基于高效轨道角动量态分离方法的复用系统方案研究

轨道角动量（OAM,orbital angular momentum）态可载荷信息,单个OAM态具有无穷大容量且不同OAM态间相互正交.基于OAM态复用的通信系统成为光通信和量子光学领域的研究热点之一.将高效OAM态分离方法应用于OAM态复用系统中,给出一种高效的OAM态通信复用方案.由于这种OAM态分离方法的特点,新方案可从OAM叠加态中同时解调出复用系统中不同轨道角动量态的载体信息,有效节省了复用系统接收端的解调设备,降低了OAM态复用系统的实现成本.数值仿真结果表明当系统信噪比大于23 dB时,系统误码率可以降至于10-4以下,本方案是一可行的OAM态复用方案.     

Analytical approach of developing the expression of output of all-optical frequency encoded different logical units and a way-out to implement the logic gates

To implement different all optical logic operations, encoding/decoding of optical signal is a very important issue. Since now there are so many types of optical signal encoding and decoding techniques have been adopted, such as intensity encoding, polarization encoding, phase encoding, symbolic substitution technique etc. All these existing techniques have their own limitations. In this context one may mention the frequency encoding/decoding technique. The basic inherent advantage of frequency encoding technique over all other existing techniques is that as the frequency of a signal is the fundamental character of it, it always preserves its identity throughout the communication of the signal, irrespective of reflection, refraction attenuation etc. Again, different optical signal has different distinct frequency which may be encoded as a distinct state of a logic system to represent the information. Adopting this technique it is possible to implement binary logic system as well as higher order logic system such as tristate logic, quaternary logic system etc. The major advantages of multivalued logic system over Boolean logic system are that in multivalued logic system the states of information is very more and as result information storage capacity is high. Again in multivalued logic system carry free and borrow free operation can be implemented which is less time consuming and therefore speed of operation is very fast. We have already developed methods of implementation of different all-optical frequency encoded logic as well as different optical processor. In this communication we propose an analytical approach to develop the expression of the outputs of frequency encoded different binary logic expression in terms of input frequencies from the stand point of basic laws of reflection, transmission and frequency conversion property of optical devices and of course mention the way-out to implement these logic operations.     

Improved online fountain codes based on shaping for left degree distribution

In this paper, an improved encoding scheme for online fountain codes is proposed with the joint optimization of variable node degree and check node degree is proposed. The coding scheme can be divided into the build-up phase and the completion phase. In the build-up phase, left degree distribution is exploited to guarantee optimal performance phase by modifying the traditional coding scheme of choosing input symbols uniformly at random. A memory-based selecting of the source symbols is employed to decrease the number of connected components, which can thus produce the dimension increasement of the linear subspace of a decoding graph constructed in the build-up phase. The upper bound on coding overhead is also derived from the analysis of random graph theory. Compared with conventional online fountain codes, it can be seen from the simulation results that the proposed scheme can provide significant performance improvement with respect to both coding overhead and feedback cost. Moreover, the lower encoding/decoding complexities may make the proposed scheme more practical in energy-constrained applications such as distributed storage.     

Cascading runlength-limited sequences

In magnetic or optical storage devices, it is often required to map the data into runlength-limited sequences. To ensure that cascading such sequences does not violate the runlength constraints, a number of merging bits are inserted between two successive sequences. A theory is developed in which the minimum number of merging bits is determined, and the efficiency of a runlength-limited fixed-length coding scheme is considered     

激光跨介质通信中跳时隙的编解码方法

跨介质无线光信道环境下散射吸收效应的出现会产生光强闪烁和光束漂移,造成激光光束传输性能下降,对数据传输产生干扰。为降低信息传输丢失概率、实现快速帧同步,提出一种跳时隙的脉冲位置调制编解码方法,通过研究跳时隙PPM编解码、信息组帧和传输技术,探讨系统实现方案。测试结果表明,采用跳时隙PPM字节组帧的信息传输技术,可进一步提升无线光信号传输抗干扰能力,收发双方依据约定的跳时隙通信规则,包括时隙类型组合、帧同步方式,有利于减小系统信息传输中被截获破译的机率,从而实现快速可靠通信。     

