We have used DCM/polyimide guest-host films for a series of device demonstrations, including demonstrations of high speed, low voltage digital and analog switching. Although useful for such demonstrations, DCM tends to out diffuse at polyimide cure temperatures, motivating the search for related compounds with similar activity, transparency, processibility, and greater thermal stability. We have designed, synthesized, and characterized a series of chromophores with related molecular structures. Like DCM, all of these chromophores share the dicyanomethylene [>C=C(CN)2] acceptor group. Some of these compounds are conventional donor-acceptor chromophores, while others fall into the class of lambda-shaped donor-acceptor-donor (DAD) compounds. An acceptor-donor-acceptor (ADA) chromophore has also been prepared and characterized. The donor-acceptor analog studies utilize a variation on the Knoevenagel condensation reaction used to make DCM, substituting isophorone for 4-pyranone to avoid the formation of mixtures. These reactions lead to the DCI series of compounds. We will describe progress in our investigations of these series of compounds.

In the course of development of any new technology the issues of device stability and reliability are inevitably encountered and must be summarily dealt with. The development of organic and polymeric nonlinear optical media has been no exception and has now evolved to a stage wherein solutions to a few performance issues are of crucial importance. Discussions here focus on just two of these critical problems. First, we describe a preliminary study intended to identify some of the variables involved in optical damage. The goal here is to identify suitable photochemically stable chromophores and polymers and to elucidate any processing and environmental influences which contribute to damage. Second, the thermal stability of nonlinear optical chromophores has already attracted much attention and significant progress has been made in enhancing the thermal stability of many systems. Our most recent effort has concentrated on chromophores with a variety of different configurations and combinations of nitrile acceptor groups, some of which possess both large nonlinearities and excellent thermal stability. Some newer aspects of a thermal stability screening protocol which are particularly useful for these thermally stable chromophores and polymers are also described.

The design and synthesis of a family of calix[4]arene-based nonlinear optical (NLO) chromophores are discussed. 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. These nonlinear optical super-chromophores were subsequently fabricated into covalently bound self-assembled 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, and the average molecular alignment, ψ. We find a value of d33 = 60 pm/V at a fundamental wavelength of 890 nm, and ψ˜ 36° with respect to the surface normal.

We have developed two new classes of highly active and thermally stable nonlinear optical (NLO) chromophores based on the use of efficient thiophene conjugating units, a N,N-diphenylamino electron-donating group, and a 1,1′-dicyanovinyl substituted electron-accepting group. We have also developed a facile and generally applicable method to functionalize NLO chromophores onto high temperature polymers to demonstrate both high electro-optic (E-O) coefficients and long-term alignment stability at 100 °C.

Chromophores capable of undergoing conformational changes when exposed to ultraviolet or visible light have been synthesized with functional groups permitting attachment to polymer matrices. One class of such chromophores, containing reactive functionalities at both ends of the chromophore, are referred to as double-end crosslinkable (DEC) chromophores. These chromophores are used in the synthesis of hardened nonlinear optically active lattices and in the fabrication of buried channel nonlinear optical waveguides by photoprocessing; development of such waveguides represents a critical step in the production of polymeric electro-optic modulators. Such chromophores are also crucial to the phenomena of laser-assisted poling (also known as photochemically-induced poling). Finally, these chromophores are attached to the surface of polystyrene beads permitting the realization of room temperature spectral hole burning exploiting morphology-dependent resonances. Such resonances provide the basis of wavelength coding for the development of high density optical memories.

