JP2019029785A - Optical receiving apparatus and optical communication system - Google Patents

Abstract

To provide an optical receiving apparatus and an optical communication system in which the phase shift between a received signal and a threshold signal is kept within a practically sufficient range with a simple circuit configuration.SOLUTION: In an optical receiving apparatus for receiving a signal transmitted by modulating data into an optical signal by using optical communication quantum cryptography by multilevel intensity modulation, a relationship between the number of thresholds for determining the upper and lower limits of a voltage level of an electric signal obtained by converting the received optical signal is set to satisfy 2≤threshold number≤base number-1 correspondingly to the base of the optical signal that encrypts the data. In addition, the assignment is made such that the threshold value for determining the upper and lower limits of the voltage level on the lower voltage level side than the threshold value for determining the upper and lower limits of the voltage level is used to make a pair of voltage levels corresponding to the same or more bases as compared with the threshold value for determining the upper and lower limits of the voltage level on the higher voltage level side.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an optical receiving apparatus and an optical communication system, and in particular, when data is modulated into an optical signal by multi-value intensity modulation and transmitted / received, the receiving apparatus has a simple configuration while suppressing deterioration in transmission characteristics. The present invention relates to an optical receiving device and an optical communication system that can perform the same.

  Yuen quantum cryptography, also called optical communication quantum cryptography (Y-00) communication, is a communication technology that spreads optical quantum fluctuations (quantum shot noise) using a special modulation method, making it impossible for an eavesdropper to receive an optical signal accurately. 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 send data is a pseudo-in accordance with an encryption key. Randomly determined by random numbers. Actually, the optical signal of M value is designed so that the distance between the signals is so small that it cannot be identified by the quantum fluctuation, so that the 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).

  In communication using Yuen quantum cryptography, an optical signal encrypted as in the optical receiver described in Patent Document 1 is converted into an electrical signal, and 0/1 bit information is read by a threshold corresponding to the base. Yes. At this time, in the conventional optical receiving apparatus, thresholds are prepared as many as the number of bases.

  However, when high-speed transmission is performed, a phase shift between the received signal and the threshold signal cannot be ignored. Therefore, when a signal with a high bit rate is handled, an error occurs.

  In Patent Document 2, in order to correct such a phase shift, a PLL (Phase Locked Loop) circuit is provided to correct the phase shift and prevent an error in received data.

JP 2006-303927 A JP 2011-1888073 A

  In the receiving apparatus of Patent Document 2 of the above-described prior art, the phase is matched by a PLL circuit in order to absorb the phase shift between the received signal and the threshold signal. However, for this purpose, a PLL circuit must be provided in the receiving apparatus, which increases the circuit scale.

  An object of the present invention is to provide an optical receiving apparatus and an optical communication system which have a simple circuit configuration and can suppress a phase shift between a received signal and a threshold signal within a practically sufficient range.

  The configuration of the optical receiver according to the present invention is preferably an optical receiver that receives a signal that is transmitted by modulating data into an optical signal using optical communication quantum cryptography based on multilevel intensity modulation. Corresponding to the base of the optical signal to be encrypted, the relation of the number of thresholds for determining the upper and lower of the voltage level of the electric signal converted from the received optical signal is 2 ≦ threshold number ≦ base number−1. Is.

  According to the present invention, it is possible to provide an optical receiving apparatus and an optical communication system in which a phase shift between a received signal and a threshold signal is kept within a practically sufficient range with a simple circuit configuration.

