Fiber optic Michelson sensor and arrays with passive elimination of polarization fading and source feedback isolation

A polarization-independent fiber optic interferometric sensor system comprising:

• optical source means for providing light of a first polarization state;
• a polarization beamsplitter having first and second input ports and first and second output ports and being coupled to said optical source means, said polarization beamsplitter being responsive to the application of said light of said first polarization state to said first input port for coupling said light from said first input port to said first output port;
• means coupled to said first output port for conveying said light of said first polarization state from said first output port to a distal end of said conveying means, said conveying means having a birefringence which changes the polarization state of said light of said first polarization state to a first arbitrary polarization state at said distal end of said conveying means;
• a fiber Michelson interferometer including:
• an optical coupler having third and fourth output ports and a third input port coupled to the distal end of said conveying means, sensing and reference fiber arms having different associated birefringences and being coupled at respective proximal ends thereof to said third and fourth output ports of said optical coupler for passing first and second portions of said light of said first arbitrary polarization state therethrough to produce respective second and third arbitrary polarization states at respective distal ends of said sensing and reference arms, and first and second Faraday rotator mirror assemblies respectively disposed at the distal ends of said sensing and reference fiber arms for converting said first and second portions of light of said second and third arbitrary polarization states into first and second portions of light of fourth and fifth arbitrary polarization states, said optical coupler combining said first and second portions of said fourth and fifth polarization states into a beam of light and allowing said beam of light to pass through said conveying means to produce said second polarization state at said first output port, said beam of light of said second polarization state passing through said polarization beam splitter to substantially only said second input port;
• and
• output means coupled to said second input port of said polarization beamsplitter and being responsive to any interference pattern contained in said beam of light for developing an electrical signal that has a peak-to-peak amplitude proportional to the visibility of said interference pattern.

A polarization-independent fiber optic interferometric sensor system comprising:

• optical source means for providing a pulse of light of a first polarization state;
• a polarization beamsplitter having first and second input ports and first and second output ports and being coupled to said optical source means, said polarization beamsplitter being responsive to the application of said pulse of light of said first polarization state to said first input port for coupling said pulse of light from said first input port to said first output port;
• an input fiber having a birefringence and having proximal end coupled to said first output port;
• a plurality of serially-coupled optical couplers serially disposed along said input fiber;
• a plurality of delay elements, each of delay T, interleaved between adjacent ones of said plurality of optical couplers;
• a plurality of fiber Michelson interferometers respectively coupled to said plurality of optical couplers, each of said fiber Michelson interferometers including:
• a coupler having third and fourth output ports and a third input port coupled to an associated one of said plurality of serially-coupled optical couplers, said birefringence of said input fiber changing the polarization state of said pulse of light of said first polarization state to an associated first arbitrary polarization state at said coupler, sensing and reference arms having difference associated birefringences and being respectively coupled at proximal ends thereof to said third and fourth output ports of said coupler for passing first and second portions of said light of said first arbitrary polarization state therethrough to produce respective second and third arbitrary polarization states at respective distal ends of said sensing and reference arms, and first and second Faraday rotator mirror assemblies respectively coupled to distal ends of said sensing and reference arms for converting said first and second portions of light of said associated second and third arbitrary polarization states into first and second portions of associated fourth and fifth arbitrary polarization states, said optical coupler combining said first and second portions of said associated fourth and fifth polarization states into an associated pulse of light and allowing said associated pulse of light to pass through its associated one of said plurality of serially-coupled optical couplers into said input fiber, said associated pulse from each of said plurality of serially-coupled optical couplers combining into a sequence of pulses along said input fiber which pulses return through associated ones of said delay elements to said first output port of said polarization beamsplitter, each pulse in said sequence of pulses having said second polarization state upon its arrival at said first output port, said sequence of pulses of light sequentially passing through said polarization beamsplitter to said second input port;
• and
• output means coupled to said second input port of said polarization beamsplitter and being responsive to any interference pattern contained in any one of said sequence of pulses of light for developing an associated electrical signal that has a peak-to-peak amplitude proportional to the visibility of said interference pattern.

A polarization-independent fiber optic interferometric sensor system comprising:

• optical source means for providing consecutive first and second pulses of light of a first polarization state;
• a polarization beamsplitter having first and second input ports and first and second output ports and being coupled to said optical source means, said polarization beamsplitter being responsive to the application of said consecutive first and second pulses of light of said first polarization state to said first input port for coupling said consecutive first and second pulses of light from said first input port to said first output port;
• an input fiber having a birefringence and having a proximal end coupled to said first output port;
• a plurality of optical couplers serially disposed along said input fiber for respectively tapping off portions of the light in each of said consecutive first and second pulses of light;
• a plurality of delay sensing coils, each of delay T, interleaved between adjacent ones of said plurality of optical couplers;
• a plurality of Faraday rotator mirror assemblies, each said Faraday rotator mirror assembly reflecting light applied thereto back with a change in polarization;
• a plurality of fiber arms respectively coupled between associated ones of said plurality of optical couplers and associated ones of said plurality of Faraday rotator mirror assemblies, said pluralities of optical couplers, fiber arms, Faraday rotator mirror assemblies and delay sensing coils forming a plurality of fiber Michelson interferometers, each of said fiber Michelson interferometers including:
• a first arm having an associated first optical coupler coupled by way of an associated first fiber arm to an associated first said Faraday rotator mirror assembly;
• and
• a second arm having said associated first optical coupler serially coupled by way of an adjacent said delay sensing coil to an associated second optical coupler, and an associated second fiber arm coupled between said associated second optical coupler and an adjacent second Faraday rotator mirror assembly, said first and second Faraday rotator mirror assemblies in each of said plurality of fiber Michelson interferometers changing the polarization states of the portions of the light in each of said consecutive first and second pulses of light and returning such light by way of said input fiber to said first output port of said polarization beamsplitter, each of said consecutive first and second pulses of light from each Faraday rotator mirror assembly having said second polarization state upon its arrival at said first output port and passing through said polarization beamsplitter to said second input port;
• and
• output means coupled to said second input port of said polarization beamsplitter and being responsive to any interference pattern contained in any one of said sequence of pulses of light for developing an associated electrical signal that has a peak-to-peak amplitude proportional to the visibility of said interference pattern;
• wherein, in each one of said plurality of fiber Michelson interferometers, only the first pulse of the two pulses of light reflected off of said second Faraday rotator mirror assembly will overlap the second pulse of the two pulses of light reflected off of said first Faraday rotator mirror assembly to produce an interference pattern at said output means.