Optical Fiber Devices Research Articles

Opto-Electron Eng, 2018, 45(9)] Hollow-core photonic bandgap fibers: properties and sensing technology

In this paper, the unique properties of the hollow-core photonic bandgap fiber (HC-PBF) are reviewed, and a variety of sensing and device applications of this type of fiber in recent years are introduced. Low-loss light transmission in air core is an important characteristic of the HC-PBF, which provides light-matter interaction channel with high energy density and long interaction distance. In addition, the air-propagation of the light in fiber also reduces the impacts of fiber material properties (such as infrared absorption, thermos-optical effect) on propagating light, hence offers an efficient platform for the sensing applications such as trace gas / liquid detection, optical fiber gyro sensing. The fine micro-structure in HC-PBF exhibits novel mechanical and thermal properties, which would be beneficial to the sensing applications such as sound wave and vibration detection. The HC-PBF’s porous structure can also be locally modified by using various post-processing techniques, such as local heat treatment, micromachining and selective filling, which would enable further function extension or performance enhancement. The flexibility of the fiber has been used to develop new optical fiber devices, such as grating, polarizer and polarization interferometer. At present, the development of HC-PBF sensing technology has greatly expanded the sensing ability and application range of optical fiber. It is an important direction for the development of all-optical devices and optical integration technology.

Fiber-optic device for mode division

In this paper, we describe a simple device for mode division based on fused quartz fiber-optic coupler. An equivalent circuit of a photonic lantern for such a device is considered. The experimental test data of the device samples are presented. As test samples showed, this technology allows to obtain satisfactory parameters for simple and inexpensive devices with one multimode port and 2-5 single-mode ports.

Clinical evaluation of an optical fiber-based probe for the assessment of central arterial pulse waves.

The aim of this study, enrolling 118 patients, was to clinically evaluate the accuracy of carotid pulse waveform acquisition with a new non-invasive optical fiber probe using invasive and non-invasive pressure readings as references. Pulse waves were acquired simultaneously in the ascending aorta and right common carotid; for the non-invasive study, the pulses were sequentially acquired using the optical fiber device and the Complior Analyse® (Alam Medical, France) device in the right carotid artery. For all subjects, the pulse waveforms assessed using the optical fiber sensor and the references were superimposed to analyze the deviation and point-by-point correlation. Augmentation index and central pressure were compared using intraclass correlation and Bland-Altman analyses with a confidence interval of 95%. For the invasive study, the acquired waves presented a mean deviation of 11 ± 3% and a mean intraclass correlation of 0.97 ± 0.02. Concerning the augmentation index and central systolic pressure, correlations of 0.79 (p < 0.001) and 0.94 (p < 0.001) were found, respectively. In the non-invasive comparison, the assessed mean deviation between the morphologies of the waves was 13 ± 5%, with correlation coefficients of 0.91 (p < 0.001) for the augmentation index and 0.98 (p < 0.001) for central systolic pressure. The results show that the optical fiber probe results were highly correlated with those obtained using the reference techniques in terms of the pulse waveforms, central systolic pressure (cSP), and augmentation index assessment.

Measurement of deformations of structural elements technical systems of aircraft by fiber optic devices

The article deals with the measurement of deformations of structural elements of technical systems. The analysis of damages and deformations arising in the elements of aircraft structures during operation is carried out. The conducted researches of the fiber-optical sensor (VOD) based on the Fabry-Perot interferometer confirmed its accuracy and reliability of operation, since the interferometer base is significantly less than the length of the fastening element. The influence of the change in ambient temperature on the change in the base is negligible. Thus, the application of the method of fiber-optic low-coherence interferometry makes it possible to provide high accuracy and reliable measurement of the deformations of the structural elements of technical systems in the process of their research, design, manufacture and operation, which makes it possible to recommend the use of the Fabry-Perot interferometer as primary transducers (sensors) as part of measuring systems. The manufacturing technology has been developed and the sensitivity of the VOD temperature sensors made on the basis of the Fabry-Perot interferometer has been tested, which have shown their reliability and future application in automated measuring systems.

