Optical signal transmitter

Abstract

An optical signal transmitter includes first and second modulation units, a combiner, and a control unit. The first and second modulation units generate first and second modulated optical signals, respectively. The combiner combines the first and second modulated optical signals to generate a polarization multiplexed optical signal. The control unit controls at least one of the first and second modulation units so that the optical powers of the first and second modulated optical signals become approximately equal to each other.

1 . An optical signal transmitter comprising:
 a first modulation unit configured to generate a first modulated optical signal;   a second modulation unit configured to generate a second modulated optical signal;   a combiner configured to combine the first and second modulated optical signals to generate a polarization multiplexed optical signal; and   a control unit configured to control at least one of the first and second modulation units so that optical powers of the first and second modulated optical signals become approximately equal to each other.   
     
     
         2 . The optical signal transmitter according to  claim 1 , wherein
 the first and second modulation units respectively have a drive circuit generating a drive signal for modulating an optical signal in accordance with transmission data, and   the control unit controls an amplitude of the drive signal of at least one of the first and second modulation units.   
     
     
         3 . The optical signal transmitter according to  claim 1 , wherein
 the first and second modulation units respectively have a modulator using an electro-optic effect, and   the control unit controls a bias of the modulator of at least one of the first and second modulation units.   
     
     
         4 . The optical signal transmitter according to  claim 1 , wherein
 the first and second modulation units respectively have an optical attenuator, and   the control unit controls the optical attenuator of at least one of the first and second modulation units.   
     
     
         5 . The optical signal transmitter according to  claim 1 , further comprising:
 a first monitor unit configured to obtain a first monitor value representing an optical power of the first modulated optical signal that is output from the first modulation unit; and   a second monitor unit configured to obtain a second monitor value representing an optical power of the second modulated optical signal that is output from the second modulation unit, wherein   the control unit controls at least one of the first and second modulation units so that the first and second monitor values become approximately equal to each other.   
     
     
         6 . The optical signal transmitter according to  claim 5 , wherein
 the first and second modulation units respectively have a modulator using an electro-optic effect and a bias control circuit controlling an operating point of the modulator, and   the first and second monitor units are respectively realized using a photodetector for the bias control circuit.   
     
     
         7 . The optical signal transmitter according to  claim 1 , wherein
 the first and second modulation units respectively have a phase modulator and an intensity modulator connected in series with the phase modulator;   each intensity modulator has a intensity modulation driver circuit generating an intensity modulation drive signal for intensity modulation in accordance with a clock signal; and   the control unit controls an amplitude of an intensity modulation drive signal of the intensity modulator of at least one of the first and second modulation units.   
     
     
         8 . An optical signal transmitter comprising:
 a first light source;   a first modulation unit configured to modulate an optical signal generated by the first light source to generate a first modulated optical signal;   a second light source;   a second modulation unit configured to modulate an optical signal generated by the second light source to generate a second modulated optical signal;   a combiner configured to combine the first and second modulated optical signals to generate a polarization multiplexed optical signal; and   a control unit configured to control at least one of the first and second light sources so that optical powers of the first and second modulated optical signals become approximately equal to each other.   
     
     
         9 . An optical signal transmitter comprising:
 a first modulation unit configured to generate a first modulated optical signal;   a second modulation unit configured to generate a second modulated optical signal;   a combiner configured to combine the first and second modulated optical signals to generate a polarization multiplexed optical signal; and   a control unit configured to control at least one of the first and second modulation units, wherein   the first and second modulated optical signals have a same symbol rate and have timings shifted with respect to each other by a predetermined time; and   the control unit controls at least one of the first and second modulation units in accordance with the symbol rate component in the polarization multiplexed optical signal.   
     
     
         10 . The optical signal transmitter according to  claim 9 , wherein
 the control unit controls at least one of the first and second modulation units so as to minimize the symbol rate component in the polarization multiplexed optical signal.   
     
     
         11 . An optical signal transmitter comprising:
 a first light source;   a first modulation unit configured to modulate an optical signal generated by the first light source to generate a first modulated optical signal;   a second light source;   a second modulation unit configured to modulate an optical signal generated by the second light source to generate a second modulated optical signal;   a combiner configured to combine the first and second modulated optical signals to generate a polarization multiplexed optical signal; and   a control unit configured to control at least one of the first and second light sources, wherein   the first and second modulated optical signals have a same symbol rate and have timings shifted with respect to each other by a predetermined time; and   the control unit controls at least one of the first and second light sources in accordance with the symbol rate component in the polarization multiplexed optical signal.   
     
     
         12 . An optical signal transmitter comprising:
 an intensity modulation unit configured to adjust an intensity of first and second wavelength components;   a demultiplexer configured to extract the first and second wavelength components;   a first modulation unit configured to generate a first modulated optical signal from the first wavelength component obtained by the demultiplexer;   a second modulation unit configured to generate a second modulated optical signal from the second wavelength component obtained by the demultiplexer;   a multiplexer configured to multiplex the first and second modulated optical signals to generate a multiplexed optical signal; and   a control unit configured to control the intensity modulation unit so that optical powers of the first and second modulated optical signals become approximately equal to each other.   
     
     
         13 . The optical signal transmitter according to  claim 12 , wherein
 the intensity modulation unit has an LN modulator; and   the control unit controls a bias of the LN modulator.   
     
     
         14 . The optical signal transmitter according to  claim 12 , wherein
 the multiplexer performs polarization multiplexing of the first and second modulated optical signals.   
     
     
         15 . An optical signal transmitter comprising
 a first modulation unit configured to generate a first modulated optical signal;   a second modulation unit configured to generate a second modulated optical signal;   a combiner configured to combine the first and second modulated optical signals to generate a polarization multiplexed optical signal; and   a control unit configured to control at least one of the first and second modulation units in accordance with a received signal quality of the polarization multiplexed optical signal.