WO2021255911A1 - Transmitter, receiver, spatial optical frequency transmission system, and spatial optical frequency transmission method - Google Patents

Transmitter, receiver, spatial optical frequency transmission system, and spatial optical frequency transmission method Download PDF

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Publication number
WO2021255911A1
WO2021255911A1 PCT/JP2020/024082 JP2020024082W WO2021255911A1 WO 2021255911 A1 WO2021255911 A1 WO 2021255911A1 JP 2020024082 W JP2020024082 W JP 2020024082W WO 2021255911 A1 WO2021255911 A1 WO 2021255911A1
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Prior art keywords
light
reference light
frequency
transmitter
beam splitter
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PCT/JP2020/024082
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French (fr)
Japanese (ja)
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大樹 佐久間
薫 新井
隆太 杉山
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日本電信電話株式会社
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Priority to PCT/JP2020/024082 priority Critical patent/WO2021255911A1/en
Priority to JP2022531211A priority patent/JP7472977B2/en
Publication of WO2021255911A1 publication Critical patent/WO2021255911A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/112—Line-of-sight transmission over an extended range

Definitions

  • the present invention relates to a transmitter, a receiver, a spatial optical frequency transmission system, and a spatial optical frequency transmission method for transmitting reference signal light having a reference optical frequency between a remote transmitter and a receiver via space.
  • Non-Patent Document 1 In various fields such as scientific measurement, communication, and navigation, there is a need for technology for highly accurate transmission of reference frequency signals between transceivers that are separated from each other in remote areas.
  • an optical frequency transmission system that transmits signal light of a reference optical frequency through space instead of transmission by optical fiber.
  • Non-Patent Document 1 A system based on the spatial optical frequency transmission method of Non-Patent Document 1 will be described.
  • This system includes a transmitter that transmits reference signal light (also referred to as reference light) separated from each other into space, and a receiver that receives the reference light and returns it to the transmitter.
  • the reference light which is a light wave of a reference frequency, is transmitted from the transmitter to the receiver via space.
  • the receiver returns back signal light (also referred to as back light) obtained by frequency-shifting the received reference light by AOM (Acousto Oputic Modulator) to the transmitter.
  • AOM Acoustic Oputic Modulator
  • the transmitter detects a phase fluctuation from the beat signal, which is the difference between the folded light and the reference light, and performs a frequency shift with respect to the reference light so that the transmission side can cancel the phase fluctuation according to the detected phase fluctuation. ..
  • the frequency of the reference light received on the receiving side becomes constant, so that the reference light having a constant frequency can be transmitted from the receiver to a communication terminal such as a user via an optical fiber.
  • the reference light is reflected by the Faraday mirror of the receiver, and at this time, the frequency f1 of the reference light is shifted by the AOM and returned to the transmitter as the return light of the frequency f2. That is, the frequencies f1 and f2 of the reference light and the return light are changed to distinguish them.
  • the folded light having a frequency of f2 noise due to unnecessary reflected light from the receiver is suppressed.
  • AOM is an active optical device using mechanical vibration by ultrasonic waves. For this reason, there are problems that the reliability is low and the power consumption is high because the failure is more likely to occur than the passive optical device.
  • the present invention has been made in view of such circumstances, and an object of the present invention is to prevent failures, improve reliability, and suppress power consumption.
  • the transmitter of the present invention reflects and transmits a beam splitter that reflects and transmits a reference light of a plane wave at a reference frequency, and a first reference light corresponding to the reference light reflected by the beam splitter.
  • a first spiral phase plate that is spiral and converts to a second reference light in a predetermined OAM (Orbital Angular Momentum) mode, and a second reference light that has passed through the beam splitter and is converted to a first reference light of a plane wave.
  • OAM Organic Angular Momentum
  • a second spiral phase plate that converts back light a specific device that propagates only plane wave light and passes only the first reference light and the second turn back light that are plane waves converted by the second spiral phase plate, and the above.
  • a beat detector that outputs the difference between the frequency of the beat signal obtained by combining the first reference light and the second folded light and the reference frequency, and the beam splitter is transmitted so that the difference becomes 0 or constant. It is characterized by including a frequency shifter that shifts the frequency of the reference light, and an optical antenna that transmits the reference light output from the frequency shifter to the receiver via space.
  • FIG. 1 is a block diagram showing a configuration of a spatial optical frequency transmission system using a transmitter and a receiver according to an embodiment of the present invention.
  • the spatial optical frequency transmission system (also referred to as a system) 100 shown in FIG. 1 includes a transmitter 10 and a receiver 30 that are separated from each other at a remote location or the like.
  • the transmitter 10 has a function of transmitting a reference light (reference signal light) 1 which is a light wave of a reference frequency to space and receiving a return light (return signal light) 7 from a receiver 30.
  • a reference light reference signal light
  • return light return signal light
  • the receiver 30 receives the reference light 1 from the transmitter 10 and transmits the received reference light 1 to the user terminal 42 having communication and information processing functions via the optical fiber 41. Further, the receiver 30 has a function of reflecting the received reference light 1 and returning the reflected light 7 due to the reflection to the transmitter 10 via the space.
  • the transmitter 10 includes an isolator 12 that receives the reference light emitted from the reference light source 11, a beam splitter 13, a Faraday rotator 14, a first spiral phase plate 15, a second spiral phase plate 16, and a lens 17. , A single-mode fiber 18, a reference oscillator 19, a beat detector 20, an oscillator control unit 21, a variable oscillator 22, a frequency shifter 23, and an optical antenna 24.
  • the reference light source 11 may be provided in the transmitter 10.
  • the beat detector according to the claim includes a reference oscillator 19, an oscillator control unit 21, and a variable oscillator 22.
  • the receiver 30 includes an optical antenna 31, a beam splitter 32, a Faraday rotator 33, a third spiral phase plate 34, and a lens 35.
  • the system 100 is realized by using spiral phase plates (first to third spiral phase plates 15, 16, 34) other than AOM, which is an active optical device applied in the above-mentioned conventional technique.
  • the spiral phase plate is formed of a phase plate made of a spiral glass material, and converts a single-frequency plane wave into a light wave having a swirling wavefront. This conversion is realized by the optical orbital angular momentum (OAM: Orbital Angular Momentum).
  • OAM optical orbital angular momentum
  • the wavefront state of the light wave is called OAM mode.
  • spiral phase plates There are two types of spiral phase plates: one that reflects a plane wave and converts it into a spiral beam, which is a light wave having a spiral wavefront, and one that passes it and converts it into a spiral beam.
  • the spiral phase plate is a passive optical device because it only receives and reflects or passes light and does not require any other control.
  • the isolator 12 passes the reference light 1 "0" in only one direction and exits to the beam splitter 13 through the space.
  • the beam splitter 13 reflects or passes the reference light 1 "0".
  • the light reflected by the beam splitter 13 with the reference light 1 "0" is referred to as reference light 2 "0" (first reference light).
  • the Faraday rotator 14 rotates the reference light 2 "0" reflected by the beam splitter 12 in the one polarization direction and outputs it to the first spiral phase plate 15 via space. Further, the Faraday rotator 14 rotates the reference light 2 “+1”, which will be described later, reflected by the first spiral phase plate 15 in the inverse polarization direction, and outputs the light to the beam splitter 13 through the space.
  • the reference light 2 "+1" (second reference light) is emitted.
  • the reference light 2 "+1” is transmitted from space through the beam splitter 13 via the Faraday rotator 14, and is further incident on the second spiral phase plate 16 via space.
  • the second spiral phase plate 16 is converted into the reference light 2 "0" by transmitting the incident reference light 2 "+1". Further, the second spiral phase plate 16 converts the folded light 7 "0” by transmitting the folded light 7 "+1" (first folded light) described later, and transmits the unnecessary reflected light 8 "0” described later. By doing so, it is converted into unnecessary reflected light 8 "-1".
  • this conversion is designed to be converted to reference light 2 "0", unnecessary reflected light 8 "-1", and return light 7 "0", that is, (0, -1, 0).
  • it may be designed to be (0, + 1,0), (0, -2, 0), or the like. That is, the reference light 2 and the return light 7 may be in the 0 mode, and the unnecessary reflected light 8 “-1” may be in the OAM mode other than the 0 mode.
  • the lens 17 collects the reference light 2 “0”, the folded light 7 “0”, or the unnecessary reflected light 8 “-1” transmitted from the space through the second spiral phase plate 16 and condenses the single mode fiber 18. It is incident on.
  • the single mode fiber 18 as a device (specific device)
  • the reference oscillator 19 outputs a reference electric RS (Reference Signal) signal 3 to the beat detector 20 via wiring.
  • RS Reference Signal
  • the beat detector 20 converts an optical beat signal obtained by combining the reference light 2 "0" and the return light 7 "0” into an electric signal, and then compares the frequency of this electric signal with the reference frequency f0 of the RS signal 3.
  • the frequency difference signal 4 which is the difference is output.
  • the oscillator control unit 21 detects the frequency fluctuation amount from the frequency difference signal 4, and the variable oscillator 22 cancels the frequency fluctuation amount corresponding to 1/2 of the frequency fluctuation amount by the control signal 5 (variable signal 6). Control to output.
  • the frequency shifter 23 shifts the frequency of the reference light 1 "0" according to the variable value of the variable signal 6.
  • the optical antenna 24 transmits the reference light 1 "0" output from the frequency shifter 23 to the space.
  • the optical antenna 31 of the receiver 30 receives the reference light 1 "0" transmitted from the optical antenna 24 of the transmitter 10.
  • the received reference light 1 "0" is reflected by the beam splitter 32 through the space and becomes a component of the return light 7 "0". This component is output from the space to the third spiral phase plate 34 through the space via the Faraday rotator 33.
  • the third spiral phase plate 34 reflects the component of the folded light 7 "0" and emits the folded light 7 "+1".
  • the folded light 7 "+1” is reflected from the space by the beam splitter 32 via the Faraday rotator 33, and the positive and negative of the OAM mode is inverted by this reflection to become the folded light 7 "-1", which is the space from the optical antenna 31. Will be sent to.
  • the unnecessary reflected light 8 “0” reflected in the receiver 30 is also transmitted from the optical antenna 31.
