Characteristics of Smart Concrete with Fiber Optical Bragg Grating Sensor

Based on the advantages of the fiber Bragg grating sensing technology,this paper presents a principle of a novel smart concrete with fiber optical Bragg grating sensor,analyses the theory and characteristics,illustrates the key technology and method to make the fiber Bragg grating sensor for the smart concrete,and proves the feasibility with experiments.The results indicate that the smart concrete with fiber Bragg grating sensors is feasible in the structure monitoring and damage diagnosing in the long run.

Convention of Optical Vortices in Two-Helix Long-Period Fiber Gratings

An effective method to fabricate two-helix long-period fiber gratings （TH-LFGs） is presented. Based on the coupling mode theory, the conversion of optical vortices （OVs） in TH-LFGs are analyzed in detail. The conversions of OVs with different topological charges： 0 → ±2 and 1 → 3 are simulated as three examples and the conversion efficiency higher than 98% can be realized.

NOVEL FIBER GRATING SENSOR DEMODULATION TECHNIQUE BASED ON OPTICAL WAVELET FILTERING

The optical wavelet filter is designed. It can filter and choose frequency swiftly. It can realize demodulation of distributed fiber Bragg grating（FBG） measurement system. Its scanning resolution and scanning period depend on wavelet function. Wavelet function is controlled by computer. Compared to conventional scan filter, optical wavelet filtering has some advantages such as simple structure, high scan frequency, high resolution and good linearity. At last, the error of optical wavelet filter scanning procedure is analyzed. Scanning step length refers to the shifting of optical wavelet window＇s central frequency. It affects system precision directly. If scanning step length is different, the measured signal is different. The methods of reducing step length guarantee scanning periodic time are presented.

Extraordinary Optical Confinement in a Silicon Slot Waveguide with Metallic Gratings

We present a silicon slot waveguide with metallic gratings embedded on the silicon surface in the slot region. The dependence of the optical coupling between two silicon wires on the width of the metal gap and the slot size are studied in detail. The results show that the optical field in the slot region with metallic gratings is significantly enhanced compared with the traditional slot waveguide due to the surface plasmon polaritons coupling on metallic gratings. The extraordinary optical confinement is attributed to the low effective dielectric constant of metallic gratings. The effective dielectric constant decreases with the increasing wavelength, and reaches the minimum when the width of the metal gap is about 0.01 times the wavelength.

Transmission resonance and color generation of metal-dielectric subwavelength gratings in visible regions

Metal-dielectric subwavelength gratings under s-polarized and p-polarized visible radiation are studied for discovering their intriguing behaviors of spectral resonance and color property.The dependence of their resonance and color on grating parameters as well as angle of incidence and position of plane of incidence is also analyzed.For s-polarized light,the behavior of spectral resonance with single peak and higher peak efficiency is found.While transmission spectra for p-polarized light are not able to achieve a behavior like that of s-polarization,creating a perceived color is feasible.Moreover,a security grating with distinctive color shifts has been designed and its resonant properties as well as related color variation have also been provided.

Tunable wavelength filters using polymer long-period waveguide gratings based on metal-cladding directly defined technique

In this work, long-period waveguide grating-based tunable wavelength filters using organic–inorganic grafting poly（methyl methacrylate）（PMMA） materials are designed and fabricated by metal-cladding directly defined technique.The thermal stabilities and optical properties of the organic–inorganic grafting PMMA core materials are analyzed. Structures and performance parameters of the waveguide gratings and self-electrode heaters are designed and simulated. The contrast of the filter is about 15 d B and the resonant wavelength can be tuned by different electric powers applied to the metal-cladding self-electrode heaters. The temperature sensitivity is 3.5 nm/℃ and the switching time is about 1 ms. The technique is very suitable for realizing the optoelectronic integrated wavelength-division-multiplexing systems.

Surface Plasmon Resonance Sensors Based on Polymer Optical Fiber

Surface Plasmon Resonance （SPR） is a powerful technique for directly sensing in biological studies, chemical detection and environmental pollution monitoring. In this paper, we present polymer optical fiber application in SPR sensors, including wavelength interrogation surface enhanced Raman scattering SPR sensor and surface enhanced Raman scattering （SERS） probe. Long-period fiber gratings are fabricated on single mode polymer optical fiber （POF） with 120 μm period and 50% duty cycle. The polarization characteristic of this kind of birefringent grating is studied. Theoretical analysis shows it will be advantageous in SPR sensing applications.

