JP4590645B2 - Optical-optical switching method, optical-optical switching element, and manufacturing method thereof - Google Patents

Description

The present invention relates to a light-light switching method using two-photon absorption characteristics, a two-photon absorption switching element, that is, a light-light switching element using two-photon absorption characteristics, and a method for manufacturing the same.

In recent years, there has been a remarkable increase in the amount of information in the information-oriented society, and it is expected to construct optical communication and optical information processing systems using light to cope with this. In particular, in optical communication and optical information processing systems, an optical switch, an optical repeater, and the like are expected. To realize this, a switching element using light, a logic circuit using these, and the like are required. A switching element using light and a logic circuit using these elements are required to respond at high speed in a wide wavelength region.

An optical-optical switch that controls on / off of signal light with control light is disclosed in Patent Literature 1, Patent Literature 2, and Patent Literature 3.

The optical-optical switch described in Patent Document 1 and Patent Document 2 uses a semiconductor having a one-photon absorption characteristic, and the optical-optical switch in Patent Document 3 uses a quasi-one-dimensional transition metal compound having a two-photon absorption characteristic. is doing.

FIG. 1A is a conceptual diagram showing one-photon absorption characteristics.

The one-photon absorption characteristic is that when light having an energy equal to or higher than the band gap between the upper conduction band and the lower valence band in FIG. The characteristic is that electrons transition from the electron band to the conduction band.

The optical-optical switch described in Patent Document 1 utilizes a one-photon absorption characteristic, and the band gap energy of a semiconductor thin film is 80 meV or less smaller than the photon energy corresponding to the wavelength of light such as control light or signal light. It is what I did. In order to obtain high-speed response, this optical-optical switch uses not a band edge wavelength (basic absorption edge) but a shorter wavelength (band internal wavelength), and therefore uses a sample grown at a low temperature. It is not necessary.

Here, the saturable absorption characteristic utilizing one-photon absorption is a band gap that is a band filling effect caused by high density carriers generated by strong photoexcitation density occupying the density of states, or a many-body effect caused by high density carriers. This is caused by the renormalization effect of the above, and the phase space filling effect based on the Wannier exciton. Therefore, a recombination process must be performed in order for the electrons excited from the valence band to the conduction band to return to the original state.

However, since the optical-optical switch of Patent Document 1 does not speed up the recombination process at the band edge of the excited carrier after all, the excited carriers (electrons, holes) accumulate at the band edge. However, there is a problem that a “pattern effect” occurs in which characteristics deteriorate when continuously used.

The optical-optical switch described in Patent Document 2 utilizes a one-photon absorption characteristic. In a semiconductor thin film crystal made of a III-V compound semiconductor manufactured on a semiconductor substrate, the thin film crystal has a growth temperature of 150 ° C. to The thin film is grown under the condition that it is in the range of 450 ° C., the beam intensity ratio V / III of the group V element to the group III element is in the range of 2 to 200, and is doped with a dopant of Be or C. The crystal shows only a steep response having a time constant of about 1 ps in the transient characteristic of absorption saturation at the band edge wavelength, and other slow responses are made to be negligibly small. In other words, in order to obtain a wide wavelength band / ultra-high speed, a slow response component is removed using a semiconductor material that has been subjected to Be or C doping and low-temperature growth.

However, in the method of intentionally introducing crystal defects in the thin film described in Patent Document 2, the growth temperature, the amount of dopant, etc. must be individually adjusted according to each semiconductor material, and the recombination rate is finite. For this reason, there is a problem that a “pattern effect” in which carrier accumulation occurs easily during continuous pulse irradiation.

The optical-optical switch using the one-photon absorption characteristics described in Patent Document 1 and Patent Document 2 also has a problem that a high-speed response to various wavelengths in the range of 1200 nm to 1700 nm which is extremely useful as an optical communication wavelength is not realized. .

Furthermore, some optical nonlinear materials using one-photon absorption may be difficult to use because they are hindered by simultaneous two-photon absorption.

On the other hand, the two-photon absorption characteristic of a material is a characteristic in which, when light with high light intensity is applied, the transition probability (two-photon absorption) using two photons increases, and the light absorption coefficient of the material increases. FIG. 1B is a conceptual diagram showing two-photon absorption characteristics. As shown in FIG. 1B, when light with high light intensity is applied, two photons are absorbed and an electron transits from a valence band to a conduction band.

The two-photon absorption characteristics in InP are described in the following Non-Patent Document 1, and the two-photon absorption characteristics in GaAs and InP are described in Non-Patent Document 2 below. The application is neither described nor suggested. Further, GaAs cannot be said to have substantially two-photon absorption characteristics, and its application to light-light switching is difficult.

The optical-optical switch described in Patent Document 3 uses a quasi-one-dimensional transition metal oxide as a nonlinear optical material in a light-optical switch that turns on and off another light with light, and uses pump light (control light) and probe light ( The sum of the photon energy of the signal light is set in the vicinity of the peak of two-photon absorption. In the optical-optical switch described in Patent Document 3, the energy (wavelength) of each two-photon is changed, and the energy sum of two-photons with high two-photon absorption efficiency is studied. Then, the time response of two-photon absorption at the energy sum value of the two-photons is examined.

The optical-optical switch using the two-photon absorption characteristics described in Patent Document 3, that is, the optical-optical switching element, has a non-linear optical material of Sr ₂ CuO ₃ or SrCuO ₂ and cannot change the composition. Wavelength dependence and two-photon absorption characteristics) cannot be optimized, it is difficult to produce an optical waveguide because it cannot grow on a substrate, and it is not suitable for device integration.

The wavelength of the signal light in the optical-optical switch is preferably in the normal optical communication wavelength range (1200 nm-1700 nm), and particularly preferably in the vicinity of the most frequently used 1550 nm (= 0.8 eV). However, in Patent Document 3, there is no measurement result of transmittance change which is a two-photon absorption characteristic when the wavelength of the signal light is 1550 nm (= 0.8 eV), and the wavelength of the signal light is in the optical communication wavelength range (1300 nm− Even if it is in the range of 1600 nm), the measurement result of the transmittance change which is a two-photon absorption characteristic at 1.38 μm, that is, 1380 nm (= 0.9 eV) has a large response component with a slow response of τ = 1.8 ps. Since there is a slow component, there is a problem that the transmittance of the next signal light is affected.

JP 2003-84321 A JP 2003-270596 A Japanese Patent No. 3533137 D. Vignaud et al., “Two-photoabsorption in InP substrates in the 1.55 μm range”, Appl. Phys. Lett. , 2004, 85, 2, 239-241 C. C. Lee et al., “Two-photoabsorption and photoconductivity in GaAs and InP”, Appl. Phys. Lett. , 20: 1, 18-20

Therefore, the present invention has been made to solve the above-described problems, and even when continuously used, a “pattern effect” is unlikely to occur, has a wide wavelength band in the optical communication wavelength region, and has a high-speed response. Light-to-light switching method capable of optical switching; “pattern effect” is less likely to occur even when continuously used, and the likelihood of material design is high. In other words, optical properties (wavelength dependence and Photon absorption characteristics) are easy to optimize, and there are no restrictions on fabrication conditions, that is, there is no need to set conditions such as dopants and quantum levels, so fabrication on the substrate is easy, and device integration is possible. It is an object of the present invention to provide an optical-optical switching element and a method for manufacturing the optical-optical switching element that can efficiently and easily manufacture the optical-optical switching element.

The above-described object is achieved by a light-light switching method, a light-light switching element, and a manufacturing method thereof using the following two-photon absorption characteristics.

The invention of the first group of the present application relates to a light-light switching method using the following two-photon absorption characteristics.

[1] In a light-light switching method in which signal light is turned on / off with control light, a semiconductor having two-photon absorption characteristics is irradiated with signal light having low light intensity, and control light having high light intensity is intermittently emitted. A light-light switching method comprising: irradiating, blocking the passage of the signal light by two-photon absorption generated when the control light is irradiated, and allowing the signal light to pass when the control light is not irradiated.
[2] The signal light and the control light are expressed by the equation [hc / λ _signal + hc / λ _control ≧ hc / λ _gap (where h: Planck constant, c: speed of light, λ _signal : wavelength of signal light, λ _control : wavelength of control light, λ _gap : wavelength of fundamental absorption edge of the semiconductor)].
[3] The semiconductor has a two-photon absorption characteristic in which the wavelength of the fundamental absorption edge is 1700 nm or less, is in the range of 1200 nm to 1700 nm, and is greater than or equal to the wavelength of the fundamental absorption edge. ] Or the optical-optical switching method according to [2].
[4] The light-light switching method according to any one of [1] to [3], wherein the semiconductor is a compound semiconductor composed of a group III element and a group V element.
[5] The group III element is at least one of In, Ga, and Al, and the group V element is at least one of As, P, and N (except GaAs) [4] ] The light-light switching method of description.
[6] The compound semiconductor is InP, In _x Ga _1-x As (x is larger than 0 and 0.8 or smaller), In _y Al _1-y As (y is 0 or larger and 0.82 or smaller), In _z Ga _{1 -Z} N (z is 0 or more and 1 or less) and In _(1-ab) Ga _a Al _b As _(1-c) N _c (a, b, a + b are 0 or more and 1 or less, c is greater than 0 and 1 Or a, b, a + b is greater than 0 and less than 1, and c is 0 or more and 1 or less (except for the case where both compositions overlap). ] The light-light switching method of description.
[7] The compound semiconductor is InP, In _x Ga _1-x As (x is larger than 0 and 0.53 or smaller), In _y Al _1-y As (y is 0 or larger and 0.69 or smaller), In _z Ga _{1 -Z} N (z is 0 or more and 0.75 or less) and In _(1-ab) Ga _a Al _b As _(1-c) N _c (a, b, a + b are 0 or more and 1 or less, c is 0 Largely less than 1, or a, b, a + b is larger than 0 and smaller than 1, and c is 0 or more and 1 or less (except when both compositions overlap). [5] The light-light switching method according to [5].
[8] The light-light switching method according to any one of [4] to [7], wherein the semiconductor is a single crystal.

