JP2007243929A - Data transmitting apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data communication apparatus which cause an eavesdropper to take a significantly increased time to analyze a cipher text and consequently realize highly concealable data communication. <P>SOLUTION: A branch unit 114 in a modulation section 112a branches an optical wave 20 outputted from a light source 113 and outputs respective branched lights to a first optical path 117 and a second optical path 118 with an optical path length difference. An optical modulation section 116 modulates an optical wave propagated through at least one of the first optical path 117 and the second optical path 118 by a multi-level signal 13. An interference section 119 interferes an optical wave outputted from the first optical path 117 with an optical wave from the second optical path 118 each other and outputs the interfered optical wave as a modulated signal 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus and method for performing cryptographic communication to prevent illegal eavesdropping and interception by a third party, and more specifically, a specific encoding / decoding (modulation / demodulation) scheme between authorized senders and receivers. The present invention relates to a data transmission apparatus and a data transmission method for performing data communication by selecting and setting the.

  Conventionally, in order to communicate only with specific persons, key information for encoding / decoding is shared between transmission / reception, and information data (plain text) to be transmitted is mathematically calculated based on the key information. In other words, a configuration is adopted in which secret communication is realized by performing computation / reverse computation. FIG. 17 is a block diagram showing a configuration of a conventional data communication apparatus based on such a configuration.

  In FIG. 17, the conventional data communication apparatus has a configuration in which a data transmission apparatus 9001 and a data reception apparatus 9002 are connected by a transmission path 913. The data transmission apparatus 9001 includes an encoding unit 911 and a modulation unit 912. The data reception device 9002 includes a demodulation unit 914 and a decoding unit 915.

  In the data transmission device 9001, information data 90 and first key information 91 are input to the encoding unit 911. The encoding unit 911 encodes (encrypts) the information data 90 based on the first key information 91. The modulation unit 912 converts the information data 90 encoded by the encoding unit 911 into a modulation signal 94 having a predetermined modulation format, and sends the modulation signal 94 to the transmission path 913.

  In the data receiving device 9002, the demodulator 914 demodulates the modulated signal 94 transmitted via the transmission path 913 by a predetermined demodulation method. The decryption unit 915 receives second key information 96 that is the same as the first key information 91. The decrypting unit 915 decrypts (decrypts) the modulated signal 94 based on the second key information 96 and outputs information data 98.

  Here, an eavesdropping action by a third party will be described using the eavesdropper receiving device 9003. In FIG. 17, an eavesdropper receiving device 9003 includes an eavesdropper demodulation unit 916 and an eavesdropper decoding unit 917. The eavesdropper demodulation unit 916 demodulates the modulation signal 94 propagating through the transmission path 913 using a predetermined demodulation method. Based on the third key information 99, the eavesdropper decoding unit 917 attempts to decode the signal demodulated by the eavesdropper demodulation unit 916. Here, the eavesdropper decryption unit 917 attempts to decrypt the signal demodulated by the eavesdropper demodulation unit 916 on the basis of the third key information 99 different from the first key information 91. It cannot be played correctly. That is, since the eavesdropper decryption unit 917 does not share correct key information with the data transmission device 9001, the information data 98 cannot be reproduced correctly.

Such mathematical encryption (or also called calculation encryption or software encryption) technology based on mathematical operations can be applied to an access system or the like as described in Patent Document 1, for example. That is, in a PON (Passive Optical Network) system in which an optical signal transmitted from one optical transmitter is branched by an optical coupler and distributed to optical receivers at a plurality of optical subscriber houses, each optical receiver includes: A signal for a subscriber other than the desired optical signal is input. Therefore, in the PON system, by using different key information for each subscriber and encrypting information data for each subscriber, leakage and wiretapping of each other's information is prevented, and safe data communication is realized.
JP-A-9-205420 Translated by Keiichiro Ishibashi, “Cryptography and Network Security: Theory and Practice”, Pearson Education, 2001 Mayumi Adachi et al., "Encryption Technology Encyclopedia", Softbank Publishing, 2003

  However, in a conventional data communication device based on mathematical cryptography, an eavesdropper can combine all possible combinations of ciphertext (modulated signal or encrypted information data) without sharing key information. In principle, cryptanalysis is possible by trying to apply key information-based operations (brute force attacks) and special analysis algorithms. In particular, the recent improvement in processing speed of computers has been remarkable, and if a computer based on a new principle such as a quantum computer is realized in the future, there has been a problem that a ciphertext can be wiretapped within a finite time.

  Therefore, an object of the present invention is to provide a highly confidential data communication device that significantly increases the time required for an eavesdropper to analyze a ciphertext.

  The present invention is directed to a data transmitting apparatus that encrypts information data using predetermined key information and performs secret communication with a receiving apparatus. In order to achieve the above object, a data transmission apparatus according to the present invention includes a multi-level code generation unit that generates a multi-level code sequence whose signal level changes substantially randomly based on predetermined key information, A multi-level processing unit that synthesizes the value code string and the information data and generates a multi-level signal having a plurality of levels corresponding to the combination of the multi-level code string and the information data, and a predetermined modulation process on the multi-level signal And a modulation unit that outputs the signal as a modulation signal. The modulation unit branches the light wave output from the light source and outputs a branched light to the first optical path and the second optical path having optical path length differences, and the first optical path and the second optical path. Among the optical paths, an optical modulator that modulates an optical wave propagating through at least one optical path with a multi-level signal and an optical wave output from the first optical path and the second optical path interfere with each other, and the interfered optical wave And an interference unit that outputs the modulated signal.

  Moreover, the data transmission device of the present invention may be configured to include a modulation unit as described below. The modulation unit branches the light wave output from the light source and outputs a branched light to the first optical path and the second optical path having optical path length differences, and the first optical path and the second optical path. An interference unit that causes the light waves output from the optical path to interfere with each other and outputs the interfered light waves as a combined wave, and an optical modulation unit that modulates the combined wave output from the interference unit with a multilevel signal.

  Moreover, the data transmission device of the present invention may be configured to include a modulation unit as described below. The modulation unit branches the output of the light modulation unit that modulates the light wave output from the light source with a multi-level signal and the light modulation unit into a first optical path and a second optical path that have optical path length differences from each other. A branching unit that outputs light and an interference unit that causes the light waves output from the first optical path and the second optical path to interfere with each other and outputs the interfered light waves as modulation signals.

  Moreover, the data transmission device of the present invention may be configured to include a modulation unit as described below. The modulation unit includes a light transmission unit disposed in the propagation path of the light wave output from the light source, and a light modulation unit that modulates the light wave output from the light transmission unit with a multi-value signal. The light transmission unit transmits the light wave output from the light source with a predetermined transmittance, and reflects the light wave output from the first transmission reflection unit with a predetermined transmission rate. A second transmission / reflection part that transmits at a transmittance and reflects at a predetermined reflectance, and an optical path having a predetermined optical path length disposed between the first transmission / reflection part and the second transmission / reflection part. Composed.

  Preferably, the optical path length difference between the first optical path and the second optical path is equal to or greater than the coherent length of the light wave input to the modulation unit. Alternatively, the optical path length difference between the first optical path and the second optical path may be generated by a delay unit arranged in at least one of the optical paths.

