JP2010114662A - Optical transmission device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent cryptogram using multi-value intensity modulation from eavesdropping thereof by further reinforcing security for data decoding of optical communication quantum cryptogram. <P>SOLUTION: This optical transmission device includes: a first pseudo random number generating section for generating a first running key by using a first encryption key; a multi-value modulation signal generating section for generating data to be transmitted as a multi-value signal of a bit unit by using the first running key by the first pseudo random number generating section; a second pseudo random number generating section for generating a second running key by using a second encryption key; a first modulator for changing a phase or frequency of an optical carrier wave of the data to be transmitted by using the second running key by the second random number generating section, and a second modulator for receiving the optical carrier wave whose phase or frequency is changed by the first modulator and generating an optical signal obtained by changing a light intensity base of the optical carrier wave by the multi-value signal generated by the multi-value modulation signal generating section, and randomly changes the frequency or phase of the optical carrier wave by the second running key with time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical transmission apparatus and an optical transmission method, and more particularly to enhancement of security against eavesdropping of encryption in optical communication quantum cryptography using multilevel intensity modulation.

In optical communication quantum cryptography, light fluctuation (quantum shot noise) is diffused by modulation, and an optical signal cannot be accurately identified by an eavesdropper. Common key quantum cryptography is known that makes it impossible.
In this common key quantum cryptography, a set of M binary optical signals carrying transmission data, called a base, is prepared, and a pseudorandom number according to the encryption key is used to determine which base is used for data transmission. It is a method that decides irregularly by.
Actually, the data is identified from the encrypted signal received by an eavesdropper by reducing the distance between the M-value signals with respect to the time direction of the phase and frequency by quantum fluctuations of a plurality of M values of light. The data is not decrypted (decryption is correctly established).

Encryption based on the above principle is called Yuen quantum cryptography according to Yuen-2000 cryptographic communication protocol (abbreviated as Y-00 protocol). Currently, as a communication system that embodies this Y-00 protocol, P.I. Kumar and H. Yuen et al. Announced the optical phase modulation method of Non-Patent Document 1.
This Y-00 protocol is higher in the strength of security for data decryption than the conventional stream cipher in wired / wireless communication that does not utilize the quantum fluctuation of light (referred to as classic Y-00). Protocol.

Moreover, the light intensity modulation method of Non-Patent Document 2 has been announced by members of Tamagawa University. FIG. 1 shows an outline of the system configuration of a Yuen quantum cryptography transceiver described in Non-Patent Document 2. In this system, a transmitter 100 that transmits an optical signal and a receiver 105 that receives the optical signal are connected via a passage 104 that is a transmission path such as an optical fiber.
The transmitter 100 includes a transmission data generation unit 103 that generates transmission data, a pseudo-random number generation unit 102 that generates a pseudo-random number when a cryptographic key K is input, and a running key generated by the pseudo-random number generation unit 102. And a multi-level light generation unit 101 that generates transmission data from the transmission data generation unit 103 as a multi-level signal in bit units using a key. The receiver 105 may be a direct detection general-purpose receiver or a heterodyne receiver with high decoding accuracy for noise in the same system.

FIG. 2 shows the relationship between data and threshold values for an authorized recipient who shares encryption key information with a transmitter and an eavesdropper who does not share encryption key information.
The transmitter 100 converts the binary data into a multi-level signal level based on the encryption key information. For example, assuming a case where the signal level is converted into an 8-level signal level, the authorized receiver knows which of the bases A to D the signal is in since the encryption key is shared with the transmitter, and the signal transition The threshold value can be set to any one of threshold value 1 to threshold value 4 as shown in FIG. Here, a pair of A signal levels “4” and “8”, a pair of B signal levels “3” and “7”, a pair of C signal levels “2” and “6”, and a signal level “D” of “D” A pair of “1” and “5” is called a binary base having one set.

Since the eavesdropper does not share the encryption key with the transmitter, the eavesdropper cannot recognize the signal level. For this reason, as shown in (b), it is necessary to recognize levels from a large number of thresholds between adjacent signal levels.
For example, assuming that the level is recognized from seven threshold values, the main noises of the close detection method are “quantum fluctuation (quantum shot noise)” and “thermal noise”, and the heterodyne noise is “quantum fluctuation (quantum fluctuation). Shot noise) ”.

