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In coherent optics transmission systems, the digital signal processor (DSP) application-specific integrated circuit (ASIC) is the most power-hungry part of the optical transceiver. Already in the edge of transistor technology, to achieve the power budget, we must look for opportunities to further optimize the designs. This letter explores a dynamic duty cycle for reducing the consumption in the pipeline of such DSP ASICs. We exploit the characteristics of estimator algorithms to introduce a dynamic duty cycle, reducing the mean consumption of designs originally constrained only for worst-case scenarios. We present the methodology to implement duty cycle control using the carrier frequency offset estimator (CFE) algorithm as case study, achieving in simulation level from 22% to 74% power consumption reduction in this algorithm, varying on-chip operation conditions. [ABSTRACT FROM AUTHOR]

Multi-core fibers (MCF) and multichannel optical waveguides have garnered significant attention as viable technologies for enhancing transmission capacity. However, the assembly of multichannel optical components encounters certain challenges, particularly in terms of alignment and takt time. To address these issues, this study proposed and demonstrated an optical coupling method using near-infrared (NIR) light-induced self-written (LISW) optical waveguide technology to simultaneously connect 4-core MCFs. All-solid LISW optical self-coupling between 4-core MCFs was achieved by employing an advanced selective polymerization process using light at 1310 nm wavelength. The resin used was characterized by the presence of an NIR dye in the monomer. The LISW optical waveguide core formation time was approximately 10 s, and the simultaneous 4-core formation was achieved within a short time. The average insertion loss (IL) of the all-solid LISW optical waveguide was 0.2 dB, and both the average IL of each channel and IL variation per channel were reduced compared with those of the butt joint. Thus, the LISW optical self-coupling compensated for the misalignment that occurred in the butt joint. Therefore, the LISW optical waveguide can also be used for the simultaneous optical self-coupling of multiple channels and is an effective method for reducing the fabrication time.

Naturally occurring mass transport events can endanger human life and infrastructure integrity, especially in mountain areas often affected by landslides, debris flows, and avalanches. Currently available hazard detection systems can greatly help with the timely warning (within a few seconds) of ongoing, potentially dangerous events, but can often be inaccurate, unreliable and, due to the need for in-situ power supply, difficult to operate. Modern optical fiber sensing techniques, on the other hand, can provide exceptional accuracy but require longer measurement time and increased complexity and cost, which makes them unsuitable for such time- and cost-sensitive applications. In this paper, we present an on-field demonstration of a previously developed polarization-based optical fiber early-warning system. A mountain gully in the Valle d'Aosta region, in Italy, is used as a validation testbed to show the reliability of our approach in detecting anomalous vibration phenomena, and its robustness against the background noise associated, for instance, with car traffic or animal wildlife in the monitored area. Our findings show that the rate of variation of the state of polarization induced by real-life, hazardous rockfall events on the optical fiber is orders of magnitudes higher than the average variation rate recorded in normal conditions, thus making the proposed system a promising alternative in the mountain hazards sensors world. Moreover, we show that the system has great potential for increased accuracy in the monitoring of event dynamics by using different optical fibers in separate sections of the site, which can also be a source of additional cost reduction.

The mountain scenario is often subject to catastrophic events such as rockfalls and avalanches, potentially dangerous for both people and civil infrastructures. Early-warning alarm systems that in case of such events can immediately turn on a traffic light on a mountain road and send remote alarms to control rooms, have already been developed in the geotechnical engineering sector, but all have some limitations and/or very high costs. In this work we propose an immediate-warning monitoring system based on fiber polarization sensing. Anomalies such as rockfalls and avalanches would change the instantaneous birefringence of the fiber installed in the area to be monitored, and can be sensed by looking at the state of polarization at the fiber output. The novelty of our paper is the development of an algorithm that is able to detect dangerous events, which we experimentally emulated on a reduced scale physical model of a mountain slope, in which fibers have been buried in different configurations. Our findings show that the system can correctly sense all the experimentally generated rockfall phenomena and for all the installed fiber configurations, and it is also robust to false alarms, provided that the monitoring algorithm main parameters are properly set.

Accurate monitoring of the internal statuses is highly valuable for the management of the lithium-ion battery (LIB). This article proposes a thermal-model-based method for multistate joint observation, enabled by a novel smart battery design with an embedded and distributed temperature sensor. In particular, a novel smart battery is designed by implanting the distributed fiber optical sensor internally and externally. This promises a real-time distributed measurement of LIB internal and surface temperature with a high space resolution. Following this endeavor, a low-order joint observer is proposed to coestimate the thermal parameters, heat generation rate, state of charge, and maximum capacity. Experimental results disclose that the smart battery has space-resolved self-monitoring capability with high reproducibility. With the new sensing data, the heat generation rate, state of charge, and maximum capacity of LIB can be observed precisely in real time. The proposed method validates to outperform the commonly-used electrical-model-based method regarding the accuracy and the robustness to battery aging. [ABSTRACT FROM AUTHOR]

A novel super-structure long-period fiber grating (SLPFG) is proposed for bending measurement with high sensitivity. The experimental and simulated results show that the number of multimode fibers (MMF) in one period influences the excited coupling mode and its coupling efficiency. Meanwhile, the bend sensitivity is increased by optimizing the number of MMFs and reaches $17.237\,\,\text {dB}/\text {m}^{-{1}}$. More importantly, the temperature cross-sensitivity is one order of magnitude lower than most fiber bending sensors. [ABSTRACT FROM AUTHOR]

This article highlights an intensity variation-based force sensor for polymer optical fiber (POF) that relies on the twisting structure. The sensing phenomena of the sensor rely on cladding mode frustrated total internal reflection (CMFTIR). A portion of two POFs is twisted in the middle where the light source is connected with illuminating fiber, and the power meter is connected with the forward end of the second fiber. Thus, the force measurement is taken from the second fiber by observing the variation of coupled intensity in which the applied force is up to 0–20 N. The sensor is analyzed on straight fiber, twisted fiber with bend, and without bend (considering the sensor’s sensitivity). The experimental results show that the sensor has higher sensitivity in the twisted with-bend structure, and the bending radius also affects the sensor sensitivity. Moreover, a multipoint and multiaxis force sensor is also presented. The POF is twisted up to 100 cm for multipoint sensing, and force is applied at five different points, whereas the cascading scheme is adopted for multiaxis to achieve the individual response of each axis. This study provides an alternative way to measure force based on intensity changes and has an additional advantage of being cheaper than fiber Bragg gratings and other systems. [ABSTRACT FROM AUTHOR]

