20 February 2014 Intra-fiber mode combining schemes, demonstrating high power brightness preservation and coherent-coupling brightness enhancement
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We demonstrate intra-fiber couplers performance that is close to complete brightness preservation up to 3kW. Furthermore, when mutually coherent sources were used, the same couplers were able to achieve brightness enhancement with almost no beam quality (BQ) deterioration. The couplers are based on an adiabatic, all-fiber, mode coupling device preserving the lowest spatial mode orders. Brightness levels that approach the theoretical limits were achieved by compressing the participating modes into a tight cross section. Incoherent combination is shown for 2×1, 3×1 and 7×1 combined elements. Additionally, we present a solution for preserving the beam propagation factor of the coupler by using a specialty engineered core delivery fiber. The fabricated components are fully fiber- integrated, hence, without free-space limitations. An overall transmission of <90% was obtained, while the coupler-delivery connection is responsible for less than 0.5% loss. Consequently, relatively low temperatures were observed in the combiner package. Alternatively, utilizing two mutually coherent sources, a quadratic brightness factor improvement was demonstrated. The scheme does not require polarization preserving fibers, and achieved rugged 'in-phase' mode-locking. This allows for a significantly simplified scheme, compared to common coherent combining methods. Prospect on future trends relating to nonlinearities and thermal load management are discussed.
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Yariv Shamir, Roey Zuitlin, Yaakov Glick, Matitya Aviel, Noam Shafir, Revital Feldman, Asaf Dahan, Benayahu Urbach, Daniel Levy, Eyal Shekel, Yoav Sintov, "Intra-fiber mode combining schemes, demonstrating high power brightness preservation and coherent-coupling brightness enhancement", Proc. SPIE 8963, High-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications III, 89630H (20 February 2014); doi: 10.1117/12.2058099; https://doi.org/10.1117/12.2058099

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