A flexible receiver with fiber optical parametric amplifier in OCDMA-FSO communication system

A new receiver is proposed, which uses the fiber optical parametric amplifier（FOPA） in optical code division multiple access（OCDMA） over free space optic（FSO） communication system. The noise tolerance as the performance index in this receiver is derived. The receiver can not only improve the noise tolerance but also change the pump data conveniently for adapting to the length variation of the coding sequence under a complex and fast-changing weather condition. The influence of different factors on the noise tolerance is analyzed, and a significant improvement of about 18.77 d B for the noise tolerance can be achieved when the pump power and the length of coding sequence are 5 W and 256, respectively.     

Revisiting the doppler filter of LEO satellite GNSS receivers for precise velocity estimation

The theoretical aspects of the precise velocity determination of Low Earth Orbit (LEO) satellites’on board Global Navigation Satellite Systems (GNSS) receivers are derived. It shows that the receiver’s Phase Lock Loop (PLL) is required to feature extremely small group delay within its low frequency band, which is in contrast to existing work that proposed wide band linear phase filters. Following this theory, a Finite Impulse Response (FIR) filter is proposed. To corroborate, the proposed FIR filter and an Infinite Impulse Response (IIR) filter lately proposed in literals are implemented in a LEO satellite onboard GNSS receiver. Tests are conducted using a third party commercial GPS signal generator. The results show that the GNSS receiver with the proposed FIR achieves 11 mm/s R.M.S precision, while the GNSS receiver with the IIR filter has a filter-caused velocity error that can not be ignored for space borne GNSS receivers.     

基于服务器系统模型的光网络容量分析

In this paper, a new architecture of optical networks -- the optical network based on server system is considered. From the point of this new architecture, the network can be modeled as a server system with three type servers -- the access server, the node server and the link server. The network performances such as cost, energy consume and network capacity can be affected by the capability of these three type servers. New ILP formulations are proposed to analyze the network capacity under two types of node severs, with and without wavelength converter. Computer simulations are conducted to evaluate the effectiveness of these new formulations. The study has shown that the network can achieve the same throughput under the two types of node servers and the network throughput increases when the maximum allowed variation increases.     

Progress of Terahertz Devices Based on Graphene

Graphene is a one-atom-thick planar sheet of sp2-hybridized orbital bonded honeycomb carbon crystal. Its gapless and linear energy spectra of electrons and holes lead to the unique carrier transport and optical properties, such as giant carrier mobility and broadband flat optical response. As a novel material, graphene has been regarded to be extremely suitable and competent for the development of terahertz （THz） optical devices. In this paper, the fundamental electronic and optic properties of graphene are described. Based on the energy band structure and light transmittance properties of graphene, many novel graphene based THz devices have been proposed, including modulator, generator, detector, and imaging device. This progress has been reviewed. Future research directions of the graphene devices for THz applications are also proposed.     

Effect of PMD—induced Pulse Broadening on Sensitivity and Frequency Spectrum

The PMD-induced pulse broadening may cause the degradation of receiver sensitivity and has negative effects on the power spectrum of received signals,The expressions of PMD-induced pulse broadening effects on receiver sensitivity are derived based on the concept of mean square pulse width.The effects of PMD on the spectrum of received power are analyzed in detail.Finally,the scheme is discussed with which the power of a certain frequency component is extracted as a feedback control signal in a PMD compensation system.     

Novel two-layer motion estimation for video coding

In this paper,we proposed a novel Two-layer Motion Estimation （TME） which searches motion vectors on two layers with partial distortion measures in order to reduce the overwhelming computational complexity of Motion Estimation （ME） in video coding.A layer is an image which is derived from the reference frame such that the sum of a block of pixels in the reference frame determines the point of a layer.It has been noticed on different video sequences that many motion vectors on the layers are the same as those searched on the reference frame.The proposed TME performs a coarse search on the first layer to identify the small region in which the best candidate block is likely to be positioned and then perform local refined search on the next layer to pick the best candidate block in the located small area.The key feature of TME is its flexibility of mixing with any fast search algorithm.Experimental results on a wide variety of video sequences show that the proposed algorithm has achieved both fast speed and good motion prediction quality when compared to well known as well as the state-of-the-art fast block matching algorithms.     

