R. Reinisch

Enhanced light transmission by hole arrays

The extraordinary optical transmission of a metallic film pierced by a two-dimensional subwavelength hole array, observed by Ebbesen et al, is explained using rigorous electromagnetic analysis and a phenomenological approach. The analysis is based on Lis Fourier-modal method extended to crossed gratings, which reduces the diffraction problem to the search for eigenvalues and eigenvectors of a particular matrix. The computation of the eigenvalues allows us to find a new channel for light transmission through the subwavelength holes, which differs from the transmission channel in the one-dimensional case (lamellar or rectangular-rod grating). It is demonstrated that the enhanced transmission is due to the excitation of a surface plasmon on the lower metallic surface.

Second-harmonic-generation-induced optical bistability in prism or grating couplers

We deal with second-harmonic generation in chi((2)) nonlinear-optical resonators such as prism or grating couplers. The theoretical study is performed within the framework of a recently developed coupled-mode analysis leading to a set of equations governing the amplitudes of pump and second-harmonic frequency fields. We predict analytically that second-harmonic generation in prism or grating couplers may lead to optical bistability. We believe this to be the first demonstration of such an effect in chi((2)) optical resonators.

Observation of stimulated surface-enhanced Raman scattering through grating excitation of surface plasmons

We report on an experiment with surface-enhanced Raman scattering on gratings overcoated by copper phtalocyanine that shows that, because of the resonant excitation of surface plasmons, a stimulated Raman scattering process occurs. The corresponding threshold value of the pump power is rather low, of the order of 40 mW. This observation was made with a thin (5-nm) film of copper phtalocyanine. The theoretical study is developed by coupled-mode analysis that makes full use of the electromagnetic resonant feature of this nonlinear interaction.

Phase matching in Čerenkov second-harmonic generation: a leaky-mode analysis

Use of leaky modes allows us to demonstrate very simply that ?erenkov second-harmonic generation is not free of phase matching. The ?erenkov phase-matching condition is derived for what is to our knowledge the first time. The way to overcome the difficulty linked with the divergence at infinity of the leaky modes is discussed.

Phase-matched guided-wave optical bistability in chi ((2)) optical resonators.

We treat χ(2) optical resonators, such as prism or grating couplers, illuminated not only by the field at the fundamental frequency but also by the one at the second harmonic. We show that optical bistability may exist even when phase matching is fulfilled. This kind of optical bistability involves a new nonlinear resonance.

Nonlinear zeros in second-harmonic generation at grating couplers

In a study concerned with second-harmonic generation at grating couplers, Kull et al. [Opt. Lett. 16, 1930 (1991)] observed a curious phenomenon in which the second-harmonic efficiency exhibits dips, instead of peaks, when the angle of incidence of the pump beam is scanned through its resonant value. This surprising result has not been explained. It is our aim to show that this effect is closely related to the existence of nonlinear zeros.

Numerical optimization of grating-enhanced second-harmonic generation in optical waveguides

Rigorous electromagnetic theory is combined with a phenomenological approach to permit optimization of grating-enhanced second-harmonic generation (SHG) in optical waveguides. Provided that the absorption losses in the optically nonlinear layer are not high, maximum SHG is observed when phase matching occurs between the incident wave at the pump frequency and guided waves at both the pump and the signal frequencies. Different coupling mechanisms are considered, and a procedure for determining the optimal groove depth and period of the grating is discussed. The phenomenological approach permits deeper physical insight into the problem and a considerable saving of computation time. Direct phase matching is shown to result in stronger SHG than indirect phase matching (performed through the grating vector), even if the former includes coupling between waveguide modes of different orders.

M-line spectroscopy for nonlinear waveguide characterization

The nonlinear M-line technique is based on the analysis of the nonlinear change in the shape of the dark line associated with the excitation of guided waves. It is an easy technique for the determination of Kerr properties of thin films which can constitute optical waveguides. Full spatio-temporal nonlinear modelization tools have been developed recently for nonlinear waveguide couplers which are used for the determination of the complex nonlinear coefficient of new organic materials.

Electromagnetic Resonance Induced Nonlinear Optical Phenomena

It is well known that efficient nonlinear optical interactions require strong nonlinear polarizations.1,2 This is achieved by increasing the nonlinear susceptibility and/or the electromagnetic field inside the nonlinear medium. The former requires a material study whereas the latter, in which we are interested, requires an electromagnetic study.