Enabling technologies for SCM basedoptically fed wireless communication systems

Basic configurations and system requirements for subcarrier multiplexing (SCM)-based optically fed wireless communication systems are summarized. The key issues for their fast deployment are improving performance and reducing the initial introduction cost. Major enabling technologies are introduced such as development of highly linear LDs, the multiple-LD method to improve carrier-to-noise ratio (CNR), super wideband frequency modulation to obtain a large power margin, and low-cost feeder design with a Fabry–Perot LD and multimode fiber. The introduction of optical feeders, which will increase the flexibility of the wireless system, is inevitable for providing multimedia services.     

Fricke and polymer gel 2D dosimetry validation using Monte Carlo simulation

Complexity in modern radiotherapy treatments demands advanced dosimetry systems for quality control. These systems must have several characteristics, such as high spatial resolution, tissue equivalence, three-dimensional resolution, and dose-integrating capabilities. In this scenario, gel dosimetry has proved to be a very promising option for quality assurance. In this study, the feasibility of Fricke and polymer gel dosimeters suitably shaped in form of thin layers and optically analyzed by visible light transmission imaging has been investigated for quality assurance in external radiotherapy. Dosimeter irradiation was carried out with a 6-MV photon beam (CLINAC 600C). The analysis of the irradiated dosimeters was done using two-dimensional optical transmission images. These dosimeters were compared with a treatment plan system using Monte Carlo simulations as a reference by means of a gamma test with parameters of 1 mm and 2%. Results show very good agreement between the different dosimetric systems: in the worst-case scenario, 98% of the analyzed points meet the test quality requirements. Therefore, gel dosimetry may be considered as a potential tool for the validation of other dosimetric systems.     

时间触发总线验证技术研究

TTP协议定义了一种高确定性,无冲突,高安全的通信总线,能够满足包括飞行控制等的安全关键实时控制系统的应用要求。时间触发总线验证技术根据TTP协议规范要求,针对研制的节点进行测试,包括基本通信测试、时钟同步、故障注入等不同的测试场景,充分验证被测节点的各项功能、性能。通过这些测试,表明被测节点各项指标都满足研制需求,可用于安全关键实时控制系统。     

Computer modeling of optical shadow-casting processor

Computing employing optical signal presupposes information being encoded optically. Many digital optical computing system employs pixel patterns to represent different logic level. Cellular logic, symbolic substitution, morphological and image processing could be performed on such pattern-coded information. Such systems have generally been analyzed by geometric optics. In this work, we propose to model such computing systems using laws of electromagnetic propagation. Results predicted by both geometric optics and the computer model are provided for a pattern-coded full adder/subtracter implementation. The model is general enough to be extended to other systems with more complicated coding pattern and could serve as design tool for optimizing a computing system using pattern-coded logic.     

Diffusion-induced Ramsey narrowing

Diffusion-induced Ramsey narrowing is characterized and identified as a general phenomenon, in which diffusion of coherence in and out of an interaction region such as a laser beam induces spectral narrowing of the associated resonance line shape. Illustrative experiments and an intuitive analytical model are presented for this spectral narrowing effect, which occurs commonly in optically interrogated atomic systems and may also be relevant to quantum dots and other solid-state spin systems.     

基于石墨烯的光学控制窄带太赫兹开关

本文提出了一种光控太赫兹开关,该开关采用覆盖单层石墨烯的十字金属谐振器超表面。利用石墨烯表面电导率模型和有限元法计算了这种复合结构的光谱特性。模拟结果表明,在0.2 W/mm²的光泵浦后,传输谱（调制深度为36.8%,Q-因子为250）出现了窄带共振衰减现象。另外,这种衰减的调制深度可以通过改变泵浦强度微调节。因此,光学可调谐太赫兹开关的设计将有助于太赫兹通信应用的功能组件开发。     

Implementation and Evaluation of Age-Aware Downlink Scheduling Policies in Push-Based and Pull-Based Communication

As communication systems evolve to better cater to the needs of machine-type applications such as remote monitoring and networked control, advanced perspectives are required for the design of link layer protocols. The age of information (AoI) metric has firmly taken its place in the literature as a metric and tool to measure and control the data freshness demands of various applications. AoI measures the timeliness of transferred information from the point of view of the destination. In this study, we experimentally investigate AoI of multiple packet flows on a wireless multi-user link consisting of a transmitter (base station) and several receivers, implemented using software-defined radios (SDRs). We examine the performance of various scheduling policies under push-based and pull-based communication scenarios. For the push-based communication scenario, we implement age-aware scheduling policies from the literature and compare their performance with those of conventional scheduling methods. Then, we investigate the query age of information (QAoI) metric, an adaptation of the AoI concept for pull-based scenarios. We modify the former age-aware policies to propose variants that have a QAoI minimization objective. We share experimental results obtained in a simulation environment as well as on the SDR testbed.     

