A Fiber Fizeau Interferometer for Measuring Minute Biological Displacements

A laser interferometer has been developed which was used to measure vibratory displacements of the cricket's posterior tympanic membrane with a sensitivity of less than 0.1 A. A special feature is the incorporation of an optical fiber in two of its arms, which makes possible its use in hard-to-access areas. Another feature is its Fizeau configuration, which enables one to eliminate much undesirable noise by combining both the reference arm and the object arm within the same length of fiber. Numerical results are given over the auditory spectrum for two different conditions of the space behind the cricket's posterior tympanic membrane.