JP2019185058A - Optical modulation circuit, optical transmitter and optical modulation method - Google Patents

Abstract

To provide an optical modulation circuit which can make a modulator, such as a MZ optical modulator, operate optimally according to the modulation system of an inputted signal, and to provide an optical transmitter and an optical modulation method.SOLUTION: An optical modulation circuit 10 includes storage means 20 for registering a plurality of types of modulation amplitude information corresponding to the modulation system, data output means 30 for extracting the modulation amplitude information corresponding to the modulation system of an inputted data signal from the storage means 20, and outputting the data signal while adjusting the amplitude thereof based on the modulation amplitude information thus extracted, and modulation means 40 for receiving continuous light and the data signal having an adjusted amplitude, modulating the continuous light by the data signal having an adjusted amplitude, and outputting a modulation signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical modulation circuit, an optical transmitter, and an optical modulation method, and more particularly to an optical modulation circuit, an optical transmitter, and an optical modulation method in which a Mach-Zehnder optical modulator is disposed.

  As an optical modulator used in an optical transmitter or the like, there is an MZ type optical modulator in which an optical waveguide type Mach-Zehnder (MZ) interferometer is incorporated with an optical phase modulator. An optical transmitter using an MZ type optical modulator is disclosed in, for example, cited documents 1-3.

  Patent Document 3 discloses an optical transmitter that can optimally operate an MZ type optical modulator regardless of the dispersion pre-equalization amount by performing DC bias control while performing correction according to the dispersion pre-equalization amount. Is disclosed.

  On the other hand, in recent years, CFP2 (100G Form-factor Pluggable) modules for metro network and data center applications have been applied as next-generation digital coherent transceivers. In the CFP2 module, an MZ type optical modulator, a driver, a light source, and the like are arranged in a pluggable transceiver, and a signal from a frame generation circuit passes through a relatively long distance wiring and is input to the driver.

  When frame generation circuits with various modulation schemes are connected to a pluggable transceiver, it is necessary to cause the MZ type optical modulator arranged in the pluggable transceiver to perform an optimum operation according to the modulation scheme of the frame generation circuit to be connected. Occurs.

JP 2014-160985 A International Publication No. 2011/104838 JP 2008-236512 A

  However, in the optical transmitters of Patent Documents 1-3, it is not considered that the MZ type optical modulator is applied to frame generation circuits of various modulation schemes.

  The present invention has been made in view of the above problems, and provides an optical modulation circuit, an optical modulator, and the like that can cause a modulator such as an MZ type optical modulator to perform an optimum operation according to a modulation method of an input signal. An object is to provide a transmitter and an optical modulation method.

  In order to achieve the above object, an optical modulation circuit according to the present invention includes a storage unit in which a plurality of modulation amplitude information corresponding to a modulation method is registered, and the modulation amplitude information corresponding to the modulation method of an input data signal. Data output means for extracting from the means, adjusting the amplitude of the data signal based on the extracted modulation amplitude information, and outputting the continuous light and the data signal with the adjusted amplitude. Modulation means for modulating the amplitude-adjusted data signal and outputting a modulated signal.

  In order to achieve the above object, an optical transmitter according to the present invention is adapted to a storage means in which a plurality of modulation amplitude information corresponding to a modulation scheme are registered, and an optical output means for generating and outputting continuous light. Frame generation means for outputting a data signal framed in accordance with the modulation method, modulation amplitude information corresponding to the applied modulation method is extracted from the storage means, and the data is based on the extracted modulation amplitude information Data output means for adjusting and outputting the amplitude of the signal, bias control means for generating and outputting a bias voltage, and using the bias voltage, the continuous light is modulated by the data signal having the adjusted amplitude, Modulation means for outputting a modulation signal.

