JP6560862B2 - Optical transmitter - Google Patents

Description

  The present invention relates to an optical transmission apparatus, and more particularly to an optical transmission apparatus suitable for easily generating a multilevel signal at low cost when data is modulated into an optical signal by multilevel intensity modulation.

  Yuen quantum cryptography is also called optical communication quantum cryptography (Y-00) communication, and is a communication technology that spreads quantum fluctuations (quantum shot noise) of light by modulation and makes it impossible to receive an optical signal accurately by an eavesdropper. Application to common key quantum cryptography has been proposed. In this common key quantum cryptography, a binary optical signal carrying binary transmission data is set as one set (referred to as a base), a plurality of M bases are prepared, and which base is used to transmit data. Randomly determined by pseudo-random numbers according to the encryption key. Actually, the optical M-value signal is designed so that the distance between the signals is so small that it cannot be identified by the quantum fluctuation, so that an eavesdropper cannot read the data information from the received signal at all.

  Since the optical modulator / demodulator of the authorized transmitter / receiver switches the binary M bases in accordance with a common pseudo-random number and communicates, the authorized receiver reads data by binary signal determination with a large inter-signal distance. Can do. Errors due to quantum fluctuations can be ignored, and accurate communication is possible between authorized senders and receivers. The encryption based on this optical modulation method is called Yuen quantum encryption based on Yuen-2000 encryption communication protocol (abbreviated as Y-00 protocol). The principle of communication using Yuen quantum cryptography and the configuration of a transmission / reception device are disclosed in, for example, Patent Document 1 and Patent Document 2.

JP 2006-303927 A JP 2010-114662 A

  As described above, in the optical transceiver according to the Y-00 protocol, the transmission light level of transmission data is randomly changed (multilevel modulation) according to the encryption key, and the interval between the light levels is reduced to a level where quantum fluctuations overlap. Communicating.

  As described above, in the optical transceiver according to the Y-00 protocol, the multi-value number is one of the important elements for maintaining the encryption strength.

  However, in the conventional apparatus, a DAC (Digital Analog Converter) having an n-bit resolution is added, in which n-bit signals having different signal levels are added to generate a target multi-value number 2 ^ n-1. ) Was used. In such a conventional method, it is essential to change the circuit configuration, and there is a problem that the multi-value number cannot be easily increased.

  Hereinafter, a method for increasing the number of multilevels represented by signals according to the prior art will be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic diagram for explaining a method of increasing the multi-value number using an adder. FIG. 6 is a schematic diagram for explaining a technique for increasing the multi-value number using a DAC.

  Now, as shown in FIG. 5A, there are signals 1 to 9, and these signals are added by an adder as appropriate using an adder to generate a multilevel signal. Here, a value is expressed by each voltage as a multilevel signal. In this case, as shown in FIG. 5B, when the signal 10 is added, it is necessary to add a signal source and review the configuration of the adder. In addition, since it is necessary to redesign the substrate, there is a problem that man-hours and costs are increased.

  Next, as shown in FIG. 6A, there are signals 1 to 9, and these signals are converted from digital signals to analog signals by a DAC to generate a multilevel signal. Also in this case, as shown in FIG. 6B, when the signal 10 is added, it is necessary to add a signal source and change the type of DAC and peripheral circuits (clock configuration, etc.). In addition, since the method uses an existing DAC, the upper limit of the multi-level number depends on the performance of the DAC, and thus it is difficult to easily change the multi-level number.

  As described above, when the multi-value number is increased by the conventional method, the demerits in man-hours and costs are hindered. In particular, in the case of a drastic change in specifications, there has been a problem that the circuit configuration and the type of IC used in the DAC may need to be fundamentally improved and may not be realized.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to easily generate a multilevel signal at low cost when modulating data into an optical signal by multilevel intensity modulation. The object is to provide an optical transmitter.

  The configuration of the optical transmission apparatus of the present invention is an optical transmission apparatus that modulates data into an optical signal using optical communication quantum cryptography based on multilevel intensity modulation, and generates a Running key based on a common key A running key generator, a multi-value signal generator that generates a multi-value signal from transmission data based on a running key generated by the running key generator, a light source generator, and a running key generated by the running key generator Based on the key, the light source control unit for controlling the optical signal level of the light source generated by the light source generation unit and the optical signal input from the light source generation unit are different from the multi-level signal input from the multi-level signal generation unit. And an optical signal modulator that modulates an optical signal having an optical signal level.

  The light source control unit controls the light source generation unit by changing a current, changing a voltage, or switching laser diodes having different light intensities.

  According to the present invention, it is possible to provide an optical transmission apparatus that can easily generate a multilevel signal at low cost when data is modulated into an optical signal by multilevel intensity modulation.

