A multilayer MIMD data-flow processor using spectral hole burning, photon echo, mutually coherent reconstruction beams for holograms, and algorithmic origami is sketched very roughly. It should allow low power consumption, significant parallelism, great flexibility, and high speed (picosecond gates). More importantly, it may allow us practical access to the high resolution of molecules relative to wires and beams of light.

We have been developing a two-photon 3-D memory expected to provide a Tbit storage capacity and a 1 ms access time for secondary storage. Even with this new technology, there still exists a four order of magnitude gap in access times between electronic RAMS and secondary storage. In addition to the existing permanent storage approach, we have begun working on systems, key components, and materials for a dynamic parallel-access 3-D two photon memories that will bridge the gap in primary memory technologies. Over the past three years our team has been developing a write-once mass-storage memory based on two-photon bond dissociation of spirobenzopyran molecules for long lifetime storage. A cache memory must have fast write-erase capability. To achieve this we are beginning to investigate highly sensitive two-photon materials which spontaneous decay (self-erase) to the off state. These materials will be incorporated into dynamic memory systems which continually refresh the memory contents, as in an electronic DRAM. The resulting memory is expected to provide a data capacity of 1 Gbit/cm³ with a 10 ns to 1 microsecond(s) access time and a 10 Tbit/s data rate. In this presentation the latest results of the parallel-access 3-D volume memory using two-photon storage is discussed. We cover material and system considerations for both types of parallel-access memories: fast-access primary storage and large-capacity secondary storage.

The speed of modern supercomputers is primarily limited by the relatively slow speed of memory. Research over the past years has focused on developing optical memory systems that, by nature of optics, promise to achieve high speed and high memory capacity. Three- dimensional optical memory systems are well known for their storage capacity and achievable short access time. But the early attempts to exploit 3-dimensional media were limited to photorefractive crystals such as lithium niobate, due to the unavailability of any other suitable medium (alternative media are precluded by their diffraction limited storage densities and non- erasable characteristics). Although volume phase holograms can be recorded in photorefractive crystals, these materials have many obvious flaws such as strong scattering, phase distortion, self diffraction, fast decay, and low refractive index modulation. There have also been continuous efforts to develop new 3-D media (such as photon echo, photorefractive polymers, bacteriorhodusphin, memory access cache, etc., but none can be applied in real world 3-D device because these materials are still in the early stage of development.

Photoinduced orientation and recording of erasable holographic gratings in a new photoresponsive amorphous polymer containing azobenzene groups were studied. Using linearly polarized white light and Ar⁺ laser beam at 488 nm, orientation of azobenzene groups perpendicular to the polarization direction of the incident light was observed in polymer films. Holographic gratings with high diffraction efficiency were recorded by polarized Ar⁺ laser beams at 488 nm. These gratings were stable at room temperature. Writing of multiple gratings at the same spot on the polymer films also was investigated. The holographic gratings can be erased by heating the samples above the glass transition temperature and can be rewritten on the same spot. This was performed for fifty cycles.

The prospect of high density three-dimensional optical memory has encouraged development efforts. Research has focused on storing Bragg angle multiplexed hologram page storage and two-photon bit storage volumes. Physical Optics Corporation (POC) has investigated alternative multilayer 3-D memories based on a vectorial organic recording medium. POC's approach incorporates polarization vector switching to independently address layers in the third dimension. POC's methodology has been to fully characterize the molecular and bulk properties of the vectorial organic recording medium, optimize material performance for memory applications including cache and integrated waveguide, and investigate suitable three- dimensional optical memory storage architectures. Here we report on a promising architecture which we have recently demonstrated.

Current properties requirements indicate that for second-order guest host polymeric materials to be both useful in an engineering sense and cost effective they must possess much greater thermal stability. This increased thermal stability is required to maintain both molecular alignment and intrinsic second-order nonlinearity during device fabrication and interface with current state-of-the-art microelectronic systems. In this presentation a new molecular design and synthetic strategy is presented to produce second-order chromophores with much higher thermal stability. Preliminary results of electric field induced second harmonic generation (EFISH) experiments on these compounds are revealed and a discussion of the use of these new molecules as second-order materials is presented.

A number of liquid crystalline cyclic pentamethylsiloxane compounds were synthesized containing high concentrations of covalently attached disperse red 1(4-[N-ethyl, N- hydroxyethylamino]-4'-nitroazobenzene) pendant groups. Corona poling (1.0 (mu) A/-5 kV) was used to align these pendant groups in thin films (1 - 2 micrometers ) produced by spin coating onto ITO covered glass substrates. The measured second harmonic (SH) intensities of these films were comparable to 1 mm thick, y-cut quartz. The initial rise in the SH signal at 25 degree(s)C occurred in less than 10 seconds. This was followed by an additional 20 - 50% increase in the signal over the next 1 - 15 minutes to a final equilibrium value. The SH signal of compounds in the smectic or nematic phase increased to a value of 0.7 - 1.0 X the quartz standard upon heating. An upper temperature limit for each material was observed prior to the dielectric breakdown of the film. The SH intensity typically decayed back to its prepoling value within one hour for films that were poled at 25 degree(s)C. Long term SH stability was observed in films that were poled at elevated temperatures. The intensity of the SH signal was found to be a function of the composition, liquid crystalline phase, and temperature.

