Light frequency stabilizer

A frequency-stabilized laser source comprising,

• a laser with a frequency-control port, an operating frequency of the laser being variable in response to a frequency control signal applied to the frequency control port;
• a birefringent element having a longitudinal axis, the birefringent element having an optical axis oriented to retard phase of polarized light propagating through the element substantially parallel to the longitudinal axis by a phase retardation amount proportional to a frequency of the polarized light;
• a polarizer disposed to receive phase-retarded light from the birefringent element, the polarizer transmitting a portion of the phase-retarded light, a magnitude of the transmitted portion being determined by the phase retardation amount;
• a first optical detector disposed to detect the transmitted portion of light, the first optical detector generating a first signal in response to the transmitted portion detected;
• and
• a feedback circuit disposed to receive the first signal and provide the frequency control signal to the laser frequency control port.

An optical communications system, comprising:

• a transmitting unit including a light frequency stabilization unit disposed to stabilize frequency of at least one optical signal, the frequency stabilization unit including
• i) a birefringent element having a longitudinal axis, the birefringent element having an optical axis oriented to retard phase of polarized light propagating through the element substantially parallel to the longitudinal axis by a phase retardation amount proportional to a frequency of the polarized light,
• ii) a polarizer disposed to receive phase-retarded light from the birefringent element, the polarizer transmitting a portion of the phase-retarded light, a magnitude of the transmitted portion being determined by the phase retardation amount,
• iii) a first optical detector disposed to detect the transmitted portion of light, the first optical detector generating a first signal in response to the transmitted portion detected, and
• iv) an electronic error circuit that generates a frequency stabilization signal in response to the first signal;
• a receiving unit;
• and an optical transport system coupled to carry optical signals from the transmitting unit to the receiving unit.

A method for generating a light frequency stabilization signal, comprising:

• retarding polarized light, using a birefringent element, by an amount that is proportional to a frequency of the polarized light;
• analyzing the phase-retarded light with a polarization analyzer to produce an analyzed light beam;
• measuring power of the analyzed light beam with a first detector to generate a first signal indicative of light frequency;
• generating the light frequency stabilization signal in response to the first signal.

A method for stabilizing the frequency of a laser, comprising:

• retarding phase of polarized light, generated by the laser, by an amount that is proportional to a light frequency;
• analyzing the phase-retarded light with a polarizer to produce an analyzed light beam;
• measuring power of the analyzed light beam with a first detector to generate a first signal indicative of laser frequency
• generating a laser feedback signal in response to the first signal;
• and adjusting frequency of the laser according to the feedback signal so as to stabilize the frequency of the laser.