JP2018004979A - Optical modulation device and optical modulation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily take a power balance between I phase and Q phase.SOLUTION: An optical modulation device comprises an amplitude modulation section 100 for modulating an amplitude of an optical signal to be input, a phase modulation section 110 for modulating a phase of the optical signal in which an amplitude is modulated by the amplitude modulation section 100, a bias drive section 120 for applying a reverse bias voltage to an output electrode of the phase modulation section 110, a current detection section 130 for detecting current flowing in the output electrode of the phase modulation section 110 and a control section 140 for controlling an amplitude modulated by the amplitude modulation section 100 so as to take a power balance between I phase and Q phase on the basis of a value of the current detected by the current detection section 130.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical modulation device and an optical modulation method.

In recent high-speed optical communications, a modulated optical signal is applied to a modulator that modulates an optical signal by applying a high-frequency analog signal from the outside as a modulation signal and controlling the phase relationship of the light using the modulation signal. A phase modulation method using a signal as a transmission signal is used. Examples of the modulator used for the phase modulation include a LN (LiNbO3) modulator, a semiconductor modulator, and the like, which are Mach-Zehnder optical modulators.
Using these modulators, in the modulation format combined with polarization multiplexing, the occupancy rate of the wavelength spectrum can be reduced by quadrature amplitude modulation (QAM) and electrical compensation at the transmission end for the purpose of improving frequency utilization efficiency. Lowering modulation schemes are attracting attention. For these various analog modulation signals, it is necessary to optimally control the modulator bias voltage and the driving amplitude.

  On the other hand, in order to increase the density of transmission capacity, in recent years, development of pluggable optical transceivers as analog coherent optics has been progressing. Since this pluggable optical transceiver has a small volume, it is difficult to mount a commonly used LN modulator. Therefore, there are an increasing number of cases where a small-sized semiconductor modulator is used for the pluggable optical transceiver.

FIG. 7 is a diagram illustrating an example of the structure of a general Mach-Zehnder optical modulator. The optical signal is generated using the Mach-Zehnder optical modulator shown in FIG. A wavelength tunable light source is input to a Mach-Zehnder type modulator (hereinafter referred to as DP-MZM), branched in the waveguide, and input to the modulation section of Inner 931. The Inner 931 has a bias electrode in each branched waveguide. In the example illustrated in FIG. 7, the Inner 931 includes electrodes of XIP901, XIN902, XQP903, XQN904, YIP905, YIN906, YQP907, and YQN908 in a plurality of waveguides. The RF 932 is connected to the subsequent stage of the Inner 931, and the Outer 933 is connected to the subsequent stage. In the example illustrated in FIG. 7, the Outer 933 controls the phase between the I phase (In Phase) and the Q phase (Quadrature Phase). Further, the Outer 933 has electrodes of XMP 911, XMN 912, YMP 913, and YMN 914 in a plurality of waveguides. Further, a π / 2 phase shifter 921 is provided at the tip of the output of the X-polarized outer 933.
In the example shown in FIG. 7, phase modulation is realized by applying a bias voltage to each electrode of Inner 931 and Outer 933 and applying a high frequency modulation signal to the electrode of RF 932 while maintaining an optimal bias state. . In this modulator structure, monitor terminals 941 and 942 are arranged for the X polarization and the Y polarization, respectively, and the output power of each polarization can be monitored.

  Further, a technique for changing the optical output power by controlling the drive amplitude has been considered (for example, see Patent Documents 1 and 2).

JP 2014-206633 A Special table 2015-528257 gazette

  In the technique described above, only one monitor terminal is provided for each of the X polarization and the Y polarization. Therefore, power balance between XY polarized waves can be obtained, but power between I phase and Q phase cannot be separately monitored. Therefore, there is a problem that it is difficult to maintain the power balance by monitoring the power balance between the I phase and the Q phase during operation. Furthermore, in multi-level modulation formats such as QAM (Quadrature Amplitude Modulation), the inter-symbol distance is smaller than that of QPSK (Quadrature Phase Shift Keying), and therefore, characteristic degradation due to power imbalance between I-phase and Q-phase becomes more remarkable. . Therefore, it is a very important control to balance the power between the I phase and the Q phase and between the XY polarized waves.

