Long period fiber gratings produced by the electric arc technique have found an increasing interest by the scientific community due to their ease to fabricate, virtually enabling the inscription in any kind of fiber, low cost, and flexibility. In 2005 we have presented the first review on this subject. Since then, important achievements have been reached such as the identification of the mechanisms responsible for gratings formation, the type of symmetry, the conditions to increase fabrication reproducibility, and their inscription in the turning points with grating periods below 200 μm. Several interesting applications in the sensing area, including those sensors working in reflection, have been demonstrated and others are expected, namely, related to the monitoring of extreme temperatures, cryogenic and high temperatures, and high sensitivity refractometric sensors resulting from combining arc-induced gratings in the turning points and the deposition of thin films in the transition region. Therefore, due to its pertinence, in this paper we review the main achievements obtained concerning arc-induced long period fiber gratings, with special focus on the past ten years.
1. Introduction
The concept of long period fiber gratings (LPFGs) was introduced in 1996 by Vengsarkar et al. in which a periodic modulation of the core refractive index was induced by UV laser radiation [1]. Since the grating periodicity is of the order of hundreds of micrometers several techniques have been used for LPFGs fabrication not only through exposure to UV, CO2, and IR femtosecond laser radiation [1–3] but also based on ion beam implantation, etching, mechanical arrangements, acoustic waves, broadband UV light, and electric arc discharges [4, 5]. Among the different available techniques the electric arc has paved its way during the past two decades since it is a simple, flexible, and low cost technique that enables the writing of gratings in all kinds of fibers. Furthermore, as is the case for CO2 and IR femtosecond laser radiation, the arc discharge technique also overcomes several limitations of the technique based on UV laser radiation [6] and enables the fabrication of several optical fiber components [7]. In fact, based on the number of publications, arc-induced gratings compares well with those fabricated by using laser radiation. Presently, and apart from Africa, it is a technique spread all over the world (see Figure 1; there are also some traces of research activity in Turkey and Iraq). More than two-tenths of research groups, by their own or in consortiums, have been studying LPFGs produced by the electric arc technique (in Figure 1 the flags dimensions are proportional to the number of publications in international journals and conferences) resulting in more than 250 papers. INESC TEC, in Portugal, accounts for about 40% of the publications (see Figure 2). It can be said that the fabrication of LPFGs started in 1994 by Poole et al. where they have used a two-step process involving ablation of the fiber cladding by CO2 radiation followed by annealing through arc discharges [8]. LPFGs based solely on arc discharges are due to Dianov et al. in 1997 [9]. In the following years a scarce number of publications were registered and despite the peak in 1998, the take-off occurred in 2001 by Rego et al. [6] followed by Humbert and Malki [10] that led to an increasing interest until 2007, also with important contributions from research groups in Japan [11], UK [12], and Brazil [13]. From 2008 up to 2012 there was a decrease in the number of publications despite the contribution of research groups from Mexico [14] and Canada/Poland [15]. In the past three years we have been climbing the technique’s notoriety with growing interest in Asia, namely, in Malaysia [5].
Worldwide research on arc-induced gratings.
Publications concerning arc-induced gratings in international journals and conferences.
In the early days, publications were essentially related to the fabrication in different kinds of fibers, the study of the gratings properties, and the discussion of the mechanisms of formation, being those issues reviewed in 2005 [4]. In the last decade we registered the consolidation of the knowledge concerning the formation mechanisms, the improvement of the reproducibility of the technique, the implementation of several sensors, namely, for the simultaneous measurement of temperature and strain, the development of refractometric sensors based on coated LPFGs and, more recently, to the inscription of arc-induced gratings in the turning points. At these points, the slope of the phase matching curves, for each cladding mode resonance, reaches its maximum value. On the other hand, near the turning points the slope steeply increases and changes from positive to negative and, for each grating period, there are two resonance wavelengths for each cladding mode. These are the regions where LPFGs show the highest sensitivities [16]. Therefore, by properly addressing issues related to the reproducibility of the technique associated with electrodes degradation and environmental parameters that impact the optimum arc discharge conditions and also the required LPFG engineering development associated with their intrinsic cross sensitivities to other physical parameters such as temperature, strain, and bending, it is expected that arc-induced gratings continue their worldwide spreading leading, in the near future, to commercial devices in the sensing area.
In the following sections, we begin by reviewing the underlying mechanisms of arc-induced gratings formation. Afterwards, the fabrication of long period fiber gratings, in particular, in the turning points is discussed. The main properties of LPFGs, which include the thermal behavior and the dependence on the external refractive index, are also presented. Finally, we analyze three important applications in the sensing area, namely, the simultaneous measurement of temperature and strain, flow measurement, and refractometric sensors.
2. Mechanisms of Gratings Formation
A long period fiber grating is a wavelength selective filter whose transmission spectra exhibit several resonances resulting from coupling between the core mode and the different copropagating cladding modes at wavelengths that obey the resonance condition [1]: λres=ncoeff-ncl,meffΛ, where λres represents the resonance wavelengths, Λ represents the grating period, and ncoeff and ncl,meff represent the effective refractive index of the core mode and the effective refractive index of the cladding modes, respectively. The theoretical equations governing the intrinsic properties of LPFGs, such as, transmission loss and resonance wavelengths or their temperature and external refractive index dependence, can be found elsewhere [5, 17–20]. For almost two decades that the underlying mechanisms of arc-induced gratings are under debate and in this context the estimation of the temperature reached by the fiber during an arc discharge allowed a proper discussion on the mechanisms responsible for their formation [21–23]. Figure 3 shows that for the typical fabrication parameters used, namely, electric current and time of the arc discharge, the fiber reaches a peak temperature of about 1400°C in less than half a second (estimated from Figure 3(b)) [23]. The latter result is also important in order to limit heat diffusion along the fiber since it prevents the use of short grating periods, due to overlap of the effects caused by the adjacent arc discharges.
(a) Temperature profile in the fiber during the arc discharge and (b) and its time dependence (it corresponds to a 50 μm Pt/Rh thermocouple inserted in a 56/125 μm silica capillary) [23].
Several works have been published focused on stress and refractive index profile measurements [24–28]. The main conclusions are that the arc discharge (considering typical fabrication parameters) relaxes intrinsic stresses in the fiber core and cladding but in regions that are larger than the grating period being, therefore, the refractive index modulation not enough to explain the grating formation. On the other hand, an increase of the refractive index of the cladding and a decrease of the core-cladding difference were observed which impacts the position of the resonance wavelengths. The conclusions concerning the core region are not so straightforward and results may depend on the fiber and also on the fabrication conditions. In 2006, it was demonstrated through simulation and by measuring the near field intensity distributions that depending on the fiber, LPFGs could couple to cladding modes of different symmetries [29]. Further studies revealed that the arc discharge is directional, possessing a temperature gradient that induces asymmetric microdeformations in the fiber [30]. These microdeformations can account for the formation of the gratings and, simultaneously, the average reduction of the fiber cross section also leads to a displacement towards shorter wavelengths of the resonances (see Figure 4(a)). It should be stressed that five years earlier the periodic modulation of the fiber was already pointed out as a potential origin of LPFGs formation [31, 32], although in the case of a symmetric perturbation it would require a severe deformation of the fiber cross section (~17%) in order to obtain strong gratings [17]. Therefore, both changes, the geometrical and the refractive indices, caused by the arc, need to be taken into account for the correct simulation of arc-induced gratings (see Figure 4(b)).
