Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator

The passive quadrature demodulator (PQD) eliminates the phase stretcher and feedback electronics frequently used in fiber interferometric sensors by passively extracting the desired signal using two distinct interferometers which differ in phase by
\pi/2
. A fusion technique is described to fabricate a fiber PQD which is sufficiently stable with respect to temperature, polarization, and wavelength to maintain the sensitivity of interferometric sensors constant to 0.25 dB.