Comprehensive theoretical model for multi-harmonic dispersion-tuned mode-locking (DTML) for use in swept-source OCT

In this study, a comprehensive theoretical model for the multi-harmonic dispersion-tuned mode-locking (DTML) regime for swept-source OCT (SS-OCT) is presented for the first time. The principle of wavelength tuning in this regime is described in detail, along with a derivation of the tuning bandwidth formula and scaling guidelines that predict the trade-offs between the tuning bandwidth and coherence performance. A comparison of the optical fields stored inside a conventional single-harmonic DTML cavity, a multi-harmonic DTML cavity, and an FDML cavity is also presented. As experimental validation of the multi-harmonic concept, OCT images of a finger tip and the retina of a volunteer are captured at a sweep rate close to 1 MHz with a 30 nm tuning bandwidth.