Single Optical Fiber Research Articles

Range limitations of optical frequency domain reflectometry with all-grating fiber for distributed strain and temperature sensing

In distributed strain or temperature sensing applications such as structural health monitoring, optical frequency domain reflectometry (OFDR) is often used to interrogate all-grating fiber (AGF), which consists of many weak, nominally identical Bragg gratings spatially multiplexed on a single optical fiber. In order to investigate the limits of OFDR-based distributed strain sensing using AGF, we develop a model that considers the critical fact that these Bragg gratings are not identical. We find that while the “auto-correlation term” significantly impacts OFDR measurements of the complex coupling coefficient, it typically does not cause a significant error in distributed strain or temperature measurements. On the other hand, the breakdown of the Born approximation generally limits the sensing range of AGF. Our model is verified by measurements on all-grating fiber using a commercially available OFDR. We propose and verify novel solutions to extend the sensing range of AGF by controlling the properties of the non-identical Bragg gratings.

Parameter Simulation and Design of an Airborne Hyperspectral Imaging LiDAR System

With continuous technological development, the future development trend of LiDAR in the field of remote sensing and mapping is to obtain the elevation and spectral information of ground targets simultaneously. Airborne hyperspectral imaging LiDAR inherits the advantages of active and passive remote sensing detection. This paper presents a simulation method to determine the design parameters of an airborne hyperspectral imaging LiDAR system. In accordance with the hyperspectral imaging LiDAR equation and optical design principles, the atmospheric transmission model and the reflectance spectrum of specific ground targets are utilized. The design parameters and laser emission spectrum of the hyperspectral LiDAR system are considered, and the signal-to-noise ratio of the system is obtained through simulation. Without considering the effect of detector gain and electronic amplification on the signal-to-noise ratio, three optical fibers are coupled into a detection channel, and the power spectral density emitted by the supercontinuum laser is simulated by assuming that the signal-to-noise ratio is equal to 1. The power spectral density emitted by the laser must not be less than 15 mW/nm in the shortwave direction. During the simulation process, the design parameters of the hyperspectral LiDAR system are preliminarily demonstrated, and the feasibility of the hyperspectral imaging LiDAR system design is theoretically guaranteed in combination with the design requirements of the supercontinuum laser. The spectral resolution of a single optical fiber of the hyperspectral LiDAR system is set to 2.5 nm. In the actual prototype system, multiple optical fibers can be coupled into a detection channel in accordance with application needs to further improve the signal-to-noise ratio of hyperspectral LiDAR system detection.

Characteristics of rising temperatures through laser irradiation using a temperature sensor integrated optical fiber probe for soft tissue ablation

A new structure composed of silica optical fibers for soft tissue ablation is proposed and fabricated in this study. Laser irradiation and temperature monitoring are simultaneously performed using a wavelength-division multiplexing technique with a single optical fiber probe. A 1.55-μm wavelength range light is used for temperature measurement. The fabricated Fabry–Perot interference temperature sensor comprising a glass capillary and a graded-index multimode fiber exhibits good temperature sensor characteristics. The probe end is terminated with a glass capillary having a declined glass cap. This portion suppresses the reflected light backward to the incident fibers. Because the reflected light at this portion does not affect the interference of internal reflected light, regardless of the outer medium, stable temperature measurement is confirmed. A 1.48-μm laser irradiation method is investigated as a thermal source for soft tissue ablation. The characteristics of rising temperatures through laser irradiation of chicken-breast meat are investigated and indicate sufficient temperature increases for thermal ablation of soft tissue. A good estimation of the thermal protein denaturation region is achieved through a simple analytical equation using the measured value at the fiber tip temperature sensor.

Measurement of droplet size and velocity based on a single tapered fiber optical reflectometer

A single optical fiber probe (OFP) is used to measure the velocity and size of droplet falling in the air. By analyzing the interference waves formed by two reflected lights from the droplet surface and the fiber core interface, the fiber optical reflectometer (FOR) is mainly studied in this paper. The wave optics simulation was firstly applied to verify the FOR principle of velocity measurement. Then an experiment system which can generate droplets with different velocities and sizes was designed. Through comparing the results of OFP with photography method, the absolute relative error of chord length measured was within 1.3%. During the study, it was observed that the intensity of oscillation waves is closely related to the contact position between probe and droplet, so a method for predicting droplet diameter by OFP is proposed. Compared with photography method, the root mean square error of the predicted diameter is 0.051 mm.

Time-transformation technique for generation of optical pulse multiplets in a single mode anomalous dispersion optical fiber.