A family of new polymeric nonlinear optical materials with high second order non-linearities, good thermo-oxidative and reorientational stability, and low waveguide losses have been prepared from a series of chromophores containing hydrazone moieties. These new polymerizable chromophores can be readily prepared by the acid-catalyzed condensation of substituted arylhydrazines with functionalized ketones or aldehydes to give molecules that have μ3 values up to 2440 × 10−48 esu (1579 nm) in solution. Thermoplastic polycarbonates and poly(hydroxy ethers) containing hydrazone chromophores have been prepared with Tg's ranging from 135 °C to 285 °C. Epoxy systems crosslinked with amino-functional arylhydrazones, have high d33 values and high glass transition temperatures, albeit with lower relative thermo-oxidative stability. Simple Mach-Zehnder modulators and registered multi-level structures based on these polymers have been reported previously. One device, prepared from a hydrazone-containing poly(hydroxy ether), has an r33 value of 10 pm/V (1320 nm), and retains most of that activity to 140 °C.

This paper presents a summary of the benefits and limits of active polymer waveguide devices and an overview of the use of active EO polymers in modulation devices with reduced length.

Relaxation dynamics of poly(methyl methacrylate) (PMMA) and doped PMMA systems are investigated as a function of processing temperature and frequency. Polymer relaxations and changes in local mobility are responsible for chromophore reorientation and lead to a loss in second-order nonlinear optical (NLO) properties. Studying polymer relaxations enables the temporal and thermal stability of the NLO polymer systems to be more accurately and readily predicted. The polymer dynamics are studied by correlating mechanical and dielectric relaxations to polymer and chromophore relaxations that occur during chromophore reorientation in second harmonic generation experiments. Dielectric and mechanical relaxation techniques enable polymer relaxation dynamics to be observed over a broad frequency range. The plasticization effect of the NLO chromophores on the polymer relaxation dynamics is also investigated.

We use the low temperature fluorescence spectra of organic multiple quantum well samples consisting of the archetype materials, 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA); 3,4,7,8 naphthalenetetracarboxylic dianhydride (NTCDA), and 3,4,9,10 perylenetetracarboxylic-bis-benzimidazole (PTCBI), to study the effects of quantum confinement on the lowest energy excited and ground electronic states of these molecular crystals. Both the Franck-Condon and the dominant ground state vibronic mode energies are observed to undergo significant shifts with decreasing PTCDA layer thicknesses (ranging from 500Å to 10Å) in PTCDA/NTCDA MQWs, while no such effects are observed for PTCBI/NTCDA MQWs. These results are interpreted in the context of confinement of spatially extended excitons in ultra thin PTCDA layers, whereas the considerably smaller radius PTCBI excitons are not affected over the range of layer thicknesses investigated. These results unambiguously rule out previous hypotheses suggesting that binding of small radius excitons to interfaces results in the blue shifts previously observed in the absorption spectra of PTCDA-based MQWs.

This contribution describes the synthesis and properties of three classes of model NLO chromophore-functionalized high-Tg polymers which test current ideas about architecture-Tg- χ(2) performance relationships. Condensation of bismaleimides with diallylamino-functionalized donor-acceptor chromophores yields polable matrices with Tg values as high as 325°C and χ(2) responses as high as 0.7 × 10-7 esu (27 pm/V; λohigh as 0.7 × 10-7 esu (27 pm/V; λo = 1064 nm; 1.17 eV). Likewise, = 1064 nm; 1.17 eV). Likewise, condensation of o,o'-diallylbisphenol A with bismaleimides followed by chromophore functionalization yields an analogous series of polyimides with Tg values as high as 260°C and χ(2) response as high as 1.0 × 10-7 esu (42 pm/V at λo = 1064 nm). Polymerization of a bis(4-aminophenyl)lophine chromophore with bismaleimides or diisocyanates yields polymers with Tg values as high as 350°C and χ(2) = 0.62 × 10-7 esu (25 pm/V at λo = 1064 nm). All members of the above series exhibit minor to negligible decay in χ(2) response on aging in air at 100°C for 1000 h. The lophine-based material exhibits only ∼10% χ(2) decay on aging for 100 h at 200 °C under N2.

This contribution describes the synthesis and properties of NLO-active self-assembled chromophoric multilayers. The stilbazolium self-assembled multilayers were prepared by new topotactic approaches based on siloxane self-assembly technology. X-ray photoelectron spectroscopy (XPS), advancing aqueous contact angle (θa) measurements, transmission optical spectroscopy, polarized second harmonic generation (SHG), and specular X-ray rellectivity (XRR) show that the resulting self-assembled chromophoric superlattices have very high structural regularity and very large second-order nonlinear optical susceptibility.

