RTP晶体光学和电学性能研究

磷酸钛氧铷(RbTiOPO4,RTP)晶体是一种新型的、有重要应用前景的电光材料。采用分光光度计、Nd:YAG锁模激光器、耐压测试仪等设备,对其光学和电学性质进行了全面测试研究,包括透过谱、折射率、消光比、电阻率、电光系数等。测试结果表明:RTP材料具有透过谱宽、吸收损耗小、消光比大、电阻率高、电光系数大、半波电压低等优点,综合性能优异,所得实验数据将为高性能RTP电光调制器件的精确设计和优化提供参考。     

Optical stress sensor based on electro-optic compensation for photoelastic birefringence in a single crystal

An optical stress sensor is proposed by using a single crystal with both electro-optic and photoelastic effects. Different from previous crystal-based stress sensors, the proposed sensor is based on electro-optic compensation for stress-induced birefringence and does not need an additional quarter-wave plate or modulator, because the stress-sensing element is simultaneously used as an electro-optic compensator. Candidate sensing materials include electro-optic crystals of the 3?m symmetry group and all glass with large Kerr coefficients. A primary experiment has demonstrated that the stress-induced birefringence in lithium niobate crystal can be compensated by its electro-optic birefringence. The proposed stress sensor is compact and low cost, and it is possible to achieve closed-loop stress measurement.     

Structural evolution, dielectric and electro-optic properties of sol-gel derived potassium titanyl phosphate thin films

Transparent potassium titanyl phosphate (KTiOPO₄) thin films were prepared by a sol-gel coating technique. The structural evolution of the KTP thin films was examined by means of DTA/TGA, FT-IR, XRD and SEM. The effect of UV irradiation on the crystallization behavior was investigated and it was found that the UV irradiation decreases the crystallization temperature of the KTP thin films and dried gels. The dielectric and electro-optic properties were evaluated. The dielectric measurement results show that the KTP thin films have a low dielectric constant of 12 in the temperature range of 25–100 °C and frequency range of 1–1000 kHz. The electro-optic results indicate that the KTP thin films exhibit a quadratic electro-optic effect and may have potential applications for electro-optic devices.     

非线性光学活性分子的线性电光效应

报道了反射型电光调制法研究６种偶氮化合物的线性电光效应,分析了给体－受体强度、掺杂浓度对线性电光系数的影响。结果表明,掺杂偶氮化合物４－「２－羟乙基苯甲氨基」－４－硝基偶氮苯的极化聚合物薄膜具有较强的线性电光效应,其线性电光系数随参杂浓度的增大而增大。     

Fabrication and analysis of a low-loss in-fiber active polymer waveguide

We present a method for fabricating an in-fiber electro-optic polymer waveguide within a D-shaped optical fiber. A combined process of selective chemical etching and spin coating creates a 2-cm in-fiber poly(methyl methacrylate)-DR1 dye polymer waveguide section with an overall insertion loss of micro 1.6 dB at 1550 nm. Numerical simulations show that, for in-fiber polymer waveguides to have low loss, the polymer layer's thickness must be kept below a certain value so that it will not support slab waveguide modes. Long transition regions between the unetched fiber and the polymer waveguide section also reduce loss. We analyze the efficiency of an in-fiber polymer waveguide by simulating its theoretical performance as an electro-optic modulator.     

Improvement of the interferometric method for measuring electro-optic coefficients of poled polymer thin films

The interferometric method for measuring the linear electro-optic coefficients of polymer films has been improved. This improved method is based on using the antipiezoelectric effect of a quartz crystal to compensate for the change in the optical path length that is due to the electro-optic effect of a polymer film. The electro-optic coefficients of six kinds of new poled polymer film have been determined at a wavelength of 633 nm by this new method. This technique offers a simple, rapid, and highly sensitive method for measuring the electro-optic coefficients of polymer films.     

Correction of low-frequency measurements of the quadratic electro-optic effect for electrostatic stresses

Electrostatic stresses that can influence the observed signal with stress-optical constants form a contribution to the quadratic electro-optic (Kerr) effect measured at low frequencies. A new formula is proposed to correct for the influence of these stresses in order to obtain the true Kerr constant.     

Characterization of dielectric and electro-optic properties of PLZT 9/65/35 films on sapphire for electro-optic applications

Lead lanthanum zirconate titanate (PLZT) thin films were deposited on r-plane sapphire at low temperatures by RF triode magnetron sputtering using lead compensated hot-pressed targets. To obtain fully perovskite phase in the films, two types of post-deposition processing were investigated: rapid thermal annealing (RTA) and furnace annealing (FA). Dielectric and electro-optic properties of PLZT films were found to be strongly dependent on annealing conditions. The peak dielectric constant of the films were 1200 and 2800 with Curie temperatures of 110 degrees C and 190 degrees C after RTA and FA processing, respectively. The dielectric losses in the films were fairly low; tan deltas were less than 0.02 after RTA and less than 0.04 after FA processing. The films showed good optical transmission characteristics after annealing and an anomalously large effective quadratic electro-optic effect was observed in one furnace annealed film.     

