Surface shape measurement for a multilayered object by synthesis of optical coherence function

An interferometric system is proposed by synthesis of the optical coherence function for measuring surface shapes of multiple planes in a multilayered transparent object. By stepwise optical frequency modulation of a laser source, the system synthesizes the optical coherence function into a delta function-like peak at an arbitrary depth, and the depth of the peak can be adjusted by changing the frequency modulation parameter. In this way, the interference of a reference with the reflection at each target surface can be selectively extracted, and the shapes of the target surfaces can then be obtained by means of fringe analysis such as the Fourier transform (FT) method. An experimental demonstration is presented and performance degradation factors are discussed.