JPH03190290A - Frequency detector - Google Patents

Abstract

PURPOSE:To enable frequency change of a light source to be detected highly efficiently in a very small space by allowing frequency of light to be detected by using the semiconductor/superconductor proximity effect. CONSTITUTION:When white parallel rays 9 are allowed to enter a comb-type cycle structure 4 which is formed with a metal or a dielectric body as a material at a constant angle, the reflected rays differ in terms of wavelength and frequency according to the reflection angle. By using this phenomenon and semiconductor/superconductor proximity effect, light wavelength or light speed are divided by wavelength, thus enabling obtained frequency to be detected. Therefore, frequency change of light source can be detected highly efficiently in a very small space.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an element that controls the semiconductor/superconductor proximity effect by changing the concentration of electrons or holes under light irradiation and detects the frequency of light with high resolution. The present invention relates to an ultra-compact, low-input frequency detector suitable for use in communication networks and optical integrated circuits.

[Conventional technology]

Aiming for application to ultra-high-speed, low-power electronic integrated circuits, research is actively being conducted on superconducting transistors that utilize semiconductor/superconductor proximity effects. The principle of the above-mentioned transistor is to control the leakage length of the wave function of the superconducting Cooper pair into the semiconductor by changing the concentration of electrons or holes in the semiconductor. This principle is discussed in detail in Solid State Physics, Volume 23 (19884), page 153. Based on this principle, the concentration of electrons or holes in a semiconductor sandwiched between superconductors is changed by applying a gate voltage, and the wave function of the Cooper pair is smeared from the superconductor at both ends of the semiconductor. It is possible to control the superconducting tunnel current caused by the overlap of the long portions and perform transistor operation. The basic concept of a superconducting transistor that operates in this way is published in the Journal of Applied Physics (J
, Appl, Phys,) Volume 51, (1980)
p. p. 2736-2743, and the operation confirmation was subsequently reported in Physical Review (Phys. Rev.) Vol. 833 (1986) p. 2042. Physical Review Letters (Phys. Rev, Lett,) Volume 20 (1968) p p
1286-1289, an attempt was made to control the superconducting tunnel current by changing the electron or hole density by injecting electrons and holes by light irradiation instead of applying a gate voltage, and fabricated a pb/cdS/Pb junction. death,
It has been reported that the tunneling current between superconductors PB was successfully changed by irradiating the CdS layer, which is a semiconductor, with light.

[Problem to be solved by the invention]

The above-mentioned conventional technology performs transistor operation by controlling the semiconductor/superconductor proximity effect by gate voltage or light irradiation. It is necessary to pursue the possibility of applying the semiconductor/superconductor proximity effect to devices with functions completely different from those of conventional electronic integrated circuits, taking advantage of the high-speed and lossless properties of superconducting current. be. An object of the present invention is to provide a novel frequency detector that detects the frequency of light using the semiconductor/superconductor proximity effect, which has not been covered within the scope of the prior art described above. In the fields of optical communications and optical integrated circuits, it is necessary to perform communications, optical modulation, and logical operations using highly monochromatic laser light sources. In such cases, fluctuations in the wavelength, or in other words, frequency, from the light source have a significant impact on the operating characteristics.Using the element based on the present invention, changes in the frequency of the light source can be detected with high efficiency and in a small space. can.

[Means to solve the problem]

