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Transient modal instabilities in high power fibre lasers

Transient modal instabilities in high power fibre lasers
Transient modal instabilities in high power fibre lasers
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.
Scarnera, V.
a7e33d06-60f4-4bf7-81bc-1b1e48ea691a
Ghiringhelli, F.
773894f2-f092-452f-84ae-98e3b64aca3f
Durkin, M. K.
c9917856-22d8-40b0-ad28-21c484ca30ed
Codemard, C. A.
3aa50483-b61c-4e7e-b178-c9a88bb47bef
Zervas, M. N.
1840a474-dd50-4a55-ab74-6f086aa3f701
Scarnera, V.
a7e33d06-60f4-4bf7-81bc-1b1e48ea691a
Ghiringhelli, F.
773894f2-f092-452f-84ae-98e3b64aca3f
Durkin, M. K.
c9917856-22d8-40b0-ad28-21c484ca30ed
Codemard, C. A.
3aa50483-b61c-4e7e-b178-c9a88bb47bef
Zervas, M. N.
1840a474-dd50-4a55-ab74-6f086aa3f701

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).

Record type: Conference or Workshop Item (Paper)

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.

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More information

Published date: 30 October 2017
Venue - Dates: Conference on Lasers and Electro-Optics Europe (CLEO EUROPE), 2017-06-25 - 2017-06-29

Identifiers

Local EPrints ID: 437520
URI: http://eprints.soton.ac.uk/id/eprint/437520
PURE UUID: 18bc76f9-8a3b-4071-9ee4-4a75998cbcc9
ORCID for V. Scarnera: ORCID iD orcid.org/0000-0001-8646-7063
ORCID for M. N. Zervas: ORCID iD orcid.org/0000-0002-0651-4059

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Date deposited: 03 Feb 2020 17:32
Last modified: 09 Jan 2022 02:41

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Contributors

Author: V. Scarnera ORCID iD
Author: F. Ghiringhelli
Author: M. K. Durkin
Author: C. A. Codemard
Author: M. N. Zervas ORCID iD

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