湍流大气对无线光通信影响分析及解决方案

分析了湍流大气光传输特性,讨论了光信号闪烁对宽带光无线通信误码率的影响及解决方案。从湍流大气的经典功率谱模型与修正功率谱模型出发,分析了Rytov指数与光场波长的变化关系,讨论了其对传输光场强度起伏的影响,以及分别在球面波与平面波时的差异。从实验上模拟考察了湍流大气对宽带光通信的影响,提出了一种新的从光链路上矫正波前畸变、减弱信号闪烁进而降低通信系统误码率的技术方案。该方案基于遗传算法和无模型盲优化的方式,以Zernike多项式系数为向量,对波前畸变进行编码,根据畸变波前的Zernike多项式的系数实现波前重构。其特点是没有预先测量波前相位畸变信息,而是采用施特列耳比作为遗传算法的适应度评判标准,通过优化达到最佳的波前畸变补偿效果。分析结果表明,该方案对中等强度以下的湍流大气光传输具有明显改善效果。     

Polarization- and Phase-Sensitive Low-Coherence Interferometry Setup for the Characterization of Integrated Optical Components

A novel phase-sensitive and polarization-sensitive scheme to implement an optical low-coherence interferometry (OLCI) system is presented. With respect to conventional phase-sensitive OLCI, in our system the interference fringes of the coherent light used to recover phase information are conveniently detected by the same photodetector acquiring the low-coherence signal. This strategy guarantees the intrinsic synchronization of the two signals at any acquisition speed, makes measurements more robust against long-term fluctuations in the experimental setup, and reduces the measurement time without affecting phase accuracy. The residual phase error after the phase recovery procedure is less than 0.01 rad, to the authors' knowledge one of the best results reported so far for OLCI measurements. Polarization sensitivity is achieved in the same setup by means of polarization selective retarders (PSRs) employed to couple light into and out of the device under test. This scheme enables to retrieve the time and frequency domain response of an optical device for both the polarization states from a single data acquisition. The presented technique is extremely versatile; it can be implemented by using either fiber or free space optics and applied to the characterization of generic optical devices. Its effectiveness is demonstrated by reporting the measurement of the amplitude and phase response of integrated optical devices based on ring resonators.      

Digital Applications of Thermoplastic Recording

Thermoplastic films' unique combination of thermal, electrical, and optical properties results in a versatile information storage medium which finds both digital and analog applications. As a digital storage medium, thermoplastic is best suited as a file memory where large capacity and rapid read access is a necessity. Reading and writing rates are completely independent. The fabrication of either sequential or random access devices using tapes or plates is possible. These couple high density capability with electron beam agility to provide large capacity storage and outstanding performance with regards to data transfer rates and read access. The recording medium consists of a substrate for mechanical carriage, a conductive film for heat developing, and the thermoplastic film. The recording process consists of writing line charges with a data-modulated electron beam and then developing with heat. The surface grooves which are formed can be read optically with a flying spot scanner. The position feedback Information inherent in the recorded data allows tracking along a single groove regardless of density.     

Modal Analysis of the Quasi-Optical Performance of Phase Gratings

This paper is concerned with the analysis of phase gratings as passive quasi-optical multiplexing devices. One important application of such components is in the local oscillator injection chain of heterodyne array receivers. Gaussian beam mode analysis can be applied as a powerful tool when modelling the optical performance of phase gratings in a real submillimeter system of finite throughput and bandwidth. In our experimental investigations we have concentrated on the Dammann Grating (DG) which is a binary optical component and thus straightforward to manufacture. A number of quartz gratings were fabricated and carefully tested to evaluate the practical limitations of such quasi-optical components. Because of its convenient refractive index quartz can be used to produce gratings with very low reflection losses. The results presented confirm DGs to be particularly suitable multiplexers for sparse arrays of finite bandwidth.     