(a) Resonance wavelengths as a function of the geometric modulation and (b) transmission spectrum of an asymmetric 540 μm LPFG induced in the SMF28 fiber: experimental (solid line) and simulation (dashed line) [32].
In the case of the B/Ge codoped fibers typical cladding modes are symmetric (Figure 5(a)), unless the fiber is placed under tension in a region of the arc with lower average temperature and higher temperature gradient (which is also an optimum point to increase the reproducibility of the technique) where, with optimized fabrication parameters, gratings with different symmetries are written simultaneously [33]. In Figure 5(b), the resonances at shorter wavelengths belong to asymmetric cladding modes whilst the others are due to coupling to symmetric cladding modes, in accordance with the simulations. Moreover, the latter modes vanish at higher temperatures, so they are not a consequence of permanent geometrical changes. These superimposed gratings showing a dual set of resonances results from two different mechanisms: microdeformations and densification [34].
(a) Spectrum of a symmetric 415 μm LPFG induced in the B/Ge codoped fiber using an external tension of 5.1 g and 60 discharges with 8.5 mA and 0.5 s; (b) spectrum of a 540 μm grating with a dual set of resonances inscribed simultaneously in the B/Ge codoped fiber after downshifting ~20 μm the fiber relatively to the arc and using an external tension of 23 g and 60 discharges of 9 mA and 0.5 s [33].
In the case of pure silica-core fibers it was also demonstrated that microdeformations can be responsible for the formation of the gratings [35]. During these investigations the knowledge regarding mechanically induced LPFGs was very important for the sake of comparison between both types of gratings [36]. Figure 6 shows the dispersion curves for symmetric and asymmetric modes being the latter at shorter wavelengths in accordance with the theory. For our particular setup, where the arc discharge is directional, and considering Ge-doped fibers such as the SMF28 from Corning, coupling occurs for asymmetric cladding modes. The comparison between arc-induced and mechanical-induced gratings (MLPFGs) is presented in Figure 7. It can be observed that the resonances of arc-induced gratings are located at shorter wavelengths, which can be attributed to the changes caused by the arc in terms of a reduction of the average core diameter and also due to annealing of intrinsic stresses that lead to a change of the refractive index of the core and cladding regions, as discussed previously. As far as the inscription of LPFGs in photonic crystal fibers is concerned this topic is discussed, for instance, in [11, 37].
Resonant wavelength versus grating period for the lowest cladding modes. The experimental data was fitted considering both types of perturbations: symmetric and asymmetric [17].
Resonance wavelengths, corresponding to coupling to asymmetric cladding modes, as a function of the grating period [36].
3. Fabrication and Characterization of Arc-Induced LPFGs
Generally speaking, arc-induced gratings are fabricated by placing an uncoated fiber, under tension, between the electrodes of a splicing machine [6], being it then submitted to an arc discharge with an electric current of 7 to 15 mA and a duration ranging from 200 ms up to 2 s. Afterwards the fiber is displaced by the grating period, typically from 400 μm to 700 μm, and the whole process arc discharge/fiber displacement is repeated 20 to 50 times. Along the years several modifications to the set-up were implemented, in part, to increase the reproducibility [17, 30]. Other improvements were also claimed by other researchers through modification of commercial fiber splicers [15, 38–43] or by developing their own high voltage power supply [31, 32, 44–46]. All advancements led us to a compactness, flexible and reproducible technique that enables the fabrication, virtually in all kinds of fibers, of low loss LPFGs with considerable short grating periods. However, as far as high sensitivity LPFGs based sensors are concerned, it was necessary to inscribe LPFGs in the turning points and this goal was reached in the last couple of years, first by Smietana et al. [47, 48] by writing LPFGs below 200 μm in B/Ge codoped fibers and later by Colaço et al. [49] that were able to inscribe LPFGs below 200 μm in the SMF28e fiber and below 150 μm in the 1250/1550 B/Ge codoped fiber, establishing a new record for the shortest grating period achieved for arc-induced gratings. This goal resulted from the development of a dedicated high voltage power supply (see Figure 8).
Experimental set-up (mechanical arrangement and high voltage power supply) used to fabricate arc-induced gratings in the turning points.
Figure 9 shows the spectra of gratings arc-induced in the SMF28e fiber and also in the B/Ge codoped fiber. The fabrication parameters were set as electric current of 12.7 mA, 600 ms arc duration, 2 g pulling weight, and 400 arc discharges, for the SMF28e fiber. It should be stressed that we are working in the limits of the electric arc technique since it was only possible to write a week grating even after 400 arc discharges. Even so, this result is quite impressive since previously in this fiber the shortest period was larger than 300 μm [15]. For the grating inscribed in the Fibercore fiber we used the following fabrication parameters: electric current of 13.8 mA, 308 ms arc duration, 2 g pulling weight, and 142 arc discharges. Note, however, that we have also produced gratings (Λ=180μm) in this fiber with resonance strength of about 20 dB by applying only 122 arc discharges (see Figure 10).
Transmission spectra of LPFGs near the turning points, inscribed in the (a) SMF28 fiber, (b) B/Ge codoped fiber [49].
Transmission spectra of a 180 μm-LPFGs inscribed in the B/Ge codoped fiber.
LPFGs have been arc-induced in different types of fibers including Ge-free fibers [24, 50, 51], photonic crystal fibers [52–58], flat cladding fibers [59], and cladding-etched fibers [14, 60, 61] and in adiabatic tapers [62]. Modifications to the technique include applying no tension, applying compression, or even pressurizing the hollow core fibers during the arc discharges [5, 19, 55, 63]. LPFGs have been produced with random period [64], superimposed with different periods [65] or with phase-shifts resulting from changing the fabrication parameters during their inscription [66]. In B/Ge codoped fibers the choice of the fabrication parameters also allowed fabricating simultaneously LPFGs with different symmetry [33].
Arc-induced LPFGs have been characterized as a function of the variation of physical parameters such as strain and temperature [40, 66–72], bending and torsion [73], pressure [74, 75], and external refractive index [76–86]. They were also exposed to gamma radiation [51]. The polarization dependence loss was also investigated [87] and the results demonstrate why they have a minute success in optical communications. As far as sensing is concerned three important characterizations were performed. First, one of the major potential applications of arc-induced gratings results from their ability to resist to high temperatures as was demonstrated by the fact that they survived at temperatures of 1000°C for about two weeks (see Figure 11). Further improvements are nevertheless expected by isolating the grating from external environment (to prevent in-diffusion of oxygen at high temperatures) and avoiding the use of unwanted external pulling tensions. This can be reached by inserting the grating into a silica capillary [68].
Evolution of the grating spectrum during the heat treatment at 1000°C for 12 days [68].
On the other hand, it was recently demonstrated that arc-induced gratings are also good candidates to perform at cryogenic temperatures [72]. A phase-shifted LPFG, working in reflection, was produced by polishing the fiber after cutting it at a distance from the grating of about a quarter of the period (Figure 12(a)). As can be observed in Figure 12(b), the temperature sensitivity obtained in the 4 K–30 K range is considerably higher than for other approaches such as embedded FBGs. Currently, further research is ongoing in order to improve their sensitivity and reproducibility.
(a) Reflection spectrum of the phase-shifted LPFG at room temperature; (b) wavelength of the two Dips and the Peak of the phase-shifted LPFG working in reflection, inscribed in the B/Ge codoped fiber, as a function of temperature [72].
