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Highlights • Requirements for the recently proposed OTDR-based testing system are clarified. • Measurement system is enhanced through the use of coherent detection. • Measurement range of over 40 km is achieved while satisfying the requirements. Abstract This paper clarifies the requirements for applying 1-μm-band mode-detection optical time domain reflectometry (OTDR) to the loss monitoring of trunk cables with the goal of detecting slight changes in macro/micro-bending that are missed by conventional OTDR. In light of the requirements, the measurement system is enhanced through the use of coherent detection to fulfill the required range performance. Moreover, the enhanced system modulates the optical frequency and the state of polarization of the probe light during the measurement to suppress amplitude fluctuations in the backscattered waveforms. A field test is carried out to confirm the performance of the enhanced measurement system. The results demonstrate that the measurement range of over 40 km is achieved while amplitude fluctuations are reduced to as low as 0.02 dB. [ABSTRACT FROM AUTHOR]

Highlights • In our manuscript, we proposed and fabricated a temperature sensor based on the angled fiber end face, in which the angle is 30°. • Compared to the previous sensors, the structure of our proposed sensor was simple and it was easy to be fabricated and easy to be used. • The advantage of small size makes it possible to be used in many places. • The experiments show that the sensor has a good temperature response in a large temperature range (−40 °C–900 °C). • In this paper, we not only proposed and fabricated a new structure sensor but also demonstrated its temperature performance experimentally. Abstract We proposed a simple structure optical fiber temperature sensor, which is easy to be fabricated and used. The fiber sensor is made by polishing the optical fiber end to be 30° angle and its operating principle is based on Michelson interferometer. In order to demonstrate the performance of the fabricated temperature sensor, we carried out low temperature experiment (−40 °C–140 °C) and high temperature experiment (250 °C–900 °C) with two different kinds of thermostats. The results show us that the temperature sensitivity of the sensor increases with increasing temperature both in the low temperature range (−40 °C–140 °C) and in the high temperature range (250 °C–900 °C). The measured temperature sensitivity is 9.5 pm/°C at −40 °C and the measured temperature sensitivity is 17.86 pm/°C at 900 °C. [ABSTRACT FROM AUTHOR]

Highlights • This paper present a novel refractive index sensor based on tapered optical fiber. • The sensitivity can be enhanced by using micro-tapered long-period fiber grating. • The sensing characterises has been indicated numerically as well as experimentally. • Proposed sensor features a low cost, a simple structure and a high sensitivity. Abstract A novel micro-tapered long-period fiber grating refractive index sensor is demonstrated in this study. Its transmission characteristics are investigated numerically and experimentally. The sensor is fabricated by inscribing periodical micro-tapers in a biconical single mode optical fiber (SMF-28) using a low cost electric arc heating technique. The periodical tapering in SMF enables the fundamental core mode to be coupled into the cladding modes resulting a resonant wavelength in the transmission spectrum. The resonant wavelength shifts linearly with the variation of surrounding refractive index. The refractive index sensitivity of 8188 nm/RIU has been experimentally achieved which is much higher than the previously reported refractive index sensitivity values for the sensors based on long period fiber grating. The effects of varying the number of periodical tapers, amount of grating period and waist diameter on the sensitivity have been analysed both numerically and experimentally. Our presented sensor features a low cost, a simple structure and a high sensitivity. The results presented in this study would be useful in both chemical and bio-sensing applications. [ABSTRACT FROM AUTHOR]

Highlights • We study disaster survivability issue for telecom networks. • We illustrate the conflict between resource utilization and connection reliability. • We propose a reliability threshold based service bandwidth recovery (RBR) scheme. • RBR can make a good trade-off between resource utilization and connection reliability. Abstract As natural disasters (e.g., earthquake, tsunami, hurricane, etc.) frequently threaten and damage the widely-deployed telecom infrastructure, maintaining the connectivity, transmission bandwidth, and reliability of various service connections becomes a crucial concern in post-disaster telecom networks (such as optical backbone networks). Based on a probabilistic failure model, in this paper we proposed a reliability threshold based service bandwidth recovery (RBR) scheme for recovering the bandwidth and reliability of the impacted service connections after a disaster. Here, the impacted service connections include the ones completely disrupted and/or the ones undisrupted but their reliability decreased beyond the corresponding reference thresholds. Since there is severe lack of bandwidth resource in the post-disaster network, some connections are difficult to obtain enough bandwidth. Under the resource crunch case, RBR employs relaxation policies based on reliability thresholds to explore reliable routes for the impacted connections and to optimize their bandwidth resource utilization. Simulation results show that RBR scheme can make a good trade-off between the bandwidth resource utilization and service connection reliability. It can also achieve satisfactory performance in terms of connection loss ratio, traffic loss ratio, and average connection reliability. [ABSTRACT FROM AUTHOR]

Highlights • The first DBA algorithm to support the differentiated QoS and SLA in NG-EPON. • A novel MUMS two-dimensional priority queue model for NG-EPON is designed. • The ONU flexible configuration for multi-type users and services is supported. • The flexibility of the multi-transceiver ONUs has been fully developed and used. Abstract Recently, the IEEE 802.3 Ethernet Working Group has been working to explore new solutions for the next-generation Ethernet passive optical network (NG-EPON). It's desirable for NG-EPON to support the coexistence of multi-type users and multi-type services (MUMS) on a single access platform. Moreover, in the future, ONU may be equipped with multiple transceivers to break through bandwidth limit of a single wavelength and then achieve greater throughput per ONU. In this paper, a two-dimensional priority queue model is designed for buffer differentiation management. Then, a dynamic bandwidth allocation (DBA) algorithm including joint grant sizing and scheduling is presented to carry out differentiated bandwidth allocation among MUMS. By providing different aggregated data rates and setting scalable wavelength resource pools for different users and services, flexible ONU configurations are allowed. By using time-order filling (ToF) and wavelength-order filling (WoF) in combination to realize grant scheduling, the flexibility of multi-transceiver ONUs gets further exploited. Finally, the simulation demonstrates the effectiveness of the proposed algorithm. Not only each type of service/user can get reasonable network access capacity that matches its bandwidth requirements, but the overall network performance also gets improved compared with other DBAs for NG-EPON. [ABSTRACT FROM AUTHOR]

