Waveguide fabrication using organic nonlinear optical materials

A detailed perceptive on the growth and characterization studies of para amino hippuric acid (PAHA) single crystals

Single crystals of para amino hippuric acid (PAHA) were grown by slow evaporation technique. The spectral and its structural properties of the crystals were studied by FT-IR, micro-Raman and factor group analysis. The optical transparency in the UV-Visible regions was found to be good for non-linear optics (NLO) applications. Thermogravimetric analysis (TGA) and Differential Thermal Analysis (DTA) showed that the compound decomposes beyond 300°C. The dielectric behavior of the compound predicts low dielectric loss at high frequency applied whereas in the case of mechanical behavior of the specimen hardness increases with increasing applied load. After certain weight increase, hardness gets saturated in the region of ≥110. Relative second harmonic efficiency of the compound is found to be 1.8 times greater than that of potassium di-phosphate reference.

Investigations on the vibrational modes and non-linear optical properties of 4-Fluoro Chalcone crystal

Organic Nonlinear Optical (NLO) crystals of 4-fluorochalcone (4FC) were synthesized and grown by slow evaporation solution growth method. The grown crystals have been characterised by powder X-ray diffraction, factor group analysis, FTIR, FT-Raman, UV-Vis Spectroscopy, powder SHG and Vickers microhardness tests. Theoretical quantum chemical analysis were performed to determine the first order hyperpolarizability (β) and HOMO-LUMO analysis of the title compound were computed by GAUSSIAN 03 package.

Fabrication of channel waveguides in dye-doped polymer films by a beam-processing machine based on photo induced bleaching

Irreversible changes in the refractive index of a dye-doped polymer film by photo induced bleaching were measured with a Mach-Zehnder interferometer. The decrease in the refractive index of the film for various laser powers and various radiation times has been investigated. A beam-processing machine with two simultaneous outputs has been designed to make use of this change in the refractive index to fabricate a channel waveguide. This method is simple and one step, and does not involve any solvent or mask; and also due to photobleaching, the pattern is not reversible.

Investigations on the physico chemical properties of 4-bromochalcone single crystals for nonlinear optical applications

Good quality yellow transparent single crystals of 4-bromochalcone (4BC) crystal have been synthesized and grown by slow evaporation solution growth method. The UV-Vis spectra was recorded for the grown crystal. The thermal behavior of the title crystal was studied. Fourier transform infrared and Raman spectral studies were performed for analyzing and assigning the vibrations and to identify the functional groups. The relative SHG efficiency of the material was investigated to explore the NLO characteristics for the first time in the literature. The SHG efficiency of the material is found to be 1.14 times greater than urea. Hyperpolarizability and HOMO-LUMO analysis of 4-bromochalcone (4BC) were performed with the help of Density Functional Theory (DFT) calculations using Gaussian 03 software.

Thiophene dendrimers as entangled photon sensor materials

The ability to do spectroscopy with a small number of entangled photons is an important development in the area of materials and sensing. This report investigates the effects of increasing thiophene dendrimer generation on the cross-section for both entangled (sigmaE) and random (deltaE) two-photon absorption cross-sections. Nonlinear optical properties of dendrimers are an interesting area of study because of potential applications in optical signal processing and remote sensing, and the use of a nonlinear optical material as a sensor for entangled photons offers great possibilities for applications in quantum lithography. Entangled two-photon absorption (ETPA) experiments and two-photon excited fluorescence (TPEF) experiments vary by at least 10 orders of magnitude in the photon flux used to probe the material. ETPA cross-sections from liquid samples as well as those of thin-film samples are investigated. An increase in sigmaE and de;taR with increasing dendrimer generation is observed, suggesting that the thiophene groups within the dendrimer nonlinearly absorb in a cooperative manner, which is further evidenced in the variation of cross-section per thiophene group. The nonlinear spectroscopic features obtained by the TPEF measurements were also obtained by the ETPA experiments, despite the fact that 10 orders of magnitude fewer photons are used in the latter technique. All dendrimer generations investigated in this work are found to have great potential for applications in quantum optical devices.