As shown in FIG. 3, when attention is paid to the signal level 7 and the signal level 8 in the receiver, the heterodyne method (one-dot chain line) has a narrower noise center around the signal than the direct detection method. Therefore, signal errors are improved and reduced.
From this fact, it is assumed that a heterodyne receiver is used as a receiver used by an eavesdropper in order to eavesdrop and decode data using the effect of reducing signal errors.
Data decryption by an eavesdropper using a heterodyne receiver is assumed to be performed by a procedure including the following configuration.

(Step 1) The received signal having the optical carrier frequency f ₁ (Hz) and the output of the local oscillator having the optical carrier frequency f ₂ (Hz) are mixed (multiplied) by the multiplexer.
(Step 2) The mixed optical signal is converted into an electrical signal by the optical / electrical converter.
(Step 3) The low frequency component of the optical carrier frequency is extracted and amplified by the calculation formula (| f ₁ −f ₂ |) by the band pass filter of the intermediate frequency amplifier.
(Step 4) The low frequency component extracted by the band pass filter is reproduced by the demodulator.

  Here, if the optical power of the local transmitter is made larger than the optical power of the received signal, the influence of thermal noise generated in the circuit on the receiver side can be ignored. Therefore, it is possible to obtain a state having only quantum fluctuations (quantum shot noise) that are necessarily generated.

If security against data decoding using a heterodyne receiver can be ensured, safety can be ensured even in the case of eavesdropping using a direct detection receiver.
For example, according to Non-Patent Document 3, when it is assumed that there is a phase error between the local oscillator and the signal, and that the phase error is a Gaussian distribution having a variance σ ² , the code error rate greatly depends on the standard deviation σ. It says that. That is, it can be seen that a system that cannot decode data can be created by adding phase noise to the signal.

  However, according to Non-Patent Document 4, the optical carrier wave of the transmitter has a single frequency, and the code error rate is evaluated using the receiver of the eavesdropper as a direct detection method. A result of a code error rate of 0.1 or more at (dBm) (dBm is 0 dB = 1 mW in absolute value expression based on mW) is obtained. This means that the probability of data error is one-tenth or more. When a heterodyne receiver is used, the reception sensitivity is better than the direct detection method. There is a possibility.

  Further, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-303927), since the optical carrier wave has a single frequency, similarly to Non-Patent Document 4, when a heterodyne receiver is used, data can be decoded. There is sex.

G. A. Barbosa, E .; Corndorf, P.M. Kumar, H.C. P. Yuen, “Secure communication using mesoscopic coherent state,” Phys. Rev. Lett. vol-90, 229011, (2003) O. Hirota, K.K. Kato, M.M. Sohma, T .; Usuda, K .; Harasawa, “Quantum stream cipher based on optical communication” SPIE Proc. on Quantum Communications and Quantum Imaging vol-5551, (2004) Takayoshi Ohkoshi and Kazuo Kikuchi, “Coherent Optical Communication Engineering”, Ohmsha, 1989 Shigeto Tsuji et al., “Light intensity modulation system 2.5 Gbit / s development of optical communication quantum cryptography transmission device (Y-00)”, 2006 IEICE General Conference, B-10-41. JP 2006-303927 A

  An object of the present invention is to further enhance the security of optical communication quantum cryptography against data decryption and to prevent eavesdropping of the cipher by multilevel intensity modulation.

  The optical transmission apparatus according to the present invention is preferably an optical transmission apparatus that modulates data into an optical signal and transmits the optical signal using optical communication quantum cryptography based on multilevel intensity modulation, and generates a first Running key. A multi-level modulation signal that generates data to be transmitted as a multi-level signal in bit units using the first pseudo-random number generator for generating the first pseudo-random number generator and the first running key generated by the first pseudo-random number generator A generating unit; a random key generating unit that generates a random key; and a first modulator that changes a phase or frequency of an optical carrier wave of data to be transmitted using the random key generated by the random key generating unit; Receiving the optical carrier wave whose phase or frequency has been changed by the first modulator, and changing the light intensity base of the optical carrier wave by the multi-value signal generated by the multi-value modulation signal generator signal A second modulator for generating, configured as an optical transmission apparatus characterized by having.

In a preferred example, the random key generation unit is a second pseudo random number generation unit that generates a second Running key using a second encryption key,
The first modulator changes the phase or frequency of the optical carrier wave of data to be transmitted, using the second Running key generated by the second pseudorandom number generator.

