High speed wavelength-swept laser source with simple configuration for optical coherence tomography

Abstract

This paper reports on a high-speed, wavelength-swept laser operating at 1310nm for optical coherence tomography (OCT) applications. The simple and reliable laser comprises a pigtailed semiconductor optical amplifier (SOA) and a wavelength-scanning filter in a fiber ring cavity configuration. The tunable filter consists of a diffraction grating and polygon mirror scanner in Littrow configuration. A photodiode is used to generate a start trigger signal synchronized to the start of each frequency sweep. Intracavity prisms plays important role to provide constant and narrow laser linewidth and linear frequency sweep at the same time. The laser exhibits a peak power of over 20mW. The tuning range of the laser is as wide as 120nm maximum, and 100nm FWHM at a scanning frequency of 20kHz. Coherence length was measured to be 4mm. By utilizing a novel double pass configuration in the scanning filter an improvement in coherence length to 7mm is also achieved. OCT system configured with the light source exhibits 106dB sensitivity and 12μm axial resolution in imaging.