Showing papers on "Optical fiber published in 2021"

Space-division multiplexing for optical fiber communications

Abstract: Research on space-division multiplexing (SDM) came to prominence in early 2010 being primarily proposed as a means of multiplying the information-carrying capacity of optical fibers at the same time as increasing efficiency through resource sharing. Proposed SDM transmission systems range from parallel single-mode fibers with shared amplifier pump lasers to the full spatial integration of transceiver hardware, signal processing, and amplification around a fiber with over 100 spatial channels comprising multiple cores each carrying multiple modes. In this paper, we review progress in SDM research. We first outline the main classifications and features of novel SDM fibers such as multicore fibers (MCFs), multimode fibers, few-mode MCFs, and coupled-core MCFs. We review research achievements of each fiber type before discussing digital-signal processing, amplifier technology, and milestones of transmission and networking demonstrations. Finally, we draw comparisons between fiber types before discussing the current trends and speculate on future developments and applications beyond optical data transmission.

Fiber-Optic Seismology

Abstract: Distributed acoustic sensing (DAS) is an emerging technology that repurposes a fiber-optic cable as a dense array of strain sensors. This technology repeatedly pings a fiber with laser pulses, meas...

Singlemode-Multimode-Singlemode Fiber Structures for Sensing Applications—A Review

Abstract: A singlemode-multimode-singlemode (SMS) fiber structure consists of a short section of multimode fiber fusion- spliced between two SMS fibers. The mechanism underpinning the operation of an SMS fiber structure is multimode interference and associated self-imaging. SMS structures can be used in a variety of optical fiber systems but are most commonly used as sensors for a variety of parameters, ranging from macro-world measurands such as temperature, strain, vibration, flow rate, RI and humidity to the micro-world with measurands such as proteins, pathogens, DNA and specific molecules. While traditional SMS structures employ a short section of standard multimode fiber, a large number of structures have been investigated and demonstrated over the last decade involving the replacement of the multimode fiber section with alternatives such as a hollow core fiber or a tapered fiber. The objective of replacing the multimode fiber has most often been to allow sensing of different measurands or to improve sensitivity. In this paper, several different categories of SMS fiber structures, including traditional SMS, modified SMS and tapered SMS fiber structures are discussed with some theoretical underpinning and reviews of a wide variety of sensing examples and recent advances. The paper then summarizes and compares the performances of a variety of sensors which have been published under a number of headings. The paper concludes by considering the challenges faced by SMS based sensing schemes in terms of their deployment in real world applications and discusses possible future developments of SMS fiber sensors.

Ultrasensitive detection of endocrine disruptors via superfine plasmonic spectral combs.

Abstract: The apparent increase in hormone-induced cancers and disorders of the reproductive tract has led to a growing demand for new technologies capable of detecting endocrine disruptors. However, a long-lasting challenge unaddressed is how to achieve ultrahigh sensitive, continuous, and in situ measurement with a portable device for in-field and remote environmental monitoring. Here we demonstrate a simple-to-implement plasmonic optical fiber biosensing platform to achieve an improved light–matter interaction and advanced surface chemistry for ultrasensitive detection of endocrine disruptors. Our platform is based on a gold-coated highly tilted fiber Bragg grating that excites high-density narrow cladding mode spectral combs that overlap with the broad absorption of the surface plasmon for high accuracy interrogation, hence enabling the ultrasensitive monitoring of refractive index changes at the fiber surface. Through the use of estrogen receptors as the model, we design an estradiol–streptavidin conjugate with the assistance of molecular dynamics, converting the specific recognition of environmental estrogens (EEs) by estrogen receptor into surface-based affinity bioassay for protein. The ultrasensitive platform with conjugate-induced amplification biosensing approach enables the subsequent detection for EEs down to 1.5 × 10−3 ng ml−1 estradiol equivalent concentration level, which is one order lower than the defined maximal E2 level in drinking water set by the Japanese government. The capability to detect EEs down to nanogram per liter level is the lowest limit of detection for any estrogen receptor-based detection reported thus far. Its compact size, flexible shape, and remote operation capability open the way for detecting other endocrine disruptors with ultrahigh sensitivity and in various hard-to-reach spaces, thereby having the potential to revolutionize environment and health monitoring. An optical fiber biosensor displaying superfine plasmonic spectral combs and enhanced by conjugate-induced amplification enables the detection of environmental estrogens down to pg/mL estradiol equivalent concentration level.