  Preferably, the interference unit is output from an amplitude adjustment unit that attenuates an amplitude of a light wave propagating through at least one of the first optical path and the second optical path, and the first optical path and the second optical path. It is comprised with the synthetic | combination part which synthesize | combines a light wave.

  The interference unit is output from a polarization adjustment unit that adjusts a polarization state of a light wave propagating through at least one of the first optical path and the second optical path, and the first optical path and the second optical path. You may comprise with the synthetic | combination part which synthesize | combines a light wave.

  Preferably, the amplitude adjusting unit varies the attenuation amount of the input light wave based on a control signal input from the outside. The polarization adjusting unit varies the deflection state of the input light wave based on a control signal input from the outside. The optical path length of the optical path having the predetermined optical path length is at least 0.5 times the coherent length of the light wave output from the light source.

  Preferably, the modulation unit further includes an interference control unit that performs feedback control of a multiplexing ratio in the interference unit based on an interference noise amount included in a light wave output from at least one of the interference unit and the light modulation unit.

  The interference control unit includes a detection unit that photoelectrically converts an input light wave and detects interference noise, and a control unit that outputs a control signal to the interference unit based on a detection result of the detection unit.

  The present invention is also directed to a data transmission method for encrypting information data using predetermined key information and performing secret communication with a receiving apparatus. In order to achieve the above object, the data transmission method of the present invention includes a multi-level code generation step for generating a multi-level code sequence in which the signal level changes substantially randomly based on predetermined key information, and a multi-level code generation step. A multi-value processing step for synthesizing the value code string and the information data to generate a multi-value signal having a plurality of levels corresponding to the combination of the multi-value code string and the information data; and a predetermined modulation process for the multi-value signal. And a modulation step of outputting as a modulation signal. However, the modulation step branches the light wave output from the light source, outputs a branched light to the first optical path and the second optical path having optical path length differences, and the first optical path and the first optical path. An optical modulation step for modulating a light wave propagating through at least one of the two optical paths with a multi-level signal and an optical wave output from the first optical path and the second optical path are caused to interfere with each other. An interference step of outputting a light wave as a modulation signal.

  In addition, the data transmission method of the present invention may include a modulation step as shown below. The modulation step branches the light wave output from the light source and outputs a branched light to the first optical path and the second optical path having optical path length differences from each other; the first optical path and the second optical path; The method includes an interference step of causing the light waves output from the optical path to interfere with each other and outputting the interfered light waves as a synthesized wave, and an optical modulation step of modulating the synthesized wave with a multilevel signal.

  In addition, the data transmission method of the present invention may include a modulation step as shown below. The modulation step includes an optical modulation step for modulating the light wave output from the light source with a multi-level signal, and a light wave modulated with the multi-level signal for branching to a first optical path and a second optical path having optical path length differences from each other. A branching step for outputting the branched light, and an interference step for causing the light waves output from the first optical path and the second optical path to interfere with each other and outputting the interfered light waves as modulation signals.

  In addition, the data transmission method of the present invention may include a modulation step as shown below. The modulation step includes a light transmission step for transmitting the light wave output from the light source, and a light modulation step for modulating the light wave output from the light transmission step with a multilevel signal. The light transmission step transmits the light wave output from the light source with a predetermined transmittance, and reflects the light wave output from the first transmission / reflection step with a predetermined reflectance. A second transmission / reflection step that outputs the light wave output from the optical path having an optical path length and transmits the light wave output from the optical path at a predetermined transmittance, and reflects the light wave at a predetermined reflectance.

  The data transmitting apparatus of the present invention encodes and modulates information data into a multilevel signal based on the key information, demodulates and encodes the received multilevel signal based on the same key information, and generates a signal pair of the multilevel signal. Optimize the noise power ratio. Thereby, the time required for the analysis of the ciphertext can be significantly increased, and highly confidential data communication can be performed. In addition, by sending a modulated signal that is a composite wave of two light waves that have passed through the long path and short path, it is difficult to avoid before and after detection, and noise with excellent controllability is generated. Thus, it is possible to provide a safe data communication device that gives decisive degradation to the received signal quality at the time of eavesdropping by a third party and makes it difficult to decode and decode the multilevel signal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing an example of the configuration of a data communication apparatus according to the first embodiment of the present invention. In FIG. 1, the data communication apparatus according to the first embodiment has a configuration in which a data transmission apparatus 1101 and a data reception apparatus 1201 are connected by a transmission path 110. The data transmission device 1101 includes a multi-level encoding unit 111 and a modulation unit 112. The multi-level encoding unit 111 includes a first multi-level code generation unit 111a and a multi-level processing unit 111b. The data reception device 1201 includes a demodulation unit 211 and a multilevel decoding unit 212. The multilevel decoding unit 212 includes a second multilevel code generation unit 212a and a multilevel identification unit 212b. The transmission line 110 can be a metal line such as a LAN cable or a coaxial cable, or an optical waveguide such as an optical fiber cable. The transmission path 110 is not limited to a wired cable such as a LAN cable, and may be a free space capable of propagating a radio signal.

  FIG. 2 is a flowchart showing an example of the operation of the data transmission apparatus 1101 according to the first embodiment of the present invention. FIG. 3 is a schematic diagram for explaining a transmission signal waveform of the data communication apparatus according to the first embodiment of the present invention. FIG. 4A is a schematic diagram for explaining names of transmission signal waveforms of the data communication apparatus according to the first embodiment of the present invention. FIG. 4B is a schematic diagram illustrating the transmission signal quality of the data communication apparatus according to the first embodiment of the present invention. The operation of the data communication apparatus according to the first embodiment of the present invention will be described below with reference to the drawings.

  Referring to FIG. 2, the first multi-level code generation unit 111a generates a multi-level code sequence 12 whose signal level changes substantially in a random manner based on predetermined first key information 11 ( Step S101). The multi-level processing unit 111b receives the multi-level code string 12 and the information data 10. The multi-level processing unit 111b synthesizes the multi-level code sequence 12 and the information data 10 according to a predetermined procedure, and outputs the multi-level signal 13 having a plurality of levels corresponding to the combination of the multi-level code sequence 12 and the information data 10. Generate (step S102). For example, when the level of the multilevel code sequence 12 changes to C1 / C5 / C3 / C4 with respect to the time slot t1 / t2 / t3 / t4 (see FIG. 3B), A multilevel signal whose level changes to L1 / L8 / L6 / L4 by adding the information data 10 (see FIG. 3A) to the multilevel code sequence 12 with the level of the multilevel code sequence 12 as a bias level. 13 (see FIG. 3C) is generated. The modulation unit 112 modulates the multilevel signal 13 in a predetermined modulation format, and outputs the modulated signal 14 to the transmission line 110 as a modulated signal 14 (step S103).

  Here, as shown in FIG. 4A, the amplitude of the information data 10 is “information amplitude”, the total amplitude of the multilevel signal 13 is “multilevel signal amplitude”, and the level C1 / C2 / C3 of the multilevel code sequence 12 The first set of levels (L1, L4) / (L2, L5) / (L3, L6) / (L4, L7) / (L5, L8) that can be taken by the multilevel signal 13 corresponding to / C4 / C5 The fifth “base” and the minimum signal point distance of the multi-level signal 13 are referred to as “step width”, respectively.