In another preferred example, the random key generation unit includes a noise source that generates noise, and an amplification unit that amplifies noise generated from the noise source,
The first modulator changes the phase or frequency of the optical carrier wave of data to be transmitted using the noise amplified by the noise amplification unit.

  Preferably, the first modulator is a frequency modulator having a plurality of n lasers, a plurality of laser drivers for driving the lasers, and a plurality of couplers for combining the outputs of the lasers. An arbitrary plural m (where m <n) of the plural n laser drivers is selected by the second Running key from the second pseudorandom number generator, and the laser driven by the selected laser driver is selected. The outputs are combined by the coupler, and the combined optical carrier is output to the second modulator.

  Preferably, different keys are used for the first and second running keys, and the first modulator changes the frequency or phase of the optical carrier by switching over time and at random. .

  Preferably, the first pseudo-random number generator and the second pseudo-random number generator are configured by different hardware circuits, and the first modulator changes the frequency or phase of the optical carrier over time. And change at random.

  Preferably, the first modulator is a frequency modulator, and the frequency modulator has an intermediate frequency amplifier included in a heterodyne receiver that receives the transmitted optical signal by applying the second Running key. An optical carrier having a frequency outside the frequency band of the band-pass filter is output.

Preferably, the first modulator is a frequency modulator, and the frequency modulator is configured to apply the second Running key by:
When assuming the frequency fc (Hz) of the optical carrier wave and the frequency variation Δfc (Hz),
fc−Δfc to fc + Δfc
In the frequency range (Hz), an optical carrier wave having a frequency that changes with time is randomly output.

Preferably, the first modulator is a phase modulator, and the phase modulator is configured to apply the second Running key by:
When the phase φc (radian) of the optical carrier and the phase variation Δφc (radian) are set,
φc−Δφc to φc + Δφc (t)
Output an optical carrier wave having a phase that changes with time in a random range.

Preferably, the first modulator is a Mach-Zehnder phase modulator,
The multilevel voltage of the second Running key is input to the electrical signal input port of the Mach-Zehnder phase modulator, and the phase of the optical carrier is randomly changed according to the multilevel voltage value of the second Running key.

  The optical transmission method according to the present invention is preferably an optical transmission method in which data is modulated into an optical signal and transmitted using optical communication quantum cryptography based on multi-level intensity modulation, and a first Running key is generated. First pseudo-random number generation step, and multi-level modulation signal generation step for generating data to be transmitted as a multi-level signal in bit units using the first Running key generated by the first pseudo-random number generation step A random key generation step for generating a random key, a first modulation step for changing the phase or frequency of an optical carrier wave of data to be transmitted using the random key generated by the random key generation step, By receiving the optical carrier wave whose phase or frequency has been changed by the first modulation step, the multi-level signal generated by the multi-level modulation signal generation step Configured as a light transmission method characterized in that it comprises a second modulation step of generating an optical signal obtained by changing the light intensity basis of the optical carrier wave, a.

  In a preferred example, the optical transmission method according to the present invention is an optical transmission method in which data is modulated into an optical signal and transmitted using optical communication quantum cryptography based on multilevel intensity modulation, and the first encryption key is used. Using the generated first running key to generate data to be transmitted as a multi-value signal in bit units, and using the second encryption key, A step of generating a second Running key, a step of changing a phase or frequency of an optical carrier of data to be transmitted using the generated second Running key, and an optical carrier whose phase or frequency is changed And generating an optical signal in which the optical intensity base of the optical carrier is changed by the multilevel signal generated in the generating step of the multilevel modulation signal. That is configured as a light transmission method.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to further strengthen the safety | security with respect to the data decoding of optical communication quantum cryptography, and to prevent the eavesdropping of the encryption by multi-value intensity | strength modulation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
Before describing an embodiment of the present invention, a configuration of a general heterodyne receiver will be described with reference to FIG.
In FIG. 4, a received signal f 1 that is an optical signal transmitted from a transmission device is combined with a predetermined frequency f 2 generated by a local transmitter 201 by a multiplexer 200, and an electrical signal is output by an optical / electric converter 202. Is converted to The electrical signal is resonated and amplified by the intermediate frequency amplifier 203 at a specific resonance frequency (bandpass characteristic), and demodulated by the demodulator 204 to generate normal reception data.