Crack monitoring in reinforced concrete beams by distributed optical fiber sensors

Abstract: This paper investigates the use of distributed optical fiber sensors (DOFS) based on Optical Frequency Domain Reflectometry of Rayleigh backscattering for Structural Health Monitoring purposes in civil engineering structures. More specifically, the results of a series of laboratory experiments aimed at assessing the suitability and accuracy of DOFS for crack monitoring in reinforced concrete members subjected to external loading are reported. The experiments consisted on three-point bending tests of concrete beams, where a polyamide-coated optical fiber sensor was bonded directly onto the surface of an unaltered reinforcement bar and protected by a layer of silicone. The strain measurements obtained by the DOFS system exhibited an accuracy equivalent to that provided by traditional electrical foil gauges. Moreover, the analysis of the high spatial resolution strain profiles provided by the DOFS enabled the effective detection of crack formation. Furthermore, the comparison of the reinforcement strain profiles with measurements from a digital image correlation system revealed that determining the location of cracks and tracking the evolution of the crack width over time were both feasible, with most errors being below +/- 3 cm and +/- 20 mu m, for the crack location and crack width, respectively.

Generation of polarization and phase singular beams in fibers and fiber lasers

Abstract: Cylindrical vector beams and vortex beams, two types of typical singular optical beams characterized by axially symmetric polarization and helical phase front, possess the unique focusing property and the ability of carrying orbital angular momentum. We discuss the formation mechanisms of such singular beams in few-mode fibers under the vortex basis and show recent advances in generating techniques that are mainly based on long-period fiber gratings, mode-selective couplers, offset-spliced fibers, and tapered fibers. The performances of cylindrical vector beams and vortex beams generated in fibers and fiber lasers are summarized and compared to give a comprehensive understanding of singular beams and to promote their practical applications.

Low-chirp isolator-free 65-GHz-bandwidth directly modulated lasers

Abstract: Today, in the face of ever increasing communication traffic, minimizing power consumption in data communication systems has become a challenge. Direct modulation of lasers, a technique as old as lasers themselves, is known for its high energy efficiency and low cost. However, the modulation bandwidth of directly modulated lasers has fallen behind those of external modulators. In this Article, we report wide bandwidths of 65–75 GHz for three directly modulated laser design implementations, by exploiting three bandwidth enhancement effects: detuned loading, photon–photon resonance and in-cavity frequency modulation–amplitude modulation conversion. Substantial reduction of chirp (α < 1.0) as well as isolator-free operation under a reflection of up to 40% are also realized. A fast data transmission of 294.7 Gb s−1 over 15 km of a standard single-mode fibre in the O-band is demonstrated. This was achieved without an optical fibre amplifier due to a high laser output power of 13.6 dBm. Directly modulated semiconductor lasers are shown to be able to operate with bandwidths exceeding 65 GHz thanks to a cavity design that harnesses photon–photon resonances.

Advances in Optical Fiber Sensors Based on Multimode Interference (MMI): A Review

Abstract: In recent years, optical fiber sensors based on multimode interference (MMI) have attracted increasing interest and developed into various sensors used in many practical applications. This review presents MMI-based fiber sensors with a specific focus on the probe structures, measurement methods, and sensing properties of different structures. The fundamentals of MMI-based fiber sensors are briefly described. Further, five main categories of SMS structure-based fiber sensors are reviewed, including conventional SMS fiber sensors, MMI-based sensors with no-core fiber (NCF), MMI-based sensors with etched/polished fiber, MMI-based sensors with tapered fiber, and cascades of MMI-based fiber sensors. Besides, their probe structures, sensing properties, practical fields, and measurement sensitivities are summarized. Finally, the current challenges and technique outlook of the MMI-based fiber sensors are pointed out, which gives the potential solutions for the existing problems and future development. This work indicates that the MMI-based fiber sensors bring the possibilities of applying multi-mode fiber (MMF) in different measurement fields with high sensitivities, easy fabrication, and low cost. With the appearance and development of new SMS fiber sensors, it will contribute significant value to scientific research and industrial applications.

