JP2003046445A - Optical signal receiver and optical signal reception method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantum receiver where the level of an output signal is not biased to either '0' or '1' even when quantization efficiency of two detectors has a deviation. SOLUTION: The optical signal (quantum) receiver 1 of this invention is provided with a signal output device 107 that changes a coding method, where even at a receiver side a PMB 102 is used to apply N-value (4-value) modulation to the interpolation signal, the N-value signal is divided into first and second groups comprising N/2 value signals and a detection signal of two photon detectors (Avalanche Photo Diodes APD1 905 and 2 906) is converted into an output signal, depending on the first group and the second group. As a result, the output signal wherein the deviation due to the optical detectors is cancelled is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal receiving device and an optical signal receiving method for canceling deviations in quantum efficiency.

[0002]

2. Description of the Related Art A "quantum receiver" will be described below as an example of an "optical signal receiver". In addition, a “quantum transmitter” will be described as an example of the “optical signal transmitter”. FIG. 5 shows a configuration diagram of a conventional quantum receiver. Figure 5
In the 900, the conventional BB84 protocol ("B
"B84 Protocol" is Charles H. Benn
Quantum receiver (optical signal receiver) that implements the quantum key distribution method proposed by ett, Gilles Brassard in 1984). Quantum receiver 90
0 receives an optical signal 910 from a quantum transmitter (not shown). The optical signal 910 is “0”, “π”, “π / 2”, “−” by the phase modulator (PMA) of the quantum transmitter.
The phase modulation of “π / 2” is randomly (1/4
The optical signal includes a modulated optical signal 950 that has been applied (at a ratio of 1) and an unmodulated optical signal 960 that has not been subjected to phase modulation. 901 inputs the optical signal 910,
It is a coupler that separates a modulated optical signal 950 and an unmodulated optical signal 960. Reference numeral 902 denotes a phase modulator (PMB) that inputs the unmodulated optical signal 960, performs phase modulation, and outputs the present modulated optical signal 970. The phase modulator 902 performs phase modulation of “0” and “π / 2” on the unmodulated optical signal 960. 908 indicates “0” and “π” for the phase modulator 902.
A modulation voltage applicator for applying a phase modulation of "/ 2". 9
Reference numeral 03 is a detour (delay buffer) provided for adjusting the timing of the modulated optical signal 950. Numeral 904 inputs and combines the modulated optical signal 950 and the current modulated optical signal 970, induces interference between the current modulated optical signal 970 and the modulated optical signal 950, and outputs the interfered optical signals 980 and 990. The coupler 904 that does this. 905 and 906 are detectors, and the detector 905 is the APD1 (APD is Avalanc).
e Photo Diode), and the detector 906
Be APD2. APD1 905 and APD2 90
Reference numeral 6 is a detector that outputs detection results that are contradictory to each other. For example, the APD1 905 detects a photon having an optical path phase difference of 0. On the other hand, the APD2 906 detects photons having an optical path phase difference of π. When the photon is detected by the APD1 905, the output signal is set to "1", and when the photon is detected by the APD2 906, the output signal is set to "0". Also, APD1
The quantum efficiency of “1” in 905 is “η1”, and A
The quantum efficiency of “0” in PD2 906 is “η2”. In the conventional quantum receiver that implements the BB84 protocol, assuming that the quantum efficiencies (η1 and η2) are equal, two (N / 2 (N is an even number)) modulations are performed by the phase modulator 902, and APD1 905 and APD29
The signal is detected at 06.

