WO2017064749A1 - Quantum cryptography device and signal light polarization compensating method - Google Patents

Quantum cryptography device and signal light polarization compensating method Download PDF

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WO2017064749A1
WO2017064749A1 PCT/JP2015/078887 JP2015078887W WO2017064749A1 WO 2017064749 A1 WO2017064749 A1 WO 2017064749A1 JP 2015078887 W JP2015078887 W JP 2015078887W WO 2017064749 A1 WO2017064749 A1 WO 2017064749A1
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interferometer
temperature
polarization
waveguide
quantum cryptography
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PCT/JP2015/078887
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French (fr)
Japanese (ja)
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健志 浅井
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三菱電機株式会社
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Priority to PCT/JP2015/078887 priority Critical patent/WO2017064749A1/en
Priority to JP2016522819A priority patent/JP5992132B1/en
Publication of WO2017064749A1 publication Critical patent/WO2017064749A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/12—Transmitting and receiving encryption devices synchronised or initially set up in a particular manner

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  • the present invention relates to a quantum cryptography device having a pressure applying mechanism that applies pressure to a waveguide of a receiving interferometer of a receiver, and a polarization compensation method for signal light applied to the quantum cryptography device.
  • a secret key can be shared between transceivers that perform communication.
  • noise is added to the signal light in the transmission path and the polarization state changes randomly, the interference intelligibility of the optical system deteriorates, resulting in a decrease in device performance.
  • the device performance is, for example, performance such as secret key generation speed or communication distance.
  • an asymmetric Mach-Zehnder interferometer is used as a reception side interferometer, and the waveguide side difference is controlled by controlling the birefringence of the waveguide in the reception side interferometer.
  • the beat length is a distance until the polarization state of incident light returns to the same polarization state again. Control of the birefringence is realized, for example, by adjusting the temperature of the waveguide of the receiving interferometer with a heater or the like.
  • the present inventor has focused on the following problems.
  • In order to increase the communication speed of the quantum cryptography device it is necessary to increase the driving frequency of the quantum cryptography device.
  • the temperature required to make the waveguide length difference an integral multiple of the beat length is the receiving interferometer. It may not be within the allowable temperature range that can be set. As a result, in the receiving interferometer, the waveguide length difference cannot be made an integral multiple of the beat length, and deterioration of the interference intelligibility of the optical system cannot be suppressed.
  • the present invention has been made in order to solve the above-described problems, and a quantum cryptography device and a polarization of signal light capable of suppressing deterioration of interference intelligibility of an optical system while increasing a communication speed.
  • the purpose is to obtain a compensation method.
  • a quantum cryptography apparatus is a quantum cryptography apparatus that performs communication subjected to quantum cryptography processing between a transmitter having a transmission-side interferometer and a receiver having a reception-side interferometer. Pressure is applied to the temperature adjustment unit that can adjust the temperature so that the temperature becomes a polarization-independent temperature that makes the waveguide length difference of the receiving interferometer an integral multiple of the beat length, and the waveguide of the receiving interferometer Thus, a pressure applying mechanism that adjusts the polarization-independent temperature is provided.
  • the polarization compensation method for signal light in the present invention is applied to a quantum cryptography apparatus that performs communication subjected to quantum cryptography processing between a transmitter having a transmission interferometer and a receiver having a reception interferometer.
  • a method for compensating the polarization of signal light wherein the temperature of the receiving interferometer is adjusted to a polarization-independent temperature in which the waveguide length difference of the receiving interferometer is an integral multiple of the beat length.
  • a step of adjusting the polarization-independent temperature by applying pressure to the waveguide of the reception-side interferometer.
  • the temperature of the reception interferometer is received.
  • the temperature is adjusted so that the difference between the waveguide lengths of the side interferometer is an integral multiple of the beat length and the polarization-independent temperature, and the pressure is applied to the waveguide of the reception side interferometer. It is configured to adjust the wave-independent temperature.
  • FIG. 1 is a configuration diagram illustrating a quantum cryptography apparatus according to Embodiment 1 of the present invention.
  • the quantum cryptography device includes a transmitter 10, a receiver 20, and a transmission path 30.
  • the transmitter 10 and the receiver 20 are connected via a transmission line 30.
  • an optical fiber can be used as the transmission line 30.
  • the driving cycle ⁇ 1 of the quantum cryptography device is expressed by the following equation (1) using the driving frequency ⁇ of the quantum cryptography device.
  • the delay amount ⁇ 2 of the interferometer includes a waveguide length difference ⁇ L which is a difference between a waveguide corresponding to a long arm and a short arm in the interferometer, and a vacuum.
  • ⁇ L waveguide length difference
  • n refractive index
  • signal light in order to perform communication between the transceivers of the quantum cryptography apparatus, signal light must not overlap between adjacent bits. That is, as illustrated in FIG. 1, the signal light a and the signal light b must not overlap. Therefore, the relationship of the following formula (3) must be satisfied between the driving cycle ⁇ 1 and the delay amount ⁇ 2 .
  • the drive frequency ⁇ is increased in order to increase the communication speed of the quantum cryptography device, the drive period ⁇ 1 is decreased. Therefore, the delay amount ⁇ 2 needs to be decreased to satisfy the expression (3). In order to reduce the delay amount ⁇ 2 , it is necessary to reduce the waveguide length difference ⁇ L as can be seen from the equation (2).
  • Equation (4) can be transformed into equation (5) below.
  • Formula (5) can be deform
  • the birefringence index B is defined as the following formula (7), and when the formula (6) is substituted into the formula (7), the birefringence index B is expressed as the following formula (8).
  • the temperature T is expressed as the following equation (10).
  • m is an integer
  • the temperature T when Expression (4) is satisfied becomes discrete at intervals of the temperature width ⁇ T pi shown in Expression (11) below.
  • the temperature T when the equation (4) is satisfied that is, the polarization-independent temperature in which the waveguide length difference of the receiving interferometer is an integral multiple of the beat length, jumps at equal intervals of the temperature width ⁇ T pi.
  • the possible values of the polarization-independent temperature are discrete at intervals of the temperature width ⁇ T pi .
  • the temperature width ⁇ T pi is inversely proportional to the waveguide length difference ⁇ L. That is, the relationship between the temperature width ⁇ T pi and the waveguide length difference ⁇ L is expressed as the following equation (12).
  • the interferometer is set to an extremely high temperature or set to an extremely low temperature, members used in the interferometer will be damaged. For this reason, there are usually an upper limit value and a lower limit value in the allowable temperature range that can be set by the interferometer, and the temperature range from the lower limit value to the upper limit value is the allowable temperature range.
  • the polarization-independent temperature is a discrete value. As such, it may not be within the allowable temperature range of the interferometer.
  • the temperature width ⁇ T pi increases as can be seen from equation (12). .
  • the temperature of the interferometer cannot be set to a polarization-independent temperature necessary for making the waveguide length difference ⁇ L an integral multiple of the beat length, and the degradation of the intelligibility of the optical system is suppressed. I can't.
  • the communication intelligibility is degraded while the communication speed is increased. Can be suppressed.
  • the transmitter 10 includes a light source 11, an optical attenuator 12, a transmission side interferometer 13, and a transmission side phase modulator 14.
