# Tunable dual-comb from an all-polarization-maintaining single-cavity dual-color Yb:fiber laser

## TL;DR

This paper presents a tunable dual-comb system using an all-polarization-maintaining, dual-color Yb fiber laser with independent mode-locking, spectral overlap, and RF comb generation, suitable for spectroscopy.

## Contribution

It introduces a novel dual-color fiber laser with tunable repetition rate difference and wavelength shift capabilities for flexible dual-comb applications.

## Key findings

- Achieved dual-color operation within a single cavity.
- Demonstrated RF comb generation with tunable line spacing.
- Validated the system's use in spectroscopy by measuring etalons.

## Abstract

We demonstrate dual-comb generation from an all-polarization-maintaining dual-color ytterbium (Yb) fiber laser. Two pulse trains with center wavelengths at 1030 nm and 1060 nm respectively are generated within the same laser cavity with a repetition rate around 77 MHz. Dual-color operation is induced using a tunable mechanical spectral filter, which cuts the gain spectrum into two spectral regions that can be independently mode-locked. Spectral overlap of the two pulse trains is achieved outside the laser cavity by amplifying the 1030-nm pulses and broadening them in a nonlinear fiber. Spatially overlapping the two arms on a simple photodiode then generates a down-converted radio frequency comb. The difference in repetition rates between the two pulse trains and hence the line spacing of the down-converted comb can easily be tuned in this setup. This feature allows for a flexible adjustment of the tradeoff between non-aliasing bandwidth vs. measurement time in spectroscopy applications. Furthermore, we show that by fine-tuning the center-wavelengths of the two pulse trains, we are able to shift the down-converted frequency comb along the radio-frequency axis. The usability of this dual-comb setup is demonstrated by measuring the transmission of two different etalons while the laser is completely free-running.

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Source: https://tomesphere.com/paper/1906.03029