JP2013009136A - Optical phase control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical phase control circuit which surely executes synchronous detection on minute modulation components, making it possible to exert stable operating point control of an optical modulator.SOLUTION: An AGC amplifier 26 has its lower limit cutoff frequency of loop band set to be higher than the frequency of a minute modulation signal b4, and amplifies, in a variable gain amplifier 31, an electric signal b8 after being photoelectric converted so that it will be equal to a target amplitude value b10 on the basis of a gain control signal b9-1. In a peak detection circuit 32, it detects the output amplitude of the variable gain amplifier, and, in an integrator, it outputs as a gain control signal an output signal b9 which is derived by integrating a difference between the output amplitude and the target amplitude value to the variable gain amplifier and also outputs it as a synchronous detection signal b9-1 to a synchronous detector 27. The synchronous detector determines the direction of operating point control by synchronously detecting the synchronous detection signal, while a control circuit 28 outputs an operating point control signal on the basis of the determined direction of control, and an adder 29 outputs to the optical modulator an operating point control signal b6 consisting of the operating point control signal which has had a minute modulation signal superposed thereon.

Description

  The present invention relates to an optical phase control circuit applied to an optical transmission device, an optical reception device, or the like constituting an optical communication system using phase modulation.

  With the recent increase in capacity and distance of optical communication systems, optical communication systems using phase modulation have begun to spread widely. The conventional intensity modulation method assigns information to the light intensity and transmits and receives signals, whereas the phase modulation method assigns information to the light phase and transmits and receives signals. And multi-valued are easy, and the optical spectrum can be effectively used and long-distance transmission is possible. In the phase modulation system, a differential phase shift keying (DPSK) system that performs demodulation using optical phase differences before and after a transmission signal and a quaternary differential phase shift keying (DQPSK) system have been put into practical use. RZ-DPSK, RZ-DQPSK, or the like, which applies pulse modulation to the phase modulation signal, is used to further increase sensitivity and improve nonlinear resistance.

  In these optical communication systems, a configuration in which Mach-Zehnder type modulators are combined in parallel or in series is used in an optical transmitter, and in order to demodulate differential phase-modulated light into intensity-modulated light in an optical receiver. Delay interferometers are used. In the optical modulator on the transmission side, the operating point differs depending on individual differences, environmental temperature, etc., and the operating point varies with time due to DC drift, etc., so automatic bias control (ABC) that always controls each operating point to the optimum point ) A circuit is required. In the delay interferometer on the receiving side, the operating point differs depending on the wavelength and the environmental temperature. Further, in order to compensate for the wavelength fluctuation and the temperature fluctuation, always optimum control by the wavelength tracking circuit is required. That is, the delay interferometer is provided with an optical phase adjuster which is a kind of optical modulator, and it is necessary to always control the operating point of the optical phase adjuster to the optimum point.

  As these control methods, a method of applying a minute modulation to a transmission signal by superimposing a minute modulation signal on an operation point control signal of a transmission-side optical modulator or a reception-side delay interferometer (optical phase adjuster) is adopted. (Patent Document 1).

  FIG. 13 shows an example of the configuration of a conventional optical phase control circuit used in an optical transmitter. As shown in FIG. 13, in the optical modulator 1 of the optical transmission device, the phase-modulated light is obtained by phase-modulating the continuous light a <b> 1 output from the light source 2 based on the data signal a <b> 2 input via the driver circuit 3. And transmits this phase-modulated light as a transmission signal a3 to an optical receiver (not shown).

  At this time, in the optical phase control circuit, in order to control the operating point (bias point) of the optical modulator 1, the optical signal (phase modulated light) is minutely modulated by the minute modulation signal a4 output from the minute modulation signal generator 4. multiply. That is, the adder 11 adds (superimposes) the minute modulation signal a4 output from the minute modulation signal generator 4 to the operation point control signal a6 of the optical modulator 1 output from the control circuit 10, thereby operating point. A control signal a 7 is generated, and this operating point control signal a 7 is output to the optical modulator 1. In the optical modulator 1, since the operating point is controlled by the operating point control signal a7 on which the minute modulation signal a4 is superimposed, minute modulation is applied to the optical signal (phase-modulated light).

  The optical signal after this minute modulation is branched, one optical signal a3-1 is output to the transmission path of the optical communication system, and the other optical signal a3-2 is used in the optical phase control circuit for operating point control. In the optical phase control circuit, the optical signal a3-2 is subjected to photoelectric conversion by photoelectric conversion means (monitor photodiode (PD) 5, transimpedance amplifier (TIA) 6) and peaked from the electric signal a5 amplified by the amplifier 7. The minute modulation signal a4 is extracted by the detection circuit 8, and synchronous detection is performed on the minute modulation signal a4 by the same minute modulation signal a4 in the synchronous detector 9. Based on the result, the control circuit 10 operates the operating point (bias point) control signal a6. Is generated. An operating point control signal a7 is generated by adding (superimposing) the minute modulation signal a4 to the operating point control signal a6 by the adder 11 as described above, and the operating point control on which the minute modulation signal a4 is superimposed. The signal a7 is output to the optical modulator 1. In the optical receiver, the operating point control signal on which the minute modulation signal is superimposed is output to the optical phase adjuster of the delay interferometer.

  The principle of control by synchronous detection is shown in FIG. As shown in FIG. 14, the signal amplitude after photoelectric conversion becomes minimum when the operating point (bias point) of the optical modulator 1 is optimal (2), and increases as it deviates from the optimal point (2). Here, when the modulation point is applied to the operating point (bias point) of the optical modulator 1 by the low-frequency minute modulation signal d, the operating point (bias point) varies with time, so that the signal amplitude also varies. Become. As shown in FIG. 14, this amplitude variation is half the period of the minute modulation signal d at the optimum operating point (bias point) (2), and the point (1) (larger one where the bias is shifted smaller). At the point (3) deviated to, the phase is the same as that of the minute modulation signal d (the opposite phase). Therefore, the direction of controlling the operating point (bias point) of the optical modulator 1 can be found by observing the change in amplitude fluctuation, and the optimum operating point (bias point) can be found. The same applies to the optical phase adjuster of the delay interferometer.

International publication: WO2005 / 088886 A1

However, the following problem exists in the operating point control method using the above-described minute modulation signal.
(1) Wide dynamic range required for a minute signal detection circuit In a phase modulation type optical transmitter or the like, the structure of the optical modulator becomes complicated, and the loss of the optical modulator and the loss variation increase. Regarding the loss of the optical modulator, for example, in a polarization multiplexing QPSK modulator, the standardized insertion loss is as large as 14 dB at the maximum, and the variation of the loss is added to this. Furthermore, in the case of the RZ system that applies pulse modulation to phase-modulated light, it is necessary to consider loss variation on the order of nearly one digit.
Also, the variation in the conversion efficiency of the monitor PD must be taken into consideration. The optical modulator is provided with a monitor PD for controlling the optical modulator. If the intensity of continuous light input to the optical modulator is the same, the monitor PD increases as the loss of the optical modulator increases. The received light intensity at is weakened. In general, since the light received by the monitor PD is leaked light at the coupling portion of the Mach-Zehnder modulator, the variation in conversion efficiency due to the variation in coupling efficiency is extremely large. The conversion efficiency of the monitor PD has a variation of one digit. Considering the above, the total loss variation is close to two digits.

