Single Photon Detection Technology in Underwater Wireless Optical Communication:Modulation Modes and Error Correction Coding Analysis

This study explores the application of single photon detection(SPD)technology in underwater wireless optical communication(UWOC)and analyzes the influence of different modulation modes and error correction coding types on communication performance.The study investigates the impact of on-off keying(OOK)and 2-pulse-position modulation(2-PPM)on the bit error rate(BER)in single-channel intensity and polarization multiplexing.Furthermore,it compares the error correction performance of low-density parity check(LDPC)and Reed-Solomon(RS)codes across different error correction coding types.The effects of unscattered photon ratio and depolarization ratio on BER are also verified.Finally,a UWOC system based on SPD is constructed,achieving 14.58 Mbps with polarization OOK multiplexing modulation and 4.37 Mbps with polarization 2-PPM multiplexing modulation using LDPC code error correction.

Training-based symbol detection with temporal convolutional neural network in single-polarized optical communication system

In order to reduce the physical impairment caused by signal distortion,in this paper,we investigate symbol detection with Deep Learning(DL)methods to improve bit-error performance in the optical communication system.Many DL-based methods have been applied to such systems to improve bit-error performance.Referring to the speech-to-text method of automatic speech recognition,this paper proposes a signal-to-symbol method based on DL and designs a receiver for symbol detection on single-polarized optical communications modes.To realize this detection method,we propose a non-causal temporal convolutional network-assisted receiver to detect symbols directly from the baseband signal,which specifically integrates most modules of the receiver.Meanwhile,we adopt three training approaches for different signal-to-noise ratios.We also apply a parametric rectified linear unit to enhance the noise robustness of the proposed network.According to the simulation experiments,the biterror-rate performance of the proposed method is close to or even superior to that of the conventional receiver and better than the recurrent neural network-based receiver.

Green indoor optical wireless communication systems:Pathway towards pervasive deployment

The Optical Wireless Communication(OWC)offers the high capacity of optical fiber communication with the flexibility of wireless communication.Since it works in the optical region of the ElectroMagnetic(EM)spectrum,it guarantees safety and security which are critical in radio and microwave frequency communication.The principal objective of this paper is to analyze the indoor OWC systems on these guaranteed features,and safety and security are jointly denoted by the term green.The high obstacle impermeability of optical signals and their directivity strengthen the security of indoor OWC data transmission.The confidentiality and authenticity of optical wireless data can also be preserved with the Quantum Key Distribution(QKD).This paper provides a technological overview and a review of literature about the OWC system that helps to identify the challenges in the path of a ubiquitous deployment of green wireless communication systems.Significant advancements in the sources and detectors are discussed together with the coding,modulation and multiplexing techniques for making highly robust OWC links.The ubiquitous deployment of green OWC necessitates the development of optical transmitters and receivers,performance enhancement techniques,incorporation of uplink and energy harvesting abilities,and safety and security enhancement techniques.Hence,a special emphasis is placed on these aspects and their challenges towards the green implementation.Furthermore,the paper explores some significant indoor applications based on the OWC that have great impacts on the Next Generation Networks(NGN)and the Internet of Things(IoT).

Efficient stochastic parallel gradient descent training for on-chip optical processor

In recent years,space-division multiplexing(SDM)technology,which involves transmitting data information on multiple parallel channels for efficient capacity scaling,has been widely used in fiber and free-space optical communication sys-tems.To enable flexible data management and cope with the mixing between different channels,the integrated reconfig-urable optical processor is used for optical switching and mitigating the channel crosstalk.However,efficient online train-ing becomes intricate and challenging,particularly when dealing with a significant number of channels.Here we use the stochastic parallel gradient descent(SPGD)algorithm to configure the integrated optical processor,which has less com-putation than the traditional gradient descent(GD)algorithm.We design and fabricate a 6×6 on-chip optical processor on silicon platform to implement optical switching and descrambling assisted by the online training with the SPDG algorithm.Moreover,we apply the on-chip processor configured by the SPGD algorithm to optical communications for optical switching and efficiently mitigating the channel crosstalk in SDM systems.In comparison with the traditional GD al-gorithm,it is found that the SPGD algorithm features better performance especially when the scale of matrix is large,which means it has the potential to optimize large-scale optical matrix computation acceleration chips.

