Investigation of the linear electro-optic effect for the guest–host polymer DR13/PEK-c thin films

The polyetherketone (PEK-c) guest–host polymer thin films doped with disperse red 13 were prepared by spin-coating method. The corona poling condition was optimized by the poling profiles. The polymer films were poled by corona-onset poling at elevated temperature, and the corona poling setup includes a grid voltage making the surface-charge distribution uniform. The linear electro-optic coefficients of the poled polymer films have been determined at λ=632.8 nm by using a new simple interferometric technique, which is based on compensating the change of the optical length due to the electro-optic effect of the poled polymer film by the anti-piezoelectric effect of a quartz crystal.     

Investigation of the polyetherketone guest–host DR1/PEK-c polymer films by real-time monitoring of the second-harmonic generation

The real-time monitoring of the second-harmonic generation (SHG) was used to optimize the poling condition and to study the nonlinear optical (NLO) properties of the polyetherketone (PEK-c) guest–host polymer films. The high second-order NLO coefficient χ₃₃⁽²⁾=11.02 pm/v measured at 1.064 μm was achieved when the weight percent of DR1 guest in the polymer system is 20%. The NLO activity of the poled DR1/PEK-c polymer film can maintain more than 80% of its initial value when temperature is under 100°C, and the normalized second-order NLO coefficient can maintain more than 85% after 2400 s at 80°C.     

Determination of the absorption for incident light propagating parallel through the guest–host polymer film waveguide

Guest–host polymer thin films of polymethyl methacrylate (PMMA) incorporated with (4′-nitrobenzene)-3-azo-9-ethylcarbazole (NAEC) were fabricated by spin coating and then poled by the method of corona-onset poling at elevated temperature. The absorption mechanism of the polymeric film, which is very important for the optical transmission losses and directly relates to the orientation of chromophore NAEC in polymer PMMA, was investigated in detail. From the UV–visible absorption spectra for NAEC/PMMA film before and after being poled, we determined the change of absorption coefficient κ with the wavelength and approximately calculated the maximum absorption A_max as 3.46 for incident light propagating parallel through the film, i.e. the ordinary polarized light, which cannot be directly measured in the spectrophotometer.     

Investigations of the E-O behavior in the poled polymer waveguide

The electro-optic (E-O) properties of the slab polymer waveguide induced by electric poling have been studied experimentally. The thin film waveguide was prepared by a synthesized polymer polypelargonamide and poled by applying voltage between the electrodes. I–V curves and E-O characteristics of the polymer films were in-situ measured during poling. In order to evaluate the molecular dipole orientation under the poling field, the absorption spectra of this film was observed by FTIR. The E-O performance of the polymer slab film was also estimated by the Mach–Zehnder interferometer.     

键合型DANS聚合物光波导电晕极化及其二阶非线性衰减

对键合型DANS聚合物薄膜光波导的电晕极化过程及其二阶非线性衰减特性进行了研究.采用本文给出的电晕极化参数,制成了具有较长极化寿命的极化聚合物薄膜光波导,为进一步研究其二阶非线性光学性质奠定了基础.     

Determination of the macroscopic optical properties for the NAEC/PEK-c guest–host polymer films

The polyetherketone (PEK-c) guest–host polymer films doped with (4′-nitro)-3-azo-9-ethyl-carbazole (NAEC) were prepared. The films were poled by corona-onset poling at elevated temperature (COPET). The orientational order parameter of the chromophores NAEC in poled polymer film was determined by measuring the absorption spectra of the films before and after being poled. By using the two-level model, the measured dispersion of the refractive index of the polymer film, and the dispersion of the first hyperpolarizability of chromophore NAEC, the dispersion of the macroscopic second-order nonlinear optical (NLO) and linear electro-optic (EO) coefficients was evaluated for the NAEC/PEK-c guest–host polymer film.     

Fabrication of χ{2) Grating in Poled Polymer Waveguide Based on Direct Laser Beam Writing

A simple method is described for fabricating high resolution χ⁽²⁾ grating in poled polymer waveguide. It is found that the second-order nonlinearity of corona-poled polymer thin film is erased after visible laser (450 nm) irradiation. The mechanism of the erasure of χ^{2) is discussed. High resolution χ⁽²⁾ grating structure in several poled polymer waveguides is demonstrated by direct writing with a cw He-Cd laser.On leave from the Department of Optical Instruments, Zhejiang University, Hangzhou, Zhejiang Province, 310027, P.R. of China.     