The invention of the second group of the present application relates to an optical-optical switching element utilizing the following two-photon absorption characteristics, that is, a two-photon absorption switching element.

[9] An optical-optical switching element comprising a semiconductor having two-photon absorption characteristics, control light input to the semiconductor, signal light propagation means, and signal light propagation means transmitted through the semiconductor.
[10] The optical-optical switching element according to [9], wherein the propagation means for the control light and the signal light is a waveguide and is connected to the semiconductor.
[11] The optical-optical switching element according to [10], wherein the signal light and control light input waveguide and the signal light output waveguide are in opposite positions across the semiconductor.
[12] The signal light input waveguide and the signal light output waveguide are in opposing positions with the semiconductor interposed therebetween, and the control light input waveguide is the signal light input waveguide and the signal light output waveguide. The optical-optical switching element according to [10], wherein the optical-optical switching element is connected to the semiconductor so as to cross a straight line connecting the two.
[13] The optical-optical switching element according to [11] or [12], wherein the semiconductor is sandwiched or surrounded by a clad having a lower refractive index.
[14] The optical-optical switching element according to [11] or [12], wherein each waveguide and the semiconductor are formed on a substrate.
[15] The optical-optical switching element according to [14], wherein the semiconductor is sandwiched or surrounded by a clad having a lower refractive index.
[16] The semiconductor, the cladding, and the waveguide are both layered, and the semiconductor, the cladding is a lower cladding layer, a semiconductor layer, and an upper cladding layer, and the waveguide is a lower cladding layer, a core layer, The optical-optical switching element according to [15], which is formed on the substrate in the order of the upper cladding layer.
[17] The optical-optical switching element according to [11] or [12], wherein the semiconductor is square or rectangular in plan view.
[18] The semiconductor is substantially T-shaped in a plan view, and the signal light input waveguide and the signal light output waveguide are connected to opposite positions with a substantially T-shaped horizontal line portion interposed therebetween, for control purposes. The optical-optical switching element according to [10], wherein the waveguide is connected to a lower end of a substantially T-shaped vertical line.
[19] The light according to [9], wherein the wavelength of the fundamental absorption edge is not more than 1700 nm, has a two-photon absorption characteristic in the range of 1200 nm to 1700 nm and not less than the wavelength of the fundamental absorption edge. An optical switching element;
[20] The optical-optical switching element according to [9] or [19], wherein the semiconductor having the two-photon absorption characteristics is a compound semiconductor composed of a group III element and a group V element.
[21] The group III element is at least one of In, Ga, and Al, and the group V element is at least one of As, P, and N (except GaAs) [20] ] The optical-optical switching element of description.
[22] The compound semiconductor is InP, In _x Ga _1-x As (x is larger than 0 and 0.8 or smaller), In _y Al _1-y As (y is 0 or larger and 0.82 or smaller), In _z Ga _{1 -Z} N (z is 0 or more and 1 or less) and In _(1-ab) Ga _a Al _b As _(1-c) N _c (a, b, a + b are 0 or more and 1 or less, c is greater than 0 and 1 Or a, b, a + b is greater than 0 and less than 1, and c is 0 or more and 1 or less (except when both compositions overlap). ] The optical-optical switching element of description.
[23] The compound semiconductor is InP, In _x Ga _1-x As (x is larger than 0 and 0.53 or smaller), In _y Al _1-y As (y is 0 or larger and 0.69 or smaller), In _z Ga _{1 -Z} N (z is 0 or more and 0.75 or less) and In _(1-ab) Ga _a Al _b As _(1-c) N _c (a, b, a + b are 0 or more and 1 or less, c is 0 Largely less than 1, or a, b, a + b is larger than 0 and smaller than 1, and c is 0 or more and 1 or less (except when both compositions overlap). [21] The light-optical switching element according to [21].
[24] The two-photon absorption switching element according to [11] or [12], wherein a distance between the pair of waveguides is in a range of 100 nm to 500 μm.
[25] The optical-optical switching element according to any one of [20] to [23], wherein the semiconductor is a single crystal.

[17] may be “the optical-optical switching element according to any one of [13] to [16], wherein the semiconductor is square or rectangular in a plan view”.
In the above [18], “the semiconductor is substantially T-shaped in a plan view, and the signal light input waveguide and the signal light output waveguide are connected to opposite positions across a substantially T-shaped horizontal line portion. In addition, the light-optical switching element according to any one of [13] to [16], wherein the control waveguide is connected to a lower end of a substantially T-shaped vertical line.
In the above [19], “the wavelength of the fundamental absorption edge is 1700 nm or less, has a two-photon absorption characteristic in the range of 1200 nm to 1700 nm and above the wavelength of the fundamental absorption edge [10 ] To the optical-optical switching element according to any one of [18].
In the above [20], the light according to any one of [10] to [18], wherein the semiconductor having the two-photon absorption property is a compound semiconductor composed of a group III element and a group V element. It may be an “optical switching element”.
In the above [24], “the two-photon absorption switching element according to any one of [13] to [18], wherein the distance between the pair of waveguides is in a range of 100 nm to 500 μm”. There may be.

The invention of the third group of the present application relates to a light-optical switching element utilizing the following two-photon absorption characteristics, that is, a method for manufacturing a two-photon absorption switching element.

[26] The method for manufacturing an optical-optical switching element according to [14], comprising a step of forming a semiconductor having a two-photon absorption characteristic on a substrate and a step of forming a waveguide.
[27] The light according to [16], comprising a step of laminating a lower clad layer, a semiconductor layer, and then an upper clad layer on a substrate, and a step of laminating a lower clad layer for a waveguide, a core layer, and then an upper clad layer. -Manufacturing method of an optical switching element.
[28] The light-optical switching according to [26], comprising a step of forming a semiconductor layer and a step of forming a waveguide on a semiconductor crystal wafer having two-photon absorption characteristics using an epitaxy growth method. Device manufacturing method.
[29] The manufacturing of the optical-optical switching element according to [28], wherein the step of forming the semiconductor layer having the two-photon absorption characteristics uses either a molecular beam epitaxy method or a metal organic chemical deposition method. Method.
[30] (1) A semiconductor lower cladding layer having a two-photon absorption characteristic is formed on a substrate, and a semiconductor core layer having a refractive index larger than that of the cladding layer and having a two-photon absorption characteristic is formed on the lower cladding layer. Next, a step of forming an upper clad layer for a semiconductor having two-photon absorption characteristics on the core layer, (2) on the upper clad layer (however, except for a region where a substantially T-shaped waveguide is to be formed in plan view) ) Forming a resist layer; (3) etching and removing the upper clad layer, the core layer and the lower clad layer in a region where a waveguide is to be formed; and (4) forming a waveguide on the resist layer. A waveguide lower cladding layer is formed on a substrate in a predetermined region, a waveguide core layer is formed on the waveguide lower cladding layer, and then the waveguide upper cladding layer is formed on the waveguide core layer. Forming (5) the resist (6) a step of forming a resist layer on a substantially T-shaped waveguide region and an upper clad layer for a semiconductor having two-photon absorption characteristics in plan view; Etching and removing a semiconductor upper clad layer having a two-photon absorption characteristic, a semiconductor core layer having a two-photon absorption characteristic, and a semiconductor lower clad layer having a two-photon absorption characteristic, which are not covered with a resist layer, 8) The method for producing an optical-optical switching element according to [17], wherein [12] is cited, the method comprising a step of removing the resist layer.

In the above [26], “the light according to any one of [15] to [25], comprising a step of forming a semiconductor having a two-photon absorption characteristic on a substrate and a step of forming a waveguide”. The manufacturing method of an optical switching element "may be sufficient.
In the above [27], “consisting of a step of laminating a lower clad layer, a semiconductor layer and then an upper clad layer on a substrate and a step of laminating a lower clad layer for a waveguide, a core layer and then an upper clad layer [17] ]-[25] The manufacturing method of the optical-optical switching element in any one of [25].