  • a light pulse is emitted from the light source 11. This light pulse passes through the optical attenuator 12 to reduce the intensity of light per pulse to a single photon level. Since the optical intensity of the signal light only needs to be at a single photon level when it is output from the transmitter 10, the optical attenuator 12 is provided at the subsequent stage of the transmission interferometer 13 or the transmission side phase modulator 14. You may arrange
  • the optical pulse enters the input port In1 of the transmission interferometer 13 and is divided into two optical pulses inside the transmission interferometer 13.
  • One of the light pulses propagates through a long arm corresponding to the first waveguide, and the other propagates through a short arm corresponding to the second waveguide having a shorter waveguide length than the first waveguide.
  • the optical signals are further divided into two, and two optical pulses separated in time are output from the output ports Out 1 and Out 2 of the transmission interferometer 13.
  • the dual optical pulse output from the output port Out2 of the transmission side interferometer 13 is not used thereafter. Subsequently, the duplex optical pulse output from the output port Out1 enters the transmission-side phase modulator 14.
  • the transmission-side phase modulator 14 adds a relative phase difference between the two series of optical pulses.
  • the phase modulation amount ⁇ A to be given, for example, one of four modulation amounts ( ⁇ / 2, 0, ⁇ / 2, ⁇ ) is selected at random.
  • the transmitter-side phase modulator 14 may include a polarizer that includes a polarizer inside, but a polarizer may be separately provided after the output of the transmitter-side phase modulator 14. Finally, the duplex optical pulse output from the transmission-side phase modulator 14 enters the transmission path 30.
  • the receiver 20 includes a reception-side phase modulator 21, a reception-side interferometer 22, a first photon detector 23, and a second photon detector 24.
  • the duplex optical pulse output from the transmission path 30 is input to the reception-side phase modulator 21.
  • the reception-side phase modulator 21 as in the operation of the transmission-side phase modulator 14, a relative phase difference is added between the two series of optical pulses.
  • phase modulation amount ⁇ B for example, any one of ( ⁇ / 2, 0, ⁇ / 2, ⁇ ) is selected at random.
  • the phase modulation amount ⁇ B given by the reception-side phase modulator 21 may be originally selected at random from (0, ⁇ / 2).
  • each of the duplex optical pulses is divided into two pulses, one propagating through the long arm 221 corresponding to the first waveguide, and the other being the first waveguide.
  • the signal is output to the output ports Out1 and Out2 of the receiving interferometer 22.
  • the temperature inside the reception interferometer 22 is also kept constant, and the delay amount is the same as the delay amount between the two series of optical pulses generated in the transmission interferometer 13. Set to the resulting temperature.
  • the front pulse among the pulses propagated through the long arm 221 interferes with the rear pulse among the pulses propagated through the short arm 222, and is output as a triplet optical pulse. .
  • the interfered optical pulse that is, the middle pulse of the triplet optical pulse
  • the output port Out1 or Out2 of the reception-side interferometer 22 depends on the phase modulation amount added by the transmission-side phase modulator 14 It is determined by ⁇ A and the phase modulation amount ⁇ B added by the receiving side phase modulator 21.
  • the polarization state of the light pulse on which the interference state is incident can be made independent of
  • the middle pulse of the triplet optical pulses output from the receiving interferometer 22 is detected by the first photon detector 23 or the second photon detector 24.
  • FIG. 2 is a configuration diagram showing the receiving interferometer 22 according to the first embodiment of the present invention.
  • the receiving interferometer 22 includes a long arm 221 corresponding to the first waveguide, a short arm 222 corresponding to the second waveguide having a shorter waveguide length than the first waveguide, A first pressure applying mechanism 223 that applies pressure to the arm 221 and a second pressure applying mechanism 224 that applies pressure to the short arm 222 are configured.
  • the first pressure applying mechanism 223 and the second pressure applying mechanism 224 can be configured using, for example, a piezoelectric element.
  • the birefringence of the long arm 221 and the short arm 222 is controlled by a temperature adjustment unit (not shown) that can adjust the temperature of the receiving interferometer 22.
  • the waveguide length difference with the short arm 222 is appropriately adjusted so as to be an integral multiple of the beat length. That is, the temperature adjustment unit adjusts the temperature so that the temperature of the reception interferometer 22 becomes a polarization-independent temperature in which the waveguide length difference of the reception interferometer 22 is an integral multiple of the beat length.
  • the beat length is a distance until the polarization state of incident light returns to the same polarization state again as described above.
  • the interference state between the TE polarization and the TM polarization in the signal light matches. That is, even if signal light in an arbitrary polarization state caused by the polarization fluctuation of the transmission path 30 is incident on the reception-side interferometer 22, it is possible to suppress degradation of interference clarity.
  • the temperature width ⁇ T pi becomes large. That is, if the waveguide length difference of the receiving interferometer 22 is small, there is a high possibility that there is no polarization-independent temperature having a discrete value within the allowable temperature range of the receiving interferometer 22. In addition, when the polarization-independent temperature does not exist within the allowable temperature range of the reception-side interferometer 22, the temperature of the reception-side interferometer 22 cannot be set to the polarization-independent temperature. It cannot be adjusted so that the waveguide length difference of the side interferometer 22 is an integral multiple of the beat length.
  • the present inventor applied the pressure for compressing at least one of the waveguides of the long arm 221 and the short arm 222 to thereby provide the receiving interferometer 22. It was found that the polarization-independent temperature can be changed regardless of the difference in the waveguide length. Also, it is possible to adjust how much the polarization-independent temperature is changed by the value of the pressure applied to the waveguide. Therefore, if the value of the pressure applied to the waveguide is controlled, a polarization-independent temperature exists within the allowable temperature range of the receiving interferometer 22 regardless of the difference in the waveguide length of the receiving interferometer 22. To be able to.
  • the mechanism by which the polarization-independent temperature changes by applying pressure to the waveguide will be described.
  • the property that the birefringence changes by applying pressure to the object is called photoelasticity.
  • the effect of this photoelasticity is utilized.
  • Equation (9) changes.
  • the first pressure applying mechanism 223 and the second pressure applying mechanism 224 are provided in the reception-side interferometer 22 so as to apply pressure to at least one of the long arm 221 and the short arm 222. It is composed.
  • the polarization-independent temperature can exist within the allowable temperature range of the side interferometer 22. Therefore, when adjusting the difference in waveguide length of the receiving interferometer 22 to be an integral multiple of the beat length, the first pressure applying mechanism 223 and the second pressure applying mechanism 224 are controlled, so that the receiving side Regardless of the waveguide length difference of the interferometer 22, the temperature of the receiving interferometer 22 can be set to a polarization-independent temperature.
  • first pressure applying mechanism 223 and the second pressure applying mechanism 224 are provided as pressure applying mechanisms.
  • any one of the first pressure applying mechanism 223 and the second pressure applying mechanism 224 is provided as a pressure applying mechanism, and configured to apply pressure to the waveguide of either the long arm 221 or the short arm 222. Also good.
  • a quantum cryptography apparatus that performs communication subjected to quantum cryptography processing between a transmitter having a transmission interferometer and a receiver having a reception interferometer
  • Pressure is applied to the temperature adjustment unit that can adjust the temperature so that the temperature becomes a polarization-independent temperature that makes the waveguide length difference of the receiving interferometer an integral multiple of the beat length, and the waveguide of the receiving interferometer
  • a pressure applying mechanism for adjusting the polarization-independent temperature.