(2) Degradation of code error rate characteristics due to minute modulation signal Since the minute modulation signal superimposed on the operating point control signal interferes with the original data modulation, the code error rate characteristic is affected or is affected. Only a very small amplitude modulation signal can be superimposed on the operating point control signal.

  To deal with the above two problems, the conventional optical phase control circuit employs a configuration in which the amplifier 7 is connected to the subsequent stage of the TIA 6 as shown in FIG. However, with the combination of the fixed gain amplifier 7, it is difficult to ensure the dynamic range as described below. FIG. 15 shows an example of detection signal amplification by the fixed gain amplifier 7. FIGS. 15A and 15B show output waveforms with respect to the minimum input intensity and the maximum input intensity, respectively, and the minimum input intensity is 1/100 of the maximum input intensity. In a fixed gain amplification system, sufficient amplitude cannot be obtained with the minimum input intensity, but the output is saturated with respect to the maximum input intensity, and a minute modulation signal is obtained from any output by peak detection. Is difficult.

  In other words, in the prior art, a small modulation signal of about several Hz to several MHz that is much lower than the modulation frequency of the optical signal is superimposed on the control signal that determines the operating point of the optical modulator or optical phase adjuster, Peak detection and synchronous detection of the signal output from the optical modulator and optical phase adjuster to extract the minute modulation signal again, and the operation of the optical modulator and optical phase adjuster from the amplitude change of the minute modulation signal before and after this A point shift was detected. However, since the signal size at the stage of synchronous detection is not guaranteed in the prior art, the extraction of the minute modulation signal may not be successful. In addition, if the intensity of the minute modulation signal is increased with a certain margin, the minute modulation signal does not affect the data signal superimposed on the optical signal, and the code error rate is deteriorated.

  Therefore, in view of the above circumstances, an object of the present invention is to provide an optical phase control circuit capable of reliably performing synchronous detection of a minute modulation component and performing stable operation point control of an optical modulator.

An optical phase control circuit according to a first aspect of the present invention for solving the above problem is an optical phase control circuit for controlling an operating point of an optical modulator,
An automatic gain control amplifier, a synchronous detector, a control circuit, a minute modulation signal generator, and an adder are provided.
The automatic gain control amplifier has a variable gain amplifier, a peak detection circuit, and an integrator, and the lower limit cutoff frequency of the loop band is set higher than the frequency of the minute modulation signal output from the minute modulation signal generator. In the variable gain amplifier, on the basis of the gain control signal output from the integrator, the optical signal output from the optical modulator or the device including the optical modulator is optically converted by the photoelectric conversion means. The electrical signal that has been electrically converted is amplified to a target amplitude value, the peak detection circuit detects the output amplitude of the variable gain amplifier, and the integrator detects the output amplitude detected by the peak detection circuit. An output signal obtained by integrating the difference from the target amplitude value is output to the variable gain amplifier as the gain control signal and the synchronous detection as a signal for synchronous detection Also output to,
The synchronous detector operates the optical modulator by synchronously detecting the synchronous detection signal output from the integrator based on the small modulation signal output from the small modulation signal generator. Determine the control direction of the point,
In the control circuit, based on the control direction determined by the synchronous detector, outputs an operating point control signal for controlling the operating point of the optical modulator to be an optimum point,
In the adder, the minute modulation signal output from the minute modulation signal generator is superimposed on the operation point control signal output from the control circuit, and the operation point control signal on which the minute modulation signal is superimposed is Output to the optical modulator,
It is comprised as follows.

The optical phase control circuit of the second invention is an optical phase control circuit for controlling the operating point of the optical modulator,
A plurality of stages of automatic gain control amplifiers connected in series, a synchronous detector, a control circuit, a minute modulation signal generator, and an adder,
Each of the multiple-stage automatic gain control amplifiers has a variable gain amplifier, a peak detection circuit, and an integrator, and a larger target amplitude value is set in the subsequent-stage automatic gain control amplifier, and the multiple-stage automatic gain control amplifiers. The automatic gain control amplifier at the end of the control amplifier is configured such that the lower limit cutoff frequency of the loop band is set higher than the frequency of the minute modulation signal output from the minute modulation signal generator, and the plurality of stages of automatic gain control amplifiers The automatic gain control amplifier other than the tail of the lower limit cutoff frequency of the loop band is set lower than the frequency of the minute modulation signal output from the minute modulation signal generator,
In the first automatic gain control amplifier among the plurality of stages of automatic gain control amplifiers, the variable gain amplifier includes the optical modulator or the optical modulator based on a gain control signal output from the integrator. An electrical signal obtained by photoelectrically converting an optical signal output from the device provided by the photoelectric conversion means is amplified so as to become a target amplitude value, and the peak detection circuit detects an output amplitude of the variable gain amplifier, In the integrator, an output signal obtained by integrating the difference between the output amplitude detected by the peak detection circuit and the target amplitude value is output to the variable gain amplifier as the gain control signal,
In the automatic gain control amplifiers other than the top of the plurality of stages of automatic gain control amplifiers, the variable gain amplifier uses the variable gain in the preceding stage automatic gain control amplifier based on the gain control signal output from the integrator. The signal output from the amplifier is amplified so as to have a target amplitude value, the peak detection circuit detects the output amplitude of the variable gain amplifier, and the integrator detects the output amplitude detected by the peak detection circuit An output signal obtained by integrating the difference between the target amplitude value and the target amplitude value is output to the variable gain amplifier as the gain control signal, and the integrator in the last automatic gain control amplifier outputs the output signal. The signal is also output to the synchronous detector as a signal for synchronous detection,
In the synchronous detector, the synchronous detection signal output from the integrator of the last automatic gain control amplifier is synchronously detected based on the minute modulation signal output from the minute modulation signal generator. By determining the control direction of the operating point of the optical modulator,
In the control circuit, based on the control direction determined by the synchronous detector, outputs an operating point control signal for controlling the operating point of the optical modulator to be an optimum point,
In the adder, the minute modulation signal output from the minute modulation signal generator is superimposed on the operation point control signal output from the control circuit, and the operation point control signal on which the minute modulation signal is superimposed is Output to the optical modulator,
It is comprised as follows.

  An optical phase control circuit according to a third aspect of the present invention is the optical phase control circuit according to the first or second aspect, wherein the optical modulator is provided in an optical transmission device, and continuous light output from a light source is based on a data signal. For phase modulation.

  An optical phase control circuit according to a fourth aspect of the present invention is the optical phase control circuit according to the first or second aspect, wherein the device including the optical modulator is provided in the optical receiving device for receiving the phase-modulated light. It is a delay interferometer, and the optical modulator is an optical phase adjuster provided in the delay interferometer.