FIG. 6 is a diagram showing the results of detecting the phase-modulated optical signals by the respective detectors. In FIG. 6, S101 indicates the value of the phase modulation by the phase modulator on the side of the quantum transmission device, which is not shown in FIG. The phase modulation by the phase modulator (PMA) on the side of the quantum transmitter is four values (φ) of “0”, “π / 2”, “π”, and “−π / 2”.
Phase modulation according to A) is performed. S102 shows the value of the phase modulation by the phase modulator (PMB) 902 of FIG. The phase modulation performed by the phase modulator 902 is “0”, “π
Phase modulation is performed by the binary value (φB) of “/ 2”. S103
Indicates the interference result Δφ by the coupler 904, and is obtained by the expression “φA−φB = Δφ”. S
104 shows the detection result of APD1 905,
When the interference result Δφ = 0, it is assumed that a photon having an optical path phase difference of 0 is detected, and the detection result when Δφ = 0 is detected is “1”. When Δφ = π, the detection result is “0” because it is a photon with an optical path phase difference of π (because it is not a photon with an optical path phase difference of 0). The detection result in the case of Δφ = π / 2 and Δφ = −π / 2 is unclear whether it is a photon with an optical path phase difference of 0 or a photon with an optical path phase difference of π, and the detection result of “1/0” It is either (1 or 0, that is, undefined).
S105 shows the detection result of the APD2 906. If the interference result Δφ = π, it is assumed that a photon with an optical path phase difference π is detected, and the detection result when Δφ = π is “1”. ". When Δφ = 0, the detection result is “0” because it is a photon having an optical path phase difference of 0 (not a photon having an optical path phase difference of π). When Δφ = π / 2 and Δφ = −π / 2, the detection result is a photon with an optical path phase difference of 0 or an optical path phase difference of π.
It is unknown whether it becomes any of the photons of (1) or (1) or “0” (that is, undefined). S106 is an output signal, which is APD1 905.
When the detection result of is "1", the value of the output signal is "1",
When the detection result of the APD 2906 is "1", the value of the output signal is "0". S107 shows the appearance ratio of the output signal. The input ratio of the photons having the optical path phase difference of 0 to the APD1 905 and the input ratio of the photons having the optical path phase difference of π to the APD2 906 should be equal, but the quantum efficiency (detection by the APD1 905 of detecting the photons having the optical path phase difference of 0 The efficiency) η1 is different from the quantum efficiency (detection efficiency) η2 at which the APD2 906 detects a photon having an optical path phase difference π. Therefore,
The ratio when the output signal value of the APD1 905 is "1" is "η1", and the ratio when the output signal value of the APD1 905 is "0" is "η2". AP
The value of the output signal of D1 905 and APD2906 is "1 /
The cases of "0" and "0/1" are ignored later, and thus are not included in the ratio of "η1" and "η2" here. S1
Reference numeral 08 denotes the overall appearance ratio of the output signal values “1” and “0”, which is “1: 0 = η1: η2”. S101 and S102 in FIG. 6 are inputs of the coupler 904, and S1
03 is the output of the coupler 904, and S104 is APD1.
905 is the detection result, S105 is APD2 90
6 is the detection result of 6. The output signal of S106 is APD1
905 and APD2 906 detection results.
As shown in FIG. 6, the output signal of S106 is "1" when φA of PMA of S101 is either "π / 2" or "-π / 2" and φB of PMB is "0". I don't know if it will be "" or "0". Therefore, it is invalid as an output signal. When φA of PMA in S101 is either “0” or “π” and φB of PMB is “0”, the output signal is validated. Also, PMA φA
Is either “0” or “π”, and when φB of PMB is “π / 2”, it is unknown whether it will be “1” or “0”. Therefore, it is invalid as an output signal. When φA of PMA is either “π / 2” or “−π / 2” and φB of PMB is “π / 2”, the output signal is valid. An output signal to be validated is extracted from FIG. 6 and shown in FIG.

[0004]

The conventional quantum receiver is constructed as described above and produces an output signal. BB8
In the conventional quantum receiver that implements the four protocols, assuming that the quantum efficiencies (η1 and η2) are equal, binary modulation is performed by the phase modulator 902, and signals are detected by the APD1 905 and the APD2 906. There is. However, in this case, if the quantum efficiency is biased, the value of the output signal is biased to either "0" or "1".

The present invention solves the above problems and has the following objects. Provided is a quantum receiving device in which the output signal value is not biased to either "0" or "1" even if the quantum efficiencies of the two detectors are biased.