  An object of the present invention is to provide an optical modulation device and an optical modulation method that solve the above-described problems.

The light modulation device of the present invention comprises:
An amplitude modulator for modulating the amplitude of the input optical signal;
A phase modulator that modulates the phase of an optical signal whose amplitude is modulated by the amplitude modulator;
A bias driver for applying a reverse bias voltage to the output electrode of the phase modulator;
A current detector for detecting a current flowing through the output electrode;
Based on the value of the current detected by the current detection unit, the amplitude modulated in the amplitude modulation unit is controlled so as to balance the power between the I phase (In Phase) and the Q phase (Quadrature Phase) of the optical signal. And a control unit.
Further, the light modulation method of the present invention includes:
Processing to modulate the amplitude of the input optical signal;
Processing to modulate the phase of the optical signal whose amplitude is modulated;
Applying a reverse bias voltage to the output electrode of the circuit that modulates the phase;
A process of detecting a current flowing through the output electrode;
A process for controlling the amplitude in the circuit for modulating the amplitude so as to balance the power between the I phase (In Phase) and the Q phase (Quadrature Phase) of the optical signal based on the detected current value; Do.

  As described above, in the present invention, the power balance between the I phase and the Q phase can be easily obtained.

It is a figure which shows 1st Embodiment of the optical modulation apparatus of this invention. It is a figure which shows 2nd Embodiment of the optical modulation apparatus of this invention. It is a figure which shows an example of the detail of a bias drive part, an electric current detection part, and a control part which were shown in FIG. It is a figure which shows an example of the correlation of the polarity of the voltage of each electrode of Inner. It is a figure which shows 4th Embodiment of the optical modulation apparatus of this invention. It is a figure which shows an example inside the thick frame line shown in FIG. It is a figure which shows an example of the structure of a general Mach-Zehnder type optical modulator.

  In the present invention, there is provided a method for maintaining the power balance of light output from the four modulation units in the modulator for the purpose of maintaining the optical transmission signal characteristic in an optimum state by using characteristics specific to the semiconductor modulator. suggest.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)

FIG. 1 is a diagram showing a first embodiment of an optical modulation device according to the present invention.
As shown in FIG. 1, the light modulation device according to this embodiment includes an amplitude modulation unit 100, a phase modulation unit 110, a bias drive unit 120, a current detection unit 130, and a control unit 140. FIG. 1 shows an example of main components related to the present embodiment among the components included in the light modulation device of the present invention.

  The amplitude modulation unit 100 modulates the amplitude of the input optical signal. The phase modulation unit 110 modulates the phase of the optical signal whose amplitude is modulated by the amplitude modulation unit 100. The bias driver 120 applies a reverse bias voltage to the output electrode of the phase modulator 110. The current detection unit 130 detects a current flowing through the output electrode of the phase modulation unit 110. Based on the value of the current detected by the current detection unit 130, the control unit 140 controls the amplitude modulated by the amplitude modulation unit 100 so as to balance the power between the I phase and the Q phase of the optical signal.

Thus, the amplitude modulated by the amplitude modulation unit 100 is adjusted so that the control unit 140 balances the power between the I phase and the Q phase of the optical signal based on the value of the current flowing through the output electrode of the phase modulation unit 110. In order to control, the power balance between IQ and XY polarization can be taken.
(Second Embodiment)

FIG. 2 is a diagram showing a second embodiment of the light modulation device of the present invention.
As shown in FIG. 2, the light modulation device in this embodiment includes an RF 101, an Outer 111, and an Inner 151.
First, the wavelength tunable light source is branched into an X polarization and a Y polarization, and each polarization is branched into an I phase (XI, YI) and a Q phase (XQ, YQ). The Furthermore, each branches to the P side and the N side. The modulation unit of Inner 151 includes bias electrodes XIP201, XIN202, XQP203, XQN204, YIP205, YIN206, YQP207, and YQN208. Subsequent to each electrode in the Inner 151, an RF 101 that is an amplitude modulation unit that modulates the amplitude of the input optical signal is provided. The RF 101 includes an electrode corresponding to each electrode in the Inner 151. At the subsequent stage of the RF 101, an Outer 111 that is a phase modulation unit is provided. Specifically, output electrodes XMP 211, XMN 212, YMP 213, and YMN 214 are provided for each of the I phase and the Q phase after each electrode in the RF 101. Further, in the subsequent stage, a π / 2 phase shifter 221 is provided on the X polarization side in order to multiplex the X polarization and the Y polarization. The configuration so far is the same as the structure of the general Mach-Zehnder type optical modulator shown in FIG. In this embodiment, the XMP 211 is used as a monitor terminal for X-I, the XMN 212 as X-Q, the YMP 213 as Y-I, and the YMN 214 as Y-Q monitor terminals.

