Transparent Dielectric Metasurfaces for Spatial Mode Multiplexing

Guest Editorial

Nowadays, the coherent optical communication system plays an important role in communication field because of large capability and bandwidth. A coherent optical communication, based on high-order modulation and digital signal processing technologies, consists of optical transmitters, optical fiber lines, optical amplifiers and optical receivers. In the high-speed coherent optical communication system, the phase noise from the transmitter laser and the local oscillator laser can significantly degrade the performance of the signal transmission and detection, especially for the systems using high-order modulation format, such as m-ary phase shift keying (mPSK) and m-ary quadrature amplitude modulation (m-QAM). Therefore, investigations on laser phase noise compensation algorithm based on digital signal processing technologies has become more and more significant. In this work, a multi-ring carrier phase recovery algorithm is developed for compensating the laser phase noise in optical fiber communication systems using high-order modulation formats. Degradations on the performance of communication systems due to the laser phase noise have been investigated. The system performance using the proposed algorithm and the conventional Viterbi-Viterbi algorithm were also evaluated in 9-channel and 15- channel, 32-Gbaud, Nyquist-spaced QPSK, 16-QAM, 64-QAM and 256-QAM coherent transmission systems with considering the impact of the laser phase noise. It is found that the phase noise leads to stricter constraints on the linewidths of transmitter-side and receiver-side lasers, and it can greatly degrade the achievable information rates in communication systems. Besides, compared to the conventional Viterbi-Viterbi algorithm, which is usually applied in the QPSK system, our proposed algorithm can also well mitigate the laser phase noise in 16-QAM, 64-QAM and 256-QAM optical communication systems.
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Deep neural networks (DNNs) have been applied to recover signals in optical communication systems and have shown competence of mitigating linear and nonlinear distortions. However, as the data throughput increases, the heavy computational cost of DNNs impedes them from rapid and power-efficient processing. In this paper, we propose an optical communication signal recovery technology based on a photonic convolutional processor, which is realized by dispersion delay unit and wavelength division multiplexing. Based on the photonic convolutional processor, we implement an optoelectronic convolutional neural network (OECNN) for signal post-equalization and experimentally demonstrate on 16QAM and 32QAM of an optical wireless communication system. With system parameters optimization, we verify that the OECNN can achieve accurate signal recovery where the bit error ratio (BER) is below the 7% forward error correction threshold of 3.8×10-3 at 2Gbps. With adding the OECNN-based nonlinear compensation, compared with only linear compensation, we improve the quality (Q) factor by 3.35 dB at 16QAM and 3.30 dB at 32QAM, which is comparable to that of an electronic neural network. This work proves that the photonic implementation of DNN is promising to provide a fast and power-efficient solution for optical communication signal processing.

