JP7651502B2 - Optical Switch - Google Patents

Description

An embodiment of the present invention relates to an optical switch that controls the opening and closing of an electrical circuit by irradiating it with light.

Optical switches, which open and close electrical circuits by irradiating them with light, have advantages over switching controls using electrical signals in terms of high-speed response, noise reduction, electrical isolation, etc. For this reason, various applications of optical switches are being considered. In particular, optical switches that use high-speed pulsed lasers are expected to provide faster switching control than general switching elements that use electrical signals.

Such optical switches work on the principle that when light with higher energy than the band gap is incident on a semi-insulating semiconductor, the photoconductive effect excites electrons in the valence band to the conduction band, generating carriers and lowering the electrical resistance. Conventional optical switches use one-photon absorption, and irradiate a laser beam perpendicularly onto an area of the substrate surface sandwiched between a pair of electrodes formed on the semi-insulating semiconductor.

JP 2003-209269 A

To improve the high voltage durability of optical switches, it is necessary to increase the distance between the electrodes and improve insulation. Optical switches that use single-photon absorption have the property that the laser light is absorbed in a concentrated manner on the surface of the substrate. For this reason, in the conventional method of irradiating the substrate with a pulsed laser perpendicularly, the carriers generated in the optical switch are limited to the surface area of the substrate. For this reason, when the distance between the electrodes is increased in conventional optical switches, the electrical resistance cannot be sufficiently reduced when the electrical circuit is closed, making it difficult to stably control the opening and closing of high voltage currents.

The embodiment of the present invention has been made in consideration of these circumstances, and aims to provide an optical switch that generates carriers over a wide area of the volumetric region of the substrate when irradiated with light, even when the distance between the electrodes is increased, and can stably control the opening and closing of high-voltage, large currents.

The optical switch according to the embodiment includes a semiconductor substrate whose electrical resistance decreases when light rays are absorbed, a pair of electrodes that apply an electric field to the semiconductor substrate in a direction along the substrate surface, and a light source that irradiates the light rays to an edge of the semiconductor substrate in a direction along the substrate surface.

An optical switch according to an embodiment includes a semiconductor substrate whose electrical resistance decreases when a light beam is absorbed, a pair of electrodes that apply an electric field to the semiconductor substrate in a direction along the substrate surface, a light source that irradiates the light beam onto an edge of the semiconductor substrate in a direction along the substrate surface, and a pair of mirrors that are disposed at the opposing edges of the semiconductor substrate and reflect the light beam to each other, causing it to resonate inside the semiconductor substrate .
In addition, an optical switch according to an embodiment includes a semiconductor substrate whose electrical resistance decreases when a light beam is absorbed, a pair of electrodes that apply an electric field to the semiconductor substrate in a direction along the substrate surface, a light source that irradiates an edge of the semiconductor substrate with the light beam in a direction along the substrate surface, and a pair of mirrors that are disposed at the opposing edges of the semiconductor substrate and reflect the light beam against each other, causing it to travel back and forth multiple times inside the semiconductor substrate.

1A is a top view of an optical switch in an OFF state according to a first embodiment of the present invention, and FIG. 1A is a top view of an optical switch in an ON state according to a first embodiment, and FIG. 11A is a top view of an optical switch in a second embodiment, showing an OFF state; FIG. 13A is a top view of an optical switch in a second embodiment, showing an ON state; FIG.

First Embodiment
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1(A) is a top view of an optical switch 10A (10) showing an OFF state in a first embodiment of the present invention, and Fig. 1(B) is a longitudinal cross-sectional view thereof. Fig. 2(A) is a top view of an optical switch 10A (10) showing an ON state in the first embodiment, and Fig. 2(B) is a longitudinal cross-sectional view thereof.

As shown in Figures 1 and 2, the optical switch 10A includes a semiconductor substrate 20 in which electrical resistance decreases when a light ray 17 is absorbed, changing the insulating region 13 (Figure 1) to a conductive region 14 (Figure 2), a pair of electrodes 16 (16a, 16b) that apply an electric field to the semiconductor substrate 20 in a direction along the substrate surface 21 (21a, 21b), and a light source 11 that irradiates the light ray 17 from edge 22a to edge 22b of the semiconductor substrate 20 in a direction along the substrate surface 21.

When the semiconductor substrate 20 absorbs the light ray 17, it excites electrons from the valence band to the conduction band, and the electrical resistance decreases due to the generation of carriers. Then, the light ray 17 incident from the light source 11 and passing through the inside of the semiconductor substrate 20 forms a carrier movement path (conductive region 14). The carrier movement path thus formed serves as a waveguide for the light ray 17, since the light ray 17 is reflected or totally reflected at the interface (the interface with the insulating region 13 of the semiconductor substrate 20 or the atmosphere).

