Evaluation of a swept-laser optical coherence tomography light source based on a novel quantum-dot based semiconductor optical amplifier

We describe a simple swept-laser design that characterizes the emission bandwidth, linewidth, spectral shape and output noise. A short cavity Littmann configuration is used in which the semiconductor optical amplifier (SOA) lasing wavelength is tuned by a galvanometer with an 830 grooves per mm diffraction grating. A 3dB coupler extracts light from the cavity formed by the grating and end-mirror and the optical output uses to illuminate a balanced swept source optical coherence tomography (SS-OCT) interferometer incorporating a circulator, 3dB coupler, dispersion compensator and balanced detector. The SOA (SOA-1200-70-PM-20sB, Innolume GmbH) uses a novel III-V semiconductor quantum-dot gain medium. ASE is emitted between 1150nm and 1300nm at a drive current of 700mA. When used in the Littmann cavity laser a coherence length of about 10mm is produced, which is tunable over 60nm. The peak output power is 12mW. The swept-laser has been incorporated into a fiber-based SS-OCT system and used to image biological tissues. Axial resolution in air is 12 microns. Images of human palmar skin in-vivo are demonstrated, showing good resolution and contrast, with the stratum corneum, epidermis, rete ridges and epidermal-dermal junction visualized.