Passive quadrature phase detection system for coherent fiber optic systems

A method of sensing, comprising:

• interfering two optical signals;
• detecting interference between said signals at first and second locations so as to provide first and second output signals having a phase bias therebetween which is independent of the interference between the signals;
• and
• selecting the locations such that said phase bias is fixed and insensitive to environmental influence, wherein said selecting step comprises selecting said first location to be at a near field pattern of the optical signals and selecting said second location to be at a far field pattern of the optical signals.

A method of sensing, comprising:

• interfering two optical signals;
• detecting interference between said signals at first and second locations so as to provide first and second output signals having a phase bias therebetween which is independent of the interference between the signals;
• and
• selecting the locations such that said phase bias is fixed and insensitive to environmental influence, wherein said selecting step comprises selecting two locations to provide a Guoy effect phase shift between the two locations.

An apparatus comprising:

• an interferometric device which provides interference between interfering light waves;
• a first detector for detecting a single optical output signal comprised of said light waves;
• and
• a second detector for detecting said single optical output signal, said first and second detectors being disposed such that said optical output signal at said second detector is shifted in phase relative to said optical output signal at said first detector to provide a phase bias between said optical output signal at said first detector and said optical output signal at said second detector, said first and second detectors being disposed such that said phase bias is stable and insensitive to environmental influence.

An apparatus comprising:

• an interferometric device having an optical output signal which is responsive to interference between interfering optical signals;
• a first detector for detecting said optical output signal;
• and
• a second detector for detecting said optical output signal, said first and second detectors being disposed such that said optical output signal at said second detector is shifted in phase relative to said optical output signal at said first detector to provide a phase bias between said optical output signal at said first detector and said optical output signal at said second detector, said first and second detectors being disposed such that said phase bias is stable and insensitive to environmental influence, wherein said phase bias is caused by a Guoy effect phase shift.

An apparatus comprising:

• an interferometric device having an optical output signal which is responsive to interference between interfering optical signals;
• a first detector for detecting said optical output signal;
• and
• a second detector for detecting said optical output signal, said first and second detectors being disposed such that said optical output signal at said second detector is shifted in phase relative to said optical output signal at said first detector to provide a phase bias between said optical output signal at said first detector and said optical output signal at said second detector, said first and second detectors being disposed such that said phase bias is stable and insensitive to environmental influence, wherein said first detector is disposed in a near field pattern of said optical output signal and said second detector is disposed in a far field pattern of said optical output signal.