Patent ID: 9641257
Date: 2017-05-02
CPC Classifications: G02F,H04B

Claim:
1. An optical transmitter for modulating light from a light source to generate an optical transmission signal with use of a data sequence as an electric signal, the optical transmitter comprising: a mapper that includes a processor programmed with a look-up table having multi-level degree information and corresponding modulation loss and that maps the data sequence to be converted into multi-level data based on the modulation multi-level degree information indicating multi-level degree of the modulation, wherein the multi-level degree is adaptively changed; a D/A converter that converts the multi-level data output from the mapper into an analog signal; an optical modulator, to be driven based on the analog signal output from the D/A converter, that modulates the light from the light source; and a bias controller that includes a processor and that sets control polarity of DC bias control of the optical modulator based on the modulation loss determined from the modulation multi-level degree information, wherein the bias controller sets the control polarity of the DC bias control of the optical modulator to be positive, when the modulation loss is determined from the multi-level degree information to be less than a threshold, and the bias controller sets the control polarity of the DC bias control of the optical modulator to be negative, when the modulation loss is determined from the multi-level degree information to be equal to or larger than the threshold.