Apparatus and method for controlling polarization of an optical signal

A method of controlling the state of polarization of an optical signal, the method comprising:

• receiving an optical signal having an input state of polarization;
• separating the optical signal into a first principal mode of polarization and a second principal mode of polarization;
• and
• introducing at least three stages of phase shift between the first and second modes of polarization to align the first and second modes of polarization with a desired output state of polarization;
• wherein each of the at least three stages of phase shift are introduced by one of at least three phase shift stages, at least one phase shift stage sharing a beam splitter with at least one other phase shift stage, wherein the beam splitter that is shaped comprises a partially transmitting mirror.

A polarization controller, comprising

• a polarization beam splitter operable to separate an optical signal into a first and a second principal mode of polarization;
• and
• at least two stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters;
• wherein at least one of the phase shifters comprises a micro-electro-optic system (MEMS) device comprising a moveable mirror layer operable to receive one of the principal modes of polarization and to change its position to contribute to a relative phase difference between the first and second principal modes.

A method of controlling the state of polarization of an optical signal, the method comprising:

• receiving an optical signal having an input state of polarization;
• separating the optical signal into a first principal mode of polarization and a second principal mode of polarization;
• and
• introducing at least two stages of phase shift between the first and second modes of polarization to align the first and second modes of polarization with a desired output state of polarization;
• wherein each of the at least two stages of phase shift are introduced by one of at least two phase shift stages, at least one phase shift stage sharing a beam splitter with at least one other phase shift stage, at least one phase shift stage comprising a micro-electro-optic system (MEMS) device operable to change its position to alter the phase of the fist principal mode relative to the phase of the second principal mode.

A polarization controller, comprising:

• at least two stages of phase shifters each operable to receive a first and a second principal mode of polarization of an optical signal, and to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters;
• wherein each of the phase shift stages comprises a micro-electro-mechanical system (MEMS) device including a moveable mirror layer operable to change its position to contribute to a relative phase shift between the first and second modes, wherein the MEMS device comprises:
• an inner conductive layer;
• a conductive moveable mirror layer disposed outwardly from the inner conductive layer and forming a space between the moveable mirror layer and the inner conductive layer;
• wherein the moveable mirror layer is operable to move relative to the inner conductive layer in response to a voltage difference between the moveable mirror layer and the inner conductive layer.

An endlessly rotatable polarization controller, comprising:

• a first polarization beam splitter operable to receive an input optical signal having an input state of polarization and to separate the signal into a first and a second principal mode of polarization;
• and
• at least three stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters, wherein the beam splitter that is shared comprises a partially transmitting mirror, the at least three stages of phase shifters comprising a first stage coupled to the first polarization beam splitter and a last stage coupled to a second polarization beam splitter;
• wherein the second polarization beam splitter is operable to receive phase shifted copies of the first and second principal modes, and to align the phase shifted copies of the principal modes to an output state of polarization.

A polarization mode dispersion (PMD) compensator, comprising:

• a first polarization beam splitter operable to receive an input optical signal and to separate the signal into a first and a second principal mode of polarization;
• and
• at least three stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one, other of the phase shifters, wherein the beam splitter that is shared comprises a partially transmitting mirror, the at least three stages of phase shifters comprising a first stage coupled to the first polarization beam splitter and a last stage coupled to a second polarization beam splitter;
• wherein the second polarization beam splitter is operable to receive phase shifted copies of the first and second principal modes, and to align the phase shifted copies of the principal modes to principal axes of a fixed delay element coupled to the second polarization beam splitter.

A method of mitigating polarization mode dispersion, comprising:

• separating an optical sigal into a first principal mode of polarization and a second principal mode of polarization, one of the first and second modes comprising a leading mode and one of the first and second modes comprising a lagging mode;
• introducing at least three stages of phase shift between the leading and lagging modes of polarization to align the leading mode with a slow principal axis of a fixed delay element and the lagging mode with a fast principal axis of the fixed delay element;
• and
• communicating the leading mode parallel to the slow axis and the lagging mode parallel to the fast axis;
• wherein each of the at least three stages of phase shift are introduced by one of at least three phase shift stages, at least one phase shift stage sharing a beam splitter with at least one other phase shift stage, wherein the beam splitter that is shared comprises a partially transmitting mirror.

