# US 2013/0156444 A1 · Optical modulation device and control method in optical modulation device

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- Number: US 2013/0156444 A1
- Document ID: US20130156444A1
- Status: Published application
- Kind: A1
- Application number: 13/654,913
- Filed: 2012-10-18
- Published: 2013-06-20
- Earliest claimed: 2011-12-16
- Assignees: Fujitsu Optical Components Limited
- Inventors: Tamotsu AKASHI
- Web page: https://patentgrep.com/patent/US20130156444A1

## CPC

- G02F 1/0123: {Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops}
- H04B 10/50575: {to control the modulator DC bias}
- G02F 1/212: {Mach-Zehnder type}
- H04B 10/5057: {using a feedback signal generated by analysing the optical output}
- 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 driver applies a drive signal based on a data signal to a modulation unit, the modulation unit modulates the light input from an LD by the drive signal, and a bias control unit calculates a bias voltage value so as to make the f0 element closer to “0,” according to a detection result in a synchronization detection unit, and supplies a bias voltage of the calculated voltage value to the modulation unit. The bias control unit stops ABC control when the data signal is in a state different from a predefined state during the ABC control, and, after the stop of the ABC control, restarts the ABC control using, as an initial value, a bias voltage value calculated before the stop of the ABC control.

## Claims

### Claim 1

An optical modulation device comprising:
a modulation unit that modulates an input light by a drive signal to output an optical signal;
a drive unit that applies the drive signal based on a data signal to the modulation unit; and
a first bias control unit that performs a bias control to adjust an operating point of a bias voltage of the drive signal such that an optical intensity in a modulation curve of the modulation unit decreases according to a bias voltage value sequentially calculated by the first bias control unit, stops the bias control when the data signal is in a different state different from a predefined state during the bias control and, after the stop of the bias control, restarts the bias control using, as an initial value, a bias voltage value calculated by the first bias control unit before the stop of the bias control.

### Claim 2 (depends on 1)

The optical modulation device according to claim 1, wherein
the first bias control unit performs the bias control to adjust the operating point to a point at which the optical intensity in the modulation curve is minimum.

### Claim 3 (depends on 1)

The optical modulation device according to claim 1, wherein
the first bias control unit performs the bias control to adjust the operating point to an intermediate point between a point at which the optical intensity in the modulation curve is maximum and a point at which the optical intensity in the modulation curve is minimum.

### Claim 4 (depends on 1)

The optical modulation device according to claim 1, wherein
the first bias control unit accepts an input of an alarm signal indicating the different state and stops the bias control according to the alarm signal (a) when the data signal continuously input in the drive unit is stopped, (b) when an amplitude of the data signal is out of a predetermined range, (c) when a frequency of the data signal is out of a predetermined range, (d) when the data signal includes a noise equal to or greater than a threshold, (e) when a part of multiple data items lacks in the data signal generated by multiplexing the multiple data items, (f) a phase difference between the multiple data items is equal to or greater than a threshold, (g) when a mark ratio in the multiple data items is out of a predetermined range, (h) when an amplitude of any of the multiple data items is out of a predetermined range, (i) when a frequency of any of the multiple data items is out of a predetermined range, or (j) when any of the multiple data items includes noise equal to or greater than a threshold.

### Claim 5 (depends on 1)

The optical modulation device according to claim 1, wherein
the first bias control unit stops the bias control and fixes a bias voltage value in a case of the different state and, after the stop, restarts the bias control using the fixed bias voltage value as the initial value.

### Claim 6 (depends on 1)

The optical modulation device according to claim 1, wherein
the first bias control unit stores the bias voltage value sequentially calculated by the first bias control unit in a memory and, after the stop, restarts the bias control using, as the initial value, a latest bias voltage value stored in the memory.

### Claim 7 (depends on 1)

The optical modulation device according to claim 1, further comprising:
a generation unit that generates the data signal by multiplexing multiple data items; and
an initialization unit that initializes the generation unit after the stop.

### Claim 8 (depends on 1)

The optical modulation device according to claim 1, further comprising an amplitude control unit that performs an amplitude control to sequentially change an amplitude of the drive signal according to an amplitude value sequentially calculated by the amplitude control unit, stops the amplitude control when the data signal is in the different state during the amplitude control and, after the stop of the amplitude control, restarts the amplitude control using, as an initial value, an amplitude value calculated by the amplitude control unit before the stop of the amplitude control.

### Claim 9 (depends on 1)

The optical modulation device according to claim 1,
wherein the modulation unit comprises an I arm that outputs an optical signal of an I element and a Q arm that outputs an optical signal of a Q element, and
the optical modulation device further comprises a second bias control unit that performs a π/2 bias control to sequentially control a bias voltage applied to the modulation unit such that a phase difference between the optical signal of the I element and the optical signal of the Q element is π/2 according to a bias voltage value sequentially calculated by the second bias control unit, stops the π/2 bias control when the data signal is in the different state during the π/2 bias control and, after the stop of the π/2 bias control, restarts the π/2 bias control using, as an initial value, a bias voltage value calculated by the second bias control unit before the stop of the π/2 bias control.

### Claim 10

A control method for an optical modulation device, the method comprising:
performing a bias control to adjust an operating point of a bias voltage of a drive signal based on a data signal such that an optical intensity in a modulation curve of a modulation unit decreases according to a bias voltage value sequentially calculated, the modulation unit modulating an input light by the drive signal to output an optical signal, the drive signal being applied to the modulation unit;
stopping the bias control when the data signal is in a state different from a predefined state during the bias control; and
after the stop, restarting the bias control using, as an initial value, a bias voltage value calculated before the stop.