We report an experimental observation of optical second-harmonic generation in an amorphous silicon–nitride based planar microcavity. The spectral dependence of the second-harmonic signal is investigated as a function of both wavelength and polarization state of the fundamental beam. The second-harmonic signal is enhanced by two orders of magnitude at the Fabry–Perot resonance. We ascribe the origin of the optical nonlinearity to surface second-harmonic generation occurring at the interfaces of the multilayered structure, where the resonant enhancement is due to the high intracavity fundamental light intensity and to the increase of the photonic density of states. Analysis of polarization dependence shows that interfacial second-order nonlinearity results from a distribution of dipoles directed perpendicularly to the plane of the film and distributed accordingly to an ∞mm point group symmetry.

Abstract:We carry out wavelength-dependent second harmonic interference experiments using thin films of an organic dye as nonlinear optical sources. While the measured difference of refractive index between the fundamental and second harmonic wavelengths follows the theoretical expectation for air in a wide spectral region, anomalous dispersion is observed when the second harmonic light lies in the absorption band of the dye. The sensitivity of the technique to small refractive index variations may prove useful for sensing applications as well as for testing models of light dispersion in weakly dispersing and absorbing media. Metrologia 31, 315-6 (1994). 15. J. C. Owens, "Optical refractive index of air: dependence on pressure, temperature and composition,"Appl. Opt. 6, 51-59 (1967). 16. E. R. Peck and K. Reeder, ""Dispersion of air,"" J. Opt. Soc. Am. 62, 958-962 (1972

Photonic crystals (PCs) are an ideal framework to control optical nonlinear interactions. Since 1995, it has been shown that within a PC one may enhance, [1][2][3] phase match, [4,5] or hold a non-vanishing second-order interaction even if the material is centrosymmetric. [6] More recently, it has been pointed out that the structuring of the dielectric together with modulation of the second-order nonlinear susceptibility may lead to a backward parametric oscillation, [7] a nonlinear effect predicted many years ago that has not yet been observed. All such control over the nonlinear interaction is possible in 1D, 2D, or 3D PCs. Among them, 2D photonic structures are, perhaps, the most interesting, because such structures could, in principle, be easier to integrate into optoelectronic devices meant for light amplification, light generation at other frequencies, optical-data processing, or any kind of sensing. [8][9][10][11] The fabrication of 2D PCs using top-down procedures such as electron-beam lithography has been applied successfully in several kinds of semiconductors. [12][13][14] Unfortunately, patterning of inorganic crystals applying, for instance, focused-ionbeam bombardment and subsequent reactive-ion etching is limited to small depth/diameter ratios. [15] Developing procedures that would be more efficient in patterning inorganic crystals is very interesting for the fabrication of new light modulators that could take full advantage of the nonlinear optic and electro-optic coefficients of such materials. [16] On the other hand, neither the viability nor cost-effectiveness of integrating some very expensive nonlinear semiconductors in silicon-based devices have been clearly demonstrated. There are alternative routes to pattern inorganic nonlinear optical materials, such as KTiOPO 4 (KTP) or LiNbO 3 routes based on a periodical poling followed by a selective domain etching.[17]Although periodical poling has been applied with different degrees of success to obtain 1D arrays with a sub-micrometer period in some nonlinear materials, [18] it is still difficult to accurately control the size of small domains. Moreover, after poling one ends up with a stand-alone sample that would, certainly, be difficult to embed in any silicon-based device. We present here a completely novel combination of both topdown and bottom-up approaches to grow 2D PCs of KTP. These crystals are grown in ordered macroporous silicon templates. An additional benefit of such an approach is that, while being simple, the silicon matrix and the structured nonlinear material, which would eventually be used to modulate or generate light, forms an integral unit. To fabricate such a hybrid structure, an ordered silicon matrix of air holes and a KTP substrate were kept closely bound in a growth solution of KTP. We observed that KTP columns grew inside the air holes of the silicon matrix following the crystalline orientation of the substrate. Finally, the potential of the 2D array of KTP columns to control the nonlinear interaction was demonstrated by ...

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We demonstrate coherent optical coupling between molecular and plasmon resonances that are well separated in energy. In the presence of metallic nanoparticles, the second harmonic spectrum of organic dyes no longer peaks at the absorption wavelength but is instead blueshifted by 25 nm towards the localized plasmon resonance. The phase of the light generated by the dyes displays a large modulation across the plasmon resonance and no change across the molecular one. The second harmonic signal contributed by the nanoparticles, which is peaked at the plasmon frequency when no molecules are present, similarly displays a shift towards the molecular resonance in their presence. A model based on the interplay of the nonlinear optical near fields is able to account for these observations.