Sol-gel derived composite materials of polyvinylpyrrolidone (PVP), SiO2 and TiO2 were studied to achieve low optical propagation loss and high thermal stability in slab waveguides. PVP is a thermally crosslinkable polymer. However, the thermal crosslinking and thermal decomposition take place around the same temperature, 200 °C, resulting in high optical propagation loss. The incorporation of sol-gel processed SiO2 prevents thermal decomposition of PVP and produces remarkably low optical propagation loss even after being baked at 230 °C. We have achieved 0.2 dB/cm optical propagation loss at 633 nm. Furthermore, little index change was observed at 110 °C for 1,000 hours after initial slight increase. Impregnation of sol-gel processed TiO2 into the PVP/SiO2 system was also studied to increase refractive index. A broad manipulation of refractive index, from 1.49 to 1.65, with an optical propagation loss of less than 0.6 dB/cm at 633 nm was accomplished by a careful selection of Ti alkoxide and optimized reaction conditions. PVP/SiO2 slab waveguides were then used to fabricate channel waveguides by using a laser densification technique utilizing metal lines as light absorbent and an Ar laser. An optical propagation loss of 0.9 dB/cm was achieved at 633 nm.

Spatial light modulator (SLM) technology based on commodity silicon fabrication processes and employing a thin, ferroelectric liquid crystal light modulating layer at the chip's surface, has advanced to the point of producing high-performance, practically useful devices. Electrically addressed display devices with 256 × 256 resolution, 100: 1 contrast, and 10 kHz frame rate, as well as optically addressed, “smart” SLMs that perform spatio-temporal filtering on images, have resulted in the course of the author's involvement with Displaytech, Inc.

The silicon technology infrastructure is a juggernaut that produces regular and significant advances in capability. An optoelectronics technology based on foundry silicon can exploit these advances directly and realize rapid improvements. The gains in the density, speed, and optical performance of the Si/FLC devices presented here, illustrate this perspective.

The favorable speed-power performance of these devices is due to an excellent match in the “terminal characteristics” of FLC materials with those of fine-line MOSFETs. The impact of these characteristics on overall device performance is discussed in some depth.

Ferroelectric metallomesogens are a new type of ferroelectric liquid crystal which have unique properties arising from the presence of metal atoms. Here we report an overview of results based on the wide range of structural changes, either in the metallic centre or in the organic part, that these compounds offer.

Ferroelectric salicylaldiminate derivatives, imine ortho-palladated dinuclear complexes and ortho-metallated imine-β-diketone mononuclear compounds give rise to chiral smectic C ordered materials with macroscopic polarizations up to 200 nC.cm-2 while their response times are in the range of ms.

Depending on the metal and the structure of the metallomesogens, additional properties such as paramagnetic behavior as well as non-linear optical reponses are described for these new materials. Thus, imine-β-diketone compounds of Pd(II) and Pt(II) are the first metallomesogens ever reported which show second harmonic generation. deff values in the range of 0.03 to 0.06 pm.V-1 at 10 °C below the transition to the SmC* phase have been measured for these materials under phase matching conditions.

Among soft organic nonlinear optical materials is a class of recently developed: χ(2)_ enhanced ferroelectric liquid crystals (FLCs). The FLC phase nonlinear susceptibility is enhanced by synthesizing onto the molecules constituting the FLC phase a moiety with an increased hyperpolarizability. The hyperpolarizability of the FLC molecules couples into the permanent, thermodynamically stable, polar order of the FLC phase resulting in a material with an enhanced nonlinear susceptibility. Like other soft organics, the linear and nonlinear optical materials characteristics can be altered by chemical synthesis and mixing.

