Standard Single-mode Optical Fiber Research Articles

Production process monitoring and post-production strain measurement on a full-size carbon-fibre composite aircraft tail cone assembly using embedded optical fibre sensors

Multiplexed optical fibre sensors were embedded into a carbon-fibre-reinforced-preform during the industrial production of a full-sized, one-piece tail cone assembly for a regional jet aircraft. Optical fibre Fresnel sensors monitored both the infusion of the resin, via measurement of the refractive index-dependent attenuation in the reflected light signal, and the degree of cure of the resin, via measurement of the chemical cure reaction-dependent change in refractive index. The resin cure was also monitored by optical fibre Bragg gratings (FBGs) fabricated in high linearly birefringent optical fibre, which measured through-thickness strain development, while FBGs in standard single mode optical fibre measured longitudinal strain development. The magnitudes and profiles of the transverse and longitudinal strains developed during the curing process were consistent across different locations on the tail cone. Typical transverse and longitudinal strains, related to cure reaction-induced shrinkage, were −1500 ± 17 μϵ and −500 ± 5 μϵ, respectively. Post-production, the same embedded FBG sensors were used subsequently to monitor structural strains when the tail cone was subjected to vacuum pressure loading. The longitudinal strains measured using the embedded FBG sensors were generally in good agreement with the longitudinal strains measured by the surface-bonded resistance foil strain gauge (RFSG) sensors, both qualitatively and quantitatively. The in-plane transverse and circumferential strains, oriented collinearly, were measured by the embedded FBGs and appropriately oriented surface-bonded RFSG sensors, respectively, and were, qualitatively, in good agreement.

Ultracompact optical fiber acoustic sensors based on a fiber-top spirally-suspended optomechanical microresonator.

Acoustic wave sensors with a high sensitivity and small size are highly desired for a wide variety of important and emerging applications such as photoacoustic gas sensing and bio-imaging. Here we present an ultracompact optical fiber acoustic sensor based on an optomechanical resonator that is directly in situ printed on the end face of a standard single-mode optical fiber by using an optical 3D μ-printing technology. The fiber-top optomechanical microresonator is composed of a microscale suspended polymer micro-disk that forms a Fabry-Perot interferometric cavity, together with the optical fiber end face, and acts as the acoustic wave-sensitive micromechanical resonator simultaneously. The microbeams for suspending the micro-disk are devised with a spiral structure to overcome the small-size imposed low deflection amplitude so as to improve its sensitivity to acoustic waves. The sensor with a high sensitivity of 118.3 mV/Pa and low noise equivalent acoustic signal level of 0.328µPa/Hz1/2 at audio frequency is experimentally demonstrated. Moreover, with a resonance amplification mechanism, the sensitivity can be enhanced by 40.1 times when the frequency of the acoustic wave matches with the natural resonance frequency of the optomechanical resonator. Such an ultrasmall fiber-tip acoustic sensor has not only a miniaturization-induced broad bandwidth, but also a structure-enhanced ultrahigh sensitivity and thus is very promising in various acoustic wave-based sensing, imaging, and testing applications.

3D Printing Technology for Tapered Optical Fiber Protection With Gas Sensing Possibilities

We present a new procedure for protecting micro-optical fibers (tapered fibers) by using the 3-dimension (3D) printing technology. A standard single-mode optical fiber was tapered down to the diameter of 1 µm and embedded in a polymeric matrix obtained by an additive manufacturing routine. We show that the proposed structure protects the fiber taper against environmental humidity while keeping permeability to gas flow and the possibility of the realization of gas detection experiments. To our knowledge, this is the first time 3D printed casings were applied to protect fiber tapers from humidity deterioration. We envisage this new approach will allow the development of new fiber taper devices to better resist in humid environments.

