David W. Vahey

A nonlinear coupled‐wave theory of holographic storage in ferroelectric materials

A theory is presented that describes the time evolution of the diffraction properties of holographically formed thick phase gratings in ferroelectrics, particularly in iron‐doped lithium niobate. The theory is based upon a model that relates the instantaneous electromagnetic fields in a grating to the refractive index in a manner consistent with the work of Young et al.; that is, the index modulation amplitude is proportional to the product of the amplitudes of the writing fields, while index maxima and intensity maxima are spatially shifted by some fraction of a fringe. The model leads to coupled nonlinear equations for the writing fields that are analogous to the linear equations of Kogelnik, and in certain limits, yield identical results. Closed‐form solutions of the coupled nonlinear equations are found to describe the interaction between writing beams observed by Staebler and Amodei, as well as the time evolution of diffraction efficiency observed by Amodei et al. In conjunction with the latter exper...

Focal properties of geodesic waveguide lenses

The focal properties of uncorrected geodesic lenses in ion‐exchanged glass waveguides are reported. A 13.8‐mm‐focal‐length lens resolved by beams with an angular separation of 27.6 mrad, while a 28‐mm‐focal‐length lens resolved beams with an angular separation of only 3.3 mrad. Intensity profiles of the focal region of the former lens revealed a 40‐μ spot size when the input aperture was 5 mm, and a spot size of 7.7 μ when the aperture was reduced to 1 mm. This value is close to the diffraction‐limited spot size of 5.7 μ.

Integrated Optics Devices Utilizing Thick Phase Gratings

Thick phase gratings have a variety of possible uses as device components in integrated optical systems. The applications make use of one or more of the unique properties of these gratings: high diffraction efficiency, good angular selectivity, and straightforward fabrication. In planar waveguides, the diffraction efficiency and angular selectivity desired for a particular application determine the length of the grating along the waveguide surface. We have holographically recorded 2 mm gratings having peak diffraction efficiencies in excess of 50% and angular selectivities less than 2 mrad by intersecting guided waves in a sample of photorefractive LiNbO3. Such gratings provide the central element in a number of actual and contemplated waveguide devices, including mirrors, beam splitters, lenses, switches, modulators, and interferometers.

Sources of scattering of guided light in Ti-diffused LiNbO3 optical waveguides

Abstract In-plane scattering in Ti-diffused LiNbO3 waveguides has been studied in order to determine sources of scattering in this material. The observed variation of scattering with direction of propagation suggests that anisotropic refractive-index variations in the waveguide are the dominant source of scattering, rather than surface roughness. Some of the scattering is found to be associated with a granular layer caused by Ti diffusion, possibly indicative of Li-Ti-0 compound formation near the surface. Scattering from this source is reduced by using less Ti diffusant and/or by polishing the finished waveguide. Electrooptic and photorefractive experiments to determine the importance of antiphase microdomains as sources of residual scattering in LiNbO3 waveguides yield conflicting results.

In-Plane Scattering In LiNbO3 Waveguides

Experimental observations of the in-plane scattered energy distribution in Ti-diffused LiNb03 waveguides have been performed with a view toward determining and subsequently eliminating sources of scattering in this material. Results suggest that scattering from refractive-index variations is more important than scattering from surface roughness in commercial samples. However, scattering from contaminants at or near the surface exists and can be reduced by using less Ti diffusant and/or by polishing the finished waveguide. Variations in scattering as a function of propagation direction and mode polarization suggest that the scattering centers are anisotropic with regard to either their refractive index, their shape or both. Diagnostic experiments to ascertain the nature of these scatterers, including electrooptic, photorefractive, and thermal studies, are described.