The light modulation device shown in FIG. 2 further includes a bias drive unit 121, a current detection unit 131, and a control unit 141. FIG. 2 shows an example of main components related to the present embodiment among the components included in the light modulation device of the present invention.
The bias drive unit 121 applies a reverse bias voltage to the XMP 211, XMN 212, YMP 213, and YMN 214 that are output electrodes of the Outer 111. At this time, the bias drive unit 121 applies reverse bias voltages to the I-phase output electrodes (XMP211 and YMP213) and the Q-phase output electrodes (XMN212 and YMN214) of the Outer 111 for each of the X polarization and the Y polarization.
The current detection unit 131 detects a current flowing through the XMP 211, XMN 212, YMP 213, and YMN 214 that are output electrodes of the Outer 111. At this time, the current detection unit 131 detects the current flowing through the I-phase output electrodes (XMP211 and YMP213) and the Q-phase output electrodes (XMN212 and YMN214) of the Outer 111 for each of the X polarization and the Y polarization.
Based on the value of the current detected by the current detection unit 131, the control unit 141 controls the amplitude modulated in the RF 101 so as to balance the power between the I phase and the Q phase of the optical signal. At this time, the control unit 141 may control the amplitude modulated in the RF 101 so that the magnitude of the I-phase output and the magnitude of the Q-phase output are the same. Alternatively, the control unit 141 may control the amplitude modulated in the RF 101 so that the magnitude of the I-phase output and the magnitude of the Q-phase output have predetermined values. Specifically, the control unit 141 adjusts the drive amplitude of XI based on the current of the XMP 211 detected by the current detection unit 131. In addition, the control unit 141 adjusts the X-Q drive amplitude based on the current of the XMN 212 detected by the current detection unit 131. The control unit 141 adjusts the Y-I drive amplitude based on the current of the YMP 213 detected by the current detection unit 131. Further, the control unit 141 adjusts the Y-Q drive amplitude based on the current of the YMN 214 detected by the current detection unit 131. Further, the control unit 141 controls the voltage of the bias drive unit 121.

FIG. 3 is a diagram illustrating an example of the details of the bias driving unit 121, the current detection unit 131, and the control unit 141 illustrated in FIG. The current detection unit 131 includes a resistor 132, an AMP 133, and an ADC 134.
The resistors 132 are resistors having a resistance value of about 0.1 to 1Ω, and a total of four resistors are provided, one for each of XMP211, XMN212, YMP213, and YMN214.
The amplifiers AMP 133 are connected to each of the XMP 211, XMN 212, YMP 213, and YMN 214, and a total of four are connected, and the voltage drop in the resistor 132 is converted from voltage to current.
The ADC 134, which is an analog-digital converter, converts the output of the AMP 133 from an analog signal to a digital signal and outputs it to the control unit 141. By using this ADC 134, the optical output from the Inner 151 can be monitored.
A total of four amplifiers AMP122 are provided corresponding to XMP211, XMN212, YMP213, and YMN214, respectively, and the amplified voltages are applied to XMP211, XMN212, YMP213, and YMN214, respectively. This AMP 122 may be included in the bias drive unit 121.
The DRV-IC 142 is a driver. The DRV-IC 142 may be included in the control unit 141. The DRV-IC 142 transmits a signal for adjusting amplitude modulation to the RF 101 in accordance with an instruction from the control unit 141.

