Nonlinear Distributed Coupling into Guided Waves

Abstract

Thin-film waveguides are a very attractive material geometry for performing nonlinear optics experiments for a number of reasons. They provide diffractionless propagation in one or more dimensions. Furthermore, efficient interactions are possible at low powers becasue of beam confinement to dimensions of the order of the wavelength of light. The application of second-order nonlinear interactions to optical waveguides is a well-developed field.^1,2 In contrast to this, interest and progress in third-order nonlinear guided wave phenomena is much more recent. Demonstrated to date have been degenerate four wave mixing in CS₂-covered³ and semiconductor-doped glass⁴ waveguides, coherent anti-Stokes Raman scattering with monolayer sensitivity,⁵ nonlinear waveguiding phenomena,^6,7 and a variety of phenomena related to distributed coupling into nonlinear waveguides.^8-17 One of the disadvantages of distributed coupling via prisms or gratings is decreased coupling efficiency^11,12,16 at high laser powers, making efficient nonlinear interactions more difficult to achieve. On the other hand, the distributed coupling does lead to interesting phenomena including optical limiting,¹² optical bistability,^13,14 switching,^{10,12–15,17} and measurement of waveguide nonlinearities.^8–10,12,16 In this paper we summarize our experiments on nonlinear distributed couplers in various time regimes.