Abstract:Visible Light Communication (VLC) attracts more and more interest since the combination of optical wireless communication with LED.LED array also becomes much popular in order to improve indoor lighting,so the VLC-MIMO based on LED array has arisen.The baseband processing of the VLC system is introduced in this paper,followed by two VLC-MIMO systems and the research progresses of Space-Time Block Code in VLC-MIMO.The physical channel processing and multiple antenna technology in long term evolution are discussed,and the future development of VLC system is predicted.

Abstract:In order to satisfy the service demands with different granularities and maximize the spectral efficiency of wavelength division multiplexing transmission,the optical network is evolving to agile and energy-efficient one.Consequently,the flexible optical transmission techniques based on bandwidth variable transceivers (BVT) have attracted worldwide attention and research interest.We review recent progresses of flexible optical transmission techniques including transmitter-side adaptive modulation,variable bit-rate loading and receiver-side corresponding modulation formats identification.Finally,we outline the prospects and future challenges in this area.

Abstract:Distributed fiber sensors based on phase-sensitive optical time domain reflectometer (Φ-OTDR) show great potential applications in the field of perimeter security intrusion and structural health monitoring.This paper reviews the principle of Φ-OTDR for sensing,and the recent development of Φ-OTDR in aspects of light source,sensing head,detection method,multiplexing technology and signal processing.

Abstract:The progress of graphene-silicon optoelectronic devices is reviewed.With the development of science and technology,the demand on aspects of information capacity,transmission speed,processing speed,energy consumption and production cost is growing quickly.In recent years,low-cost,high-speed and high-density integrated silicon-based optoelectronic technology has been booming.Soon after its discovery,graphene has attracted much attention for its marvelous optical and electrical properties.Recently,the research of graphene-silicon based optoelectronic devices has rapidly become a research hotspot,and has made a breakthrough.Compared with traditional silicon-based optoelectronic devices,graphene-silicon-based optoelectronic devices have many advantages such as low power consumption,small temperature drift,large bandwidth and controllable bandgap.The present work is a review of the development of graphene-silicon-based optoelectronic devices including optical modulator,photodetector,polarization controller and so on.

Abstract:As a new wireless communication technology combined illumination with communication,visible light communication has become attractive recently.Optical antenna plays a significant role in visible light communication system for it can optimize the light intensity distribution,enhance the received optical power,and improve the signal to noise ratio of the system.Research on optical antenna is mainly focused on the transmitting antenna or the receiving antenna.Transmitting antenna is usually combined with LED optical design,which can be divided into collimation type,uniform illumination type,and focus type according to the light intensity distribution.Receiving antenna uses composite parabolic concentrator (CPC),Fresnel lens or other optical components as the optical receiving front end to enhance the received optical power.In this paper,the research of optical antenna at home and abroad is introduced.The optical performance of the optical antenna is evaluated and compared,and finally the development trend of the optical antenna is forecasted.

Abstract:Various indoor positioning techniques have been developed and widely applied in both manufacturing processes and people's lives.Due to the electromagnetic interference and multipath effects,traditional Wi-Fi,Bluetooth and other wireless locating technologies are difficult to achieve high accuracy.Modulated white LED can provide both illumination and location information to achieve highly accurate indoor positioning.In this paper,we first introduce several modulation methods of visible light positioning systems and compare the characteristics of different modulation methods.Then,we propose a viable indoor positioning scheme based on visible light communications and discuss two different demodulation methods.In the following,we introduce several positioning algorithms used in visible light communication system.Finally,the problems and prospects of the visible light communication based indoor positioning are discussed.

Abstract:In the field of microwave photonics,microwave photonic phase shifter plays a key role in signal processing technology.The main component of this technology is the modulator,which can be driven by electrical signal or radio frequency signal to control the optical signal.Then the phase response of the optical signal can be adjusted through optical device.Thus the phase shift of the optical signal can be achieved in the electronic domain.It has the advantages of high linearity,good tenability and wide band,etc.In this paper,the mechanism of microwave photonic phase shifter is introduced briefly,and then several typical schemes and their latest applications are summarized.It is pointed out that microwave photonic phase shifter is expected to lead to an innovation in the field of microwave photonics.

Abstract:With the deepening study of nonlinear effect in optical fiber,the distributed optical fiber sensor has been widely studied and applied.In this paper,the application of optical fiber sensor is introduced.To realize different types of fiber distributed sensing,the principle of three kinds of scattered light based on Brillouin scattering,Raman scattering,and Rayleigh scattering is summarized.Finally,the future development direction of fiber distributed sensing is prospected.

Abstract:Due to the relatively low sampling rate of current commercial polarization state analyzers,a specialized measurement system will need to be built with the use of high-speed real-time digital oscilloscopes if the detection of polarization state for a high-speed signal is required.At this point,the system calibration becomes particularly important,and the calibration method will directly decide the measurement accuracy.A calibration method is proposed for an optical fiber high-speed polarization state detection system.This method is theoretically analyzed by Mueller matrix,and then it is proved that the calibration method is feasible and accurate,of which the measurement error is less than ±3%.