[0006]

An optical signal receiving device according to the present invention receives an optical signal, and a phase-modulated optical signal already phase-modulated with N (N is an even number) value is still phase-modulated. A splitter for separating the unmodulated optical signal and the unmodulated optical signal into two optical signals, and the unmodulated optical signal separated by the separator is subjected to N-value phase modulation, and the phase-modulated optical signal is subjected to current modulation light. The phase modulator output as a signal and the current modulated optical signal output by the phase modulator and the already-modulated optical signal separated by the separator are combined to induce interference between the currently-modulated optical signal and the already-modulated optical signal. And two detectors that detect the optical signal output from the coupler and output a detection signal, generate an N-valued signal and cause the phase modulator to perform N-valued phase modulation, and N value generated by receiving detection signals from two detectors Characterized by comprising a signal and a signal processing unit for generating and outputting an output signal from the detection signal received from the two detectors.

The optical signal receiving apparatus according to the present invention is
The optical signal is a photon train, and the detector is a photodetector for detecting photons.

The optical signal receiving apparatus according to the present invention is
The signal processing device divides an N-valued signal into a first group and a second group of N / 2-valued signals, and performs phase modulation based on the N / 2-valued signals belonging to the first group. In this case, the output signal encoding method used in the above case and the output signal encoding method used in the case where the phase modulation is performed based on the N / 2-valued signal belonging to the second group are replaced.

The optical signal receiving apparatus according to the present invention is
The signal processing device divides an N-valued signal (N ≧ 4) into a first group and a second group of N / 2-valued signals, and based on the N / 2-valued signals belonging to the first group. In the case where phase modulation is performed by a predetermined encoding algorithm, a binary signal is obtained and used as an output signal, and phase modulation is performed based on the N / 2-valued signal belonging to the second group. Is characterized by inverting a binary signal obtained by using the same algorithm as the above-mentioned predetermined encoding algorithm and using it as an output signal.

The optical signal receiving apparatus according to the present invention is
In the signal processing device, among four-valued signals of 0, π / 2, π, and -π / 2, 0 and π / 2 are the first group, and π and -π / 2 are the second group. It is characterized by