The manufacturing method of the optical-optical switching element may be as follows.
[31] (1) A semiconductor lower cladding layer having a two-photon absorption characteristic is formed on a substrate, and a semiconductor core layer having a refractive index larger than that of the cladding layer and having a two-photon absorption characteristic is formed on the lower cladding layer. Next, a step of forming a semiconductor upper clad layer having a two-photon absorption characteristic on the core layer, (2) on the upper clad layer (however, a waveguide that is a substantially T-shaped vertical line in plan view) A step of forming a resist layer in a region excluding the region), (3) a step of etching and removing the upper clad layer, the core layer, and the lower clad layer in the region where the waveguide is to be formed, and (4) on the resist layer A waveguide lower cladding layer is formed on a substrate in a waveguide formation region, a waveguide core layer is formed on the waveguide lower cladding layer, and then the waveguide upper layer is formed on the waveguide core layer. A step of forming a cladding layer, (5) (6) A resist layer is formed on the upper clad layer for the waveguide and the upper clad layer for the semiconductor having the two-photon absorption characteristics (however, it is a substantially T-shaped horizontal line in plan view). (7) etching a semiconductor upper cladding layer having a two-photon absorption characteristic, a semiconductor core layer having a two-photon absorption characteristic, and a semiconductor lower cladding layer having a two-photon absorption characteristic that are not covered with the resist layer. And (8) the light-light described in [17] (however, rectangular in plan view), characterized by comprising (8) a step of removing the resist layer. A method for manufacturing a switching element.
[32] (1) A semiconductor lower cladding layer having a two-photon absorption characteristic is formed on a substrate, and a semiconductor core layer having a refractive index larger than that of the cladding layer and having a two-photon absorption characteristic is formed on the lower cladding layer. Then, forming a semiconductor upper cladding layer having a two-photon absorption characteristic on the core layer, (2) forming a substantially T-shaped resist in plan view on the upper cladding layer, (3) Etching and removing a semiconductor upper clad layer having a two-photon absorption characteristic, a semiconductor core layer having a two-photon absorption characteristic, and a semiconductor lower clad layer having a two-photon absorption characteristic, which are not covered with a resist layer, 4) The method for producing an optical-optical switching element according to [18], comprising a step of removing the resist layer.

According to the optical-optical switching method of the invention of the first group of the present application, “pattern effect” hardly occurs even when continuously used, and has a wide wavelength band property in a normal optical communication wavelength range, and high-speed response optical-optical switching. Is possible. The optical-optical switching elements of the invention of the second group of the present application are less likely to produce a “pattern effect” even when continuously used, can respond at high speeds at normal optical communication wavelengths, and have a high likelihood of material design. By changing the material composition, it is easy to optimize the optical properties (wavelength dependence and two-photon absorption characteristics), and the manufacturing conditions are less restrictive. In other words, it is not necessary to set conditions such as dopants and quantum levels. The above fabrication is easy, and device integration is possible. In addition, the light-optical switching element can be efficiently and easily manufactured by the method for manufacturing a light-optical switching element according to the third group of the present invention.

The figure for demonstrating the one-photon absorption characteristic and the two-photon absorption characteristic. The figure explaining the light-light switching operation | movement using a two-photon absorption characteristic. Diagram showing the relationship between the InGaAs composition ratio and the fundamental absorption edge wavelength for each growth temperature 1 is a schematic cross-sectional view of an optical-optical switching element A according to an embodiment. 1 is a schematic perspective view of an optical-optical switching element B according to an embodiment. FIG. 1 is a schematic perspective view of an optical-optical switching element C according to an embodiment. FIG. 1 is a schematic perspective view of an optical-optical switching element D according to an embodiment. 1 is a schematic perspective view of an optical-optical switching element E according to an embodiment. 1 is a schematic perspective view of an optical-optical switching element F according to an embodiment. FIG. 1 is a schematic perspective view of an optical-optical switching element G according to an embodiment. The figure which shows the manufacturing method of the optical-optical switching element C which concerns on embodiment. The figure which shows the manufacturing method of the optical-optical switching element D which concerns on embodiment. The figure which shows the manufacturing method of the optical-optical switching element E which concerns on embodiment. Schematic which shows the measuring system for measuring a light transmittance change. Schematic which shows the measurement system in a pump probe method. The figure which shows the two-photon absorption characteristic at the time of using InP. Shows a two-photon absorption characteristics when the In _0.53 Ga _0.47 As. The figure which shows the change of the absorption coefficient at the time of changing _{x of} InxGa1 _- xAs. The figure which shows the change of the absorption coefficient at the time of mixing a dopant with a compound semiconductor layer.

Explanation of symbols

A ... Two-photon absorption switching element, B ... Two-photon absorption switching element, C ... Two-photon absorption switching element, D ... Two-photon absorption switching element, E ... Two-photon absorption switching element, F ... Two-photon absorption switching element, G ... Two-photon absorption switching element,
PC: Planned waveguide formation region, PD: Waveguide formation planned region, QC: Semiconductor formation planned region having two-photon absorption characteristics, QD: Semiconductor formation planned region having two-photon absorption characteristics, QE: Two-photon absorption characteristics Semiconductor formation planned area,
DESCRIPTION OF SYMBOLS 1A ... Semiconductor having two-photon absorption characteristics, 20A ... Input waveguide, 20LA ... Lower cladding layer of input waveguide, 20MA ... Core layer of input waveguide, 20HA ... Upper cladding layer of input waveguide, 21A ... Output waveguide, 21LA... Lower clad layer of output waveguide, 21MA... Core layer of output waveguide, 21HA... Upper clad layer of output waveguide, 3A.
1B: Semiconductor having two-photon absorption characteristics, 20B: Input waveguide, 20LB: Lower cladding layer of input waveguide, 20MB: Core layer of input waveguide, 20HB: Upper cladding layer of input waveguide, 21B ... output waveguide, 21LB ... lower clad layer of output waveguide, 21MB ... core layer of output waveguide, 21HB ... upper clad layer of output waveguide, 22B ... waveguide for control light input, 22LB ... control Lower clad layer of optical input waveguide, 22 MB: Core layer of control light input waveguide, 22 HB: Upper clad layer of control light input waveguide,
1C: a semiconductor having a two-photon absorption characteristic, 1LC: a semiconductor lower cladding layer having a two-photon absorption characteristic, 1MC: a semiconductor core layer having a two-photon absorption characteristic, 1HC: an upper cladding layer for a semiconductor having a two-photon absorption characteristic, 20C: input waveguide, 20LC: lower cladding layer of input waveguide, 20MC: core layer of input waveguide, 20HC: upper cladding layer of input waveguide, 21C: output waveguide, 21LC: output Lower clad layer of waveguide, 21MC ... Core layer of output waveguide, 21HC ... Upper clad layer of output waveguide, 22C ... Waveguide for control light input, 22LC ... Lower clad layer of waveguide for control light, 22MC: Control light input waveguide core layer, 22HC: Control light input waveguide upper clad layer, 2C: Waveguide, 2LC: Waveguide lower clad layer, 2MC The core layer of the waveguide, the upper cladding layer of 2HC ... waveguide, 3C ... structural substrate,
1D: a semiconductor having a two-photon absorption characteristic, 1LD: a lower cladding layer for a semiconductor having a two-photon absorption characteristic, 1MD: a semiconductor core layer having a two-photon absorption characteristic, 1HD: an upper cladding layer for a semiconductor having a two-photon absorption characteristic, 22D: Control light input waveguide, 22LD: Lower clad layer of control light input waveguide, 22MD: Core layer of control light input waveguide, 22HD: Upper clad layer of control light input waveguide, 2D: Conduction Waveguide, 2LD ... lower clad layer of waveguide, 2MD ... core layer of waveguide, 2HD ... upper clad layer of waveguide, 3D ... structural substrate,
DESCRIPTION OF SYMBOLS 1E ... Semiconductor having two-photon absorption characteristics, 1LE ... Lower cladding layer for semiconductor having two-photon absorption characteristics, 1ME ... Semiconductor core layer having two-photon absorption characteristics, 1HE ... Upper cladding layer for semiconductor having two-photon absorption characteristics, 3E ... structural substrate,
DESCRIPTION OF SYMBOLS 1F ... Semiconductor with two-photon absorption characteristics, 20F ... Input waveguide, 21F ... Output waveguide, 22F ... Control light input waveguide, 3F ... Structural substrate, 4F ... Splitter 1G ... Two-photon absorption characteristics Semiconductors, 20G ... input waveguides, 21G ... output waveguides, 3F ... structure substrate, 4G ... branch filter, 5G ... lens 6C ... resist layer, 7C ... resist layer, 6D ... resist layer, 7D ... resist layer , 6E ... resist layer, 7E ... resist layer

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The light-light switching method according to the invention of the first group of the present application does not absorb a photon when a semiconductor material having a two-photon absorption characteristic is irradiated with only light having low light intensity that does not cause two-photon absorption. Phenomenon that light can be transmitted through the material, but when light with high light intensity is irradiated at the same place as light with low light intensity, two-photon absorption occurs and light with low light intensity cannot be transmitted. Invented with a focus on. This light-light switching method is a light-light switching method in which signal light is turned on / off with control light, and a semiconductor having two-photon absorption characteristics is irradiated with signal light having low light intensity, and control with high light intensity is performed. It is characterized in that light is intermittently irradiated, the passage of the signal light is blocked by two-photon absorption generated when the control light is irradiated, and the signal light is allowed to pass when the control light is not irradiated. At this time, the signal light and the control light are expressed by the equation [hc / λ _signal + hc / λ _control ≧ hc / λ _gap (where h: Planck constant, c: speed of light, λ _signal : wavelength of signal light, λ It is desirable to satisfy the relationship: _control : wavelength of control light, λ _gap : wavelength of the fundamental absorption edge of the semiconductor).

