Optical switch

Abstract

To enable an optical switch to operate efficiently even when a trigger light is of low intensity.SOLUTION: An optical switch includes: a semiconductor substrate 11; a pair of electrodes 12A and 12B disposed on the semiconductor substrate; and a power supply 13 connected to the electrodes and configured to generate a potential difference between the pair of electrodes. The semiconductor substrate is composed of a semi-insulating semiconductor and includes, on one side surface thereof, a trigger light introduction surface 14 configured to introduce trigger light 1 thereinto. A carrier generation region 16 is disposed inside a portion corresponding to the pair of electrodes, where carriers are generated by passage of the trigger light and an electric resistance value is reduced. The semiconductor substrate 11 includes, at a position opposite to the one side surface, a total reflection surface 15 configured to totally reflect the trigger light introduced thereinto. It is configured so that the trigger light 1 introduced into the semiconductor substrate 11 from the trigger light introduction surface 14 and totally reflected by the total reflection surface 15 passes through the carrier generation region 16 multiple times.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to an optical switch that uses light to open and close a circuit. [Background technology]

[0002] Optical switches, which open and close circuits using light rather than electrical signals, are used in a variety of applications, such as for faster response than electrical control, noise reduction, and electrical isolation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-209269 A [Patent Document 2] JP 2005-191074 A [Patent Document 3] Japanese Utility Model Application Publication No. 58-166627 [Patent Document 4] Japanese Patent Application Publication No. 7-22603 [Non-patent literature]

[0004] [Non-Patent Document 1] F. Lacassie et. Al., “Two photon absorption in semi-insulating gallium arsenide photoconductive switch irradiated by a picosecond infrared laser” The European Physical Journal - Applied Physics, Volume 11, Issue 3, September 2000, pp. 189 - 195 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses a photoconductive switch that uses the photoconductive effect, in which electrons in the valence band are excited to the conduction band when light with a wavelength shorter than the bandgap wavelength of a semi-insulating semiconductor is irradiated, and carriers are injected, lowering the electrical resistance. By using high-speed pulsed laser light or the like as trigger light, this photoconductive switch can perform a closing operation faster than normal switching elements controlled by electrical signals, and can also be used at high voltages because the withstand voltage of the substrate made of a semi-insulating semiconductor is high.

[0006] On the other hand, in conventional photoconductive switches, the number of carriers is limited because the laser light is absorbed only on the substrate surface, making it difficult to increase the current or sufficiently reduce the electrical resistance. A photoconductive switch that uses two-photon absorption to solve this problem has been proposed in Non-Patent Document 1. In two-photon absorption type photoconductive switches, the absorption length is long, so the excitation light penetrates the semi-insulating semiconductor substrate, and the region into which the carriers are injected becomes a volume rather than a surface, making it possible to inject a large amount of carriers.

[0007] However, a long absorption length also leads to the majority of incident light being transmitted, resulting in a decrease in light utilization efficiency. FIG. 7 shows a conventional two-photon absorption photoconductive switch 100. A pair of positive and negative electrodes 101A and 101B are disposed on a semiconductor substrate 102. The pair of electrodes 101A and 101B are connected to a power source 103, which applies a voltage difference between the electrodes 101A and 101B. When trigger light 104 is incident on a trigger light introduction surface 105 disposed on a side surface of the semiconductor substrate 102, the incident trigger light 104 passes through a carrier generation region 106 of the semiconductor substrate 102, and a part of the incident trigger light 104 is two-photon absorbed in the carrier generation region 106. This reduces the electrical resistance value of the carrier generation region 106, causing the photoconductive switch 100 to perform a closing operation. When the photoconductive switch 100 performs a closing operation, a current flows between the electrodes 101A and 101B via the semiconductor substrate 102.

[0008] As described above, in the two-photon absorption type photoconductive switch 100, most of the trigger light 104 is not absorbed and does not contribute to opening or closing the photoconductive switch 100, and is emitted to the outside of the semiconductor substrate 102 from the opposite side of the semiconductor substrate 102, etc. As described above, the two-photon absorption type photoconductive switch 100 has a long absorption length, and most of the trigger light 104 is emitted, reducing the utilization efficiency of the trigger light 104, which increases the intensity (output) required for the trigger light 104 to operate the photoconductive switch 100.