An optical signal receiving method according to the present invention receives an optical signal, and an already-modulated optical signal which has already undergone N (N is an even number) phase modulation and an unmodulated optical signal which has not yet undergone phase modulation. And a separation step of separating the optical signal into two optical signals, and a phase modulation in which an unmodulated optical signal separated by the separation step is subjected to N-value phase modulation and the phase-modulated optical signal is output as a current modulation optical signal. And a coupling step of coupling the current modulated optical signal output by the phase modulation step and the already-modulated optical signal separated by the separation step, and inducing interference between the currently-modulated optical signal and the already-modulated optical signal. A detection step of detecting an optical signal output from the step and outputting a detection signal; and a step of generating an N-value signal for phase modulation of the N-value in the phase modulation step, and receiving the detection signal from the detection step,
And a signal processing step of generating and outputting an output signal from the generated N-value signal and the detection signal received from the detection step.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. Hereinafter, an example of the optical signal receiving device of the present invention will be described using a quantum receiving device. FIG. 1 shows a configuration diagram of the quantum transmitter and the quantum receiver according to the first embodiment. In FIG. 1, 2 is a quantum transmitter, 1 is a quantum receiver, and 3 is a communication path (optical fiber cable) connecting the quantum transmitter 2 and the quantum receiver 1. The quantum transmitter 2 generates an optical signal and transmits the generated optical signal to the quantum receiver 1 via the communication path 3. The configuration of the quantum transmitter 2 will be briefly described. The quantum transmitter 2 comprises a laser 201 and a coupler 202. The coupler 202 inputs the optical signal emitted from the laser 201 and splits the input optical signal into two. Reference numeral 203 denotes a phase modulator (PMA), and 208
Is a modulation voltage applicator that applies a modulation voltage to the PMA 203. The PMA 203 is predetermined to input either one of the optical signals separated by the coupler 202, and has the N value (N is an even number) of the N value (N is an even number) applied by the modulation voltage applying unit 208 to the input optical signal. Phase modulation is randomly applied at equal ratios (1 / N) (here, phase modulation of “0”, “π”, “π / 2”, and “−π / 2” is applied). Here, the optical signal subjected to the N-valued phase modulation is referred to as an already-modulated optical signal, and the optical signal separated by the coupler 202 and not subjected to the N-valued phase modulation is referred to as an unmodulated optical signal. Reference numeral 205 denotes a coupler, which inputs and combines the modulated optical signal and the unmodulated optical signal. An attenuator 206 inputs the optical signal coupled by the coupler 205, attenuates the optical signal to the level of one photon, and outputs the optical signal to the communication path 3. The quantum receiver 1 receives an optical signal from the communication path 3. The received optical signal is an optical signal containing a modulated optical signal and an unmodulated optical signal. Next, the configuration of the quantum receiving device 1 will be described. 101 is a coupler,
The optical signal transmitted from the quantum transmitter 2 via the communication path 3 is input to the modulated optical signal 150 and the unmodulated optical signal 160.
The optical signals are separated into and (separation step). Reference numeral 102 is a phase modulator (PMB), and reference numeral 108 is a modulation voltage applicator that applies a modulation voltage to the PMB 102. PMB1
02 is the unmodulated optical signal 1 separated by the coupler 101
Enter 60. The already-modulated optical signal 150 does not pass through the bypass 103, which is a delay fiber provided for timing adjustment, and is subjected to phase modulation again. PMB
Reference numeral 102 randomly applies the N-valued (N is an even number) phase modulation applied by the modulation voltage application unit 108 to the unmodulated optical signal 160 at an equal ratio (1 / N) (phase modulation step). Here, the N value is “0”, “π”, “π”.
4 values of "/ 2" and "-π / 2". The four values to which the phase modulation is applied are the same as the N values to which the phase modulation is performed by the PMA 203 of the quantum transmitter 2. The optical signal that is phase-modulated by the PMB 102 is called a current modulation optical signal 170. Reference numeral 104 denotes a coupler, which inputs and combines the current modulated optical signal 170 and the modulated optical signal 150 that has passed through the bypass 103, and induces interference between the current modulated optical signal 170 and the modulated optical signal 150 ( Bonding step). 105 and 106 are
The detector is APD1 105 (APD is Avala
nche Photo Diode), 106
Be APD2. APD1 105 and APD2 10
6 detects one of photons having an optical path phase difference of 0 and the other detects a photon having an optical path phase difference of π (detection step). A
The probability (quantum efficiency) that the PD 1105 detects an optical signal of a photon having an optical path phase difference of 0 is η1, and the probability that the APD 2 106 detects an optical signal of a photon having an optical path phase difference of π (quantum efficiency).
Is η2. Reference numeral 107 denotes a signal processing device, which causes the modulation voltage applicator 108 to generate an N value. Here, for example, four values 00, 01, 10, and 11 corresponding to “0”, “π”, “π / 2”, and “−π / 2” are randomly set at equal ratios (1 / N). generate. The signal processing device 107 causes the PMB 102 to perform N-value phase modulation, and at the same time, APD1 105 and AP.
The detection result is input from D2 106 and an output signal is generated based on the detection result (signal processing step).