Cracked tooth syndrome in irradiated patients with head and neck cancer

The aim of this study was to assess the presence of enamel craze lines (ECLs), part of the spectrum of the so-called cracked tooth syndrome, on the surface of teeth irradiated in vivo. Forty teeth extracted from patients with head and neck cancer were paired, matched, and equally divided into 4 groups: noncarious irradiated (G1); noncarious control (G2); radiation-related caries (RRC) (G3), and carious control (G4). Samples were examined for ECL detection with a fiberoptic transillumination device and photographed, and ECL mean size, number, and patterns of topographic distribution in tooth crown were determined. Groups were compared accordingly: G1 versus G2; G3 versus G4. We analyzed 538 ECLs, of which 30.1% were found in noncarious irradiated teeth, 19.3% in noncarious controls, 27.6% in RRC, and 23% in carious controls. Non-carious irradiated teeth presented higher quantities of ECL than non-carious control (P < 0.05). Higher incidences of ECLs were identified in specific enamel topographies of anterior G1 and G3 samples (P <.05). There was no correlation between ECL size/numbers and radiation isodose delivery to teeth. Increased incidence of ECLs may indicate weakened enamel structure in irradiated teeth, and this may play a role in the onset and progression of RRC.

Versatile Approach for Reducing Propagation Loss in Wet-Electrospun Polymer Fiber Waveguides.

Wet-electrospun (WES) polymer micron and submicron fibers are promising building blocks for small, flexible optical fiber devices, such as waveguides, sensors, and lasers. WES polymer fibers have an inherent cylindrical geometry similar to that of optical fibers and a relatively large aspect ratio. Furthermore, WES fibers can be produced using low-cost and low-energy manufacturing techniques with large-area fabrication and a large variety of materials. However, the high propagation loss in the fibers, which is normally on the order of tens or thousands of decibels per centimeter in the visible light region, has impeded the use of these fibers in optical fiber devices. Here, the origin of propagation losses is examined to develop a comprehensive and versatile approach to reduce these losses. The excess light scattering that occurs in fibers due to their inhomogeneous density is one of the primary factors in the propagation loss. To reduce this loss, the light transmission characteristics were investigated for single WES polymer fibers heated at different temperatures. The propagation loss was significantly reduced from 17.0 to 8.1 dB cm–1 at 533 nm wavelength, by heating the fibers above their glass transition temperature, 49.8 °C. In addition, systematic verification of the possible loss factors in the fibers confirmed that the propagation loss reduction could be attributed to the reduction of extrinsic excess scattering loss. Heating WES polymer fibers above their glass transition temperature is a versatile approach for reducing the propagation loss and should be applicable to a variety of WES fibers. This finding paves the way for low-loss WES fiber waveguides and their subsequent application in small, flexible optical fiber devices, including waveguides, sensors, and lasers.

3D printed fiber optic faceplates by custom controlled fused deposition modeling.

A 3D printing technique for manufacturing air-clad coherent fiber optic faceplates is presented. The custom G-code programming is implemented on a fused deposition modeling (FDM) desktop printer to additively draw optical fibers using high-transparency thermoplastic filaments. The 3D printed faceplate consists of 20000 fibers and achieves spatial resolution 1.78 LP/mm. Transmission loss and crosstalk are characterized and compared among the faceplates printed from four kinds of transparent filaments as well as different faceplate thicknesses. The printing temperature is verified by testing the transmission of the faceplates printed under different temperatures. Compared with the conventional stack-and-draw fabrication, the FDM 3D printing technique simplifies the fabrication procedure. The ability to draw fibers with arbitrary organization, structure and overall shape provides additional degree of freedom to opto-mechanical design. Our results indicate a promising capability of 3D printing as the manufacturing technology for fiber optical devices.

In-situ ultrasensitive label-free DNA hybridization detection using optical fiber specklegram

In this work, we present a compact and ultrasensitive bio-molecule sensor based on fiber specklegram, achieving a DNA detection sensitivity of 10−16 M. To our knowledge, the new device is the most sensitive fiber-optic DNA sensor reported to date. Importantly, the well-known temperature cross-sensitivity issue in many fiber-optic devices has been entirely removed by the introduction of a reference fiber-optic channel embedded in microfluidic channels. In the experiment, we demonstrate label-free DNA hybridization detection at different concentrations, where normalized intensity inner product of the collected specklegrams are calculated and used for determining the DNA concentration. The result shows the exact ssDNA concentration can be precisely determined with a single experiment in 60 min. The new fiber sensor presents distinctive advantages over traditional bio-sensors in terms of sensitivity, precision and cost, which may find many practical applications in health and medicine, e.g., point-of-care testing and disease diagnosis.

