JP2012074980A - Optical transmission device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure safety by correcting a distribution shape of quantum shot noise, keeping an influence degree of the quantum noise uniform independently of a distance from a true optical signal level, and extending an optical signal level interval.SOLUTION: An optical transmission device has: a second pseudo-random number generating unit generating a second pseudo-random number sequence using a seed key held by the transmission device; a weighted pseudo-random number generating unit generating a pseudo-random number sequence from the second pseudo-random number sequence, to which an occurrence probability is weighted according to a constant rule; a diffusion unit changing a signal level sent from a modulation level selecting unit selecting a modulation level of a transmission data signal to a higher signal level or a lower signal level depending on the pseudo-random number generated by the weighted pseudo-random number generating unit; and a multivalued optical modulating unit generating a multivalued modulation signal depending on the signal level generated by the diffusion unit. The weighted pseudo-random number generating unit performs weighting in a larger amount as a diffusion amount of quantum shot noise becomes larger, and changes input and output characteristics of the second pseudo-random number sequence so as to form a flat part in a distribution shape of the quantum shot noise.

Description

  The present invention relates to an optical transmission apparatus and method, and more particularly to an optical quantum cryptography transmission apparatus and method using optical intensity multilevel modulation typified by Yuen quantum cryptography.

  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 Literature 1 and Patent Literature 2.

JP 2006-303927 A JP 2010-111462 A

  The optical communication quantum cryptography actively uses the quantum shot noise of light to prevent eavesdropping by causing an error when an eavesdropper detects a plurality of adjacent optical signal levels. In this case, the amount of noise generated during reception and the distribution shape greatly affect the safety. As shown in FIG. 1, the naturally obtained quantum shot noise has a small amount of noise, and the distribution of noise amplitude and occurrence probability has a bell shape. For this reason, it is difficult to uniformly cause errors in a plurality of optical signal levels. Therefore, it is desired to correct the noise amount so that the quantum shot noise is uniformly distributed.

  The purpose of the present invention is to correct the distribution shape of the quantum shot noise, to keep the influence of the quantum noise uniform regardless of the distance from the true optical signal level, and to increase the normality by widening the optical signal level interval. It is to secure the safety by suppressing the influence on the recipient.

The optical transmission apparatus according to the present invention is preferably an optical transmission apparatus that transmits optical quantum cryptography using optical intensity multilevel modulation.
A first pseudo-random number generator that generates a first pseudo-random number sequence using a shared key shared between the transmitting and receiving devices as a seed key;
A base selection unit that selects a base from the first pseudo-random number sequence generated by the first pseudo-random number generation unit;
A modulation level selection unit that selects a signal level in accordance with binary data to be transmitted and base allocation from the base selected by the base selection unit to a multilevel level;
A second pseudo-random number generation unit that generates a second pseudo-random number sequence from a seed key possessed by the transmission device;
A weighted pseudo-random number generation unit that generates a pseudo-random number sequence in which the occurrence probability is weighted according to a certain rule from the second pseudo-random number sequence generated by the second pseudo-random number generation unit;
A diffusion unit that changes the signal level output from the modulation level selection unit to upper and lower signal levels by a pseudorandom number generated by the weighted pseudorandom number generation unit;
A multi-level optical modulation unit that generates a multi-level optical modulation signal according to the signal level output from the diffusion unit.

  In a preferred example, the weighted pseudo-random number generation unit generates a second pseudo-random number generated by the second pseudo-random number generation unit with a weight that increases the probability of occurrence as the amount to be varied by the diffusion unit increases. By adding to the random number sequence, the probability when the same fluctuation amount is generated only by the quantum noise is compensated, and the influence degree of the quantum noise is made uniform.

  Preferably, the weighted pseudo-random number generation unit generates a pseudo-random number sequence in relation to a binary conversion unit that converts an input random number into binary data and the binary data from the binary conversion unit. A correction table is provided that stores data for changing the input / output characteristics of the second pseudo-random number sequence in a non-linear manner so that the weighting increases as the diffusion amount of the quantum shot noise increases.