[0009] The embodiments of the present invention have been made in consideration of the above circumstances, and an object of the present invention is to provide an optical switch that can operate efficiently even when the intensity of the trigger light is low. [Means for solving the problem]

[0010] An optical switch in an embodiment of the present invention has a semiconductor substrate, a pair of electrodes provided on the semiconductor substrate, and a power source connected to the electrodes to generate a potential difference between the pair of electrodes, the semiconductor substrate being made of a semi-insulating semiconductor and having a trigger light introduction surface on one side for introducing trigger light into the interior, and a carrier generation region is provided inside corresponding to the pair of electrodes in which carriers are generated by the passage of the trigger light and a value of electrical resistance is reduced, the semiconductor substrate having a total reflection surface at a position opposite to the one side for totally reflecting the trigger light introduced into the interior, and the trigger light introduced into the semiconductor substrate from the trigger light introduction surface and totally reflected by the total reflection surface is configured to pass through the carrier generation region multiple times. Effect of the Invention

[0011] According to an embodiment of the present invention, even a low intensity trigger light can operate efficiently. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a plan view showing a photoconductive switch as an optical switch according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 11 is a plan view showing a photoconductive switch as an optical switch according to a second embodiment. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] 5 is an explanatory diagram illustrating the state of incidence and reflection of trigger light on the semiconductor substrate in FIG. 4 in an enlarged manner. [Figure 6] FIG. 11 is a plan view showing a photoconductive switch as an optical switch according to a third embodiment. [Figure 7] 7A and 7B show a conventional two-photon absorption photoconductive switch, in which (A) is a plan view and (B) is a cross-sectional view taken along line VIIB-VIIB in FIG. 7A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [A] First embodiment (Figs. 1 and 2) Fig. 1 is a plan view showing a photoconductive switch as an optical switch according to the first embodiment. The photoconductive switch 10 as an optical switch shown in Fig. 1 is a switch that opens and closes a circuit using light (trigger light 1), and is configured with a semiconductor substrate 11, a pair of positive and negative electrodes 12A and 12B provided on the front and back surfaces of the semiconductor substrate 11, respectively, and a power source 13 connected to these electrodes 12A and 12B to generate a potential difference between these electrodes 12A and 12B.

[0014] The electrodes 12A and 12B are made of an electrical conductor such as gold, aluminum, ITO (Indium-Tin Oxide), Ni, or Ti. The electrodes 12A and 12B may also be made by laminating the above conductors. When the photoconductive switch 10 is closed, a current flows between the electrodes 12A and 12B via the semiconductor substrate 11 due to a potential difference applied between the electrodes 12A and 12B by the power source 13.

[0015] The semiconductor substrate 11 is made of a semi-insulating semiconductor such as Si, GaAs, SiC, GaN, or diamond, and has a trigger light introducing surface 14, a total reflection surface 15 (first total reflection surface 15A, second total reflection surface 15B), and a carrier generation region 16.

[0016] The trigger light introducing surface 14 is formed on one side of the semiconductor substrate 11, and the angle of incidence of the trigger light 1 is set to be smaller than the critical angle, which is a condition for total reflection, thereby introducing the trigger light 1 into the semiconductor substrate 11. The trigger light introducing surface 14 may also be set at a Brewster's angle with respect to the trigger light 1 to suppress reflection of the trigger light 1, which is p-polarized light, at the trigger light introducing surface 14, thereby improving the transmittance of the trigger light 1. Furthermore, the trigger light introducing surface 14 may be coated with an anti-reflection coating for the trigger light 1.

