Optical Fiber-based System Research Articles

Long-range fiber-based laser Doppler vibrometer using Faraday rotator for polarization-rotation compensation

In this paper, we report a method for extending distance of an optical fiber-based laser Doppler vibrometer system. This method uses a Faraday rotator (FR) to compensate polarization rotation in an installed long-range optical fiber. The construction of the proposed system is simple and achieved only by adding the FR to the sensing head unit, leading to stable and highly reliable vibration measurement even by using a long-range optical fiber exceeding kilometer. Experiments by using 100-m and 10-km long standard single mode fibers with emulated polarization rotation verified advantages of the proposed method; the system performances retained almost the same values even when the polarization state of reflected light was randomly rotated in installed optical fibers.

Field tests for performance evaluation of a new spent-fuel verification system in heavy water reactor

The optical fiber-based measurement system has been utilized for inspecting CANDU-type spent fuel at the Wolsung site in South Korea under the nuclear safeguards of the International Atomic Energy Agency (IAEA). In our previous studies, we developed a new spent-fuel verification system to address issues of the existing instrument. While our prior work primarily focused on equipment development, we had not yet conducted comprehensive field tests to assess its performance. Recently, we conducted field tests at the Wolsung Unit 4 to thoroughly evaluate the newly developed spent-fuel verification system's performance. This paper discusses the results of these field tests, with a focus on signal sensitivity, the system's capability to distinguish neighboring spent-fuel bundles, and the optical fiber background signals. Additionally, we conducted experiments to assess how different scintillation materials impact the system's performance, including p-terphenyl organic scintillator, PVT plastic scintillator, and lithium glass scintillator. The experimental results demonstrated that the new instrument equipped with the p-terphenyl organic scintillator outperformed the existing system. The p-terphenyl scintillator emerged as the superior choice among the three radiation scintillators. Signals that were previously undetectable using the Li glass scintillator were observed in the signals obtained with the p-terphenyl and PVT plastic scintillators. The remarkable performance of the new verification instrument is attributed mainly to the p-terphenyl's high light output and low decay time. The newly developed verification system is expected to streamline IAEA safeguards inspection efforts, reducing both time and the burden on nuclear operators. This report represents the first successful application of the p-terphenyl scintillator as a radiation detector in a wet spent fuel pool. The experimental findings presented in this paper are anticipated to be valuable for researchers working on radiation detectors suitable for high radiation environments in water.

Scalable optical fiber reactor for photocatalytic H2 production: Addressing scattering issues

Scattering is one of the main challenges in scaling up photocatalytic water splitting using the most prevalent powder catalysts. This can be overcome by decoupling the reaction medium from light transmission, as in the case of optical fibers. Here we explore utilizing optical fibers coated with 5 wt% CuO supported on TiO2 for photocatlytic H2 production from water-methanol mixtures. CuO/TiO2 is a well studied photo catalyst in which photoreduced Cu species are known to act as sensitizers for inducing visible light activity. Lower activity of sequentially coated systems indicates that appropriate interfaces of active Cu and TiO2 with water are desirable. The scalability of such optical fiber-based systems along with potential in non-potable turbid water media are demonstrated. Maximum activity of 22 μmoles of H2 in 8 h was obtained with 50 mg of catalyst coated on optical fibers, which increases linearly with increase in fiber numbers, whereas, drastic reduction in activity is observed in powder catalyst upon increasing the catalyst quantity. A one-to-one comparison of 700 mg of catalyst in powder form and coated on optical fibers indicates more than one order enhancement in activity in the optical fiber based system. In addition, ∼70% retention in activity in highly turbid non-potable water was observed as compared to powdered system which shows complete reduction in the activity by 99.99%.

Utilization of smartphones for the evaluation of Gr/Ni nanostructures magnetically controlled based on optical fibers surface plasmons.

In the suggested optical fiber-based magnetoplasmonic system, we investigated the magnetic properties of graphene/nickel nanostructures. The plasmonic mode changes under the magnetic field observed in the intensity diagrams over time. To be accessible, cheap, and portable, we used a smartphone as a detector and processor. Considering the ambient noise and the light source, it was reported that the intensity of the changes improved up to 5 times. Further, the clad corrosion experiment carried out by pure dimethyl ketone in an intensity modulation by a smartphone camera and 10 seconds suggested removing fluorine polymer clad.

