Non linear optical (NLO) polymers have great potential to be fabricated into integrated electro-optic (E/O) devices for use as high speed electro-optic (E/O) switches, modulators and interconnects in computer and communication systems [1,2]. The fabrication of practical integrated E/O devices requires a material system that meets the final device requirements and can be processed using standard fabrication technologies [3]. Applications of polymer E/O devices in electronic systems have been limited by the relatively low thermal stability and poor processability of non linear optical (NLO) polymers. This paper describes a thermally stable electro-optic material system and the fabrication process to make compact integrated E/O devices for application in electronic systems. This material system consists of high thermal stability polyimide core and cladding materials. The active NLO material is a side chain polyimide that uses a new high activity and high thermal stability chromophore.

Novel approaches to second-order nonlinear optical (NLO) side-chain polyquinolines and polyimides are described. The syntheses and the characterization of the polymers are detailed. The electro-optical coefficients (r33), temporal stability of dipole alignment, and other physical properties of the NLO polymers are presented.

A new class of nonlinear optical (NLO) polyimides incorporating a thermally stable chromophore has been synthesized and characterized. These polymers exhibit large and extremely

Thin films of the organic nonlinear optical materials 4‘-nitrobenzylidene-3-acetamino-4- methoxy-aniline (MNBA), and 2-cyclooctylamino-5-nitropyridine (COANP) have been deposited by organic molecular beam epitaxy. Homoepitaxial growth has been demonstrated for both materials. MNBA thin films were grown heteroepitaxially on lattice-matched ethylenediammonium terephthalate (EDT) substrates. Under optimum growth conditions, similar to those valid for homoepitaxial growth of the same material, i.e. at substrate temperatures of 80°C, and growth rates of 0.1 Å/s, highly oriented films were deposited in an island growth mode. Nonlinear optical second-harmonic generation experiments confirmed the macroscopic orientation of the deposited MNBA thin films. Growth experiments with MNBA and COANP on inorganic substrates lead to amorphous or polycrystalline films, depending primarily on the substrate temperature. A spontaneous recrystallization process, occurring in COANP thin films under ambiant conditions, led to the formation of macroscopic nonlinear optically active domain structures.

A new class of second order nonlinear optical chromophores resulted from the replacement of the most reactive CN group in tricyanovinylthiophene derivatives with aryl units, have been designed and synthesized. It was shown that these chromophores provide excellent tradeoffs among many relevant properties such as molecular nonlinearity, linear absorption at 830 nm, inherent thermal stability, chemical stability in processing solvents as well as host polymer matrices at high temperatures and attenuation at 830 nm.

The phenomenon of second harmonic generation has been studied from the earliest days of nonlinear optics.[l] To date the most impressive results in terms of conversion efficiency for as low an input power as possible have been obtained in channel waveguides made from inorganic materials.[2] However, when their second order nonlinearities (10s of pm/V) are compared with those of organic materials (10s → 100s pmn/V), it is clear that organic materials should eventually produce much better harmonic conversion efficiencies. [3]

The realization of photonics technology rests on the development of multifunctional materials, which simultaneously satisfy many functional requirements. Towards this goal, we present here, the preparation of novel multifunctional nanostructured composites using the sol-gel process. Two specific applications: optical limiting, and two-photon pumped lasing in these composite materials will be discussed.

We have been able to dope two optical limiting materials in a single bulk and retain the optical limiting effects at each of their characteristic wavelengths. The materials selected for this purpose were C60 which shows optical limiting behavior at a wavelength of 532 nm and bisbenzothiazole 3,4-didecyloxy thiophene (BBTDOT) which exhibits a strong two-photon absorption induced optical limiting at 800 nm. The resulting glass acts as a multi-wavelength optical limiter.

In addition, we present results of two-photon pumped upconverted lasing at 600 nm in a nanostructured composite glass doped with a new dye, trans-4-[P-(N-ethyl-Nhydroxylethylamino) styryl]-N-methylpyridinium tetraphenylborate (ASPT). The pump source was a Q-switched Nd:YAG laser producing 1064 nm pulses of ˜ 10 ns duration.