  In order to achieve the above object, an optical modulation method according to the present invention is an optical modulation method using an optical modulation circuit including a storage unit in which a plurality of modulation amplitude information corresponding to a modulation scheme is registered, and is input Modulation amplitude information corresponding to the modulation method of the data signal is extracted from the storage means, the amplitude of the data signal is adjusted based on the extracted modulation amplitude information, and the amplitude of the input continuous light is adjusted Modulate with data signal.

  According to the above-described aspect of the present invention, a modulator such as an MZ type optical modulator can be caused to perform an optimum operation according to the modulation method of the input signal.

1A is a block configuration diagram of an optical modulation circuit 10 and FIG. 1B is a block configuration diagram of an optical transmitter 80 according to a first embodiment. It is a block block diagram of the optical modulation circuit 100 which concerns on 2nd Embodiment. It is a block block diagram of the optical modulator 200 which concerns on 2nd Embodiment. It is a block block diagram of the power acquisition circuit 300 which concerns on 2nd Embodiment. It is a figure which shows an example of the modulation amplitude of the transfer curve and modulation | alteration signal in case the QPSK modulation system is applied of the optical modulator 200 which concerns on 2nd Embodiment. It is a figure which shows an example of the modulation curve of the optical modulator 200 which concerns on 2nd Embodiment in case the QAM modulation system is applied, and a modulation signal. It is a figure which shows the operation | movement procedure of the optical modulation circuit 100 which concerns on 2nd Embodiment.

<First Embodiment>
A first embodiment of the present invention will be described. FIG. 1A shows a block configuration diagram of the light modulation circuit according to the present embodiment. In FIG. 1A, the light modulation circuit 10 includes a storage unit 20, a data output unit 30, and a modulation unit 40.

  A plurality of pieces of modulation amplitude information corresponding to the modulation method are registered in the storage unit 20. For example, in the storage unit 20 according to the present embodiment, modulation amplitude information for generating a modulation signal having a modulation amplitude corresponding to the 2Vπ operation is registered in association with a QPSK (Quadrature Phase Shift Keying) modulation method. Yes. Further, the storage means 20 is associated with a QAM (Quadrature Amplitude Modulation) modulation method, a desired modulation amplitude smaller than the modulation amplitude corresponding to the 2Vπ operation, for example, the modulation amplitude corresponding to the 2 × 0.9Vπ operation, Modulation amplitude information for generating a modulation signal having

  This is because, in the case of the QPSK modulation method, the amplitude variation of the input signal can be almost ignored by using a limiting type driver, and the operation with the maximum modulation amplitude is possible. This is because it is not possible to use a driver of the Ting type. In the case of the QAM modulation method, it is necessary to apply a linear type driver required for multi-level signal amplification such as a pulse amplitude waveform modulation (PAM) method, and the linear type driver has a variation in the amplitude of the input signal. Since the signal is amplified by the gain of the driver, it is necessary to operate with a modulation amplitude that is less affected by the modulation distortion.

  The data output means 30 receives a framed data signal from a frame generation means or the like (not shown) according to the applied modulation method. Then, the data output means 30 extracts modulation amplitude information corresponding to the applied modulation method from the storage means 20, and adjusts the amplitude of the input data signal based on the extracted modulation amplitude information to modulate the modulation means. Output to 40.

  The modulation means 40 receives continuous light and a data signal with adjusted amplitude output from the data output means 30. Then, the modulation means 40 modulates the input continuous light with the data signal whose amplitude is adjusted, and outputs a modulation signal.

  In the optical modulation circuit 10 configured as described above, the data output means 30 optimally adjusts the amplitude of the data signal based on the modulation amplitude information corresponding to the modulation method. For example, the data output means 30 uses the modulation amplitude information corresponding to the modulation method when a modulation method such as a QAM modulation method, in which modulation distortion occurs due to an increase in modulation amplitude, is applied. Reduce the amplitude of the data signal. When the modulation means 40 modulates using the data signal input from the data output means 30, a modulation signal having an optimum modulation amplitude with little influence of modulation distortion is output. That is, the light modulation circuit 10 according to the present embodiment can cause the modulation unit 40 to perform an optimum operation according to the modulation method of the input signal.