According to one aspect of the present invention, the semiconductor/superconductor junction has a structure in which linear superconductors are periodically repeated;
When irradiating such a periodic structure and its vicinity with parallel light, the angle of incidence of the parallel light with respect to the bonded surface is unique;
The generation of charge carriers such as electrons and holes in the semiconductor due to the irradiation of parallel light and the resulting increase in the length of the Cooper pairs in the superconductor seeping into the semiconductor are caused by the irradiation of parallel light of a specific wavelength or frequency. A frequency detector is provided which can detect the wavelength or frequency of the parallel light by detecting the current flowing through the periodic structure of the superconductor. It is preferable that the frequency of the parallel light is approximately equal to or slightly higher than the optical absorption edge frequency of the semiconductor. According to a limited aspect of the invention, there is provided a frequency detector, said frequency detector having means for directing collimated light by means of an optical fiber or a rod lens. It is desirable that the parallel light be incident on the periodic structure more or less obliquely. According to another limited aspect of the invention, a frequency detector is provided, the frequency detector comprising a high temperature superconducting material as a superconductor. Preferably, the detector is operated at a temperature below liquid nitrogen temperature. According to yet another limited aspect of the invention, there is provided a frequency detector having at least one other metal layer at the superconductor/semiconductor interface in the frequency detector. According to another limited aspect of the present invention, the frequency detector has means for positioning incident light by fixing an optical fiber or lens using a step structure formed on a semiconductor surface. provided. The above step is 1mm
A certain degree is desirable. [Operation] When a white parallel light beam is incident at a certain angle on a comb-shaped periodic structure made of metal or dielectric material,
A phenomenon is observed in which the wavelength or frequency of reflected light rays differs depending on the reflection angle. Using this phenomenon, it is possible to create a device that obtains the spectrum of light including any frequency. This phenomenon is based on light diffraction. Using this phenomenon and the semiconductor/superconductor proximity effect, it is possible to divide the wavelength of light or the speed of light by the wavelength and detect the resulting frequency. The principle of frequency detection in the present invention will be explained using FIG. An element is fabricated in which a diffraction grating made by processing a superconductor film into a comb shape is provided on a light absorber such as a semiconductor. In this element, as shown in FIG. 1(,)(b), a wavelength λ is applied. , frequency ν. A monochromatic parallel ray of light is incident. At this time, it is necessary to pay attention to the parallelism of the incident light. This is because poor parallelism reduces frequency resolution. Let θ be the angle of incidence measured from the normal to the surface of the light absorber. Now, in order for the incident light to be diffracted by the above-mentioned diffraction grating and enter the light absorber, the phase difference of the light diffracted on each grating must be 2.
Must be an integer multiple of π. When the approach angle is φ measured from the above normal line, the condition is as follows. d(sinθ−(1/n)sinφ)=N·λ. Here, d, n, and N are the unit length of the diffraction grating, the refractive index of the light absorber, and a positive integer, respectively. Generally, higher-order terms with N greater than 1 are very weak and can be ignored. Furthermore, if the thickness of the superconductor is larger than the incident wavelength, φ is almost zero. Therefore, the above formula % formula % is obtained. Since d is determined at the time of device fabrication, θ and λ. have a one-to-one correspondence, and if θ is fixed, the above equation is the only λ. Holds true only for. Under conditions where the above equation holds true (hereinafter referred to as 2-diffraction conditions), the light intensity in the light absorber is no longer zero, and a tunnel current flows due to the semiconductor/superconductor proximity effect. By connecting a superconducting diffraction grating to a DC electrode and an ammeter and detecting this tunnel current, it is possible to know whether the diffraction conditions are met. The frequency of the incident light, i.e. the wavelength λ in the above equation
. If the current is fluctuating, the detected current will fluctuate significantly. This can be used to determine changes in wavelength. Figure 1 (c
) shows the current response when the incident frequency is changed. Check the diffraction conditions of the element. is set to match the frequency of the semiconductor laser, and the frequency is changed by slightly changing the current of the semiconductor laser. Δν indicates the frequency resolution of the element. 1.5μm wavelength i.e. 2X105GHz
For the light source, if θ is 20 degrees, d is 4.4 μm
It will be about. It is also possible to amplify the detection voltage and drive other semiconductor lasers. In this case, frequency fluctuations can be monitored as changes in light intensity. [Example 1] The present invention will be explained in detail with reference to Examples below. Example 1 As shown in FIGS. 1(a) and 1(b), the substrate 1 was made of InP, and the light absorber 2 was made of In. 4□SGa,'□5A s,
, 'pH'3 layer MBE (molecular beam epitaxy)
The film is grown to a thickness of 2 μm using the method. Then, 3μm