The principle of the light-to-light switching method according to the invention of the first group of the present application is as shown in FIG. When the control light of a certain pulse train ((b) in the figure) is irradiated to the same location on the semiconductor, only the signal light that does not overlap in time with the control light appears as output light ((c) in the figure) and overlaps the control light. The signal light is absorbed by the semiconductor. The signal light may be intermittent or continuous and is not particularly limited. The control light is desirably intermittent, for example, a pulse train. In this case, it is desirable that the time change is steep and at the same time the intensity of the control light necessary to realize this operation is as small as possible. Here, the light intensity Is of the signal light is preferably 10 nJ / cm ² <Is <1 μJ / cm ² , and the light intensity Ic of the control light is preferably 1 μJ / cm ² ≦ Ic <10 J / cm ² , More preferably, 10 μJ / cm ² <Ic <100 mJ / cm ² . The lower limit of the light intensity of the signal light is a light intensity that satisfies the error rate ε <10 ⁻¹¹ in optical communication. The wavelengths of the signal light and the control light to be used are equal to or greater than the wavelength of the basic absorption edge of the semiconductor to be used, and are within the wavelength range having the two-photon absorption characteristics of the semiconductor. The control light and signal light are preferably laser light in terms of light intensity and time width of the light pulse.

The irradiation time of the control light and the pulse width when the control light is pulsed light are not particularly limited, but are within a range where the semiconductor having the two-photon absorption characteristics is not broken. Since the control light has a high light intensity, the semiconductor is destroyed and processed when the irradiation time (pulse time width) becomes long even at the same intensity. This fine condition varies depending on various factors such as the sample and the repetition period of the laser. Laser ablation in the range of the control light intensity (1 μJ / cm ² ≦ Ic <10 J / cm ² ) described in [0036] (Evaporation of some or all of the constituent elements when the semiconductor is heated with a laser) Should not happen. Therefore, when 1 μJ / cm ² ≦ Ic <100 μJ / cm ² , the pulse width may be 100 ps or more, but when 100 μJ / cm ² ≦ Ic <1 mJ / cm ² , the pulse width is 100 ps or less to 10 ps or less ( In the case of 100 μJ / cm ² , it is 100 ps or less, in the case of 1 mJ / cm ² , it is 10 ps or less, and between 100 μJ / cm ² and 1 mJ / cm ² , the intermediate value between 100 ps and 10 ps (the control light intensity and the pulse width are In the case of 1 mJ / cm ² ≦ Ic <10 mJ / cm ² , the pulse width is set to 10 ps or less to 1 ps or less, and 10 mJ / cm ² ≦ Ic. <pulse width in the case of 100 mJ / cm ² to 1ps below ~0.1ps following field ^{100mJ / cm 2 ≦ Ic <10J} / cm 2 It is desirable that the pulse width below 0.1 ps.

Since the wavelength of light used in normal optical communication is in the range of 1200 nm to 1700 nm, the wavelength of the fundamental absorption edge of the semiconductor having the two-photon absorption characteristics is smaller than 1200 nm, and the semiconductor has a two-photon range from 1200 nm to 1700 nm. It is most desirable to have absorption properties. With such a semiconductor, signal light and control light having a wavelength within an extremely wide range of 1200 nm to 1700 nm can be used for optical-optical switching. In addition, when the wavelength of the fundamental absorption edge of the semiconductor having the two-photon absorption characteristic is in the middle of 1200 nm to 1700 nm, for example, even when the basic absorption edge of the semiconductor having the two-photon absorption characteristic is 1500 nm, the wavelength is 1500 nm to 1700 nm. If it has photon absorption characteristics, signal light and control light having a wavelength in the range of 1500 nm to 1700 nm can be used for light-light switching. In the future, even when the lower limit of the wavelength of light used in optical communication is shifted to less than 1200 nm, for example, 1000 nm, the basic absorption edge of the semiconductor having the two-photon absorption characteristics is 1000 nm, and the two-photon is 1000 nm to 1700 nm. If it has absorption characteristics, signal light and control light having a wavelength in the range of 1000 nm to 1700 nm can be used for light-light switching.

The semiconductor having the two-photon absorption characteristic is preferably a compound semiconductor composed of a group III element and a group V element. The group III element is preferably at least one of In, Ga, and Al, and the group V element is preferably at least one of As, P, and N. Here, the group III element and the group V element are preferably in a ratio of 1: 1. Since GaAs does not substantially have a two-photon absorption characteristic, it is not included in a semiconductor having a two-photon absorption characteristic or a compound semiconductor.

At least one of In, Ga, and Al may be one of In, Ga, and Al, or may be a combination of two of In, Ga, and Al, or a combination of three of In, Ga, and Al. But you can. At least one of As, P, and N may be one of As, P, and N, may be a combination of two of As, P, and N, and may be a combination of three of As, P, and N But you can.

Wherein the compound semiconductor _{is, InP, In x Ga 1-} x As, In y Al 1-y As, In z Ga 1-z N, and _{In (1-a-b)} Ga a Al b As (1- _{c) In} order to obtain a desirable two-photon absorption characteristic in which one-photon absorption does not occur even with any of _Nc , it is extremely desirable that the ratio of each element is within a predetermined range.

In the case of InP, it is highly desirable that the ratio of In to P is 1: 1, and in the case of In _y Al _1-y As, y is preferably in the range of 0 to 0.69, and In _z In the case of Ga _1-z N, z is preferably in the range of 0 to 0.75, and preferably in the range of 0.4 to 0.75. In the case of In _x Ga _1-x As, x is preferably in the range of more than 0 and not more than 0.53, and more preferably in the range of not less than 0.05 and not more than 0.53. However, since the wavelength of the fundamental absorption edge depends on the growth temperature of the semiconductor layer, the desired range may be affected by the growth temperature of the semiconductor. In particular, in the case where an In _x Ga _1-x As crystal is used as the semiconductor layer, when the crystal growth temperature (Tg) is 380 ° C., it is preferably in the range of more than 0 and 0.27 or less. Of course, even if x is 0.53 which is larger than 0.27, the fundamental absorption edge becomes 1700 nm, and light-light switching is possible at 1700 nm. When the crystal growth temperature (Tg) is 100 ° C., it is desirable that the crystal growth temperature (Tg) is in the range of more than 0 and 0.53 or less. Of course, even if x is 0.8, which is larger than 0.53, the fundamental absorption edge is 1700 nm, and light-light switching is possible at 1700 nm.

Specifically, a compound semiconductor having a two-photon absorption characteristic at a wavelength of the fundamental absorption edge of 1700 nm or less, within a range of 1200 nm to 1700 nm and above the wavelength of the fundamental absorption edge, is InP, In _x Ga _{1− x} As (growth temperature 380 ° C., x is greater than 0 and less than or equal to 0.53), In _x Ga _1-x As (growth temperature 100 ° C., x is greater than 0 and less than or equal to 0.8), In _y Al _1-y As (y is 0 or 0.82) or _in z _{Ga 1-z} N (the z 0 or more and 1 or _{less), in (1-a-} b) Ga a Al b As (1-c) N _c (a, b, a + b is 0 or more and 1 or less, c is greater than 0 and less than 1, or a, b, a + b is greater than 0 and less than 1, c is 0 or more and 1 or less, provided that both compositions overlap A compound comprising at least one composition of It is a semiconductor. Since it is desirable to have a two-photon absorption characteristic in the entire range of 1200 nm to 1700 nm, the basic absorption edge is 1200 nm or less, and the two-photon absorption characteristic is in the range of 1200 nm to 1700 nm and above the wavelength of the basic absorption edge. The compound semiconductor which has is desirable. Specifically, InP, In _x Ga _1-x As (growth temperature 380 ° C., x is greater than 0 and 0.27 or less), In _x Ga _1-x As (growth temperature 100 ° C., x is Greater than 0 and less than 0.53), In _y Al _1-y As (y is 0 or more and 0.69 or less) or In _z Ga _1-z N (z is 0 or more and 0.75 or less), In _{(1- ab)} Ga _a Al _b As _(1-c) N _c (a, b, a + b is 0 or more and 1 or less, c is greater than 0 and less than 1, or a, b, a + b is greater than 0 and less than 1, c is 0 or more and 1 or less, except for the case where both compositions overlap).

In the composition of the compound semiconductor, the ratio of the sum of group III (In, Ga, Al) and the sum of group V (As, P, N) is 1: 1 in each case, but the error range is In terms of the ratio of the sum of Group III (In, Ga, Al) and the sum of Group V (As, P, N), Group III: Group V = 49.9: 50.1-50.1: 59.9 More preferably, it is III group: V group = 49.99: 50.01-50.01: 49.99 more desirably. In addition, it describes in the following Table 1 and FIG. 3 about the relationship between a compound semiconductor material and a fundamental absorption edge. FIG. 3 shows the relationship between the InGaAs composition ratio and the fundamental absorption edge wavelength for each growth temperature.

