JP5336534B2 - Optical resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure the Q value of an optical resonator using a one-dimensional photonic crystal having a bar-like structure, and to minimize temperature rise near the center by decreasing thermal resistance of the resonator. <P>SOLUTION: A side slab (105) of finite width having a high heat conductivity and thinner than a one-dimensional photonic crystal (101) having a bar-like structure composed of a high refractive index material (Si, or the like), arranged periodically with a columnar or a polygonal prism structure (107) composed of a low refractive index material (air, or the like), is arranged in contact with the one-dimensional photonic crystal, and a thermal diffusion structure (106) having a high heat conductivity is arranged on the outside of the side slab. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to an optical resonator, and more particularly to an optical resonator that suppresses a temperature rise near the center.

  2. Description of the Related Art Semiconductor laser elements that operate using a stimulated emission phenomenon generated in a semiconductor material using a semiconductor as a material are widely used in various industries. A semiconductor laser (hereinafter referred to as a photonic crystal laser) in which an optical resonator is formed of a photonic band gap material can have a much smaller element size than a conventional optical resonator. Improvement of the resonator structure has progressed, making it possible to confine light effectively in the volume of the third power of the wavelength of light (for optical communication, about 1.55 micrometers), and at the same time to the loss of light and the waveguide It is possible to increase the Q value, which represents the small amount of leakage due to spillage, from tens of thousands to about one million. A laser that is more compact than a vertical cavity surface emitting laser (VCSEL) that is known to have a low threshold in terms of area can be realized.

  Since the resonator Q value is equal to or greater than that of a conventional laser and the volume is smaller, the amount of electrons and holes (hereinafter referred to as carriers) necessary for laser oscillation, and the oscillation threshold (in the case of output and current injection operations) Current) becomes smaller. In principle, the oscillation threshold value can be made smaller than that of the surface emitting laser as long as the carrier is efficiently provided to the resonator. The threshold current is determined not only by the optical resonator structure and element temperature, but also by the current confinement structure and the structure and characteristics of the electronic element such as a resistor and an electrode. Is not included in the scope).

  In the photonic crystal laser, the threshold of pumping light power becomes extremely small under the condition where carriers are supplied by light. Assuming photoexcitation, there is a method of selectively selecting the position of the active layer by a selective growth technique as a method for efficiently concentrating optical carriers in the resonator portion. The active layer can be designed to absorb and amplify light while confining carriers therein. Only the active layer portion can absorb the excitation light by selecting the operating wavelength, the excitation wavelength, and the material. In addition, if quantum dots and quantum wells are used in the active layer, the laser will be highly efficient. The threshold power of the laser has dropped to at least the μW level. In addition to lasers, principle verification or verification has been performed in the configuration of optical elements such as modulators, optical switches, and optical memories using photonic crystal resonators. The inventors have also reported that a modulator and an optical switch have been realized in the Si photonic crystal resonator by a high-speed optical bistable phenomenon due to the carrier plasma effect. Furthermore, we succeeded in realizing a long memory time by changing the material and structure to an InGaAsP quantum well active layer having a larger carrier plasma effect and an InP photonic crystal that generates less heat due to surface recombination.

  The advantage of the photonic crystal resonator in the modulator / optical switch is that it operates at a very low power as a result of the enhancement of the carrier plasma effect by the resonator Q value and the small confinement volume. These low power operations are also realized by utilizing the modulation of the carrier (plasma) by light. In recent years, not only photonic crystals but also ring resonators composed of high-refractive-index thin-wire waveguides with a sub-micron cross-sectional dimension have been reduced in power due to the enhancement effect of small volume resonators and high Q values. .

Eiichi Kuramochi et al., "Ultrahigh-Q one-dimensional photonic crystal nanocavities with modulated mode-gap barriers on SiO2 claddings and on air claddings," OPTICS EXPRESS, Vol.18, No.15, pp.15859-15869, 2010 July 12, Internet <http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-15-15859> LD. Haret et al., "Extremely low power optical bistability in silicon demonstrated using 1D photonic crystal nanocavity," OPTICS EXPRESS, Vol.17, No.23, pp.21108-21117, November 4, 2009, Internet <http : //www.opticsinfobase.org/oe/abstract.cfm? URI = oe-17-23-21108> B. Schmidt et al., "Compact electro-optic modulator on silicon-on-insulator substrates using cavities with ultra-small modal volumes," OPTICS EXPRESS, Vol.15, No.6, pp3140-3148, March 19, 2007 Japan, Internet <http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-6-3140> Y. Tanaka et al., "Investigation of point-defect cavity formed in two-dimensional photonic crystal slab with one-sided dielectric cladding," Applied Physics Letters, Vol. 88, 011112, June 2006, Internet <http: / /apl.aip.org/resource/1/applab/v88/i1/p011112_s1?isAuthorized=no>

  It is desirable to electrically drive an optical element such as a laser switch. In the case of electric drive, a small and inexpensive device can be configured by combining with a universal semiconductor electronic chip, and it can be driven with low power consumption, whereas in the case of optical drive, a laser light source, a light modulation device, etc. This is because a light driving device is required separately, so that practicality is limited. Photonic crystal resonator-based optical devices have already achieved excellent performance under light excitation and drive conditions, while some surface-emitting photonic crystal lasers (horizontal direction) The fact that good performance is not obtained except for light confinement indicates a high degree of difficulty.

