Recently developed micro- and nano-structured optical fiber sensors, with particular reference to surface plasmon resonance (SPR) fiber sensors and photonic crystal fiber (PCF) sensors are reviewed. SPR fiber sensors can have diverse structures such as D-shape, cladding-off, fiber tip or tapered fiber structures. Some of the recently developed novel structures include the use of various types of fiber gratings in SPR fiber sensors. PCF sensors cover diverse recent developments on photonic-bandgap fiber, holey fiber, hole-assisted fiber and Bragg fiber sensors. Major applications of these include gas sensors and bio-sensors. These micro- and nano-structured fiber sensors have attracted considerable research and development interest, because of their distinct advantages, which include high sensitivity, small sensor head footprint and the flexibility of the optical fibers. They are also of academic interest, and many novel ideas are continuously developed.
It is proposed that using Ethernet in the fronthaul, between base station baseband unit (BBU) pools and remote radio heads (RRHs), can bring a number of advantages, from use of lower-cost equipment, shared use of infrastructure with fixed access networks, to obtaining statistical multiplexing and optimised performance through probe-based monitoring and software-defined networking. However, a number of challenges exist: ultra-high-bit-rate requirements from the transport of increased bandwidth radio streams for multiple antennas in future mobile networks, and low latency and jitter to meet delay requirements and the demands of joint processing. A new fronthaul functional division is proposed which can alleviate the most demanding bit-rate requirements by transport of baseband signals instead of sampled radio waveforms, and enable statistical multiplexing gains. Delay and synchronisation issues remain to be solved.
► An all-fiber mid-infrared supercontinuum source emitting over 1.9–4.8 μm. ► The laser includes commercial off-the-shelf parts and a chalcogenide fiber. ► Demonstrated 10 dB spectral flatness from 2.0 to 4.6 μm, and −20 dBm from 1.9 to 4.8 μm. ► The system output average power is 565 mW at 10 MHz. ► The long wavelength edge limit is caused by an extrinsic absorption in the fiber. An all-fiber based supercontinuum source with emission covering the wavelength range of 1.9–4.8 μm is demonstrated. The laser source is based on a combination of silica commercial off-the shelf components and a chalcogenide-based nonlinear optical fiber. The system provides 10 dB spectral flatness from 2.0 to 4.6 μm, and −20 dBm points from 1.9 to 4.8 μm. The output power is 565 mW but scalable by scaling the repetition rate. The limit on the long wavelength edge of the system is identified as an extrinsic absorption feature in the fiber used; confirming the system could be scaled to generated a broadband source even further in the infrared.
We give an overview of the current status of fiber-based noise-like pulse (NLP) research conducted over the past decade, together with presenting the newly conducted, systematic study on their temporal, spectral, and coherence characteristics in nonlinear polarization rotation (NPR)-based erbium-doped fiber ring cavity configurations. Firstly, our study includes experimental investigations on the characteristic features of NLPs both in the net anomalous dispersion regime and in the net normal dispersion regime, in comparison with coherent optical pulses that can alternatively be obtained from the same cavity configurations, i.e., with the conventional and dissipative solitons. Secondly, our study includes numerical simulations on the formation of NLPs, utilizing a simplified, scalar-field model based on the characteristic transfer function of the NPR mechanism in conjunction with the split-step Fourier algorithm, which offer a great help in exploring the interrelationship between the NLP formation and various cavity parameters, and eventually present good agreement with the experimental results. We stress that if the cavity operates with excessively high gain, i.e., higher than the levels just required for generating coherent mode-locked pulses, i.e., conventional solitons and dissipative solitons, it may trigger NLPs, depending on the characteristic transfer function of the NPR mechanism induced in the cavity. In particular, the NPR transfer function is characterized by the critical saturation power and the linear loss ratio. Finally, we also report on the applications of the fiber-based NLP sources, including supercontinuum generation in a master-oscillator power amplifier configuration seeded by a fiber-based NLP source, as one typical example. We expect that the NLP-related research area will continue to expand, and that NLP-based sources will also find more applications in the future.
Over the last five years, the number of demonstrations of mode-locked thulium-doped fiber lasers with output wavelengths around 2 μm has increased rapidly. Mode-locked Tm-doped fiber lasers now provide pulse energies above 150 μJ and durations less than 30 fs (although not simultaneously). Applications for these sources are continuously being developed as they become commercially available and currently include medicine, environmental sensing, materials processing, and defense. A review of previously demonstrated mode-locked thulium-doped fiber lasers up to the state-of-the-art will be presented along with the aforementioned applications of these sources.