According to the optical phase control circuit of the present invention, the dynamic range can be expanded by the automatic gain control amplifier and the integrator of the automatic gain control amplifier regardless of whether the optical phase control circuit is applied to, for example, an optical transmission device or an optical reception device of an optical communication system. It is possible to perform highly sensitive detection of a minute modulation signal component by.
Further, by connecting a plurality of stages of automatic gain control amplifiers having different loop bandwidths in series, it is possible to further expand the dynamic range and extract a minute modulation signal with the last automatic gain control amplifier.
In addition, when applied to an optical receiver, a small modulation component (intensity modulation component) by a small modulation signal superimposed on a reception signal is detected as an error from a target amplitude value, and an automatic gain control amplifier is used as a gain control signal. By feeding back to (1), the minute modulation amplitude can be reduced, and the influence on the code error rate characteristic can be reduced.

It is a block diagram of the optical transmitter provided with the optical phase control circuit which concerns on Example 1 of Embodiment of this invention. It is a figure which shows the amplitude fluctuation suppression effect by an automatic gain control (AGC) amplifier. It is a figure explaining the state where the amplitude fluctuation suppression by AGC amplifier does not work. It is a figure which shows the waveform of the gain control signal of an AGC amplifier. It is a block diagram of the optical transmitter provided with the optical phase control circuit based on Embodiment 2 of this invention. It is a figure which shows the relationship between the transfer characteristic of 1st and 2nd AGC amplifier, and the frequency of a minute modulation signal. It is a figure which shows the output waveform (state with a small optical modulator bias) at the time of minimum input intensity reception. It is a figure which shows the output waveform (state with a small optical modulator bias) at the time of maximum input intensity reception. It is a block diagram of the optical receiver provided with the optical phase control circuit which concerns on Example 3 of Embodiment of this invention. It is a figure explaining the operation principle of the said Example 3. It is a figure which shows a phase modulation light receiving waveform. It is a block diagram of the optical receiver provided with the optical phase control circuit which concerns on Example 4 of this invention. It is a block diagram of the optical receiver provided with the conventional optical phase control circuit. It is a figure explaining the principle of synchronous detection. It is a figure which shows the example of detection signal amplification by fixed gain amplifier.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

<Embodiment 1>
The optical phase control circuit according to the first embodiment of the present invention provided in the optical transmission device will be described with reference to FIGS.

  As shown in FIG. 1, the main signal unit of the optical transmission device includes a light source 21 that emits continuous light b <b> 1, an optical modulator 22, and a driver circuit 23. The control unit to be controlled includes a minute modulation signal generator 30, a monitor photodiode (PD) 24, a transimpedance amplifier (TIA) 25, an automatic gain control (AGC) amplifier 26, a synchronous detector 27, and a control circuit. 28 and an adder 29. The AGC amplifier 26 includes a variable gain amplifier 31, a peak detection circuit 32, and an integrator 33.

  The optical modulator 22 of the optical transmitter generates phase-modulated light by phase-modulating the continuous light b1 output from the light source 21 based on the data signal b2 input via the driver circuit 23, and this phase modulation Light (transmission signal b3-1) is transmitted to an optical receiver (not shown).

  At this time, in the optical phase control circuit, the optical signal (phase modulated light) is minutely modulated by the minute modulation signal b4 output from the minute modulation signal generator 30 for controlling the operating point (bias point) of the optical modulator 22. Apply (intensity modulation). In other words, the adder 29 adds (superimposes) the minute modulation signal b4 output from the minute modulation signal generator 30 to the operation point control signal b5 of the optical modulator 22 output from the control circuit 28, so that the light An operating point control signal b6 for the modulator 22 is generated, and this operating point control signal b6 is output to the optical modulator 22. In the optical modulator 22, since the operating point is controlled by the operating point control signal b6 on which the minute modulation signal b4 is superimposed, the optical signal (phase modulated light) is subjected to minute modulation (intensity modulation).

  The optical signal after this minute modulation is branched, one branched optical signal b3-1 is output to the transmission line of the optical communication system, and the other optical signal b3-2 is used for controlling the operating point by an optical phase control circuit. Used.

  In the optical phase control circuit, the optical signal b3-2 output from the optical modulator 22 is photoelectrically converted into an electrical signal b8 by photoelectric conversion means (monitor PD24, TIA25). Specifically, the optical signal b3-2 is received by the monitor PD 24 to be a current signal b7, and the voltage signal b8 corresponding to the current signal b7 is TIA25. The output signal b8 of the TIA 25 is amplified by the AGC amplifier 26 so as to have a desired amplitude value (target amplitude value b10).

The AGC amplifier 26 can keep the output amplitude of the variable gain amplifier 31 constant (that is, the amplitude can be controlled constant), and the lower limit cutoff frequency of the loop band of the minute modulation signal b4 output from the minute modulation signal generator 30 is It is set higher than the frequency.
In the AGC amplifier 26, the variable gain amplifier 31 converts the electrical signal b8 photoelectrically converted by the photoelectric conversion means based on the gain control signal b9-1 output from the integrator 33 to the target amplitude value b10. Amplify so that
The peak detection circuit 32 detects the output amplitude of the variable gain amplifier 31. That is, the peak detection circuit 32 converts the amplitude information of the output signal b11 of the variable gain amplifier 31 into voltage information b12.
The integrator 33 compares the output amplitude (voltage information b12) detected by the peak detection circuit 32 with the target amplitude value b10, and the difference (error signal) between the output amplitude (voltage information b12) and the target amplitude value b10. ) Is output to the variable gain amplifier 31 as the gain control signal b9-1. Based on the gain control signal b9-1, the variable gain amplifier 31 amplifies the signal b8 after photoelectric conversion to the target amplitude value b10 as described above (that is, the gain of the variable gain amplifier 31 is increased as described above). The difference (error signal) is controlled to be zero). Further, the integrator 33 outputs the output signal b9 to the synchronous detector 27 as the synchronous detection signal b9-2.

  That is, when the optical signal output from the optical modulator 22 is branched and photoelectrically converted and then amplified to the target amplitude value b10 by the AGC amplifier 26, the amplitude fluctuation due to the minute modulation signal b4 is an error from the target amplitude value b10. The gain control signal b9-1 (synchronous detection signal b9-2) obtained by integrating the error by the integrator 33 is also used as the detection value of the minute modulation signal b4.

The synchronous detector 27 performs synchronous detection on the signal b9-2 for synchronous detection output from the integrator 33 based on the minute modulation signal b4 output from the minute modulation signal generator 30, whereby the optical modulator 22 is detected. The control direction of the operating point (bias point) is determined.
The control circuit 28 outputs an operating point control signal b5 for controlling the operating point (bias point) of the optical modulator 22 to be an optimal point based on the control direction determined by the synchronous detector 27.
In the adder 29, as described above, the minute modulation signal b4 output from the minute modulation signal generator 30 is superimposed on the operating point control signal b5 output from the control circuit 28, and this minute modulation signal b4 is superimposed. The point control signal b6 is output to the optical modulator 22.

  Here, the principle of the minute modulation signal detection by the AGC amplifier 26 will be described with reference to FIGS.

