Modifying electrooptics of orthoconic antiferroelectric liquid crystal cells by manufacturing procedures

Orthoconic antiferroelectric liquid crystals (AFLCs) having 45° tilt angle have been proposed to overcome the problem of reduced contrast usually exhibited by regular antiferroelectric displays. However, the pitch of the helix induced by chirality is customarily short in existing orthoconic materials, making it difficult to achieve surface stabilized configurations when the material’s pitch is smaller than the cell thickness. In this work, the influence of different manufacturing procedures on the electrooptical behaviour of orthoconic AFLCs is studied. Using the same orthoconic AFLC mixture, aligning surfaces and manufacturing protocol, we have observed two dissimilar responses, true orthoconic behaviour, and orthoconic V-shape response. The electrooptical response depends ultimately on the rubbing strategy adopted in either case.     

基于正交频分复用无源光网络的动态带宽分配算法研究

介绍了一种应用于未来大容量、多业务接入场景下的称为光正交频分复用无源光网络的下一代接入网技术,并提出了一种基于此结构的称为基于服务质量需求的固定周期流水线轮询动态带宽分配算法.该算法通过应用二级带宽分配机制、带宽预申请机制和最小带宽申请优先原则等方法,有效地保障了在大容量、多业务接入场景下各个业务不同的服务质量需求.为研究其性能,建立了该算法的仿真模型并进行了对比仿真.仿真结果显示该算法以低时延和低抖动有效地支持快速转发业务,同时平衡了确保转发业务和尽力而为业务之间的优先性和相对公平性,并且实现了不同光网络单元间的同优先级业务带宽分配的公平性.与传统的动态带宽分配算法算法相比,基于服务质量需求的固定周期流水线轮询动态带宽分配算法具有执行效率高、算法复杂度低、性能良好等优点,并且能够更好地适应光正交频分复用无源光网络的特性,发挥网络最大的性能.     

基于正交频分复用无源光网络的动态带宽分配算法研究

介绍了一种应用于未来大容量、多业务接入场景下的称为光正交频分复用无源光网络的下一代接入网技术,并提出了一种基于此结构的称为基于服务质量需求的固定周期流水线轮询动态带宽分配算法.该算法通过应用二级带宽分配机制、带宽预申请机制和最小带宽申请优先原则等方法,有效地保障了在大容量、多业务接入场景下各个业务不同的服务质量需求.为...     

A Wavelength and Bandwidth Assignment Algorithm to Support Guaranteed Bandwidth Levels in Hybrid Time Division Multiplexing/Wavelength Division Multiplexing Ethernet Passive Optical Networks

Abstract

A novel bandwidth assignment algorithm in wavelength division multiplexing Ethernet passive optical networks, called a dynamic wavelength assignment service level agreement, is proposed to efficiently provide subscriber differentiation. Simulation results show that the dynamic wavelength assignment service level agreement outperforms other bandwidth allocation algorithms in wavelength division multiplexing Ethernet passive optical networks, as it makes a fairer bandwidth distribution than other methods and is able to overcome the non-allowed packet fragmentation of the Ethernet passive optical network standard. Consequently, it greatly increases the achieved throughput and always ensures a minimum guaranteed bandwidth to every priority subscriber. Furthermore, the new algorithm obtains lower mean packet delay and packet loss rate for the highest priority subscribers when compared with other bandwidth distribution schemes in wavelength division multiplexing Ethernet passive optical networks.     

Orthoconic antiferroelectric liquid crystals containing biphenyl,terphenyl, or naphthyl mesogenic unit

Three homologous series of orthoconic (45 degree tilt) antiferroelectric liquid crystals containing either naphthyl or terphenyl groups as mesogenic unit have been synthesized and their mesomorphic behaviour investigated by DSC and polarized light microscopy, and their properties discussed. X-ray diffraction studies have shown the presence of a de Vries-type smectic A phase which does not exhibit a layer shrinkage on transition to the ferroelectric smectic C phase. Mixtures of the new materials have been formulated and their electro-optical properties investigated for their use in surface stabilized orthoconic antiferroelectric liquid crystal (SSOAFLC) devices     

光纤光栅多参数桥梁结构监测系统的研究

从土木工程应用的实际情况出发,利用光纤光栅传感器具有波长绝对编码和易于复用的特点,提出工程化同时测量温度、应变和压力的全光栅型低成本分布式传感方案。设计了基于连续波调频技术的光纤光栅多参量桥梁结构监测系统,将光频域反射复用与波分复用技术相结合,实现分布式光栅传感网络的寻址,提高了系统复用容量。实验表明：所设计的传感系统能够准确监测结构重要部位的内部应变及车流量等参数,为桥梁结构的静、动载测试提供了准确的数据,同时也为桥梁的工作状态评估和健康诊断提供了依据。     

Features of the smectic e phases in some strongly polar biphenyls and tolanes

Four compounds with the isothiocyanate terminal group (–NCS) in tolane or biphenyl molecules, revealing E phase in a broad temperature range, have been investigated by means of the DSC, polarizing microscope, miscibility and X-ray methods. The investigations have confirmed that internal smectic E phase in those compounds was not identical and it has been characterized by different distortions of the orthoconic cell and interlayer correlation.     

