Swept Source OCT Beyond the Coherence Length Limit

We present a simple modification to a swept source optical system that overcomes the limitations in the depth range associated with the short coherence length of fast swept lasers. It is based on a wavelength dependent delay induced by a diffraction grating pair with negative dispersion incorporated in a reference arm of a Mach-Zehnder optical coherence tomography interferometer. The experimental depth range in air obtained was as large as 1.6 cm for a source coherence length of 4 mm.