The compound semiconductor may or may not contain a dopant such as Be, Fe, or Cr. This is because the influence of the dopant is hardly seen in the two-photon absorption characteristics. However, when a dopant is introduced, the one-photon absorption characteristic in the semiconductor layer is hindered. Therefore, in order to emphasize only the two-photon absorption characteristic, it is preferable to include the dopant. In that case, it is preferable to contain about 10 ¹⁶ to 10 ²⁰ cm ⁻³ in terms of impurity concentration. A compound semiconductor composed of a group III element and a group V element, in particular, the group III element is at least one of In, Ga, and Al, and the group V element is at least one of As, P, and N. III Since compound semiconductors composed of group elements and group V elements do not require precise adjustment of the dopant, the likelihood of material design can be ensured.

The compound semiconductor is loosely limited in manufacturing conditions in the following points.
(1) No need to form quantum levels
Many optical-optical switches using absorption saturation due to one-photon absorption use quantum levels or excitons, and for this purpose, quantum wells must be fabricated. In order to fabricate quantum wells, the fabrication conditions for quantum wells (well layer composition / width, barrier layer composition / width) must be set strictly, and fluctuations during their growth must be suppressed. If even one of the parameters is shifted, the quantum level is also shifted. However, the compound semiconductors are not necessary because they are unnecessary, and the yield is improved industrially.
(2) The composition of the compound semiconductor in which the composition fluctuation during the growth does not become a problem only needs to satisfy the conditions described in [0039] to [0044]. Therefore, there is no problem even if the composition ratio between a plurality of elements fluctuates somewhat during growth (usually, fluctuation of x during growth is suppressed to ± 0.05 or less).
(3) As shown in FIG. 3, it is not necessary to adjust the growth temperature strictly. As shown in FIG. 3, even at 250 ° C., which is half the normal growth temperature (500 ° C. to 600 ° C.), the wavelength of the fundamental absorption edge It can be seen from the fact that it has not changed much. The growth temperature only needs to be in a range where no one-photon absorption occurs.
(4) It does not depend on the impurity concentration (usually the same as the doping concentration, but if it includes an unintended impurity concentration, the total concentration with the concentration) and the carrier concentration. Therefore, it is not necessary to control the impurity concentration, and the production is simple. The growth temperature (the carrier concentration often changes as the growth temperature changes) is as described above.
The compound semiconductor can control the fundamental absorption edge wavelength of the semiconductor and the wavelength range showing the two-photon absorption characteristics by changing the combination of the group III element and the group V element, the element ratio, or the growth temperature. -Convenient for preparing optical switching elements.

The semiconductor may be single crystal, polycrystalline, or amorphous, but is preferably single crystal. If it is polycrystalline or amorphous, the steepness of the fundamental absorption edge is lost and the wavelength of the fundamental absorption edge is shortened. However, if one of the two wavelengths used for two-photon absorption is shortened, two-photons can be obtained even if polycrystalline or amorphous. This is because absorption can be caused.

The light-optical switching element using the two-photon absorption characteristic according to the invention of the second group of the present application, that is, the two-photon absorption switching element is a semiconductor having a two-photon absorption characteristic, and means for propagating control light and signal light input to the semiconductor And means for propagating signal light transmitted through the semiconductor. The semiconductor is as described above. The shape of the semiconductor is not particularly limited, and examples thereof include a thin film shape on a substrate, a layer shape grown on the substrate, a flake shape, a tape shape, a string shape, and a chip shape. The height and width of the semiconductor in the plane perpendicular to the light traveling direction are both preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 10 μm or less from the viewpoint of suppressing light diffusion. The best height and width are around 1 μm. The length of the semiconductor in the light traveling direction is preferably in the range of 100 nm to 500 μm. The propagation means for the control light and the signal light may be any means as long as it can propagate the control light and the signal light emitted from the light source to the semiconductor, and can propagate the signal light transmitted through the semiconductor. ), An optical fiber (for example, made of quartz glass), an optical fiber array, a lens array, and a lens. If a semiconductor having a two-photon absorption characteristic is formed into a waveguide shape, that is, the semiconductor is used as a core and is sandwiched or surrounded by a clad having a lower refractive index (for example, a compound semiconductor having a lower refractive index than the core compound semiconductor). For example, it can be a signal light propagation means, or it can be a signal light propagation means and a control light propagation means.

In the case of forming a semiconductor layer on a substrate, it is possible to form the above-mentioned single semiconductor layer, or to stack a plurality of thin films made of these semiconductors.

The substrate is not particularly limited as long as it is flat, and various substrates can be used. However, a structural substrate (for example, a sapphire plate or a quartz plate) is preferable, and two-photon absorption characteristics are more preferable. A structure substrate on which a semiconductor layer can be grown. For example, when a molecular beam epitaxy method (MBE method) described later or a crystal growth method such as a metal organic chemical deposition method (MOCVD method) is used, the semiconductor substrate used for the crystal growth can be used as it is. The substrate is not particularly limited, but it is desirable that the lattice constant matches or is as close as possible to that of the semiconductor to be grown and has the same crystal structure. Accordingly, a compound semiconductor is desirable, and more desirably a compound semiconductor based on a semiconductor element having two-photon absorption characteristics.

A two-photon absorption switching element A according to a preferred embodiment of the invention of the second group of the present application includes a semiconductor layer 1A having a two-photon absorption characteristic formed on a structural substrate 3A, and control light and signal for the semiconductor layer 1A. The input optical waveguide 20A for introducing light and the output optical waveguide 21A disposed opposite to the input optical waveguide with the semiconductor layer interposed therebetween (see FIG. 4). Although not shown, the signal light and the control light are merged before the semiconductor 1A (for example, the signal light waveguide and the control light waveguide arranged in parallel as shown in FIG. 9). Is a case where a directional coupler is used to bring the waveguides close to each other). As long as the semiconductor layer 1A having the two-photon absorption characteristics, the input waveguide 20A, and the output waveguide 21A are provided, the two-photon absorption switching element functions. However, from the viewpoint of mechanical stability and manufacturability, the two-photon It is highly desirable that the absorption switching element is formed and fixed on the structure substrate 3A (see FIG. 4).

It is desirable that the distance between the tip of the input waveguide 20A and the tip of the output waveguide 21A that are arranged to face each other with the semiconductor 1A having the two-photon absorption characteristic in the range of 100 nm to 500 μm. When such a range is employed, a range of 1200 nm to 1700 nm that is extremely useful as an optical communication wavelength can be made longer than the basic absorption edge. In addition, since two-photon absorption is excellent in high speed, optical non-linear devices such as light-optical switching elements and light control devices manufactured using semiconductors having such two-photon absorption characteristics can be used in a wide wavelength range. High speed operation is possible.

The input waveguide 20A and the output waveguide 21A are not particularly limited as long as light of a desired wavelength can be propagated, and preferably from the core layer 20MA (21MA) and the core layer 20MA (21MA). Consists of a structure sandwiched or surrounded by a pair of clad layers 20LA and 20HA (21LA and 21HA) having a low refractive index (see FIG. 4). Note that the light-optical switching element of FIG. 4 employs a configuration in which both control light having high light intensity and signal light having low light intensity are simultaneously propagated from the input waveguide 20A. The optical-optical switching element having this configuration propagates only signal light having low light intensity from the input waveguide 20A to the semiconductor layer 1A, thereby transmitting the signal light to generate output light, and thereby generating a signal having low light intensity. The switching function is exhibited by blocking the signal light by causing two-photon absorption by propagating light and control light having high light intensity from the input waveguide 20A to the semiconductor layer 1A.

The optical-optical switching element B of FIG. 5 includes an input waveguide 20B that propagates signal light with low light intensity and an input waveguide 22B for control of two-photon absorption characteristics that propagates control light with high light intensity. The control light input waveguide 22B is connected to the semiconductor layer 1B so as to be orthogonal to a straight line connecting the signal light input waveguide 20B and the signal light output waveguide 21B. ing. The input waveguide 22B may cross at an angle with respect to the straight line at an angle of 45 ° to less than 90 °, for example.

Since the output waveguide 21B is for propagating the output light when the signal light is transmitted through the semiconductor layer 1B disposed between it and the input waveguide 20B, it faces the input waveguide 20B. It is important that they are formed in pairs. A semiconductor layer 1B having two-photon absorption characteristics is disposed between the input waveguide 20B and the output waveguide 21B. From the relationship of light loss, the input waveguide 20B, the semiconductor layer 1B, and the output The waveguide 21B and the semiconductor layer 1B are preferably directly connected without interposing an air layer, and more preferably integrally formed. When not integrally molded, it is preferable that the optical path coupling adhesive, the optical waveguide forming resin, and the like are used for close contact. In addition, the distance between these opposing waveguides is not particularly limited as long as light can be transmitted. However, the range in which light can be sufficiently blocked and the loss of light in a state where the transition probability is high. In consideration of an allowable range, the thickness is desirably in the range of 100 nm to 500 μm, and more desirably in the range of 100 nm to 100 μm. The same applies to the optical-optical switching element of the type shown in FIG.

6 includes a lower clad layer 1LC on a structural substrate 3C, a semiconductor layer 1MC having a refractive index larger than that of the clad layer and having two-photon absorption characteristics on the lower clad layer 1LC, the semiconductor layer A laminated body 1C is formed by laminating the upper clad layer 1HC in this order on 1MC, and the signal light input waveguide 20C and the signal light output waveguide 21C are formed at positions facing each other with the laminated body 1C interposed therebetween. The control light input waveguide 22C is connected to the laminated body 1C so as to cross at a right angle to a straight line connecting the pair of signal light waveguides. Is a preferred embodiment of the optical-optical switching element. Since the signal light and the control light cross at the semiconductor layer 1MC in the stacked body 1C, the semiconductor 1MC serves as a switching unit.

