Ryohei HANAYAMA, Kenichi HIBINO¹, Shin'ichi WARISAWA and Mamoru MITSUISHI

School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
¹Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, 1-2 Namiki, Tsukuba 305-8564, Japan

(Received December 24, 2003; Accepted May 27, 2004)

Wavelength scanned interferometry allows the simultaneous measurement of top surface shape and optical thickness variation of a transparent object consisting of several parallel surfaces. Interference signals from these surfaces can be separated in frequency space, and their phases are detected by discrete Fourier analysis. However, these signal frequencies are shifted from the detection frequency by the refractive index dispersion of the object and a nonlinearity of the wavelength scanning. The Fourier analysis is sensitive to the detuning of the signal frequency and suffers from the multiple-beam interference noise. Conventional error-compensating algorithms cannot be applied to an object consisting of more than three reflecting surfaces. We derive a new 2N-1 sample error-compensating algorithm, which allows the phase detection of any order of harmonic frequency among the interference signals. The new algorithm suppresses the effect of signal frequency detuning as well as the multiple-beam interference noise and can be applied to the measurement of complex objects consisting of more than three reflecting surfaces.

Key words: phase measurement, Fizeau interferometer, wavelength-scanned interferometer, optical thickness, optical parallel