It is a block diagram of the optical communication system by a Y-00 protocol. It is a figure which shows the relationship between the optical communication system in this embodiment, a base, and a threshold value. It is a block diagram of the optical receiver in case the number of thresholds = n. It is a block diagram of the optical receiver in the case of base number = 8 and threshold value = 2. It is a figure which shows the relationship between a base and a threshold value when the number of bases = 8 and the number of threshold values = 2. It is a truth table of Basis Selector 5 in the case of base number = 8 and threshold number = 2. It is a block diagram of an optical receiver in the case of base number = 8 and threshold number = 3. It is a figure which shows the relationship between a base and a threshold value when the number of bases = 8 and the number of threshold values = 3. It is a truth table of Basis Selector 5 in the case of base number = 8 and threshold number = 3. It is a block diagram of an optical receiver in the case of base number = 8 and threshold number = 4. It is a figure which shows the relationship between a base and a threshold value when the number of bases = 8 and the number of threshold values = 4. It is a truth table of Basis Selector5 when the number of bases = 8 and the number of thresholds = 4. It is the graph which showed the relationship of Power Penalty when changing the threshold number.

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

[Outline and configuration of optical communication system]
First, the outline and configuration of an optical communication system based on the Y-00 protocol will be described with reference to FIG.
In the optical communication system based on the Y-00 protocol, an electric signal is converted into an optical signal, and a transmission path such as an optical fiber between the optical transmission device 100 and the optical reception device 200 is encrypted and transmitted. Although not shown in FIG. 1, in an actual system, a plate transmission device that inputs transmission data as an electrical signal to the optical transmission device 100 and a data reception device that inputs data output from the optical reception device 200 Is connected.

  As illustrated in FIG. 1, 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 encryption key 102 is digital data that is shared between the optical transmission device 100 and the optical reception device 200 (encryption key 202) and serves 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 encryption key 102 as original data.

  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 modulator 110 multi-value modulates the output light of the light source generator 108 to generate an optical multi-value 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. 1, the optical receiving device 200 includes a running key generation unit 204, a threshold generation unit 206, an O / E conversion unit 208, and a discriminator 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.

[Basic idea of the present invention and relationship between base and threshold]
Next, it is a figure which shows the basic idea of this invention, and the relationship between a base and a threshold value using FIG.
The optical communication system according to the present embodiment has a configuration in which the optical transmission device 100 to the optical reception device 200 transmit information using an optical signal via an optical fiber. As illustrated in FIG. 2, the optical transmission device 100 includes an E / O conversion mechanism that converts an electrical signal into an optical signal, and the optical reception device 200 includes an O / E conversion mechanism that converts an optical signal into an electrical signal. And a discriminator.

  In optical communication quantum cryptography (Y-00) communication, as described above, encryption is performed using a base that is a set of binary optical signals for intensity modulation.

When the base is is N is, as shown in FIG. 2, i-th basis is the optical power of the low side _{P ol (i),} the optical power of the high side as _{P oh (i), (P} ol _(I) , P _{oh (i)} ) (i = 1,..., N).

On the optical receiver 200 side, an optical signal is converted into an electrical signal by an O / E conversion mechanism. The basis (P _{ol (i)} , P _{oh (i)} ) (i = 1,..., N) at that time Is converted into an electric signal, a pair of voltage levels becomes (V _{l (i)} , V _{h (i)} ) (i = 1,..., N).

Here, V _{l (i)} is the low-side voltage output by the O / E conversion mechanism corresponding to the low-side optical power _{Pol (i)} , and V _{h (i)} is the high-side optical power. This is a high-side voltage output by the O / E conversion mechanism corresponding to _{Pol (i)} . Then, the discriminator on the optical receiving device 200 side determines whether the transmitted data is on the low side or the high side by a threshold value that identifies a voltage corresponding to any base determined by encryption. .

Here, when the threshold corresponding to the voltage level pair (V _{l (i)} , V _{h (i)} ) is V _{th (i)} , V _{th (i)} is V _{l (i)} and V _{h ( The} voltage level is approximately in the middle of _i) .

In the conventional optical receiving apparatus, thresholds are prepared by the number N of bases, and data identification is performed. However, in the optical receiving apparatus of this embodiment, as shown in FIG. It is regarded as a group, and data identification is performed for a voltage pair corresponding to the base with one threshold. That is, when the threshold value is V _{th (j)} (j = 1,..., N) and n is the number of threshold values, n <N.

