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

Abstract

It is hard to overstate the utility of lasers in modern technology. Optical-fiber-based lasers are of particular value thanks to their combination of small form factors, afforded by the coilability of the thin strands of fiber and high beam-quality output. The optical fiber geometry also possesses a relatively high surface-area-to-volume ratio, rendering thermal management somewhat more straightforward than in other bulk laser types. Regardless, the generation of heat during the lasing process can still be problematic for a myriad of reasons, and conventional methods of thermal management do not comport with the potential compactness and elegance of fiber lasers as technological solutions. This Perspective summarizes recent advances in glass science and optical fiber engineering to support the provocative premise that heat generation in future laser systems can be entirely managed by a combination of fiber materials and novel laser physics. Letting the fiber manage heat itself would have significant impacts on enhancing system performance while greatly reducing size, weight, power-consumption, and cost.

Single-mode radiation-balanced Yb-doped silica fiber laser and amplifier

“…A fit of this measured dependence to the model of ASF cooling in a single-mode fiber placed in air [8] permitted to infer the fiber's residual absorption coefficient (αba = 25 dB/km) and critical quenching concentration Nc = 1.61x10 27 Yb 3+ /m 3 . This latter value ranks among the best (highest) reported for a silica fiber [3].…”

“…The fiber has a core diameter of 7.8 µm, a numerical aperture of 0.098, and a V number of 2.26 at 1064 nm (single mode). It is doped with 1.61x10 26 Yb 3+ /m 3 , a high value among fibers exhibiting cooling properties [3]. The core was also doped with a high concentration of Al (1.6 wt.% Al2O3) to increase the Yb2O3 solubility in the host glass and reduce quenching.…”

“…In recent years, rapid progress in various applications, notably quantum technologies, has generated an increased demand for advancements in laser technology, especially lasers and amplifiers with a high-power stability, high-beam quality, and low-frequency noise [1,2]. These desirable attributes are generally constrained by the generation of heat in the active fiber due to the quantum defect [3,4], which induces undesirable effects ranging from power and frequency instabilities at lower power to self-focusing and transverse-mode instabilities instability at higher power levels. Conventional heat-remediation techniques like forced-air cooling or liquid cooling are efficacious, but they increase weight, size, and cost, and they introduce vibrations and non-uniform cooling that can adversely affect the laser mode, power, and frequency stability.…”

“…Residual absorption of pump and signal photons by impurities also generates heat in proportion to the pump power. Recent progress in Yb-doped silica fabrication [3] has led to the advent of glass compositions with high Yb concentrations, low quenching, and reduced residual absorbing impurities, in both bulk glass [9,10] and fibers [3,11]. These material breakthroughs have enabled significant cooling achievements, including a temperature change of -67 K in an aluminosilicate rod fiber with a 900-µm core [9], and -70 mK in a small-core aluminosilicate fiber in air [11], both measured from room temperature.…”