An intelligent optical fiber-based prewarning system for oil and gas pipelines

The total length of the global oil and gas pipelines has increased rapidly during the last decades. Subsequently, prewarning systems for pipeline intrusion damage incidents have become significantly important. The traditional remote optical fiber prewarning systems however often have high false-alarm and missing alarm rates due to the complex environment that reduces signal recognition accuracy. To address this issue, in this paper we analyze the signal characteristics of various dangerous events and then use dimensional signals in the space-time domain to develop a novel signal recognition method based on object detection. Our objective is to improve recognition accuracy and reduce the false alarm rate. Our experiments and test scenarios confirm that the recognition accuracy of this method is greater than 98%. We also examined the proposed method on Pipechina MaFang to MiYun with a total length of 41 km, and show that it significantly improves signal recognition and further provides good adaptability under various interferences.

Application of an optical fiber-based system for mass movement monitoring

Application of an optical fiber-based system for mass movement monitoring

A Study on Material Dispersion around Zero Material Dispersion Wavelength of Different Material Composition based Optical Fiber

The Optical Fiber-based communication system has established its proficiency and inevitability towards regular progress and advancement worldwide. The most attractive wavelength for optical fiber communication is 1.55 μm, as it represents the lowest loss. The other challenging parameter ‘Material Dispersion’ gets reduced to ‘Zero’ at 1.27 μm wavelengths for conventional pure silica-based Optical Fiber. To improve the system towards a better unification between the loss and dispersion, the Dispersion Shifted Fiber (DSF) has been introduced. The Dispersion Flattened Fiber has introduced the concept of flat dispersion over a wide range of wavelengths. But the effective combination of the mechanisms to compensate for all the challenges is yet to be established properly. The said mechanisms are complex to design and implement. So, there is an immense scope to search for an alternative to get control over the loss and dispersion. At present, a fair number of material compositions of optical fiber are reported with different specifications. Our study on some of these fiber compositions has produced some interesting data towards the broader flatness and the minimum dispersion effect over a considerable range of wavelengths around the Zero Material Dispersion Wavelength (ZMDW). It helps to have more effective wavelength division Multiplexing (WDM). In this paper, we have studied different prospective options of optical fiber doping profiles to explore and propose an effective and optimized alternative among the available fiber profiles. We have studied the samples of pure SiO2 fibers along with B2O3 and GeO2 doped fibers and samples of Fluoride-based ABCY and ZBLAN glass Fibers to propose an effective combination of materials among the available options to get the optimized conjugation of loss and dispersion. Our report on the comparative study of different fiber materials has produced some effective results to have minimum material dispersion at the lowest loss wavelength to invite worldwide attention from system designers.

Optical Energy-Difference Conservation in a Synthetic Anti-PT-Symmetric System.

Anti-parity-time (APT) symmetry is associated with various effects beyond the fundamental limitations implied in the standard Hermitian-Hamiltonian dynamics. Here, we create an optical APT-symmetric system in a synthetic frequency domain using a conventional fiber without intrinsic gain or loss and experimentally reveal photonic APT-symmetric effects, including energy-difference conservation and synchronized power oscillation, which have not yet been confirmed experimentally in the optical domain. The optical fiber-based APT-symmetric system has a long interaction length because of its negligible loss, and the APT-symmetric Hamiltonian is precisely tunable with optical pumping density and phase mismatch. On this basis, we observe the phase transition at exceptional points, energy-difference conservation, and synchronized power oscillation. Our results provide a robust theoretical and experimental framework connecting the emerging non-Hermitian physics with technologically important nonlinear fiber-optic interactions.

An optical fiber-based monitoring system to study the seepage flow below the landside toe of a river levee

The development of innovative monitoring systems to mitigate the risk associated to river levee failure is a recent challenge involving synergic effort of public institutions, specialized companies and academics. The present study examines a 350 m stretch of Adige river levees, located in the Province of Bolzano (Italy) close to the village of Salorno, interested in the recent past by moderate piping phenomena and subjected to subsequent interventions for seepage control (cut-off diaphragm wall). As is customary, the levee body and its foundation soil were investigated through geophysical and geotechnical surveys. The arising results provided a multi-dimensional characterization of the levee and the nearby soil water-meadows likely to be affected by preferential paths for piping. The detection of those paths entailed the joined use of piezometers and distributed optical fiber sensing (DFOS) system, the latter installed in a shallow trench on the landside. In the last days of October 2018, Northeastern Italy was hit by a tremendous storm and the Adige river was subjected to a relevant double flooding event. This exceptional circumstance, entirely recorded by the monitoring system, gives the chance to provide insight into the seepage process undermining the levee stability.

