Variable lightwave functional circuit and variable lightwave functional apparatus

A variable lightwave functional apparatus comprising:

• an acousto-optical modulator for outputting wavelength multiplexed light containing a plurality of pulses having a first wavelength interval;
• a coupler arranged at an output of said acousto-optical modulator;
• a polarization branching/coupling device having a first port to a third port, for branching the output form said coupler, which is entered from said first port into the polarization branching/coupling device, to both said second port and said third port;
• an optical amplifier connected to said second port of said polarization branching/coupling device;
• and
• a variable lightwave functional circuit arranged between said second port of said polarization branching/coupling device and said optical amplifier;
• wherein:
• multi-wavelength oscillation light is outputted from said coupler by laser light from said acousto-optical modulator, and
• said variable lightwave functional circuit comprising:
• an applying unit for applying lateral pressure;
• a polarization-maintaining optical fiber having a polarization axis, for inducing a polarization mode coupling by applying the lateral pressure to a predetermined position by said applying unit;
• and
• a branching/coupling device having a first port to a fourth port, for branching laser light inputted from the first port to both said second port and said third port, and also for projecting laser light inputted from said second port to the fourth port;
• wherein:
• one end of said polarization-maintaining optical fiber is connected to one of said second port and said third port in such a manner that the polarization axis is inclined at a predetermined angle to an axial direction parallel to a branching plane of said branching/coupling device;
• the other end of said polarization-maintaining optical fiber is connected to the other of said second port and said third port in such a manner that the polarization axis is made coincident with said axial direction parallel to said branching plane of said branching/coupling device;
• laser light is entered from the first port of said branching/coupling device via the third port to said polarization-maintaining optical fiber;
• said polarization-maintaining optical fiber changes a characteristic related to either a transmission wavelength or a repetition frequency of a pulse stream by the induced polarization mode coupling in response to either a single condition of a position, a quantity, and a magnitude of lateral pressure applied by said applying unit, or plural conditions thereof and said polarization-maintaining optical fiber projects the laser light whose characteristic has been changed from said fourth port of said branching/coupling device.