  • the receiving-side interference is applied by the pressure application mechanism so that the polarization-independent temperature is within the allowable temperature range of the receiving interferometer regardless of the waveguide length difference of the receiving interferometer.
  • the value of pressure applied to the meter's waveguide can be controlled. Further, in the quantum cryptography apparatus having such a configuration, it is possible to suppress the deterioration of the interference intelligibility of the optical system while increasing the communication speed, and the secret key sharing speed can be increased.

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  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Optical Communication System (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

A quantum cryptography device for performing a quantum-encrypted communication between a transmitter (10) having a transmission-side interferometer (13) and a receiver (20) having a reception-side interferometer (22) is configured to perform a temperature adjustment such that the temperature of the reception-side interferometer (22) is a polarization-independent temperature that causes the waveguide length difference of the reception-side interferometer (22) to be equal to an integral multiple of the beat length, and the quantum cryptography device is further configured to apply a pressure to the waveguide of the reception-side interferometer (22), thereby adjusting the polarization-independent temperature.

Description

量子暗号装置および信号光の偏波補償方法Quantum encryption device and polarization compensation method for signal light
　本発明は、受信機の受信側干渉計の導波路に圧力を付与する圧力付与機構を備えた量子暗号装置、および量子暗号装置に適用される信号光の偏波補償方法に関するものである。 The present invention relates to a quantum cryptography device having a pressure applying mechanism that applies pressure to a waveguide of a receiving interferometer of a receiver, and a polarization compensation method for signal light applied to the quantum cryptography device.
　量子暗号を行うと、通信を行う送受信機間で秘密鍵を共有することができる。しかしながら、伝送路中で信号光にノイズが加わり、偏光状態がランダムに変化すると、光学系の干渉明瞭度が劣化し、結果として、装置性能が低下する。なお、装置性能とは、例えば、秘密鍵の生成速度または通信距離などの性能である。 When quantum cryptography is performed, a secret key can be shared between transceivers that perform communication. However, if noise is added to the signal light in the transmission path and the polarization state changes randomly, the interference intelligibility of the optical system deteriorates, resulting in a decrease in device performance. The device performance is, for example, performance such as secret key generation speed or communication distance.
　そこで、光学系の干渉明瞭度の劣化を抑制することで装置性能の低下を抑えることを実現するための手法が提案されている。具体的には、このような干渉明瞭度の劣化を防ぐためには、信号光の偏波補償を行うこととなる。 Therefore, a method has been proposed for realizing a reduction in apparatus performance by suppressing deterioration of the interference intelligibility of the optical system. Specifically, in order to prevent such deterioration of interference clarity, signal light polarization compensation is performed.
　従来の偏波補償方式の１つとしては、非対称Ｍａｃｈ－Ｚｅｈｎｄｅｒ干渉計を受信側干渉計として使用し、受信側干渉計において、導波路の複屈折率を制御することで、導波路長差をビート長の整数倍となるように適切に調整する方式がある（例えば、非特許文献１参照）。なお、ビート長とは、入射した光の偏光状態が再び同一の偏光状態に戻るまでの距離である。複屈折率の制御は、例えば、ヒーター等で受信側干渉計の導波路の温度を調整することで実現される。 As one of the conventional polarization compensation methods, an asymmetric Mach-Zehnder interferometer is used as a reception side interferometer, and the waveguide side difference is controlled by controlling the birefringence of the waveguide in the reception side interferometer. There is a method of appropriately adjusting so as to be an integral multiple of the beat length (for example, see Non-Patent Document 1). The beat length is a distance until the polarization state of incident light returns to the same polarization state again. Control of the birefringence is realized, for example, by adjusting the temperature of the waveguide of the receiving interferometer with a heater or the like.
　本発明者は従来技術の課題について検討した結果、次のような課題に着目した。量子暗号装置の通信速度を大きくするためには、量子暗号装置の駆動周波数を大きくする必要がある。しかしながら、量子暗号装置の駆動周波数を大きくするのに従って、受信側干渉計の導波路長差を大きくする必要がある。 As a result of examining the problems of the prior art, the present inventor has focused on the following problems. In order to increase the communication speed of the quantum cryptography device, it is necessary to increase the driving frequency of the quantum cryptography device. However, it is necessary to increase the waveguide length difference of the receiving interferometer as the driving frequency of the quantum cryptography device is increased.
　したがって、受信側干渉計において、複屈折率を制御するために温度を調整するように構成する場合、導波路長差をビート長の整数倍にするのに必要な温度が、受信側干渉計で設定可能な許容温度範囲内に存在しない可能性がある。その結果、受信側干渉計において、導波路長差をビート長の整数倍にすることができず、光学系の干渉明瞭度の劣化を抑制することができない。 Therefore, when the receiving interferometer is configured to adjust the temperature to control the birefringence, the temperature required to make the waveguide length difference an integral multiple of the beat length is the receiving interferometer. It may not be within the allowable temperature range that can be set. As a result, in the receiving interferometer, the waveguide length difference cannot be made an integral multiple of the beat length, and deterioration of the interference intelligibility of the optical system cannot be suppressed.
　このように、量子暗号装置において、通信速度の高速化と、光学系の干渉明瞭度の劣化の抑制とを両立することが困難であるという問題がある。 As described above, in the quantum cryptography apparatus, there is a problem that it is difficult to achieve both high communication speed and suppression of degradation of the interference intelligibility of the optical system.
　本発明は、上記のような課題を解決するためになされたものであり、通信速度を高速化しつつ、光学系の干渉明瞭度の劣化を抑制することのできる量子暗号装置および信号光の偏波補償方法を得ることを目的とする。 The present invention has been made in order to solve the above-described problems, and a quantum cryptography device and a polarization of signal light capable of suppressing deterioration of interference intelligibility of an optical system while increasing a communication speed. The purpose is to obtain a compensation method.
　本発明における量子暗号装置は、送信側干渉計を有する送信機と、受信側干渉計を有する受信機との間で量子暗号処理された通信を行う量子暗号装置であって、受信側干渉計の温度が、受信側干渉計の導波路長差をビート長の整数倍とする偏波無依存温度となるように温度調整可能な温度調整部と、受信側干渉計の導波路に圧力を付与することで、偏波無依存温度を調整する圧力付与機構と、を備えたものである。 A quantum cryptography apparatus according to the present invention is a quantum cryptography apparatus that performs communication subjected to quantum cryptography processing between a transmitter having a transmission-side interferometer and a receiver having a reception-side interferometer. Pressure is applied to the temperature adjustment unit that can adjust the temperature so that the temperature becomes a polarization-independent temperature that makes the waveguide length difference of the receiving interferometer an integral multiple of the beat length, and the waveguide of the receiving interferometer Thus, a pressure applying mechanism that adjusts the polarization-independent temperature is provided.
　また、本発明における信号光の偏波補償方法は、送信側干渉計を有する送信機と、受信側干渉計を有する受信機との間で量子暗号処理された通信を行う量子暗号装置に適用される信号光の偏波補償方法であって、受信側干渉計の温度が、受信側干渉計の導波路長差をビート長の整数倍とする偏波無依存温度となるように温度調整するステップと、受信側干渉計の導波路に圧力を付与することで、偏波無依存温度を調整するステップと、を備えたものである。 Further, the polarization compensation method for signal light in the present invention is applied to a quantum cryptography apparatus that performs communication subjected to quantum cryptography processing between a transmitter having a transmission interferometer and a receiver having a reception interferometer. A method for compensating the polarization of signal light, wherein the temperature of the receiving interferometer is adjusted to a polarization-independent temperature in which the waveguide length difference of the receiving interferometer is an integral multiple of the beat length. And a step of adjusting the polarization-independent temperature by applying pressure to the waveguide of the reception-side interferometer.
