Electric Arc Discharge Technique Research Articles

Tapered fiber optic refractive index sensor using speckle pattern imaging

In this study, a low-cost and compact refractive index (RI) sensor based on speckle pattern imaging has been proposed and demonstrated numerically and experimentally. We have proven that speckle pattern images recorded with a CCD camera placed at the end of the tapered optical fiber (TOF) are highly sensitive to the RI of the medium to be measured. The effects of the waist diameter and length of the tapered region, which is the sensing part of the fiber, on sensitivity were investigated using the beam propagation method (BPM). It has been seen that the numerical results have compatible with the experimental results. Tapered fiber sensor was fabricated by electric arc discharge technique using step index multimode fiber (SI-MMF) with core and cladding diameters of 105 and 125 μm. The sensor sensitivity increases as the waist diameter decreases and the waist length increases. The sensor, which waist diameter is reduced to 10 μm, is sensitive to RI changes of the order of 10-4. It has been clearly seen that the proposed sensor based on speckle pattern imaging is highly sensitive to RI change.

Sensitivity Enhancement in Long Period Gratings by Mode Transition in Uncoated Double Cladding Fibers

This work deals with long period gratings (LPGs) fabricated in double cladding fibers (DCFs) with W-type refractive index profile and analyzes their surrounding refractive index (SRI) sensitivity. The W-type fiber presents an outer cladding with refractive index higher than the inner one, thus some cladding modes can be guided in the ring-shaped outer cladding without interacting with the core mode. However, the transition phenomenon from outer- to inner-cladding of these modes can be induced, through the reduction of the external cladding thickness (i.e. fiber diameter). As a matter of fact, here we demonstrate for the first time the mode transition phenomenon without any additional coating on the fiber. The result is a significant enhancement of the SRI sensitivity, as well as the possibility to tune the SRI range with maximum sensitivity gain. It is illustrated by numerical analysis and experimentally verified by considering LPGs written in pure-silica core with F-doped inner cladding and silica outer cladding fiber, by means of the electric arc discharge technique. The case study is focused on the SRI sensitivity in water-like environment as for biological applications. Proof of concept results have demonstrated that, by proper selection of the outer diameter through chemical etching, the gain in SRI sensitivity reaches from 40 to 60 as compared with unetched fiber, with maximum sensitivity around 420 nm/RIU with water as surrounding material.

High strain rate behavior of graphene-epoxy nanocomposites

This work consists of the synthesis of high purity graphene nanoflakes (GNF), the manufacturing of GNF-epoxy nanocomposites and the mechanical characterization of the nanocomposite at high and quasi static strain rates, (2750/s - 1.E−5/s). GNF were synthesized by using the electric arc discharge technique. Thermogravimetry/Differential Thermal Analysis (TG/DTA) of synthesized graphene reveals high purity and high crystallinity. Raman spectra and the broad Brunauer-Emmet-Teller (BET) specific surface area indicate that the synthesized graphene has several layers. Following the solution mixing manufacturing process of GNF-epoxy nanocomposites, the influences of strain rate on the mechanical behaviors are investigated under quasi static and dynamic loadings. High strain rate uniaxial compression tests (1270–2750/s) using Split Hopkinson Pressure Bar (SHPB) and quasi static compression tests (1.E−3 and 1.E−5/s) of GNF-epoxy with two graphene contents (0.1 and 0.5 wt %) are performed at room temperature. The maximum elasticity modulus achieved by the GNF-epoxy with 0.5 wt% at the strain rate of 2350/s corresponds to a 68% increase compared to the neat epoxy. The yield strength of the material is doubled under dynamic loading conditions compared to the quasi static loading.

Arc-Induced Long Period Gratings in Erbium-Doped Fiber

In this paper, we report about the fabrication of long period gratings (LPGs) directly into an Erbium-doped fiber, by using the electric arc discharge technique. The attention is focused on the writing process and the resulting properties, by considering gratings with different periods and measuring their spectra over a wide wavelength range. The LPGs show high order attenuation bands with tunable resonance wavelengths and depths up to 30 dB, while the lengths of the final devices are in range 20-45 mm. The polarization-dependent loss of these LPGs is also measured, for the first time in this kind of fiber. As further novelty, the influence of surrounding refractive index, applied strain, and temperature is investigated and discussed in comparative manner. Based on the achieved results, this fabrication procedure can be adapted to a specific application, for example in optical communications, signal processing, and sensing fields.

