Numerical and experimental investigations of spatial soliton squeezing

Abstract

We describe numerical and experimental investigations of the use of soliton spectral filtering in the spatial domain. As is well known, the nonlinear Schrodinger equation description of optical soliton propagation in single-mode fibers applies equally well to spatial solitons in nonlinear planar waveguides. Therefore, we can expect that the photon-number squeezing methods that work for temporal solitons in optical fibers apply equally well to spatial solitons. The spatial-soliton equivalent of spectral filtering is to use a spatial slit to remove the edge portions of the spatial soliton after it emerges from the planar waveguide. To optimize the experimental configuration, we have modeled the spatial-soliton propagation using a numerical quantum propagation code. Our results show that optimal squeezing is obtained at propagation distances of several soliton periods for solitons with the order N/spl sim/1.2. To experimentally demonstrate photon number squeezing by spatial filtering of spatial solitons, we have fabricated an AlGaAs planar waveguide that is 1.5 /spl mu/m thick and 1-3 cm long. For our device, the bandgap is in the vicinity of 0.8 /spl mu/m, so by using short pulses from a color-center laser tuned to 1.5- to 1.6-/spl mu/m wavelengths, we can excite reasonably large nonlinearities due to two-photon and three-photon resonances in the bandgap. This allows us to create spatial solitons. Spatial solitons created by color-center laser pulses are spatially windowed by slits at the output of the planar waveguide. The spatially filtered pulses are transmitted to a balanced mixer-detector arrangement that allows measurement of the noise of the windowed pulses relative to the shot-noise level.