In this way, the optical output from the Inner 151 is monitored using the output electrode of the Outer 111, and the modulation of the amplitude in the RF 101 is controlled based on the monitored result. Therefore, it operates in proportion to the optical output power passing through each path, regardless of whether or not a high-frequency signal is applied to the electrode of RF101. That is, it is possible to achieve power balance without depending on modulation or non-modulation by the RF 101. Further, even when the light modulation device is in operation, the current can be monitored without affecting other controls in the light modulation device. These current values are calibrated in advance at the time of product manufacture, the control unit 141 calculates the monitor value obtained by the ADC 134 so as to maintain this current, controls the control signal to the DRV-IC 142, and controls the modulation signal. Make it bigger or smaller. Thereby, it is possible to balance the output light power from each Inner. Furthermore, since it is possible to balance the output light power of XI, XQ, YI, and YQ, the power balance not only between the I phase and the Q phase but also between the XY polarized waves is the same. Can be easily taken.
(Third embodiment)

FIG. 4 is a diagram showing an example of the correlation of the polarity of the voltage of each inner electrode.
As shown in FIG. 4, when the dynamic range of each inner electrode ranges from a negative voltage to a positive voltage, a region in which one electrode is a positive voltage (forward bias) and the other voltage is a negative voltage (reverse bias) ( In FIG. 4, F / R, R / F) occur. Here, one electrode is a first electrode (XIP, XQP, YIP, YQP), and the other electrode is a second electrode (XIN, XQN, YIN, YQN). One electrode may be the second electrode and the other electrode may be the first electrode.
Even in such a case, by monitoring the correlation between the first electrode and the second electrode in advance, the monitor value of the quasi-bias electrode is converted based on the monitor result of the reverse-bias electrode. can do.
(Fourth embodiment)

FIG. 5 is a diagram showing a fourth embodiment of the light modulation device of the present invention.
As shown in FIG. 5, the light modulation device in this embodiment includes an RF 101, a bias drive unit 121, a current detection unit 131, a control unit 141, an inner 152, and an outer 112. The electrode provided in the inner 152 and the electrode provided in the outer 112 are the same as the electrode provided in the inner 151 and the electrode provided in the outer 111 in the second embodiment.

FIG. 6 is a diagram showing an example of the inside of the thick frame line shown in FIG.
As shown in FIG. 6, a monitor-dedicated electrode 231 is provided in the vicinity of YQP 207 which is an input electrode of Inner 152 of the phase modulation unit. In addition, a monitor-dedicated electrode 232 is provided in the vicinity of the YMN 214 that is the output electrode of the outer 112 of the phase modulation unit. Similarly, monitor dedicated electrodes are provided in the vicinity of other electrodes (XIP201, XIN202, XQP203, XQN204, YIP205, YIN206, YQN208, XMP211, XMN212, YMP213). At this time, the current detection unit 131 detects a current flowing through each monitor dedicated electrode. Thereby, the optical power can be monitored without being affected by the bias control voltage.
Note that a monitor-dedicated electrode may be provided after combining in the I phase and the Q phase.

A part or all of the above embodiment can be described as in the following supplementary notes, but is not limited thereto.
(Appendix 1)
An amplitude modulator for modulating the amplitude of the input optical signal;
A phase modulator that modulates the phase of an optical signal whose amplitude is modulated by the amplitude modulator;
A bias driver for applying a reverse bias voltage to the output electrode of the phase modulator;
A current detector for detecting a current flowing through the output electrode;
Based on the value of the current detected by the current detection unit, the amplitude modulated in the amplitude modulation unit is controlled so as to balance the power between the I phase (In Phase) and the Q phase (Quadrature Phase) of the optical signal. A light modulation device.
(Appendix 2) The bias drive unit applies a reverse bias voltage to the output electrodes of the I phase and the Q phase of the phase modulation unit for each of the X polarization and the Y polarization,
The light modulation device according to appendix 1, wherein the current detection unit detects a current flowing through each of the output electrodes of the I phase and the Q phase of the phase modulation unit for each of the X polarization and the Y polarization.
(Supplementary note 3) In the supplementary note 1 or the supplementary note 2, the control unit controls the amplitude modulated in the amplitude modulation unit so that the magnitude of the output of the I phase is the same as the magnitude of the output of the Q phase. The light modulation device described.
(Supplementary note 4) The control unit controls the amplitude to be modulated in the amplitude modulation unit so that the magnitude of the output of the I phase and the magnitude of the output of the Q phase have predetermined values. The light modulation device according to attachment 2.
(Additional remark 5) The said electric current detection part detects any said electric current based on the value of the voltage drop in the resistor with a predetermined resistance value connected to the said output electrode, Any one of Additional remark 1 to 4 The light modulation device according to 1.
(Supplementary note 6) The light modulation device according to any one of supplementary notes 1 to 5, wherein the bias driving unit applies a voltage amplified by a voltage amplifier to the output electrode.
(Supplementary note 7) A monitor-dedicated electrode is provided near the input electrode or the output electrode of the phase modulation unit,
The light modulation device according to any one of appendices 1 to 6, wherein the current detection unit detects a current flowing through the monitor-dedicated electrode.
(Appendix 8) A process for modulating the amplitude of an input optical signal;
Processing to modulate the phase of the optical signal whose amplitude is modulated;
Applying a reverse bias voltage to the output electrode of the circuit that modulates the phase;
A process of detecting a current flowing through the output electrode;
A process for controlling the amplitude in the circuit for modulating the amplitude so as to balance the power between the I phase (In Phase) and the Q phase (Quadrature Phase) of the optical signal based on the detected current value; The light modulation method to be performed.