Highlights • For inter-DCI applications, a cost effective solution for high capacity transmission over 80 km SSMF is required. • In this paper, the optimal driving conditions of electro absorption modulated integrated lasers are investigated for transmitting real-time PAM-4 optical signal over 80 km SSMF. • The required OSNR and dispersion tolerance as a function of EAM driving conditions are measured and utilized for transmitting 100 Gigabit Ethernet traffic. • This technique can be applied for optimizing multi-level modulation transmission which use optical transmitter with non-linear transfer curve. Abstract We report on an electro-absorption modulator (EAM) integrated laser (EML) based real-time 112 Gbit/s (2 × 56.25 Gbit/s) 4-level pulse amplitude modulation (PAM-4) signal transmission in the C-band over 80 km of standard single-mode fiber (SSMF). Various operating conditions of the EAM were investigated to find the optimum driving conditions for PAM-4 modulation. When the EAM reverse bias was set to the inflection point of the transfer curve, which was −2.35 V, we obtained a bit error ratio (BER) of 4 × 10−8, which is well below the forward error correction (FEC) limit. The results demonstrate the feasibility of using EMLs for implementation in PAM-4 transceivers for inter-datacenter interconnection (inter-DCI) applications. [ABSTRACT FROM AUTHOR]

Highlights • Proposes the method intended to determine coupling coefficients between fibers in (1 + 1)GTWave. • Analytical expressions are obtained for the determination of coupling coefficients. • Presents experimental results, coupling coefficient values and analysis of the results. Abstract This paper proposes a theoretical and experimental method to determine the effective coupling coefficients for the pump radiation in (1 + 1)GTWave fibers and also gives mathematical expressions derived from analytical solutions for the pump radiation power distribution to estimate values thereof. The conditions for carrying out experiments to measure effective coupling coefficients, as well as results of these measurements are presented. [ABSTRACT FROM AUTHOR]

Highlights • Explains how to bias a dual-ring fiber optical gyroscope for max sensitivity. • This dual-ring optical gyro has unacceptable cross-sensitivity between rotation axes. • Points out errors on the transmission formula of a dual-ring fiber optical resonator. Abstract A recent paper by Gu and Liu reported a fiber double-ring resonator gyroscope that can simultaneously measure rotation in two orthogonal axes, with a sensitivity predicted to be 35 times larger than that of an interferometric fiber optic gyroscope (IFOG). Because the two rings have different lengths, the gyroscope could not be biased properly, and the authors remark that as a result, its sensitivity to a small rotation rate is reduced. We stress that this sensor actually responds quadratically to a small applied rotation rate, and that it is therefore essentially insensitive to a small rotation rate. We point out that it could easily be biased properly and this major issue is eliminated by using two rings with nominally equal lengths. We also show that in general, and unlike claimed, this sensor does not measure rotation on orthogonal axes independently. This cross-sensitivity between axes worsens significantly when the sensor is properly biased, and it is then much too strong for inertial navigation of aircraft. A conceptual method that might reduce this cross-sensitivity is suggested. A simple physical argument is also presented to explain why this gyroscope was entirely expected to be more sensitive than an IFOG, and shows that as a result of algebraic errors, the predicted factor of 35 is actually only at most 11. [ABSTRACT FROM AUTHOR]

Highlights • On-line temperature measurement of FBGs in fiber lasers is proposed and demonstrated. • The real-time temperature of FBGs is precisely given by the lasing wavelength. • It opens new chances for study of high-power fiber lasers. Abstract We propose an on-line measurement approach for the temperature of fiber Bragg gratings (FBGs) inside a fiber laser. To demonstrate this method, a narrow linewidth fiber ring laser is set up employing a π-phase shift FBG and a highly reflective FBG, and then the core-temperature is obtained by detecting the operating wavelength of the laser due to the temperature characteristics of the FBGs. This paper provides a real-time, rapid method to detect the core-temperature of FBGs in fiber lasers, which can be used in study of high power fiber lasers. [ABSTRACT FROM AUTHOR]

Highlights • Thermal resistance network model based on an analytic method is established. • Active optical fiber is discretized into multiple eccentric heat sources. • Analytic values are consistent with the change trend of experimental data. • Fiber placement has a certain effect on the temperature uniformity of fiber lasers. Abstract Long optical fiber is usually coiled on the surface of the substrate. Spreading thermal resistance is an important factor affecting thermal properties of optical fiber in this encapsulation way. This paper adopts a concise general analytic method to calculate spreading thermal resistance of the eccentric heat source formed in the rectangular channel. The on-site testing of active doped double clad fiber(DDCF)laser is also carried out. It is observed that the output light efficiency is high after the fiber loses heat through the plate which conforms to the needs of normal fiber laser light output efficiency of 70%–80%. The analytic value is in line with the changing trend of the experimental value, with the error of the temperature measurement points within ±8.8%. The third segment rules out the influence of the optical fiber coupler location and the temperature of coupling point. When the pump power ranges from 4.4 W to 31.07 W, the error range between the experiment and analytics is within −4.14% to −0.82%. The layout plan of the fiber has a certain effect on the temperature uniformity of the fiber laser. It is demonstrated that the analytic method and mathematical assumption are reliable in the cooling design of the optical fiber. [ABSTRACT FROM AUTHOR]

Highlights • A novel scheme is proposed to suppress receiver IQ mismatch and phase noise in PDM CO-OFDM system. • The mathematic model including receiver IQ mismatch, channel distortion and phase noise is deduced. • Part of residual IQ mismatch after GSOP can be eliminated. • The proposed method has a high tolerance of the amplitude and phase mismatches. • The complexity has been analyzed for the proposed method and the compared method. Abstract Receiver in-phase/quadrature (IQ) mismatch as well as phase noise are hard to mitigate at the receiver in polarization division multiplexed (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) system and so far this problem hasn't been properly solved yet. In this paper, a novel scheme is proposed to suppress receiver IQ mismatch and phase noise. In this scheme, through combining the pilot structure with Gram Schmidt orthogonalization procedure (GSOP) algorithm we can estimate the phase noise as well as channel distortion and eliminate the effect of part of the residual IQ mismatch. Numerical simulation shows that the proposed method has better performance than compared method at 100 Gb/s after 480 km transmission. What's more, the calculation complexity is also analyzed. [ABSTRACT FROM AUTHOR]

Silicon photonic integration is an enabling technology for power- and cost-effective optical interconnects in exascale performance computers and datacenters which require extremely low power consumption and dense integration for a higher interface bandwidth density. In this paper, we experimentally demonstrate a fully integrated optical transceiver network on a silicon substrate using heterogeneous integration. High performance on-chip lasers, modulators and photodetectors are enabled by transferring III–V materials to a pre-patterned silicon substrate. Wavelength division multiplexed transceivers with eight wavelength channels are monolithically-integrated on a single chip, forming an optical network-on-chip circuit with total transmission capacity up to 8 × 8×40 Gbps, and bandwidth density over 2 Tbps/cm. We show that the heterogeneous silicon integration provides the design flexibility and scalability for high-speed optical communication systems. [ABSTRACT FROM AUTHOR]

