Exceptional-point-enhanced sensing in an all-fiber bending sensor

An exceptional-point(EP)enhanced fiber-optic bending sensor is reported.The sensor is implemented based on paritytime(PT)-symmetry using two coupled Fabry-Perot(FP)resonators consisting of three cascaded fiber Bragg gratings(FBGs)inscribed in an erbium-ytterbium co-doped fiber(EYDF).The EP is achieved by controlling the pumping power to manipulate the gain and loss of the gain and loss FP resonators.Once a bending force is applied to the gain FP resonator to make the operation of the system away from its EP,frequency splitting occurs,and the frequency spacing is a nonlinear function of the bending curvature,with an increased slope near the EP.Thus,by measuring the frequency spacing,the bending information is measured with increased sensitivity.To achieve high-speed and high-resolution interrogation,the optical spectral response of the sensor is converted to the microwave domain by implementing a dual-passband microwave-photonic filter(MPF),with the spacing between the two passbands equal to that of the frequency splitting.The proposed sensor is evaluated experimentally.A curvature sensing range from 0.28 to 2.74 m^(−1) is achieved with an accuracy of 7.56×10^(−4 )m^(−1 )and a sensitivity of 1.32 GHz/m^(−1),which is more than 4 times higher than those reported previously.

Investigation of frost heave prevention using permeable subgrade structure

This paper set up a series of comprehensive targets based on the concept of＇anti-freeze filler＇, which include reasonable water retention rate, frost heave characteristics, and compaction characteristics of filling material. Then, a type of permeable graded gravel is proposed, suitable for high-speed railway subgrade. A series of in-door water retention, permeability, and frost heave tests were performed under different graded conditions. Water retention, permeability, and frost heave characteristic of dif- ferent graded filling materials can be determined, in order to define the gradation range of permeable graded gravel. Relying on the frost-heave monitoring record of high speed railway in Northeast China, a series of experimental studies were per- formed, which included on-site filler production, compaction test, and the anti-frost effect test, in order to improve the pro- duction and compaction techniques of permeable graded gravel. From the research of this paper, the use of permeable graded gravel subgrade as the anti-frost structure for the high-speed railway subgrade in cold areas is feasible.

Large-capacity and low-loss integrated optical buffer

Trapping light in a photonic integrated circuit can findmany applications, such as optical storage, optical-packetswitching, optical sensing and microwave photonics. Althoughthere are many ways to implement an integrated opticalbuffer, such as the use of ring resonators, photonic crystals,Bragg gratings and spiral waveguides, it is still challenging torealize optical buffers with long storage time and low loss.Photonic integrated circuits with small size are of interest forimplementing optical buffers. In general, three materials systemsare employed to implement integrated optical buffers, silicon,silicon nitride and indium phosphide. However, it is hardto implement optical buffers with a storage time over tens ofnanoseconds due to the intrinsic high loss of these materials.

Investigation of insulation layer dynamic characteristics for high-speed railway

Dynamic performance of insulation is one of the key parameters during the insulation application for high-speed railway subgrade. This paper conducted laboratory and field tests for the materials and dynamic load, especially for thermal performance, elastic deformation, and accumulated deformation of insulation materials. Experiment results show that mechanical properties of insulation layer structure are stable, which satisfies the requirements of the high speed railway.

Investigation of monitoring system for high-speed railway subgrade frost heave

This paper presents methods for monitoring frost heave, device requirements, testing principals, and data analysis re- quirements, such as manual leveling observation, automatic monitoring （frost heave, frost depth, and moisture）, track dynamic detection, and track status detection. We focused on the requirements of subgrade frost heave monitoring for high speed railways, and the relationship of different monitoring methods during different phases of the railway. The com- prehensive monitoring system of high speed railway subgrade frost heave provided the technical support for dynamic design during construction and safe operation of the rail system.

Preface to the Special Issue on Semiconductor Optoelectronic Integrated Circuits

The past 20 years have witnessed the rapid growth of photonic integration circuits(PIC)technology,which has been warmly embraced by both academia and the industry.Powered by the advanced development in material growth,processing,and design capability,the PIC technology now covers multiple material platforms,including III–V(InP,GaAs),silicon,silica,lithium niobate on insulator(LNOI)polymer,etc.The integration level has evolved from a single functional device to thousands of components on-chip.The increase in the performance and the complexity of the PICs have become an energetic booster for communication and information technology.