Physical Principles of Developing Pressure Sensors Using Refractive Index Changes in Optical Fiber Microbending

The paper deals with the physical principles of development of pressure sensors using changes in the refractive index in the optical fiber microbending. The development of a simplified fiber-optic based pressure sensor is considered to be relevant for the mining industry if used as a temperature-compensated pressure sensor to avoid known disadvantages of various optical interferometers. An important point is the use of a G.652 standard single-mode optical fiber, which is also used as a guide for electrical signal transmission. The proposed information measurement system is capable of making remote measurements of the rock pressure on the powered support. The ground expressions are given to describe a physical process of the pressure measurement based on the photoelastic effect observed at microbending. The obtained results of the field experiments prove changes in the diffraction spot configuration at the optical fiber end depending on microbending. The finite element program Ansys Static Structural is used for a simulation of the mechanical stress on the optical fiber causing its microbending. The proposed sensor can detect not only pressure, but also temperature and rock mass microdisplacement and can be used for geotechnical monitoring of mine openings representing the danger of gas and coal dust explosion.

Impact of Thermal-Induced Turbulent Distribution Along FSO Link on Transmission of Photonically Generated mmW Signals in the Frequency Range 26–40 GHz

Microwave photonics is a promising solution to transmit millimeter wave (mmW) signals for the 5th generation (5G) mobile communications as part of a centralized radio access network (C-RAN). In this paper, we experimentally evaluate the impact of turbulent free space optics links on photonically generated mmW signals in the frequency range of $\text{26}-\text{40}\text{ GHz}$ . We analyze the remote generation of mmW signals over hybrid links based on free-space optics (FSO) and standard single mode optical fiber (SSMF) with $ - \text{39.97}\;\text{dBm}$ received electrical power and phase noise level at $\text{100}\;\text{kHz}$ as low as $ - \text{95.92}\;\text{dBc}\;\text{Hz}$ at $\text{26}\;\text{GHz}$ . Different thermal distributions along the FSO link have been implemented and Gamma-Gamma model has been employed to estimate the thermally induced turbulence. The results show high electrical power decrease and fluctuation of the generated mmW signal according to the particular level of the turbulence in terms of refractive index structure parameter and thermal distribution along the FSO link. $\text{8}\;\text{Gb}/\text{s}$ 16-quadrature amplitude modulation (QAM) data transmission at $\text{42}\;\text{GHz}$ has been demonstrated over the hybrid link with minimal error vector magnitude (EVM) value of $\text{5}{\%}$ whereas turbulent FSO link introduced up to $\text{5}\;\text{dB}$ power penalty.

Fast and direct measurement of the linear birefringence profile in standard single-mode optical fibers.

Phase birefringence in optical fibers typically fluctuates over their length due to geometrical imperfections induced from the drawing process or during installation. Currently commercially available fibers exhibit remarkably low birefringence, prompting a high standard for characterization methods. In this work, we detail a method that uses chirped-pulse phase-sensitive optical time-domain reflectometry to directly measure position-resolved linear birefringence of single-mode optical fibers. The technique is suitable for fiber characterization over lengths of tens of kilometers, relying on a fast measurement ($ {\sim} 1\,\, {\rm s} $∼1s) with single-ended access to the fiber. The proposed method is experimentally validated with three different commercial single-mode optical fibers.

100 Gb/s (4 × 25 Gb/s) real-time coherent UDWDM-PON with a large power budget

We propose a 100-Gb/s coherent ultra-dense wavelength-division multiplexing passive optical network (UDWDM-PON) structure with a large power budget by placing an erbium-doped fiber amplifier at the optical line terminal side for amplification of optical signals in both the uplink and downlink. Then we experimentally demonstrate a real-time 4 × 25 - G b / s coherent UDWDM-PON at 12.5-GHz spacing over 50-km standard single-mode optical fiber. A high sampling rate analog-to-digital converter is designed for the 25-Gb/s real-time coherent optical module. Experimental results show that 100-Gb/s bidirectional transmission can be realized. The downlink power budget can be more than 44 dB, which can support more than 1000 users based on the proposed structure. The effects of several parameters have also been investigated in the experimental demonstration. The 24-h real-time performance evaluation for bidirectional transmission is conducted to prove the feasibility of real-time field-programmable gate array based transceivers in the proposed UDWDM-PON structure. An off-line experimental demonstration is also conducted to verify the feasibility of burst-mode operation in the uplink.

