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 so
urce, the system synthesizes the optical coherence function into a delta fu
nction-like peak at an arbitrary depth, and the depth of the peak can be ad
justed by changing the frequency modulation parameter. In this way, the int
erference of a reference with the reflection at each target surface can be
selectively extracted, and the shapes of the target surfaces can then be ob
tained by means of fringe analysis such as the Fourier transform (FT) metho
d. An experimental demonstration is presented and performance degradation f
actors are discussed.