Methods of and apparatus for calibrating precisely spaced multiple

Abstract

A Bragg reflection filter wavemeter is used to measure transverse holographic gratings and optical fibers and utilizes a first interferometer which is always fixed with respect to the optical fiber and a second adjustable interferometer. The optical fiber and first interferometer are mounted on a translating support while the second interferometer includes a pair of angularly adjustable mirrors for changing the angle at which the object and reference beams thereof intersect the fiber. Since the fiber is mounted on a movable support, the position of the support can be continually adjustable so that the reference and object beams always intersect the fiber at the same point, regardless of the angle assumed by the reflecting mirrors. The resulting interference patterns are projected by an objective lens to the far field in which a linear scanning, photodiode array is moved. The photodiode array includes a first photodiode which is sensitive only to the interference patterns from the first laser beam and a second photodiode sensitive to the interference patterns from the second laser beam. The photodiodes are connected to a counter which provides ratios of interference line counts which are then multiplied by wavelength to provide precise modulation spacings so as to establish wavelength standards.