Medical control of a pulse wave fiber optic sensors

The modern level of development of systems of measurement, processing and data transmission promote creation of optical multiple parameter medical diagnostic systems. One of intensively developed directions is creation of fiber-optical diagnostic systems on the basis of fiber optic sensors. Fiber optic sensors are characterized by high sensitivity to mechanical oscillations of a surface of a body of the patient under power influence of a blood flow. This property creates premises for design miniature, steady against noises, safe sensors of micromovements. Their fixing on a body of the patient allows to reveal a number of the vital parameters characterizing normal and critical condition of the patient. Results of a research of fiber optic sensors of pressure on the basis of standard single-mode optical SMF-28 fiber are presented in article. The principle of operation of sensors consists in use of physical properties of the fiber - the impact which had in some pressure point on throughput characteristic. The purpose of the real work is the research of a possibility of use of fiber optic sensors of the tunnel, flexural and microflexural types on Bragg’s grid for control of a pulse wave providing more exact determination of parameters of a pulse wave. The offered monitoring systems of a status of patients on the basis of fiber optic sensors in medicine are very perspective.

A Refractive Index Sensor Based on a Fabry–Perot Interferometer Manufactured by NIR Laser Microdrilling and Electric Arc Fusion

In-line Fabry–Perot cavities manufactured by a new technique using electric arc fusion of NIR laser microdrilled optical fiber flat tips were studied herein for refractive index sensing. Sensors were produced by creating an initial hole on the tip of a standard single-mode telecommunication optical fiber using a Q-switched Nd:YAG laser. Laser ablation and plasma formation processes created 5 to 10 micron cavities. Then, a standard splicing machine was used to fuse the microdrilled fiber with another one, thus creating cavities with lengths around 100 micrometers. This length has been proven to be necessary to obtain an interferometric signal with good fringe visibility when illuminating it in the C-band. Then, the sensing tip of the fiber, with the resulting air cavity, was submitted to several cleaves to enhance the signal and, therefore, its response as a sensor, with final lengths between tens of centimeters for the longest and hundreds of microns for the shortest. The experimental results were analyzed via two signal analysis techniques, fringe visibility and fast Fourier transform, for comparison purposes. In absolute values, the obtained sensitivities varied between 0.31 nm−1/RIU and about 8 nm−1/RIU using the latter method and between about 34 dB/RIU and 54 dB/RIU when analyzing the fringe visibility.

Highly sensitive fiber optic temperature and strain sensor based on an intrinsic Fabry-Perot interferometer fabricated by a femtosecond laser.

In this Letter, we report on a simple, but highly sensitive sensor based on two intrinsic Fabry-Perot interferometers (FPIs) inscribed in a standard single-mode optical fiber. A brief theoretical study on the Vernier effect is presented, in which a simulation of the sensitivity magnification factor dependence on the FPI's length is performed. Based on the simulation results, the FPIs were fabricated using a custom micromachining setup that integrates a near-infrared femtosecond laser and a motorized XYZ platform. Using the Vernier effect, sensitivities of 145pm/με and 927pm/°C were obtained for strain and temperature, respectively. The sensor's performance combined with its versatile and customizable configuration allows real-time and in situ strain and temperature monitoring under harsh environments.

Enhanced Distributed Fiber Optic Vibration Sensing and Simultaneous Temperature Gradient Sensing Using Traditional C-OTDR and Structured Fiber with Scattering Dots.

We present results demonstrating several beneficial effects on distributed fiber optic vibration sensing (DVS) functionality and performance resulting from utilizing standard single mode optical fiber (SMF) with femtosecond laser-inscribed equally-spaced simple scattering dots. This modification is particularly useful when using traditional single-wavelength amplitude-based coherent optical time domain reflectometry (C-OTDR) as sensing method. Local sensitivity is increased in quasi-distributed interferometric sensing zones which are formed by the fiber segments between subsequent pairs of the scattering dots. The otherwise nonlinear transfer function is overwritten with that of an ordinary two-beam interferometer. This linearizes the phase response to monotonous temperature variations. Furthermore, sensitivity fading is mitigated and the demodulation of low-frequency signals is enabled. The modification also allows for the quantitative determination of local temperature gradients directly from the C-OTDR intensity traces. The dots’ reflectivities and thus the induced attenuation can be tuned via the inscription process parameters. Our approach is a simple, robust and cost-effective way to gain these sensing improvements without the need for more sophisticated interrogator technology or more complex fiber structuring, e.g., based on ultra-weak FBG arrays. Our claims are substantiated by experimental evidence.

