Coherent optical signal processing

A coherent optical signal processing instrument, comprising:

• a collimator including:
• a first fiber input;
• a second fiber input;
• the collimator having the first and second fibers as inputs to a collimating lens, wherein the collimating lens is configured to generate a nonparallel collimating lens output beam pair comprising a first collimating lens output beam and a second collimating lens output beam that define a crossing angle and that intersect at a crossing point;
• and
• a biprism configured to convert the nonparallel first and second collimating lens output beams into first and second collimator output beams, wherein the first and second collimator output beams are generally parallel and are separated by a preselected spacing;
• a polarization-multiplexer including:
• an input plate pair including a first birefringent plate;
• and a second birefringent plate;
• and
• an output plate pair including a third birefringent plate and a fourth birefringent plate;
• wherein the first birefringent plate includes an input configured to receive the first input beam;
• a first output configured to transmit an ordinary beam of a first input beam;
• and a second output configured to transmit an extraordinary beam of the first input beam;
• wherein the second birefringent plate includes an input configured to receive a second input beam;
• a first output configured to transmit an ordinary beam of the second input beam;
• and a second output configured to transmit an extraordinary beam of the second input beam;
• wherein the first collimator output beam is the first input beam of the first birefringent plate;
• and
• further wherein the second collimator output beam is the second input beam of the second birefringent plate.
• wherein the third birefringent plate includes a first input configured to receive the first input beam ordinary beam;
• and a second input configured to receive the second input beam extraordinary beam;
• and an output configured to transmit a first output beam comprising the first input beam ordinary beam and the second input beam extraordinary beam;
• and
• wherein the fourth birefringent plate includes a first input configured to receive the first input beam extraordinary beam;
• and a second input configured to receive the second input beam ordinary beam;
• and an output configured to transmit a second output beam comprising the first input beam extraordinary beam and the second input beam ordinary beam;
• and further wherein
• the first input beam and the second input beam are generally parallel, and the first output beam and the second output beam are generally parallel;
• and
• a photodiode detector device coupled to receive the first and second output beams.