Congji Zha

In Situ Second Harmonic Generation in Disperse Red 1-Doped Polymer and Sol-Gel Films

ABSTRACT We investigated linear optical and second-order nonlinear optical (NLO) properties of films of poly(bisphenol A carbonate) resin, and a newly synthesised titania/silica/hybrid sol-gel polymer resin doped with Disperse Red 1 (DR1) molecular chromophore. DC electric field induced second harmonic generation (SHG) technique has been used to monitor in situ the polar alignment and relaxation of orientation of the guest molecules in the corona-poled films. The temporal behaviour of the second harmonic signal was remarkably different in these two polymers both during poling and when the poling field was turned off. A fast decay of the second harmonic intensity was observed at room temperature in 3 wt% DR1-doped sol-gel film, and a long relaxation time constant was found in 13 wt% DR1-doped polycarbonate film. Resonantly enhanced deff coefficient of about 9 pm/V was found in the sol-gel film, and 25 pm/V in the polycarbonate film at the fundamental wavelength 1053 nm. The d33 values were about 20 pm/V, and 60 pm/V in these films, respectively. The SHG results were used to estimate the average rotation mobility parameter of DR1 molecules in the host polymers.

Preparation and Spectroscopy of Aluminosilicate Films Deposited on Graphite Surfaces via an Anhydrous Sol-Gel Route

Anhydrous aluminosilicate sols with Al : Si molar ratio ranging from 1 : 10 to 1 : 5 were prepared by a two-step anhydrous sol-gel process, in which tetraethoxysilane (TEOS) is pre-hydrolysed by formic acid, followed by addition of aluminium ethoxide. Unlike the case of aqueous sol-gel routes, where the Si–O–Al network homogeneity is greatly restricted by precipitation of Al(OH)3, this anhydrous route yields clear, homogeneous sols. The sol formation and densification processes were investigated by infrared spectroscopy and X-ray powder diffraction (XRD) techniques, and the existence of Al–O–Si linkages was confirmed. To demonstrate an application of the anhydrous sol-gel process, aluminosilicate films were deposited onto graphite surfaces by dip coating and densified at 800°C under nitrogen, and their protective effect was evaluated.

Optical Properties and Structural Transitions in Ge-As-Se Glasses

The optical and structural properties of Ge-As-Se glasses have been studied using Raman, UV-Vis-IR, Z-scan and DSC techniques, and the effect of composition on structural transition, optical band gap and nonlinearity is described.

Properties and structure of Ag-doped As2Se3 glasses

Ag-doped As2Se3 glasses were prepared by the melt-quenching method and the influence of silver doping on the glass structure and optical properties was studied using Raman and UV-Vis-IR spectroscopy and differential scanning calorimetry. For Ag concentrations less than 15 at%, introduction of Ag into As2Se3 glasses mainly leads to the formation of Ag-Se covalent bonds, resulting in destruction of the glass network. This manifests itself by a decrease in the glass transition temperature and low frequency shifts in the As-Se Raman band. When the Ag concentration was higher than 25 at%, some Ag atoms exist in the glass matrix as coordinative bonds, resulting in a slight increase in the glass transition temperature and high frequency shifts in the Raman peaks. The relationship between the glass structure and properties is discussed.

Wavelength dispersion of Verdet constant in Ge 22 As 20 Se 58 , Ge 33 As 12 Se 55 and As 2 S 3 chalcogenide thin films

The Verdet constants of amorphous thin films of chalcogenide glasses of three different compositions were determined across a range of wavelengths from the visible to the infrared. The Verdet constant of Ge₂₂As₂₀Se₅₈ was found to be 30 times greater than silica.

Optical characterization of Ge-As-Se glasses containing high content of germanium

Optical properties of chalcogenide glasses, Ge_xAs_ySe_100-x-y (33les x les39 and 12les y les16) were studied by using Raman, UV-vis-IR and PDS spectroscopic techniques, and the relationships between structure, composition and optical property were discussed.

Nonlinear materials for integrated ultra-fast all-optical devices

This research focuses on several aspects of chalcogenide all-optical processors. This study has chosen glasses in the Ge-As-Se system with the aim of optimising glass composition to obtain low loss, high nonlinearity and glass stability, whilst complementary efforts are focussed on the production, optimisation and application of chalcogenide waveguide devices to all-optical of high-speed telecommunication signals. Devices have been characterised in realistic telecommunications conditions with the eventual aim being to validate performance at rates up to 640 Gb/s.

Highly Optical Nonlinear Ag-doped As 2 Se 3 Glasses: Preparation and Characterization

Ag-doping in chalcogenide glasses can significantly increase the materials optical nonlinearity. This paper describes our study on Ag-doped As2Se3 glasses. The effect of Ag doping on the glass structure and optical properties have been discussed.

Optimization of the Structural and Optical Properties of Ge-As-Se Glasses

In this study Ge_XAs_ySe_100x+y glasses with 0lesx<40 and 12lesy40 are characterized to determine the effects of varying composition on parameters such as the nonlinear refractive index (n₂), glass transition temperature (T_g) and the optical absorption band edge (E_g). The linear absorption losses were studied using photo-thermal deflection spectroscopy (PDS). We found that increasing the Ge concentration increases the linear absorption loss, ranging from ~ 0.05 dB/cm for Ge₅As₃₈Se₅₇ to > 0.1 dB/cm for Ge > 33% (Ge₃₃As₁₂Se₅₅) at 1550 nm. A modified Z-Scan technique was developed to measure the nonlinear refractive index (n₂) at 1500 nm. The conventional closed aperture is replaced by an InGaAs camera to image the output beam. Image analysis is done using Lab VIEW software and the on axis transmission is measured and extracted as a Z-scan.

Influence of TiO2 on Second Harmonic Generation in Disperse Red -1 doped Organic-Inorganic Hybrid Thin Films

Disperse Red 1 (DR1) doped TiO2-SiO2 inorganic-organic hybrid polymers were prepared by an anhydrous sol-gel process and second harmonic generation (SHG) of the fundamental 1053nm in these polymeric thin films was measured using Maker-fringe method. The nonlinear optical activity of DR1 in the thin films was studied by corona poling at different temperature (from room temperature to 140°C), and the stability of SHG after switching off corona power was evaluated by analyzing the SHG decay dynamics. Experimental results showed that the stability of the SHG of DR1 significantly increases with the cross-linkage degree of the TiO 2 SiO 2 hybrid polymer network, and that the second harmonic coefficient d 33 increases as the DR1 concentration increases. TiO 2 -doping can promote the polymerization of unsaturated C=C double bonds in the hybrid thin films during in-situ hot poling, enhancing the cross-linkage of the network of the hybrid material, and resulting in a great improvement of the stability of SHG. The excellent stability of second harmonic generation in the hybrid polymer thin films suggests that TiO 2 -doped inorganic-organic hybrid polymer is promising for chromophore doping for nonlinear optical applications.