Thermally Stimulated Desorption Optical Fiber-Based Interrogation System: An Analysis of Graphene Oxide Layers’ Stability

Thin graphene oxide (GO) film layers are being widely used as sensing layers in different types of electrical and optical sensor devices. GO layers are particularly popular because of their tuned interface reflectivity. The stability of GO layers is fundamental for sensor device reliability, particularly in complex aqueous environments such as wastewater. In this work, the stability of GO layers in layer-by-layer (LbL) films of polyethyleneimine (PEI) and GO was investigated. The results led to the following conclusions: PEI/GO films grow linearly with the number of bilayers as long as the adsorption time is kept constant; the adsorption kinetics of a GO layer follow the behavior of the adsorption of polyelectrolytes; and the interaction associated with the growth of these films is of the ionic type since the desorption activation energy has a value of 119 ± 17 kJ/mol. Therefore, it is possible to conclude that PEI/GO films are suitable for application in optical fiber sensor devices; most importantly, an optical fiber-based interrogation setup can easily be adapted to investigate in situ desorption via a thermally stimulated process. In addition, it is possible to draw inferences about film stability in solution in a fast, reliable way when compared with the traditional ones.

A Differential Pilot Protection Scheme for MMC-Based DC Grid Resilient to Communication Failure

Primary single-end line protection strategies of modular multilevel converter (MMC)-HVdc systems are difficult to make a tradeoff between fast detection speed and high reliability. To improve reliability, the pilot protection schemes based on communication and data exchange can be adopted. However, the communication-based schemes suffer from potential communication failure problems, such as data error, data loss, and time synchronization error. To avoid blocking of protection devices during communication failures, a resilience-oriented differential pilot protection method is proposed in this article. To address the problem of synchronization error, a startup element based on the multiresolution morphological gradient (MMG) of traveling wave (TW) is proposed. For the problems of data error and data loss in communication, the sampled data are preprocessed by morphological filtering (MF). Also, the correlation of TWs is used to identify the internal and external faults; the ratio of the morphological gradient of pole voltages is adopted to discriminate the faulty poles. A four-terminal MMC-based dc grid model is built in PSCAD/EMTDC interfaced with the optical fiber-based communication system built in MATLAB/Simulink. The simulation results show that the protection scheme can effectively identify the faults against serious communication problems of 1‰ bit error rate and 5% data loss.

Surface Plasmon Resonance Sensing Characteristics of Thin Copper and Gold Films in Aqueous and Gaseous Interfaces

The sensing properties of thin copper (Cu) films near the surface plasmon resonance (SPR), were re-evaluated for the metal-air and metal-water interfaces and compared with gold (Au) films. For this, we used three different SPR sensing designs, i.e., a prism-based set-up, an optical fiber-based system, and a grating coupler-based solution. Optimum SPR-excitation conditions are restricted to a Cu-metal film thickness of 45± 5 nm for the ATR set-up in aqueous solution. The impacts of the surface Cu-oxide layer were discussed and prevented employing an Au ultra-thin protective overlayer. This strategy proved to be efficient for non-reversible binding. Cu-SPR responsivities are higher for the prism-based set-up (quite similar to Au-SPR ones) than the ones for the optical fiber-based system and a grating coupler-based solution. In contrast to thin Au films, bovine serum albumin (BSA) and other proteins do not bind irreversibly onto thin Cu-films. Our findings confirm the suitability of thin copper films for selected SPR sensing applications.

Simultaneous measurement of SO2 and NO2 concentration using an optical fiber-based LP-DOAS system

SO2 and NO2 are the most important pollution in atmosphere. An optimized long path (LP) differential optical absorption spectroscopy (DOAS) system of high light intensity at an ultraviolet (UV) wavelength is proposed and used to measure the concentration of SO2 and NO2 simultaneously. In contrast to the traditional DOAS, the system adopted a Y-type optical fiber structure instead of a combination of mirrors in the telescope. The UV light intensity test shows that the light intensity of UV can arrive to above 80% of the max measuring range when the light path reaches 135 m, and the integral time of the spectrograph is only 15 ms. The system is proved to be efficacious through laboratory calibration. The maximum error of SO2 calibration is 4.19%, and is 5.22% for NO2. The error of the SO2 and NO2 mixture calibration is within 10%. Field measurement is implemented in a wastewater treatment plant in winter. The measurement light path is 738 m. The concentration of SO2 varies from 6 μg/m3 (2.26 ppb) to 20 μg/m3 (7.52 ppb), and the concentration of NO2 varies from 100 μg/m3 (53.2 ppb) to 200 μg/m3 (106.4 ppb) approximately. The results are in accordance with the data from a monitoring station nearby in magnitude order and variation tendency mostly.