　本発明によれば、送信側干渉計を有する送信機と、受信側干渉計を有する受信機との間で量子暗号処理された通信を行う量子暗号装置において、受信側干渉計の温度が、受信側干渉計の導波路長差をビート長の整数倍とする偏波無依存温度となるように温度調整するように構成するとともに、受信側干渉計の導波路に圧力を付与することで、偏波無依存温度を調整するように構成する。これにより、通信速度を高速化しつつ、光学系の干渉明瞭度の劣化を抑制することのできる量子暗号装置および信号光の偏波補償方法を得ることができる。 According to the present invention, in a quantum cryptography apparatus that performs communication subjected to quantum cryptography processing between a transmitter having a transmission interferometer and a receiver having a reception interferometer, the temperature of the reception interferometer is received. The temperature is adjusted so that the difference between the waveguide lengths of the side interferometer is an integral multiple of the beat length and the polarization-independent temperature, and the pressure is applied to the waveguide of the reception side interferometer. It is configured to adjust the wave-independent temperature. As a result, it is possible to obtain a quantum cryptography device and a signal light polarization compensation method capable of suppressing the deterioration of the interference intelligibility of the optical system while increasing the communication speed.
本発明の実施の形態１における量子暗号装置を示す構成図である。It is a block diagram which shows the quantum cryptography apparatus in Embodiment 1 of this invention. 本発明の実施の形態１における受信側干渉計を示す構成図である。It is a block diagram which shows the receiving side interferometer in Embodiment 1 of this invention.
　以下、本発明による量子暗号装置、および量子暗号装置に適用される信号光の偏波補償方法を、好適な実施の形態にしたがって図面を用いて説明する。なお、図面の説明においては、同一部分または相当部分には同一符号を付し、重複する説明を省略する。また、実施の形態１では、送信側干渉計を有する送信機と受信側干渉計を有する受信機との間で量子暗号処理された２連光パルスを用いた通信を行う量子暗号装置に対して本願発明を適用した場合を例示する。 Hereinafter, a quantum cryptography device according to the present invention and a polarization compensation method for signal light applied to the quantum cryptography device will be described with reference to the drawings according to a preferred embodiment. In the description of the drawings, the same portions or corresponding portions are denoted by the same reference numerals, and redundant description is omitted. Further, in the first embodiment, for a quantum cryptography device that performs communication using a double light pulse subjected to quantum cryptography processing between a transmitter having a transmission side interferometer and a receiver having a reception side interferometer The case where this invention is applied is illustrated.
　実施の形態１．
　図１は、本発明の実施の形態１における量子暗号装置を示す構成図である。図１において、量子暗号装置は、送信機１０、受信機２０および伝送路３０を備える。送信機１０および受信機２０は、伝送路３０を介して接続されている。伝送路３０としては、例えば、光ファイバを用いることができる。 Embodiment 1 FIG.
FIG. 1 is a configuration diagram illustrating a quantum cryptography apparatus according to Embodiment 1 of the present invention. In FIG. 1, the quantum cryptography device includes a transmitter 10, a receiver 20, and a transmission path 30. The transmitter 10 and the receiver 20 are connected via a transmission line 30. For example, an optical fiber can be used as the transmission line 30.
　ここで、送信機１０および受信機２０の各構成要素の詳細について説明する前に、本発明者が着目した従来技術の課題について説明する。 Here, before describing the details of each component of the transmitter 10 and the receiver 20, problems of the prior art focused by the present inventor will be described.
　まず、量子暗号装置の駆動周期τ1と、量子暗号装置に用いられる干渉計の遅延量τ2の関係について説明する。送信機の光源から出力される信号光の駆動周期τ1は、量子暗号装置の駆動周波数νを用いて、以下の式（１）で表される。 First, the relationship between the driving cycle τ 1 of the quantum cryptography device and the delay amount τ 2 of the interferometer used in the quantum cryptography device will be described. The driving period τ 1 of the signal light output from the light source of the transmitter is expressed by the following equation (1) using the driving frequency ν of the quantum cryptography device.
Figure JPOXMLDOC01-appb-M000001
Figure JPOXMLDOC01-appb-M000001
　また、干渉計の遅延量τ2は、干渉計におけるロングアーム（Ｌｏｎｇ　ａｒｍ）に相当する導波路とショートアーム（Ｓｈｏｒｔ　ａｒｍ）に相当する導波路との差である導波路長差ΔＬと、真空中の光速度ｃと、干渉計の導波路の屈折率ｎとを用いて、以下の式（２）で表される。 The delay amount τ 2 of the interferometer includes a waveguide length difference ΔL which is a difference between a waveguide corresponding to a long arm and a short arm in the interferometer, and a vacuum. Using the medium light velocity c and the refractive index n of the waveguide of the interferometer, it is expressed by the following equation (2).
Figure JPOXMLDOC01-appb-M000002
Figure JPOXMLDOC01-appb-M000002
　ここで、量子暗号装置の送受信機間で通信を行うためには、隣接するビット間で信号光が重なってはいけない。すなわち、図１で例示するように、信号光ａと、信号光ｂとが重なってはいけない。したがって、駆動周期τ1と遅延量τ2との間で、以下の式（３）の関係を満たさなければならない。 Here, in order to perform communication between the transceivers of the quantum cryptography apparatus, signal light must not overlap between adjacent bits. That is, as illustrated in FIG. 1, the signal light a and the signal light b must not overlap. Therefore, the relationship of the following formula (3) must be satisfied between the driving cycle τ 1 and the delay amount τ 2 .
Figure JPOXMLDOC01-appb-M000003
Figure JPOXMLDOC01-appb-M000003
　量子暗号装置の通信速度を高速化するために駆動周波数νを高くする場合、駆動周期τ1が小さくなるので、式（３）を満たすように遅延量τ2も小さくする必要がある。また、遅延量τ2を小さくするには、式（２）から分かるように導波路長差ΔＬを小さくする必要がある。 When the drive frequency ν is increased in order to increase the communication speed of the quantum cryptography device, the drive period τ 1 is decreased. Therefore, the delay amount τ 2 needs to be decreased to satisfy the expression (3). In order to reduce the delay amount τ 2 , it is necessary to reduce the waveguide length difference ΔL as can be seen from the equation (2).
　ここで、受信側干渉計で信号光が干渉する際の、ＴＥ偏波の位相φTEおよびＴＭ偏波の位相φTMが以下の式（４）を満たすとき、ＴＥ偏波およびＴＭ偏波の干渉度合いが同じになる。換言すると、導波路長差ΔＬがビート長の整数倍のとき、式（４）を満たす。 Here, when the phase φ TE of the TE polarization and the phase φ TM of the TM polarization when the signal light interferes with the receiving side interferometer satisfy the following formula (4), the TE polarization and the TM polarization The degree of interference is the same. In other words, when the waveguide length difference ΔL is an integral multiple of the beat length, Expression (4) is satisfied.