7 includes a lower clad layer 1LD on a structure substrate 3D, a semiconductor layer 1MD having a refractive index larger than that of the clad layer on the lower clad layer 1LD and having a two-photon absorption characteristic, and the semiconductor layer. A laminate 1D is formed by laminating an upper clad 1HD layer in this order on 1MD. The laminate 1D forms a T-shaped horizontal line in plan view, and the control light input waveguide 22D is seen in plan view. It is connected to this laminated body 1D so as to form a T-shaped vertical line, and is a preferred embodiment of a rectangular optical-optical switching element according to claim 17 (however, it is rectangular in plan view). . In this optical-optical switching element, signal light that has propagated through a waveguide (not shown) is input to a portion corresponding to a substantially T-shaped horizontal line (that is, the left end of 1MD), and control light is transmitted to a substantially T-shaped vertical line. In the portion corresponding to (that is, the upper end of 22MD). A crossing portion of the signal light and the control light in the laminate 1D becomes a switching portion.

In the optical-optical switching element E of FIG. 8, a lower cladding layer 1LE is stacked on a structural substrate 3E, and a semiconductor layer 1ME having a higher refractive index than the cladding layer and having two-photon absorption characteristics is stacked on the lower cladding layer 1LE. The upper clad layer 1HE is laminated on the semiconductor layer 1ME, and the laminated body 1E is T-shaped in a plan view, which is a preferred embodiment of the optical-optical switching element according to claim 18. In this optical-optical switching element, signal light that has propagated through a waveguide (not shown) is input to a portion corresponding to a T-shaped horizontal line (that is, the left end of 1ME) and propagates through a waveguide (not shown). Control light is input to the portion corresponding to the vertical line of the T-shape (that is, the upper end of 1ME ′). A crossing portion of the signal light and the control light in the laminate 1E becomes a switching portion.

The optical-optical switching element F according to FIG. 9 includes a structure substrate 3F, a semiconductor layer 1F having a two-photon absorption characteristic formed on the structure substrate 3F, an input waveguide 20F, and the input waveguide 20F. A plurality of output waveguides 21F arranged in the opposite example with the semiconductor layer 1F interposed therebetween, and arranged between the output waveguide 21F and the semiconductor layer 1F, the input waveguides 20F are connected to the output waveguides 21F. And a branching filter 4F that branches according to the wavelength when light from the light propagates. The input waveguide 20F is joined to the two-photon absorption characteristic control waveguide 22F that propagates strong light on the front side of the semiconductor layer 1F, and signal light and control light are connected to the semiconductor layer 1F through the same waveguide. Is configured to propagate. With such a configuration, for example, light having a plurality of wavelengths is propagated from the input waveguide 3F, is incident on the semiconductor layer 1F and transmitted at the same time, and is branched according to the wavelength by the branching filter 4F. Only light in the range can be extracted. When this two-photon absorption switching element is used, only one kind of strong light for control is required, and there is an advantage that a plurality of wavelengths can be controlled with an extremely simple configuration. As another specific example, the input waveguide 20F and the control waveguide 22F are not joined, and an aspect like a directional coupler in which the input waveguide and the control waveguide are formed close to each other is also possible. is there. In addition, when a duplexer having no wavelength branching function is used, a lens 5G is used instead of a mode in which a band pass filter or the like is arranged in the middle of each output waveguide, or a waveguide 22F for controlling two-photon absorption characteristics. There is a mode in which light-to-light switching is enabled by irradiating the semiconductor layer 1G with control light having high light intensity through (see FIGS. 9 and 10).

The manufacturing method of the light-light switching element using the two-photon absorption characteristic which is the invention of the third group of the present application, ie, the two-photon absorption switching element
[24] The method for producing an optical-optical switching element according to [13], comprising a step of forming a semiconductor having a two-photon absorption characteristic on a substrate and a step of forming a waveguide.
[25] The light according to [15], comprising a step of laminating a lower clad layer, a semiconductor layer, and then an upper clad layer on a substrate, and a step of laminating a lower clad layer for a waveguide, a core layer, and then an upper clad layer. -Manufacturing method of an optical switching element.
[26] The light-optical switching according to [25], comprising a step of forming a semiconductor layer and a waveguide by using an epitaxy growth method on a semiconductor crystal wafer having two-photon absorption characteristics. Device manufacturing method.
[27] The process for forming a semiconductor layer having two-photon absorption characteristics uses either a molecular beam epitaxy method or a metal organic chemical deposition method. Method.
However, specific examples thereof are as follows. The semiconductor is as described above.

Hereinafter, a method for manufacturing the optical-optical switching element of FIG. 6 will be described with reference to FIG. In FIG. 11, center columns (1 ′) and (8 ′) show plan views, and left columns (1) to (8) show YY ′ line cross sections of the plan views, and right columns (1 ″). ˜ (8 ″) represents a cross section taken along line XX ′ of the plan view.

This manufacturing method is
(1) A lower clad layer 1LC made of Al _p Ga _1-p As (for a semiconductor having two-photon absorption characteristics) is formed on 3C on a structural substrate made of GaAs by, for example, chemical vapor deposition (CVD), On the lower cladding layer 1LC, a semiconductor core layer 1MC having a two-photon absorption characteristic made of In _x Ga _1-x As (x is larger than 0 and 0.53 or smaller) is formed by, for example, chemical vapor deposition (CVD). Forming an upper clad layer 1HC (for a semiconductor having a two-photon absorption characteristic) made of Al _p Ga _1-p As, for example, by chemical vapor deposition (CVD), for example, on the core layer 1MC; (2) A photoresist is applied on the upper clad layer 1HC (except for a substantially T-shaped waveguide formation planned area PC in a plan view) by, for example, a photolithography method, exposed, Developing to form a resist pattern layer 6C; (3) the upper cladding layer 1HC, the core layer 1MC, and the lower cladding in the waveguide formation region PC by an etching method such as a dry etching method or a wet etching method. (4) Al _q Ga _1-q As is formed on the resist pattern layer 6C and the substrate 1 in the waveguide formation planned area PC by, for example, chemical vapor deposition (CVD). A waveguide lower cladding layer 2LC made of Al _p Ga _1-p As is formed on the waveguide lower cladding layer 2LC by, for example, chemical vapor deposition (CVD). form and then on the waveguide core layer 2MC, for example, chemical vapor deposition upper waveguide consisting of _Al q _{Ga 1-q} As the chemical vapor deposition (CVD) A step of forming the lad layer 2HC (where 0 ≦ p <q ≦ 1), (5) a step of lifting off the resist pattern layer 6C and its upper layer portion 2C, and (6) an upper clad layer 2HD for a waveguide ( A step of forming a resist pattern layer 7C by applying, exposing and developing a photoresist, for example, by a photolithography method on the waveguide formation planned region PC) and on the semiconductor upper cladding layer 1HC having the two-photon absorption characteristics; 7) An upper cladding layer 1HC (for a semiconductor having two-photon absorption characteristics) that is not covered with the resist pattern layer 7C by an etching method such as dry etching or wet etching, and a semiconductor core layer 1MC having two-photon absorption characteristics And a step of etching and removing the lower cladding layer 1HC (for a semiconductor having two-photon absorption characteristics), and (8) the resist A step of removing the patterned layer 7C.

A method for manufacturing the optical-optical switching element of FIG. 7 will be described with reference to FIG. In FIG. 12, center columns (1 ′) and (8 ′) show plan views, and left columns (1) to (8) show YY ′ line cross sections of the plan view, and right columns (1 ″). ˜ (8 ″) represents a cross section taken along line XX ′ of the plan view.
This manufacturing method is
(1) On the structural substrate 3D made of GaAs, a lower cladding layer 1LD made of Al _p Ga _1-p As (for a semiconductor having two-photon absorption characteristics) is formed by, for example, chemical vapor deposition (CVD), On the lower cladding layer 1LD, a semiconductor core layer 1MD having a two-photon absorption characteristic made of In _x Ga _1-x As (x is larger than 0 and 0.53 or smaller) is formed by, for example, chemical vapor deposition (CVD). Forming and then forming an upper clad layer 1HD made of Al _p Ga _1-p As (for a semiconductor having two-photon absorption characteristics) on the core layer 1MD by, for example, chemical vapor deposition (CVD); (2) A photoresist is applied on the upper clad layer 1HD (excluding a waveguide formation planned region PD which is a substantially T-shaped vertical line in a plan view) by, for example, photolithography. A step of forming a resist pattern layer 6D by exposure and development; (3) the upper cladding layer 1HD, the core layer 1MD, and the core layer 1MD in the waveguide formation region PD by an etching method such as a dry etching method or a wet etching method; (4) Al _q Ga _{1− is} formed on the resist pattern layer 6D and the substrate 3D in the waveguide formation region PD by, for example, chemical vapor deposition (CVD). A waveguide lower clad layer 2LD made of _q As is formed, and a waveguide core made of Al _p Ga _1-p As is formed on the lower clad layer 2LD for waveguide by, for example, chemical vapor deposition (CVD). forming a layer 2MD, then on the waveguide core layer 2MD, made of _Al q _{Ga 1-q} As, for example, by chemical vapor deposition (CVD) guided A step of forming the upper cladding layer 2HD for use, (5) a step of lifting off the resist pattern layer 6D and its upper layer portion 2D, and (6) on the upper cladding layer 2HD for waveguide (waveguide formation scheduled region PD) and two photons A step of forming a resist pattern layer 7D by applying, exposing, and developing a photoresist on the upper cladding layer 1HD for semiconductor having absorption characteristics (however, a substantially T-shaped horizontal line in plan view) by, for example, photolithography. (7) Upper cladding layer 1HD (for a semiconductor having two-photon absorption characteristics) not covered with the resist pattern layer 7D by an etching method such as a dry etching method or a wet etching method, a semiconductor core having two-photon absorption characteristics Etching and removing the layer 1MD and the lower cladding layer 1LD (for semiconductors having two-photon absorption characteristics), (8) A step of removing the serial resist pattern layer 7D.

