# US 2013/0155482 A1 · Optical modulation device and optical modulation method

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- Number: US 2013/0155482 A1
- Document ID: US20130155482A1
- Status: Published application
- Kind: A1
- Application number: 13/663,758
- Filed: 2012-10-30
- Published: 2013-06-20
- Earliest claimed: 2011-12-16
- Assignees: Fujitsu Optical Components Limited
- Inventors: Akihiro TOYA; Tsuyoshi Morishita
- Web page: https://patentgrep.com/patent/US20130155482A1

## CPC

- G02F 1/0123: {Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops}
- H04B 10/50572: {to control the modulating signal amplitude including amplitude distortion}
- H04B 10/50575: {to control the modulator DC bias}
- H04B 10/50577: {to control the phase of the modulating signal}
- H04B 10/5561: {Digital phase modulation}
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- H04B: TRANSMISSION

## Abstract

In an optical modulation device, a first drive signal and a first bias signal are applied to a phase modulation unit, a second drive signal and a second bias signal are applied to a phase modulation unit, and a third bias signal is applied to a π/2 phase shift unit. A control unit adjusts the third bias signal in a first adjustment period, adjusts the first drive signal and the first bias signal in a second adjustment period next to the first adjustment period, and adjusts the second drive signal and the second bias signal in a third adjustment period next to the second adjustment period. The control unit starts the second adjustment period before a gap between the current value of an adjustment reference signal and a target value is filled, and starts the third adjustment period before a gap in the second adjustment period is filled.

## Claims

### Claim 1

An optical modulation device comprising:
a first modulation unit that includes: a first modulator that forms a first optical modulation signal by modulating a light based on a first drive signal and a first bias signal; a second modulator that forms a second optical modulation signal by modulating a light based on a second drive signal and a second bias signal; and a phase shifter that makes a phase difference between the first optical modulation signal and the second optical modulation signal closer to π/2 by shifting a phase of the first optical modulation signal with respect to the second optical modulation signal based on a third bias signal;
a former that forms an adjustment reference signal based on a synthesized signal synthesizing the first optical modulation signal phase-shifted in the phase shifter and the second optical modulation signal; and
a controller that adjusts amplitudes of the first drive signal and the second drive signal and voltages of the first bias signal, the second bias signal and the third bias signal, based on a gap between a current value of the adjustment reference signal and a target value,
wherein the controller performs an adjustment in a plurality of adjustment periods and starts a second adjustment period next to a first adjustment period before the gap in the first adjustment period is filled.

### Claim 2 (depends on 1)

The optical modulation device according to claim 1, wherein the controller adjusts the third bias signal in the first adjustment period, adjusts the first drive signal and the first bias signal in the second adjustment period and adjusts the second drive signal and the second bias signal in a third adjustment period next to the second adjustment period.

### Claim 3 (depends on 2)

The optical modulation device according to claim 2, wherein
the first drive signal and the second drive signal are superimposed over a first pilot having a first frequency,
the first bias signal and the second bias signal are superimposed over a second pilot having a second frequency,
the third bias signal is superimposed over a third pilot, and
the controller controls a length of the first adjustment period to be equal to or greater than one cycle of the third pilot and equal to or less than a time constant at the time of adjustment of the third bias signal, controls a length of the second adjustment period to be equal to or greater than one cycle of the first pilot and equal to or less than a time constant at the time of adjustment of the first drive signal and the first bias signal, and controls a length of the third adjustment period to be equal to or greater than one cycle of the second pilot and equal to or less than a time constant at the time of adjustment of the second drive signal and the second bias signal.

### Claim 4 (depends on 1)

The optical modulation device according to claim 1, further comprising:
a second modulation unit that includes: a third modulator that forms a third optical modulation signal by modulating a light based on a third drive signal and a fourth bias signal; a fourth modulator that forms a fourth optical modulation signal by modulating a light based on a fourth drive signal and a fifth bias signal; and a second phase shifter that makes a phase difference between the third optical modulation signal and the fourth optical modulation signal closer to π/2 by shifting a phase of the third optical modulation signal with respect to the fourth optical modulation signal based on a sixth bias signal; and
a second former that forms a second adjustment reference signal based on a second synthesized signal synthesizing the third optical modulation signal phase-shifted in the second phase shift unit and the fourth optical modulation signal,
wherein the controller performs adjustment processing based on the first adjustment reference signal and adjustment processing based on the second adjustment reference signal in parallel.

### Claim 5 (depends on 1)

The optical modulation device according to claim 1, wherein the controller starts the first adjustment period before the light is emitted.

### Claim 6 (depends on 5)

The optical modulation device according to claim 5, wherein, when a target voltage value of the third bias signal is out of an allowable range, the controller changes the target voltage value to a predetermined value in the allowable range.

### Claim 7 (depends on 5)

The optical modulation device according to claim 5, wherein, when a target voltage value of the first bias signal is out of an allowable range, the controller unit changes the target voltage value to a predetermined value in the allowable range.

### Claim 8 (depends on 5)

The optical modulation device according to claim 5, wherein, when a target voltage value of the first drive signal is out of an allowable range, the controller changes the target voltage value to a minimum value in the allowable range.

### Claim 9

An optical modulation method comprising:
forming a first optical modulation signal by modulating a light based on a first drive signal and a first bias signal;
forming a second optical modulation signal by modulating a light based on a second drive signal and a second bias signal;
making a phase difference between the first optical modulation signal and the second optical modulation signal closer to π/2 by shifting a phase of the first optical modulation signal with respect to the second optical modulation signal based on a third bias signal;
forming an adjustment reference signal based on a synthesized signal synthesizing the phase-shifted first optical modulation signal and the second optical modulation signal;
adjusting amplitudes of the first drive signal and the second drive signal and voltages of the first bias signal, the second bias signal and the third bias signal, based on a gap between a current value of the adjustment reference signal and a target value; and
performing the adjustment in a plurality of adjustment periods and starting a second adjustment period next to a first adjustment period before the gap in the first adjustment period is filled.