We review the molecular third-order polarizability of a series of compact two-dimensional cyanoethynylethene derivatives and show that the best molecules have a nonlinearity that is only by a factor of 50 lower than the fundamental limit derived by Kuzyk, which is revealed to be a quite useful concept in discussing the observed trends in molecular nonlinearities. We also show that the nonlinearity of this family of molecules contains a large two-photon contribution, and that the best molecules have a very high specific third-order polarizability, meaning that they pack a large nonlinearity in a relatively small size.

We report on the first experimental observation of a large spatial lateral shift in the interaction of obliquely oriented spatial-dark soliton stripes. We demonstrate by numerical simulations that this new effect can be attributed to the specific features of optical media with nonlocal nonlinear response.

Using sum rules and a new dipole-free sum-over-states expression, we introduce a method for calculating the fundamental limits of the dispersion of the real and imaginary parts of all electronic nonlinear-optical susceptibilities. As such, these general results can be used to study any nonlinear optical phenomena at any wavelength, making it possible to push both applications and our understanding of such processes to the limits. These results reveal the ultimate constraints imposed by nature on our ability to control and use light.

Modulating the electronic, magnetic and optical properties at the molecular level using an external trigger has been extended to the field of nonlinear optics. The switching molecule is designed to have a complexation site or a redox active unit which can guarantee electronic communication over the whole conjugated system. The alteration of the nonlinear property is then induced by the modulation of the internal charge-transfer due to the response of the molecule to the external stimulus. This can be achieved by cation binding, protonation/deprotonation or electrochemically.

Azo-functionalized hyperbranched polymers 1 and 2, and linear polyacetylene 3 are synthesized by palladium-catalyzed coupling of triiodoarenes with a diethynylazobenzene, and post functionalization, respectively. These polymers are soluble, film-forming, and morphologically stable (T_g > 180 ^oC). The poled polymer films of 1 and 2 exhibit high second-harmonic generation coefficients (d₃₃ up to 177 pm/V), thanks to the chromophore-separation and site-isolation effects of hyperbranched architectural structure of the polymers in the three-dimensional space. The poled film of polymer 3 shows the trade-off of nonlinearity-transparency-orientation thermal stability. The poled films are all orientationally and thermally stable due to the facile cross-linking of the multiple acetylenic triple bonds in the hyperbranched polymer and the rigid backbone in the linear polyacetylene, respectively.

Photonic have crystals shown promise in a variety of applications. Recently, there has been a great interest in designing and building three-dimensional (3D) photonic crystals whose fabrication can be integrated with standard CMOS processes. In this paper, we explore both of these areas in more detail. We first present techniques for modeling 3D photonic crystals and the analysis of practical lattice configurations. We then discuss our process for fabricating such structures built on standard lithography methods. We conclude by showing how these techniques have been used to design and build practical photonic crystal structures capable integration with CMOS circuitry.

The engineering of a well-designed passband inside the stopband of a self-assembled colloidal crystal superlattice and its effect on the steady-state emission properties of infiltrated fluorophores is reported here. The superlattice was constructed by convective self-assembly of slabs of silica spheres of two distinct diameters. This resulted in an effective passband in between the two stopbands of the total photonic crystal structure as seen in transmission. Because of the passband there is a narrow spectral range with an increased density of states for photon modes. This is seen as a decrease in the suppression of emission (an enhancement of the emission) for the narrow spectral range where the effective passband manifests itself. These experiments indicate that the threshold for lasing can possibly be lowered by spectrally narrowing the emission of fluorophores infiltrated in suitably engineered self-assembled photonic crystal superlattices, and are therefore important towards the realization of efficient all-optical integrated circuits from functionalized photonic superlattices and heterostructures.

