Multiple-wavelength light source and method of controlling oscillation frequencies thereof

A multiple-wavelength light source comprising:

• a plurality of semiconductor laser devices;
• a plurality of optical waveguides for leading laser beams emitted from said semiconductor laser devices to respective desired paths;
• a plurality of diffraction gratings disposed in said optical waveguides, respectively, and serving as external cavities for said semiconductor laser devices, whereby laser beams having respective wavelengths determined by structural details of said diffraction gratings can be output;
• an optical wavelength multiplexer/demultiplexer for multiplexing the laser beams emitted from said semiconductor laser devices into a laser beam;
• an optical branching circuit for branching the laser beam from said optical wavelength multiplexer/demultiplexer into as many laser beams as the number of desired wavelengths;
• a wavelength filter for extracting laser beams of desired wavelengths from the laser beams from said optical branching circuit;
• a photodetector for detecting the laser beams from said wavelength filter and outputting voltages depending on respective detected power levels of the laser beams;
• a plurality of heaters disposed near said diffraction gratings, respectively, for varying temperatures of said diffraction gratings;
• and
• a heater current control circuit for supplying currents to said heaters, respectively, for maximizing the output voltages from said photodetectors.

A multiple-wavelength light source comprising:

• a plurality of semiconductor laser devices;
• a plurality of optical waveguides for leading laser beams emitted from said semiconductor laser devices to respective desired paths;
• a plurality of diffraction gratings disposed in said optical waveguides, respectively, and serving as external vavities for said semiconductor laser devices, whereby laser beams having respective wavelengths determined by structural details of said diffraction gratings can be output;
• a frequency modulating circuit for modulating currents injected into said semiconductor laser devices with different frequencies;
• an optical wavelength multiplexer/demultiplexer for multiplexing the laser beams emitted from said semiconductor laser devices into a laser beam;
• an optical branching circuit for branching the laser beam from said optical wavelength multiplexer/demultiplexer into as many laser beams as the number of desired wavelengths;
• a photodetector for detecting the laser beams from said optical branching circuit and outputting voltages depending on respective detected power levels of the laser beams;
• a plurality of electric filters for extracting modulation frequency components from the output voltages from said photodetectors;
• a plurality of heaters disposed near said diffraction gratings, respectively, for varying temperatures of said diffraction gratings;
• and
• a heater current control circuit for supplying currents to said heaters, respectively, for maximizing the output voltages from said photodetectors.

A method of controlling oscillation frequencies of a multiple-wavelength light source to control oscillation wavelengths thereof, said multiple-wavelength light source comprising:

• a plurality of semiconductor laser devices;
• a plurality of optical waveguides for leading laser beams emitted from said semiconductor laser devices to respective desired paths;
• a plurality of diffraction gratings disposed in said optical waveguides, respectively, and serving as external cavities for said semiconductor laser devices, whereby laser beams having respective wavelengths determined by structural details of said diffraction gratings can be output;
• said method comprising the steps of:
• providing a plurality of heaters disposed near said diffraction gratings, respectively, for varying temperatures of said diffraction gratings;
• multiplexing the laser beams emitted from said semiconductor laser devices into a laser beam;
• demultiplexing the laser beam into a plurality of laser beams having desired wavelengths;
• detecting the demultiplexed laser beams and outputting voltages depending on detected power levels of the laser beams;
• and
• supplying currents to said heaters, respectively, in order to maximize said voltages.

A method of controlling oscillation frequencies of a multiple-wavelength light source to control oscillation wavelengths thereof, said multiple-wavelength light source comprising:

• a plurality of semiconductor laser devices;
• a plurality of optical waveguides for leading laser beams emitted from said semiconductor laser devices to respective desired paths;
• a plurality of diffraction gratings disposed in said optical waveguides, respectively, and serving as external cavities for said semiconductor laser devices, whereby laser beams having respective wavelengths determined by structural details of said diffraction gratings can be output;
• said method comprising the steps of:
• providing a plurality of heaters disposed near said diffraction gratings, respectively, for varying temperatures of said diffraction gratings;
• multiplexing the laser beams emitted from said semiconductor laser devices into a laser beam;
• branching the laser beam into as many laser beams as the number of desired wavelengths;
• extracting laser beams of desired wavelengths from the divided laser beams;
• detecting the extracted laser beams and outputting voltages depending on detected power levels of the laser beams;
• and
• supplying currents to said heaters, respectively, in order to maximize said voltages.

A method of controlling oscillation frequencies of a multiple-wavelength light source to control oscillation wavelengths thereof, said multiple-wavelength light source comprising:

• a plurality of semiconductor laser devices;
• a plurality of optical waveguides for leading laser beams emitted from said semiconductor laser devices to respective desired paths;
• a plurality of diffraction gratings disposed in said optical waveguides, respectively, and serving as external cavities for said semiconductor laser devices, whereby laser beams having respective wavelengths determined by structural details of said diffraction gratings can be output;
• said method comprising the steps of:
• providing a plurality of heaters disposed near said diffraction gratings, respectively, for varying temperatures of said diffraction gratings;
• modulating currents injected into said semiconductor laser devices with different frequencies;
• multiplexing the laser beams emitted from said semiconductor laser devices into a laser beam;
• branching the laser beam into as many laser beams as the number of desired wavelengths;
• outputting signals depending on detected power levels from the branched laser beams;
• extracting modulation frequency components from said signals;
• and
• supplying currents to said heaters, respectively, in order to maximize voltages of the extracted modulation frequency components.