[0017] First total reflection surface 15A and second total reflection surface 15B of total reflection surface 15 are provided at a position facing trigger light introducing surface 14 on semiconductor substrate 11, and are continuous with surface H perpendicular to the front or back surface of semiconductor substrate 11. Furthermore, first total reflection surface 15A and second total reflection surface 15B cause trigger light 1 introduced into semiconductor substrate 11 to be incident at an incident angle equal to or greater than the critical angle which is a condition for total reflection, thereby totally reflecting trigger light 1 introduced into semiconductor substrate 11.

[0018] For example, the angles (incidence angle of trigger light 1) between first total reflection surface 15A, where trigger light 1 first arrives, and second total reflection surface 15B, where trigger light 1 arrives after being reflected by first total reflection surface 15A, are both set to 45 degrees. Here, when semiconductor substrate 11 is made of SiC and trigger light 1 is the second harmonic of an Nd:YAG laser with a wavelength of 532 nm, the critical angle for total reflection of trigger light 1 is 22 degrees. Therefore, trigger light 1 introduced into semiconductor substrate 11 passes through carrier generation region 16, is totally reflected by first total reflection surface 15A, and then totally reflected by second total reflection surface 15B, and passes through carrier generation region 16 again.

[0019] Carrier generation region 16 is provided in the interior of semiconductor substrate 11 corresponding to a pair of electrodes 12A and 12B, i.e., in a region sandwiched between electrodes 12A and 12B inside semiconductor substrate 11. When trigger light 1 passes through carrier generation region 16, the valence band is excited to the conduction band, carriers are generated, and the electrical resistance value decreases. Trigger light 1 introduced into semiconductor substrate 11 from trigger light introduction surface 14 passes through carrier generation region 16, and then trigger light 1 totally reflected by total reflection surface 15 (first total reflection surface 15A, second total reflection surface 15B) passes through carrier generation region 16 again, so that trigger light 1 passes through carrier generation region 16 multiple times.

[0020] The trigger light 1 incident from the trigger light introduction surface 14 of the semiconductor substrate 11 and introduced into the semiconductor substrate 11 is preferably a laser light including a pulsed laser light. The wavelength of this trigger light 1 is set to be longer than one time and not more than two times the band gap wavelength of the semi-insulating semiconductor constituting the semiconductor substrate 11.

[0021] For example, the band gap wavelengths of Si, GaAs, SiC, GaN, and diamond constituting the semiconductor substrate 11 are 1117 nm, 867 nm, 384 nm, 364 nm, and 226 nm, respectively. Therefore, the laser light as the trigger light 1 is preferably an Er:YAG laser when the semiconductor substrate 11 is made of Si, and is preferably an Er:YAG laser, an Nd:YAG laser, an Nd:YVO4 laser, an Yb:YAG laser, or an Yb fiber laser when the semiconductor substrate 11 is made of GaAs, and is preferably a second harmonic of the Nd:YAG laser, an Nd:YVO4 laser, an Yb:YAG laser, or an Yb fiber laser when the semiconductor substrate 11 is made of SiC or GaN, and is preferably a third harmonic of the Nd:YAG laser, an Nd:YVO4 laser, an Yb:YAG laser, or an Yb fiber laser when the semiconductor substrate 11 is made of diamond. The trigger light 1 may also be light from a flash lamp, a semiconductor laser corresponding to each wavelength, or light from a light emitting diode, etc.

[0022] The trigger light 1 may be set to a wavelength longer than twice and equal to or less than three times the band gap wavelength of the semi-insulating semiconductor constituting the semiconductor substrate 11. For example, the laser light as the trigger light 1 is preferably an Nd:YAG laser, an Nd:YVO4 laser, an Yb:YAG laser, or an Yb fiber laser when the semiconductor substrate 11 is made of SiC or GaN, and is preferably a second harmonic of an Nd:YAG laser, an Nd:YVO4 laser, an Yb:YAG laser, or an Yb fiber laser when the semiconductor substrate 11 is made of diamond. In this case, the trigger light 1 may be light from a flash lamp, a semiconductor laser corresponding to each wavelength, or light from a light emitting diode or the like.

[0023] Next, the operation of the photoconductive switch 10 configured as above will be described. In a normal state, the photoconductive switch 10 is open, and a potential difference is applied in advance by the power source 13 between the pair of electrodes 12A, 12B.