Design, Fabrication and Characterization of an InP-Based Tunable Integrated Optical Pulse Shaper

In this paper a tunable integrated semiconductor optical pulse shaper is presented. The device consists of a pair of arrayed waveguide gratings with an array of electrooptical phase modulators in between. It has been fabricated in InP-InGaAsP material for operation at wavelengths around 1.55 mum. Multimode inputs to the waveguide gratings are used to flatten their optical passband. We have used a new short-pulse characterization technique to fully characterize pulse shaping by the device, i.e., both the power and the phase profile. A fourfold decrease in pulse ringing was observed for the devices with flattened passbands. Moreover these devices showed a 25% increase in pulse peak power. The possibilities for using the device as a dispersion (pre-) compensator have been investigated. Pulse reconstruction could be obtained for dispersion values of up to 0.2 ps/nm. The fabrication technology of the pulse shaper is compatible with the fabrication of integrated mode-locked lasers, which makes further integration of complete arbitrary pulse generators possible.     

Improved optical coding method for orthogonal ASK/DPSK modulation format

Orthogonal ASK/DPSK labeling, which encodes label information on optical carriers in a modulation format, is regarded as a competing scheme to subcarrier multiplexed optical labeling. However, the inherent cross-talk limits the extinction ratio (ER) of the payload and label sensitivity. In this paper, two optical coding methods-Manchester coding and 8B10B coding-which can remarkably improve the system quality to obtain acceptable ER are discussed. A novel optical packet encoding methodmark-insertion coding-is demonstrated to significantly reduce cross-talk between the amplitude shift keying ASK) payload and the differential phase shift keying (DPSK) label through spectrum shaping. The performance of mark-insertion coding depends on the number of inserted 'marks'. Finally, the transmission over a 40 km single mode fiber (SMF) is compared with optical label swapping for a. 40 Gbit/s ASK payload and 2.5 Gbit/s DPSK label under these coding schemes. The experimental result is consistent with the theoretical analysis.     

用光束轨道角动量实现相位信息编码

光束轨道角动量的本征态可实现高维量子信息的传输,将此特性用于信息的编码,可以提高数据编码的密度.提出了对八台阶结构相位编码的方法,根据相位旋转角的不同,来控制入射光束的相位延迟,进而实现相位信息的编码.讨论了基模高斯光束经过不同台阶后的螺旋谱分布,通过阵列功率探测器检测特定编码台阶结构对应的螺旋谱,区分不同的编码数据态,实现相位信息的解码.每个存储单元理论上可编码24 bits数据信息,是四台阶结构编码信息的3倍.     

Full Complex Amplitude Digital Holograms： Design, Fabrication and Optical Characterization

Diffractive optical elements have a large number of industrial applications, such as beam shaping and optical filtering. Traditionally, these elements modulate the phase of the incoming light or its amplitude, but not both. To overcome this limitation, full complex-amplitude modulation diffractive optical elements were developed. Well-established integrated circuit fabrication steps were employed to fabricate the devices with high precision. Using this approach, the new element‘s optical performances are improved also for near field operations. With this device it is possible to obtain 100% efficient spatial filtering and low noise reconstructed images.     

Send a hologram [photorefractive materials]

As computers and the Internet become faster and faster, more and more information is transmitted, received, processed, and stored everyday. The demand for high-speed, large-capacity information systems is pushing scientists and engineers to explore all possible approaches, including electrical and optical means. Photorefractive materials and devices are becoming viable alternatives for information systems. Photorefractive materials, including traditional electrooptic photorefractive crystals as well as photopolymers and photosensitive glasses, have demonstrated their potential in information systems. In this article we describe several applications of various photorefractive materials in information storage, processing, and communication systems. Specifically, we briefly discuss the applications of the traditional electrooptic photorefractive crystals and photopolymers in volume holographic data storage (VHDS) and information processing. Then, we discuss our recent works on the applications of photopolymers, holographic polymer dispersed liquid crystals (H-PDLC), and photosensitive glasses in photonic devices for optical fiber communications.     

