Sine-cosine optical frequency encoder devices based on optical polarization properties

An optical frequency encoder device for measuring an optical frequency of light, comprising:

• an input port that receives light at an optical frequency to be measured;
• an input optical polarizer in an optical path of the received light to output light in an input optical polarization;
• an optical differential delay (DGD) device oriented to have two orthogonal optical polarization axes of the DGD device to be at 45 degrees with respect to the input optical polarization and located to receive the light from the input optical polarizer to cause a delay between light components in two orthogonal optical polarization axes of the DGD device;
• an optical beam splitter placed to receive light out of the DGD device and to split the received light out of the DGD device into a first beam along a first optical path and a second beam along a different second optical path;
• a first optical polarizer in the first optical path to receive from the first beam to produce a first polarized beam in a first polarization;
• a first optical detector in the first optical path to receive the first polarized beam to produce a first detector signal;
• a second optical polarizer placed in the second optical path of the second beam to produce a second polarized beam at a second polarization that is perpendicular to the first polarization;
• a second optical detector placed in the second optical path to receive the second polarized light beam and to produce a second detector signal;
• a quarter wave plate that is placed in front of one of either the first optical polarizer or the second optical polarizer, wherein fast and slow polarization axes of the quarter wave plate are oriented relative to polarization axes of the DGD device to cause the first detector signal and the second detector signal to be sinusoidal signals with a relative phase difference close to 90 degrees and that vary with a retardation value between two orthogonal polarizations of the DGD device;
• and
• a processor coupled to receive the first and second detector signals and to process the first and second detector signals to determine the optical frequency.

An optical frequency encoder device for measuring an optical frequency of light, comprising:

• an input port that receives light at an optical frequency to be measured;
• an input optical polarization device placed in an optical path of the received light and structured to interact with optical polarization of the received light to output first and second light beams with orthogonal optical polarizations;
• a polarization rotator placed in the first light beam to rotate polarization by 90 degrees;
• an optical differential delay (DGD) device coupled to receive the first and second light beams to cause a delay between the first and second light;
• an input optical polarizer placed between the polarization rotator and the DGD device and structured to have a polarization axis at 45 degrees with respect to two orthogonal optical polarization axes of the DGD device;
• an optical beam splitter placed to receive light out of the DGD device and to split the received light out of the DGD device into a first beam along a first optical path and a second beam along a different second optical path;
• a first optical polarizer in the first optical path to receive from the first beam to produce a first polarized beam in a first polarization;
• a first optical detector in the first optical path to receive the first polarized beam to produce a first detector signal;
• a second optical polarizer placed in the second optical path of the second beam to produce a second polarized beam at a second polarization that is perpendicular to the first polarization;
• a second optical detector placed in the second optical path to receive the second polarized light beam and to produce a second detector signal;
• a quarter wave plate that is placed in front of one of either the first optical polarizer or the second optical polarizer, wherein fast and slow polarization axes of the quarter wave plate are oriented relative to polarization axes of the DGD device to cause the first detector signal and the second detector signal to be sinusoidal signals with a relative phase difference close to 90 degrees and that vary with a retardation value between two orthogonal polarizations of the DGD device;
• and
• a processor coupled to receive the first and second detector signals and to process the first and second detector signals to determine the optical frequency.