Photonic smart bandage for wound healing assessment

Abstract: Chronic wounds affect around 2% of the world population with an annual multi-billion dollar cost to the healthcare system. This background pushes the development of new therapies and procedures for wound healing and its assessment. Among them, the potential of hydrogen (pH) assessment is an important indicator of the wound healing stage and condition. This paper presents the development of the first optical fiber-embedded smart wound dressing for pH assessment. An intrinsically pH-sensitive optical fiber is fabricated using a polydimethylsiloxane (PDMS) precursor doped with rhodamine B dye. Raman and Fourier transform infrared (FTIR) spectroscopies are performed in order to verify the presence of rhodamine B and PDMS in the fiber samples. Then, the fiber is embedded in gauze fabric and hydrocolloid wound dressing. In addition, such low Young’s modulus of PDMS fiber enables its use as a highly sensitive pressure sensor, where the results show that the fiber-embedded bandage can measure pressures as low as 0.1 kPa with a high linearity in the range of 0 to 0.3 kPa. The smart bandage is subjected to different pH, which resulted in a wavelength shift of 0.67 nm/pH when the absorption peak at 515 nm was analyzed. Furthermore, pH increase leads to linear decrease of the transmitted optical power (R2 of 0.998), with rise and fall times below 20 s and 30 s, respectively. Therefore, the proposed optical fiber-embedded smart bandage enables the simultaneous assessment of pressure and pH on the wound region.

High speed pulse generators with electro-optic modulators based on different bit sequence for the digital fiber optic communication links

Abstract: The paper outlines the simulation of various pulse generators for the enhancement of optical fiber access transmission networks within flow rate of 10 Gbps and transmission range of 100 km. The pulse generators are gaussian, hyperbolic secant, triangle, sine, raised cosine in the transmission stage. Proposed pulse generators are mixed with both electro-absorption modulator (EAM) and mach-zehnder modulator (MZM) for efficient transmission. We have compared the max. the quality factor with using proposed pulse generators against nonreturn to zero (NRZ) return to zero (RZ) pulse generators in the previous research works for different bit sequences. The signal power amplitude is tested for both optical fiber and PIN photodetector optical time-domain visualizer and RF spectrum analyzer by using in the optimum cases for different bit sequence. It is observed that proposed pulse generators/EAM have presented an efficient increase in Q-factor value compared with proposed pulse generators/MZM for different bit sequences.

High speed modulated wavelength division optical fiber transmission systems performance signature

Abstract: This study presents modulated-wavelength division radio signals over fiber with mixed modulation techniques in the transmitter stage. Hybrid optical sources are used to achieve optimal performance and enhancement for an optical fiber communication network. The proposed modulation techniques work at a frequency of 250 GHz. Optical quadrature phase shift keying (OQPSK) and phase modulation (PM) techniques were merged to create OQPSKPM. This was in addition to the minimum shift keying (MSK) modulation scheme that was applied in the proposed model. The modulated wavelength division multiplexing design to four subscribers was examined with a single mode optical fiber at a 1550 nm wavelength. The proposed and previous simulation models were executed, investigated and measured on important operating parameter quantities that expressed the behavior of the optical fiber network in detail, like maximum quality factor, minimum bit error rate, and output power. The obtained simulation results demonstrated the priority of the proposed simulation model.

Review of Femtosecond-Laser-Inscribed Fiber Bragg Gratings: Fabrication Technologies and Sensing Applications

Abstract: Fiber Bragg grating (FBG) is the most widely used optical fiber sensor due to its compact size, high sensitivity, and easiness for multiplexing Conventional FBGs fabricated by using an ultraviolet (UV) laser phase-mask method require the sensitization of the optical fiber and could not be used at high temperatures Recently, the fabrication of FBGs by using a femtosecond laser has attracted extensive interests due to its excellent flexibility in creating FBGs array or special FBGs with complex spectra The femtosecond laser could also be used for inscribing various FBGs on almost all fiber types, even fibers without any photosensitivity Such femtosecond-laser-induced FBGs exhibit excellent thermal stability, which is suitable for sensing in harsh environment In this review, we present the historical developments and recent advances in the fabrication technologies and sensing applications of femtosecond-laser-inscribed FBGs Firstly, the mechanism of femtosecond-laser-induced material modification is introduced And then, three different fabrication technologies, ie, femtosecond laser phase mask technology, femtosecond laser holographic interferometry, and femtosecond laser direct writing technology, are discussed Finally, the advances in high-temperature sensing applications and vector bending sensing applications of various femtosecond-laser-inscribed FBGs are summarized Such femtosecond-laser-inscribed FBGs are promising in many industrial areas, such as aerospace vehicles, nuclear plants, oil and gas explorations, and advanced robotics in harsh environments