光纤通信已经成为目前通信网络发展的主流方向。但是随着光纤通信系统向着超远距离、超大容量、超高速率的方向发展，光纤色散已经成为其巨大的阻碍。如何有效地控制光通信系统中产生的色散，使光信号在大容量、高速率、长距离传输中无误码地到达接收端，已经成为人们迫切需要解决的问题。对光通信系统中的色散进行监测并进行动态补偿的研究，使得超大容量、超长距离、超高速率的光纤通信系统成为可能，有助于最终实现全光智能自动交换网络。在众多测量光纤色散的方法中，调制相移法具有结构简单，可靠性强等优点。本文中，我们对使用调制相移法测量光纤色散进行了研究和仿真，讨论了在不同光纤长度和不同调制频率下，影响调制相移法测量结果精度的因素。通过适当地选取调制频率，我们可以使用调制相移法测得不同光纤长度下色散的精确值。另外在本文中，我们通过仿真验证了调制相移法可以测量具有任意色散–波长曲线的光纤。因此在实际应用中，调制相移法是可以应用于高精度光纤色散的测量。 Optical fiber communication is the mainstream of communication development at present. However, with the development of optical fiber communication system which trending towards ultra-long length, ultra-large capacity and ultra-high speed, fiber dispersion turned to be a great obstacle. How to control the dispersion created in the optical communication system effectively while force optical signal to reach the receiving end in high-capacity, high-rate and error-free long-distance transmission has increasingly become a research focus of optical fiber communication systems. It is a great significance to research about monitor and dynamic compensate dispersion in the optical communication systems, so that the ultra-large capacity, ultra-long length and ultra-high speed optical fiber communication systems would not be impossible, all-optical intelligent network with automatic switching functions would come true. Among the varieties of methods to measure fiber dispersion, the phase-modulation shift method is the unique one, which has the advantages of simple structure, high reliability. In this paper, we make a research and simulate to use the phase-modulation shift method, meanwhile we also discuss about the factors which affect the accuracy of the results in the different fiber lengths and modulation frequencies. By the means that selecting appropriate modulation frequency, we can use modulation phase shift method to measure the exact value of dispersion comes out from different lengths of fiber. Moreover, this paper also proves that the phase-modulation shift method is able to measure the optical fiber with arbitrary dispersion-wavelength curve, which is already verified by our simulation. Therefore, the phase-modulation shift method is well to be applied to take practice in the high-precision fiber dispersion measurement.

The efficient and accurate evaluation of the transmission performance of high-capacity optical communication systems has always attracted significant research attentions. The enhanced Gaussian noise (EGN) model is considered as an excellent solution to predict the system performance taking into account linear and nonlinear transmission impairments. Since the conventional form of the EGN model is complicated and intractable for a fast computation, the closed-form simplification has been regarded as a direction to significantly reduce the computational complexity. However, the accuracy of such a closed-form EGN model becomes a main concern in the application of ultra-wideband optical communication systems. In this work, we have investigated the accuracy of the closed-form EGN model for ultra-wideband optical fiber communication systems, where the performance of the system using electronic dispersion compensation, multi-channel nonlinearity compensation and full-field nonlinearity compensation has been evaluated in terms of symbol rate, number of channels and signal power. Our work will provide an insight on the application of the EGN model in next-generation ultra-wideband long-haul optical fiber communication networks.

The exponential growth of data in the information era has pushed conventional optical communication technology to its limitations, including inefficient spectral utilization, slow data rate, and inherent security vulnerabilities. Here, a transformative high-speed organic spectral wireless communication (SWC) technology enabled by a flexible, miniaturized, and high-performance organic hyperspectrometer is proposed that integrates ultrahigh-speed data transmission with hardware-level encryption. By synergistically combining organic photodetector arrays with tunable responsivities and spectral-tunable organic filters, the organic hyperspectrometer achieves a broad spectral detection range of 400 to 900 nm, resolution of 1.08 nm, accuracy of 0.60 nm, and response time of 684 ns. Unlike prior optical wireless communication systems, the organic hyperspectrometer-based SWC platform uniquely decodes high-speed encrypted data at the hardware level, which is a breakthrough in secure, high-speed, and high-capacity communication. Harnessing the full visible-to-near-infrared spectrum, the SWC system achieves a theoretical data rate of 9.1 Gbits s-1, ranking as the highest-speed organic optical communication system. Furthermore, the intrinsic flexibility and bandgap-tunability of organic materials enable unparalleled portability, adaptability, and scalability of organic SWC, establishing a scalable framework for terahertz-scale data transmission. These advancements mark a pivotal leap toward secure, high-speed, and ultracompact optical networks for the future data- and AI-driven era.

