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This article presents a new interrogation technique for serial fiber optical sensor networks. A hybrid code-division multiplexing (CDM)-wavelength-division multiplexing (WDM) scheme allows interrogating 2000 serial fiber-Bragg grating (FBG) sensors in a network with a length of 50 m. Furthermore, an interrogation of 477 sensors over a length of 150 m is shown. The work focuses on influences given by the above-mentioned sensor networks, such as reflectance, multiple reflections, and overlapping FBG spectra, as well as on specifications of used equipment. Since CDM relies on orthogonal codes, an autocorrelation function of a code is presented that suits for the interrogation of the previous mentioned sensor networks. A simulation of the interrogation scheme allowed for the study of the overall sensor network performance and the impact of its different components. The promising results were reproduced in a testbed. Furthermore, strain calibration measurements showed a high level of accuracy. The proposed hybrid CDM-WDM interrogation scheme can deal with sensor network lengths from a few meters to the range of a few kilometers with massive numbers of freely distributable sensors in the fiber. It is a promising approach in the field of FBG based optical sensing.

Utilizing a Coherent-Correlation-OTDR, 2000 draw tower gratings in 100 meter fiber with a spatial resolution of 50 mm were successfully interrogated. Spooling of the fiber results in variations of the FBG reflection spectra.

The soluble cytoplasmic ATPase motor protein SecA powers protein transport across the Escherichia coli inner membrane via the SecYEG translocon. Although dimeric in solution, SecA associates monomerically with SecYEG during secretion according to several crystallographic and cryo-EM structural studies. The steps SecA follows from its dimeric cytoplasmic state to its active SecYEG monomeric state are largely unknown. We have previously shown that dimeric SecA in solution dissociates into monomers upon electrostatic binding to negatively charged lipid vesicles formed from E. coli lipids. Here we address the question of the disposition of SecA on the membrane prior to binding to membrane embedded SecYEG. We mutated to cysteine, one at a time, 25 surface-exposed residues of a Cys-free SecA. To each of these we covalently linked the polarity-sensitive fluorophore NBD whose intensity and fluorescence wavelength-shift change upon vesicle binding report on the the local membrane polarity. We established from these measurements the disposition of SecA bound to the membrane in the absence of SecYEG. Our results confirmed that SecA is anchored in the membrane interface primarily by the positive charges of the N terminus domain. But we found that a region of the nucleotide binding domain II is also important for binding. Both domains are rich in positively charged residues, consistent with electrostatic interactions playing the major role in membrane binding. Selective replacement of positively charged residues in these domains with alanine resulted in weaker binding to the membrane, which allowed us to quantitate the relative importance of the domains in stabilizing SecA on membranes. Fluorescence quenchers inside the vesicles had little effect on NBD fluorescence, indicating that SecA does not penetrate significantly across the membrane. Overall, the topology of SecA on the membrane is consistent with the conformation of SecA observed in crystallographic and cryo-EM structures of SecA-SecYEG complexes, suggesting that SecA can switch between the membrane-associated and the translocon-associated states without significant changes in conformation. ispartof: JOURNAL OF MOLECULAR BIOLOGY vol:434 issue:12 ispartof: location:Netherlands status: published

This contribution demonstrates a massive hybrid code-division multiplexing (CDM)-wavelength-division multiplexing (WDM) scheme that interrogates 2×2000 serial fiber-Bragg gratings (FBGs). The overlapping FBG spectra lead to maximum deviation errors of only 8 pm at a reflectance of 1 %.

This contribution shows the interrogation of 4000 serial fiber-Bragg gratings (FBGs) by means of a hybrid code-division multiplex (CDM) - wavelength-division multiplex (WDM) scheme. A strain measurement shows no influence of a strained WDM-section to another non-strained WDM-section. Polarization effects are diminished by the implementation of a semi-conductor optical amplifier.