  2A and 2B are respectively amplified by the photoelectrically converted data signal b8 (input signal of the AGC amplifier 26) modulated by the minute modulation signal b4 and the AGC amplifier 26 (variable gain amplifier 31). Data signal b11 (output signal of the AGC amplifier 26). As described above, the amplitude information of the output signal b11 of the AGC amplifier 26 (variable gain amplifier 31) is converted into the voltage information b12 by the peak detection circuit 32. The integrator 33 compares the voltage information b12 with the target amplitude value b10, integrates the difference as an error signal, and outputs the output signal b9 obtained by the integration to the variable gain amplifier 31 as the gain control signal b9-1. Thus, the gain of the variable gain amplifier 31 is controlled so that the difference (error signal) becomes zero. That is, as shown in FIGS. 2C and 2D, if the conversion voltage (voltage information b12) is larger than the target amplitude value b10, the gain of the variable gain amplifier 31 is reduced, and the conversion voltage (voltage information b12). Is smaller than the target amplitude value b10, the gain of the variable gain amplifier 31 is increased so that the output amplitude of the variable gain amplifier 31 is controlled to match the target amplitude value b10.

  Here, by adjusting the time constant of the integrator 33, the frequency band included in the gain control signal b9-1 can be set, and the loop band of the AGC amplifier 26 can be arbitrarily designed. FIG. 2E shows a loop band (transfer function) of the AGC amplifier 26. Since the feedback works so as to compensate for the frequency component below the lower limit cutoff frequency of the loop band of the AGC amplifier 26 determined by the time constant of the integrator 33, this fluctuation is generated in the output of the variable gain amplifier 31. It does not appear. On the contrary, the frequency component higher than the lower limit cutoff frequency of the loop band of the AGC amplifier 26 does not catch up with the feedback and is amplified as it is and appears at the output of the variable gain amplifier 31.

  Therefore, as shown in FIG. 2E, when the frequency of the minute modulation signal b4 is lower than the lower limit cutoff frequency of the loop band of the AGC amplifier 26, the minute modulation component (intensity modulation component) by the minute modulation signal b4 is changed. Return works to counteract. That is, the gain control signal b9-1 is reverse to the minute modulation component (intensity modulation component) by the minute modulation signal b4 in addition to the signal for amplifying the output amplitude of the variable gain amplifier 31 to the desired value (target amplitude value b10). A phase signal appears. Therefore, by monitoring the gain control signal b9-1, a minute modulation component (intensity modulation component) based on the minute modulation signal b4 can be extracted. Further, the output signal b11 of the AGC amplifier 26 (variable gain amplifier 31) is obtained by amplifying the input signal b8 (FIG. 2 (a)) subjected to minute modulation (intensity modulation) to a desired amplitude (target amplitude value b10). However, a minute modulation component (intensity modulation component) by the minute modulation signal b4 is removed from the voltage waveform (shown by a solid line in FIG. 2B) (indicated by a dotted line in FIG. 2B). Waveform).

In contrast, FIG. 3 shows a case where the frequency of the minute modulation signal b4 is higher than the lower limit cutoff frequency of the loop band of the AGC amplifier 26, as shown in FIG. FIGS. 3A to 3D show the same parts as FIGS. 2A to 2D, respectively. In this example, although the minute modulation component (intensity modulation component) by the minute modulation signal b4 appears at the output of the AGC amplifier 26 (variable gain amplifier 31) (FIG. 3B), this minute modulation component ( Since the intensity modulation component) is cut in the band of the integrator 33, the gain control signal b9-1 does not show a signal that cancels this fluctuation, that is, a signal having a phase opposite to that of the minute modulation component (intensity modulation component). As a result, the output signal b11 of the AGC amplifier 26 (variable gain amplifier 31) has amplified the minutely modulated (intensity modulated) input signal b8 (FIG. 3A) to a desired amplitude (target amplitude value b10). However, a minute modulation component (intensity modulation component) is also superposed on this (FIG. 3B).
In FIG. 2 (e) and FIG. 3 (e), the signal frequency is represented by a single frequency for simplicity, but the present invention can also be applied to those having a bandwidth.

  From the above, in the first embodiment, by setting the lower limit cutoff frequency of the loop band of the AGC amplifier 26 to be lower than the frequency of the minute modulation signal b4, the gain control signal b9-1 is added to the minute modulation signal b4. The component of appears. FIG. 4 shows the waveform of the gain adjustment signal b9-1 of the AGC amplifier 26 (variable gain amplifier 31) obtained by calculation for the first embodiment. The frequency of the minute modulation signal 4 was 3 MHz. As is clear from the figure, at the bias optimum point (optimum operating point), a double wave of the frequency of the minute modulation signal b4 is obtained, and the phase of the detected minute modulation signal is inverted at this point. . Desired control can be performed by detecting the presence or absence of this phase inversion by synchronous detection, determining the control direction, and setting a state in which a double wave is generated. At the same time, since the AGC amplifier 26 performs constant output amplitude control, the dynamic range of the input signal can be widened.

  In the first embodiment, the TIA 25 is connected to the output of the monitor PD 24. Alternatively, a similar effect can be obtained by connecting a relatively large resistor to perform current-voltage conversion.

<Embodiment 2>
The optical phase control circuit according to the second embodiment of the present invention provided in the optical transmission device will be described with reference to FIGS.

  As shown in FIG. 5, in the second embodiment, in order to further expand the dynamic range, a first AGC amplifier 41 (corresponding to the first AGC amplifier) connected in series and a second AGC amplifier are further expanded. 42 (corresponding to the last AGC amplifier). The component of the minute modulation signal c2 is extracted from the gain control signal c1-1 of the second AGC amplifier 42. Other configurations are the same as those in the first embodiment.

  More specifically, the main signal unit of the optical transmission apparatus includes a light source 43 that emits continuous light c3, an optical modulator 44, and a driver circuit 45, and controls to control the optical modulator 44. The unit includes a minute modulation signal generator 46, a monitor PD 47, a TIA 48, two AGC amplifiers 41 and 42, a synchronous detector 49, a control circuit 50, and an adder 51. The first AGC amplifier 41 includes a variable gain amplifier 61, a peak detection circuit 62, and an integrator 63. The second AGC amplifier 42 includes a variable gain amplifier 71, a peak The detection circuit 72 and the integrator 73 are provided.

  The optical modulator 44 of the optical transmitter generates phase-modulated light by phase-modulating the continuous light c3 output from the light source 43 based on the data signal c4 input via the driver circuit 45, and this phase modulation Light (transmission signal c5-1) is transmitted to an optical receiver (not shown).

  At this time, in the optical phase control circuit, the optical signal (phase modulated light) is minutely modulated by the minute modulation signal c2 output from the minute modulation signal generator 46 for controlling the operating point (bias point) of the optical modulator 44. Apply (intensity modulation). In other words, the adder 51 adds (superimposes) the minute modulation signal c2 output from the minute modulation signal generator 46 to the operating point control signal c6 of the optical modulator 44 output from the control circuit 50, so that the light An operating point control signal 76 for the modulator 44 is generated, and this operating point control signal c 7 is output to the optical modulator 44. In the optical modulator 44, since the operating point is controlled by the operating point control signal c7 on which the minute modulation signal c2 is superimposed, the optical signal (phase modulated light) is subjected to minute modulation (intensity modulation).

  The optical signal after the minute modulation is branched, one branched optical signal c5-1 is output to the transmission line of the optical communication system, and the other optical signal c5-2 is used by the optical phase control circuit for operating point control. Used.

