Optical source isolator with polarization maintaining optical fiber and aspheric collimating and focusing lens

An optical system for use in a fiber optic gyroscope having an optical fiber ring comprising;

• a substrate;
• a source of substantially monochromatic circularly polarized input light mounted on said substrate, wherein said source is a light emitting diode (LED);
• a polarizing beamsplitter mounted on said substrate;
• a first lens mounted on said substrate and positioned to receive light from said source of monochromatic light, said first lens being aspheric;
• said aspherical lens collimating into a circular cross-section beam and focusing light from said monochromatic light source into said beamsplitter, said beamsplitter transmitting said input light linearly polarized in a first plane through it to form a linearly polarized output beam and reflecting said input light linearly polarized in a plane orthogonal to said first plane;
• a non-reciprocal (NR) device mounted on said substrate and positioned to receive said linearly polarized output beam and pass it through said NR device in a first direction while rotating the plane of polarization of said light passing through it in said first direction by 45 degrees in one direction
• a pigtail fiber optic connector connected to said fiber optic ring;
• a second lens mounted on said substrate and positioned to focus light emitted from said nonreciprocal device into said fiber optic pigtail connector, and to focusing return light emitted from said fiber optic connector into said nonreciprocal device, whereby light is passed in a second direction through said non-reciprocal device and has its plane of polarization rotated an addition 45 degrees;
• said light emitted from said non-reciprocal device in said second direction being incident upon said beamsplitter with a plane of polarization rotated 90 degrees with respect to the plane of polarization of light emitted from said beamsplitter being arranged to reflect return light rotated by said 90 degrees away from said light source;
• a photodetector element mounted on said substrate and positioned to receive light passing in said second direction into said polarizing beamsplitter which has been reflected away from said light source,
• wherein said pigtail connector includes:
• a single mode polarization maintaining (PM) optical fiber extending from an input/output I/0 and along a fiber axis, and associated means for positioning said I/0 end whereby said I/O end is aligned to receive light passing from said NR device in said one direction, and for passing light propagating in said second direction from said PM fiber to said NR device.

An optical system comprising:

• A. a rigid substrate
• B. a polarizing beamsplitter having a first input axis, a second input axis, a first output axis and a second output axis, said first and second output axes being substantially parallel, said first output axis and said second input axis being coincident, and said beamsplitter being adapted to:
• i. pass light incident along said first input axis and polarized in a first input polarization plane along a first output axis,
• ii. reflect light incident along said first input axis and polarized in a second polarization plane being orthogonal to said second polarization plane, said first output axis being angularly offset with respect to said second output axis,
• iii. reflect light incident along said second input axis and polarized in said second polarization plane along a third output axis, said third output axis, being angularly offset with respect to said first and second output axes,
• C. a non-reciprocal (NR) device defining a non-reciprocal propagation path extending therethrough along an NR axis, whereby the polarization plane of light incident on said NR device and passing along said NR axis through said NR device in one direction is rotated by an angle substantially equal to 45 degrees in a first direction from said polarization plane, and the polarization plane of light incident on said NR device and passing along said NR axis through said NR device in the direction opposite to said one direction is rotated by an angle substantially equal to 45 degrees in said first direction from said polarization plane,
• D. means for affixing said polarizing beamsplitter and said NR device to said substrate in a serial configuration whereby first output axis of said polarizing beamsplitter is substantially coaxial with said second input axis of said polarizing beamsplitter and said NR axis of said NR device, and whereby light passing along said second output axis from said polarizing beamsplitter is directed to said propagation path of said NR device along said NR axis, and light passing along said propagation path of said NR device along said NR, axis toward polarizing beamsplitter is directed along said second input axis.
• E. a single mode polarization maintaining (PM) optical fiber extending from an input/output (I/0) end along a fiber axis, and associated means for positioning said I/O end whereby said I/0 end is opposite NR device and adapted to receive light passing from said NR device in said one direction and for passing light to said NR device in said direction opposite to said one direction, and whereby said fiber axis is substantially aligned with said NR axis,
• F. an aspheric lens positioned along said input axis before said polarizing beamsplitter including means for collimating light applied thereto into a circular section cross beam directed to be incident on and focused into said polarizing beamsplitter, and
• G. an optical source including generating means for generating light and directing said generating light to be incident on said polarizing beamsplitter along said first input axis;
• wherein said generating means is a light emitting diode (LED) directed to be incident on and focused into said polarizing beamsplitter.