  • the optical antenna 24 of the transmitter 10 and the optical antenna 31 of the receiver 30 are arranged. It is also possible to transmit the reference light 1 "0" as a high-order mode.
  • step S1 shown in FIG. 2 the reference light 1 “0” of the reference frequency is emitted from the reference light source 11.
  • the emitted reference light 1 “0” is reflected and transmitted by the beam splitter 13 via the isolator 12 in step S2.
  • the reflected reference light 1 "0” becomes the reference light 2 "0” output to the Faraday rotator 14.
  • the transmitted reference light 1 “0” is output to the frequency shifter 23.
  • step S3 the reference light 2 "0" is rotated in the unipolarization direction by the Faraday rotator 14 and then output to the first spiral phase plate 15.
  • step S4 the reference light 2 "0" is reflected by the first spiral phase plate 15 and is emitted as the reference light 2 "+1".
  • step S5 the emitted reference light 2 “+1” is rotated by the Faraday rotator 14 in the direction of inverse polarization with that of step S3, and then passes through the beam splitter 13 and is incident on the second spiral phase plate 16. Be done. At this time, it is assumed that the folded light 7 “+1” and the unnecessary reflected light 8 “0” from the receiver 30 reflected by the beam splitter 13 are also incident on the second spiral phase plate 16.
  • step S6 the incident back light 7 “+1” and unnecessary reflected light 8 “0” from the receiver 30, and the reference light 2 “+1” in step S5 are transmitted through the second spiral phase plate 16. Due to the phase modulation action of -1, the folded light 7 “0”, the unnecessary reflected light 8 "-1", and the reference light 2 "0" are output.
  • step S7 the output return light 7 "0", unnecessary reflected light 8 "-1", and reference light 2 "0" are condensed by the lens 17 and incident on the single mode fiber 18. Since the single mode fiber 18 passes only the light in the “0” mode, the folded light 7 “0” and the reference light 2 “0” pass through and are input to the beat detector 20.
  • step S8 in the beat detector 20, the optical beat signal to which the input return light 7 “0” and the reference light 2 “0” are combined is converted into an electric signal. Further, the beat detector 20 outputs a frequency difference signal 4 based on a comparison between the frequency of the converted electric signal and the reference frequency f0 of the RS signal 3.
  • step S9 shown in FIG. 3 the oscillator control unit 21 controls the variable processing of the variable value of the variable signal 6 oscillated by the variable oscillator 22 by the control signal 5 corresponding to the frequency fluctuation of the frequency difference signal 4. do.
  • the variable signal 6 is output to the frequency shifter 23.
  • step S10 in the frequency shifter 23, the frequency of the reference light 1 "0" is shifted by the frequency corresponding to the variable value -3 of the variable signal 6 and output to the optical antenna 24.
  • step S11 the reference light 1 "0" is transmitted from the optical antenna 24 to the optical antenna 31 of the receiver 30 via space.
  • step S12 the reference light 1 "0" received by the optical antenna 31 is reflected by the beam splitter 32 and becomes a folded light 7 "0" component to the third spiral phase plate 34 via the Faraday rotator 33. It is output.
  • step S13 the folded light 7 "0" component is reflected by the third spiral phase plate 34 and emitted as the folded light 7 "+1".
  • the emitted return light 7 "+1" is reflected by the beam splitter 13 via the Faraday rotator 14 in step S14, becomes the return light 7 "-1", and is transmitted from the optical antenna 31 to the space. ..
  • the unnecessary reflected light 8 "-1" is also transmitted from the optical antenna 31.
  • step S15 the transmitted return light 7 "-1" is received by the optical antenna 24 of the transmitter 10.
  • the received return light 7 “-1” is reflected by the beam splitter 13 via the frequency shifter 23. Due to this reflection, the folded light 7 “-1” is inverted to become the folded light 7 "+1", and is incident on the second spiral phase plate 16. At this time, it is assumed that the reference light 2 "+1" transmitted through the beam splitter 13 is also incident on the second spiral phase plate 16.
  • Both the incident return light 7 "+1" and the reference light 2 "0" are processed in the same manner as described above in steps S6 to S8.
  • the beat signal 4 having a frequency f0 is output from the beat detector 20 to the oscillator control unit 21.
  • step S9 the oscillator control unit 21 controls the variable processing of the variable value of the variable signal 6 oscillated by the variable oscillator 22 by the control signal 5 corresponding to the frequency f0 of the beat signal 4.
  • the variable value of the variable signal 6 from the variable oscillator 22 becomes 0 and is output to the frequency shifter 23.
  • step S10 in the frequency shifter 23, since the variable value of the variable signal 6 is 0, the reference frequency of the reference light 1 “0” is not shifted, and the reference light 1 “0” of the reference frequency as it is is the optical antenna. It is output to 24.
  • the reference light 1 "0" having this reference frequency is received by the optical antenna 31 of the receiver 30, passes through the beam splitter 32, is condensed by the lens 35, is incident on the optical fiber 41, and is incident on the optical fiber 41 via the optical fiber 41. It is transmitted to the user terminal 42.
  • the transmitter 10 of the system 100 reflects and transmits the reference light 1 “0” of the plane wave at the reference frequency, and the reference light corresponding to the reference light 1 “0” reflected by the beam splitter 13. It is provided with a first spiral phase plate 15 that reflects 2 “0” and converts it into a spiral and predetermined OAM mode reference light 2 “+1”.
  • the transmitter 10 transmits the reference light 2 “+1” transmitted through the beam splitter 13 and converts it into the reference light 2 “0” of the plane wave, and the reference light 1 transmitted from the transmitter 10 via space.
  • a second light “0” is folded back by the receiver 30 and is transmitted through the folded light 7 "+1” in the OAM mode in which the positive and negative are inverted due to reflection by the beam splitter 13 and converted into the folded light 7 "0” of a plane wave.
  • a spiral phase plate 16 is provided.
  • the transmitter 10 propagates only the light of the plane wave, and passes only the reference light 2 “0” and the return light 7 “0”, which are the plane waves converted by the second spiral phase plate 16, and the single mode fiber 18.
  • the beat detector 20 that outputs the frequency difference between the reference light 2 “0” and the folded light 7 “0", and the reference light 1 "0” that has passed through the beam splitter 13 so that the frequency difference becomes 0 or constant.
  • the configuration includes a frequency shifter 23 that shifts the frequency, and an optical antenna 24 that transmits the reference light 1 “0” output from the frequency shifter 23 to the receiver 30 via space.
  • the reference light 2 "0" corresponding to the reference light 1 "0” of the reference frequency and the folded light 7 “0” in which the reference light 1 "0” is folded back by the receiver 30 are used.
  • the frequency difference from “0” can be set to 0 or constant. Therefore, the transmitter 10 transmits the constant frequency reference light 1 "0” to the receiver 30 via the space, and the transmitted constant frequency reference light 1 "0” is received by the receiver 30 after being received by the user. It can be transmitted to the terminal 42. Since the transmitter 10 that performs this processing is configured by using two spiral phase plates 15 and 16 which are passive optical devices, it is compared with an active optical device that utilizes mechanical vibration by ultrasonic waves such as a conventional AOM. , Since failure is less likely to occur, reliability can be improved. Further, since it is a passive optical device, power consumption can be suppressed as compared with an active optical device.
  • the second spiral phase plate 16 is the unnecessary reflected light 8 “0” reflected by the receiver 30 when the reference light 1 “0” transmitted from the transmitter 10 through the space is turned back by the receiver 30.
  • -1 is transmitted, converted into unnecessary reflected light 8“ -1 ”in a predetermined OAM mode, and output to the single mode fiber 18.
  • the unnecessary reflected light 8 “-1” in the OAM mode converted by the second spiral phase plate 16 cannot pass through the single mode fiber 18 propagating only the plane wave. Therefore, the unnecessary reflected light 8 "-1" can be removed on the input side of the single mode fiber 18.
  • the reference light 1 “0” from the transmitter 10 is reflected by the beam splitter 32 and the folded light 7 “+1” component is transferred to the folded light 7 “+1” in the OAM mode on the spiral phase plate. It is converted to "+1", and the folding light 7 "+1” is converted to the folding light 7 "0” in the OAM mode by the beam splitter 13 and transmitted to the transmitter 10. Since the receiver 30 that performs this processing is configured by using the spiral phase plate 34 that is a passive optical device, failure is less likely to occur as compared with a conventional active optical device such as AOM, so that reliability can be improved and further. Compared to active optical devices, power consumption can be reduced.
  • a beam splitter that reflects and transmits the reference light of a plane wave at a reference frequency and a first reference light corresponding to the reference light reflected by the beam splitter are reflected, and a predetermined OAM (Orbital Angular Momentum) is spirally formed.
  • the first spiral phase plate that converts to the second reference light in the mode) and the second reference light that has passed through the beam splitter are transmitted and converted to the first reference light of the plane wave, and transmitted from the transmitter via space.
  • With the second spiral phase plate that the reference light is folded back by the receiver and is transmitted through the first folded light in the OAM mode whose positive and negative are inverted by the reflection by the beam splitter and converted into the second folded light of the plane wave.
  • the specific device that propagates only the light of the plane wave and passes only the first reference light and the second folded light, which are the plane waves converted by the second spiral phase plate, and the first reference light and the second folded light.
  • a beat detector that outputs the difference between the frequency of the beat signal that combines the waves and the reference frequency, and a frequency shifter that shifts the frequency of the reference light that has passed through the beam splitter so that the difference is 0 or constant.
  • the transmitter is provided with an optical antenna for transmitting the reference light output from the frequency shifter to the receiver via space.
  • the frequency difference between the first reference light corresponding to the reference light of the reference frequency and the second folded light in which the reference light is folded back by the receiver can be set to 0 or constant. Therefore, the reference light having a constant frequency can be transmitted from the transmitter to the receiver via the space, and the transmitted reference light having the constant frequency can be transmitted to the user terminal after being received by the receiver. Since the transmitter that performs this processing is configured by using two spiral phase plates that are passive optical devices, a failure occurs as compared with an active optical device that uses mechanical vibration by ultrasonic waves such as the conventional AOM. Since it becomes difficult, reliability can be improved. Further, since it is a passive optical device, power consumption can be suppressed as compared with an active optical device.
