Dynamic characteristics of optical intersecting-waveguidemodulators/switches with curved electrodes

The dynamic behavior of optical modulators/switches in the form of intersecting waveguides with curved electrodes is formulated. It is shown that the electrode curvature is very effective in achieving reflected pulses in good resemblance to the incident ones. Further, the speed of operation is found to be high and is shown to depend upon the commonly known capacitance of the device and the time required for refractive index variations to settle down; and also upon the relative pulsewidths of the optical and modulating signals and the extent of their synchronization. The intersection angle is found to influence the propagation delays of the spatial components, which are equalized by properly chosen structural parameters, to achieve unbroadened and undistorted output pulses. The flexibility in the bandwidth of even a fabricated device, through adjustment of the driving conditions, is demonstrated and the capability of such devices to handle a very wide range of optical pulsewidths is clarified     

Extinction ratios and scattering losses of opticalintersecting-waveguide switches with curved electrodes

Optical intersecting-waveguide switches with curved electrodes are analyzed. It is shown that the electrode-curvature in the form of a logarithmic spiral results in reflected field distributions in good resemblance to the incident one with reduced transverse shifts. Large extinction ratios and low scattering losses with small voltage-length product are, therefore, achievable. It is concluded that electrode curvature in the form of a logarithmic spiral is effective in realization of low insertion loss, high extinction ratios and small size optical switches     

Overlap integral factors in integrated optic modulators andswitches

Coplanar strip and complementary coplanar strip electrodes are often used in integrated optical switches and modulators using the optical directional coupler. The field analysis of these electrodes is performed to determine the optimum overlap integral between the optical field and the modulating electromagnetic field. The optimal placement of the electrodes with respect to the optical channel waveguides is presented as a function of electrode width and spacing     

Analytical method for calculation of stresses and material birefringence in polarization-maintaining optical fiber

An analytical method is presented for the calculation of 1 thermal stress and the material birefringence in polarization-maintaining 1 optical fiber. The method is based on the thermoelastic displacement c potential in which the principle of superposition applies. The method is applicable to any fiber structure. Its application to fibers with isolated stress-producing regions and a variety of core shapes is demonstrated. The optimum fiber parameters required to achieve maximum material birefringence for fibers with circular or bow-tie shaped stress regions are given. It is also shown that the thermal stresses tend to make the bow-tie fiber more crack-resistant than the fiber with circular stress lobes.     

Fast 2×2 Mach-Zehnder optical space switches usingInGaAsP-InP multiquantum-well structures

We report fast 2×2 Mach-Zehnder optical space switches by using quantum confined Stark effect in InGaAsP-InP multiquantum-well structures that are ultracompact, require low voltages, and employ a simple RF drive with RC time-constant limited lumped electrodes. Cut-off frequencies in excess of 10 GHz are observed suitable for a variety of fast optical switching applications     

A Dual-Mode Electrochromic Platform Integrating Zinc Anode-Based and Rocking-Chair Electrochromic Devices

The complementary electrochromic device, where the optical transmittance changes upon the flow of cations back and forth between anodic and cathodic electrodes, operates in a rocking-chair fashion if it can inherently self-discharge. Herein, the first demonstration of a dual-mode electrochromic platform having self-coloring and self-bleaching characteristics is reported, which is realized by sandwiching zinc metal within a newly-designed Prussian blue (PB)-WO₃ rocking-chair type electrochromic device. It is demonstrated that the redox potential differences between the zinc metal and the WO₃/PB electrodes endow the self-color-switching of these electrodes. By employing a hybrid electrolyte of Zn²⁺/K⁺, it is further shown that the colored PB-WO₃ rocking-chair device is capable of spontaneously bleaching when the anodic and cathodic electrodes are coupled. This dual-mode light-control strategy enables the electrochromic devices to exhibit four distinct optical states with the highest optical contrast of 72.6% and fast switching times (<5 s for the bleaching/coloration processes). Furthermore, the built-in voltage of the dual-mode electrochromic devices not only promotes energy efficiency, but also augments the bistability of the devices. It is envisioned that the broad implication of the present platform is in the development of self-powered smart windows, colorful displays, optoelectronic switches, and optical sensors.     

Switch energies of electronic and optical switches: a simplecomparative study

A comparison of the switch energies of electrically controlled optical absorption switches and electronic switches is performed. It is shown that in the investigated case with quantum box based absorption switches, the switch energies of the optical switches are generally orders of magnitude larger than those of the electronic switches for very high frequencies. Consequences on integration of optical devices as well as on the potential for photonic switching and processing are briefly discussed     

35 GHz bandwidth photonic space switch with travelling waveelectrodes on InP

A 2×2 Mach-Zehnder interferometer based switch with a large optical bandwidth of 35 GHz is reported. The design and the characteristics of switches with travelling wave electrodes are discussed. The realised travelling wave electrode design meets the demands for ultrahigh-speed demultiplexing beyond 100 Gbit/s     

MEMS 光开关技术的研究进展

近年来国际上出现的一些新型MEMS光开关，包括其结构、驱动方式、规模等。并且通过对基于各种不同工作机理的光开关之问，性能、结构及可实行产业化程度等各方面数据的分析比较，认为MEMS光开关在现代光通讯领域具有较好的应用发展前景。     

General solutions for stress-induced polarization in optical fibers

General solutions of thermal stresses and material birefringence in polarization-maintaining optical fibers are presented. The solutions give the stresses and birefringence at every point in the cross section of various fibers. The fundamental solution of the stress field is constructed by using the complex variable method in elasticity. When the cores, inner claddings, or stress-inducing regions are ellipses, circles, or bow-tie shapes, exact closed-form solutions can be found. The average core birefringence and center core birefringence of elliptical core, elliptical cladding, twin core, Panda, and bow-tie fibers are calculated and compared. Among these fibers, the bow-tie fiber shows the highest birefringence     