Single‑Layer ZnO Hollow Hemispheres Enable High‑Performance Self‑Powered Perovskite Photodetector for Optical Communication

The carrier transport layer with reflection reduction morphology has attracted extensive attention for improving the utilization of light.Herein,we introduced single-layer hollow ZnO hemisphere arrays(ZHAs)behaving light trapping effect as the electron transport layer in perovskite photodetectors(PDs).The singlelayer hollow ZHAs can not only reduce the reflection,but also widen the angle of the effective incident light and especially transfer the distribution of the optical field from the ZnO/FTO interface to the perovskite active layer confirmed by the 3D finitedifference time-domain simulation.These merits benefit for the generation,transport and separation of carriers,improving the light utilization efficiency.Finally,our optimized FTO/ZHA/CsPbBr3/carbon structure PDs showed high self-powered performance with a linear dynamic range of 120.3 dB,a detectivity of 4.2×10^(12) Jones,rise/fall time of 13/28μs and the f_(−3) dB of up to 28 kHz.Benefiting from the high device performance,the PD was demonstrated to the application in the directional transmission of encrypted files as the signal receiving port with super high accuracy.This work uniquely utilizes the features of high-performance self-powered perovskite PDs in optical communication,paving the path to wide applications of all-inorganic perovskite PDs.

Novel graphene enhancement nanolaser based on hybrid plasmonic waveguides at optical communication wavelength

Surface plasmon polariton （SPP） nanolaser, which can achieve an all-optical circuit, is a major research topic in the field of micro light source. In this study, we examine a novel SPP graphene nanolaser in an optoelectronic integration field. The proposed nanolaser consists of metallic silver, two-dimensional （2D） graphene and high refractive index semiconductor of indium gallium arsenide phosphorus. Compared with other metals, Ag can reduce the threshold and propagation loss. The SPP field, excited by coupling Ag and InGaAsE can be enhanced by the 2D material of graphene. In the proposed nanolaser, the maximum value of propagation loss is approximately 0.055 dB/~tm, and the normalized mode area is con- stantly less than 0.05, and the best threshold can achieve 3380 cm l simultaneously. Meanwhile, the proposed nanolaser can be fabricated by conventional materials and work in optical communication （1550 nm）, which can be easily achieved with current nanotechnology. It is also an important method that will be used to overcome the challenges of high speed, miniaturization, and integration in optoelectronic integrated technology.

Petahertz communication:Harmonizing optical spectra for wireless communications

With the rapid deployment of Next-Generation Networks(NGN),the research community has initiated discussions on an entirely new suite of optical enabling techniques.To pave the way for the development of future wireless networks,this article aims to unify the existing infrared,visible light,and ultraviolet subbands while also exploring the potential of the Petahertz(PHz)band to support extremely bandwidth-thirsfy telepresence style applications.Our focus is on the emerging Petahertz Communication(PetaCom)framework,scenario-dependent propagation channels,modulation schemes,system performance,multiple access techniques,and networking.We conclude with a range of PetaCom challenges and open research issues.

Research on Dispersion Compensation of 40 GB/s Optical Duo-Binary Coded Transmission System

A 40 Gb/s high speed optical transmission system is designed, and the different dispersion compensation schemes are adopted to realize the transmission of the optical duo-binary (ODB) signals over 120 km optical fiber. Optical duo-binary signals are generated by using a precoder, two low- pass filters (LPF) and one mach-zehnder modulator (MZM). Through combination of dispersion compensation fiber (DCF) and single mode fiber (SMF) in the transmission link, four different dispersion compensation schemes (pre-compensation, post-compensation and hybrid compensation (pre+ post) and hybrid compensation (post+ pre)) were compared. Analyzing Q factor, BER, eye diagrams and receiver sensitivity in several dispersion compensation schemes, the simulation results are: the cut-off frequency of LPF affects the transmission performance, and the hybrid compensation (post+ pre) scheme is the optimal dispersion compensation method.