Design of integrated 1×2, 1×4 low driving voltage polymer electro-optic switches based on Y-fed directional couplers

Two integrated 1 × 2 and 1 × 4 polymer electro-optic switches based on Y-fed directional couplers are designed and optimized in terms of the coupled mode theory, electro-optic modulation theory, conformal transforming method and image method. The principle of the 1 × 2 electro-optic switch is described. Parameters including the core size, buffer layer thickness, electrode thickness, electrode width and electrode gap are optimized. Simulation results show that the length of the designed 1 × 2 switch is about 3.126 mm, the driving voltages of the two branches are as low as 0.891 and ?0.891 V, respectively, the crosstalk and insertion loss are less than ?30 and 1.42 dB, respectively, within the operation wavelength from 1527 to 1574 nm. Under the same driving voltages, the 1 × 4 optical switch with a total length of less than 7 mm can be switched by altering the voltages applied on the electrodes of the three Y-fed directional couplers. Simulation results from the beam propagation method (BPM) indicate that the two designed devices exhibit favorable switching functions.     

Proposal for electro-optic multiplier based on dual transverse electro-optic Kerr effect

A novel electro-optic multiplier is proposed, which can perform voltage multiplication operation by use of the Kerr medium exhibiting dual transverse electro-optic Kerr effect. In this kind of Kerr medium, electro-optic phase retardation is proportional to the square of its applied electric field, and orientations of the field-induced birefringent axes are only related to the direction of the field. Based on this effect, we can design an electro-optic multiplier by selecting the crystals of 6/mmm, 432, and m3m classes and isotropic Kerr media such as glass. Simple calculation demonstrates that a kind of glass-ceramic material with a large Kerr constant can be used for the design of the proposed electro-optic multiplier.     

Drying temperature effects on microstructure, electrical properties and electro-optic coefficients of sol-gel derived PZT thin films

Transparent lead zirconium titanate (PZT) thin film is suitable for a variety of electro-optic application, and the increasing of the electro-optic coefficient of PZT film is one of the important factors for this application. In this study, the main processing variable for improving an electro-optic coefficient was the drying temperature: 300, 350, 450 and 500°C in sol-gel derived PZT thin films. The highest linear electro-optic coefficient (1.65×10⁻¹⁰ (m/V)) was observed in PZT film dried at 450°C. The PZT film showed the highest perovskite content, polarization (P_max=49.58 μC/cm², P_r=24.8 μC/cm²) and dielectric constant (532). A new two-beam polarization (TBP) interferometer with a reflection configuration was used for electro-optic testing of PZT thin films which allows measurement of the linear electro-optic coefficient of thin film with strong Fabry–Perot (FP) effect usually present in PZT thin film.     

Effect of polarization state on electro-optic coupling and its application to polarization rotation

The effect of the polarization state on electro-optic coupling is studied by using the wave coupling theory of the linear electro-optic effect. The numerical results show that the polarization state obviously influences the electro-optic coupling. The conditions for realizing perfect coupling are emphasized. As an application of perfect coupling, a novel polarization rotator, which can rotate the polarization of a light beam with an arbitrary angle but keep the output intensity unchanged, is presented.     

Enhanced absorption and electro-optic Pockels effect of electrostatically self-assembled CdSe quantum dots

The spectrum and electro-optic properties of CdSe quantum dots are studied. Spectrum wavelength shifts that are due to the quantum size effect and to the electro-optic Stark effect are investigated. It is found that CdSe quantum dot-polymer composites formed by an electrostatic self-assembly (ESA) technique exhibit high internal electric fields. Using the second-order perturbation theory of the 1s-1s energy shift (Stark effect), we estimate the internal field of the ESA film to be as high as 2.6 x 10(8) V/m. This value results in a much higher absorption coefficient and electro-optic coefficients for ESA films than for their bulk crystal counterparts or for spin-coated film samples. The relationships among unusual spectra, film structure, and high electro-optic response are analyzed. These results are useful both for understanding the physical mechanisms of semiconductor quantum dots and for developing high-performance photonic devices.     

Dynamic behavior of electro-optic and strain-optic effects in ferroelectrics with diffuse phase transitions

The transverse electro-optic effect under the step-function electric field in PMN single crystals and PLZT ceramics has been investigated. The time and temperature dependences of the electro-optic coefficients g₁₁–g₁₂ and R₁₁–R₁₂ have been determined. The strain-optic contribution to the total electro-optic effect has been evaluated. The influence of the polar phase regions on the electro-optic properties and their clamping is discussed.     

