JP2009239791A - Optical receiver and optical testing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receiver and an optical testing device provided with the optical receiver, can set phases of two branches to target phases in a short period of time, in the optical receiver having two branches. <P>SOLUTION: An optical receiver 1 includes: an I branch 10a provided with a delay interferometer 11a, a balanced photo-detector 12a and a data reproduction circuit 14a; a Q branch 10b provided with a delay interferometer 11b, a balanced photo-detector 12b and a data reproduction circuit 14b; a signal processor 15; and phase adjusters 16a, 16b. The signal processor 15 uses a signal S1 obtained from the pre-stage of the data reproduction circuit 14a and data D1 obtained from the post-stage thereof and a signal S2 obtained from the pre-stage of the data reproduction circuit 14b and data D2 obtained from the post-stage thereof to obtain phase signals C1, C2 indicating the absolute value of phase errors from respective target phases of the I branch 10a and the Q branch 10b. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical receiving apparatus that receives a phase-modulated optical signal and an optical test apparatus that includes the apparatus.

  In recent years, research and development have been actively conducted to realize large capacity and long distance of optical transmission systems. In particular, DPSK (Differential Phase Shift Keying) and DQPSK (Differential Quadrature Phase Shift Keying) are used to increase the maximum transmission speed of optical transmission systems from 10 Gbps (bit per second) to 40 Gbps. The practical application of an optical transmission system using a phase modulation method such as shift modulation is expected.

In Patent Document 1 below, an optical DQPSK receiver including two branches provided with an interferometer, a balanced photodetector, and a data recovery circuit is obtained from the preceding stage of the data recovery circuit provided in one branch. Phase error (π / 4 or −π / 4) of one branch with respect to the other branch using a signal obtained by multiplying the obtained signal by a signal obtained from the subsequent stage of the data reproduction circuit provided in the other branch A technique for detecting a deviation amount from (a) is disclosed.
JP 2007-20138 A

  By the way, in the technique disclosed in Patent Document 1 described above, the phase error between the branches is only obtained as the magnitude of the voltage, and the absolute value of the phase error cannot be obtained. Therefore, in a control system that adjusts the phase difference between branches to a predetermined phase difference (π / 4 or −π / 4) based on the detected phase error (voltage value), it is detected that the control gain is set too large. Depending on the phase error, oscillation occurs and normal control cannot be performed. Therefore, the control gain is suppressed to a small value in order to realize stable control.

  For this reason, the conventional technique has a problem that it takes time to set the phase difference between the branches to the target phase difference. The above control is performed, for example, when the optical receiver is turned on or when the optical receiver is initialized. If time is required for such control, the optical receiver is turned on (or restarted). There is a problem that it takes a long time until it becomes ready for use after it is turned on.

  The present invention has been made in view of the above circumstances, and an optical receiving apparatus capable of setting the phase of each branch in a light receiving apparatus having two branches to a target phase in a short time, and an optical device including the apparatus. An object is to provide a test apparatus.