Graphic User Interface for Modeling States of Polarization in Fiber Optics

In this paper a design of a graphical user interface (GUI), to observe polarization states changes on a standard single-mode optical fiber (SMF-28) that has been twisted, is presented. Here, we modify two different groups of parameters: 1) the input polarizationellipticity injected to an optical fiber; this is, the tilt or the angle of propagation and the intensity on each electric field or the shift phase; the other group is 2) the birefringence fiber values, mainly induced by mechanicalefforts, since its fabrication either by pinching, bending or in general by manipulating it; obtaining simulated results that describes the output polarized light at the end of the fiber. The results are depicted on the Poncaire Sphere and Stokes parameters graphics. Moreover, the GUI was developed in Visual-Basic, used for the interface windows, and it was connected to Matlab, used like mathematic engine.

Towards athermal Brillouin strain sensing based on heavily germania-doped core optical fibers

Owing to their interesting linear and nonlinear optical properties, germania-based core optical fibers are being widely used in a wide range of applications ranging from nonlinear optics to optical sensing. We here examine both the strain and temperature coefficients of stimulated Brillouin scattering in heavily doped core optical fibers with ultrahigh GeO2 doping level up to 98-mol. %. Our results show that the temperature dependence of the Brillouin gain spectrum becomes almost negligible (CT = 0.07 MHz/°C) for high doping content, while its Brillouin strain coefficient remains significant (Cε = 21.4 kHz με−1) compared to that of standard single-mode optical fibers (Cε = 48.9 kHz με−1). It is further shown that the temperature coefficient tends to zero when removing the fiber coating, indicating that those athermal highly GeO2-doped-core optical fibers could advantageously be used for Brillouin fiber strain sensing.

Investigation of MoS2 on coated titanium surface plasmon resonance side-polished optical fiber sensor

In this paper, we propose a rigorous configuration of 2D-material using MoS2 coated on titanium (Ti) surface plasmon resonance (SPR) optical fiber sensor. The present configuration is included side-polished optical fiber sensor, titanium (Ti) coating, MoS2 and sensing medium. The SPR sensing device uses a standard single-mode optical fiber with locally removed cladding and a thin Ti film supporting a surface plasma wave (SPW). We perform the performance characteristics of the design sensor in terms of sensitivity, detection accuracy and quality factor. Addition of MoS2 layer on the Ti-SPR will increase the overall sensitivity of the device. The polishing region is covered by metallic layer acted as active sensing medium as the interaction between the SPW, fiber mode and consequently the fiber mode attenuation which depends strongly on the refractive index of analytes. Variations of analytes used such as water, 60% alcohol, sodium chloride, glucose and sucrose can be determined by monitoring changes in the wavelength at which the resonant attenuation of the fiber mode occurs.

Influence of molten-state duration time on torsion sensitivity for fiber sensors based on helical long-period gratings: An experimental study

Abstract In this paper, we report an experimental study to systematically and quantitatively investigate the effect of molten-state duration time (MSDT) upon the torsion sensitivity for fiber sensors based on helical long-period fiber gratings (H-LPGs). During the fabrication processes to twist the standard single-mode optical fibers (SMFs) in molten states, we have found that there exists a logarithmic function relationship between the sensitivity of H-LPG-based torsion sensors and the manufacturing MSDT. When the average MSDT to fabricate each grating period increases from 24 to 72 s, the torsion sensitivity increases from minimally 0.0735 nm/(rad/m) to maximally 0.1105 nm/(rad/m) within a twist rate of −20.9 to +20.9 rad/m. This empirical study can potentially provide a constructive guideline for the fabrication and testing of H-LPG-based fiber torsion sensors.

