Controls of spectral shape and dispersion mismatch for high-resolution optical coherence tomography

The longitudinal resolution of an optical coherence tomography (OCT) system is conventionally defined as the full-width at half maximum (FWHM) of the interference fringe envelope, which depends on the center wavelength as well as the spectral width of the light source. One can obtain an FWHM of an interference fringe envelope larger or smaller than that resulted from a Gaussian spectrum of the same spectral FWHM when the light source spectrum is non-Gaussian distributed. In this paper, we first study the dependencies of OCT resolution on the spectral shape and dispersion mismatch with numerical simulations. We will demonstrate the capability of enhancing the longitudinal resolution of an OCT system with a proper control of spectral distribution and dispersion mismatch. Then, in experiments we built an OCT system with its light source generated from nonlinear optics effects of 12-fsec Ti:sapphire laser pulses in an optical fiber. With proper control of dispersion mismatch between the sample and reference arms, the FWHM of the interference fringe envelope was smaller than that of a Gaussian spectrum with the same spectral FWHM by a factor of two. Furthermore, the side lobes were suppressed with a process algorithm to significantly improve the longitudinal resolution.