Mode-locked and tunable fiber laser at the 3.5 ${\mu}$m band using frequency-shifted feedback

TL;DR

This paper presents a tunable, mode-locked fiber laser operating at 3.5 μm with broad wavelength tuning and stable pulse generation, marking the longest wavelength for such lasers and enabling environmental sensing applications.

Contribution

The authors demonstrate the first widely tunable, stable, mode-locked fiber laser at 3.5 μm with the longest wavelength achieved in rare-earth doped fiber lasers.

Findings

Achieved wavelength tuning over 215 nm range.

Maximum average power of 208 mW at 3612 nm.

Stable mode-locking with 53 ps pulses.

Abstract

We report on a mid-infrared mode-locked fiber laser that uses an acousto-optic tunable filter to achieve frequency-shifted feedback pulse generation with frequency tuning over a 215 nm range. The laser operates on the 3.5 ${\mu}$m transition in erbium-doped zirconium fluoride-based fiber and utilizes the dual-wavelength pumping scheme. Stable, self-starting mode-locking with a minimum pulse duration of 53 ps was measured using a two-photon absorption autocorrelator. The longest wavelength demonstrated was 3612 nm and a maximum average power of 208 mW was achieved. This is the longest wavelength rare-earth doped mode-locked fiber laser demonstrated to the best of the authors' knowledge. The broad tunability promises potential uses for environmental sensing applications.