It is a block diagram of the optical communication system by the Y-00 protocol containing the optical transmitter which concerns on 1st embodiment. It is the schematic diagram which demonstrated the signal processing of the optical transmitter which concerns on 1st embodiment in contrast with the prior art. It is the schematic diagram explaining the other signal processing of the optical transmitter which concerns on 1st embodiment. It is a block diagram of the optical communication system by the Y-00 protocol containing the optical transmitter which concerns on 2nd embodiment. It is a schematic diagram for demonstrating the method of increasing a multi-value number using an adder. It is a schematic diagram for demonstrating the method of increasing a multi-value number using DAC. It is a block diagram of the optical communication system by the Y-00 protocol based on a prior art.

  Embodiments according to the present invention will be described below with reference to FIGS.

[Conventional technology]
First, the configuration of an optical communication system based on the Y-00 protocol according to the prior art will be described with reference to FIG. The optical communication system based on the Y-00 protocol according to the prior art is a system that converts an electrical signal into an optical signal and encrypts and transmits a transmission path such as an optical fiber between the optical transmitter 100 and the optical receiver 200. Although not shown in FIG. 7, in an actual system, a transmission apparatus that inputs transmission data as an electrical signal to the optical transmission apparatus 100 and a reception apparatus that inputs transmission data output from the optical reception apparatus 200. Is connected.

  As illustrated in FIG. 7, the optical transmission device 100 includes a running key generation unit 104, a multilevel signal generation unit 106, a light source generation unit 108, and an optical modulation unit 110. The shared key 102 is an encryption key shared between the optical transmission device 100 and the optical reception device 200 (shared key 202), and is digital data used as a basis for determining the transition pattern of the multilevel signal.

  The running key generation unit 104 generates a running key having a pseudo random number (random pattern) property using the shared key 102 as original data. This is a one-time key that is generated to enhance the cryptographic strength. The multilevel signal generation unit 106 converts transmission data (digital data) into a multilevel signal according to the Running key.

  On the other hand, the light source generator 108 is composed of, for example, a laser diode and generates light having a certain level of intensity. Then, the light modulation unit 110 modulates the output light of the light source in accordance with the multilevel signal, and generates an optical multilevel signal. For example, in the case of intensity modulation, the optical multilevel signal is expressed by a difference in light intensity. This encrypted optical multilevel signal is sent to the optical receiver 200 via the transmission path.

  Next, as illustrated in FIG. 7, the optical receiving device 200 includes a running key generation unit 204, a threshold generation unit 206, an O / E (Optical / Electrical) conversion unit 208, and an identifier 210. In the optical receiver 200, the optical multilevel signal sent via the transmission path is converted into an electrical multilevel signal by the O / E converter 208.

  Here, although not described in detail, a threshold value to be input to the discriminator 210 is generated by the threshold generation unit 206 using a common Running key by a synchronization process between the optical transmission device 100 and the optical reception device 200. The

  The discriminator 210 identifies the electrical multilevel signal output from the O / E conversion unit using the input threshold value, and restores the transmission data. For data identification when intensity modulation is used for light modulation, reference is made to FIG.

Embodiment 1
Next, the optical transmission apparatus of the optical communication system according to the first embodiment will be described with reference to FIG.
FIG. 1 is a configuration diagram of an optical communication system based on the Y-00 protocol including an optical transmission device. The optical transmission device 100a includes a light source control unit 120 in addition to the running key generation unit 104, the multilevel signal generation unit 106a, the light source generation unit 108a, and the light modulation unit 110 that are included in the optical transmission device 100 according to the related art. is there.

  In the optical transmission device 100a according to the present embodiment, the Running key output from the Running key generation unit 104 is input to the light source control unit 120, and the light source control unit 120 determines the light source generation unit according to the value of the input Running key. The optical signal level (light intensity) of 108a is controlled. As a result, the optical signal level that has been constant in the prior art is made variable, and the optical modulation unit 110a performs optical modulation by combining the signals from the light source generation unit 108a and the multilevel signal generation unit 106a.

  The light source control unit 120 controls the light source generation unit 108a to make the optical signal level of the generated light source variable. The method of making the current flowing through the laser diode variable, and providing a modulation unit for the laser diode are added. A method of changing the voltage, a method of switching by providing a plurality of laser diodes having different light intensities, and the like can be considered.

  Next, signal processing of the optical transmission apparatus according to the first embodiment will be described with reference to FIGS. FIG. 2 is a schematic diagram illustrating the signal processing of the optical transmission device in comparison with the prior art. FIG. 3 is a schematic diagram illustrating another signal processing of the optical transmission device.