The effects of molecular reorientation on the absorption of intense light by organic-dye solutions

Abstract Equations are presented for the spectral and orientational distribution of unexcited dye molecules in the field of an intense giant laser pulse. The solute dye molecules are linear oscillators that may be broadened either homogeneously or inhomogeneously, and may reorient by sudden jumps over large angles or by small angular steps (brownian rotational motion). The equations are employed to analyze the intensity dependence of fluorescence polarization observed by Mourou and Denariez-Roberge for the system cryptocyanine-glycerin. Their data are consistent with an excited-state deactivation time T 1 = 0.4 ± 1.0 ns and a rotational diffusion constant D = 20/ T 1 = 5.0 × 10 9 s −1

Development Of An Integrated-Optics Multichannel Data Processor

An integrated optical system for comparing one set of voltage signals to a reference set will be described. The processor utilizes a hologram written in an outdiffused LiNb03 waveguide to effectively subtract the input signal voltage set from one or many reference sets as a means of pattern recognition. Parallel processing in a one-dimensional format should make possible comparison rates of 100 MHz for data sets containing as many as 100 information channels. The envisioned system contains the following components: A end-fired laser, a metallized-photoresist grating beam splitter and two polished-edge mirrors to form an integrated interferometer, a waveguide hologram in the area of beam recombination, and a lens to project the processed beam onto a butt-coupled detector. In the reference arm of the interferometer, a simple electrode pair is utilized to generate the phase shift required for holographic subtraction, while in the signal arm, a more complicated N-channel electrode structure is employed to electrooptically convert voltage information to spatial phase information on the guided wave. Efforts to build and characterize a three-channel system with integrated beam splitter, mirror, electrodes, and hologram are presented.

Effects of anisotropic and curvature losses on the operation of geodesic lenses in Ti:LiNbO 3 waveguides

The effects of curvature and anisotropy (leaky-mode) losses on the performance of geodesic lenses in Ti-diffused waveguides in LiNbO(3) are examined. A model for the lenses is developed that is equivalent to the usual Fraunhofer diffraction theory, modified to account for the path-dependent losses. Numerical calculations show that the curvature losses are dominant and require fabrication of waveguides having well-confined fundamental modes. Higher-order modes are effectively attenuated by the lenses. The leaky-mode losses have the beneficial effect of reducing the side-lobe intensity in the focal plane.

Optical gating by bleaching‐induced polarization anisotropy in organic dyes

A light gate based on optically induced polarization anisotropy in cryptocyanine‐glycerin compares favorably with a CS2 light gate tested under similar conditions. The organic‐dye device is more transmissive at giant‐pulse excitation levels up to 10 MW/cm2, where both devices gated 1% of an incident probe beam, and is less sensitive to variations in the intensity of exciting light. A theory based on the anisotropic orientational distribution of excited dye molecules during bleaching is used to explain the data. Fair agreement is obtained if one accounts for the birefringence as well as the absorption anisotropy induced by the exciting pulse.

Noncontact profiling techniques for intraocular lens edge measurements.

Two techniques, focal spot projection and fringe projection, have been developed for profiling the edges of anterior-chamber style intraocular lenses (IOL). The techniques are based on measurement of the trajectory of reflected light when an incident beam is focused and stepped across the edge surface (spot projection) or when two focused beams combine to form an optical interference pattern on the edge (fringe projection). The optical configurations for performing the projection techniques are described along with the mathematical relationship between the reflected-beam trajectories and the edge profile. An automated system for the implementation of focal spot projection was developed. The system has the capability of positioning the IOL edge at the focal point of the incident beam, acquiring trajectory data via stepper motors and a TV camera, processing the data to generate a profile, and displaying the profile on the computer video monitor or in hard-copy form via a printer. On one lens tested, three profiles corresponding to different locations along the IOL edge could be generated without user intervention. However, the user has the option of manually positioning the IOL to permit greater versatility. The typical 300-microm wide IOL edges are profiled to a resolution of approximately 20 microm. To constrain optical and microprocessor hardware costs, compromises were made in operating speeds so that approximately 20 min is required per profile. With current trends in integrated circuit technology future generations of the system could be made faster and prove useful as a QC tool for the IOL industry. Furthermore, the present device can be used in determining appropriate IOL profile standards.