In order to solve the above problems, an optical receiver according to the first aspect of the present invention includes a delay interferometer (11a, 11b), a balanced photodetector (12a, 12b), and a data recovery circuit (14a, 14b). In the optical receiver (1) including the first and second branches (10a, 10b) provided respectively, the signal (S1) obtained from the previous stage of the data recovery circuit provided in the first branch and the subsequent stage The first signal (A1) is obtained by multiplying the obtained signal (D1), and the signal (S1) obtained from the previous stage of the data reproduction circuit provided in the first branch and the second branch are provided. In addition, the mixer unit (23, 34) that obtains the second signal (B1) by multiplying the signal obtained from the subsequent stage (D2) of the data reproduction circuit, and the first and second obtained by the mixer unit. The first angle calculator (25a, 36a) for calculating the absolute value of the phase error from the first target phase of the first branch using the signal, and the phase error calculated by the first angle calculator And a first phase adjustment unit (16a) that adjusts the phase of the delay interferometer provided in the first branch using an absolute value.
According to the present invention, the signal obtained from the previous stage of the data reproduction circuit provided in the first branch and the signal obtained from the subsequent stage are multiplied to generate the first signal, and the data reproduction provided in the first branch. The signal obtained from the previous stage of the circuit and the signal obtained from the subsequent stage of the data recovery circuit provided in the second branch are multiplied to generate a second signal. The first and second signals are used to generate the second signal. The absolute value of the phase error from the first target phase is calculated by the first angle calculator, and the phase of the delay interferometer provided in the first branch is adjusted by the first adjuster using this absolute value.
Further, in the optical receiver according to the first aspect of the present invention, the mixer unit includes a signal (in addition to the first and second signals) obtained from a previous stage of the data recovery circuit provided in the second branch ( S2) and the signal (D2) obtained from the subsequent stage are multiplied to obtain a third signal (A2), and the signal (S2) obtained from the preceding stage of the data reproduction circuit provided in the second branch; The fourth signal (B2) is obtained by multiplying the signal (D1) obtained from the subsequent stage of the data recovery circuit provided in the first branch, and the third and fourth signals are used to A second angle calculator (25b, 36b) that calculates an absolute value of the phase error from the second target phase of the two branches, and the absolute value of the phase error calculated by the second angle calculator The delay provided in the two branches Is characterized by comprising a second phase adjusting unit for adjusting the phase of the interferometer (16b).
The optical receiver according to the first aspect of the present invention includes a signal obtained from a front stage and a rear stage of the data recovery circuit provided in the first branch, and a front stage of the data recovery circuit provided in the second branch. And low-pass filters (21a, 21b, 22a, 22b, 33a to 33c) for reducing the frequency of the signal obtained from the subsequent stage, respectively.
In the optical receiver according to the first aspect of the present invention, the mixer unit is provided in the second branch and the signal (D1) obtained from the subsequent stage of the data recovery circuit provided in the first branch. A switch (31) for selecting one of the signals (D2) obtained from the subsequent stage of the data reproduction circuit, and a signal (S1) obtained from the previous stage of the data reproduction circuit provided in the first branch The first mixer (34a) that multiplies the signal selected by the switch and the signal selected by the switch, the signal (S2) obtained from the previous stage of the data reproduction circuit provided in the second branch, and the signal selected by the switch And a second mixer (34b) for multiplying.
The optical receiver according to the second aspect of the present invention includes first and second delay interferometers (11a, 11b), balanced photodetectors (12a, 12b), and data recovery circuits (14a, 14b), respectively. In the optical receiver (2) including the second branch (10a, 10b), the signal (D1) obtained from the subsequent stage of the data recovery circuit provided in the first branch and the data provided in the second branch A logic operation unit (40) that performs a predetermined logic operation using a signal obtained from the subsequent stage (D2) of the reproduction circuit, and a signal (S1) obtained from the preceding stage of the data reproduction circuit provided in the first branch And a mixer unit (5) that multiplies the signal (S2) obtained from the previous stage of the data reproduction circuit provided in the second branch and the operation results (D11 to D13) of the logic operation unit. ) And the result of multiplication in the mixer unit, a first angle calculator (25a) that calculates an absolute value of a phase error from the first target phase of the first branch, and the first angle calculator And a first phase adjustment unit (16a) for adjusting the phase of the delay interferometer provided in the first branch using the calculated absolute value of the phase error.
An optical test apparatus according to the present invention is an optical test apparatus that receives a phase-modulated optical signal transmitted from an optical transmission apparatus and tests the optical transmission apparatus. It is a feature.

  According to the present invention, the data reproduction circuit provided in the first branch obtains the first signal by multiplying the signal obtained from the previous stage of the data reproduction circuit provided in the first branch and the signal obtained from the subsequent stage. The second signal is obtained by multiplying the signal obtained from the previous stage and the signal obtained from the subsequent stage of the data recovery circuit provided in the second branch, and the first target of the first branch is obtained using these first and second signals. The absolute value of the phase error from the phase is calculated, and the phase of the delay interferometer provided in the first branch is adjusted using this absolute value. Therefore, there is an effect that the phase of each branch in the optical receiving apparatus having two branches can be set to the target phase in a short time.

  Hereinafter, an optical receiver and an optical test apparatus according to embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram showing the main configuration of the optical receiver according to the first embodiment of the present invention. As shown in FIG. 1, the optical receiver 1 of this embodiment includes delay interferometers 11a and 11b, balanced photodetectors 12a and 12b, amplifiers 13a and 13b, data recovery circuits 14a and 14b, a signal processing unit 15, and Phase adjustment units 16a and 16b (first and second phase adjustment units) are provided, and a phase-modulated optical signal L1 input from the outside is received. In the present embodiment, it is assumed that the phase-modulated optical signal L1 is an optical signal modulated by the DQPSK system, and the optical receiver 1 receives an optical signal modulated by the DQPSK system.

  The delay interferometer 11a, the balanced photodetector 12a, the amplifier 13a, and the data recovery circuit 14a are provided in the I branch 10a (first branch), and the delayed interferometer 11b and the balanced photodetector 12b. The amplifier 13b and the data recovery circuit 14b are provided in the Q branch 10b (second branch). The phase adjustment unit 16a is provided for the I branch 10a, and the phase adjustment unit 16b is provided for the Q branch 10b.

  The delay interferometer 11a is a Mach-Zehnder interferometer that splits incident light into two and interferes each branched light through different optical paths (upper arm and lower arm), and includes an optical delay element in the upper arm. 17a is provided, and a phase shift element 18a is provided on the lower arm. The delay time of the optical delay element 17a is one symbol time of the phase-modulated optical signal L1, which is an optical signal modulated by the DQPSK method. This one symbol time is a time obtained by doubling the time obtained by the reciprocal of the bit rate of the phase modulated optical signal L1. Further, the phase amount (that is, the phase shift amount) of the phase shift element 18a is “π / 4”.