Distributed Strain Monitoring of Railway Composite Bogies Using a Brillouin Optical Correlation Domain Analysis System

The structural deformation of a bogie frame manufactured using a composite material was monitored in real time using a distributed optical fiber sensor. The bogie frame contained an internally embedded standard single-mode optical fiber. Performance tests were conducted by applying a vertical load to the middle of the side beams on each side of the composite bogie frame. The strain distribution was monitored using an optical fiber sensor. A distributed optical fiber sensor system based on the Brillouin optical correlation domain analysis (BOCDA) technique with a 3 cm spatial resolution was used. The distributed strain measured using the optical fiber correlated well with the finite element (FE) analysis data, confirming that the composite bogie frame was fabricated as designed. For a vertical load of 182 kN, the maximum strain, which occurred in the middle of the side frame, increased by 1.3 times, as compared with a vertical load of 140 kN. The experiment was able to verify the balance and the structural stability of the left- and right-hand-side beams. Furthermore, it could confirm that there was a concentrated load where the side beam and the crossbeam meet, owing to a mismatch during the assembly of the composite bogie frame.

Multiple off-axis fiber Bragg gratings for 3D shape sensing.

Point-by-point femtosecond laser processed fiber Bragg gratings are arranged around the edge of a standard single-mode optical fiber core. The relative amplitudes of at least three such fiber Bragg gratings are utilized to detect the central position of the mode field within the fiber core and calculate the local curvature of the fiber. An analytical approximation is given, and an experimental validation is performed.

Fabrication of Long Period Gratings by Periodically Removing the Coating of Cladding-Etched Single Mode Optical Fiber Towards Optical Fiber Sensor Development.

Here, we present a novel method to fabricate long period gratings using standard single mode optical fibers (SMF). These optical devices were fabricated in a three-step process, which consisted of etching the SMF, then coating it with a thin-film and, the final step, which involved removing sections of the coating periodically by laser ablation. Tin dioxide was chosen as the material for this study and it was sputtered using a pulsed DC sputtering system. Theoretical simulations were performed in order to select the appropriate parameters for the experiments. The responses of two different devices to different external refractive indices was studied, and the maximum sensitivity obtained was 6430 nm/RIU for external refractive indices ranging from 1.37 to 1.39.

Photonic Generation and Transmission of Linearly Chirped Microwave Pulses With High TBWP by Self-Heterodyne Technique

This paper shows the generation of linearly chirped microwave pulses employing the photonic self-heterodyne technique, leading to ultrawideband signals with time-bandwidth products up to 74 000. By using low-frequency electronics to drive a distributed feedback laser diode, optical chirping is generated predominantly by thermal effect. Combining laser chirping, delay-optimized self-heterodyning, and saturated optical amplification yields to linearly chirped pulses with 2–25.2-GHz wide spectrum and better than ±3 dB flatness. A simple theoretical model showing the tradeoff between maximum attainable bandwidth and time-bandwidth product was developed and experimentally verified. Undistorted transmission along >40 km standard single-mode optical fiber is also shown.

Optical Fiber-Tip Sensors Based on In-Situ µ-Printed Polymer Suspended-Microbeams.

Miniature optical fiber-tip sensors based on directly µ-printed polymer suspended-microbeams are presented. With an in-house optical 3D μ-printing technology, SU-8 suspended-microbeams are fabricated in situ to form Fabry–Pérot (FP) micro-interferometers on the end face of standard single-mode optical fiber. Optical reflection spectra of the fabricated FP micro-interferometers are measured and fast Fourier transform is applied to analyze the cavity of micro-interferometers. The applications of the optical fiber-tip sensors for refractive index (RI) sensing and pressure sensing, which showed 917.3 nm/RIU to RI change and 4.29 nm/MPa to pressure change, respectively, are demonstrated in the experiments. The sensors and their optical µ-printing method unveil a new strategy to integrate complicated microcomponents on optical fibers toward ‘lab-on-fiber’ devices and applications.