Radiation resistant fiber Bragg grating in random air-line fibers for sensing applications in nuclear reactor cores.

This paper reports the testing results of radiation resistant fiber Bragg grating (FBG) in random air-line (RAL) fibers in comparison with FBGs in other radiation-hardened fibers. FBGs in RAL fibers were fabricated by 80 fs ultrafast laser pulse using a phase mask approach. The fiber Bragg gratings tests were carried out in the core region of a 6 MW MIT research reactor (MITR) at a steady temperature above 600°C and an average fast neutron (>1 MeV) flux >1.2 × 1014 n/cm2/s. Fifty five-day tests of FBG sensors showed less than 5 dB reduction in FBG peak strength after over 1 × 1020 n/cm2 of accumulated fast neutron dose. The radiation-induced compaction of FBG sensors produced less than 5.5 nm FBG wavelength shift toward shorter wavelength. To test temporal responses of FBG sensors, a number of reactor anomaly events were artificially created to abruptly change reactor power, temperature, and neutron flux over short periods of time. The thermal sensitivity and temporal responses of FBGs were determined at different accumulated doses of neutron flux. Results presented in this paper reveal that temperature-stable Type-II FBGs fabricated in radiation-hardened fibers can survive harsh in-pile conditions. Despite large parameter drift induced by strong nuclear radiation, further engineering and innovation on both optical fibers and fiber devices could lead to useful fiber sensors for various in-pile measurements to improve safety and efficiency of existing and next generation nuclear reactors.

An All-Solid Athermal Multimode-Interference Cascaded Device for Wavelength-Locking

We demonstrate a passive, material-based athermalization of all-fiber architectures consisting of cascaded multimode-interference (MMI) devices. Specifically, the athermal MMI filter used for in-line thermo-optic compensation consists of a no-core multimode fiber, which is spliced between two single-mode fibers, and is partly covered with a polymer coating. The design of the temperature-compensation unit is straightforward and its fabrication is simple. The applicability of our approach is experimentally verified by fabricating wavelength-locked MMI lasers with a temperature sensitivity lower than 1.0 pm/°C, which is several times smaller than that achieved with other fiber-optic devices and is comparable to that targeted in silicon photonics.

Cancellation of birefringence in DBR laser through principal axis offset by a rotation of 90°

The cancellation of birefringence in the distributed Bragg reflector based on 90° rotation offset method is demonstrated. It is found that the birefringence, which causes the peak bifurcation has been eliminated and a single peak is produced at each resonance in the output spectrum. This modification is an economic solution for eliminating the birefringence of the optical fibre devices.

Fiber optic sensors for sub-centimeter spatially resolved measurements: Review and biomedical applications

Abstract 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 trapping and micromanipulation with a photonic lantern-mode multiplexer.

We demonstrate a simple approach based on a photonic lantern spatial-mode multiplexer and a few-mode fiber for optical and manipulation of multiple microspheres. Selective generation of linearly polarized (LP) fiber modes provides light patterns useful for trapping one or multiple microparticles. Furthermore, rotation of the particles can be achieved by switching between degenerate LP modes, as well as through polarization rotation of the input light. Our results show that emerging fiber optic devices such as photonic lanterns can provide a versatile and compact means for developing optical fiber traps.

Complications following intracranial pressure monitoring in children: a 6-year single-center experience.

OBJECTIVE Intracranial pressure (ICP) monitoring is an important tool in the neurosurgeon's armamentarium and is used for a wide range of indications. There are many different ICP monitors available, of which fiber-optic intraparenchymal devices are very popular. Here, the authors document their experience performing ICP monitoring from 2005 to 2015 and specifically complication rates following insertion of the Microsensor ICP monitor. METHODS A retrospective case series review of all patients who underwent ICP monitoring over a 10-year period from 2005 to 2015 was performed. RESULTS There were 385 separate operations with an overall complication rate of 8.3% (32 of 385 cases). Hardware failure occurred in 4.2% of cases, the CSF leakage rate was 3.6%, the postoperative hemorrhage rate was 0.5%, and there was 1 case of infection (0.3% of cases). Only patients with hardware problems required further surgery as a result of their complications, and no patient had any permanent morbidity or mortality from the procedure. Younger patients (p = 0.001) and patients with pathologically high ICP (13% of patients with high ICP vs 6.5% of patients with normal ICP; p = 0.04) were significantly more likely to have complications. There was no significant difference in the complication rates between general neurosurgical patients and craniofacial patients (7.6% vs 8.8%, respectively; p = 0.67). CONCLUSIONS Intraparenchymal ICP monitoring is a safe procedure associated with low complications and morbidity in the pediatric craniofacial and neurosurgical population and should be offered to appropriate patients to assess ICP with the reassurance of the safety record reported in this study.

