Raymond K. Kostuk

Low-density parity check codes and iterative decoding for long-haul optical communication systems

A forward-error correction (FEC) scheme based on low-density parity check (LDPC) codes and iterative decoding using belief propagation in code graphs is presented in this paper. We show that LDPC codes provide a significant system performance improvement with respect to the state-of-the-art FEC schemes employed in optical communications systems. We present a class of structured codes based on mutually orthogonal Latin rectangles. Such codes have high rates and can lend themselves to very low-complexity encoder/decoder implementations. The system performance is further improved by a code design that eliminates short cycles in a graph employed in iterative decoding.

Investigation of the effect of finite grating size on the performance of guided-mode resonance filters

We evaluate the effect of finite aperture gratings on the spectral and efficiency characteristics of guided-mode resonance filters. A simple analytical model based on the attenuation properties of the waveguide and a fixed length of the grating aperture is developed. The results from this model are in good agreement with experimental filters formed with subwavelength period photoresist gratings and solgel waveguides.

Polarization properties of substrate-mode holographic interconnects

The polarization properties of cascaded substrate-mode holographic optical elements are analyzed and demonstrated. The design criteria for polarization selective and nonselective elements are given and verified with experimental volume holograms formed in dichromated gelatin emulsions. Using the experimental grating parameters, it is estimated that a reconfigurable optical bus with eight nodes can be made. Improved control of hologram construction parameters can increase this to more than 500 nodes. Use of this device with a reconfigurable interchange coupler and a multistage optical bus is also examined.

Optimization of multiplexed holographic gratings in PQ-PMMA for spectral-spatial imaging filters

Holographic gratings formed in thick phenanthrenquinone- (PQ-) doped poly(methyl methacrylate) (PMMA) can be made to have narrowband spectral and spatial transmittance filtering properties. We present the design and performance of angle-multiplexed holographic filters formed in PQ-PMMA at 488 nm and reconstructed with a LED operated at approximately 630 nm. The dark delay time between exposure and the preillumination exposure of the polymer prior to exposure of the holographic area are varied to optimize the diffraction efficiency of multiplexed holographic filters. The resultant holographic filters can enhance the performance of four-dimensional spatial-spectral imaging systems. The optimized filters are used to simultaneously sample spatial and spectral information at five different depths separated by 50 microm within biological tissue samples.

Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-microm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouards method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (< 0.2 nm) and high side-lobe suppression (<-- 30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (< 0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.

Lamellar gratings as polarization components for specularly reflected beams

Abstract High spatial frequency lamellar gratings are shown to function as phase compensators, quarter-wave and half-wave retarders, and polarization rotators that operate on specularly reflected (zeroth-order) beams. These gratings are designed using rigorous coupled-wave and modal grating diffraction theories. Controlling the geometrical parameters of these gratings allows for engineering the phase retardation and polarization conversion introduced to a reflected beam. Fabrication and operational tolerances for these elements are discussed. Wavelength and polar angle of incidence variation affect the performance of these elements more strongly than variations in other geometrical and operational parameters.

Energy collection efficiency of holographic planar solar concentrators

We analyze the energy collection properties of holographic planar concentrator systems. The effects of solar variation on daily and annual energy collection are evaluated. Hologram diffraction efficiency, polarization, crosstalk in cascaded elements, and constraints imposed by the radiance theorem, as well as solar illumination characteristics, are considered. A planar holographic solar concentrator configuration is designed and modeled to maximize energy collection efficiency during the course of a year without the need for tracking. Results indicated that nearly 50% of the available energy illuminating hologram areas can be collected by photovoltaic cells without the need of tracking.

Reducing alignment and chromatic sensitivity of holographic optical interconnects with substrate-mode holograms

The alignment and chromatic sensitivity of holographic optical elements for use in optical interconnect systems are quantified. The effects of these image degrading parameters are related to the frequency and power requirements for CMOS compatible detectors in an optical interconnect system. Techniques for reducing the magnitude of these problems with substrate-mode holograms are described, and experimental results demonstrating these designs are presented.

Analysis and design of holographic solar concentrators

The diffraction and the dispersion properties of holographic optical elements are examined for use as solar concentrators for photovoltaic and hybrid photovoltaic/thermal energy conversion systems. The diffraction angle and efficiency are computed for folded optical geometries that are potentially useful for low concentration ratio systems that can reduce the cost of residential solar energy systems. An investigation of the collection efficiency of a holographic planar concentrator and a spectrum splitting concentrator are analyzed with different construction parameters. It is found that collection angles of 40o and spectral bandwidth of 70 nm result with folded optical geometries for single volume holograms.

Ghost-pulse reduction in 40-Gb/s systems using line coding

At high bit rates, four-wave mixing and nonlinearities in the optical channel give rise to ghost pulses. In this letter, we propose the application of modulation codes to tackle this effect.