Transient modal instabilities in high power fibre lasers

Scarnera, V., Ghiringhelli, F., Durkin, M. K., Codemard, C. A. and Zervas, M. N. (2017) Transient modal instabilities in high power fibre lasers. Conference on Lasers and Electro-Optics Europe (CLEO EUROPE). 25 - 29 Jun 2017. (doi:10.1109/CLEOE-EQEC.2017.8087025).

Abstract

Transverse modal instability (TMl) [1] is proving to be a major power-scaling limitation in high-power fibre lasers (HPFLs) [2]. The origin of TMI is predominantly thermal and a number of theoretical models have been introduced to explore its characteristics [3-9]. The majority of TMI reports so far deal with fibre amplifiers in MOPA configurations [3-14], and only a small numbers of recent reports refer to TMI in single-cavity HPFLs [15-16]. In addition, most of the experimental TMI work is carried out under steady-state pumping conditions and the transient TMI response is largely overlooked [17]. TMI threshold reduces in the presence of backreflections in amplifiers [18], and, therefore, TMI effects are expected to be more pronounced in single-cavity HPFL oscillators.In this work, we explore for the first time the transient behaviour of power instabilities in single-cavity HPFLs with modulated (ON/OFF) pumping (quasi-CW (QCW) operation). Fig. 1(a) shows the schematic of the tested HPFL. The ends of the Yb-doped signal fibre of a GTWaveTM [19-20] are spliced (S) with singlemode (SM) pigtails with a high reflector (HR) and output coupler (OC) fibre Bragg gratings inscribed in their cores. The fundamental mode (FM) of the active fibre is matched to the SM pigtails. Higher-order modes (HOMs) supported by or thermally induced in the active fibre are scattered into the pigtail cladding at the splices (S), and a cladding-mode stripper (CMS) in the output pigtail is used to strip them out and monitor their power. The combined pump diodes are modulated with variable repetition rates and ON/OFF duty cycles and are launched into the pump fibres of the GTWaveTM. The fundamental mode (FM) at the output and HOMs at the CMS are monitored with high-speed photodetectors.

This record has no associated files available for download.

Contributors

Author: V. Scarnera

Author: M. N. Zervas

Download statistics