A power source (not shown) and an object to which power is to be supplied (not shown) are connected in series to the pair of electrodes 16 (16a, 16b). When power is supplied from the power source (not shown) to the electrodes 16 (16a, 16b), an electric field is applied in a direction along the substrate surface 21 of the semiconductor substrate 20. The electrodes 16 are formed of a metal such as gold or aluminum, and may also be formed by stacking multiple metals.

When light beam 17 is emitted from light source 11, pair of electrodes 16 (16a, 16b) become conductive with each other, and the electrical circuit including optical switch 10 becomes closed. When light beam 17 from light source 11 is stopped, pair of electrodes 16 (16a, 16b) become insulated, and the electrical circuit including optical switch 10 becomes open. In the figure, each of pair of electrodes 16 (16a, 16b) is shown as being disposed on one side of substrate surface 21a, but may be disposed on both sides of substrate surface 21a, 21b, respectively.

The light source 11 is configured to have multiple irradiation ports 12 from which multiple light beams 17 are output, but may also be configured to output one light beam 17 from one irradiation port 12. Specifically, Nd:YAG laser, Yb:YAG laser, Yb fiber laser, flash lamp, semiconductor laser, and light emitting diode are preferably used as the light source 11.

The irradiation port 12 of the light source 11 opens from the edge 22a to the edge 22b of the semiconductor substrate 20, and irradiates a light beam 17 in a direction along the substrate surface 21. In the figure, the irradiation direction of the light beam 17 is shown as being along the electric field direction formed by the pair of electrodes 16 (16a, 16b), but it may be set to intersect with this electric field direction. In addition, the irradiation direction of the light beam 17 may be either forward or reverse to the polarity direction of the electric field.

Semiconductor substrate 20 is preferably made of Si, GaAs, SiC, GaN, or diamond. Here, the wavelengths of electromagnetic waves having the equivalent energy to the band gaps of Si, GaAs, SiC, GaN, and diamond (hereinafter referred to as "equivalent wavelengths") are 1117 nm, 867 nm, 384 nm, 364 nm, and 226 nm, respectively.

Two-photon absorption is achieved by setting the wavelength of light 17 to be longer than but less than twice the equivalent wavelength of the band gap of semiconductor substrate 20. Here, two-photon absorption means that two photons of light 17 are simultaneously absorbed by semiconductor substrate 20, and electrons that exceed the band gap between the valence band and the conduction band are excited.

Examples of the light beam 17 that undergoes two-photon absorption in a semiconductor substrate 20 made of Si or GaAs include Nd:YAG laser, Yb:YAG laser, and Yb fiber laser. Examples of the light beam 17 that undergoes two-photon absorption in a semiconductor substrate 20 made of SiC or GaN include the second harmonic of a Nd:YAG laser, Yb:YAG laser, and Yb fiber laser. Examples of the light beam 17 that undergoes two-photon absorption in a semiconductor substrate 20 made of diamond include the third harmonic of a Nd:YAG laser, Yb:YAG laser, and Yb fiber laser. Light beam 17 having a wavelength that undergoes two-photon absorption can be output at will from a light source 11 such as a flash lamp, semiconductor laser, or light-emitting diode.

Three-photon absorption is achieved by setting the wavelength of light 17 to be longer than twice but less than three times the equivalent wavelength of the band gap of semiconductor substrate 20. Three-photon absorption means that three photons of light 17 are simultaneously absorbed by semiconductor substrate 20, exciting electrons that exceed the band gap between the valence band and the conduction band.

Examples of the light beam 17 that undergoes three-photon absorption in a semiconductor substrate 20 made of SiC or GaN include a Nd:YAG laser, a Yb:YAG laser, and a Yb fiber laser. Examples of the light beam 17 that undergoes three-photon absorption in a semiconductor substrate 20 made of diamond include the second harmonic of a Nd:YAG laser, a Yb:YAG laser, and a Yb fiber laser. Light source 11 such as a flash lamp, a semiconductor laser, or a light-emitting diode can output any light beam 17 having a wavelength that undergoes three-photon absorption.

In single-photon absorption, the absorption length is short and the laser cannot penetrate the semiconductor as shown in the figure, so the only option is to irradiate the laser directly between the electrodes from the front, resulting in a conductive region 14 where carriers are generated as a surface. On the other hand, in multi-photon absorption such as two-photon absorption or three-photon absorption, the absorption length is long, so the light ray 17 penetrates deep into the semiconductor substrate 20, and the conductive region 14 where carriers are generated becomes a volume rather than a surface, lowering the electrical resistance of the optical switch 10.