FIBER OPTIC TEMPERATURE MEASURING SYSTEM

This paper presents a fiber optic temperature measuring system used for measuring the temperature in many occasions. The system is of reflective type and composed of thermostatic bimetal plate, lever piston framework, optical grating and optical fiber probes. When the temperature changes, the thermostatic bimetal plate deforms. Through lever piston framework, the optical grating produces displacement in the upright direction. Thus the change of the temperature is transformed into the upright displacement of the optical grating. Optical fiber probes are used for detecting the number of streak lines of the optical grating′s displacement depending on the change of temperature. The detected signal can be transmitted to the control center through optical fiber cable up to distance of 1 km. The measurable range of this system reaches 100℃ with accuracy of ±0.2℃.

Field measurement of strain response for typical asphalt pavement

In order to reveal the changing law of the mechanical response of asphalt pavements under the action of vehicle load and provide references for the design of durable pavements,three typical asphalt pavement structures with flexible base(S1),combined base(S2),and semi-rigid base(S3)were selected to perform field strain tests under static and dynamic load using the fiber Bragg grating optical sensing technology.The changing characteristics of the strain field along the horizontal and depth directions of pavements were analyzed.The results indicate that the most unfavorable asphalt pavement layers were the upper-middle surface layer and the lower base layer.In addition,the most unfavorable loading positions on the surface layer and the base layer were the center of wheel load and the gap center between two wheels,respectively.The most unfavorable layer of the surface layers gradually moved from the lower layer to the upper layer with the increase of base layer modulus.The power function relationships between structural layer strain and vehicle speed were revealed.The semi-rigid base asphalt pavement was the most durable pavement type,since its strain value was lower compared to those of the other structures.

Multi-wavelength fiber ring laser based on a chirped moiré fiber grating and a semiconductor optical amplifier

A simple and cost-effective multi-wavelength fiber ring laser based on a chirped Moire fiber grating （CMFG） and a semiconductor optical amplifier （SOA） is proposed. Stable triple-wavelength lasing oscillations at room temperature are experimentally demonstrated. The measured optical signal-to-noise ratio （SNR） reaches the highest value of 50 dB and the power fluctuation of each wavelength is less than 0.2 dB within a 1-h period. To serve as a wavelength selective element, the CMFG possesses excellent comb-like filtering characteristics including stable wavelength interval and ultra-narrow passband, and its fabrication method is easy and flexible. The lasing oscillation shows a narrower bandwidth than SOA-based multi-wavelength fiber lasers utilizing some other kinds of wavelength selective components. Methods to optimize the laser performance are also discussed.

A novel durable intelligent fiber reinforced polymer anchor with embedded optical fiber Bragg grating sensors

Anchors are the key members of the geotechnical anchorage engineering, it is urgent to monitor their behavior in service for preventing the potential risks. This paper proposes a novel durable intelligent fiber reinforced polymer （FRP） anchor to understand the behavior of the anchor in the field application. Series of optical fiber Bragg grating （FBG） sensors were embedded into the central axis along the anchor to sense itself axial strain variations. An evolution model of axial strain was also developed to evaluate the behavior along the anchor. A demonstration test was carried out to test its self-sensing properties in the laboratory. The experimental results indicated that the embedded FBG sensors monitored the behavior, e.g. axial strairl/interfacial damage evolutions along the anchor and displacement/applied load at the pulling end effectively, without influence from the interfacial compression and slip effects.

Improved optical enhancement using double-width plasmonic gratings with nanogaps

Plasmonic grating structures have been shown effective at increasing near-field optical enhancement. A doublewidth plasmonic grating design is introduced, where each period has two alternating metal widths separated by a nanogap. With this new design, analysis has shown that plasmonic resonances couple between each metal section,resulting in even greater optical enhancement compared with single-width gratings. The geometry that gives the greatest optical enhancement has been determined with a computational model. This work demonstrates that the increased enhancement is due to hybridized modes that couple between the two grating segments.

A Novel Sensor for Detecting the Vibration

The micro-cantilever beam with a twin long period optic fiber grating sensitive to the strain and the vibration is designed to use as the sensor head.The micro-displacement of wavelength caused by strain or vibration is amplified in the system.Special cladding material is used to eliminate the interference brougth about the temperature.The designing structure is enabled to detect the micro-information.