The design, fabrication, optical and mechanical characteristics, and reliability of several kinds of the latching-type single-mode-fiber (SMF) switch are reported. Practical applications of these switches to optical fiber communication systems and optical testing and sensing systems are also demonstrated. In the developed switches, a movable fiber is actuated by the magnetic attraction force produced between permanent magnets and a micromagnetic-alloy pipe fixed around the fiber. The ultralight micropipes (0.13 (i.d.)-0.18 (o.d.)/spl times/5/sup L/ mm, 400 /spl mu/g) were successfully massproduced by a fiber-micromachining technique based on metallizing and etching of sacrificial fibers. We used a refractive-index-matching oil in the switches to reduce insertion loss and reflected light. The several hundred fabricated 1/spl times/2 standard SMF switches exhibited excellent optical characteristics, such as typical insertion loss of 0.36 dB, return loss of 49 dB and crosstalk of -70 dB. They exhibited stable latching-type operation with loss changes of below 0.1 dB during 10/sup 5/ switching operations with minimum driving power of 9 mW and switching time of 2 ms. The switches were subjected to endurance (10/sup 8/ switching operations), heat cycles, shock and vibration, and long-term (6.5 years) intermittent operation tests, and revealed no significant optical or mechanical degradation. A 1/spl times/8 latching-type SMF switch was constructed using seven 1/spl times/2 switches cascaded in three stages and uniform insertion losses of below 0.7 dB and return losses of over 47 dB at each of eight ports were obtained. The 1/spl times/2 and 1/spl times/8 switches have been applied to NTT's optical communication systems. We fabricated a compact and cost-effective wavelength switch by installing microfilter chips in the 1/spl times/2 switch and confirmed stable latching-type wavelength switching between 1.3- and 1.55-/spl mu/m optical signals. We also designed and fabricated a polarization-maintaining switch using polarization maintaining and absorption reducing (PANDA) fibers and confirmed stable polarization maintaining switching operations. These switches are applicable not only to optical fiber communication systems, but also to optical testing and sensing systems.

Self-powered photoelectrochemical (PEC) photodetectors have emerged as promising candidates for optical communication systems owing to the natural compatibility with aqueous environments, simple fabrication processes, excellent detection sensitivity, and flexibly tunable photoresponse. However, existing PEC-based optical communication devices predominantly operate in a single-channel mode (either visible or ultraviolet spectrum), making them inherently vulnerable to signal interception and information leakage. This work presents the first experimental demonstration of secure dual-wavelength optical communication systems employing self-powered PEC photodetectors based on a type-I In2Te3/Se heterostructure. This self-powered photodetector shows strong visible-NIR photoresponse, excellent operational stability, fast response of hundreds of microseconds, and high photoresponsivity. Based on this, we developed a dual-wavelength optical communication architecture, comprising a 550/1030 nm free-space transmission system and a 450/550 nm underwater optical communication system to facilitate high-precision encrypted data transmission. These results demonstrate the feasibility of developing dual-band self-powered PEC photodetectors for multiscenario encrypted optical communication applications.

Study on the regulation of amplitude for the optical soliton through nonlinear effects in the optical communication system

Clouds are key driver in the performance of free space optical communication (FSOC) systems. Clouds are composed of liquid water and/or ice crystals and depending on the physical thickness can produce atmospheric fades easily exceeding 10 dB. In these more common cases, impacts on FSOC systems may be severe. On the other hand, there are times when cloud fades may be as low as 1 or 2 dB as a result of thin, ice crystal based cirrus clouds. In these cases, the impacts on FSOC communication collectors may be limited. The ability to characterize the distribution and frequency of clouds are critical in order to understand and predict atmospheric impacts. A cloud detection system has been developed and applied to produce high resolution climatologies in order to investigate these impacts. The cloud detection system uses geostationary, multi-spectral satellite imagery at horizontal resolutions up to one kilometer and temporal resolutions up to fifteen minutes. Multispectral imagery from the visible wavelengths through the longwave infrared is used to produce individual cloud tests which are combined to produce a composite cloud analysis. The result represents a high spatial and temporal resolution climatology that can be used to derive accurate Cloud Free Line of Sight (CFLOS) statistics in order to quantify atmospheric effects on optical communication systems. The Lasercom Network Optimization Tool (LNOT) is used along with a mission CONOPS and the cloud database to find configuration of geographically diverse ground sites which provide a high availability system.