When controlling the opening and closing of a high-voltage current in the optical switch 10, the distance between the electrodes must be increased in consideration of the dielectric strength. By utilizing multiphoton absorption, which has a long absorption length, it is possible to generate carriers over a wide area of the volumetric region of the semiconductor substrate 20 by irradiating light 17 from the edge 22 in a direction along the substrate surface 21. This allows stable opening and closing of a large high-voltage current even if the distance between the electrodes 16 (16a, 16b) in the optical switch 10 is increased.

As shown in FIG. 1, when the light source 11 is not irradiated, an insulating region 13 is formed in the semiconductor substrate 20, and therefore the optical switch 10 is in an open state. Then, as shown in FIG. 2, a voltage is applied from a power source (not shown) to a pair of electrodes 16 (16a, 16b). When a light ray 17 is irradiated from the light source 11 in a direction along the substrate surface 21 of the semiconductor substrate 20 from the edge 22, if the wavelength of the light ray 17 is longer than the equivalent wavelength of the band gap, the light ray 17 is not absorbed by one photon and penetrates the semiconductor substrate 20. Then, when multiphoton absorption occurs in the semiconductor substrate 20, electrons in the valence band are excited to the conduction band, carriers are generated, and a conductive region 14 is formed.

When the light beam 17 is continuous light, the conductive region 14 is maintained during the irradiation period and the optical switch 10 closes the electrical circuit, and when the irradiation is stopped, the insulating region 13 is maintained and the optical switch 10 opens the electrical circuit. On the other hand, when the light beam 17 is pulsed light, the optical switch 10 controls the opening and closing of the electrical circuit at the response frequency of the rising edge of the pulsed light during the irradiation period. The optical switch 10 can widen the gap between the electrodes 16 (16a, 16b) and therefore can pass a high current at a high voltage, and its excellent high-speed response allows stable control even when the electrical circuit is opened and closed at the response frequency of the rising edge.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to Fig. 3 and Fig. 4. Fig. 3(A) is a top view of an optical switch 10B (10) showing an OFF state in the second embodiment, and Fig. 3(B) is a vertical cross-sectional view thereof. Fig. 4(A) is a top view of an optical switch 10B (10) showing an ON state in the second embodiment, and Fig. 4(B) is a vertical cross-sectional view thereof.

The optical switch 10B of the second embodiment has a semiconductor substrate 20, a pair of electrodes 16 (16a, 16b), and a light source 11 that are common to the optical switch 10A of the first embodiment, and further has a pair of mirrors 19 (19a, 19b). In Figures 3 and 4, parts that have the same configuration or function as Figure 1 are indicated by the same reference numerals, and duplicated explanations will be omitted.

The pair of mirrors 19 (19a, 19b) are disposed on the opposing edges 22 (22a, 22b) of the semiconductor substrate 20. The pair of mirrors 19 (19a, 19b) reflect the light beam 17 to each other, causing it to go back and forth between the mirrors 19 (19a, 19b) multiple times inside the semiconductor substrate 20, or to resonate. When the light beam 17 goes back and forth between the mirrors 19 (19a, 19b) multiple times, a 100% reflecting mirror is used, and the reflecting mirror 19 is installed so that the light beam 17 is shifted by the beam diameter. When resonating, a partially reflecting (90-99%) mirror 19 is installed so that it reflects the light vertically in parallel.

The pair of mirrors 19 (19a, 19b) are set so that the distance between them is an integer multiple of the wavelength of the light beam 17 so that multiple round trips or a resonant state is maintained. The pair of mirrors 19 (19a, 19b) can be formed by coating each of the opposing edges of the semiconductor substrate 20. In this case, the distance adjuster (not shown) can be a temperature control mechanism that changes the temperature of the semiconductor substrate 20, or a pressure mechanism that changes its length by applying pressure.

The pair of mirrors 19 (19a, 19b) can also be positioned physically away from the edge of the semiconductor substrate 20. In this case, the spacing adjuster (not shown) can be a stage mechanism that moves the pair of mirrors 19 (19a, 19b) over a small distance with high precision.

As shown in FIG. 3, when the light source 11 is not irradiated, the optical switch 10 is in an open state because an insulating region 13 is formed on the semiconductor substrate 20. Then, as shown in FIG. 4, when a voltage is applied from a power source (not shown) to a pair of electrodes 16 (16a, 16b), a light beam 17 is emitted from the light source 11 in a direction along the substrate surface 21 from one mirror 19a.