  The demodulator 211 demodulates the modulated signal 14 transmitted via the transmission path 110 and reproduces the multilevel signal 15. The second multi-level code generation unit 212 a shares the second key information 16 that is the same as the first key information 11 in advance, and generates the multi-level code sequence 17 based on the second key information 16. . The multilevel identifying unit 212b identifies the multilevel signal 15 (binary determination) using the multilevel code string 17 as a threshold value, and reproduces the information data 18. Here, the modulation signal 14 in a predetermined modulation format transmitted and received by the modulation unit 112 and the demodulation unit 211 via the transmission path 110 is obtained by modulating an electromagnetic wave (electromagnetic field) or a light wave with the multilevel signal 13. Is.

  The multi-level processing unit 111b may generate the multi-level signal 13 using any method other than the method of generating the multi-level signal 13 by adding the multi-level code sequence 12 and the information data 10. . For example, the multilevel processing unit 111 b may generate the multilevel signal 13 by amplitude-modulating the level of the multilevel code sequence 12 based on the information data 10. Alternatively, the multi-level processing unit 111b sequentially reads the levels of the multi-level signal 13 corresponding to the combination of the information data 10 and the multi-level code sequence 12 from the memory in which the level of the multi-level signal 13 is stored in advance. A value signal 13 may be generated.

  3 and 4A, the level of the multi-level signal 13 is expressed in eight stages, but the level of the multi-level signal 13 is not limited to this notation. Further, although the information amplitude is expressed as three times or an integer multiple of the step width of the multi-level signal 13, the information amplitude is not limited to this notation. Further, in FIGS. 3 and 4A, each level of the multilevel code sequence 12 is arranged so as to be approximately the center of each level of the multilevel signal 13, but each level of the multilevel code sequence 12 is limited to this arrangement. Is not to be done. For example, each level of the multilevel code string 12 may not be substantially the center of each level of the multilevel signal 13, or may match each level of the multilevel signal 13. In the above description, it is assumed that the multi-level code sequence 12 and the information data 10 have the same change rate and are in a synchronous relationship, but one change rate is faster than the other change rate ( (Or low speed) or asynchronous.

  Next, the wiretapping operation of the modulated signal 14 by a third party will be described. A third party who is an eavesdropper uses the configuration in conformity with the data receiving device 1201 provided by an authorized receiver or a higher performance data receiving device (hereinafter, referred to as an eavesdropper data receiving device) to output the modulated signal 14. It is assumed that it will be deciphered. The eavesdropper data receiving apparatus reproduces the multilevel signal 15 by demodulating the modulated signal 14. However, since the eavesdropper data receiving apparatus does not share key information with the data transmitting apparatus 1101, unlike the data receiving apparatus 1201, the multilevel code string 17 cannot be generated from the key information. For this reason, the eavesdropper data receiving device cannot perform binary determination of the multilevel signal 15 with the multilevel code string 17 as a reference.

  As an eavesdropping operation that can be considered in such a case, there is a method of simultaneously identifying all levels of the multilevel signal 15 (generally called “brute force attack”). That is, the eavesdropper data receiving apparatus prepares threshold values for all signal points that can be taken by the multilevel signal 15, performs determination of the multilevel signal 15, and analyzes the determination result to obtain correct key information or information. Attempt to extract data. For example, the eavesdropper data receiving apparatus performs multilevel determination on the multilevel signal 15 with each level C0 / C1 / C2 / C3 / C4 / C5 / C6 of the multilevel code string 12 shown in FIG. Therefore, it tries to extract correct key information or information data.

  However, in an actual transmission system, noise is generated due to various factors, and this noise is superimposed on the modulation signal 14, whereby the level of the multilevel signal 15 is temporally and instantaneously shown in FIG. 4B. fluctuate. In such a case, the SN ratio of the signal to be determined (multilevel signal 15) determined by the authorized receiver (data reception device 1201) is determined by the ratio between the information amplitude of the multilevel signal 15 and the amount of noise. On the other hand, the SN ratio of the determination target signal (multilevel signal 15) determined by the eavesdropper data receiving apparatus is determined by the ratio between the step width of the multilevel signal 15 and the amount of noise.

  For this reason, when the noise level of the determined signal is the same, the eavesdropper data receiving device has a relatively smaller SN ratio than the data receiving device 1201, and transmission characteristics (error rate) ) Will deteriorate. That is, the data communication apparatus of the present invention can make eavesdropping difficult by using this characteristic to induce an identification error with respect to a brute force attack using all third-party thresholds. In particular, if the data communication device sets the step width of the multi-level signal 15 to the same order or smaller than the noise amplitude (that is, the spread of the noise intensity distribution), the multi-level determination by a third party is a fact. It is impossible to achieve the ideal prevention of eavesdropping.

  The noise superimposed on the signal to be judged (multi-level signal 15 or modulated signal 14) is a thermal noise (Gaussian property) possessed by a spatial field or electronic parts when electromagnetic waves such as radio signals are used for the modulated signal 14. When light waves are used, in addition to thermal noise, fluctuations in the number of photons (quantum noise) when photons are generated can be used. In particular, since a signal using quantum noise cannot be subjected to signal processing such as recording or duplication, the data communication apparatus sets the step width of the multilevel signal 15 based on the amount of noise. Therefore, it is impossible to eavesdrop on a third party, and the absolute safety of data communication can be ensured.

  As described above, according to the data communication apparatus according to the first embodiment of the present invention, when the information data to be transmitted is encoded as a multilevel signal, the distance between the signal points of the multilevel signal is determined with respect to the noise amount. To prevent eavesdropping by a third party. This provides a safer data communication device that gives decisive degradation to the received signal quality at the time of eavesdropping by a third party and makes it difficult for the third party to decode and decode the multilevel signal. be able to.

  As shown in FIG. 5, the multi-level encoding unit 111 superimposes each step width (S1 to S7) of the multi-level signal 13 on the fluctuation amount of each level of the multi-level signal 13, that is, each level. It may be varied according to the noise intensity distribution. Specifically, the multilevel encoding unit 111 sets the signal points of the multilevel signal 13 so that the SN ratios determined between two adjacent signal points of the determination target signal input to the multilevel identification unit 212b substantially match. Distribute the distance between them. Further, the multi-level encoding unit 111 sets the step widths of the multi-level signal 13 equally when the amount of noise superimposed on each level is equal.

  In general, when a light intensity modulation signal using a semiconductor laser (LD) as a light source is assumed as the modulation signal 14 output from the modulation unit 112, the modulation depends on the level of the multilevel signal 13 input to the semiconductor laser. The fluctuation range (noise amount) of the signal 14 changes. This is because the semiconductor laser emits light based on the principle of stimulated emission using spontaneous emission light as “seed light”, and the amount of noise included in the modulation signal output from the semiconductor laser is the amount of induced emission light. It is defined by the relative ratio with the amount of spontaneous emission. In other words, the higher the pumping rate of the semiconductor laser (the bias current injected into the semiconductor laser), the greater the ratio of the amount of stimulated emission light, and the smaller the amount of noise. Conversely, the lower the pumping rate of the semiconductor laser, the greater the amount of spontaneous emission, and the greater the amount of noise. Therefore, as shown in FIG. 5, the multilevel encoding unit 111 sets the step width to be large in a region where the level of the multilevel signal 13 is small, and to set the step width to be nonlinear in a region where the level of the multilevel signal 13 is large. Thus, the SN ratio between adjacent signal points of the signal to be determined can be made substantially uniform.