Radio wave propagation in arch-shaped tunnels: Measurements and simulations by asymptotic methods

Several wireless communication systems are developed for communication needs between train and ground and between trains in the railway or mass transit domains. They are developed for operational needs for security and comfort. In order to deploy these systems in specific environments, such as tunnels, straight or curved, rectangular or arch-shaped section, specific propagation models have to be developed. A modelisation of the radio wave propagation in straight arch-shaped tunnels is realized by using asymptotic methods, such as Ray Tracing and Ray Launching, combined with the tessellation of the arched section. A method of interpolation of the facets' normals was implemented in order to minimize the error made when using the tessellation. Results obtained are validated by comparison to the literature and to measurement results.     

A comparison of optically and electronically controlled optical switches

Electronically and optically controlled optical switches are compared with respect to switch energy requirements. Only switches based on optical phase change are treated, since these have the largest flexibility. Further, only switches that preserve input wavelength at the output are considered, due to cascadeability requirements. It is argued that as long as ‘all-optical’ switches need electronically controlled switches for information transfer to the optical signals controlling the all-optical switch, this will compromise any other advantages that the all-optical switch and the corresponding systems might have. A further application for all-optical switches, which currently are orders of magnitude faster than electronically controlled ones, would be in banks of electronically controlled slower all-optical switches which are all-optically multiplexed to drive all-optical switches to data rates not currently achievable by electronically controlled switches. It is argued that such systems will be complex, requiring sophisticated electronic synchronization and being inferior to corresponding wavelength division multiplexing systems. Power dissipation and switch energy are analyzed for two different physical mechanisms for controllably changing the refractive index in the all-optical and electronically controlled optical switches: Pockels and Kerr effects as well as the plasma or free carrier effect and the relative merits of electronically and optically controlled optical switches using these are discussed. It is shown that, in the former case, (Pockels and Kerr effects) using representative data, electronically controlled switches are generally more power efficient than the all-optical counterparts.     

异面带状线馈电的宽带双极化蝶形天线

针对通信与雷达系统对双极化与宽带天线的要求,提出了一种基于带状线馈电的双极化蝶形天线。通过两对互相正交的蝶形阵子实现了天线的双极化,并采用一种新型的微带线转异面带状线的巴伦给两对正交蝶形阵子平衡馈电。异面带状线为平衡传输线,满足了蝶形阵子对于平衡馈电的要求。在馈电点处由同轴线对微带线馈电,经渐变微带线转化为异面带状线,最后由两组异面带状线给两对正交蝶形阵子馈电。测得该天线实现了69.23%的阻抗带宽,在6.8~14GHz频带内电压驻波比(VSWR)小于2。为使天线单向辐射且改善天线增益,将天线放置于反射吸收腔内。测得天线在6.8~18GHz的频宽内VSWR基本小于3,天线增益在8~12GHz频带内大于0.11dB,天线前后瓣比大于15dB。因此,所提出的双极化蝶形天线可用于宽带通信系统中。     

异面带状线馈电的宽带双极化蝶形天线

针对通信与雷达系统对双极化与宽带天线的要求,提出了一种基于带状线馈电的双极化蝶形天线。通过两对互相正交的蝶形阵子实现了天线的双极化,并采用一种新型的微带线转异面带状线的巴伦给两对正交蝶形阵子平衡馈电。异面带状线为平衡传输线,满足了蝶形阵子对于平衡馈电的要求。在馈电点处由同轴线对微带线馈电,经渐变微带线转化为异面带状线,最后由两组异面带状线给两对正交蝶形阵子馈电。测得该天线实现了69.23%的阻抗带宽,在6.8～14 GHz频带内电压驻波比(VSWR)小于2。为使天线单向辐射且改善天线增益,将天线放置于反射吸收腔内。测得天线在6.8～18 GHz的频宽内VSWR基本小于3,天线增益在8～12 GHz频带内大于0.11 dB,天线前后瓣比大于15 dB。因此,所提出的双极化蝶形天线可用于宽带通信系统中。     

Beam steering and deflecting device using step-based micro-blazed grating

The rapidly evolving demands of optical communications and optical switching systems have created a new market for high capacity all-optical beam steering and deflecting techniques. One technology potentially capable of realizing such systems uses the multistep micro-blazed grating optical beam deflectors based on binary and multiple-phase modulation methods. The micro-optical element has been fabricated by introducing very large scale integration (VLSI), stepping photolithography and reactive ion etching (RIE), which can realize beam steering, deflecting, splitting, and switching in free space, and its diffraction properties are determined by the blazed-grating parameters, such as the number of steps, grating depth, grating period, as well as blazed profile. The theoretical analysis and primarily experimental result show that this phase-type element has the advantages of high diffractive efficiency, low cross talk, small feature size, and high reliability due to nonmechanical beam steering without any moving parts. Hence it is ideally suited to applications in optical communication and optical interconnection network.     

