Laser with phase controlling region and method for driving the same

A method for driving a laser, said method comprising the steps of:

• (A) preparing a laser including:
• (1) a first region with a first waveguide, said first waveguide including a first diffraction grating;
• (2) a second region with a second waveguide, said second waveguide including a second diffraction grating;
• and
• (3) a phase controlling region with a third waveguide, said phase controlling region including control means for controlling an effective refractive index of said third waveguide, wherein said phase controlling region, said second region, and said first region are serially coupled in this order, and are constructed such that a coupling coefficient of the diffraction grating of said second region adjacent to said phase controlling region is smaller than a coupling coefficient of the diffraction grating of said first region, and said first and second diffraction gratings have a common value of pitch,
• wherein a reflective layer is provided on one end of the phase controlling region;
• and
• (B) changing a current injected into or a reverse voltage applied to the phase controlling region to change at least one of a polarization mode and a wavelength of light output from the laser.

A light transmitter comprising:

• (A) a laser including:
• (1) a first region with a first waveguide, said first waveguide including a first diffraction grating;
• (2) a second region with a second waveguide, said second waveguide including a second diffraction grating;
• and
• (3) a phase controlling region with a third waveguide, said phase controlling region including control means for controlling an effective refractive index of said third waveguide, wherein said phase controlling region, said second region, and said first region are serially coupled in this order, and are constructed such that a coupling coefficient of the diffraction grating of said second region adjacent to said phase controlling region is smaller than a coupling coefficient of the diffraction grating of said first region, and said first and second diffraction gratings have a common value of pitch,
• wherein a reflective layer is provided on one end of said phase controlling region;
• (B) control means for controlling light output from said laser in accordance with a transmission signal;
• and
• (C) a mode selector for selecting a component of a desired mode from the light output from said laser.

An optical communication system for communicating over a light transmission line that transmits a signal from a transmitter side to a receiver side, said system comprising:

• (A) a light transmitter for transmitting light of a signal through the light transmission line including:
• (1) a laser including:
• (a) a first region with a first waveguide, said first waveguide including a first diffraction grating;
• (b) a second region with a second waveguide, said second waveguide including a second diffraction grating;
• and
• (c) a phase controlling region with a third waveguide, said phase controlling region including control means for controlling an effective refractive index of said third waveguide, wherein said phase controlling region, said second region, and said first region are serially coupled in this order, and are constructed such that a coupling coefficient of the diffraction grating of said second region adjacent to said phase controlling region is smaller than a coupling coefficient of the diffraction grating of said first region, and said first and second diffraction gratings have a common value of pitch,
• wherein a reflective layer is provided on one end of the phase controlling region;
• (2) control means for controlling light output from said laser in accordance with a transmission signal;
• and
• (3) a mode selector for selecting a component of a desired mode from the light output from said laser;
• and
• (B) a receiver for receiving and detecting an intensity-modulated signal transmitted from the laser through the light transmission line.