双轴晶体电光调制器的最优设计

运用新的线性电光效应的耦合波理论，对双轴晶体KTP电光调制器的温度特性进行了理论研究.找到了一个入射光波矢的方向，在该方向上，出射光光强不随温度的变化而变化，而且此方向在一定的角度范围内变动，温度的稳定性是可以保持的.还进一步对晶体的通光长度和外加电场的方向进行了筛选，实现了双轴晶体KTP电光调制器的最优设计. 关键词： 电光效应 耦合波理论 电光调制器 最优设计     

A cascaded traveling-wave electrooptic modulator

A novel configuration for a wide-band and low-drive power electrooptic modulator is proposed. The device is based on the compensation for the velocity difference between the electrical and optical signals by adjusting their relative delay between two succussive modulators. A cascaded traveling-wave optical modulator having a band-width of approximately 3 GHz and a required power of 150 mW for 30% linear modulation has been constructed.     

Active antireflection coating electrooptic modulator

A new type of multiple quantum well (MQW) reflection modulator, based on the multilayer active antireflection coating (A-ARC) is proposed and compared theoretically with the conventional MQW modulator based on the asymmetric Fabry-Perot etalon (AFP). It is shown that both a large on-off ratio and a low operating voltage can be achieved. It will be demonstrated that the A-ARC device matches the performance of the recently reported asymmetric Fabry-Perot modulator while requiring smaller device thickness. It will also be shown that A-ARC MQW modulators exhibit superior tolerance to the unavoidable thickness variations, thus allowing fabrication of large-area uniform arrays of modulators.     

A novel type of electrooptic light modulator

A new type of electrooptic modulator is presented. The modulation of optical waves is obtained by variation of one of the parameters ruling the excitation conditions of a guided mode during the coupling of an optical beam into a planar structure. The performances obtained with a prism coupler are discussed.     

Barium doping-induced polar nanoregions in lead germanate single crystal

The results of measurement of the linear and nonlinear dielectric susceptibilities of pure and Ba-doped lead germanate, (Pb_{1? x} Ba _x )₅Ge₃O₁₁ with x = 0, 0.02 and 0.05, single crystals are presented. The change in the sign of the third-order dielectric susceptibility, χ ₃, as predicted by the thermodynamic theory of the continuous phase transitions, is observed in pure crystal. On the contrary, in the Ba-doped crystals, the third-order dielectric susceptibility is positive and shows a peak near the temperature, which corresponds to the position of the peak of the linear dielectric susceptibility, χ ₁. This result indicates that the Ba-doped lead germanate crystals do not show features typical of a continuous phase transition. In B-doped lead germanate crystal, the scaled nonlinear sucsebtibility, a ₃, shows ferroelectric relaxor-type behavior.     

A novel type of electrooptic light modulator

A new type of electrooptic modulator is presented. The modulation of optical waves is obtained by variation of one of the parameters ruling the excitation conditions of a guided mode during the coupling of an optical beam into a planar structure. The performances obtained with a prism coupler are discussed.     

Non-linear electrooptic effect in antiferroelectric liquid crystal

Electrooptic phenomena caused by weak electric fields, much lower than those needed for the helix unwinding, in helical smectic liquid crystals were studied in thin planar samples. The investigations were performed in chiral liquid crystal 4-(1-methyl-heptyloxycarbonyl) phenyl 4′-(3-butanoyloxy propyl-1-oxy) biphenyl-4-carboxylate which exhibits antiferro-electric properties. We have found that electric field applied to a helical smectic liquid crystal caused two effects. First, the helix was deformed and the position of effective optic axis changed by an angle proportional to the field strength. The second effect, quadratic in field, causes the change in the shape of the indicatrix. As a consequence, the relative changes in the light intensity caused by external electric field consist of two components. The first component represents the modulation with the fundamental frequency and the second one with the doubled frequency (second harmonic of the electrooptic effect). The ab- solute values of the first- and second-order electrooptic coefficients have been determined and their temperature dependence discussed.     

Optical pulse generation by using quasi-velocity-matched guided-wave electrooptic phase modulator

A quasi-velocity-matched guided-wave electrooptic modulator was fabricated using a periodically domain-inverted LiTaO₃. Band modulation characteristics around the designed modulation frequency and the generation of optical sidebands of about 100 GHz were confirmed experimentally. The trains of optical pulses below 20 ps were also generated by the compression of the optical sidebands from the modulator. It should lead to the construction of integrated optical pulse generators.     

用电光相位调制器显示超声行波波前

本文提出了一种用连续激光器,在时间相关理论依据下,以电光相位调制显示超声行波波前的新方法;并考虑到运动相位和静止相位的差异,提出了一种特殊的空间滤波技术,从而显示了超声行波的高对比像.     