Here, the target is limited to a photonic crystal nanoresonator (hereinafter referred to as a nanoresonator) that confines light in a minute volume having a scale of several times the wavelength or less. The definition of nanocavity is that the Q value (intrinsic value ignoring coupling with the outside: excluding the decrease due to the gain mechanism of the active layer) is 10,000 or more, and the confined mode volume is 3 (λ / n) ³ ( λ is a wavelength and n is a refractive index) or less. Such a resonator is difficult to realize by a principle other than the photonic crystal. In nanoresonators, in comparison with larger resonators, it is possible in principle to significantly reduce chip volume and area and to greatly reduce operating power. Energy conversion is expected.

  In this application, the problem in the one-dimensional rod-like photonic crystal (hereinafter referred to as 1D crystal) is taken up. Conventional nanocavities have been realized mainly in two-dimensional slab type photonic crystals (hereinafter referred to as 2D crystals). 1D crystal resonators are simpler and easier to process than 2D crystal resonators, and have high compatibility with nano-optical waveguides that are being developed as silicon photonics, especially on silicon on insulator (SOI) substrate platforms. However, it has not received much attention due to insufficient performance such as Q value.

  With regard to 1D crystal resonators, the inventors have recently made appropriate designs based on the principle of confining light by locally modulating the spacing and radius of the holes near the center of the resonator and generating a mode gap at the waveguide mode end. As a result, it was clarified that the same performance as that of the 2D crystal resonator can be achieved (see Non-Patent Document 1). On the other hand, in the 1D crystal resonator, it has been clarified that the thermal resistance becomes very large and heat is easily collected at the center of the resonator (Non-patent Document 2). In order to introduce an effective waveguide mode in the 1D crystal, it is necessary to keep the refractive index of the material surrounding the rod-shaped portion sufficiently lower than that of the rod-shaped portion. For example, the low refractive index portion is made of a material having low thermal conductivity such as air, dielectric, or polymer. The conventional design has a good heat conductor only in a thin rod-shaped portion, and there is no other way for heat and the thermal resistance is increased.

  An increase in thermal resistance causes an increase in element temperature in an element that generates heat in the resonator portion. In a light emitting element such as a laser, it is necessary to dispose a gain medium in the resonator portion and supply carriers to the gain medium. Some of the carriers do not contribute to light emission, cause non-radiative recombination, and generate heat. Even in the non-light emitting element, part of the carriers supplied for refractive index modulation similarly generates heat. Particularly in a photonic crystal, an etching surface existing on the side wall of a hole constituting the crystal supplies a non-radiative recombination center and easily generates heat. In electric drive, Joule heat generation due to electric resistance is also a problem. In the case of a semiconductor laser, in principle, the oscillation threshold increases as the element temperature increases. In optical switches, modulation, and memory devices that use optical nonlinear effects (including optical bistable phenomena) due to the carrier plasma effect, it becomes difficult to control the resonator wavelength by refractive index modulation, which is the operating principle, due to wavelength changes due to temperature rise. There's a problem.

  Thus, a certain amount of heat generation is unavoidable in the 1D crystal resonator element that is electrically driven. Therefore, in order to realize a high-performance optical element, it is necessary to reduce the thermal resistance and improve the exhaust heat performance. However, a countermeasure for increasing the thermal resistance in the conventional 1D crystal resonator has not been considered.

  Although the increase in thermal resistance has been taken up as a problem of conventional 1D crystal resonators, another important thermal characteristic is thermal relaxation time. This is the time constant when heat is exponentially relaxed. General semiconductor structures have an exponential thermal response due to the nature of the heat conduction equation. We have reported that the experimental relaxation time is about 100 ns in a silicon 2D crystal resonator. Using this value as a reference, a conventional 1D and 2D crystal resonator was used, and numerical analysis was performed using the commercial software Comsol. The result was published in Non-Patent Document 2. In the 2D crystal resonator, the calculated value of the thermal resistance almost coincided with the experimental value, and it was confirmed that the calculated result was reliable. It should be noted that in the 1D crystal resonator having a large thermal resistance, the thermal relaxation time also increased significantly, which is several times that of the 2D crystal resonator. An increase in the thermal relaxation time slows down the response speed of an optical element such as an optical switch element utilizing the thermo-optic effect, and thus becomes an obstacle to realizing a high-speed optical element. Thus, the conventional 1D crystal resonator also has a problem in terms of thermal relaxation time.

