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By introducing material gain within a bulk nonlinear medium, it is possible to taper adiabatically a self-guided beam and to preserve its planar wave front. The amount of tapering can be controlled externally by varying the gain through the intensity of a pump beam. This self-guided beam induces a tapered (linear) waveguide, which in turn can guide a low-power (signal) beam. Two counterpropagating self-guided beams induce tapered, mismatched (linear) couplers that allow for all-optical, tunable, adiabatic power splitting without waveguide fabrication.
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Snyder et al. (1992) studied this question.
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