Highly sensitive measurement of surrounding refractive index using tapered trench–assisted multicore fiber

Abstract In this study, a surrounding refractive index (SRI) sensor based on tapered trench-assisted multicore fiber (TAMCF) is proposed and experimentally demonstrated. A segment of TAMCF was spliced between two single mode fibers (SMF28). Electric arc discharge technique was employed to fabricate a tapered sensor with a SMF28–tapered TAMCF–SMF28 structure. Numerical beam propagation was used to investigate the benefit of tapering on TAMCF. Tapering allows coupling of light in the center and outer cores, thereby enhancing the sensitivity of the sensor. Two sensors were fabricated with waist lengths of 10 and 15 mm and a waist diameter of 25 µm. The sensitivity of sensors at different SRI ranges was investigated using a set of honey/water solutions with precisely controlled concentrations. The measured SRI sensitivity was up to 35089.28 nm/RIU (refractive index unit) in SRI range from 1.4430 to 1.4442, which is higher than previously reported studies using other kinds of MCF sensors. SRI sensitivity was enhanced with the increase in waist length of the tapered TAMCF. The fabricated sensors have demonstrated good linearity in terms of spectral wavelength shift versus SRI variations.

Random Rotational Entire-Angle Sensor Using Two Chemical Etching Intrinsic Fabry–Pérot Interferometers

We demonstrate a full range rotational angle sensor system using two chemical etching intrinsic Fabry–Perot interferometers (FPIs) fabricated by an electrical arc discharge technique. The use of magnetic scale, combined packaged FPI detectors, allows the exploration of position characteristic with direction discrimination. Numerical simulation is employed for optimizing the distance $(d)$ between the detector and the circle magnetic scale. Experiments and numerical simulation show the interference dip shifts of FPI have sinusoidal relation with the rotational angle, as d ranging from 1 to 2.5 mm. Measurements showed five times ( $d=1$ ) and four times ( $d=1.5$ ) of magnitude greater than FBG detectors, with the linearity of 0.993 and 0.999, respectively. The sinusoidal function variations are displayed by two detectors with a phase difference of 90 degrees, which help to discriminate rotational direction. Moreover, two detectors have a low temperature cross-sensitivity of 2.3 pm/C°. The important advantage of our rotational angle sensor is their angle measurement range without limitation.

Development of High Purity, Few-Layer Graphene Synthesis by Electric Arc Discharge Technique

Development of High Purity, Few-Layer Graphene Synthesis by Electric Arc Discharge Technique

Arc-Induced Long Period Gratings from Standard to Polarization-Maintaining and Photonic Crystal Fibers.

In this work, we report about our recent results concerning the fabrication of Long Period Grating (LPG) sensors in several optical fibers, through the Electric Arc Discharge (EAD) technique. In particular, the following silica fibers with both different dopants and geometrical structures are considered: standard Ge-doped, photosensitive B/Ge codoped, P-doped, pure-silica core with F-doped cladding, Panda type Polarization-maintaining, and Hollow core Photonic crystal fiber. An adaptive platform was developed and the appropriate “recipe” was identified for each fiber, in terms of both arc discharge parameters and setup arrangement, for manufacturing LPGs with strong and narrow attenuation bands, low insertion losses, and short length. As the fabricated devices have appealing features from the application point of view, the sensitivity characteristics towards changes in different external perturbations (i.e., surrounding refractive index, temperature, and strain) are investigated and compared, highlighting the effects of different fiber composition and structure.

Long Period Gratings in unconventional fibers for possible use as radiation dosimeter in high-dose applications

In this work, we conducted experimental and theoretical investigations on gamma radiation sensitivity of Long Period Gratings (LPGs), fabricated by electric arc discharge technique in two different single mode optical fibers, designed to be radiation resistant, with the aim to understand their behavior under irradiation and their radiation hardness as a function of core/cladding dopants. The first fiber is sold by the manufacturer to be used in harsh environments and has doped core and pure-silica cladding, while the second one is radiation-hardened with pure-silica core and F-doped silica cladding. Gamma irradiation was performed at a 60Co source with a 0.2 kGy/h dose rate, until a total absorbed dose close to 30 kGy was reached. During the experiments, the LPGs spectral changes were recorded in real-time, moreover pre- and post- irradiation investigations were done to establish the impact of gamma radiation over fiber refractive index modification and LPGs temperature sensitivity. The LPG in pure-silica core fiber proved its radiation hardness exhibiting changes in resonant wavelength position lower than 0.2 nm, on the contrary the LPG written in doped-core fiber showed high sensitivity to radiation with a wavelength shift of 5.7 nm at the end of the irradiation. The outcomes of this experimentation, along with our previous results on gamma irradiated LPGs, are useful for the design of an all LPG-based temperature compensated radiation dosimeter.