Figure JPOXMLDOC01-appb-M000004
Figure JPOXMLDOC01-appb-M000004
　干渉計の導波路の温度Ｔを考慮したＴＥ偏波の屈折率ｎTE（Ｔ）およびＴＭ偏波の屈折率ｎTM（Ｔ）と、導波路長差ΔＬと、各偏波の波長λとを用いると、式（４）は、以下の式（５）のように変形することができる。また、式（５）は、以下の式（６）のように変形することができる。 The TE-polarized refractive index n TE (T) and the TM-polarized refractive index n TM (T) in consideration of the waveguide temperature T of the interferometer, the waveguide length difference ΔL, and the wavelength λ of each polarized wave Is used, equation (4) can be transformed into equation (5) below. Moreover, Formula (5) can be deform | transformed like the following formula | equation (6).
Figure JPOXMLDOC01-appb-M000005
Figure JPOXMLDOC01-appb-M000005
　複屈折率Ｂは、以下の式（７）のように定義され、式（７）に式（６）を代入すると、複屈折率Ｂは、以下の式（８）のように表される。 The birefringence index B is defined as the following formula (7), and when the formula (6) is substituted into the formula (7), the birefringence index B is expressed as the following formula (8).
Figure JPOXMLDOC01-appb-M000006
Figure JPOXMLDOC01-appb-M000006
　ここで、複屈折率Ｂを、定数Ｂ0およびαを用いて、温度Ｔの一次の項まで展開すると、以下の式（９）のように表される。 Here, when the birefringence B is expanded to the first order term of the temperature T using the constants B 0 and α, it is expressed as the following formula (9).
Figure JPOXMLDOC01-appb-M000007
Figure JPOXMLDOC01-appb-M000007
　また、式（９）に式（８）を代入すると、温度Ｔは、以下の式（１０）のように表される。式（１０）において、ｍは整数であるので、式（４）を満たすときの温度Ｔは、以下の式（１１）で示す温度幅ΔＴpiの間隔で離散的となる。 Further, when the equation (8) is substituted into the equation (9), the temperature T is expressed as the following equation (10). In Expression (10), since m is an integer, the temperature T when Expression (4) is satisfied becomes discrete at intervals of the temperature width ΔT pi shown in Expression (11) below.
Figure JPOXMLDOC01-appb-M000008
Figure JPOXMLDOC01-appb-M000008
　このように、式（４）を満たすときの温度Ｔ、すなわち、受信側干渉計の導波路長差をビート長の整数倍とする偏波無依存温度は、温度幅ΔＴpiの等間隔でとびとびの値をとる。換言すると、偏波無依存温度がとりうる値は、温度幅ΔＴpiの間隔で離散的となる。また、式（１１）から分かるように、温度幅ΔＴpiは、導波路長差ΔＬに対して反比例する。すなわち、温度幅ΔＴpiと、導波路長差ΔＬとの関係は、以下の式（１２）のように表される。 As described above, the temperature T when the equation (4) is satisfied, that is, the polarization-independent temperature in which the waveguide length difference of the receiving interferometer is an integral multiple of the beat length, jumps at equal intervals of the temperature width ΔT pi. Takes the value of In other words, the possible values of the polarization-independent temperature are discrete at intervals of the temperature width ΔT pi . As can be seen from the equation (11), the temperature width ΔT pi is inversely proportional to the waveguide length difference ΔL. That is, the relationship between the temperature width ΔT pi and the waveguide length difference ΔL is expressed as the following equation (12).
Figure JPOXMLDOC01-appb-M000009
Figure JPOXMLDOC01-appb-M000009
　ここで、干渉計を極端に高温に設定する場合、または極端に低温に設定する場合、干渉計に使用されている部材等が破損してしまう。そのため、通常、干渉計で設定可能な許容温度範囲には、上限値および下限値が存在し、下限値から上限値までの温度範囲が許容温度範囲となる。 Here, if the interferometer is set to an extremely high temperature or set to an extremely low temperature, members used in the interferometer will be damaged. For this reason, there are usually an upper limit value and a lower limit value in the allowable temperature range that can be set by the interferometer, and the temperature range from the lower limit value to the upper limit value is the allowable temperature range.
　また、この許容温度範囲内の下限値から上限値までの温度幅ΔＴsと、温度幅ΔＴpiとの関係ついて、ΔＴpi＞ΔＴsの場合、偏波無依存温度は、離散的な値であるので、干渉計の許容温度範囲内に存在しないことがある。 Further, regarding the relationship between the temperature range ΔT s from the lower limit value to the upper limit value within the allowable temperature range and the temperature range ΔT pi , when ΔT pi > ΔT s , the polarization-independent temperature is a discrete value. As such, it may not be within the allowable temperature range of the interferometer.
　以上の考察をまとめると、従来技術においては、量子暗号装置の通信速度を高速化するために導波路長差ΔＬを小さくした場合、式（１２）から分かるように、温度幅ΔＴpiが大きくなる。また、温度幅ΔＴpiが大きくなるにしたがって、偏波無依存温度が干渉計の許容温度範囲内に存在しない場合が生じうる。この場合、干渉計の温度を、導波路長差ΔＬをビート長の整数倍にするのに必要な偏波無依存温度に設定することができず、光学系の干渉明瞭度の劣化を抑制することができない。 To summarize the above considerations, in the prior art, when the waveguide length difference ΔL is reduced in order to increase the communication speed of the quantum cryptography device, the temperature width ΔT pi increases as can be seen from equation (12). . Further, as the temperature width ΔT pi increases, there may occur a case where the polarization-independent temperature does not exist within the allowable temperature range of the interferometer. In this case, the temperature of the interferometer cannot be set to a polarization-independent temperature necessary for making the waveguide length difference ΔL an integral multiple of the beat length, and the degradation of the intelligibility of the optical system is suppressed. I can't.
　このように、従来技術では、量子暗号装置において、通信速度の高速化と、光学系の干渉明瞭度の劣化の抑制とを両立することが困難であるという問題がある。 As described above, in the conventional technology, there is a problem that it is difficult for the quantum cryptography device to achieve both the increase in communication speed and the suppression of the degradation of the intelligibility of the optical system.
　これに対して、本発明では、受信機の受信側干渉計の導波路に圧力を付与する圧力付与機構を備えて構成することで、通信速度を高速化しつつ、光学系の干渉明瞭度の劣化を抑制することができる。 On the other hand, in the present invention, by including a pressure applying mechanism that applies pressure to the waveguide of the receiving interferometer of the receiver, the communication intelligibility is degraded while the communication speed is increased. Can be suppressed.
　次に、送信機１０および受信機２０の各構成要素の詳細について説明する。
＜送信機１０の説明＞
　送信機１０は、光源１１、光減衰器１２、送信側干渉計１３および送信側位相変調器１４を有する。 Next, details of each component of the transmitter 10 and the receiver 20 will be described.
<Description of transmitter 10>
The transmitter 10 includes a light source 11, an optical attenuator 12, a transmission side interferometer 13, and a transmission side phase modulator 14.
