# Soliton microcomb based spectral domain optical coherence tomography

## TL;DR

This paper investigates the use of soliton microcombs generated in photonic chipscale resonators as a novel illumination source for spectral domain optical coherence tomography, demonstrating advantages in bandwidth, noise performance, and potential for advanced imaging techniques.

## Contribution

It introduces the application of soliton microcombs in SD-OCT, showing their superior bandwidth, lower noise floor, and potential for improved imaging and circular ranging capabilities.

## Key findings

- Soliton microcombs can exceed the bandwidth of commercial SLDs.
- Soliton states exhibit a noise floor about 3 dB lower than SLDs at the same power.
- Experimental SD-OCT imaging demonstrates the viability of soliton microcombs for biomedical imaging.

## Abstract

Spectral domain optical coherence tomography (SD-OCT) is a widely used and minimally invaive technique for bio-medical imaging [1]. SD-OCT typically relies on the use of superluminescent diodes (SLD), which provide a low-noise and broadband optical spectrum. Recent advances in photonic chipscale frequency combs [2, 3] based on soliton formation in photonic integrated microresonators provide an chipscale alternative illumination scheme for SD-OCT. Yet to date, the use of such soliton microcombs in OCT has not yet been analyzed. Here we explore the use of soliton microcombs in spectral domain OCT and show that, by using photonic chipscale Si3N4 resonators in conjunction with 1300 nm pump lasers, spectral bandwidths exceeding those of commercial SLDs are possible. We demonstrate that the soliton states in microresonators exhibit a noise floor that is ca. 3 dB lower than for the SLD at identical power, but can exhibit significantly lower noise performance for powers at the milliWatt level. We perform SD-OCT imaging on an ex vivo fixed mouse brain tissue using the soliton microcomb, alongside an SLD for comparison, and demonstrate the principle viability of soliton based SD-OCT. Importantly, we demonstrate that classical amplitude noise of all soliton comb teeth are correlated, i.e. common mode, in contrast to SLD or incoherent microcomb states [4], which should, in theory, improve the image quality. Moreover, we demonstrate the potential for circular ranging, i.e. optical sub-sampling [5, 6], due to the high coherence and temporal periodicity of the soliton state. Taken together, our work indicates the promising properties of soliton microcombs for SD-OCT.