Increased demands for web and cloud-based services have been driving exponential growth of datacenter bandwidth. This paper discusses, from Google’s perspective, emerging challenges and possible technical solutions for scaling intra-datacenter and intra-campus interconnection network bandwidth. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the current situations of optical fibers used for terrestrial and submarine transmission systems as well as up-to-date R&D on these fibers. The current fibers include standard single mode fibers (SMFs), non-zero dispersion shifted fibers (NZ-DSFs), and dispersion managed lines (DMLs). Even though these fibers show quite high and matured properties, the internet traffic is continuously growing, and around 2015–2020, it is expected that the current transmission fibers would become inadequate. To prepare for the future ultra high-capacity transmission, there are three important R&D directions for transmission fibers. (1) Reducing non-linearity by means of enlarging Aeff and/or reducing attenuation loss. It is very important in the case of transmission systems using new multi-level signal formats. (2) Expanding the transmission band more than the current C- and/or L-Band by utilizing new transmission fibers. For example, holey fibers (HFs), which have an endlessly single mode (ESM) property, are one of the interesting candidates of the new transmission fibers. (3) Using Space Division Multiplexing (SDM) by using multi-core fibers. The multi-core fiber literally multiples the core number within a fiber dimension, which enables multiple transmission capacity per one fiber. In addition to the developments of transmission fibers, component fibers have also been studied and developed. Examples of R&D on these component fibers will be also discussed in the latter part of this paper. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the work carried out in the recent years on sensors which exploit optical fibre nanotapers (OFN). After a brief introduction on the morphology, fabrication and properties of OFN, this paper will review the various OFN sensors. This type of sensors are extremely compact and relatively robust, are usually unperturbed by electromagnetic interference and can be interrogated remotely. In this review sensors will be grouped in three categories according to their morphology: linear sensors, resonant sensors and tip sensors. While linear and resonant sensors exploit the fraction of power propagating in the evanescent field (outside the nanotaper physical boundary), tip sensors exploit light confined within the nanotaper to excite/detect variations within a very limited area. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we have proposed an efficient wavelength rerouting algorithm for dynamic provisioning of lightpath. In wavelength-division multiplexed (WDM) networks rerouting of lightpath can be used to improve throughput and to reduce blocking probability. We have proposed a Lightpath Rerouting Algorithm (LRRA) for dynamic traffic in WDM optical networks. The results have shown that LRRA can improve blocking performance of the network. In this paper, low complexity algorithm has been developed which is used for the calculation of blocking probability of network. The proposed algorithm has also been applied on the realistic network such as NSFnet for calculation and optimization of blocking probability of the network. The results have also shown that the proposed algorithm can be implemented to huge networks for good blocking performance of the network. [Copyright &y& Elsevier]

Abstract: This paper introduces a new chromatic dispersion monitoring technique using optical asynchronous sampling and double sideband filtering. We present simulation results that relate chromatic dispersion with the ratio between the maximum amplitude of the signal and the average optical output power, yielding in a method which is power transparent. We also show theoretical investigation and theoretical results that prove the approach used in this paper. [Copyright &y& Elsevier]

Abstract: In this paper, we have proposed an efficient wavelength rerouting algorithm for dynamic provisioning of lightpath. In wavelength division multiplexed (WDM) networks rerouting of lightpath can be used to improve throughput and to reduce blocking probability. We have proposed a shortest path wavelength rerouting (SPWRR) algorithm for dynamic traffic in WDM optical networks. The results have shown that SPWRR algorithm can improve blocking performance of the network. In this paper, low complexity algorithm has been developed which is used for the calculation of blocking probability of network. The proposed algorithm has also been applied on the realistic network such as NSFnet for calculation and optimization of blocking probability of the network. [Copyright &y& Elsevier]

Abstract: This paper proposes a hybrid subcarrier multiplexing/optical spectrum code division multiplexing (SCM/OSCDM) system for the purpose of combining the advantages of both techniques. Optical spectrum code division multiple-access (OSCDMA) is one of the multiplexing techniques that is becoming popular because of the flexibility in the allocation of channels, ability to operate asynchronously, enhanced privacy and increased capacity in bursty nature networks. On the other hand, subcarrier multiplexing (SCM) technique is able to enhance the channel data rate of OSCDMA systems. In this paper, a newly developed detection technique for the OSCDM called spectral direct decoding (SDD) detection technique is compared mathematically with the AND subtraction detection technique. The system utilizes a new unified code construction named KS (Khazani–Syed) code. The results characterizing the bit-error-rate (BER) show that SDD offers a significant improved performance at BER of 10−9. [Copyright &y& Elsevier]

Abstract: Polarization Mode Dispersion (PMD) compensation has been a matter of investigation of several papers in literature. The proposed solutions belong basically to two large families: electronic compensators and optical compensators. Both PMD compensator schemes have advantages and disadvantages: electronic PMD compensators are usually simple to include in line-terminal, potentially low-cost, very fast, and FEC compatible but their development is strongly dependent on IC technology capability that at this time allows device developments up to the 10 Gbit/s bit rates area. Furthermore, they are strongly dependent on modulation formats, and they can operate only on a single channel. Conversely, optical compensators are independent of bit rate and modulation format and potentially they can compensate more channels simultaneously; their major drawbacks are the longer response time and the complexity in the feedback signal process within the control algorithm. In this paper we consider an optical Polarization Mode Dispersion Compensator (PMDC) that is simple to realize and easy to include at limited costs in each EDFA module (distributed compensation) as well as a single-stage front-end compensator. Numerical analysis of the PMDC and experimental results confirm the utility of the PMDC proposed and its capability in compensating DGD larger than 20 ps in NRZ and RZ 40 Gbit/s optical systems. [Copyright &y& Elsevier]

• This paper proposes a FBG acceleration sensor based on the double-mass block structure. • The resonance frequency of the sensor is 1000 Hz, and the sensitivity of the sensor is 26.7 pm/g at 250 Hz. • The sensor has a simple structure, low cost and easy to fabricate. A double-mass block acceleration sensor based on Fiber Bragg Grating (FBG) is proposed to meet the needs of acceleration sensors in vibration monitoring. The proposed sensor is composed of FBG, beam and double mass block, and the FBG is fixed in the middle of the upper surface of the dual mass block by epoxy glue. Through theoretical analysis and experimental verification, the resonant frequency, sensitivity and lateral anti-interference ability of the sensor have been investigated. The experimental results show that the natural frequency of the sensor is 1000 Hz, the sensitivity is 26.7 pm/g when the frequency is 250 Hz, and the lateral anti-interference degree is less than 6%. And the sensor structure in this paper is simple and easy to fabricate. Therefore, it has a great application prospect in the vibration monitoring of bridges, roads and buildings. [ABSTRACT FROM AUTHOR]