Design for Y-branch waveguides with wide angle and low loss

A novel method to design Y-branch waveguides is proposed by using total internal reflection, and the optical properties areanalyzed. The simulated results show that the optical loss values of two Y-branch waveguides with the branching angles of 12° and 30° are only 0.310 dB and 0.645 dB, respectively. Compared with conventional Y-branch waveguides, the opticalperformance of the proposed ones is well improved, which has many advantages such as wide angle, low loss, simplestructure and easy for fabrication.     

Performance of non-coherent receiver with UWB PPM signal in multipath channels

Mainly due to its implementation simplicity, the non-coherent Ultra-Wide Band （UWB） receiver is attractive for lower data rate applications, which gains much attention again in recent years. In this paper, a General Likelihood Ratio Test （GLRT） based non-coherent receiver on UWB Pulse-Position-Modulation （PPM） signal in multipath channels is derived, and a novel structure is proposed as well. Subsequently, the closed-form expressions of asymptotic error-rate performance related to the non-coherent receiver are also derived and verified.     

Design and simulation of a novel CMOS superimposed photodetector

A novel superimposed photodetector(PD)is put forward.The photodetector can obtain a couple of differential photocur-rent signals from one input optical signal.The light injection efficiency and the vertical work distance of this new photode-tector are much higher than those of the others.The superimposed photodetctor is designed based on the standard 0.18μm CMOS process.The responsivity,bandwidth and transient response of the photodetector are simulated by a commercial simulation software of ATLAS.The responsivities of two obtained photocurrent signals are 0.035 A/W and 0.034 A/W,while the bandwidths are 3.8 GHz and 5.2 GHz,respectively.A full differential optical receiver which uses the superim-posed photodetector as input is simulated.The frequency response and 4 Gbit/s eye diagram of the optical receiver are also obtained.The results show that the two output signals can be used as the differential signal.     

Design and Implementation of a Cueing Wideband Digital EW Receiver

A cueing wideband digital Electronic Warfare （EW） receiver is presented. The proposed receiver, which is to measure the instantaneous frequency and bandwidth of the intercept short-duration pulse radar signals that cue and match the corresponding ones, meets the requirements of good sensitivity and dynamic range for EW and can save hardware resources greatly as well. In addition, real-time signal processing, which is the main bottleneck for covering a wide instantaneous frequency band for EW receiver, is better solved in the proposed design structure. The highly efficient implementation and good parameter estimation algorithms are proposed as welL Theoretical analysis and experimental results show that this structure is feasible.     

空间光通信广角接收馈源研究进展

为了将光通信一些优越性能应用于空间光探测、空间光通信和民用个人通信,在目前光纤只有非常小的数值孔径的情况下,需要对微弱空间光信号进行厂角接收,以便使接收角度达数十度、以致半个空间的光信号能进入光纤接收系统。然后可以对其中光信号进行光放大和处理。文章将空间光厂角接收馈源分为传统接收馈源和耦合入纤接收馈源两大类,着重于讨论后者。前者由于受制于光学系统和传统滤波器对视场角的限制,其灵敏度和视场角难以同时得到提高。而后者有望解除这些限制,真正实现对微弱空间光信号的非扫描式广角接收,应该是今后的发展方向,具有广泛应用前景。空间光厂角接收的实现将有力促进空间光通信、个人通信和光探测技术的发展,加大空间通信的带宽,对未来通信将产生不可估量的影响。     