  In the optical phase control circuit, the optical signal c5-2 is photoelectrically converted into an electrical signal c9 by photoelectric conversion means (monitor PD47, TIA48). More specifically, the optical signal c5-2 is received by the monitor PD 47 to be a current signal c8, and the TIA 48 is set to a voltage signal c9 corresponding to the current signal c8. Then, the output signal b9 of the TIA 48 is amplified by the first AGC amplifier 41 in the previous stage so as to have a desired amplitude value (first target amplitude value c10), and the output signal c12 of the first AGC amplifier 41 is further increased. Then, it is amplified by the second AGC amplifier 42 in the subsequent stage so as to have a desired amplitude value (second target amplitude value c11). The second target amplitude value c11 is set to a value larger than the first target amplitude value c10.

  The first AGC amplifier 41 has a lower limit cut-off frequency of the loop band that can keep the output amplitude of the variable gain amplifier 61 constant (that is, the amplitude can be controlled constant) and is output from the minute modulation signal generator 46. It is set lower than the frequency of the signal c2. The second AGC amplifier 42 has a lower limit cut-off frequency of the loop band that can keep the output amplitude of the variable gain amplifier 71 constant (that is, the amplitude can be controlled constant) and is output from the minute modulation signal generator 46. It is set higher than the frequency of the signal c2.

In the first AGC amplifier 41, the variable gain amplifier 61 converts the electrical signal c9 obtained by photoelectric conversion by the photoelectric conversion means based on the gain control signal c13 output from the integrator 63 to the first target amplitude. Amplification is performed to obtain a value c10.
The peak detection circuit 62 detects the output amplitude of the variable gain amplifier 61. That is, the peak detection circuit 62 converts the amplitude information of the output signal c12 of the variable gain amplifier 61 into voltage information c14.
The integrator 63 compares the output amplitude (voltage information c14) detected by the peak detection circuit 62 with the first target amplitude value c10, and this output amplitude (voltage information c14) and the first target amplitude value c10. An output signal obtained by integrating the difference (error signal) is output to the variable gain amplifier 61 as a gain control signal c13. In the variable gain amplifier 61, as described above, based on the gain control signal c13, the signal c9 after photoelectric conversion is amplified so as to become the first target amplitude value c10 (that is, the gain of the variable gain amplifier 61 is The difference (error signal) is controlled to be zero).

Next, in the second AGC amplifier 42, the variable gain amplifier 71 outputs from the variable gain amplifier 61 in the first AGC amplifier 41 in the previous stage based on the gain control signal c <b> 1-1 output from the integrator 73. The signal c12 is amplified so as to become the second target amplitude value c11.
The peak detection circuit 72 detects the output amplitude of the variable gain amplifier 71. That is, the peak detection circuit 72 converts the amplitude information of the output signal c15 of the variable gain amplifier 71 into voltage information c16.
The integrator 73 compares the output amplitude (voltage information c16) detected by the peak detection circuit 72 with the second target amplitude value c11, and this output amplitude (voltage information c16) and the second target amplitude value c11. An output signal c1 obtained by integrating the difference (error signal) with respect to is output to the variable gain amplifier 71 as a gain control signal c1-1. Based on the gain control signal c1-1, in the variable gain amplifier 71, as described above, the signal c12 output from the variable gain amplifier 61 in the first AGC amplifier 41 in the previous stage is converted to the second target amplitude value c11. (That is, the gain of the variable gain amplifier 71 is controlled so that the difference (error signal) becomes zero). Further, the integrator 73 outputs the output signal c1 to the synchronous detector 49 as the synchronous detection signal c1-2.

  That is, the optical signal output from the optical modulator 44 is branched and photoelectrically converted, then amplified to the first target amplitude value c10 by the first AGC amplifier 41, and the second AGC amplifier 42 When amplifying up to the target amplitude value c11 of 2, the amplitude variation due to the minute modulation signal c2 is detected as an error from the target amplitude value c11, and this error is integrated by the integrator 73 to obtain the gain control signal c1-1 (synchronization). The detection signal c1-2) is also used as a detection value of the minute modulation signal c2.

The synchronous detector 49 synchronously detects the synchronous detection signal c1-2 output from the integrator 73 on the basis of the minute modulation signal c2 output from the minute modulation signal generator 46, whereby the optical modulator 44 is detected. The control direction of the operating point (bias point) is determined.
The control circuit 50 outputs an operating point control signal c6 for controlling the operating point (bias point) of the optical modulator 44 to be an optimum point based on the control direction determined by the synchronous detector 49.
In the adder 51, as described above, the minute modulation signal c2 output from the minute modulation signal generator 46 is superimposed on the operating point control signal c6 output from the control circuit 50, and the minute modulation signal c4 is superimposed. The point control signal c7 is output to the optical modulator 22.

  FIG. 6 shows the relationship between the loop band of each AGC amplifier 41, 42 and the frequency of the minute modulation signal c2 in this configuration. The lower limit cutoff frequency of the loop band of the first AGC amplifier 41 determined by the time constant of the integrator 63 is lower than the frequency of the minute modulation signal c2, and the second AGC amplifier is determined by the time constant of the integrator 73. The lower limit cutoff frequency of the 42 loop band is set high. 2 and 3, in the first AGC amplifier 41, the component (intensity modulation component) of the minute modulation signal c2 does not appear in the gain adjustment signal c13, and the output signal c12 of the variable gain amplifier 61 does not. The component of the minute modulation signal c2 (intensity modulation component) remains superimposed. On the other hand, in the second AGC amplifier 42, the component (intensity modulation component) of the minute modulation signal c2 appears in the gain adjustment signal c1-1, and the component of the minute modulation signal c (from the output signal c15 of the variable gain amplifier 71) ( The control works so that the intensity modulation component) is canceled out.

  FIG. 7 shows the output c9 of the TIA 48 and the second AGC amplifier 42 (variable gain amplifier 71) when the optical phase control circuit of the second embodiment is applied to the quadrature control ABC circuit of the QPSK modulator. Of the output c15 and the waveform of the gain control signal c1-1. Here, the input of the monitor PD 47 is the minimum reception intensity, the frequency of the minute modulation signal c2 is 3 MHz, and the operating point (bias point) is shifted from the optimum point to the smaller side. FIG. 8 shows the same calculation as in FIG. 7 with the input of the monitor PD 47 as the maximum reception intensity. The minimum reception strength is 1/100 of the maximum reception strength.

From these comparisons,
Even if the reception intensity is different by two digits, the output amplitude of the second AGC amplifier 42 (variable gain amplifier 71) is a desired amplitude (second target amplitude value c11) by the first and second AGC amplifiers 41 and 42. Can be amplified to
Under either condition, the component (intensity modulation component) of the 3 MHz minute modulation signal c appears in the gain control signal c1-1 of the second AGC amplifier 42;
・ This makes it possible to control the operating point of the optical modulator with a very wide dynamic range.
I understand.