In this paper, we report on an offshore field validation of a FBG based optical fiber sensor for simultaneous monitoring of hydrostatic pressure and temperature. The sensor consists of a femtosecond laser induced grating written in a Butterfly microstructured fiber. The sensor has an extremely low cross-sensitivity between temperature and pressure which makes it ideal for monitoring large transients in pressure or temperature, like is the case in wireline intervention. Pressure and temperature readings from the FBG based optical fiber sensor are compared with the readings from a battery powered electrical quartz gauge during an offshore wireline intervention job in an oil well. Good agreement was found between both measurements.

Much is known about the structure, function, and stability of the SecA motor ATPase that powers the secretion of periplasmic proteins across the inner membrane of Escherichia coli. Most studies of SecA are carried out in buffered sodium or potassium chloride salt solutions. However, the principal intracellular salt of E. coli is potassium glutamate (KGlu), which is known to stabilize folded proteins and protein-nucleic acid complexes. Here we report that KGlu stabilizes SecA, including its dimeric state, and increases its ATPase activity, suggesting that SecA is likely fully folded, stable, and active in vivo at 37°C. Furthermore, KGlu also stabilizes a precursor form of the secreted maltose-binding protein.

The influence of hydrogen gas on Fiber Bragg Grating (FBG)-based optical fiber sensors has been validated experimentally. More in particular, the focus was on FBGs written in the so-called Butterfly Micro Structured Fiber that targets simultaneous pressure and temperature monitoring with a minimum in cross-sensitivity to be used in, for example, downhole applications for the oil and gas market. The hydrogen-induced pressure and temperature errors from this type of sensor have been quantified as a function of the partial hydrogen pressure. The induced errors can be related to the diffusion of the hydrogen into the microstructure and to refractive index changes due to the presence of the hydrogen in the micro holes and penetration of it into the fiberglass. Furthermore, we have also shown that the hydrogen-induced errors scale with the partial hydrogen pressure. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

In this paper, a packaged FBG based optical fiber sensor written by femtosecond laser pulses in highly birefringent micro-structured optical fiber (MS-FBG sensor) is presented and validated for simultaneous pressure and temperature monitoring. The MS-FBG sensor is capable of separating the temperature information from pressure information without the need for an additional transduction mechanism and this with a negligible pressure-temperature cross-sensitivity. However, in order to use the sensor for downhole applications, a ruggedized sensor housing is required that not only offers mechanical protection to the fiber, but also provides pressure transfer from the well fluid to the sensing element without inducing an additional pressure-temperature cross-sensitivity. In this article, the design of the sensor housing is reported as well as the lab-scale validation up to a temperature and pressure of 150 °C and 700 bar, respectively.

In this paper, we evaluate different thermal treatments in order to stabilize fiber Bragg gratings written by a femtosecond pulsed laser in specialty highly birefringent micro-structured optical fiber, targeting pressure monitoring at high pressure and high temperature environments. We have obtained a pressure sensitivity of 3.30 pm/bar up to 1400 bar and 290 degrees C. An effective thermal treatment has been experimentally implemented, yielding a nearly unchanged reflectivity at high temperature in combination with stable temperature and pressure readings: a standard deviation of 0.42 bar in the pressure reading was observed over 7 days at 280 degrees C. (C) 2017 Optical Society of America

In this paper, we demonstrate that femtosecond laser pulse written fiber Bragg gratings (FBGs) fabricated in specialty highly birefringent micro-structured optical fiber (MSF) can be used for high pressure and high temperature monitoring in downhole applications. The design of the micro-structure allows encoding the pressure information into the spectral separation between the two Bragg peaks reflected by the obtained MS-FBG. We obtained a differential pressure sensitivity of 3.30 pm/bar over a pressure range from atmospheric up to 1400 bar and at temperatures between 40 °C and 290 °C. Owing to the negligible differential pressure-temperature cross-sensitivity of 6.06E-3 bar/°C, the proposed MS-FBG sensor is an ideal candidate for pressure monitoring in the presence of high temperature transients.