  The balanced photodetector 12a receives the interference light output from the delay interferometer 11a and outputs a light reception signal. The amplifier 13a outputs a signal S1 that is an analog signal obtained by amplifying the received light signal output from the balanced photodetector 12a. The data reproduction circuit 14a reproduces data D1 from the signal S1 from the amplifier 14a. The signal S1 obtained from the previous stage of the data reproduction circuit 14a and the data D1 obtained from the subsequent stage of the data reproduction circuit 14a have a frequency of about 20 GHz and are input to the signal processing unit 15. .

  The delay interferometer 11b is a Mach-Zehnder interferometer having the same configuration as that of the delay interferometer 11a. The upper arm is provided with an optical delay element 17b, and the lower arm is provided with a phase shift element 18b. Yes. The delay time of the optical delay element 17b is set to the same time as the delay time of the optical delay element 17a (one symbol time of the phase-modulated optical signal L1). On the other hand, the phase amount (that is, the phase shift amount) of the phase shift element 18b is “−π / 4” unlike the phase amount of the phase shift element 18a.

  The balanced photodetector 12b receives the interference light output from the delay interferometer 11b and outputs a light reception signal. The amplifier 13b outputs a signal S2 that is an analog signal obtained by amplifying the received light signal output from the balanced photodetector 12b. The data reproduction circuit 14b reproduces data D2 from the signal S2 from the amplifier 14b. The signal S2 that is a signal obtained from the previous stage of the data reproduction circuit 14b and the data D2 that is a signal obtained from the subsequent stage of the data reproduction circuit 14b have a frequency of about 20 GHz and are input to the signal processing unit 15. . Although not shown in FIG. 1, the data D1 and D2 reproduced by the data reproduction circuits 14a and 14b are transmitted to a data processing unit (not shown) that processes received data in addition to the signal processing unit 15. Is also entered.

  The signal processing unit 15 uses the input signals S1 and S2 and the data D1 and D2 to input a deviation amount (phase error from the first target phase) from the phase shift amount “π / 4” of the delay interferometer 11a. While calculating the absolute value, the absolute value of the shift amount (phase error from the second target phase) from the phase shift amount “−π / 4” of the delay interferometer 11b is calculated, and the absolute value of each shift amount is calculated. The phase signals C1 and C2 shown are output. The phase adjustment unit 16a uses the phase signal C1 output from the signal processing unit 15 to adjust the phase amount of the delay interferometer 11a provided in the I branch 10a (the phase amount of the phase shift element 18a). Similarly, the phase adjustment unit 16b uses the phase signal C2 output from the signal processing unit 15 to adjust the phase amount of the delay interferometer 11b provided in the Q branch 10b (the phase amount of the phase shift element 18b).

  Next, the internal configuration of the signal processing unit 15 will be described. FIG. 2 is a block diagram showing an internal configuration of the signal processing unit 15. As shown in FIG. 2, the signal processing unit 15 includes low-pass filters (LPF) 21a, 21b, 22a, 22b, a mixer unit 23 (mixers 23a-23d), averaging processing units 24a-24d, and angle calculation units 25a, 25b. (First and second angle calculation units). The low-pass filters 21a and 21b reduce the frequency of the input signals S1 and S2 to about 100 MHz. Similarly, the low-pass filters 22a and 22b reduce the frequency of the input data D1 and D2 to about 100 MHz.

  It is easy for the mixers 23a to 23d to reduce the frequencies of the signals S1 and S2 and the data D1 and D2 using the low-pass filters 21a, 21b, 22a, and 22b without complicating the circuit configuration of the mixers 23a to 23d. This is to realize multiplication. Here, if the transmission frequency band of the low-pass filters 21a, 21b, 22a, and 22b is lowered, the configuration of the mixers 23a to 23d can be simplified. However, if the transmission frequency band is too low, the sensitivity deteriorates, so the frequency is set to about 100 MHz. It is desirable to do.

  The mixer 23a multiplies the signal S1 through the low-pass filter 21a and the data D1 through the low-pass filter 22a to output a signal A1 (first signal), and the mixer 23b outputs the signal S2 through the low-pass filter 21b and the low-pass filter. The signal A2 (third signal) is output by multiplying the data D2 via 22b. The mixer 23c multiplies the signal S1 through the low-pass filter 21a and the data D2 through the low-pass filter 22b to output a signal B1 (second signal), and the mixer 23d outputs the signal S2 through the low-pass filter 21b and the low-pass filter. The signal B2 (fourth signal) is output by multiplying the data D1 via 22a.