We report on electrooptical modulation with a sub 1Volt sensititivity in a photonic crystal slab waveguide resonator which contains a nanostructured nonlinear optical polymer. This modulation effect is based on the electronic displacement polarization in a noncentrosymmetric medium (Pockels-effect) and is therefore inherently by more than three orders of magnitude faster than any other reported electrooptic modulation effect in nanophotonics. We also show concepts for extremely high and zero dispersion as well as for time delay in photonic crystal waveguides. Tuning can be achieved by hybrid combination of Si-based PCs and organic EO-materials.

Photonic crystals have now started to make the transition from basic to applied research, with new materials systems and device results being published on a frequent basis. While a number of photonic crystals have been made using organic materials, the lack of high index organic materials has impeded their development. We have investigated several novel high index organic systems for use in both 2-D and 3-D photonic crystals. 2-D photonic crystal templates were made by a rapid multibeam interference method in the photoresist SU-8, using 532nm laser radiation. These samples, typically on glass, were then infiltrated by a number of methods including from solution and melt, as well through chemical vapor deposition. Solutions of a titanium precursor with a cured refractive index of 2.1 at 633nm were infiltrated and cured in the SU-8 structure, with the infiltrant deposited by both by spin coating and casting. The resulting structure was shown to preserve the six-fold symmetry of the initial photonic crystal and subsequent firing at high temperature effectively removed the SU-8 template. We have also explored the infiltration of nanoamorphous carbon into the photonic crystals using chemical vapor deposition. This material, which is essentially a carbon-silicon ceramic, has exceptional infrared optical properties with a refractive index > 2 for wavelengths beyond 2 μm. The SU-8 polymer template has been shown to survive the CVD deposition process and the resulting infiltrated structure also preserves the initial PC symmetry. A series of metal-like PCs with a full range of properties is enabled by the ability to dope the nanoamorphous carbon with metals that possess exceptional refractive indices in the infrared regions of interest. We have also investigated the potential for nonlinear optical devices based upon azobenzene copolymer infiltrated silicon PCs and demonstrate the excellent properties of this material with respect to all-optical effects.

We have investigated photorefractive (PR) properties of a polymer composite with low glass-transition temperature (T_g) in a symmetric reflection geometry. A diffraction efficiency of more than 30% is observed in 105μm thick devices. In low T_g photorefractive polymers, poling of the nonlinear optical chromophores at room temperature leads to birefringence in the material. The birefringence will alter the Bragg condition, as the propagation vectors for object and reference beams as well as the readout angle are influenced. We observed the Bragg-mismatch effect that caused a reduction in diffraction efficiency as the external field is increased. We have varied the angle of readout beam slightly at each bias field to get the highest efficiency.

We report results of two ongoing investigations that seek to characterize the photophysics of organometallic complexes under one- and two-photon excitation. In the first line of investigation we explore the properties of the triplet state in a complex that contains four individual platinum-acetylide chromophores linked via a tetraphenylmethane unit. Although the individual platinum-acetylide chromophores are not conjugated in the tetramer, transient absorption studies provide clear evidence that triplet-triplet annihilation is very efficient when the complex is excited by sequential two-photon absorption. In a second line of study we have carried out preliminary photophysical studies of an Ir(III) complex that contains a highly conjugated organic ligand that is designed to exhibit a large two-photon absorption cross section. One photon excitation of the Ir(III) complex in the visible region produces a long-lived triplet state that absorbs strongly in the visible and near-infrared regions. Preliminary experiments suggest that the long-lived triplet can be efficiently produced via two-photon absorption in the near-infrared region.

The materials used as media for volumetric storage by means of two photon absorption processes have been studied. The spectroscopic properties, transient spectra and kinetics of several composite molecules are described. The media consist of a photo-chromic moiety that is chemically bonded to a strongly fluorescing dye. Experimental data presented here show that this composite molecule performs as a write/read/erase molecular optical storage medium with non-destructive read-out. The optical head used to record and access the stored information is also depicted.