  In addition, preferably, it further includes a noise generation unit for improving the complexity of the weighted pseudo random number generation unit, and the spreading unit converts the signal level output from the modulation level selection unit into the weighted pseudo random number generation unit. The signal level is changed to the upper and lower signal levels by the pseudo random number generated by the random number generator and the noise signal generated by the noise generator.

The optical transmission apparatus according to the present invention is preferably an optical transmission method for transmitting an optical quantum cryptography using light intensity multilevel modulation,
A first pseudo-random number generation step of generating a first pseudo-random number sequence using a shared key shared between the transmitting and receiving devices as a seed key;
A base selection step of selecting a base from the generated first pseudorandom number sequence;
A binary level data to be transmitted, and a modulation level selection step for selecting a signal level in accordance with the base allocation from the base selected by the base selection to the multilevel level;
A second pseudo-random number generation step of generating a second pseudo-random number sequence using a seed key possessed by the transmitting device;
A weighted pseudo-random number generation step for generating a pseudo-random number sequence in which the occurrence probability is weighted with a certain rule from the second pseudo-random number sequence generated in the second pseudo-random number generation step;
A diffusion step of changing the signal level sent from the modulation level selection to the upper and lower signal levels by the pseudorandom number generated in the weighted pseudorandom number generation step;
A multi-level light modulation step for generating a multi-level light modulation signal according to the signal level generated by the diffusion;
In the weighted pseudo-random number generation step, the input and output characteristics of the pseudo-random number sequence are changed so as to form a flat portion in the distribution shape of the quantum shot noise by increasing the weight as the diffusion amount of the quantum shot noise increases. It is comprised as an optical transmission method characterized by this.

  In a preferred example, in the weighted pseudorandom number generation, a weight that increases the probability of occurrence as the amount to be varied by the diffusion increases is added to the pseudorandom number sequence generated by the second pseudorandom number generation. Thus, the probability when the same fluctuation amount occurs only with the quantum noise is compensated, and the influence degree of the quantum noise is made uniform.

  Preferably, the method further comprises a noise generation step for improving the complexity of the weighted pseudorandom number generation step, wherein the spreading step uses the signal level sent from the modulation level selection as the weighted pseudorandom number generation. The signal level is changed to upper and lower signal levels by the pseudo random number generated in the step and the noise signal generated in the noise generation step.

  According to the present invention, it is possible to widen the optical signal level interval while maintaining a certain level of safety, and it is possible to extend the transmission distance with the same number of optical signal levels (reduction of influence on authorized receivers). . Further, the optical signal level interval can be widened while maintaining a certain level of safety, and the number of optical signal levels can be reduced without changing the transmission distance (simplification of the configuration). In addition, since the noise distribution shape is flat, it is possible to suppress changes in safety against fluctuations in the optical signal level interval.

The figure which shows the distribution state of general quantum shot noise. The figure which shows the distribution state of the quantum shot noise correct | amended by one Example. The block diagram which shows the structural example of the Y-00 transmission apparatus by one Example. The block diagram which shows the structural example of the weighted pseudorandom number generation part 36 by one Example. FIG. 4 is a diagram illustrating an example of weighted pseudorandom number generation according to the first embodiment. FIG. 6 is a diagram illustrating a configuration example of a correction data table of the weighted pseudorandom number generation unit 36 according to the first embodiment. FIG. 10 is a diagram illustrating an example of weighted pseudorandom number generation according to the second embodiment. FIG. 10 is a diagram illustrating a configuration example of a correction data table of a weighted pseudorandom number generation unit 36 according to the second embodiment. The block diagram which shows the structural example of the noise generation part 38 of the Y-00 transmission apparatus by one Example. The block diagram which shows the structural example of the Y-00 transmission apparatus by another Example.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows a general quantum shot noise distribution state in Y-00 communication. The number of photons detected when laser light is measured follows a bell-shaped detection probability (Poisson distribution), so that the detection probability is higher in the vicinity of the expected detection value and decreases as the distance increases. Therefore, there is a problem that a discrimination error is less likely to occur as the signal level is farther from the signal light.

