JP2023070255A - Optical transmitter and optical communication system - Google Patents

Abstract

To provide an optical transmitter capable of stably maintaining the characteristics of transmitted signal light, and an optical communication system equipped with this optical transmitter.SOLUTION: An optical transmitter (1) includes an optical modulator (20) that outputs signal light, a driver amplifier unit (103) that amplifies the voltage of an electric signal that is a data signal and applies it to electrodes (44, 45, 54, 55), an amplitude monitor unit (104) that monitors the amplitude of the voltage of the amplified electrical signal, a DC bias application unit (105) that applies a DC bias voltage (VB) to the electrode, and a DC bias control unit (106), and the DC bias control unit (106) performs first control to adjust a DC bias voltage (VB) according to the monitored amplitude, and after that, second control is performed to adjust the DC bias voltage (VB) such that the error rate detected by the optical receiver (70) that receives the signal light is minimized.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to optical transmitters and optical communication systems.

In recent years, in order to realize large-capacity optical transmission, a polarization multiplexed phase modulation method using digital coherent technology, which can increase the data rate per wavelength to 100 Gbps or 400 Gbps, has been adopted. As the polarization multiple phase modulation method, DP-QPSK (Dual Polarization-Quadrature Phase Shift Keying) modulation using an MZ (Mach-Zehnder) type optical modulator and DP-16QAM (Dual Polarization Quadrature Amplifier Modulation) are used. on), etc. ing.

As an optical transmitter that employs DP-QPSK modulation or 16QAM, there is one that has a laser light source and a QPSK modulator, which is a semiconductor optical modulator that phase-modulates the laser light (see, for example, Patent Document 1). This optical transmitter performs phase adjustment by applying a voltage to each phase adjustment electrode of Ich (In-phase channel), Qch (Quadrature-phase channel), and Pch (Phase channel), and transmits a data signal to RF (Radio frequency) An RF signal amplified by a driver amplifier is applied to the modulation electrodes, and a DC bias voltage adjusted by the DC bias controller is applied to the modulation electrodes.

Japanese Patent No. 6251977

However, there is a problem that the required RF drive voltage (that is, half-wave voltage) Vπ, which is determined by the DC bias voltage of the modulation electrode of the semiconductor optical modulator, is attenuated due to aged deterioration of the RF driver amplifier.

An object of the present disclosure is to provide an optical transmitter that can stably maintain the characteristics of transmitted signal light, and an optical communication system that includes this optical transmitter.

An optical transmitter of the present disclosure has an optical waveguide and an electrode that applies an electric field to the optical waveguide, modulates laser light input to the optical waveguide with the electric field, and outputs the modulated light as signal light. a modulation unit, a driver amplifier unit that amplifies the voltage of an electric signal that is a data signal and applies the amplified electric signal to the electrodes, an amplitude monitor unit that monitors the amplitude of the voltage of the amplified electric signal; a DC bias application unit that applies a DC bias voltage to the electrode; and a DC bias control unit that controls the DC bias application unit, wherein the DC bias control unit controls the amplitude monitored by the amplitude monitor unit. performing a first control for adjusting the DC bias voltage according to, after the first control, receiving an error rate detected by an optical receiver that receives the signal light, and minimizing the error rate The second control is performed to adjust the DC bias voltage as follows.

According to the optical transmitter and optical communication system of the present disclosure, it is possible to stably maintain the characteristics of the transmitted signal light.

1 is a block diagram schematically showing configurations of an optical transmitter and an optical communication system according to Embodiment 1; FIG. 5 is a flow chart showing operations related to DC bias voltage control of the optical transmitter according to Embodiment 1; FIG. 3 is a block diagram schematically showing configurations of an optical transmitter and an optical communication system according to Embodiment 2; 10 is a flow chart showing operations related to DC bias voltage control of the optical transmitter according to the second embodiment;

An optical transmitter and an optical communication system according to embodiments will be described below with reference to the drawings. The following embodiments are merely examples, and the embodiments can be combined as appropriate and each embodiment can be modified as appropriate.