室内MIMO ACO-OFDM可见光通信系统接收机设计

设计了一种在室内可见光MIMO通信系统(MIMO-VLC)中使用具有两个不同视场角(FOV)的光电二极管(PD)的角度分集光接收机(2FOV-ADR),其兼具两个不同视场角的接收机(2-FOV)和传统角度分集接收机(ADR)的优点,实现了更优的接收性能。对将LED灯用作数据发射器的典型室内可见光通信场景进行仿真,结果表明,2FOV-ADR均衡器输出端的最小信噪比(minSNR)要高于2-FOV接收机和传统ADR,实现了室内97%的位置的minSNR在45 dB以上,相比于前两种接收机,这一比例分别提高了96%和32%。最后,对使用非对称限幅光正交频分复用(ACO-OFDM)作为调制方案的系统,计算总误码率(BER),给出了迫零和最小均方误差均衡器的结果。结果表明,对于所考虑的室内位置,2FOV-ADR都具有最低的误码率。     

Analysis of diffuse optical wireless channels employing spot-diffusing techniques, diversity receivers, and combining schemes

In this letter, the performance of an indoor optical wireless spot-diffusing system using various multibeam transmitter configurations, in association with direction diversity and combining techniques, is assessed and compared under the impact of multipath dispersion and ambient light noise through theoretical analysis and computer simulation. Computer simulation for three different multibeam transmitter configurations and a conventional diffuse transmitter is carried out. Diversity receiver and wide field-of-view (FOV) receiver configurations are evaluated in conjunction with the proposed configurations. For the diversity-detection case, a receiver comprising an array of narrow FOV detectors (three and seven segments) oriented in different directions is used to maximize the collected signals and minimize noise. A novel line-strip multibeam system (LSMS) is investigated with single and diversity receiver configurations, and is compared with other spot-diffusing methods. Combining schemes, including selection combining, maximum ratio combining, and equal gain combining are employed for the presented configurations. Our results indicate that the performance improvement obtained through the use of LSMS with a three-direction diversity receiver is about 20 dB signal-to-noise ratio enhancement over the conventional diffuse system, and 26 dB when combining techniques are used. Root mean square delay-spread performance for the proposed configurations, at different positions on the communication floor, are also evaluated and compared.     

双自由曲面大视场头盔显示光学系统设计

视场大小是评价头盔显示器在虚拟现实等领域的关键性能指标,为了克服视场增加带来各类像差急剧增大的困难,提出了一种基于双自由曲面的大视场头盔显示光学系统。首先,分析了双椭球结构实现大视场与低畸变的基本原理,指出了其难以校正除畸变以外其他像差的原因。接着,提出根据系统对称性和光路走向采用竖直方向对称、水平方向不对称的自由曲面反射镜校正离轴像差,完成了基于双自由曲面反射镜的大视场头盔显示光学系统设计。系统视场范围为106.3(H)80(V),最大相对畸变为6.97%,出瞳直径8 mm,点眼距19 mm。单目系统向外倾斜8时,双目视场范围为122.3(H)80(V),双目重叠视场为90.3(H)80(V),瞳距在55~71 mm范围内可调节。对系统性能分析结果表明:相比双椭球结构,系统成像质量得到较大提高;视场范围和相对畸变满足虚拟现实领域的应用要求。     

大扫描视场红外椭球形整流罩光学系统设计方法

应用椭球形整流罩的飞行器具有良好的空气动力学特性,但由于头罩的非旋转对称结构特性,后续红外搜索/跟踪成像系统难以同时实现大扫描视场与良好成像质量.为解决这一难题,提出一种基于拱形校正元件和动态校正器的椭球形整流罩光学系统设计方法,使用该方法设计的中波红外头罩光学系统具有±54°的超大扫描视场,且成像质量在整个扫描和瞬时视场内接近衍射极限.     