100 Amplitude modulation unit 101 RF
110 Phase modulator 111, 112 Outer
120, 121 Bias driver 122, 133 AMP
130, 131 Current detection unit 132 Resistance 134 ADC
140,141 Control unit 142 DRV-IC
151,152 Inner
201 XIP
202 XIN
203 XQP
204 XQN
205 YIP
206 YIN
207 YQP
208 YQN
211 XMP
212 XMN
213 YMP
214 YMN
221 π / 2 phase shifter 231 and 232 Monitor dedicated terminal

Claims (8)

An amplitude modulator for modulating the amplitude of the input optical signal;
A phase modulator that modulates the phase of an optical signal whose amplitude is modulated by the amplitude modulator;
A bias driver for applying a reverse bias voltage to the output electrode of the phase modulator;
A current detector for detecting a current flowing through the output electrode;
Based on the value of the current detected by the current detection unit, the amplitude modulated in the amplitude modulation unit is controlled so as to balance the power between the I phase (In Phase) and the Q phase (Quadrature Phase) of the optical signal. A light modulation device. The light modulation device according to claim 1,
The bias drive unit applies a reverse bias voltage to the output electrodes of the I phase and the Q phase of the phase modulation unit for each of the X polarization and the Y polarization,
The current detection unit is an optical modulation device that detects a current flowing through each of the output electrodes of the I phase and the Q phase of the phase modulation unit for each of the X polarization and the Y polarization. The light modulation device according to claim 1 or 2,
The control unit is an optical modulation device that controls the amplitude modulated in the amplitude modulation unit so that the magnitude of the output of the I phase is the same as the magnitude of the output of the Q phase. The light modulation device according to claim 1 or 2,
The control unit is an optical modulation device that controls an amplitude modulated in the amplitude modulation unit so that a magnitude of the output of the I phase and a magnitude of the output of the Q phase become predetermined values. In the light modulation device according to any one of claims 1 to 4,
The said current detection part is a light modulation apparatus which detects the said electric current based on the value of the voltage drop in the resistor with a predetermined resistance value connected to the said output electrode. The light modulation device according to any one of claims 1 to 5,
The bias driving unit is an optical modulation device that applies a voltage amplified using a voltage amplifier to the output electrode. The light modulation device according to any one of claims 1 to 6,
In the vicinity of the input electrode of the phase modulation unit or in the vicinity of the output electrode, a monitor dedicated electrode,
The current detection unit is a light modulation device that detects a current flowing through the monitor-dedicated electrode. Processing to modulate the amplitude of the input optical signal;
Processing to modulate the phase of the optical signal whose amplitude is modulated;
Applying a reverse bias voltage to the output electrode of the circuit that modulates the phase;
A process of detecting a current flowing through the output electrode;
A process for controlling the amplitude in the circuit for modulating the amplitude so as to balance the power between the I phase (In Phase) and the Q phase (Quadrature Phase) of the optical signal based on the detected current value; The light modulation method to be performed.

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