  First, the principle of the transmission apparatus according to the present invention will be described. If the data is encrypted by the characteristic multi-level intensity modulation on the transmitting device side, even if the eavesdropper receives the encrypted data according to the present invention using the heterodyne receiver of FIG. (I.e., establishment of correct decoding) is extremely difficult.

As an example, when the frequency fc (Hz) of the optical carrier wave and the frequency variation Δfc (Hz),
fc−Δfc to fc + Δfc (Hz) (1)
These are varied over time and randomly in the frequency range (Hz) of (1).

As another example, when the phase φc (radian) of the optical carrier and the phase variation Δφc (radian) are set,
φc−Δφc to φc + Δφc (t) (2)
These are varied with time and randomly in the phase range (radian) of (2).

For example, in the case of frequency variation,
| f ₁ − f ₂ | (Hz) (3)
In this case, according to (3), the frequency band outside the bandpass filter of the intermediate frequency amplifier 203 can be set (FIG. 4).

Even when using a pseudo-random number sequence or using an external noise source by changing the data decryption over time and at random, it is equivalent under certain conditions to enhance security against encryption. can do.
The condition is that the frequency variation Δfc (Hz) of the optical carrier or the phase variation Δφc (radian) of the optical carrier can be varied over a wide range from the frequency variable range of the local transmitter of the receiver. thing. Furthermore, the phase variation Δφc (radian) can be varied at a high speed at which the local oscillator cannot respond.

  As shown in FIG. 5, the function of the frequency or phase variation is realized by a modulation mechanism 500 that modulates the frequency or phase of an optical carrier wave (continuous light) generated from the laser 59 of the transmission apparatus. A detailed example of the frequency or phase modulation mechanism 500 will be described later with reference to FIGS. Here, I would like to describe the schematic configuration of the transmission apparatus.

  The transmission apparatus uses a pseudo-random number generator 512 that generates a running key from the encryption key 513, and a multi-value modulation that generates transmission data as a multi-value signal in bit units using the running key generated by the pseudo-random number generator 512. The optical signal generation unit 511 and the optical signal whose phase or frequency is modulated from the frequency or phase modulation mechanism 500 are received, and the light intensity base of the optical signal is generated by the multilevel signal generated by the multilevel modulation electrical signal generation unit 511. And an intensity modulator 52 that generates an optical signal in which is changed. Here, the pseudo-random number generator 512 and the multi-level modulated electric signal generator 511 have the same functions as those of a conventional optical transmitter (for example, FIG. 1).

Next, frequency fluctuation and phase fluctuation of the optical carrier wave will be described with reference to FIG.
In FIG. 6, (a) is a reference optical carrier, (b) is an optical carrier whose Δfc (Hz) frequency is changed with respect to the reference optical carrier, and (c) is a Δφc (radian) phase is changed with respect to the reference optical carrier. The optical carrier made to show is shown.
When the frequency or phase of the reference optical carrier is varied with time on the transmission device side, the heterodyne receiver (FIG. 4) does not resonate at the specific resonance frequency f2 with respect to the received optical signal. For this reason, correct decryption (sapping) of the received signal is not established, and the security of encryption of transmission data can be further enhanced.

[Example 1]
FIG. 7 shows a configuration example of a transmission apparatus that varies the frequency of the reference optical carrier according to one embodiment.
In FIG. 7, a pseudo-random number generator 712 that generates a running key 1 from an encryption key 713 and a running key 1 generated by the pseudo-random number generator 712 are used to generate transmission data as a multi-value signal in bit units. The value modulation electric signal generation unit 711 and the intensity modulator 72 that generates an optical signal in which the light intensity base of the optical signal is changed are the encryption key 513, the pseudo random number generation unit 512, the multi-level modulation electric signal generation unit in FIG. 511 and the intensity modulator 52.

  Furthermore, a pseudorandom number generator 72 that generates the Running key 2 using the encryption key 2 (73) and a frequency modulator 70 are provided. The frequency modulator 70 has a plurality of (n) lasers (LDs), a plurality of laser drivers 702 for driving them, and a plurality of couplers 704 for adding continuous light as the output of the laser 703. Configured.

According to the Running key 2 generated by the pseudorandom number generator 72, at least two laser drivers 702 are selected, and the corresponding lasers 703 are turned on / off over time. The continuous light thus generated is added by the coupler 704 over time, and is added to the intensity modulator 303.
Thereby, the continuous light given to the intensity modulator 52 becomes a signal whose frequency fluctuates as f _{1 to} f ₃ ... With respect to the continuous light (a) of the reference frequency as shown in FIG.

