Dror Sarid

High‐efficiency prism coupler for optical waveguides

A single prism has been used to simultaneously couple light into and out of an optical waveguide, with a guiding length of 1 cm. The method, which is simple and reproducible, utilizes two optimized gaps for the coupling regions. Coupling efficiencies in excess of 90% have been achieved.

Recovery of the refractive-index profile of an optical waveguide from the measured coupling angles

A method is presented for calculating the profile of the refractive index of an optical waveguide, n(x) = n(0) + f(x), from the measured coupling angles for any physically justified functional form of f(x). As an example, we present the results of a Ti in-diffused LiNbO(3) waveguide for which f(x) fits the sum of two Gaussians.

Light scattering on internal reflection from surface acoustic waves

The intensity of light scattered by surface acoustic waves (SAW) on internal reflection has been calculated for the geometry where the incident and scattered light are in a plane perpendicular to the SAW wave vector. The calculation was carried out for an arbitrary piezoelectric crystal having a free or metallized surface. Measurements on a y‐cut LiNbO3 crystal and a z‐propagating SAW give good agreement with the theory.

Prism coupling into clad uniform optical waveguides

The theory of prism coupling into multilayered dielectric slab waveguides is presented. In addition to including the possibility of high index cladding, the present theory also extends the region of validity of previously reported work to cover the regime of ’’strong coupling’’. The limiting conditions for validity of the present theory are that both αm/k and αm±p/k be much smaller than either unity or ‖βm−βm±p‖, where m is the mode under consideration, αm is the leakage of that mode, and ‖βm−βm±p‖ is the separation of the effective indices of adjacent modes. A numerical example is presented in which the coupling efficiency into a uniform or slab waveguide with Δn=0.002 is calculated for various cladding thicknesses with a cladding index of 2.5. The introduction of cladding is found to reduce coupling efficiency in this example due to increased phase mismatch between the incident and ’’ideal’’ beams.

The line shape of the light scattered by surface acoustic waves upon total internal reflection

The light which is scattered by a surface acoustic wave, upon total internal reflection and at a grazing angle, exhibits a pronounced structure which varies as the polarization of the light is rotated and differs for a free or metallized surface. A theory is presented which accounts accurately for the various line shapes measured on a y‐z LiNbO3 crystal.

Prism‐waveguide coupling efficiency for waveguides with an arbitrary refractive‐index profile

Using the WKB approximation, we generalize Ulrich’s solution to the optimum coupling efficiency of a prism‐waveguide coupler, so that it can be applied to a waveguide with an arbitrary refractive‐index profile. As an example, we give an analytic solution to a waveguide having an exponential refractive‐index profile.

On the theory of the prism waveguide coupler in the strong coupling regime

It is shown that under practical assumptions both ray and wave theories of the prism waveguide coupler can be applied to the whole range of the coupling strength parameter 0⩽h⩽1, and yield identical results. A numerical example is given, which shows the range of validity of the weak coupling approximation.

Direct measurement of the partial waves of a surface acoustic wave by means of light scattering

We report the direct measurement of each of the partial waves which constitute a surface acoustic wave propagating on a y‐z LiNbO3 crystal by means of light scattering on internal reflection. It is shown both theoretically an experimentally that each of the partial waves has a wave vector pointing in a different direction. We could account theoretically for the shape of the scattered light which is split into several components. Each component corresponds to a single partial wave.