Design of a New Family of Narrow Linewidth Mid-Infrared Lasers

TL;DR

This paper proposes a new design for narrow linewidth mid-infrared lasers using Pi-phase-shifted fiber Bragg gratings, enabling low-threshold, high-coherence sources suitable for sensing and spectroscopy across 2.5 to 9.5 micrometers.

Contribution

It introduces a practical design for mid-infrared distributed feedback Raman fiber lasers with ultra-narrow linewidths using low-phonon-energy glass fibers.

Findings

Anticipated linewidths below 1 MHz

Threshold pump powers as low as a few milliwatts

Feasibility across a broad wavelength range of 2.5 to 9.5 micrometers

Abstract

We describe the design of a new family of high spectral brightness narrow linewidth (NLW) mid-infrared (MIR) lasers of < 1 MHz anticipated linewidths with potential for operation at any target wavelength between 2.5 and 9.5 um. More specifically, we analyze the potential performance characteristics of mid-infrared distributed feedback (DFB) Raman fiber lasers (RFLs) based on Pi-phase-shifted (PPS) Fiber Bragg Gratings (FBGs) written in appropriately chosen low-phonon-energy glass fibers. In particular, we calculate anticipated threshold pump powers for optimal laser designs and pump wavelengths for single frequency (fundamental mode) operation of specific mid-infrared DFB-RFLs operating at chosen target wavelengths, and show that these pump powers can be as low as a few milliWatts for MIR DFB-RFLs fabricated with appropriate low-loss small mode area single mode fibers. As such, we clearly establish the PPS-DFB RFL platform as a very practical approach for constructing a broad range of narrow linewidth MIR coherent sources for numerous applications, including proximal and remote sensing of molecules and various high spectral brightness and long coherence length MIR applications.