• An overburden failure volume calculation model based on the BOTDA was established. • The optical fiber mechanical models in different zone of overburden are established. • This research is a combination of mining engineering and fiber optic sensing. The determination of overburden failure volume is a great challenge because of the complexity and concealment of mining fractures. Taking the 61,601 working face of Longwanggou Coal Mine as the engineering background, this paper established a two-dimensional model of 3000 mm × 200 mm × 1350 mm (length × width × height) in the laboratory. By adopting the Brillouin optical time-domain analysis (BOTDA) technology, considering the fiber deformation and the coordination of rock strata, Of deformation and damage state of overburden strata above the mined-out area, discusses the strata deformation partitioning features and characteristics of fiber optic monitoring strain curve partition interaction relations, is derived based on the above theoretical calculation formula of the rock damage volume, comparing the calculated results with measured results, verify the accuracy of volume calculation formula of mined-out area. The results show a good correspondence between the strain zoning characteristics monitored by optical fiber and the deformation zoning characteristics of overburden. Based on considering the discordant deformation between the overlying rock mass and the optical fiber sensor, the range and degree of overlying mining rock can be obtained through the inversion of the horizontal optical fiber monitoring results to reflect the position and degree of rock strata movement and deformation with the optical fiber. By analyzing the development process of the vertical fiber optic strain curve, it can be found that the rock strata with different propelling distances and different heights bear different tensile stresses, which have remarkable range characteristics. By comparing the results of the calculation model proposed in this paper with the monitored values of the model, it is found that the void volume size of goaf is the same, and the relative error is less than 9%. The results show that the model is reliable in calculating the failure volume of overburden rock in goaf. [ABSTRACT FROM AUTHOR]

• PPP-BOTDA-based monitoring approach of concrete structure crack is presented. • PPP-BOTDA-based experiments for crack location and propagation process are implemented. • A PPP-BOTDA-based semi-empirical model monitoring crack is proposed. Cracks are the most common lesion in water-wading structures such as dams and sluices, which have an important impact on the durability of concrete materials and the safety of structures. The emergence of cracks is also regarded as a precursor to the destruction of buildings. However, the randomness and concealment of cracks are strong, which bring great difficulty to real-time and accurate capture. This paper focuses on Pulse Pre-Pump Brillouin Optical Time Domain Analysis (PPP-BOTDA) and studies the principle and realization method of PPP-BOTDA optical fiber sensing for concrete structure strain. On this basis, several groups of monitoring experiment for crack initiation location and propagation process of concrete structures are carried out. In the paper, the relationship between force-light-opening is studied and the influence of angle between optical fiber and crack on monitoring results is analyzed. Finally, a monitoring model for concrete cracks based on optical fiber strain sensing is constructed. [ABSTRACT FROM AUTHOR]

Abstract: Two important tasks with respect to the optimized configuration of an optical communications system are those of the performance evaluation and the receiver decision threshold estimation. In this paper, a new training-based BER and threshold estimation technique is proposed relaxing the assumption of Gaussian distributed received signals. The proposed method is similar in philosophy to the Gaussian Approximation one, and is system-independent and simulation-based. This means that the probability density function (pdf) of the sampled electrical current is estimated based on training data provided via simulations without any assumptions on the specific configuration of the communications system under consideration. The novelty of the paper is that for the first time a combination of a generalized form of the gamma distribution together with the noncentral chi-square distribution have been used for the modeling of the pdfs of the spaces and the marks, respectively. [Copyright &y& Elsevier]

Abstract: This paper reports on a novel design of a remote sensor for temperature detection based on surface plasmon resonance and optical fiber technology. We theoretically analyze the performance of proposed sensor under different conditions related to its constituents, i.e., optical fiber, metallic layer, sensing region, and launched light. The effect of the related parameters such as numerical aperture, fiber length, core diameter, FWHM of the Gaussian input on sensor is analyzed along with its physical explanation. The numerical results presented in this paper leads to a significant optimization of the important design parameters to achieve a high temperature detection accuracy and sensitivity of a fiber optic remote sensor. [Copyright &y& Elsevier]

This paper studies optical solitons and its perturbations that is governed by the generalized nonlinear Schro¨dinger's equation with non-Kerr law nonlinearities. The quasi-stationarity is applied, for the first time, to the non-Kerr law nonlinearity and an approximate solution is obtained. A few special cases of the non-Kerr law nonlinearities are considered. The study is conducted with nonlinear damping and saturable amplifiers which are treated as perturbation terms. Finally, the paper concludes with some numerical results. [Copyright &y& Elsevier]

In this paper, a high-sensitivity magnetic field sensor is proposed. The sensor consists of a spindly optical fiber taper (SOFT) coated with magnetic fluid. The SOFT structure is made through fusing taper method and connected to a fiber loop for magnetic field sensing. The experiment results show that the sensor is barely dependent on laser wavelength within the range of 1520 nm to 1575 nm. When the magnetic field of 180 Oe is applied, the transmission change reaches up to 3.324 dB at 1550 nm. Additionally, the magnetic field sensitivity of the sensor is − 23. 4 μ s /Oe in the linear region of 10 Oe−80 Oe. Compared with the traditional fiber optic magnetic field sensor with the fiber loop ring-down (FLRD), the proposed SOFT sensor could achieve higher magnetic field sensitivity. • A spindly optical fiber taper (SOFT) structure is proposed to measure magnetic field. • The SOFT sensor has good magnetic field response ability while maintaining low loss. • The optimization of the fiber loop parameters is studied. • We could achieve higher magnetic field sensitivity compared with the previous sensors. [ABSTRACT FROM AUTHOR]

• The physical-layer security of the IM-QNRC with CMA is quantitatively analysed. • The NMN and the PCG are used as metrics to assess the security. • The QNRC system combined with CMA can realize higher anti-interception communication. By applying intensity modulation, the quantum noise random cipher (QNRC) hides the signal amplitude in quantum noise to prevent eavesdropping. It is an essential topic for evaluating the secret performance of the QNRC system. In this paper, the physical-layer security of the QNRC based on intensity modulation (IM-QNRC) with chaos masking (CMA) is quantitatively analysed. The model of the transmission system is built. Additionally, the noise-mask-signal number (NMN) and the probability of correctly guessing data for the interceptor (PCG) are used as metrics to assess the security of the physical layer. The general expression of PCG for an eavesdropper is derived. A comprehensive evaluation and comparison of the security metrics versus several system parameters are carried out. Based on simulation, the mixing of chaos masking reduces the PCG of the QNRC system with suitable parameters by approximately 8 orders of magnitude. The QNRC system combined with CMA can realize higher anti-interception communication. [ABSTRACT FROM AUTHOR]

