Two-photon holography in a 3D photopolymer host-guest matrix.

We demonstrate for the first time two-photon induced holographic recording at an arbitrary point in three dimensional photopolymeric cube by overlapping two coherent pulses from a 200 femtosecond Ti: Sapphire tunable laser operating at 710 nm. Spatial overlap is achieved by a novel pupil division method. The polymer material is made of epoxy host, which is fully polymerized and filled with liquid photopolymerisable formulation comprising acrylate type monomer and two-photon photoinitiator. Measured diffraction efficiency is measured to be 3.5%.

Two-photon holography in 3-D photopolymer host-guest matrix: errata.

: Correction to References. Commercial codes of the chemicals are added.

Cationic two-photon induced polymerization with high dynamic range.

Cationic-induced two-photon photo-polymerization is demonstrated at 710 nm, using an isopropylthioxanthone / diarylidonium salt initiating system for the cationic polymerization of an epoxide. In-situ monitoring of the polymer conversion using interferometry allows for determination of the polymerization threshold J2th, polymerization rate R and its dependence of initiator's concentration z. Best J2th achieved is 1 GW/cm 2 , with a dynamic range of > 100, i.e. the material can be fully polymerized at intensities > 100 times the threshold level without damage. The R is found to be proportional to the m=1.7 power of the intensity, or R =[C(J-J2th)]m =[C(J-J2th)]1.7 , which implies a significantly stronger localization of the photochemical response than that of free radical photoinitiators. Both R and J2th significantly improve when the concentration z of the initiator (onium salt) increases, reduction of J2th exhibiting z -m trend.

A scalable optoelectronic neural system using free-space optical interconnects.

The design of a scalable, fully connected 3-D optoelectronic neural system that uses free-space optical interconnects with silicon-VLSI-based hybrid optoelectronic circuits is proposed. The system design uses a hardware-efficient combination of pulsewidth-modulating optoelectronic neurons and pulse-amplitude-modulating electronic synapses. Low-area, high-linear-dynamic-range analog synapse and neuron circuits are proposed. SPICE circuit simulations and an experimental demonstration of the free-space optical interconnection system are included.

Characterization of dielectric and electro-optic properties of PLZT 9/65/35 films on sapphire for electro-optic applications.

Lead lanthanum zirconate titanate (PLZT) thin films were deposited on r-plane sapphire at low temperatures by RF triode magnetron sputtering using lead compensated hot-pressed targets. To obtain fully perovskite phase in the films, two types of post-deposition processing were investigated: rapid thermal annealing (RTA) and furnace annealing (FA). Dielectric and electro-optic properties of PLZT films were found to be strongly dependent on annealing conditions. The peak dielectric constant of the films were 1200 and 2800 with Curie temperatures of 110 degrees C and 190 degrees C after RTA and FA processing, respectively. The dielectric losses in the films were fairly low; tan deltas were less than 0.02 after RTA and less than 0.04 after FA processing. The films showed good optical transmission characteristics after annealing and an anomalously large effective quadratic electro-optic effect was observed in one furnace annealed film.

Deposition and characterization of thin ferroelectric lead lanthanum zirconate titanate (PLZT) films on sapphire for spatial light modulators applications.

Ferroelectric lead lanthanum zirconate titanate (PLZT) films are deposited on R-plane sapphire using RF triode magnetron sputtering. Perovskite PLZT films with the desired composition (9/65/35) are obtained using compensated deposition techniques around 500 degrees C and postdeposition annealing at 650 degrees C. The deposited films exhibit good optical and electrooptical properties. The room temperature dielectric constant of the films was 1800 at 10 kHz. The refractive index of the films was in the range of 2.2-2.5. The films showed a quadratic electrooptic effect with R=0.6 x10(-16) m(2)/V(2). The development of PLZT on silicon-on-sapphire smart spatial light modulators using these films is also explored.

Activity of the HMGB1-derived immunostimulatory peptide Hp91 resides in the helical C-terminal portion and is enhanced by dimerization.

