<title>High-resolution tomography for scattering media by synthesis of optical coherence function</title>

Abstract

A technique named synthesized optical coherence tomography (SOCT) has been developed as an alternative method of the well-known optical coherence tomography (OCT) for cross- sectional imaging of scattering objects. The SOCT is based on the principle of the synthesis of optical coherence function. Instead of the low coherence light source in the OCT, the SOCT uses a super structure grating (SSG) distributed Bragg reflector tunable laser diode as the light source. By stepwise optical frequency modulation, a comb-shaped power spectrum is obtained; thus the optical coherence function is synthesized into a delta-function-like peak at an arbitrary location. When the injection currents to the SSG sections and the phase control section are modulated synchronically and in a proper relation, an equally spaced frequency tuning of a range of near 40 nm is obtained, corresponding to a spatial resolution of several tens of microns theoretically. The location of the coherence peak can be adjusted by the spacing in the frequency modulation and scanned by the simultaneous phase modulation in the reference wave. The longitudinal scattering distribution of the object under test is thus obtained without mechanically driven reference. Two-dimensional tomography was demonstrated in a basic experiment with lateral scanning mechanism.