[Configuration of Optical Receiving Device when Threshold Number = n]
Next, the configuration of the optical receiving apparatus when the threshold number = n in this embodiment will be described with reference to FIG.
As shown in FIG. 3, the optical receiver 200 includes an O / E converter 1, a linear amplifying unit 2, a comparator 3 (comparator), a multiplexer 4, a base selector 5, a seed key 6, an LFSR (linear feedback shift register) 7, S / P converter 8 and Decoder 9.

  The O / E converter 1 converts the optical signal from the optical transmission device 100 into an electrical signal. Next, the linear amplification unit 2 linearly amplifies the electric signal output from the O / E conversion unit 1.

Next, the comparator 3 (comparator) compares the electric signal linearly amplified by the linear amplifier 2 with the threshold value V _{th (j)} .
Here, the threshold _values of V _{th (1)} , V _{th (2)} ,..., V _{th (n)} of the comparator 3 are fixed (fixed threshold _values ), and V _{th (1)} is a threshold value for a voltage level pair having a low voltage level. _{Vth (n)} is a threshold for a voltage level pair with a high voltage level (hereinafter referred to as an “MSB side threshold”).

  Seed Key 6 is an encryption key, and the same encryption key as that owned by optical transmission apparatus 100 is used. In LFSR7, a Running key obtained by expanding the encryption key is generated. The LFSR 7 must be the same as the LFSR used in the running key generation unit 104 of the optical transmission device 100. The S / P converter 8 performs serial-parallel conversion on the output signal of the LFSR 7.

  In Basis Selector 5, the Comparator output corresponding to the base created by Seed Key 6 and LFSR 7 is selected, and Multiplexer 4 is controlled so that the output compared with the fixed threshold is input to Decoder 9.

  Multiplexer 4 assigns a comparator output corresponding to the base to decoder 9.

  The decoder 9 restores the randomization performed by the optical transmission device 100 and demodulates the data.

[Configuration of Optical Receiver and Selection of Threshold when Base Number = 8 and Threshold Number = 2]
Next, the configuration of the optical receiving apparatus and the selection of the threshold when the number of bases is 8 and the number of thresholds is 2 will be described with reference to FIGS.
The configuration of the optical receiver 200 when the number of bases = 8 and the number of thresholds = 2 corresponds to the case where n = 2 in FIG. 3, as shown in FIG. In the S / P converter 8 outputs A, B, and C of the signal, the first basis selection unit 51 of the Basis Selector5, it outputs _{S 1,} the second base selector 52, and outputs the _{S 2.}

The output of LSFR7, the relationship between the bases, and the output of Basis Selector 5 are as shown in FIG. Here, eight base numbers are # 0 to # 7.
Here, the output of LSFR 7 and the output of Basis Selector 5 are expressed by the following (Equation 1).

As shown in FIG. 5, when the number of bases = 8 and the number of thresholds = 2, the four bases of base numbers # 0 to # 3 on the LSB side are V _{th (1)} as shown in FIG. The determination of 0/1 is made, and the four bases of the base numbers # 4 to # 7 on the MSB side are determined to be 0/1 with _{Vth (2)} .

[Configuration of Optical Receiver and Selection of Threshold when Base Number = 8 and Threshold Number = 3]
Next, the configuration of the optical receiving apparatus and the selection of the threshold when the number of bases is 8 and the number of thresholds is 3 will be described with reference to FIGS.
The configuration of the optical receiver 200 when the number of bases = 8 and the number of thresholds = 3 corresponds to the case where n = 3 in FIG. 3, as shown in FIG. In the S / P converter 8, and outputs A, B, and C of the signal, the first basis selection unit 51 of the Basis Selector5, it outputs _{S 1,} the second base selector 52, and outputs a _{S 2,} In the third basis selection unit 53, and outputs the _{S 3.}

The output of LSFR7, the relationship between the bases, and the output of Basis Selector 5 are as shown in FIG. Here, eight base numbers are # 0 to # 7.
Here, the output of LSFR 7 and the output of Basis Selector 5 are expressed by the following (Formula 2).