Embodiment 1.
FIG. 1 is a block diagram schematically showing configurations of an optical transmitter 1 and an optical communication system 3 according to Embodiment 1. As shown in FIG. The optical transmitter 1 includes an optical modulation section 20, an RF driver amplifier 103 as a driver amplifier section, an amplitude monitor section 104 as a voltage measuring instrument, a DC bias application section 105 as a DC voltage application circuit, and a bias control circuit. and a DC bias control unit 106 as a . Further, in Embodiment 1, the optical transmitter 1 includes a laser light source 10, a phase control section 101 as a phase control circuit, a light intensity detector 80 for monitoring the intensity of an output signal, and a data generation section 102. have.

The optical modulator 20 has an optical waveguide and electrodes 41 to 45 and 51 to 55 that apply an electric field to the optical waveguide. The received light is output as signal light (also referred to as "output light"). The optical modulator 20 has an MZ (Mach-Zender) type optical modulator. For example, the optical modulation unit 20 includes an optical branching unit 30, which is an optical branching element that branches the light incident from the laser light source 10 into two, and an MZ type Ich that modulates the light branched by the optical branching unit 30. Optical modulator (also referred to as "first optical modulator") 40 and MZ-type Qch optical modulator (also referred to as "second optical modulator") 50, optical modulator 40 and optical modulator and a light synthesizing unit 60 which is a light synthesizing element for synthesizing the output light of 50 . Signal light output from the optical transmitter 1 is received by the optical receiver 70 through the optical transmission line.

The RF driver amplifier 103 amplifies the voltage of the electrical signal, which is the data signal output from the data generator 102, and applies the amplified electrical signal to electrodes (eg, electrodes 44, 45, 54, 55). The amplitude monitor section 104 monitors the voltage amplitude of the electric signal amplified by the RF driver amplifier 103 . The DC bias application unit 105 applies a DC bias voltage VB to electrodes (eg, electrodes 45 and 55). The DC bias control section 106 controls the DC bias applying section 105 to set the DC bias voltage VB.

The optical modulator 20, for example, modulates input light with DP-QPSK or 16QAM. In the optical modulator 20, the optical splitter 30 splits the input laser beam into two laser beams, and the split laser beams are input to the Ich optical modulator 40 and the Qch optical modulator 50, respectively. The two laser beams optically modulated by the optical modulator 40 and the optical modulator 50 are polarization-combined by the optical combiner 60, and the polarization-combined laser beam is output as output light. The output light output from the optical transmitter 1 is received by the optical receiver 70 .

A data signal output from the data generator 102 is amplified by the RF driver amplifier 103 and input to the optical modulator 20 . The electrical signal output from the DC bias application unit 105 and the electrical signal output from the phase control unit 101 are input to the optical modulation unit 20, thereby modulating the laser light. The modulated laser light is transmitted as signal light and received by the optical receiver 70 . The optical receiver 70 calculates BER (Bit Error Rate), which is an error rate, and transmits the BER to the optical transmitter 1 .

DC bias control section 106 performs first control to adjust DC bias voltage VB according to the amplitude monitored by amplitude monitor section 104 (steps S102 to S104 in FIG. 2 described later), and after the first control , receives the error rate detected by the optical receiver 70 that receives the signal light, and performs second control to adjust the DC bias voltage VB so that the error rate is minimized (steps S105 to S110 in FIG. 2 described later). ).

FIG. 2 is a flow chart showing the operation related to DC bias voltage control of the optical transmitter 1 according to the first embodiment. First, the RF driver amplifier 103 amplifies the RF signal, which is the data signal output from the data generator 102 (step S101). Next, the amplitude monitor section 104 detects the RF amplitude output from the RF driver amplifier 103 (step S102).

