Fig. 1: The principle of dissipative Kerr soliton enabled spectral domain optical coherence tomography (OCT).
From: Soliton microcomb based spectral domain optical coherence tomography
a A dissipative Kerr soliton (DKS), based on the system shown in b, where a continuous-wave laser drives nonlinear frequency conversion, through four-wave mixing (FWM), cross-phase modulation (XPM) and self-phase modulation (SPM) in a photonic chip-based Si3N4 microresonator. Here, the generated pulse train is comprised of discrete and equally spaced frequency components as determined by the free spectral range of the non-linear cavity. In particular, this process creates a frequency comb via the dual balance between non-linearity and dispersion on one hand, and loss and gain on the other. Eventually, the discrete components of this microresonator frequency comb (or continuous source as in traditional OCT) are dispersively projected onto a charged-coupled device (CCD) array as shown in c, after passing through a standard OCT setup as seen in d. Experimental data for a variety of free spectral ranges (Green 1 THz, Red 200 GHz, and Blue 100 GHz) typical of microresonator DKS are shown in e, along with an inset microscope photograph of a ~1 THz microresonator, and a scanning electron microscopy photograph of a typical bus waveguide in Si3N4.
