Comparison Of Phase Modulation Schemes For Coherently Combined Fiber Amplifiers

Abstract

Optical linewidth broadening through both white noise (WNS) and pseudo-random binary sequence (PBRS) phase modulation are effective techniques for suppressing stimulated Brillouin scattering (SBS) in high-power fiber amplifiers. However, detailed studies comparing both coherent beam combining and SBS suppression of these phase modulation schemes have not been reported. In this study, a passive fiber cutback experiment is performed comparing the SBS threshold enhancement factor of a PRBS and WNS broadened seed as a function of linewidth and fiber length. Particularly, assuming an optimal PRBS pattern is chosen, pseudorandom modulation provides superior SBS suppression than WNS for a given fiber length and signal linewidth. Furthermore, two WNS and PRBS modulated 150 W fiber lasers are coherently combined to measure and compare the combining efficiency, beam quality, and coherence as a function of optical path length difference. Notably, the discrete spectral density of PRBS modulation provides a re-coherence effect where the lasers periodically come back into phase. Overall, this may reduce path length matching complexity in coherently combined fiber laser systems.

Publication Date

10-19-2015

Publication Title

Optics Express

Volume

23

Issue

21

Number of Pages

27046-27060

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1364/OE.23.027046

Socpus ID

84957045883 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/84957045883

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