Optical fiber structures for bending sensing have attracted extensive attention in recent years with their unique advantages. In this article, innovative C-shaped-core long-period fiber gratings (C-LPFGs) with two resonant peaks are proposed and experimentally tested. This special fiber microstructure is achieved by methods of CO2-laser polishing and oxyhydrogen-flame heating. During the process of heating, the core at polished area micro-bends to the surface of the structure due to the surface tension effect, which forms a “C”-shaped core. Each microbending Section of core results in partial energy leaking into the cladding to excite the cladding modes. As the number of periods increases, stronger effective refractive index modulation forms multiple resonant peaks. According to the experimental results, sensors with 17 periods represent excellent contrast and repeatability of two resonant peaks. The bending sensitivity of the proposed structure achieves −24.01/−21.3 nm/m−1 at 0° and −4.88/−10.17 nm/m−1 at 90° of Dip $_{1/2}$. Furthermore, the temperature sensitivity of both dips is 64/33 pm/°C, and the total length of the sensor is only 0.85 cm. With considerable bending sensitivity, the compact sensor possesses latent potential in fields of dual-parameter measurement in the future. [ABSTRACT FROM AUTHOR]

Traditional optical voltage transformers (OVTs) based on electro-optical and inverse piezoelectric effects are gradually exposing their accuracy and reliability issues. In contrast, fibers for measuring electricity have unique properties and significant advantages in the high-voltage power industry, especially fiber optic current sensor (FOCS), which has been widely used in the field of high-voltage measurement. As a result, a novel fiber optical voltage sensor (FOVS) is proposed, which uses FOCS to measure the current flowing through the capacitive voltage divider (CVD) and then calculates the primary voltage proportional to it. In order to solve the inherent temperature- and wavelength -dependent errors and achieve high accuracy, a novel closed-loop signal processing method, which aims to minimize the influence of temperature-sensitive components such as CVD, quarter waveplate, and sensing fiber on the measurement accuracy of the system, is presented. A 110-kV FOVS prototype with a rated voltage of 110/ $({3})^{1/2}$ kV and a rated frequency of 50 Hz is developed and tested. The results show that after temperature and wavelength correction, the accuracy reaches the metering class of 0.2% and protection class of 3P specified in GB/T20840.7-2007 [ABSTRACT FROM AUTHOR]

The realization of multiple demodulation sche- mes of fiber Bragg grating (FBG) sensor is important for its engineering application. Here, we proposed a new edge filter that is formed by cascading dispersion compensation fiber (DCF) and no-core fiber (NCF) structure between two single-mode fibers (SMFs) for demodulation of quasi-distributed FBG sensor. The edge filter can be suitable for FBG with different center wavelengths by changing its structure parameters to achieve a wide range of FBG demodulation. In order to verify the performance of the edge filter, a demodulation system for quasi-distributed FBG sensor is successfully designed by introducing an optical time-domain reflectometer (OTDR), the wavelength shift of FBG caused by the change of temperature and strain is converted into power change through the edge filter, so as to realize temperature and strain demodulation. In the experiment, two FBG sensors separated by 500 m were set at the end of a 3000-m optical fiber for temperature and strain monitoring. The results show that the temperature sensitivity is 0.23 dB/°C from 50 °C to 100 °C, and the strain sensitivity is 0.01658 dB/ $\mu \epsilon $ from 0 to $669.6\,\mu \epsilon $. The edge filter for FBG demodulation has the advantages of high sensitivity, adjustable structural parameters, low cost, and independent multipoint/multiparameter demodulation. [ABSTRACT FROM AUTHOR]

This study investigated lightning-induced damage of optical fiber overhead ground wires (OPGWs) through damage measurements, numerical simulations and influencing factor analysis. A high-precision damage measurement method was proposed to calculate the lightning damage volume based on laser profile scanning and a developed data processing program. The time-and-space-varying current and heat flows obtained from an arc magnetohydrodynamic model were loaded on OPGWs by stepwise segmental injection to establish a coupled arc-thermal-electric model and simulate the heating and damage behavior of OPGWs. The comparisons indicated that the simulated metal phase transition region agreed well with the actual damage distribution, and the area surrounded by the aluminum melting point isotherm provided a good prediction of the arc sweep damage. The hysteresis of the temperature rise suggested that lightning damage was dominated by heat flow conduction rather than the Joule heating effect. Furthermore, the continuing current was the main cause of severe damage. The damage volume increased linearly with increasing charge transfer. As the discharge gap increases, the arc loading intensity decreases, but the damage volume undergoes a non-monotonic change, which is due to the complex variations in the arc attachment area regulated by the discharge gap and current intensity. [ABSTRACT FROM AUTHOR]

This paper demonstrates that relatively inexpensive acrylate coated FBGs can survive short exposure times to high temperatures in a pultrusion process and monitor relatively low magnitude bending and axial tension strains in a composite material. However, under higher sustained axial loads, the observed interfacial failure of the optical fiber and the host material resulted in a significant reduction of the indicated strains during constant elongation. These findings are analyzed by experimental measurements supported by finite element simulations. The optimal placement of embedded optical fibers in the rods is discussed based on the limitations of the rods and the mechanical strength of the commercially available optical fibers. [ABSTRACT FROM AUTHOR]

A high-sensitivity and high-resolution refractive index (RI) sensor with ultrawide measurement range based on no core fiber (NCF) with large offset splicing and microwave photonic filter (MPF) interrogation is demonstrated theoretically and experimentally for the first time. In the sensor, an inline Mach–Zehnder interferometer (MZI) based on NCF with large offset splicing is used as the sensing head, and a single-passband MPF is designed to interrogate the sensing signal. Compared with the traditional interrogation in optical domain, the MPF interrogation converts the periodic interference pattern in optical spectrum into the nonperiodic bandpass frequency response in radio frequency (RF) domain, so the measurement range is unlimited in principle. Owing to the large offset splicing in the inline MZI structure, the sensitivity of the sensor as high as −1.1054 GHz/RIU is obtained in the experiment. More importantly, MPF interrogation improves the resolution by an order of magnitude to $9\times10$ −7 RIU. Meanwhile, the sensitivity and the resolution of the sensor are easily adjusted by changing the length of dispersive media. The high sensitivity and high resolution of the sensor have potential applications in ultralow concentration biochemical detection field. [ABSTRACT FROM AUTHOR]