High-performance unidirectional electrooptic modulator based on polymeric highly multi-mode waveguides

A unidirectional electrooptic modulator based on an asymmetrical highly multi-mode waveguide coupler is proposed. Firstly, the energy distributions of all the modes within two highly multi-mode waveguides are analyzed with eigenstate theory. Then, to achieve high switching performance in a guided-wave coupler, a dumping wall is placed on the larger waveguide of an asymmetric pair of waveguides, so that the larger waveguide has a dumping effect. This dumping effect makes the asymmetric highly multi-mode waveguide coupler possess a highly efficient unidirectional coupling process. Due to the large cross-section of the waveguide, a new modulation electrode structure is built. Based on this dumping effect, the unidirectional coupling process is theoretically modeled. Furthermore, in both scenarios, i.e., the unmodulated state and the electrooptically modulated state, the unidirectional coupling efficiencies are studied. As a result, not only can a high unidirectional coupling efficiency of 100% be achieved, but a high electrooptic modulation depth more than 90% can also be implemented in theory, and a high thermooptic modulation depth more than 90% under a low modulation voltage of 30 volts is also experimentally achieved. This device can be used for multi-mode optical interconnection systems such as data communication and fiber sensor networks.     

掺杂铁电钛酸钡的拉曼散射研究

掺杂铁电钛酸钡的拉曼散射研究张明生，陈强，尹真（南京大学现代分析中心和固体微结构物理国家重点实验室南京２１００９３）ＲａｍａｎＳｃａｔｔｅｒｉｎｇＳｔｕｄｙｏｆｔｈｅＤｏｐｅｄＢａｒｉｕｍｔｉｔａｎａｔｅ￥ＺｈａｎｇＭｉｎｇ；ＳｈｅｎｇＣｈｅｎ；Ｑｉ...     

Short-term reversible changes in the dielectric dispersion of a barium titanate single crystal

An effect of spontaneous fluctuation of the dispersion frequency was detected during investigations of the dielectric dispersion of a BaTiO₃ single crystal while measuring under the electric field only. A decrease in the dispersion frequency by three orders of magnitude and its subsequent return to the previous value was observed. A possible mechanism of this phenomenon is suggested, which involves the dynamics of the screening process.     

Ultrafast opto-terahertz photonic crystal modulator

We present an agile optically controlled switch or modulator of terahertz (THz) radiation. The element is based on a one-dimensional photonic crystal with a GaAs wafer inserted in the middle as a defect layer. The THz electric field is enhanced in the photonic structure at the surfaces of the GaAs wafer. Excitation of the front GaAs surface by ultrashort 810 nm laser pulses then leads to an efficient modulation of the THz beam even at low photocarrier concentrations (approximately 10(16) cm(-3)). The response time of the element to pulsed photoexcitation is about 130 ps.     

Elastic compliances of barium titanate crystal

The elastic compliances of barium titanate have been calculated on the basis of the point dipole model taking account of the dipole-dipole interactions and the proper interatomic forces. The results obtained are discussed.     

Effects of crystallographic orientation on electrooptic spatial light modulator amplitude and phase responses

The effects of crystallographic orientation on output amplitude and signal-dependent phase distortions in electrooptic spatial light modulators such as the PROM and PRIZ are described.     

A planar electrooptic beam splitter/modulator with a pair of parallel electrodes

A new planar electrooptic beam splitter with a pair of parallel electrodes is proposed and its characteristics are demonstrated on LiNbO₃. At a voltage up to 80 V and a 9.5 m electrode separation, the two output beams can be scanned over a total angle of 3° in the guide plane. The structure can also be applied to amplitude modulation, requiring 15 V for complete on-off modulation. The device permits convenient fabrication and has a potential to operate at high speeds.     

Design considerations and analysis of velocity mismatch effects in an electrooptic Fabry-Perot modulator

The influence of velocity mismatch effects on the design and performance of an integrated optic Fabry-Perot travelling wave modulator fabricated in LiNbO₃ is studied analytically. It is shown that despite the velocity mismatch the performance of this system is significantly better than equivalent single pass systems.     

A bistable liquid crystal electro-optic modulator

A new liquid crystal hybrid bistable optical device is described. Optical bistability has been observed and the use of this device for optical logic elements and ultralinear modulation applications demonstrated. The transient response of the device for optical logic elements and ultralinear modulation applications demonstrated. The transient response of the device has also been studied and a “critical slowing down” phenomenon observed.     

Orthogonally polarized single sideband modulator

A modulator design capable of producing a new constant intensity modulation format is proposed. The modulator consists of a Mach-Zehnder interferometer containing two polarization modulators. By shifting the relative phase of the electrical drive signal applied to each polarization modulator by 90 degrees a modulation consisting of a carrier and a single sideband, polarized orthogonal to the carrier, is produced.