In the above description of FIG. 1, the "modulated optical signal", "unmodulated optical signal", and "currently modulated optical signal" have been described. The "unmodulated optical signal" and "currently modulated optical signal" will be described in detail. On the quantum transmitter 2 side, the optical signal emitted from the laser 201 is separated into two by the coupler 202. One is for the short path with the phase modulator 203, and the other is for the detour 20.
Take a long route with 4. The two separated optical signals merge again at the coupler 205, but are guided to the communication path 3 with a timing shift by the passage time corresponding to each optical path. The two optical signals that have reached the quantum receiving device 1 through the communication path 3 are separated into two by the coupler 101. One goes through the short path with the phase modulator 102, and the other goes through the long path with the detour 103. The optical signals separated into a total of four are combined by the coupler 104, and the optical detector A
The PD1 105 and the APD2 106 are shifted in time. Here, the “short optical signal” in which the short path is selected by both the quantum transmitter 2 and the quantum receiver 1 and the “long optical signal in which the long path is selected by both the quantum transmitter 2 and the quantum receiver 1. Is too fast or too slow in time, and the photodetectors APD1 105 and APD2 106
Therefore, they are not used in the present invention. The “short-long optical signal” and the “long-short optical signal”, which have selected the short path only in either the quantum transmitter 2 or the quantum receiver 1, arrive at the coupler 104 at the same time, causing interference. In the present invention, the terms “modulated optical signal”, “unmodulated optical signal”, and “currently modulated optical signal” are used, focusing only on the two optical signals that induce this interference. The “modulated optical signal” is an “short optical signal”, which is an optical signal that has been subjected to phase modulation by the phase modulator 203 of the quantum transmitter 2.
The “unmodulated optical signal” is a “long and short optical signal”, which is an optical signal before being subjected to phase modulation by the phase modulator 102 of the quantum receiving device 1. The “current modulation optical signal” is a “long and short optical signal”, which is an optical signal that has been subjected to phase modulation by the phase modulator 102 of the quantum receiving device 1.

FIG. 2 shows the quantum receiver 1 extracted from FIG. The difference between FIG. 5 and FIG. 2 of the conventional example is that the signal processing device 107 of the quantum receiving device 1 of the present invention shown in FIG. 2 has four values (“0”, “π”, “π / 2”, “−”). π
This is to control the PMB 102 so as to perform the 4-valued phase modulation of “/ 2”, and the PMB 102 performs the 4-valued phase modulation. FIG. 3 is a diagram showing the detection results of APD1 and APD2 of the first embodiment and the value of the output signal generated by the signal processing device. In FIG. 3, S 201 is the modulated optical signal 150 received from the quantum transmitter 2, and the detour 10
It is a value that is input to the coupler 104 through 3. S20
Reference numerals 2 are phase modulation values φA and φB of the current modulation optical signal 170 that are phase-modulated by the PMB 102, and are values input to the coupler 104. S201 and S202 represent combinations of all signals input to the coupler 104. In S203, the induction of interference of the coupler 104 in the combination of the optical signals of S201 and S202 is represented by “φA−φB = Δφ”. For example, "φ
When A = π / 2 ”and“ φB = π ”,“ Δφ = π / 2 ”. S204 represents the detection result of the optical signal by the APD1 105, and S205 represents the detection result of the optical signal by the APD2 106. As mentioned above, APD1 1
05 detects a photon having an optical path phase difference of 0, and APD 210
6 detects a photon having an optical path phase difference π. Therefore, AP
If the D1 105 and the APD2 106 are operating correctly, the detection results will be contradictory. APD1
When 105 detects a photon having an optical path phase difference of 0, it outputs "1" as a detection result. When the APD2 106 detects a photon having an optical path phase difference of π, it outputs "1" as the detection result. When the APD1 105 and the APD2 106 are operating correctly, the detection result of the APD1 105 is “1” and the detection result of the APD2 106 is “0”. In addition, the interference result Δφ is “π / 2” or “−π /
2 ”, APD1 105 and APD2 10
The detection result of No. 6 is "1/0" or "0/1" and is indefinite. In S206, the signal processing device 107 performs S204 and S.
The detection result of 205 is input, and an output signal is generated based on the input detection result according to a predetermined condition. Here, when the value of “φB” in S202 is “π” or “−π / 2”, the signal processing device 107 outputs the same value as the detection result of the APD2 106 in S205. Then, the value of “φB” in S202 is “0” or “π / 2”.
If so, the same value as the detection result of the APD1 105 in S204 is output. That is, the signal processing device 107
When the phase modulation φB by the MB 102 is “0” and “π / 2” (first group), “π” and “−π / 2”
In the case of (2nd group), the value of the output signal is reversed. S207 indicates the appearance ratio of the output signal generated by the signal processing device 107, and the probability (quantum efficiency) that the APD1 105 detects a photon having an optical path phase difference of 0 is "η.
1 ”, and the probability (quantum efficiency) of detecting a photon having an optical path phase difference π of the APD2 106 is“ η2 ”(η1 ≠ η).
2). S208 shows the partial appearance ratio of the output signal, and the value of "φB" of S202 is "0" or "π / 2".
The probability when the output signal is 1 and the probability when the output signal is 0 is “1: 0 = η1: η2”. The value of “φB” in S202 is “π” or “−π /
The probability when the output signal is 1 when it is “2” and the probability when the output signal is 0 is “1: 0 = η2: η1”. Therefore, the overall appearance ratio of the output signal in S209 is “1: 0 = η1 + η2: η2 + η1 = 1: 1”.
“Φ (first group)” in FIG.
S203 when the value of "B" is "0" or "π / 2"
The contents of steps S208 to S208 are the same as the conventional steps S103 to S1 of FIG.
It is the same as the content of 08. This is because the value for phase modulation is the same as that of the conventional phase modulator 902. S201 to S209 indicated by "B (second group)" in FIG.
The value of is a content not described in the conventional FIG.
This is because the values for phase modulation (“π”, “−π / 2”) do not exist in the phase modulation by the conventional phase modulator 902. FIG. 4 shows S202 and S2 of FIG.
04, S205, and S206 are extracted and illustrated. The appearance ratio of “1” and “0” in the output signal of S206 is “η1 + η2: η2 + η1 = 1: 1”. Therefore, even if the appearance ratio of either of the output signals 0 and 1 is biased due to the difference between η1 and η2 as in the conventional example, the quantum receiving device 1 can output “1” and “0” of the output signals. Can be output with the same appearance ratio.