  FIG. 2 shows a distribution state of quantum shot noise corrected according to the present invention. According to the present invention, the conventional bell-shaped distribution (dotted line) is corrected to a rectangular (or trapezoidal) distribution (solid line). That is, by modulating the light level based on a predetermined conversion rule, the quantum shot noise is diffused, and a flat portion (portion indicated by W) is formed in the distribution shape. As a result, it is possible to generate a discrimination error uniformly in a certain range W regardless of the distance from the signal light.

  As described above, in the normal quantum shot noise having a bell shape (FIG. 1), a certain degree of influence is shown in a narrow portion near the expected value, and this range dominates the entire optical signal level interval. On the other hand, the present invention can widen the optical signal level interval by correcting the distribution shape of the quantum shot noise as shown in FIG. The transmission distance depends on the optical signal amplitude. If the optical signal level interval becomes 10 times, the optical signal amplitude becomes 10 times at the same number of optical signal levels, and the transmission distance can be extended.

Next, a specific configuration for correcting the distribution shape of quantum shot noise to a flat shape will be described. FIG. 3 shows a configuration block of the encryption unit of the Y-00 transmission apparatus according to an embodiment.
The Y-00 encryption unit generates a pseudo-random number sequence 31 at a high speed using the shared key shared between the transmitting and receiving apparatuses as a seed key 1, and the pseudo-random number sequence generated by the pseudo-random number generation unit 31. A base selection unit 32 for selecting a base, a binary level plaintext data to be transmitted, and a modulation level selection unit for selecting a signal level in accordance with the base allocation (mapping) from the base selected by the base selection unit 32 to a multilevel level 33, a pseudo-random number generation unit 35 that generates a pseudo-random number sequence at high speed from the seed key 2 of the transmission device, and a pseudo-random number sequence that is weighted with a certain rule from the pseudo-random number sequence generated by the pseudo-random number generation unit 35 Weighted pseudo random number generator 36, noise generating unit 38 for improving the complexity of weighted pseudo random number generator 36, and signal level output from modulation level selector 33 are weighted. A multilevel light modulation signal is generated based on a pseudorandom number generated by the pseudorandom number generation unit 36 and a signal level output from the diffusion unit 37 and the signal level output from the diffusion unit 37 to change the signal level up and down by the noise signal generated by the noise generation unit 38. The multi-level light modulator 34 is included.
Here, with respect to the configuration of the weighted pseudo-random number generation unit 36, refer to FIGS. 4 to 6 (Example 1) and FIGS. 7 to 8 (Example 2), and the configuration of the noise generation unit 38 is illustrated in FIG. This will be described later with reference to FIG.

  With the above configuration, the weighted pseudo-random number generation unit 36 adds a weight to the pseudo-random number generation of the pseudo-random number generation unit 35 such that, for example, the greater the amount to be changed by the diffusion unit 37, the greater the occurrence probability. It is possible to compensate the probability when the same fluctuation amount is generated only by the quantum noise, and to make the influence degree of the quantum noise uniform.

Here, the configuration of the noise generator 38 will be described with reference to FIG.
The noise generation unit 38 is an optical power control unit 91 that controls the power of a noise generation optical signal prepared independently of the multi-level optical modulation unit 34, and an optical signal is transmitted by the optical power control signal from the optical power control unit 91. An electrical / optical conversion unit 92 that converts the signal into an optical signal, an optical / electrical signal conversion unit 93 that converts the output optical signal into an electrical signal and outputs a noise signal, and an average of the output noise signal It has a low-pass filter 94 that monitors to be constant. A randomly varying analog electric signal output from the optical / electrical signal conversion unit 93 is given to the diffusion unit 37 as a noise signal.
Since the optical signal has quantum fluctuations, quantum shot noise occurs even when the noise light is changed to electricity, and the detection voltage varies randomly. This becomes a noise signal. When the optical / electrical converter 93 has a sufficiently wide band than the signal speed of the transmission / reception device, the generated noise signal becomes a noise having intrinsic randomness.