  Here, the optimum average intensity can be applied as the modulation amplitude information. In this case, the light modulation circuit 10 further includes an intensity measurement unit that acquires the average intensity of the modulation signal output from the modulation unit 40. Then, the data output means 30 extracts the optimum average intensity corresponding to the applied modulation method from the storage means 20, and the average intensity of the modulation signal measured by the intensity measurement means matches the extracted optimum average intensity. Thus, the amplitude of the data signal is adjusted.

  In addition, a bias control unit that generates a bias voltage for making the operating point of the modulation unit 40 coincide with the NULL point and outputs the bias voltage to the modulation unit 40 may be disposed in the optical modulation circuit 10. In this case, the modulation unit 40 modulates the input continuous light with the data signal whose amplitude is adjusted, using the bias voltage input from the bias control unit, and outputs a modulation signal.

  Note that the above-described optical modulation circuit 10 may be disposed in the optical transmitter. A block diagram of the optical transmitter 80 in this case is shown in FIG. The optical transmitter 80 in FIG. 1B is configured by adding a bias control unit 50, an optical output unit 60, and a frame generation unit 70 to the optical modulation circuit 10 in FIG.

  The bias control unit 50 generates a bias voltage for making the operating point of the modulation unit 40 coincide with the NULL point, and outputs the bias voltage to the modulation unit 40. The light output means 60 generates continuous light and outputs it to the modulation means 40.

  On the other hand, the frame generation means 70 outputs a data signal framed in accordance with the adapted modulation method to the data output means 30. The data output unit 30 adjusts the amplitude of the data signal input from the frame generation unit 70 according to the modulation amplitude information extracted from the storage unit 20 and outputs the adjusted data signal to the modulation unit 40.

  Then, the modulation means 40 modulates the continuous light input from the light output means 60 by using the bias voltage input from the bias control means 50 by the data signal having the amplitude adjusted from the data output means 30. And outputs a modulated signal.

  Note that the storage unit 20, the data output unit 30, the modulation unit 40, the bias control unit 50, and the optical output unit 60 may be configured as a pluggable transceiver separate from the frame generation unit 70. In this case, the pluggable transceiver is applied to the modulation means 40 by adjusting the amplitude of the data signal input from the frame generation means 70 connected in the data output means 30 according to the applied modulation method. It is possible to perform the optimum operation according to the modulation method.

<Second Embodiment>
A second embodiment will be described. FIG. 2 shows a block configuration diagram of the light modulation circuit according to the present embodiment. In FIG. 2, the optical modulation circuit 100 includes an optical modulator 200, a power acquisition circuit 300, a storage element 400, a control circuit 500, an auto bias control circuit 600, and a driver circuit 700.

  The optical modulator 200 is driven by the driving bias voltage applied from the auto bias control circuit 600, optically modulates the input continuous light based on the data string input from the driver circuit 700, and outputs a modulation signal. . An example of a block diagram of the optical modulator 200 is shown in FIG. 3, the optical modulator 200 according to the present embodiment includes an optical demultiplexer 210, a first Mach-Zehnder (MZ) type optical modulator 220, a second MZ type optical modulator 230, and an optical phase adjustment unit 240. And an optical multiplexer 250.

  The optical demultiplexer 210 splits the inputted continuous light into two, and outputs one to the first MZ type optical modulator 220 and the other to the second MZ type optical modulator 230.

  The first MZ type optical modulator 220 is driven by the driving bias voltage Vx applied from the auto bias control circuit 600, and modulates one continuous light input using the data string DATAx input from the driver circuit 700. , Output a modulated signal of X polarization.

  The second MZ type optical modulator 230 is driven by the driving bias voltage Vy applied from the auto bias control circuit 600, and modulates the other continuous light input using the data string DATAxy input from the driver circuit 700. , Y modulation signal is output.