<Embodiment 3>
In the foregoing first and second embodiments, the optical phase control circuit of the present invention is used to optimize the operating point of the optical modulator provided in the optical transmitter. In this third embodiment and later-described fourth embodiment, as another application example of the optical phase control circuit of the present invention, desired interference light is output from a delay interferometer provided in the optical receiver. An example in which the optical phase control circuit of the present invention is used to optimize the operating point (phase adjustment point) of the optical phase adjuster provided in the delay interferometer will be described. When the operating point (phase adjustment point) of the optical phase adjuster provided in the delay interferometer is changed, the light phase changes, but the delay interferometer changes the light intensity (modulation). Thus, it is possible to detect whether or not the operating point (phase adjustment point) of the optical phase adjuster is optimal.
First, the optical phase control circuit according to the third embodiment of the present invention provided in the optical receiver will be described with reference to FIGS.

  As shown in FIG. 9, the optical receiving apparatus in the third embodiment is a DPSK receiving circuit using a delay interferometer, and includes a delay interferometer 81, a balanced PD 82, a TIA 83, and an AGC amplifier 84. And a control unit (synchronous detector 85, control circuit 86, adder 87, minute modulation signal generator 88). The configuration of the AGC amplifier 84 and the configuration of the control unit are the same as those in the first embodiment. The delay interferometer 81 is provided with an optical phase adjuster 89 for controlling the transmission frequency, and a minute modulation signal d1 output from the minute modulation signal generator 88 is superimposed on the optical phase adjuster 89.

  In the optical phase control circuit, first, an optical signal output from a delay interferometer 81 (corresponding to a device equipped with an optical modulator) provided with an optical phase adjuster 89 is converted into a photoelectric conversion means (balanced PD 82, TIA 83). Is converted into an electric signal d2. Specifically, an optical signal output from the delay interferometer 81 to each of the ports 90 and 91 is received by the balanced PD 82 to be a current signal d3, and a voltage signal d2 corresponding to the current signal d3 by the TIA 83.

Then, the output signal d2 of the TIA 83 is amplified by the AGC amplifier 84 so as to have a desired amplitude value (target amplitude value d4).
The AGC amplifier 84 can maintain the output amplitude of the variable gain amplifier 92 constant (that is, the amplitude can be controlled constant), and the lower limit cutoff frequency of the loop band of the minute modulation signal d1 output from the minute modulation signal generator 88 is It is set higher than the frequency.
In this AGC amplifier 84, in the variable gain amplifier 92, the electrical signal d2 photoelectrically converted by the photoelectric conversion means based on the gain control signal d5-1 output from the integrator 94 becomes the target amplitude value d4. Amplify to.
The peak detection circuit 93 detects the output amplitude of the variable gain amplifier 92. That is, the peak detection circuit 93 converts the amplitude information of the output signal d6 of the variable gain amplifier 92 into voltage information d7.
The integrator 94 compares the output amplitude (voltage information d7) detected by the peak detection circuit 93 with a target amplitude value d4, and a difference (error signal) between the output amplitude (voltage information d7) and the target amplitude value d4. ) Is output to the variable gain amplifier 92 as a gain control signal d5-1. Based on the gain control signal d5-1, the variable gain amplifier 92 amplifies the signal d2 after photoelectric conversion to the target amplitude value b10 as described above (that is, the gain of the variable gain amplifier 31 is increased as described above). The difference (error signal) is controlled to be zero). Further, the integrator 94 outputs the output signal d5 to the synchronous detector 85 as a synchronous detection signal d5-2.

  That is, when the intensity-modulated light demodulated from the phase-modulated light by the delay interferometer 81 is photoelectrically converted by the balance type PD 82 and then amplified to the target amplitude value d4 by the AGC amplifier 84, the amplitude fluctuation due to the minute modulation signal d1 is detected as the target amplitude value A gain control signal d5-1 (synchronous detection signal d5-2), which is detected as an error from d4 and integrated by the integrator 94, is also used as a detection value of the minute modulation signal d1.

The synchronous detector 85 synchronously detects the synchronous detection signal d5-2 output from the integrator 94 on the basis of the minute modulation signal d1 output from the minute modulation signal generator 88, thereby providing an optical phase adjuster. The control direction of 89 operation points (phase adjustment points) is determined.
The control circuit 86 outputs an operating point control signal d8 for controlling the operating point (phase adjusting point) of the optical phase adjuster 89 to be the optimum point based on the control direction determined by the synchronous detector 85. To do.
In the adder 87, the minute modulation signal d1 output from the minute modulation signal generator 88 is superimposed on the operating point control signal d8 output from the control circuit 86, and the operating point control signal d9 is superimposed on the minute modulation signal d1. Is output to the optical phase adjuster 89.

Further detailed description will be given based on FIG. 10 and FIG. FIG. 10A shows the relationship between the phase adjustment value of the delay interferometer 81 and the transmission characteristics. The optimum operating point (phase adjustment point) indicated by a dotted line in FIG. 10A is the transmission characteristic maximum (or minimum) of the delay interferometer 81, that is, the input peak intensity to each port 90, 91 of the balanced PD 82. This is the maximum (or minimum) point. In this state, the output amplitude of the receiving circuit is maximized.
As the operating point deviates from the optimum point, the input peak intensity to the ports 90 and 91 of the balanced PD 82 becomes smaller and the ports on the opposite side (from the first port 90 to the second port 91 and the second port) are reduced. The leakage light from 91 to the first port 90) increases. At this time, the output amplitude of the receiving circuit is also smaller than the amplitude at the optimum operation point.
Since the minute modulation signal d1 used in the control constantly vibrates the operating point (phase adjustment point) of the optical phase adjuster 89, the reception amplitude periodically attenuates or increases (in FIG. 10B). Waveform).

  In the conventional configuration, this fluctuation is detected as a minute modulation component (intensity modulation component), and the operating point is controlled to the optimum point. (Modulation component) remains superimposed. As described above, this results in interference with the data signal and degrades the code error rate characteristic.

On the other hand, in the present invention, an amplitude variation due to minute modulation (intensity modulation) is detected, and the control direction is determined by synchronously detecting a control signal for compensating for the amplitude variation. Therefore, suppression of the minute modulation component (intensity modulation component) and extraction of the minute modulation component (intensity modulation component) can be realized simultaneously from the output waveform.
FIG. 11 is a comparison of the output waveform according to the present invention and the output waveform according to the conventional configuration. From FIG. 11, it can be seen that the minute modulation signal seen in the output of the conventional configuration is significantly suppressed in the output of the configuration according to the present invention as described above.

<Embodiment 4>
Based on FIG. 12, the optical phase control circuit according to the fourth embodiment of the present invention provided in the optical receiver will be described.

  As shown in FIG. 12, in the fourth embodiment, in order to further expand the dynamic range, a first AGC amplifier 101 (corresponding to the first AGC amplifier) connected in series and a second AGC amplifier 102 (corresponding to the last AGC amplifier). The component of the minute modulation signal e2 is extracted from the gain control signal e1-1 of the second AGC amplifier 102. Other configurations are the same as those in the third embodiment.