  The present invention has been made in view of such a problem, and an object of the present invention is to add a side slab and a thermal diffusion structure to the 1D crystal resonator element, thereby increasing the temperature near the center of the resonator. An object of the present invention is to provide an optical resonator that suppresses the rise.

  In order to solve the above-described problems, an optical resonator according to the present application includes a one-dimensional photonic crystal having a rod-like structure made of a high-refractive index material in which cylindrical or polygonal column structures made of a low-refractive index material are periodically arranged. A rod-like structure), a low refractive index medium surrounding the rod-like structure, a side slab, and a heat diffusion structure. The side slab has high thermal conductivity, is thinner than the rod-like structure, and has a finite width. The thermal diffusion structure has high thermal conductivity, and is disposed at a position where the side slab is sandwiched between the thermal diffusion structure and the rod-shaped structure.

The invention according to claim 1 is an optical resonator, a one-dimensional photonic crystal having a rod-like structure made of a high-refractive index medium in which a cylindrical or polygonal column structure made of a low-refractive index material is periodically arranged. One or a plurality of side slabs made of a material having high thermal conductivity, which is disposed in contact with the one-dimensional photonic crystal, which is thinner than the one-dimensional photonic crystal and has a finite width, and the side slab And a low-refractive index medium surrounding the one-dimensional photonic crystal, and the thermal diffusion structure is made of a semiconductor material. And a metal layer made of a metal having a higher thermal conductivity than that of the semiconductor material .

According to a second aspect of the present invention, in the optical resonator according to the first aspect , the high refractive index medium, the side slab, and the semiconductor material are silicon, and the low refractive index surrounding the one-dimensional photonic crystal. The low refractive index material of the medium and the cylindrical or polygonal column structure is a material having a refractive index lower than that of air or a silicon oxide film, and the thickness of the thermal diffusion structure is thicker than the side slab. Features.

According to a third aspect of the present invention, in the optical resonator according to the first aspect , the high refractive index medium, the side slab, and the semiconductor material are InP, and the low refractive index surrounding the one-dimensional photonic crystal. The refractive index medium and the low refractive index material of the cylindrical or polygonal column structure are materials having a refractive index equal to or lower than that of air or a silicon oxide film, and the thermal diffusion structure is thicker than the side slab. And

According to a fourth aspect of the present invention, in the optical resonator according to the third aspect of the present invention, the optical resonator further includes a heat transfer body made of a material having higher thermal conductivity than InP or InP manufactured on a semiconductor substrate, and the thermal diffusion The structure is arranged in contact with the heat transfer body.

The invention according to claim 5 is an optical resonator, a one-dimensional photonic crystal having a rod-like structure made of a high-refractive index medium in which a cylindrical or polygonal column structure made of a low-refractive index material is periodically arranged. One or a plurality of side slabs made of a material having high thermal conductivity, which is disposed in contact with the one-dimensional photonic crystal, which is thinner than the one-dimensional photonic crystal and has a finite width, and the side slab And a low-refractive index medium surrounding the one-dimensional photonic crystal, and the high-refractive index medium is made of InP. consists of a layer serving and of InGaAsP layers, said side slab is composed of a layer of air between the two layers and the two layers of InP, the thermal diffusion structure, InP Tona And a low refractive index medium surrounding the one-dimensional photonic crystal and a low refractive index material having a cylindrical or polygonal column structure have a refractive index lower than that of air or a silicon oxide film. The heat diffusion structure is thicker than the side slab.

  As described above, according to the present invention, in the 1D crystal optical nanoresonator, it is possible to reduce the resonator thermal resistance while maintaining a necessary and sufficient Q value, and to suppress the temperature rise near the center of the resonator. Become. By implementing the present invention, it is possible to improve the characteristics of optical elements such as lasers, optical switches, and optical memories that have a heat generation process such as non-radiative recombination and Joule heat during operation and whose performance is limited by temperature rise. Become. In addition, when the element is electrically driven, the side slab can be used as a current conducting wire, so that the compatibility with the electric drive is higher than many conventional 1D crystal resonator designs.

  The structure of the optical resonator of the present application is also effective for an optical resonator in a hollow silicon thin film provided on an air layer. However, particularly in the case of an SOI structure with a silicon oxide film, it is compatible with silicon photonics. There are advantages such that the manufacturing process can be simplified, the structural vulnerability associated with the hollow structure can be eliminated, and the like. In view of the fact that it is difficult to realize a high-performance 2D crystal resonator with an oxide film (see Non-Patent Document 4), the present invention is extremely useful as a base of optoelectronic elements in silicon photonics.