光伏帮扶项目是如何实现政策效应的?——基于六村庄的田野调查分析

光伏扶贫是脱贫攻坚时期产业扶贫的重要方式之一,也是巩固脱贫成果、防止返贫的重要举措。本文基于对六个村庄的田野调查数据,通过分析光伏扶贫对于收入分配、产业发展和就业以及公共事务和基层治理等方面的效应,探讨光伏帮扶项目如何实现其政策效应。结果显示,村集体通过合理优化光伏收入分配机制,不仅实现了对无劳动能力贫困人口的兜底保障脱贫的战略目标,也促进了农村产业发展,增加了农业就业机会。同时,通过使用光伏帮扶收入设置公益性岗位,推动了农村公益而事业的发展,提高了村干部的威信和基层治理水平。

中国社会救助绩效评价指标体系构建研究——以城市居民最低生活保障制度为例

社会救助绩效评估工作开展较晚,并且早期主要围绕着最低生活保障制度进行探索。总体看来,现有社会救助绩效评估体系可以分为基于民政业务和跨民政业务两种模式。本文以最低生活保障为例构建指标体系,采用层次分析法赋予指标权重,在收集了沈阳市和广州市的相关数据对绩效指标体系进行验证分析之后,提出相关政策建议。

转型时期中国城镇亚贫困问题与相关社会政策研究

城镇亚贫困者是那些收入高于绝对贫困线但低于相对贫困线的人。由于我国目前城镇社会两极化非常严重,加上最低生活保障线的标准过低,亚贫困群体具有相当大的规模。城镇亚贫困问题是我国改革开放以后在社会经济转型过程中逐渐形成的。这些社会转型因素主要包括劳动收入分配制度改革、劳动就业方式的改变、社会保障制度改革、住房和教育制度的改革等等。本文在分析亚贫困问题产生的制度根源基础上,提出应当按照群体分类的原则分清目前城镇不同就业群体的社会政策受益,在此基础上依靠改革和完善社会政策体系来应对城镇亚贫困问题。

中国自然灾害生活救助标准的历史发展与政策启示

中国古代社会在救灾过程中就已经形成了一整套有效的自然灾害生活救助措施和方法。但在救助标准制定问题上,中国从古至今鲜有相关理论进行探讨。从古代社会至今中国历朝历代都对自然灾害采取种种生活救助措施并有一定的救助标准。总体看来,这些救助措施和标准之间有较强的相似性。古代至民国时期的官府自然灾害生活救助款物也会按照一定标准发放,但是很少有关于标准的制度性的规定。计划经济时期由于经济困难和自然灾害频繁等原因,自然灾害的生活救助主要是尽量避免饿死人的物质分配。与计划经济相适应,当时在巨灾面前还采取过实物供应制发放救灾物质。改革开放以后,国家在中央层面制定了全国统一的自然灾害生活救助标准,但是这些标准主要是基于实践经验的总结,而缺少科学的标准制定方法和论证。

Reconfigurable single-shot incoherent optical signal processing system for chirped microwave signal compression

We propose and demonstrate a reconfigurable and single-shot incoherent optical signal processing system for chirped microwave signal compression, using a programmable optical filter and a multiwavelength laser(MWL). The system is implemented by temporally modulating a specially shaped MWL followed by a suitable linear dispersive medium. A microwave dispersion value up to 1.33 ns/GHz over several GHz bandwidth is achieved based on this approach. Here we demonstrate a singleshot compression for different linearly chirped microwave signals over several GHz bandwidth. In addition, the robustness of the proposed system when input RF signals are largely distorted is also discussed.