Next, the DC bias control unit 106 sets the amplitude of the voltage of the RF signal detected by the amplitude monitor unit 104 to a half-wave phase modulation voltage (" It is also called a "half-wave voltage".) It is determined whether or not it is equal to Vπ (step S103). DC bias control unit 106 adjusts DC bias voltage VB when the amplitude of the voltage of the RF signal is not equal to Vπ (NO in step S103). Specifically, if the amplitude of the voltage of the RF signal is smaller than Vπ, the DC bias control unit 106 adjusts the DC bias voltage VB to reduce Vπ, and if the amplitude of the voltage of the RF signal is larger than Vπ, the DC bias control unit 106 adjusts the DC bias voltage. The bias voltage VB is adjusted to increase Vπ (step S104).

When the voltage amplitude of the RF signal is equal to Vπ (YES in step S103), DC bias control section 106 receives the BER measured by optical receiver 70 (step S105).

The DC bias control unit 106 changes the DC bias voltage VB to a predetermined value (eg, +A [V]) (step S106), and determines whether or not the BER measured by the optical receiver 70 has been improved. (Step S107). If the BER measured by the optical receiver 70 is improved (YES in step S107), the DC bias control unit 106 again changes the DC bias voltage VB to a predetermined value (for example, +A [V]). Then (step S106), it is determined whether or not the BER measured by the optical receiver 70 has been improved (step S107).

If the BER measured by the optical receiver 70 is not improved (NO in step S107), the DC bias control unit 106 changes the DC bias voltage VB to a predetermined value (eg -A [V]). (Step S108), it is determined whether or not the BER measured by the optical receiver 70 has been improved (Step S109). If the BER measured by the optical receiver 70 is improved (YES in step S109), the DC bias control unit 106 again sets the DC bias voltage VB to a predetermined value (eg -A [V]). After the change (step S108), it is determined whether or not the BER measured by the optical receiver 70 is improved (step S109).

If the BER measured by the optical receiver 70 is not improved (NO in step S109), the DC bias control unit 106 changes the DC bias voltage VB to a predetermined value (for example, +A [V]) ( step S110). Note that the processing may be performed by exchanging the plus and minus signs of "+A" and "-A" in steps S106 to S110.

As described above, according to the optical transmitter 1 and the optical communication system 3 according to Embodiment 1, since the amplitude of the output of the RF driver amplifier 103 can be monitored, Gain attenuation can be compensated, and the effect of ensuring signal characteristics can be obtained.

Further, according to the optical transmitter 1 and the optical communication system 3 according to the first embodiment, even when the amplitude or gain of the output of the RF driver amplifier 103 is increased due to parts replacement, etc., the amplitude of the RF signal is kept equal to Vπ. It is possible to

Embodiment 2.
FIG. 3 is a block diagram schematically showing configurations of the optical transmitter 2 and the optical communication system 4 according to the second embodiment. In FIG. 3, the same reference numerals as those shown in FIG. 1 are attached to the same or corresponding configurations as those shown in FIG. The optical transmitter 2 and the optical communication system 4 according to the second embodiment add a semiconductor optical amplifier 90 and an optical amplification controller 107, which are optical amplifiers for amplifying the optical output power, in the subsequent stage of the optical modulator 20. This is different from the optical transmitter 1 and the optical communication system 3 according to the first embodiment.

Embodiment 2 is similar to Embodiment 1 in that the amplitude of the voltage output from RF driver amplifier 103 is monitored by amplitude monitor section 104 and fed back to DC bias control section 106 . In the second embodiment, the optical amplification controller 107 controls the gain of the semiconductor optical amplifier 90 provided after the optical modulator 20 based on the power detected by the optical intensity detector 80 . By increasing the DC bias voltage VB in the DC bias control section 106, the modulation loss in the optical modulation section 20 increases. The light intensity detector 80 detects the decrease, and the optical amplification controller 107 controls the semiconductor optical amplifier 90 so as to compensate for the decreased gain.

FIG. 4 is a flow chart showing operations related to DC bias voltage control of the optical transmitter 2 according to the second embodiment. In FIG. 4, steps S101 to S110 are the same as steps S101 to S110 in FIG.