Acquisition performance analysis for intersatellite optical communications with vibration influence

A stable and accurate pointing,acquisition system is an important part of initially building intersatellite optical communication links.Satellite platform vibration can cause the system instability and reduce the system precision in building and maintenance of a satellite optical communication system.In this paper,vibration influence is consciously discussed by acquisition time for intersatellite optical communications.Analytical expression of acquisition possibility is derived,taking the scan parameters and platform vibration into account,and vibration influence on the multi-scan acquisition time is also presented.The theoretical result calculated by the proposed analytical expression is approximate to the result by the Monte Carlo simulation.

Proposed Different Signal Processing Tools for Efficient Optical Wireless Communications

Optical Wireless Communication(OWC)is a new trend in communication systems to achieve large bandwidth,high bit rate,high security,fast deployment,and low cost.The basic idea of the OWC is to transmit data on unguided media with light.This system requires multi-carrier modulation such as Orthogonal Frequency Division Multiplexing(OFDM).This paper studies optical OFDM performance based on Intensity Modulation with Direct Detection(IM/DD)system.This system requires a non-negativity constraint.The paper presents a framework for wireless optical OFDM system that comprises(IM/DD)with different forms,Direct Current biased Optical OFDM(DCO-OFDM),Asymmetrically Clipped Optical OFDM(ACO-OFDM),Asymmetrically DC-biased Optical OFDM(ADO-OFDM),and Flip-OFDM.It also considers channel coding as a tool for error control,channel equalization for reducing deterioration due to channel effects,and investigation of the turbulence effects.The evaluation results of the proposed framework reveal enhancement of performance.The performance of the IM/DD-OFDM system is investigated over different channel models such as AWGN,log-normal turbulence channel model,and ceiling bounce channel model.The simulation results show that the BER performance of the IM/DD-OFDM communication system is enhanced while the fading strength is decreased.The results reveal also that Hamming codes,BCH codes,and convolutional codes achieve better BER performance.Also,two algorithms of channel estimation and equalization are considered and compared.These algorithms include the Least Squares(LS)and the Minimum Mean Square Error(MMSE).The simulation results show that the MMSE algorithm gives better BER performance than the LS algorithm.

Vehicle Positioning Based on Optical Camera Communication in V2I Environments

Demand for precise vehicle positioning(VP)increases as autonomous vehicles have recently been drawing attention.This paper proposes a scheme for positioning vehicles on the move based on optical camera communication(OCC)technology in the vehicle-to-infrastructure(V2I)environment.Light-emitting diode(LED)streetlights and vehicle cameras are used as transmitters and receivers respectively.Regions of streetlights are detected and traced by examining images that are obtained from cameras of vehicles.Then,a scheme for analyzing visible light data extracted from the images is proposed.The proposed vehicle positioning scheme uses information on angles between vectors that are formed under the collinearity conditions between the absolute coordinates of at least three received streetlights,and the coordinates of an image sensor.The experiments are performed under stationary state and moving state at a speed of 5 and 20 km/h.To verify the reliability of the proposed scheme,a comparison is made between the actual and estimated location of the camera in the stationary state.In addition,the path of a moving vehicle and the estimated path of the vehicle are compared to check the performance of the scheme.The performance of the proposed technique is analyzed and experimental demonstration confirms that the proposed OCC-based VP scheme achieves positioning accuracy of under 1 m.

Printable Optical Filters for Visible Optical Communications

The design, production and characterization of tailored printable optical filters for visible optical communications are demonstrated. As result, the average color difference between the specified and the produced filters is 32.6, quantified in terms of CIELAB coordinates.

Optical Wireless Communications

The optical spectrum can serve as a good spectrum resource for wideband wireless communications. The advantages of optical wireless communications （OWC） mainly lie in two aspects： the potential large transmission bandwidth due to the high-frequency carrier, and thecommunication security due to no radio-frequency radiation. Thus OWC can be applied in the seenarios where the radio silence is required or the radio frequency radiation may cause explosions, for example in the battle field or some special ar- eas in the storehouses.

Short-Range Optical Wireless Communications for Indoor and Interconnects Applications

Optical wireless communications have been widely studied during the past decade in short-range applications, such as indoor highspeed wireless networks and interconnects in data centers and high-performance computing. In this paper, recent developments in high-speed short-range optical wireless communications are reviewed, including visible light communications （VLCs）, infrared indoor communication systems, and reconfigurable optical interconnects. The general architecture of indoor high-speed optical wireless communications is described, and the advantages and limitations of both visible and infrared based solutions are discussed. The concept of reconfigurable optical interconnects is presented, and key results are summarized. In addition, the challenges and potential future directions of short-range optical wireless communications are discussed.