We present the generation of optical pulse multiplets in the temporal domain from a single pulse using the time-transformation technique for the first time, to the best of our knowledge. The generation of a pair of compressed, well-spaced, and identical Gaussian pulses from a third-order super-Gaussian input pulse when propagated through an anomalous dispersion fiber is reported. Detailed analysis on the effect of variation of input energy, pulse parameters, and optical gain in view of doublet formation leading to the possibility of high effective repetition rate (ERR) at smaller propagating length is reported. The formation of triplets and quadruplets from different input pulse shapes is investigated.

32-CHANNEL DWDM SYSTEM WITH DIFFERENT AMPLIFIERS AND MODULATIONS

Wavelength Division Multiplexing is a technology that has enabled the transmission of huge amounts of data at high transfer rates over a single optical fiber. The capacity of an optical channel is usually affected by the shape of signal, nonlinear characteristics and dispersion. In this article, we focus on the DWDM system, optical amplifiers, and optical modulations in 32-channel DWDM system, which was designed in the OptiSystem program. We evaluate the parameters BER (Bit Error Rate) and Q factor for 40 Gb/s systems with changing amplifiers.

Damage detection in composite aircraft wing-like test-box using distributed fiber optic sensors

Structural Health Monitoring Systems for the aircraft structures are intended to detect the location and size of the damage with minimum downtime of the aircraft. As the damage produces localized strain changes, a sensor network of many sensors bonded/embedded throughout the structure is required for damage diagnosis. This paper describes a distributed fiber optic sensor's demonstration to detect the disbond damage in a typical aircraft wing-like structure where a single optical fiber can cover a large area. Distributed fiber optic sensor is being bonded along the bolt line of the test-box. Controlled disbond are created by the removal of the bolts. In the pristine state, the strain signature/map is measured under applied load, which act as a reference in this case. In this approach, localized strain signature difference between the reference and disbond-structure is used to detect the damage. A non-dimensional quantity damage index (DI) is calculated based on the normalized sum of the square magnitude of strain difference of all sensors to indicate the damage severity. We have found that the DI value greater than or equal to 0.2 indicates the damage region through the iterative approach. Further, the algorithm is validated by loading the structure with disbond at different load levels. The maximum error in the disbond estimation is found to be ∼11 mm. This system and methodology hold immense promise for a ground-based method for detecting damage (disbond) in the aircraft/unmanned aerial vehicle structures (UAV).

Analysis and experiment on simultaneous measurement of strain and temperature by etched and un-etched FBG pair

This paper presents analysis and experiment on simultaneous measurement of strain and temperature using pair of etched and un-etched fiber Bragg grating (FBG) fabricated in a single mode glass optical fiber. The intrinsic sensitivity for strain and temperature of FBG explicitly depends on the clad diameter. The mechanical properties of glass optical fiber such as Young’s modulus and Poisson’s ratio change with cladding diameter. This in turn will change the strain optic coefficient and thermal expansion coefficient of the optical fiber. Analytically, it is shown that the change in refractive index, Young’s modulus, Poisson’s ratio and thermal expansion coefficient was 0.04, 58.2 GPa, 0.29 and 0.99 × 10−6/°C respectively as the cladding diameter was decreased from 125 µm to 11 µm. The results obtained for strain and temperature sensitivity from the analysis are verified with experimental results. Experimentally, as the fiber clad diameter is reduced from 125 µm to 25 µm via hydrofluoric (HF) etching, the average strain sensitivity increases from 1.06 pm/µɛ to 1.20 pm/µɛ for the maximum applied strain of around 5500 µɛ and also the average temperature sensitivity increases from 11.48 pm/°C to 11.80 pm/°C for the maximum applied temperature of 150 °C. The temperature and strain can be measured simultaneously with high accuracy by using these sensitivity coefficients for two gratings.

Multi-Wavelength Ultra-Weak Fiber Bragg Grating Arrays for Long-Distance Quasi-Distributed Sensing