When the light ray 17 passes through one mirror 19a and strikes the edge 22a of the semiconductor substrate 20, it is reflected by the opposing mirror 19b, and this reflected wave is then reflected by the mirror 19a again, and this reflection is repeated. Because the distance between the pair of mirrors 19 (19a, 19b) is set to an integer multiple of the wavelength of the light ray 17, the repeated reflected wave travels back and forth between the mirrors 19 (19a, 19b) or resonates many times inside the semiconductor substrate 20, amplifying its intensity.

This increases the frequency of multiphoton absorption throughout the entire interior of the semiconductor substrate 20, and also increases the volume of the conductive region 14 where carriers are generated, significantly lowering the electrical resistance of the optical switch 10. If the reflectivity of the semi-transparent mirror 19 (19a, 19b) is 99%, assuming that the light is not absorbed by the semiconductor substrate 20, the intensity of the light ray 17, which travels back and forth between the mirrors 19 (19a, 19b) multiple times or resonates, becomes 100 times that of before it is incident.

In addition, by making the mirror 19b, which is located on the opposite side of the light source 11 out of the pair of mirrors 19 (19a, 19b), a total reflection mirror, the intensity of the light beam 17 can be further amplified by traveling back and forth between the mirrors 19 (19a, 19b) multiple times or by resonance. As a result, in the second embodiment, even if the irradiation intensity of the light beam 17 is reduced compared to the first embodiment, carriers can be sufficiently generated over a wide area of the volume region of the semiconductor substrate 20. As a result, even if the distance between the electrodes 16 (16a, 16b) in the optical switch 10 is widened, a high voltage and large current can be stably opened and closed.

According to at least one of the optical switch embodiments described above, by irradiating the edge of the semiconductor substrate with a light beam in a direction along the substrate surface, carriers are generated over a wide area of the volumetric region of the substrate when light is irradiated, making it possible to stably control the opening and closing of a high-voltage current, even if the distance between the electrodes is increased.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

10 (10A, 10B)...optical switch, 11...light source, 12...illumination port, 13...insulating region, 14...conductive region, 16 (16a, 16b)...electrode, 17...light beam, 19 (19a, 19b)...mirror, 20...semiconductor substrate, 21 (21a, 21b)...substrate surface, 22 (22a, 22b)...edge.

Claims (12)

a semiconductor substrate whose electrical resistance decreases when light is absorbed;
A pair of electrodes for applying an electric field to the semiconductor substrate in a direction along a substrate surface;
a light source that irradiates the light beam onto an edge of the semiconductor substrate in a direction along a surface of the substrate;
a pair of mirrors disposed on opposite edges of the semiconductor substrate for reflecting the light beam to each other and causing resonance within the semiconductor substrate . a semiconductor substrate whose electrical resistance decreases when light is absorbed;
A pair of electrodes for applying an electric field to the semiconductor substrate in a direction along a substrate surface;
a light source that irradiates the light beam onto an edge of the semiconductor substrate in a direction along a surface of the substrate;
a pair of mirrors disposed on opposite edges of the semiconductor substrate for reflecting the light beam to each other and for making a plurality of round trips within the semiconductor substrate . 3. The optical switch according to claim 1 ,
An optical switch in which the wavelength of the light is set to be longer than or equal to twice the wavelength of an electromagnetic wave having an energy equivalent to the band gap of the semiconductor substrate. 3. The optical switch according to claim 1 ,
An optical switch in which the wavelength of the light is set to be longer than twice the wavelength of an electromagnetic wave having energy equivalent to the band gap of the semiconductor substrate, but not longer than three times the wavelength. 5. The optical switch according to claim 1 ,
An optical switch, wherein the light beam is a continuous light or a pulsed light . 6. The optical switch according to claim 1 ,
The optical switch has a pair of mirrors, the mirror located opposite to the light source being a total reflection mirror. 7. The optical switch according to claim 1 ,
An optical switch in which an adjuster for adjusting the distance between the pair of mirrors is provided. 7. The optical switch according to claim 1 ,
An optical switch in which the pair of mirrors are coated on each of the opposing edges of the semiconductor substrate. 9. The optical switch according to claim 1,
An optical switch in which the direction of application of the electric field and the direction of irradiation of the light beam are either a forward direction, a reverse direction, or a cross direction with respect to each other. 10. The optical switch according to claim 1 ,
An optical switch in which each of the pair of electrodes is provided on one or both of the substrate surfaces. 11. The optical switch according to claim 1 ,
The semiconductor substrate is selected from the group consisting of Si, GaAs, SiC, GaN and diamond. 12. The optical switch according to claim 1 ,
The light source is selected from the group consisting of a Nd:YAG laser, a Yb:YAG laser, a Yb fiber laser, a flash lamp, a semiconductor laser, and a light emitting diode.

Images