  In the present invention, a method of separating and introducing a side slab portion that performs light confinement and a heat diffusion structure having high heat exhaust performance is adopted. As shown in the second verification example below, this method is particularly effective in a medium having a relatively low thermal conductivity such as InP.

  The optical resonator of the present invention is based on a 1D crystal, and is less susceptible to the vertical asymmetry of the structure compared to a 2D crystal resonator. The position of the side slab is not below the 1D crystal part as shown in FIG. It can be said that it is excellent in adaptability to various processing technologies for realizing resonators and optical elements. Similarly, since it is difficult to be affected by the vertical asymmetry, the upper and lower low refractive index media may be different as in the example of FIG. Therefore, it has excellent compatibility with various materials.

It is a sketch of the basic composition of the optical resonator which concerns on this invention. It is sectional drawing of the optical resonator of 1st embodiment of this invention. It is a figure which shows the calculation of Q value and the experimental result of the optical resonator of 1st embodiment of this invention. It is a figure which shows the calculation of the thermal resistance of the optical resonator of 1st embodiment of this invention, and an experimental result. It is a figure which shows the calculation result of the thermal relaxation time of the optical resonator of 1st embodiment of this invention. It is sectional drawing of the optical resonator of 2nd embodiment of this invention. It is a figure which shows the calculation of the thermal resistance of the optical resonator of 2nd embodiment of this invention, and an experimental result. It is a figure which shows the calculation result of the thermal relaxation time of the optical resonator of 2nd embodiment of this invention. It is sectional drawing of the optical resonator of 3rd embodiment of this invention. It is sectional drawing of the optical resonator of 4th embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As described above, according to the present application, a rod-shaped structure made of a high-refractive index material, a low-refractive index medium surrounding the same, a side slab having a high thermal conductivity, thinner than the rod-shaped structure, and having a finite width, There is provided an optical resonator additionally provided with a heat diffusion structure having a high thermal conductivity disposed on the outside thereof. The rod-like structure is a 1D crystal (one-dimensional rod-like photonic crystal) made of a high-refractive index material periodically arranged in a cylindrical or polygonal column structure made of a low-refractive index material.

  FIG. 1 shows a sketch of the basic configuration of an optical resonator according to the present invention. The optical resonator shown in FIG. 1 has a rod-like structure 101 made of a high refractive index material, a side slab 105 and a thermal diffusion structure 106 with high thermal conductivity on a substrate 104. The optical resonator shown in FIG. 1 has a low refractive index medium 103 between a substrate 104, a rod-shaped structure 101, and a side slab 105, and a low-refractive index medium 102 is disposed on the upper portion of the rod-shaped structure 101. . That is, the low refractive index medium is arranged so as to surround the rod-like structure 101. A cylindrical or polygonal column structure made of a low refractive index material is periodically arranged inside the rod-shaped structure 101 which is a 1D crystal having a rod-shaped structure. A low refractive index medium 103 may be disposed between the thermal diffusion structure 106 and the substrate 104.

  In FIG. 1, the side slab 105 functions as a heat exhaust path that transfers heat in the rod-like structure 101 that is a 1D crystal to the outside. Even if the material has a high refractive index, the side slab has a low effective refractive index combined with the upper and lower low-refractive index media 102 and 103 by reducing the thickness sh (the length in the y direction in the figure, hereinafter the same). Therefore, a sufficient light confinement effect can be obtained for the rod-like structure in the horizontal direction (x direction in the figure). A realistic side slab material that has high thermal conductivity and does not hinder light confinement in the resonator is limited to semiconductors such as silicon and InP as well as the rod-shaped structure.

  Although the side slab structure itself has been proposed as a method for realizing an electrical pin structure (see Non-Patent Document 3), no consideration has been given to heat dissipation. Further, a design guideline for keeping the resonator Q value high while ensuring heat dissipation has not been presented. In the present invention, a finite width sw (length in the x direction in the figure, the same applies hereinafter) is set in the side slab. When sh is thin and the sw width is wide, the thermal resistance increases. Conversely, when sh is thick and sw is narrow, the optical confinement in the horizontal direction is weakened, and the resonator Q value is lowered. According to the present invention, it is possible to significantly improve the heat dissipation of the 1D crystal resonator with respect to the conventional design while ensuring the optical resonator performance by optimizing sh and sw as in the following examination example. Become.