Theory-inspired development of organic electro-optic materials

Real-time, time-dependent density functional theory (RTTDDFT) and pseudo-atomistic Monte Carlo-molecular dynamics (PAMCMD) calculations have been used in a correlated manner to achieve quantitative definition of structure/function relationships necessary for the optimization of electro-optic activity in organic materials. Utilizing theoretical guidance, electro-optic coefficients (at telecommunication wavelengths) have been increased to 500 pm/V while keeping optical loss to less than 2 dB/cm. RTTDDFT affords the advantage of permitting explicit treatment of time-dependent electric fields, both applied fields and internal fields. This modification has permitted the quantitative simulation of the variation of linear and nonlinear optical properties of chromophores and the electro-optic activity of materials with optical frequency and dielectric permittivity. PAMCMD statistical mechanical calculations have proven an effective means of treating the full range of spatially-anisotropic intermolecular electrostatic interactions that play critical roles in defining the degree of noncentrosymmetric order that is achieved by electric field poling of organic electro-optic materials near their glass transition temperatures. New techniques have been developed for the experimental characterization of poling-induced acentric order including a modification of variable angle polarization absorption spectroscopy (VAPAS) permitting a meaningful correlation of theoretical and experimental data related to poling-induced order for a variety of complex organic electro-optic materials.     

Quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 transparent ceramics under both DC and AC bias

The basic quadratic electro-optic properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) transparent ceramics have been studied under both DC and AC electric field bias. The contribution of piezoelectric resonance to electro-optic effect for this quadratic electro-optic ceramics material has been experimentally demonstrated and theoretically analyzed. It is found that, at the piezoelectric resonance frequencies, the piezoelectric induced electro-optic effect dominates and leads to a dramatically high sensitivity for weak electric signal detection. About 20 dB signal-to-noise ratio is attained when detecting AC electric field strength of 1 V/m with optimized DC bias. Besides, the effects of AC frequency and amplitude on halfwave voltage V(π) of PMN-PT are investigated.     

Very large electro-optic responses in H-bonded heteroaromatic films grown by physical vapour deposition

A crucial goal for modern telecommunications systems is development of very high-speed components for broadband (>100 GHz), all-optical signal/information processing. The core component of such technologies is the electro-optic modulator, which encodes electrical signals onto fibre-optic transmissions. A significant challenge therefore is obtaining materials that have large electro-optic responses and that can be readily fabricated into devices at low cost. We report here on the realization of high-response heteroaromatic organic chromophores that can be straightforwardly self-organized from the vapour phase into intrinsically acentric, high-quality, micrometre-scale films. These pi-conjugated electro-optically active films (with second-order susceptibilities up to approximately 100 pm V(-1)) are thermally stable and conveniently grown by a simple physical vapour deposition process in a few hours. Supramolecular acentricity is achieved without electric field poling, enforced by biomimetic heterocycle-hydroxycarbonyl head-to-tail hydrogen-bonding.     

Effects of rigid structures containing (meth)acrylate monomers and crosslinking agents with different chain length on the morphology and electro-optical properties of polymer-dispersed liquid crystal films

ABSTRACT

This contribution investigates the preparation of polymer-dispersed liquid crystal (PDLC) films based on meth(acrylate) monomers containing rigid structures. The current study specifically focuses on comparison of the monomers on the basis of meth(acrylate) side group, flexible/rigid structures and rigidity. We find that methacrylate monomers exhibit more preferable electro-optic properties than that of the acrylate monomers. Furthermore, through the systematic variation of rigidity, composition of the monomers and chain length of crosslinking agents, both the morphologies and electro-optic properties of these films are found to be adjustable. A composite film is demonstrated by employing moderately rigid monomer (tetrahydrofurfuryl methacrylate) with low driving voltage (21.0?V) and high contrast ratio (87.5). Therefore, the studies here provide a new approach to optimize the electro-optical properties of the PDLC films by introducing monomers with rigid structures.     

Hydrothermal growth of AIIBVI semiconductors

Hydrothermal method is used for growing ZnO, ZnS and HgS single crystals. This method is more advantageous compared to the other ones and enables one to obtain large bulky crystals of technically convenient habit with low concentration of defects. Some physical properties of these single crystals were studied and active elements for the new advanced piezoelectric, electro-optic and laser devices are reported.     

Large-angle electro-optic laser scanner on LiTaO(3) fabricated by in situ monitoring of ferroelectric-domain micropatterning

We report on a horn-shaped electro-optic scanner based on a ferroelectric LiTaO(3) wafer that is capable of scanning 632.8-nm light by an unprecedented 14.88 degrees angle for extraordinary polarized light and by 4.05 degrees for ordinary polarized light. The device concept is based on micropatterning ferroelectric domains in the shape of a series of optimized prisms whose refractive index is electric field tunable through the electro-optic effect. We demonstrate what we believe is a novel technique of using electro-optic imaging microscopy for in situ monitoring of the process of domain micropatterning during device fabrication, thus eliminating imperfect process control based on ex situ monitoring of transient currents.