Synthetic polypeptides containing Disperse Red 1 (4-[N-ethyl, N- hydroxyethylamino]-4'-nitroazobenzene) nonlinear optical side chains were synthesized. The extent of side chain modification was ca. 10% and higher modifications were expected to produce crystallization of the polar NLO molecule and polymer insolubility. These polymers displayed a lyotropic liquid crystalline phase above a concentration of 15 - 20% (w/w) in dichloromethane. Corona poling (1.0 (mu) A/-5 kV) was used to align the Disperse Red 1 molecules of modified poly[L-glutamic acid] or modified poly[(gamma) -methyl-L-glutamate] thin films (1 - 2 micrometers ) that were produced by spin coating onto ITO covered glass substrates. Decay of the second harmonic (SH) signal was the slowest for films aligned by corona-onset poling at elevated temperatures (COPET) and the fastest for films aligned at room temperature. The SH intensities at 532 nm were comparable to the 1 mm thick, y-cut quartz standard and the (I_s^2(omega)/I_q^2(omega))^1/2 values were measured as a function of the film temperature during corona poling. The biexponential decay model was used to describe the trends in SH decay.

The synthesis and preliminary characterization of new polypeptide-bound chromophores are reported. These polymers were made for the purpose of assembling (beta) -sheets at an air- water surface, and processing them into nonlinear optical films by Langmuir-Blodgett (LB) deposition. These films should be amenable to integration on semiconductor wafers, e.g., as active optical waveguides for phase shifting.

Second harmonic generation by NLO-active organic chromophores is used to monitor the poling dynamics and temporal stability of three kinds on `guest-host' materials: (1) helical polypeptides, (2) random coil polymers, and (3) smectic thermotropic liquid crystals. In (1) sidechain NLO-active chromophores reorient without changing the polymer backbone, whereas in (2) there is a two stage reorientation, sidechains followed by backbone. For the liquid crystal, (3) the mean field gives rise to a threshold poling potential and the polar chromophore orientation appears to be stabilized by the apolar but anisotropic mesogen orientational order.

The optical limiting behavior of trans-diphenyl-1,3-butadiene (DPB), 2,2'-3- methyldithienylethylene (MDTE), 2,2'-dithienyl-1,3-butadiene (DTB) and trans- 2,2'-dibenzthienylethylene (DBTE) in chloroform was studied. Solutions of these compounds are nonresonant at 532 nm. The effects of laser beam spot size at 532 nm on the onset of limiting and the temporal profiles of the transmitted laser pulses were examined. The results indicate two photon absorption as the major contributor to the optical limiting. Two photon absorption cross sections were estimated from the optical limiting data.

Saccharide materials are potential candidates for frequency conversion applications. In addition to being chiral, which ensures crystallization in a space-group relevant for three-wave mixing processes, they generally possess useful physical and optical properties. We have examined the powder second harmonic generation efficiencies of both saturated saccharides and sugars with simple polar (pi) -functionalities. Powder efficiencies of up to 5 times that of sucrose were observed for simple saturated sugars, whereas values of 18 times sucrose (or 0.45 X urea) were observed for unsaturated saccharide derivatives. We have noted that for both classes of material, there is a tendency for more efficient nonlinear compounds to reside in a monoclinic rather than an orthorhombic space-group. We have also noted that there appears to be a correlation between the phase-matching potential and the crystal symmetry.

Attempts are being made to produce nonlinear optical (NLO) polymers by capitalizing on self- alignment properties of peptides by the formation of a beta pleated sheet. Such polymers contain both hydrophilic chromophores and hydrophobic side chains in which selective wetting on a water surface using Langmuir-Blodgett techniques creates a first-order approximation of the oriented film. Assembly to the planar beta pleated sheet structure should further enhance the oriented chromophoric structure of the extended mass. However, this requires stabilization through both hydrogen bonding and through energetically stable conformations. It is this stabilization which will favor the enhanced chromophore alignment during the deposition processes. Previous experimental peptides using leucine-based hydrophobic groups and dinitrophenyl-based hydrophilic chromophores have shown limited success in formation of the oriented films. Because it is desirable to be able to predict the effects of the side chain on orientational properties we have added molecular modeling to our general synthetic strategies, in order to analyze the possible affects of the primary structure on the beta sheet.