Energy gaps and interaction blockade in confined quantum systems

We investigate universal properties of strongly confined particles that turn out to be dramatically different from what is observed for electrons in atoms and molecules. For a large class of harmonically confined systems, such as small quantum dots and optically trapped atoms, many-body particle addition and removal energies, and energy gaps, are accurately obtained from single-particle eigenvalues. Transport blockade phenomena are related to the derivative discontinuity of the exchange-correlation functional. This implies that they occur very generally, with Coulomb blockade being a particular realization of a more general phenomenon. In particular, we predict a van der Waals blockade in cold atom gases in traps.     

基于平行偏振光注入的1550nm波段垂直腔表面发射激光器获取窄线宽光子微波的理论和实验研究

提出一种基于1550 nm垂直腔表面发射激光器(1550 nm-VCSEL)获取高质量微波信号的全光方案.在该方案中,采用波长位于VCSEL中被抑制模式的中心波长附近、振动方向与VCSEL中主导模式相同的偏振光注入(即平行注入)1550 nm-VCSEL获取高频微波,并借助双光反馈对该高频微波的线宽进行窄化.一方面,基于VCSEL的自旋反转模型,从理论上分析了采用该方案产生微波信号的可行性;另一方面,通过构建相应的实验系统,对该方案产生的微波的特性进行初步实验研究.实验结果表明:在合适的注入条件下,1550 nm-VCSEL能够产生30 GHz左右的微波信号,但该信号的线宽较宽(百兆水平);引入双光反馈后,微波线宽可被压窄两个数量级以上,得到了线宽低于1 MHz、信噪比大于40 d B的微波信号.     

Chaotic breathers in delayed electro-optical systems

We show that in integro-differential delayed dynamical systems, a hybrid state of simultaneous fast-scale chaos and slow-scale periodicity can emerge subsequently to a sequence of Hopf bifurcations. The resulting time trace thereby consists in chaotic oscillations "breathing" periodically at a significantly lower frequency. Experimental evidence of this type of dynamics in delayed dynamical systems is achieved with a Mach-Zehnder modulator optically fed by a semiconductor laser and is subjected to a delayed nonlinear electro-optical feedback. We also propose a theoretical understanding of the phenomenon.     

A Review of Diffuse Discharge Opening Switches

The basic operation principles of externally controlled diffuse discharges with respect to their application as opening switches are discussed. Discharge sustainment by electron and UV ionization and additional control mechanisms, such as photodetachment and optically enhanced attachment, are considered. Special emphasis is given electron-beam (e-beam) controlled switches. For such systems, design criteria are discussed and a summary of experimental switch results is presented.     

Electrooptical oscillator using an integrated cutoff modulator

An integrated optical cutoff modulator is fed back electrically. In this way an electrooptical oscillator is built applicable as optical clock generator or electrical switchable oscillator for optical communication systems. Its center frequency is 380 MHz with a stability of 6 × 10^-5. The mode structure of the oscillator is investigated.     

Capacity limits of information transport in fiber-optic networks

The instantaneous optical Kerr effect in optical fibers is a nonlinear phenomenon that can impose limits on the ability of fiber-optic communication systems to transport information. We present here a conservative estimate of the "fiber channel" capacity in an optically routed network. We show that the fiber capacity per unit bandwidth for a given distance significantly exceeds current record experimental demonstrations.     

Terahertz band: Next frontier for wireless communications

This paper provides an in-depth view of Terahertz Band (0.1–10 THz) communication, which is envisioned as a key technology to satisfy the increasing demand for higher speed wireless communication. THz Band communication will alleviate the spectrum scarcity and capacity limitations of current wireless systems, and enable new applications both in classical networking domains as well as in novel nanoscale communication paradigms. In this paper, the device design and development challenges for THz Band are surveyed first. The limitations and possible solutions for high-speed transceiver architectures are highlighted. The challenges for the development of new ultra-broadband antennas and very large antenna arrays are explained. When the devices are finally developed, then they need to communicate in the THz band. There exist many novel communication challenges such as propagation modeling, capacity analysis, modulation schemes, and other physical and link layer solutions, in the THz band which can be seen as a new frontier in the communication research. These challenges are treated in depth in this paper explaining the existing plethora of work and what still needs to be tackled.     

Accurate sensitivity in optically preamplified direct detection

We present a novel model for calculating the bit error rate in optical communication systems in the case of on-off keying intensity modulation and optically preamplified direct detection. The model accounts for the intersymbol interference and is based on the Laguerre photon-count probability distribution predicted by photodetection theory. For a non-return-to-zero modulation format an accurate value of the sensitivity for a quantum-limited receiver of 33.9 photons/bit is obtained.