Small AC Driving Voltage for MZI-Based GaAs–GaAlAs Electrooptic Modulators/Switches With Coplanar Electrodes

We report a method to achieve a small ac driving voltage for high-speed multimode interference Mach-Zehnder interferometer GaAs-GaAlAs electrooptic modulators and switches with coplanar electrodes for polarization-insensitive operation. By biasing the devices in the reverse break-down region, the ac driving voltage can be as small as 3 V. Such a small ac driving voltage is important for high-speed optical modulators and switches. The physics behind this small ac driving voltage is also discussed.     

Capacitance tomography sensor without CMOS switches

Usually, CMOS switches are used to select excitation and detection electrodes in electrical capacitance tomography (ECT) systems. However, these switches cause charge injection or coupling leakage problems. An ECT sensor is described which does not use any switches directly connected to the measurement electrodes. The potentials on the electrodes are digitally controlled and the excitation field of the sensor is totally flexible. Experimental results show that the circuit performs well as either an excitation or a detection channel     

领结型和椭圆型保偏光纤的应力和模式分析

应用有限元方法对领结型和椭圆型保偏光纤的热应力双折射特性和模式双折射进行了分析,给出了这两种保偏光纤的应力和双折射分布规律.对领结型保偏光纤,研究了纤芯的双折射和模式双折射随着应力区离纤芯距离的变化规律;对椭圆型保偏光纤,研究了纤芯的应力双折射和模式双折射随包层椭圆度的变化规律;分析了光纤应力区结构对纤芯双折射大小和均匀性的影响,并将应力诱导双折射与模式理论计算结果进行了比较.     

Analytical solution of bow-tie fibres

In the letter we attempt to treat theoretically the complicated profile structure of a polarising bow-tie fibre. The mathematical steps taken in our analysis include the use of a Fourier expansion of the index profile and an iterative technique to obtain the Green functions of the optical field. Numerical examples show that a bow-tie fibre with the usual profile structure has higher leaky losses than the predicted leaky losses of an anisotropic step-index model.     

Integrated optic electrooptic modulator electrode analysis

Integrated optical (IO) switches and modulators are based on the electrooptic effect obtained by applying a voltage between electrodes fabricated on the surface of a crystal (for example, LiNbO3). In this paper, we calculate the change in the optical propagation constant in single modeZ-cut LiNbO3:Ti-diffused waveguides for a variety of electrode configurations. These calculations are compared to experimental data from IO devices. The calculations predict the observed variations in switching voltage with wavelength and electrode separation.     

Research Progress on Multimode Interference Switches

Optical switches are key components for constructing optical communication networks, so it is necessary to design optical switches and optical switch arrays with high performance and low cost. As one type of optical switches, the multimode interference（MMl） switches have received considerable attention due to their unique merits. The structures and operation principles of various types of MMI switches are introduced, and the recent progresses of MMI switches are also discussed.     

Compact and dynamic optical bypass-exchange switch

A novel, compact and dynamic optical bypass-exchange switch is presented. It is based on a planar optics configuration with polarization-sensitive linear grating holographic optical element, and a polarization rotator light modulator. Representative switches were designed, fabricated and experimentally evaluated. The results indicate that relatively low crosstalk level can be reached to make such switches suitable for practical optical interconnect networks.     

Carrier Diffusion and Recombination in Photonic Crystal Nanocavity Optical Switches

Carrier dynamics in silicon photonic crystal (PhC) nanocavities are studied numerically. The results agree well with previous experimental demonstrations. It is shown that the presence of carrier diffusion makes fast switching possible, which is an advantage of nanocavity switches over other types of larger carrier based nonlinear optical switches. In particular, diffusion is effective in PhC nanocavity switches, which makes the switching recovery time even faster than that of silicon waveguide-based optical switches. In addition, calculations suggest that the thermo-optic effect can be reduced if the carriers are extracted within a few 100 ps by introducing a p-i-n structure.     

等离子体电极普克尔盒的并联驱动

高功率大型惯性约束聚变(ICF)激光驱动器大多采用等离子体电极普克尔盒(PEPC)抑制多程放大器的自激振荡和隔离反激光。采用并联驱动技术有利于实现等离子体电极普克尔盒电光开关小型化和降低成本，并可提高激光系统可靠性和稳定性。等离子体电极普克尔盒的并联驱动包括等离子体电极的并联驱动和普克尔盒充电的并联驱动。分析了等离子体电极电光开关并联驱动的途径和问题，通过采用电阻隔离和二极管退耦措施实现了预电离并联驱动，进而实现了等离子体电极的同步驱动；通过调节开关脉冲发生器输出波形及传输电缆长度，可实现普克尔盒充电的并联驱动，并给出了实验结果。     

Analytic solution for the birefringence produced by thermal stress in polarization-maintaining optical fibers

Polarization-maintaining optical fibers are usually made by inducing a large anisotropic thermal stress in the core so that it appears highly birefringent. A simple analytic solution has been found for the birefringence in terms of the cross-sectional distribution of the high-expansion material used to create the thermal stress. The analysis is able to predict optimal structures which efficiently utilize the available stress and thus maximize the birefringence. It is shown that the optimum structure has a cross-sectional geometry resembling a bow-tie. Design rules are given whereby the dimensions may be chosen and these are verified in a simple experiment.