Three-dimensional hyperspectral imaging with optical microcombs

TL;DR

This paper introduces a novel 3D hyperspectral imaging technique using microcombs, enabling rapid, high-resolution, label-free chemical and spatial analysis of micro-sized particles, with potential environmental sensing applications.

Contribution

The work presents the first application of microcombs for 3D hyperspectral imaging, combining amplitude and phase analysis for high-speed, precise, and scalable chemical and spatial diagnostics.

Findings

Achieved over 1.2 million pixels per second imaging throughput.

Demonstrated micrometre-scale spatial and nanometre-scale axial resolution.

Successfully characterized microplastics in a real-world environmental context.

Abstract

Optical frequency combs have revolutionised time and frequency metrology [1, 2]. The advent of microresonator-based frequency combs ('microcombs' [3-5]) is set to lead to the miniaturisation of devices that are ideally suited to a wide range of applications, including microwave generation [6, 7], ranging [8-10], the precise calibration of astronomical spectrographs [11], neuromorphic computing [12, 13], high-bandwidth data communications[14], and quantum-optics [15, 16] platforms. Here, we introduce a new microcomb application for three-dimensional imaging. Our method can simultaneously determine the chemical identity and full three-dimensional geometry, including size, shape, depth, and spatial coordinates, of particulate matter ranging from micrometres to millimetres in size across nearly $10^5$ distinct image pixels. We demonstrate our technique using millimetre-sized plastic specimens (i.e. microplastics measuring less than 5 mm). We combine amplitude and phase analysis and achieve a throughput exceeding $1.2~10^6$ pixels per second with micrometre-scale precision. Our method leverages the defining feature of microcombs - their large line spacing - to enable precise spectral diagnostics using microcombs with a repetition frequency of 1 THz. Our results suggest scalable operation over several million pixels and nanometre-scale axial resolution. Coupled with its high-speed, label-free and multiplexed capabilities, our approach provides a promising basis for environmental sensing, particularly for the real-time detection and characterisation of microplastic pollutants in aquatic ecosystems [17].