Volume Holographic Reflection Endoscope for In-Vivo Ovarian Cancer Clinical Studies.

We present the design for an endoscopic system capable of imaging tissues of the ovary at two selected imaging depths simultaneously. The method utilizes a multiplexed volume hologram to select wavefronts from different depths within the tissue. It is the first demonstration of an endoscopic volume holographic imaging system. The endoscope uses both gradient index (GRIN) optical components and off the shelf singlet lenses to relay an image from the distal tip to the proximal end. The endoscope has a minimum diameter of 3.75 mm. The system length is 30 cm which is connected to a handle that includes the holographic components and optics that relay the image to a camera. Preliminary evaluation of the endoscope was performed with tissue phantoms and calibrated targets, which shows lateral resolution ≈ 4 µm at an operating wavelength of 660 nm. The hologram is recorded in phenanthraquinone doped poly methacrylate and is designed to produce images from two tissue depths. One image is obtained at the tissue surface and the second 70 µm below the surface. This method requires no mechanical scanning and acquires an image at the camera frame rate. The preliminary ex-vivo results show good correlation with histology sections of the same tissue sections.

Interconnect characteristics of fiber image guides.

We investigated various factors that influence the transmission of high-density and high-bandwidth signals propagated through fiber image guides. The effects of signal power uniformity, optical cross talk, mode dispersion, and modal noise were considered. A model for power uniformity and optical cross talk is provided that we used to evaluate the channel density of several coupling modes. Also, modal noise was experimentally measured for several conditions of coupling to the fiber image guide. A commercially available fiber image guide was evaluated in the context of these performance considerations and was experimentally tested. The resultant minimum signal channel based on these criteria was found to consist of three fiber elements. The limit on transmission length that is due to modal dispersion was estimated at 1.65 m at 2.5-Gbits/s and at 42 cm at 10-Gbits/s data rates. Optical cross talk and modal noise were found to place a lower limit on the signal channel density. These characteristics compare favorably with electrical interconnect densities that are projected for tape automated bonding and flip-chip bonding techniques used at the chip-to-module and chip-to-board packaging levels.

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.

Dynamic hologram recording characteristics in DuPont photopolymers.

Hologram formation and diffusion reactions in photopolymer films are examined at different stages of exposure and at different spatial frequencies. Different properties of the grating formation process are evaluated from efficiency data, including the relative rates of diffusion and photoinitiated polymerization, dye absorption, and residual efficiency enhancement after UV curing. It was also found that gratings with larger periods (approximately 1.4 microm) are susceptible to erasure effects with postexposure laser illumination. In addition, crossed gratings were found to have an extended dynamic range. This effect can have a significant impact on the number of holograms formed with rotational or peristrophic multiplexing.

Resonant waveguide-grating switching device with nonlinear optical material.

The design and analysis of a dielectric guided-mode resonance filter (GMRF) utilizing a nonlinear material for the waveguide is presented. Small changes to the parameters of a GMRF have a large impact on its resonance. A nonlinear material can provide a small change in the refractive index of the waveguide, altering the resonance of the device and resulting in modulation of the transmitted and reflected output of the filter. Numerical results show that nonlinear switching from 100% transmission to 100% reflection can be accomplished with less than 100 kW/cm(2) using a simple design.

Error correction for free-space optical interconnects: space-time resource optimization.

We study the joint optimization of time and space resources withinfree-space optical interconnect (FSOI) systems. Both analyticaland simulation results are presented to support this optimization studyfor two different models of FSOI cross-talk noise: diffraction froma rectangular aperture and Gaussian propagation. Under realisticpower and signal-to-noise ratio constraints, optimum designs based onthe Gaussian propagation model achieve a capacity of 2.91 x10(15) bits s(-1) m(-2), while therectangular model offers a smaller capacity of 1.91 x10(13) bits s(-1) m(-2). We alsostudy the use of error-correction codes (ECC) within FSOIsystems. We present optimal Reed-Solomon codes of various length, and their use is shown to facilitate an increase in both spatialdensity and data rate, resulting in FSOI capacity gains in excess of8.2 for the rectangular model and 3.7 for the Gaussian case. Atolerancing study of FSOI systems shows that ECC can provide toleranceto implementational error sources. We find that optimally codedFSOI systems can fail when system errors become large, and we present acompromise solution that results in a balanced design in time, space, and error-correction resources.

Scalar diffraction theory approach to estimating multimode-waveguide field-amplitude mode distributions.

We introduce a method to estimate the coupling coefficients of the guided field amplitude and the corresponding angular bandwidth in a multimode slab waveguide. This scalar diffraction theory approach is simpler than the more rigorous electromagnetic treatment and is directly applicable to communications systems that use large (dimensions or numerical aperture) waveguides, as in substrate-mode interconnects. Moreover, this method provides conceptual insight as to a parameter's effect on the field-amplitude mode distribution and angular bandwidth.

Connection cube modules for optical backplanes and fiber networks.

A modular free-space optical system, called the connection cube, for connecting arrays of electro-optic transceivers and fiber-array connectors is presented. The connection cube module provides bidirectional data transfer between four processing nodes on a cube face and can be used as a basic building block for optical backplanes and interconnect networks. An experimental system for connecting four processing nodes is presented and used to examine alignment and packaging issues. An analysis of the dimensional requirements and scaling capability for systems based on this module is conducted. This analysis shows that, when the connection cube module is adapted to vertical-cavity surface-emitting-laser-based point-to-point fiber-array links currently under development, it can connect up to 14 processing nodes with an aggregate data transfer capacity of 112 Gbits/s with 19.6-W power consumption.