We have previously shown that an 18 amino acid long peptide, named Hp91, whose sequence corresponds to a region within the endogenous protein HMGB1, activates dendritic cells (DCs) and acts as adjuvant in vivo by potentiating Th1-type antigen-specific immune responses. We analyzed the structure-function relationship of the Hp91 peptide to investigate the amino acids and structure responsible for immune responses. We found that the cysteine at position 16 of Hp91 enabled formation of reversible peptide dimmers, monomer and dimmer were compared for DC binding and activation. Stable monomers and dimers were generated using a maleimide conjugation reaction. The dimer showed enhanced ability to bind to and activate DCs. Furthermore, the C-terminal 9 amino acids of Hp91, named UC1018 were sufficient for DC binding and Circular dichroism showed that UC1018 assumes an alpha-helical structure. The ninemer peptide UC1018 induced more potent antigen-specific CTL responses in vivo as compared to Hp91 and it protected mice from tumor development when used in a prophylactic vaccine setting. We have identified a short alpha helical peptide that acts as potent adjuvant inducing protective immune responses in vivo.

HMGB1-derived peptide acts as adjuvant inducing immune responses to peptide and protein antigen.

There is a need for new adjuvants that will induce immune responses to subunit vaccines. We show that a short peptide, named Hp91, whose sequence corresponds to an area within the endogenous molecule high mobility group box (HMGB1) protein 1 potentiates cellular immune responses to peptide antigen and cellular and humoral immune responses to protein antigen in vivo. Hp91 promoted the in vivo production of the immunomodulatory cytokines, IFN-γ, TNF-α, IL-6, and IL-12 (p70), as well as antigen-specific activation of CD8+ T cells. These results demonstrate the ability of a short immunostimulatory peptide to serve as an adjuvant for subunit vaccines.

Partial response precoding for parallel-readout optical memories.

The data density that can be resolved in optical memories is limited by the inherent band-limited nature of optical systems. We show how a precoding technique used in serial communications, called partial response precoding, can be applied to parallel readout optical memories to precompensate for the spatial data broadening that occurs as result of this band limiting. We experimentally demonstrate a factor-of-15 improvement in average worst-case contrast ratio and an order-of-magnitude improvement in average contrast ratio. Over 50% more area was needed to achieve the same contrast ratio in a system without precoding.

Three-dimensional optical data storage in a fluorescent dye-doped photopolymer.

We propose a new, to our knowledge, monolithic multilayer optical storage medium in which data may be stored through the diffusional redistribution of fluorescent molecules within a polymer host. The active portion of the medium consists of a photopolymer doped with a fluorescent dye that is polymerized at the focal point of a high-numerical-aperture lens. We believe that as fluorescent molecules bond to the polymer matrix they become more highly concentrated in the polymerized regions, resulting in the modulated data pattern. Since data readout is based on detection of fluorescence rather than index modulation as in other photopolymer-based memories, the problems of media shrinkage and optical scatter are of less concern. An intensity threshold observed in the recording response of this material due to the presence of inhibitor molecules in the photopolymer allows for the three-dimensional confinement of recorded bits and therefore multilayer recording. The nonlinear recording characteristics of this material were investigated through a simple model of photopolymerization and diffusion and verified experimentally. Both single-layer and multilayer recordings were demonstrated.

Three-dimensional holographic stamping of multilayer bit-oriented nonlinear optical media.

The requirements and limitations on the use of a volume holographic element for the simultaneous optical stamping of multilayer data into a three-dimensional (3D) bit-oriented material that exhibits a suitable sensitivity threshold are investigated. The expected performance of such a holographic stamping element is examined through a model of the coherent noise effects that result from the interference of the many data layers with one another. We show that higher signal-to-noise values may be achieved through the use of semicoherent light during the readout of the hologram. The main limitations to this technique arise from the bandwidth requirements on the holographic element, the degree of nonlinearity required of the bit-oriented media, and the tolerance requirements for the optical exposure levels. As a demonstration of the concept, a two-layer stamping element is fabricated and used to simultaneously stamp two layers of data into a 3D dye-doped photopolymer storage medium.

Speed and energy analysis of digital interconnections: comparison of on-chip, off-chip, and free-space technologies.

We model and compare on-chip (up to wafer scale) and off-chip(multichip module) high-speed electrical interconnections withfree-space optical interconnections in terms of speed performance andenergy requirements for digital transmission in large-scalesystems. For all technologies the interconnections are firstmodeled and optimized for minimum delay as functions of theinterconnection length for both one-to-one and fan-outconnections. Then energy requirements are derived as functions ofthe interconnection length. Free-space optical interconnectionsthat use multiple-quantum-well modulators or vertical-cavitysurface-emitting lasers as transmitters are shown to offer aspeed-energy product advantage as high as 30 over that of the electrical interconnection technologies.