Abstract:In order to increase the effective area of image sensor and to avoid the interruption of communications in optical camera communications (OCC),a novel non-line-of-sight (NLOS) OCC scheme is proposed,which uses a high-resolution image sensor to receive completely a data packet within a single frame.The NLOS channel profits the mitigation of the blooming effect from the optical source,and also the increment of effective area of an image sensor for communications.Furthermore,the high-accuracy synchronization scheme has been adopted for the integration of multiple pixel columns to mitigate the signal loss in an NLOS channel.High-resolution image sensor has been applied for fast signal variation,as well as the increment of both synchronization accuracy and the data rate.The performances of OCC system with the data rate of 2.15 kpbs and a link range of 1.5 m has been verified experimentally.It has shown that a data packet of 16 bits could be reliably received within a single frame,which is applicable for indoor positioning and navigation,photonics labeling,and so on.

Abstract:We present an ARQ-FSO system,which consists of pulse position modulation (PPM) hard decision and a novel automatic repeat request (ARQ) protocol.Instead of traditional ARQ's data error detection,the PPM hard decision results are used to find data error.Then the transmitter only retransmits the failed decoded portion of the packet.These measures can eliminate the information redundancy of traditional ARQ and enhance the system efficiency.Theoretical analysis shows that the ARQ-FSO system can effectively improve the BER performance of the direct hard decision PPM system.Additionally,the proposed system significantly improves the average throughput efficiency compared with traditional ARQ systems.These characteristics make this ARQ-FSO system suitable to apply in low BER and low complexity FSO communications.

Abstract:Mode division multiplexed (MDM) in few mode fibers has gained attraction due to its potential to achieve ultra-high capacity beyond the nonlinear Shannon limit of the single mode fiber.Meanwhile,polarization division multiplexing (PDM) can make the system transmission capacity doubled without changing the fiber link.The combination of MDM and PDM can provide much more capacity up to several hundreds Gbit/s.However,it cannot be ignored that the effect of mode coupling and differential mode group delay on optical signals exists in transmission and mitigating these impairments is required in this multiplexing.This paper focuses on the frequency domain least mean square (LMS) digital equalization for MDM with PDM in few mode fiber system.A modified frequency domain LMS algorithm is proposed,which is operated with a butterfly finite impulse response (FIR) filter by means of modifying equations according to average power in each frequency bins.Simulation results show that the modified algorithm can improve the convergence speed and the system performance compared with traditional algorithm.

Abstract:Optical signal suffers from fluctuations in both intensity and phase due to the random refractive index variations induced by atmospheric turbulence.Meanwhile,system performance degradation due to urban fog/haze also should not be ignored.Given slowly time-varying characteristics of turbulent phase variations and laser phase noise,decision-aided,maximum likelihood (DAML) phase estimation algorithm is employed in free space coherent optical communication system to improve system performance.Then,BER performance of DAML system with DQPSK modulation is investigated considering the influences of atmospheric turbulence,laser phase noise and weather conditions.Transmission distance and wavelength selectivity is also analyzed in fog/haze weather.Simulation results show that turbulent phase noise can be ignored with less than 0.1 dB signal-to-noise ratio penalty compared with no turbulence.And in fog and haze weathers,free space coherent optical communication with DAML algorithm has longer transmission distance than OOK IM/DD free space optical communication,at least 500 meters.DAML system with 1 550 nm wavelength has better performance than that with 850 nm wavelength in haze and light fog weathers.But system performance is independent of wavelength in thick fog weather when visibility is less than 200 meters.

Abstract:In this paper,we investigate and compare the performance of three digital signal processing (DSP) based transmission technologies for indoor visible light communication (VLC).These schemes include orthogonal frequency division multiplexing (OFDM),single carrier frequency domain equalization (SCFDE),and single-carrier frequency division multiplexing (SCFDM).Particularly,we analyze their peak-to-average power ratio (PAPR) and computational complexity for comparison.Our results indicate that SCFDE and SCFDM system have relatively low PAPR while SCFDM has the highest complexity.Besides,we present a hardware prototype for the three modulation methods using a white LED lamp.Experimental results show that,due to their low PAPR,SCFDE and SCFDM outperform OFDM in aspects of bit error rate (BER) and Q factor performances in VLC transmission.

Abstract:Feature extraction of instantaneous frequency is the key for fault diagnosis of rotating machines,considering that the vibration signals of bearing are usually potential and very weak for dynamic response.A new STFT-SC (Short Time Fourier Transform and Seam Carving) feature extraction method is thus proposed which can estimate instantaneous frequency of vibration signal of rolling bearings.Seam Carving method,usually applied in the field of image processing,is revised according to the characteristics of the rolling bearing.Instantaneous frequency of the vibration signal is estimated using the STFT,then the first order Seam route is solved using the energy gradients of Seam Carving and dynamic planning method;finally,the first order signal is reconstructed and compared with the simulated signal.Results show that the proposed STFT-SC method is effective and quick for estimation of vibration signal even under interference of strong noise and adjacent order components of signal.

Abstract:The lightning characteristics and variation trends in Sanming of Fujian provinceare analyzed based on lightning monitoring data from 1981 to 2013,and the vulnerability risk zoning of lightning disaster are made for period of 2003-2013.Lightning vulnerability indicators,including cloud to ground lightning density(N_g),the frequency of lightning disaster(P),economic vulnerability module(D),and vital vulnerability module(L),are selected as indexes for risk assessment of regional lightning disaster and comprehensive evaluation of the vulnerability of Sanming city and its 10 counties.The weights of the lightning vulnerability indicators are calculated based on investigation and questionnaire.Finally,Sanming's lightning vulnerability zoning map is made,which provides scientific basis and valuable reference for the reasonable planning of lightning disaster prevention and reduction in Sanming.