• LEAF optical fiber Brillouin signature allows temperature and strain discrimination. • Irradiation exposure of LEAF improves temperature and strain discrimination. • Measurement only requires one fiber and one Brillouin-based interrogation technique. • Temperature and strain sensitivities of LEAF are affected by the irradiation. • Suitable technique under irradiation depending on the application. In this paper, we investigate the accessible performances in terms of strain and temperature discrimination using Brillouin Optical Time Domain Analysis (BOTDA) combined with the LEAF fiber (from Corning) when exposed to γ-rays up to doses of 1 MGy(SiO 2). This optical fiber offers a multipeak Brillouin Gain Spectrum (BGS) with unique dependencies of each of its peaks over temperature and strain. The discrimination capability evolution of LEAF is investigated at high γ doses and dose rates to evaluate the radiation effects on the sensing performances. Gamma irradiation leads to modifications of the LEAF BGS signature through two main effects. First, the Radiation Induced Attenuation (RIA) of this germanosilicate optical fiber limits the BGS amplitude, sensing range and capability for discrimination over BGS amplitude. Second, radiations modify the Brillouin scattering properties by slightly changing the refractive indices and the acoustic velocities of the fiber core and cladding leading to a small change in temperature and strain dependences as well as a limited Radiation Induced Brillouin Frequency Shift (RI-BFS) causing a direct error on the measured parameters. Results exhibit an overall decrease of temperature and strain uncertainties through discrimination process after 1 MGy irradiation reaching 0. 9 ° C and 29 μ ε for 0.1 MHz frequency uncertainty. [ABSTRACT FROM AUTHOR]

• A compact, high-sensitivity magnetic field sensor is experimentally demonstrated. • Higher M factor of the Vernier effect due to the usage of hybrid interferometers. • Experimental results show that a linear sensitivity of 811.53 pm/mT is reached. This paper presents and demonstrates an ultra-sensitive magnetic field sensor using a hybrid interferometer. The sensor is created by combining a Sagnac loop interferometer (SI) and a Fabry-Perot interferometer (FPI). The difference in the free spectrum ranges of the two cavities generates a Vernier effect, which amplifies the sensitivity. Experimental results indicate that the sensitivity of the single FP cavity is 25 pm/mT, while the sensitivity of the hybrid sensor is 811.53 pm/mT, which is about 32 times higher than that of a single individual FPI. The sensor can be applied in harsh environment such as mine, oil well and other fields. [ABSTRACT FROM AUTHOR]

• Composite concentric mandrel optical fiber hydrophone specifically for the submarine sonar applications. • The special features are high sensitivity, higher natural frequency and hydrostatic pressure tolerance. • A composite material based on aluminium, hard plastic HDPE and soft plastic Syntactic Foam provides both structural stabilities required at operational depths and good compliance with acoustic pressure improving sensitivity. • A detailed design using finite element analysis revealed not only an optimum hydrophone configuration but also the effect of material mechanical properties and the geometry. • An omni directional directivity pattern is obtained. • The optical components connected with the hydrophone viz. coupler and reflector (faraday mirror) can be packed inside the air cavity space. • The interconnection of multiple hydrophones on to a single fiber is possible just by the splicing methods. The optical fiber hydrophones are well suited for the submarine passive sonar applications taking into consideration of their high sensitivity, fully electrically passive characteristics etc. and are definitely an equivalent replacement for Lead Zirconate and Lead Titanate ceramic hydrophones. In this paper, finite element analysis of several sets of cases of concentric hybrid material-based air-backed OF mandrel hydrophones are analysed and tuned to their geometric dimensions and their mechanical properties for design optimization, suitable for submarine sonar applications. A finite element method is adopted for analysis, strain and sensitivity calculations using ANSYS software. An inverse dependency of the sensitivity and the natural frequency were observed and was overcome by an innovative method where a hybrid inner hollow tube, combining both Aluminium and high-density polyethylene materials, were used, improving both the stiffness property and compliance of the mandrel and thereby improving both the natural frequency and pressure sensitivity. The harmonic analysis was carried out at 5 KHz acoustic pressure, by adding hydrostatic pressures of 2 MPa, 3 MPa and 4 MPa and obtained satisfying results. The acoustic directivity of this OF mandrel hydrophone was estimated, plotted and an omni directional pattern was obtained. [ABSTRACT FROM AUTHOR]

The all-fiber voltage sensor is difficult for application because of its complex structure, difficult signal demodulation, and sensitivity to the environment. In this paper, a wavelength modulated all-fiber voltage sensor with a simple structure is designed and proposed using straight tapered single-mode fiber and stacked piezoelectric crystal as a voltage sensing unit. The simulation analysis of its performance shows that it can realize the voltage measurement of 0 kV ∼ 10.41 kV, and the accuracy can reach 0.2%. Additionally, the tapered fiber has good strain sensitivity and temperature insensitivity, and its sensitivity is up to 0.03206 nm / μ ε with low bending loss. [ABSTRACT FROM AUTHOR]

This paper presents a respiratory frequency system composed by a polymer optical fiber sensor using a smartphone as the interrogator and a remote access to information through a Web server. The system developed a locally-based signal processing method for a dedicated designed application while ensuring remote access using the Thingspeak Web server and application. To check the sensor accuracy, tests with known respiratory rates of 30, 35 and 40 Breaths per Minute (BPM), respectively, are performed using a metronome. The sensor is manually stretched on the metronome beats frequency and the results achieved by the system were of 30.3599, 35.88 and 41.4 BPM. Furthermore, tests are performed in volunteers to check system performance in a real environment, where the volunteers are asked to breathe normally so their respiratory rate could be counted manually and compared to the values delivered by the experimental system in a given period. The error rate verified in the validation experiments are less than 2%. To verify the remote access to information, it is checked whether the respiratory rate data measured by the acquisition system is accordingly sent and visualized by Thingview: the application used in this prototype. The frequency read on the app is the same as measured by the sensor, which shows the suitability of the proposed approach for remote sensing applications with cloud integration. • Local data acquisition using a smartphone and dedicated platform. • Smartphone-integrated optical fiber sensor for real-time respiration monitoring. • Remote Access to information using free web server and application. [ABSTRACT FROM AUTHOR]

Thulium-doped fiber laser (TDFL) devices are a promising laser source technology for applications in the wavelength of 2000 nm, such as spectroscopy, sensing, medical, among many others. Several pulse regimes employing different approaches have been constantly demonstrated in the scientific literature. Particularly, the development of new saturable absorber (SA) materials with exceptional nonlinear optical properties has become an efficient methodology for generating short pulses in fiber laser cavities at 2000 nm. Looking for clarifying the current state of the art of TDFL technology at 2000 nm, we review in this paper the main achievements of TDFLs in the last five years (2022–2018) based on SA materials. Nonlinear optical properties of these materials, experimental setup arrangements, as well as new avenues are addressed in this review for the advancements in source laser technologies operating at 2000 nm. • A review of the thulium-doped fiber lasers based on saturable absorbers is done. • Nonlinear optical properties of the saturable absorber materials are addressed. • Experimental setups, as well as future perspectives, are also discussed. [ABSTRACT FROM AUTHOR]

