Abstract
The x(2) cascading nonlinearity1 is attracting new attention for applications as diverse as ultrafast switching, optical transistor action, and one- and two-dimensional spatial soli-tons. One advantage of this off-resonant process with x'-1 materials is that we need a relatively small light intensity for inducing a particular nonlinear phase shift when compared with conventional x<",) processes. One limitation ihat has previously been believed to be serious is the temporal walkoff that occurs between fundamental and second-harmonic (SH) pulses in dispersive media. For example, the maximum propagation length used in early experiments was limited to 1.9 times the walk-off length (I„,alt._0ffV because the fundamental pulse was assumed to no longer interact with the SH pulse when the fundamental pulse walks off beyond the SH pulse. Because they exhibit very short walk-off lengths because of their strong refractive-in des dispersion, semiconductors are apparently unsuitable for cascading despite their large nonlinearities [(&"'e!s10Ûs pm/Vj and potential for integration. In fact, the cascading phase shift in strong walk-off regimes has never been investigated, either experimentally or theoretically. And, to the contrary of currently held opinion, this paper shows that a significant cascading phase shift occurs even in a strong walk-off regime, based on numerical simulations. As an example, the operating conditions for a semiconductor-based Mach-Zehnder switch are estimated.
© 1997 Optical Society of America
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