Optical transmitter and optical transmission method

Patent metadata

Field	Value
Publication number	US-2020033642-A1
Application number	US-201816493363-A
Country	US
Kind code	A1
Filing date	Mar 15, 2018
Priority date	Mar 28, 2017
Publication date	Jan 30, 2020
Grant date	—

Abstract

To clarify the characteristics of an optical modulator having output asymmetry due to a non-linear effect, an optical transmitter includes: a light source which outputs light of a predetermined wavelength; a modulator which modulates the light output from the light source using a modulation signal; a modulator drive unit which outputs a modulation signal to the modulator; a control unit which outputs a low-frequency signal to the modulator and a modulator driver, amplitude-modulates the modulation signal using the low-frequency signal, intensity-modulates the amplitude-modulated modulation signal using the low-frequency signal, and receives a monitor signal including a low-frequency signal component; and a detection unit which extracts a low-frequency component of an optical signal output from the modulator, and outputs the low-frequency component as a monitor signal.

First claim

What is claimed is:

1 . An optical transmitter comprising:
a light source configured to output light of a predetermined wavelength; a modulator configured to modulate the light outputted from the light source by a modulation signal; a modulator driver configured to output the modulation signal to the modulator; a controller configured to output a low-frequency signal to the modulator and the modulator driver, amplitude-modulate the modulation signal with the low-frequency signal, intensity-modulate the amplitude-modulated modulation signal with the low-frequency signal, and receive a monitor signal including a component of the low-frequency signal; and a detector configured to extract a low-frequency component of an optical signal outputted from the modulator and output the extracted low-frequency component as the monitor signal.

2 . The optical transmitter according to claim 1 , wherein
the controller performs the amplitude modulation and the intensity modulation such that the low-frequency signal is superimposed only on one of an envelope on a positive side and an envelope on a negative side of the amplitude-modulated and intensity-modulated modulation signal.

3 . The optical transmitter according to claim 1 , wherein
the controller
performs first amplitude modulation and intensity modulation such that the low-frequency component is superimposed only on the envelope on the positive side of the amplitude-modulated and intensity-modulated modulation signal, and
performs second amplitude modulation and intensity modulation such that the low-frequency component is superimposed only on the envelope on the negative side of the amplitude-modulated and intensity-modulated modulation signal.

4 . The optical transmitter according to claim 1 , wherein
the controller detects transfer characteristics of the modulator, based on the monitor signal.

5 . The optical transmitter according to claim 4 , wherein
the controller has a function of switching at least one of a wavelength and output power of the light source, and detects the transfer characteristics of the modulator with execution of the switching.

6 . The optical transmitter according to claim 4 , wherein
the controller sets driving conditions of the modulator, based on the detected transfer characteristics.

7 . The optical transmitter according to claim 6 , wherein
the controller sets the driving conditions, based on at least one of a bias voltage applied to the modulator, a driving amplitude of the modulation signal, and predistortion of the modulation signal.

8 . The optical transmitter according to claim 1 , wherein the modulator comprises:
a terminator configured to terminate the modulation signal; an optical modulator configured to modulate the light outputted from the light source, based on the terminated modulation signal; a splitter configured to split a part of output of the optical modulator; and a converter configured to convert the split output light into an electrical signal and output the electrical signal to the detector.

9 . An optical transmission method comprising:
outputting light of a predetermined wavelength; modulating, by a modulator, the light outputted from the light source by a modulation signal; outputting the modulation signal to the modulator; amplitude-modulating the modulation signal with the low-frequency signal; intensity-modulating the amplitude-modulated modulation signal with the low-frequency signal; outputting, as a monitor signal, a low-frequency component of an optical signal outputted from the modulator; and detecting transfer characteristics of the modulator, based on the monitor signal.

10 . The optical transmission method according to claim 9 , wherein
the amplitude modulation and the intensity modulation are performed such that the low-frequency signal is superimposed only on one of an envelope on a positive side and an envelope on a negative side of the amplitude-modulated and intensity-modulated modulation signal.

11 . The optical transmitter according to claim 2 , wherein
the controller
performs first amplitude modulation and intensity modulation such that the low-frequency component is superimposed only on the envelope on the positive side of the amplitude-modulated and intensity-modulated modulation signal, and
performs second amplitude modulation and intensity modulation such that the low-frequency component is superimposed only on the envelope on the negative side of the amplitude-modulated and intensity-modulated modulation signal.

12 . The optical transmitter according to claim 2 , wherein
the controller detects transfer characteristics of the modulator, based on the monitor signal.

13 . The optical transmitter according to claim 3 , wherein
the controller detects transfer characteristics of the modulator, based on the monitor signal.

14 . The optical transmitter according to claim 11 , wherein
the controller detects transfer characteristics of the modulator, based on the monitor signal.

15 . The optical transmitter according to claim 12 , wherein
the controller has a function of switching at least one of a wavelength and output power of the light source, and detects the transfer characteristics of the modulator with execution of the switching.

16 . The optical transmitter according to claim 13 , wherein
the controller has a function of switching at least one of a wavelength and output power of the light source, and detects the transfer characteristics of the modulator with execution of the switching.

17 . The optical transmitter according to claim 2 , wherein the modulator comprises:
a terminator configured to terminate the modulation signal; an optical modulator configured to modulate the light outputted from the light source, based on the terminated modulation signal; a splitter configured to split a part of output of the optical modulator; and a converter configured to convert the split output light into an electrical signal and outputting the electrical signal to the detector.

18 . The optical transmitter according to claim 3 , wherein the modulator comprises:
a terminator configured to terminate the modulation signal; an optical modulator configured to modulate the light outputted from the light source, based on the terminated modulation signal; a splitter configured to split a part of output of the optical modulator; and a converter configured to convert the split output light into an electrical signal and outputting the electrical signal to the detector.

19 . The optical transmitter according to claim 4 , wherein the modulator comprises:
a terminator configured to terminate the modulation signal; an optical modulator configured to modulate the light outputted from the light source, based on the terminated modulation signal; a splitter configured to split a part of output of the optical modulator; and a converter configured to convert the split output light into an electrical signal and outputting the electrical signal to the detector.

20 . The optical transmitter according to claim 19 , wherein
the controller has a function of switching at least one of a wavelength and output power of the light source, and detects the transfer characteristics of the modulator with execution of the switching.

Assignees

• Nec Corp

Inventors

• Komatsu Hirokazu

Classifications

• H04B10/50572

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

• H04B10/5561

  Digital phase modulation · CPC title

• G02F1/0123 Primary

  Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops · CPC title

• H04B10/54

  Intensity modulation · CPC title

• H04B10/58

  Compensation for non-linear transmitter output · CPC title