Long coherence length and linear sweep without an external optical k-clock in a monolithic semiconductor laser for inexpensive optical coherence tomography

Abstract

We demonstrate a new swept-wavelength laser for optical coherence tomography using a monolithic semiconductor device with no moving parts. The laser is based on a Vernier-Tuned Distributed Bragg Reflector (VTDBR) structure. We show highly-linear sweeps at 200 kHz sweep repetition rates, with peak output power of 20 mW. Using a test interferometer, we demonstrate point-spread functions with 45-55 dB dynamic range. The source provides long coherence length (> 40mm) at up to 200 kHz sweep rates. The laser system has sufficient linearity in optical frequency and stability over time to provide an electronic sample trigger clock (an Electronic K-Clock) that denotes equal optical frequency intervals during the sweep. The laser tuning mechanism is all-electronic, easily adjustable and programmable. We demonstrate both flat and Gaussian power vs. wavelength profiles, programmable sweep rates with the same device, and an adjustable duty cycle of up to 85% at full speed. Because the laser is a monolithic semiconductor structure based on reliable, wafer-scale processes, the manufacturing cost of the laser will decrease rapidly in volume production.