Fiber Bragg grating (FBG) array, consisting of a number of sensing units in a single optical fiber, can be practically applied in quasi-distributed sensing networks. Serious signal crosstalk occurring between large-serial of identical FBGs, however, has limited the further increase in the number of sensing units, thus restricting applications only for short-distance sensing networks. To reduce the signal crosstalk, we design two novel types of 10-kilometer-long FBG arrays with 10 000 equally spaced gratings, written on-line using a customized grating inscription system, which is affiliated to a drawing tower. Main factors causing signal crosstalk, such as spectral shadowing and multiple reflections, are firstly investigated in theory. Consistent with the theoretical findings, experimental results are proving that ultra-weak (the reflectivity of ∼−40 dB) and multi-wavelength gratings of a number more than 10 000 can be readily identified, with satisfied low crosstalk. The maximum attenuation of grating signal and minimum signal-to-noise ratio (SNR) in a single-wavelength array are 10.69 dB and 5.62 dB, respectively. As a comparison, by increasing the number of central wavelengths to three, the attenuation can be effectively reduced to 5.54 dB and the minimum SNR has been improved to 8.14 dB. The current study significantly enhances the multiplexing capacity of FBG arrays and demonstrates promising potentials for establishing large-capacity quasi-distributed sensing networks.

Whispering gallery mode excitation using exposed-core fiber.

Whispering gallery modes (WGMs) in micro-resonators are of interest due to their high Q-factors. Ultra-thin fiber tapers are widely deployed to couple light into micro-resonators but achieving stable and practical coupling for out-of-lab use remains challenging. Here, a new WGM coupling scheme using an exposed-core silica fiber (ECF) is proposed, which overcomes the challenge of using fragile fiber tapers. Microspheres are deposited onto the exposed channel for excitation via the evanescent field of the fiber's guided modes. The outer jacket of the ECF partially encapsulates the microspheres, protecting them from external physical disturbance. By varying the mode launching conditions in this few-mode ECF, in combination with a Fano resonance effect, we demonstrate a high degree of tunability in the reflection spectrum. Furthermore, we show multi-particle WGM excitation, which could be controlled to occur either simultaneously or separately through controlling the ECF mode launching conditions. This work can bring value towards applications such as optical switches and modulators, multiplexed/distributed biosensing, and multi-point lasing, integrated in a single optical fiber device that avoids fiber post-processing.

Twin lossy mode resonance on a single D-shaped optical fiber.

This Letter presents the fabrication of dual lossy mode resonance (LMR) refractometers based on titanium dioxide (TiO2) and tin oxide (SnO2) thin films deposited on a single side-polished D-shaped optical fiber. For the first time, to the best of our knowledge, two independent LMRs are obtained in the same D-shaped optical fiber, by using a step-shaped nanostructure consisting of a first section of TiO2 with a thickness of 120 nm and a second section with a thickness of 140 nm (120 nm of TiO2 and 20 nm of SnO2). Each section is responsible for generating a first-order LMR with TM-polarized light (LMRTM). TiO2 is deposited by atomic layer deposition and SnO2 by electron-beam deposition. The theoretical results show that the depth of each of the resonances of the dual LMR depends on the length of the corresponding section. Two experimental devices were fabricated with sections of different lengths, and their sensitivities were studied, achieving values ∼4000nm/refractiveindexunit (RIU) with a maximum of 4506 nm/RIU for values of the SRI between 1.3327 and 1.3485.

Water Pollution Fiber Sensor Based on Surface Plasmon Resonance Technique; Implementation and Characterization

In this work, a single fiber optic fiber was developed as a water pollution sensor based on the Surface Plasmon Resonance Phenomenon based upon the Mach - Zehender Interferometry (MZI) technology. The sensor submitted was developed to detect water pollutants. The SPR sensors were prepared by coating a golden metallic film which thickness 42 nm on a chemically etched single-mode fiber with a thickness of 20 micrometers, which achieved the best results of sensitivity to water pollution, the results of the high sensitivity of the optical fiber sensor were obtained based on the surface plasmon resonance phenomenon. The experimental results showed high sensitivity, reaching 1315 pm/mol.l−1 for a salty solution with distilled water, 1705 pm/mol.l−1 for the salty solution with tap water, as well as 2222 pm/mol.l−1 for sugar solution with distilled water, and 1925 pm/mol.l−1 for sugar solution with tap water. This means that these sensors which are based on SPR could be very useful in the field of water pollution detection.

Optical and scintillation properties of Ce:Y3Al5O12 single crystal fibers grown by laser heated pedestal growth method

The single crystal scintillating optical fibers acting as the scintillators and light conductors show potential application in scintillating fiber array detectors with high spatial resolution. In this paper we report the growth of 0.2 at% Ce:Y3Al5O12 single crystal fiber. The crystalline phase, surface morphology of the axial-section and cross-section, optical and scintillation properties of the as-grown fiber were investigated. The Ce:Y3Al5O12 single crystal fiber has a pure YAG phase, a uniform distribution of cerium in the axial-section and cross-section surface. Emission spectrum is composed of broad bands ranging from 440 to 700 nm. In addition, the single crystal fiber has a high light yield of 26115 ± 2000 photons/MeV, low energy resolution of 9.44% @662 keV and decay time of a fast component of 78 ns and a slow component of 301 ns. The intensity ratio of fast to slow components is roughly 8:1.