杨氏双缝干涉实验测量涡旋光束的轨道角动量

研究了平面波经过螺线型相位板后产生的涡旋光束,经双缝干涉后在干涉场中干涉条纹的分布情况。详细介绍了涡旋光束的拓扑荷数对干涉条纹分布的影响。发现同平面波的竖直干涉条纹相比较,涡旋光束的干涉条纹,从顶部向底部看去,沿着横向出现移动,并且移动的大小和方向与拓扑荷数的取值有关。通过观测干涉条纹,可以得到涡旋光束的拓扑荷数。涡旋光束由于携带轨道角动量可应用于新型的光信息编码与传输,研究结果可望在这种新型的光信息编码与传输中得到应用。     

Converged Wireless and Wireline Access System Based on Optical Phase Modulation for Both Radio-Over-Fiber and Baseband Signals

We propose and experimentally investigate a scheme for transmitting a phase-modulated radio-over-fiber (RoF) signal along an existing fiber infrastructure without degradation of the existing baseband signal. Optical phase encoding of both signals, namely a baseband 21.4-Gb/s nonreturn-to-zero differential quaternary phase-shift keyed signal and a 5.25-GHz RoF carrying 1.25 Gb/s, enables the use of identical optical receiver structures. The experimental results show that both receivers achieve error-free operation after 80-km standard single-mode fiber transmission. The proposed scheme has potential applications for converged wireless and wireline optical access networks.      

一种新型芴类衍生物的双光子光致漂白三维光存储

基于光致漂白的双光子吸收三维光信息存储原理,以钛蓝宝石飞秒脉冲激光在一种新型光致漂白材料芴类衍生物BMOSF中进行光致漂白双光子信息写入和读出的实验研究,实现了6层光信息存储,信息点间距和信息层间距分别为8和10μm;采用MATLAB软件对6层信息点进行信号强度识别和信号点强度对比.实验表明,芴类衍生物BMOSF可以用...     

Nonuniform Spectral Phase Encoding in Optical CDMA Networks

We utilize a nonuniform encoding scheme for spectral phase encoding in optical code-division-multiple-access networks. This method improves the orthogonality of encoded waveforms between multiple users under synchronous transmission by compensating for the nonideal spectral shape of the subpicosecond mode-locked laser pulse source. Simulation results demonstrate five orders of magnitude of bit-error-rate reduction compared with the traditional uniform encoding scheme     

Low-complexity video coding via power-rate-distortion optimization

Wireless multimedia sensor networks (WMSNs) have been potentially applicable for several emerging applications. The resources, i.e., power and bandwidth available to visual sensors in a WMSN are, however, very limited. Hence, it is important but challenging to achieve efficient resource allocation and optimal video data compression while maximizing the overall network lifetime. In this paper, a power-rate-distortion (PRD) optimized resource-scalable low-complexity multiview video encoding scheme is proposed. In our video encoder, both the temporal and interview information can be exploited based on the comparisons of extracted media hashes without performing motion and disparity estimations, which are known to be time-consuming. We present a PRD model to characterize the relationship between the available resources and the RD performance of our encoder. More specifically, an RD function in terms of the percentages for different coding modes of blocks and the target bit rate under the available resource constraints is derived for optimal coding mode decision. The major goal here is to design a PRD model to optimize a “motion estimation-free” low-complexity video encoder for applications with resource-limited devices, instead of designing a general-purpose video codec to compete compression performance against current compression standards (e.g., H.264/AVC). Analytic results verify the accuracy of our PRD model, which can provide a theoretical guideline for performance optimization under limited resource constraints. Simulation results on joint RD performance and power consumption (measured in terms of encoding time) demonstrate the applicability of our video coding scheme for WMSNs.