A polarization mode dispersion compensator, comprising:

• a variable delay line;
• and
• a polarization controller coupled to the variable delay line and operable to receive an optical signal having an input state of polarization and to align an output state of polarization of the optical signal to the variable delay line, the polarization controller comprising:
• a polarization beam splitter operable to separate the optical signal into a first and a second principal mode of polarization;
• and
• at least two stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters;
• wherein at least one of the phase shifters comprises a micro-electro-optic system (MEMS) device comprising a moveable mirror layer operable to receive one of the principal modes of polarization and to change its position to contribute to relative phase difference between the first and second principal modes.

A method of mitigating polarization mode dispersion, comprising:

• separating an optical signal into a first principal mode of polarization and a second principal mode of polarization, one of the first and second modes comprising a leading mode and one of the first and second modes comprising a lagging mode;
• introducing at least two stages of phase shift between the leading and lagging modes of polarization to align the leading mode with a slow principal polarization axis of a variable delay element and the lagging mode with a fast principal polarization axis of the variable delay element;
• and
• communicating the leading mode parallel to the slow axis and the lagging mode parallel to the fast axis;
• wherein each of the at least two stages of phase shift are introduced by one of the at least two phase shift stages, at least one phase shift stage sharing a beam splitter with at least one other phase shift stage, at least one phase shift stage comprising a micro-electro-optic system (MEMS) device operable to change its position to alter the phase of the first principal mode relative to the phase of the second principal mode.

A variable delay line, comprising:

• a first polarization maintaining fiber;
• a first polarization beam splitter coupled to the first polarization maintaining fiber, the first polarization beam splitter operable to receive an input optical signal and to separate the signal into a first and a second principal mode of polarization;
• and
• at least three stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters, wherein the beam splitter that is shared comprises a partially transmitting mirror, the at least three stages of phase shifters comprising a first stage coupled to the first polarization beam splitter and a last stage coupled to a second polarization beam splitter;
• wherein the second polarization beam splitter is operable to receive phase shifted copies of the first and second principal modes, and to align the phase shifted copies of the principal modes to principal axes of a second polarization maintaining fiber coupled to the second polarization beam splitter.

A method of providing variable delay between modes of polarization in an optical signal, comprising

• receiving an optical signal from a first polarization maintaining fiber,
• separating the optical signal into a first principal mode of polarization and a second principal mode of polarization, one of the first and second modes comprising a leading mode and one of the first and second modes comprising a lagging mode;
• introducing at least three stages of phase shift between the leading and lagging modes of polarization to align the leading mode with a slow principal axis of a second polarization maintaining fiber and the lagging mode with a fast principal axis of the second polarization maintaining fiber;
• and
• communicating the leading mode parallel to the slow axis and the lagging mode parallel to the fast axis;
• wherein each of the at least three stages of phase shift are introduced by one of at least three phase shift stages, at least one phase shift stage sharing a beam splitter with at least one other phase shift stage, wherein the beam splitter that is shared comprises a partially transmitting mirror.

A system operable to facilitate polarization multiplexing of multiple signal wavelengths, the system comprising:

• a wavelength division demultiplexer operable to receive an optical signal carrying substantially orthogonally polarized neighboring wavelength signals and to substantially separate the neighboring wavelength signals from one another;
• and
• an array of phase shift based polarization controllers coupled to the wavelength division demultiplexer, each operable to receive one wavelength and adjust the state of polarization of the wavelength to facilitate separation of the wavelength from its neighboring wavelengths;
• wherein each of the phase shift-based polarization controllers comprises:
• a first polarization beam splitter operable to receive an input wavelength signal having an input state of polarization and to separate the signal into a fist and a second principal mode of polarization;
• and
• at least three stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters, wherein the beam splitter that is shared comprises a partially transmitting mirror, the at least three stages of phase shifters comprising a first stage coupled to the first polarization beam splitter and a last stage coupled to a second polarization beam splitter;
• wherein the second polarization beam splitter is operable to receive phase shifted copies of the first and second principal modes, and to align the phase shifted copies of the principal modes to an output state of polarization.

A system operable to facilitate coherent optical communication, the system comprising:

• a local oscillator operable to generate a local optical signal;
• an optical mixer operable to receive an incident optical signal and the local optical signal and to combine the incident optical signal with the local optical signal to generate a combined signal;
• and
• a polarization controller operable to receive either the local optical signal or the incident optical signal and to adjust the state of polarization of the received signal to ensure that the received signal is not polarized orthogonally to the other signal when the signals are combined at the optical mixer;
• wherein the polarization controller comprises:
• a first polarization beam splitter operable to receive an input wavelength signal having an input state of polarization and to separate the signal into a first and a second principal mode of polarization;
• and
• at least three stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters, wherein the beam splitter that is shared comprises a partially transmitting mirror, the at least three stages of phase shifters comprising a first stage coupled to the first polarization beam splitter and a last stage coupled to a second polarization beam splitter;
• wherein the second polarization beam splitter is operable to receive phase shifted copies of the first and second principal modes, and to align the phase shifted copies of the principal modes to an output state of polarization.

