We proposed recently a new «Smart Grids Plus» concept for digital energy grids design. These grids, in addition to layers of intelligent energy grids and information communication channels, include a layer of diagnostic monitoring based on a passive fiber optic sensor networks. Sensor networks have a hybrid TWDM structure – information exchange channels and integrated fiber optical sensors – core, based on a new technology for address interrogation and multiplexing – special addressable fiber Bragg gratings, combined for arbitrary topologies - point and quasi-distributed. Some examples of diagnostic monitoring nets for temperature control of complete switchgear contacts (point) and bus bars (quasi-distributed) are considered. Their principles of operation are discussed. The main advantages of these sensor networks are using of addressable fiber Bragg gratings simultaneously as sensors and multiplexing elements, and using of PON structure simultaneously as sensor and communication networks.
We present an approach to design and optimize a high angular dispersion spectrograph optical scheme. Such an instrument can be built using two volume-phase holographic gratings mounted one after another and simple focusing optics. However, this solution may suffer from high angular and spectral selectivity on the second grating. We propose a design technique combining simple raytracing with diffraction efficiency optimization based on analytical and numerical computations. As an example, we demonstrate a few versions of a compact spectrograph for the 830 to 870 nm near infrared range. Its spectral resolution is up to 0.01 nm, and after the optimization, the efficiency can reach 64.9%, while remaining very uniform for the entire range. Also, by the use of grisms instead of gratings, it is possible to make the optical design axial while keeping almost the same performance and eliminating misalignment issues.
One of the promising methods for generating continuous sub-terahertz radiation is the method of photomixing, when the photoconductive material is excited by the emission of two optical continuous lasers with frequencies separated by terahertz frequencies. It should be noted that for effective photomixing the polarization, frequencies and phases of the optical beams introduced into the mixer must be constant, otherwise it is necessary to additionally use a complex system of phase synchronization. In connection with the complexity of such an implementation, variants based on the conversion of single-frequency and broadband laser radiation into two-frequency ones were investigated. The first of these is modulation and consists in the external modulation of single-frequency laser radiation in the electro-optical Mach-Zehnder modulator. The second one is broadband with the allocation of two wavelengths using two rectangular fiber Bragg gratings with a small difference in width. The studies were carried out to create a terahertz photoconductor, the distinguishing feature of which is the use of heterostructures grown on a GaAs substrate in the low-temperature regime as a photoconductive material in the form of a thick gradient layer In(x)Al(1-x)As (x = 0 → 1) with artificially created local deformations and with photoconductive composite InGaAs / InAs / InGaAs quantum wells.
This article deals with problem of carbon brush`s length measurements. There are many applications where regular inspection is not feasible because of a number of factors including, for example, time, labor, cost and disruptions due to down time. Thus, there is a need for a system that can monitor the brush`s length to calculate it`s wear rate, while the component is in operation or without removing of the component from its operational position. We propose a novel method for characterization of carbon brush`s length. This method based on the usage of advantages of the multiplicative response of FBGs and FBG arrays: spectral parameters depend on several aspects, such as grating`s period, refractive index, it`s physical length and so on. We are the first, in our point of view, who proposed to use third parameter for sensing application and prospectively all three parameters for complex measurement: the change of FBG`s length is used to measure length of the brush and it`s wear rate, grating`s central wavelength shift for temperature (due to refractive index change) and mechanical stress (due to grating`s period variations) measurements. The results of modelling and experiments are presented.
This work presents results of experimental approbation of earlier on proposed modified fiber optic stress sensor based on a few-mode effects occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is concerned with a passage to quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm lengths improved by fiber Bragg grating (FBG) written on preliminary formed precision macrostructure defects in silica multimode graded-index optical fibers and special offset launching conditions providing laser-based excitation of higher-order modes. The “arms” of quasi-interferometer are two equalized lengths of MMF Cat. OM2 with great central dip of refractive index profile and strong pulse splitting due to high differential mode delay (DMD). We tested FBGs with Bragg wavelength both 1310 nm and 1550 nm written over tapers or up-tapers preliminary formed in short pieces of MMF Cat. OM2+/OM3 and further jointed to the end of one of the arms before output Y-coupler. Researches were focused on comparison analysis of pulse responses under changing of selected excited mode mixing and power diffusion processes due to stress distributed action to sensor fiber depending. Here we considered FBGs not only as particular wavelength reflector during spectral response measurement but also as local periodic microstructure defect which strongly effects on few-mode signal components mixing process also improved by combination with macro-defect like taper or up-taper that should provide response variation. Some results pulse response measurements produced for different scheme configuration and their comparison analysis are represented.