A method for manufacturing the optical-optical switching element of FIG. 8 will be described with reference to FIG. In FIG. 13, the central columns (1 ′) and (4 ′) are plan views, and the left columns (1) to (4) are cross-sectional views taken along line YY ′ of the plan view, and the right columns (1 ″). ˜ (4 ″) represents a cross section taken along line XX ′ of the plan view.
This manufacturing method is
(1) On a structural substrate 3E made of InP, it is made of In _y Al _1-y As (0 ≦ y ≦ 0.69, preferably y = 0.52), for example, by chemical vapor deposition (CVD). A lower cladding layer 1LE (for a semiconductor having a two-photon absorption characteristic) is formed, and In _x Ga _1-x As (x is larger than 0) is formed on the lower cladding layer 1LE by, for example, chemical vapor deposition (CVD). The semiconductor core layer 1ME having a two-photon absorption characteristic of 0.53 or less) is formed, and then In _y Al _1-y As (0 ≦ 0) is formed on the core layer 1ME by, for example, chemical vapor deposition (CVD). a step of forming an upper cladding layer 1HE (for a semiconductor having a two-photon absorption characteristic) consisting of y ≦ 0.69 (preferably y = 0.52), (2) a photolithograph, for example, on the upper cladding layer 1HE A step of applying, exposing and developing a photoresist by a method to form a resist pattern layer 6E having a substantially T-shape in plan view; (3) an etching method such as a dry etching method or a wet etching method; Etching and removing semiconductor upper cladding layer 1HE having two-photon absorption characteristics, semiconductor core layer 1ME having two-photon absorption characteristics, and semiconductor lower cladding layer 1LE having two-photon absorption characteristics not covered with layer 6E Then, (4) a step of removing the resist pattern layer 6E.

In each of the above manufacturing methods, each of the cladding layers for a semiconductor having the two-photon absorption characteristics, the semiconductor core layer having the two-photon absorption characteristics, each of the cladding layers for the waveguide and the core layer are compound semiconductor thin films. Is a compound semiconductor thin film crystal epitaxial film. The chemical vapor deposition method (CVD method), molecular beam epitaxy method (MBE method), metal organic chemical vapor deposition method (MOCVD method), metal organic chemical vapor deposition method (MOVPE method), etc. The conventional method such as the epitaxial crystal growth method is exemplified.

Hereinafter, in order to confirm the performance of the light-light switching element using the two-photon absorption characteristics according to the second embodiment of the present invention, that is, the two-photon absorption switching element, a compound semiconductor layer is actually formed, and the characteristics are It was measured. This will be specifically described below.

In this example, a compound semiconductor layer was formed on a structural substrate using a solid source molecular beam epitaxial method.
More specifically, a compound semiconductor layer was formed based on the conditions in Table 2 below. In both cases, the growth rate was 1 μm / h, and the degree of vacuum during growth was 2 × 10 ⁻⁶ Torr.

For each compound semiconductor layer created above, first, the excitation intensity density dependence of the light transmittance change was measured. FIG. 14 shows this measurement system.

In this measurement system, a laser light pulse is introduced into a sample (compound semiconductor layer) through a variable ND, a glass plate, and an objective lens through a single mode optical fiber, and the output light is measured with an optical power meter. In addition, the reflected light from a glass plate is measured with the optical power meter as a reference.

Similarly, the response speed of two-photon absorption was determined for each of the semiconductor layers by the pump / probe method, which is a conventional method. FIG. 15 shows this measurement system.

The measurement results by these measurement systems are shown in FIGS. In the following ΔαL, α is generally a light absorption coefficient. However, if L (the thickness of the sample) is the same, αL can be said to be a light absorption coefficient in a relative sense. This is called a change in coefficient.

First, FIG. 16A shows a change ΔαL of the light absorption coefficient when the sample number 1 (InP) is measured as the semiconductor layer 2 and the excitation light intensity density is changed. . The horizontal axis represents the excitation light intensity density (μJ / cm ² ), and the vertical axis represents the change ΔαL of the light absorption coefficient. DerutaarufaL the excitation light intensity density _{I 0,} the transmitted light intensity density is taken as I, are intended to be calculated in _{ΔαL = -ln (I / I 0} ). As a result, in the case of a compound semiconductor layer made of InP, it is confirmed that ΔαL increases from 1630 nm to 1700 nm as the excitation light intensity density increases. -It turns out that it can fully be used as an optical switching element. FIG. 16B shows the transmittance change ΔT / T when the sample number 1 (InP) is measured as the semiconductor layer 2 and the delay time is changed. The horizontal axis represents the delay time (ps), and the vertical axis represents the transmittance change ΔT / T. The light intensity of the signal light is 0.9 μJ / cm ² and the light intensity of the control light is 190 μJ / cm ² . In FIG. 16A, only the data at 1630 nm to 1700 nm is shown, but FIG. 16B shows the response speed in the range of 1390 to 1650 nm. The half width of the response speed is 0.25 ps, which is a very fast response characteristic. Therefore, it is well understood that a two-photon absorption characteristic sufficient as an optical-optical switching element appears in the normal optical communication wavelength range of 1390 to 1700 nm.

In FIG. 16B, the delay time is negative (the signal light is ahead of the control light and the sample is before the control light) around the time origin (delay time 0 ps; the time when the signal light and the control light are completely overlapped in time). The waveform in the time domain in which the time domain and the delay time are positive (when the signal light is incident on the sample after the control light) is symmetrical. There is no slow response component as in Patent Document 3 in the time region where the delay time is positive. In general, a waveform with a negative delay time shows a fast response waveform that is the same as a laser waveform even in a system with a pattern effect or a slow recovery speed, but they have a slow response component in the positive delay time region. Appears in the waveform and is not symmetrical about the time origin. From the above, it can be seen that there is no pattern effect in this embodiment.

Next, FIG. 17A shows the case where measurement is performed using In _0.53 Ga _0.47 As of the sample number 3 as the semiconductor layer 2, and the absorption coefficient when the excitation light intensity density is changed. The change ΔαL in FIG. Except for the compound semiconductor material, it is substantially the same as FIG. 15A.

According to FIG. 17A, like InP, an increase in ΔαL accompanying an increase in excitation light intensity density can be confirmed at 1630 nm to 1700 nm, and In _0.53 Ga _0.47 As has excellent two-photon absorption characteristics. It was confirmed that

FIG. 17B shows a case where the sample number 3 (In _0.53 Ga _0.47 As) is measured as the semiconductor layer 2 and the transmittance change ΔT / T when the delay time is changed. Indicates. The horizontal axis represents the delay time (ps), and the vertical axis represents the transmittance change ΔT / T. The light intensity of the signal light is 0.9 μJ / cm ² and the control light intensity is 190 μJ / cm ² . According to FIG. 17B, the full width at half maximum at the peak of the response is 0.25 ps, and it was confirmed that a high-speed response can be realized. Of course, as in FIGS. 16A and 16B, it can be seen from FIGS. 17A and 17B that the two-photon absorption characteristics are well exhibited at 1390 nm to 1700 nm, which is a normal optical communication wavelength region. It turned out that it can use suitably as a light-light switching element in the range of 1390 nm-1700 nm.

In FIG. 17B, at the time origin, the delay time is negative (the signal light is earlier than the control light), centering on (delay time 0 ps; time when the signal light and the control light are completely overlapped in time). The waveform in the time domain when the light is incident on the sample and the delay time are positive (when the signal light is incident on the sample after the control light) are symmetrical. There is no slow response component as in Patent Document 3 in the time region where the delay time is positive. In general, a waveform with a negative delay time shows a fast response waveform that is the same as a laser waveform even in a system with a pattern effect or a slow recovery speed, but they have a slow response component in the positive delay time region. Appears in the waveform and is not symmetrical about the time origin. From the above, it can be seen that there is no pattern effect in this embodiment.

Therefore, in order to confirm the desirable range of x in In _x Ga _1-x As, the absorption coefficient when the excitation light intensity density is changed for a compound semiconductor in which the value of x is variously changed in the range of 0 to 0.53. The change ΔαL was examined. The result is shown in FIG. The compound semiconductor materials with various values of x correspond to sample numbers 2 to 6 in Table 1 above. The wavelength of the excitation light is 1700 nm.