  • the second spiral phase plate transmits unnecessary reflected light reflected by the receiver when the reference light transmitted from the transmitter through the space is turned back by the receiver, and has a predetermined OAM mode.
  • the unnecessary reflected light in the OAM mode converted by the second spiral phase plate cannot pass through a specific device that propagates only a plane wave. Therefore, unnecessary reflected light can be removed on the input side of the specific device.
  • An optical antenna that receives the reference light of a plane wave transmitted from the transmitter via space, a beam splitter that reflects and transmits the reference light received by the optical antenna, and a reference that is reflected by the beam splitter.
  • a third spiral phase plate that reflects the folded light component corresponding to the light and converts it into the first folded light in a predetermined OAM mode in a spiral manner is provided, and the first folded light converted by the third spiral phase plate is provided. Is converted into the second folded light in the OAM mode in which the positive and negative are inverted by the reflection by the beam splitter, and the light is returned from the optical antenna to the transmitter via space.
  • the folding light component in which the reference light from the transmitter is reflected by the beam splitter is converted into the first folding light in the OAM mode by the third spiral phase plate, and the first folding light is converted. Is converted into the second return light in OAM mode by the beam splitter and transmitted to the transmitter. Since the receiver that performs this processing is configured by using a third spiral phase plate that is a passive optical device, failure is less likely to occur compared to an active optical device such as a conventional AOM, so reliability can be improved and further. Compared to active optical devices, power consumption can be suppressed.
  • a spatial optical frequency transmission system including the transmitter according to (1) or (2) above and the receiver according to (3) above.

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Abstract

A transmitter (10) of a spatial optical frequency transmission system (100) is provided with first and second helical phase plates (15, 16) that are passive optical devices, and sets, to 0 or a fixed level, a frequency difference between reference light (2 "0") corresponding to standard light (1 "0") at a standard frequency and return light (7 "0") obtained by returning of the standard light (1 "0") by a receiver (30). Accordingly, the standard light (1 "0") at a fixed frequency from the transmitter (10) is transmitted to the receiver (30) via a space, and the transmitted standard light (1 "0") at the fixed frequency can be transmitted to a user terminal (42) after reception by the receiver (30).

Description

送信機、受信機、空間光周波数伝送システム及び空間光周波数伝送方法Transmitter, receiver, spatial optical frequency transmission system and spatial optical frequency transmission method
　本発明は、離間した送信機及び受信機間で基準となる光周波数の基準信号光を、空間を介して伝送する送信機、受信機、空間光周波数伝送システム及び空間光周波数伝送方法に関する。 The present invention relates to a transmitter, a receiver, a spatial optical frequency transmission system, and a spatial optical frequency transmission method for transmitting reference signal light having a reference optical frequency between a remote transmitter and a receiver via space.
　科学計測や通信、ナビゲーション等の様々分野において、遠隔地等に離間した送受信機間で基準となる周波数信号を高精度に伝送する技術が必要とされている。近年、周波数伝送技術の適用領域拡大に向け、光ファイバによる伝送ではなく、空間を介して基準となる光周波数の信号光を伝送する光周波数伝送システムがある。この種の技術として、非特許文献１に記載のものがある。 In various fields such as scientific measurement, communication, and navigation, there is a need for technology for highly accurate transmission of reference frequency signals between transceivers that are separated from each other in remote areas. In recent years, with the aim of expanding the application range of frequency transmission technology, there is an optical frequency transmission system that transmits signal light of a reference optical frequency through space instead of transmission by optical fiber. As a technique of this kind, there is one described in Non-Patent Document 1.
　非特許文献１の空間光周波数伝送方式によるシステムを説明する。このシステムは互いに離間した基準信号光（基準光ともいう）を空間へ送信する送信機と、基準光を受信して送信機へ折り返す受信機とを備える。送信機から基準周波数の光波である基準光を、空間を介して受信機へ送信する。受信機では、ＡＯＭ（Acousto Oputic Modulator：音響光学変調）によって、受信した基準光を周波数シフトさせた折返し信号光（折返し光ともいう）を送信機へ返信する。 A system based on the spatial optical frequency transmission method of Non-Patent Document 1 will be described. This system includes a transmitter that transmits reference signal light (also referred to as reference light) separated from each other into space, and a receiver that receives the reference light and returns it to the transmitter. The reference light, which is a light wave of a reference frequency, is transmitted from the transmitter to the receiver via space. The receiver returns back signal light (also referred to as back light) obtained by frequency-shifting the received reference light by AOM (Acousto Oputic Modulator) to the transmitter.
　送信機では、折返し光と基準光との差分であるビート信号から位相変動を検知し、この検知した位相変動に応じて、送信側で位相変動を相殺可能な周波数シフトを基準光に対して行う。これにより受信側で受信される基準光の周波数が一定となるので、受信機からユーザ等の通信端末機へ光ファイバで一定周波数の基準光を伝送できる。 The transmitter detects a phase fluctuation from the beat signal, which is the difference between the folded light and the reference light, and performs a frequency shift with respect to the reference light so that the transmission side can cancel the phase fluctuation according to the detected phase fluctuation. .. As a result, the frequency of the reference light received on the receiving side becomes constant, so that the reference light having a constant frequency can be transmitted from the receiver to a communication terminal such as a user via an optical fiber.
　このような方式のシステムでは、受信機のファラデーミラーで基準光を反射し、この際にＡＯＭにより基準光の周波数ｆ１をシフトして周波数ｆ２の折返し光として送信機へ返信している。つまり、基準光と折返し光の周波数ｆ１，ｆ２を変えて区別している。この周波数ｆ２の折返し光とすることで、受信機からの不要な反射光によるノイズを抑制している。 In such a system, the reference light is reflected by the Faraday mirror of the receiver, and at this time, the frequency f1 of the reference light is shifted by the AOM and returned to the transmitter as the return light of the frequency f2. That is, the frequencies f1 and f2 of the reference light and the return light are changed to distinguish them. By using the folded light having a frequency of f2, noise due to unnecessary reflected light from the receiver is suppressed.
　しかし、上記非特許文献１のシステムにおいて、ＡＯＭは超音波による機械的な振動を利用したアクティブ光デバイスである。このため、パッシブ光デバイスに比べて故障が起こり易いため信頼性が低く、更に、消費電力が高いといった課題があった。 However, in the system of Non-Patent Document 1 above, AOM is an active optical device using mechanical vibration by ultrasonic waves. For this reason, there are problems that the reliability is low and the power consumption is high because the failure is more likely to occur than the passive optical device.
　本発明は、このような事情に鑑みてなされたものであり、故障を起こり難くして信頼性を向上させ、消費電力を抑制することを課題とする。 The present invention has been made in view of such circumstances, and an object of the present invention is to prevent failures, improve reliability, and suppress power consumption.
　上記課題を解決するため、本発明の送信機は、基準周波数で平面波の基準光を反射及び透過するビームスプリッタと、前記ビームスプリッタで反射された基準光に対応する第１参照光を反射して、螺旋状で所定のＯＡＭ（Orbital Angular Momentum）モードの第２参照光に変換する第１螺旋位相板と、前記ビームスプリッタを透過した第２参照光を透過して平面波の第１参照光に変換すると共に、送信機から空間を介して送信された基準光が受信機で折り返され、且つ前記ビームスプリッタでの反射により正負が反転したＯＡＭモードの第１折返し光を透過して、平面波の第２折返し光に変換する第２螺旋位相板と、平面波の光のみを伝搬し、前記第２螺旋位相板で変換された平面波である第１参照光及び第２折返し光のみを通す特定デバイスと、前記第１参照光と前記第２折返し光とを合波したビート信号の周波数と、基準周波数との差分を出力するビート検出器と、前記差分が０又は一定となるように、前記ビームスプリッタを透過した基準光の周波数をシフトする周波数シフタと、前記周波数シフタから出力される基準光を空間を介して受信機へ送信する光アンテナとを備えることを特徴とする。 In order to solve the above problems, the transmitter of the present invention reflects and transmits a beam splitter that reflects and transmits a reference light of a plane wave at a reference frequency, and a first reference light corresponding to the reference light reflected by the beam splitter. , A first spiral phase plate that is spiral and converts to a second reference light in a predetermined OAM (Orbital Angular Momentum) mode, and a second reference light that has passed through the beam splitter and is converted to a first reference light of a plane wave. At the same time, the reference light transmitted from the transmitter through the space is folded back by the receiver and transmitted through the first folded light in the OAM mode in which the positive and negative are inverted due to the reflection by the beam splitter, and the second plane wave is transmitted. A second spiral phase plate that converts back light, a specific device that propagates only plane wave light and passes only the first reference light and the second turn back light that are plane waves converted by the second spiral phase plate, and the above. A beat detector that outputs the difference between the frequency of the beat signal obtained by combining the first reference light and the second folded light and the reference frequency, and the beam splitter is transmitted so that the difference becomes 0 or constant. It is characterized by including a frequency shifter that shifts the frequency of the reference light, and an optical antenna that transmits the reference light output from the frequency shifter to the receiver via space.
　本発明によれば、故障を起こり難くして信頼性を向上させ、消費電力を抑制できる。 According to the present invention, failure is less likely to occur, reliability is improved, and power consumption can be suppressed.
本発明の実施形態に係る送信機及び受信機を用いた空間光周波数伝送システムの構成を示すブロック図である。It is a block diagram which shows the structure of the space optical frequency transmission system which used the transmitter and the receiver which concerns on embodiment of this invention. 本実施形態の空間光周波数伝送システムの処理動作を説明するための第１のフローチャートである。It is a 1st flowchart for demonstrating the processing operation of the space optical frequency transmission system of this embodiment. 本実施形態の空間光周波数伝送システムの処理動作を説明するための第２のフローチャートである。It is a 2nd flowchart for demonstrating the processing operation of the space optical frequency transmission system of this embodiment.
　以下、本発明の実施形態を、図面を参照して説明する。
＜実施形態の構成＞
　図１は、本発明の実施形態に係る送信機及び受信機を用いた空間光周波数伝送システムの構成を示すブロック図である。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Structure of Embodiment>
FIG. 1 is a block diagram showing a configuration of a spatial optical frequency transmission system using a transmitter and a receiver according to an embodiment of the present invention.