  The point of the present invention is to separate the side slab 105 that performs light confinement from the heat diffusion structure 106 outside thereof. By separating the thermal diffusion structure 106 from the side slab 105, an optimum structure for thermal diffusion can be pursued regardless of the optical resonator design. Specifically, the thickness of the semiconductor structure can be increased. It is also possible to dispose a metal film having high thermal conductivity. In the case of an optical resonator arranged on a semiconductor substrate, it is also effective in some circumstances to directly connect the heat diffusion structure to the substrate.

<First embodiment>
Below, the result of having proved the effectiveness of this invention by numerical simulation and experiment is shown.
FIG. 2 shows the configuration of the optical resonator of the first verification example, and FIGS. 3 to 5 show the verification results. In the optical resonator shown in FIG. 2, the 1D crystal 201, the side slab 205, and the thermal diffusion structure 206 are made of a silicon thin film. These are disposed on the silicon substrate 204 via a silicon oxide film layer (low refractive index medium) 203. This structure is aligned with the SOI substrate (203, 204). The 1D crystal 201 and the thermal diffusion structure 206 can be realized using the SOI layer as it is. The upper low refractive index medium 202 is air, and the crystal hole 207 and the side slab 205 made of air can be processed by dry etching the SOI layer from the upper surface. The resonator design is based on a mode gap 1D crystal resonator (cylindrical hole ladder type) with a very high Q value disclosed in Non-Patent Document 1, based on a lattice constant α of 350 nm, a hole radius of reference r0 = 105 nm, and a modulation parameter. Was set to m = 17. The height of the 1D crystal 201 and the thermal diffusion structure 206 was 210 nm, the width of the 1D crystal 201 was 580 nm, and the thickness of the silicon oxide film layer 203 was 2 μm. The optical resonator performance of this structure was evaluated by numerical analysis by a three-dimensional finite difference time domain method (FDTD) and measurement of a sample obtained by processing an SOI substrate by electron beam lithography. In the calculation, the refractive indexes of silicon, silicon oxide film, and air were set to 3.4, 1.46, and 1.0, respectively.

FIG. 3 shows the dependence of the resonator Q value on the height sh of the side slab. Here, the width sw of the side slab was set to 1.2 μm. Although the Q value decreases with increasing sh, the calculation confirmed that the Q value exceeded 1 million even at sh = 60 nm, and the experiment also confirmed that the Q value exceeded 100,000 at sh = 50 nm. The Q value of 100,000 is sufficient for normal optical device applications. The mode volume was a value less than 1 (λ / n) ³ in the FDTD calculation result. It has been demonstrated that a high-performance 1D crystal resonator can be realized in the structure of FIG.

  Next, the thermal resistance and thermal relaxation time of this structure were examined. Using the same model as in Non-Patent Document 2, analysis was performed with commercial software Comsol. In the analysis, the thermal conductivities of silicon and silicon oxide film were 163 and 1.5 (unit: W / m / K), respectively, and air was a thermal insulator. FIG. 4 shows the sh dependence of the thermal resistance. The thermal resistance decreased monotonously as the side slab became thicker. When they were compared with the sh dependence of the thermal resistance obtained experimentally from the measurement results of the thermo-optical characteristics of the resonator sample, they agreed well. From this, it was clarified that the thermal resistance can be improved by providing appropriate sh and sw by this structure. In this structure, since the silicon oxide film is used as the low refractive index medium, the thermal resistivity without the side slab remains at a slightly higher level. When the low refractive index medium examined in Non-Patent Document 2 is all air, the thermal resistance is further increased by a factor of five.

  Next, the calculation result regarding the thermal relaxation time is shown in FIG. This also showed sh dependence similar to thermal resistance, and it was shown that the thermal response speed can be accelerated by the side slab. In any case, it was found that the improvement effect by adopting the side slab was several times at maximum when sw = 1.2 μm, and several tens of times when the silicon oxide film 203 was removed and replaced with an air layer compared to non-adoption. . FIG. 5 shows that the relaxation time is shortened as the sw is narrowed. Although the setting of sh and sw is also limited by the optical resonator performance, a sufficiently large thermal performance improvement is obtained in sh and sw in the range of operating as a useful nanoresonator shown in FIG.

  The feature of silicon is that it has a high thermal conductivity approaching that of metal. Therefore, sufficient heat dissipation performance can be obtained even with a relatively thin (210 nm) silicon thin film employed in this structure as the thermal diffusion structure. That is, as compared with the design in which the side slab portion as shown in Non-Patent Document 3 is not limited and the thickness of the thermal diffusion structure is the same as sh, the thermal relaxation time is reduced to half or less, and the thermal resistance is also 15% or more. Can be expected to decrease.

