Millimetre-Wave Comb Generated by an Optical Microcomb

TL;DR

This paper introduces a novel millimetre-wave baseband comb source generated from an optical microcomb, enabling coherent, stable, and spectrally tunable signals for advanced wireless and sensing applications.

Contribution

It presents the first direct generation of a millimetre-wave baseband comb from an optical microcomb with high phase coherence and without external amplification.

Findings

Achieved a 50 GHz repetition rate millimetre-wave comb covering the sub-terahertz region.

Demonstrated stable, zero carrier-envelope offset combs suitable for time-domain spectroscopy.

Showed spectral tailoring of microwave output via multisoliton states.

Abstract

Metrological-grade millimetre wave baseband comb sources covering the subterahertz window are a key building block for next-generation wireless communications, precision sensing, and positioning systems. While optical microcombs have set new benchmarks in ultra-low phase noise single-frequency microwave generation, to date, no microcomb source has directly produced a millimetre-wave baseband comb. Here, we present a 50 GHz repetition rate carrier-envelope offset estabilised millimetre-wave baseband comb source covering the sub-terahertz region, generated from an optical microcomb source. Our microresonator-filtered microcomb enables direct, coherent downconversion via photoconductive antennas, even without external amplification. The metrological-grade optical soliton source produces single-cycle, naturally zero carrier-envelope offset millimetrewave baseband combs. It supports time-domain spectroscopy without any need to temporally align the source and detection pulses, as the ultra-high phase coherence allows significant differences between the optical paths of the source and detection pulses, which we tested over 8m, finding no degradation even in freerunning operation. Finally, the multisoliton operation regime provides a simple way of spectrally tailoring the microwave output by selecting different optical soliton states.