Three-port interferometer in silicon-on-insulator for wavelength monitoring and displacement measurement

The wavelength of a narrow-band optical signal can be accurately tracked by means of an interferometer having a fixed path length difference. For example, a low-cost Fiber Bragg Grating (FBG) interrogation system which tracks the FBG reflection wavelength over time can be based on such an interferometer. Alternatively, an interferometer is operated at fixed wavelength to monitor displacement, as applied in metrology.