R. Normandin

Picosecond signal processing with planar, nonlinear integrated optics

The convolution of picosecond optical signals is demonstrated via the nonlinear mixing of guided waves in a Ti in‐diffused LiNbO3 waveguide. Various applications are discussed.

Enhanced second‐harmonic generation by counter‐propagating guided optical waves

Second‐harmonic light generated by mixing oppositely propagating guided waves in LiNbO3 waveguides was enhanced ∼500‐fold by varying the refractive index of the medium above the LiNbO3 surface.

Field analysis of harmonic generation in thin-film integrated optics

Harmonic generation of light in thin-film optical waveguides is analyzed theoretically by evaluating the total electromagnetic fields that satisfy the polarization driven wave equation and the electromagnetic boundary conditions at both interfaces. Analytical expressions are given for the amplitude of the growing wave component of the total fields. The results agree with those of normal mode analysis only in the limit of phase-matched harmonic generation. This analysis is believed to be applicable to a large range of wave interaction phenomena in integrated optics.

Analysis of parameteric mixing and harmonic generation of surface acoustic waves

The parametric mixing and harmonic generation of surface acoustic waves (SAW) has been treated by a new formalism in which the nonlinear wave equation and boundary conditions are rigorously satisfied at the sum and difference frequencies. The key features are analytical expressions for the spatial structure of modes which can be synchronously driven by volume forces and surface‐boundary conditions. After a propagation distance of a few acoustic wavelengths, the acoustic fields evolve into a linearly growing normal‐mode SAW. Equations are derived from which the nonlinear interaction cross sections can be evaluated and numerical results are given for a number of materials. Good agreement was obtained between experiment and theory for y‐x and x‐y α‐quartz in the limit that the piezoelectricity is neglected.

Optical damage thresholds of thin‐film and in‐diffused waveguides

The behavior of a number of glass and Ti in‐diffused LiNbO3 waveguides was investigated as a function of laser power, and the damage thresholds were evaluated and compared to the bulk material values.

Overlap‐integral analysis of surface‐acoustic‐wave harmonic generation

It is verified that the overlap‐integral and total‐field approaches to the analysis of harmonic generation of surface acoustic waves produce identical results.

Exact analysis of mode interaction phenomena in integrated optics: Application to acousto‐optics

A new theory of coherent mode interactions in integrated optics is described with particular reference to light scattering by surface waves. This analysis is characterized by exact solutions to polarization‐driven wave equations and electromagnetic boundary conditions.

Surface‐wave generation by nonlinear mixing of bulk waves

The nonlinear interaction between bulk acoustic waves at a surface to produce surface acoustic waves is analyzed theoretically. In this analysis both the nonlinear wave equation and boundary conditions are rigorously satisfied by the total acoustic fields. Shear‐wave incidence is treated in detail for isotropic fused quartz and numerical cross sections are evaluated for different angles of incidence. Maximum surface‐wave generation is predicted for geometries corresponding to bulk waves, shear or longitudinal, traveling parallel to the surface.

Signal processing with surface waves via the double acousto‐optic interaction

Optical diffraction by two successive surface acoustic waves was used to achieve various signal‐processing operations. Expressions were derived for the frequency spectrum and bilinearity factor associated with this double interaction and these formulas were verified experimentally using Fabry‐Perot interferometry. An aperture function formalism was used to demonstrate that the doubly diffracted field corresponds in form to that required for real‐time convolution. The addition of a simple lens system extended the capability of this technique to a full range of processing functions. The following operations were demonstrated for pulses of the order of 1 μs: squaring convolution, squaring correlation, variable time expansion, variable time compression, time inversion, and image scanning. This processor is characterized by large bandwidth since the diffraction takes place in the Raman‐Nath limit up to GHz frequencies.