Side illumination fluorescence emission characteristics from a dye doped polymer optical fiber under two-photon excitation

Two-photon excited (TPE) side illumination fluorescence studies in a Rh6G-RhB dye mixture doped polymer optical fiber (POF) and the effect of energy transfer on the attenuation coefficient is reported. The dye doped POF is pumped sideways using 800 nm, 70 fs laser pulses from a Ti:sapphire laser, and the TPE fluorescence emission is collected from the end of the fiber for different propagation distances. The fluorescence intensity of RhB doped POF is enhanced in the presence of Rh6G as a result of energy transfer from Rh6G to RhB. Because of the reabsorption and reemission process in dye molecules, an effective energy transfer is observed from the shorter wavelength part of the fluorescence spectrum to the longer wavelength part as the propagation distance is increased in dye doped POF. An energy transfer coefficient is found to be higher at shorter propagation distances compared to longer distances. A TPE fluorescence signal is used to characterize the optical attenuation coefficient in dye doped POF. The attenuation coefficient decreases at longer propagation distances due to the reabsorption and reemission process taking place within the dye doped fiber as the propagation distance is increased.

Layer-by-layer deposited organic/inorganic hybrid multilayer films containing noncentrosymmetrically orientated azobenzene chromophores

Organic/inorganic hybrid multilayer films with noncentrosymmetrically orientated azobenzene chromophores were fabricated by the sequential deposition of ZrO2 layers by a surface sol-gel process and subsequent layer-by-layer (LbL) adsorption of the nonlinear optical (NLO)-active azobenzene-containing polyanion PAC-azoBNS and poly(diallyldimethylammonium chloride) (PDDA). Noncentrosymmetric orientation of the NLO-active azobenzene chromophores was achieved because of the strong repulsion between the negatively charged ZrO(2) and the sulfonate groups of the azobenzene chromophore in PAC-azoBNS. Regular deposition of ZrO(2)/PAC-azoBNS/PDDA multilayer films was verified by UV-vis absorption spectroscopy and quartz crystal microbalance measurements. Both UV-vis absorption spectroscopy and transmission second harmonic generation (SHG) measurements confirmed the noncentrosymmetric orientation of the azobenzene chromophores in the as-prepared ZrO2/PAC-azoBNS/PDDA multilayer films. The square root of the SHG signal (I(2omega)(1/2)) increases with the increase of the azobenzene graft ratio in PAC-azoBNS as the number of deposition cycles of the ZrO(2)/PAC-azoBNS/PDDA films remains the same, while the second-order susceptibility chi(zzz)(2) of the film decreases with the increase of the azobenzene graft ratio. Furthermore, the present method was successfully extended to realize the noncentrosymmetric orientation of azobenzene chromophores in multilayer films when small organic azobenzene compounds with carboxylic acid and/or hydroxyl groups at one end and sulfonate groups at the other end were used. The present method was characterized by its simplicity and flexibility in film preparation, and it is anticipated to be a facile way to fabricate second-order nonlinear optical film materials.

Nonlinear silicon-on-insulator waveguides for all-optical signal processing

Values up to gamma=7 x 10(6)/(W km) for the nonlinear parameter are feasible if silicon-on-insulator based strip and slot waveguides are properly designed. This is more than three orders of magnitude larger than for state-of-the-art highly nonlinear fibers, and it enables ultrafast all-optical signal processing with nonresonant compact devices. At lambda=1.55 microm we provide universal design curves for strip and slot waveguides which are covered with different linear and nonlinear materials, and we calculate the resulting maximum gamma.

Vibrational spectroscopic studies of an organic non-linear optical crystal 8-hydroxyquinolinium picrate

8-hydroxyquinolinium picrate (8-HQP) was synthesized by the addition of equimolar quantities of 8-hydroxyquinoline (8-HQ) and picric acid (PA). Single crystals were grown from N,N dimethyl formamide (DMF) by restricted evaporation method at room temperature. The solubility of 8-HQP was determined in different solvents at various temperatures. The structural characterization of the grown crystals was carried out by X-ray diffraction. Vibrational modes were classified on the basis of group theoretical analysis and the spectral bands were compared with those of parent compounds in order to propose a tentative assignment by recording FT-IR, FT-Raman and polarized Raman spectra in different crystal orientations. The crystal possess lower cut-off at 230 nm and good transparency as confirmed by optical transmittance studies.