All-fiber ring-cavity based frequency swept laser source for frequency domain OCT

Abstract

We develop a high-speed tunable, quasi-continuous-wave laser source for frequency domain (FD) optical coherence tomography (OCT). The laser resonance is realized within a unidirectional all-fiber ring cavity consisting of a fiber coupler, two fiber isolators, a semiconductor optical amplifier (SOA), and a fiber Fabry-Perot tunable filter (FFP-TF) for frequency tuning. Light output from the coupler is further amplified and spectral shaped by a booster SOA terminated at both ends with two isolators. The developed laser source provides up to 8000 sweeps per second over a full-width wavelength tuning range of 120 nm at center wavelength of 1320 nm with an average power of 9 mW, yielding an axial resolution of 13.6 \mu m in air and a maximum sensitivity of about 112 dB for OCT imaging. The instantaneous linewidth is about 0.08 nm, enabling OCT imaging over an axial range of 3.4 mm in air. For optimization consideration based on this custom-built swept laser, experimental study on imaging quality relevant parameters of the swept laser with sine and ramp driving waveforms to the FFP-TF is conducted, and investigation of the swept laser on the cavity length is done. Implementing the laser source in our established swept source based OCT (SS-OCT) system, real-time structural imaging of biological tissue is demonstrated.