A thick Nb film is grown on the light absorber 2 by sputtering. The superconductor layer is processed into a diffraction grating section 4 including 500 thin wire sections 3 and an electrode section 5 using electron beam exposure and dry etching. Au 14 on the electrode part 5
is formed to a thickness of 300 nm. Light from a semiconductor laser that emits light with an oscillation wavelength of 1.5 μm, that is, a frequency of 2×10 sGHz, is extracted through an optical fiber 6. The extracted light 7 is converted into parallel light 9 by a rod lens 8 and is irradiated onto the diffraction grating section 4 . The unit period length d of the diffraction grating is 4.39 μm, the incident angle θ is 20 degrees, and the diffraction conditions are made to match light with a frequency of 2×10' GHz. The width of the thin line portion 30 is 2.5 μm. By irradiating this light at liquid helium temperature, electrons and holes 12 are generated in the light absorber 2, and a tunnel current flows between the superconductors forming the diffraction grating section 4. Connecting between the electrode parts 5 with a DC power supply 10 and an ammeter 11,
Detect this current. By changing the current injected into the semiconductor laser and changing the frequency of the incident light, the results shown in Figure 1 (
The results shown in C) were obtained. 9. is 2X105G
Hz, ΔY is 500 GHz, and the frequency resolution is 50
0 GHz, Δv/'sr 0 is 0.25%. The maximum value of the current is 100 μA. As microfabrication technology advances in the future, it will be possible to further improve the frequency resolution, and it will be possible to reduce Δv/v to about 0.01%. In this example, an InP-based compound semiconductor is used as the material, but the substrate 1 is made of semi-insulating GaAs.
A similar device can also be realized by using a GaAs layer for the light absorber 2. In this case, the wavelength and frequency of the incident light are 850 nm and 3.5×10 5 GHz. Although the examples below refer to specific materials, the comments here apply equally. Example 2 In this example, as shown in FIG. 2, a diffraction grating portion 28 was fabricated using a high temperature superconductor YBC◯ film 26 as the superconducting material of the thin wire portion 27. As in Example 1, I was applied to the substrate 21.
nP is used, and the light absorber 22 has a thickness of 2 μm.
sGa, No. 2 S A S No. 0 p, 43rd layer MBE
It was produced by the method. On top of that, as a buffer metal, W
3Qnm of Si23, 30m of Mo24, and further Au
A device similar to that of Example 1 was produced by growing 80 layers of No. 25 by sputtering. The characteristics at liquid nitrogen temperature are the same as in Example 1. Example 3 In this example, in order to accurately set the angle of incident light,
As shown in FIG. 3, the rod lens 35 was installed so as to be in contact with a side wall 36 etched into a mesa shape. The height of the side walls is 1 mm. An InP substrate 31 is processed into a mesa shape, and a 0.5 μm InP buffer layer 32 and a 2 μm thick InP buffer layer 32 and a 2 μm thick InP buffer layer 32 are formed thereon.
A S a', Pl, 41 layer 33 is produced by MBE method,
The diffraction grating 34 was constructed using a Nb film as a superconducting material. The characteristics at liquid helium temperature are the same as in Example 1. Embodiment 4 As shown in FIG. 4(, ), a part of the signal light 47 propagating through the leading wavepath 42 is taken out as detection light 48 and propagated through the leading wavepath 43. A superconducting diffraction grating for frequency detection is provided on the end face of the optical waveguide 43. Figure 4 (
a) is a view of the device viewed from above; Superconducting thin wire 4
6 has a width of 2.5 μm, and the length of one period of the diffraction grating composed of the superconducting thin wire 46 and the light absorber 44 is <4.3, which is the same as in Example 1.
9 μm, the incident angle is 20 degrees, and the diffraction conditions are suitable for light with a wavelength of 1.5 μm, that is, 2×10 sGHz. In,' on the InP substrate 41. G ao'5 AS II's P 1)'5 layer is grown and processed using conventional lithography and etching techniques to form optical waveguides 42,43. Leading wave path 4
2 has a thickness and width of 2 μm. On the other hand, the thickness and width of the leading waveguide 43 are 2 μm and 10 μm. Then, N
A film b is formed on a substrate by sputtering, and processed into the shape shown in FIG. 4 using electron beam exposure and dry etching. As the light absorber 44, In. '7. G
The aO'□, A sO', and PO' layers are grown to a thickness of 2 μm by MBE and etched into the shape shown in the figure. For the electrode 45, 30 nm of Au
Form. FIG. 4(b) shows a view of the above-mentioned diffraction grating section viewed obliquely from above. When light with a wavelength of 1.5 μm, ie, 2×10′ GHz, from a semiconductor laser was incident, and the frequency was varied by changing the injection current, results similar to those of Example 1 were obtained at the liquid helium temperature. Example 5 Using the element of Example 1, an element for extracting frequency changes by changes in light intensity was constructed. As shown in FIG. 5(a), light with a frequency of 2 x 10' GHz is guided through an optical fiber 51 to an optical amplifier 53, and the amplified light is incident on a rod lens 54 through an optical fiber 52 to become parallel light 55. incident on the frequency detector 50. A DC power supply 56 and a resistor 57 are connected to the frequency detector 50, and the resistor 5
7 is amplified through an amplifier 58 and supplied as a driving voltage for another semiconductor laser 59. Output light 6
By changing the frequency of the incident light while measuring the zero intensity, the intensity spectrum shown in FIG. 5(b) is obtained. The maximum intensity is 10 mW. Other characteristics are the same as in Example 1. [Effect of the Invention 1 According to the present invention, the frequency of light can be detected using the semiconductor/superconducting proximity effect.