  The optical phase adjustment unit 240 shifts the phase of the Y-polarized modulation signal output from the second MZ type optical modulator 230 by π / 2 and outputs the result.

  The optical multiplexer 250 receives the X-polarized modulated signal output from the first MZ-type optical modulator 220 and the Y-polarized modulated signal output from the optical phase adjusting unit 240 and shifted in phase by π / 2. Combine and output as modulated signal.

  The power acquisition circuit 300 detects the light intensity of the modulation signal output from the optical modulator 200, acquires the average intensity of the modulation signal output from the light modulator 200 from the detected light intensity, and outputs the average intensity to the control circuit 500. To do. An example of a block diagram of the power acquisition circuit 300 is shown in FIG. In FIG. 4, the power acquisition circuit 300 according to the present embodiment includes a photodiode (PD) 310, an IV converter 320, a low-pass filter (LPF) 330, and an analog-digital converter 340.

  For example, the PD 310 is disposed on the output port of the optical modulator 200 and outputs a current value corresponding to the light intensity of the modulation signal output from the optical modulator 200.

  The IV converter 320 converts a current value corresponding to the light intensity of the modulation signal output from the PD 310 into a voltage value, and outputs the voltage value to the LPF 330 and the analog-digital converter 340.

  The LPF 330 detects the average intensity of the modulation signal output from the optical modulator 200 by removing the modulation component from the voltage value of the input light intensity, and outputs it to the analog-to-digital converter 340.

  The analog-to-digital converter 340 converts the voltage value of the light intensity input from the IV converter 320 into a digital value and converts the average intensity of the modulation signal input from the LPF 330 into a digital value. It outputs to the control circuit 500 as intensity information.

  In the memory element 400, the optimum point of the light average intensity is registered in advance for each of a plurality of modulation methods. For example, for the QPSK modulation method, the light average intensity of the light intensity at the time of 2Vπ operation described later is registered as the optimum point. For the QAM modulation method, the light average intensity of the light intensity at the time of 2 × 0.9 Vπ operation described later is registered as the optimum point.

  The control circuit 500 generates bias control information for making the operating point of the optical modulator 200 coincide with the NULL point based on the light intensity information input from the power acquisition circuit 300 and outputs the bias control information to the auto bias control circuit 600. . Further, the control circuit 500 reads the optimum point of the light average intensity corresponding to the modulation method at that time from the storage element 400. Then, the control circuit 500 reads the optical average intensity of the modulation signal output from the optical modulator 200 from the storage element 400 based on the optical average intensity information input from the power acquisition circuit 300. Amplitude information for matching the signal is generated and output to the driver circuit 700.

  The auto bias control circuit 600 generates drive bias voltages Vx and Vy based on the bias control information input from the control circuit 500, and generates the generated drive bias voltage Vx in the first MZ type optical modulator 220. The drive bias voltage Vy thus applied is applied to the second MZ type optical modulator 230. By applying the drive bias voltages Vx and Vy generated by the auto bias control circuit 600 based on the bias control information to the optical modulator 200, the optical modulator 200 is driven with the NULL point as a bias point.

  The driver circuit 700 receives transmission data encoded in accordance with the applied modulation scheme. The driver circuit 700 adjusts the electrical amplitude of the input transmission data based on the amplitude information input from the control circuit 500, and the data strings DATAx and DATAy are adjusted to the first MZ type optical modulator 220 and the second MZ type optical modulator 230. To each output.