[0024] Next, trigger light 1 is irradiated. Since the angle of incidence of trigger light 1 with respect to trigger light introducing surface 14 is set to be smaller than the critical angle, which is a condition for total reflection, trigger light 1 penetrates inside semiconductor substrate 11. For example, the refractive index of SiC of semiconductor substrate 11 for the wavelength 532 nm, which is the second harmonic of the Nd:YAG laser that is trigger light 1, is 2.78, and the critical angle is 22 degrees.

[0025] After entering semiconductor substrate 11, trigger light 1 passes through carrier generation region 16, and some of the light is absorbed, reducing the electrical resistance value of carrier generation region 16, but the majority of the light is transmitted and reaches first total reflection surface 15A.

[0026] The trigger light 1 totally reflected by the first total reflection surface 15A is incident on the second total reflection surface 15B and totally reflected, and then passes through the carrier generation region 16 again, further decreasing the electrical resistance value of the carrier generation region 16. As the trigger light 1 passes through the carrier generation region 16 twice and the electrical resistance value of the carrier generation region 16 decreases, the photoconductive switch 10 is closed, and a current flows between the pair of electrodes 12A and 12B.

[0027] As configured as above, the first embodiment provides the following effect (1). (1) The trigger light 1 introduced from the trigger light introduction surface 14 into the semiconductor substrate 11 and totally reflected by the total reflection surface 15 (first total reflection surface 15A, second total reflection surface 15B) is configured to pass through the carrier generation region 16 of the semiconductor substrate 11 multiple times. Therefore, a larger amount of the trigger light 1 is absorbed in the carrier generation region 16, and therefore a larger amount of carriers are generated in the carrier generation region 16, decreasing the electrical resistance value. As a result, even if the trigger light 1 has a low intensity (low output), the photoconductive switch 10 can be efficiently closed. On the other hand, when the intensity (output) of the trigger light is constant, the electrical resistance value during the closing operation of the photoconductive switch 10 can be set to a lower value.

[0028] [B] Second embodiment (Figs. 3 to 5) 3 is a plan view showing a photoconductive switch as an optical switch according to the second embodiment. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0029] A photoconductive switch 20 as an optical switch of the second embodiment differs from the first embodiment in that a total reflection surface 22 in a semiconductor substrate 21 made of a semi-insulating semiconductor is formed parallel to the trigger light introducing surface 14 on a plane including the front or back surface of the semiconductor substrate 21 as shown in Fig. 3, and is set at an angle α (for example, α = θ) that is equal to or greater than the critical angle θ of the trigger light 1 with respect to a plane H perpendicular to the front or back surface of the semiconductor substrate 21 as shown in Fig. 4 and Fig. 5. For example, when the semiconductor substrate 21 is made of SiC and the trigger light 1 is the second harmonic of a Nd:YAG laser with a wavelength of 532 nm, the critical angle θ of the trigger light 1 is 22 degrees.

[0030] Furthermore, the total reflection surface 22 is set at an angle such that the angle of incidence (90°-2θ) at which the trigger light 1 totally reflected by this total reflection surface 22 is incident on the front or back surface of the semiconductor substrate 21 is equal to or greater than the critical angle θ. Furthermore, the total reflection surface 22 is set at an angle such that the angle of incidence β at which the trigger light 1 totally reflected once or multiple times by the front or back surface of the semiconductor substrate 21 is incident on the trigger light introducing surface 14 is an angle 2θ that is equal to or greater than the critical angle θ.

[0031] Since the total reflection surface 22 is set as described above, the trigger light 1 introduced into the semiconductor substrate 21 from the trigger light introduction surface 14 is repeatedly totally reflected at the total reflection surface 22, the front or back surface of the semiconductor substrate 21, and the trigger light introduction surface 14, and passes back and forth through the carrier generation region 16 of the semiconductor substrate 21 multiple times, thereby reducing the electrical resistance value of this carrier generation region 16.

