Apparatus and method for reducing phase errors in an interferometer

A method of reducing phase errors in an interferometer having an interferometer loop comprised of single mode birefringent waveguide which propagates light in two orthogonal polarization modes, said interferometer providing an output signal having both orthogonal and non-orthogonal light wave components, said method comprising:

• utilizing a light source having a coherence length which is at least about a hundred times less than the optical path length difference around said loop for said two modes to reduce phase errors caused by interference between non-orthogonal light wave components of said signal;
• propagating light from said source through birefringent waveguide disposed between the source and the loop such that, upon entering said loop, light in one polarization mode is substantially incoherent with respect to light in the other polarization mode to reduce phase errors caused by interference between non-orthogonal light wave components of said signal;
• and
• spatially averaging orthogonal light wave components of said signal under conditions of global orthogonality to reduce phase errors resulting from orthogonal light wave components of said signal.

An interferometer which provides an optical output signal, said interferometer comprising:

• an interferometer loop comprised of birefringent waveguide which propagates light in first and second orthogonal polarization modes, the birefringence of said waveguide causing light in said first and second modes to propagate around said loop in first and second propagation times, respectively corresponding to first and second optical path lengths, respectively, said first optical path length being different from said second optical path length to provide an optical path length difference therebetween;
• a light source providing light for input to said loop, said light having a coherence length which is at least about a hundred times less than the optical path length difference for said first and second modes to reduce phase errors caused by non-orthogonal components of said output signal;
• an optical propagation path between said light source and said loop, said optical propagation path comprised of birefringent waveguide which propagates light in two polarization modes, the birefringence of said waveguide causing light in said two orthogonal polarization modes to propagate from said source to said loop in third and fourth propagation times corresponding to third and fourth optical path lengths, respectively, said third and fourth optical path lengths having an optical path length difference therebetween which is equal to at least one coherence length of the source to reduce phase errors caused by non-orthogonal components of said output signal;
• a first coupler for coupling light between said optical propagation path and said loop, said coupler coupling light from said loop to said optical propagation path to form said optical output signal, said optical output signal propagating in said optical propagation path in two orthogonal polarization modes;
• and
• a detector sized and positioned to intercept the optical output signal so as to detect light from both of the orthogonal polarization modes, such that light wave components in orthogonal modes of said optical output signal are spatially averaged so as to reduce phase errors resulting from orthogonal components of said signal.