　送信機１０では、まず光源１１から光パルスが発せられる。この光パルスは、光減衰器１２を通過することで、１パルスあたりの光の強度を単一光子レベルにまで減光する。信号光の光強度は、送信機１０から出力される際に単一光子レベルになっていればよいので、光減衰器１２は、送信側干渉計１３の後段、または送信側位相変調器１４の後段に配置してもよい。 In the transmitter 10, first, a light pulse is emitted from the light source 11. This light pulse passes through the optical attenuator 12 to reduce the intensity of light per pulse to a single photon level. Since the optical intensity of the signal light only needs to be at a single photon level when it is output from the transmitter 10, the optical attenuator 12 is provided at the subsequent stage of the transmission interferometer 13 or the transmission side phase modulator 14. You may arrange | position in a back | latter stage.
　光パルスは、次に、送信側干渉計１３の入力ポートＩｎ１へと入射し、送信側干渉計１３の内部で２つの光パルスに分割される。それぞれの光パルスの一方は、第１の導波路に相当するロングアームを伝播し、他方は、第１の導波路よりも導波路長の短い第２の導波路に相当するショートアームを伝播した後、さらに２つずつに分割され、送信側干渉計１３の出力ポートＯｕｔ１およびＯｕｔ２から、時間的に離れた２連光パルスが出力される。 Next, the optical pulse enters the input port In1 of the transmission interferometer 13 and is divided into two optical pulses inside the transmission interferometer 13. One of the light pulses propagates through a long arm corresponding to the first waveguide, and the other propagates through a short arm corresponding to the second waveguide having a shorter waveguide length than the first waveguide. Thereafter, the optical signals are further divided into two, and two optical pulses separated in time are output from the output ports Out 1 and Out 2 of the transmission interferometer 13.
　ここで、送信側干渉計１３内部の温度は、ヒーター等を用いることによって、一定に保っておく必要がある。これは、上述した２連光パルス間の遅延量を一定に保っておくことに相当し、遅延量が一定でない場合、光学系の干渉明瞭度が減少する。 Here, it is necessary to keep the temperature inside the transmitting interferometer 13 constant by using a heater or the like. This corresponds to keeping the delay amount between the above-described two light pulses constant. When the delay amount is not constant, the intelligibility of the optical system decreases.
　また、送信側干渉計１３の出力ポートＯｕｔ２から出力された２連光パルスは、以降使用されない。続いて、出力ポートＯｕｔ１から出力された２連光パルスは、送信側位相変調器１４へと入射する。 In addition, the dual optical pulse output from the output port Out2 of the transmission side interferometer 13 is not used thereafter. Subsequently, the duplex optical pulse output from the output port Out1 enters the transmission-side phase modulator 14.
　送信側位相変調器１４では、２連光パルスの間に相対的な位相差を付加する。与える位相変調量φAは、例えば、（－π／２，０，π／２，π）の４つの変調量のいずれか１つをランダムに選択したものとする。送信側位相変調器１４には、その内部に偏光子を含むものを使用してもよいが、送信側位相変調器１４の出力の後に別途、偏光子を配置してもよい。最後に、送信側位相変調器１４から出力された２連光パルスは、伝送路３０へと入射する。 The transmission-side phase modulator 14 adds a relative phase difference between the two series of optical pulses. As the phase modulation amount φ A to be given, for example, one of four modulation amounts (−π / 2, 0, π / 2, π) is selected at random. The transmitter-side phase modulator 14 may include a polarizer that includes a polarizer inside, but a polarizer may be separately provided after the output of the transmitter-side phase modulator 14. Finally, the duplex optical pulse output from the transmission-side phase modulator 14 enters the transmission path 30.
＜受信機２０の説明＞
　受信機２０は、受信側位相変調器２１、受信側干渉計２２、第１の光子検出器２３および第２の光子検出器２４を有する。 <Description of Receiver 20>
The receiver 20 includes a reception-side phase modulator 21, a reception-side interferometer 22, a first photon detector 23, and a second photon detector 24.
　受信機２０では、まず伝送路３０から出力された２連光パルスが受信側位相変調器２１へと入力される。受信側位相変調器２１では、送信側位相変調器１４の動作と同様に、２連光パルスの間に相対的な位相差を付加する。 In the receiver 20, first, the duplex optical pulse output from the transmission path 30 is input to the reception-side phase modulator 21. In the reception-side phase modulator 21, as in the operation of the transmission-side phase modulator 14, a relative phase difference is added between the two series of optical pulses.
　与える位相変調量φBは、例えば、（－π／２，０，π／２，π）のいずれかをランダムに選択したものとする。受信側位相変調器２１で与える位相変調量φBは、本来ならば、（０，π／２）からランダムに選択したものとすればよい。 As the phase modulation amount φ B to be given, for example, any one of (−π / 2, 0, π / 2, π) is selected at random. The phase modulation amount φ B given by the reception-side phase modulator 21 may be originally selected at random from (0, π / 2).
　次に、受信側位相変調器２１から出力された２連光パルスは、受信側干渉計２２の入力ポートＩｎ１へと入射する。送信側干渉計１３の動作と同様に、２連光パルスのそれぞれが２つのパルスずつに分割され、一方が第１の導波路に相当するロングアーム２２１を伝播し、他方が第１の導波路よりも導波路長の短い第２の導波路に相当するショートアーム２２２を伝播した後、受信側干渉計２２の出力ポートＯｕｔ１およびＯｕｔ２に出力される。 Next, the double light pulse output from the reception-side phase modulator 21 enters the input port In1 of the reception-side interferometer 22. Similar to the operation of the transmission side interferometer 13, each of the duplex optical pulses is divided into two pulses, one propagating through the long arm 221 corresponding to the first waveguide, and the other being the first waveguide. After propagating through the short arm 222 corresponding to the second waveguide having a shorter waveguide length, the signal is output to the output ports Out1 and Out2 of the receiving interferometer 22.
　このとき、送信側干渉計１３と同様に受信側干渉計２２の内部の温度も一定に保ち、かつ、送信側干渉計１３で生じた２連光パルス間の遅延量と同じ分の遅延量を生じさせる温度に設定する。このように構成することで、ロングアーム２２１を伝播したパルスのうちの前方のパルスと、ショートアーム２２２を伝播したパルスのうちの後方のパルスが干渉し、３連光パルスとなって出力される。 At this time, similarly to the transmission interferometer 13, the temperature inside the reception interferometer 22 is also kept constant, and the delay amount is the same as the delay amount between the two series of optical pulses generated in the transmission interferometer 13. Set to the resulting temperature. With this configuration, the front pulse among the pulses propagated through the long arm 221 interferes with the rear pulse among the pulses propagated through the short arm 222, and is output as a triplet optical pulse. .
　干渉した光パルス、すなわち、３連光パルスの真ん中のパルスが、受信側干渉計２２の出力ポートＯｕｔ１およびＯｕｔ２のどちらから出力されるかは、送信側位相変調器１４で付加される位相変調量φAと、受信側位相変調器２１で付加される位相変調量φBとで決まる。 Whether the interfered optical pulse, that is, the middle pulse of the triplet optical pulse, is output from the output port Out1 or Out2 of the reception-side interferometer 22 depends on the phase modulation amount added by the transmission-side phase modulator 14 It is determined by φ A and the phase modulation amount φ B added by the receiving side phase modulator 21.
