High performance polarization controller and polarization sensor

An apparatus for measuring the state of polarization of a light beam comprising in optical series

• a first beamsplitter to produce a first sample beam and to transmit the first remaining light beam,
• a retarder means to transform state of polarization of the first remaining light beam,
• a second beamsplitter to produce from the transformed light beam a second sample beam and to transmit the second remaining light beam, and
• a first detector to measure the intensity of the first sample beam, and
• a second detector to measure the intensity of the second sample beam,
• wherein the first and second beamsplitters and the retarder means are disposed such that the intensity of the first sample beam corresponds to one of the Poincare latitude and longitude, and the intensity of the second sample beam corresponds to the other one of the Poincare latitude and longitude.

An apparatus for measuring the state of polarization of a light beam comprising in optical series

• a first beamsplitter to produce a first sample beam and transmit the first remaining light beam,
• wherein the first beamsplitter is arranged to preferentially sample light having a first state of polarization and transmits at least 80 percent of the light having the first state of polarization and transmits substantially all of light polarized orthogonally to the first state of polarization,
• a second beamsplitter to produce from the first remaining beam a second sample beam and to transmit the second remaining light beam,
• wherein the second beamsplitter is arranged to preferentially sample light having a second state of polarization and transmits at least 80 percent of the light having the second state of polarization and transmits substantially all of the light polarized orthogonally to the second state of polarization,
• a first photodetector to measure the intensity of the first sample beam,
• a second photodetector to measure the intensity of the second sample beam,
• wherein the first and second beamsplitters are disposed such that the signal from the first photodetector varies linearly and monotonically as a function of the state of polarization of the input light along a first arc on the Poincare sphere and the signal from the second photodetector varies linearly and monotonically as a function of the state of polarization of the input light along a second arc on the Poincare sphere, and the first and second arcs are substantially orthogonal.

A method of sensing the state of polarization of a light beam comprising separating from the light beam a first sample beam and transmitting the first remaining light beam,

• separating from the first remaining light beam a second sample beam and transmitting the second remaining light beam, and
• measuring the intensity of the first sample beam, and
• measuring the intensity of the second sample beam,
• wherein the separation of the first sample beam is performed to preferentially sample light having a first linear polarization and the separation of the second sample beam is performed to preferentially sample light having a second linear polarization,
• wherein the first and second separation each transmit in excess of 80 percent of the light having the polarization that is preferentially sampled, and each separation transmits substantially all of the light having the orthogonal polarization, and
• wherein the first and second separations are performed such that the intensity of the first sample beam varies linearly and monotonically as a function of the state of polarization of the light beam along a first arc on the Poincare sphere and the intensity of the second sample beam varies linearly and monotonically as a function of the state of polarization of the light beam along a second arc on the Poincare sphere and the two arcs are substantially orthogonal.

Apparatus to control the state of polarization of a beam of light, comprising a polarization sensor and a polarization modulator,

• wherein the polarization modulator transforms the state of polarization of light passing therethrough and comprises a first adjustment means that adjusts the state of polarization of light along a first adjustment arc on the Poincare sphere according to a first control signal, and a second adjustment means that adjusts the state of polarization of light along a second adjustment arc on the Poincare sphere according to a second control signal,
• wherein the polarization sensor comprises in optical series a first beamsplitter to produce a first sample beam and transmit the first remaining light beam,
• a second beamsplitter to produce from the first remaining beam a second sample beam and to transmit the second remaining light beam,
• a first photodetector to measure the intensity of the first sample beam,
• a second photodetector to measure the intensity of the second sample beam,
• wherein the first and second beamsplitters are disposed such that the measured intensity at the first photodetector varies linearly and monotonically as a function of the state of polarization of the input light along a first sensing arc on the Poincare sphere and the measured intensity at the second photodetector varies linearly and monotonically as a function of the state of polarization of the input light along a second sensing arc on the Poincare sphere which is substantially orthogonal to the first sensing arc, and
• circuitry that derives the first and second control signals from the measured intensities at the first and second photodetectors.

A method of controlling the state of polarization of a light beam comprising the steps of modulating the polarization to create a transformed beam and measuring the state of polarization of one of the light beam and the transformed light beam;

• where the modulation is achieved by
• applying a first polarization transformation that alters the state of polarization along a first transformation arc on the Poincare sphere and then
• applying a second polarization transformation that alters the state of polarization along a second transformation arc on the Poincare sphere;
• where the measurement of state of polarization is achieved by
• separating from the beam to be measured a first sample beam and transmitting the first remaining light beam,
• separating from the first remaining light beam a second sample beam and transmitting the second remaining light beam,
• measuring the intensity of the first sample beam, and measuring the intensity of the second sample beam;
• and the state of polarization is controlled by
• adjusting the first and second polarization transformations according to the measurement of the intensity of the first and second sample beams.

A method of sensing the state of polarization of a light beam comprising separating from the light beam a first sample beam and transmitting the first remaining light beam,

• separating from the first remaining light beam a second sample beam and transmitting the second remaining light beam, and
• measuring the intensity of the first sample beam, and
• measuring the intensity of the second sample beam,
• wherein the separation and measurement of the first sample beam is performed to preferentially measure light having a first linear polarization and the separation and measurement of the second sample beam is performed to preferentially measure light having a second linear polarization,
• wherein the separation of the first and second sample beams is performed such that the intensity of the first sample beam varies linearly and monotonically as a function of the state of polarization of the light beam along a first arc on the Poincare sphere and the intensity of the second sample beam varies linearly and monotonically as a function of the state of polarization of the light beam along a second arc on the Poincare sphere and the two arcs are substantially orthogonal.