  Even when an optical modulation signal is used as the modulation signal 14, the SN ratio of the reception signal is mainly determined by shot noise under the condition that the noise due to the spontaneous emission light and the thermal noise used in the optical receiver are sufficiently small. Will be. Under such conditions, the amount of noise included in the multilevel signal 13 increases as the level of the multilevel signal 13 increases. Therefore, contrary to the case of FIG. 5, the multilevel encoding unit 111 sets a small step width in a region where the level of the multilevel signal 13 is small and a large step width in a region where the level of the multilevel signal 13 is large. By doing so, the S / N ratio between adjacent signal points of the signal to be determined can be set substantially uniformly. As a result, decisive deterioration can be equally applied to the received signal quality at the time of eavesdropping by a third party, so that the decoding / decoding of the multilevel signal by the third party can be made more difficult.

(Second Embodiment)
FIG. 6 is a block diagram showing an example of the configuration of the data communication apparatus according to the second embodiment of the present invention. In FIG. 6, the data communication apparatus according to the second embodiment of the present invention has a configuration in which a data transmission apparatus 1102 and a data reception apparatus 1201 are connected by a transmission line 110. The data transmission apparatus 1102 includes a first multi-level code generation unit 111a, a multi-level processing unit 111b, and a modulation unit 112a. The data reception device 1201 includes a demodulation unit 211, a second multi-level code generation unit 212a, and a multi-level identification unit 212b.

  As shown in FIG. 6, the configuration of the data communication apparatus according to the second embodiment is different from the data communication apparatus according to the first embodiment in the configuration of the modulation unit 112a. In FIG. 6, the modulation unit 112 a includes a light source 113, a branching unit 114, a delay unit 115, an optical modulation unit 116, and an interference unit 119. The interference unit 119 includes an amplitude adjustment unit 120 and a synthesis unit 121. Hereinafter, the same reference numerals are assigned to the same configurations as those in the first embodiment, and the data communication apparatus according to the second embodiment will be described focusing on the different configurations.

  The light wave 20 emitted from the light source 113 is incident on the branching unit 114, and is branched into the first optical path 117 and the second optical path 118 having optical path length differences. In the present embodiment, the first optical path 117 from the branching unit 114 via the delay unit 115 to the interference unit 119 is a long path, and the second optical path from the branching unit 114 to the interference unit 119 via the light modulation unit 116. The optical path 118 is a short path.

  FIG. 7A is a schematic diagram illustrating an optical multiplexed signal waveform of the data transmission apparatus 1102 according to the second embodiment of the present invention. Referring to FIG. 7A, among the light waves branched by branching unit 114, light wave a <b> 1 that passes through a long path is emitted to interference unit 119 after receiving a predetermined delay time Δt by delay unit 115. On the other hand, the light wave a2 branched by the branching unit 114 and passing through the short path is modulated based on the multilevel signal 13 by the light modulating unit 116 and then emitted to the interference unit 119 as the light wave b2. Of the light waves incident on the interference unit 119, the light wave a1 passing through the long path is attenuated to a predetermined amplitude by the amplitude adjustment unit 120 and then emitted to the synthesis unit 121 as the light wave b1. In the synthesizer 121, the light wave b 1 passing through the long path and the light wave b 2 passing through the short path are combined and sent to the transmission path 110 as the modulation signal 14.

  In the data receiving apparatus 1201, the demodulator 211 reproduces the multilevel signal 15 by demodulating the modulated signal 14 received via the transmission path 110, and reproduces the information data 18 in the multilevel decoder 212.

  Note that the phase relationship between the two light waves incident on the combining unit 121 is preferably uncorrelated. In this embodiment, this relationship can be easily realized by setting the optical path length in the delay unit 115 to be equal to or longer than the coherent length (coherence length) of the light source 113.

  As for the configuration of the short path and the long path, as described above, in addition to the method of configuring the delay unit 115 in the long path and configuring the optical modulation unit 116 in the short path, the delay unit 115 and the optical modulation in the long path. The unit 116 may be configured. In the present embodiment, the number of branches in the branching unit 114 is 2. However, the number of branches may be larger than 2.

  FIG. 7B is a flowchart showing an example of the operation of the modulation unit 112a according to the second embodiment of the present invention. Referring to FIG. 7B, branching unit 114 branches light wave 20 output from light source 113, and outputs the respective branched lights to first optical path 117 and second optical path 118 having optical path length differences from each other. (Step S1031). The light modulation unit 116 modulates the light wave propagating through at least one of the first optical path 117 and the second optical path 118 with the multilevel signal 13 (step S1032). The interference unit 119 causes the light waves output from the first optical path 117 and the second optical path 118 to interfere with each other, and outputs the interfered light waves as the modulation signal 14 (step S1033).

  Next, an eavesdropping operation by a third party will be described. The third party square-detects a part or all of the modulation signal 14 which is a composite wave of two light waves passing through the long path and the short path by the light receiving element, and demodulates the multilevel signal. At this time, quantum noise and interference noise of two light waves are superimposed on the demodulated multilevel signal. FIG. 8 is a schematic diagram for explaining superimposed noise by the data transmission apparatus 1102 according to the second embodiment of the present invention.

Of the noise superimposed on the multilevel signal, the quantum noise is a fluctuation that is inevitably generated when a light wave is used for the modulation signal, and becomes manifest as a fluctuation in the number of electrons (that is, a shot noise current) after detection. (See FIG. 8 (a)). This distribution of the number of electrons (that is, the average number of electrons N) is known to follow the Poisson distribution shown in Equation (1).

In addition, the interference of two uncorrelated light waves (same wavelength) traveling in the same direction among the noises superimposed on the multilevel signal is an interference having a distribution that is polarized around the average number of electrons N after detection. It becomes manifest as noise (FIG. 8B). The probability density function when this interference noise is normalized by the average number of electrons N is expressed by equation (2), where R is the ratio of the electric field amplitudes of both light waves. In particular, the two poles in the amplitude distribution of interference noise (in other words, the highest number of electrons generated when the average number of electrons is N) are given by N (1-2R) and N (1 + 2R). . Therefore, the difference (N · 4R) between the two poles is determined by the average number of electrons N and the electric field amplitude ratio R of both light waves.

  That is, the distribution of the number of electrons after detection by a third party who is an eavesdropper is a distribution in which the average number of electrons N is centered by interference noise and the tail spreads around each spire value by shot noise. (Fig. 8 (c)). This superposed noise is difficult to avoid before / after detection due to the unavoidability of quantum noise and the difficulty of separating / removing interference noise. Further, as shown in Expression (2), the distribution of noise that becomes apparent after detection depends on the average number of electrons N proportional to the signal light intensity and the electric field amplitude ratio R of the two light waves. Therefore, by setting the electric field amplitude ratio R, it is possible to freely set the amount of noise that is difficult to avoid. The setting of the electric field amplitude ratio R can be easily realized by setting the coupling ratio of two light waves in the combining unit 121, for example.