  For example, when n lasers 703 having the same output power are used, any two lasers 703 that are turned on simultaneously with time are denoted by LD-i and LD-j, respectively, and the other (n-2) The laser 703 is turned off.

  When the output of the laser 703 that is simultaneously turned on with time is represented by (4),

強度変調器５２の入力信号は、（５）となる。

The input signal of the intensity modulator 52 is (5).

ここで、（６）は、変換された光搬送波周波数（Ｈｚ）、（７）は、同包短線成分の周波数（Ｈｚ）である。

Here, (6) is the converted optical carrier frequency (Hz), and (7) is the frequency (Hz) of the enclosed short line component.

図８は、レーザ７０３およびレーザドライバ７０２の動作速度とヘテロダイン受信機の局部発信器２０１の応答速度による光搬送波周波数の関係を示す。
レーザ７０３およびレーザドライバ７０２の動作速度は光搬送波周波数が０．１ｆ_１になる速度が３５（ｐｓ）、ヘテロダイン受信機の局部発信器２０１の応答速度が０．１ｆ_２になる速度が１４０（ｐｓ）である。

FIG. 8 shows the relationship between the operating speed of the laser 703 and the laser driver 702 and the optical carrier frequency according to the response speed of the local oscillator 201 of the heterodyne receiver.
The operating speed of the laser 703 and the laser driver 702 is 35 (ps) when the optical carrier frequency is 0.1 f ₁ and 140 (ps) when the response speed of the local oscillator 201 of the heterodyne receiver is 0.1 f _2. ).

The optical carrier frequency at time t is f ₁ , the local oscillator frequency is f ₂ ^′ ,

つまり、レーザ７０３およびレーザドライバ７０２の動作速度がヘテロダイン受信機の局部発信器２０１の応答速度より速い場合、光搬送波の周波数の変化にヘテロダイン受信機が追従できなくなる。そのために、式（８）の場合は中間周波増幅器２０３（図４）のバンドパスフィルタの周波数帯域外にすることが可能となる。従って、レーザの出力レベルは小さくなり、受信信号は正確に復号化はできない。

That is, when the operating speed of the laser 703 and the laser driver 702 is higher than the response speed of the local oscillator 201 of the heterodyne receiver, the heterodyne receiver cannot follow the change in the frequency of the optical carrier. Therefore, in the case of Expression (8), it is possible to make the frequency band outside the band pass filter of the intermediate frequency amplifier 203 (FIG. 4). Accordingly, the output level of the laser becomes small, and the received signal cannot be accurately decoded.

  On the other hand, even when the operating speed of the laser 703 and the laser driver 702 is slower than the response speed of the local oscillator 203 of the heterodyne receiver, if the fluctuation range of (6) is larger than the operating frequency range of the local oscillator 201, the bandpass It becomes possible to make it outside the frequency band of the filter. Therefore, even when a heterodyne receiver is used, correct decryption (encryption eavesdropping) can be prevented.

Next, examples will be described using specific numerical values.
The transfer function H (f) of the bandpass filter of the intermediate frequency amplifier 203 is

ｆ：周波数（Ｈｚ）、ｆ₀＝|ｆ₁−ｆ₂|:中間周波数（Ｈｚ）、Ｑ：尖鋭度(１０〜１００)、
Ｖｏｕｔ：復調器出力レベル（Ｖ）、Ｖｉｎ：中間周波増幅器入力レベル（Ｖ）、
Ｇ：中間周波増幅器の利得（倍）
レーザ５０４の周波数をＩＴＵ-Ｔ Ｒｅｃｏｍｍｅｎｄａｔｉｏｎ Ｇ．６９２で規定されているＬＤ５０４の周波数を用い、Ｑ＝１００、Ｖｉｎ＝０．１（Ｖ）、Ｇ＝１０（倍）、ｆ₂＝１９３．３３９（ＴＨｚ）の中間周波増幅器２０３を想定する。

f: frequency (Hz), f ₀ = | f ₁ −f ₂ |: intermediate frequency (Hz), Q: sharpness (10 to 100),
Vout: demodulator output level (V), Vin: intermediate frequency amplifier input level (V),
G: Gain of intermediate frequency amplifier (times)
The frequency of the laser 504 is changed to ITU-T Recommendation G. Assume an intermediate frequency amplifier 203 using the frequency of the LD 504 defined in 692, Q = 100, Vin = 0.1 (V), G = 10 (times), and f ₂ = 193.339 (THz).