The synthesis and photochemical reaction of N-benzoyl oxazines was investigated. The materials were found to be photosensitive and capable of generating oxazine dye upon light irradiation. The early step of the reaction may include homolytical bond cleavage between the oxazine nitrogen and benzoyl carbon atoms via an excited singlet state and formation of oxazine and benzoyl radicals. Subsequent reaction steps include disproportionation of the oxazine dimer species formed through recombination of two oxazine radicals, which led to the formation of oxazine dye cation and oxazine anion pair. At the present time direct electron transfer between two oxazine radicals cannot be excluded. These molecules are potential media for optical storage and other applications.

The last little more than five years have seen an outstanding advance in the design of NLO-active organic molecules with octopolar symmetry, despite the often pessimistic predictions for the practical application potential of organic molecular materials. This contribution aims to review the latest developments, and, with special emphasis on efficient bulk materials based on functional molecules, tries to point out promising developments and strategies in order to promote organic molecular materials as useful candidates in modern nonlinear optics.

Conjugated chromophores with permanent dipole moments can be aligned by heating a thin polymer film containing chromophores in an external electric field. The heated "guest-host" system is then cooled in the field to maintain the chromophores' alignment. Dielectric breakdown and charge transfer, however, often limit the external electric field to about 100 V/μm of film thickness. It was hypothesized that electrical pulses could increase the voltage of the poling field without damaging the sample films. This was achieved by combining an amplified waveform from a function generator with the DC poling field. Pulse amplitudes were varied from 10 to 10³ V. Pulse frequencies were varied from 10^-1 to 10³ Hz with a duty cycle of up to 50% of the pulse period. Pulse amplitudes were found to have optimum effects at less than 15% of the DC field at low frequencies, 0.1-10 Hz, with a sinusoidal pulse shape. It was found that this technique induced up to a 20% improvement in optical properties without damaging the sample films.

The reorientational mobilities of molecules in nonlinear optical (NLO) polymers poled by thermal-assisted (TAP) and photo-assisted (PAP) electric-field poling are compared by measuring the temporal development of the NLO properties under a secondary poling voltage at a temperature below the glass transition temperature of the polymer. By comparing the experimental results with a theoretical model that is based on independent chromophores with a distribution of relaxation times, it was found that the secondary poling profile for a polymer poled by PAP is very well described by the theory. This shows that the chromophores can indeed be regarded as independent to each other as far as their relaxations are concerned. The secondary poling profile for a polymer poled by TAP, on the other hand, did not agree with the theory. The discrepancy of the behaviors between the two poling methods suggests that the relaxation patterns observed for polymers poled by TAP may be affected by factors not intrinsic to the polymer properties. This result may have an impact on the assessment of the long-term reliability of photonic devices based on thermally poled NLO polymers.

Chromophore-polymer composite materials for electro-optical applications are rendered active at the χ⁽²⁾ level of susceptibility by inducing chromophore alignment through the interaction of the chromophore dipole moment with an external electric field, a process referred to as "poling". To provide insight into the molecular details of the poling process, single molecule microscopy studies of DCM (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4Hpyran) and RhB (Rhodamine B) in poly(methyl acrylate) (PMA) above T_g of the polymer host are performed. Electric fields of 50 V/μm are employed consistent with typical experimental conditions. The effect of environment is studied through comparative studies or RhB reorientation in oxidative and inert atmospheres. Single-molecule rotational dynamics are monitored through the time-evolution of the fluorescence anisotropy. Anisotropy correlation functions demonstrate non-exponential decay consistent with previous studies of molecular rotation dynamics in polymer melts. The rotational dynamics of DCM are found to be weakly perturbed in the presence of a 50 V/μm electric field consistent with the modest alignment potential created by the electric field relative to the amount of available thermal energy. The relevance of these findings to current models of the poling process is discussed.