Under acid stress, Escherichia coli induce expression of CadA (lysine decarboxylase) and CadB (lysine/cadaverine antiporter) in a lysine-rich environment. The ToxR-like transcriptional activator CadC controls expression of the cadBA operon. Using a novel signal peptidase I (SPase I) cleavage assay, we show that CadC is a type II single-span membrane protein (S-SMP) with a cytoplasmic DNA-binding domain and a periplasmic sensor domain. We further show that, as long assumed, dimerization of the sensor domain is required for activating the cadBA operon. We prove this using a chimera in which the periplasmic domain of RodZ-a type II membrane protein involved in the maintenance of the rod shape of E. coli-replaces the CadC sensor domain. Because the RodZ periplasmic domain cannot dimerize, the chimera cannot activate the operon. However, replacement of the transmembrane (TM) domain of the chimera with the glycophorin A TM domain causes intramembrane dimerization and consequently operon activation. Using a low-expression protocol that eliminates extraneous TM helix dimerization signals arising from protein over-expression, we enhanced dramatically the dynamic range of the β-galactosidase assay for cadBA activation. Consequently, the strength of the intramembrane dimerization of the glycophorin A domain could be compared quantitatively with the strength of the much stronger periplasmic dimerization of CadC. For the signal peptidase assay, we inserted an SPase I cleavage site (AAA or AQA) at the periplasmic end of the TM helix. Cleavage occurred with high efficiency for all TM and periplasmic domains tested, thus eliminating the need for the cumbersome spheroplast-proteinase K method for topology determinations.

Measuring strain in an unobtrusive and distributed way is of key importance to many avionics applications. Optical sensing technologies based on fiber Bragg gratings (FBGs) enable multiplexed strain measurements while offering precise location tracking. These precise and multiplexed strain measurements are enabling monitoring of more advanced parameters such as curvature and shape [1,2].

Optical sensors based on Fiber Bragg Gratings (FBGs) are used in several applications and industries. Several inscription techniques and type of fibers can be used. However, depending on the writing process, type of fiber used and the packaging of the sensor a Polarization Dependent Frequency Shift (PDFS) can often be observed with polarized tunable laser based optical interrogators. Here we study the PDFS of the FBG peak for the different FBG types. A PDFS of 20pm was observed across the FBGs. To mitigate and reduce this effect we propose a polarization mitigation technique which relies on a synchronous polarization switch to reduce the effect typically by a factor greater than 4. In other scenarios the sensor itself is designed to be birefringent (Bi-FBG) to allow pressure and/or simultaneous temperature and strain measurements. Using the same polarization switch we demonstrate how we can interrogate the Bi-FBGs with high accuracy to enable high performance of such sensors to be achievable.

Fiber Bragg grating inscription with a deep ultraviolet (DUV) femtosecond laser and two-beam interferometry allows grating inscription in germanium-free fibers without classical UV photosensitivity. Therefore such a writing technology is a promising solution for the fabrication of fiber Bragg gratings in the active fiber material to realize a fully integrated all-fiber solution. In this paper we report on the use of the DUV femtosecond laser fiber Bragg grating technology to build a grating-stabilized fiber laser with high spectral purity. Output powers up to 158 W at 1083 nm and a slope efficiency of 76% have been demonstrated.

Using a combination of phase mask and interferometric inscription technique we have generated 1st order fiber Bragg gratings (FBGs) with resonance wavelengths in a wide range of the visible spectrum (VIS). We use a modified Talbot interferometer which offers great flexibility in Bragg wavelength, spatial grating length and reflectivity. Gratings with shortest grating lengths of less than 1mm and with reflectivities of more than 70% have been produced. Peak reflectivities of up to 99% have been achieved in the visible spectrum. FBGs in the visible spectral range require structure sizes in the sub 100 nm scale. Potential applications are in the field of laser and sensor technology.