As shown in FIG. 8, when the number of bases = 8 and the number of thresholds = 3, the relationship between the bases # 0 to # 2 on the LSB side is V _{th (1)} as shown in FIG. The bases # 6 to # 7 on the MSB side are determined to be 0/1 with V _{th (3)} , and base numbers # 3 to # 5 in the middle are determined. _Are determined to be 0/1 by V _{th (2)} .

Here, a method for assigning a threshold to a base will be described.
First, the base number is divided by the threshold number, and a quotient number (integer) base is assigned to each threshold value. Assigning a base to a threshold means that a 0/1 decision on that base is made based on that threshold. The bases that have not been assigned so much are sequentially assigned from the LSB side (base on the low voltage level side) to the MSB side (base on the high voltage level side).

This will be specifically described below when the base number = 8 and the threshold number = 3.
First, the quotient of base number / threshold number = int (8/3) = 2, and two bases are assigned to V _{th (1)} , V _{th (2)} , and V _{th (3)} .

Next, the base number / the remainder of the threshold number = the base number mod threshold number = 8 mod 3 = 2 is calculated.
Further, one base is assigned to each of the threshold value V _{th (1)} on the LSB side and the intermediate threshold value V _{th (2)} .

Therefore, the number of bases assigned to the threshold value V _{th (1)} on the LSB side is three, the number of bases assigned to the intermediate threshold value V _{th (2)} is three, and the threshold value V _{th (} The number of bases assigned to ₃₎ is two.

[Configuration of Optical Receiver and Selection of Threshold when Base Number = 8 and Threshold Number = 4]
Next, the configuration of the optical receiving apparatus and the selection of the threshold when the base number = 8 and the threshold number = 4 will be described with reference to FIGS.
The configuration of the optical receiver 200 when the number of bases = 8 and the number of thresholds = 4 corresponds to the case where n = 4 in FIG. 3, as shown in FIG. The S / P conversion unit 8 outputs A, B, and C signals, the first basis selection unit 51 of the Basis Selector 5 outputs S ₁ , and the second basis selection unit 52 outputs S ₂ and the third basis. the selection unit 53 outputs the _{S 3,} the second basis selection unit 54, and outputs the _{S 4.}

The output of LSFR7, the relationship between the bases, and the output of Basis Selector5 are as shown in FIG. Here, eight base numbers are # 0 to # 7.
Here, the output of LSFR 7 and the output of Basis Selector 5 are expressed by the following (Equation 3).

As shown in FIG. 11, when the number of bases = 8 and the number of thresholds = 4, the relationship between the bases # 0 and # 1 on the LSB side is V _{th (1) as shown} in FIG. The two bases of base numbers # 6 and # 7 on the MSB side are determined to be 0/1 with V _{th (4)} , and the base numbers # 2 and # 3 in between are determined. Two bases are determined to be 0/1 at V _{th (2)} , and two bases of base numbers # 4 and # 5 are determined to be 0/1 at V _{th (3).} Become.

[Consideration of relationship between base number and threshold number and characteristics of optical receiver of this embodiment]
Next, the relationship between the base number and the threshold number will be described using the calculation result of FIG.
Based on the condition of base number = 2048 and BER (Bit Error Rate) = 1E-12, the power penalty when the optical input / output power of the optical receiver with threshold number = 2048 is set as a reference (0 [dB]) is As shown in FIG. According to this graph, the threshold number> 10 or more is 0.1 [dB] or less, and a sufficiently good result is obtained. When the threshold number = 2, 2.65 [dB], and when the threshold number = 3, 1. 42 [dB]. Therefore, the inventor thinks that there is no problem if a threshold number of 2 or more is taken under this condition.

  As described above, in the optical receiving apparatus of this embodiment, the relationship between the base number and the threshold number is as shown in the following (formula 4).

