G. I. Stegeman

High‐resolution spectroscopy for optical probing of continuously generated surface acoustic waves

Under conditions of continuous acoustic generation, light scattered from oppositely directed surface acoustic waves on y‐cut z‐propagating lithium niobate was frequency analyzed with a high‐resolution Fabry‐Perot interferometer. The following parameters were measured at 105 MHz: acoustic power standing‐wave ratio, reflection coefficient for both sending and receiving transducers, low‐power acoustic damping coefficients, surface wave propagation velocity, and nonlinear harmonic growth. We note that the method used has an advantage over other methods since it is to a large extent independent of the optical quality of the propagation surface.

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.

Nonlinear surface‐wave interactions: Parametric mixing and harmonic generation

The nonlinear interaction of surface acoustic waves propagating in the same direction has been treated from the rigorous theory of thermoelasticity. Exact expressions were derived for the nonlinear volume forces and surface stresses, and the nonlinear cross sections were calculated under two separate assumptions. First, the work done by the nonlinear forces and surface stresses on a normal‐mode surface wave was evaluated and assumed to be totally converted into surface‐wave energy. In the second approach, a linear analytic solution was formulated which simultaneously satisfies the nonlinear wave equation and maintains a stress‐free boundary condition. Numerical values for the strength of second‐harmonic generation were calculated for 24 materials. The characteristics of nonlinear surface‐wave generation were compared with those of nonlinear bulk‐wave generation and significant differences were found. Coupled amplitude equations were derived to treat the case of multiharmonic generation. Finally, a charact...

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.

Normal‐mode surface waves in the pseudobranch on the (001) plane of gallium arsenide

It is shown that two directions exist on the (001) plane of gallium arsenide for which the pseudobranch reduces to normal‐mode surface waves; one corresponds to the usual saggital‐plane surface waves along [110] and the second to a nonsaggital‐plane SAW at 32.89 ° from the x axis.

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.

Theory of non phase-matched second harmonic generation of surface plasmons☆

Abstract Non phase-matched harmonic generation of surface plasmons has been analysed using total field solutions which satisfy the nonlinear current driven Maxwells Equations and electromagnetic boundary conditions. The results are compared with a recent calculation by Mills.

Theory of light scattering by surface acoustic waves on reflection and transmission

A general approach to the theory of light scattering by surface acoustic waves on reflection from and transmission through a surface is described. The appropriate polarization‐driven‐wave equation is solved exactly, and total solutions are found which also satisfy all the electromagnetic boundary conditions across the acoustically corrugated interface. This formalism is vectorial in character and is valid for all scattering angles. The scattering of both ’’s’’‐ and ’’p’’‐polarized incident light is treated analytically and numerically for Rayleigh waves on an isotropic medium (fused quartz) and Y‐Z lithium niobate and for Bleustein‐Gulyaev waves on Y‐X cadmium sulphide. The results deviate significantly from the predictions of previous scalar theories for scattering angles greater than a few degrees.

Probing of surface acoustic wave devices with large‐diameter laser beam

The theory of dark field imaging technique as applied to acousto‐optic interactions has been developed and then used in studies of linear and nonlinear surface acoustic waves and volume acoustic waves. The theory is consistently expressed in terms of phase transmittance function. Experimental results show how the technique can be applied in the case of multimode propagation to unfold the complex frequency spectra of spurious modes in surface wave devices, and how to discriminate between different harmonics in the case of nonlinear acoustic propagation.

Brillouin spectrum of single‐mode optical fibers

Experimental and theoretical results are presented for the Brillouin spectrum of single‐mode optical fibers in the 180° scattering geometry. It is shown that for core diameters less than 10 μm both the Brillouin frequency shift and spontaneous linewidth are influenced by the nature of the normal acoustic‐mode spectrum and wave‐vector nonconservation in the acousto‐optic interaction. The velocity and lifetime of longitudinal phonon excitations in the core are evaluated, and the consequences to stimulated Brillouin scattering assessed.