After step S110, in the optical transmitter 2 according to the second embodiment, the optical intensity detector 80 detects the output optical power of the optical modulation section 20 (step S201), and the optical amplification control section 107 detects the output optical power It is determined whether or not the power is lower than a preset value (step S202). If the output light power is lower than the preset value (YES in step S202), the optical amplification controller 107 increases the gain of the semiconductor optical amplifier 90 by, for example, a predetermined value (step S203). The optical amplification control unit 107 repeats the processing of steps S202 and S203 until the output optical power becomes higher than a preset value.

As described above, according to the optical transmitter 2 and the optical communication system 4 according to the second embodiment, since the semiconductor optical amplifier 90 is provided after the optical modulation section 20, by controlling the DC bias voltage VB, It is possible to compensate for the increased optical loss, and the effect is obtained that the optical output power of the transmitter can be maintained. As a result, the required optical power can be continuously output from the transmission path or the opposing optical receiver, and signal characteristics can be ensured at the same time as in the first embodiment.

Further, according to the optical transmitter 2 and the optical communication system 4 according to the second embodiment, even if the optical loss compensation due to other factors or the optical transmitter output power required for the system changes, the desired optical output can be obtained. Power can be matched.

Also, an erbium-doped optical fiber amplifier may be used instead of the semiconductor optical amplifier 90 for amplifying the optical output.

The data generation unit 102, the DC bias control unit 106, the phase control unit 101, and the like can be formed by a processing circuit. The processing circuit includes a memory for storing programs and a CPU (Central Processing Unit) for executing programs. and processors such as

Except for the above points, the second embodiment is the same as the first embodiment.

Embodiment 3.
The optical transmitter and the optical communication system according to the third embodiment obtain the relationship between the wavelength of the laser light and the DC bias voltage VB in advance and store it as a table. Differs from a transmitter and an optical communication system. In Embodiment 3, the DC bias voltage VB is set by referring to a table of DC bias voltages VB for wavelengths obtained in advance. In other words, in the third embodiment, the DC bias control unit 106 acquires and holds in advance a table of the DC bias voltage VB for each wavelength of the laser light to be used. Then, the table is used to adjust the DC bias voltage VB so that the amplitude monitored by the amplitude monitor 104 becomes equal to the half-wave voltage Vπ.

As described above, according to the optical transmitter and the optical communication system according to the third embodiment, by determining the value of the DC bias voltage VB with respect to the working wavelength in advance, when the wavelength of the laser light source is changed, Also, it is possible to obtain the effect that the transmission characteristics and the optical output power can be maintained.

Except for the above points, the third embodiment is the same as the first or second embodiment.

Embodiment 4.
The optical transmitter and optical communication system according to Embodiment 4 differ from the optical transmitter and optical communication system according to Embodiment 3 above in that Vπ is adjusted for each wavelength of laser light. The optical transmitter according to the fourth embodiment changes the wavelength of the laser light emitted from the laser light source 10 from the shortest wavelength to the longest wavelength within the applicable range of the device so that the desired Vπ is obtained at each wavelength. A DC bias voltage VB is calculated. After that, the optical transmitter according to the fourth embodiment checks the BER of the received signal with the optical receiver 70, changes the DC bias voltage VB, and determines the DC bias voltage VB that minimizes the BER. By storing in advance the table of the wavelength of the laser light versus the DC bias voltage VB obtained by the above method, it is possible to set the DC bias voltage VB required when the wavelength of the laser light source 10 is changed. becomes. In other words, in the fourth embodiment, the DC bias control unit 106 presets the DC bias voltage VB that minimizes the error rate of the signal received by the optical receiver 70 for each wavelength of the laser light used. It is obtained and stored as a table, and the table is used to adjust the DC bias voltage VB so that the amplitude monitored by the amplitude monitor unit 104 is equal to the half-wave voltage Vπ with respect to the wavelength of the laser light used. .

