Half a century of optics in computing--a personal perspective [Invited].

Optical signal processing and computing was triggered by the invention of the laser. Starting practically in 1960, it really took off with the introduction of the spatial-matched filter in 1964. Almost half a century later, research and engineering activity in the field continues unabated but in directions that could not have been anticipated in those early days.

Detecting motion through dynamic refraction.

Refraction causes random dynamic distortions in atmospheric turbulence and in views across a water interface. The latter scenario is experienced by submerged animals seeking to detect prey or avoid predators, which may be airborne or on land. Man encounters this when surveying a scene by a submarine or divers while wishing to avoid the use of an attention-drawing periscope.

Conformationally locked chromophores as models of excited-state proton transfer in fluorescent proteins.

Members of the green fluorescent protein (GFP) family form chromophores by modifications of three internal amino acid residues. Previously, many key characteristics of chromophores were studied using model compounds. However, no studies of intermolecular excited-state proton transfer (ESPT) with GFP-like synthetic chromophores have been performed because they either are nonfluorescent or lack an ionizable OH group.

Selection of dark modes in resonators with conical reflectors.

Selection of modes containing different dark regions was studied in resonators with conical reflectors. The possibility of selecting whole subgroups of such modes was shown in circularly symmetric resonators. To handle single-mode selection employing extra intracavity spatial filters, modified integral equations and a numerical method of their analysis are proposed.

Absorption enhancement by matching the cross-section of plasmonic nanowires to the field structure of tightly focused beams.

Nanostructured materials, designed for enhanced light absorption, are receiving increased scientific and technological interest. In this paper we propose a physical criterion for designing the cross-sectional shape of plasmonic nanowires for improved absorption of a given tightly focused illumination. The idea is to design a shape which increases the matching between the nanowire plasmon resonance field and the incident field.

Material classification of nanoparticles by focused beam scattering.

Advanced science and technology frequently encounters the need to detect particles in the micrometer and nanometer range of a given composition. While the scattering process of light by small particles is well documented, most conventional analytic methods employ wide illumination of large ensembles of particles. With such an approach, no information can be obtained about single particles due to their weak interaction.

Scattering of singular beams by subwavelength objects.

In recent years, there has been a mounting interest in better methods of measuring nanoscale objects, especially in fields such as nanotechnology, biomedicine, cleantech, and microelectronics. Conventional methods have proved insufficient, due to the classical diffraction limit or slow and complicated measuring procedures. The purpose of this paper is to explore the special characteristics of singular beams with respect to the investigation of subwavelength objects.

Plasmonic resonance scattering from silver nanowire illuminated by tightly focused singular beam.

We investigate scattering features of tightly focused singular beams by placing a cylindrical nanowire in the vicinity of a line phase singularity. Applying an illumination wavelength corresponding to silver cylinder plasmonic resonance, we compare the scattering response with that of a perfect conductor. The rigorous modeling employs a 2D version of the Richards-Wolf focusing method and the source model technique.

Characterization of the order-disorder dielectric transition in the hybrid organic-inorganic perovskite-like formate Mn(HCOO)(3)[(CH(3))(2)NH(2)].

We have found that the hybrid organic-inorganic perovskite-like formate Mn(HCOO)(3)[(CH(3))(2)NH(2)] shows a dielectric transition around 190 K. According to single crystal X-ray diffraction, the compound shows rhombohedral symmetry at room temperature and monoclinic symmetry at low temperature (100 K), and the main difference between both structures is that the (CH(3))(2)NH(2)(+) (DMA) cations are disordered in the high temperature phase but cooperatively ordered in the low temperature one. The vibrational spectra of this compound reveal that significant changes take place in the vibrations ascribed to the DMA cation (changes in the frequency of certain vibrations, splitting of particular vibrations, and changes in the intensities), while no significant changes have been observed in those attributed to the formate anion.

Pattern generation with an extended focal depth.

The depth of focus of light patterns can be extended, within given tolerances, beyond the classical limits. For a quantitative evaluation we introduce a degree of depth-of-focus extension and a three-dimensional energy-distribution efficiency. The basic limitations involved in depth-of-focus extension are discussed.

Singular beam microscopy.

Optical singularities are localized regions in a light field where one or more of the field parameters, such as phase or polarization, become singular with associated zero intensity. Singular beam microscopy exploits the fact that the strong variations of the optical field around the singularities are highly sensitive to changes in their neighborhood. As a consequence, analysis of the light field scattered from the object during a scanning process can yield useful information about the object features.

Vision through semireflecting media: polarization analysis.