Assay systems based on the ToxR protein are widely used to investigate interaction of transmembrane domains that come from natural proteins or are isolated from combinatorial libraries. The principle of this method is that self-interaction of any given transmembrane domain, which is expressed within a ToxR chimeric protein, drives ToxR–ToxR assembly in a bacterial inner membrane. In current versions of the system, ToxR–ToxR interaction drives transcription activation of the cholera toxin (ctx) promoter and thereby induces expression of downstream reporter genes in appropriately constructed bacterial strains. Here, we describe the application of other known ToxR-regulated promoters. We show that interacting transmembrane domains also promote ToxR-driven activation of the ompU promoter. Conversely, these interactions efficiently repress transcription from the constitutively active ompT promoter. We present novel Escherichia coli strains whose chromosomes harbor fusions of ompU or ompT promoters with different reporter genes. Depending on the used promoter, self-interaction of transmembrane domains induces or represses reporter enzyme expression in these cells. These strains extend current applications of the ToxR protein and may find use in mapping transmembrane helix–helix interfaces and selection of transmembrane domains with medium affinities.

The ability to decouple strain from temperature is being explored using Bragg gratings written in highly birefringent fiber in combination with a high accuracy interrogator. Both the birefringent preform as well as the interrogator have been optimized in order to reach maximum measurement accuracy. The results from calibration measurements will be presented together with the estimated stability.

The ToxR transcription activator system is a genetic tool widely used to examine homotypic interactions of alpha-helical transmembrane domains that drive or support oligomerization of integral membrane proteins. Here, we present a variant of this system that was developed to investigate heterotypic interactions. In this system, a homotypically interacting transmembrane domain within the ToxR protein is coexpressed with a potential competitor that is embedded within an inactivated ToxR mutant. Successful heterotypic interaction competes with homotypic interaction in a dominant-negative fashion as revealed by reduced reporter gene transcription. We expect that this system will be useful for the characterization of transmembrane domains whose homotypic and heterotypic interactions compete with each other.

The principles underlying the folding of integral membrane proteins are uncovered in an increasingly detailed way. Experimental determination of high-resolution structures followed by analysis of packing reveal structural similarities as well as differences to soluble globular proteins. At the same time, protein/protein interactions at the level of membrane-embedded domains have been investigated for different model proteins. More recently, self-interacting transmembrane helices have been selected from combinatorial libraries in vitro to study the mechanistic basis of protein/protein interaction in membranes in a systematic way. With an emphasis on the latter approach, this review discusses insights emerging from an integrated view on the recent advances.

Thermally regenerated fiber Bragg gratings written in photosensitive fibers with nanosecond laser pulses without hydrogen loading have been shown to become temperature stable up to 600 °C. In this paper, we give an experimental analysis of the refractive index development for fabricating the gratings and for the thermal regeneration process. Furthermore, we identify a thermal induced type IIa (type In) behavior of the refractive index to be responsible for the regeneration. The variation of refractive index modulation and the average index in the grating region is discussed. With additional annealing it is possible to improve the temperature stability beyond 1000 °C. © 2010 Elsevier B.V. All rights reserved.

Today fiber Bragg gratings are commonly used in sensing technology as well as in telecommunications. Numerous requirements must be satisfied for their application as a sensor such as the number of sensors per system, the measurement resolution and repeatability, the sensor reusability as well as the sensor costs. In addition current challenges need to be met in the near future for sensing fibers to keep and extend their marketability such as the suitability for sterilization, hydrogen darkening or the separation of strain and temperature (or pressure and temperature). In this contribution we will give an outlook about trends and future of the fiber Bragg gratings in sensing technologies. Specifically, we will discuss how the use of draw tower grating technology enables the production of tailored Bragg grating sensing fibers, and we will present a method of separating strain and temperature by the use of a single Bragg grating only, avoiding the need for additional sensors to realize the commonly applied temperature compensation.