  When the driver circuit 700 adjusts the electrical amplitude of the transmission data based on the amplitude information input from the control circuit 500, the optical modulator 200 outputs a modulation signal optimally modulated according to the modulation method. For example, when the QPSK modulation method is applied, the optical modulator 200 outputs a modulation signal having a modulation amplitude corresponding to the 2Vπ operation. FIG. 5 shows the transfer curve of the optical modulator 200 and the modulation amplitude of the modulation signal output from the optical modulator 200 when the QPSK modulation method is applied. As shown in FIG. 5, the light intensity of the modulation signal is highest during 2Vπ operation. On the other hand, when the QAM modulation method is applied, the optical modulator 200 outputs a modulation signal having a modulation amplitude corresponding to 2 × 0.9 Vπ operation. FIG. 6 shows the transfer curve of the optical modulator 200 and the modulation amplitude of the modulation signal output from the optical modulator 200 when the QAM modulation method is applied. In FIG. 6, by reducing the modulation factor in the case of the QAM modulation method, the light intensity of the modulated signal can be lowered, and the adverse effect on the signal quality due to the modulation distortion can be reduced.

  The optical modulation circuit 100 configured as described above matches the optical average intensity of the modulation signal output from the optical modulator 200 acquired by the power acquisition circuit 300 with the optimal point of the optical average intensity read from the storage element 400. Amplitude information is generated, and the amplitude of the transmission data is adjusted using the amplitude information. By outputting the transmission data whose electrical amplitude is adjusted based on the amplitude information to the optical modulator 200, the optical modulator 200 outputs a modulation signal whose modulation amplitude is optimally adjusted according to the modulation method.

  Next, an operation procedure of the light modulation circuit 100 according to the present embodiment will be described with reference to FIG. In FIG. 7, the optical modulator 200 optically modulates the input continuous light based on the data string input from the driver circuit 700 by the driving bias voltage applied from the auto bias control circuit 600, and converts the modulated signal into a modulated signal. Output (S101).

  The power acquisition circuit 300 measures the light intensity of the modulation signal output from the optical modulator 200, and further acquires the average intensity of the modulation signal. Then, the power acquisition circuit 300 outputs the measured light intensity and the acquired light average intensity to the control circuit 500 as light intensity information and light average intensity information (S102).

  Based on the input light intensity information, the control circuit 500 generates bias control information for making the operating point of the optical modulator 200 coincide with the NULL point, and outputs the bias control information to the auto bias control circuit 600 (S103). The auto bias control circuit 600 generates a drive bias voltage based on the bias control information input from the control circuit 500, and applies it to the optical modulator 200 (S104).

  On the other hand, the control circuit 500 reads the optimum point of the light average intensity corresponding to the modulation method at that time from the storage element 400 (S105). Then, the control circuit 500 matches the optical average intensity of the modulation signal output from the optical modulator 200 with the optimal point of the optical average intensity read from the storage element 400 based on the input optical average intensity information. Amplitude information is generated and output to the driver circuit 700 (S106).

  For example, when the optical average intensity of the modulation signal output from the optical modulator 200 is smaller than the optimum point of the optical average intensity read from the storage element 400, the control circuit 500 outputs amplitude information with an increased gain to the driver circuit 700. To do. On the other hand, when the optical average intensity of the modulation signal output from the optical modulator 200 is larger than the optimum point of the optical average intensity read from the storage element 400, the control circuit 500 outputs amplitude information with a reduced gain to the driver circuit 700. To do.

  The driver circuit 700 adjusts the electrical amplitude of the input transmission data based on the amplitude information input from the control circuit 500, and outputs the data string to the optical modulator 200 (S107). Accordingly, for example, when the QPSK modulation method is applied, a modulation signal having a modulation amplitude corresponding to the 2Vπ operation is output from the optical modulator 200, and when the QAM modulation method is applied, the optical modulator 200 is applied. To output a modulation signal having a modulation amplitude corresponding to 2 × 0.9 Vπ operation.

  As described above, since the optical modulation circuit 100 according to the present embodiment optimally adjusts the amplitude of the data signal based on the modulation amplitude information corresponding to the modulation method in the driver circuit 700, the optical modulator 200 Optimal operation according to the method can be performed.

