30 May 2003 Oblique point-diffraction source for interferometer design
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We describe an oblique point-diffraction source, which is made from a single-mode optical fiber whose end is specially cut with an oblique face angle of 28.8° to the optical axis of the fiber. Analytical and empirical investigations reveal that, like ordinary fibers cut with zero face angle, the oblique fiber generates a high-quality spherical wave into free space by means of point diffraction at its end, but the diffracted wave has a propagation angle of 45° to the surface normal. This inclined nature of point diffraction is useful in many optical designs because it allows the returning wave of the original diffracted wave to be reflect at a right angle at the end face of the oblique fiber without additional optics. An exemplary use of the oblique fiber is demonstrated in an enhanced optical design of Fizeau interferometer, in which the troublesome combination of a pinhole and a beam splitter is effectively replaced only with a single oblique fiber. Another example is shown in a phase-shifting diffraction interferometer that has been specially designed for testing concave mirrors of low f-numbers. The use of oblique fibers enables to use the entire full numerical aperture of the diffracted wave from a single-mode fiber for optical testing without any overlap between the reference and the test waves.
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Hagyong Kihm, Hagyong Kihm, Seung-Woo Kim, Seung-Woo Kim, "Oblique point-diffraction source for interferometer design", Proc. SPIE 5144, Optical Measurement Systems for Industrial Inspection III, (30 May 2003); doi: 10.1117/12.500253; https://doi.org/10.1117/12.500253

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