The transmembrane (TM) helices of most type II single-span membrane proteins (S-SMPs) of Escherichia coli occur near the N-terminus, where the cell's targeting mechanisms can readily identify it as it emerges from the ribosome. However, the TM helices of a few S-SMPs, such as RodZ, occur a hundred or more residues downstream from the N-terminus, which raises fundamental questions about targeting and assembly. Because of RodZ's novelty and potential usefulness for understanding TM helix insertion in vivo, we examined its membrane targeting and assembly. We used RodZ constructs containing immunotags before the TM domain to assess membrane insertion using proteinase K digestion. We confirmed the N(in)-C(out) (type II) topology of RodZ and established the absence of a targeting signal other than the TM domain. RodZ was not inserted into the membrane under SecA depletion conditions or in the presence of sodium azide, which is known to inhibit SecA. Insertion failed when the TM proton gradient was abolished with Carbonyl cyanide m-chlorophenyl hydrazone. Insertion also failed when RodZ was expressed in SecE-depleted E. coli, indicating that the SecYEG translocon is required for RodZ assembly. Protease accessibility assays of RodZ in other E. coli depletion strains revealed that insertion is independent of SecB, YidC, and SecD/F. Insertion was found to be only weakly dependent on the signal recognition particle pathway: insertion was weakly dependent on the Ffh but independent of FtsY. We conclude that membrane insertion of RodZ requires only the SecYEG translocon, the SecA ATPase motor, and the TM proton motive force.

The idea of fabricating fiber Bragg gratings (FBGs) during the drawing of a fiber dates back more than 20 years. Because of the high technology requirements it took more than 10 years to develop the method into a reliable process. During the last five years the improvements in the technical development enabled a cost effective industrial production of draw tower gratings (DTG®s) for the use in fiber optic sensing and telecommunication. We report about new possibilities and the production of low reflective DTGs for the use of optical frequency domain reflectometry (OFDR). Furthermore we describe the design, fabrication and testing of a polarization maintaining fiber with DTG inscription. This special fiber type can be used for the separating of strain and temperature.

Single-span membrane proteins (SSMPs) are the most abundant membrane proteins in virtually all organisms. SSMPs with N-terminus outside the cell are referred to as Type I MPs, while those with the N-terminus inside are referred to as Type II MPs. It is generally assumed that insertion occurs co-translationally via the signal recognition particle (SRP) pathway. The positive-inside rule determines TypeI/II MPs. The TM segment of Type I MPs is generally preceded by a cleavable signal sequence to facilitate the Nout-Cin topology. The TM segment of both types of proteins generally occurs early in the amino acid sequence, allowing recognition by SRP as it emerges from the ribosome. Secreted periplasmic proteins have a signal sequence, but are secreted post-translationally through the translocon by the SecA translocase.We are studying an unusual class of Type II MPs that lack identifiable signal sequences and whose TM segments can occur hundreds of residues downstream from the N-terminus. One such protein is RodZ, which is a cytoskeletal protein involved in maintaining the rod shape of E. coli. What pathway does this protein use? Several prediction programs and our experimental studies of RodZ with deleted TM segment (RodZ-ΔTM) confirm the absence of a native targeting signal. Proteinase K treatment of spheroplasts reveal that RodZ has Nin-Cout (Type II) topology, consistent with previous studies. Classic N-terminal cleavable signal sequences, such as DsbA or MalE, do not affect the topology of RodZ. We have determined that RodZ insertion is strongly SecA dependent, because RodZ is not incorporated into the membrane under SecA-depletion conditions or in the presence of sodium azide, which is known to inhibit SecA. This result is important, because it is now possible to study the energetics of TM helix insertion by SecA.

A fiber optic Bragg grating (FBG) sensor and interrogation scheme has been designed to capture the momentary peak pressure forces in the nip of two adjacent paper machine rolls. The spatial distribution of these nip forces along circumference and length of the roll, for production speeds of up to 2000 m/min are investigated. Additionally, this FBG sensor system measures the temperature distribution in the roll cover. FBG sensor embedding has been optimized for the implementation of pressure force measurements in various roll cover materials. High strength draw tower grating (DTG) sensor arrays were used for the embedding process combined with spectrometric interrogation and autonomous power supply technologies. This results in an extremely robust fiber optic sensor system for operation at rotation speeds of 700 rpm, equivalent to centrifugal accelerations of 300 G. These measurements enable immediate quality control during various stages of the high-speed paper production process. © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

