Optical transmitter and bias control method for optical modulator
First Claim
1. 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.
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Accused Products
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.
10 Citations
9 Claims
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1. An optical transmitter comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A bias control method for an optical modulator, comprising:
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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.
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Specification