We demonstrate that the aggregation tendency of dye molecules in a host polymer can be significantly reduced by exploiting non-covalent interactions between the host polymer and guest dye molecules. Such interactions occur spontaneously with no need for chemical synthesis, and could thus be utilized to combine the ease of processing of traditional guest-host systems with the high dye concentrations achievable in covalently linked systems. We studied the aggregation properties of the common azo-dye Disperse Red 1 in polymers with different functional groups. Compared to a nonpolar polymer (polystyrene), dye aggregation tendency is substantially reduced in polar polymer matrices containing hydrogen-bond donating [poly(vinylphenol)] or hydrogen-bond accepting [poly(4-vinylpyridine)] functional sites. Furthermore, by forming a polyelectrolyte-dye complex [Disperse Red 1/poly(styrenesulfonic acid)], a dye monomer can be attached to approximately each polymer unit, resulting in dye concentration of 63 wt. %. Complexation through proton transfer was further studied by using a fluorescent dye 5-phenyl-2-(4-pyridyl)oxazole. Our results indicate that polymer-dye complexes could provide a facile route for new type of optical materials, with potential applications in various fields of optics and photonics.

A method of chemical synthesis that allows for the facile attachment of a wide variety of chemical compounds, including highly active nonlinear optical chromophores, to polyimides has been developed recently at the Naval Air Warfare Center, Weapons Division. The synthesis of these compounds is presented, along with a discussion of their relevant physical and chemical properties, alone and in comparison to equivalent guest/host materials. Examples of attached chromophores include the well-known Disperse Red 1, along with high-activity chromophores of more recent interest such as FTC and CLD. The synthesis of structures that contain both attached chromophores and chemical functionalities that enable thermal cross-linking of the polyimides is also discussed.

The use of DNA as a functional biomaterial for optical device applications is becoming a fast-expanding technology. Various researchers are investigating salmon DNA as the primary ingredient in the design of optical waveguide devices. The interaction of the indicator dye molecule, Bromocresol Purple (BCP) with the unique homogeneous double helical structure of DNA for potential electro-optic and chemical sensing applications is reported.

We fabricated single mode optical waveguides made of perfluoropolymers with extremely low propagation loss at communication wavelengths reaching even 1650 nm, and found they showed high reliability. The used materials are poly(perfluorinated butenyl vinyl ether) and the chemically-related materials. In the previously reported trial, we used the doped core in order to adjust the refractive index. The propagation loss was low enough for us to use at 1310 and 1550 nm, but the existence of dopant limited the loss reduction. In this paper we report on the perfluoropolymer optical waveguides with dopant-free core. The propagation loss was 0.03-0.04 dB/cm at both 1550 and 1650 nm. The spectral measurement showed that their propagation losses are lower than 0.1 dB/cm all over the communication wavelengths. High durability to humidity was also shown. As an application of this optical waveguide, we demonstrated the 1x32 splitter.

Fluorinated poly(arylene ether)s are attractive for the fabrication of optical waveguide devices for photonic applications due to their low optical attenuation and high thermal stability. A variety of waveguide devices have been fabricated in these polymers through thermal crosslinking followed by a reactive ion etch process. This work reports on the use of a novel fluorinated poly(arylene ether ketone) incorporating tetrafluorostyrol groups for photo-crosslinking. This new molecular design allows sufficient photosensitivity to fabricate waveguides through a UV direct patterning and wet-etch method, offering a fast, convenient and economic approach to making polymer photonic devices. Data concerning the polymer molecular structure and choice of suitable photo-initiators for the fabrication of the devices are presented in this paper. Based upon the optical and thermal properties of the resultant materials it appears that similar degrees of polymer crosslinking can be achieved using the photo-curing process as those using a thermal crosslinking process. High quality waveguide devices with smooth, well-defined sidewalls are demonstrated. Optical characterization of these devices suggests that the waveguide quality is comparable to that of waveguides fabricated using a dry etch process.

