Modal sensitivity analysis for single mode operation in large mode area fiber

Benoit Sévigny; Xiaoxing Zhang; Marc Garneau; Mathieu Faucher; Yannick Keith Lizé; Nigel Holehouse

doi:10.1117/12.775101

25 February 2008 Modal sensitivity analysis for single mode operation in large mode area fiber

Benoit Sévigny, Xiaoxing Zhang, Marc Garneau, Mathieu Faucher, Yannick Keith Lizé, Nigel Holehouse

Proceedings Volume 6873, Fiber Lasers V: Technology, Systems, and Applications; 68730A (2008) https://doi.org/10.1117/12.775101
Event: Lasers and Applications in Science and Engineering, 2008, San Jose, California, United States

Abstract

Most of the current large mode area (LMA) fibers are few-moded designs using a large, low numerical aperture (N.A.) core, which promotes mode coupling between core modes and increases bending losses (coupling with claddingmodes), which is undesirable both in terms ofmode area and beamquality. Furthermore, short LMA fiber lengths and small cladding diameters are needed to minimize nonlinear effects and maximize pump absorption respectively in high-power pulsed laser systems. Although gain fiber coiling is a widely used technique to filter-out unwanted modes in LMA fibers, coupling between modes can still occur in component leads and relay fibers. In relay fiber, light coupled into higher-order modes can subsequently be lost in the coiling or continue as higher-order modes, which has the overall effect of reducing the effective transmission of the LP₀₁ mode and degrading the beam quality. However, maximum transmission of the LP₀₁ mode is often required in order to have the best possible beam quality (minimal M²). Launching in an LMA fiber with a mode field adapter (MFA)¹ provides an excellent way of ensuring maximum LP₀₁ coupling, but preservation of this mode requires highmodal stability in the output fiber. Small cladding, low N.A. LMA fibers have the disadvantage of being extremely sensitive to external forces in real-life applications, which is unwanted for systems where highly sensitive mode coupling can occur. In this paper, we present a detailed experimental and theoretical analysis of mode coupling sensitivity in LMA fibers as a function of fiber parameters such as N.A., core diameter and cladding diameter. Furthermore, we present the impact of higher N.A. as a solution to increase mode stability in terms of its effect on peak power, effective mode area and coupling efficiency.

Citation Download Citation

Benoit Sévigny, Xiaoxing Zhang, Marc Garneau, Mathieu Faucher, Yannick Keith Lizé, and Nigel Holehouse "Modal sensitivity analysis for single mode operation in large mode area fiber", Proc. SPIE 6873, Fiber Lasers V: Technology, Systems, and Applications, 68730A (25 February 2008); https://doi.org/10.1117/12.775101

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