  The optical modulation circuits 10 and 100 described above can be disposed in, for example, an optical transceiver, an optical transmission circuit, a digital coherent optical transceiver, a digital coherent optical transmission circuit, an optical modulator control circuit, or the like.

  The present invention is not limited to the above-described embodiment, and design changes and the like within a range not departing from the gist of the present invention are included in the present invention.

DESCRIPTION OF SYMBOLS 10 Optical modulation circuit 20 Memory | storage means 30 Data output means 40 Modulation means 50 Bias control means 60 Optical output means 70 Frame generation means 80 Optical transmitter 100 Optical modulation circuit 200 Optical modulator 210 Optical demultiplexer 220 1st MZ type optical modulator 230 2nd MZ type optical modulator 240 Optical phase adjustment unit 250 Optical multiplexer 300 Power acquisition circuit 310 PD
320 IV converter 330 LPF
340 Analog to Digital Converter 400 Memory Element 500 Control Circuit 600 Auto Bias Control Circuit 700 Driver Circuit

Claims (10)

Data output means for adjusting the amplitude of the data signal based on the target light intensity according to the modulation method of the input data signal;
A modulation means for modulating the continuous light input by the data signal having an adjusted amplitude and outputting a modulated signal;
A light modulation circuit comprising: The data output means adjusts the amplitude of the data signal based on a target light intensity corresponding to a modulation method of the data signal among the plurality of target light intensities associated with a plurality of modulation methods. The light modulation circuit according to 1. Further comprising intensity measuring means for measuring the average intensity of the output modulation signal;
The target light intensity is an optimal average intensity,
The data output means adjusts the amplitude of the data signal based on the optimum average intensity corresponding to the modulation method of the input data signal;
The light modulation circuit according to claim 1. Bias control means for generating and outputting a bias voltage;
The modulating means modulates the continuous light with the data signal having the amplitude adjusted, using the output bias voltage.
The light modulation circuit according to claim 1. A second intensity measuring means for measuring the light intensity of the output modulation signal;
The bias control means generates a bias voltage for making the operating point of the modulation means coincide with a NULL point based on the measured light intensity;
The light modulation circuit according to claim 4. The modulating means includes
Branching means for branching the input continuous light into two;
A first Mach-Zehnder optical modulator that modulates the one branched continuous light with the data signal using the bias voltage and outputs a first modulated signal;
A second Mach-Zehnder optical modulator that modulates the other branched continuous light with the data signal using the bias voltage and outputs a second modulated signal;
Combining means for combining the first modulated signal and the second modulated signal to output a modulated signal;
Comprising
The light modulation circuit according to claim 4 or 5. The modulating means modulates the continuous light with the data signal having the adjusted amplitude,
When a QPSK modulation method is applied, a modulation signal having a modulation amplitude corresponding to 2Vπ operation is output,
When a QAM modulation method is applied, a modulated signal having a modulation amplitude smaller than the modulation amplitude corresponding to the 2Vπ operation is output.
The light modulation circuit according to claim 6. Light output means for generating and outputting continuous light;
Frame generating means for outputting a framed data signal according to the modulation method being adapted;
Modulation amplitude information corresponding to the applied modulation scheme is extracted from the storage means, and the amplitude is adjusted based on the target light intensity corresponding to the modulation scheme of the data signal based on the extracted modulation amplitude information. Data output means for outputting;
Bias control means for generating and outputting a bias voltage;
Modulating means for modulating the continuous light with the data signal having the adjusted amplitude by using the bias voltage and outputting a modulated signal;
An optical transmitter. The optical transmitter according to claim 8, wherein the frame generation unit, the data output unit, and the modulation unit are configured to be pluggable. Based on the target light intensity corresponding to the modulation method of the input data signal, the amplitude of the data signal is adjusted,
Modulating the input continuous light by the data signal with the amplitude adjusted;
Light modulation method.

Images