200 W Self-Organized Coherent Fiber Arrays Hans Bruesselbach, Monica Minden, J. L. Rogers, D. C. Jones, M. S. Mangir HRL Laboratories, LLC 3011 Malibu Cyn Rd, Malibu, CA 90265 Phone: 310-317-5204 Fax: 310-317-5268 email: hwBruesselbach@hrl.com Abstract: We report producing 200 W coherent fiber laser arrays without active control. This outcome is obtained via self-organization using a non-fiber coupler for two- to ten- laser arrays. © 2005 Optical Society of America OCIS Codes: 060.4370 Nonlinear optics, fibers 060.2320 Fiber optics amplifiers and oscillators 1. Introduction Lasers are nonlinear oscillators capable of complex dynamical behaviors. Studies of nonlinear systems have shown that under the correct conditions self-organization phenomena cause groups of dissimilar nonlinear oscillators to passively form in-phase states, without any active control. These studies have further shown that both the correct inherent dynamics and proper oscillator connectivity are required for in- phase states to self-organize. Fiber lasers offer the desirable characteristics of high efficiency, high power per weight, good thermal characteristics, and simple infrastructure; their limited individual output can be overcome by allowing them to form arrays. We report our experimental demonstration of up to 200 W output from fiber laser arrays. Using a different physical architecture than our initial work [1], we again confirm that fiber laser arrays can self- organize coherent and in-phase states. We observe that self-organization occurs only when the intensity in the fiber is not so large that the optical phase is disrupted by cross phase modulation, as well as when the gain is not so saturated that the Kramers-Kronig-mediated phase adjustment is not also saturated. 2. The Experiment 50% 50% 50% 50% 50% 50% 50% 50% 20% Fiber #1 Fiber #2 Fiber #3 Fiber #4 Fiber #5 Fiber #6 Fiber #7 Fiber #8 Fiber #9 Fiber #10 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 l / 4 l / 2 Splice Grating Pump Splice Grating Pump Splice Grating Pump Splice Grating Pump Splice Grating Pump Splice Grating Pump Splice Grating Pump Splice Grating Pump Splice Grating Pump Splice Grating Pump R 16% 20% 50% 50W 50W 80W 17W 2W <1W (a) (b) Fig. 1: (a) Experimental layout in which up to ten fiber lasers are combined. Fiber lasers are described in text. Optical path lengths external to fibers the same for all lasers. Lenses collimate the beams emerging from fibers. Their polarization are adjusted by the wave plates. Beams then are directed by fold mirrors (not shown) to mirrors (reflectivities indicated) which are chosen to provide uniform all-to-all coupling between the lasers, adjustable by changing the reflectivity of the mirror labeled “R”. The 0.4 nm wide gratings overlap spectrally; they were temperature controlled and tuned to center at 1073.5±0.2 nm. (b) The measured output power is shown when only lasers #9 & 10 are operating, at 50 W, as discussed in Section 3 of text. Fig. 1 shows the coupling approach used – an external mirror arrangement. Table I summarizes the fiber lasers’ properties. Separate experiments were done with two different sets of ten Yb-doped cladding- pumped fiber lasers. Each fiber laser uses a diode pump laser bank, which is fiber coupled, with standard industrial 400 µm-core fiber, into a lens module which end-couples this fiber into either the Crystal Fibre™ or, with a different lens module, the Nufern™ fiber. Each Crystal Fibre™ laser, Fig. 2, has a section of non-Yb air-guided fiber to guide the pump; the nearly 100% reflectivity grating is written into its Ge-doped