Sensitivity-optimized long-period fiber gratings for refractive index and temperature sensing

ABSTRACTA long-period fiber grating sensor was fabricated by periodically changing the structure of single-mode fiber with an electric arc discharge technique. After the fabrication, the refractive index and temperature sensitivities were optimized by etching the cladding with hydrofluoric acid solution. The experimental results illustrate that the thinner cladding shows relatively higher refractive index and temperature sensitivities for the same order cladding mode, which are accordant with that of numerical simulation. After the long-period fiber grating was etched for 15 min, average refractive index sensitivities of 214 nm/refractive index unit (RIU) (1.3333 – 1.3931) and 1987 nm/RIU (1.4115–1.4555) were achieved. An extremely higher refractive index sensitivity of 2731 nm/RIU appears near 1.4555. By systematically studying the temperature sensing characteristic of cladding-etched long-period fiber grating in this work for the first time, the temperature sensitivity can reach as high as 144.23 pm/°C when the ambient temperature changes from 30 to 80°C. This work provides a theoretical reference for the fabrication of a high-sensitivity refractive index and temperature sensor based on arc-induced long-period fiber grating.

Arc-induced Long Period Gratings in standard and speciality optical fibers under mixed neutron-gamma irradiation

In this paper, for the first time, the effects of mixed neutron and gamma flux on the spectral and sensing responses of Long Period Gratings (LPGs) are thoroughly analyzed. Six LPGs written by means of Electric Arc Discharge (EAD) technique in standard and speciality fibers, including radiation-hardened ones, were tested. The EAD technique was chosen because it enables the writing of gratings both in standard and not photosensitive fibers. The experiments have been carried out in a “TRIGA” pulsed nuclear reactor and the LPGs were irradiated by a gamma-ray dose-rate of 9 Gy/s and a mean 1.2∙1012 n/(cm2s) neutron flux. Real time monitoring was performed for a comparative investigation of LPGs’ response, in terms of radiation sensitivity and wavelength shift. Experiments show that LPG in a radiation-resistant fiber exhibits resonant wavelength shift higher than LPG in standard fiber. The changes of temperature sensitivity due to radiation were experimentally established by comparison of pre- and post-radiation characterization, indicating that radiation effects induce a slight increase of the temperature sensitivity, except for the LPG in pure-silica fiber. Theoretical and numerical analysis was combined with experimental data for evaluation LPGs’ parameters changes, such as refractive index and thermo-optic coefficient, after exposure to radiation.

Sensing Characteristics of Arc-Induced Long Period Gratings in Polarization-Maintaining Panda Fiber

We present and discuss an investigation of the sensing features of long period gratings fabricated in a polarization-maintaining Panda optical fiber, by means of the electric arc discharge technique. In particular, the investigation regards the resonant wavelength shift of first three cladding modes as function of three environmental parameters, such as strain, temperature, and surrounding medium refractive index. We also investigate and discuss the variations of the sensing behavior as a function of the polarization input state. The achieved results show that the sensitivity of each resonant wavelength to environmental parameters is modulated by the cladding mode order and by polarization input light, with some appealing characteristics. For instance, the lowest order cladding mode in slow polarization state is practically insensitive to temperature and surrounding refractive index, but sensitive to strain. Temperature and strain sensitivities show opposite signs with the input light polarization. Sensitivity to surrounding refractive index is higher in the case of fast polarization state. These results represent a concrete perspective of the possibility that this device can act as a 3-parameter sensor.

Single-mode all-fiber structured modal interference for temperature and refractive index sensing

A new type of optical fiber sensor based on an asymmetric structured microfiber modal interferometer is proposed and demonstrated. The sensor head is simply made of single-mode fiber using the electrical arc discharge technique. Owing to the reflection spectrum dips formed by the interference between the cladding modes and the core mode, measurements of temperature and the refractive index (RI) can be obtained by monitoring the wavelength shifts of the interference spectrum. Experiments show that the sensor exhibits a good response to temperature and the ambient RI variation, with maximum sensitivities of 0.079 nm °C−1 and −49.957 nm/RIU, respectively. The merits of its cost-effective and simple fabrication makes this sensor a promising device for sensing applications.

Nano silica diaphragm in-fiber cavity for gas pressure measurement

We demonstrate an ultrahigh-sensitivity gas pressure sensor based on the Fabry-Perot interferometer employing a fiber-tip diaphragm-sealed cavity. The cavity is comprised of a silica capillary and ultrathin silica diaphragm with a thickness of 170 nm, with represents the thinnest silica diaphragm fabricated thus far by an electrical arc discharge technique. The resulting Fabry-Perot interferometer-based gas pressure sensor demonstrates a gas pressure sensitivity of about 12.22 nm/kPa, which is more than two orders of magnitude greater than that of a similarly configured fiber-tip air bubble sensor. Moreover, our gas pressure sensor has a low temperature cross-sensitivity of about 106 Pa/°C, and the sensor functions well up to a temperature of about 1000 °C. As such, the sensor can potentially be employed in high-temperature environments.