  More specifically, first, an optical signal output from the delay interferometer 104 (corresponding to the apparatus including the optical modulator in the first and second embodiments) provided with the optical phase adjuster 103 is converted into a photoelectric conversion means. Photoelectric conversion is performed by (balance type PD105, TIA106) to obtain an electric signal e3. Specifically, an optical signal output from the delay interferometer 104 to each of the ports 107 and 108 is received by the balanced PD 105 as a current signal e4 and a voltage signal e3 corresponding to the current signal e4 by the TIA 106. Then, the output signal e3 of the TIA 106 is amplified by the first AGC amplifier 101 in the previous stage so as to have a desired amplitude value (first target amplitude value e5), and the output signal e7 of the first AGC amplifier 101 is further increased. Then, it is amplified by the second AGC amplifier 102 in the subsequent stage so as to have a desired amplitude value (second target amplitude value e6). The second target amplitude value e6 is set to a value larger than the first target amplitude value e5.

The first AGC amplifier 101 includes a variable gain amplifier 111, a peak detection circuit 112, and an integrator 113. The second AGC amplifier 102 includes a variable gain amplifier 121, a peak detection circuit, and the like. 122 and an integrator 123 are provided.
As in the case of the second embodiment (see FIG. 6), the first AGC amplifier 101 can keep the output amplitude of the variable gain amplifier 111 constant (that is, the amplitude can be controlled constant). Is set lower than the frequency of the minute modulation signal e2 output from the minute modulation signal generator 109, and the second AGC amplifier 102 can keep the output amplitude of the variable gain amplifier 121 constant ( In other words, the lower limit cutoff frequency of the loop band in which constant amplitude control is possible is set higher than the frequency of the minute modulation signal e2 output from the minute modulation signal generator 109.

In the first AGC amplifier 101, the variable gain amplifier 111 converts the electrical signal e3 photoelectrically converted by the photoelectric conversion means based on the gain control signal e8 output from the integrator 113 to the first target amplitude value e5. Amplify so that
The peak detection circuit 112 detects the output amplitude of the variable gain amplifier 111. That is, the peak detection circuit 112 converts the amplitude information of the output signal e7 of the variable gain amplifier 111 into voltage information e9.
The integrator 113 compares the output amplitude (voltage information e9) detected by the peak detection circuit 112 with the first target amplitude value e5, and this output amplitude (voltage information e9) and the first target amplitude value e5. An output signal obtained by integrating the difference (error signal) is output to the variable gain amplifier 111 as a gain control signal e8. Based on the gain control signal e8, the variable gain amplifier 111 amplifies the signal e3 after photoelectric conversion to the first target amplitude value e5 as described above (that is, the gain of the variable gain amplifier 111 is The difference (error signal) is controlled to be zero).

Next, in the second AGC amplifier 112, the variable gain amplifier 121 outputs the variable gain amplifier 111 in the first AGC amplifier 101 in the previous stage based on the gain control signal e1-1 output from the integrator 123. The signal e7 is amplified so as to become the second target amplitude value e6.
The peak detection circuit 122 detects the output amplitude of the variable gain amplifier 121. That is, the peak detection circuit 122 converts the amplitude information of the output signal e10 of the variable gain amplifier 121 into voltage information e11.
The integrator 123 compares the output amplitude (voltage information e11) detected by the peak detection circuit 122 with the second target amplitude value e6, and this output amplitude (voltage information e11) and the second target amplitude value e6. Is output to the variable gain amplifier 121 as a gain control signal e1-1. Based on the gain control signal e1-1, in the variable gain amplifier 121, as described above, the signal e7 output from the variable gain amplifier 111 in the first AGC amplifier 101 in the previous stage is converted to the second target amplitude value e6. (That is, the gain of the variable gain amplifier 121 is controlled so that the difference (error signal) becomes zero). Further, the integrator 123 outputs the output signal e1 to the synchronous detector 110 as a synchronous detection signal e1-2.

  That is, the intensity-modulated light demodulated from the phase-modulated light by the delay interferometer 104 is photoelectrically converted by the balance type PD 105, amplified by the first AGC amplifier 101 to the first target amplitude value e 5, and then the second AGC amplifier 102. When the amplitude is amplified to the second target amplitude value e6, the amplitude fluctuation due to the minute modulation signal e2 is detected as an error from the target amplitude value e6, and this error is integrated by the integrator 123 to obtain the gain control signal e1-1. (Signal e1-2 for synchronous detection) is also used as a detection value of the minute modulation signal d1.

The synchronous detector 110 synchronously detects the synchronous detection signal e1-2 output from the integrator 123 based on the minute modulation signal e2 output from the minute modulation signal generator 109, thereby providing an optical phase adjuster. The control direction of the operating point (phase adjustment point) 103 is determined.
The control circuit 114 outputs an operating point control signal e12 for controlling the operating point (phase adjusting point) of the optical phase adjuster 103 to be an optimum point based on the control direction determined by the synchronous detector 110. To do.
In the adder 112, the minute modulation signal e2 output from the minute modulation signal generator 109 is superimposed on the operating point control signal e12 output from the control circuit 114, and the operating point control signal e13 is superimposed on the minute modulation signal e2. Is output to the optical phase adjuster 103.

  In the second and fourth embodiments, two AGC amplifiers are used. However, the present invention is not limited to this, and the dynamic range may be expanded using three or more AGC amplifiers. That is, the optical phase control circuit of the present invention includes three or more (for example, three stages) AGC amplifiers connected in series, a synchronous detector, a control circuit, a minute modulation signal generator, and an adder. It may be a configuration.

This case is the same as the case where the AGC amplifier has two stages. That is, each of the three or more stages of AGC amplifiers is configured to include a variable gain amplifier, a peak detection circuit, and an integrator. A larger target amplitude value is set for the latter AGC amplifier.
Of the three or more stages of AGC amplifiers, the last AGC amplifier (the third stage in the case of three stages) has a lower limit cutoff frequency of the loop band, which is a minute modulation signal output from the minute modulation signal generator. The AGC amplifiers other than the last of three or more stages of AGC amplifiers (in the case of three stages, the first stage (first) and the second stage) have a lower cutoff frequency of the loop band. The frequency is set lower than the frequency of the minute modulation signal output from the minute modulation signal generator.
Also, in the first (first stage) AGC amplifier among the three or more stages of AGC amplifiers, the variable gain amplifier uses an optical modulator or an optical modulator based on a gain control signal output from the integrator. An electrical signal obtained by photoelectrically converting an optical signal output from a device (delay interferometer) having a photoelectric conversion means by a photoelectric conversion means is amplified so as to become a target amplitude value. An output amplitude is detected, and the integrator outputs an output signal obtained by integrating a difference between the output amplitude detected by the peak detection circuit and the target amplitude value to the variable gain amplifier as the gain control signal. To do.
In the AGC amplifiers other than the top of the plurality of stages of AGC amplifiers (in the case of three stages, the second stage and the third stage (tail)), in the variable gain amplifier, the gain output from the integrator Based on the control signal, the variable gain in the AGC amplifier at the front stage (in the case of three stages, the first stage for the second stage (second stage) and the second stage for the last stage (third stage)) The signal output from the amplifier is amplified so as to have a target amplitude value, the peak detection circuit detects the output amplitude of the variable gain amplifier, and the integrator detects the output amplitude detected by the peak detection circuit And an output signal obtained by integrating the difference between the target amplitude value and the target amplitude value is output to the variable gain amplifier as the gain control signal, and in the AGC amplifier at the end (third stage in the case of three stages) The integrator outputs the output signal. Examples signal synchronous detection also outputs to the synchronous detector.
In the synchronous detector, based on the minute modulation signal output from the minute modulation signal generator, the signal for synchronous detection of the AGC amplifier at the tail (third stage in the case of three stages) is synchronously detected. By doing so, the control direction of the operating point of the optical modulator (or optical phase adjuster in the case of a delay interferometer) is determined. The control circuit outputs an operating point control signal for controlling the operating point of the optical modulator (or optical phase adjuster in the case of a delay interferometer) based on the control direction determined by the synchronous detector. . In the adder, the minute modulation signal output from the minute modulation signal generator is superimposed on the operation point control signal output from the control circuit, and the operation point control signal on which the minute modulation signal is superimposed is Output to an optical modulator (or optical phase adjuster if a delay interferometer).