Another intrinsic property of LPFGs is their dependence on the external refractive index which affects the effective refractive index of the cladding modes and, therefore, in particular, changes their resonance wavelengths [18]. The gratings sensitivity depends on the order of the cladding modes and reaches its maximum close to the so-called turning points. In these regions the slope of the phase matching curves changes from positive to negative, and for each grating period, there are two resonance wavelengths for each cladding mode. This is due to the dependence on wavelength of the core and cladding effective refractive indices. For a particular grating period, the phase matching condition can be satisfied for more than one resonance wavelength since as the wavelength increases the effective refractive index of the cladding mode decreases faster than that of the core [88]. An arc-induced inscribed in the B/Ge codoped fiber in the turning points was characterized as a function of water-glycol mixtures and a sensitivity of about 1000 nm/RIU was obtained by considering the shift of the resonance at shorter wavelengths (Figure 13). Further improvements are expected as will be discussed in the next section.
Transmission spectra as a function of the external refractive index for a LPFGs in the turning points, inscribed in the B/Ge codoped fiber (Λ=192μm) [49].
4. Applications of Arc-Induced Gratings
LPFGs find application in optical communications and sensing areas. However, as far as arc-induced gratings are concerned only few works related to optical communications have been published, namely, those related to their performance as filters in optical sources and in the equalization of optical fiber amplifiers [39, 89–92]. The reason may lay in the fact they are intrinsically polarization dependent [87], therefore, impacting negatively in communication systems. A way to mitigate this issue would be the fabrication of helical arc-induced gratings, since, as demonstrated for LPFGs fabricated by CO2 laser radiation, they exhibit low polarization dependent loss (PDL) [93–95]. Clearly this topic requires further study and, therefore, in this section we shall present only applications in the sensing area. In this field a diversity of applications have been published, namely, related to the measurement of physical parameters, such as temperature and strain [66, 96, 97], displacement [98], bending [99–102], torsion [73], or pressure [103, 104]. An important achievement related to arc-induced gratings is concerned with the demonstration that by changing the fabrication parameters not only the resonance wavelengths change but also their sensitivity to physical parameters are modified. Based on that, a sensor for the simultaneous measurement of temperature and strain was implemented by changing the fabrication parameters during the grating inscription, that is, for the first 15 discharges, an external tension of 22.8 g and a current of 9 mA during 1 s were used followed by 40 discharges using an external tension of 1.2 g and an electric current of 11 mA during 1 s. This resulted in a phase-shifted grating in which two neighbor resonances, in the third telecommunication window, exhibited different sensitivities to temperature and strain [66]. Figure 14 shows the evolution of the grating spectrum during the fabrication process, where the fabrication parameters used are also presented.
Evolution of the grating spectrum during the fabrication process: (dash line) normal grating spectrum obtained after 15 arc discharges; (solid line) phase-sifted grating obtained after 40 more arc discharges but with different fabrication parameters [66].
Other more unusual applications include sensors performing as inclinometers [105] and flowmeters [106]; they have been used for the determination of metal thermal conductivity [107] and oxidation [108] and also to follow reactive ion etching processes [109]. The optical flowmeter [106] is a particular interesting application that comprises the use of an LPFG, a FBG, and a metallic thin film. Figure 15 shows the sensing head used to measure the air flow. The LPFG couples light to the cladding at a wavelength that is absorbed by the metallic film in which, being in the FBG region, its resonance shifts towards longer wavelengths due to the heating process. Afterwards, the air flow removes the heat from the film at a rate that depends on the air velocity and that translates into the movement of the FBG signature. Topics concerning interrogation techniques are discussed in [110–115].
Sensor head used for air flow measurement [106].
LPFGs are intrinsically sensitive to changes of the external refractive index and, therefore, they are used as refractometers [14, 18, 47, 48, 61, 65, 81, 116–151]. As discussed in [18] standard arc-induced LPFGs are limited to resolutions of about 10−3 in changes of the refractive index and, therefore, several techniques such as tapering, etching, and bending or by implementing interferometric configurations have been applied in order to improve their resolution. Another limitation is related to the value of the ambient refractive index to be monitored since the sensitivity increases as it approaches the cladding refractive index but, in general, one works with aqueous solutions with a refractive index around 1.33. Moreover, the resonance wavelengths do not change for external medium with a refractive index above that of the cladding. These constraints can be overcome by using thin films and recently several applications based on coated arc-induced LPFGs have been proposed [123–134]. Some examples include monitoring the quality of fried oils [125] and olive oil [126], measure humidity [127], CO2 [131], or detect the presence of E. coli [132]. Figure 16 exemplifies the use of titanium dioxide coatings in order to be able to detect changes in olive oil which possesses a refractive index above that of the cladding.
LPFG coated with a TiO2 thin film [126].
Another recent milestone was the possibility to arc-induce gratings in the turning points [47, 48] with periods as short as 148 μm [49]. Therefore, and despite the fact that cross sensitivity issues need to be properly addressed, the combination of strong arc-induced gratings in the vicinity of the turning points coated with thin films in the transition region opens the possibility of reaching resolutions of the order of 10−6 [135]. Furthermore, it was demonstrated that the initial coupling strength of the grating is determinant in order to avoid the fading out of the resonance in the transition region [136]. Recently, Del Villar also demonstrated that additionally to the previous methods, the etching of the fiber cladding can be used to further increase the sensitivity of the gratings reaching potential sensitivities of the order of 1.4 × 105 nm/RIU [137]. Smietana et al. demonstrated the possibility of tuning the characteristics of LPFGs coated with diamond-like carbon nano-layers by using reactive ion etching [138, 139]. Finally, it should be stressed that these gratings can work in reflection configuration [72]. Thus, we have now all means to produce high sensitivity optical refractometers based on coated arc-induced gratings.
5. Conclusions
In this paper we review the issues related to arc-induced gratings, addressing both the research groups that are working worldwide with the technology and their main achievements. In particular, we highlighted the issues concerning the reproducibility of the technique, the mechanisms of gratings formation, and the possibility of inscribing LPFGs in the turning points. We are now in the presence of a technology with a degree of development that enables the fabrication, at a reduced cost, of high sensitivity refractometric sensors and also temperature sensors for extreme environments, namely, to perform at cryogenic and high temperatures. On the other hand, the mass production of sensors based on arc-induced gratings will require the control of the environment where the discharges occur, in order to prevent or mitigate electrodes degradation, and the intrinsic gratings cross sensitivity to other physical parameters also demands for some product engineering attention.
Conflict of Interests
The author declares that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
This work is financed by the ERDF, European Regional Development Fund, through the Operational Programme for Competitiveness and Internationalisation, COMPETE 2020 Programme, and by National Funds through the FCT, Fundação para a Ciência e a Tecnologia (Portuguese Foundation for Science and Technology) within Project “POCI-01-0145-FEDER-006961.” The author would like to thank O. Ivanov, P. Caldas, C. Colaço, and J. L. Santos for their contribution and valuable comments. The author also would like to thank L. Coelho for supplying Figure 16.