Next, the configuration of the weighted pseudorandom number generator 36 will be described with reference to FIG.
The weighted pseudo random number generation unit 36 includes a binary conversion unit 41 that converts input data (random numbers) into binary data, and a correction table 42, and the output of the correction table 42 is a pseudo random number.
The correction table 42 stores data that changes the input / output characteristics of the pseudo-random number sequence in a non-linear manner, and FIG. 6 shows a configuration example thereof. The table is indexed by binary 8-bit input data from −128 to +127, and correction data is output.

[Example 1]
FIG. 5 shows an example of weighted pseudorandom number generation in the weighted pseudorandom number generator 36. FIG. 6 shows a table configuration for generating the weighted pseudorandom numbers of FIG.
In order to diffuse the quantum shot noise and form the flat portion W having a distributed shape, weighting may be performed so that the probability of occurrence increases as the diffusion amount increases (that is, ± 3 to 4).
Therefore, as in the table shown in FIG. 6, the contents of the table are configured so that the small diffusion amount (diffusion amount −1 to +1) is small and the large diffusion amount (diffusion amount ± 4) is large.
With this table configuration, the input / output characteristics of the pseudo-random number sequence can be converted nonlinearly.

[Example 2]
FIG. 7 shows an example of weighted pseudorandom number generation in the weighted pseudorandom number generation unit 36, and FIG. 8 shows a table configuration for generating the weighted pseudorandom number.
In this example, the table is configured so that only diffusion amounts of 0 and ± 4 are generated.

[Example 3]
FIG. 10 shows a configuration example of a Y-00 transmission apparatus according to another embodiment.
In the configuration example shown in FIG. 3, the modulation level including the plaintext data is spread by the signal from the weighted pseudorandom number generation unit 36 and the noise signal from the noise generation unit 38. On the other hand, in the example of FIG. 10, the noise signal from the noise generation unit 38 is converted into a digital signal by the A / D conversion unit 39 ′ and provided to the weighted pseudorandom number generation unit 36 ′. The weighted pseudo random number generation unit 36 ′ generates a weighted pseudo random number by superimposing the pseudo random number generated by the pseudo random number generation unit 35 and the noise signal from the noise signal generation unit 38. The diffusion unit 37 ′ controls the modulation of the multilevel light in the multilevel light modulation unit 34 by diffusing the modulation signal with a pseudo random number.

  In the first embodiment, after performing digital diffusion using the output of the weighted pseudo-random number generator, analog diffusion is performed immediately before the multilevel light modulation unit 34 using an analog noise signal output from the noise generation unit 38. is doing. For this reason, the first embodiment requires a wideband analog circuit. On the other hand, in the third embodiment, the analog noise signal generated by the noise generation unit 38 is converted into a digital noise signal by the A / D conversion unit 39 ′, and this is added to the output of the pseudorandom number generator 35 and weighted. This is input to the attached pseudorandom number generator 36 '. For this reason, once A / D conversion is performed, it can be realized by a technique similar to the conventional Y-00 technique.

