Self-referencing fiber optic rotary displacement sensor

A fiber optic rotary displacement sensor has been developed in which an optical retardation plate is used to encode angular displacement on a broadband optical signal as a modulated notch minimum. As the waveplate is rotated, the optical beam experiences a variable linear retardation. The signal wavelength at which the retardation is exactly one-half wave exhibits a minimum intensity transmission. The wavelength of the intensity minimum is then a function of the rotation of the retardation plate. Determination of the wavelength of these intensity minima is based on measurements acquired with a grating-CCD configuration. Source variations (wavelength and power) are monitored by illuminating a portion of the grating-CCD. Normalization is obtained by referencing the modulated signal, obtained from the remaining CCD pixels, to the source emission. A theoretical prediction of the sensor’s performance is developed and compared with experiments performed in the near IR spectral region using large core multimode optical fiber. Temperature compensation of the system will also be discussed.