Structure design and application of hollow core microstructured optical fiber gas sensor: A review

Abstract: Gas sensors play an important role in the increasing trend of industrial automation in recent years. Hollow core microstructured optical fibers have become a popular material for gas sensors because of their unique structure and excellent performance. In this paper, the hollow-core microstructured optical fiber gas sensors are divided into two types (interferometric type and absorptive type) according to the sensing principle. The corresponding principles and structures are introduced and discussed respectively. We focus on the research progress and key performance of hollow core microstructured optical fiber based gas sensors reported in the past 10 years to compare and discuss their advantages and disadvantages, as well as their future development prospects.

Power control strategies and network performance assessment for C+L+S multiband optical transport

Abstract: Spatial-division multiplexing (SDM) and band-division multiplexing (BDM) have emerged as solutions to expand the capacity of existing C-band wavelength-division multiplexing (WDM) optical systems and to deal with increasing traffic demands An important difference between these two approaches is that BDM solutions enable data transmission over unused spectral bands of already-deployed optical fibers, whereas SDM solutions require the availability of additional fibers to replicate C-band WDM transmission On the other hand, to properly design a multiband optical line system (OLS), the following fiber propagation effects have been taken into account in the analysis: (i) stimulated Raman scattering (SRS), which induces considerable power transfer among bands; (ii) frequency dependence of fiber parameters such as attenuation, dispersion, and nonlinear coefficients; and (iii) utilization of optical amplifiers with different doping materials, thus leading to different characteristics, eg, in terms of noise figures This work follows a two-step approach: First, we aim at maximizing and flattening the quality of transmission (QoT) when adding L- and ${\rm L} {+} {\rm S}$-bands to a traditional WDM OLS where only the C-band is deployed This is achieved by applying a multiband optimized optical power control for BDM upgrades, which consists of setting a pre-tilt and power offset in the line amplifiers, thus achieving a considerable increase in QoT, both in average value and flatness Second, the SDM approach is used as a benchmark for the BDM approach by assessing network performance on three network topologies with different geographical footprints We show that, with optical power properly optimized, BDM may enable an increase in network traffic, slightly less than an SDM upgrade but still comparable, without requiring additional fiber cables

No-core optical fiber sensor based on surface plasmon resonance for glucose solution concentration and temperature measurement

Abstract: The accuracy of the surface plasmon resonance (SPR) optical fiber sensor is affected by the change of ambient temperature Therefore, we propose a simple dual channel SPR optical fiber sensor, which can measure both glucose concentration and ambient temperature The proposed sensor is a two-channel structure based on a no-core optical fiber (NCF): one channel is coated with gold film and polydimethylsiloxane (PDMS) to sense the ambient temperature, and the other is coated with silver film to sense glucose concentration The experimental results show that the sensor's sensitivity for sensing glucose concentration is 2882 nm / %, and for sensing temperature is -2904 nm / °C By monitoring the real-time temperature, the accuracy of glucose concentration detection was improved The proposed sensor has a simple and compact structure, and it is suitable for sensing glucose solution or other analyte solutions that need temperature compensation

Optical fiber sensors for glucose concentration measurement: A review

Abstract: In the past few decades, glucose sensors have attracted continuous attention due to demands in diabetes diagnosis, component analysis, biological detection and environmental monitoring. Optical fiber sensors (OFS) as ideal platforms for glucose detection, presents good biocompatibility, small size, anti-electromagnetic interference, chemical inertness and distinct advantages in remote and real-time monitoring. In this paper, we give a briefly review of the current research progress of optical fiber glucose sensor (OFGS). Three detection principles are described firstly, including oxidation reaction and covalent binding, relationship between concentration and refractive index (RI). Furthermore, several methods in measurement such as Surface plasmon resonance (SPR) method, fiber grating method, modal interference method, and fluorescence method are investigated. Finally, we discuss the shortcomings on OFGS and provide an outlook for OFGS.

