Variable wavelength light source using a laser, wavelength control method, optical communication system and optical communication method

A method of driving a variable wavelength light source comprising (a) a semiconductor laser comprising a substrate, a plurality of semiconductor layers laminated on the substrate, the plurality of semiconductor layers including an active layer and constituting a laser resonator, a diffraction grating periodically formed along a resonance direction of the laser resonator, and a plurality of electrodes for injecting current into the semiconductor layers, the plurality of electrodes being arranged in tandem in the resonance direction, wherein the semiconductor laser selectively outputs either one of light of a first polarization mode having a predetermined wavelength and polarized in a predetermined direction and light of a second polarization mode having a wavelength different from that of the first polarization mode light and polarized in a direction orthogonal to the predetermined direction in correspondence to an amount of current injected from at least one of the plurality of electrodes, and first and second electrodes arranged in tandem in the resonance direction, and (b) a light selecting element for switchably selecting either one of the first and second polarization mode light which are outputted from the semiconductor laser, said method comprising the steps of:

• injecting current, according to a signal in which a modulation signal is superimposed on a bias signal, into the semiconductor layers from the second electrode, and thereby outputting light modulated in accordance with the modulation signal between the first and second polarization modes from the semiconductor laser;
• and
• varying an amount of current, according to the bias signal, to be injected into the semiconductor layers from the second electrode, and thereby varying the respective wavelengths of the first and second polarization mode light outputted from the semiconductor laser.

A method of driving a variable wavelength light source comprising (a) a semiconductor laser comprising a substrate, a plurality of semiconductor layers laminated on the substrate, the plurality of semiconductor layers including an active layer and constituting a laser resonator, a diffraction grating periodically formed along a resonance direction of the laser resonator, and a plurality of electrodes for injecting current into the semiconductor layers, the plurality of electrodes being arranged in tandem in the resonance direction, wherein the semiconductor laser selectively outputs either one of light of a first polarization mode having a predetermined wavelength and polarized in a predetermined direction and light of a second polarization mode having a wavelength different from that of the first polarization mode light and polarized in a direction orthogonal to the predetermined direction in correspondence to an amount of current injected from at least one of the plurality of electrodes and (b) a light selecting element for switchably selecting either one of the first and second polarization mode light which are outputted from the semiconductor laser, said method comprising the steps of:

• selecting either one of the first and second polarization mode light with the light selecting element;
• and
• in correspondence to the polarization mode of light selected by the light selecting element selected in said selecting step, driving the semiconductor laser in accordance with either one of a modulation signal having the same phase as an information signal and the modulation signal having a phase opposite to that of the information signal.

An optical communication system comprising:

• a variable wavelength light source comprising:
• (a) a semiconductor laser comprising:
• a substrate,
• a plurality of semiconductor layers laminated on the substrate, said plurality of semiconductor layers including an active layer and constituting a laser resonator,
• a diffraction grating periodically formed along a resonance direction of said laser resonator, and
• a plurality of electrodes for injecting current into said semiconductor layers, said plurality of electrodes being arranged in tandem in the resonance direction,
• wherein said semiconductor laser selectively outputs either one of light of a first polarization mode having a predetermined wavelength and polarized in a predetermined direction and light of a second polarization mode having a wavelength different from that of said first polarization mode light and polarized in a direction orthogonal to said predetermined direction in correspondence to an amount of current injected from at least one of said plurality of electrodes;
• and
• (b) a light selecting element for switchably selecting either one of said first and second polarization mode light which are outputted from said semiconductor laser;
• an optical transmitter for transmitting the light selected by said light selecting element as an optical signal;
• and
• an optical receiver for receiving the optical signal transmitted from said optical transmitter.