  The present invention relates to an optical phase control circuit applied to an optical transmission device, an optical reception device, or the like constituting an optical communication system using phase modulation, and an optical modulator in an optical transmission device or a delay interferometer in an optical reception device. It is useful when applied to the case where stable operating point control is performed for an optical phase adjuster or the like.

21 Light source 22 Optical modulator 23 Driver circuit 24 Monitor PD
25 TIA
26 AGC amplifier 27 Synchronous detector 28 Control circuit 29 Adder 30 Small modulation signal generator 31 Variable gain amplifier 32 Peak detection circuit 33 Integrator 41 First AGC amplifier 42 Second AGC amplifier 43 Light source 44 Optical modulator 45 Driver Circuit 46 Minute modulation signal generator 47 Monitor PD
48 TIA
49 Synchronous detector 50 Control circuit 51 Adder 61 Variable gain amplifier 62 Peak detection circuit 63 Integrator 71 Variable gain amplifier 72 Peak detection circuit 73 Integrator 81 Delay interferometer 82 Balanced PD
83 TIA
84 AGC amplifier 85 Synchronous detector 86 Control circuit 87 Adder 88 Minute modulation signal generator 89 Optical phase adjuster 90 First port 91 Second port 92 Variable gain amplifier 93 Peak detection circuit 94 Integrator 101 First AGC Amplifier 102 Second AGC amplifier 103 Optical phase adjuster 104 Delay interferometer 105 Balanced PD
106 TIA
Reference Signs List 107 first port 108 second port 109 minute modulation signal generator 110 synchronous detector 111 variable gain amplifier 112 peak detection circuit 113 integrator 114 control circuit 121 variable gain amplifier 122 peak detection circuit 123 integrator

Claims (4)

An optical phase control circuit for controlling the operating point of the optical modulator,
An automatic gain control amplifier, a synchronous detector, a control circuit, a minute modulation signal generator, and an adder are provided.
The automatic gain control amplifier has a variable gain amplifier, a peak detection circuit, and an integrator, and the lower limit cutoff frequency of the loop band is set higher than the frequency of the minute modulation signal output from the minute modulation signal generator. In the variable gain amplifier, on the basis of the gain control signal output from the integrator, the optical signal output from the optical modulator or the device including the optical modulator is optically converted by the photoelectric conversion means. The electrical signal that has been electrically converted is amplified to a target amplitude value, the peak detection circuit detects the output amplitude of the variable gain amplifier, and the integrator detects the output amplitude detected by the peak detection circuit. An output signal obtained by integrating the difference from the target amplitude value is output to the variable gain amplifier as the gain control signal and the synchronous detection as a signal for synchronous detection Also output to,
The synchronous detector operates the optical modulator by synchronously detecting the synchronous detection signal output from the integrator based on the small modulation signal output from the small modulation signal generator. Determine the control direction of the point,
In the control circuit, based on the control direction determined by the synchronous detector, outputs an operating point control signal for controlling the operating point of the optical modulator to be an optimum point,
In the adder, the minute modulation signal output from the minute modulation signal generator is superimposed on the operation point control signal output from the control circuit, and the operation point control signal on which the minute modulation signal is superimposed is Output to the optical modulator,
An optical phase control circuit configured as described above. An optical phase control circuit for controlling the operating point of the optical modulator,
A plurality of stages of automatic gain control amplifiers connected in series, a synchronous detector, a control circuit, a minute modulation signal generator, and an adder,
Each of the multiple-stage automatic gain control amplifiers has a variable gain amplifier, a peak detection circuit, and an integrator, and a larger target amplitude value is set in the subsequent-stage automatic gain control amplifier, and the multiple-stage automatic gain control amplifiers. The automatic gain control amplifier at the end of the control amplifier is configured such that the lower limit cutoff frequency of the loop band is set higher than the frequency of the minute modulation signal output from the minute modulation signal generator, and the plurality of stages of automatic gain control amplifiers The automatic gain control amplifier other than the tail of the lower limit cutoff frequency of the loop band is set lower than the frequency of the minute modulation signal output from the minute modulation signal generator,
In the first automatic gain control amplifier among the plurality of stages of automatic gain control amplifiers, the variable gain amplifier includes the optical modulator or the optical modulator based on a gain control signal output from the integrator. An electrical signal obtained by photoelectrically converting an optical signal output from the device provided by the photoelectric conversion means is amplified so as to become a target amplitude value, and the peak detection circuit detects an output amplitude of the variable gain amplifier, In the integrator, an output signal obtained by integrating the difference between the output amplitude detected by the peak detection circuit and the target amplitude value is output to the variable gain amplifier as the gain control signal,
In the automatic gain control amplifiers other than the top of the plurality of stages of automatic gain control amplifiers, the variable gain amplifier uses the variable gain in the preceding stage automatic gain control amplifier based on the gain control signal output from the integrator. The signal output from the amplifier is amplified so as to have a target amplitude value, the peak detection circuit detects the output amplitude of the variable gain amplifier, and the integrator detects the output amplitude detected by the peak detection circuit An output signal obtained by integrating the difference between the target amplitude value and the target amplitude value is output to the variable gain amplifier as the gain control signal, and the integrator in the last automatic gain control amplifier outputs the output signal. The signal is also output to the synchronous detector as a signal for synchronous detection,
In the synchronous detector, the synchronous detection signal output from the integrator of the last automatic gain control amplifier is synchronously detected based on the minute modulation signal output from the minute modulation signal generator. By determining the control direction of the operating point of the optical modulator,
In the control circuit, based on the control direction determined by the synchronous detector, outputs an operating point control signal for controlling the operating point of the optical modulator to be an optimum point,
In the adder, the minute modulation signal output from the minute modulation signal generator is superimposed on the operation point control signal output from the control circuit, and the operation point control signal on which the minute modulation signal is superimposed is Output to the optical modulator,
An optical phase control circuit configured as described above. In the optical phase control circuit according to claim 1 or 2,
The optical phase control circuit according to claim 1, wherein the optical modulator is provided in an optical transmission device and is for phase-modulating continuous light output from a light source based on a data signal. In the optical phase control circuit according to claim 1 or 2,
The apparatus provided with the optical modulator is a delay interferometer provided in the optical receiver for receiving phase-modulated light, and the optical modulator is an optical phase adjuster provided in the delay interferometer. An optical phase control circuit.

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