We demonstrate volume Bragg gratings inscribed in S-TIH53 glass. S-TIH53 is in the proper meaning not photosensitive; therefore we used a fs-laser system for the inscription process. The grating structure was formed in a Talbot interferometer and was investigated with help of the external Bragg reflection method. With this method we could measure the reflectivity profile and thereto the size of the grating. To ensure that the generated gratings are no surface or absorption gratings the probes were investigated by a microscope and absorption measurements and heating experiments were done.

Special fiber Bragg grating (FBG) sensor embedding and interrogation schemes have been designed to capture the momentary peak pressure forces in the nip of adjacent paper machine rolls, and the spatial distribution of these nip forces along circumference and length of the roll, for production speeds of up to 2000 m/min. Additionally, this FBG sensor system measures the temperature distribution in the roll cover. FBG sensor embedment has been investigated and optimized for the implementation of pressure force measurements in various roll cover materials. These measurements enable immediate quality control during various stages of the production process. Draw Tower Grating sensor arrays, simultaneously performing spectrometric interrogation, and autonomous power supply technologies result in an extremely robust fiberoptic sensor system operating at rotation speeds of 700 rpm, equivalent to centrifugal accelerations of 300 G.

The idea of fabricating fiber Bragg gratings during the drawing process of an optical fiber dates back almost 20 years. The application of a transverse holographic writing method on a fiber draw tower offers a promising solution for a highly effective Bragg grating production. Because of the high technology requirements it took more than 10 years to develop the method into a reliable process. The improvements in the technical development during the last five years enable today a cost efficient industrial production of draw tower grating (DTG®) arrays. In this paper we report about new possibilities of the improved process with respect to the grating type (type I gratings, type II gratings), the coating type (2ORMOCER®, metals) and the fiber diameter (125μm, 80μm and below). Furthermore, we present an example for the application of draw tower fiber Bragg gratings in sensing technologies for medical applications.

Regeneration of fiber Bragg gratings has been shown to be an effective method for improving the temperature stability well beyond the limit of conventional gratings. Strong gratings, which require a high number of laser pulses, have been used mostly in the past for the additional regeneration process. Specific production methods such as draw tower inscription allow only single laser pulse illumination. Such a process can provide, however, versatile and cost effective Bragg grating arrays for sensor applications. Therefore, a combination of single pulse gratings and a regeneration process is of great practical interest. We have demonstrated that an increase of the temperature stability up to 800°C for arrays of single pulse gratings is possible. Furthermore we observe a stronger regeneration for 800 nm wavelength gratings with considerably higher reflectivity after the thermal process compared to gratings for the 1550nm wavelength range.

This Letter presents simulation and experimental results that explore bending insensitivity of fiber Bragg gratings in suspended-core optical fibers. The implementation of thin silica bridge in the fibers enhances index contrast of the fiber core and reduces bending-induced strain transfer to the fiber core. This fiber design lead to a reduction of over 7 times in strain-induced fiber Bragg grating resonant peak shifts in the suspended-core fiber compared with that in standard telecommunication fiber, and an 0.14 dB bending loss at a bending radius of 6.35 mm.

Regeneration of two types of gratings is demonstrated using post-hydrogen loading. This increases the flexibility of the regeneration process by allowing access to gratings that are written with hydrogen and also reducing the demands for immediate regeneration after grating writing.

Fiber Bragg gratings (FBGs) are attractive as reflector elements in fully integrated all-fiber laser systems. Furthermore, FBGs made with femtosecond laser technology allow to reduce splice connections in the fiber, since no special photosensitive fibers are required. Fiber Bragg grating inscription with deep ultraviolet femtosecond laser (267 nm) and two beam interferometry allows to target germanium-free and non-photosensitive fibers while maintaining versatility in the choice of the output wavelength of the fiber laser. This concept offers the potential of gratings with high spatial resolution, great flexibility and good homogeneity and complements the methods of point-by-point inscription at 800 nm or of phase-mask inscription with 400 nm femtosecond laser exposure. We report on the application of the interferometric fiber Bragg grating inscription technology to build a grating-stabilized fiber laser with high beam purity. Output powers up 160 W have been achieved.