• A high sensitivity salinity sensor based on tapered optical fiber is proposed. • The tapered optical fiber salinity sensor based on SPR effect possesses the highest sensitivity of 0.708 nm/‰. • The protection of gold film makes the sensor have long-term effectiveness and high repeatability. High sensitivity detection of seawater salinity has important practical significance. SPR fiber optic sensors based on tapered fiber optic have high sensitivity to refractive index and are widely used in fields such as physics, chemistry, and biology. In this paper, a tapered fiber optic was prepared using a fusion tapering process, and the morphology of the SPR sensor was optimized by adjusting three important parameters: taper length, waist diameter, and coating thickness. The influence of these factors on the sensor performance was studied through simulations. Based on the quality factor as the main evaluation criterion, a tapered fiber optic SPR sensor with a taper length of 27 mm, waist diameter of 25 μm, and coating thickness of 40 nm (Au) was selected through experiments. This sensor was used to detect seawater salinity, and its sensitivity reached 0.708 nm/‰ with good linearity. The experiment also proved the long-term effectiveness of the sensor. [ABSTRACT FROM AUTHOR]

Multidimensional optical modulation (MOM) is one of the promising techniques for spectrally efficient optical access network transmissions. However, inter-dimensional interference (IDI) in MOM limits the signal-to-interference-plus-noise ratio (SINR) giving trade-off between each dimension. In this paper, we propose IDI-tolerant four-dimensional (4-D) set-partitioning quadrature amplitude modulation with M−ary differential phase shift keying (SP-QAM-MDPSK) based on direct-detection (DD) systems. We compared the proposed scheme with QAM-MDPSK without set-partitioning and experimentally demonstrate SP-16QAM-16DPSK over 20-km single-mode fiber, results in nearly 3 dB signal-to-noise ratio (SNR) gain at 3 × 10 - 2 symbol error rate (SER) compared to 16QAM-4DPSK, which shows that SP-QAM-MDPSK is tolerant to the possible IDI. [ABSTRACT FROM AUTHOR]

• The delayed resource allocation is developed for AR requests. • A resource allocation sorting strategy based on the relative flexibility of requests is proposed. • The strategy makes full use of the time characteristics of AR request to determine the allocation order of requests. • The simulation results show that the proposed algorithm is better than the benchmark algorithm. With the advantages of fine granularity spectrum allocation (SA) and large capacity, elastic optical networks (EONs) are considered as the most promising development direction of optical network in the future. The emergence of two-dimensional (2-D) fragmentation during dynamic SA of EONs not only reduces the availability of resources but also increases the blocking probability of requests. In addition, the advance reservation (AR) request has the characteristics of resource reservation and time flexibility, which further complicates the fragmentation issue. To solve the above issues, in this paper, a fragmentation-aware routing, modulation and spectrum assignment (RMSA) algorithm for AR requests is proposed. First, delayed resource allocation is developed for AR requests. Second, a resource allocation sorting strategy based on the relative flexibility of requests is proposed. The strategy makes full use of the time characteristics of AR request to determine the allocation order of requests. In addition, from the perspective of the impact on adjacent resources, a 2-D path resource model is introduced to evaluate the impact of 2-D fragmentation from the perspective of resource matching degree and resource connectivity. Moreover, simulation results show that the proposed algorithm is better than the benchmark algorithm in terms of blocking probability, resource utilization and fragmentation rate. [ABSTRACT FROM AUTHOR]

• SPR-based optical fiber sensor for salinity measurement. • FBG sensors for salinity assessment through thermal responses. • Combination of SPR and FBG sensors for higher accuracy in salinity estimation. This paper presents a novel optical fiber sensor system for salinity monitoring using data fusion in different optical fiber sensors approaches. In this case, a surface Plasmon resonance (SPR) sensor in a D-shaped optical fiber is developed in conjunction with a fiber Bragg grating (FBG). The SPR sensors are able to detect the liquid sample salinities through the refractive index variation of the different samples. In contrast, the FBG sensors estimate the salinity through the thermal dynamics of the samples. Results show a sensitivity of 164.0 nm/% and 12.5 pm/°C for the SPR and FBG sensors, respectively. Thus, the combination between the SPR and FBG sensors result in an improvement of the salinity monitoring of different samples, where a root mean squared error of 0.001% is obtained. [ABSTRACT FROM AUTHOR]

• An actual DML-based MB-OFDM UWBoF system was constructed and investigated. • The ISFA algorithm is applied to improve the SNR and channel estimation accuracy of the DML-based MB-OFDM UWBoF system. • OCT precoding is employed to average the SNR of DML-based MB-OFDM UWBoF systems. In this paper, an intensity-modulated direct-detection (IM/DD) multiband orthogonal-frequency-division-multiplexing ultra-wideband over fiber (MB-OFDM UWBoF) transmission system using a low-cost directly modulated laser (DML) is analyzed and experimentally verified. Precoding techniques and inter-symbol frequency-domain averaging (ISFA) algorithm are used in this experiment. Precoding techniques are used to suppress the noise introduced by DML and the power fading due to the imperfect frequency response of optoelectronic devices and frequency selective fading. Orthogonal Circular Matrix Transform (OCT) precoding and Discrete Fourier Transform (DFT) precoding were compared when the ISFA algorithm was used. In this scheme, for a single-mode fiber (SMF) link at a distance of 20 km, the 64 Quadrature amplitude modulation (QAM) mapped MB-OFDM UWBoF system using OCT precoding with ISFA and DFT precoding with ISFA scheme can improve the sensitivity of the optical receiver by 0.4 dBm and 0.284 dBm, respectively, compared to no precoding with ISFA at a BER of 3.8e-3. The minimum BER of the 64QAM mapped MB-OFDM UWBoF system scheme with OCT precoding and ISFA scheme is 2.56e-5, which achieves two orders of magnitude improvement compared to the BER threshold of the 7% hard-decision forward error correction (HD-FEC, 3.8e-3). [ABSTRACT FROM AUTHOR]