  In the optical receiving apparatus according to the prior art, the base number = the threshold number, and the threshold value is generated by a DA (Digital Analog) converter.

In the optical receiving apparatus of the present embodiment, the threshold value has a fixed threshold value V _{th (j)} (j = 1,..., N) in the comparator 3 under the condition of the above (formula 4). In addition, with a simple circuit configuration, a phase shift between the received signal and the threshold signal hardly occurs even in high-speed transmission.

In addition, many bases and thresholds are assigned to the bases on the LSB side. As a result, the number of bases for determining 0/1 increases where the extinction ratio is large, so that improvement in transmission characteristics can be expected.
In addition, since the encryption method and the structure of the optical transmission device are not changed, the encryption strength does not decrease as compared with the prior art.

DESCRIPTION OF SYMBOLS 100 ... Optical transmission apparatus, 102 ... Encryption key (transmission apparatus side), 200 ... Optical reception apparatus, 202 ... Encryption key (reception apparatus side), 104 ... Running key generation part (transmission apparatus side), 204 ... Running key generation part (Receiving device side) 106 ... multi-value signal generation unit 108 108 light source generation unit 110 light modulation unit 206 threshold generation unit 208 O / E conversion unit 210 discriminator
DESCRIPTION OF SYMBOLS 1 ... O / E conversion part, 2 ... Linear amplification part, 3 ... Comparator, 4 ... Multiplexer, 5 ... Basis Selector, 6 ... Seed Key, 7 ... LFSR, 8 ... S / P conversion part, 9 ... Decoder

Claims (8)

An optical receiver that receives a signal transmitted by modulating data into an optical signal using optical communication quantum cryptography based on multilevel intensity modulation,
Corresponding to the base of the optical signal for encrypting data, the relationship between the number of thresholds and the number of bases for determining the voltage level of the electrical signal converted from the received optical signal is 2 ≦ threshold number ≦ base number An optical receiver characterized by being -1.   The threshold for determining the upper and lower of the voltage level pair on the lower voltage level relative to the threshold for determining the upper and lower of the voltage level is higher than the threshold for determining the upper and lower of the voltage level pair on the higher voltage level. 2. The optical receiving apparatus according to claim 1, wherein a pair of voltage levels corresponding to the same or many bases is assigned so as to be determined.   2. The optical receiving apparatus according to claim 1, further comprising a comparator for determining whether the voltage level is higher or lower, wherein the comparator performs voltage level determination using a fixed number of voltage generation means equal to the number of thresholds.   The optical receiving apparatus according to claim 1, further comprising: a multiplexer, wherein the multiplexer includes a threshold number of switches, and selects a threshold value for determining a voltage level by the switch. An optical transmission device that modulates data into an optical signal and transmits it using an optical communication quantum cryptography based on multilevel intensity modulation and an optical reception device that receives a signal transmitted from the optical transmission device are connected via an optical communication path An optical communication system,
In the optical receiver, the relationship between the number of thresholds and the number of bases for determining the rise and fall of the voltage level of the electrical signal converted from the received optical signal corresponding to the base of the optical signal for encrypting data is 2 An optical communication system, wherein ≦ threshold number ≦ base number−1.   In the optical receiver, the threshold for determining the up / down of the voltage level pair on the lower voltage level relative to the threshold for determining the up / down of the voltage level is higher or lower than the voltage level pair on the higher voltage level side. 6. The optical communication system according to claim 5, wherein a voltage level pair corresponding to the same or more bases than the threshold value for determination is assigned so as to be determined.   6. The optical receiver according to claim 5, further comprising a comparator for determining whether the voltage level is higher or lower, wherein the comparator performs voltage level determination using a fixed number of voltage generating means equal to the number of thresholds. The optical communication system described.   6. The optical communication system according to claim 5, wherein the optical receiver includes a multiplexer, and the multiplexer has a switch corresponding to the threshold number, and selects a threshold value for determining a voltage level by the switch.

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