In the conventional example, the number of optical signals transmitted by the optical signal transmitter is four.
In contrast to (N) -valued (phase) modulation, 2 is used in the optical signal receiving device.
Two photon detectors (AP
D1905, APD2 906) detection signal,
“1” if detected by APD1 905, APD2
When detected in 906, "0" is assigned and encoded, and the signal is output. Therefore, there is a problem that when the quantum efficiency is biased, it is directly reflected as the bias of the output signal. On the other hand, in the optical signal receiving apparatus according to the second embodiment of the present invention, the N (4) value modulation of the transmitting apparatus is also subjected to the N (4) value modulation in the receiving apparatus, and two photon detectors (APD1105, APD2 106) are provided. ) The encoding method for converting the detection signal into an output signal is changed from the conventional method (in the present invention, phase modulation of "0" and "π / 2",
By reversing the encoding method with the phase modulation of "π" and "-π / 2"), an optical signal receiving device and an optical signal receiving device that can obtain an output signal with the bias of the photon detector canceled I explained how. In the example of the optical signal receiving apparatus described above, since the appearance ratios of the output signals are both “1” and “0”, which is equal to the average quantum efficiency of the two photon detectors (APD1 105, APD2 106), the output Unbiased signals.

The optical signal receiving apparatus described in the first embodiment receives the optical signal and separates the received optical signal into the first optical path and the second optical path (coupler 101).
, A coupler (coupler 104) that couples the two separated optical signals and induces interference, and a delay fiber (detour 1) provided for timing adjustment in the separated first optical path.
03), corresponding to the fact that the quantum transmitter performs the phase modulation on the N value in the second optical path, the phase modulator (PMB102) for performing the phase modulation on the N value and the output port of the coupler inducing interference. There are two photon detectors (APD1 105, APD2 106) for detecting photons, and a modulation voltage applicator (modulation voltage applicator) that can apply an N-value modulation voltage to the N-value modulation of the phase modulator. 108) and a signal processing device (signal processing device 107) which sends an N-valued signal to the modulation voltage applying device and forms an output signal from the sent signal and the detection signals received from the two photon detectors. It is characterized by

In the optical signal receiving method described in the first embodiment, the separating step of separating the incident optical signal into the first optical path and the first optical path, and the first optical path (detour path). ), A phase modulation step of subjecting the optical signal flowing in the second optical path to N-valued phase modulation, and a delayed optical signal of the first optical path subjected to phase modulation Second
According to the confluence interference (coupling) step of merging the optical signals of the optical path of No. 1 to induce interference, the detection step of detecting the optical signal after the interference, and the N value modulation applied in the phase modulation step, the optical signal is detected in the detection step. And a signal processing step of encoding a detection signal converted into an electric signal into a digital signal.

