Time Domain Discrete Fourier Domain Mode Locked Laser with k-Space Uniform Comb Lines

Frequency comb swept lasers or wavelength stepped swept lasers with comb filters have been proposed in optical domain subsampling or circular-ranging optical coherence tomography (OCT) to achieve high axial scan rate and extended imaging range with a given acquisition bandwidth. However, the comb filters lack flexibility in varying the free spectral range (FSR). In this article, we propose and demonstrate a novel discrete Fourier domain mode locked (FDML) laser by using intracavity optical intensity modulation. Swept signals with comb lines uniformly distributed in the frequency domain is generated with tailor-made pulse patterns according to the sweep trace of the swept filter. Discrete k-space uniform swept signals with different FSRs and pulse durations are generated in the same laser. The FDML laser discretized by temporal modulation is more stable than that with a comb filter. The discrete FDML lasers will be potential sources of OCT and the fast-developing swept source LiDAR.