• 1:3 scale laboratory train model. • Rail track stability, rail-wheel contact stress in laboratory rail test rig. • Vertical force of wheel to axial strain on the rail measurement using optical sensors. • Train axle peak detection, rolling contact fatigue analysis using FBG in laboratory train test rig. • Fiber Bragg grating sensing technology in rail transport. Railway and train condition monitoring are two critical components in assuring passenger safety and comfort during their journey. In this work, a new laboratory downscale rail test rig has been designed and developed for exploring rail-wheel interaction and axle peak detection using fiber Bragg grating (FBG) optical sensors. This paper describes the laboratory setup's development process which includes numerical analysis of rail model, review of different experimental techniques, followed by 1:3 scaled model, mechanical and functional analysis of the railway setup with the grating sensor. By employing various data processing techniques axle peak detection of train was done and strain/stress transfer was calculated by the train passage to the rail track which was ∼100.86 µɛ. Total wavelength shit in the FBG sensor was 0.133 nm due to wheel load and sensitivity value was calculated approximately 1.36 pm/µɛ for the wavelength/strain changes. Characteristics of 1:3 laboratory rail test rig such as track retention, number of wheels, axle peak detection, rail-wheel rolling contact, stress/strain track deformation can be obtained in real time with fiber Bragg grating sensors. [ABSTRACT FROM AUTHOR]

• An innovative structure design and sensing theory combination were proposed. • High sensitivity temperature sensor was achieved by PDMS microcavity. • Simple basic SMSMS structure lowered the fabrication difficulty. • Combined SMSMS + PDMS cavity structure brought sensing improvement for about 7 times. • Two combined sensors can cross-correct within the intersected detection range. • With simple manufacture steps, higher temperature sensitivity and bigger sensing range are achieved. In this paper, an optic-fiber temperature sensor is proposed with an innovative structure design and sensing theory combination. The structure design is consisted of classic SMSMS structure and a polydimethylsiloxane (PDMS) microcavity, which is formed by inserting single mode fibers (SMF) and multimode fibers (MMF) from both ends of a hollow core fiber (HCF) filled with uncured PDMS. By adjusting the length (L) of the cavity into proper value, the reflection temperature sensitivity reaches up to −567.86 pm/℃, and the transmission sensitivity reaches −120.69 pm/℃. Due to the presence of the PDMS microcavity, the reflection spectrum achieved highly sensitive temperature Fabry-Perot interferometer (FPI) sensor. Moreover, a Mach-Zehnder interferometer (MZI) temperature sensor also formed by monitoring the transmission spectrum, and its temperature sensitivity is elevated about 7 and 1.2 times compared with the pure splicing SMSMS and the splicing + PDMS coating structure. By deploying the PDMS microcavity, FPI sensor and MZI sensor were combined inside one device with significant temperature sensing performance, and these two combined sensors can cross-correct within the intersected detection range. With simple manufacture steps, higher temperature sensitivity and bigger sensing range are achieved. [ABSTRACT FROM AUTHOR]

• Fabricated POF composed of bisphenol-A acrylate for perceptual detection. • Analyzed four sensitivity zone (temperture, humidity, pressure and bending angle) of the BAA-POF sensor. • BAA-POF was proved for application in activity perception of the elbow joint. In this paper, a flexible optical sensor based on bisphenol-A acrylate polymer fiber (BAA-POF) is fabricated and demonstrated. The BAA-POF is composed of bisphenol-A acrylate monomers and additives in a certain proportion. When the pressure is applied to the BAA-POF, or the BAA-POF is bent by an angle, the sensor can perceive variations of the output spectrum loss caused by the sensor sensing accordingly. Experimental results show that the sensor has good linear responses to pressure and bending perception with negligible temperature and humidity cross-impact. The pressure sensitivity is 1.24 dB/N and the bending sensitivity is 0.08 dB/°. Moreover, the sensor is also proved for application in activity perception of the elbow joint. [ABSTRACT FROM AUTHOR]

• Two different structures of reflected fiber ethanol probes were compared. • Relationship of sensitivity and morphology parameters have been discussed. • Microfiber taper ethanol probe has been experimentally demonstrated. • Ethanol sensitivity of 7.18 × 10-4 dBm/ppm was obtained during 0–200 ppm. Reflected fiber probes can efficiently detect different environmental parameters in the narrow space. In this paper, the coreless fiber and the microfiber taper cascade-spliced structures were coated with the sensitive materials. Their refractive index sensing performance was studied and compared. The microfiber taper shows a sensitivity of −36.581 dBm/RIU, which is significantly higher than that of the coreless fiber structure with the same length (-9.482 dBm/RIU). The reflected microfiber taper ethanol gas sensor was made by surface-modified with the mixtures containing zinc oxide nanosheets and UV glue with low refractive index. In experiment, as the ethanol concentration increased, the intensity of the reflection spectrum increased, resulting in the sensitivity of 7.18 × 10-4 dBm/ppm. This miniature fiber structure can be integrated into the conventional optical fiber system to develop the miniature detectors with high performance. [ABSTRACT FROM AUTHOR]

• We proposed layered QAM signal realized by constellation layering technique. • We proposed super-channel transmission based on self-homodyne comb. • This scheme reduces the system costs and mitigate the laser phase noise. • The layered 80QAM can achieve a SNR gain of 2.7 dB compared with ordinary 80QAM. • The total data rate of the system can reach 1.57 Tbit/s. In this paper, polarization division multiplexing-layered 80-ary quadrature amplitude modulation-orthogonal frequency division multiplexing (PDM-layered 80QAM-OFDM) is proposed and demonstrated in super-channel system based on self-homodyne comb. The composition of the super-channel is derived from the optical comb generated by a single laser-driven dual polarized Mach-Zehnder modulator (DP-MZM) modulated by odd sideband suppression. Since the optical comb generated by the transmitter is used as a local oscillator (LO) signal for self-homodyne coherent detection. This scheme effectively reduces the system cost and alleviates the performance constraints caused by phase noise. Moreover, the bit error rate (BER) and generalized mutual information (GMI) of layered 24QAM/48QAM/80QAM-OFDM are evaluated to obtain the highest transmission rate and the laser linewidth tolerance of the system. The results show that in Additive White Gaussian Noise (AWGN) channel, layered QAM signal realized by low-complexity constellation layering technique can significantly improve the BER performance at a small entropy cost compared with ordinary QAM signals. Meanwhile, the layered 80QAM can achieve a signal-to-noise ratio (SNR) gain of 2.7 dB. In addition, after 40 km standard single mode fiber (SSMF) transmission, the total data rate of the system can reach 1.57 Tbit/s and the corresponding spectral efficiency (SE) is 12 bit/s/Hz when the BER of the super-channel system meets soft decision-forward error correction (SD-FEC) threshold. [ABSTRACT FROM AUTHOR]