VengsarkarA. M.LemaireP. J.JudkinsJ. B.BhatiaV.ErdoganT.SipeJ. E.Long-period fiber gratings as band-rejection filters1996141586410.1109/50.4761372-s2.0-0029733122CoelhoJ. M. P.SilvaC.NespereiraM.AbreuM.RebordãoJ.Writing of long period fiber gratings using CO2 laser radiation2015chapter 9Rijeka, CroatiaInTech287314AhmedF.JoeH.-E.MinB.-K.JunM. B. G.Characterization of refractive index change and fabrication of long period gratings in pure silica fiber by femtosecond laser radiation20157411912410.1016/j.optlastec.2015.05.018RegoG.MarquesP. V. S.SantosJ. L.SalgadoH. M.Arc-induced long-period gratings2005243-424525910.1080/014680305909229752-s2.0-18144428367TanS.-Y.YongY.-T.LeeS.-C.Abd RahmanF.Review on an arc-induced long-period fiber grating and its sensor applications201529670372610.1080/09205071.2015.1021019RegoG.OkhotnikovO.DianovE.SulimovV.High temperature stability of long-period fiber gratings produced using an electric arc200119101574157910.1109/50.9561452-s2.0-0035481435RegoG.Review paper: fibre optic devices produced by arc discharges2010121111300210.1088/2040-8978/12/11/1130022-s2.0-78349255878PooleC. D.PresbyH. M.MeesterJ. P.Two-mode fibre spatial-mode converter using periodic core deformation199430171437143810.1049/el:199409482-s2.0-0028499030DianovE. M.KarpovV. I.GrekovM. V.GolantK. M.VasilievS. A.MedvedkovO. I.KhrapkoR. R.Thermo-induced long-period fibre gratingsProceedings of the 23rd European Conference on Optical Communications (ECOC '97)September 1997Edinburgh, UK5356HumbertG.MalkiA.Electric-arc-induced gratings in non-hydrogenated fibres: fabrication and high-temperature characterizations20024219419810.1088/1464-4258/4/2/3132-s2.0-0036501138MorishitaK.MiyakeY.Fabrication and resonance wavelengths of long-period gratings written in a pure-silica photonic crystal fiber by the glass structure change200422262563010.1109/jlt.2004.8243892-s2.0-1942422106DobbH.KalliK.WebbD. J.Temperature-insensitive long period grating sensors in photonic crystal fibre2004401165765810.1049/el:200404332-s2.0-2942700237FalateR.KamikawachiR. C.MüllerM.KalinowskiH. J.FabrisJ. L.Fiber optic sensors for hydrocarbon detection2005105243043610.1016/j.snb.2004.06.0332-s2.0-14744296463Martinez-RiosA.Monzon-HernandezD.Torres-GomezI.Highly sensitive cladding-etched arc-induced long-period fiber gratings for refractive index sensing2010283695896210.1016/j.optcom.2009.10.1082-s2.0-74549140285SmietanaM.BockW. J.MikulicP.ChenJ.Increasing sensitivity of arc-induced long-period gratings—pushing the fabrication technique toward its limits201122101520110.1088/0957-0233/22/1/0152012-s2.0-79251592542ShuX.ZhangL.BennionI.Sensitivity characteristics of long-period fiber gratings200220225526610.1109/50.9832402-s2.0-0036474602RegoG.2006Porto, PortugalUniversity of PortoRegoG.A review of refractometric sensors based on long period fibre gratings201320131491341810.1155/2013/9134182-s2.0-84893821358Estudillo-AyalaJ. M.Mata-ChávezR. I.Hernández-GarcíaJ. C.Rojas-LagunaR.Long period fiber grating produced by arc discharges2012chapter 12Rijeka, CroatiaInTech29531610.5772/26703AndréP. S.Sá FerreiraR. A.CorreiaC. M. L.KalinowshyH.Xiang-JunX.PintoJ. L.Demodulating the response of optical fibre long-period gratings: genetic algorithm approach20062392480248210.1088/0256-307x/23/9/0362-s2.0-33748450750RegoG.SantosL. M. N. B. F.SchröderB.MarquesP. V. S.SantosJ. L.SalgadoH. M.In situ temperature measurement of an optical fiber submitted to electric arc discharges20041692111211310.1109/lpt.2004.8315592-s2.0-4444275480RegoG. M.MarquesP. V. S.SantosJ. L.SalgadoH. M.Estimation of the fibre temperature during the inscription of arc-induced long-period gratings2006259262062510.1016/j.optcom.2005.09.0352-s2.0-31644437446RegoG.SantosL. M. N. B. F.SchröderB.Estimation of the fibre temperature during an Arc-discharge20085082020202510.1002/mop.235552-s2.0-46049088966DürrF.RegoG.MarquesP. V. S.SemjonovS. L.DianovE. M.LimbergerH. G.SalathéR. P.Tomographic stress profiling of arc-induced long-period fiber gratings200523113947395310.1109/JLT.2005.8577632-s2.0-30344473984RegoG.DürrF.MarquesP. V. S.LimbergerH. G.Strong asymmetric stresses arc-induced in pre-annealed nitrogen-doped fibres200642633433510.1049/el:200639192-s2.0-33645221790SévignyB.LeducM.FaucherM.GodboutN.LacroixS.Characterization of the large index modification caused by electrical discharge in optical fibersProceedings of the Conference on Lasers and Electro-Optics (CLEO '07)May 2007Baltimore, Md, USAIEEE1210.1109/cleo.2007.44528022-s2.0-82955188825AbrishamianF.DragomirN.MorishitaK.Refractive index profile changes caused by arc discharge in long-period fiber gratings fabricated by a point-by-point method201251348271827610.1364/AO.51.0082712-s2.0-84870942912RegoG.CarvalhoJ. C. C.MarquesP. V. S.Fernandez FernandezA.DürrF.LimbergerH. G.Stress profiling of arc-induced long-period gratings written in pure-silica-core fibers585517th International Conference on Optical Fibre SensorsAugust 2005Bruges, Belgium884887Proceedings of SPIE10.1117/12.624285RegoC.IvanovO. V.MarquesP. V. S.Demonstration of coupling to symmetric and antisymmetric cladding modes in arc-induced long-period fiber gratings20061421959495992-s2.0-33750292381IvanovO. V.RegoG.Origin of coupling to antisymmetric modes in arc-induced long-period fiber gratings20071521139361394110.1364/oe.15.0139362-s2.0-35348947025ChungC.LeeH.Wavelength characteristics of arc-induced long-period fiber grating by core and cladding diameter modulation2Proceedings of the 14th Annual Meeting of the IEEE Lasers and Electro-Optics Society (LEOS '01)November 2001San Diego, Calif, USA7787792-s2.0-0035651581KimM. W.LeeD. W.HongB. I.ChungH. Y.Performance characteristics of long-period fiber-gratings made from periodic tapers induced by electric-arc discharge20024023693732-s2.0-0036002777RegoG.IvanovO. V.Two types of resonances in long-period gratings induced by arc discharges in boron/germanium co-doped fibers200732202984298610.1364/ol.32.0029842-s2.0-39749085427GrubskyV.FeinbergJ.Rewritable densification gratings in boron-doped fibers200530111279128110.1364/ol.30.0012792-s2.0-20444473400RegoG.IvanovO.Investigation of the mechanisms of formation of long-period gratings arc-induced in pure-silica-core fibres201128482137214010.1016/j.optcom.2010.12.0832-s2.0-79951853161RegoG.Long-period fiber gratings mechanically induced by winding a string around a fiber/grooved tube set20085082064206810.1002/mop.235722-s2.0-46049105603PetrovićJ. S.WebbD. J.MezentsevV.DobbH.KalliK.BennionI.Nondestructive index profiling of long period gratings in photonic crystal fibres200638991392010.1007/s11082-006-9026-82-s2.0-33947127393NamS. H.ZhanC.LeeJ.HahnC.ReichardK.RuffinP.DengK.