Optical transmitter and method of controlling optical modulator

Patent metadata

Field	Value
Publication number	US-10122507-B2
Application number	US-201615172289-A
Country	US
Kind code	B2
Filing date	Jun 3, 2016
Priority date	Jul 28, 2015
Publication date	Nov 6, 2018
Grant date	Nov 6, 2018

Abstract

An optical transmitter has an optical modulator with a Mach-Zehnder interferometer, a pilot signal generator configured to generate a pilot signal to be superimposed on a drive signal for driving the optical modulator or on a substrate bias voltage applied to the optical modulator, and a controller configured to detect a ratio between a pilot component and a direct current component contained in a light output from the optical modulator and control at least one of an amplitude of the drive signal and a level of the substrate bias voltage such that the ratio becomes a constant value.

First claim

What is claimed is:

1. An optical transmitter comprising:
an optical modulator with a Mach-Zehnder interferometer,
a pilot signal generator configured to generate a pilot signal to be superimposed on a drive signal for driving the optical modulator or on a substrate bias voltage applied to the optical modulator,
a monitor circuit that detects a ratio between a pilot component and a direct current component contained in a light output from the optical modulator; and
a processor that controls at least one of an amplitude of the drive signal for driving the optical modulator and a level of the substrate bias voltage applied to the optical modulator such that the ratio becomes a constant value,
wherein the ratio between the pilot component and the direct current component is maintained constant so as to achieve a predetermined optical phase modulation depth of a main signal output from the optical modulator, the ratio being determined according to a modulation scheme of the optical transmitter.

2. The optical transmitter as claimed in claim 1 ,
wherein the monitor circuit has a photo detector configured to convert the light output from the optical modulator into an electrical signal, a first monitor configured to detect the direct current component from the electrical signal, and a second monitor configured to detect the pilot component from the electrical signal, and
the processor maintains the ratio between the pilot component and the direct current component at the constant value.

3. The optical transmitter as claimed in claim 1 , wherein
the processor maintains a power level of the direct current component at a constant level and controls a power level of the pilot component so as to be a predetermined level.

4. The optical transmitter as claimed in claim 3 , further comprising:
a light level adjuster configured to adjust an output level of the optical modulator;
wherein the processor adjusts a gain or an attenuation of the light level adjuster such that the power level of the direct current component becomes the constant level.

5. The optical transmitter as claimed in claim 1 ,
wherein the optical modulator is a semiconductor optical modulator.

6. A method of controlling an optical modulator, comprising:
superimposing a pilot signal onto a drive signal for driving an optical modulator with a Mach-Zehnder interferometer or onto a substrate bias voltage applied to the optical modulator;
detecting a ratio between a pilot component and a direct current component contained in a light output from the optical modulator; and
controlling an amplitude of the drive signal or a level of the substrate bias voltage such that the ratio becomes a constant value,
wherein the ratio between the pilot component and the direct current component is maintained constant so as to achieve a predetermined optical phase modulation depth of a main signal output from the optical modulator, the ratio being determined according to a modulation scheme of the optical transmitter.

7. The method as claimed in claim 6 , wherein
a power of the direct current component is controlled to a constant level and a power level of the pilot component is controlled so as to be a predetermined level.

Assignees

• Fujitsu Optical Components Ltd

Inventors

• Nishimoto Hiroshi

Classifications

• H04B2210/075

  using a pilot tone · CPC title

• H04L27/0008

  arrangements for allowing a transmitter or receiver to use more than one type of modulation (negotiating modulation type for two-way transmission paths H04L5/1453) · CPC title

• H04B10/50572

  to control the modulating signal amplitude including amplitude distortion · CPC title

• H04L5/0008

  Wavelet-division · CPC title

• H04B10/5053

  using a parallel, i.e. shunt, combination of modulators · CPC title