As described in Patent Document 1 or Non-Patent Document 4, when one LD having a single frequency 193.4 (THz) is used, the intermediate frequency is f ₀ = | 193.4-193.3339 | = 1 ( GHz), (9)
| H (f) | = 1. From (10), Vout = 1 (V).

From the case of using two LDs with f _LD-i = 193.4 (THz) and f _LD-j = 192.7 (THz), (6), f _s = (193.4 + 192.7) / 2 = 193 .05 (THz), (9) becomes | H (f) | = 2.86 × 10 ⁻⁵ , and (10) gives Vout = 2.86 × 10 ⁻⁵ (V), and the demodulator 204 (FIG. 4). ) Is hardly input, and data demodulation cannot be expected.

The case where the operating speed of the laser 703 and the laser driver 702 is slower than the response speed of the local transmitter 201 of the heterodyne receiver will be described using specific numerical values.
When the variable range of the optical carrier frequency is 193.4 (THz) ± 0.1 (THz) and the frequency variable range of the local oscillator 201 is 193.399 (THz) ± 0.05 (THz), the intermediate frequency is , | (193.4 ± 0.1) − (193.339 ± 0.05) | = −49 (GHz) to 51 (GHz). When the condition of the intermediate frequency amplifier 203 is the above, Vin = 0.2 (mV), and the signal input to the demodulator 204 is input only to the extent that cannot be expected for data demodulation.

  In this embodiment, the encryption key 713 and the encryption key 73, and the pseudo random number generator 712 and the pseudo random number generator 72 function well even in the same circuit. However, from the viewpoint of enhancing security by optical communication quantum encryption, it is preferable to make the encryption key 1 and the encryption key 2 different and / or to configure the pseudo-random number generation units 1 and 2 with different hardware circuits. Moreover, it is desirable that the pseudo random number generator 1 and the pseudo random number generator 2 operate independently and asynchronously.

In the above example, the two laser drivers 702 are selected with the Running key 2. However, the number is not limited to two, and may be three or more.
Further, although the output power of each laser 703 is assumed to be equal, the output power of each laser may be appropriately different.

[Example 2]
FIG. 9 shows a configuration example of a transmission apparatus that varies the phase of the reference optical carrier wave according to another embodiment (embodiment 2).
An optical carrier wave (continuous light) always output from the laser 59 is input to the phase modulator 90.
For example, the output of the Running key 2 is a multi-value voltage, and when a random voltage value is set in 1024 steps from +0 to +4 (Vpp), the step unit is 4 (Vpp) / 1024 ( Step) ≈3.9 m (Vpp / step). Therefore, it is desirable to use a Mach-Zehnder phase modulator for the phase modulator 90.

  Specifically, when the multi-value voltage of the running key 2 is input to the electrical signal input port of the Mach-Zehnder phase modulator, the phase of the continuous light from the LD 59 is randomly changed according to the multi-value voltage value of the running key 2. Can be changed.

  The configuration of the pseudo-random number generator 72 that generates the Running key 2 using the encryption key 73 is the same as that shown in FIG. The pseudo random number generation unit 711 that generates the Running key 1 using the encryption key 713 and the multi-value modulation electrical signal generation unit 711 that changes the tone of the multi-value signal using the Running key are the same as those in FIG.

  According to this example, as shown in FIG. 11, a multilevel phase modulated signal light (b) that is phase-modulated by Δφ0 to Δφc (radian) is generated by the phase modulator 90 with respect to the reference optical carrier wave (a). Then, the multilevel phase-modulated signal light is subjected to multilevel intensity modulation by the intensity modulator 92 and transmitted to the optical fiber 104.

  As described above, according to a preferred embodiment, the frequency difference between the optical carrier and the local oscillator 201 in the heterodyne receiver (FIG. 4) is set outside the frequency band of the intermediate frequency amplifier 203 (first embodiment), or heterodyne. By controlling the phase so that the operating speed of the laser driver 59 is faster than the response speed of the local transmitter 201 in the receiver (Example 2), it is possible to enhance the security against encryption by multi-value intensity modulation. it can. Thus, even when a heterodyne receiver is used, correct decryption (cipher wiretapping) can be prevented.