[Brief explanation of drawings]

FIG. 1(a) is a perspective view of a frequency detector according to an embodiment of the present invention, FIG. 1(b) is a side sectional view of the main part of the detector, and FIG.
) is a current spectrum diagram showing the operating characteristics of the above detector, FIG. Cross section, 3rd
4(a) is a top view of the detector element portion of still another embodiment of the present invention, and FIG. 4(b) is a sectional view of the detector element portion of still another embodiment of the present invention. Perspective view of main parts, Figure 5 (
FIG. 3A is a schematic configuration diagram of a frequency detector according to still another embodiment of the present invention, and FIG. 2B is a frequency characteristic diagram of the detector according to the above embodiment. Explanation of symbols 1...Substrate, 2...Light absorber, 3...Thin line part,
4... Diffraction grating section, 5... Electrode section, 6... Optical fiber, 7... Extraction light, 8... Rod lens, 9
... Parallel light, 10 ... DC power supply, 11 ... Ammeter, 12 ... Electrons and holes, 13 ... Normal to the surface of light absorber 2, 14 ... Au, 21 ···substrate,
22...Light absorber, 23.24.25...Buffer metal, 26...YBCO127...Thin line part, 28...
... Diffraction grating portion, 31... Substrate, 32... Buffer layer, 33... Light absorber, 34... Diffraction grating, 35...
...Rod lens, 36...Mesa-shaped etched side wall, 41...Substrate, 42.43...Optical waveguide, 4
4... Light absorber, 45... Au, 46... Superconducting thin wire, 47... Signal light, 48... Detection light, 50...
・Frequency detection element, 51.52... Optical fiber, 53
... Optical amplifier, 54 ... Rod lens, 55 ...
Parallel light, 56... DC power supply, 57... Resistance, 58.
··amplifier.

Claims (1)

[Claims] 1. A semiconductor/superconductor junction having a structure in which linear superconductors are periodically repeated, and when the periodic structure and its vicinity are irradiated with parallel light, The angle of incidence of the parallel light with respect to the junction surface is unique, and the generation of charge carriers such as electrons and holes in the semiconductor by the irradiation of the parallel light and the resulting transfer of Cooper pairs in the superconductor into the semiconductor. An increase in the seepage length occurs resonantly only for parallel light of a specific wavelength or frequency, and at this time, by detecting the current flowing through the periodic structure of the superconductor, the wavelength or frequency of the parallel light can be changed. Frequency detector to know. 2. The frequency detector according to claim 1, wherein the parallel light is guided by an optical fiber or a rod lens. 3. The frequency detector according to claim 1, wherein the superconductor is made of a high temperature superconducting material. 4. The frequency detector according to claim 3, further comprising at least one other metal layer at the superconductor/semiconductor interface. 5. having periodically repeated semiconductor/superconductor junctions;
A frequency detector that performs optical-to-electrical conversion. 6. Frequency detector consisting of a diffraction grating made of superconductor. 7. The frequency detector according to claim 6, wherein the diffraction grating made of the superconductor is formed on the surface of the semiconductor. 8. The frequency detector according to claim 1, wherein the optical fiber or lens is fixed using a stepped structure formed on the semiconductor surface to position the incident light. 9. The frequency detector according to claim 1, which has a branched optical waveguide formed on the semiconductor surface, extracts a part of the light traveling through the optical waveguide, and detects the wavelength or frequency of the light. 10. The frequency detector according to claim 9, wherein the periodic structure made of a semiconductor/superconductor junction is connected to the end face of the optical waveguide. 11. Using the current or voltage generated during frequency detection,
Claim 1 or 9, further comprising driving another light source and detecting the wavelength or frequency of the incident light as the intensity of the light emitted from the other light source.
Frequency detector as described. 12. A frequency detector that has a periodic structure made of superconductor and reads the frequency of one light as the intensity of another light.