  The averaging processing units 24a and 24b perform averaging processing on the signals A1 and A2 obtained by the mixers 23a and 23b, respectively. The averaging processing units 24c and 24d average the signals B1 and B2 obtained by the mixers 23c and 23d. Each process is performed. The angle calculation unit 25a calculates the absolute value of the shift amount from the phase shift amount “π / 4” of the delay interferometer 11a using the signals output from the averaging processing units 24a and 24c, and calculates the absolute value of the shift amount. A phase signal C1 indicating the value is output. Similarly, the angle calculation unit 25b calculates the absolute value of the deviation amount from the phase shift amount “−π / 4” of the delay interferometer 11b using the signals output from the averaging processing units 24b and 24d, A phase signal C2 indicating the absolute value of the shift amount is output.

The angle calculation unit 25a uses the following equation (1) to indicate the phase signal C1 indicating the absolute value of the shift amount from the phase shift amount “π / 4” of the delay interferometer 11a and the phase shift amount of the delay interferometer 11b. A phase signal C2 indicating the absolute value of the deviation amount from “−π / 4” is obtained.

上記（２）式右辺の変数Ａ_０は位相変調光信号Ｌ１の振幅に応じた値を取る変数であり、変数θは遅延干渉計１１ａの位相であり、変数ｎはシンボル点のデータの値である。尚、上記変数θは０度〜９０度の値を取り、変数ｎは０，１，２，３のうちの何れかの値を取る変数である。 Here, the principle by which the phase signals C1 and C2 can be obtained using the above equation (1) will be described. Since the phase signals C1 and C2 are obtained on the same principle, only the phase signal C1 will be described here. First, the received light signal (signal S1 output from the amplifier 13a) output from the balanced photodetector 12a by causing the phase interferometer 11a to interfere with the phase-modulated optical signal L1 that is an optical signal modulated by the DQPSK method is as follows. (2).

The variable A _{0 on the} right side of the above equation (2) is a variable that takes a value corresponding to the amplitude of the phase-modulated optical signal L1, the variable θ is the phase of the delay interferometer 11a, and the variable n is the data value of the symbol point. is there. The variable θ takes a value from 0 degrees to 90 degrees, and the variable n is a variable that takes one of 0, 1, 2, and 3.

When the light receiving signal S1 represented by the above equation (2) is reproduced (demodulated) by the data reproducing circuit 14a, data D1 represented by the following equation (3) is obtained.

Multiplying the signal S1 shown in the above equation (2) by the data D1 shown in the above equation (3) to obtain the time average, the following equation (4) is obtained.

Similarly, a light reception signal (signal S2 output from the amplifier 13b) output from the balanced photodetector 12b by causing the phase modulation optical signal L1 to interfere with the delay interferometer 11b is expressed by the following equation (5): When the light receiving signal S2 is reproduced (demodulated) by the data reproducing circuit 14b, data D2 represented by the following equation (6) is obtained. In the following formula (5), the phase of the delay interferometer 11b is set to −π / 4.

The following equation (7) is obtained by multiplying the signal S1 represented by the above equation (2) and the data D2 represented by the above equation (6) to obtain a time average.

上記（８）式からtan（Δθ）＝−Ｂ１／Ａ１なる式が求められ、この式から前述した（１）式が得られる。以上から、ミキサ２３ａで得られる信号Ａ１とミキサ２３ｃで得られる信号Ｂ１から位相信号Ｃ１を求められるのが分かる。 Now, assuming that the amount of deviation from the phase “π / 4” in the delay interferometer 11a is Δθ, and θ = π / 4 + Δθ, the following equation (8) is obtained.

From the above equation (8), an equation of tan (Δθ) = − B1 / A1 is obtained, and the above-described equation (1) is obtained from this equation. From the above, it can be seen that the phase signal C1 can be obtained from the signal A1 obtained by the mixer 23a and the signal B1 obtained by the mixer 23c.

  3 and 4 are simulation results showing the relationship between the phase shift amount in the delay interferometer 11a and the phase signal C1 obtained by the angle calculation unit 25a. Referring to FIG. 3, when the amount of phase shift in the delay interferometer 11a is within ± 45 degrees, the graph showing the relationship between the amount of phase shift and the phase signal C1 passes through the vicinity of the origin and rises to the right. It is a straight line, and it can be seen that the phase signal C1 obtained by the angle calculator 25a is substantially equal to the phase shift amount in the delay interferometer 11a.

  Referring to FIG. 4, when the target phase is in the range of −180 degrees to −135 degrees, and when the target phase is in the range of 135 degrees to 180 degrees, the target phase is opposite in inclination direction. Shows a change similar to that in the case where is within ± 45 degrees. For this reason, care is required when control is performed to make the shift amount Δθ from the phase “π / 4” in the delay interferometer 11a zero, but to control to +180 degrees or −180 degrees.