Knowledge of the optical properties of the biological spores in air is essential to the development of remote sensing capabilities of biological aerosols. Recently Developed Mid-Infrared (2 to 33 μm) Variable Angle Spectroscopic Ellipsometry has been used to evaluate the optical properties of composite bacterial Spores thin films at Air/ZnS Interfaces. Bacterial-spores thin films was studied in attempt to determine the optical constants of biological spores and the appropriate dielectric Effective Medium Theories that well describe these composite systems. It is shown most of the spores lying down on the interfaces. We compared the optical constants of an individual bacterial spore calculated from the ellipsometric data and a number of static and dynamic dielectric Effective Medium Theory models that considering the effects of sizes, shapes, and electrical and magnetic dipole interactions of the spores. These measurements and assessments show the validity of the models in describing the optical properties of the bacterial-spore composite materials.

Biophotonic sensors based on polymer waveguide with Bragg reflection grating are demonstrated in this work. Waveguide Bragg reflectors were designed by using the effective index method and the transmission matrix method. The grating pattern was formed by exposing laser interference pattern on a photoresist. On top of the inverted rib waveguide, the grating was inscribed into the core layer by the O₂ plasma etching. In order to perform the bio-molecule detection experiment, a calixarene molecule was self-assembled on top of thin Au film deposited on the waveguide Bragg reflector. To measure the response of the sensor, several PBS solutions with different concentrations of potassium ion from 1 pM to 100 μM were dropped on the sensor surface. The shift of Bragg reflection wavelength was observed from the PBS solution with lowest potassium concentration, 1 pM.

There is a long history of using light to change the shape of a material. More than a decade ago, our group proposed and demonstrated that the length of an optical fiber should change due to a guided mode in analogy to the refractive index change due to the Optical Kerr Effect. The mechanisms that we postulated as being responsible included photothermal heating and photoisomerization. In the present studies, we report on a polymer optical fiber cantilever, which is excited by launching a light beam off-axis into the fiber. In measurements of the degree of bending as a function of time after the light beam is turned on or turned off, we find that there are two distinct time responses, each of different magnitude. We show that the dynamics of photobending is consistent with coupling between the photothermal heating and photoisomerization mechanisms. More interestingly, we find that a collective release of stress must be invoked to describe the observations. We propose new kinetic models of the phenomena, and show that they are consistent with the data.

Electro-optic (EO) polymer modulators have demonstrated high speed external modulation of optical signals. Additionally, EO polymers have closely matched refractive indices at optical and microwave wavelengths, which enables high bandwidth operation. An EO polymer includes a polymer matrix and an organic "push-pull" chromophore that can be modified to give poled polymers with high EO activity. This high EO activity and optical-microwave velocity match offer the promise of accomplishing broadband, high speed optical modulation with low drive voltage. Such optical signal modulation is critical for applications in phased array radar and RF photonics. Practical issues such as electrode design, optical fiber coupling, and hermetic packaging are critical in final device performance. Herein, we report on high-speed electrode parameters as well as electro-optic performance versus frequency of packaged modulators fabricated with novel, highly photostable chromophores.

We demonstrate a simple method for monitoring all-optical poling in real time. The susceptibility pattern created by two collinear beams, a writing beam at the fundamental frequency and a seed beam at the secondharmonic frequency, is reconstructed by two-beam second-harmonic generation due to the writing beam and a non-collinear probe beam at the fundamental frequency. This leads to spatial separation of the seeding and signal beams, and allows easy detection of the signal during the seeding period. When the probe beam is sufficiently weak, it does not distort the collinear poling process. Furthermore, the method provides a significantly stronger signal than monitoring based on a probe beam alone.