Further, in the optical signal receiving method, the N-valued modulation is in pairs of N / 2 each, and the N-valued modulation is paired with the detected signals generated from the two photon detectors. If so (a pair of “0” and “1”), the signal processing step is characterized by performing bit inversion operation as a digital signal and performing encoding.

In the above description, the N value is set to "0", "π".
It is set to four values of "/ 2", "π", and "-π / 2", but N ≧ 4
Moreover, if N is an even number, other values may be used.

[0020]

As described above, according to the optical signal receiving apparatus of the present invention, the already-modulated optical signal which has already undergone the N-value phase modulation and the unmodulated optical signal which has not yet undergone the phase modulation in the optical signal transmitting apparatus. Signal and generate an N-valued signal to cause the phase modulator to perform N-valued phase modulation to phase-modulate the unmodulated optical signal and receive and generate detection signals from two detectors. A signal processing device for generating and outputting an output signal from the N-valued signal and the detection signals received from the two detectors was provided. Therefore, it is possible to obtain an output signal in which the bias of the quantum efficiency of the two detectors is eliminated.

The optical signal is a photon train, and the photodetector detects photons. Therefore, there is an effect that the optical signal receiving device of the present invention can be used in a system using the quantum mechanical property of photons.

Further, the signal processing device converts an N-value signal into N /
A first group of binary signals and a second group, which are used to encode an output signal when phase modulation is performed based on N / 2-valued signals belonging to the first group; The encoding method of the output signal used when the phase modulation is performed based on the N / 2-valued signals belonging to the two groups is replaced. Therefore, the quantum efficiency viewed from the output signal becomes the average of the quantum efficiencies of the two detectors for both “0” and “1” of the digital signal, and is equal, and therefore, the bias of the output signal can be eliminated. .

Further, the signal processing device is 0, π / 2, π,
Of the four-valued signals of −π / 2, 0 (horizontal) and π / 2 were set as the first group, and π (vertical) and −π / 2 were set as the second group. The above four values are the same as the four values which are phase-modulated by the four values by the optical signal transmission device which the optical signal reception device receives. Therefore, there is an effect that the same phase modulation function can be used on the optical signal transmitting device side and the optical signal receiving device side.

According to the optical signal receiving method of the present invention, an N-valued signal is received by receiving an already-modulated optical signal that has already been N-phase-modulated and an unmodulated optical signal that has not been phase-modulated yet. The phase modulator modulates the non-modulated optical signal by applying phase modulation of N value to the phase modulator and receives the detection signal from the two detectors and receives the generated N value signal and the two detectors. And a signal processing step of generating and outputting an output signal from the detected signal. Therefore, it is possible to obtain an output signal in which the bias of the quantum efficiency of the two detectors is eliminated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a quantum transmitter and a quantum receiver according to a first embodiment.

FIG. 2 is a configuration diagram of the quantum receiving device according to the first embodiment.

FIG. 3 is a diagram showing an input value and an output value of each component of the quantum receiving device according to the first embodiment.

FIG. 4 is a diagram showing a phase modulation value, a detection result, and an output signal value according to the first embodiment.

FIG. 5 is a block diagram showing the configuration of a conventional quantum receiving device.

FIG. 6 is a diagram showing an input value and an output value of each component of the conventional quantum receiving device.

FIG. 7 is a diagram showing a phase modulation value, a detection result, and an output signal value of a conventional example.