  Next, the operation of the optical receiver 1 according to the present embodiment will be described. When the phase-modulated optical signal L1 is incident on the optical receiver 1, it is branched into, for example, an I branch 10a and a Q branch 10b with an intensity ratio of 1: 1. The branched light branched to the I branch 10a enters the delay interferometer 11a and is further branched to the upper arm side and the lower arm side. The branched light branched to the upper arm side is delayed by one symbol time of the phase-modulated optical signal L1 by the optical delay element 17a, and the branched light branched to the lower arm side has a phase of “π / 4” by the phase shift element 18a. "Will change the phase. Thereafter, these branched lights are interfered, and the interference light is received by the balanced photodetector 12a. The light reception signal output from the balanced photodetector 12a is amplified by the amplifier 13a and output as the signal S1. This signal S1 is input to the signal processing unit 15 and also to the data reproduction circuit 14a. When the signal S1 is input to the data recovery circuit 14a, the data D1 is recovered and input to the signal processing unit 15.

  The branched light branched to the Q branch 10b is incident on the delay interferometer 11b and further branched to the upper arm side and the lower arm side. The branched light branched to the upper arm side is delayed by one symbol time of the phase-modulated optical signal L1 by the optical delay element 17b, and the phase of the branched light branched to the lower arm side is “−π / The phase changes by 4 ”. Thereafter, these branched lights are interfered, and the interference light is received by the balanced photodetector 12b. The light reception signal output from the balanced photodetector 12b is amplified by the amplifier 13b and output as the signal S2. This signal S2 is input to the signal processing unit 15 and also to the data reproduction circuit 14b. When the signal S2 is input to the data recovery circuit 14b, the data D2 is recovered and input to the signal processing unit 15.

  The signal S1 input to the signal processing circuit 15 is input to the mixers 23a and 23c via the low pass filter 21a, and the signal S2 input to the signal processing circuit 15 is input to the mixers 23b and 23d via the low pass filter 21b. . The data D1 input to the signal processing circuit 15 is input to the mixers 23a and 23d via the low-pass filter 22a, and the data D2 input to the signal processing circuit 15 is input to the mixers 23b and 23c via the low-pass filter 22b. Is done.

  The mixer 23a multiplies the signal S1 via the low-pass filter 21a and the data D1 via the low-pass filter 22a to output the signal A1 from the mixer 23a, and the mixer 23b outputs the signal S2 via the low-pass filter 21b to the low-pass filter 21b. The signal A2 is output from the mixer 23b by multiplying the data D2 via the filter 22b. The mixer 23c multiplies the signal S1 through the low-pass filter 21a and the data D2 through the low-pass filter 22b to output the signal B1 from the mixer 23c, and the mixer 23d outputs the signal S2 through the low-pass filter 21b and the low-pass filter 21b. The data D1 through the filter 22a is multiplied and the signal B2 is output from the mixer 23d.

  The signals A1 and B1 are input to the averaging processing units 24a and 24c, averaged, and then input to the angle calculation unit 25a. The signals A2 and B2 are input to the averaging processing units 24b and 24d, averaged, and then input to the angle calculation unit 25b. Then, the angle calculation units 25a and 25b obtain the phase signals C1 and C2 using the above-described equation (1), respectively. These phase signals C1 and C2 are output to the phase adjusters 16a and 16b, respectively, and the phase amount of the delay interferometer 11a provided in the branch 10a (the phase amount of the phase shift element 18a) is adjusted to “π / 4”. In addition, the phase amount of the delay interferometer 11b provided in the Q branch 10b (the phase amount of the phase shift element 18b) is adjusted to “−π / 4”.

  FIG. 5 is a diagram showing a simulation result indicating the time required for the phase adjustment of the delay interferometer. FIG. 5A is a diagram showing a simulation result in the conventional optical receiver, and FIG. 5B is a diagram showing the present embodiment. It is a figure which shows the simulation result in the optical receiver. First, referring to FIG. 5A showing a conventional simulation result, it takes about 120 seconds until the phase of the delay interferometer falls within ± 1 degree of the target phase “π / 4”. It can also be seen that the graph showing the time phase change of the delay interferometer is gentle overall. These can be attributed to the fact that the control gain is suppressed in order to prevent oscillation in the control system that controls the delay interferometer.

  On the other hand, referring to FIG. 5B showing the simulation result of the present embodiment, it takes only about 50 seconds until the phase of the delay interferometer falls within ± 1 degree of the target phase “π / 4”. It can be seen that it is less than half of FIG. Compared with FIG. 5 (a), the phase of the delay interferometer has greatly changed from the start of the adjustment of the delay interferometer until it falls within ± 1 degree of the target phase “π / 4”. I understand that. This is because in the present embodiment, the phase signals C1 and C2 indicating the absolute value of the deviation amount from the target phase are obtained, and the control gains of the oscillation phase adjusting units 16a and 16b can be increased. From the above, in this embodiment, the respective phases of the I branch 10a and the Q branch 10b can be set to the target phase in a short time.