We measured the third-harmonic spectrum for a series of both centrosymmetric and noncentrosymmetric squaraine dyes in chloroform. By fitting the experimental dispersion of the third order susceptibility, γ, to a four-level sum-over-states model, we determined the strength and location of the lowest lying two-photon-like transition. In each case, we find that the lowest two-photon-like state appears just above the dominant linear absorption peak in energy and that the transition moment to that state makes a significant contribution to the nonlinearity, as do transition moments to one or more higher-lying two-photon-like states in the ultraviolet. The spectra of one centrosymmetric dye contains an additional feature evidencing a nonzero dipole moment difference between the ground and first excited state dipole moments (δμ) that we attribute to a conformational asymmetry. A noncentrosymmetric squaraine dye shows a similar feature, which, as expected, arises from its δμ. Effects of symmetry breaking are described.

Electroactive polymers such as poly [p-phenylene vinylene] (PPV) and poly [2,5-thienylene vinylene] (PTV) have been shown to yield highly conductive materials upon oxidative doping,1 and to display enhanced third order nonlinear optical response.2 Optical absorption spectra for either neutral or doped polymers, however, are quite broad, extending well into the visible for the neutral polymer and into the near infrared (NIR) for the doped polymers, with little evident fine structure. For certain nonlinear optical (NLO) applications, this can lead to undesirable absorption losses and resonance phenomena. We would like to describe how copolymers incorporating oligomeric dithienylpolyene segments may be designed so as to give some degree of control over the polymer absorption characteristics in either neutral or oxidized form.

Integrated optic zero-gap directional couplers (ZGDC‘s) offer orders of magnitude shorter device lengths than conventional directional couplers. Researchers are currently striving to simultaneously optimize several properties of nonlinear optical (NLO) polymers that are viewed essential for the fabrication of commercially viable polymer electro-optic devices, including high electro-optic activity, low propagation loss and high temperature poling retention. Fabrication of zero-gap directional couplers using NLO polymers show the potential to realize devices with interaction lengths as short as 100 μm, operating at TFL level switching voltages. Hence, NLO polymer ZGDC‘s will possess the ability to tolerate large propagation losses. This can allow the low propagation loss constraint for NLO materials to be relaxed significantly. Polymers with high electro-optic activity that might be rejected because of high propagation loss, could potentially be utilized for ZGDC switches. In addition, by using these devices as stand alone switches for the present (i.e., not integrating them with electronic circuits) the de-poling temperature constraint can also be significantly relaxed since neither solder baths nor high density interconnect (HDI) processes will be needed. These relaxed constraints should improve the chances for introduction of viable NLO polymer devices that can compete in the market place today, without being forced to wait for a material in which all properties have been optimized.

Self-assembled molecular architechtures of nonlinear optical (NLO) chromophores and their super-chromophores are discussed. The chromophores are derivatives of azobenzene sulfonates and the super chromophores are derivatives of calix[4]stilbazole and calix[4]stilbazolium. The studies of azobenzene sulfonates are aimed at understanding the surface coverage and molecular orientation in polar self-assembled monolayers (SAMs). The optimized molecular orientation was found to be 32±3 degree and the maximum surface coverage is approximately 2–4 molecules per nm2 depending on the molecular cross-section. The calixarene chromophores are macrocyclic compounds consisting of four simple D-π-A units bridged by methylene groups. These molecules were synthesized such that four D-π-A units of the calix[4]arene were aligned along the same direction with the calixarene in a cone conformation. Both simple and super-chromophores were subsequently fabricated into covalently bound selfassembled monolayers on the surfaces of fused silica and silicon. Spectroscopic second harmonic generation (SHG) measurements were carried out to determine the absolute value of the dominant element of the second-order nonlinear susceptibility, d33 = 60 pm/V at a fundamental wavelength of 890 nm. Furthermore, SHG imaging was employed to investigate the pattemed SAMs of NLO super chromophores.

We report the synthesis, and optical characterization of the planar binuclcar phthalocyanines metal free (-1)( H2Pc)2(t-bu)6 and (-l)(VOPc)2(t-bu)6. Several of their optical properties, including linear absorption, concentration dependence, electroabsorption, and transient optical response were measured.

We calculate the pump-probe spectrum of an ensemble of ID molecular aggregates, taking into account coherent exciton transport and exciton-exciton interactions. Comparison with recent experiments show that small radius biexcitons may be optically induced in PIC J-aggregates.