  4 and 5, the analysis calculation area is set to 20 μm × 20 μm, and the width of the thermal diffusion structure 206 is from 20 μm to the width of the 1D crystal 201 (Wpc = 580 nm). Also, the sum of the widths (sw × 2) of the two side slabs 205 was subtracted and divided by 2 (a value less than 10 μm). As a boundary condition at the end of the calculation area, heat is deprived instantly. It can be regarded as approximately equivalent to the case where a sufficiently large metal or a good heat conductor such as silicon is arranged outside the boundary. The width of the thermal diffusion structure 206 in the actually manufactured optical resonator is at least 40 μm or more, and greatly extends beyond the calculation area in the analysis. The heat diffused in the heat diffusion structure is finally transferred to the substrate or air and then dissipated.

  The optical resonator according to the first embodiment has been shown and described with reference to FIGS. This is an example embodiment on an SOI platform. The present invention is also effective when the silicon oxide film layer 203 of FIG. 2 is removed to form an air layer. In particular, the thermal relaxation time is shorter when there is no silicon oxide film layer having a very low thermal conductivity. The removal of the silicon oxide film layer 203 can be realized by etching with hydrogen fluoride, for example.

<Second Embodiment>
FIG. 6 shows the configuration of the optical resonator of the second verification example, and FIGS. 7 to 8 show the verification results. Here, the high refractive index material constituting the 1D crystal 601, the side slab 605, the thermal diffusion structure 606, and the substrate 604 is changed from silicon to InP. InP and mixed crystal material systems based on it are important materials used in semiconductor lasers, light receivers, modulators, and the like. Although a structure with an oxide film such as SOI can be realized even in InP, it is not common in InP substrates and is not common, so here, an example in which the lower refractive index layer 603 is an air layer is used. I picked up.

  Note that InP has a much lower thermal conductivity (68 W / m / K) than silicon. First, the width sw and the film thickness sh of the side slab 605 need to be optimized more strictly. In addition, unlike the case of using silicon as a material for the thermal diffusion structure 606, thermal conduction in an InP layer having a thickness of 200 to 300 nm becomes a bottleneck. In order to further improve the exhaust heat performance, (1) the InP film thickness of this part is greatly increased, (2) heat is transferred directly to the substrate (InP) by InP or other high thermal conductivity medium, and (3) It is necessary to take measures such as adding a metal film having a very high thermal conductivity to the thermal diffusion structure. In this verification example, (1) and (2) are adopted, and a heat transfer portion 608 made of InP connecting the InP substrate 604 and the heat diffusion structure 606 made of InP is disposed. In the structure of FIG. 6, the thickness of the lower low-refractive index layer 603 (also referred to as the air layer 603) and the heat transfer portion 608 is 1 μm, and the thickness (height) of the 1D crystal 601 and the heat diffusion structure 606 is 210 nm. . The change of the thermal resistance and the thermal relaxation time when the thickness sh and the width sw of the side slab 605 were changed was numerically analyzed. In the present study, the lower refractive index layer 603 serving as the air layer and the end of the side slab 605 are matched, but this matching is not always necessary. FIG. 7 is a diagram in which the thermal resistance is plotted assuming that the thermal resistance in the case of no side slab is 1. In the comparison when the width sw of the side slab 605 is 1.2 μm, the thermal resistance when the thickness sh is 50 nm is 1/8 of the thermal resistance when there is no side slab, and the effectiveness of this verification example is clearly shown. It was. Although the thermal resistance is greatly increased as shown in the figure due to the difference in thermal conductivity as compared to the equivalent structure of silicon (silicon nanoresonator), the thermal resistance of the InP nanoresonator can be increased by the present invention to a typical silicon nanoresonator. There is a prospect of restraining within 2 times.

  FIGS. 8A and 8B show the sh and sw dependence of the thermal relaxation time, respectively. Similar to thermal resistance, the thermal relaxation time showed a large monotonic change. Since the relaxation time without the side slab exceeds 500 ns, a reduction of one digit or more can be obtained.

  7 and 8 show that the sw dependence of the thermal resistance and thermal relaxation time in the case of InP is larger than that in the case of silicon, indicating that the heat conduction in the InP slab is a bottleneck. Similar to silicon, the effect of maximizing sh in an allowable range and minimizing sw is extremely large. In addition, the effect of adopting the heat transfer portion 608 made of InP is great, and the heat resistance is doubled by a maximum as compared with the case where the heat transfer portion 608 is replaced with an air layer instead of InP, and the relaxation time is further improved.

In the structure of FIG. 6, when sh = 50 nm, sw = 1.0 μm, the width of the 1D crystal 601 is 525 nm, and the thickness (height) h of the 1D crystal 601 and the thermal diffusion structure 606 is 300 nm, the thermal resistance is The unit of 7 was 0.11. Based on the mode gap 1D crystal resonator (cylindrical hole ladder type) disclosed in Non-Patent Document 1, the lattice constant α is set to 400 nm, the hole radius is set to the reference r0 = 150 nm, and the modulation parameter m = 6.85. When the model arranged in this structure was analyzed by the FDTD method with a refractive index of InP of 3.17, a resonator mode having a Q value of about 200,000 and a mode volume of less than 1 (λ / n) ³ was obtained. It was. As described above, it has been numerically verified that a practical nanoresonator having excellent thermal performance can be obtained in this verification example.

