Sci‐PM Fri ‐ 01: Application of broadly tunable asymmetric multiple‐quantum‐well (AMQW) lasers to optical coherence tomography (OCT)

Optical coherence tomography (OCT) requires a broad‐band light source for time domain OCT or a broadly tunable light source for Fourier domain OCT. People use an LED or an SLD for time domain OCT and use a swept laser for Fourier domain OCT. Asymmetric multiple‐quantum‐well (AMQW) lasers have superiority in obtaining a broad and flat gain spectrum, thus it should be possible to achieve both broadband and high‐power operation with AMQW lasers. We show in this work that with a DOE applied short external cavity system, an AMQW laser could work as both a tunable laser for Fourier domain OCT and as a broad‐band light source for time domain OCT. The former application is straight‐forward. We put our new idea in the latter application. If one uses a Fourier domain approach and integrates in time the output of the detector while the wavelength of the source is tuned rapidly, the tunable light source will appear as an incoherent light source with a depth resolution that is inversely proportional to the spectral width that the laser is tuned over. Therefore the depth resolution can be increased by broader spectral width. With our AMQW laser, the maximum tuning range is as broad as 100 nm, with a corresponding depth resolution of 10.6 μm in air with center wavelength of 1.55 μm. The maximum depth that could be measured depends on the spacing of the longitudinal modes of the laser and is 550 μm for a laser with mode‐spacing of 1 nm.