　図１に示す空間光周波数伝送システム（システムともいう）１００は、互いが遠隔地等に離間する送信機１０と受信機３０とを備える。 The spatial optical frequency transmission system (also referred to as a system) 100 shown in FIG. 1 includes a transmitter 10 and a receiver 30 that are separated from each other at a remote location or the like.
　送信機１０は、基準周波数の光波である基準光（基準信号光）１を空間へ送信すると共に、受信機３０からの折返し光（折返し信号光）７を受信する機能を備える。 The transmitter 10 has a function of transmitting a reference light (reference signal light) 1 which is a light wave of a reference frequency to space and receiving a return light (return signal light) 7 from a receiver 30.
　受信機３０は、送信機１０から基準光１を受信し、この受信した基準光１を、光ファイバ４１を介して通信及び情報処理機能を備えるユーザ端末機４２へ送信する。更に、受信機３０は、受信した基準光１を反射し、この反射による折返し光７を、空間を介して送信機１０へ返信する機能を備える。 The receiver 30 receives the reference light 1 from the transmitter 10 and transmits the received reference light 1 to the user terminal 42 having communication and information processing functions via the optical fiber 41. Further, the receiver 30 has a function of reflecting the received reference light 1 and returning the reflected light 7 due to the reflection to the transmitter 10 via the space.
　送信機１０は、基準光源１１から出射される基準光を受信するアイソレータ１２と、ビームスプリッタ１３と、ファラデー回転子１４と、第１螺旋位相板１５と、第２螺旋位相板１６と、レンズ１７と、シングルモードファイバ１８と、基準発振器１９と、ビート検出器２０と、発振器制御部２１と、可変発振器２２と、周波数シフタ２３と、光アンテナ２４とを備えて構成されている。なお、基準光源１１は、送信機１０に備えられていてもよい。なお、請求項記載のビート検出器は、基準発振器１９、発振器制御部２１及び可変発振器２２を含んで構成される。 The transmitter 10 includes an isolator 12 that receives the reference light emitted from the reference light source 11, a beam splitter 13, a Faraday rotator 14, a first spiral phase plate 15, a second spiral phase plate 16, and a lens 17. , A single-mode fiber 18, a reference oscillator 19, a beat detector 20, an oscillator control unit 21, a variable oscillator 22, a frequency shifter 23, and an optical antenna 24. The reference light source 11 may be provided in the transmitter 10. The beat detector according to the claim includes a reference oscillator 19, an oscillator control unit 21, and a variable oscillator 22.
　受信機３０は、光アンテナ３１と、ビームスプリッタ３２と、ファラデー回転子３３と、第３螺旋位相板３４と、レンズ３５とを備えて構成されている。 The receiver 30 includes an optical antenna 31, a beam splitter 32, a Faraday rotator 33, a third spiral phase plate 34, and a lens 35.
　本実施形態では、前述の従来技術で適用されていたアクティブ光デバイスであるＡＯＭ以外の螺旋位相板（第１～第３螺旋位相板１５，１６，３４）を用いてシステム１００を実現した。 In the present embodiment, the system 100 is realized by using spiral phase plates (first to third spiral phase plates 15, 16, 34) other than AOM, which is an active optical device applied in the above-mentioned conventional technique.
　螺旋位相板は、螺旋状のガラス材による位相板により形成され、単一周波数の平面波を、渦を巻いた波面を有する光波に変換するものである。この変換は、光軌道角運動量（ＯＡＭ：Orbital Angular Momentum）で実現される。その光波の波面状態をＯＡＭモードと呼ぶ。 The spiral phase plate is formed of a phase plate made of a spiral glass material, and converts a single-frequency plane wave into a light wave having a swirling wavefront. This conversion is realized by the optical orbital angular momentum (OAM: Orbital Angular Momentum). The wavefront state of the light wave is called OAM mode.
　螺旋位相板には、平面波を反射して螺旋状の波面を有する光波である螺旋ビームに変換するものと、通過させて螺旋ビームに変換するものがある。螺旋位相板は、光を受けて反射又は通過させるのみであり、その他の制御が必要ないことから、パッシブ光デバイスである。 There are two types of spiral phase plates: one that reflects a plane wave and converts it into a spiral beam, which is a light wave having a spiral wavefront, and one that passes it and converts it into a spiral beam. The spiral phase plate is a passive optical device because it only receives and reflects or passes light and does not require any other control.
　螺旋位相板の巻き数が増える程に、螺旋ビームの光強度分布が外周側に移行して円環状となり、円環状の径が大きくなってゆく。光強度分布による円環状の径が大きくなる程にＯＡＭモードが大きくなる。螺旋ビームの光強度は、円環状の１周における０（始点）～２π（終点）の位相変調を1単位としており、０～２πでは、ｍ＝＋１となる。ｍはＯＡＭモードの次数である。０～４πでは、ｍ＝＋２となる。 As the number of turns of the spiral phase plate increases, the light intensity distribution of the spiral beam shifts to the outer peripheral side to form an annular shape, and the diameter of the annular shape increases. The larger the diameter of the annular shape due to the light intensity distribution, the larger the OAM mode. The light intensity of the spiral beam has a phase modulation of 0 (start point) to 2π (end point) in one circumference of the ring as one unit, and m = + 1 at 0 to 2π. m is the order of the OAM mode. From 0 to 4π, m = +2.
　平面波ではｍ＝「０」である。ｍ＝「０」は、平面波の中心部分が最大の光強度となっている。ｍ＝＋１以上になると、中心部分の光強度が外周側に寄るが、この状態では、中心部分の光強度が無くなる。また、ｍ＝「－１」のように、マイナスは、渦の回転がｍ＝「＋１」の逆回転になることを表す。 For plane waves, m = "0". When m = "0", the central portion of the plane wave has the maximum light intensity. When m = +1 or more, the light intensity of the central portion shifts to the outer peripheral side, but in this state, the light intensity of the central portion disappears. Further, like m = "-1", minus means that the rotation of the vortex becomes the reverse rotation of m = "+1".
　送信機１０側の基準光源１１は、レーザを用いて構成されており、基準周波数の平面波であるｍ＝「０」の基準光（レーザ光）を空間を介してアイソレータ１２へ出射する。ｍ＝「０」の平面波の基準光を基準光１「０」と表す。「０」や「＋１」等はＯＡＭモードを示す。 The reference light source 11 on the transmitter 10 side is configured by using a laser, and emits a reference light (laser light) of m = "0", which is a plane wave of a reference frequency, to the isolator 12 via a space. The reference light of a plane wave with m = "0" is represented as the reference light 1 "0". “0”, “+1” and the like indicate the OAM mode.
　アイソレータ１２は、基準光１「０」を一方向にのみに通過させ、空間を介してビームスプリッタ１３へ出射する。 The isolator 12 passes the reference light 1 "0" in only one direction and exits to the beam splitter 13 through the space.
　ビームスプリッタ１３は、基準光１「０」を反射又は通過させる。基準光１「０」がビームスプリッタ１３で反射された光を、参照光２「０」（第１参照光）と呼ぶ。 The beam splitter 13 reflects or passes the reference light 1 "0". The light reflected by the beam splitter 13 with the reference light 1 "0" is referred to as reference light 2 "0" (first reference light).
　ファラデー回転子１４は、ビームスプリッタ１２で反射された参照光２「０」を一偏光方向に回転させ、空間を介して第１螺旋位相板１５へ出力する。また、ファラデー回転子１４は、第１螺旋位相板１５で反射した後述の参照光２「＋１」を逆偏光方向に回転させ、空間を介してビームスプリッタ１３へ出力する。 The Faraday rotator 14 rotates the reference light 2 "0" reflected by the beam splitter 12 in the one polarization direction and outputs it to the first spiral phase plate 15 via space. Further, the Faraday rotator 14 rotates the reference light 2 “+1”, which will be described later, reflected by the first spiral phase plate 15 in the inverse polarization direction, and outputs the light to the beam splitter 13 through the space.
　第１螺旋位相板１５は、ｍ＝「＋１」の位相変調作用を有する反射型の螺旋位相板である。この第１螺旋位相板１５は、参照光２「０」を反射すると、参照光２「＋１」（第２参照光）を出射する。この参照光２「＋１」は、空間からファラデー回転子１４を介してビームスプリッタ１３を透過し、更に空間を介して第２螺旋位相板１６に入射される。 The first spiral phase plate 15 is a reflection type spiral phase plate having a phase modulation action of m = "+1". When the first spiral phase plate 15 reflects the reference light 2 "0", the reference light 2 "+1" (second reference light) is emitted. The reference light 2 "+1" is transmitted from space through the beam splitter 13 via the Faraday rotator 14, and is further incident on the second spiral phase plate 16 via space.
　第２螺旋位相板１６は、ｍ＝「－１」の位相変調作用を有する透過型の螺旋位相板である。この第２螺旋位相板１６は、入射された参照光２「＋１」を透過することで参照光２「０」に変換する。更に、第２螺旋位相板１６は、後述の折返し光７「＋１」（第１折返し光）を透過することで折返し光７「０」に変換し、後述の不要反射光８「０」を透過することで不要反射光８「－１」に変換する。 The second spiral phase plate 16 is a transmission type spiral phase plate having a phase modulation action of m = "-1". The second spiral phase plate 16 is converted into the reference light 2 "0" by transmitting the incident reference light 2 "+1". Further, the second spiral phase plate 16 converts the folded light 7 "0" by transmitting the folded light 7 "+1" (first folded light) described later, and transmits the unnecessary reflected light 8 "0" described later. By doing so, it is converted into unnecessary reflected light 8 "-1".
　この変換では、図示のように参照光２「０」、不要反射光８「－１」、折返し光７「０」への変換、つまり、（０，－１，０）となるように設計しているが、（０，＋１，０）や（０，－２，０）等となるように設計してもよい。つまり、参照光２及び折返し光７が０モードで、不要反射光８「－１」が０モード以外のＯＡＭモードであればよい。 In this conversion, as shown in the figure, it is designed to be converted to reference light 2 "0", unnecessary reflected light 8 "-1", and return light 7 "0", that is, (0, -1, 0). However, it may be designed to be (0, + 1,0), (0, -2, 0), or the like. That is, the reference light 2 and the return light 7 may be in the 0 mode, and the unnecessary reflected light 8 “-1” may be in the OAM mode other than the 0 mode.
