Lasers and SLEDs for optical coherence tomography

Optical coherence tomography (OCT) allows for the generation of 3D tomographic images of sub-surface structures in-vivo. This non-destructive, non-ionising process has found application in biological science and clinical diagnosis. Specifically, two versions of the OCT technique have proved optimal for different applications. For retinal imaging through a long length of water, near infrared wavelength super-luminescent diodes (SLEDs) with silicon array detector spectrometer systems have dominated. For imaging turbid media such as skin, Rayleigh scattering favours a longer wavelength in order to achieve suitable penetration depth. As such, the silicon detector is no longer suitable and the optimum system is now based on a swept-wavelength laser with an InGaAs single element detector. The gain element in the swept source laser is a semiconductor optical amplifier (SOA) where rapid sweeping is essential. In both cases, the amplifier chips are largely identical in design, and broadband gain is of prime importance. We discuss the developments of these gain chips towards achieving cellular resolution.