The idea of Bragg gratings, generated during the drawing process of a fiber dated back almost 20 years ago. The technical improvement of the DTG process results today in high reliable and cost effective Bragg gratings for versatile application in the optical fiber sensor market. Due to the single pulse exposure of the fiber, the gratings behave typically like type I gratings with respect to their temperature stability. This means that such gratings only work up to temperatures lower than 300 °C. To increase temperature stability we combined DTG arrays with hydrogen loading and a thermal regeneration process which enables their use in high temperature environment. The regenerated draw tower gratings are suitable for temperatures up to 900°C.

This paper presents simulation and experimental results of orientation-dependent transverse load fiber sensors using fiber Bragg gratings written in four-hole suspended core fibers. Resonant peak shifts and splitting of fiber Bragg gratings were studied as functions of the applied transverse load and its orientation. Both simulation and experimental results revealed that response of fiber Bragg grating in suspended core fibers are sensitive to both orientation and magnitude of transverse strains.

The idea of fabricating fiber Bragg gratings already during the drawing of a fiber dates back almost 20 years. The application of a transverse holographic writing method on a draw tower offers a promising solution for a highly effective Bragg grating production. Because of the high technology requirements it took more than 10 years to develop the method into a reliable process. During the last five years the improvements in the technical development enables cost effective industrial production of draw tower gratings (1DTG®). In this paper we report about new possibilities of the improved process with respect to the grating type (type I gratings, type II gratings), the coating type (2ORMOCER®, metals) and the fiber type and diameter (125μm, 80μm and below). Furthermore, we present examples for the application of draw tower fiber Bragg gratings in sensing technologies for medical applications.

Various spectral-encoded fiber optic sensor concepts and advanced system solutions for application in energy facility monitoring have been investigated. The technological maturity, high performance and reliability of multiplexed fiber Bragg grating (FBG) sensor arrays and networks for the measurement of temperature, dynamic strain, air flow, and magnetic field distributions in electric power generators increasing their efficiency will be demonstrated by selected examples of field testing under harsh environmental conditions. For high-temperature combustion monitoring in gas turbines, beside silica FBGs with enhanced temperature stability also sapphire FBGs and Fabry-Perot sensors have been tested and evaluated as well as fiber-based black-body thermal radiation sensors. Finally, the potential of FBG sensors for application in cryo-energetic facilities such as super-conductive high-power motors and experimental nuclear fusion reactors will be discussed.

Fiber Bragg grating based fiber lasers are promising for stable all fiber laser solutions. Standard methods for fiber Bragg gratings in fiber lasers apply germanium doped passive fibers which are connected to the amplifier section of the fiber laser with a splice. The connection is usually recoated using a low-index polymer coating to maintain guidance properties for the pump light. At high pump powers the spliced connections are affected by absorbed pump light and are prone to thermal degradation. Fiber Bragg gratings made with femtosecond laser exposure allow the direct inscription of resonator mirrors for fiber lasers into the amplifying section of the fiber laser. Such a technology has a number of advantages. The number of splices in the laser cavity is reduced. Fiber Bragg grating inscription does not relay on hydrogenation to increase the photosensitivity of the fiber. This is of special interest since hydrogen loading in large mode area fibers is a time consuming procedure due to the diffusion time of hydrogen in silica glass. Finally, one gets direct access to fiber Bragg gratings in air-clad fibers. In this paper we use a two beam interferometric inscription setup in combination with an frequency tripled femtosecond laser for grating inscription. It allows to write fiber Bragg gratings in rare earth doped fibers with a reflection wavelength span that covers the Ytterbium amplification band. Reflections with values higher than 90% have been realized.