　レンズ１７は、第２螺旋位相板１６を透過して空間から入射される参照光２「０」、折返し光７「０」又は不要反射光８「－１」を集光してシングルモードファイバ１８へ入射する。 The lens 17 collects the reference light 2 “0”, the folded light 7 “0”, or the unnecessary reflected light 8 “-1” transmitted from the space through the second spiral phase plate 16 and condenses the single mode fiber 18. It is incident on.
　シングルモードファイバ１８は、ｍ＝０以外の高次モード（例えば、ｍ＝「＋１」や「－１」）を通さず、「０」モードのみを通す。このため、シングルモードファイバ１８は、参照光２「０」、折返し光７「０」を通し、不要反射光８「－１」を通さない。 The single mode fiber 18 does not pass through a higher order mode other than m = 0 (for example, m = "+1" or "-1"), but passes only in the "0" mode. Therefore, the single mode fiber 18 passes the reference light 2 “0” and the return light 7 “0”, and does not pass the unnecessary reflected light 8 “-1”.
　なお、デバイス（特定デバイス）としてのシングルモードファイバ１８に代え、ＯＡＭモード＝「０」の光のみを伝搬する（通す）空間フィルタ等の特定デバイスを用いてもよい。 Instead of the single mode fiber 18 as a device (specific device), a specific device such as a spatial filter that propagates (passes) only the light of OAM mode = "0" may be used.
　基準発振器１９は、基準となる電気のＲＳ（Reference Signal）信号３を、配線を介してビート検出器２０へ出力する。 The reference oscillator 19 outputs a reference electric RS (Reference Signal) signal 3 to the beat detector 20 via wiring.
　ビート検出器２０は、参照光２「０」及び折返し光７「０」を合波した光ビート信号を電気信号へと変換後、この電気信号の周波数とＲＳ信号３の基準周波数ｆ０とを比較した差分である周波数差信号４を出力する。 The beat detector 20 converts an optical beat signal obtained by combining the reference light 2 "0" and the return light 7 "0" into an electric signal, and then compares the frequency of this electric signal with the reference frequency f0 of the RS signal 3. The frequency difference signal 4 which is the difference is output.
　発振器制御部２１は、周波数差信号４から周波数変動量を検知し、制御信号５により可変発振器２２が周波数変動量の１／２に相当する周波数変動量を相殺する周波数信号（可変信号６）を出力するように制御する。 The oscillator control unit 21 detects the frequency fluctuation amount from the frequency difference signal 4, and the variable oscillator 22 cancels the frequency fluctuation amount corresponding to 1/2 of the frequency fluctuation amount by the control signal 5 (variable signal 6). Control to output.
　周波数シフタ２３は、可変信号６の可変値に応じて、基準光１「０」の周波数をシフトする。 The frequency shifter 23 shifts the frequency of the reference light 1 "0" according to the variable value of the variable signal 6.
　光アンテナ２４は、周波数シフタ２３から出力された基準光１「０」を、空間へ送信する。 The optical antenna 24 transmits the reference light 1 "0" output from the frequency shifter 23 to the space.
　受信機３０の光アンテナ３１は、送信機１０の光アンテナ２４から送信された基準光１「０」を受信する。この受信された基準光１「０」は、空間を介してビームスプリッタ３２で反射され、折返し光７「０」の成分となる。この成分が空間からファラデー回転子３３を介して空間を通り第３螺旋位相板３４へ出力される。 The optical antenna 31 of the receiver 30 receives the reference light 1 "0" transmitted from the optical antenna 24 of the transmitter 10. The received reference light 1 "0" is reflected by the beam splitter 32 through the space and becomes a component of the return light 7 "0". This component is output from the space to the third spiral phase plate 34 through the space via the Faraday rotator 33.
　第３螺旋位相板３４は、ｍ＝「＋１」の位相変調作用を有する反射型の螺旋位相板である。この第３螺旋位相板３４は、折返し光７「０」の成分を反射し、折返し光７「＋１」を出射する。この折返し光７「＋１」は、空間からファラデー回転子３３を介してビームスプリッタ３２で反射され、この反射によりＯＡＭモードの正負が反転して折返し光７「－１」となり、光アンテナ３１から空間へ送信される。この際、光アンテナ３１からは、受信機３０内で反射した不要反射光８「０」も送信される。 The third spiral phase plate 34 is a reflection type spiral phase plate having a phase modulation action of m = "+1". The third spiral phase plate 34 reflects the component of the folded light 7 "0" and emits the folded light 7 "+1". The folded light 7 "+1" is reflected from the space by the beam splitter 32 via the Faraday rotator 33, and the positive and negative of the OAM mode is inverted by this reflection to become the folded light 7 "-1", which is the space from the optical antenna 31. Will be sent to. At this time, the unnecessary reflected light 8 “0” reflected in the receiver 30 is also transmitted from the optical antenna 31.
　なお、このようなシステム１００においては、送信機１０の第１及び第２螺旋位相板１５，１６の配置を工夫することで、送信機１０の光アンテナ２４と受信機３０の光アンテナ３１間において、基準光１「０」を高次モードとして伝送することも可能である。 In such a system 100, by devising the arrangement of the first and second spiral phase plates 15 and 16 of the transmitter 10, the optical antenna 24 of the transmitter 10 and the optical antenna 31 of the receiver 30 are arranged. It is also possible to transmit the reference light 1 "0" as a high-order mode.
＜実施形態の動作＞
　次に、実施形態に係るシステム１００の動作を、図２及び図3に示すフローチャートを参照して説明する。 <Operation of the embodiment>
Next, the operation of the system 100 according to the embodiment will be described with reference to the flowcharts shown in FIGS. 2 and 3.
　図2に示すステップＳ１において、基準光源１１から基準周波数の基準光１「０」が出射される。この出射された基準光１「０」は、ステップＳ２において、アイソレータ１２を介してビームスプリッタ１３で反射及び透過される。反射された基準光１「０」は、ファラデー回転子１４へ出力される参照光２「０」となる。透過された基準光１「０」は、周波数シフタ２３へ出力される。 In step S1 shown in FIG. 2, the reference light 1 “0” of the reference frequency is emitted from the reference light source 11. The emitted reference light 1 "0" is reflected and transmitted by the beam splitter 13 via the isolator 12 in step S2. The reflected reference light 1 "0" becomes the reference light 2 "0" output to the Faraday rotator 14. The transmitted reference light 1 "0" is output to the frequency shifter 23.
　ステップＳ３において、上記参照光２「０」は、ファラデー回転子１４で一偏光方向に回転させられた後、第１螺旋位相板１５へ出力される。 In step S3, the reference light 2 "0" is rotated in the unipolarization direction by the Faraday rotator 14 and then output to the first spiral phase plate 15.
　ステップＳ４において、参照光２「０」が第１螺旋位相板１５で反射され、参照光２「＋１」となって出射される。 In step S4, the reference light 2 "0" is reflected by the first spiral phase plate 15 and is emitted as the reference light 2 "+1".
　この出射された参照光２「＋１」は、ステップＳ５において、ファラデー回転子１４で上記ステップＳ３と逆偏光方向に回転させられた後、ビームスプリッタ１３を透過して第２螺旋位相板１６に入射される。この際、第２螺旋位相板１６には、ビームスプリッタ１３で反射された受信機３０からの折返し光７「＋１」及び不要反射光８「０」も入射されたとする。 In step S5, the emitted reference light 2 “+1” is rotated by the Faraday rotator 14 in the direction of inverse polarization with that of step S3, and then passes through the beam splitter 13 and is incident on the second spiral phase plate 16. Be done. At this time, it is assumed that the folded light 7 “+1” and the unnecessary reflected light 8 “0” from the receiver 30 reflected by the beam splitter 13 are also incident on the second spiral phase plate 16.
　ステップＳ６において、入射された受信機３０からの折返し光７「＋１」及び不要反射光８「０」と、上記ステップＳ５の参照光２「＋１」とは、第２螺旋位相板１６を透過する際の－１の位相変調作用により、折返し光７「０」、不要反射光８「－１」、参照光２「０」となって出力される。 In step S6, the incident back light 7 “+1” and unnecessary reflected light 8 “0” from the receiver 30, and the reference light 2 “+1” in step S5 are transmitted through the second spiral phase plate 16. Due to the phase modulation action of -1, the folded light 7 "0", the unnecessary reflected light 8 "-1", and the reference light 2 "0" are output.
　ステップＳ７において、その出力された折返し光７「０」、不要反射光８「－１」、参照光２「０」は、レンズ１７で集光されてシングルモードファイバ１８へ入射される。シングルモードファイバ１８は、「０」モードの光のみを通過させるため、折返し光７「０」及び参照光２「０」が通過してビート検出器２０に入力される。 In step S7, the output return light 7 "0", unnecessary reflected light 8 "-1", and reference light 2 "0" are condensed by the lens 17 and incident on the single mode fiber 18. Since the single mode fiber 18 passes only the light in the “0” mode, the folded light 7 “0” and the reference light 2 “0” pass through and are input to the beat detector 20.
　ステップＳ８において、ビート検出器２０では、入力された折返し光７「０」及び参照光２「０」が合波された光ビート信号が電気信号に変換される。更に、ビート検出器２０では、変換された電気信号の周波数とＲＳ信号３の基準周波数ｆ０との比較による周波数差信号４を出力する。 In step S8, in the beat detector 20, the optical beat signal to which the input return light 7 “0” and the reference light 2 “0” are combined is converted into an electric signal. Further, the beat detector 20 outputs a frequency difference signal 4 based on a comparison between the frequency of the converted electric signal and the reference frequency f0 of the RS signal 3.
