Fiber Interferometer

Fiber Coupled 90° Optical Hybrid

The FCOH is a passive, micro-optics-based 90° optical hybrid designed for coherent optical signal demodulation, including BPSK and QPSK formats. It functions by mixing the incoming signal (S) with a local oscillator reference signal (L), generating four optical outputs corresponding to the vector sums and differences of the two inputs: S+L, S−L, S+jL, and S−jL. These outputs represent four quadrature states in the complex optical field space. The signals are then directed to two pairs of balanced photodetectors, enabling differential detection of the in-phase (I) and quadrature (Q) components. This configuration allows the extraction of both amplitude and relative phase information through digital signal processing.