Fiber-optic circuit for direct phase conversion with two outputs in quadrature

The authors model and demonstrate a fiber-optic circuit configuration that maps optical phase shifts into electrical phase shifts in the fundamental and second harmonics of an imposed modulation frequency. This optical circuit allows simple electronic phase detectors to extract these phase shifts, which are demonstrated to be linear over a full 2π radians, opposite in slope, and offset by π/2 from each other in a phase relation similar to quadrature