We characterized the radiation response in the visible domain of a new multimode graded-index (GI) phosphosilicate optical fiber (GIMMF), exposed to the harsh environment (pulses of 14-MeV neutrons, X-rays, and $\gamma $ -rays) associated with laser experiments at the OMEGA facility. The growth of permanent radiation-induced attenuation (RIA) was measured in situ after a series of laser shots involving a large production of 14-MeV neutrons (yields > $10^{{14}}$ n per shot). RIA linearly increases with accumulated neutron fluence without recovery between shots. The obtained results allow a precise evaluation of this GIMMF vulnerability when implemented as part of laser or plasma diagnostics. Our work also reveals the potential of this class of optical fiber to serve as a radiation monitor in the radiation-rich mixed environments of megajoule class laser facilities and to provide a very fast and online estimation of the accumulated deposited dose at various locations of their experimental halls. In our experimental test configuration at OMEGA, 14-MeV neutrons are estimated to contribute to about 55% of the total deposited dose on the fibers, and the other optical losses are related to X-ray and $\gamma $ -ray contributions. Those measurements could be, for example, benchmarked to the radiation maps obtained by Monte Carlo simulation tools, potentially facilitating the evaluation of the aging of diagnostics, components, and systems as well as their maintenance operations. [ABSTRACT FROM AUTHOR]

Distributed acoustic sensors (DASs) are able to monitor in real-time acoustic excitation and mechanical vibration of the external environment for many kilometers along the length of the optical fiber. In the oil industry, the technology allows the monitoring of well structural health, identifying flow profile, acquiring seismic data, updating reservoir information, and feeding geological models. The spatial resolution of DAS is a limiting factor on the quality of information gathered. In this article, we propose and analyze a novel method of measuring local dynamic strain of structures using DAS. The method uses serpentine configurations to measure the frequency spectrum of the in-phase strain signals at discrete regions of the structure, enabling DAS to determine, among other vibration parameters, the strain frequency response function (SFRF). An experimental study of the sensor application with different arrangements in a small structure has been performed. The structure in the experiment consists of a free–free aluminum beam of approximately 2.7 m. Experiment results show agreement with numerical results developed by the finite element method (FEM) and using reference sensors, demonstrating a significant improvement of the DAS SFRF accuracy using the serpentine configuration and up to 12.9 dB increase in peak-to-noise ratio (PNR) for low excitation forces. The recovered response enabled the reconstruction of mode shapes. [ABSTRACT FROM AUTHOR]

A fiber-optic hydrophone based on extrinsic Fabry–Perot (F-P) interferometer is proposed. The sensitive element of the hydrophone is an Archimedes spiral metal diaphragm, and the inner surface of the diaphragm and the end face of the optical fiber form the F-P cavity. Due to the grooved surface of the sensitive diaphragm, the hydrophone is minimally affected by hydrostatic pressure. The geometry structure of sensor and finite element method (FEM) modeling is presented. Experiments of underwater acoustic response and sensitivity calibration of the hydrophone are carried out and the experimental phase results are demodulated by the orthogonal phase demodulation method based on birefringent crystals and polarization technology. The experiment results show that the hydrophone has a relatively flat signal-to-noise ratio (SNR) and sensitivity within 1–20 kHz, and the average sensitivity is −172.52 dB (re. 1 rad/ $\mu $ Pa) @ 1–20 kHz. We believe that this type of hydrophone has the potential to be applied in the field of underwater acoustic communication. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate a distributed temperature and curvature sensing method based on spontaneous Raman backscattered lights in a few-mode optical fiber. A loop structure is used to demodulate the distributed temperature information using the Raman anti-Stokes (AS) scattering lights. And the fiber curvature is estimated by the loss of Raman Stokes (S) light. This system can measure temperature and curvature at the same position of the fiber simultaneously. The experimental results show that the temperature uncertainty and spatial resolution can reach up to 0.24 °C and 1.8 m on 6 km sensing fiber. Besides, the maximum measurement error is 0.11 cm within the curvature measurement range of 0.5–3 cm. [ABSTRACT FROM AUTHOR]

A fiber surface plasmon resonance (SPR) curvature sensor has the advantage of being insensitive to axial strain and temperature, but there are still difficulties in multichannel cascade and curvature direction identification. In this article, a multichannel directional recognition SPR curvature sensor based on D-type double-clad multimode fiber was proposed. The asymmetric structure of D-type multimode fiber can well realize directional curvature sensing. When the light in the multimode core leaks to the silica clad, due to the existence of plastic clad, it can still continue to transmit. When the refractive index of UV curable adhesive coated in different sensing areas is different, wavelength-division multiplexing multichannel sensing can be realized. When the sensing probe is bent to be convex, the maximum intensity sensitivity is 0.0057 a.u./m−1, the resonance wavelength is redshift, and the wavelength sensitivity is 0.6114 nm/m−1. When the sensor probe is bent to be concave, the maximum intensity sensitivity is 0.0043 a.u./m−1, the wavelength is blueshift, and its highest sensitivity is 0.5831 nm/m−1. In addition, this article also realizes a three-channel directional recognition SPR curvature sensor based on a D-type double-clad multimode fiber, which provides a new scheme for multichannel directional curvature measurement. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) is a common defect to determine the quality of high-voltage power equipment insulation systems. Localization of PD is very important for equipment maintenance and risk assessment. A localization algorithm of received signal strength (RSS) using demodulating PD optical signal is proposed. This is based on the optical effects caused by PD, which influence the optical signal that is transmitted through an optical fiber sensor placed inside the equipment. Compared with plastic fluorescent fiber, SiO2 cladding YAP:Ce crystal core fluorescent fiber (SYCF) with high luminous efficiency, low loss, and strong anti-electromagnetic interference capability is selected as the sensing unit to detect the received optical signal strength of PD, through the all-fiber optic sensing system to achieve the PD location in 3-D space. Based on the optical RSS localization method, the range of localization deviation of PD under 37-kV applied voltage is measured and studied. The average localization deviation and the error are 6.9 cm and 7.4%, respectively. Comparing the optical signal location method based on RSS with other methods of PD localization, the advantages and accuracy of the optical location method proposed in this article are outstanding. Therefore, the all-fiber system with SYCF via optical signal has a wide application prospect in the spatial localization of PD. [ABSTRACT FROM AUTHOR]

Reliability evaluation of electronic systems in space environment is a critical issue. In this work, reliability evaluation of superluminescent diode (SLD) systems, which are sensitive to both displacement damage effects and charge–discharge effects, was investigated by the Bayesian network model. Displacement equivalence model of the SLDs is verified by the irradiation results of 5-MeV protons and 1-MeV electrons. Charge–discharge effects of SLDs are induced by 110-keV electrons. Orbital energy spectra and cumulative distribution functions for the equivalent irradiation fluence are calculated by self-built software. Based on the experimental and calculated results, the Bayesian networks under various conditions are established. The probabilities of the type of faults prone in the system under each condition can then be analyzed and quantified. The proposed method provides a good idea for on-orbit reliability evaluation of complex systems. [ABSTRACT FROM AUTHOR]

