Discrete Step Wavemeter

摘要

Tunable lasers are used in optical metrology, but their intrinsic tuning accuracy is sometimes inadequate and an external wavemeter is then required to measure the wavelength more accurately. In this paper, we present the design of a discrete step wavemeter to measure the wavelength of the light from a tunable laser during the operation of a multi-wavelength interferometric shape measuring system. This relatively low-cost wavemeter is embedded in the metrology system and consists of a discrete set of small retroreflectors mounted at different ranges on a super-invar base, which eases alignment and allows it to be insensitive to temperature changes. During operation, interference patterns from the retroreflectors are captured by a camera for each phase shift and commanded wavelength and analyzed to determine the actual wavelength. The phase measurement uses a least square fitting algorithm. A Fourier Transform peak finding measurement technique is used for phase unwrapping. Both numerical simulation and experiments indicate improved system performance using this internal wavemeter technique.