Writing of internal gratings in optical glass with a femtosecond laser

The writing of an internal diffraction grating in optical glass plate is demonstrated using low-density plasma formation excited by a high-intensity femtosecond Ti:sapphire laser. The same diffraction efficiency at ±1,±2, and 0 order is achieved by multiple layers writing. The dependences of diffractive efficiency on the irradiated energy, the speed of writing, the numerical aperture (NA) of the focusing objective, and materials are investigated in detail. The grating is birefringent. It is attributed to residual stress interaction between glass and femtosecond laser pulse.

Non-uniform strain measurement along a f iber Bragg grating using optical frequency domain reflectometry

A novel method of measuring non-uniform strain along a fiber Bragg grating(FBG) using optical frequency domain reflectometry(OFDR) is proposed and experimentally demonstrated. This method can overcome the problems of traditional non-uniform strain measurement methods for FBGs, i.e., the likelihood of chirping and multiple peaking in the spectrum when FBG is subjected to inhomogeneous strain fields. Wavelength interrogation is realized by OFDR with a narrow-line-width tunable laser as the optical source. When non-uniform strain distributions along areas adjacent to structural damage are measured by this method, good agreement is obtained between measurements and theoretical simulation results.

Long-period grating inscription on polymer functionalized optical microfibers and its applications in optical sensing

We demonstrated long-period grating(LPG) inscription on polymer functionalized optical microfibers and its applications in optical sensing. Optical microfibers were functionalized with ultraviolet-sensitive polymethyl methacrylate jackets and, thus, LPGs could be inscribed on optical microfibers via point-by-point ultraviolet laser exposure. For a 2 mm long microfiber LPG(MLPG) inscribed on optical microfibers with a diameter of 5.4 μm, a resonant dip of 15 d B at 1377 nm was observed. This MLPG showed a high sensitivity of strain and axial force, i.e.,-1.93 pm∕με and-1.15 pm∕μN, respectively. Although the intrinsic temperature sensitivity of the LPGs is relatively low, i.e.,-12.75 pm∕°C, it can be increased to be-385.11 pm∕°C by appropriate sealing. Benefiting from the small footprint and high sensitivity, MLPGs could have potential applications in optical sensing of strain,axial force, and temperature.

Optical true time-delay for two-dimensional phased array antennas using compact fiber grating prism

A two-dimensional(2D) optical true-time delay(TTD) beam-forming system using a compact fiber grating prism(FGP) for a planar phased array antenna(PAA) is proposed. The optical beam-forming system mainly consists of a TTD unit based on the same compact FGP, one tunable laser for elevation beam steering, and a controlled wavelength converter for azimuth beam steering. A planar PAA using such 2D optical TTD unit has advantages such as compactness, low bandwidth requirement for tunable laser sources, and potential for large-scale system implementations. The proof-of-concept experiment results demonstrate the feasibility of the proposed scheme.

Generation of regular optical vortex arrays using double gratings

In order to generate high quality regular optical vortex array(OVA),we present an experimental method for generating OVA using phase only liquid crystal spatial light modulator(LC-SLM)assisted two gratings.In the scheme,holograms of two grating are displayed on the screen of two LC-SLMs respectively;the diffraction optical fields are captured by a CCD camera.The simulated and experimental results show that the regular OVA can be generated by using double diffraction gratings.The generated OVAs have a constant topological charge of±1.The method can provide a useful pathway to produce regular OVA for some applications in optical communication,particle trapping and optical metrology.

Optical Properties of High Sensitivity Fiber Bragg Grating on Temperature Sensor

In this paper, the spectrum shift properties of the center reflection wavelength detected to be based on the FBG sensor with ambient temperature change. The basic theoretical methods and numerical simulation for the spectral properties of uniform Bragg grating is analyzed by using coupling mode theory which is optical properties of high sensitivity fiber Bragg grating on temperature sensor in accordance with experiment.

Line-narrowed electro-optic periodically-poled-lithium-niobate Q-switched laser with intra-cavity optical parametric oscillation using a grazing-incidence grating

We report a line-narrowed electro-optic periodically-poled-lithium-niobate （PPLN） Q-switched laser with intra-cavity optical parametric oscillation using a grazing-incidence grating, producing 8-ns, 5-#J pulses at 10-kHz repetition rate when pumped with a 10-W diode laser at 808 rim. The output wavelength is centered at 1554.3 nm with a 0.03-nm spectral width. Wavelength tuning is achieved by rotating a mirror and changing the crystal temperature.