We review recent advances in distributed fiber optic sensing (DFOS) and their applications. The scattering mechanisms in glass, which are exploited for reflectometry-based DFOS, are Rayleigh, Brillouin, and Raman scatterings. These are sensitive to either strain and/or temperature, allowing optical fiber cables to monitor their ambient environment in addition to their conventional role as a medium for telecommunications. Recently, DFOS leveraged technologies developed for telecommunications, such as coherent detection, digital signal processing, coding, and spatial/frequency diversity, to achieve improved performance in terms of measurand resolution, reach, spatial resolution, and bandwidth. We review the theory and architecture of commonly used DFOS methods. We provide recent experimental and field trial results where DFOS was used in wide-ranging applications, such as geohazard monitoring, seismic monitoring, traffic monitoring, and infrastructure health monitoring. Events of interest often have unique signatures either in the spatial, temporal, frequency, or wavenumber domains. Based on the temperature and strain raw data obtained from DFOS, downstream postprocessing allows the detection, classification, and localization of events. Combining DFOS with machine learning methods, it is possible to realize complete sensor systems that are compact, low cost, and can operate in harsh environments and difficult-to-access locations, facilitating increased public safety and smarter cities. [ABSTRACT FROM AUTHOR]

In order to overcome the capacity limitations of current lightwave systems based on the single-mode optical fiber, massively parallel transmission in the spatial domain [space-division multiplexing (SDM)] supported by extended parallelism in the frequency domain (ultrawideband (UWB) systems) must be used. This article reviews key aspects of parallel transmission systems as the only significant capacity scaling option going forward and discusses the various tradeoffs on an architectural level and a hardware integration level. In doing so, this article also serves as an introduction to the more detailed accounts of fiber-optic systems and their future scaling within this Special Issue of the Proceedings of the IEEE. [ABSTRACT FROM AUTHOR]

Optical communication systems form the backbone of today’s communication and information society. Approximately six billion kilometers of optical fiber are installed around the globe today, enough to wrap a string of glass as thin as a human hair around the globe about 150000 times, or 20 times from Earth to Sun and back. Over just a single such strand of optical fiber, cutting-edge optical communication systems are able to carry tens of terabits per second over trans-Pacific distances, taking a mere 50 ms to link North America with South-East Asia. Today’s globally installed base of optical communication transponders is collectively capable to transmit several ten exabits per second of information (1 Ebit = $10^{{18}}$ bits), sending signals over short links between tens of meters and a kilometer within a data center, over tens of kilometers in links connecting datacenters, in cellular wireless fronthaul and backhaul, and in fiber-to-thehome applications, over hundreds of kilometers in metropolitan and regional networks, and over thousands of kilometers in trans-continental and submarine backbones. In short, almost every bit of information we touch or consume today, whether it belongs to an Internet search, to a streamed video, or to a mobile phone call, lives some parts of its life as an infrared photon within a gigantic global fiber-optic communications infrastructure. [ABSTRACT FROM AUTHOR]

Forthcoming capacity scaling requirements of optical networks and advances in optical fiber communications beyond the omnipresent single-mode fiber operating over the conventional band introduces new opportunities and challenges for exploiting the expanded spectral and spatial resources available for fiber-optic network designs. The spectral and spatial degrees of freedom introduce utilization tradeoffs that can be leveraged under different applications. After briefly reviewing the supporting network building elements (emerging fiber types, multiplexers, optical switches, and amplifiers), we consider networking scenarios such as intra/inter datacenter, terrestrial, undersea, and wireless 5G/6G hauling networks and identify the best utilization plan and key attributes that can be harnessed by the offered spectral and spatial degrees of freedom for each scenario and how optical switching can be employed therein for traffic management. Networks supporting these scenarios are experiencing tremendous traffic growth pushing their existing implementations to their physical capacity-distance limits. New network builds must offer significant capacity multipliers in an efficient and cost-effective manner, requiring new switching solutions for supporting the unabated traffic growths foreseen in the years to come. We discuss how space-division multiplexed networks can help address this challenge in key communication scenarios. [ABSTRACT FROM AUTHOR]

Since the 1980s, the single-core optical fiber cable has been the essential data transmission wiring media, with ongoing increases in deployments. Its use case has broadened, with transmission distances ranging from meters to 10000s km, including intrabuilding, fiber-to-the-home (FTTH), terrestrial, and even submarine trunk lines. Currently, optical fiber cable deployment is strongly driven by cloud-based storage, X as a Service (XaaS), and worldwide data center (DC) functionality with the optical interconnection of massive servers on DC campuses. Hence, it is quite natural that the optical fiber cable industry has developed ultrahigh fiber count, high density, and small diameter optical fiber cable, e.g., 6912-fiber-count cable. With high-density cables, massive data capacity can be installed at one time while saving limited space in an underground duct. High-density cable designs have been developed not just by cable structure optimization but through the process of bundling fibers and the use of high-grade optical fibers. Moreover, many enabling technologies have been developed to support the deployment of ultrahigh fiber count cables, such as fiber identification, connectors, mass fusion splicing, and storage systems for fusion splicing points. In this article, state-of-the-art technologies and prospects for ultrahigh-count and ultrahigh-density optical fiber cables and enabling technologies are explained. [ABSTRACT FROM AUTHOR]

Mode-division multiplexing (MDM) using few-mode fibers (FMFs) appears as a promising technology to increase fiber capacity by a few orders of magnitude and sustain the traffic demand for the decades to come. The potential of MDM lies in its ability to exploit multiple modes within a single optical fiber strand. Since 2011 and the first promising demonstrations, impressive progress has been made. In this article, we will show how the most recent advances in design and fabrication have improved the performance of FMFs and MDM systems, and allowed to turn research demonstrations into practical deployments. [ABSTRACT FROM AUTHOR]

Wavelength-division multiplexing (WDM) has historically enabled the increase in the capacity of optical systems by progressively populating the existing optical bandwidth of erbium-doped fiber amplifiers (EDFAs) in the $C$ -band. Nowadays, the number of channels—needed in optical systems—is approaching the maximum capacity of standard $C$ -band EDFAs. As a result, the industry worked on novel approaches, such as the use of multicore fibers, the extension of the available spectrum of the $C$ -band EDFAs, and the development of transmission systems covering $C$ - and $L$ -bands and beyond. In the context of continuous traffic growth, ultrawideband (UWB) WDM transmission systems appear as a promising technology to leverage the bandwidth of already deployed optical fiber infrastructure and sustain the traffic demand for the years to come. Since the pioneering demonstrations of UWB transmission a few years ago, long strides have been taken toward UWB technologies. In this review article, we discuss how the most recent advances in the design and fabrication of enabling devices, such as lasers, amplifiers, optical switches, and modulators, have improved the performance of UWB systems, paving the way to turn research demonstrations into future products. In addition, we also report on the advances in UWB optical fibers, such as the recently introduced nested antiresonant nodeless fibers (NANFs), whose future implementations could potentially provide up to 300-nm-wide bandwidth at less than 0.2 dB/km loss. [ABSTRACT FROM AUTHOR]