　次に、図３に示すステップＳ９において、発振器制御部２１は、周波数差信号４の周波数変動に対応した制御信号５により、可変発振器２２で発振される可変信号６の可変値の可変処理を制御する。可変信号６は、周波数シフタ２３へ出力される。 Next, in step S9 shown in FIG. 3, the oscillator control unit 21 controls the variable processing of the variable value of the variable signal 6 oscillated by the variable oscillator 22 by the control signal 5 corresponding to the frequency fluctuation of the frequency difference signal 4. do. The variable signal 6 is output to the frequency shifter 23.
　ステップＳ１０において、周波数シフタ２３では、基準光１「０」の周波数が、可変信号６の可変値－３に対応する周波数だけシフトされ、光アンテナ２４へ出力される。 In step S10, in the frequency shifter 23, the frequency of the reference light 1 "0" is shifted by the frequency corresponding to the variable value -3 of the variable signal 6 and output to the optical antenna 24.
　ステップＳ１１において、基準光１「０」が、光アンテナ２４から空間を介して受信機３０の光アンテナ３１へ送信される。 In step S11, the reference light 1 "0" is transmitted from the optical antenna 24 to the optical antenna 31 of the receiver 30 via space.
　ステップＳ１２において、光アンテナ３１で受信された基準光１「０」は、ビームスプリッタ３２で反射され、折返し光７「０」成分となってファラデー回転子３３を介して第３螺旋位相板３４へ出力される。 In step S12, the reference light 1 "0" received by the optical antenna 31 is reflected by the beam splitter 32 and becomes a folded light 7 "0" component to the third spiral phase plate 34 via the Faraday rotator 33. It is output.
　ステップＳ１３において、折返し光７「０」成分が第３螺旋位相板３４で反射され、折返し光７「＋１」となって出射される。 In step S13, the folded light 7 "0" component is reflected by the third spiral phase plate 34 and emitted as the folded light 7 "+1".
　この出射された折返し光７「＋１」は、ステップＳ１４において、ファラデー回転子１４を介してビームスプリッタ１３で反射され、折返し光７「－１」となって、光アンテナ３１から空間へ送信される。なお、受信機３０内で反射した不要反射光８「０」がある場合、不要反射光８「－１」も光アンテナ３１から送信される。 The emitted return light 7 "+1" is reflected by the beam splitter 13 via the Faraday rotator 14 in step S14, becomes the return light 7 "-1", and is transmitted from the optical antenna 31 to the space. .. When there is unnecessary reflected light 8 "0" reflected in the receiver 30, the unnecessary reflected light 8 "-1" is also transmitted from the optical antenna 31.
　ステップＳ１５において、その送信された折返し光７「－１」が、送信機１０の光アンテナ２４で受信される。この受信された折返し光７「－１」は、周波数シフタ２３を介してビームスプリッタ１３で反射される。この反射により折返し光７「－１」は反転して折返し光７「＋１」となり、第２螺旋位相板１６に入射される。この時、ビームスプリッタ１３を透過した参照光２「＋１」も第２螺旋位相板１６に入射されたとする。 In step S15, the transmitted return light 7 "-1" is received by the optical antenna 24 of the transmitter 10. The received return light 7 "-1" is reflected by the beam splitter 13 via the frequency shifter 23. Due to this reflection, the folded light 7 "-1" is inverted to become the folded light 7 "+1", and is incident on the second spiral phase plate 16. At this time, it is assumed that the reference light 2 "+1" transmitted through the beam splitter 13 is also incident on the second spiral phase plate 16.
　この入射された折返し光７「＋１」と参照光２「０」との双方は、上記ステップＳ６～Ｓ８で上記同様に処理される。この処理において、その双方の周波数差が０であったとすると、ビート検出器２０から周波数ｆ０のビート信号４が発振器制御部２１へ出力される。 Both the incident return light 7 "+1" and the reference light 2 "0" are processed in the same manner as described above in steps S6 to S8. In this process, assuming that the frequency difference between the two is 0, the beat signal 4 having a frequency f0 is output from the beat detector 20 to the oscillator control unit 21.
　次に、ステップＳ９において、発振器制御部２１は、ビート信号４の周波数ｆ０に対応した制御信号５により、可変発振器２２で発振される可変信号６の可変値の可変処理を制御する。この制御では可変発振器２２からの可変信号６の可変値が０となって周波数シフタ２３へ出力される。 Next, in step S9, the oscillator control unit 21 controls the variable processing of the variable value of the variable signal 6 oscillated by the variable oscillator 22 by the control signal 5 corresponding to the frequency f0 of the beat signal 4. In this control, the variable value of the variable signal 6 from the variable oscillator 22 becomes 0 and is output to the frequency shifter 23.
　次に、ステップＳ１０において、周波数シフタ２３では、可変信号６の可変値が０なので、基準光１「０」の基準周波数はシフトされず、そのままの基準周波数の基準光１「０」が光アンテナ２４へ出力される。この基準周波数の基準光１「０」は、受信機３０の光アンテナ３１で受信後に、ビームスプリッタ３２を透過し、レンズ３５で集光されて光ファイバ４１に入射され、光ファイバ４１を介してユーザ端末機４２へ送信される。 Next, in step S10, in the frequency shifter 23, since the variable value of the variable signal 6 is 0, the reference frequency of the reference light 1 “0” is not shifted, and the reference light 1 “0” of the reference frequency as it is is the optical antenna. It is output to 24. The reference light 1 "0" having this reference frequency is received by the optical antenna 31 of the receiver 30, passes through the beam splitter 32, is condensed by the lens 35, is incident on the optical fiber 41, and is incident on the optical fiber 41 via the optical fiber 41. It is transmitted to the user terminal 42.
　このようにステップＳ６～Ｓ１５の処理を繰り返すことにより、基準光１「０」が送信機１０から受信機３０へと伝送される際に生じる周波数変動が補正され、一定周波数の基準光１「０」をユーザ端末機４２へ送信できる。 By repeating the processes of steps S6 to S15 in this way, the frequency fluctuation generated when the reference light 1 "0" is transmitted from the transmitter 10 to the receiver 30 is corrected, and the reference light 1 "0" having a constant frequency is corrected. Can be transmitted to the user terminal 42.
＜実施形態の効果＞
　本実施形態の空間光周波数伝送システム１００の作用効果について説明する。 <Effect of embodiment>
The operation and effect of the spatial optical frequency transmission system 100 of the present embodiment will be described.
　（１ａ）システム１００の送信機１０は、基準周波数で平面波の基準光１「０」を反射及び透過するビームスプリッタ１３と、ビームスプリッタ１３で反射された基準光１「０」に対応する参照光２「０」を反射して、螺旋状で所定のＯＡＭモードの参照光２「＋１」に変換する第１螺旋位相板１５とを備える。 (1a) The transmitter 10 of the system 100 reflects and transmits the reference light 1 “0” of the plane wave at the reference frequency, and the reference light corresponding to the reference light 1 “0” reflected by the beam splitter 13. It is provided with a first spiral phase plate 15 that reflects 2 “0” and converts it into a spiral and predetermined OAM mode reference light 2 “+1”.
　また、送信機１０は、ビームスプリッタ１３を透過した参照光２「＋１」を透過して平面波の参照光２「０」に変換すると共に、送信機１０から空間を介して送信された基準光１「０」が受信機３０で折り返され、且つビームスプリッタ１３での反射により正負が反転したＯＡＭモードの折返し光７「＋１」を透過して、平面波の折返し光７「０」に変換する第２螺旋位相板１６を備える。 Further, the transmitter 10 transmits the reference light 2 “+1” transmitted through the beam splitter 13 and converts it into the reference light 2 “0” of the plane wave, and the reference light 1 transmitted from the transmitter 10 via space. A second light "0" is folded back by the receiver 30 and is transmitted through the folded light 7 "+1" in the OAM mode in which the positive and negative are inverted due to reflection by the beam splitter 13 and converted into the folded light 7 "0" of a plane wave. A spiral phase plate 16 is provided.
　更に、送信機１０は、平面波の光のみを伝搬し、第２螺旋位相板１６で変換された平面波である参照光２「０」及び折返し光７「０」のみを通すシングルモードファイバ１８と、参照光２「０」と折返し光７「０」との周波数差を出力するビート検出器２０と、周波数差が０又は一定となるように、ビームスプリッタ１３を透過した基準光１「０」の周波数をシフトする周波数シフタ２３と、周波数シフタ２３から出力される基準光１「０」を空間を介して受信機３０へ送信する光アンテナ２４とを備える構成とした。 Further, the transmitter 10 propagates only the light of the plane wave, and passes only the reference light 2 “0” and the return light 7 “0”, which are the plane waves converted by the second spiral phase plate 16, and the single mode fiber 18. The beat detector 20 that outputs the frequency difference between the reference light 2 "0" and the folded light 7 "0", and the reference light 1 "0" that has passed through the beam splitter 13 so that the frequency difference becomes 0 or constant. The configuration includes a frequency shifter 23 that shifts the frequency, and an optical antenna 24 that transmits the reference light 1 “0” output from the frequency shifter 23 to the receiver 30 via space.
　この構成によれば、送信機１０において、基準周波数の基準光１「０」に対応する参照光２「０」と、その基準光１「０」が受信機３０で折り返された折返し光７「０」との周波数差を０又は一定にできる。このため、送信機１０から一定周波数の基準光１「０」を空間を介して受信機３０へ送信し、この送信された一定周波数の基準光１「０」を、受信機３０で受信後にユーザ端末機４２へ送信できる。この処理を行う送信機１０を、パッシブ光デバイスである２つの螺旋位相板１５，１６を用いて構成したので、従来のＡＯＭのような超音波による機械的な振動を利用したアクティブ光デバイスに比べ、故障が起こり難くなるので信頼性を向上できる。更に、パッシブ光デバイスであるため、アクティブ光デバイスに比べ、消費電力を抑制できる。 According to this configuration, in the transmitter 10, the reference light 2 "0" corresponding to the reference light 1 "0" of the reference frequency and the folded light 7 "0" in which the reference light 1 "0" is folded back by the receiver 30 are used. The frequency difference from "0" can be set to 0 or constant. Therefore, the transmitter 10 transmits the constant frequency reference light 1 "0" to the receiver 30 via the space, and the transmitted constant frequency reference light 1 "0" is received by the receiver 30 after being received by the user. It can be transmitted to the terminal 42. Since the transmitter 10 that performs this processing is configured by using two spiral phase plates 15 and 16 which are passive optical devices, it is compared with an active optical device that utilizes mechanical vibration by ultrasonic waves such as a conventional AOM. , Since failure is less likely to occur, reliability can be improved. Further, since it is a passive optical device, power consumption can be suppressed as compared with an active optical device.
