Optical phase modulator for high resolution phase measurements

An optical phase modulator for producing two polarized-modulated laser beams from a laser source comprising:

• a first length of a polarization preserving fiber-optic conductor having an input for receiving a polarized laser beam and an output;
• a second length of a polarization preserving fiber-optic conductor having an input and an output;
• an input polarizer for polarizing a laser beam as it passes into the input of the first fiber-optic conductor so that the direction of its polarization forms a 45.degree. angle to an axis X in an orthogonal X-Y coordinates in the cross-section of said first fiber-optic conductor;
• an input optical coupler which connects together the first and second fiber-optic conductors, the input optical coupler having a means for splitting a polarized laser beam propagating into the first fiber-optic conductor input into a first component which further propagates through the first fiber-optic conductor and a second component which further propagates through the second fiber-optic conductor;
• an optical phase shifter connected to said first fiber-optic conductor for phase modulating the said first component;
• an output optical coupler connecting the first and second fiber-optic conductors so that each output of each fiber-optic conductor has a complementary coherent mixture of said first component and said second component with an orthogonal direction of linear polarization, the output of said first fiber-optic conductor producing a first optical beam and the output of the second fiber-optic conductor producing a second optical beam;
• and
• a quarter-wave plate structure for introducing a phase delay, said quarter-wave plate structure having a first window and a second window, said first window being aligned with the output of said first fiber-optic conductor for producing a first polarized-modulated optical beam and the second window being aligned with the second fiber-optic conductor for producing a second polarized modulated beam.