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Second harmonic conversion enhancement in 2-D planar photonic crystals Jiang, Weiyang

Abstract

Two dimensional (2D) periodic texture in a thin GaAs semiconductor waveguide is used to dramatically enhance the second harmonic conversion efficiency of infrared laser radiation incident on the structure from above. A square lattice of through-holes was etched into a 140 nm thick layer of GaAs supported on a ~ 1 μm thick alumina cladding layer. The pitch of 770 nm, and hole diameter of 320 nm, were chosen so that fundamental light at a wavelength of ~ 2 μm could resonantly excite the lowest order band of leaky photonic eigenstates characteristic of the strongly textured membrane. The energy of the fundamental and second harmonic are both less than the band gap energy of the GaAs, thus avoiding any linear absorption. Used in this way, the structure acts effectively like a nonlinear cavity, where strong internal fields are generated in the GaAs waveguide core layer when the incident light excites a leaky photonic eigenstate. The 2nd order polarization excited in the GaAs can also be resonant with photonic eigenstates at twice the fundamental frequency and in-plane wavevector. Both model calculations and experimental results (obtained by J. Mondia at the University of Toronto) clearly demonstrate that the second harmonic conversion efficiency is dramatically influenced when the fundamental and/or the second harmonic fields are resonant with photonic bands. Peak enhancements of over 1000 times are observed under the "doubleresonance" condition when both the fundamental and second harmonic fields excite photonic eigenstates, and the enhancement clearly tracks the in-coming and out-going dispersion of the photonic bands.

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