Realization of optical fiber regenerated gratings by rapid cooling and split annealing

Rapid cooling, or quenching, during regeneration of seed gratings in standard single-mode silica optical fiber is explored. It is shown that regeneration can be broken up into stages in time. The novel, to the best of our knowledge, method of ``split annealing'' offers a unique tool for optimiz-ing regeneration and studying fundamental glass science within a one-dimensional bi-material system. We demon-strate regeneration at temperatures as high as T= 1200 degrees C for the first time as well as opening up an approach suited to batch processing of regenerated gratings. (c) 2022 Optica Publishing Grou

Optimum Placement of Long Gauge FBG Sensor in Reinforced Concrete Bridge: A Case Study

In the world today, civil infrastructure plays a major role in the advancement of the modern age. They are huge in scale, complex in their behaviour and create great impact in everyday life. To ensure safety of these structures, assessment of their structural integrity is an important and challenging task. The sole purpose of structural health monitoring is to detect damage in the structures and suggest suitable rehabilitation measures. Various sensors are employed to achieve the task of damage detection and establish a warning system to avoid failure of the structures. For large structures, long-gauge Fibre Bragg Grating (FBG) sensors which are sensitive to the global behaviour, can be suitably used for this purpose. However, health monitoring of a structure with large number of sensors is expensive and hence there is a need to optimize the number of sensors deployed to minimize the cost of the exercise without compromising on performance assessment. For this purpose, several optimization algorithms are available in literature. In this study, the Effective Independence Method (EIM) which optimizes the response of the structure based on modal analysis, is used to derive the Optimum sensor placement (OSP) protocol for a reinforced concrete (RC) bridge-deck in Poland, the geometry of which has been taken from literature. This will enable the placement of 40 long gauge FBG sensors in regions for efficient damage response in the bridge-deck. Further, the optimum orientation of the sensors is further validated with a finite element model of the bridge-deck, where a moving load is applied, and strains are recorded in the sensing fibre in both longitudinal (along length) and transverse (along breadth) alignments. It has been found that long gauge FBG sensors placed in the transverse direction are more efficient in damage detection than when they are placed longitudinally

Development of Canadian Water Quality Index (WQI) of Vidhyadhari, an Estuarine River in Eastern India

Surface water represents one of the most utilized sources for water distribution systems globally, despite the fact that rapid urbanization and industrialization has reduced its cleanliness. As a result, the end-user's health is seriously impacted by the dirty water. Nevertheless, it is clear that many developing nations, including India, pay little regard to or care about this crucial issue. The Vidhyadhari River has become a receiver of high organic and bacteriological load of entire Kolkata City through Basanti canal. As a result, the purpose of this investigation is to evaluate how rapid urbanization and industrialization has changed the water quality of Vidhyadhari River using Canadian Water Quality Index (WQI). We have used seasonal water quality data collected at two monitoring stations (Haroa bridge and Malancha) from 2011 to 2020 to study the water quality of Vidhyadhari River. Results of the study indicated that the annual WQI value of Haroa brigde ranged between 21.62 (very bad) and 62.89 (medium) with an average of 27.29 (bad), whereas annual WQI value of Malancha station ranged between 15.44 (very bad) and 43.09 (bad) with an average of 18.77 (very bad). In comparison to downward location, the water quality of Vidhyadhari River was somehow good at upstream i.e., Haroa brigde. According to WQI, the water quality of Vidhyadhari River fall into bad to very bad category, which indicated deterioration of river water quality. Factor analysis revealed that both stations are predominated by hardness cluster (hardness, calcium, magnesium and chloride) followed by cluster of total dissolved solids (TDS), sulphate and ammonia. Sewer, excessive human activity, industrial discharges, poor sanitation, and urban runoff outflow can be extrapolated as the main causes for the deterioration of Vidhyadhari River water quality. This study emphasized the significance of implementing measurement actions, introduction of watershed characteristics and implications for developing water management strategies

Long period fiber grating for biosensing: an improved design methodology to enhance add-layer sensitivity

We present our theoretical study on the design of LPFG sensor where its add-layer sensitivity is enhanced. addlayer sensitivity quantifies the sensitivity of the sensor to the changes taking place within few tens of nanometers around the receptor molecules. Two different methodologies: the use of dual overlay layer and tailoring of the intermodal separation between two cladding modes, have been used to enhance the add-layer sensitivity. Using coupled mode analysis we compute several examples to carry out a detailed comparative analysis between the results obtained, focusing on the cladding mode near mode transition.This work was supported by Council of Scientific Research (CSIR), India during the 12th Five Year Plan. Project Nos. ESC-0102 and ESC-0110. The author I. D. Villar thankfully acknowledge the support of the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) (TEC2016-78047-R) and the Government of Navarre through the project with reference 2017/PI044