We present an approach to recovering scenes deteriorated by reflections off a semi-reflecting medium. The approach is based on imaging through a polarizer at two different orientations. We analyze the image-formation process, taking into account changes in reflection and polarization properties owing to internal reflections within the medium.

Optics inspired logic architecture.

Conventional architectures for the implementation of Boolean logic are based on a network of bistable elements assembled to realize cascades of simple Boolean logic gates. Since each such gate has two input signals and only one output signal, such architectures are fundamentally dissipative in information and energy. Their serial nature also induces a latency in the processing time.

Paradigms for bit-oriented holographic information storage.

One of the difficulties encountered during the many years of research on holographic information storage was the lack of an easy theoretical way to assess proposed paradigms. I exploit the fact that for bit-oriented holographic storage, Gaussian beams are usually involved. For this case I show that the reconstructed wave can be represented as a superposition of simple Gaussian beams, regardless of the exact recording condition, and a virtual source for this wave can be determined.

Simple online recognition of optical data strings based on conservative optical logic.

Optical packet switching relies on the ability of a system to recognize header information on an optical signal. Unless the headers are very short with large Hamming distances, optical correlation fails and optical logic becomes attractive because it can handle long headers with Hamming distances as low as 1. Unfortunately, the only optical logic gates fast enough to keep up with current communication speeds involve semiconductor optical amplifiers and do not lend themselves to the incorporation of large numbers of elements for header recognition and would consume a lot of power as well.

Laser-mode selection by a combination of biprism-like reflectors with narrow amplitude masks.

In recent work the laser mode selectivity induced separately by a biprism-like reflector and by an absorbing strip was investigated by numerical analysis. It was shown that each of these elements in an otherwise conventional resonator was suitable to cause the laser to oscillate preferentially on the first odd mode that contains a line singularity, which is a useful dark beam (i.e.

Achieving stabilization in interferometric logic operations.

Interferometric systems with amplitude beam splitters can implement reversible operations that, on detection, become Boolean operators. Being passive, they consume no energy, do not limit the operating bandwidth, and have negligible latency. Unfortunately, conventional interferometric systems are notoriously sensitive to uncontrolled disturbances.

Two regions of mode selection in resonators with biprismlike elements.

A resonator structure in which one reflector is replaced by a biprismlike reflecting surface is investigated theoretically. It is shown that such a modification leads to two regions of parameters, each with different regimes of mode selection. The first region has an improved laser power output because of the nearly flat-top mode shape.

Tunable, oblique incidence resonant grating filter for telecommunications.

We have designed a tunable, oblique-incidence resonant grating filter that covers the C band as an add-drop device for incident TE-polarized light. We tune the filter by tilting a microelectromechanical systems platform onto which the filter is attached. The fabrication tolerances as well as the role of finite incident-beam size and limited device size were addressed.

Generalized Bragg selectivity in volume holography.

The diffraction efficiency of holographically recorded volume gratings was extensively studied, and it can be accurately predicted as long as the recording wave fronts are simple. The derivation of the diffraction efficiency when complicated wavefronts or images are involved is much more tedious and less explored. In this work we derive operator expressions that can be used to analyze these processes regardless of the shape of the wavefront and the nature of the optical systems through which they propagate.

Propagation-invariant wave fields with finite energy.

Propagation invariance is extended in the paraxial regime, leading to a generalized self-imaging effect. These wave fields are characterized by a finite number of transverse self-images that appear, in general, at different orientations and scales. They possess finite energy and thus can be accurately generated.

Polarization and statistical analysis of scenes containing a semireflector.

We present an approach to recover scenes deteriorated by reflections off a semireflecting medium (e.g., a glass window).

On-axis computer-generated holograms for three-dimensional display.

The feasibility of on-axis synthetic near-field amplitude holograms for three-dimensional display applications is demonstrated. An iterative optimization algorithm is used that generates an object-dependent diffuser that utilizes the phase and, to some extent, amplitude freedoms in the reconstruction plane. The discrimination between twin images and undiffracted terms is thus improved.

Resolution enhancement by extrapolation of the optically measured spectrum of surface profiles.

Surface features are measured by the analysis of the diffracted field intensity distribution generated by a scanning Gaussian beam. The measured data are shown to represent the amplitude of the Gabor expansion coefficients of the complex function embossed by the surface onto the reflected wave front. The surface is reconstructed by use of a custom-designed algorithm based on generalized projections, with a resolution exceeding the classical diffraction limit.

Self-imaging with finite energy.

General solutions and conditions are presented for paraxial waves that image themselves with different scales through free propagation. These waves, represented as superpositions of Gauss-Laguerre modes, have finite energy and thus finite effective width. The self-imaging wave fields described by Montgomery [J.