Two-loop-based low-coherence multiplexing fiber-optic sensor network with a Michelson optical path demodulator

A two-loop-based low-coherence multiplexing fiber-optic sensor network is proposed and demonstrated. It greatly extends the multiplexing capacity of this kind of sensor. A practical implementation of this scheme uses a popular amplified spontaneous emission light source and standard single-mode fiber, which are commonly used in the communications industry. The sensor's two-loop topology is completely passive. Absolute length measurements can be obtained for each sensing fiber segment for use in measuring the quasi-distribution strain or temperature. For large-scale smart structures this technique not only extends the multiplexing potential but also provides a redundancy for the sensing system. This means that the two-loop sensor network can break down at several points and the sensing system will still work even if some of the embedded two-loop sensors have been destroyed. The robustness of the nine-sensor two-loop sensing network is investigated and discussed.     

Four-dimensional scheduling for uplink dynamic bandwidth allocation in OFDM-PON

Orthogonal frequency division multiplexing passive optical network (OFDM-PON) has been considered a promising access solution to meet the variable bandwidth demand. In this paper, a novel scheduling for dynamic bandwidth allocation (DBA) at medium access control (MAC) layer is proposed for uplink transmission of OFDM-PON. In order to utilize the bandwidth efficiently, scheduling in four dimensions is adopted in the proposed DBA algorithm. Four dimensions stand for frequency domains, time domains, modulation formats and power allocations. The algorithm is quite flexible. Simulation results and analysis show that the proposed algorithm can efficiently utilize the OFDM bandwidth and make the system highly energy-efficient.     

OFDMA-based LAN emulation in long-reach hybrid PON system

A novel long-reach, hybrid wavelength-division multiplexing (WDM) and time-division multiplexing (TDM) passive optical network (PON) architecture which supports local area network (LAN) emulation among customers is proposed. Orthogonal frequency division multiplexing access (OFDMA) technology is used in optical network units (ONUs) to transmit the LAN data. The optical LAN data from an ONU is converted into the electrical signal and combined with TDM downstream access data in the extended box for delivery to other ONUs. This scheme has many advantages on LAN emulation, such as dynamic allocation of LAN bandwidth, no bandwidth cost of TDM business, supporting multiple concurrent LAN services and so on. Simulations are performed to verify the scheme. Tolerance of dispersion and factors that influence the performance of various independent services are all investigated and analyzed.     

分布反馈式光纤激光水听器拖曳线列阵实验研究

为了进一步增大光纤拖曳阵的探测距离,研制了缆径为16mm的32元分布反馈式光纤激光水听器拖曳线列阵.阵元在10~2 000Hz频率范围内的平均声压灵敏度为-142.7dB(re 1rad/μPa),波动幅度小于±2dB.基于声光调制器的时分、波分联合复用技术实现了32元光纤激光水听器的多路复用,各个阵元之间以及各个通道之间的串扰均小于-40dB,并完成了静态和动态拖曳湖上实验.实验结果表明,研制的32元分布反馈式光纤激光水听器拖曳线列阵无论是在静态,还是在6~16节的动态拖曳状态,都能对目标形成稳定的波束指向,与GPS轨迹记录完全一致,展现了分布反馈式光纤激光水听器拖曳线列阵在工程上的应用前景.     

Energy-Efficient Next-Generation Passive Optical Networks Based on Sleep Mode and Heuristic Optimization

Abstract

In this article, an energy-efficiency mechanism for next-generation passive optical networks is investigated through heuristic particle swarm optimization. Ten-gigabit Ethernet–wavelength division multiplexing optical code division multiplexing–passive optical network next-generation passive optical networks are based on the use of a legacy 10-gigabit Ethernet–passive optical network with the advantage of using only an en/decoder pair of optical code division multiplexing technology, thus eliminating the en/decoder at each optical network unit. The proposed joint mechanism is based on the sleep-mode power-saving scheme for a 10-gigabit Ethernet–passive optical network, combined with a power control procedure aiming to adjust the transmitted power of the active optical network units while maximizing the overall energy-efficiency network. The particle swarm optimization based power control algorithm establishes the optimal transmitted power in each optical network unit according to the network pre-defined quality of service requirements. The objective is controlling the power consumption of the optical network unit according to the traffic demand by adjusting its transmitter power in an attempt to maximize the number of transmitted bits with minimum energy consumption, achieving maximal system energy efficiency. Numerical results have revealed that it is possible to save 75% of energy consumption with the proposed particle swarm optimization based sleep-mode energy-efficiency mechanism compared to 55% energy savings when just a sleeping-mode-based mechanism is deployed.     