Time multiplexed super resolution of multicore fiber endoscope using multimode fiber illumination patterns

Abstract Optical fibers’ flexible mechanics and thin diameter makes them highly desirable for imaging in the field of optical endoscopy. Their ability to efficiently convey light towards an external imaging sensor outside the subject’s body, allows an optical fiber-based system to achieve high-resolution optical imaging from inside the body. Typically, commercial systems consist of a single core illumination fiber and a multi-core imaging fiber. Each of the cores acts like a fiber in itself, and serves as a single pixel in the final image. To eliminate core-to-core light coupling, each core has to be separated from its neighbor with a sufficient length. This creates a pixelated image having reduced resolution for small overall fiber diameter and it is being damaged by pixelization artifacts. In this paper we describe a method that uses a multimode illumination fiber to project different high-resolution patterns on the inspected sample. Images of the different patterns illuminating the inspected sample are then taken using a multi-core imaging fiber, and a post processing algorithm eliminates the pixelization effects and increases the imaging resolution. The advantage of the proposed concept is that the overall endoscope can have overall very thin diameter which consists from a very thin low-resolution multi-core fiber and a diameter of a projection multi-mode fiber which is also being very thin.

New daylight fluctuation control in an optical fiber-based daylighting system

Daylighting systems have recently been developed as another way to harness solar energy and contribute to the reduction of greenhouse gas emissions. Various technologies can be used in daylighting systems. These technologies differ with respect to the sunlight collection systems and sunlight transmission systems they employ, but have solar luminaires in common. Many factors, such as the fluctuations in the intensity of solar irradiance, limit the efficiency of daylighting systems. This study presents the design, construction and assessment of a daylight fluctuations control for enclosed spaces with no direct access to daylight from side openings. A new control algorithm is proposed for this purpose based on daylighting monitoring and a low cost microcontroller. It also allows communication between several solar luminaires based on long range wireless solutions. The main components of the proposed daylight fluctuation control are: the luminaire, mirror, shaft, frame, stepper motor driver, stepper motor, light sensor, limit switch, XBee and microcontroller. The system uses solar luminaries and dimmable lamps. Tests performed in the laboratory on the system have shown positive results. The different dimming profiles perceived have a linear zone; hence, the perceived changes in brightness are correct. The Just Noticeable Difference is less than 200 (lx). And, the solar luminaire efficiency has good results that vary between 71.60% and 76.44%, depending on the used step angle.

Guided Wave-based System for Real-time Cure Monitoring of Composites using Piezoelectric Discs and Phase-shifted Fiber Bragg Gratings.

A real-time, in-process cure monitoring system employing a guided wave-based concept for carbon fiber reinforced polymer (CFRP) composites was developed. The system included a single piezoelectric disc that was bonded to the surface of the composite for excitation, and an embedded phase-shifted fiber Bragg grating (PS-FBG) for sensing. The PS-FBG almost simultaneously measured both quasi-static strain and the ultrasonic guided wave-based signals throughout the cure cycle. A traditional FBG was also used as a base for evaluating the high sensitivity of the PS-FBG sensor. Composite physical properties (degree of cure and glass transition temperature) were correlated to the amplitude and time of arrival of the guided wave-based measurements during the cure cycle. In addition, key state transitions (gelation and vitrification) were identified from the experimental data. The physical properties and state transitions were validated using cure process modeling software (e.g., RAVEN®). This system demonstrated the capability of using an embedded PS-FBG to sense a wide bandwidth of signals during cure. The distinct advantages of a fiber optic-based system include multiplexing of multiple gratings along a single optical fiber, small size compared to piezoelectric sensors, ability to embed or surface mount, utilization in harsh environments, electrically passive operation, and electromagnetic interference (EMI) immunity. The embedded PS-FBG fiber optic sensor can monitor the entire life-cycle of the composite structure from curing, post-cure/assembly, and in-service creating "smart structures".