As human society to the information in the process of moving and growing demand for bandwidth communications capacity, the optical of new modulation formats increasingly attention and quickly play an important role in optical communications. How can the system bit error rate within a certain degree of stability while still maintaining high-speed long-distance dispersal system, has been a popular issue is the optical communications industry. Starting from the optical modulation format herein, the generation process of the system introduced various optical signal modulation format, the optical signal through the optical fiber was studied and the performance of the simulation, on the basis of the design of advanced optical modulation formats in an optical fiber communication system .

The application of very fast image detectors to the fine tracking system of free space optical (FSO) communication has been demonstrated in several projects. In the near surface of the earth, the influence of the atmosphere on the optical communication system must be considered. The optical communication system must be designed to be able to suppress the influence of atmospheric turbulence. The authors have used the high-speed CMOS image sensor for the fine tracking system of 15 km FSO communication demonstration. In this study, the authors present the atmospheric influence on the fine tracking detector, and find out the tracking algorithm for the fine tracking detector to detect the centre of the received spot. On analysis of atmosphere turbulence influenced and the experiment data, the authors find that using centroid algorithm in the fine tracking system is better than the centre of mass algorithm. They proposed a new centroid algorithm in the fine tracking system and use this algorithm in the demonstration system. They found it can minimise the atmosphere turbulence influence.

Over the last 20 years, the process of measuring and recording a place or position on the surface of the earth has gone through a revolutionary change. There has been a switch from alidades to GPS, from slide rules to pentium computers, from manual to automatic recording and processing of spatial data. The changes include introduction and implementation of two satellite surveying systems (Transit and GPS), transfer of computations to high-speed computers, and processing and graphic presentation of spatial data in real time. Within the GPS domain, techniques have been developed to overcome degradation of the data by the government and to permit positioning to an accuracy of 2–3 mm in some cases.

We propose and experiment an integration system of fiber-wireless communication and free space optical (FSO) communication based on nonlinear noise compensation. This integration system, combining the benefits of FSO communication and high-frequency wireless communication, as well as the high-frequency efficiency and anti-interference to multipath fading of the multicarriers orthogonal frequency division multiplexing (OFDM) modulation, can increase the capacity and flexibility of the system. The nonlinear equalizer is employed to compensate the distortion caused by the beating between OFDM signal subcarriers in the combination system. Up to 1-Gbaud 16QAM discrete multitone (DMT) OFDM signal can be first transmitted over the distance of 100-m single-mode fiber (SMF), then delivered over the distance of 100-m FSO link, and finally, transmitted over the distance of 4 m wireless. The bit-error-ratio (BER) of the OFDM signal in the integration system can be less than the hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10−3. The experiment shows that the nonlinear equalizer can work well compatible with the combination system and can improve the transmission performance by 0.7-dB receiving sensitivity in the combination system.

Unidirectional transmission of optical waveguides in optical communication bands has been a difficult problem in the field of optical communication. In this paper, the valley Hall effect is utilized to enhance the transmission efficiency of optical wave in optical communication system. Valley photonic crystal is selected as the main material of optical waveguide in optical communication band. Valley photonic crystal is composed of air columns periodically arranged according to the honeycomb lattice in the dielectric material, which shows the valley Hall topological effect in transverse electric wave mode. By introducing the energy valley degree of freedom into the photonic crystal, the light wave is transmitted locally on the dielectric material at the interface, and the control of the dielectric material realizes the regulation of light transmission. The Chern number of optical waveguide topology in the optical communication band, the exchange phenomenon occurs at the same energy band position and realizes efficient unidirectional transmission of optical waveguides in optical communication bands. The experimental results show that the optical communication band optical waveguide based on the valley Hall effect has unique unidirectional transmission characteristics and robustness to cornering and is capable of realizing unidirectional optical transmission in optical communication systems.