A Survivable Wavelength Division Multiplexing Passive Optical Network with Both Point-to-Point Service and Broadcast Service Delivery

Abstract

A survivable wavelength division multiplexing passive optical network enabling both point-to-point service and broadcast service is presented and demonstrated. This architecture provides an automatic traffic recovery against feeder and distribution fiber link failure, respectively. In addition, it also simplifies the protection design for multiple services transmission in wavelength division multiplexing passive optical networks.     

Ultra-High-Capacity Passive Optical Network Systems with Free-Space Optical Communications

Abstract

This article experimentally demonstrates a hybrid fiber–free-space passive optical network that enables high spectral density, aggregated capacity, and total throughput through ultra-dense wavelength-division multiplexing baseband and radio-over-fiber channels. Ultra-dense wavelength-division multiplexing 10-Gb/s Nyquist-shaped 16-ary quadrature amplitude modulation, 10-Gb/s radio-over-fiber orthogonal frequency-division multiplexing, and 8.75-Gb/s baseband orthogonal frequency-division multiplexing signals per user were transmitted through a maximum 40-km passive optical network, which includes a 6-m free-space optics link with acceptable performance.     

Color holographic display based on azo-dye-doped liquid crystal (Invited Paper)

A multiplexed holographic display video has been achieved by using a passive azo-dye-doped liquid crystal （LC） cell. Holograms formed in this cell can be refreshed in the order of several milliseconds. By angular multiplexing technique, dynamically multiplexed holographic videos are realized. Moreover, the reconstructed RGB images are merged into a color image, which illustrates the possibility of a color holographic three-dimensional （3D） display by holographic multiplexing of the LC cell.     

Influence of a helical pitch on orthoconic antiferroelectric liquid crystals performance

Orthoconic antiferroelectric liquid crystals, whose half cone angle is 45°, are of interest in display technology because they are capable of providing greyscale in passively addressing waveform while exhibiting very good contrast. However, orthoconic antiferroelectrics having short pitch are difficult to be aligned, this makes surface stabilized alignment unfeasible. In this case, dynamic behaviour is usually poor, avoiding electronic addressing with standard electronics. In this work, we report the helical pitch measurements of OAFLC mixtures and we compare electrooptical performance of high and low pitch OAFLCs.     

Generalised multiple-lateral-mode rate equation modelling of lasers with selective quantum-well intermixing for improved beam quality

A numerical model in terms of rate equations for lateral mode amplitudes for analysing static and dynamic properties of moderately broad stripe (tens of microns) laser diodes is proposed and used for modeling lasers with longitudinally or laterally intermixed passive areas. Introduction of passive diffractive regions is shown to offer some improvement of the laser beam, and the potential of further improvement of the beam by Intermixing lateral fringes along the stripe is discussed.     

Experimental Demonstration of SCM-PON Monitoring with Baseband Embedded OTDR

The combination of subcarrier multiplexing and passive optical networks can provide an efficient and cost-effective solution for fiber and wireless convergence in access networks. Moreover, to reduce operational expenditures, a reliable monitoring technique should provide in-service evaluation of the physical layer. Here, we perform the experimental demonstration of an SCM-PON system with baseband embedded optical time-domain reflectometer monitoring. Different modulation formats were tested to evaluate the penalty generated by the monitoring system. Based on the long-term evolution downlink test model (E-TM 3.1), our results show negligible power penalty while achieving a ~12-dB dynamic range with 10-m spatial resolution.     

基于时分复用和窄波长扫描激光的长距离光纤布喇格光栅传感系统

提出了一种通过提高长距离光纤布喇格光栅传感系统容量,从而实现多传感点参量测量的新方法.采用时分复用、窄波长范围扫描激光方式,将多个中心波长相近的低反射率光纤布喇格光栅放置于系统的不同位置,构成准分布式光纤传感系统,实现了多个传感点参量的同时测量.同时提出了采用掺铒光纤和喇曼混合放大方法来延长传感距离.在系统的中间加入一个喇曼泵浦进行喇曼放大以此补偿光纤布喇格光栅反射的信号,系统末端的掺铒光纤利用前面喇曼泵浦剩余的泵浦功率产生自发辐射光并放大传感信号,使得整个系统的传感距离延长.实验证实：将三只中心波长均在1 580 nm附近,反射率均小于4%的光纤布喇格光栅,分别放置在系统的不同位置,在200 km处获得了15 dB的信噪比,反射信号明显|并且在200 km处的静态应变和温度实验中,线性度均达到了0.999以上.     

On the elimination of DC in reconstructed wavefronts from in-line holograms

New experimental results to demonstrate that the annoying DC in the reconstructed wavefronts from in-line holograms could be successfully eliminated are presented in this paper. The complete elimination of DC has been achieved by making proper use of a Mach-Zehnder interferometer. The results for an in-line hololens and an in-line Fourier transform hologram are discussed. Contribution No. 8 from Laboratories for Coherent Optics and Electrooptical Research.