| 摘要 |
An optical transmitter has an optical modulator (1,2,3,4) and a control apparatus (60,7). The optical modulator has a branching section (1) that branches input light (CW) and supplies it to 2xN phase modulating sections (21,22,23,24). In a coupling section (3) light from the output of the 2xN phase modulating sections (2-1,2-2) is coupled to obtain a quadrature amplitude modulated signal light (16QAM) with a 4 N value (N‰¥2). An optical phase adjusting section (5) of the modulator can adjust the optical phase of light from two specific modulation sections (2-1) with respect to light from the remaining modulation sections (2-2).
The control apparatus monitors the power of the quadrature amplitude modulated signal light (16QAM) in a monitoring section (60) and a phase difference controlling section (7) detects time fluctuations in the power of the light signal and applies a bias voltage (DC-P) to the optical phase adjusting section (5) of the modulator in a feedback control loop.
The power ratio of phase modulated lights may be variably adjusted by applying a bias voltage (DC_A) to an optical power adjusting section (5) of the modulator.
The main application of the invention is in optical transmission systems. |