  The optical resonator according to the second embodiment has been described above with reference to FIGS. The processing of this structure is mainly for InP materials. Crystal holes and side slab portions can be realized by combining high-precision electron beam lithography and processing by dry etching. A portion made of InP including the heat transfer portion 608 can be realized by a crystal growth technique on the InP substrate 604. The arrangement of the air layer 603 is difficult only by simple crystal growth or etching techniques. A combination of techniques such as selective etching / selective growth, regrowth after the processing process, etc. that are already in widespread use is necessary. For example, first, InGaAsP, which is a sacrificial layer material, is grown on the entire surface of the InP substrate 604, and then etched away leaving a portion that becomes the air layer 603. Next, InP in the heat transfer section 606 is selectively regrown, and then InP in the 1D crystal 601, the side slab 605, and the thermal diffusion structure 606 is regrown on the entire surface of the substrate. Next, the crystal hole 607 and the side slab 605 are processed by electron beam lithography and dry etching. Finally, the InGaAsP sacrificial layer left as a portion to become the air layer 603 is removed by selective etching to form the air layer 603, which is completed. In addition to the examples described here, there are combinations and procedures for realizing this structure.

<Third embodiment>
FIG. 9 shows the configuration of the third embodiment of the present invention. The heat diffusion structure portion is changed from the structure of FIG. First, it is assumed that the InP heat transfer section (608 in FIG. 6) is not adopted and the entire structure is a hollow structure on the air layer 903 (mechanical support is performed far from the resonator outside the illustrated range). On the other hand, a metal layer 907 is formed on the InP layer 905. The configuration for forming the metal layer 907 corresponds to the configuration described in the second embodiment (3) in which a metal film having a very high thermal conductivity is added to the thermal diffusion structure. In the present embodiment, Al, Au, Ag, Cu or the like having higher thermal conductivity than InP is preferable as the metal. When the metal layer was set to 160 nm thick Au (thermal conductivity 400 W / m / K) and numerical analysis was performed, the thermal resistance was slightly inferior to the results of the second embodiment shown in FIGS. And an improvement in relaxation time was obtained. The advantage of the third embodiment over the second embodiment is that selective re-growth is not necessary for the production of the air layer portion 903 and the processing can be simplified. Formation of the metal layer 907 can be easily realized by a combination of a general film forming method such as vacuum deposition and patterning by a lift-off method or the like. When the optical element is electrically driven, the metal layer 907 can be used as an electrode.

  The thermal diffusion structure 206 in the resonator configuration described in the first embodiment is replaced with a silicon thin film, and a silicon thin film and a metal (Al, Au, Ag, Cu, etc.) layer having higher thermal conductivity than silicon. Even in this configuration, improvement in thermal resistance and relaxation time can be obtained as in the present embodiment. In addition, instead of InP, the thermal diffusion structure 606 in the resonator configuration described in the second embodiment is replaced with an InP layer and a metal (Al, Au, Ag, Cu, etc.) layer having higher thermal conductivity than InP. Even if it comprises, the improvement of thermal resistance and relaxation time is obtained similarly to this embodiment.

<Fourth embodiment>
FIG. 10 shows a configuration of an optical resonator according to the fourth embodiment. The 1D crystal 1001 includes a lower InP layer 1009, an intermediate InGaAsP layer 1010, and a part of the upper InP layer 1011, and a crystal hole 1012 passes therethrough. The side slab 1002 is composed of a part of the InP layers 1009 and 1011 and supports the 1D crystal 1001 and serves as a path for heat and current. The side slab 1002 functions to confine light in the 1D crystal 1001 from the horizontal direction together with the intermediate air layer 1006. The air layers 1004 and 1005 serve to confine light in the 1D crystal 1001 from above and below. The thermal diffusion structure 1003 is composed of portions of the InGaAsP layers 1008 and 1010 and the InP layers 1009 and 1011 that are outside the side slab 1002, supports the 1D crystal 1001 and the side slab 1002, and diffuses heat in the horizontal and substrate directions.