[Second Embodiment]
FIG. 6 is a block diagram showing a configuration of a signal processing unit provided in the optical receiver according to the second embodiment of the present invention. The configuration other than the signal processing unit is the same as the configuration shown in FIG. That is, the optical receiving apparatus of this embodiment is configured to include the signal processing unit 30 shown in FIG. 6 instead of the signal processing unit 15 shown in FIG. As shown in FIG. 6, the signal processing unit 30 provided in the optical receiver of the present embodiment includes a switch 31, capacitors 32 a to 32 c, low pass filters 33 a to 33 c, mixers 34 a and 34 b (first and second mixers), an average Conversion processing units 35a and 35b and angle calculation units 36a and 36b (first and second angle calculation units), and the configuration is simplified by reducing the number of low-pass filters and mixers. The switch 31 and the mixers 34a and 34b are included in the mixer unit 34.

  The switch 31 has three input terminals: an input terminal to which data D1 is input, an input terminal to which data D2 is input, and an input terminal that is electrically grounded. Select one and connect it to the output. The switch 31 can be realized by an electronic switch using, for example, a transistor. The electrically grounded input terminal is selected when correcting the offset of the mixers 34a and 34b. Capacitors 32a and 32b remove the DC components of input signals S1 and S2, respectively. The capacitor 32c is connected to the output terminal of the switch 31, and removes the DC component of the signal selected by the switch 31.

  The low-pass filters 33a, 33b, and 33c reduce the frequency of the data selected by the signal S1, the signal S2, and the switch 31 to about 100 MHz, respectively. The mixer 34a multiplies the signal S1 via the capacitor 32a and the low-pass filter 33a and the data selected by the switch 31 and the data via the capacitor 32c and the low-pass filter 33c. The mixer 34b multiplies the signal S2 via the capacitor 32b and the low-pass filter 33b and the data selected by the switch 31 and the data via the capacitor 32c and the low-pass filter 33c.

  Averaging processing units 35a and 35b perform averaging processing on the signals obtained by the mixers 34a and 34b, respectively. The angle calculation unit 36a calculates the absolute value of the shift amount from the phase shift amount “π / 4” of the delay interferometer 11a using the signal output from the averaging processing unit 35a, and calculates the absolute value of the shift amount. The phase signal C1 shown is output. Similarly, the angle calculation unit 36b calculates the absolute value of the shift amount from the phase shift amount “−π / 4” of the delay interferometer 11b using the signal output from the averaging processing unit 35b, and the shift amount. A phase signal C2 indicating the absolute value of is output.

  In the above configuration, when the phase-modulated optical signal L1 is incident on the optical receiver, it is branched into the I branch 10a and the Q branch 10b as in the first embodiment, and after being interfered by the delay interferometers 11a and 11b, respectively, the balanced type Light is received by the photodetectors 12a and 12b. The received light signals output from the balanced photodetectors 12a and 12b are amplified by the amplifiers 13a and 13b and output as signals S1 and S2, respectively. These signals S1 and S2 are input to the signal processing unit 30 shown in FIG. 6 and to the data reproduction circuits 14a and 14b, respectively. Then, the data D1 and D2 are reproduced from the signals S1 and S2, respectively, and input to the signal processing unit 30.

  When the data D1 and D2 are input to the signal processing unit 30, either one is selected by the switch 31. Here, if the data D1 is selected, the selected data D1 is input to the mixers 34a and 34b through the capacitor 32c and the low-pass filter 33c in this order. The signal S1 input to the signal processing unit 30 is input to the mixer 34a through the capacitor 32a and the low-pass filter 33a in order, and the signal S2 input to the signal processing unit 30 is sequentially input through the capacitor 32b and the low-pass filter 33b. Input to the mixer 34b.

  In the mixer 34a, the signal S1 passing through the capacitor 32a and the low-pass filter 33a is multiplied by the data D1 passing through the capacitor 32c and the low-pass filter 33c, and the mixer 34a corresponds to the signal A1 described in the first embodiment. A signal is output. In the mixer 34b, the signal S2 via the capacitor 32b and the low-pass filter 33b is multiplied by the data D1 via the capacitor 32c and the low-pass filter 33c, and the mixer 34b corresponds to the signal B2 described in the first embodiment. A signal is output. The signal (signal A1) output from the mixer 34a is input to the averaging processor 35a and averaged and then input to the angle calculator 36a, and the signal (signal B2) output from the mixer 34b is averaged. After being input to 35b and averaged, it is input to the angle calculator 36b.

  Next, if the data D2 is selected by switching the switch 31, the selected data D2 is input to the mixers 34a and 34b through the capacitor 32c and the low-pass filter 33c in this order. In the mixer 34a, the signal S1 passing through the capacitor 32a and the low-pass filter 33a is multiplied by the data D2 passing through the capacitor 32c and the low-pass filter 33c, and the mixer 34a corresponds to the signal B1 described in the first embodiment. A signal is output. In the mixer 34b, the signal S2 via the capacitor 32b and the low-pass filter 33b is multiplied by the data D2 via the capacitor 32c and the low-pass filter 33c, and the mixer 34b corresponds to the signal A2 described in the first embodiment. A signal is output.