-L.YinS.Bend-insensitive ultra short long-period gratings by the electric arc method and their applications to harsh environment sensing and communication200513373173710.1364/opex.13.0007312-s2.0-14744298008CacciariI.BrenciM.FalciaiR.Nunzi ContiG.PelliS.RighiniG. C.Reproducibility of splicer-based long-period fiber gratings for gain equalization20073320320610.1007/s11801-007-6195-z2-s2.0-34347207953SmietanaM.BockW. J.MikulicP.Comparative study of long-period gratings written in a boron co-doped fiber by an electric arc and UV irradiation201021202530910.1088/0957-0233/21/2/0253092-s2.0-76149087491García-de-la-RosaL. A.Torres-GómezI.Martínez-RíosA.Monzón-HernándezD.Reyes-GómezJ.Background loss minimization in arcinduced long-period fiber gratings201049606500110.1117/1.34479202-s2.0-77953593015YinG.WangY.LiaoC.ZhouJ.ZhongX.WangG.SunB.HeJ.Long period fiber gratings inscribed by periodically tapering a fiber201426769870110.1109/LPT.2014.23029012-s2.0-84897878784YinG.WangY.LiaoC.ZhouJ.ZhongX.LiuS.WangQ.LiZ.SunB.HeJ.WangG.Improved arc discharge technique for inscribing compact long period fiber gratings915723rd International Conference on Optical Fiber Sensors, 91577X1June 2014Proceedings of SPIE10.1117/12.2059261InS.ChungC.LeeH.The resonance wavelength-tuning characteristic of the arc-induced LPFGs by diameter modulation1Proceedings of the 15th International Conference on Optical Fiber SensorsMay 2002Portland, Ore, USAIEEE13113410.1109/ofs.2002.1000519LeeS. C.YongY. T.YeapK. H.RahmanF. A.An asymmetric tapered long period fiber grating: fabrication and characterizationProceedings of the IEEE 4th International Conference on Photonics (ICP '13)October 2013Melaka, Malaysia212410.1109/icp.2013.66870572-s2.0-84893630551ChoM. P.LinH. S.YongY. T.PhuaY. N.YongT. K.RahmanF. A.Characterisation of continuous arc discharge system as a fusion heat source for fused fiber componentsProceedings of the 4th Annual IEEE International Conference on Cyber Technology in Automation, Control, and Intelligent Systems (IEEE-CYBER '14)June 2014Hong KongIEEE27027310.1109/cyber.2014.69174732-s2.0-84910655872SmietanaM.DebowskaA. K.MikulicP.BockW. J.Refractive index sensing with high temperature nano-coated electric arc-induced long-period gratings working at dispersion turning pointProceedings of the 18th Microoptics Conference (MOC '13)October 2013Tokyo, Japan122-s2.0-84894207708DebowskaA. K.SmietanaM.MikulicP.BockW. J.High temperature nano-coated electric-arc-induced long-period gratings working at the dispersion turning point for refractive index sensing201453808ME0110.7567/JJAP.53.08ME012-s2.0-84905976484ColaçoC.CaldasP.ChibanteR.RegoG.Arc-induced gratings in the turning points963424th International Conference on Optical Fibre SensorsSeptember 2015Curitiba, BrazilProceedings of SPIE10.1117/12.2194274RegoG.FalateR.SantosJ. L.SalgadoH. M.FabrisJ. L.SemjonovS. L.DianovE. M.Arc-induced long-period gratings in aluminosilicate glass fibers200530162065206710.1364/OL.30.0020652-s2.0-24344500502RegoG.Fernandez FernandezA.GusarovA.BrichardB.BerghmansF.SantosJ. L.SalgadoH. M.Effect of ionizing radiation on the properties of arc-induced long-period fiber gratings200544296258626310.1364/ao.44.0062582-s2.0-27844562112DobbH.KalliK.WebbD. J.Measured sensitivity of arc-induced long-period grating sensors in photonic crystal fibre2006260118419110.1016/j.optcom.2005.10.0222-s2.0-33644650561PetrovicJ. S.DobbH.MezentsevV. K.KalliK.WebbD. J.BennionI.Sensitivity of LPGs in PCFs fabricated by an electric arc to temperature, strain, and external refractive index20072551306131210.1109/JLT.2007.8939122-s2.0-34248571856KimS.KimG. H.HwangK.-J.LimS. D.LeeK.KimS. H.LeeS. B.JeongJ.-M.Investigation of an arc-induced long period fiber grating inscribed in a photonic crystal fiber with two large air holes200913442843310.3807/josk.2009.13.4.4282-s2.0-76849117334IadiciccoA.CampopianoS.CusanoA.Long-period gratings in hollow core fibers by pressure-assisted arc discharge technique201123211567156910.1109/LPT.2011.21645182-s2.0-84867290273IadiciccoA.RanjanR.CampopianoS.Fabrication and characterization of long-period gratings in hollow core fibers by electric arc discharge20151553014302010.1109/JSEN.2014.2383175IredaleT. B.SteinvurzelP.EggletonB. J.Electric-arc-induced long-period gratings in fluid-filled photonic bandgap fibre2006421373974010.1049/el:200613652-s2.0-33745434657HuangW.-B.LiuL.-W.WangY.-L.LiuW.-F.LeeC.-L.Dispersion control in liquid core arc-induced long-period fiber gratingsProceedings of the 15th OptoElectronics and Communications Conference (OECC '10) Technical DigestJuly 2010Sapporo, Japan655657ZhengZ.-Z.LiC.-M.LeeC.-L.HorngJ.-S.Arc-induced long period fiber gratings based on flat-clad fibersProceedings of the Progress in Electromagnetics Research Symposium (PIERS '13)March 2013Taipei, Taiwan525527ZulkiflyM. Z. R. M.RahmanF. A.WongH. Y.Arc-induced long period fiber gratings (LPFG) characterization: comparison between cladding etched and non-etched LPFGProceedings of the 1st International Conference on Photonics (ICP '10)July 2010Langkawi, MalaysiaIEEE1310.1109/icp.2010.56044312-s2.0-78349287740IadiciccoA.CampopianoS.CutoloA.PawlowskiM. L. K.BockW. J.CusanoA.Refractive index sensitivity in thinned UV and arc induced long-period gratings: a comparative study200812354369Martínez-RiosA.Monzón-HernándezD.Salceda-DelgadoG.Arc-induced long-period fiber gratings inscribed in asymmetric adiabatic tapers8621Optical Components and Materials XMarch 2013San Francisco, Calif, USAProceedings of SPIE10.1117/12.2001864Mata-ChávezR. I.Martinez-RiosA.Torres-GomezI.Alvarez-ChavezJ. A.Selvas-AguilarR.Estudillo-AyalaJ.Wavelength band-rejection filters based on optical fiber fattening by fusion splicing200840467167510.1016/j.optlastec.2007.08.0102-s2.0-37249010948Martinez-RiosA.Torres-GomezI.Monzon-HernandezD.Salceda-DelgadoG.Duran-RamirezV. M.Anzueto-SanchezG.Random