Host polymers play an important role in determining the thermal, optical and electrical properties of guest-host electro-optic (EO) polymers. In this study, a series of novel polymers, polyaryletherketones (PEKs) and polyarylethersulfones (PES'), were synthesized. After an initial screening on EO modulator fabrication-related properties, a PEK, LP120, was identified as a good candidate to host the highly stable chromophores (DH6 and DH52) developed in the company. Further optimization indicated that solvents in chromophore/polymer solutions have a strong impact on the quality of spin-coated films. DH6/LP120 and DH52/LP120 films spun from cyclopentanone gave lower optical losses of 1.97 and 1.55 dB/cm, respectively, when compared with 2.84 dB/cm for DH6/APC and 1.96 dB/cm for DH52/APC. Moreover, poling efficiencies as being reflected by EO coefficient were also improved by using LP120 compared to APC.

Polymeric electro-optical modulators have the advantages in bandwidth, driving voltage, and cost over lithium niobate modulator for potential industrial, military and space applications. There are strict requirements on electro-optical polymer materials to be used for practical device fabrication: large EO response, high thermal and photochemical stability, low optical loss, high long-term stability and good processibility. Lots of progress in material design, modification and optimization has been made based on theoretical calculation and actual material processing. However it is very challenging to put all good properties into one material. We report the development of a chromophore series based on 3,4-ethylenedioxythiophene structure and two host polymers based on 4,4'-(3,3,5-trimethylcyclohexylidene) diphenol monomer. EO activity and optical loss at different chromophore loadings were systematically studied and compared on various guest/host combinations. Specifically, DH-52/APC system was compared with DH-6/APC system, showing improved overall electrical and optical properties. LP-116, with higher glass transition temperature than that of APC, exhibits excellent mechanical property and compatibility with various chromophore guests. Especially, DH-67/LP- 116 has optical loss of 0.87 dB/cm. This indicates that LP-116 can substitute APC as an improved host polymer and DH- 52/LP-116 is highly feasible for the fabrication of EO devices with enhanced performance.

Very efficient Faraday rotation has been observed in regioregular polyalkoxythiophene. These observations could be a first step towards a new type of application of conjugated polymers.

The orientation relaxation upon photo-induced isomerization of azo-dyes was studied. All-optical poling (AOP) and photo-induced birefringence, which are based on the mechanism of angular selective photo-isomerization, were employed to manipulate the angular distribution of azo-dyes (Disperse-red 1) doped in three different amorphous polymers: (poly(methyl methacrylate) PMMA, poly(carbonate) PC and poly(sulfone) PSU), with different glass transition temperature (T_g). In the case of AOP, quasi-permanent macroscopic second-order nonlinear optical susceptibility χ⁽²⁾ was inscribed in the dye-doped centro-symmetric polymer systems, while in the case of photo-induced birefringence, quasi-permanent birefringence Δn was inscribed in the dye-doped isotropic polymer systems. Relaxation of χ⁽²⁾ and Δn were monitored upon different duration of AOP and photo-induced birefringence preparation. Experimental results show that azo-dye orientation relaxation follows the duration of the photo-nduced isomerization process: the longer the photo-induced isomerization process, the slower the relaxation of the inscribed χ⁽²⁾ and Δn. In addition, retardation of the orientation relaxation does not follow a simple relation with hardness (T_g) of the polymer host. Causes of the orientation relaxation retardation are discussed.

Theoretical models for photoinduced birefringence and chiral structure formation in achiral azobenzene-containing materials were proposed considering phototriggered molecular reorientation via trans-cis-trans photoisomerization cycles of azobenzene. The photoisomerization cycles were expressed by two rate equations of the orientation distributions of trans- and cis-forms. Phototriggered molecular reorientation by illuminating linearly polarized light was verified theoretically. The photoinduced helical structure formation was simualted by elliptically polarized light. The molecular rotation angle was dependent on the sign of the ellipticity. The time evolution of the helical structure formation was consistent with the experimental result that reported by other papers.

