paper

Sub-nominal resolution Fourier transform spectrometry with chip-based combs

arXiv:2303.13074 · doi:10.1002/lpor.202300724

Abstract

Chip-based optical frequency combs address the demand for compact, bright, coherent light sources of equidistant phase-locked lines. Traditionally, the Fourier Transform Spectroscopy (FTS) technique has been considered a suboptimal choice for resolving comb lines in chip-based sensing applications due to the requirement of long optical delays, and spectral distortion from the instrumental line shape. Here, we develop a sub-nominal resolution FTS technique that precisely extracts the comb's offset frequency in any spectral region directly from the measured interferogram without resorting to nonlinear -to- interferometry. This in turn enables MHz-resolution spectrometry with millimeter optical retardations. Low-pressure MHz-wide absorption lines probed by widely-tunable chip-scale mid-infrared OFCs with electrical pumping are fully resolved over a span of tens of nanometers. This versatile technique paves the way for compact, electrostatically-actuated, or even all-on-chip high-fidelity FTS, and can be readily applied to boost the resolution of existing commercial instruments several hundred times.

arXiv commentMain text: 8 pages, 4 figures; supplementary document: 7 pages, 8 figures

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