This article describes the design principles of optoelectronic system (OES) for instantaneous frequency measurement (IFM) of microwave signals based on the use of amplitude-phase modulation conversion of single optical carrier into symmetrical dual-frequency signal for additional frequency separation, its modulation by unknown frequency and subsequent “frequency-amplitude” measurement conversion in Fiber Bragg Grating (FBG) with Gaussian reflection profile. Such approach allows increasing of measurement resolution at low frequencies.
This work presents method for performing precision macro-structure defects “tapers” and “up-tapers” written in conventional silica telecommunication multimode optical fibers by commercially available field fusion splicer with modified software settings and following writing fiber Bragg gratings over or near them. We developed technique for macrodefect geometry parameters estimation via analysis of photo-image performed after defect writing and displayed on fusion splicer screen. Some research results of defect geometry dependence on fusion current and fusion time values re-set in splicer program are represented that provided ability to choose their “the best” combination. Also experimental statistical researches concerned with “taper” and “up-taper” diameter stability as well as their insertion loss values during their writing under fixed corrected splicer program parameters were performed. We developed technique for FBG writing over or near macro-structure defect. Some results of spectral response measurements produced for short-length samples of multimode optical fiber with fiber Bragg gratings written over and near macro-defects prepared by using proposed technique are presented.
In this paper, we consider a number of different methods that form the modern approach to the development of aircraft GTE’s noise suppression systems at service conditions. The herein-presented efficient noise suppression system on the base of fiber optic sensors makes it possible to reduce pulsations at the exhaust nozzle exit and noise levels at the engine outlet section.
The problems of synthesis and application of fiber Bragg gratings with special spectrum shapes in measurement and information channels of quazi-distributed fiber optic systems for climatic test systems are introduced. In particular, gratings with concave, triangular symmetric and triangular asymmetric spectrum shapes are considered, also the new poly-harmonic methods of its interrogation are presented. Projects of system decisions and results of experimental researches of its blocks are discussed.
This work is concerned with fiber Bragg grating (FBG) writing technique developed for graded-index multimode optical fibers applied in measurement systems based on a few-mode effects. We present some results of experimental approbation of proposed technique with Bragg wavelength 1310 and 1550 nm on samples of graded-index multimode optical fibers 50/125 of both new-generations Cat. OM2+/OM3 and old Cat. OM2 with preliminary measured refractive index profiles. While the first group fibers of Cat. OM2+/OM3 was characterized by almost ideal smooth graded refractive index profile and some fiber profile samples of this group contains thin central peak, the second fiber group profiles of Cat. OM2 differ by great central core defects representing dip or thick peak. Results of described FBG spectral response measurements under excitation of laser pigtailed by single-mode fiber are represented.
Aspects of the paper relate to a wear monitoring system for smart photonic carbon brush. There are many applications in which regular inspection is not feasible because of a number of factors including, for example, time, labor, cost and disruptions due to down time. Thus, there is a need for a system that can monitor the wear of a component while the component is in operation or without having to remove the component from its operational position. We propose a new smart photonic method for characterization of carbon brush wear. It is based on the usage of advantages of the multiplicative response of FBG and LPFG sensors and its double-frequency probing. Additional measuring parameters are the wear rate, the brush temperature, the engine rotation speed, the hangs control, and rotor speed. Sensor is embedded in brush. Firstly the change of sensor length is used to measure wear value and its central wavelength shift for temperature ones. The results of modeling and experiments are presented.
This work presents results of experimental researches of fiber Bragg gratings (FBG) operating in a few-mode regime.
We tested FBGs written on silica graded-index multimode fibers 50/125 Cat. OM2+/OM3 with Bragg wavelength 1550
nm by using them in a set of developed experimental schemes based on excitation of multimode fibers by corresponding
laser sources. The researches were focused on analysis of both spectral and pulse responses under changing of selected
mode mixing and power diffusion processes due to tension and/or stress local and distributed action to FBG or sensor
fiber. Results of spectral and pulse response measurements at the output of schemes with installed described FBGs are
represented.
This work presents results of experimental approbation of modified fiber optic stress sensor based on a few-mode effects
occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is
concerned with adding of quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm
lengths improved by fiber Bragg grating (FBG) and special offset launching conditions providing laser-based excitation
of higher-order modes. We tested FBGs written on graded-index MMFs 50/125 with Bragg wavelength 1550 nm connected
to different parts of proposed scheme. Researches are focused on comparing analysis of both spectral and pulse
responses under changing of selected mode mixing and power diffusion processes due to stress local and distributed action
to sensor fiber depending on scheme configuration. Here we considered FBGs not only as particular wavelength
reflector during spectral response measurement but also as local periodic microstructure defect strongly effecting few-mode
signal components mixing process that provides pulse response variation. Some results of spectral and pulse response
measurements produced for different scheme configuration and their comparison analysis are represented.
In this paper we consider the integrated approach to development of the aero-acoustical methods for diagnostics of aircraft gas-turbine engine flow-through passages by using as the base the passive fiber-optic and location technologies.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.