Deep-red double-clad fiber laser at 717 nm

Oxxius deep-red fiber laser sources today

Published in Optics Letters in 2023, this paper reports a deep-red Pr:ZBLAN fiber laser at 717 nm delivering 0.71 W of output power with 9.0% slope efficiency — pumped by a ∼442 nm GaN diode laser. The gain fiber is a 0.8 mol% PrF₃-doped ZBLAN double-clad fiber with a 7.5 µm single-mode core and a double D-shaped inner cladding, allowing efficient pump coupling from a multimode GaN diode while maintaining single-mode output at 716.7 nm. This Optics Letters paper is the peer-reviewed journal companion to the ASSL 2022 conference presentation of the same results, providing the detailed simulation framework that establishes guidelines for scaling this architecture toward watt-level deep-red output.

The 717 nm wavelength occupies a spectral region of growing relevance for life science imaging. It lies within the optimal excitation window for several deep-red fluorophores used in super-resolution microscopy and single-molecule imaging, while also benefiting from reduced tissue scattering compared to visible wavelengths below 650 nm. For neuroscience applications, 717 nm is well-matched to red-shifted channelrhodopsin variants used in optogenetics. The combination of single-mode output and watt-approaching power levels makes this source a compelling candidate for high-sensitivity fluorescence excitation in next-generation instruments.

Enabling technology: Oxxius GaN pump modules

The 442 nm GaN pump diode module used in this experiment represents the class of high-brightness blue diode sources that Oxxius develops and manufactures for exactly this application. The spatial brightness of the pump is the critical parameter governing both threshold and slope efficiency in single-clad and double-clad fiber laser geometries at 717 nm. Oxxius’s High-Power Diode Modules at 442 nm provide the beam quality and power stability required to drive Pr:ZBLAN fiber lasers to the output levels demonstrated in this and companion publications.

Abstract

We report on a double-clad fiber laser operating on the ^3P_0 → ^3F_4 Pr^3+ transition (in the deep-red spectral range) pumped by a GaN diode laser at ∼442 nm. It employs a 0.8-mol% PrF_3-doped ZBLAN double-clad fiber with a 7.5-µm core, a double D-shaped inner cladding, and a length of 3.0 m. The laser delivers a maximum output power of 0.71 W at 716.7 nm with a slope efficiency of 9.0% (versus the launched pump power) and a laser threshold of 0.90 W. The laser emission is partially polarized. The laser performance is simulated providing a guideline for watt-level deep-red fiber laser sources.