  Next, a third party who is an eavesdropper prepares thresholds for all signal points that can be taken by the demodulated multilevel signal by performing a brute force attack, and performs simultaneous determination of the multilevel signal, and the determination result By trying to extract correct key information or information data. For example, the eavesdropper performs multi-level determination on a multi-level signal using the multi-level code string level C0 / C1 / C2 / C3 / C4 / C5 / C6 shown in FIG. Identify the level of the value signal. However, since noise that is difficult to avoid before and after detection is superimposed, as shown in FIG. 9, the bipolar noise centered on each multi-level is substantially equal to the multi-level signal. Overlapping. For example, since the determination result identified at the level C3 of the multilevel code string can give the possibility of the multilevel level of L3 / L6 in addition to the possibility of the multilevel level of L4 / L5 adjacent to the determination result, The eavesdropping can be made more difficult by causing the identification error in the multi-level determination operation by the person to be more difficult and specifying the multi-level level by analyzing the determination result.

  As described above, according to the present embodiment, it is difficult to avoid before / after detection by sending a modulated signal that is a composite wave of two light waves that have passed through a long path and a short path. Providing a secure data communication device that generates noise with excellent controllability, decisively degrades the received signal quality when eavesdropping by a third party, and makes decoding and decoding difficult. can do.

(Third embodiment)
FIG. 10 is a block diagram showing an example of the configuration of the data transmission device 1103 according to the third embodiment of the present invention. As shown in FIG. 10, the configuration of the data transmission device 1103 according to the third embodiment is different from the configuration of the data transmission device 1101 according to the first embodiment in the configuration of the modulation unit 112b. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The data communication apparatus according to the third embodiment will be described focusing on the different components.

  In FIG. 10, the modulation unit 112 b includes a light source 113, a branch unit 114, a delay unit 115, an optical modulation unit 116, and an interference unit 119. The interference unit 119 includes an amplitude adjustment unit 120 and a synthesis unit 121. In the modulation unit 112b, the light wave 20 emitted from the light source 113 is incident on the branching unit 114, and the branching unit 114 splits the first optical path 117 and the second optical path 118 having an optical path length difference. The In the present embodiment, the first optical path 117 from the branching unit 114 via the delay unit 115 to the interference unit 119 is a long path, and the second optical path 118 that directly connects the branching unit 114 and the interference unit 119 is a short path. And

  FIG. 11A is a schematic diagram for explaining the wavelength arrangement of an optical multiplexed signal in the data transmission apparatus 1103 according to the third embodiment of the present invention. Referring to FIG. 11A, among the light waves branched by branching unit 114, a light wave passing through a long path is emitted to interference unit 119 after being subjected to a predetermined delay time Δt by delay unit 115. On the other hand, the light wave b <b> 2 branched by the branching unit 114 and passing through the short path is emitted to the interference unit 119. Among the light waves incident on the interference unit 119, the light wave that has passed through the long path is attenuated to a predetermined amplitude by the amplitude adjustment unit 120 and then emitted to the synthesis unit 121 as the light wave b1. The light wave b1 passing through the long path and the light wave b2 passing through the short path are combined by the combining unit 121, modulated in a batch based on the multilevel signal 13 by the light modulating unit 116, and then modulated signal 14 (c1 + c2). ) To the transmission line 110.

  FIG. 11B is a flowchart illustrating an example of the operation of the modulation unit 112b according to the third embodiment of the present invention. Referring to FIG. 11B, branching unit 114 branches light wave 20 output from light source 113, and outputs the respective branched lights to first optical path 117 and second optical path 118 having optical path length differences from each other. (Step S1131). The interference unit 119 causes the light waves output from the first optical path 117 and the second optical path 118 to interfere with each other, and outputs the interfered light waves as a synthesized wave (step S1132). The optical modulation unit 116 modulates the combined wave output from the interference unit 119 with the multilevel signal 13 and outputs the modulated signal 14 (step S1133).

  As described above, according to the present embodiment, the electric field amplitude of the two light waves included in the modulation signal is obtained by collectively modulating the combined wave of the two light waves that have passed through the long path and the short path with the multilevel signal. Since the ratio R can always be made constant irrespective of the signal stream of the multilevel signal, it is easy to manage noise superimposed on the multilevel signal when demodulating the modulation signal. In addition, this superposed noise is difficult to avoid before / after detection due to the unavoidability of quantum noise and the difficulty of separating / removing interference noise. It is possible to make the identification error more difficult and to specify the multi-value level by analyzing the determination result, thereby making it difficult to eavesdrop.

(Fourth embodiment)
FIG. 12 is a block diagram showing an example of the configuration of the data transmission apparatus 1104 according to the fourth embodiment of the present invention. As shown in FIG. 12, the configuration of the data transmitting apparatus 1104 according to the fourth embodiment of the present invention is different from the data transmitting apparatus 1101 according to the first embodiment in the configuration of the modulation unit 112c. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The data communication apparatus according to the fourth embodiment will be described focusing on the different components.

  In FIG. 12, the modulation unit 112 c includes a light source 113, a branch unit 114, a delay unit 115, an optical modulation unit 116, and an interference unit 119. The interference unit 119 includes an amplitude adjustment unit 120 and a synthesis unit 121. In the modulation unit 112c, the light wave 20 emitted from the light source 113 is incident on the light modulation unit 116, modulated by the light modulation unit 116 based on the multilevel signal 13, and then has an optical path length difference in the branching unit 114. The light is branched into the first optical path 122 and the second optical path 123 and emitted. In the present embodiment, the first optical path 122 from the branching unit 114 via the delay unit 115 to the interference unit 119 is a long path, and the second optical path 123 that directly connects the branching unit 114 and the interference unit 119 is a short path. A route.

  FIG. 13A is a schematic diagram illustrating the wavelength arrangement of an optical multiplexed signal in the data transmission device 1104 according to the fourth embodiment of the present invention. Referring to FIG. 13A, among the light waves branched by branching unit 114, the light wave passing through the long path is emitted to interference unit 119 after being subjected to a predetermined delay time Δt by delay unit 115. On the other hand, the light wave b <b> 2 branched by the branching unit 114 and passing through the short path is emitted to the interference unit 119. Among the light waves incident on the interference unit 119, the light wave that has passed through the long path is attenuated to a predetermined amplitude by the amplitude adjustment unit 120 and then emitted to the synthesis unit 121 as the light wave b1. In the combining unit 121, the light wave b 1 passing through the long path and the light wave b 2 passing through the short path are combined and sent to the transmission path 110 as the modulation signal 14.

  FIG. 13B is a flowchart illustrating an example of the operation of the modulation unit 112c according to the fourth embodiment of the present invention. Referring to FIG. 13B, the light modulation unit 116 modulates the light wave 20 output from the light source 113 with the multilevel signal 13 (step S1231). The branching unit 114 branches the light wave 20 modulated by the multi-level signal 13 and outputs the respective branched lights to the first optical path 122 and the second optical path 123 that have optical path length differences from each other (step S1232). The interference unit 119 causes the light waves output from the first optical path 122 and the second optical path 123 to interfere with each other, and outputs the interfered light waves as the modulation signal 14 (step S1233).

