Optical transmitter and bias control method for optical modulator
AssigneeFujitsu Optical Components Limited
InventorIori Shirakawa
Life of this patent
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Abstract
An optical transmitter has an optical modulator having Mach-Zehnder interferometers, modulator drivers configured to drive the optical modulator by a drive signal, a low frequency generator configured to generated a low frequency signal that changes a ratio of a driving amplitude with respect to a half-wave voltage of the optical modulator, a photodetector configured to detect a portion of output light of the optical modulator, a detector configured to detect a low frequency component contained in a detected signal from the photodetector using the low frequency signal, and a bias voltage controller configured to control a bias voltage for the optical modulator such that the detected low frequency component becomes the maximum and in-phase with the superimposed low frequency signal.
Claims9
An optical transmitter comprising:
- an optical modulator having Mach-Zehnder interferometers;
- modulator drivers configured to drive the optical modulator;
- a low frequency generator configured to generate a low frequency signal that changes a ratio of a driving amplitude over a half-wave voltage of the optical modulator;
- a photodetector configured to detect a portion of output light of the optical modulator;
- a detector configured to detect a low frequency component contained in a detected signal from the photodetector using the low frequency signal;
- and
- a bias voltage controller configured to control a bias voltage for the optical modulator such that the detected low frequency component becomes the maximum and in-phase with the low frequency signal;
- an amplitude detector configured to detect an amplitude level of output signals from the modulator drivers;
- and
- an amplitude controller configured to control a magnitude of the low frequency signal to be superimposed on a drive signal for driving the optical modulator based upon a detection result of the amplitude detector.
A bias control method for an optical modulator, comprising:
- when driving an optical modulator having Mach-Zehnder interferometers, supplying a low frequency signal for changing a ratio of a driving amplitude over a half-wave voltage of the optical modulator;
- detecting a low frequency component contained in an output of the optical modulator using the low frequency signal;
- and
- controlling a bias voltage for the optical modulator such that the low frequency component becomes the maximum and in-phase with the low frequency signal;
- detecting an amplitude level of output signals from the modulator drivers;
- and
- controlling a magnitude of the low frequency signal to be superimposed on a drive signal for driving the optical modulator based upon a detection result of the amplitude level of the output signals from the modulator drivers.
Dependencies are inferred from the claim text.