Optical fibre sensor for simultaneous temperature and relative humidity measurement: Towards absolute humidity evaluation

Temperature and humidity are essential parameters in monitoring the health of patients in critical care. An optical fibre sensor has been developed for simultaneous measurement of relative humidity (RH) and temperature at a single optical fibre tip based on the reflected intensity. Combining these measurements enables absolute humidity values to be obtained. The fibre tip is first modified with a coating of poly(allylamine hydrochloride) (PAH) / silica nanoparticles (SiO2 NPs) for relative humidity (RH) measurement and then coated with thermochromic liquid crystal (TLC) for temperature measurement. Experimental results demonstrate that the RH and temperature sensitivity are respectively 0.43 %/RH% (intensity at a wavelength of 650 nm) from 55 to 90% RH (R2 = 0.973) and 3.97 nm/°C from 28 to 46 °C (R2>0.99). Moreover, the proposed sensor has low crosstalk between each of the sensing parameters, with a response time of 3.1 s temperature (30–38 °C) and 13.2 s for relative humidity (20–80 %). In comparison to grating based optical fibre sensors the proposed sensor is low-cost with a simple manufacturing process which has the potential to find widespread use in healthcare applications.

Stimulated Brillouin scattering mitigation using optimized phase modulation waveforms in high power narrow linewidth Yb-doped fiber amplifiers.

We demonstrate the mitigation of stimulated Brillouin scattering (SBS) in a double-clad single mode Yb-doped optical fiber amplifier through external phase modulation of narrow linewidth laser radiation using optimized periodic waveforms from an arbitrary waveform generator. Such optimized phase modulation waveforms are obtained through a multi-objective Pareto optimization based on a comprehensive model for SBS in high power narrow linewidth fiber amplifiers using Brillouin parameters determined from controlled measurements. The ability of our approach to mitigate SBS is tested experimentally as a function of RMS linewidth of the modulated optical radiation, and we measure an enhancement in SBS threshold with respect to optical linewidth of ∼ 10 GHz-1. Furthermore, we discuss the dependence of the SBS threshold enhancement on key parameters such as the amplifier length and the period of the optimized waveforms. Through simulations we find that waveforms of sufficiently long periods and optimized for a relatively long fiber (10 m) are effective for SBS suppression for shorter fibers as well. We also investigate the effect of increase in the bandwidth and amplitude of the modulation waveform on the SBS threshold enhancement observed at higher optical linewidth.

Detection of X-Rays Radiation Effect on Radiation Sensors Based on Optical Fiber Technology

This study aims to investigate the characteristics of optical fiber sensors under X-rays radiation. The Radiation-Induced Absorption (RIA) and Radiation-Induced Refractive-Index Change (RIRIC) in the UV-VIS domain were investigated. Single and multi-mode optical fibers (SMFs & MMFs) have been used for this purpose. The outer diameters of these fibers were reduced from (125 to 50 and 55μm for SMF and MMF respectively) via chemical etching process then dipped into (3 wt % concentration) of germanium (Ge) solution to produce the sensing part of the fibers. Due to the applied X-rays radiation, an attenuation of the spectrum and a redshift in peak wavelength were achieved. Both sensors show good responsivity to the applied radiation and the MMFs sensors showed higher wavelength shifting as compared to SMFs sensors.

Testing of a Polarimetric Current Sensor in the Frequency Domain.

This paper proposes an original model of a polarimetric current sensor, in which the measuring coil was made of a single mode telecommunication optical fiber ITU-T G.652, G.653, G.655, and G.657. This sensor was subjected to the commercialization process, which was carried out by a company combining the functionality of a technology transfer center with the capabilities of the Startit Fund Sp. z o.o. The published results included the analysis of the implementation readiness, the analysis of the market potential, the valuation of the industrial property rights of the invention and indicated further directions of scientific research on the sensor, which include the frequency analysis of measurement signals. This prompted the conduct of relevant scientific research. In this paper, the idea of measurement of current using polarimetric current sensor with optical fiber coil has been briefly characterized. It shows the definition and basic properties of the Discrete Fourier Transform (DFT). It discusses the technique of determining the value of each harmonic of signal at the input and output of polarimetric current sensor. The value of measurement errors and total harmonic distortion (THD) have been calculated. The general conclusions for disturbances in the processing realized in polarimetric current sensor have been formulated. In addition, the impact of the molar concentration of the dopant GeO2 in the core of the single mode telecommunication optical fibers and the impact of the number of turns of the measuring coil on the distortion accompanying the process of processing have been determined. Therefore, it can be concluded that the key result obtained during the research is the confirmation of the fact that single mode telecommunication optical fibers can be used to build the measuring coil of a polarimetric sensor used for measuring alternating currents. This means that the considered sensor, when measuring this type of currents, does not introduce additional distortions and distortions of their waveforms.

