Optical coherence tomography (OCT) is an emerging technology for producing real-time, high-resolution cross-sectional medical images of tissue with a resolution of a few microns. The analogy of OCT is traditional ultrasound with the difference that the resolution is about hundred times lower due to the longer wavelength of ultrasound waves compared to the optical waves used in OCT. The near infrared light used in OCT penetrates human tissue typically only a few millimeters before absorption and scattering become too high. Most OCT systems used today are in the field of ophthalmology (e.g., retina or cornea examinations) or in combination with endoscopy, for example for cardiovascular medicine. Other medical applications of OCT like dental or skin tissue examinations are still in development but show the potential of OCT being deployed in other areas of medicine.

Today’s ophthalmic OCT systems use SLEDs in the 800-to-900-nm wavelength range for retinal applications and SLEDs in the 1300-nm regime for cornea examinations. New wavelengths like the 1050-nm low-absorption window of water have been recently proposed for retinal OCT as well. Non-ophthalmic medical OCT is typically operating in the 1300-nm regime.

Time-domain (TD-) OCT systems require SLEDs with good spectral shape, for example first-order Gaussian, such that the coherence function features good sidelobe suppression. Spectral-domain (SD-) OCT systems perform anyway advanced signal processing such that sidelobes are less critical. Still, spectral shape matters in order to have a rather constant power spectral density over a wide wavelength range. For this reason, high-resolution SD-OCT systems use SLEDs having a spectrum with a flat-top shape and a bandwidth of 50 to 100 nm.

EXALOS is the leading supplier of high-bandwidth and high-power SLEDs for ophthalmic and medical OCT applications allowing resolutions down to two microns in tissue.