Ram Voorakaranam

An Updatable Holographic Display for 3D Visualization

Among the various methods to produce three-dimensional (3D) images, holography occupies a special niche. Indeed, holograms provide highly realistic 3D images with a large viewing angle capability without the need for special eyewear. Such characteristics make them valuable tools for a wide range of applications such as medical, industrial, military, and entertainment imaging. To be suitable for an updatable holographic display, a material needs to have a high diffraction efficiency, fast writing time, hours of image persistence, capability for rapid erasure, and the potential for large display area-a combination of properties that has not been realized before.

A Silicon-Polymer Hybrid Modulator—Design, Simulation and Proof of Principle

Optimal dimensions are found for the silicon waveguide in an electro-optic (EO) polymer cladding-based silicon waveguide modulator. The confinement factor as well as the effective index of the mode are taken into account. The influence of the coplanar electrode spacing and electrode height on performance are examined and a figure of merit formula for choosing the optimal device geometry is shown. The design space for both 1550 nm and 1310 nm wavelengths is explored. With the optimal 275 nm waveguide width and 4 μm electrode spacing, a Vπ of a few volts can be achieved even with moderate r33 EO polymers. Experimental results on a fabricated modulator are shown and compared with the predicted performance.

Silica/Electro-Optic Polymer Optical Modulator With Integrated Antenna for Microwave Receiving

A silica/electro-optic (EO) polymer phase modulator is proposed for microwave radiation receiver with the use of a bowtie antenna. Waveguide design optimization is presented for a waveguide with an EO polymer core and silica/sol-gel cladding. Electrode effects on the insertion loss and poling efficiency are also analyzed and conditions for low-loss and high poling efficiency established. The bowtie antenna is simulated and shows a broadband response with a maximum at 5 GHz and a 3 dB-bandwidth of approximately 12 GHz. A fiber splicing technique is presented that reduces coupling loss between SMF-28 and the waveguide. Experimental results for a fabricated device with microwave-response between 10-14 GHz are shown with carrier to first sideband intensity difference of up to -36 dB.

Materials for an Updatable Holographic 3D Display

Holography is a powerful technique for providing high-resolution, realistic three-dimensional (3D) images without the need for special eyewear. A material that takes full advantage of the potential of holography, including updatability, has not existed. Here, the first updatable holographic 3D display based on a photorefractive polymer is summarized. The performance characteristics of these materials are measured, and how they relate to the development of additional display enhancements such as pulsed writing, white light viewing, and large viewing angle, are discussed.

Are stereograms holograms? A human perception analysis of sampled perspective holography

In this paper, we analyze the optical performance of a commonly used 1-step recording geometry for stereograms and compare it to the fully fringe rendered case, taking a published optical model of the human eye into account. We compare our results to a model that conserves wavefront curvature. We then demonstrate how to optimize hogel sampling parameters as a function of image depth, size, and viewer distance. We conclude that stereograms suffer from little degradation from a viewing distance larger than 2 meters, but that nearer field images can significantly benefit by adding a second order phase correction.

Complementary grating dynamics in photorefractive polymers with Alq3

The electron transporting molecule tris(8-hydroxyquinoline) aluminum (Alq3) was introduced into a photorefractive composite in a low density to study the effects of electron traps on the performance. Compared to a control sample, Alq3 samples exhibited higher dielectric strength, over-modulation at reduced voltage, and increased writing speed. Transient measurements indicated grating revelation via decay of a competing grating. The dynamics are consistent with a bipolar charge transport model. Overall, Alq3 improves the sensitivity, trapping, and breakdown voltage without significant losses in absorption or phase stability.

Corrections to “A Silicon-Polymer Hybrid Modulator—Design, Simulation, and Proof of Principle” [Dec 13 4067-4072]

In the article, “A Silicon-polymer hybrid modulator—Design, simulation and proof of principle”(Himmelhuber, R. ibid, vol. 31, no. 24, pp. 4067–4072, Dec. 2013], an error was found in the code used for calculating the line capacitance of a the CPS electrode design.

Avenues for expanded applicability in photorefractive based holographic 3D displays

The first updatable three-dimensional holographic display based on a photorefractive polymer device, exhibiting a fast response, long persistency, and phase stability is discussed. Material and optical setup changes for new and broader applications are outlined.