[Explanation of symbols]

1 quantum receiver, 2 quantum transmitter, 3 communication channel, 1
01, 104 coupler, 102 phase modulator (PM
B), 103, 204 detour, 105 APD1 (photodetector), 106 APD2 (photodetector), 107 signal processing device, 108, 208 modulation voltage applicator, 150
Modulated optical signal, 160 unmodulated optical signal, 170 current modulated optical signal, 201 laser, 202, 205 coupler, 203 phase modulator (PMA), 206 attenuator, 900 quantum receiver, 901, 904 coupler, 903 bypass circuit, 905 APD1, 906 AP
D2,908 Modulation voltage applicator, 910,980,99
0 optical signal, 950 pre-modulated optical signal, 960 unmodulated optical signal, 970 present modulated optical signal.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04B 10/142 10/152 // H04L 9/38 (72) Inventor Yuichi Ishizuka 2-3-2 Marunouchi, Chiyoda-ku, Tokyo No. Sanryo Electric Co., Ltd. (72) Inventor Junichi Abe No. 2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. F-term (reference) 2H079 AA02 BA03 CA04 FA01 HA11 KA11 KA19 KA20 2K002 AA02 AB18 5J104 AA05 5K002 AA02 AA04 CA14 CA15 DA06

Claims (6)

[Claims] 1. An optical signal is received and is converted into two optical signals, an already-modulated optical signal that is already phase-modulated with N (N is an even number) value and an unmodulated optical signal that is not yet phase-modulated. Demultiplexer that separates, phase modulator that performs N-value phase modulation on the unmodulated optical signal that is separated by the separator, and outputs the phase-modulated optical signal as the current modulated optical signal, and output by the phase modulator The combined current modulated optical signal and the modulated optical signal separated by the splitter are combined to induce interference between the present modulated optical signal and the modulated optical signal, and the optical signal output from the coupler Two detectors that perform detection and output a detection signal, and an N value signal is generated to cause a phase modulator to perform N value phase modulation, and a detection signal is received from the two detectors and generated N The value signal and the detection signals received from the two detectors Optical signal receiving apparatus characterized by comprising a signal processing unit which generates and outputs et output signal. 2. The optical signal receiving device according to claim 1, wherein the optical signal is a photon train, and the detector is a photodetector for detecting photons. 3. The signal processing device divides an N-valued signal (N ≧ 4) into a first group and a second group of N / 2-valued signals, and N / 2 belonging to the first group. Value signal encoding method used when phase modulation is performed based on a value signal, and output signal encoding method used when phase modulation is performed based on an N / 2 valued signal belonging to a second group Method to replace the method.
The optical signal receiving device described. 4. The signal processing device converts N-valued signals into N / N signals.
When the phase modulation is performed on the basis of the N / 2-valued signals belonging to the first group, the signals are divided into a first group and a second group of binary-valued signals. When a value signal is obtained and used as an output signal, and phase modulation is performed based on the N / 2-valued signal belonging to the second group, it is obtained by using the same algorithm as the above predetermined encoding algorithm. The optical signal receiving device according to claim 1, wherein the value signal is inverted to be an output signal. 5. The signal processing device comprises 0, π / 2, π,
5. The optical signal according to claim 4, wherein among the four-valued signals of −π / 2, 0 and π / 2 are a first group, and π and −π / 2 are a second group. Receiver. 6. An optical signal which is received and is converted into two optical signals, that is, an already-modulated optical signal that is already phase-modulated with N values (N is an even number) and an unmodulated optical signal that is not yet phase-modulated. Separation step of separating, phase modulation step of performing N-value phase modulation on the unmodulated optical signal separated by the separation step, and outputting the phase-modulated optical signal as the present modulation optical signal, output by the phase modulation step Of the optical signal output from the combining step and the combining step of inducing interference between the present modulated optical signal and the already-modulated optical signal by combining the present modulated optical signal and the already-modulated optical signal separated in the separating step. A detection step of performing detection and outputting a detection signal; and a step of generating an N-valued signal for phase modulation of the N-value in the phase modulation step, receiving the detection signal from the detection step, and generating the generated N-valued signal. Received from the detection process An optical signal receiving method is characterized in that a signal processing step of and generate output signals from the output signal output.