All-optical switch based on photonic crystal microcavity with multi-resonant modes

We present a design of all-optical switches based on one-dimensional photonic crystals (1D PhC) doped with nonlinear optical materials. The 1D PhC switch structure is composed of a PhC cavity sandwiched by two accessional PhC microcavities. The center PhC cavity has two resonant frequencies with nearly the same quality factors (Q), while the accessional PhC cavities have the same resonant frequency, which is equal to one of the resonant frequencies of the center cavity. The two accessional PhC cavities cause reduction of Q value in this resonant frequency and result in different Q values of two modes. We realize all-optical switch effect by selecting pump light wavelength at the low Q mode and probe light wavelength at the other mode. The theoretical simulations by using the finite difference time domain method show that the pump light intensity required to realize optical switch effect in the designed switch is 50 times smaller than that in one-dimensional photonic crystals cavity with only one resonant mode.     

The synthesis of generalised Mach–Zehnder optical switches based on multimode interference (MMI) couplers

The space-division switching properties of a generalised Mach–Zehnder photonic switch are examined in this paper. It is shown for the first time that such an N × N switch can only produce N independent point-to-point switching states. A method that unambiguously identifies these states and thereby provides a synthesis technique for the design of these switches is presented.     

N × N集成光开关阵列模型

报道了由2N个1 × N 多模干涉马赫-曾德尔光开关组成的N × N光开关阵列结构,分析了这种结构的开关阵列优势和局限性.用场传输矩阵方法建立了1 × N多模干涉光开关的光场传输方程.给出了光开关阵列从任一输入端输入、从任一输出端输出时阵列开关的工作条件.在上述原理及理论基础上分析了4×4光开关阵列的结构和工作条件.     

An ultra-fast all-optical RS flip-flop based on nonlinear photonic crystal structures

In this paper, an all-optical RS flip-flop was proposed using nonlinear Kerr effect in photonic crystals. The proposed structure is composed of a core section and two optical switches. The core section consists of two cross-connected resonant cavities whose resonant mode are at wavelengths 1586 and 1620 nm. The cavities were designed such that the resonance of one cavity prevents the signal coupling through the other one. For designing the switch sections, a bias port was used to keep data when there is no input for the flip-flop. Therefore, when both input ports are inactive, the previous state of the flip-flop will be kept. Total footprint and maximum frequency of the proposed structure are obtained 361 μm² and 320 GHz, respectively.     

Ultra-fast optical switches using 1D polymeric photonic crystals

We report fabrication of ultra-fast optical switches operated at a wavelength of 1064 nm using spin-coated one-dimensional polymeric photonic crystals doped with nonlinear-optical dyes. The optical switches are controlled either by an applied electric-field voltage or by a pump light by use of two different optical-configurations. The response time of the electro-optic switch and the all-optical switch are limited by the applied voltage and the laser used, respectively. The polymeric photonic crystals can be easily fabricated with low cost.     

Photonic dispersions of semiconductor-quantum-dot-array-based photonic crystals in primitive and face-centered cubic lattices

We study the energy dispersions of photonic crystals based on the semiconductor-quantum-dot arrays. It has been shown that for the most commonly used semiconductor materials, and as compared with the primitive cubic lattice, the photonic crystal in a face-centered cubic (fcc) lattice exhibits a very promising energy dispersion relationship with an overall photonic bandgap. The bandgap is most prominent along the Λ(Γ–L) line inq space. The results explain the difficulties in fabricating photonic crystals in fcc lattices. They explain also the experimental works of Vlasov et al. [Physical Review B55, R13357–13360 (1997)], where it has been demonstrated that for CdS nanocrystals embedded in fcc porous silica matrices the photonic bandgaps are observed for any direction of the radiation incidence, being most pronounced for the [111] direction.     

Advancements in passive planar lightwave circuits and hybrid integration devices

Planar silica device technology provides the ability to filter, route, switch, and attenuate optical signals for Wavelength Division Multiplexing (WDM) based photonic networks. As network capacity expands there is a requirement to increase the complexity, scale and density of the functions whilst reducing cost. It is also important that both the optical performance and long term stability of the devices are not compromised. The following paper reviews recent progress on these types of devices for large-scale manufacture, concentrating on key performance parameters for filter type structures and hybrid integrated devices such as insertion loss and polarisation dependent loss (PDL). To cite this article: J.R. Bonar et al., C. R. Physique 4 (2003).     

Photonic switches and switch arrays on LiNbO3

In recent years there has been tremendous progress in lithium niobate-based photonic switches. The various switch configurations proposed and implemented, and their characteristics, are reviewed. A summary of the device technology is given. Performance analysis based on different architecture and the size of arrays that can be relalized are discussed.Indian Institute of Science, Bangalore, India     

Design and simulation of a novel 32 × 32 photonic bandgap power switch based on SOI waveguide

In this paper, we propose a novel 32 × 32 photonic bandgap (PBG) power switch based on silicon-on-insulator (SOI) substrate. The 32 × 32 PBG power switch merges the design concept of PBG structure and multimode interference (MMI) structure. With controlling the voltages of 256 blocks for changing the refractive index, we can demonstrate that the light propagation direction can be switched to the assigned output port as a 32 × 32 power switch. According to the simulations, the power switching control tables are searched and selected for successful switching. The size of our designed 32 × 32 PBG switch can be reduced to 252 × 6040 μm which is much smaller than the conventional opto-electronic switches.     