period arc-induced long-period fiber gratings20124441176117910.1016/j.optlastec.2011.11.0372-s2.0-84655162266SilvaG. E.SantosP. J. C.SantosJ. L.Optical fiber refractive index sensor with reduced thermal sensitivity based on superimposed long-period gratings915723rd International Conference on Optical Fiber Sensors, 91571SJune 20141Proceedings of SPIE10.1117/12.2059661RegoG.FalateR.IvanovO.SantosJ. L.Simultaneous temperature and strain measurements performed by a step-changed arc-induced long-period fiber grating20074691392139610.1364/AO.46.0013922-s2.0-34247469944RegoG.Long-period gratings arc-induced in B/GE codoped fibers. Thermal behavior and uniform exposure to UV-radiation2008501687110.1002/mop.230142-s2.0-38049165690RegoG.CaldasP.IvanovO.SantosJ. L.Investigation of the long-term stability of arc-induced gratings heat treated at high temperatures2011284116917110.1016/j.optcom.2010.08.0432-s2.0-78649668259RegoG.Annealing of arc-induced gratings at high temperatures2009451997297410.1049/el.2009.17672-s2.0-70249109697Mata-ChávezR. I.Martínez-RiosA.Estudillo-AyalaJ. M.Vargas-RodríguezE.Rojas-LagunaR.Hernández-GarcíaJ. C.Guzmán-ChávezA. D.Claudio-GonzálezD.Huerta-MascotteE.High temperature optical fiber sensor based on compact fattened long-period fiber gratings20131333028303810.3390/s1303030282-s2.0-84875189492GengT.ZiD.YangW.TongC.The LPFG temperature characteristic research based on electric heating methodProceedings of the IEEE International Conference on Optoelectronics and Microelectronics (ICOM '13)September 2013Harbin, China293210.1109/icoom.2013.66264832-s2.0-84888988359MartinsR.CaldasP.TeixeiraB.AzevedoJ.MonteiroJ.BeloJ. H.AraujoJ. P.SantosJ. L.RegoG.Cryogenic temperature response of reflection-based phase-shifted long-period fiber gratings201533122511251710.1109/jlt.2014.2381236CaldasP.RegoG.IvanovO. V.SantosJ. L.Characterization of the response of a dual resonance of an arc-induced long-period grating to various physical parameters201049162994299910.1364/AO.49.0029942-s2.0-77955995537BockW. J.ChenJ.MikulicP.EftimovT.A novel fiber-optic tapered long-period grating sensor for pressure monitoring20075641176118010.1109/tim.2007.8999042-s2.0-34547883830SadeghiJ.ZibaiiM. I.KheiriM.AhmadlouA.LatifiH.GhezelaiaghM. H.Hybrid long period fiber grating for measuring refractive index and pressure in downhole application8311Optical Sensors and Biophotonics IIINovember 2011Proceedings of SPIE10.1117/12.904447Guzman-RamosV.Ceballos-HerreraD. E.Selvas-AguilarR.Numerical analysis of GeO2-concentration effects in arc-induced long-period fiber gratings under external refractive-index changes201421214314910.1007/s10043-014-0022-02-s2.0-84898726181KamikawachiR. C.PossettiG. R. C.MullerM.FabrisJ. L.Influence of the surrounding refractive index on the thermal and strain sensitivities of a cascaded long period grating200718103111311610.1088/0957-0233/18/10/s102-s2.0-36748999399KamikawachiR. C.PossettiG. R. C.FalateR.MullerM.FabrisJ. L.Influence of surrounding media refractive index on the thermal and strain sensitivities of long-period gratings200746152831283710.1364/ao.46.0028312-s2.0-34547252485RegoG. M.SantosJ. L.SalgadoH. M.Refractive index measurement with long-period gratings arc-induced in pure-silica-core fibres2006259259860210.1016/j.optcom.2005.09.0302-s2.0-31644447342SmietanaM.SzmidtJ.Korwin-PawlowskiM. L.BockW. J.GrabarczykJ.Application of diamond-like carbon films in optical fibre sensors based on long-period gratings2007164–71374137710.1016/j.diamond.2006.11.0182-s2.0-34047262174ŚmietanaM.MyśliwiecM.MikulicP.WitkowskiB. S.BockW. J.Capability for fine tuning of the refractive index sensing properties of long-period gratings by atomic layer deposited Al2O3 overlays20131312163721638310.3390/s1312163722-s2.0-84888607095SmietanaM.BockW. J.MikulicP.Effect of high-temperature plasma-deposited nano-overlays on the properties of long-period gratings written with UV and electric arc in non-hydrogenated fibers201324909401610.1088/0957-0233/24/9/0940162-s2.0-84883201637PillaP.GiordanoM.Korwin-PawlowskiM. L.BockW. J.CusanoA.Sensitivity characteristics tuning in tapered long-period gratings by nanocoatings200719191517151910.1109/lpt.2007.903779SmietanaM.BockW. J.MikulicP.Temperature sensitivity of silicon nitride nanocoated long-period gratings working in various surrounding media2011221111520310.1088/0957-0233/22/11/1152032-s2.0-80054771965CaldasP.JorgeP. A. S.AraújoF. M.FerreiraL. A.RegoG.SantosJ. L.Geometrical effects on the refractive index sensitivity of Mach-Zehnder fibre modal interferometers based on long-period gratings200920707520110.1088/0957-0233/20/7/0752012-s2.0-70350674102CaldasP.JorgeP. A. S.AraújoF. M.FerreiraL. A.RegoG.SantosJ. L.Effect of fiber tapering in LPG-based Mach-Zehnder modal interferometers for refractive-index sensing750320th International Conference on Optical Fibre SensorsOctober 2009Edinburgh, UKProceedings of SPIE10.1117/12.834951RegoG. M.SantosJ. L.SalgadoH. M.Polarization dependent loss of arc-induced long-period fibre gratings2006262215215610.1016/j.optcom.2005.12.0642-s2.0-33646501244GrubskyV.FeinbergJ.Long-period fiber gratings with variable coupling for real-time sensing applications200025420320510.1364/OL.25.0002032-s2.0-0001739978Anzueto-SánchezG.Martínez-RiosA.Castrellon-UribeJ.Tuning and wavelength switching erbium-doped fiber ring lasers by controlled bending in arc-induced long-period fiber gratings201218651351710.1016/j.yofte.2012.08.0042-s2.0-84868460187TrifanovI.CaldasP.NeaguL.RomeroR.BerendtM. O.SalcedoJ. A. R.PodoleanuA. G.Lobo RibeiroA. B.Combined nodymium—ytterbium-doped ASE fiber-optic source for optical coherence tomography applications2011231212310.1109/lpt.2010.20900392-s2.0-78650573210AbrishamianF.MorishitaK.Cascade connection of two long-period fiber gratings with a π-phase shift to expend the rejection bandwidths201598651251710.1587/transele.e98.c.512RegoG.Optical filters for fiber lasers and amplifiers200850489089410.1002/mop.232252-s2.0-41849150059OhS.LeeK. R.PaekU.