Space-division multiplexing (SDM) technology is a promising candidate to achieve massive parallelism in optical fiber cables and overcome the capacity limitation of the conventional single-mode fiber (SMF). Among the several kinds of SDM fiber, a weakly coupled multicore fiber (MCF) is advantageous in that it can be easily upgraded for use in existing equipment and requires no complex signal processing for optical multi-input multi-output (MIMO). In this article, we discuss the progress and standardization activity of MCF technologies from the viewpoint of accelerating the practical application of SDM technology. We first describe the possible application areas of SDM fibers and then show the recent progress of the essential technologies to construct the MCF link: the MCF itself, its splicing and connectorization, and the input/output techniques. We also discuss the availability and deployability of MCF as a large-capacity transmission medium and detail the progress on establishing a new international standard for SDM technology, which includes both historical progress and more recent endeavors on the standardization of optical fiber cables and SDM technology in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) and International Electrotechnical Commission (IEC). We close with a summary of MCF technology and its standardization activity with an eye to next-generation transmission systems and the long-term development of ultralarge capacity SDM transmission technology. [ABSTRACT FROM AUTHOR]

Since its early commercial deployment in the late 1980s, optical fiber has evolved to become the predominant carrier of the globe’s communications. Yet, after accommodating the world’s exponentially growing appetite for transmitted data for more than three decades, its ability to continue doing so is being challenged by fundamental factors. In this article, we review these factors and examine their consequences in terms of information capacity. In particular, we review the difficulties that are imposed by the nonlinear nature of fiber-optic transmission on the assessment of the capacity and on the definition of fundamental concepts, such as bandwidth and spectral efficiency. We discuss relevant approximations and regimes of operation in which bounds for the capacity can be effectively assessed while covering a broad range of applications ranging from interdatacenter communications to links spanning transoceanic distances. We relate to a broad variety of transmission schemes and discuss the potential benefits of spatial multiplexing with multimode and multicore fibers. State-of-the-art transmission experiments are also reviewed and compared with theoretical capacity bounds. [ABSTRACT FROM AUTHOR]

Randomly-coupled multi-core fiber (MCF) technology has come to attract lots of attention because of its strong applicability to long-haul transmission systems. Compared with weakly-coupled MCFs with independent cores, it can simultaneously realize higher spatial channel density and ultralow transmission loss using existing ultralow-loss single-mode fiber (SMF) core designs. The strong mode coupling characteristics of randomly-coupled MCFs can provide favorable optical properties, such as suppressed accumulation of modal dispersion (MD), mode-dependent loss (MDL), and nonlinear impairments. This article gives an overview of randomly-coupled MCF technology advancements. First, we describe the classification and design of randomly-coupled MCFs and explain what the randomly-coupled MCFs are and how they are designed. State-of-the-art randomly-coupled MCFs can accommodate four, seven, or 12 cores in a standard 125- $\mu \text{m}$ cladding while achieving ultralow transmission loss and/or small MD, which are very promising for long-haul transmission media. Next, we present the methods to characterize the optical properties of randomly-coupled MCFs and the difference compared to conventional SMF measurements. We also show the low-loss low-MDL connectivity of this type of MCF and the cabling that can suppress MD. A field-deployed randomly-coupled MCF cable testbed is also presented, which confirmed the favorable optical properties of randomly-coupled MCFs after deployment. Then, multi-core amplifier technologies are briefly summarized, and finally, we discuss the performance improvements in the transmissions over randomly-coupled MCFs and suitable application areas. [ABSTRACT FROM AUTHOR]

The ballistocardiogram (BCG) is a graphic representation of the movements of the body associated with cardiac activity. In this article, a 10-min BCG has been captured for ten different volunteers with a polymer optical fiber (POF) specklegram sensor. This transducer, which is composed of a charge-coupled device (CCD) camera, a laser emitting diode, and two meters of POF, allows capturing the BCG by analyzing how the induced speckle pattern changes over time. These changes are related to cardiac activity. Several processing methods have been compared to determine which method achieves the best performance: complex cepstrum, power of spectral density (PSD), Pam–Tompkins algorithm, wavelet, autocorrelation, Savitzky–Golay filter, mean absolute deviation, and Hilbert transform. Accuracy and resource consumption have been characterized and compared for these methods. Hilbert, PSD, and Savitzky–Golay exhibit both small errors and computational costs. This article describes a baseline for the main frequency determination of POF-based BCG signals in real-time. [ABSTRACT FROM AUTHOR]

A novel miniature magnetic-fluid (MF)-infiltrated eccentric fiber Bragg grating (EFBG) vectorial magnetic field sensor was proposed and experimentally demonstrated. An EFBG with a length of 10 mm and an eccentric distance of $2~\mu \text{m}$ was written in a standard single-mode fiber by a point-to-point femtosecond laser (FSL) writing process, which was then sealed in an MF-infiltrated glass capillary (GC) to form the magnetic-field-sensitive structure. Through the refractive index and absorption modulation of the MF under the influence of external magnetic fields, the transmission intensities at the resonant wavelengths of cladding modes are accordingly changed. Transmission at these resonant wavelengths can be used as the magnetic field sensing quantity. Experiments show that the sensor can sensitively respond to both strength and direction of the magnetic field. A sensitivity of about 0.042 dB/Oe in a magnetic field strength range of 0–120 Oe was found. [ABSTRACT FROM AUTHOR]

A surface plasmon resonance (SPR) dual-parameter sensor is designed and fabricated. It was electroless plated with silver on the surface of the core of the plastic-clad optical fiber and a gold film was plated near the end face side to produce the double SPR resonance valleys. 4-mercaptophenylboronic acid (4-MPBA) and $\beta $ -cyclodextrin ($\beta $ -CD) were coated separately on the surface of the silver and gold films. 4-MPBA can selectively recognize the structures of cis-vicinal diols, and thus can capture glucose that contains such structures. $\beta $ -CD is a class of cyclic oligosaccharides whose unique hydrophilic outer surface and lipophilic central cavity help facilitate the formation of inclusion complexes with cholesterol through multiple interactions. The sensor can detect 0–4 mM glucose and 0–500 nM cholesterol, and it has a linear response in the concentration range of 0–0.1 mM glucose and 0–15 nM cholesterol. The sensitivity of glucose and cholesterol concentration of the sensor is 89.6 and 0.994 nm/nM, respectively. The detection limits for quantifying glucose and cholesterol are $1.12~\mu \text{M}$ and 0.1 nM, respectively. The experimental results also show that the sensor has good selectivity and stability. The proposed technique can be further applied in medicine, environment, and biology monitoring. [ABSTRACT FROM AUTHOR]