　さらに、ここで設定する受信側干渉計２２内部の温度を、後述するように、偏波無依存温度となるように適切な値に設定することで、干渉の状態が入射する光パルスの偏光状態に依存しないようにすることができる。 Furthermore, by setting the temperature inside the receiving interferometer 22 set here to an appropriate value so as to become a polarization-independent temperature, as will be described later, the polarization state of the light pulse on which the interference state is incident Can be made independent of
　最後に、受信側干渉計２２から出力された３連光パルスのうちの真ん中のパルスが、第１の光子検出器２３または第２の光子検出器２４にて検出される。 Finally, the middle pulse of the triplet optical pulses output from the receiving interferometer 22 is detected by the first photon detector 23 or the second photon detector 24.
　次に、受信側干渉計２２の詳細について、図２を参照しながらさらに説明する。図２は、本発明の実施の形態１における受信側干渉計２２を示す構成図である。 Next, details of the receiving interferometer 22 will be further described with reference to FIG. FIG. 2 is a configuration diagram showing the receiving interferometer 22 according to the first embodiment of the present invention.
　図２において、受信側干渉計２２は、第１の導波路に相当するロングアーム２２１と、第１の導波路よりも導波路長の短い第２の導波路に相当するショートアーム２２２と、ロングアーム２２１に圧力を付与する第１の圧力付与機構２２３と、ショートアーム２２２に圧力を付与する第２の圧力付与機構２２４とを含んで構成される。 In FIG. 2, the receiving interferometer 22 includes a long arm 221 corresponding to the first waveguide, a short arm 222 corresponding to the second waveguide having a shorter waveguide length than the first waveguide, A first pressure applying mechanism 223 that applies pressure to the arm 221 and a second pressure applying mechanism 224 that applies pressure to the short arm 222 are configured.
　なお、第１の圧力付与機構２２３および第２の圧力付与機構２２４は、例えば、圧電素子を用いて構成することができる。 The first pressure applying mechanism 223 and the second pressure applying mechanism 224 can be configured using, for example, a piezoelectric element.
　受信側干渉計２２では、受信側干渉計２２の温度を調整可能な温度調整部（図示せず）によって、ロングアーム２２１のおよびショートアーム２２２の複屈折率を制御することで、ロングアーム２２１とショートアーム２２２との導波路長差がビート長の整数倍となるように適切に調整する。すなわち、温度調整部によって、受信側干渉計２２の温度が、受信側干渉計２２の導波路長差をビート長の整数倍とする偏波無依存温度となるように温度調整を行う。なお、ビート長とは、上述のとおり、入射した光の偏光状態が再び同一の偏光状態に戻るまでの距離である。 In the receiving interferometer 22, the birefringence of the long arm 221 and the short arm 222 is controlled by a temperature adjustment unit (not shown) that can adjust the temperature of the receiving interferometer 22. The waveguide length difference with the short arm 222 is appropriately adjusted so as to be an integral multiple of the beat length. That is, the temperature adjustment unit adjusts the temperature so that the temperature of the reception interferometer 22 becomes a polarization-independent temperature in which the waveguide length difference of the reception interferometer 22 is an integral multiple of the beat length. The beat length is a distance until the polarization state of incident light returns to the same polarization state again as described above.
　ここで、受信側干渉計２２において、導波路長差がビート長の整数倍となっていると、信号光におけるＴＥ偏波とＴＭ偏波との干渉状態が一致する。すなわち、伝送路３０の偏波変動に起因した任意の偏波状態の信号光が、受信側干渉計２２へ入射しても、干渉明瞭度の劣化を抑制することができる。 Here, in the reception-side interferometer 22, when the waveguide length difference is an integral multiple of the beat length, the interference state between the TE polarization and the TM polarization in the signal light matches. That is, even if signal light in an arbitrary polarization state caused by the polarization fluctuation of the transmission path 30 is incident on the reception-side interferometer 22, it is possible to suppress degradation of interference clarity.
　ただし、上述のとおり、量子暗号装置の通信速度を高速化するために駆動周波数を高速化し続けると、これに伴って、受信側干渉計２２の導波路長差が小さくする必要があり、その結果、温度幅ΔＴpiが大きくなってしまう。つまり、受信側干渉計２２の導波路長差が小さくすると、受信側干渉計２２の許容温度範囲内に、離散的な値をとる偏波無依存温度が存在しない可能性が大きくなる。また、受信側干渉計２２の許容温度範囲内に偏波無依存温度が存在しない場合には、受信側干渉計２２の温度を偏波無依存温度に設定することができないので、その結果、受信側干渉計２２の導波路長差がビート長の整数倍となるように調整することができない。 However, as described above, if the drive frequency is continuously increased in order to increase the communication speed of the quantum cryptography apparatus, it is necessary to reduce the waveguide length difference of the reception-side interferometer 22 accordingly. The temperature width ΔT pi becomes large. That is, if the waveguide length difference of the receiving interferometer 22 is small, there is a high possibility that there is no polarization-independent temperature having a discrete value within the allowable temperature range of the receiving interferometer 22. In addition, when the polarization-independent temperature does not exist within the allowable temperature range of the reception-side interferometer 22, the temperature of the reception-side interferometer 22 cannot be set to the polarization-independent temperature. It cannot be adjusted so that the waveguide length difference of the side interferometer 22 is an integral multiple of the beat length.
　これに対して、本発明者は、このような課題を鋭意検討した結果、ロングアーム２２１およびショートアーム２２２の少なくとも一方の導波路を圧縮するための圧力を付与することで、受信側干渉計２２の導波路長差の大きさによらず、偏波無依存温度を変化させることができることを見出した。また、導波路に付与する圧力の値によって、偏波無依存温度をどの程度変化させるかを調整することができる。したがって、導波路に付与する圧力の値を制御すれば、受信側干渉計２２の導波路長差の大きさによらず、受信側干渉計２２の許容温度範囲内に偏波無依存温度が存在するようにすることができる。 On the other hand, as a result of earnestly examining such a problem, the present inventor applied the pressure for compressing at least one of the waveguides of the long arm 221 and the short arm 222 to thereby provide the receiving interferometer 22. It was found that the polarization-independent temperature can be changed regardless of the difference in the waveguide length. Also, it is possible to adjust how much the polarization-independent temperature is changed by the value of the pressure applied to the waveguide. Therefore, if the value of the pressure applied to the waveguide is controlled, a polarization-independent temperature exists within the allowable temperature range of the receiving interferometer 22 regardless of the difference in the waveguide length of the receiving interferometer 22. To be able to.
　続いて、導波路に圧力を付与することで偏波無依存温度が変化するメカニズムについて説明する。ここで、物体に圧力を付与することで複屈折率が変化する性質を光弾性という。本願発明では、この光弾性による効果を利用している。 Subsequently, the mechanism by which the polarization-independent temperature changes by applying pressure to the waveguide will be described. Here, the property that the birefringence changes by applying pressure to the object is called photoelasticity. In the present invention, the effect of this photoelasticity is utilized.
　つまり、導波路に圧力を付与することで、導波路の光弾性によって複屈折率が変化する。具体的には、式（９）における右辺のＢ0が変化する。 That is, by applying pressure to the waveguide, the birefringence changes due to the photoelasticity of the waveguide. Specifically, B 0 on the right side in Equation (9) changes.
　また、複屈折率が変化すると、ビート長が変化するので、その結果、偏波無依存温度も変化する。具体的には、式（１０）における右辺のＢ0が変化するので、それに伴い、左辺のＴも変化する。 Further, when the birefringence changes, the beat length changes, and as a result, the polarization-independent temperature also changes. Specifically, since B 0 on the right side in Equation (10) changes, T on the left side also changes accordingly.