-C.ChungY.Fabrication of helical long-period fiber gratings by use of a Co2 laser200429131464146610.1364/ol.29.0014642-s2.0-3142718444KoppV. I.ChurikovV. M.SingerJ.ChaoN.NeugroschlD.GenackA. Z.Chiral fiber gratings20043055680747510.1126/science.10976312-s2.0-3042795664KoppV. I.ChurikovaV. M.ZhangG.SingerJ.DraperC. W.ChaoN.NeugroschlD.GenackA. Z.Chiral fiber gratings: perspectives and challenges for sensing applications66193rd European Workshop on Optical Fibre Sensors (EWOFS '07), 66190BJuly 2007Napoli, Italy1Proceedings of SPIE10.1117/12.738344FrazãoO.MarquesL. M.SantosS.BaptistaJ. M.SantosJ. L.Simultaneous measurement for strain and temperature based on a long-period grating combined with a high-birefringence fiber loop mirror200618222407240910.1109/LPT.2006.8861392-s2.0-34247203792RegoG.Simultaneous measurement of temperature and strain based on arc-induced long-period fiber gratings. A case study20085092472247410.1002/mop.236442-s2.0-48849096803BaptistaJ. M.SantosS. F.RegoG.FrazãoO.SantosJ. L.Micro-displacement or bending measurement using a long-period fibre grating in a self-referenced fibre optic intensity sensor2006260181110.1016/j.optcom.2005.10.0042-s2.0-33644656206FrazãoO.FalateR.BaptistaJ. M.FabrisJ. L.SantosJ. L.Optical bend sensor based on a long-period fiber grating monitored by an optical time-domain reflectometer2005441111050210.1117/1.2123267FalateR.FrazãoO.RegoG.IvanovO. V.KalinowskiH. J.FabrisJ. L.SantosJ. L.Bending sensitivity dependent on the phase shift imprinted in long-period fibre gratings200718103123313010.1088/0957-0233/18/10/S122-s2.0-36749002148FrazãoO.ViegasJ.CaldasP.SantosJ. L.AraújoF. M.FerreiraL. A.FarahiF.All-fiber Mach-Zehnder curvature sensor based on multimode interference combined with a long-period grating200732213074307610.1364/ol.32.0030742-s2.0-40149108796WuZ.ZhangN.ShumP.ShaoX.ZhangH.HuangT.HumbertG.AugusteJ.-L.GéromeF.DinhX. Q.Curvature sensor based on long-period grating in dual concentric core fiberProceedings of the Conference on Lasers and Electro-Optics: Applications and Technology (CLEO-AT '15)May 2015San Jose, Calif, USAATu1M.5SmietanaM.BockW. J.MikulicP.ChenJ. H.Pressure sensing in high-refractive-index liquids using long-period gratings nanocoated with silicon nitride20101012113011131010.3390/s1012113012-s2.0-78650290013KosA.ChenJ. H.BockW. J.MikulicP.Tapered long-period grating (TLPG) with Teflon AF coating for pressure sensing applicationsProceedings of the Canadian Conference on Electrical and Computer Engineering (CCECE '08)May 2008Niagara Falls, CanadaIEEE86186610.1109/CCECE.2008.4564658FrazãoO.FalateR.FabrisJ. L.SantosJ. L.FerreiraL. A.AraújoF. M.Optical inclinometer based on a single long-period fiber grating combined with a fused taper200631202960296210.1364/OL.31.0029602-s2.0-33750507947CaldasP.JorgeP. A. S.RegoG.FrazãoO.SantosJ. L.FerreiraL. A.AraújoF.Fiber optic hot-wire flowmeter based on a metallic coated hybrid long period grating/fiber Bragg grating structure201150172738274310.1364/ao.50.0027382-s2.0-79958788190SilvaG. E.CaldasP.SantosJ. C.SantosJ. L.All-fiber sensor based on a metallic coated hybrid LPG-FBG structure for thermal characterization of materials915723rd International Conference on Optical Fibre Sensors (OFS '14)June 2014Proceedings of SPIE10.1117/12.2059655CoelhoL.ViegasD.SantosJ. L.de AlmeidaJ. M. M.Real time monitoring oxidation of transition metals with long period fiber gratings963424th International Conference on Optical Fibre SensorsSeptember 2015Curitiba, BrazilProceedings of SPIE10.1117/12.2195199ŚmietanaM.KobaM.MikulicP.BockW. J.Measurements of reactive ion etching process effect using long-period fiber gratings20142255986599410.1364/OE.22.0059862-s2.0-84896331596CarvalhoJ. P.CoelhoL.PontesM. J.BarberoA. P.MartinezM. A.RibeiroR. M.WeylJ.BaptistaJ. M.GiraldiM. T. R.DiasI.SantosJ. L.FrazãoO.Long-period gratings dynamic interrogation with modulated fiber bragg gratings and optical amplification201212117918310.1109/JSEN.2011.21283052-s2.0-82555194600CarvalhoJ. P.CoelhoL.BaptistaJ. M.SantosJ. L.FrazãoO.Dynamic interrogation for optical fibre sensors based on long-period gratings2011226506520110.1088/0957-0233/22/6/0652012-s2.0-79956065765FrazãoO.CorreiaC.BaptistaJ. M.MarquesM. B.SantosJ. L.Ring fibre laser with interferometer based in long period grating for sensing applications2008281225601560410.1016/j.optcom.2008.08.0042-s2.0-52149107851ViegasD.CarvalhoJ. P.CoelhoL.SantosJ. L.AraújoF. M.FrazãoO.Long-period grating fiber sensor with in situ optical source for remote sensing201022201533153510.1109/lpt.2010.20672082-s2.0-77957570724CaldasP.JorgeP. A. S.AraújoF. M.FerreiraL. A.MarquesM. B.RegoG.SantosJ. L.Fiber modal Michelson interferometers with coherence addressing and heterodyne interrogation200847404440110.1117/1.29030892-s2.0-67649840773YongY.LeeS.RahmanF. A.Sensitization of hybrid LPFG–FBG refractometer using double-pass configuration201533859059510.1016/j.optcom.2014.11.054FalateR.FrazãoO.RegoG.FabrisJ. L.SantosJ. L.Refractometric sensor based on a phase-shifted long-period fiber grating200645215066507210.1364/ao.45.0050662-s2.0-33748697846SilvaC.CoelhoJ. M. P.CaldasP.FrazãoO.JorgeP. A. S.SantosJ. L.Optical fiber sensing system based on long-period gratings for remote refractive index measurement in aqueous environments201029316016910.1080/014680310037594932-s2.0-77952637495JesusC.CaldasP.FrazãoO.SantosJ. L.JorgeP. A. S.BaptistaJ. M.Simultaneous measurement of refractive index and temperature using a hybrid fiber bragg grating/long-period fiber grating configuration200928644044910.1080/014680309032900392-s2.0-74949138351LineshJ.LibishT. M.BobbyM. C.RadhakrishnanP.NampooriV. P. N.Periodically tapered LPFG for ethanol concentration detection in ethanol-gasoline blend201112522052122-s2.0-79955021797ChanK. P.TanC. S.TengW. S.RahmanF. A.SoonS. C.ZulkiflyZ. R.Feasibility study of long period grating as an optical biosensor for dengue virus detection—an alternative approach to dengue virus screeningProceedings of the IEEE EMBS Conference on Biomedical Engineering and Sciences (IECBES '10)December 2010Kuala Lumpur, Malaysia384210.1109/iecbes.2010.57421952-s2.0-79955387108LohM. C.RahmanF. A.KuramitzH.YongY. T.Method to sensitize an arc-induced LPFG-based sensor using double-pass configuration201456122766276910.1002/mop.287012-s2.0-84908374195LohM.YongY. T.KuramitzH.TehP. C.Abd-RahmanF.Double-pass configuration to enhance the