Temperature investigation of a multi-watt thulium-doped fiber laser

Thulium-Doped Fiber Lasers (TDFL) emitting at 2 μm wavelength are used in various applications such as imaging, telecommunication and optical countermeasures. Many of these applications require highly integrated and passively cooled lasers with low SWaP (size, weight, and power) architecture that can work in harsh environment at different temperatures. We investigated the temperature dependence of a multi-watt TDFL with a low SWaP architecture for temperatures ranging from 253 K till 573 K. Cladding-pumping with 793 nm diode lasers is used for high-power TDFLs to take advantage of the cross-relaxation effect to double the quantum efficiency. However, since the 3 H4 absorption band is relatively narrow with a 16 nm FWHM compared to the diode wavelength shift of 0.3 nm/K, these diode lasers have to be wavelength or temperature stabilized using volume Bragg gratings or Peltier elements. Both approaches either limit the applicable temperature range1 or decrease the overall efficiency. In contrast in-band core-pumping directly into the 3 F4 level offers a broad absorption band ranging from 1550 nm till 1720 nm and is therefore preferred for low SWaP TDFLs. We investigated therefore a low SWaP TDFL that is core-pumped by an in-house built erbium:ytterbium-codoped fiber laser (EYDFL) with pump wavelength of 1567 nm.