We consider how geometry and symmetry alone play a role in determining the magnitude of the hyperpolarizability. Using potential energy functions given by a superposition of force centers representing nuclei, we find that for certain specific geometries, such as asymmetric octupolar-like molecule with donors and acceptors of varying strengths at the branches, the hyperpolarizability is near the fundamental limit. The fact that the hyperpolarizability, when it is at the fundamental limit, is well approximated by a three-level model confirms the three-level ansatz. Our results suggest new design strategies for breaking beyond the apparent limit.

We investigated on cyanine dye (HQ) in Langmuir and Langmuir-Blodgett (LB) films using UV-visible spectra and second-harmonic generation (SHG) methods. UV-visible spectra indicated a uniform film transfer. The significant SHG fringe signal as a function of angle of incidence for Z-type LB films observed respectively. The second-order susceptibility χ⁽²⁾zzz, refractive indexes at 532 nm as well as the average tilt angle ψ between the molecular (dipolar) axis and surface normal, obtained by means of fitting the SHG data, are 42 pM/V^-1, 1.4841, 57° and 32 pM/V^-1, 1.4775, 53° for LB films without and with Cd²⁺ ions, respectively. These high nonlinearities are due to resonant enhancement resulting from the proximity of the second harmonic wavelength to the absorption band of the films.

Amorphous and nanostructured SiO₂:DR1 sol-gel films were prepared by dip-coating. X-ray diffraction studies were performed to determine the long-order structure obtained in the films. The optical absorption (AO) measurements were done in three different nanostructures of the SiO₂ network: lamellar, hexagonal and mixed. The AO measurements and the second harmonic generation (SHG) intensity were carried out at different orientation steps of the chromophores embedded in the films. These chromophore orientation distributions were obtained by means of the corona technique, and they depend on the corona poling time. We physically model the optical absorption and the second harmonic generation experimental results as function of the corona poling time, employing only one fitting parameter related to the matrix-chromophore interactions. The physical model and the experimental results were in an excellent agreement. The experimental results fitted by the model are shown in plots of order parameter against corona poling time and SHG intensity against corona poling time. The lamellar structure provides a larger order parameter values than those obtained for the other structures. A minimum value for the order parameter was detected by means of the optical absorption measurements at short poling times. For the SHG measurements, four different chromophore concentrations were used. As the concentration increases the measured SHG intensity increases too, but the increment is limited by the electrostatic interactions among the chromophores, which is also considered in our model.

Coupling of optical data-processing devices with microelectronics, telecocommunication and sensory functions, is among the biggest challenges in molecular electronics. Intensive research is going on to find suitable nonlinear optical materials that could meet the demanding requirements of optoelectronic applications, especially regarding high sensitivity and stability. In addition to inorganic and organic crystals, biological molecules have also been considered for use in integrated optics, among which the bacterial chromoprotein, bacteriorhodopsin (bR) generated the most interest. bR undergoes enormous absorption and concomitant refractive index changes upon initiation of a cyclic series of photoreactions by a burst of actinic light. This effect can be exploited to create highly versatile all-optical logical elements. We demonstrate the potential of this approach by investigating the static and dynamic response of several basic elements of integrated optical devices. Our results show that, due to its relatively high refractive index changes, bR can be used as an active nonlinear optical material to produce a variety of integrated optical switching and modulation effects.

Helicenes with aryl electron-withdrawing or/and electron-donating groups at one/both end/s are potential candidates for second order nonlinear optical applications. We have prepared such helicenes and related compounds. A single crystal X-ray structure showed the structure and architecture of 2,7-di-1-naphthylbenzo[1,2-b:4,3-b'] dithiophene to be racemic chiral helixes. Both terminal aryl rings contribute to the π-π stacking. Theoretically, there are two synthetic routes (A and B) for the synthesis of 2-(4-methoxylphenyl)trithia-[5]-heterohelicene and 2-(4-methoxylphenyl)-9-(4-cyanophenyl)trithia- [5]-heterohelicene. Although route A is more complicated, it is more efficient because substituents improve solubility. Introducing an electron-donating group increases the yields of all reactions in A.