  In manufacturing this structure, first, an InGaAsP layer 1008, an InP layer 1009, an InGaAsP layer 1010, and an InP layer 1011 are grown on the InP substrate 1007 in this order on the entire surface of the substrate. The thickness of each layer is, for example, 1 μm, 50 nm, 200 nm, and 50 nm in order from the bottom. The compositions of the lower InGaAsP layer 1008 and the intermediate InGaAsP layer 1010 are such that they become sacrificial layers when the air layers 1005 and 1006 are formed by selective etching with respect to InP, respectively, and the former has a considerably higher etching rate than the latter. Set to. Next, a selective etching hole 1013 penetrating from the upper surface to the InP layer 1009 is formed by dry etching or the like. Next, selective etching of InP and InGaAsP is performed using a chemical solution such as citric acid. Etching of the InP layers 1009 and 1011 is maintained as it is to a negligible extent. A part of the InGaAsP layer 1010 is removed to form an air layer 1006. Etching is stopped when the InGaAsP layer 1010 forming a part of the 1D crystal 1001 becomes narrow to a predetermined width. The lower InGaAsP layer 1008 is also etched through the hole 1013, but the etching rate is considerably higher than that of the intermediate InGaAsP layer 1010. Therefore, the 1D crystal 1001 and the InGaAsP layer 1008 under the side slab 1002 are all removed and completely replaced with the air layer 1005. The Finally, this structure is completed by processing the crystal hole 1012 by electron beam lithography and dry etching. In this structure, exhaust heat performance is improved by arranging two layers of InP side slabs on the top and bottom. In the fourth embodiment, crystal growth needs to be performed only once, and application of advanced regrowth technology / selective growth technology can be eliminated.

101, 201, 601, 901, 1001 Bar-shaped structure 102, 202, 602, 902, 1004 Low refractive index medium (above bar-shaped structure)
103, 203, 603, 903, 1005 Low refractive index medium (under the rod-shaped structure)
1006 Low refractive index medium (next to rod-like structure)
104, 204, 604, 908, 1007 Substrate 105, 205, 605, 904, 1002 Side slab 106, 206, 606, 905, 1003 Thermal diffusion structure 107, 207, 607, 906, 1012 Crystal hole 608 Heat transfer section 907 Metal layer 1008 Lower InGaAsP layer 1009, 1011 InP layer 1010 Upper InGaAsP layer 1013 Sacrificial layer etching hole

Claims (5)

An optical resonator,
A one-dimensional photonic crystal having a rod-like structure made of a high-refractive index medium in which a cylindrical or polygonal column structure made of a low-refractive index material is periodically arranged;
One or a plurality of side slabs made of a material having high thermal conductivity, arranged in contact with the one-dimensional photonic crystal, and thinner than the one-dimensional photonic crystal and having a finite width;
A thermal diffusion structure disposed in contact with the side of the side slab that is opposite to the side in contact with the one-dimensional photonic crystal;
A low refractive index medium surrounding the one-dimensional photonic crystal ,
The thermal diffusion structure is constituted by a semiconductor layer made of a semiconductor material and a metal layer made of a metal having a higher thermal conductivity than the semiconductor material . The high refractive index medium, the side slab, and the semiconductor material are silicon;
The low refractive index medium surrounding the one-dimensional photonic crystal and the low refractive index material having the cylindrical or polygonal column structure are materials having a refractive index lower than that of air or a silicon oxide film,
The optical resonator according to claim 1 , wherein the thermal diffusion structure is thicker than the side slab. The high refractive index medium, the side slab, and the semiconductor material are InP;
The low refractive index medium surrounding the one-dimensional photonic crystal and the low refractive index material having the cylindrical or polygonal column structure are materials having a refractive index lower than that of air or a silicon oxide film,
The optical resonator according to claim 1 , wherein the thermal diffusion structure is thicker than the side slab. A heat transfer body made of a material having higher thermal conductivity than InP or InP produced on a semiconductor substrate;
The optical resonator according to claim 3 , wherein the heat diffusion structure is disposed in contact with the heat transfer body. An optical resonator,
A one-dimensional photonic crystal having a rod-like structure made of a high-refractive index medium in which a cylindrical or polygonal column structure made of a low-refractive index material is periodically arranged;
One or a plurality of side slabs made of a material having high thermal conductivity, arranged in contact with the one-dimensional photonic crystal, and thinner than the one-dimensional photonic crystal and having a finite width;
A thermal diffusion structure disposed in contact with the side of the side slab that is opposite to the side in contact with the one-dimensional photonic crystal;
A low refractive index medium surrounding the one-dimensional photonic crystal;
With
The high refractive index medium includes a layer made of InP and a layer made of InGaAsP.
The side slab consists of two layers made of InP and an air layer between the two layers ,
The thermal diffusion structure includes a layer made of InP and a layer made of InGaAsP,
The low refractive index medium surrounding the one-dimensional photonic crystal and the low refractive index material having the cylindrical or polygonal column structure are materials having a refractive index lower than that of air or a silicon oxide film,
The thermal diffusion structure, the optical resonator you characterized thicker than the side slabs.

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