Phase unwrapping is the prerequisite to obtain the true phase in interferometric fiber sensing. This article proposes a method based on an unscented Kalman filter (UKF) for interferometric fiber sensors. This method can break the limitation that the traditional phase unwrapping methods fail with a high probability when the differences in phase change are more than $\pi $ radians according to the Itoh criterion. Then, the measurement range of the phase signal can be expanded. This method combines the true phase and the phase gradient into the state vector estimation for UKF. The feasibility of this method is verified theoretically and experimentally. In the specific experiment, the phase signal with a maximum absolute phase difference of $1.5\pi $ (about 4.705) between adjacent sampling points can be recovered perfectly. The time and frequency domain results using this method show better performance. This method can effectively improve the detection range of the system and reduce the sampling rate to a certain extent, which is suitable for large-scale array systems. [ABSTRACT FROM AUTHOR]

Biogenic amines (BAs) are compounds found in a vast range of food products. In recent years, there has been a crescent awareness toward food safety, followed by an increase in food regulations. Long-period fiber gratings (LPFGs) coated with titanium dioxide (TiO2) were used to monitor the optical properties of a layer of poly(ethylene-co-vinyl acetate) (PEVA) doped with maleic anhydride (MA), which was polymerized on top of TiO2. This hydrophobic polymeric structure is permeable to BA, which causes a steady increase in its effective refractive index (RI) causing a wavelength shift in the coated LPFG attenuation band. LPFG wavelength shift was observed and measured for the monoamine tyramine (TYR), to the diamines, putrescine (PUT), cadaverine (CAD), histamine (HIS), and tryptamine (TRYP), and to the polyamines, spermidine (SPED), and spermine (SPEM). It was determined that, while PEVA-coated devices present a residual sensitivity to BA, the MA greatly increases it. In fact, for PEVA only coated LPFGs, the sensitivities of 1.45 ± 0.11, 0.97 ± 0.05, 0.46 ± 0.08, and 0.94 ± 0.09 nmM−1 for PUT, CAD, HIS, and TYR, respectively, were measured. However, for PEVA-doped MA-coated LPFGs, the sensitivities are 3.34 ± 0.13, 3.06 ± 0.11, 2.62 ± 0.14, and 3.65 ± 0.23 nmM−1 for PUT, CAD, HIS, and TYR, respectively. Thus, the RI of PEVA increases with BAs in- diffusion, and MA doping further enhances the PEVA sensitivity to BA. The proposed sensor is expected to play a part in the further development of a biosensor for the quantification of BA in real foodstuff, providing a methodology for quality control. [ABSTRACT FROM AUTHOR]

In recent times, usage of fixed wireless access (FWA) is gaining momentum even though fiber based existing services such as fiber-to-the-home (FTTH) are widely used for home Internet applications. We explore a time-division multiplexing passive optical network (TDM-PON) and long term evolution advanced (LTE-A) based cost-efficient access network planning strategy for combined usage of FWA and FTTH with the same network infrastructure. The proposed fiber-wireless (FiWi) access network satisfies all feasibility constraints and users’ quality of service (QoS) requirements. The proposed planning method judiciously identifies the network architecture and user service mode (FWA/FTTH). [ABSTRACT FROM AUTHOR]

Optical fiber in-line Mach-Zehnder interferometer for strain and refractive index sensing is proposed based on a pair of multi-column diffraction gratings. In the device operation, part of the light traveling in the fiber core diffracted to the cladding region through the first set of multi-column diffraction gratings, and directed back into the fiber core by the second set of multi-column diffraction gratings after being reflected at the cladding-air interface. The rest of the light remains traveling along the core, and the two parts of light recombine and produce interference. Thus, the multi-column diffraction gratings pair essentially forms an optical fiber in-line Mach-Zehnder interferometer. The transmission spectra of different free spectral ranges can be obtained by controlling the separation of two set of multi-column diffraction gratings. The sensitivities achieved for strain and refractive index are ~−1.43 pm / $\mu \varepsilon $ and 363.41 nm/RIU (refractive index unit), respectively. As the device has a low temperature sensitivity 8.03 pm/°C, the temperature cross sensitivity can be greatly reduced. Such a device is small in size, robust in structure, and convenient in operation, and has potential in photonic applications. [ABSTRACT FROM AUTHOR]

For data communications over long distances, optical wireless satellite networks (OWSNs) can offer lower latency than optical fiber terrestrial networks (OFTNs). However, when is it beneficial to switch or crossover from an OFTN to an OWSN for lower latency data communications? In this article, we introduce a crossover function that enables to find the crossover distance, i.e., a distance between two points on the surface of the Earth beyond which switching or crossing over from an OFTN to an OWSN for data communications between these points is useful in terms of latency. Numerical results reveal that a higher refractive index of optical fiber (or $i$) in an OFTN and a lower altitude of satellites (or $h$) in an OWSN result in a shorter crossover distance. To account for the variation in the end-to-end propagation distance that occurs over the OWSN, we examine the crossover function in four different scenarios. Numerical results indicate that the crossover distance varies with the end-to-end propagation distance over an OWSN and is different for different scenarios. We calculate the average crossover distance over all scenarios for different $h$ and $i$ and use it to evaluate the simulation results. Furthermore, for a comparative analysis of OFTNs and OWSNs in terms of latency, we study three different OFTNs having different refractive indexes and three different OWSNs having different satellite altitudes in three different scenarios for long-distance intercontinental data communications, including connections between New York and Dublin, Sao Paulo and London, and Toronto and Sydney. All three OWSNs offer better latency than OFTN2 (with $i_{2}$ = 1.3) and OFTN3 (with $i_{3}$ = 1.4675) in all scenarios. For example, for Toronto–Sydney connection, OWSN1 (with $h_{1}$ = 300 km), OWSN2 (with $h_{2}$ = 550 km), and OWSN3 (with $h_{3}$ = 1100 km) perform better than OFTN2 by 18.11%, 16.08%, and 10.30%, respectively, while they provide an improvement in latency of 27.46%, 25.67%, and 20.54%, respectively, compared to OFTN3. OWSN1 performs better than OFTN1 (with $i_{1}$ = 1.1) for Sao Paulo–London and Toronto–Sydney connections by 2.23% and 3.22%, respectively, while OWSN2 outperforms OFTN1 for Toronto–Sydney connection by 0.82%. For New York–Dublin connection, all OWSNs while for Sao Paulo–London connection, OWSN2 and OWSN3 exhibit higher latency than OFTN1 as the corresponding average crossover distances are greater than the shortest terrestrial distances between cities in these scenarios. Multiple satellites (or laser intersatellite links) on its shortest paths drive up the propagation distance to the extent that OWSN3 ends up with a higher latency than OFTN1 for the Toronto–Sydney intercontinental connection scenario although the related average crossover distance is less than the shortest terrestrial distance between Toronto and Sydney. The challenges related to OWSNs and OFTNs that may arise from this work in future are also highlighted. [ABSTRACT FROM AUTHOR]