Sensitivity Analysis of Sidelobes of the Lowest Order Cladding Mode of Long Period Fiber Gratings at Turn Around Point

A new methodology to enhance the sensitivity of a long period fiber grating sensor (LPFG) at the Turn Around Point (TAP) is here presented. The LPFG sensor has been fabricated by etching the fiber up to 20.4 mu m, until the sidelobes of dispersed LP0,2 cladding mode appeared near TAP in aqueous medium. The dual peak sensitivity of the sidelobes was found to be 16,044 nm/SRIU (surrounding refractive index units) in the RI range from 1.333 to 1.3335

Sensitivity analysis of a dispersed clad mode to surrounding refractive index

The sensitivity of a specific dispersed clad mode and a normal clad mode of a Long Period Grating (LPG) near Turn Around Point (TAP) to surrounding refractive index in the range of 1.3332 - 1.3348 has been studied experimentally. We could attain a sensitivity of ∼2413 nm/RIU using LP0, 11 dispersed clad mode of a TAP-LPG with ∼3dB attenuation at resonance

Design and realization of a femtosecond-laser-inscribed fiber Bragg grating for accurate measurement of liquid level and liquid density

An exceptionally sensitive liquid level and density sensor system using Femtosecond-Laser-Inscribed Fiber Bragg Gratings is designed and demonstrated utilizing the basic Archimedes' Law of Buoyancy. The sensor works based on principles of Archimedes' law of buoyancy and basic strain sensitivity of Fiber Bragg Grating (FBG). A cylindrical mass of 22.5 cm long is suspended from one end of the FBG and whereas the other end of the fiber is fixed. The mass is partially immersed into the liquid under consideration to measure the liquid level as well as liquid density. Following Archimedes' law of buoyancy, the relative weight of the suspended mass gets reduced and the corresponding shift in Bragg wavelength is measured using an interrogator connected at the fixed end of the sensor lead fiber. The relative weight of the immersed mass also depends on the liquid density. Therefore, a change in liquid density also is reflected by the shift in Bragg wavelength. The system can be calibrated to measure the accurate liquid level and liquid density. A liquid (water) level measurement sensitivity of 5.47 to 5.60 pm/mm is achieved using the system under three times of consecutive experiments which is very close to the simulated value (5.9 pm/mm). A density measurement sensitivity of - 0.71 nm/(gm/cm3) is calculated in this system and experimentally achieved sensitivity is - 0.7 nm/(gm/cm3). The LOD (limit of detection) was also found to be 1.008 gm/cc for the density measurement and the average error during the measurement was 0.0021 nm/(gm/cm3).It is also shown that the density measurement sensitivity is highly dependent on the amount of immersed portion of the suspended mass and more amount of immersed mass is desirable for better sensitivity

Design of Superstructure Fiber Bragg Grating With Efficient Mode Coupling for Simultaneous Strain and Temperature Measurement With Low Cross-Sensitivity

An efficient fiber-optic sensor based on a superstructure fiber Bragg grating (SFBG) for simultaneous strain and temperature measurement is numerically and experimentally demonstrated. The stain-insensitivity property of a specific LPG resonance band has been used to overcome the effect of cross-sensitivity. The strain sensitivities of the FBG and LPG peaks of the proposed SFBG sensor have been obtained as 0.79 and -0.41 pm/mu epsilon, and their temperature sensitivities are found as 8.67 and 40.13 pm/degrees C, respectively. The resolutions for the strain and temperature measurements have been noted as +/- 12.83 mu epsilon and +/- 1.02 degrees C based on the wavelength resolution of an optical spectrum analyzer (FBG peak: 0.01 nm; LPG peak: 0.1 nm) and the deviations of measured values from applied ones of measurands. The proposed sensor has shown good agreement between the applied and measured measurands with good linearity and reduced cross-sensitivity

Over coupled long period grating with enhanced sensitivity to refractive index higher than that of cladding

Response characteristics of over coupled long period gratings to ambient refractive index higher than that of cladding index are investigated. For the first time change in the peak attenuation ~ 670 dB/RIU has been reported