Subcarrier Intensity Modulated Optical Wireless Communications:A Survey from Communication Theory Perspective

Subcarrier intensity modulation with direet detection is a modulatiou/detection technique tbr optical wireless communication systems, where a pre-modulated and properly biased radio frequency signal is modulated on the intensity of the optical carrier. The most important benefits of subcarrier intensity modulation are as follows： 1） it does not provide irreducible error floor like the conventional on-off keying intensity modulation with a fixed detection threshold; 2） it provides improved spectral efficiency and supports higher order modulation schemes; and 3） it has much less implementation complexity compared to coherent optical wireless communications with heterodyne or homodyne detection. In this paper, we present an up-to-date review of subcarrier intensity modulated optical wireless communication systems. We survey the error rate and outage performance of subcarrier intensity modulations in the atmospheric turbulence channels considering different modulation and coding schemes. We also explore different contemporary atmospheric turbulence fading mitigation solutions that can be employed for subcarrier intensity modulation. These solutions include diversity combining, adaptive transmission, relay assisted transmission, multiple-subcarrier intensity modulations, and optical orthogonal frequency division multiplexing. Moreover, we review the performance of subcarrier intensity modulations due to the pointing error and synchronization error.

Compensating for Nonlinear Effects in Coherent-Detection Optical Transmission Systems

Fiber nonlinearity is one of the most important limiters of capacity in coherent optical communications. In this paper, we review two nonlinear compensation methods： digital backward propagation （BP） and nonlinear electrical equalizer （NLEE） based on the timedomain Volterra series. These compensation algorithms are implemented in a singlechannel 50 Gb/s coherent optical singlecarrier frequency division multiplexed （CO-SCFDM） system transmitting over 10 × 80 km of standard singlemode fiber （SSMF）.

Toward Low-Cost Flexible Intelligent OAM in Optical Fiber Communication Networks

Low-cost,flexible and intelligent optical performance monitoring and management is a key enabling technology for network quality guarantee,especially in the era of explosive growth of communication capacity and network scale.However,to the best of our knowledge,it is extremely challenging to implement real-time performance monitoring and operations,administration and maintenance(OAM) in a highly complex dynamic network.In this paper,we propose an innovative optical identification(OID) scheme that can realize both performance monitoring and some advanced OAM sub-functions.The basic concepts,applications,challenges and evolution directions of this OID tool are also discussed.

Flipped-Exponential Nyquist Pulse Technique to Optimize PAPR in Optical Direct-Detection OFDM Systems

In this paper, we describe a novel technique based on the flipped-exponential （FE） Nyquist pulse method for reducing peak-to-average power ratio （PAPR） in an optical direct-detection orthogonal frequency-division multiplexing （DD-QFDM） system, The technique involves proper selection of the FE Nyquist pulses for shaping the different subcarriers of the OFDM. We apply this technique to a DD-OFDM transmission system to significantly reduce PAPR. We also investigate the sensitivity of a received OFDM signal with strong nonlinearity in a standard single-mode fiber （SMF）.

Call for Papers ZTE Communications Special Issue on Optical Wireless Communications

Optical wireless communication, which serves as an important alternative to the radio-frequency communication, shows great potential to a lot of applications, such as indoor communication, secure communication, and battlefield communication. It has attracted increasing research interests from both academia and industrial fields. Moreover, optical wireless communication has been applied to the indoor communication and positioning system. The upcoming special issue of ZTE Communication will focus on the cutting-edge research and application on the communication system and related signal processing in optical wireless communication. The expected publication date will be in Mar. 2016. It includes （but not limited to） the following research directions：

A New Optical Cable Communications Project

A key project of the state, the Beijing-Taiyuan-Xi’an optical cable communications trunk, is one of the 22 optical cables planned to be laid by the Ministry of Post and Telecommunications during the Eighth Five Year. Plan. This communication cable trunk covers a distance of 1771 km, starting from Beijing and going via Hebei and Shanxi to Xi’an in Shaanxi, linking two provincial capitals, one municipality directly under the jurisdiction of the central government, seven other cities and 32 counties.