According to FIG. 18, almost all except GaAs show that ΔαL increases as the excitation light intensity density increases, but GaAs does not show an increase but rather tends to decrease. This indicates that even when strong light is applied to GaAs, light is not blocked, indicating that the semiconductor layer cannot function as a two-photon absorption characteristic. Therefore, when functioning as a two-photon absorption switching element, it was confirmed that _{x of} In _x Ga _1-x As exhibited a two-photon absorption characteristic in a range larger than 0 and smaller than 0.53. This shows the same desired range as the basic absorption edge described above. Here, the lower limit of x is preferably 0.05.

Next, the change ΔαL of the absorption coefficient when the excitation light intensity density was changed was measured for the compound semiconductor doped with the dopant. Sample numbers 1 to 3 shown in Table 2 were used as samples. The measurement results are shown in FIG. In FIG. 19, although it is indicated as an InGaAs bulk thin film, it is a Be-doped In _0.53 Ga _0.47 As bulk thin film.

According to this measurement result, as in FIG. 18, in the Cr-doped GaAs substrate, ΔαL hardly increases even when the excitation light intensity density increases, whereas the Fe-doped InP substrate or Be-doped In _0.53 Ga _0. It was confirmed that the _.47 As bulk thin film sufficiently showed the two-photon absorption characteristics.

As described above, it is possible to obtain a sub-picosecond operating speed in the optical communication wavelength region by using a semiconductor having two-photon absorption characteristics, particularly the compound semiconductor, as a switch part of an optical-optical switching element. I understood.

Industrial applicability

The optical-optical switching method and optical-optical switching element of the present invention are useful for optical gates, optical modulators, wavelength converters, optical sampling oscilloscopes, routers, and the like. Furthermore, even this single two-photon absorption switching element can be used as a wavelength-division multiplexing (WDM) switching element for optical communication. If the required number of channels are used in parallel, optical time-division multiplexing (OTDM) Since it can be used as a switching element of the system, it can be used as a switching element for OTDM-WDM communication.

Claims (24)

In a light-light switching method in which signal light is turned on / off with control light,
_{In x Ga 1-x As (} x is 0.8 or less larger than _{0), In y Al 1 -y} As (y is 0 or 0.82 or _{less), In z Ga 1-z} N (z 0.4 1 or more) and In _(1-ab) Ga _a Al _b As _(1-c) N _c (a, b, a + b is 0 or more and 1 or less, c is greater than 0 and less than 1, or a, b , A + b is greater than 0 and less than 1, and c is 0 or more and 1 or less, except for the case where both compositions overlap each other, and a compound semiconductor having a two-photon absorption characteristic (however, quantum well, quantum A thin wire, a quantum effect structure such as a quantum dot and a semiconductor periodic structure are not irradiated with signal light with low light intensity, and control light with high light intensity is irradiated intermittently. The two-photon absorption generated during irradiation blocks the signal light from passing through, and the control light And wherein the passing the signal light at the time of non-irradiation, light - optical switching method. _{I n x Ga 1-x As} x in is 0.53 or less greater than _{0, In y Al 1-y} y in As is 0 or more 0.69 or less, in _In z _{Ga 1-z} N 2. The optical-optical switching method according to claim 1 , wherein z is 0.4 to 0.75. The signal light and the control light are expressed by the equation [hc / λ _signal + hc / λ _control ≧ hc / λ _gap (where h: Planck's constant, c: speed of light, λ _signal : wavelength of signal light, λ _control : 3. The optical-optical switching method according to claim 1 , wherein the relationship of the wavelength of control light, λ _gap : wavelength of the fundamental absorption edge of the compound semiconductor)] is satisfied. 4. The light-light switching method according to claim 1, wherein the compound semiconductor is a single crystal. The optical-optical switching method according to claim 1, wherein the compound semiconductor is a bulk semiconductor. _{In x Ga 1-x As (} x is 0.8 or less larger than _{0), In y Al 1 -y} As (y is 0 or 0.82 or _{less), In z Ga 1-z} N (z 0.4 1 or more) and In _(1-ab) Ga _a Al _b As _(1-c) N _c (a, b, a + b is 0 or more and 1 or less, c is greater than 0 and less than 1, or a, b , A + b is greater than 0 and less than 1, and c is 0 or more and 1 or less, except for the case where both compositions overlap each other, and a compound semiconductor having a two-photon absorption characteristic (however, quantum well, quantum A structure having a quantum effect such as a thin wire or a quantum dot and a semiconductor periodic structure) , a propagation means for control light and signal light input to the compound semiconductor, and a propagation means for signal light transmitted through the semiconductor An optical-optical switching element , which is characterized. _{I n x Ga 1-x As} x in is 0.53 or less greater than _{0, In y Al 1-y} y in As is 0 or more 0.69 or less, in _In z _{Ga 1-z} N The optical-optical switching element according to claim 6 , wherein z of said light is 0.4 or more and 0.75 or less . 8. The optical-optical switching element according to claim 6, wherein the compound semiconductor is a single crystal. The optical-optical switching element according to any one of claims 6 to 8, wherein the compound semiconductor is a bulk semiconductor. A propagation means waveguides with propagation means of the control light the signal light, characterized in that it is connected to the compound semiconductor, the light of any one of claims 6 to claim 9 - light Switching element. An input waveguide of the signal light and the input waveguide of the control light, and an output waveguide of said signal light, characterized in that on opposite position across said compound semiconductor, according to claim 10, wherein Optical-optical switching element. An input waveguide of the signal light and the output waveguide of the signal light is in the opposite position across said compound semiconductor, the input waveguide of said control light, an input waveguide of the signal light characterized in that it is connected to the compound semiconductor to intersect a line connecting the output waveguide of the signal light, according to claim 10, wherein the light - the light switching element. The compound semiconductor, characterized in that it is clamped or surrounded by the cladding refractive index is less than that, according to claim 11 or claim 12, wherein the light - the light switching element. Each waveguide and said compound semiconductor, characterized in that it is formed on the substrate, light according to claim 11 or claim 12, wherein - the light switching element. The compound semiconductor, characterized in that it is clamped or surrounded by the cladding refractive index is less than that, the light of claim 14, wherein - the light switching element. The compound semiconductor, the clad, and the waveguide are both layered. The compound semiconductor, the clad is a lower clad layer, the compound semiconductor layer, and an upper clad layer, and the waveguide is a lower clad layer and a core layer. , the order of the upper cladding layer, characterized in that it is formed on the substrate, light according to claim 15, wherein - the light switching element. 13. The optical-optical switching element according to claim 11 , wherein the compound semiconductor is square or rectangular in plan view. Said compound semiconductor is substantially T-shaped in plan view, the output waveguide between the input waveguide of the signal light the signal light, are connected to the opposite position across the horizontal portion of the substantially T-, wherein the waveguide for said control light is coupled to the lower end of a vertical line of substantially T-, according to claim 10, wherein the light - the light switching element. The distance between the pair of waveguides, characterized in that in the range of 100Nm～500myuemu, light according to claim 11 or claim 12, wherein - the light switching element. Characterized by comprising the step of forming a step and the waveguide forming the compound semiconductor on the substrate, light according to claim 14, wherein - the method for manufacturing an optical switching element. On a substrate, a lower clad layer, the compound semiconductor layer, and then the lower cladding layer for process and waveguide laminating an upper cladding layer, a core layer, and then characterized by comprising the step of laminating the upper cladding layer, wherein Item 17. A method for producing an optical-optical switching element according to Item 16. 23. The light of claim 21 , comprising a step of forming the compound semiconductor layer and a step of forming the waveguide on a compound semiconductor crystal wafer having two-photon absorption characteristics using an epitaxy growth method. Manufacturing method of optical switching element. Process is characterized by using molecular beam epitaxy or metal organic chemical deposition method, light according to claim 22, wherein forming the compound semiconductor layer - the manufacturing method of the optical switching element. (1) Forming the compound semiconductor lower cladding layer on a substrate, forming the compound semiconductor core layer having a refractive index larger than that of the cladding layer and having two-photon absorption characteristics on the lower cladding layer, and then forming the core layer A step of forming an upper clad layer for a compound semiconductor on the upper surface; (2) a step of forming a resist layer on the upper clad layer (excluding a region where a substantially T-shaped waveguide is to be formed in plan view); (3) a step of etching and removing the upper clad layer, the core layer, and the lower clad layer in the region where the waveguide is to be formed, and (4) for the waveguide on the resist layer and the substrate in the region where the waveguide is to be formed. Forming a lower cladding layer, forming a waveguide core layer on the waveguide lower cladding layer, and then forming a waveguide upper cladding layer on the waveguide core layer; (5) the resist Layer and its upper layer Futoofu to step (6) forming a resist layer in a substantially T-shaped waveguide region and the compound semiconductor for the upper clad layer in a plan view, (7) not covered with the resist layer and the compound semiconductor 13. The method according to claim 12, comprising: a step of etching and removing the upper clad layer for use, the compound semiconductor core layer and the lower clad layer for compound semiconductor, and (8) a step of removing the resist layer. The method for manufacturing an optical-optical switching element according to claim 17.

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