FDML (incl. Parallelization)

Optical coherence tomography with wavelength swept light sources (SS-OCT) requires tuneable lasers with a very unique set of performance parameters. The most critical parameters are a wide wavelength sweep range and a fast tuning rate. Initially, SS-OCT systems used conventional lasers which were reengineered in an attempt to meet the needs of OCT, but they always represented more or less of a compromise. With the introduction of Fourier Domain Mode Locking (FDML) a radically new operating regime of lasers was introduced to overcome fundamental physical limitations of OCT lasers (Huber et al., Opt Express 14(8):3225–3237, 2006; Huber R et al., Fourier domain mode locked lasers for OCT imaging at up to 290 kHz sweep rates. In: Drexler W (ed) European conference on biomedical optics, SPIE. Optical Society of America, Munich, p PDA3, 2005). Today FDML lasers are the fastest actively tuned OCT lasers and achieve sweep repetition rates far beyond other technologies. This chapter describes the idea behind FDML, its history, the most recent performance specifications and a selection of unique OCT imaging applications. FDML lasers were the first to enable real time 3D Megahertz and multi-Megahertz imaging with swept source technology and thereby opened an entirely new field of future OCT applications. A series of proof of concept experiments with MHz FDML laser is discussed and an outlook on the future of such high speed systems is presented.