Fiber optic propagation problems and signal bandwidth measurements under high temperature and high dopant germanium ratios

Abstract: This study presents fiber optic losses/dispersion and signals bandwidth measurements under high temperature and high dopant germanium ratios variations for ultra-long haul distances without amplification stage. The fiber losses, fiber dispersion, and total fiber data rates are estimated and compared with the previous results under room temperature and high germanium dopant ratios to silica glass fiber. Then the model is extended for ultra-fiber transmission distances up to 500 km under high-temperature variations without using any amplification stage. The fiber losses/dispersion coefficient is degraded, and the total fiber data rates are enhanced with the increment of high dopant ratios of germanium.

Simulative study on the cascaded stages of traveling wave semiconductor optical amplifiers based multiplexing schemes for fiber optic systems improvement

Abstract: This study has outlined the performance analysis of the cascade traveling-wave optical amplifier (Semiconductor optical amplifier [SOA]) with multiplexing techniques based on fiber communication transceiver systems. The maximum Quality factor is measured against signal power. Signal input power level is enhanced by using the suggested model with previous model. The low pass Bessel filter removes the unwanted ripples from the original signal. The suggested model has clarified better performance efficiency than the previous model.

Complex-Valued Neural Network Design for Mitigation of Signal Distortions in Optical Links

Abstract: Nonlinearity compensation is considered as a key enabler to increase channel transmission rates in the installed optical communication systems. Recently, data-driven approaches – motivated by modern machine learning techniques – have been proposed for optical communications in place of traditional model-based counterparts. In particular, the application of neural networks (NN) allows improving the performance of complex modern fiber-optic systems without relying on any a priori knowledge of their specific parameters. In this work, we introduce a novel design of complex-valued NN for optical systems and examine its performance in standard single mode fiber (SSMF) and large effective-area fiber (LEAF) links operating in relatively high nonlinear regime. First, we present a methodology to design a new type of NN based on the assumption that the channel model is more accurate in the nonlinear regime. Second, we implement a Bayesian optimizer to jointly adapt the size of the NN and its number of input taps depending on the different fiber properties and total length. Finally, the proposed NN is numerically and experimentally validated showing an improvement of 1.7 dB in the linear regime, 2.04 dB at the optimal optical power and 2.61 at the max available power on Q-factor when transmitting a WDM 30 × 200G DP-16QAM signal over a 612 km SSMF legacy link. The results highlight that the NN is able to mitigate not only part of the nonlinear impairments caused by optical fiber propagation but also imperfections resulting from using low-cost legacy transceiver components, such as digital-to-analog converter (DAC) and Mach-Zehnder modulator.

Overview of refractive index sensors comprising photonic crystal fibers based on the surface plasmon resonance effect [Invited]

Abstract: Optical fibers have been widely applied to telecommunication, imaging, lasers, and sensing. Among the different types of fibers, photonic crystal fibers (PCFs), also called microstructured optical fibers, characterized by air holes arranged along the length of fibers have experienced tremendous advance due to their unique advantages. They are regarded as a desirable platform to excite surface plasmon resonance (SPR) because of easy realization of phase matching conditions between the fundamental core mode and the plasmonic mode, which plays a critical role in miniaturization and integration of SPR sensors. In this mini-review, the current status of PCF sensors based on SPR is summarized. The theory of SPR is discussed, and simulation methods for PCF-SPR sensors are described. The important parameters including the refractive index detection range, resonance wavelength, and spectral sensitivity responsible for the sensing properties of PCF-SPR sensors are reviewed. The fabrication and the comparison of performances are also illustrated, and, finally, the challenges and future perspectives are outlined.

Label-Free Biosensors Based on Long Period Fiber Gratings: A Review

Abstract: Fiber optic label-free biosensors are currently experiencing wide diffusion, as they combine the performance of optical measurements with the advantages of optical fiber. This paper presents a comprehensive review about the design, development and testing of biosensor solutions based on in-fiber long period gratings (LPG). The attention is focused on optical transducers and methodologies allowing a significant enhancement of the sensitivity. Moreover, coating nanomaterials, bio-functionalization strategies and recognition elements providing the selectivity to the target analyte are reported in detail. The aim is to provide a detailed review concerning the state of the art about LPG-based label-free biosensors and to outline the future research trends.