Broadband Infrared Access with a Multi-Spot Diffusing Configuration: Performance

We evaluate transmission link performance for a Multi-Spot Diffusing Configuration (MSDC) for indoor wireless optical LANs. MSDC utilizes a multibeam transmitter and a composite receiver consisting of 7 narrow field-of-view (FOV) branches. Numerical evaluation is performed for two values of the receiver FOV corresponding to the cases when at least one or two diffusing spots are covered by a branch. Required optical power is used as a measure for MSDC link evaluation. The composite receiver provides angle diversity, which allows implementation of effective combining techniques. Selection Combining (SC) and Maximal Ratio Containing (MRC) methods have been analyzed. Our simulation results show that MSDC can reach much higher bit rates than a diffuse link can, without any channel equalization. MSDC link employing angle diversity receiver with larger FOV (each receiver branch capturing at least two diffusing spots) and using MRC method shows a promising performance for up to several hundreds of Mbps. System robustness against shadowing and blockage is also investigated. MSDC is more robust when an obstacle is located near the receiver, while this may cause severe problems in a diffuse link.     

Laboratory-simulation experiment for optical communication through low-visibility atmosphere using a diode laser

A laboratory-simulation experiment has been performed to determine the feasibility of exploiting the scattered (in addition to the unscattered) radiation to improve optical communication through low-visibility atmosphere. A multiple field-of-views (FOV) (0.043-0.945degfull angle) optical receiver was designed which utilizes a narrow-band interference filter (Deltalambda sim 15Å) for background-light suppression. The laser transmitter was a CW GaAlAs laser diode (lambda = 0.8486 mum) capable of emitting ∼ 7 mW power output of 15° divergent beam. Both polydisperse (particle diameters,din the range ofsim0.2-5.17 mum) and monodisperse (d sim 0.2 mum andd = 3.01 mum) latex spheres in water were used for simulating haze, fog, etc. Results include signal-to-noise ratio (SNR) and scattered-to-unscattered signal ratio as a function of field-of-view of reception for various optical thickness of the medium. Also, SNR is plotted as a function of optical thickness for various FOV's. The unique feature of this simulation is that it can simulate worst case solar background where the sun enters the FOV of receiver. Finally a new technique of estimating forward-scattering efficiency and root-mean-square forward scatter angle has also been presented with examples.     

气泡尾流光束衰减测量中的复散射校正

为了分析复散射对气泡尾流衰减测量的影响,采用小角度辐射传输方程,引入了表征复散射效应强弱的校正因子,通过数值求解分析了典型的尾流气泡尺度分布和数密度条件下复散射校正因子与接收视场角、光学厚度、光束大小和接收截面大小等参量之间的关系。结果表明,接收视场角在前向小角度范围内的变化对复散射校正因子的影响很大,而视场角较大时对复散射校正因子的影响基本相同;光学厚度的变化对复散射校正因子的影响显著,且在光学厚度小于1时,影响更明显;接收截面大小的变化在光学厚度小于1时对复散射校正因子的影响很小,但在光学厚度较大时,对复散射校正因子的影响比较明显;光束大小的变化对复散射因子的影响相对较小,且在光束束腰较大时对复散射因子的影响基本不变。该研究为尾流光束衰减测量条件的选择和优化提供了理论依据。     

New structure of optical homodyne receiver utilising a 4×4fibre directional coupler

A new structure of optical homodyne receiver based on a 4×4 fibre directional coupler is proposed. It has the characteristics of balanced detection, high receiving sensitivity, and the ability to tolerate wide laser linewidth     

Dragonfly‐Eye‐Inspired Artificial Compound Eyes with Sophisticated Imaging

The natural compound eye is a striking imaging device with a wealth of fascinating optical features such as a wide field of view (FOV), low aberration, and high sensitivity. Dragonflies in particular possess large, sophisticated compound eyes that exhibit high resolving power and information‐processing capacity. Here, a large‐scale artificial compound eye inspired by the unique designs of natural counterparts is presented. The artificial compound eye is created by a high‐efficiency strategy that combines single‐pulse femtosecond laser wet etching with thermal embossing. These eyes have a macrobase diameter of 5 mm and ≈30 000 close‐packed ommatidia with an average diameter of 24.5 μm. Moreover, the optical properties of the artificial compound eyes are investigated; the results confirm that the eye demonstrates advanced imaging quality, an exceptionally wide FOV of up to 140°, and low aberration.