　（２ａ）第２螺旋位相板１６は、送信機１０から空間を介して送信された基準光１「０」が受信機３０で折り返される際に、受信機３０で反射された不要反射光８「－１」を透過して所定のＯＡＭモードの不要反射光８「－１」に変換してシングルモードファイバ１８へ出力する構成とした。 (2a) The second spiral phase plate 16 is the unnecessary reflected light 8 “0” reflected by the receiver 30 when the reference light 1 “0” transmitted from the transmitter 10 through the space is turned back by the receiver 30. -1 ”is transmitted, converted into unnecessary reflected light 8“ -1 ”in a predetermined OAM mode, and output to the single mode fiber 18.
　この構成によれば、第２螺旋位相板１６で変換されたＯＡＭモードの不要反射光８「－１」は、平面波のみを伝搬するシングルモードファイバ１８を通ることができない。このため、シングルモードファイバ１８の入力側で不要反射光８「－１」を除去できる。 According to this configuration, the unnecessary reflected light 8 “-1” in the OAM mode converted by the second spiral phase plate 16 cannot pass through the single mode fiber 18 propagating only the plane wave. Therefore, the unnecessary reflected light 8 "-1" can be removed on the input side of the single mode fiber 18.
　（３ａ）送信機１０から空間を介して送信された平面波の基準光１「０」を受信する光アンテナ３１と、光アンテナ３１で受信された基準光１「０」を反射及び透過するビームスプリッタ３２と、ビームスプリッタ３２で反射された基準光１「０」に対応する折返し光７「＋１」成分を反射して、螺旋状で所定のＯＡＭモードの折返し光７「＋１」に変換する第３螺旋位相板３４とを備える。第３螺旋位相板３４で変換された折返し光７「＋１」を、ビームスプリッタ１３での反射により正負が反転したＯＡＭモードの折返し光７「０」に変換して、光アンテナ３１から空間を介して送信機１０へ返信する構成とした。 (3a) An optical antenna 31 that receives the reference light 1 "0" of a plane wave transmitted from the transmitter 10 via space, and a beam splitter that reflects and transmits the reference light 1 "0" received by the optical antenna 31. A third that reflects the folded light 7 "+1" component corresponding to the reference light 1 "0" reflected by the beam splitter 32 and converts it into a spiral back light 7 "+1" in a predetermined OAM mode. A spiral phase plate 34 is provided. The folded light 7 "+1" converted by the third spiral phase plate 34 is converted into the folded light 7 "0" in the OAM mode in which the positive and negative are inverted by the reflection by the beam splitter 13, and the optical antenna 31 passes through the space. It was configured to reply to the transmitter 10.
　この構成によれば、受信機３０において、送信機１０からの基準光１「０」がビームスプリッタ３２で反射された折返し光７「＋１」成分を、螺旋位相板でＯＡＭモードの折返し光７「＋１」に変換され、この折返し光７「＋１」がビームスプリッタ１３でＯＡＭモードの折返し光７「０」に変換されて送信機１０へ送信される。この処理を行う受信機３０を、パッシブ光デバイスである螺旋位相板３４を用いて構成したので、従来のＡＯＭのようなアクティブ光デバイスに比べ、故障が起こり難くなるので信頼性を向上でき、更に、アクティブ光デバイスに比べ、消費電力を抑制できる。 According to this configuration, in the receiver 30, the reference light 1 “0” from the transmitter 10 is reflected by the beam splitter 32 and the folded light 7 “+1” component is transferred to the folded light 7 “+1” in the OAM mode on the spiral phase plate. It is converted to "+1", and the folding light 7 "+1" is converted to the folding light 7 "0" in the OAM mode by the beam splitter 13 and transmitted to the transmitter 10. Since the receiver 30 that performs this processing is configured by using the spiral phase plate 34 that is a passive optical device, failure is less likely to occur as compared with a conventional active optical device such as AOM, so that reliability can be improved and further. Compared to active optical devices, power consumption can be reduced.
＜効果＞
　（１）基準周波数で平面波の基準光を反射及び透過するビームスプリッタと、前記ビームスプリッタで反射された基準光に対応する第１参照光を反射して、螺旋状で所定のＯＡＭ（Orbital Angular Momentum）モードの第２参照光に変換する第１螺旋位相板と、前記ビームスプリッタを透過した第２参照光を透過して平面波の第１参照光に変換すると共に、送信機から空間を介して送信された基準光が受信機で折り返され、且つ前記ビームスプリッタでの反射により正負が反転したＯＡＭモードの第１折返し光を透過して、平面波の第２折返し光に変換する第２螺旋位相板と、平面波の光のみを伝搬し、前記第２螺旋位相板で変換された平面波である第１参照光及び第２折返し光のみを通す特定デバイスと、前記第１参照光と前記第２折返し光とを合波したビート信号の周波数と、基準周波数との差分を出力するビート検出器と、前記差分が０又は一定となるように、前記ビームスプリッタを透過した基準光の周波数をシフトする周波数シフタと、前記周波数シフタから出力される基準光を空間を介して受信機へ送信する光アンテナとを備えることを特徴とする送信機である。 <Effect>
(1) A beam splitter that reflects and transmits the reference light of a plane wave at a reference frequency and a first reference light corresponding to the reference light reflected by the beam splitter are reflected, and a predetermined OAM (Orbital Angular Momentum) is spirally formed. The first spiral phase plate that converts to the second reference light in the mode) and the second reference light that has passed through the beam splitter are transmitted and converted to the first reference light of the plane wave, and transmitted from the transmitter via space. With the second spiral phase plate that the reference light is folded back by the receiver and is transmitted through the first folded light in the OAM mode whose positive and negative are inverted by the reflection by the beam splitter and converted into the second folded light of the plane wave. , The specific device that propagates only the light of the plane wave and passes only the first reference light and the second folded light, which are the plane waves converted by the second spiral phase plate, and the first reference light and the second folded light. A beat detector that outputs the difference between the frequency of the beat signal that combines the waves and the reference frequency, and a frequency shifter that shifts the frequency of the reference light that has passed through the beam splitter so that the difference is 0 or constant. The transmitter is provided with an optical antenna for transmitting the reference light output from the frequency shifter to the receiver via space.
　この構成によれば、送信機において、基準周波数の基準光に対応する第１参照光と、その基準光が受信機で折り返された第２折返し光との周波数差を０又は一定にできる。このため、送信機から一定周波数の基準光を空間を介して受信機へ送信し、この送信された一定周波数の基準光を、受信機で受信後にユーザ端末機へ送信させることができる。この処理を行う送信機を、パッシブ光デバイスである２つの螺旋位相板を用いて構成したので、従来のＡＯＭのような超音波による機械的な振動を利用したアクティブ光デバイスに比べ、故障が起こり難くなるので信頼性を向上できる。更に、パッシブ光デバイスであるため、アクティブ光デバイスに比べ、消費電力を抑制できる。 According to this configuration, in the transmitter, the frequency difference between the first reference light corresponding to the reference light of the reference frequency and the second folded light in which the reference light is folded back by the receiver can be set to 0 or constant. Therefore, the reference light having a constant frequency can be transmitted from the transmitter to the receiver via the space, and the transmitted reference light having the constant frequency can be transmitted to the user terminal after being received by the receiver. Since the transmitter that performs this processing is configured by using two spiral phase plates that are passive optical devices, a failure occurs as compared with an active optical device that uses mechanical vibration by ultrasonic waves such as the conventional AOM. Since it becomes difficult, reliability can be improved. Further, since it is a passive optical device, power consumption can be suppressed as compared with an active optical device.
　（２）前記第２螺旋位相板は、送信機から空間を介して送信された基準光が受信機で折り返される際に、当該受信機で反射された不要反射光を透過して所定のＯＡＭモードの不要反射光に変換して前記特定デバイスへ出力することを特徴とする上記（１）に記載の送信機である。 (2) The second spiral phase plate transmits unnecessary reflected light reflected by the receiver when the reference light transmitted from the transmitter through the space is turned back by the receiver, and has a predetermined OAM mode. The transmitter according to (1) above, wherein the transmitter is converted into unnecessary reflected light and output to the specific device.
　この構成によれば、第２螺旋位相板で変換されたＯＡＭモードの不要反射光は、平面波のみを伝搬する特定デバイスを通ることができない。このため、特定デバイスの入力側で不要反射光を除去できる。 According to this configuration, the unnecessary reflected light in the OAM mode converted by the second spiral phase plate cannot pass through a specific device that propagates only a plane wave. Therefore, unnecessary reflected light can be removed on the input side of the specific device.
　（３）送信機から空間を介して送信された平面波の基準光を受信する光アンテナと、前記光アンテナで受信された基準光を反射及び透過するビームスプリッタと、前記ビームスプリッタで反射された基準光に対応する折返し光成分を反射して、螺旋状で所定のＯＡＭモードの第１折返し光に変換する第３螺旋位相板とを備え、前記第３螺旋位相板で変換された第１折返し光を、前記ビームスプリッタでの反射により正負が反転したＯＡＭモードの第２折返し光に変換して、前記光アンテナから空間を介して前記送信機へ返信することを特徴とする受信機である。 (3) An optical antenna that receives the reference light of a plane wave transmitted from the transmitter via space, a beam splitter that reflects and transmits the reference light received by the optical antenna, and a reference that is reflected by the beam splitter. A third spiral phase plate that reflects the folded light component corresponding to the light and converts it into the first folded light in a predetermined OAM mode in a spiral manner is provided, and the first folded light converted by the third spiral phase plate is provided. Is converted into the second folded light in the OAM mode in which the positive and negative are inverted by the reflection by the beam splitter, and the light is returned from the optical antenna to the transmitter via space.