Recent advances in optoelectronic oscillators

An optoelectronic oscillator(OEO)is a microwave photonic system that produces microwave signals with ultralow phase noise using a high-quality-factor optical energy storage element.This type of oscillator is desired in various practical applications,such as communication links,signal processing,radar,metrology,radio astronomy,and reference clock distribution.Recently,new mode control and selection methods based on Fourier domain mode-locking and parity-time symmetry have been proposed and experimentally demonstrated in OEOs,which overcomes the long-existing mode building time and mode selection problems in a traditional OEO.Due to these mode control and selection methods,continuously chirped microwave waveforms can be generated directly from the OEO cavity and single-mode operation can be achieved without the need of ultranarrowband filters,which are not possible in a traditional OEO.Integrated OEOs with a compact size and low power consumption have also been demonstrated,which are key steps toward a new generation of compact and versatile OEOs for demanding applications.We review recent progress in the field of OEOs,with particular attention to new mode control and selection methods,as well as chip-scale integration of OEOs.

Recent progresses on optical arbitrary waveform generation

这份报纸在光任意的波形产生(美国线规) 上考察最近的进步技术，它能被用来为波形产生打破电子学技术的速度和带宽瓶颈。为光学地产生的主要启用技术光并且微波波形在这被介绍并且考察纸例如印射技术的 wavelength-to-time ， space-to-time 印射技术，塑造的时间的脉搏( TPS )系统，光电子振荡器( OEO )，可编程的光过滤器，光微分器和综合者和万用的电镀物品眼的调整实现。这些光美国线规技术的主要优点和挑战也被讨论。

Polarimetric parity-time symmetry in a photonic system

Parity-time(PT)symmetry has attracted intensive research interest in recent years.PT symmetry is conventionally implemented between two spatially distributed subspaces with identical localized eigenfrequencies and complementary gain and loss coefficients.The implementation is complicated.In this paper,we propose and demonstrate that PT symmetry can be implemented between two subspaces in a single spatial unit based on optical polarimetric diversity.By controlling the polarization states of light in the single spatial unit,the localized eigenfrequencies,gain,loss,and coupling coefficients of two polarimetric loops can be tuned,leading to PT symmetry breaking.As a demonstration,a fiber ring laser based on this concept supporting stable and single-mode lasing without using an ultranarrow bandpass filter is implemented.

4×4 multiple-input multiple-output coherent microwave photonic link with optical independent sideband and optical orthogonal modulation

A 4× 4 multiple-input multiple-output coherent microwave photonic （MWP） link to transmit four wireless signals with an identical microwave center frequency over a single optical wavelength based on optical independent sideband （OISB） modulation and optical orthogonal modulation with an improved spectral efficiency is proposed and experimentally demonstrated. At the transmitter, the OISB modulation and optical orthogonal modulation are implemented to generate an OISB signal using a dual-parallel Mach-Zehnder modulator （DP- MZM） driven by four microwave orthogonal frequency-division multiplexing （OFDM） signals with an identical microwave center frequency. At the receiver, the OISB signal is coherently detected at a coherent receiver where a free-running local oscillator （LO） laser source is employed. Digital signal processing is then used to recover the four OFDM signals, to eliminate the phase noise from the transmitter laser source and the LO laser source, and to cancel the unstable wavelength difference between the wavelengths of the transmitter laser source and the LO laser source. Error-free transmission of three 16 quadrature amplitude modulation （16-QAM） 1 Gbps OFDM signals and one 16-QAM 1.5 Gbps OFDM signal at a microwave center frequency of 2.91 GHz over a 10 km single-mode fiber is experimentally demonstrated.

Introduction to the Microwave Photonics feature issue

Microwave photonics is a field that studies the interaction between microwave and optical waves for the generation,processing,control,and distribution of microwave signals by means of photonics.The key advantages of using photonics for microwave applications include wide bandwidth,low loss,and large tunability.In addition,the distribution of microwave signals over optical fibers can avoid a serious problem,electromagnetic interferences,especially in an electromagnetic-complex environment.The intention of this feature issue is to provide participants in the 2013 Asia Communications and Photonics Conference(ACP2013)with an opportunity to publish an account of their microwave photonics research as a peer-reviewed archival paper.

A special issue on Photonics Research in Canada

Canada has a long standing history of contributions to the field of photonics. Photonics research occurs at a number of universities across the country as well as in government research labs. The Canadian photonics industry includes small start-ups to large scale corporations, many of which are involved in research. It is estimated that photonics is a $6 billion industry in Canada that employs more than 24000 people. Photonics clusters can be found in Vancouver, Toronto, Ottawa, Montreal, and Quebec City---cities that are also home to universities where world renowned photonics research takes place.