In the optical modulation unit 110 of the optical transmission device according to the related art, the signal level of the light source output from the light source generation unit 108 is constant. The optical signal level of this light source is Pave. Now, if six optical signal level values are generated, the difference between the optical signal levels is Δ, and the optical signal level of Pave is between i = 2 and i = 3, i The optical signal level L (i) of = 0,..., 5 is expressed by the following (formula 1) as shown in FIG.
[Equation 1]
L (i) = Pave + (i−5 / 2) Δ (Expression 1)

In the optical modulation unit 110 of the optical transmission device according to the present embodiment, the signal level of the light source output from the light source generation unit 108 is made variable to generate an optical signal having two or more optical signal levels. The optical signal levels of these light sources are Pave1 and Pave2. At this time, similarly to the optical modulator 110 of the prior art, the optical modulator 110a synthesizes a signal with a variable optical signal level from the light source even when it generates six levels of optical signal levels. As a result, as shown in FIG. 2B, it is possible to generate an optical signal having 12 optical signal levels represented by the following (Equation 2).
[Equation 2]
When i = 0, ..., 5:
L (i) = Pave1 + (i−5 / 2) Δ
When i = 6, ..., 11:
L (i) = Pave2 + (i−17 / 2) Δ (Expression 2)

Another implementation method will be described. Again, it is assumed that six levels of optical signal level values are generated, and the difference between the optical signal levels is Δ. At this time, the signal level of the light source output from the light source generation unit 108 is made variable to generate an optical signal having two optical signal levels, but the optical signal level of the light source is set to 0, ( As 1/2), as shown in FIG. 3, an optical signal having 12 optical signal levels is generated according to the following (Equation 3).
[Equation 3]
When i = 0, 2,..., 10 (even number):
L (i) = M (i / 2)
When i = 1,..., 11 (odd number):
L (i) = M ((i−1) / 2) + (1/2) Δ (Expression 3)
However, M (i) (i = 0,..., 5) is the value of the original six-stage optical signal level.

  As described above, in this embodiment, it is possible to generate an optical modulation multilevel signal by simply adding optical signal levels.

[Embodiment 2]
Next, the optical transmission apparatus of the optical communication system according to the second embodiment will be described with reference to FIG.

  FIG. 4 is a configuration diagram of an optical communication system based on the Y-00 protocol including the optical transmission apparatus according to the second embodiment.

  In the optical communication system based on the Y-00 protocol of the first embodiment, there is only one shared key. However, in this embodiment, each of the optical transmitter 100b and the optical receiver 200b has two types of shared keys. It has a key 1 and a shared key 2.

  Then, in the optical transmitter 100b, the shared key 2 is input to the running key generation unit 304, and a running key is generated. Then, according to the Running key, the light source control unit 306 controls the optical signal level (light intensity) of the light source generation unit 108a to make the optical signal level variable. In the light modulation unit 110a, the light modulation is performed by combining the signals from the light source generation unit 108a and the multilevel signal generation unit 106a, as in the first embodiment. That is, the optical transmitter 100b of the present embodiment is different in that a dedicated route of shared key 2 → Running key → control of the optical signal level of the light source is provided.

  In response to this, in the optical receiver 200b, the optical receiver 200 of the first embodiment is provided with a running key generation unit 404, and the common key 2 is input to the optical receiver 200b to obtain the running key. The threshold generator generates a classifier by referring to two types of running keys, the running key generated by the running key generator 204 to which the common key 1 is input and the running key generated by the running key generator 404. A threshold value to be input to 210 is generated.

  100, 100a, 100b ... transmitter, 102, 302 ... common key (transmitter side), 202, 402 ... common key (receiver side), 104, 304 ... Running key generator (transmitter side), 204, 404 ... Running key generator (receiver side), 106, 106a ... Multi-value signal generator, 108,108a ... Light source generator, 110,110a ... Light modulator, 120 ... Light source controller, 206,406 ... Threshold generator , 208... O / E (Optical / Electrical) converter, 210.

Claims (3)

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 running key generation unit that generates a running key having a pseudo-random property based on the common key;
Based on the Running key generated by the Running key generation unit, a binary optical signal carrying binary transmission data is set as one set (referred to as a base), and a plurality of M bases are prepared. Whether to use or send data is determined irregularly by a pseudo-random number according to the encryption key, and a multi-value signal generator for generating a multi- value signal of the optical M-value signal ;
Based on a light source generator that emits an optical signal of a certain level and a running key generated by the running key generator, a current is changed, a voltage is changed, or laser diodes having different light intensities are used. A light source controller that controls the light signal level of the light source generated by the light source generator in a plurality of stages by switching;
An optical signal modulation unit that modulates an optical signal of a certain level generated from the light source generation unit into an optical signal having a plurality of signal levels according to the multilevel signal input from the multilevel signal generation unit. An optical transmission device. 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 Running key generation unit that generates a Running key based on the first common key;
A second Running key generation unit that generates a Running key based on the second common key;
A multi-level signal generation unit that generates a multi-level signal from transmission data based on the first Running key generated by the first Running key generation unit;
Based on a light source generator that emits an optical signal of a certain level and a second running key generated by the second running key generator, changing the current, changing the voltage, or different light A light source controller that controls the optical signal level of the light source generated by the light source generator in a plurality of stages by switching the laser diode having intensity;
An optical signal modulation unit that modulates an optical signal of a certain level generated from the light source generation unit into an optical signal having a plurality of signal levels according to the multilevel signal input from the multilevel signal generation unit. An optical transmission device. The optical transmission device according to claim 1, wherein the optical signal modulation unit generates an optical modulation multilevel signal by adding optical signal levels.

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