sensitivity of a polyelectrolyte-coated arc-induced long-period fiber grating201529141908191610.1080/09205071.2015.1066715SimõesE.AbeI.OliveiraJ.FrazãoO.CaldasP.PintoJ. L.Characterization of optical fiber long period grating refractometer with nanocoating2011153233533910.1016/j.snb.2010.10.0332-s2.0-79953027713NascimentoI. M.GouveiaC.JanaS.BeraS.BaptistaJ. M.MoreiraP.BiwasP.BandyopadhyayS.JorgeP. A. S.High refractive index and temperature sensitivity LPGs for high temperature operation87858th Iberoamerican Optics Meeting and 11th Latin American Meeting on Optics, Lasers, and ApplicationsNovember 2013Proceedings of SPIE10.1117/12.2027573AbeI.OliveiraJ.SimõesE.CaldasP.FrazãoO.Monitoring the quality of frying oils using a nanolayer coated optical fiber refractometer201083129129310.1016/j.talanta.2010.08.0402-s2.0-78049374315CoelhoL.ViegasD.SantosJ. L.de AlmeidaJ. M.Detection of extra virgin olive oil thermal deterioration using a long period fiber grating sensor coated with titanium dioxide2015861211121710.1007/s11947-015-1489-9ViegasD.GoicoecheaJ.SantosJ. L.AraújoF. M.FerreiraL. A.ArreguiF. J.MatiasI. R.Sensitivity improvement of a humidity sensor based on silica nanospheres on a long-period fiber grating20099151952710.3390/s901005192-s2.0-59249104987CoelhoL.ViegasD.SantosJ. L.AlmeidaJ. M. M. M.Characterization of zinc oxide coated optical fiber long period gratings with improved refractive index sensing properties20162234551CoelhoL.ViegasD.SantosJ. L.AlmeidaJ. M. M. M. D.Enhanced refractive index sensing characteristics of optical fibre long period grating coated with titanium dioxide thin films201420292993410.1016/j.snb.2014.06.0352-s2.0-84903988924CoelhoL.QueirósR. B.SantosJ. L.CristinaM.MartinsL.ViegasD.JorgeP. A. S.DNA-Aptamer optical biosensors based on a LPG-SPR optical fiber platform for point-of care diagnostic8957Plasmonics in Biology and Medicine XI, 89570KMarch 2014Proceedings of SPIE10.1117/12.2040892GouveiaC.BaloghK.BaptistaJ. M.KovacsB.JorgeP. A. S.LPG based fiber optic sensor for carbon dioxide842122nd International Conference on Optical Fiber Sensors (OFS '12)October 2012Beijing, ChinaProceedings of SPIE10.1117/12.975279QueirósR. B.GouveiaC.FernandesJ. R. A.JorgeP. A. S.Evanescent wave DNA-aptamer biosensor based on long period gratings for the specific recognition of E. coli outer membrane proteins20146222723310.1016/j.bios.2014.06.0622-s2.0-84904041569CzaplaA.WolińskiT. R.BockW. J.Nowinowski-KruszelnickiE.DąbrowskiR.WójcikJ.Long-signature: highlighting sparse salient regions20095021657610.1080/15421400902815712JorgeP. A. S.SilvaS. O.GouveiaC.TafuloP.CoelhoL.CaldasP.ViegasD.RegoG.BaptistaJ. M.SantosJ. L.FrazãoO.Review: fiber optic-based refractive index sensing at INESC Porto20121268371838910.3390/s1206083712-s2.0-84863194087PillaP.TronoC.BaldiniF.ChiavaioliF.GiordanoM.CusanoA.Giant sensitivity of long period gratings in transition mode near the dispersion turning point: an integrated design approach201237194152415410.1364/ol.37.0041522-s2.0-84867149639ZouF.LiuY.DengC.DongY.ZhuS.WangT.Refractive index sensitivity of nano-film coated long-period fiber gratings20152321114112410.1364/oe.23.0011142-s2.0-84921758306Del VillarI.Ultrahigh-sensitivity sensors based on thin-film coated long period gratings with reduced diameter, in transition mode and near the dispersion turning point20152378389839810.1364/oe.23.008389SmietanaM.KobaM.MikulicP.BockW. J.Tuning properties of long-period gratings by plasma post-processing of their diamond-like carbon nano-overlays2014251111400110.1088/0957-0233/25/11/1140012-s2.0-84907887528SmietanaM.KobaM.MikulicP.BockW. J.Enhancing sensitivity of long-period gratings by combined fiber etching and diamond-like carbon nano-overlay deposition963424th International Conference on Optical Fiber Sensors, 963456September 2015Curitiba, BrazilProceedings of SPIE10.1117/12.2195214PatrickH. J.KerseyA. D.BucholtzF.Analysis of the response of long period fiber gratings to external index of refraction19981691606161210.1109/50.7122432-s2.0-0032166466LanX.HanQ.HuangJ.WangH.GaoZ.KaurA.XiaoH.Turn-around point long-period fiber grating fabricated by CO2 laser for refractive index sensing20131771149115510.1016/j.snb.2012.12.0062-s2.0-84872165242GargR.TripathiS. M.ThyagarajanK.BockW. J.Long period fiber grating based temperature-compensated high performance sensor for bio-chemical sensing applications20131761121112710.1016/j.snb.2012.08.0592-s2.0-84875421100HuangJ.LanX.KaurA.WangH.YuanL.XiaoH.Reflection-based phase-shifted long period fiber grating for simultaneous measurement of temperature and refractive index2013521401440410.1117/1.OE.52.1.014404ReesN. D.JamesS. W.TatamR. P.AshwellG. J.Optical fiber long-period gratings with Langmuir-Blodgett thin-film overlays200227968668810.1364/ol.27.0006862-s2.0-0036574505IshaqI. M.QuintelaA.JamesS. W.AshwellG. J.Lopez-HigueraJ. M.TatamR. P.Modification of the refractive index response of long period gratings using thin film overlays2005107273874110.1016/j.snb.2004.12.0042-s2.0-18544377023VillarI. D.MatíasI. R.ArreguiF. J.LalanneP.Optimization of sensitivity in long period fiber gratings with overlay deposition2005131566910.1364/opex.13.0000562-s2.0-13544270151CusanoA.IadiciccoA.PillaP.ContessaL.CampopianoS.CutoloA.GiordanoM.Mode transition in high refractive index coated long period gratings2006141193410.1364/opex.14.0000192-s2.0-30344446935Del VillarI.AchaerandioM.MatíasI. R.ArreguiF. J.Deposition of overlays by electrostatic self-assembly in long-period fiber gratings200530772072210.1364/OL.30.0007202-s2.0-16244376815KorposhS.SelyanchynR.YasukochiW.LeeS.-W.JamesS. W.TatamR. P.Optical fibre long period grating with a nanoporous coating formed from silica nanoparticles for ammonia sensing in water20121332-378479210.1016/j.matchemphys.2012.01.0942-s2.0-84862776805TripathiS. M.BockW. J.MikulicP.ChinnappanR.NgA.TolbaM.ZourobM.Long period grating based biosensor for the detection of Escherichia coli bacteria201235130831210.1016/j.bios.2012.03.0062-s2.0-84860508919KankaJ.Long-period gratings in photonic crystal fibers operating near the phase-matching turning point for evanescent chemical and biochemical sensing8370Fiber Optic Sensors and Applications IXMay 2012111Proceedings of SPIE10.1117/12.918677