Large coherence length swept source for axial length measurement of the eye.

We present and demonstrate a swept source with a large coherence length using a quasi-phase continuous tuning (QPCT) technique. QPCT is a method of minimizing the phase shift per round trip with respect to the tunable filter so that the resonance of lasing becomes high, resulting in high finesse of lasing during a rapid sweep. The demonstrated swept source consists of a fiber ring extended cavity laser with a diffraction grating and a polygon scanner-based tunable filter configuration. The projected beam on the diffraction grating is expanded with a multiple of beam expanders to achieve high finesse of the filter. The source demonstrated an 18 nm swept range at 1060 nm wavelength, 28 mm coherence length, and 6.2 mW peak power at a 2.5 kHz swept rate. OCT imaging results showed that a coherence length of 28 mm enables the measurement of the axial length of a pig's eye with 20 mm length in physical size.