An optical fiber-based flexible readout system for micro-pattern gas detectors

This paper presents an optical fiber-based readout system that is intended to provide a general purpose multi-channel readout solution for various Micro-Pattern Gas Detectors (MPGDs). The proposed readout system is composed of several front-end cards (FECs) and a data collection module (DCM). The FEC exploits the capability of an existing 64-channel generic TPC readout ASIC chip, named AGET, to implement 256 channels readout. AGET offers FEC a large flexibility in gain range (4 options from 120 fC to 10 pC), peaking time (16 options from 50 ns to 1 us) and sampling freqency (100 MHz max.). The DCM contains multiple 1 Gbps optical fiber serial link interfaces that allow the system scaling up to 1536 channels with 6 FECs and 1 DCM. Further scaling up is possible through cascading of multiple DCMs, by configuring one DCM as a master while other DCMs in slave mode. This design offers a rapid readout solution for different application senario. Tests indicate that the nonlinearity of each channel is less than 1%, and the equivalent input noise charge is typically around 0.7 fC in RMS (root mean square), with a noise slope of about 0.01 fC/pF. The system level trigger rate limit is about 700 Hz in all channel readout mode. When in hit channel readout mode, supposing that typically 10 percent of channels are fired, trigger rate can go up to about 7 kHz. This system has been tested with Micromegas detector and GEM detector, confirming its capability in MPGD readout. Details of hardware and FPGA firmware design, as well as system performances, are described in the paper.

Optical Fiber-Based Confocal and Interferometric System for Measuring the Depth and Diameter of Through Silicon Vias

To measure the depth and diameter of through silicon vias simultaneously, a novel method based on spectral-domain interferometer and confocal microscope is proposed and realized. Most parts of the measurement system are constructed with optical fiber components for flexible configuration and easy alignment. According to the measurement results and performance evaluation, the mean values of the diameter and depth were 6.07m and 48.255m with the expanded uncertainties of 0.20m ( $k\,= \,{\text{2}}$ ) and 37nm ( $k\,= \,{\text{2}}$ ), respectively.

Development of a PET/OMRI combined system for simultaneous imaging of positron and free radical probes for small animals.

Positron emission tomography (PET) has high sensitivity for imaging radioactive tracer distributions in subjects. However, it is not possible to image free radical distribution in a subject by PET. Since free radicals are quite reactive, they are related to many diseases, including but not limited to cancer, inflammation, strokes, and heart disease. The Overhauser enhanced magnetic resonance imaging (OMRI) is so far the only method that images free radical distribution in vivo. By combining PET and OMRI, a new hybrid imaging modality might be developed that can simultaneously image the radioactive tracer and free radical distributions. For this purpose, the authors developed a PET/OMRI combined system for small animals. The developed PET/OMRI system used an optical fiber-based PET system combined with a permanent magnet-based OMRI system. The optical fiber-based PET system uses flexible optical fiber bundles. Eight optical fiber-based block detectors were arranged in a 56 mm diameter ring to form a PET system. The LGSO blocks were located inside the field-of-view (FOV) of the OMRI, and the position sensitive photomultiplier tubes were positioned behind the OMRI to minimize the interference between the PET and the OMRI. The OMRI system used a 0.0165 T permanent magnet. The system has an electron spin resonance coil to enhance the MRI signal using the Overhauser effect to image the free radical in the FOV of the PET/OMRI system. The spatial resolution and sensitivity of the optical fiber-based PET system were 1.2 mm FWHM and 1.2% at the central FOV, respectively. The OMRI system imaged the distribution of a nitroxyl radical (NXR) solution. The interference between PET and OMRI was small. Simultaneous imaging of the positron radiotracer and the NXR solution was successfully conducted with the developed PET/OMRI system for phantom and small animal studies. The authors developed a PET/OMRI combined system with the potential to provide interesting new results in molecular imaging research, such as in vivo molecular and free radical distributions.

Precision Alignment of Optical Fibers Based on Telecentric Stereo Microvision

Optical fiber alignment plays an important role in assembling an optical fiber-based system. Proper alignment can improve optical transmission efficiency of the spliced fiber. As for traditional methods, passive alignment has its drawback of less accuracy, and the active method based on optical power sensing is complex and often cannot find the best solution. In this paper, a novel precision closed-loop method for optical fiber alignment based on telecentric lens is introduced. First, to improve the measurement accuracy of the binocular vision system, a quick and high-precision image-processing algorithm for the glass core of an optical fiber is proposed. Then, a stereo matching problem is solved by combining the epipolar constraint with the geometry constraint especially for telecentric lens, and the 3-D recovery of the optical fibers is achieved. Finally, with the help of a proposed simple eye-to-hand calibration for this microalignment system, a coarse-to-fine strategy is put forward to deal with this five-degree-of-freedom alignment task. The experimental results showed that the proposed method had high performance such as prominent precision and strong robustness in 3-D optical fiber alignment.