• Measurement of large surface displacements is crucial for SHM. • Characterization of an FBG displacement sensor based on curvature sensing is presented. • Bidirectional displacement measurement is possible with high sensitivity. • Temperature compensation technique reduces contributions due to fast temperature changes. Measurement of displacement, deformation, curvature, and other physical parameters is of great importance for adequate Structural Health Monitoring (SHM) of large surfaces. Fiber Bragg Grating (FBG) sensors have become a focus of research in academia and engineering for structural monitoring applications. This paper presents the study and characterization of a displacement FBG sensor based on curvature sensing of an array of 4 FBGs , as well as possible applications for structural monitoring, developing the sensing part, and analyzing the signals obtained to develop a sensor with good sensitivity and resolution, capable of measuring bidirectional displacements. The sensor prototype is presented to measure displacements in a range of ±30 mm with a single grating, with a sensitivity of up to 74 pm/mm, linearity to R 2 = 0. 999, and hysteresis error up to 1.27 %, with temperature compensation for displacement monitoring in case of temperature variations. [ABSTRACT FROM AUTHOR]

• This article presents an FBG-based method for submarine cable shape monitoring. • The Frenet framework is used in the paper to achieve the continuity of discrete curvature. • When the monitoring system from the article was used on the undersea landing cable, it discovered potential dangers. Submarine cables are crucial in the transmission of electricity between coastal islands. Compared with terrestrial cables, submarine cables operate under harsher environments and thus their probability of failure is higher. Therefore, the effective monitoring of submarine cables is necessary to prevent related accidents. Quasi-distributed sensing technology based on fiber Bragg gratings converts the sensing information into discrete curvature information according to the pure bending theory and subsequently reconstructs the shape of the submarine cable using discrete curvature interpolation and curve reconstruction algorithms. The fiber Bragg grating sensor is placed on the landing cable section to analyze the reconstruction effect and error, demonstrating the feasibility of the method for submarine cable monitoring. Finally, the monitoring results in extreme weather reveal potential safety hazards in the submarine landing cable. [ABSTRACT FROM AUTHOR]

• Balancing the optical powers of signals with the combination of FWM and ASE noise is one of the main challenges of optical system design and OSNR optimization of signals. • The input power values that maximize the OSNR value of the channel with the lowest OSNR value among the channels with the same power were determined. • The input power values that maximized the smallest OSNR value were obtained by both PSO with fixed inertia weight and PSO with linearly decreasing inertia weight. • The values acquired by the three methods were compared and remarkable results were obtained. In this paper, a new application of the particle swarm optimization (PSO) algorithm has been carried out in the field of the optical fiber (OF) communication system. In this theoretical work, the most suitable input channel powers to reduce the disruptive effects of four-wave mixing (FWM) occurring in OF and amplified spontaneous emission (ASE) noise from optical amplifiers are determined with the help of two different particle swarm optimization (PSO) in terms of inertia weight. The figure of merit is the optical signal-to-noise ratio (OSNR) of each channel at the output end of OF. Each of the input channel powers is optimized to maximize the OSNR of the channel with the lowest OSNR. The values obtained by both optimization methods are well good compared to those obtained with equal powers allocation (EPA). The best improvement in OSNR with PSO is obtained as 1.105846 dB (2.762778 %). Moreover, the performances of both algorithms and EPA are also comparatively evaluated in the study. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the experimental transmission of 16- and 64- quadrature amplitude modulation (QAM) Long Term Evolution - Orthogonal Frequency Division Multiplexing (LTE-OFDM) signals by using millimetre wave frequencies at 60 GHz and 25 GHz for downlink and uplink, respectively, over a heterogeneous optical fronthaul infrastructure. A directly modulated laser was employed for both links, which enables the cost-effective full-duplex system proposal. The bidirectional link consists of a 10 km of single mode fiber, a 100 m long free space optics channel and 2 m long wireless radio link, which brings flexibility for future wireless networks. The error vector magnitude (EVM) parameter is measured for a range of the received optical and electrical power as well as the signal-to-noise ratio. A comprehensive estimation of penalty factors in the different network segments is presented. The successful transmission over the whole proposed network with the EVM below the required limit of 9 % for 64-QAM with 20 MHz bandwidth is experimentally demonstrated for the received optical power of −2.7 dBm and −1 dBm for the downlink and uplink, respectively. [ABSTRACT FROM AUTHOR]

• This paper carries out a detailed literature review about this topic, including resource assignment and reinforcement learning (RL)-based algorithm in OTN. • We explore multi-modal information in OTN, and express OTN and services through image. • This paper proposes a cost-efficient routing, modulation, wavelength, and port assignment (CE-RMWPA) algorithm based on RL to optimize the cost caused by ports. • The performance of CE-RMWPA is evaluated by simulation under different-scales of service. Simulation results show that the CE-RMWPA can reduce the cost. With the rapid growth of global network traffic, more and more high-capacity network services are required. Traditional wavelength division multiplexing (WDM) networks are inadequate in terms of service scheduling and network management, so optical transport networks (OTN) have been proposed. OTN offers electric-layer switching ability to support finer granularity and higher spectrum efficiency. In OTN, we need to realize routing, modulation, wavelength, and port assignment (RMWPA) for supporting optical-electric (O/E) conversion (i.e. , O/E port). Efficient RMWPA will significantly reduce the cost of operators. In this paper, we explore multi-modal information from OTN, and image the topology and routes to capture the information of the OTN and services. We design a cost-efficient RMWPA (CE-RMWPA) algorithm based on reinforcement learning to realize RMWPA for reducing cost in OTN. The proposed algorithm can interact with the OTN environment and learn how to make improved decisions based on the environment's feedback. Simulative results demonstrate that the CE-RMWPA algorithm can achieve the optimization of RMWPA for reducing cost. [ABSTRACT FROM AUTHOR]

• Parallel pipelined design and FPGA implementation of low-complexity Volterra-DFE for PAM-4 transmission. • The feed-forward section adopts a method based on multi-level register banks. • Using a method based on pre-computation and multiplexer to transform the feedback loop into a pipelined form. • The FPGA-based structure can meet the timing requirements of 250 MHz clock and achieve a throughput of 24-Gb/s. In this paper, a high-performance parallel pipelined hardware structure of Volterra decision feedback equalizer (Volterra-DFE) for 4-level pulse amplitude modulation (PAM-4) transmission is derived and implemented for the first time. For feed-forward portion, an approach based on multi-level register banks is employed, and the feedback portion is pipelined by converting complex calculation in the loop into the form of pre-computation and multiplexer. To facilitate field programmable gate array (FPGA) implementation, this paper also studies the bit error rate (BER) performance of a low-complexity Volterra-DFE to explore the minimum feedback tap setting that can reach the forward error correction (FEC) threshold, and the experimental results show that for a three-order Volterra-DFE with 61 feed-forward taps, at least 7 feedback taps are required and the received sensitivity is −19 dBm. The resource utilization of the implemented FPGA architecture is investigated and its throughput can reach 24-Gb/s, which is of great significance to real-time optical communication systems. [ABSTRACT FROM AUTHOR]