Employment of optical fibers for RC bond-slip characterization

Some features as workability, high durability and low cost of production have contributed for reinforced concrete (RC) be largely used worldwide. However, environmental actions and the natural material decaying are the most common processes that contribute for the loss of the physical-mechanical properties of the RC structures. When the bond between the concrete and the reinforcing rebar are affected, the results can be extremely dramatic and unpredicted. In this work, an optical fiber device for the monitoring of the bond-slip of old RC structures, where less intrusive techniques need to be considered, is proposed and tested. The sensor developed is based on the fiber Bragg grating (FBG) technology, inscribed in silica optical fiber. A pull-out test was carried out in a RC specimen, following the recommendations of the Annex D of the EN 10080. The results showed that the bond-slip optical sensors are capable to measure micro-displacements, with lower intrusiveness. Therefore, they can be used for monitoring the bond-slip of old RC structures as way of to collect information, essential to assist the owners to adopt cost effective, efficient and safer maintenance measures.

Experimental Set up to Measure Dispersion in Optical Fiber Devices

Experimental Set up to Measure Dispersion in Optical Fiber Devices

Hybrid photonic-crystal fiber

This article offers an extensive survey of results obtained using hybrid photonic crystal fibers (PCFs) which constitute one of the most active research fields in contemporary fiber optics. The ability to integrate novel and functional materials in solid- and hollow-core PCFs through various post-processing methods has enabled new directions towards understanding fundamental linear and nonlinear phenomena as well as novel application aspects, within the fields of optoelectronics, material and laser science, remote sensing and spectroscopy. Here the recent progress in the field of hybrid PCFs is reviewed from scientific and technological perspectives, focusing on how different fluids, solids and gases can significantly extend the functionality of PCFs. In the first part of this review we discuss the most important efforts by research groups around the globe to develop tunable linear and nonlinear fiber-optic devices using PCFs infiltrated with various liquids, glasses, semiconductors and metals. The second part is concentrated on the most recent and state-of-the-art advances in the field of gas-filled hollow-core PCFs. Extreme ultrafast gas-based nonlinear optics towards light generation in the extreme wavelength regions of vacuum ultraviolet (VUV), pulse propagation and compression dynamics in both atomic and molecular gases, and novel soliton - plasma interactions are reviewed. A discussion of future prospects and directions is also included.

In-Line Tunable Nematic Liquid Crystal Fiber Optic Device

This paper has been focused on design, fabrication, and characterization of a new in-line tunable nematic liquid crystal fiber optic device. The application of a biconical optical fiber taper as a core surrounded by liquid crystals' molecules as cladding gives the possibility to voltage control of spectral characteristics including system losses and its polarization in an optical visible wavelength range from 500 to 700 nm. The device is based on a standard single mode telecommunication fiber and a special, nematic liquid crystalline mixture of a 1550C1 type. The temperature and time course of liquid crystal mixture investigation of the proposed element are also included in the paper.

Theoretical Approach of Soil Slope Slip Monitoring Based on Composite Optical Fiber Devices

Theoretical Approach of Soil Slope Slip Monitoring Based on Composite Optical Fiber Devices

Multifunctional Metamirror: Polarization Splitting and Focusing

Metasurfaces are paving the way to improve traditional optical components by integrating multiple functionalities into one optically flat metasurface design. We demonstrate the implementation of a multifunctional gap surface plasmon-based metasurface which, in reflection mode, splits orthogonal linear light polarizations and focuses into different focal spots. The fabricated configuration consists of 50 nm thick gold nanobricks with different lateral dimensions, organized in an array of 240 nm x 240 nm unit cells on the top of a 50 nm thick silicon dioxide layer, which is deposited on an optically thick reflecting gold substrate. Our device features high efficiency (up to ~65%) and polarization extinction ratio (up to ~30 dB), exhibiting broadband response in the near-infrared band (750-950 nm wavelength) with the focal length dependent on the wavelength of incident light. The proposed optical component can be forthrightly integrated into photonic circuits or fiber optic devices.