[0032] Next, the operation of the photoconductive switch 20 configured as above will be described. In a normal state, the photoconductive switch 20 is open, and a potential difference is applied in advance by the power source 13 between the pair of electrodes 12A, 12B.

[0033] Next, trigger light 1 is irradiated. The incident angle of the trigger light 1 with respect to the trigger light introducing surface 14 is set to be smaller than the critical angle θ, which is the condition for total reflection, so that the trigger light 1 penetrates inside the semiconductor substrate 21.

[0034] After the trigger light 1 penetrates inside the semiconductor substrate 21, it passes through the carrier generation region 16, where some of it is absorbed and reduces the electrical resistance value of the carrier generation region 16, but most of it is transmitted and reaches the total reflection surface 22.

[0035] Thereafter, trigger light 1 is totally reflected by total reflection surface 22 and enters the front or back surface of semiconductor substrate 21. Since the angle of incidence (90°-2θ) at this time is equal to or greater than the critical angle θ, trigger light 1 is repeatedly totally reflected by the front or back surface of semiconductor substrate 21 and passes through carrier generation region 16 again, further decreasing the electrical resistance value of carrier generation region 16.

[0036] Since the trigger light introducing surface 14 and the total reflection surface 22 are arranged in parallel on a plane including the front or back surface of the semiconductor substrate 21, the trigger light 1 totally reflected by the front or back surface of the semiconductor substrate 21 is incident on the trigger light introducing surface 14 at an incidence angle β (β=2θ). Since this incidence angle β is greater than the critical angle θ, the trigger light 1 is totally reflected by the trigger light introducing surface 14, totally reflected again by the front or back surface of the semiconductor substrate 21, and passes through the carrier generation region 16, further reducing the electrical resistance value of the carrier generation region 16.

[0037] As configured as above, the second embodiment also provides the same effect as the effect (1) of the first embodiment.

[0038] [C] Third embodiment (FIG. 6) 6 is a plan view showing a photoconductive switch as an optical switch according to the third embodiment. In the third embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0039] The photoconductive switch 30 as an optical switch of the third embodiment differs from the first embodiment in that, like the first embodiment, a plurality of total reflection surfaces 15 (first total reflection surface 15A, second total reflection surface 15B) are provided continuously on the semiconductor substrate 11, but trigger light 31 has a predetermined width W in the arrangement direction of the plurality of total reflection surfaces 15 (first total reflection surface 15A, second total reflection surface 15B) and is simultaneously incident on and totally reflected by the plurality of total reflection surfaces 15 (first total reflection surface 15A, second total reflection surface 15B).

[0040] Therefore, the trigger light 31 introduced into the semiconductor substrate 11 from the trigger light introduction surface 14 of the semiconductor substrate 11 passes through the carrier generation region 16 and then reaches the first total reflection surface 15A and the second total reflection surface 15B at the same time. Of the trigger light 31, the light 31U in the region on one side of the center line P (for example, the upper half region in FIG. 6) is totally reflected by the second total reflection surface 15B, then totally reflected by the first total reflection surface 15A, and passes through the carrier generation region 16 again. At the same time, of the trigger light 31, the light 31D in the region on the other side of the center line P (for example, the lower half region in FIG. 6) is totally reflected by the first total reflection surface 15A, then totally reflected by the second total reflection surface 15B, and passes through the carrier generation region 16 again. In this way, more of the trigger light 31 passes through the carrier generation region 16 of the semiconductor substrate 11.

[0041] As configured as above, the third embodiment also provides the same effect as the effect (1) of the first embodiment. Note that in the photoconductive switch 30 of the third embodiment, the multiple total reflection surfaces 15 (first total reflection surface 15A, second total reflection surface 15B) may be set at an angle α (for example, α=θ) equal to or greater than the critical angle θ of the trigger light 31 with respect to a surface H perpendicular to the front or back surface of the semiconductor substrate, like the total reflection surface 22 of the second embodiment.

