Principle of functioning of a self-compensated fibre-optical displacement sensor based on diffraction-grating-ended POF

A self-compensated displacement sensor has been realized by placing a diffraction grating on the end face of a plastic optical fibre (POF), the method serving for any highly multimode optical fibre. By measuring the output powers at two diffraction angles corresponding to two different diffraction orders, a simple way to cancel out the fluctuations of the light source and other disturbances has been achieved.