Fiber Optic Diffraction Interferometer for Testing Spherical Mirrors

摘要

Light emanating from the polished end of a single-mode fiber forms into a near-perfect spherical wave within a finite solid angle, which can readily be explained by diffraction theory. Utilizing the useful phenomenon, we in this paper present a fiber optic diffraction interferometer that has specially been devised for testing spherical mirrors. The interferometer adopts three optical fibers; one is for generating spherical reference wave, another is for illuminating the mirror under test and the other is for calibrating the interferometer. A special assembly of sliding prism driven by a PZT actuator provides necessary phase shifts with a high immunity to environmental disturbances. In conclusion, the proposed fiber optic diffraction interferometer enables us to achieve a measurement accuracy of an order of magnitude better than conventional testing schemes using the Fizeau interferometers of which measurement accuracy is ultimately limited by the reference surface to λ/50, where λ is the wavelength of the source.