　この構成によれば、受信機において、送信機からの基準光がビームスプリッタで反射された折返し光成分を、第３螺旋位相板でＯＡＭモードの第１折返し光に変換され、この第１折返し光がビームスプリッタでＯＡＭモードの第２折返し光に変換されて送信機へ送信される。この処理を行う受信機を、パッシブ光デバイスである第３螺旋位相板を用いて構成したので、従来のＡＯＭのようなアクティブ光デバイスに比べ、故障が起こり難くなるので信頼性を向上でき、更に、アクティブ光デバイスに比べ、消費電力を抑制できる。 According to this configuration, in the receiver, the folding light component in which the reference light from the transmitter is reflected by the beam splitter is converted into the first folding light in the OAM mode by the third spiral phase plate, and the first folding light is converted. Is converted into the second return light in OAM mode by the beam splitter and transmitted to the transmitter. Since the receiver that performs this processing is configured by using a third spiral phase plate that is a passive optical device, failure is less likely to occur compared to an active optical device such as a conventional AOM, so reliability can be improved and further. Compared to active optical devices, power consumption can be suppressed.
　（３）上記（１）又は（２）に記載の送信機、及び、上記（３）に記載の受信機を備えることを特徴とする空間光周波数伝送システムである。 (3) A spatial optical frequency transmission system including the transmitter according to (1) or (2) above and the receiver according to (3) above.
　この構成によれば、（１）又は（２）に記載の送信機、並びに、（３）に記載の受信機の双方と同様の作用効果が得られる。 According to this configuration, the same effects as those of both the transmitter described in (1) or (2) and the receiver described in (3) can be obtained.
　その他、具体的な構成について、本発明の主旨を逸脱しない範囲で適宜変更が可能である。 In addition, the specific configuration can be appropriately changed without departing from the gist of the present invention.
　１０　送信機
　１３，３２　ビームスプリッタ
　１５　第１螺旋位相板
　１６　第２螺旋位相板
　１８　シングルモードファイバ（特定デバイス）
　２０　ビート検出器
　２３　周波数シフタ
　２４，３１　光アンテナ
　３０　受信機
　３４　第３螺旋位相板
　１００　空間光周波数伝送システム 10 Transmitter 13, 32 Beam splitter 15 First spiral phase plate 16 Second spiral phase plate 18 Single mode fiber (specific device)
20 Beat detector 23 Frequency shifter 24,31 Optical antenna 30 Receiver 34 Third spiral phase plate 100 Spatial optical frequency transmission system

Claims (6)

  1. 　基準周波数で平面波の基準光を反射及び透過するビームスプリッタと、
    　前記ビームスプリッタで反射された基準光に対応する第１参照光を反射して、螺旋状で所定のＯＡＭ（Orbital Angular Momentum）モードの第２参照光に変換する第１螺旋位相板と、
    　前記ビームスプリッタを透過した第２参照光を透過して平面波の第１参照光に変換すると共に、送信機から空間を介して送信された基準光が受信機で折り返され、且つ前記ビームスプリッタでの反射により正負が反転したＯＡＭモードの第１折返し光を透過して、平面波の第２折返し光に変換する第２螺旋位相板と、
    　平面波の光のみを伝搬し、前記第２螺旋位相板で変換された平面波である第１参照光及び第２折返し光のみを通す特定デバイスと、
    　前記第１参照光と前記第２折返し光とを合波したビート信号の周波数と、基準周波数との差分を出力するビート検出器と、
    　前記差分が０又は一定となるように、前記ビームスプリッタを透過した基準光の周波数をシフトする周波数シフタと、
    　前記周波数シフタから出力される基準光を空間を介して受信機へ送信する光アンテナと
    　を備えることを特徴とする送信機。     A beam splitter that reflects and transmits the reference light of a plane wave at the reference frequency,
    A first spiral phase plate that reflects the first reference light corresponding to the reference light reflected by the beam splitter and converts it into a spiral second reference light in a predetermined OAM (Orbital Angular Momentum) mode.
    The second reference light transmitted through the beam splitter is transmitted and converted into the first reference light of a plane wave, and the reference light transmitted from the transmitter through space is folded back at the receiver and at the beam splitter. A second spiral phase plate that transmits the first folding light in OAM mode whose positive and negative are inverted by reflection and converts it into the second folding light of a plane wave.
    A specific device that propagates only the light of the plane wave and passes only the first reference light and the second folded light, which are the plane waves converted by the second spiral phase plate.
    A beat detector that outputs the difference between the frequency of the beat signal obtained by combining the first reference light and the second folded light and the reference frequency.
    A frequency shifter that shifts the frequency of the reference light transmitted through the beam splitter so that the difference becomes 0 or constant.
    A transmitter including an optical antenna that transmits reference light output from the frequency shifter to a receiver via space.
  2. 　前記第２螺旋位相板は、送信機から空間を介して送信された基準光が受信機で折り返される際に、当該受信機で反射された不要反射光を透過して所定のＯＡＭモードの不要反射光に変換して前記特定デバイスへ出力する
    　ことを特徴とする請求項１に記載の送信機。     When the reference light transmitted from the transmitter through the space is turned back by the receiver, the second spiral phase plate transmits the unnecessary reflected light reflected by the receiver and causes unnecessary reflection in a predetermined OAM mode. The transmitter according to claim 1, wherein the transmitter is converted into light and output to the specific device.
  3. 　送信機から空間を介して送信された平面波の基準光を受信する光アンテナと、
    　前記光アンテナで受信された基準光を反射及び透過するビームスプリッタと、
    　前記ビームスプリッタで反射された基準光に対応する折返し光成分を反射して、螺旋状で所定のＯＡＭモードの第１折返し光に変換する第３螺旋位相板と
    　を備え、
    　前記第３螺旋位相板で変換された第１折返し光を、前記ビームスプリッタでの反射により正負が反転したＯＡＭモードの第２折返し光に変換して、前記光アンテナから空間を介して前記送信機へ返信する
    　ことを特徴とする受信機。     An optical antenna that receives the reference light of a plane wave transmitted from a transmitter through space,
    A beam splitter that reflects and transmits the reference light received by the optical antenna,
    It is provided with a third spiral phase plate that reflects the folded light component corresponding to the reference light reflected by the beam splitter and converts it into the first folded light in a predetermined OAM mode in a spiral shape.
    The first folded light converted by the third spiral phase plate is converted into the second folded light in OAM mode in which the positive and negative are inverted by the reflection by the beam splitter, and the transmitter is transmitted from the optical antenna through space. A receiver characterized by replying to.
  4. 　請求項１又は２に記載の送信機、及び、請求項３に記載の受信機
    　を備えることを特徴とする空間光周波数伝送システム。     A spatial optical frequency transmission system comprising the transmitter according to claim 1 or 2 and the receiver according to claim 3.
  5. 　送信機は、
    　基準周波数で平面波の基準光をビームスプリッタで反射及び透過するステップと、
    　前記ビームスプリッタで反射された基準光に対応する第１参照光を第１螺旋位相板で反射して、螺旋状で所定のＯＡＭモードの第２参照光に変換するステップと、
    　第２螺旋位相板によって、前記ビームスプリッタを透過した第２参照光を透過して平面波の第１参照光に変換すると共に、送信機から送信された基準光が受信機で折り返され、且つ前記ビームスプリッタでの反射により正負が反転したＯＡＭモードの第１折返し光を透過して、平面波の第２折返し光に変換するステップと、
    　平面波の光のみを伝搬する特定デバイスで、前記第２螺旋位相板で変換された平面波である第１参照光及び第２折返し光のみを通すステップと、
    　前記第１参照光と前記第２折返し光とを合波したビート信号の周波数と、基準周波数との差分を出力するステップと、
    　前記差分が０又は一定となるように、前記ビームスプリッタを透過した基準光の周波数をシフトするステップと、
    　前記シフトされた基準光を受信機へ送信するステップと
    　を実行することを特徴とする空間光周波数伝送方法。     The transmitter is
    A step of reflecting and transmitting a plane wave reference light at a reference frequency with a beam splitter,
    A step of reflecting the first reference light corresponding to the reference light reflected by the beam splitter by the first spiral phase plate and converting it into a spiral second reference light in a predetermined OAM mode.
    The second spiral phase plate transmits the second reference light transmitted through the beam splitter and converts it into the first reference light of a plane wave, and the reference light transmitted from the transmitter is folded back by the receiver and the beam is used. A step of transmitting the first folded light of the OAM mode in which the positive and negative are inverted due to the reflection at the splitter and converting it into the second folded light of the plane wave.
    A step of passing only the first reference light and the second folded light, which are plane waves converted by the second spiral phase plate, in a specific device that propagates only the light of the plane wave.
    A step of outputting the difference between the frequency of the beat signal obtained by combining the first reference light and the second folded light and the reference frequency.
    A step of shifting the frequency of the reference light transmitted through the beam splitter so that the difference becomes 0 or constant.
    A spatial optical frequency transmission method comprising performing the steps of transmitting the shifted reference light to a receiver.
  6. 　受信機は、
    　送信機から空間を介して送信された平面波の基準光を光アンテナで受信するステップと、
    　前記光アンテナで受信された基準光をビームスプリッタで反射及び透過するステップと、
    　前記ビームスプリッタで反射された基準光に対応する折返し光成分を螺旋位相板で反射して、螺旋状で所定のＯＡＭモードの第１折返し光に変換するステップと、
    　前記第１折返し光を、前記ビームスプリッタでの反射により正負が反転したＯＡＭモードの第２折返し光に変換して、前記光アンテナから空間を介して前記送信機へ返信するステップと
    　を実行することを特徴とする空間光周波数伝送方法。     The receiver is
    The step of receiving the reference light of the plane wave transmitted from the transmitter through the space with the optical antenna, and
    A step of reflecting and transmitting the reference light received by the optical antenna by the beam splitter, and
    A step of reflecting the folded light component corresponding to the reference light reflected by the beam splitter by the spiral phase plate and converting it into the first folded light in a predetermined OAM mode in a spiral manner.
    The step of converting the first folded light into the second folded light in the OAM mode in which the positive and negative are inverted by the reflection from the beam splitter and returning the light from the optical antenna to the transmitter via space is executed. A spatial optical frequency transmission method characterized by.
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