[0042] Although several embodiments of the present invention have been described above, 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, changes, and combinations can be made without departing from the spirit of the invention. Furthermore, these substitutions, changes, and combinations are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0043] Reference Signs List 1... trigger light, 10... photoconductive switch (optical switch), 11... semiconductor substrate, 12A, 12B... electrodes, 13... power source, 14... trigger light introduction surface, 15... total reflection surface, 15A... first total reflection surface, 15B... second total reflection surface, 16... carrier generation region, 20... photoconductive switch, 21... semiconductor substrate, 22... total reflection surface, 30... photoconductive switch, 31... trigger light, H... vertical surface, W... width, α... angle, β... angle of incidence, θ... critical angle

Claims

1. A semiconductor substrate, a pair of electrodes disposed on the semiconductor substrate, and a power source connected to the electrodes to generate a potential difference between the pair of electrodes, the semiconductor substrate is made of a semi-insulating semiconductor and has a trigger light introduction surface on one side thereof for introducing a trigger light into the inside, and a carrier generation region is provided inside the semiconductor substrate corresponding to the pair of electrodes in which carriers are generated by the passage of the trigger light, thereby decreasing an electrical resistance value; the semiconductor substrate has a total reflection surface at a position opposite to the one side surface, the total reflection surface causing the trigger light introduced therein to be totally reflected; An optical switch characterized in that the trigger light is introduced into the semiconductor substrate from the trigger light introduction surface and totally reflected at the total reflection surface, and is configured to pass through the carrier generation region multiple times.

2. 2. The optical switch according to claim 1, wherein the total reflection surface is provided on a surface perpendicular to a front or rear surface of a semiconductor substrate.

3. 2. The optical switch according to claim 1, wherein the total reflection surface is set at an angle greater than or equal to the critical angle of the trigger light with respect to a plane perpendicular to the front or back surface of the semiconductor substrate, and is set at an angle such that the totally reflected trigger light is incident on the front or back surface of the semiconductor substrate at an angle greater than or equal to the critical angle.

4. 2. The optical switch according to claim 1, wherein the total reflection surface is set at an angle equal to or greater than the critical angle of the trigger light with respect to a plane perpendicular to the front or back surface of the semiconductor substrate, and the trigger light that is totally reflected is incident on the front or back surface of the semiconductor substrate at an angle equal to or greater than the critical angle, and the trigger light that is totally reflected on the front or back surface of the semiconductor substrate is incident on a trigger light introducing surface of the semiconductor substrate at an angle equal to or greater than the critical angle.

5. the semiconductor substrate has a plurality of total reflection surfaces; 2. The optical switch according to claim 1, wherein the trigger light has a predetermined width in a direction in which the plurality of total reflection surfaces are arranged, and is configured to be simultaneously incident on the plurality of total reflection surfaces and to be totally reflected.

6. 2. The optical switch according to claim 1, wherein the trigger light introduction surface is set at a Brewster's angle with respect to the trigger light, and the trigger light is p-polarized with respect to the trigger light introduction surface.

7. 2. The optical switch according to claim 1, wherein an anti-reflection coating against the trigger light is applied to the trigger light introduction surface.

8. 2. The optical switch according to claim 1, wherein the trigger light has a wavelength set to be greater than one time and less than or equal to two times the band gap wavelength of a semi-insulating semiconductor that constitutes a semiconductor substrate.

9. 2. The optical switch according to claim 1, wherein the trigger light has a wavelength set to be greater than twice and less than or equal to three times the band gap wavelength of the semi-insulating semiconductor that constitutes the semiconductor substrate.

10. 2. The optical switch according to claim 1, wherein the trigger light is a laser light including a pulsed laser light.

11. 2. The optical switch according to claim 1, wherein the trigger light is light from an Er:YAG laser, an Nd:YAG laser, an Ni:YVO4 laser, an Yb:YAG laser, an Yb fiber laser, a semiconductor laser, a flash lamp, or a light from a light-emitting diode.

12. 2. The optical switch according to claim 1, wherein the semi-insulating semiconductor constituting the semiconductor substrate is Si, GaAs, SiC, GaN or diamond.

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