Kerr nonlinear switch based on ultra-compact photonic crystal directional coupler

In this paper, an all optical switch based on nonlinear photonic crystal directional coupler has been simulated and analyzed by the finite difference time domain (FDTD) method. The lunched pump signal increases the refractive indices of the central row of the coupler, due to nonlinear Kerr effect, hence the coupler works in the nonlinear conditions and lightwave guides to the other output port. We have tried to increase the coupling efficiency and reduce the required power in the nonlinear status by optimizing the bends structure and increasing the interaction between dielectric and lightwave signal. Therefore, the input signal beam can be controlled to be exchanged between two output ports to earn the highest output power ratio and the smallest amount of power required for nonlinear performance, the physical length of the coupler is determined to be 20a, where a is the structure lattice constant.     

硅基光波导开关技术综述

硅基光波导开关技术是公认的低成本光交换技术,在电信网络、数据中心和高性能计算领域中都具有非常广泛的应用前景.本文系统综述了近年来硅基光波导开关技术研究取得的主要进展,首先对马赫-曾德尔干涉仪型、微环谐振型和微电子机械系统驱动波导型三种硅基光波导开关技术进行了介绍,并对不同原理的光开关技术的应用场景进行了总结;然后讨论了影响大端口光开关性能的关键技术,特别着重于拓扑架构、无源器件和光电封装等方面;最后对硅基光波导开关技术的技术挑战和研究方向进行了展望,其对未来硅基全光交换技术的实用化具有指导性意义.     

Digital optical switch based on amorphous silicon waveguide

In this paper, the performance of a digital optical switch, operating at the infrared communications wavelength of 1550 nm and based on the thermo-optic effect in amorphous silicon, are investigated. We prove that the strong thermo-optic effect of amorphous silicon, combined with the possibility of realising micrometric integrated structures, allow the design of promising integrated switches. The device, designed for low-cost photonic applications, could be easily integrated in silicon optoelectronic circuits.     

Theoretical investigation of a polymer Mach–Zehnder electro-optic switch using 2N + 1 serial-coupled microrings with ultralow-driving voltage

Universal structure and thorough analysis are proposed for a kind of (2N + 1)th order polymer microring resonator Mach–Zehnder interferometer (MRR-MZI) electro-optic (EO) switch. Formulas and expressions of output power, insertion loss and crosstalk are derived, and detailed design and optimization are carried out. Analytical results indicate that, besides the first-order MRR-MZI EO switch (N = 0), other devices for N ≥ 1 can all perform normal switching function, and 5 ≥ N ≥ 2 is preferred for dropping the crosstalk below ?10 dB. For the four MRR EO switches (N = 2–5), their switching voltages are 0.99, 0.73, 0.57 and 0.47 V, respectively; their insertion losses are within the range of 1.15–2.26 dB at bar state, whereas those are within the range of 1.95–2.42 dB at cross state; their crosstalks are within the range of 11.04–17.82 dB at bar state, whereas those are within the range of 10.34–12.51 dB at cross state. Compared with the traditional MZI EO switch, the voltage–length product (0.21 V mm) of this switching element is decreased by ~111.7 times under the same waveguide parameters. Therefore, due to small footprint size and extremely low switching voltage, this switching configuration can be densely integrated onto optoelectronic chips.     

p-Type and n-type quaterthiophene based semiconductors for thin film transistors operating in air?

The solution and solid-state properties as well as the organic thin film transistor (OTFT) behavior of α,ω-perfluorohexyl-quaterthiophene (DFH-4T) are presented and compared to those of quaterthiophene (4T) and α,ω-hexyl-quaterthiophene (DH-4T). UV/visible and fluorescence data showed the same weak effect of hexyl and perfluorohexyl substitutions on the optical properties of 4T core. Growth mechanism of DFH-4T based thin films deposited by vacuum deposition on heated Si/SiO₂ substrates has been investigated in details and demonstrated to be identical to that of DH-4T. The characterization in air of the charge transport properties of thin films based on DH-4T and DFH-4T revealed a switch from p- to n-type, respectively, depending on the nature of alkyl chains. A qualitative Schottky-type charge injection barrier model, based on HOMO and LUMO energy levels estimated from cyclic voltammograms and optical absorption spectra of DFH-4T relative to those of 4T and DH-4T, was introduced to explain such change in semiconducting properties observed under ambient conditions (temperature, light, air). In an attempt to answer to the question of “are p-type and n-type quaterthiophene derivatives appropriate semiconductors for thin film transistors operating in air?” we investigated the influence of the nature of the dielectrics to obtain OTFTs operating in air and showing environmentally stable mobility.     