For enhancing channel capacity and spectrum efficiency, vortex beam carrying orbital angular momentum (OAM) has been ardently investigated in optical communication. However, the crosstalk among OAM modes induced by mode coupling has seriously hindered the development of vortex beam communication (OBC). A novel concept of mitigating crosstalk within an OAM-mode group for a short-haul optical fiber communication (OFC) is proposed by reversing the transmission matrix. To support more OAM modes propagation, a step-index OAM fiber with ring-shaped profile is also designed and fabricated, which can support 6 vector/OAM modes propagation. A proof-of-concept experiment is performed for verifying the feasibility of the proposed concept, where a quadrature-phase-shift-keying (QPSK) signal is utilized as an excitation signal. Bit-error-ratio (BER) and constellation diagram (CD) are employed to evaluate the performance of the proposed system. The captured intensity profiles and interference diagrams demonstrate that the propagated four OAM beams within the 2rd OAM-mode group are successfully received. The measured BER and CD illustrate that the crosstalk within the mode group can be significantly mitigated. Further, although the data speed or fiber length is increased, the system performance using the proposed concept is still superior to the case without increasing fiber length or data speed when the proposed concept is missed. Therefore, the proposed concept is effective for mitigating the crosstalk and can be then used for a short-haul OAM-based OFC. [ABSTRACT FROM AUTHOR]

This article presents a novel and cost-effective vector network analyzer (VNA)-based phase-compensated channel sounder operating in the frequency range of 10–50 GHz using radio-over-fiber (RoF) techniques, which can support multilink/channel long-range phase-coherent measurements. The optical cable enables long-range channel measurements with a dynamic range of 115.7 dB at 30 GHz (for the back-to-back connection). The phase compensation scheme is utilized for stabilizing the inherent phase variations introduced by the optical fiber of the channel sounder to enable its application in multichannel/antenna measurements. A novel optical delay line and combiner scheme is proposed and implemented to separate the signals, thereby saving the port resource on the VNA for multilink/channel measurements. The proposed channel sounder is validated in back-to-back measurements under two optical cable conditions, i.e., with the presence of thermal changes and mechanical stress. The phase change could be maintained within 3° at 10–30 GHz and 7° in 30–50 GHz compared to the over 80° phase variation introduced by the cable effects at 10–50 GHz, demonstrating the robustness and effectiveness of the developed channel sounder in practice. With the proposed optical delay line and combiner scheme, multiple channels can be measured simultaneously with minimal VNA ports, significantly reducing the measurement cost and time for multilink channel measurements. Two multilink indoor channel measurements are conducted and analyzed using a virtual uniform rectangular array (URA) at 28-GHz bands. The results demonstrate the capability of the proposed channel sounder to perform high-fidelity long-range ultrawideband multilink channel measurements. [ABSTRACT FROM AUTHOR]

A quasi-distributed vibration sensing system based on a phase-sensitive optical frequency-domain reflectometer is proposed for monitoring the vibration of power transformer oil tanks. Compared with traditional accelerometers, the proposed system has high electromagnetic interference immunity. In this article, the principles of localization and vibration sensing are introduced. Then, the system layout and the vibration signal demodulation process are explained in detail. Next, the vibration sensing performance of the system is calibrated experimentally. Finally, vibration monitoring tests are carried out in a laboratory environment and on-site to verify the vibration detection capability of the system. The proposed system can be used to measure the time domain, frequency domain, and spatial distribution of oil tank vibration, which can be used for the online monitoring of the mechanical state of power transformers. [ABSTRACT FROM AUTHOR]

Partial discharge (PD) detection from protrusion defects is performed in an actual gas-insulated switchgears (GISs) based on a built-in sensor integrated with fluorescent fiber and ultrahigh frequency (UHF) antenna. The characteristics of both optical and UHF signals are analyzed in terms of inception voltage, pulse distribution, and statistical characteristics including the phase-resolved partial discharge (PRPD) pattern and PD number. In the experiment, protrusions with different curvatures are adopted to investigate the reason for the differences in the characteristics of UHF and optical signals. The results show that UHF and optical methods have different detection sensitivity for different discharge types owing to the different energies of electromagnetic waves and optical signals radiated in different discharge types. The optical method can easily detect avalanche discharge, while the UHF method can easily detect streamer discharge. This difference leads to the difference of the PD characteristics obtained by the two partial methods. For example, for the PD of small curvature protrusions, the PD inception voltage (PDIV) of the optical method is lower than that of the UHF method, because the defect triggers avalanche discharge. Moreover, the optical and UHF signal pulses are not always simultaneous in the time domain because they detect different discharge types. The PRPD patterns obtained by the optical method have a wider phase distribution than the UHF method because the optical method can detect avalanche discharge under low voltage. [ABSTRACT FROM AUTHOR]

An optical fiber sensor based on the parallel Vernier effect for temperature and transverse load measurement is reported in this paper. The sensor is composed of a novel compact fiber Michelson interferometer (MI) and a closed-cavity Fabry–Perot interferometer (FPI) connected in parallel. The fiber MI consists of a bent single-mode fiber (SMF) structure and a short length of hollow core silicon tube (HCST). A section of HCST is fused between two segments of SMF to form the fiber FPI. Two sensors in parallel can easily measure different physical parameters independently, thus realizing multi-parameter sensing. The fiber MI and FPI are used for temperature and transverse load measurement, respectively. Fiber optic MI and FPI are Vernier effect mutual reference interferometers. When MI is used for temperature sensing, FPI is the reference interferometer. When FPI is used for transverse load sensing, MI is the reference interferometer. It can improve the sensitivity of temperature and transverse load. Two samples were made and the sensing experiment was carried out. Through the sensing experiment, we get the maximum temperature sensitivity of 85.1 pm/°C in the temperature range of 30–80 °C and a transverse load sensitivity of −3.15 nm/N in the temperature range of 0–1.96 N. In addition, the sensor has the advantages of tiny size, low cost, and easy manufacture, which is suitable for temperature and transverse load sensing applications. [ABSTRACT FROM AUTHOR]