Optimization and theoretical modeling of polymer microlens arrays fabricated with the hydrophobic effect.

High-performance polymer microlens arrays were fabricated by means of withdrawing substrates of patterned wettability from a monomer solution. The f-number (f(#)) of formed microlenses was controlled by adjustment of monomer viscosity and surface tension, substrate dipping angle and withdrawal speed, the array fill factor, and the number of dip coats used. An optimum withdrawal speed was identified at which f(#) was minimized and array uniformity was maximized. At this optimum, arrays of f/3.48 microlenses were fabricated with one dip coat with uniformity of better than Deltaf/f +/- 3.8%. Multiple dip coats allowed for production of f/1.38 lens arrays and uniformity of better than Deltaf/f +/-5.9%. Average f(#)s were reproducible to within 3.5%. A model was developed to describe the fluid-transfer process by which monomer solution assembles on the hydrophilic domains. The model agrees well with experimental trends.

Biorthogonally accessed three-dimensional two-photon memory for relational database operations.

Memory bandwidth is a bottleneck for very large database machines. Parallel-access three-dimensional two-photon memories have the potential of achieving enormous throughput (>100 Gbit/s) and capacity (1 Tbit/cm(3)) [Appl. Opt. 29, 2058 (1990)] and, consequently, are well suited for this application. Our analysis shows that some operations can be completed more than 2 orders of magnitude faster with this type of memory than with a system based on serial-access storage. These particular memories have a further feature of being accessible in orthogonal directions. We show that this property, used in conjunction with a three-dimensional data-organization scheme designed for this approach, leads to improved performance by permitting the user a choice of accessing strategies for a given operation.

Parallel fuzzy inference with an optoelectronic H-tree architecture.

Fuzzy inference is a method of reasoning with imprecise information. The mathematical operations of fuzzy inference can be stated in terms of generalized vector algebra, in which multiplication and summation are generalized to min and max operations. An optoelectronic H-tree architecture is ideally suited to perform these generalized vector operations in parallel and requires only a simple imaging optical interconnection. Appropriate data encodings and electronic circuitry permit large scale, pipelined systems.

Programmable ultrashort optical pulse delay using an acousto-optic deflector.

We present an optical pulse delay (OPD) for delaying ultrashort optical pulses that uses an acousto-optic deflector as an active component. The OPD is designed to correct for chromatic dispersion caused by the significant color spectrum of ultrashort pulses. It is intended to be used as one of the components in a three-dimensional memory system based on pulse-collision addressing in two-photon materials. Calculations show that the OPD should be able to provide 65 arbitrary delays with a random access time of ˜ 1 µs for 100-fs pulses. The power efficiency of the OPD can be as high as 85% and hence permits two units to be cascaded to provide more than 4000 distinct delays. The number of delays and the access time can be optimized such that a fewer number of delays are obtained with a shorter access time, which favors high-speed operations. We provide experimental results that use a Michelson interferometer to measure three different delays, approximately 1 mm apart (equivalent to ˜3-ps time delay), obtained with 130-fs pulses. In addition we include an analysis of the performance of acousto-optic devices for both monochromatic light and ultrashort pulsed lasers. Finally, we provide the design of the optical pulse-delay system for a three-dimensional memory application.

Motionless-head parallel-readout optical-disk system: experimental results.

The motionless-head parallel-readout optical-disk system is designed to read out two-dimensional bit planes that are stored as one-dimensional Fourier-transform computer-generated holograms distributed radially on the disk active surface. Such a system, when built at full scale, could offer several potential advantages: high data-transfer rates of 1 Gbyte/s and higher, low access times of less than 15 ms, low retrieval times (the time required to read the entire memory) of less than 25 ms, and simple optical implementation. The experimental results of a scaled-down implementation of the system are presented.

Computerized design and generation of space-variant holographic filters: 2: Applications of space-variant filters to optical computing.

Holographic optical elements (HOEs) of space-variant impulse response have been designed and generated using a computerized optical system. HOEs made of dichromated gelatin have been produced and used for spatial light modulator defect removal and optical interconnects. Experimental performance and characteristics are presented.

Spatial light modulators and their applications: introduction by the guest editors.

The feature in this issue of Applied Optics includes a collection of papers originally presented at the 1990 Lake Tahoe topical meeting on Spatial Light modulators. These papers emphasize materials and devices for spatial light modulation, smart pixels, and applications.