Picosecond and nanosecond nonlinear transmission measurements were used to determine the excited singlet and triplet state absorption cross sections at 532 nm for group IVA metalloid phthalocyanines. A five-state rate-equation model is used to analyze the nonlinear transmission data. The successful simulations of the nonlinear transmission data on this series of phthalocyanines for widely differing pulse durations provide strong evidence for the validity of the excited state absorption model. Use of the heavy atom effect has allowed engineering of phthalocyanines with strongly enhanced optical limiting performance.

Ether-linked bolaform amphiphiles (Langmuir 1992 8, 637; J. Am. Chem. Soc. 1992, 9035) and novel gramicidin-porphyrin `diads' (MRS Symposium Series, Vol. 277, 1992, 93) have been synthesized. Protocols for vectorial insertion of the derivatized gramicidins into bolaform lipid vesicles have been developed and the photochemical behavior of these proteinaceous composite membranes probed in the presence of electron donors and acceptors. Photoinduced electron transfer properties of the gramicidin-porphyrin conjugates were compared in TRIS- buffered dihexadecyl-phosphate bilayer (DHP) and bolaform monolayer membrane vesicles containing dithiothreitol as sacrificial donor and methyl viologen as electron acceptor on both the inner and outer vesicle surfaces. Although the rates of methyl viologen photoreduction varied depending on the mode of diad orientation within DHP bilayer membranes, photoreduction rates were not orientation- dependent in bolaform membrane vesicles containing the gramicidin-porphyrin diad. The relevance of these results on vectorial electron transfer processes in lamellar systems and the design of integrated charge transfer components is discussed.

We report an observation of optical phase conjugate and high-order diffractions from degenerate multi-wave mixing in LB films of pure purple membrane for the first time. Based on the simplified BR photocycle, a model that describes the high-order diffractions from the population gratings versus the total incident intensity has been developed. The saturated absorption intensity and the saturated nonlinear refractive index of the LB films have been estimated by fitting method to be 0.42 W/cm², and 5 X 10^-2 cm²W, respectively. The typical response time of its nonlinearity is about several milliseconds.

It is recognized that the earliest and most prodigious development in photonics technology will be in the area of second-order nonlinear optical processes: second-harmonic generation and electro-optic modulation. Photonics applications will undoubtedly involve an integration of fast and reliable high-speed optical crossbar switches, electric field sensing devices, and beam alignment of read-write heads for optical data storage in optical computers. The requirements for such devices are very rigorous, and their development relies on employing photonics materials whose linear and nonlinear optical properties can be engineered. There are several organic materials that are being developed into viable devices due to the fact that their (chi) ⁽²) nonlinearities are much higher than those of existing dielectrics. The most recent materials applied to integrated optics have been the sol-gel processed glasses and glass/polymer nanocomposites which have the inherent advantages of being more easily processed and are cost effective. We report in this paper the recent developments of studies involving linear and nonlinear optical properties of some novel sol-gel processed inorganic oxides/organic polymer composites for nonlinear optics and photonics applications.

In order to develop polypeptide-based second order nonlinear optical materials, we have derivatized succinylated poly(l-lysine) with a spiropyran. Spin coated thin films (2 (mu) thickness) of this material on indium tin oxide-coated glass were corona-poled (6 X 10⁵ V/m) under conditions of variable temperature. The degree of alignment and nonlinear optical properties were monitored by measurement of the intensity of second harmonic signal resulting from irradiation at 1064 nm. The dark-adapted polypeptide was in the spiropyran form. The second harmonic signal intensity was 20 times greater than that of the dark-adapted sample. The results demonstrate the feasibility of development of a light- activated nonlinear optical material.

We report the background leading to the development of the first all-polyimide system (cladding/core/cladding) suitable for fabrication of electro-optic waveguide devices on silicon substrates. The cladding layers are spun from a low optical loss, commercially available polyimide that is suitable for multilayer stacks. The electro-optic material consists of this same polyimide as host to a commercially available guest chromophore and is based upon our prior work on thermoplastic polyimides. The synthesis and purification of this chromophore and an analog is discussed. We also present the materials and process development methodology with the results for this polymer system and demonstrate it by fabrication of an all-polyimide Mach- Zehnder modulator operating at 830 nm. CMOS-compatible switching using a device based on the new material has been demonstrated.

We report the femtosecond laser studies of exciton decay kinetics in stretch oriented poly(paraphenylenevinylene) (PPV) films. Stimulated emission of excitons and stimulated Raman gain have been observed after 500 nm photoexcitation with 100 fs laser pulses. These are not observed when higher energy photons are used to excite the polymer.