A polarization controller, comprising:

• a first polarization beam splitter operable to receive an input optical signal having an input state of polarization and to separate the signal into a first and a second principal mode of polarization;
• and
• at least three stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters, the at least three stages of phase shifters comprising a first stage coupled to the first polarization beam splitter and a last stage coupled to a second polarization beam splitter, at least one phase shifter comprising:
• a plurality of mirrors, each mirror operable to receive one of the principle modes of polarization and to reflect those signals toward an output for combination, at least one of the mirrors comprising a Micro-electro-optic system (MEMS) device including a plurality of adjacent mirror strips operable to receive one of the principal states of polarization, the mirror strips further operable to change their position substantially in unison in a substantially piston-like motion to create a phase shift between the first and second modes of polarization;
• and
• wherein the second polarization beam splitter is operable to receive phase shifted copies of the first and second principal modes, and to align the phase shifted copies of the principal modes to an output state of polarization.

A method of controlling the state of polarization of an optical signal, the method comprising:

• receiving an optical signal having an input state of polarization;
• separating the optical signal into a first principal mode of polarization and a second principal mode of polarization;
• and
• introducing at least three stages of phase shift between the first and second modes of polarization to align the first and second modes of polarization with a desired output state of polarization;
• wherein each of the at least three stages of phase shift are introduced by one of at least three phase shift stages, at least one phase shift stage sharing a beam splitter with at least one other phase shift stage, at least one phase shifter comprising:
• a plurality of mirrors, each mirror operable to receive one of the principle modes of polarization and to reflect those signals toward an output for combination, at least one of the mirrors comprising a Micro-electro-optic system (MEMS) device including a plurality of adjacent mirror strips operable to receive one of the principal states of polarization, the mirror strips further operable to change their position substantially in unison in a substantially piston-like motion to create a phase shift between the first and second modes of polarization.

A polarization mode dispersion (PMD) compensator, comprising:

• a first polarization beam splitter operable to receive an input optical signal and to separate the signal into a first and a second principal mode of polarization;
• and
• at least three stages of phase shifters each operable to introduce a phase shift between the first and second principal modes, at least one phase shifter comprising a beam splitter that is shared with at least one other of the phase shifters, the at least three stages of phase shifters comprising a first stage coupled to the first polarization beam splitter and a last stage coupled to a second polarization beam splitter, at least one phase shifter comprising:
• a plurality of mirrors, each mirror operable to receive one of the principle modes of polarization and to reflect those signals toward an output for combination, at least one of the mirrors comprising a Micro-electro-optic system (MEMS) device including a plurality of adjacent mirror strips operable to receive one of the principal states of polarization, the mirror strips further operable to change their position substantially in unison in a substantially piston-like motion to create a phase shift between the first and second modes of polarization;
• and
• wherein the second polarization beam splitter is operable to receive phase shifted copies of the first and second principal modes, and to align the phase shifted copies of the principal modes to principal axes of a fixed delay element coupled to the second polarization beam splitter.

A method of mitigating polarization mode dispersion, comprising:

• separating an optical signal into a first principal mode of polarization and a second principal mode of polarization, one of the first and second modes comprising a leading mode and one of the first and second modes comprising a lagging mode;
• introducing at least three stages of phase shift between the leading and lagging modes of polarization to align the leading mode with a slow principal axis of a fixed delay element and the lagging mode with a fast principal axis of the fixed delay element;
• and
• communicating the leading mode parallel to the slow axis and the lagging mode parallel to the fast axis;
• wherein each of the at least three stages of phase shift are introduced by one of at least three phase shift stages, at least one phase shift stage sharing a beam splitter with at least one other phase shift stage, at least one phase shifter comprising:
• a plurality of mirrors, each mirror operable to receive one of the principle modes of polarization and to reflect those signals toward an output for combination, at least one of the mirrors comprising a Micro-electro-optic system (MEMS) device including a plurality of adjacent mirror strips operable to receive one of the principal states of polarization, the mirror strips further operable to change their position substantially in unison in a substantially piston-like motion to create a phase shift between the first and second modes of polarization.