This paper presents an optimum design for highly birefringent hybrid photonic crystal fiber (HyPCF) based on a modified structure for broadband compensation covering the S, C, and L-communication bands i.e. wavelength ranging from 1460 to 1625 nm. The finite element method (FEM) with perfectly matched layer (PML) circular boundary is used to investigate the guiding property. It is demonstrated that it is possible to obtain broadband large negative dispersion, and dispersion coefficient varies from −388.72 to −723.1 ps nm km over S, C and L-bands with relative dispersion slope (RDS) matched to that of single mode fiber (SMF) of about 0.0036 nm at 1550 nm. According to simulation, a five-ring dispersion compensating hybrid cladding photonic crystal fiber (DC-HyPCF) is designed that simultaneously offers birefringence of order 3.79 × 10 , nonlinear coefficient of 40.1 W km at 1550 nm wavelength. In addition to this, effective area, residual dispersion, and confinement loss of the proposed DC-HyPCF are also reported and discussed.
The development of optical fibers with suspended cores has enabled the demonstration of a range of powerful new techniques for chemical and biological sensing. Here the fabrication, design and application of this new class of fibers are reviewed. The performance and potential of sensors based on these fibers is evaluated, including dip sensors for sensing small sample volumes, exposed-core fibers for real-time and distributed measurements, and surface functionalized fibers for the specific detection of chemicals and biomolecules.
The current state of research into polymer optical fiber (POF) sensors linked to safety in human life is summarized in this paper. This topic is directly related with new solutions for civil aircraft, structural health monitoring, healthcare and biomedicine fields. In the last years, the properties of polymers have been explored to identify situations offering potential advantages over conventional silica fiber sensing technology, replacing, in some cases, problematic electronic technology used in these mentioned fields, where there are some issues to overcome. POFs could preferably replace their silica counterparts, with improved performance and biocompatibility. Finally, new developments are reported which use the unique properties of POF.
Raman-based distributed temperature sensors are now used in a wide variety of industrial and scientific applications. In this paper, we set out the physical principles behind these systems and we summarise the many approaches to their design, the relevant parameters, and the significant features of employed schemes such as optical time- or frequency-domain reflectometry, with resulting implications for their performance. Recent techniques aimed at enhancing the sensing performance or overcoming known issues are also addressed such as photon counting or pulse coding. Also, current standardisation efforts are mentioned, and important applications of the technology are reviewed.
One of the current frontier of optical fiber sensors, and a unique asset of this sensing technology is the possibility to use a whole optical fiber, or optical fiber device, as a sensor. This solution allows shifting the whole sensing paradigm, from the measurement of a single physical parameter (such as temperature, strain, vibrations, pressure) to the measurement of a spatial distribution, or profiling, of a physical parameter along the fiber length. In the recent years, several technologies are achieving this task with unprecedentedly narrow spatial resolution, ranging from the sub-millimeter to the centimeter-level. In this work, we review the main fiber optic sensing technologies that achieve a narrow spatial resolution: Fiber Bragg Grating (FBG) dense arrays, chirped FBG (CFBG) sensors, optical frequency domain reflectometry (OFDR) based on either Rayleigh scattering or reflective elements, and microwave photonics (MWP). In the second part of the work, we present the impact of spatially dense fiber optic sensors in biomedical applications, where they find the main impact, presenting the key results obtained in thermo-therapies monitoring, high-resolution diagnostic, catheters monitoring, smart textiles, and other emerging applicative fields.
Optical fiber-based high-resolution fluorescence imaging techniques have promising applications in clinical practice and preclinical research using animals. Here we review the instrumentation and applications of microendoscopy based on various types of optical fibers. Single-mode fibers and double-clad fibers have been widely used for delivering light from light sources to tissues and collecting light from tissues to photodetectors. Coherent fiber bundles, cylindrical graded-index lenses, and multi-mode fibers have been employed in both beam-scanning and non-scanning microscopy. With continuing advances of optical fiber technologies, further innovations in optical microendoscopy are expected.
Today’s optical networks function are in a fairly static fashion and are built to operate within well-defined specifications. This scenario is quite challenging for next generation high-capacity systems, since network paths are not static and channel-degrading effects can change with temperature, component drift, aging, fiber plant maintenance and many other factors. Moreover, we are far from being able to simply “plug-and-play” an optical node into an existing network in such a way that the network itself can allocate resources to ensure error-free transmission. Optical performance monitoring could potentially enable higher stability, reconfigurability, and flexibility in a self-managed optical network. This paper will describe the specific fiber impairments that future intelligent optical network might want to monitor as well as some promising techniques.
