Single-cycle all-fiber frequency comb

TL;DR

This paper reports a compact, reliable all-fiber single-cycle frequency comb source that generates ultra-short pulses with broad spectra, enabling advanced light-matter interaction studies and nonlinear optics applications.

Contribution

The authors present the first all-fiber single-cycle frequency comb system, combining amplification, self-compression, and supercontinuum generation in a practical, turn-key device.

Findings

Generated 6.8 fs pulses with 215 kW peak power

Achieved over two-octave spectrum from 700 nm to 3500 nm

Produced stable few-cycle pulses from 6 μm to beyond 22 μm

Abstract

Single-cycle pulses with deterministic carrier-envelope phase enable the study and control of light-matter interactions at the sub-cycle timescale, as well as the efficient generation of low-noise multi-octave frequency combs. However, current single-cycle light sources are difficult to implement and operate, hindering their application and accessibility in a wider range of research. In this paper, we present a single-cycle 100 MHz frequency comb in a compact, turn-key, and reliable all-silica-fiber format. This is achieved by amplifying 2 $\mu$m seed pulses in heavily-doped Tm:fiber, followed by cascaded self-compression to yield 6.8 fs pulses with 215 kW peak power and 374 mW average power. The corresponding spectrum covers more than two octaves, from below 700 nm up to 3500 nm. Driven by this single-cycle pump, supercontinuum with 180 mW of integrated power and a smooth spectral amplitude between 2100 and 2700 nm is generated directly in silica fibers. To broaden applications,few-cycle pulses extending from 6 $\mu$m to beyond 22 $\mu$m with long-term stable carrier-envelope phase are created using intra-pulse difference frequency, and electro-optic sampling yields comb-tooth-resolved spectra. Our work demonstrates the first all-fiber configuration that generates single-cycle pulses, and provides a practical source to study nonlinear optics on the same timescale.