We report on our technique to evaluate the nonlinear optical properties of χ(2)-enhanced FLCs by measuring their high-frequency electro-optic r-coefficients. The technique is broad-band, readily allowing electro-optic coefficient measurement between 100 KHz and 200 MHz. Although the experimental geometry is not conducive for practical device application, it offers a compromise between ease of fabrication and magnitude of nonlinear response. This technique can also be used to evaluate other organic materials such as poled polymers.

Initial results of a project directed towards the design and synthesis of ferroelectric liquid crystal polymers (FLCPs) for second order nonlinear optics (NLO) applications are described. FLCP glasses represent a novel type of solid, a truly noncrystalline solid with thermodynamically stable polar order. FLCPs with useful magnitude of the second order susceptibility χ(2) and processability not possible with poled polymers or crystals have been obtained.

Ferroelectric liquid crystals (FLCs) are true liquids with a thermodynamically stable polar structure. Furthermore, in some systems excellent polar stereocontrol has been demonstrated (> 80% of the molecular dipole oriented along the polar axis with infinite “thermal stability”). These properties make FLCs an interesting candidate for second order NLO applications. However, until now the orientation of organic functional arrays with “large β”, typified by the disperse red 1 (DRI) chromophore, has not been demonstrated.

Herein we report the initial results of a study directed towards providing a solution to this problem. Specifically, a new FLC dopant wherein the DRI chromophore (p-nitro-p'-dialkyl-aminoazobenzene unit) is oriented along the polar axis in FLC mixtures up to 30% by weight is described. These results suggest that it will be possible to obtain FLCs with good stereocontrolled orientation of large β functional arrays. Given that hybrid VLSI silicon/FLC optical chips are under intense investigation as micro-displays, and manufacturing issues for this class of devices are being addressed in the display context, the materials presented here suggest VLSI/FLC chips may be useful as high speed electro-optic modulators as well.

Ferroelectric morphotropic phase boundary (MPB) materials based on Pb2+ - containing compositions are potentially important for optical and electronic applications because they exhibit high switchable polarization near this boundary with superior electro-optic and piezoelectric properties. In this paper we discuss these MPB materials, substrate issues, and the growth of MPB film compositions based on the PZT and PSKNN systems.

High quality lithium niobate (LiNbO3) epitaxial thin films have been grown on c-plane sapphire and LiTaO3 substrates by solid-source MOCVD using the tetramethyl-heptanedionate sources, Li(thd) and Nb(thd)4. Phase content was controllable, and stoichiometric films were reproducibly deposited over a broad temperature range from a Li(thd)-rich source. Using sapphire substrates, with which the occurrence of multiple in-plane orientations is typically a problem, LiNbO3 films with only one in-plane orientation could be prepared within a narrow range of growth conditions. XRD rocking curve FWHM values as low as 0.04°, and optical waveguiding losses near 2dB/cm (1200Å thick film, TMo mode, 632.8nm) were obtained. However, film thicknesses on sapphire were limited to 2000Å because of cracking caused by the large thermal expansion mismatch, and in such thin films, optical confinement is poor.

In contrast, LiTaO3 has almost same lattice constants and thermal expansion coefficients as LiNbO3, making it a potentially superior substrate material. Lithium niobate films up to 6000Å were successfully deposited on LiTaO3 substrates without cracking. Film quality was greatly improved, with FWHM values as low as 0.01°, and rms surface roughness less than 10 Å. Preliminary optical waveguiding losses less than 6 dB/cm for the TEo mode have been achieved.

Ferroelectric potassium niobate thin films have been deposited by conventional, low pressure metalorganic chemical vapor deposition on several types of oxide substrates. The films were epitaxial with a c-axis orientation normal to the substrate. Atomic force microscopy revealed a surface roughness of 1 - 4 nm. Transmission electron microscopy showed the film/substrate interface to be semi-coherent with lattice misfit accommodated by misfit dislocations. The nonlinear optical properties of the KNbO3 films were measured by a transmission technique. The room temperature, effective second order nonlinear coefficient was 13 pm/V.