As described above, according to the optical transmitter and the optical communication system according to the fourth embodiment, it is possible to maintain the transmission performance with high accuracy by determining the value of the DC bias voltage VB for the wavelength used in advance. can be done.

Except for the above points, the fourth embodiment is the same as the third embodiment.

1, 2 optical transmitter 3, 4 optical communication system 10 laser light source (laser light emitting element) 20 optical modulator 30 optical splitter (optical splitter) 40 optical modulator (first optical modulator) , 41 to 45 electrodes, 50 optical modulator (second optical modulator), 51 to 55 electrodes, 60 light combining section (light combining element), 70 optical receiver, 80 light intensity detector, 90 semiconductor optical amplifier, 101 phase Control section 102 Data generation section 103 RF driver amplifier (driver amplifier section) 104 Amplitude monitor section 105 DC bias application section 106 DC bias control section 107 Optical amplification control section.

Claims (10)

an optical modulator that has an optical waveguide and an electrode that applies an electric field to the optical waveguide, modulates laser light input to the optical waveguide by the electric field, and outputs the modulated light as signal light;
a driver amplifier unit that amplifies the voltage of an electric signal that is a data signal and applies the amplified electric signal to the electrodes;
an amplitude monitor unit for monitoring the amplitude of the voltage of the amplified electrical signal;
a DC bias applying unit that applies a DC bias voltage to the electrode;
a DC bias control unit that controls the DC bias applying unit;
has
The DC bias control unit
performing a first control for adjusting the DC bias voltage according to the amplitude monitored by the amplitude monitor;
After the first control, receiving an error rate detected by an optical receiver that receives the signal light, and performing a second control for adjusting the DC bias voltage so that the error rate is minimized. An optical transmitter characterized by: 2. The method according to claim 1, wherein in the first control, the DC bias control section adjusts the DC bias voltage so that the amplitude monitored by the amplitude monitor section becomes equal to a half-wave voltage. Optical transmitter as described. The optical modulation unit has an MZ type optical modulator,
3. The optical transmitter according to claim 1, wherein the MZ optical modulator has the optical waveguide and the electrodes. The optical modulation unit
an optical branching unit that branches light incident from a laser light source into two;
a first MZ optical modulator and a second MZ optical modulator that respectively modulate the light split by the optical splitter;
a light synthesizing unit for synthesizing the output lights of the first optical modulator and the second optical modulator;
has
3. The optical transmitter according to claim 1, wherein the first optical modulator and the second optical modulator each have the optical waveguide and the electrodes. further comprising a laser light source that outputs the laser light,
In the first control, the DC bias control section adjusts the DC bias voltage so that the amplitude monitored by the amplitude monitor section becomes equal to the half-wave voltage of the laser light. An optical transmitter according to any one of claims 1 to 4. an optical intensity detector that detects the intensity of the signal light output from the optical modulator;
an optical amplifier that amplifies the signal light output from the optical modulator;
an optical amplification controller that adjusts the gain of the optical amplifier based on the intensity detected by the optical intensity detector;
6. An optical transmitter according to any one of claims 1 to 5, characterized by: The DC bias control unit obtains and holds a table of the DC bias voltage in advance for each wavelength of the laser light to be used, and monitors the wavelength of the laser light to be used by the amplitude monitor unit. 7. The optical transmitter according to any one of claims 1 to 6, wherein said table is used to adjust said DC bias voltage so that said amplitude is equal to a half-wave voltage. The optical transmitter according to any one of claims 1 to 7, wherein the DC bias control section determines the DC bias voltage that minimizes the error rate received from the optical receiver. The DC bias control unit obtains in advance a DC bias voltage that minimizes the error rate of the received signal in the optical receiver for each wavelength of the laser light used, holds it in a table, and uses it. 8. The table is used to adjust the DC bias voltage so that the amplitude monitored by the amplitude monitor unit is equal to a half-wave voltage with respect to the wavelength of the laser light. The optical transmitter according to any one of Claims 1 to 3. an optical transmitter according to any one of claims 1 to 9;
An optical communication system comprising: the optical receiver;

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