The transverse nonlinear dynamics of switchings in an active system (laser with nonlinear saturable absorber on bacteriorhodopsin in a self-imaging cavity) is studied both experimentally and theoretically. The soliton-like light field structure formation and continuously cycled self-switching process are investigated.

The second hyperpolarizability, (gamma) , of the donor-acceptor polyene compounds (CH₃)₂N-(CHequalsCH)₃-CHO, 3, (CH₃CH₂CH₂CH₂)₂N- (CHequalsCH)₂-CHequalsC(CN)₂, 4, the cyanine compound [CH₂CH₂OCH₂CH₂-N-(CHequalsCH)₃-CHequalsN-CH₂CH₂OCH₂CH₂]⁺ClO₄^-, 5, and the linear polyenes CH₃- (CHequalsCH)_n-CH₃, where n equals 4, 1, or 5, 2, have been measured by third harmonic generation (THG) at 1907 nm, in a series of solvents ranging in polarity from CCl₄ to CH₃OH. It was found that 3, with the moderately strong formyl acceptor, had positive values of (gamma) which exhibit a peak as a function of solvent polarity. In contrast, 4, with the stronger dicyanovinyl acceptor, had positive (gamma) in very nonpolar solvents but increasingly negative (gamma) values in solvents of moderate to high polarity. These solvent- dependent hyperpolarizabilities are associated with a change in geometry from a highly bond length alternated, polyene-like structure for the formyl-substituted compound in nonpolar solvents, to a cyanine-like structure, with very little bond length alternation, for the dicyanovinyl-substituted compound in polar solvents.

We review the effects of variations in effective mode indices and dispersion on the design and characterization of polymeric waveguides for frequency conversion and photoinduced diffraction in integrated optics devices. Device design in each case depends critically on the effective index of refraction of light propagating in the waveguide which may be a function of the intensity and device history. In detail we report on the conditions for anomalous dispersion phase matching in nonlinear waveguides and on techniques for measuring photoinduced diffraction in prism coupled waveguides. With respect to the latter, diffraction effects due to photochromic gratings in slab waveguides of disperse red 1 in polymethylmethacrylate were studied. Optical damage in the form of diffractive mode conversion was observed when light whose wavelength was slightly longer than the absorption edge of disperse red 1 was coupled in. We also investigated the effect of mode coupling changes on the determination of diffraction efficiency and sensitivity in waveguide experiments using two crossed guided beams. Diffraction efficiencies predicted by measurements of the modulation depth in the guide are found to overstate the actual diffraction efficiencies which could be observed in this geometry. Techniques for overcoming this limitation and for improving estimates of the energy density and interaction length in the guide are noted.

In this paper we show the applicability of Hyper-Rayleigh scattering to obtain hyperpolarizabilities of ionic and biochemical compounds. It was found that dark-adapted bacteriorhodopsin and its isolated chromophore have considerable second order nonlinear optical properties. Information obtained from depolarization studies of the scattered light is discussed.

We propose and demonstrate a novel method which utilizes nonlinear optical techniques to implement parallel optical matrix-matrix multiplication. Such a matrix-matrix multiplier is capable of handling large matrices such as those with 1000 X 1000 elements. The principle of operation and experimental results are presented.

The synthesis and second-order nonlinear optical properties of acceptor substituted biologically derived (beta) -apo-8'-carotenal compounds are reported. Electric field-induced second harmonic generation (EFISH) measurements give values of (beta) (0) which are 2 - 6 times greater than for 4-N,N-dimethylamino-4'-nitrostilbene (DANS).

Polyacetylene is one of the most studied nonlinear organic materials. Its nearly one- dimensional nature and the conjugate electrons along the carbon-backbone are responsible for its unusual physical, chemical, and optical properties. Polyacetylene has attracted the attention of physicists, chemists, and optical engineers. In particular, the highly nonlinear optical properties of polyacetylene can imply efficient optoelectronic applications.

Persistent spectral hole-burning (PSHB) and its applications in data storage and processing are described. Purely electronic zero-phonon lines having very high peak values in the low temperature impurity spectra of solids are considered. Limitations for very large capacity PSHB memories put by the number of impurity molecules to store one bit are discussed. Doped with impurities optical fiber memory is proposed as a means to have low impurity concentration simultaneously with a large number of the impurities to store one bit. Bit-by-bit (digital) storage is compared to the distributed one and the advantages of the two versions of the latter -- PSHB holography and PSHB modeling of neural networks -- are considered. An experiment of simultaneous read-out over coordinates and frequency in neural network modeling is described. Requirements to PSHB materials and possibilities of the existence of materials effective at high temperatures are discussed.

The spectroscopic properties of several spiropyrans has been studied. Absorption and emission spectra has been recorded and the transient states and species identified. Reaction mechanisms responsible for the photocoloration of spiropyrans are discussed and the use of these materials for 3D memory devices is analyzed.