[Example 3]
FIG. 12 is an example in which a noise source is used in place of the generating means for the Running key 2 in the transmission apparatus of the first embodiment.
That is, in the transmitting apparatus of FIG. 7, instead of the encryption key 2 and the running key 2 that is the output of the pseudorandom number generator 72, a physical noise source 74 and a noise amplifying unit 75 that amplifies the noise are provided. The noise amplified by the unit 75 is given to the frequency modulator 70. The physical noise source 74 does not maintain regularity due to the environment due to voltage or heat, and the use of the physical noise source 74 and the noise amplifying unit 75 constitutes a transmitter with enhanced safety. be able to.

[Example 4]
FIG. 13 shows an example in which a noise source is used in place of the generating means for the Running key 2 in the transmission apparatus of the second embodiment.
That is, in the transmission apparatus of FIG. 9, a physical noise source 74 and a noise amplifying unit 75 for amplifying the noise are provided in place of the encryption key 2 and the running key 2 that is the output of the pseudo-random number generating unit 72, and noise amplification. The noise amplified by the unit 75 is given to the phase modulator 90. The physical noise source 74 does not maintain regularity due to the environment due to voltage or heat, and the use of the physical noise source 74 and the noise amplifying unit 75 constitutes a transmitter with enhanced safety. be able to.

The figure which shows the outline of the system configuration | structure of a Yuen quantum cryptography transmitter / receiver. The figure which shows the relationship between the data of a regular receiver and an eavesdropper, and a threshold value. The figure which shows the comparison of the signal level of the direct detection system and heterodyne system in a receiver. The figure which shows the structure of a general heterodyne receiver. The figure which shows the structure of the transmitter by one Example. The figure which shows the waveform of the optical carrier wave in one Example. The figure which shows the structure of the transmitter by one Example (Example 1). The figure which shows the LD operation speed and response speed to a local transmitter in one Example. The figure which shows the structure of the transmitter by one Example (Example 2). FIG. 3 is a diagram illustrating optical frequency characteristics of an optical carrier wave according to the first embodiment. FIG. 6 is a diagram illustrating phase characteristics of an optical carrier wave according to the second embodiment. FIG. 9 is a diagram illustrating a configuration of a transmission device according to a third embodiment. FIG. 10 is a diagram illustrating a configuration of a transmission device according to a fourth embodiment.

Explanation of symbols

500: Frequency or phase modulation mechanism 511: Multi-level modulation electric signal generation unit 512: Pseudorandom number generation unit 513: Encryption key 104: Optical fiber 52: Intensity modulator
70: Frequency modulator 702: LD Driver 703: LD 704: Coupler 72: Pseudorandom number generator 2, 73: Encryption key 2 713: Encryption key 1 712: Pseudorandom number generation unit 1 711: Multi-level modulation electric signal generation unit 52 : Intensity modulator 104: optical fiber 90: phase modulator 74: physical noise source 75: noise amplifier.

Claims (16)