  As described above, according to the present embodiment, the electric wave amplitude ratio R of the two light waves is substantially randomized by previously modulating the light wave with the multilevel signal and giving a predetermined optical path length difference between the branched light waves. Therefore, it is possible to make it difficult to predict the amount of noise that becomes apparent after detection by a third party. In addition, this superposed noise is difficult to avoid before / after detection due to the unavoidability of quantum noise and the difficulty of separating / removing interference noise. It is possible to make it difficult to elicit identification errors and to specify multi-level levels by analyzing the determination results, and to make eavesdropping difficult.

(Fifth embodiment)
FIG. 14 is a block diagram showing an example of the configuration of a data transmission apparatus 1105 according to the fifth embodiment of the present invention. As shown in FIG. 14, the configuration of the data transmitting apparatus 1105 according to the fifth embodiment of the present invention is different from the data transmitting apparatus according to the first embodiment in the configuration of the modulation unit 112d. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The data communication apparatus according to the fifth embodiment will be described focusing on the different components.

  In FIG. 14, the modulation unit 112 d includes a light source 113, a light transmission unit 124, and a light modulation unit 116. The light transmission unit 124 includes a first transmission reflection unit 125, a second transmission reflection unit 127, and an optical path 126 having a predetermined optical path length. The first transmission reflection unit 125 and the second transmission reflection unit 127 transmit the light wave 20 input from the light source 113 with a predetermined transmittance and reflect the light wave 20 with a predetermined reflectance.

  FIG. 15A is a schematic diagram illustrating the flow of light waves in the light transmitting section 124. Referring to FIGS. 14 and 15A, the light wave 20 emitted from the light source 113 is incident on the light transmission unit 124, is transmitted by the first transmission reflection unit 125 in the light transmission unit 124, and passes through the optical path 126. , Is incident on the second transmitting / reflecting portion 127. A part of the light wave incident on the second transmission / reflection unit 127 is transmitted based on the transmittance of the second transmission / reflection unit 127 and is input to the light modulation unit 116. In the present embodiment, the light wave directly output through the first transmission / reflection unit 125, the optical path 126, and the second transmission / reflection unit 127 is used as direct light.

  On the other hand, a part of the light wave incident on the second transmitting / reflecting part 127 is reflected based on the reflectance of the second transmitting / reflecting part 127 and propagates through the optical path 126 in the reverse direction, Based on the reflectance of the first transmission / reflection unit 125, the light is reflected again by the first transmission / reflection unit 125, and is incident on the light modulation unit 116 via the optical path 126 and the second transmission / reflection unit 127. In the present embodiment, in this way, the light wave that passes through the first transmission / reflection unit 125, the optical path 126, and the second transmission / reflection unit 127 twice and is output as the multiple reflection light.

Note that higher order reflection operations are omitted for the sake of simplicity. Here, the optical path length difference between the two light waves (direct light and multiple reflected light) is exactly one round trip of the optical path 126 (twice the optical path length of the optical path 126). The field amplitude ratio R, when the reflectance first transmitting reflecting section 125 has R _125, the reflectivity second transmissive reflective portion 127 has an R _127, defined by R = R ₁₂₅ · R _127.

  In this embodiment, the light transmission part 124 is composed of two transmission reflection parts and an optical path arranged between the two transmission reflection parts, and the two transmission reflection parts have an electric field amplitude ratio R. For example, by giving optical loss to the direct light and the multiple reflected light in the optical path in the light transmission part, a predetermined electric field amplitude ratio between the direct light and the multiple reflected light is used. May be given.

  The direct light and the multiple reflected light incident on the light modulation unit 116 are collectively modulated by the light modulation unit 116 using the multi-level signal 13 and are sent to the transmission line 110 as the modulation signal 14.

  FIG. 15B is a flowchart illustrating an example of the operation of the modulation unit 112d according to the fifth embodiment of the present invention. Referring to FIG. 15B, the light transmission unit 124 transmits the light wave 20 output from the light source 113. Specifically, in the light transmission unit 124, the first reflection / transmission unit 125 transmits the light wave 20 output from the light source 113 with a predetermined transmittance and reflects the light wave 20 with a predetermined reflectance (step S1331). The second reflection / transmission unit 127 transmits the light wave output from the optical path 126 with a predetermined transmittance and reflects the light wave with a predetermined reflectance (step S1332). The light modulation unit 116 modulates the light wave output from the light transmission unit 124 with the multi-value signal 13 and outputs the modulated signal 14 (step S1333).

  As described above, according to the present embodiment, two transmission / reflection portions are provided in an optical path, and two light waves (direct light and multiple reflected light) that have passed through optical paths having different optical path lengths are obtained using a multilevel signal. By collectively modulating, the electric field amplitude ratio R of the two light waves included in the modulated signal can always be made constant regardless of the signal stream of the multilevel signal with a simpler configuration. In addition, this superposed noise is difficult to avoid before / after detection due to the unavoidability of quantum noise and the difficulty of separation / removal of interference noise. It is possible to make the identification error in the operation induced and to specify the multi-level level by analyzing the determination result, and it is possible to make the wiretapping difficult.

(Sixth embodiment)
FIG. 16 is a block diagram showing an example of the configuration of a data transmission apparatus 1106 according to the sixth embodiment of the present invention. As shown in FIG. 16, the configuration of the data transmission device 1106 according to the sixth embodiment is different from the configuration of the data transmission device 1106 according to the first embodiment in the configuration of the modulation unit 112e. Hereinafter, the same components as those in the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted. The data communication apparatus according to the sixth embodiment will be described focusing on the different components.

  In FIG. 16, the modulation unit 112 e includes a light source 113, a branch unit 114, a delay unit 115, an optical modulation unit 116, an interference unit 119, and an interference control unit 128. The interference control unit 128 includes a control unit 129 and a detection unit 130. Note that the interference unit 119 may include an amplitude adjustment unit 120 and a synthesis unit 121 as illustrated in FIG. 16.

  Referring to FIG. 16, the light wave 20 emitted from the light source 113 is incident on the branching unit 114, where the branching unit 114 branches and exits to the first optical path 117 and the second optical path 118 having different optical path length differences. Is done. In the present embodiment, the first optical path 117 from the branching unit 114 via the delay unit 115 to the interference unit 119 is a long path, and the second optical path from the branching unit 114 to the interference unit 119 via the light modulation unit 116 is used. The optical path 118 is a short path.

  Of the light waves branched by the branching unit 114, the light wave passing through the long path is subjected to a predetermined delay by the delay unit 115 and then emitted to the interference unit 119. On the other hand, the light wave branched by the branching unit 114 and passing through the short path is modulated by the light modulation unit 116 based on the multilevel signal 13 and then emitted to the interference unit 119. Among the light waves incident on the interference unit 119, the light wave that has passed through the long path is attenuated to a predetermined amplitude by the amplitude adjustment unit 120 according to the control signal output from the control unit 129, and then is transmitted to the synthesis unit 121. Incident. In the combining unit 121, the light wave that passes through the long path and the light wave that passes through the short path are combined and incident on the detection unit 130.