In this work, a prototype of 10G Combo-PON OLT transceiver based on photonic integrated circuits (PIC) is proposed and demonstrated. Key optical components for Combo-PON OLT transceiver, including high-power DFB laser, micro-ring modulator and WDM, have been developed and validated. The Combo-PON OLT transceiver integrated four XGS-PON/GPON ports and all ports comply with I-TUT G.984.2 Class C+ standard. The advantages and disadvantages of PIC in PON application are analyzed. The analysis shows that PIC can also provide a cost and power-efficient way to implement the next generation PON transceiver for high density PON ports. [ABSTRACT FROM AUTHOR]

Recently, an exceptional point (EP) was constructed in a coupled double-ring resonator. Generally, such non-Hermitian optical systems are realized via material selection and a spatially precise layout. However, because of material limitations, some system parameters cannot be changed after the waveguide is fabricated. In this study, We demonstrate a lithium niobate-based tunable system for controlling system dispersion and loss, the resonator structure made of lithium niobate is theoretically and numerically investigated and analyzed. Lithium niobate is chosen because it exhibits good electro-optic properties. Furthermore, the real part of the potential energy term of the non-Hermitian system is regulated using external electric field. Consequently, a frequency shift of up to 149 GHz is observed in the double characteristic peak of the transmission spectrum with a contrast of up to 0.43. In addition, a gain-influenced EP is observed in a coupled dual-ring resonator system by introducing gain material. It has potential application in future optical fiber communication, optical quantum computing, and environmental sensing. [ABSTRACT FROM AUTHOR]

The receiving characteristics of the silicon photonic-integrated chip assembly consisting of transimpedance amplifiers and butt-joint waveguide germanium avalanche photodiodes with lateral separated absorption and multiplication (SAM) structures were demonstrated based on conventional complementary metal-oxide-semiconductor processes. We experimentally verified a clear open eye diagram at 10 Gbps with a reverse bias of 17 V. Receiving sensitivities of $-$ 22.8 dBm and $-$ 22.0 dBm were obtained for the best and worst polarizations, respectively, with optical signals that had wavelengths longer than those of the absorption edges of Ge at a bit rate of 10 Gbps and a wavelength of 1600 nm. The proposed waveguide butt-joint germanium avalanche photodiodes with lateral SAM structures can be used to receive long wavelengths of downstream signals with low polarization dependence in next-generation optical access network systems. [ABSTRACT FROM AUTHOR]

A D-shaped fiber-optic surface plasmon resonance (SPR) sensor with MXene (Ti3C2Tx) is proposed as the sensing enhancement material. A spin coating method was used to cover the gold film D-shaped fiber SPR sensor with a layer of MXene. Experimentally, the sensor's sensitivity, full width at half maximum (FWHM), and figure of merit (FOM) are discussed. The effect of various MXene concentrations on D-shaped fiber SPR sensors was investigated. The results demonstrate that as the MXene concentration increases, the sensitivity, FWHM, and FOM value of the D-shaped fiber SPR sensor increase as well. The MXene-based D-shaped fiber SPR sensor exhibits the highest sensitivity, measuring 3143 nm/RIU, and the highest FOM value, 15.26. Compared to the Au-film D-shaped fiber SPR sensor, Sensitivity is increased by 53.6%. The results indicate that MXene could be used to enhance the performance of SPR refractive index sensors. [ABSTRACT FROM AUTHOR]

We propose a weakly-coupled ultra-flattened chromatic dispersion few-mode photonic crystal fiber (FM-PCF) supporting 10 vector modes (HE11a, HE11b, TM01, HE21a, HE21b, TE01, HE31a, HE31b, EH11a, EH11b) which works over a large range of wavelength across the C+L band. We investigate the chromatic dispersion, minimum effective refractive index difference (minΔneff), confinement loss, bending loss and differential mode delay (DMD) of the proposed fiber under the influences of design parameters by using the finite element method (FEM). The circular holes in the first ring are replaced by elliptical holes to obtain flattened-chromatic dispersion. And an extra small rectangular defected hole is introduced in the fiber core order to achieve ultra-flattened chromatic dispersion and large minΔneff. The simulated results show that the designed weakly-coupled FM-PCF can obtain ultra-flattened (dispersion slope < 1.8 × 10−4 ns/km/nm2) and large minΔneff (> 1.6 × 10−4) in the wavelength range of 1520 nm to 1640 nm. And the proposed weakly-coupled FM-PCF also has ultra-low confinement loss (<10−9dB/km) and good bending resistance. In summary, the proposed weakly-coupled FM-PCF has the potential applications for large-capacity MDM communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a high-security three-dimensional carrier-less amplitude-phase (3D-CAP) modulation is proposed, which can be used for short-distance multi-core fiber communication. Using a brand-new 3D constellation dubbed Triple-Decker, the 3D-CAP passive optical network's bit error rate (BER) performance is improved. This constellation's constellation figure of merit can be increased by changing the three-dimensional constellation distribution through geometric shaping. To provide constellation encryption for Triple-Decker by rotation, expansion, and time slot scrambling at the physical layer in 3D-CAP passive optical network (3D-CAP-PON), a four-dimensional hyperchaotic system known as Fu's model is utilized. We successfully carried out an experiment demonstrating 25.5 Gb/s 3D-CAP transmission over a 7-core fiber communication system. Experimental results illustrate that, compared to the traditional 3D constellation, our suggested scheme can obtain 0.6 dB receiving sensitivity gain at the BER∼1 × 10−3. The achieved key space is 10120. Due to its strong security and superior performance, this scheme has a promising future in short-distance secure communication. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate an integrated passive optical network monitoring system for fault detection and localization. Fault detection technology is based on the recognition of reflection spectrum generated by each single fiber Bragg grating, which can support large-capacity user fiber fault monitoring. Fault localization method uses two different total received powers measured by an optical power meter to solve the established equation, and it shows a good accuracy compared with the OTDR measurement results. Fault detection and localization are carried out separately but share the same transmitter module. The introduction of the additional module ensures that the troubleshooting does not affect other normal user data communication. We also investigate the dynamic range requirements of the fault detection technology and the measurement error of the fault localization method. The calculation results show the required dynamic range for the recognition device can be maintained within a small range and the use of high-accuracy optical power meter can reduce the measurement error. The proposed monitoring system can simultaneously provide a large-capacity fault detection technology and high-accuracy fault localization method in a cost-sensitive passive optical network market. [ABSTRACT FROM AUTHOR]