31: Pseudorandom number generation unit 1 32: Base selection unit 33: Modulation level selection unit 34: Multi-level signal modulation unit 35: Pseudorandom number generation unit 2 36: Weighted pseudorandom number generation unit 37: Spreading unit 38: Noise generation unit

Claims (7)

In an optical transmission device that transmits optical quantum cryptography using light intensity multilevel modulation,
A first pseudo-random number generator that generates a first pseudo-random number sequence using a shared key shared between the transmitting and receiving devices as a seed key;
A base selection unit that selects a base from the first pseudo-random number sequence generated by the first pseudo-random number generation unit;
A modulation level selection unit that selects a signal level in accordance with binary data to be transmitted and base allocation from the base selected by the base selection unit to a multilevel level;
A second pseudo-random number generation unit that generates a second pseudo-random number sequence from a seed key possessed by the transmission device;
A weighted pseudo-random number generation unit that generates a pseudo-random number sequence in which the occurrence probability is weighted according to a certain rule from the second pseudo-random number sequence generated by the second pseudo-random number generation unit;
A diffusion unit that changes the signal level output from the modulation level selection unit to upper and lower signal levels by a pseudorandom number generated by the weighted pseudorandom number generation unit;
An optical transmission apparatus comprising: a multilevel optical modulation unit that generates a multilevel optical modulation signal based on a signal level output from the diffusion unit. The weighted pseudo-random number generation unit adds a weight to the second pseudo-random number sequence generated by the second pseudo-random number generation unit so that the probability of occurrence increases as the amount to be varied by the diffusion unit increases. The optical transmission apparatus according to claim 1, wherein the probability of occurrence of the same fluctuation amount only by quantum noise is compensated to make the influence of the quantum noise uniform. The weighted pseudo-random number generation unit generates a pseudo-random number sequence in relation to the binary data from the binary conversion unit that converts an input random number into binary data, and the binary data from the binary conversion unit. A correction table for storing data that changes the input / output characteristics of the second pseudorandom number in a non-linear manner so as to increase the weighting as the diffusion amount of the quantum shot noise increases,
The optical transmission device according to claim 1, wherein: A noise generator for improving the complexity of the weighted pseudorandom number generator;
The spreading unit changes the signal level output from the modulation level selection unit to upper and lower signal levels by the pseudo random number generated by the weighted pseudo random number generation unit and the noise signal generated by the noise generation unit,
The optical transmission device according to any one of claims 1 to 3. In an optical transmission method for transmitting optical quantum cryptography using light intensity multilevel modulation,
A first pseudo-random number generation step of generating a first pseudo-random number sequence using a shared key shared between the transmitting and receiving devices as a seed key;
A base selection step of selecting a base from the generated first pseudorandom number sequence;
A binary level data to be transmitted, and a modulation level selection step for selecting a signal level in accordance with the base allocation from the base selected by the base selection to the multilevel level;
A second pseudo-random number generation step of generating a second pseudo-random number sequence using a seed key possessed by the transmitting device;
A weighted pseudo-random number generation step for generating a pseudo-random number sequence in which the occurrence probability is weighted with a certain rule from the second pseudo-random number sequence generated in the second pseudo-random number generation step;
A diffusion step of changing the signal level sent from the modulation level selection to the upper and lower signal levels by the pseudorandom number generated in the weighted pseudorandom number generation step;
A multi-level light modulation step for generating a multi-level light modulation signal according to the signal level generated by the diffusion;
In the weighted pseudo-random number generation step, the input and output characteristics of the pseudo-random number sequence are changed so as to form a flat portion in the distribution shape of the quantum shot noise by increasing the weight as the diffusion amount of the quantum shot noise increases. An optical transmission method characterized by the above. The weighted pseudo-random number generation has the same variation by adding a weight that increases the probability of occurrence as the amount to be varied by the diffusion increases to the pseudo-random number sequence generated by the second pseudo-random number generation. 6. The optical transmission method according to claim 5, wherein the probability when the quantity is generated only by quantum noise is compensated for and the influence degree of quantum noise is made uniform. A noise generation step for improving the complexity of the weighted pseudorandom number generation step;
The spreading step changes the signal level sent from the modulation level selection to the upper and lower signal levels by the pseudo random number generated in the weighted pseudo random number generating step and the noise signal generated in the noise generating step,
The optical transmission method according to claim 5 or 6.

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