An optical transmission device that modulates data into an optical signal and transmits it using optical communication quantum cryptography based on multilevel intensity modulation,
A first pseudo-random number generation unit for generating a first Running key and data to be transmitted by using the first Running key generated by the first pseudo-random number generation unit. A multi-level modulation signal generation unit to generate as a signal;
A random key generating unit that generates a random key; a first modulator that changes a phase or frequency of an optical carrier wave of data to be transmitted using the random key generated by the random key generating unit;
An optical signal that has received an optical carrier whose phase or frequency has been changed by the first modulator and whose optical intensity base of the optical carrier has been changed by a multilevel signal generated by the multilevel modulation signal generator. And a second modulator for generating the optical transmitter. The random key generation unit is a second pseudo random number generation unit that generates a second Running key using a second encryption key;
The first modulator changes the phase or frequency of an optical carrier wave of data to be transmitted using the second Running key generated by the second pseudorandom number generator. 1. Optical transmission apparatus. The random key generation unit includes a noise source that generates noise, and an amplification unit that amplifies noise generated from the noise source,
2. The optical transmission apparatus according to claim 1, wherein the first modulator changes the phase or frequency of an optical carrier wave of data to be transmitted using the noise amplified by the noise amplification unit. The first modulator is a frequency modulator having a plurality of n lasers, a plurality of laser drivers for driving the lasers, and a plurality of couplers for combining the outputs of the lasers, and the second pseudorandom number A plurality of n laser drivers (where m <n) are selected by the second running key from the generator, and the output of the laser driven by the selected laser driver is output by the coupler. 4. The optical transmission device according to claim 1, wherein the combined optical carrier wave is output to the second modulator. The first running key and the second running key are different from each other, and the first modulator changes the frequency or phase of the optical carrier wave by switching over time and at random. The optical transmission device according to claim 1. The first pseudo random number generator and the second pseudo random number generator are configured by different hardware circuits, and the first modulator switches the frequency or phase of the optical carrier wave over time and randomly. 6. The optical transmission device according to claim 1, wherein the optical transmission device is changed. The first modulator is a frequency modulator;
The frequency modulator is configured to apply the second Running key,
7. The optical transmission device according to claim 1, wherein an optical carrier wave having a frequency outside the frequency band of the bandpass filter of the intermediate frequency amplifier included in the heterodyne receiver that receives the transmitted optical signal is output. . The first modulator is a frequency modulator;
The frequency modulator is configured to apply the second Running key by
When assuming the frequency fc (Hz) of the optical carrier wave and the frequency variation Δfc (Hz),
fc−Δfc to fc + Δfc
8. The optical transmission device according to claim 1, wherein an optical carrier wave having a frequency that changes over time and randomly in a frequency range (Hz) is output. The first modulator is a phase modulator;
The phase modulator is configured to apply the second Running key
When the phase φc (radian) of the optical carrier and the phase variation Δφc (radian) are set,
φc−Δφc to φc + Δφc (t)
7. An optical transmission device according to claim 1, wherein an optical carrier wave having a phase which changes with time in a phase range (radian) of at least randomly. The first modulator is a Mach-Zehnder phase modulator;
The multilevel voltage of the second running key is input to the electrical signal input port of the Mach-Zehnder phase modulator, and the phase of the optical carrier is randomly changed according to the multilevel voltage value of the second running key. The optical transmission device according to claim 1. An optical transmission method for modulating and transmitting data into an optical signal using optical communication quantum cryptography based on multilevel intensity modulation,
A first pseudo-random number generation step of generating a first Running key;
A multi-level modulation signal generation step of generating data to be transmitted as a multi-level signal in units of bits using the first Running key generated by the first pseudo-random number generation step;
A random key generation step for generating a random key;
A first modulation step of changing a phase or frequency of an optical carrier wave of data to be transmitted using the random key generated by the random key generation step;
An optical signal that has received the optical carrier whose phase or frequency has been changed by the first modulation step and has changed the light intensity base of the optical carrier by the multi-level signal generated by the multi-level modulation signal generation step. And a second modulation step for generating the optical transmission method. An optical transmission method for modulating and transmitting data into an optical signal using optical communication quantum cryptography based on multilevel intensity modulation,
Generating a first Running key using the first encryption key;
Using the generated first Running key to generate data to be transmitted as a multi-value signal in bit units;
Generating a second Running key using the second encryption key;
Changing the phase or frequency of the optical carrier wave of the data to be transmitted using the generated second Running key;
Receiving an optical carrier whose phase or frequency is changed, and generating an optical signal in which the optical intensity base of the optical carrier is changed by the multilevel signal generated in the multilevel modulation signal generating step;
An optical transmission method comprising: 12. The optical transmission method according to claim 11, wherein the frequency or phase of the optical carrier is changed over time and at random by using different keys as the first and second running keys. The frequency modulator that changes the frequency of the optical carrier has a frequency outside the frequency band of the bandpass filter of the intermediate frequency amplifier of the heterodyne receiver that receives the transmitted optical signal by applying the second Running key. 14. The optical transmission method according to claim 11, wherein an optical carrier wave is output. When the frequency modulator that changes the frequency of the optical carrier has the frequency fc (Hz) and the frequency variation Δfc (Hz) of the optical carrier by the application of the second running key,
fc−Δfc to fc + Δfc
15. The optical transmission method according to claim 11, wherein an optical carrier wave having a frequency that changes over time and randomly in a frequency range (Hz) is output. Using a Mach-Zehnder phase modulator as a modulator that changes the phase of the optical carrier,
The Mach-Zehnder phase modulator is configured to apply the second Running key by:
When the phase φc (radian) of the optical carrier and the phase variation Δφc (radian) are set,
φc−Δφc to φc + Δφc (t)
14. The optical transmission method according to claim 11, wherein an optical carrier wave having a phase that changes with time in a phase range (radian) is output in a random manner.

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