Free-space holographic optical interconnects for board-to-board and chip-to-chip interconnections.

We describe a free-space holographic optical interconnect system designed for signal communication between chips and circuit boards on a common backplane. The system uses a transparent optical substrate-mode holograms to implement chip-to-chip interconnections and free space for board-to-board interconnections. Realization of a variety of interconnect functions with substrate-mode holograms is described. A three-board holographic interconnect system is also experimentally demonstrated.

Hybrid free-space optical bus system for board-to-board interconnections.

A free-space optical bus system is described for board-to-board interconnections at the backplane level. The system uses active optoelectronic modules as the interface between the circuit boards and the electrical backplane. Substrate-mode holograms are used to implement signal broadcast operations between boards, and each board on the backplane shares common free-space channels for transmitting and receiving signals. System-design considerations are given, and the potential performance of the optical bus system is evaluated. An experimental demonstration is also presented for the signal broadcast operation through cascaded substrate-mode holograms at a data rate of 622 Mb/s.

Volume holographic phase-retardation elements.

The form birefringence of subwavelength period gratings can be applied to realize phase-retardation elements. Previous researchers used high-frequency surface relief structures or sinusoidal gratings formed in photoresist to fabricate phase-retardation elements. We present the performance of a volume holographic quarter-wave phase-retardation element formed in a dichromated gelatin emulsion for operation at 632.8 nm. To our knowledge this is the first demonstration of a retardation element exhibiting this magnitude of phase delay in a volume material. The phase properties of volume gratings are investigated by both effective medium theory and rigorous coupled-wave analysis.

Comparison of methods for determining the bias index of a dichromated gelatin hologram.

Determination of the bias refractive index of a holographic emulsion before exposure and after development is an important factor in the design of holographic optical elements. Several experimental methods are discussed for determining the bias index of a volume hologram in dichromated gelatin, and the results for each technique are presented. It is shown experimentally that these measurement methods yield different results for the same hologram, and the cause of the differences is proposed to be a variation of the bias index with depth in the hologram. An index measurement technique is also presented that accounts for variation in the bias index and is shown to yield an accurate value for the bias index.

Substrate-mode holograms used in optical interconnects: design issues.

We discuss a number of design issues that affect the performance tolerances of substrate-mode holograms used for optical interconnect systems. We examine the effects of emulsion uniformity, thickness variation, and index variation on the ability to determine the Bragg angle and the diffraction angle within the substrate accurately. The environmental stability with respect to temperature, laser irradiance, and humidity are considered. Experimental results are presented for substrate-mode holograms fabricated in spin-coated dichromated-gelatin emulsions. The coupling properties for a 1 × 2 multiplexed substrate-mode hologram with two superimposed gratings are also described.

Diffractive-optic polarization-sensing element for magneto-optic storage heads.

A cascaded planarized holographic optical sensor consisting of a combination of a leaky beam splitter and a polarization beam splitter is evaluated for possible use in magneto-optic data storage pickup heads. The performance requirements for each element are specified, and two cascaded grating designs are considered. In one design we reconstruct the gratings with the grating vector in the plane of incidence, using a half-wave plate. In the second design we reconstruct the gratings with the grating vector of the polarization beam splitter out of the plane of incidence without using a half-wave plate. The two systems are fabricated with gratings formed in dichromated gelatin emulsions, and they can detect 0.5 degrees rotations in the polarization state of an incident beam by use of a differential detection system.

Dispersion compensation for an integrated optic grating coupler utilizing a transmission volume hologram.

In this paper we show the analysis and experimental results of using a volume holographic grating to increase the wavelength bandwidth over which light is coupled into a thin-film optical waveguide. Partial matching of the dispersion relationships of a hologram fabricated in dichromated gelatin with a waveguide/grating coupler etched in glass, show an increase in the full-width half-maximum wavelength (FWHM) bandwidth from approximately 0.25 nm to greater than 5 nm.

Distributed optical data bus for board-level interconnects.

A design for a distributed free-space optical system is presented that provides interconnection of electronic processing elements at the board level of packaging. The system can be expanded to more than two boards and transfers an array of data in parallel between connection planes. The design uses binary optic microlens arrays to collimate and collect light from surface-emitting lasers, and it uses substratemode holographic window elements for directing light to and from the bus region. The use of a collection lens array for extending the alignment tolerance of the imaging system is also discussed. The paper concludes with experimental demonstrations of critical system components and performance with 64-bit data arrays.

Refractive index modulation mechanism in bleached silver halide holograms.

We present a simple technique for observing and studying the onset of microstructure in silver halide gratings, which can also be used to improve processing chemistry.

Factorial optimization of bleach constituents for silver halide holograms.

A factorial design approach to optimizing rehalogenating bleaches for silver halide holograms is presented. An advantage of this technique is that it allows simultaneous improvement in a number of hologram performance characteristics as a function of several input parameters. Interactive effects of combinations of input parameters can also be examined. A specific experiment is described in which diffraction efficiency, average light loss, thickness change, and noise grating efficiency are optimized as a function rehalogenating agent, oxiding agent, and acid concentrations of a rehalogenating bleach. Results for both Agfa 8E75HD and Ilford SP673 films are presented.

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.