Chirped-apodized Thue-Morse quasiperiodic structures for multichannel optical dispersion compensation

Nowadays, optical data transmission systems are significantly involved in telecommunication networks. Particularly, hundreds of data channels can be sent concurrently over a single optical fiber through dense wavelength division multiplexing (DWDM) and optical time division multiplexing technologies. Nevertheless, dispersion imposes main limitations for having high capacity systems with high transmission rates. This paper suggests a new dispersion compensating scheme by introducing one-dimensional chirped and apodized Thue-Morse quasiperiodic structures. Numerical investigations of the dispersion features of the proposed structure is presented. According to the acquired relatively smooth and negative slope group delay (GD) along with corresponding negative constant group velocity dispersion (GVD) of the reflection bands, it would be possible to apply the suggested structure in an efficient way in DWDM applications for multiband dispersion compensation in optical communication systems. The designed multilayer structure with short physical length and ultrahigh negative dispersion coefficient and with the free spectral range (FSR) of about 0.8 nm meets the International Telecommunication Union-Telecommunication Standardization (ITU-T) Sector requirements. Besides, the impact of main structural design parameters on the spectral features of the suggested system are presented in this paper.

High-Order Fiber Mode Beam Parameter Optimization for Transport and Rotation of Single Cells.

Optical tweezers are becoming increasingly important in biomedical applications for the trapping, propelling, binding, and controlled rotation of biological particles. These capabilities enable applications such as cell surgery, microinjections, organelle extraction and modification, and preimplantation genetic diagnosis. In particular, optical fiber-based tweezers are compact, highly flexible, and can be readily integrated into lab-on-a-chip devices. Taking advantage of the beam structure inherent in high-order modes of propagation in optical fiber, LP11, LP21, and LP31 fiber modes can generate structured radial light fields with two or more concentrations in the cross-section of a beam, forming multiple traps for bioparticles with a single optical fiber. In this paper, we report the dynamic modeling and optimization of single cell manipulation with two to six optical traps formed by a single fiber, generated by either spatial light modulation (SLM) or slanted incidence in laser-fiber coupling. In particular, we focus on beam size optimization for arbitrary target cell sizes to enable trapped transport and controlled rotation of a single cell, using a point matching method (PMM) of the T-matrix to compute trapping forces and rotation torque. Finally, we validated these optimized beam sizes experimentally for the LP21 mode. This work provides a new understanding of optimal optical manipulation using high-order fiber modes at the single-cell level.

Research of multisensor characteristics based on optical fiber

The research results of multisensors based on optical fiber, the principle of which is to change the conditions of propagation of optical radiation in the optical fiber in the places where macro-bends are formed at the points of impact, are presented in the paper. The formation of macro-bends leads to an additional attenuation of the power of optical radiation propagating through the optical fiber. A single-mode optical fiber was used with the parameters, which are supported by numerous manufacturers and comply with the recommendations of ITU-T G.655. The measurements were carried out for four wavelengths of optical radiation (1310, 1490, 1550, 1625 nm), corresponding to the transparency windows of the optical loss spectrum of the optical fiber. Using optical reflectometry methods, it was determined that the amount of attenuation of optical radiation of each macro-bend formed at the point of action of the multisensor does not depend on the number of simultaneously formed macro-bends and also does not depend on the location of the point of action along the length of the multisensor. The dependences of the attenuation of the optical radiation power introduced by the macro-bends of the optical fiber on the radius, length, or angle of the macro-bends formed at the multisensory impact points are determined experimentally. The obtained dependences also allow one to determine the optimal parameters of the formed macro-bends of the multisensor to obtain the maximum range of attenuation change for each value of the wavelength. The values of the minimum distance between the impact points, the maximum number of impact points and the optimal values of the radius and angle of the optical fiber macro-bend at the impact points are determined. The results obtained provide opportunities to continue the development of multisensors that allow us to receive information about parameters from several impact points, that are located on a single optical fiber, simultaneously.