  The signal (signal B1) output from the mixer 34a is input to the averaging processor 35a and averaged and then input to the angle calculator 36a, and the signal (signal A2) output from the mixer 34b is averaged. After being input to 35b and averaged, it is input to the angle calculator 36b. Then, the angle calculation units 36a and 36b respectively obtain the phase signals C1 and C2 using the above-described equation (1). These phase signals C1 and C2 are output to the phase adjusters 16a and 16b, respectively, and the phase amount of the delay interferometer 11a provided in the branch 10a (the phase amount of the phase shift element 18a) is adjusted to “π / 4”. In addition, the phase amount of the delay interferometer 11b provided in the Q branch 10b (the phase amount of the phase shift element 18b) is adjusted to “−π / 4”.

  Note that switching of the switch 31 is frequently performed in a short time (for example, about a fraction of 1 to several tens of seconds). Therefore, the signals A1 and B1 are input almost continuously to the angle calculation unit 36a, and the signals A2 and B2 are input substantially continuously to the angle calculation unit 36b. For this reason, also in this embodiment, the phase of the delay interferometers 11a and 11b can be adjusted to the target phase in a time of about 50 seconds as in the first embodiment. From the above, also in the present embodiment, each phase of the I branch 10a and the Q branch 10b can be set to the target phase in a short time.

[Third Embodiment]
FIG. 7 is a block diagram showing a main configuration of an optical receiver according to the third embodiment of the present invention. In FIG. 7, the same blocks as those in FIG. 1 are denoted by the same reference numerals. The optical receiver 2 shown in FIG. 7 has a configuration in which a logic operation unit 40 is added to the optical receiver 1 shown in FIG. 1 and a signal processor 50 is provided in place of the signal processor 15.

  The logical operation unit 40 includes an AND circuit 41, NOT circuits 42 and 44, and NAND circuits 43 and 45, and performs predetermined logical operations on the data D1 and D2 output from the data reproduction circuits 14a and 14b. The operation data D11 to D13 are output. In the calculation data D11 to D13, when the data D1 is taken on one of the orthogonal axes and the data D2 is taken on the other of the orthogonal axes, the points indicated by the data D1 and D2 appear in any quadrant. It shows whether or not. The operation data D11 to D13 output from the logic operation unit 40 are input to the signal processing unit 50.

  FIG. 8 is a block diagram showing an internal configuration of the signal processing unit 50. As shown in FIG. 5, the signal processing unit 50 includes low-pass filters 51 a to 51 c instead of the low-pass filters (LPF) 22 a and 22 b included in the signal processing unit 15 illustrated in FIG. 2, and a mixer unit 23 (mixers 23 a to 23 d). ), A mixer unit 52 (mixers 52a to 52d) is provided, and arithmetic circuits 53a to 53d are further added.

  The low-pass filters 51a to 51c reduce the frequencies of the input computation data D11 to D13 to about 100 MHz, respectively. The mixer 52a outputs a signal obtained by multiplying the signal S1 through the low-pass filter 21a and the operation data D12 through the low-pass filter 51b. The mixer 52b outputs a signal obtained by multiplying the signal S2 via the low-pass filter 21b and the calculation data D13 via the low-pass filter 51c. The mixer 52c outputs a signal obtained by multiplying the signal S1 through the low-pass filter 21a and the operation data D11 through the low-pass filter 51a. The mixer 52d outputs a signal obtained by multiplying the signal S2 via the low-pass filter 21b and the calculation data D11 via the low-pass filter 51a.

  The arithmetic circuit 53a calculates the difference between the signals output from the mixers 52a and 52c and outputs a signal A1 (first signal). The arithmetic circuit 53b adds the signals output from the mixers 52b and 52d. The signal A2 (third signal) is output. The arithmetic circuit 53c adds the signals output from the mixers 52a and 52c and outputs a signal B1 (second signal), and the arithmetic circuit 53d calculates the difference between the signals output from the mixers 52b and 52d. The signal B2 (fourth signal) is output. Signals A1 and A2 are input to averaging processing units 24a and 24b, respectively, and signals B1 and B2 are input to averaging processing units 24c and 24d, respectively.

  Also in the optical receiver 2 having the above configuration, the phase signal C1 indicating the absolute value of the deviation amount from the phase shift amount “π / 4” of the delay interferometer 11a is the same as in the optical receiver 1 of the first embodiment. The phase signal C2 indicating the absolute value of the deviation amount from the phase shift amount “−π / 4” of the delay interferometer 11b is obtained, and the delay interferometers 11a and 11b using the phase signals C1 and C2 are obtained. Phase adjustment is performed. For this reason, also in the present embodiment, it is possible to adjust the phases of the delay interferometers 11a and 11b to the target phase in a time of about 50 seconds as in the first embodiment. From the above, also in the present embodiment, each phase of the I branch 10a and the Q branch 10b can be set to the target phase in a short time.

  Although the optical receiver according to the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be freely changed within the scope of the present invention. For example, the optical receiver of the present invention can be provided in an optical test apparatus that receives a phase-modulated optical signal transmitted from the optical transmitter and tests the optical transmitter. By providing the optical receiving apparatus of the present invention in the optical test apparatus, it becomes possible to use the optical test apparatus in a short time after the power is turned on, so that convenience for the user can be improved.