Difunctionalized aminophenylenethienylidene-1,3-bisdicyanomethyleneindane (BDMI) derived second order push-pull chromophores and polymers have been synthesized and characterized. Preliminary studies of doped polymeric composite thin films reveal large SHG signals as well as good chemical and thermal stabilities under poling conditions.

Based on our previous work using benzocyclobutene (BCB) moieties in extended-chain polymers [1], it was thought that the construction of unsymmetrical molecules around the BCB unit might result in thermally crosslinkable NLO-active materials. The feasibility of incorporating such a functional system in donor-acceptor molecules without disrupting processability is discussed and demonstrated. The synthesis, processing, and characterization of these molecules was investigated by thermogravimetry, differential scanning calorimetry, and optical microscopy using a specially designed hot stage which makes it possible to apply an inplane electric field at elevated temperatures. The ability to rapidly and irreversibly crosslink bulk films without the generation of volatile byproducts provides a novel method for sustaining poled optical properties by locking in the desired orientation. The anisotropy of the electrically poled melt and sustained birefringence after BCB crosslinking and cooling demonstrates the achievement of molecular alignment in these new materials.

Two types of second-order nonlinear optical epoxy-based polymers functionalized with tricyanovinyl chromophores were synthesized. One was prepared by azo coupling between an epoxy prepolymer and 4-tricyanovinylaniline while the other was synthesized by reacting the epoxy prepolymer with tetracyanoethylene. The d33 for the polymers were determined to be 243 and 178 pm/V at 1.064 μm respectively. Retentions of deff value of 83% and 65% were observed after the polymers had been heated at 80°C for 1000 hours.

Nonlinear optical (NLO) LB films of polyamic acid containing a stable NLO dye were prepared and imidized either chemically or thermally. The optical properties and molecular orientation of these LB films were studied. From the absorption spectra, we infer that the derivative of the pnitroazobenzene chromophore covalently attatched to polyamic acid did not show significant aggregation. Quadratic dependence of SHG on the number of layers in polyamic acid films indicated the noncentrosymmetric organization of polar NLO chromophores. A second-order nonlinear coefficient (d33) of 23.4 pm/V was observed at 1064 nm after absorption correction. In polyimide films, SH intensity was dramatically reduced due to the collapse of the layered structure upon imidization process. In-plane isotropy of the LB films of polyamic acid and polyimide were lost upon irradiation of polarized light.

The photobleaching mechanism of nonlinear optical polymers has been investigated; the PMMA based polymers with nonlinear optical chromophores, 4-dimethylamino-4'-nitro-stilbene (DANS), 4-dimethylamino-4'-hexylsulfone-stilbene (DASS), and 4'-(2-hexyloxyethyl) ethyl amino-4-nitro azobenzene (DR-16). The photobleaching was carried out using near-UV lines. FTIR spectra and UV-VIS absorption spectra were obtained after each photobleaching. Refractive indices were measured in the photobleaching processes. The results suggest that the photobleaching mechanism of two PMMA based side-chain polymers with DANS and DASS chromophores results from the photo-oxidation and that of the PMMA based host-guest polymer with DR-16 chromophore results from the combination of the photo-degradation and the trans-cis conformational transformation.

We report the observation of photorefractive (PR) effect in a solution processable, thiophene copolymer with a side chain nonlinear optical (NLO) chromophore, poly(3- octylthiophene-co-N-(3-thenyl)-4-amino-2-nitrophenol) [POMDT]. The copolymer exhibits moderately fast photoconductivity. When doped with second order NLO active azo dye, this copolymer exhibited large second order NLO activity, and low asymmetric two beam coupling (TBC) gain. Enhanced TBC gain was observed, when this composite material was plasticized. The observed photorefractive response time is of the order of seconds. The slower response is attributed to the presence of large volume fraction of the plasticizer in the composition, which reduces the charge carrier mobility. The results from photoconductivity, second harmonic generation and two beam coupling experiments are discussed.

We report our investigation on the recording of surface relief gratings on azobenzene containing polymer films by laser beams with different polarizations. Experimental evidence shows that it is necessary to have spatial variations of both magnitude and direction of net electric field in the films to record surface relief gratings. Large surface modulation (> 3500 Å) and high diffraction efficiency (about 30%) were obtained under optimized recording conditions. In addition, polarization dependent erasure of the gratings by a single laser beam has been studied.