Second-harmonic generation in poled films of nonlinear optical polymer composites

The second-harmonic generation (SHG) has been measured for studying the molecular ordering and its relaxation process in poled states of two different nonlinear optical (NLO) polymer composites.p-Nitroaniline (pNA) and the azo dye Disperse Orange 3 (DO3) are uniformly dispersed in photopolymer matrices followed by poling. Two different composites made-up of 1 wt% of pNA and 2.5 wt% of DO3 are poled at 200 MV m^-1 and 80 MV m^-1, respectively. One of the second-order NLO coefficients,d ₃₃, was found to be 0.27 pm V^-1 for the pNA-doped film and 0.20 pm V^-1 for the DO3-doped film. While for the latter the ratiod ₃₃/d ₃₃ (3.1) is consistent with the value of 3 in the low-field approximation, for the former the value of 3.5 indicates that higher-order effects of the poling field play a significant role in the NLO process. It is suggested that the SHG relaxation dynamics is also closely related to the UV absorption of the NLO molecules in a photopolymer matrix.     

Periodic poling of optical waveguides produced by swift-heavy-ion irradiation in LiNbO<Subscript>3</Subscript>

The generation of periodically poled structures in waveguides prepared by swift-heavy-ion (SHI) irradiation, i.e. in the electronic stopping power regime, has been achieved following two different strategies. In one of them we have prepared bulk PPLN samples by an applied electrical field, followed by irradiation with F ions at 22 MeV. After the ion irradiation, a waveguide showing a high optical confinement is obtained, preserving the original PPLN structure. The second strategy consisted of electric periodic poling of previously fabricated swift-ion-irradiated waveguides. To our knowledge this method has not been, so far, successful for conventional implanted waveguides. The successful fabrication of PPLN structures on novel waveguides prepared by SHI irradiation offers a promising potential for nonlinear integrated optical devices.     

极化聚合物薄膜取向有序度及极化寿命的表征

研究了极化聚事物薄膜波导的退极化过程,提出了表征极化聚合物薄膜取向有序度和极化寿命的集成光学方法。采用集成光学中的棱镜耦合技术,测量极化前后聚合物薄膜光波导的各向异性有效折射率。通过求解各向异性介质光波导的模式本征方程,得到波导极化前后寻常光和非寻常光折射率的变化及其随时间衰减,进而得到取向有序度随时间的变化曲线。采用复合指数函数模型进行最小二乘曲线拟合,进而推测其极化寿命。实验中以键合型ＤＡＮＳ     

Influence of hydroxyl content on second-order nonlinearity in thermally poled type-III fused silica

Effects of high (∼1000 ppm) and low (∼200 ppm) hydroxyl (OH) content on second-order optical nonlinearity (χ⁽²⁾) in thermally poled type-III fused silica (KU-1) are studied. Type-III fused silica with low OH content poled under 275 °C with 6 kV for various poling durations shows much stronger intensity of second-harmonic generation (SHG) signals compared with that with high OH content poled under the same condition. A near-anodic uniform surface and uniform bulk χ⁽²⁾ profiles which are opposite in sign are calculated to be formed in the fused silica poled longer than the optimum poling duration. A two-charge-carrier model with charge injection and non-blocking electrodes is given to explain the creation of the χ⁽²⁾ profile. More OH is believed to decrease the mobility of alkali ions during poling.     

Preparation and characterization of poled nanocrystal and polymer composite PZT/PC films

Pb(Zr_0.52Ti_0.48)O₃ (PZT) nanocrystals and transparent polycarbonate (PC) composite thin films with useful properties for ferroelectric, piezoelectric and electro-optic devices were prepared by a spin-coating technique. Ultra-fine PZT (∼40–50 nm) nanocrystals with pure perovskite tetragonal phase were synthesized by a hydrothermal method. The structure and morphology of the composite thin films were studied by means of X-ray diffraction and scanning electron microscopy. To obtain the optimum electro-optic properties of poled composite films, the poling condition under an external electric field was optimized through the dielectric properties of PZT and PC polymer and effective field intensity theory. The electro-optic coefficient of the poled PZT/PC composite film is estimated to be 30.5 pm/V. The transparency spectra were measured and the optical band gaps of the unpoled, poled at 145 °C and poled at 165 °C composite thin films are estimated to be 4.26 eV, 4.21 eV and 4.18 eV, respectively. The measured dielectric constants of PZT/PC are in good agreement with the calculated values for the composite with a very small PZT volume fraction, based on the Onsager effective-field theory. This offers a reliable and indirect way to predict the dielectric constant of nanocrystals. PACS 81.40.Tv; 78.66.Sq; 78.66.Vs     

低阈值极化电压玻璃光波导电光效应的研究

采用热极化技术对掺锗玻璃条形光波导进行极化,通过光纤连接 (单模) 的Mach Zehnder Interferometer 系统测量条形波导内诱导出的电光效应,系统地研究了大气环境下极化条件(极化温度、极化时间、极化电压)对电光效应的影响.结果表明:在最佳极化条件下(406℃、-2.4 kV、20 min),波导内的电光系数为r_TM=0.059±0.001 pm/V, r_TE=0.053±0.001 pm/V,且波导结构中存在一个较低的阈值极化电压(100 V)和阈值极化温度(80℃),此时在波导样品内仍能被激发出可观察的电光效应;实验还发现采用负极化诱导方式产生的电光系数较正极化提高15%左右.     

Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d ₃₃, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r ₃₃, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.     

Characterization of the polyurea polymeric waveguides fabricated using the chemical vapor deposition process

Aromatic polyurea-based waveguides were fabricated by the evaporation and deposition of a diamino monomer and a diisocyanate monomer onto an indium tin oxide (ITO) glass substrate in a vacuum chamber. The nonlinear I–V behaviors of the polyurea film were characterized in situ during poling. Fourier transform infrared spectroscopy and the heterodyne Mach–Zehnder interference (HMZI) technique were applied to explore the electro-optic performance of the polyurea polymeric waveguide induced by an applied electric field. The Pockels coefficients were measured by a heterodyne Mach–Zehnder interference (HMZI) system to be γ₁₃=7.1 and γ₃₃=21.9 pm/V, for the TE and TM polarizations, respectively.     

Synthesis of photosensitive poly(methyl methacrylate-co-glycidyl methacrylate) for optical waveguide devices

Photosensitive poly(MMA-co-GMA) for optical waveguide was synthesized, and the refractive index of the polymer film was tuned in the range of 1.481–1.588 at 1550 nm by mixing with bis-phenol-A epoxy resin. The film, which was made by spinning coated the poly(MMA-co-GMA) with photo initiator, had good UV light lithograph sensitivity, high glass transition temperature (T _g : 153°C, after crosslinking) and good thermal stabilities (T _d : up to 324°C, after crosslinking). The optical waveguides with very smooth top surface were fabricated from the resulting polymer by direct UV exposure and chemical development. For waveguides with cladding, the propagation losses of the channel waveguides were measured to be below 3 dB/cm at 1550 nm.     

Investigation on the nonlinear optical properties of the DCNP/PEK-c guest–host polymer films

The polyetherketone (PEK-c) guest-host polymer thin films doped with 3-(1,1-dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. The polymer films were investigated with in situ second-harmonic generation (SHG) measurement. The corona poling temperature was optimized by the temperature dependence of the in situ SHG signal intensity under the poling electric field applying. The temporal and temperature stability of the second-order properties of the poled polymer film were measured by the in situ SHG signal intensity probing. The second-order NLO coefficient L₃₃⁽²⁾=32.65 pm/V at 5=1064 nm was determined by using the Maker fringe method after poling under the optimal poling condition. The dispersion of the NLO coefficient of the guest-host polymer system was determined by the measured value of L₃₃⁽²⁾ at 1064 nm and the two-level model.     

Beam delivery characteristics of optical fibres for carbon monoxide lasers

An experimental investigation has been conducted of the propagation characteristics of several types of optical fibres which are candidates for use in optical beam delivery systems for carbon monoxide lasers. Both solid core (chalcogenide) fibres and hollow core (with dielectric or dielectric coated metal) waveguides have been investigated. Such experiments have included an assessment of both the power transmission characteristics, and the effects of waveguide transmission on the optical quality of the beam at the exit of the fibre. The experiments indicated lowest loss for the chalcogenide solid core fibre with a value of 0.4 dB m⁻¹.     

Large optical second-order nonlinearity of poled WO3-TeO2 glass

Second-harmonic generation, one of the second-order nonlinear optical properties of thermally and electrically poled WO>(3)-TeO>(2) glasses, has been examined. We poled glass samples with two thicknesses (0.60 and 0.86 mm) at various temperatures to explore the effects of external electric field strength and poling temperature on second-order nonlinearity. The dependence of second-harmonic intensity on the poling temperature is maximum at a specific poling temperature. A second-order nonlinear susceptibility of 2.1 pm/V was attained for the 0.60-mm-thick glass poled at 250 degrees C. This value is fairly large compared with those for poled silica and tellurite glasses reported thus far. We speculate that the large third-order nonlinear susceptibility of WO>(3)- TeO>(2) glasses gives rise to the large second-order nonlinearity by means of a X((2)) = 3X((3)) E(dc) process.     

Second-order non-linear optical studies on CdS microcrystallite-doped alkali borosilicate glasses

CdS microcrystal-doped alkali borosilicate glasses were prepared by conventional fusion and heat-treatment method. Utilizing Maker fringe method, second-harmonic generation (SHG) was both observed from CdS-doped glasses before and after certain thermal/electrical poling. While because the direction of polarization axes of CdS crystals formed in the samples is random or insufficient interferences of generated SH waves occur, the fringe patterns obtained in samples without poling treatments showed no fine structures. For the poled samples, larger SH intensity has been obtained than that of the samples without any poling treatments. It was considered that the increase of an amount of hexagonal CdS in the anode surface layer caused by the applied dc field increased the SH intensity. The second-order non-linearity χ⁽²⁾ was estimated to be 1.23 pm/V for the sample poled with 2.5 kV at 360 °C for 30 min.