  The detection unit 130 detects the amount of superimposed noise included in the incident signal, outputs the detection result to the control unit 129, and sends the modulation signal 14 to the transmission path 110. Based on the detection result, the control unit 129 feedback-controls the amplitude attenuation amount of the amplitude adjustment unit 120 so that the superimposed noise included in the modulation signal 14 is constant, and indirectly, the two in the synthesis unit 121 The electric field amplitude ratio R of the light wave is variable. With this operation, it is possible to stably generate superimposed noise when an eavesdropper demodulates the modulation signal regardless of changes in the operating environment.

  In this embodiment, the amplitude attenuation amount of the amplitude adjusting unit 120 is controlled and the electric field amplitude ratio R is indirectly controlled. For example, the polarization of two light waves incident on the combining unit 121 is controlled, The electric field amplitude ratio R may be controlled.

  Further, in the present embodiment, the detection unit 130 is arranged at the subsequent stage of the synthesis unit 121. However, the detection unit 130 may be arranged at any position as long as it is in the optical path in which two light waves are synthesized.

  As described above, according to the present embodiment, noise that is difficult to avoid before / after detection by sending a modulated signal that is a composite wave of two light waves that have passed through a long path and a short path. Thus, it is possible to provide a safe data communication apparatus that makes it difficult to decode and decode the received signal quality at the time of eavesdropping by a third party.

  In addition, the data communication apparatus according to the first to sixth embodiments described above can be configured to combine the features of the embodiments. In addition, each process performed by the data transmission device, the data reception device, and the data communication device according to the first to twelfth embodiments described above includes a data transmission method, a data reception method, and data communication that provide a series of processing procedures. It can also be understood as a method.

  In the data communication method, the data reception method, and the data communication method described above, predetermined program data stored in a storage device (ROM, RAM, hard disk, etc.) that can execute the processing procedure described above is interpreted and executed by the CPU. May be realized. In this case, the program data may be introduced into the storage device via the storage medium, or may be directly executed from the storage medium. Note that the storage medium refers to a semiconductor memory such as a ROM, a RAM, or a flash memory, a magnetic disk memory such as a flexible disk or a hard disk, an optical disk memory such as a CD-ROM, a DVD, or a BD, and a memory card. The storage medium is a concept including a communication medium such as a telephone line or a conveyance path.

  Although the present invention has been described in detail above, the above description is merely illustrative of the present invention in all respects and is not intended to limit the scope thereof. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention.

  The data communication device according to the present invention is useful as a secure secret communication device that does not receive eavesdropping and interception.

The block diagram which shows an example of a structure of the data communication apparatus which concerns on the 1st Embodiment of this invention. The flowchart which shows an example of operation | movement of the data transmitter which concerns on the 1st Embodiment of this invention. FIG. 4 is a schematic diagram for explaining a waveform of a transmission signal of the data communication apparatus according to the first embodiment of the present invention. FIG. 4 is a schematic diagram for explaining a waveform of a transmission signal of the data communication apparatus according to the first embodiment of the present invention. Schematic diagram illustrating transmission signal quality of the data communication apparatus according to the first embodiment of the present invention. Schematic diagram illustrating another transmission signal quality of the data communication apparatus according to the first embodiment of the present invention. The block diagram which shows an example of a structure of the data communication apparatus which concerns on the 2nd Embodiment of this invention. Schematic diagram illustrating the optical multilevel signal waveform of the data transmission apparatus 1102 according to the second embodiment of the present invention. The flowchart which shows an example of operation | movement of the modulation part 112a which concerns on the 2nd Embodiment of this invention. Schematic diagram illustrating superimposed noise by the data transmission apparatus 1102 according to the second embodiment of the present invention. Schematic diagram illustrating the wavelength arrangement of an optical multilevel signal of the data transmission apparatus 1102 according to the second embodiment of the present invention. The block diagram which shows an example of a structure of the data transmitter 1103 which concerns on the 3rd Embodiment of this invention. Schematic diagram illustrating the wavelength arrangement of the optical multilevel signal of the data transmission apparatus 1103 according to the third embodiment of the present invention. The flowchart which shows an example of operation | movement of the modulation part 112b which concerns on the 3rd Embodiment of this invention. The block diagram which shows an example of a structure of the data transmitter 1104 which concerns on the 4th Embodiment of this invention. Schematic diagram illustrating the wavelength arrangement of an optical multilevel signal of a data transmission apparatus 1104 according to the fourth embodiment of the present invention. The flowchart which shows an example of operation | movement of the modulation part 112c which concerns on the 4th Embodiment of this invention. The block diagram which shows an example of a structure of the data transmitter 1105 which concerns on the 5th Embodiment of this invention. Schematic diagram showing the flow of light waves in the light transmitting section 124 The flowchart which shows an example of operation | movement of the modulation part 112d which concerns on the 5th Embodiment of this invention. The block diagram which shows an example of a structure of the data transmitter 1106 which concerns on the 6th Embodiment of this invention. Block diagram showing the configuration of a conventional data communication device

Explanation of symbols

1101 to 1106 Data transmission device 1201 Data reception device 10, 18 Information data 11, 16, 91, 96, 99 Key information 12, 17 Multi-level code string 13, 15 Multi-level signal 14, 94 Modulated signal 110 Transmission path 111 Multi-level Encoding unit 111a First multi-level code generating unit 111b Multi-level processing unit 112, 112a to 112e Modulating unit 113 Light source 114 Branching unit 115 Delay unit 116 Optical modulating unit 117 First optical path 118 Second optical path 119 Interfering unit 120 Amplitude adjusting unit 121 Combining unit 124 Light transmitting unit 125, 127 Transmitting / reflecting unit 126 Optical path 128 Interference control unit 129 Control unit 130 Detection unit 211 Demodulating unit 212 Multi-level decoding unit 212a Second multi-level code generation unit 212b Multi-level identification Part

Claims (17)