An investigation of the thermal annealing effects on the strain, stress, and force sensitivities of polymer optical fiber Bragg grating sensors is performed. We demonstrate for the first time that the fiber annealing can enhance both stress and force sensitivities of Bragg grating sensors, with the possible cause being the molecular relaxation of the polymer when fiber is raised above the -transition temperature. A simple, cost-effective, but well controlled method for fiber annealing is also presented in this work. In addition, the effects of chemical etching on the strain, stress, and force sensitivities have been investigated. Results show that fiber etching too can increase the force sensitivity, and it can also affect the strain and stress sensitivities of the Bragg grating sensors.
Over the last five years, the number of demonstrations of mode-locked thulium-doped fiber lasers with output wavelengths around 2 mu m has increased rapidly. Mode-locked Tm-doped fiber lasers now provide pulse energies above 150 mu J and durations less than 30 fs (although not simultaneously). Applications for these sources are continuously being developed as they become commercially available and currently include medicine, environmental sensing, materials processing, and defense. A review of previously demonstrated mode-locked thulium-doped fiber lasers up to the state-of-the-art will be presented along with the aforementioned applications of these sources. (C) 2014 Elsevier Inc. All rights reserved.
In this paper, we present a porous-core circular photonic crystal fiber (PC-CPCF) with ultra-low material loss for efficient terahertz wave transmission. The full vector finite element method with an ideally matched layer boundary condition is used to characterize the wave guiding properties of the proposed fiber. At an operating frequency of 1 THz, simulated results exhibit an extremely low effective material loss of 0.043 cm , higher core power fraction of 47% and ultra-flattened dispersion variation of 0.09 ps/THz/cm. The effects of important design properties such as single mode operation, confinement loss and effective area of the fiber are investigated in the terahertz regime. Moreover, the proposed fiber can be fabricated using the capillary stacking or sol-gel technique and be useful for long distance transmission of terahertz waves.
To realize the reliable and long-term strain detection, the durability of optical fiber sensors has attracted more and more attention. The packaging technique has been considered as an effective method, which can enhance the survival ratios of optical fiber sensors to resist the harsh construction and service environment in civil engineering. To monitor the internal strain of structures, the embedded installation is adopted. Due to the different material properties between host material and the protective layer, the monitored structure embedded with sensors can be regarded as a typical model containing inclusions. Interfacial characteristic between the sensor and host material exists obviously, and the contacted interface is prone to debonding failure induced by the large interfacial shear stress. To recognize the local interfacial debonding damage and extend the effective life cycle of the embedded sensor, strain transfer analysis of a general three-layered sensing model is conducted to investigate the failure mechanism. The perturbation of the embedded sensor on the local strain field of host material is discussed. Based on the theoretical analysis, the distribution of the interfacial shear stress along the sensing length is characterized and adopted for the diagnosis of local interfacial debonding, and the sensitive parameters influencing the interfacial shear stress are also investigated. The research in this paper explores the interfacial debonding failure mechanism of embedded sensors based on the strain transfer analysis and provides theoretical basis for enhancing the interfacial bonding properties and improving the durability of embedded optical fiber sensors.
A novel fiber optical fiber-magnetic sensor based on magnetic fluid is proposed in this paper. The stable nanoparticles Fe O magnetic fluid was synthesized firstly; the Fe O magnetic fluid was injected in capillaries containing etched fiber Bragg grating (FBG) as sensing element. The reflected Bragg wavelength was changed by varying the magnetic field which is perpendicular to the axial of FBG. Experimental results show that the FBG with small diameter has more sensitive wavelength shift in magnetic field. When the magnetic field increases to 25 mT, the wavelength shift of the most sensitive FBG is 86 pm, and the etched FBG shows reversible response on magnetic fields under 16 mT.
This paper overviews recent development in gas detection with micro- and nano-engineered optical fibers, including hollow-core fibers, suspended-core fibers, tapered optical micro/nano fibers, and fiber-tip micro-cavities. Both direct absorption and photoacoustic spectroscopy based detection schemes are discussed. Emphasis is placed on post-processing stock optical fibers to achieve better system performance. Our recent demonstration of distributed methane detection with a ∼75-m long of hollow-core photonic bandgap fiber is also reported.