Analysis of photonic band gap structure for the design of photonic devices

A detailed analysis, based on Kronig–Penney model and finite-difference time-domain (FDTD) method, is used to explain the air-filling factor effect on the optical properties of defect-free photonic crystals. By the use of the Kronig–Penney model, we calculated the photonic band structure for electromagnetic waves in a structure consisting of a periodic square array of dielectric rods of lattice constant a separated by air holes. Gaps in the resulting band structures are found for waves of both polarisations. We analysed the air-filling factor effect on both polarisations in low and high frequency regions. It is shown that the frequency of the lower TE (transverse-electric) band edge is independent of the air-filling factor in the low frequency region. The opposite behaviour holds for the upper band edge, growing rapidly with the air-filling factor. Using the FDTD we simulated the electric field as the pulse propagates through the structure. The results of both approaches are compared, and the operation characteristics of the measuring air-filling factor device are described. We investigate the optical properties of a single and two defects incorporated in the PC, which can be potentially applied to ultra small surface-emitting-type channel drop filter. It is shown that the frequency and polarisation of the dropped light can be controlled by changing the size and/or shape of the defect. The electric field distribution calculations show that the electric field for a given frequency is located only at the defect, which means that each defect can detect only its corresponding wavelength. To cite this article: F. Ouerghi et al., C. R. Physique 5 (2004).     

Optical switch with low-phase transition temperature based on thin nanocrystalline VOx film

An optical switch is fabricated by using micromachining technology, which is based on thin nanocrystalline vanadium oxide (VO_x) film, and it consists of four layers: a silicon (Si) substrate layer, a VO_x layer, a Si₃N₄ buffer layer, and an aurum (Au) electrode layer. By applying a switching power supply to a pair of the Au electrodes, the optical switch is controlled to exhibit from an “on” state with semi-conducting phase to an “off” state with metallic phase. The optical switch performance is investigated, and testing results show that its extinction ratio is about 14 dB, its switching response time can achieve about 1.5 ms, and the power dissipation required for stimulating switching to work can be below about 15 mW at least, which is lower than the power dissipation of conventional optical switches based on microstructure thin vanadium dioxide (VO₂) films. This kind of optical switch is potential to be applied as optical switch for optical communication.     

光子晶体异质结耦合波导光开关

以二维三角晶格光子晶体为研究对象,在该光子晶体中引入两行平行的单模线缺陷波导,以一行耦合介质柱为间距,通过调节部分耦合介质柱的折射率,构筑了光子晶体异质结耦合波导光开关结构。利用平面波展开法和定向耦合原理计算了在不同入射光频率下,缺陷波导间耦合介质柱的折射率不同时的耦合长度,确定了合适的光子晶体异质结耦合波导光开关的结构参数。利用时域有限差分法研究了该光开关中耦合介质柱的折射率变化及异质结构介质柱的位置分布对光信号输出路径的影响。结果表明,通过改变该结构中耦合介质柱的折射率可以改变光的输出路径,可实现光的开关行为。并且异质结构介质柱位置的随机分布对该光开关的影响不大,有助于光子晶体新型滤波器、定向耦合器、波分复用器以及光开关等光子器件的研究。     

细菌视紫红质光开关特性实验研究

介绍实现光子开关材料BR分子的重要性。理论上分析BR分子材料光学特性，实验观测BR分子材料在400nm和632nm光照射下的相互抑制作用，最后分析BR的光子开关特性。     

On the optically transparent WDM ATM multicast (3M) switches

We describe an architecture design and implementation of the optically transparent wavelength-division-multiplexed (WDM) asynchronous-transfer-mode (ATM) multicast (3M) switch for all optical high-speed networks. By using the WDM techniques, the wire complexity in both the switch fabric and the concentrator can be reduced from O(N²) to O(N). By using integrated photonic devices and highly parallel processing and pipeline control electronic circuits the switch is handling signals at the cell level (53 bytes) instead of at the bit level and can achieve very high speed and high throughput operation. Several key components, including a cell synchronizer, a photonic VCI over-writting unit, a wavelength converter, an optical concentrator, and a WDM memory, have also been proposed to realize this 3M switch. All of the photonic devices are highly integratable and are very suitable for building future large-scale, low-cost photonic ATM switches. A combination of both the ATM and WDM techniques will provide an ultimate version for optical networking with almost unlimited capacity.     

Slowing down the light for delay lines implementation: Design and performance

Optical delay lines are key building blocks for all-optical signal processing. Photonic crystal structures can demonstrate efficient group velocity reduction, together with a wide-bandwidth and reduced high-order group velocity dispersion. Theses structures also offer the ability for 2D integration within photonic integrated circuits. This paper presents the performances of photonic crystal structures engineered for slowing down the light, and discuss the actual limitation encountered due to fabrication imperfections. To cite this article: A. Talneau, C. R. Physique 10 (2009).