Reduced quantum defect in a Yb-doped fiber laser by balanced dual-wavelength excitation

Abstract

Two color optical pumping, both above (anti-Stokes pump or ASP) and below (Stokes pump) the lasing wavelength, was adopted to reduce the net quantum defect (QD) in a solid-state Yb-doped fiber laser. The reduction in QD was achieved by converting a substantial portion of the gain medium's phonons directly into useful photons through a dual-wavelength excitation (DWE) mechanism. Since this is achieved through the usual processes of absorption and stimulated emission associated with lasing, high efficiency can be maintained. Both time domain and power measurements are presented, demonstrating a 13.2% reduction of the system's net QD and a 13.8% reduction in the lasing threshold power. These values were limited only by the available ASP power. Laser slope efficiency, with respect to launched ASP power, was found to be as high as 38.3%. A finite difference time domain model, developed to elucidate the role of both pumps in populating the upper states, corroborated the experimental findings. The DWE concept proposed here opens the door to an “excitation-balanced” type of self-cooled fiber laser. Simulation results also suggest that the technique is scalable and conceptually applicable to other solid-state laser systems.

Prospects and challenges for all-optical thermal management of fiber lasers

“…In this case, advantages are gained from materials whose spectroscopy favors shorter wavelength operation (such as the fluorosilicates [26] and phosphosilicates [53]). Another promising approach to reducing the laser QD can be found in multi-wavelength pumping [54], referred to here as excitation balancing. This method has been introduced to solid-state lasers quite recently (2021), and therefore it has not been studied as extensively.…”

Material approaches to thermal management in advanced fiber lasers and amplifiers

“…Quantum defects below 1% have been realized in this way [18]. The second, while also benefitting from the "intrinsically low" QD in similar MCM silicate fibers, further drives low QD performance by using two wavelengths (Stokes and anti-Stokes pumping) in a pulsed configuration to create "excitation balancing" [19]. In this case, the anti-Stokes pumping is done at a wavelength greater than the lasing wavelength, ultimately contributing a negative QD to the system via conversion of phonons into light energy.…”

The uniqueness of glass for passive thermal management for optical fibers

“…Excitation-balanced lasers (ExBLs), based on a twocolor pumping scheme, have recently been developed as a new approach to an effectively reduced QD fiber laser. 59 As stated above, pumping a laser in the steady state with a wavelength longer than the intended lasing wavelength will not result in gain, prohibiting laser oscillation. In the case of an amplifier, where both a signal and pump are present together, signal energy will be transferred to the pump when 𝜆 pump > 𝜆 laser resulting in net loss.…”

“…Excitation‐balanced lasers (ExBLs), based on a two‐color pumping scheme, have recently been developed as a new approach to an effectively reduced QD fiber laser 59 . As stated above, pumping a laser in the steady state with a wavelength longer than the intended lasing wavelength will not result in gain, prohibiting laser oscillation.…”