Arc-Induced Long Period Gratings in Phosphorus-Doped Fiber

Phosphorus-doped fibers have been reported and discussed in extensive works, as well as the radiation effects on their guiding features in different spectral ranges. However, the assessment of a technique enabling the fabrication of grating devices in this fiber is still an open issue. Here, for the first time to the best of our knowledge, we report on the fabrication of long period gratings (LPGs) in P-doped optical fiber by means of electric arc discharge technique (EAD). LPGs having periods of $500~\mu \text{m}$ and of $700~\mu \text{m}$ were presented, achieving the coupling up to LP06 cladding mode, attenuation bands with depth up to 35 dB, power losses lower than 0.5 dB, and devices length less than 20 mm. The results being also compared with numerical simulations. Moreover, the sensitivity characteristics to surrounding refractive index (SRI) and temperature changes of LPGs in P-doped fibers were also investigated. The SRI sensitivity of LP06 for SRI = 1.437 was about −478 nm/RIU, slightly higher than in standard fiber. Whereas, differently from standard Ge-doped fibers, a negative temperature response was found (−116 pm/°C) opening the possibility of new applications, for example for temperature compensation solutions.

Real-time analysis of arc-induced Long Period Gratings under gamma irradiation

In this paper, we present a comparative experimental and theoretical study on gamma radiation sensitivity of Long Period Gratings (LPGs), fabricated by electric arc discharge technique, as monitored in three single mode optical fibers supplied by different manufacturers. A real-time measurement of LPGs’ wavelength shift was performed until a total dose of 35 kGy was reached, with average dose rate of 0.18 kGy/h, the irradiation being done at room temperature. In one case, a maximum radiation sensitivity of 1.34 nm/kGy was recorded for doses up to 0.5 kGy. Moreover, by combining experimental results with numerical simulations, it was found that changes occurred in the core refractive index of the irradiated optical fibers up to 2.5 ∙ 10−5. The increase of the core thermo-optic coefficient up to 1.5 ∙ 10−8/°C was observed as well.

Arc-Induced Long Period Gratings in Polarization-Maintaining Panda Fiber

In this letter, we report about the fabrication of long period gratings (LPGs) in a polarization-maintaining Panda optical fiber, by means of the electric arc discharge technique. This is the first time that LPGs are arc-induced in a polarization maintaining fiber. The dependence of the LPG’s spectral features on the input light polarization alignment is illustrated, by considering the two principal polarization states, i.e., along the fast and slow axes of the Panda fiber. Moreover, an investigation about the surrounding refractive index sensitivity, as a function of the two principal polarization states, is also reported with interesting results.

Temperature-Independent Force Sensor Based on PSLPFG Induced by Electric-Arc Discharge

A novel approach to create a phase shift in a long period fiber grating (LPFG) by using the electric-arc discharge technique is first proposed and demonstrated. We observe that an equivalent phase shift is created at the middle of the LPFG by slight tapering the grating by discharge arc. By measuring the wavelength separation of the two resonance peaks, we obtain a force sensor without any temperature crosstalk.

Photocatalytic Degradation of Methylene Blue Using TiO<sub>2</sub>/Carbon Nanoparticles Fabricated by Electrical Arc Discharge in Liquid Medium

Herein we modified TiO2 anatase with carbon material using an electrical arc discharge technique in liquid medium to produce a nanoparticle of TiO2/Carbon photocatalyst. The electrical arc discharge was performed using two graphite electrodes submerged in TiO2 suspended in ethanol by passing electrical 20-40 V (10-50 A). X-ray Diffraction (XRD) peak profile analysis shows the successful modification confirmed from the presenting peaks which represent to crystalline TiO2 and carbon element. The fabrication was then followed by the assessment of photocatalytic activity of fabricated nanoparticles in methylebe blue degradation under mercury lamp irradiation. After 60 minutes irradiation, the photocatalytic activity of TiO2/Carbon increased more than three times higher compared to the photocatalytic activity of pristine TiO2.

Asymmetrical in-fiber Mach-Zehnder interferometer for curvature measurement.

We demonstrated a compact and highly-sensitive curvature sensor based on a Mach-Zehnder interferometer created in a photonic crystal fiber. Such a Mach-Zehnder interferometer consisted of a peanut-like section and an abrupt taper achieved by use of an optimized electrical arc discharge technique, where only one dominating cladding mode was excited and interfered with the fundamental mode. The unique structure exhibited a high curvature sensitivity of 50.5 nm/m-1 within a range from 0 to 2.8 m-1, which made it suitable for high-sensitivity curvature sensing in harsh environments. Moreover, it also exhibited a temperature sensitivity of 11.7 pm/°C.