A data transmitting device that encrypts information data using predetermined key information and performs secret communication with a receiving device,
Based on the predetermined key information, a multi-level code generator for generating a multi-level code sequence whose signal level changes in a substantially random manner;
A multi-level processing unit that combines the multi-level code sequence and the information data, and generates a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation unit that performs a predetermined modulation process on the multilevel signal and outputs the modulated signal as a modulation signal;
The modulator is
A branching unit that branches the light wave output from the light source and outputs the respective branched lights to the first optical path and the second optical path that have optical path length differences from each other;
An optical modulator that modulates a light wave propagating through at least one of the first optical path and the second optical path with the multilevel signal;
A data transmitting apparatus comprising: an interference unit that causes light waves output from the first optical path and the second optical path to interfere with each other and outputs the interfered light waves as the modulation signal. A data transmitting device that encrypts information data using predetermined key information and performs secret communication with a receiving device,
Based on the predetermined key information, a multi-level code generator for generating a multi-level code sequence whose signal level changes in a substantially random manner;
A multi-level processing unit that combines the multi-level code sequence and the information data, and generates a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation unit that performs a predetermined modulation process on the multilevel signal and outputs the modulated signal as a modulation signal;
The modulator is
A branching unit that branches the light wave output from the light source and outputs the respective branched lights to the first optical path and the second optical path that have optical path length differences from each other;
An interference unit that causes the light waves output from the first optical path and the second optical path to interfere with each other, and outputs the interfered light waves as a composite wave;
A data transmission apparatus comprising: an optical modulation unit that modulates the composite wave output from the interference unit with the multilevel signal. A data transmitting device that encrypts information data using predetermined key information and performs secret communication with a receiving device,
Based on the predetermined key information, a multi-level code generator for generating a multi-level code sequence whose signal level changes in a substantially random manner;
A multi-level processing unit that combines the multi-level code sequence and the information data, and generates a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation unit that performs a predetermined modulation process on the multilevel signal and outputs the modulated signal as a modulation signal;
The modulator is
A light modulation unit that modulates a light wave output from a light source with the multi-value signal;
A branching unit that branches the output of the light modulation unit and outputs branched light to the first optical path and the second optical path having optical path length differences from each other;
A data transmitting apparatus comprising: an interference unit that causes light waves output from the first optical path and the second optical path to interfere with each other and outputs the interfered light waves as the modulation signal. A data transmitting device that encrypts information data using predetermined key information and performs secret communication with a receiving device,
Based on the predetermined key information, a multi-level code generator for generating a multi-level code sequence whose signal level changes in a substantially random manner;
A multi-level processing unit that combines the multi-level code sequence and the information data, and generates a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation unit that performs a predetermined modulation process on the multilevel signal and outputs the modulated signal as a modulation signal;
The modulator is
A light transmission part arranged in the propagation path of the light wave output from the light source;
An optical modulation unit that modulates the light wave output from the light transmission unit with the multilevel signal,
The light transmission part is
A first transmitting / reflecting unit that transmits the light wave output from the light source with a predetermined transmittance and reflects the light wave with a predetermined reflectance;
A second transmission / reflection unit that transmits the light wave output from the first transmission / reflection unit at a predetermined transmittance and reflects the light wave at a predetermined reflectance;
A data transmission apparatus comprising: an optical path having a predetermined optical path length disposed between the first transmission / reflection section and the second transmission / reflection section.   2. The data transmission device according to claim 1, wherein an optical path length difference between the first optical path and the second optical path is equal to or greater than a coherent length of a light wave input to the modulation unit.   The data transmission apparatus according to claim 1, wherein the optical path length difference between the first optical path and the second optical path is generated by a delay unit arranged in at least one of the optical paths. The interference unit is
An amplitude adjusting unit for attenuating the amplitude of a light wave propagating through at least one of the first optical path and the second optical path;
The data transmission device according to claim 1, comprising: a combining unit that combines light waves output from the first optical path and the second optical path. The interference unit is
A polarization adjusting unit that adjusts a polarization state of a light wave propagating through at least one of the first optical path and the second optical path;
The data transmission device according to claim 1, comprising: a combining unit that combines light waves output from the first optical path and the second optical path.   8. The data transmission apparatus according to claim 7, wherein the amplitude adjustment unit varies an attenuation amount of an input light wave based on a control signal input from the outside.   9. The data transmission apparatus according to claim 8, wherein the polarization adjustment unit varies a deflection state of an input light wave based on a control signal input from the outside.   The data transmission apparatus according to claim 4, wherein the optical path length of the optical path having the predetermined optical path length is at least 0.5 times or more than the coherent length of the light wave output from the light source. The modulator is
The apparatus further comprises an interference control unit that feedback-controls a multiplexing ratio in the interference unit based on an interference noise amount included in a light wave output from at least one of the interference unit or the light modulation unit. Item 5. The data transmission device according to Item 4. The interference control unit
A detection unit that photoelectrically converts an input light wave and detects interference noise;
The data transmission apparatus according to claim 12, comprising: a control unit that outputs a control signal to the interference unit based on a detection result of the detection unit. A data transmission method for encrypting information data using predetermined key information and performing secret communication with a receiving device,
A multi-level code generation step for generating a multi-level code sequence in which the signal level changes substantially randomly based on the predetermined key information;
A multi-level processing step of combining the multi-level code sequence and the information data to generate a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation step of performing a predetermined modulation process on the multi-level signal and outputting as a modulation signal;
The modulation step includes
A branching step of branching the light wave output from the light source and outputting the respective branched lights to the first optical path and the second optical path having optical path length differences from each other;
An optical modulation step of modulating a light wave propagating through at least one of the first optical path and the second optical path with the multilevel signal;
A data transmission method comprising: an interference step of causing light waves output from the first optical path and the second optical path to interfere with each other and outputting the interfered light waves as the modulation signal. A data transmission method for encrypting information data using predetermined key information and performing secret communication with a receiving device,
A multi-level code generation step for generating a multi-level code sequence in which the signal level changes substantially randomly based on the predetermined key information;
A multi-level processing step of combining the multi-level code sequence and the information data to generate a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation step of performing a predetermined modulation process on the multi-level signal and outputting as a modulation signal;
The modulation step includes
A branching step of branching the light wave output from the light source and outputting the respective branched lights to the first optical path and the second optical path having optical path length differences from each other;
An interference step of causing the light waves output from the first optical path and the second optical path to interfere with each other and outputting the interfered light waves as a synthesized wave;
A data transmission method comprising: an optical modulation step of modulating the synthesized wave with the multilevel signal. A data transmission method for encrypting information data using predetermined key information and performing secret communication with a receiving device,
A multi-level code generation step for generating a multi-level code sequence in which the signal level changes substantially randomly based on the predetermined key information;
A multi-level processing step of combining the multi-level code sequence and the information data to generate a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation step of performing a predetermined modulation process on the multi-level signal and outputting as a modulation signal;
The modulation step includes
A light modulation step of modulating the light wave output from the light source with the multi-value signal;
A branching step of branching the light wave modulated by the multi-level signal and outputting the branched light to the first optical path and the second optical path having optical path length differences from each other;
A data transmission method comprising: an interference step of causing light waves output from the first optical path and the second optical path to interfere with each other and outputting the interfered light waves as the modulation signal. A data transmission method for encrypting information data using predetermined key information and performing secret communication with a receiving device,
A multi-level code generation step for generating a multi-level code sequence in which the signal level changes substantially randomly based on the predetermined key information;
A multi-level processing step of combining the multi-level code sequence and the information data to generate a multi-level signal having a plurality of levels corresponding to a combination of the multi-level code sequence and the information data;
A modulation step of performing a predetermined modulation process on the multi-level signal and outputting as a modulation signal;
The modulation step includes
A light transmission step for transmitting light waves output from the light source;
A light modulation step of modulating the light wave output from the light transmission step with the multilevel signal,
The light transmission step includes
A first transmission / reflection step of transmitting the light wave output from the light source with a predetermined transmittance and reflecting with a predetermined reflectance;
The light wave output from the first transmission / reflection step is output through an optical path having a predetermined optical path length, and the light wave output from the optical path is transmitted with a predetermined transmittance and reflected with a predetermined reflectance. A data transmission method comprising: a second transmission / reflection step.

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