　そこで、このような知見を踏まえ、第１の圧力付与機構２２３および第２の圧力付与機構２２４を受信側干渉計２２に設け、ロングアーム２２１およびショートアーム２２２の少なくとも一方に圧力を付与するように構成している。 Therefore, based on such knowledge, the first pressure applying mechanism 223 and the second pressure applying mechanism 224 are provided in the reception-side interferometer 22 so as to apply pressure to at least one of the long arm 221 and the short arm 222. It is composed.
　このように構成することで、ロングアーム２２１およびショートアーム２２２の少なくとも一方に圧力を付与することが可能となり、導波路に付与する圧力の値を制御することで、複屈折率を制御し、受信側干渉計２２の許容温度範囲内に偏波無依存温度が存在するようにすることができる。したがって、受信側干渉計２２の導波路長差がビート長の整数倍となるように調整する際に、第１の圧力付与機構２２３および第２の圧力付与機構２２４を制御することで、受信側干渉計２２の導波路長差によらず、受信側干渉計２２の温度を偏波無依存温度に設定することができる。 With this configuration, it is possible to apply pressure to at least one of the long arm 221 and the short arm 222, and by controlling the value of the pressure applied to the waveguide, the birefringence is controlled and the reception is performed. The polarization-independent temperature can exist within the allowable temperature range of the side interferometer 22. Therefore, when adjusting the difference in waveguide length of the receiving interferometer 22 to be an integral multiple of the beat length, the first pressure applying mechanism 223 and the second pressure applying mechanism 224 are controlled, so that the receiving side Regardless of the waveguide length difference of the interferometer 22, the temperature of the receiving interferometer 22 can be set to a polarization-independent temperature.
　なお、ここでは、第１の圧力付与機構２２３および第２の圧力付与機構２２４を圧力付与機構として設ける場合を例示した。しかしながら、第１の圧力付与機構２２３および第２の圧力付与機構２２４のいずれかを圧力付与機構として設け、ロングアーム２２１およびショートアーム２２２のいずれかの導波路に圧力を付与するように構成してもよい。 Here, the case where the first pressure applying mechanism 223 and the second pressure applying mechanism 224 are provided as pressure applying mechanisms is illustrated. However, any one of the first pressure applying mechanism 223 and the second pressure applying mechanism 224 is provided as a pressure applying mechanism, and configured to apply pressure to the waveguide of either the long arm 221 or the short arm 222. Also good.
　以上、本実施の形態１によれば、送信側干渉計を有する送信機と受信側干渉計を有する受信機との間で量子暗号処理された通信を行う量子暗号装置において、受信側干渉計の温度が、受信側干渉計の導波路長差をビート長の整数倍とする偏波無依存温度となるように温度調整可能な温度調整部と、受信側干渉計の導波路に圧力を付与することで、偏波無依存温度を調整する圧力付与機構と、を備えて構成する。 As described above, according to the first embodiment, in a quantum cryptography apparatus that performs communication subjected to quantum cryptography processing between a transmitter having a transmission interferometer and a receiver having a reception interferometer, Pressure is applied to the temperature adjustment unit that can adjust the temperature so that the temperature becomes a polarization-independent temperature that makes the waveguide length difference of the receiving interferometer an integral multiple of the beat length, and the waveguide of the receiving interferometer And a pressure applying mechanism for adjusting the polarization-independent temperature.
　このような構成を実現することで、受信側干渉計の導波路長差によらず、偏波無依存温度が受信側干渉計の許容温度範囲内に収まるように、圧力付与機構で受信側干渉計の導波路に付加される圧力の値を制御することができる。また、このような構成を備えた量子暗号装置において、通信速度を高速化しつつ、光学系の干渉明瞭度の劣化を抑制することが可能となり、秘密鍵の共有速度を高めることができる。 By realizing such a configuration, the receiving-side interference is applied by the pressure application mechanism so that the polarization-independent temperature is within the allowable temperature range of the receiving interferometer regardless of the waveguide length difference of the receiving interferometer. The value of pressure applied to the meter's waveguide can be controlled. Further, in the quantum cryptography apparatus having such a configuration, it is possible to suppress the deterioration of the interference intelligibility of the optical system while increasing the communication speed, and the secret key sharing speed can be increased.

Claims (5)

  1. 　送信側干渉計を有する送信機と、受信側干渉計を有する受信機との間で量子暗号処理された通信を行う量子暗号装置であって、
    　前記受信側干渉計の温度が、前記受信側干渉計の導波路長差をビート長の整数倍とする偏波無依存温度となるように温度調整可能な温度調整部と、
    　前記受信側干渉計の導波路に圧力を付与することで、前記偏波無依存温度を調整する圧力付与機構と、
    　を備えた量子暗号装置。     A quantum cryptography device that performs communication subjected to quantum cryptography processing between a transmitter having a transmission side interferometer and a receiver having a reception side interferometer,
    A temperature adjusting unit capable of adjusting the temperature so that the temperature of the receiving interferometer is a polarization-independent temperature in which the waveguide length difference of the receiving interferometer is an integral multiple of the beat length; and
    A pressure applying mechanism that adjusts the polarization-independent temperature by applying pressure to the waveguide of the receiving interferometer;
    Quantum cryptography device with
  2. 　前記圧力付与機構は、
    　　前記偏波無依存温度が前記受信側干渉計の許容温度範囲内に収まるように前記受信側干渉計の導波路に圧力を付与する
    　請求項１に記載の量子暗号装置。     The pressure applying mechanism is
    The quantum cryptography device according to claim 1, wherein pressure is applied to a waveguide of the reception interferometer so that the polarization-independent temperature is within an allowable temperature range of the reception interferometer.
  3. 　前記圧力付与機構は、
    　　前記受信側干渉計の導波路を構成するロングアームおよびショートアームの少なくとも一方に圧力を付与する
    　請求項１または２に記載の量子暗号装置。     The pressure applying mechanism is
    3. The quantum cryptography device according to claim 1, wherein pressure is applied to at least one of a long arm and a short arm constituting the waveguide of the reception interferometer.
  4. 　前記圧力付与機構は、圧電素子を用いて構成される
    　請求項１から３のいずれか１項に記載の量子暗号装置。     The quantum cryptography apparatus according to claim 1, wherein the pressure applying mechanism is configured using a piezoelectric element.
  5. 　送信側干渉計を有する送信機と、受信側干渉計を有する受信機との間で量子暗号処理された通信を行う量子暗号装置に適用される信号光の偏波補償方法であって、
    　前記受信側干渉計の温度が、前記受信側干渉計の導波路長差をビート長の整数倍とする偏波無依存温度となるように温度調整するステップと、
    　前記受信側干渉計の導波路に圧力を付与することで、前記偏波無依存温度を調整するステップと、
    　を備えた信号光の偏波補償方法。     A polarization compensation method for signal light applied to a quantum cryptography device that performs communication subjected to quantum cryptography processing between a transmitter having a transmission interferometer and a receiver having a reception interferometer,
    Adjusting the temperature so that the temperature of the receiving interferometer is a polarization-independent temperature in which the waveguide length difference of the receiving interferometer is an integral multiple of the beat length;
    Adjusting the polarization independent temperature by applying pressure to the waveguide of the receiving interferometer;
    A polarization compensation method for signal light.
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