Resonantly enhanced second harmonic generation in a one-dimensional GaN-based photonic crystal slab
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E7.1.1
Resonantly enhanced second harmonic generation in a one-dimensional GaN-based photonic crystal slab
Jérémi Torres, Marine Le Vassor d’Yerville, David Cassagne, René Legros, Jean-Paul Lascaray, Emmanuel Centeno, Jean-Paul Albert and Dominique Coquillat Groupe d’Etude des Semi-conducteurs, UMR 5650 CNRS-Universite Montpellier II Place Eugene Bataillon, 34095 Montpellier, FRANCE
ABSTRACT We have performed investigations of resonance effects inside a gallium nitride onedimensional photonic crystal slab in order to enhance the second-harmonic generated from an beam incident on the surface of the slab. Convenient conditions on the incident beam propagation direction and polarization are first identified by experimental or theoretical linear optical studies. Giant enhancements in the second-harmonic conversion have been obtained by comparison with the unpatterned GaN layer. The combined role of the resonant coupling of the fundamental field and of the second-harmonic field has been observed by rotating the polarization of the fundamental beam.
INTRODUCTION Since their first proposal in 1987 [1, 2], photonic crystals (PhCs) structures have been the subject of an enthusiastic interest especially because of the possibility to generate photonic band gaps. These photonic band gaps are frequency ranges inside which the propagation of electromagnetic waves is forbidden, and their emergence is due to a spatial periodic modulation of the dielectric function, in a similar way as the electronic band gap of semiconductors is generated by the periodicity of the crystal atomic lattice. This property arises from a strong modification of the dispersion curves related to the periodic modulation of the dielectric constant of the structure. Beside photonic band gaps, other remarkable optical properties emerge because of the existence of high density of states regions, lying inside the allowed bands, especially close to the band edges. Inside these regions, electromagnetic modes are characterized by low group velocities and a strong concentration of the photonic modes energy inside small volumes. This leads to an enhanced optical response of the PhC structure, and is in particular expected to exalt non-linear optical processes such as frequency conversion. Here we study the second harmonic generation (SHG) process produced inside a GaN-based PhC structure. Our choice to use GaNbased structures is motivated by their ability to convert light from infrared to ultraviolet due to their wide transmission range (from 365 nm to 13.5 µm). Moreover using GaN photonic structures for efficient non-linear optical processes benefits from their high optical damage thresholds and their fairly large non linear coefficients [3] (d33~11pmV-1 for GaN, as compared with d33=25.2pmV-1 for LiNbO3). An enhancement of the nonlinearities inside GaN can be moreover expected in the presence of quantum wells inducing internal piezoelectric fields [4]. However, the use of bulk GaN material has not been possible practically due to the high dispersion and the smal
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