It is a block diagram which shows the principal part structure of the optical receiver by 1st Embodiment of this invention. 2 is a block diagram showing an internal configuration of a signal processing unit 15. FIG. It is a simulation result which shows the relationship between the phase shift amount in the delay interferometer 11a and the phase signal C1 obtained by the angle calculation unit 25a. It is a simulation result which shows the relationship between the phase shift amount in the delay interferometer 11a and the phase signal C1 obtained by the angle calculation unit 25a. It is a figure which shows the simulation result which shows the time required for the phase adjustment of a delay interferometer. It is a block diagram which shows the structure of the signal processing part provided in the optical receiver by 2nd Embodiment of this invention. It is a block diagram which shows the principal part structure of the optical receiver by 3rd Embodiment of this invention. 2 is a block diagram showing an internal configuration of a signal processing unit 50. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Optical receiver 10a I branch 10b Q branch 11a, 11b Delay interferometer 12a, 12b Balance type photodetector 14a, 14b Data reproduction circuit 16a, 16b Phase adjustment part 21a, 21b Low pass filter 22a, 22b Low pass filter 23 Mixer Unit 25a, 25b angle calculation unit 31 switch 33a-33c low pass filter 34 mixer unit 34a, 34b mixer 36a, 36b angle calculation unit 40 logic operation unit 52 mixer unit A1, A2 signal B1, B2 signal D1, D2 data D11-D13 logic Data S1, S2 signal

Claims (6)

In an optical receiver including first and second branches provided with a delay interferometer, a balanced photodetector, and a data recovery circuit,
The first signal is obtained by multiplying the signal obtained from the preceding stage of the data reproducing circuit provided in the first branch and the signal obtained from the succeeding stage, and the preceding stage of the data reproducing circuit provided in the first branch. A mixer unit that obtains a second signal by multiplying the signal obtained from the signal obtained from the subsequent stage of the data reproduction circuit provided in the second branch;
A first angle calculation unit that calculates an absolute value of a phase error from the first target phase of the first branch using the first and second signals obtained by the mixer unit;
A first phase adjusting unit that adjusts the phase of the delay interferometer provided in the first branch using the absolute value of the phase error calculated by the first angle calculating unit. Receiver device. In addition to the first and second signals, the mixer unit obtains a third signal by multiplying a signal obtained from the previous stage of the data reproduction circuit provided in the second branch and a signal obtained from the subsequent stage. At the same time, the fourth signal is obtained by multiplying the signal obtained from the previous stage of the data reproduction circuit provided in the second branch and the signal obtained from the subsequent stage of the data reproduction circuit provided in the first branch. Is,
A second angle calculation unit that calculates an absolute value of a phase error from the second target phase of the second branch using the third and fourth signals;
And a second phase adjusting unit that adjusts a phase of the delay interferometer provided in the second branch using an absolute value of the phase error calculated by the second angle calculating unit. Item 4. The optical receiver according to Item 1.   A low-pass filter that respectively reduces the frequency of the signal obtained from the preceding stage and the subsequent stage of the data reproduction circuit provided in the first branch and the signal obtained from the preceding stage and the subsequent stage of the data reproduction circuit provided in the second branch; The optical receiver according to claim 2, further comprising: The mixer unit outputs one of a signal obtained from a subsequent stage of the data reproduction circuit provided in the first branch and a signal obtained from a subsequent stage of the data reproduction circuit provided in the second branch. A switch to select,
A first mixer that multiplies a signal obtained from a previous stage of the data reproduction circuit provided in the first branch and a signal selected by the switch;
The second mixer according to claim 2, further comprising: a second mixer that multiplies a signal obtained from a previous stage of the data reproduction circuit provided in the second branch and a signal selected by the switch. Optical receiver. In an optical receiver including first and second branches provided with a delay interferometer, a balanced photodetector, and a data recovery circuit,
A logical operation unit that performs a predetermined logical operation using a signal obtained from a subsequent stage of the data reproduction circuit provided in the first branch and a signal obtained from a subsequent stage of the data reproduction circuit provided in the second branch When,
A mixer that multiplies the signal obtained from the previous stage of the data reproduction circuit provided in the first branch and the signal obtained from the previous stage of the data reproduction circuit provided in the second branch and the operation result of the logic operation unit. And
A first angle calculation unit that calculates an absolute value of a phase error from a first target phase of the first branch, using a multiplication result in the mixer unit;
A first phase adjusting unit that adjusts the phase of the delay interferometer provided in the first branch using the absolute value of the phase error calculated by the first angle calculating unit. Receiver device. In an optical test apparatus that receives a phase-modulated optical signal transmitted from an optical transmission apparatus and tests the optical transmission apparatus,
An optical test apparatus comprising the optical receiver according to any one of claims 1 to 5.

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