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You searched for subject:(Optical Fibers Photosensitivity). Showing records 1 – 2 of 2 total matches.

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Indian Institute of Science

1. Madhav, Kalaga Venu. All-Fiber Sensing Techniques For Structural Health Monitoring And Other Applications.

Degree: 2007, Indian Institute of Science

In this thesis, we explore the four aspects of fiber Bragg grating sensors: mathematical modeling of Fiber Bragg Grating response/spectral characteristics, fabrication using phase mask, application and interrogation. Applications of fiber Bragg gratings, also known as in-fiber gratings, with emphasis on their sensing capabilities, interrogation of an array of sensors and their performance in structural health monitoring scenario are documented. First, we study the process of photosensitivity phenomenon in glasses, in particular GeO2:SiO2 glasses. For mathematical modeling we consider the 1-D refractive index profile along the propagation axis of an optical fiber drawn from the preform of such glasses. These 1-D index structures exhibit a bandgap for propagation along the fiber axis. We show how the bandgap is dependent on the two structural parameters: index periodicity and effective refractive index. The mathematical model provides the characteristics of three sensor parameters -resonance wavelength also known as the Bragg wavelength (λB ), filter bandwidth (ΔλB ), and reflectivity (R). We show that the evolution of the index structure in germanosilicate glasses is dependent on the inscription parameters such as exposure time, intensity of the laser used for inscribing, the interference pattern, and coherence of the laser system. In particular, a phase mask is used as the diffffacting element to generate the required interference pattern, that is exposed on the photosensitive fiber. We present a mathematical model of the electromagnetic diffraction pattern behind the phase mask and study the effect of the limited coherence of the writing laser on the interference pattern produced by the diffracting beams from the mask. Next, we demostrate the sensing capabilities of the fiber Bragg gratings for measuring strain, temperature and magnetic fields. We report linearity of 99.7% and sensitivity of 10.35pm/◦C for the grating temperature sensor. An array of gratings assigned with non-overlapping spectral windows is inscribed in a single fiber and applied for distributed sensing of structural health monitoring of an aircraft’s composite air-brake panel. The performance of these sensors is compared with the industry standard resistance foil gauges. We report good agreement between the two gauges (FBG and RSG). In some applications it is more desirable to know the spectral content, rather than the magnitude of perturbation. Fiber Bragg gratings sensors can be used to track events that occur in a very small span of time and contain high frequencies. Such applications demand very high speed wavelength demodulation methods. We present two interrogation techniques: wavelength-shift time-stamping (WSTS) and reflectivity division multiplexing (RDM). WSTS interrogation method employs the multiple threshold-crossing technique to quantize the sensor grating fluctuations and in the process produces the time stamps at every level-cross. The time-stamps are assembled and with the a priori knowledge of the threshold levels, the strain… Advisors/Committee Members: Asokan, S.

Subjects/Keywords: Structural Health Monitoring; Optical Devices; Fiber Optics; Fiber Bragg Gratings (FBG); Optical Fibers - Photosensitivity; Fiber Bragg Grating Sensor; Fiber Bragg Grating - Mathematical Modeling; Photonic Bandgap; Fabricated Gratings; FBG Fabrication; Grating; Fiber Sensing; Reflectivity Division Multiplexing; Instrumentation

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Madhav, K. V. (2007). All-Fiber Sensing Techniques For Structural Health Monitoring And Other Applications. (Thesis). Indian Institute of Science. Retrieved from http://hdl.handle.net/2005/644

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Madhav, Kalaga Venu. “All-Fiber Sensing Techniques For Structural Health Monitoring And Other Applications.” 2007. Thesis, Indian Institute of Science. Accessed January 22, 2020. http://hdl.handle.net/2005/644.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Madhav, Kalaga Venu. “All-Fiber Sensing Techniques For Structural Health Monitoring And Other Applications.” 2007. Web. 22 Jan 2020.

Vancouver:

Madhav KV. All-Fiber Sensing Techniques For Structural Health Monitoring And Other Applications. [Internet] [Thesis]. Indian Institute of Science; 2007. [cited 2020 Jan 22]. Available from: http://hdl.handle.net/2005/644.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Madhav KV. All-Fiber Sensing Techniques For Structural Health Monitoring And Other Applications. [Thesis]. Indian Institute of Science; 2007. Available from: http://hdl.handle.net/2005/644

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


Indian Institute of Science

2. Rahman, Aashia. Germanosilicate Fibers And Bragg Gratings : Newer Efforts In Understanding Photosensitivity And Novel Methods For Strain-Temperature Discrimination.

Degree: 2009, Indian Institute of Science

The different topics covered in this thesis include photosensitivity in germanosilicate fibers/glasses and application of fiber Bragg grating sensors in simultaneous strain and temperature discrimination. Fiber Bragg Gratings are wavelength dispersive refractive index structures manufactured through ultra-violet (UV) exposure of optical fibers. Their applications range from wavelength division multiplexing filters, dispersion compensators and fiber laser resonators for telecommunication applications to different types of point or distributive sensors for a variety of applications. One aim of this thesis has been to understand the mechanism of photosensitivity in germanosilicate fibers/preforms. Studies undertaken in this part of the thesis include thermal dynamics of Fiber Bragg Gratings and nano-indentation on ultra-violet irradiated germanosilicate glass preforms. An interesting, periodic appearance of a new peak has been observed in the reflected spectrum of Bragg grating inscribed in a germanosilicate fiber during thermal treatment. The new peak occurs on the longer wavelength side of the spectrum during heating and on the shorter wavelength side during cooling, following an identical reverse dynamics. A commercial grating with 99.9% reflectivity also shows a similar decay dynamics. The observed temperature induced distortion in refractive index modulation profile has been understood in the light of compaction-densification model. It is proposed that during the fabrication process of a grating, the modulation in the thermal expansion coefficient brought about by the interference fringes results in a non-uniform expansion throughout the grating length which in turn results in the distortion of the refractive index profile with increase/decrease in temperature. Since the reflection spectrum of a grating can be approximated as the Fourier transform of the refractive index profile, any distortion in the index profile results in the observed anomalous behaviour in the reflection spectrum. Nano-indentation studies have been performed to measure the changes in mechanical properties of a glass preform subjected to different levels of ultra-violet exposure. The results reveal that short term exposure leads to an appreciable increase in the Young’s modulus suggesting the densification of the glass, confirming the compaction-densification model. However, on prolonged exposure, the Young’s modulus decreases, which provides the first direct evidence of dilation in the glass leading into the Type IIA regime. The present results rule out the hypothesis that continued exposure leads to an irreversible compaction and prove that index modulation regimes are intrinsic to the glass matrix. In the second part of the thesis, three different schemes have been proposed for the use of Fiber Bragg Gratings as strain-temperature discriminating sensors: (a) The first method is based on the measurement of the different characteristic wavelength shifts of two types of gratings. Strain and temperature sensitivities of a Type I Bragg… Advisors/Committee Members: Asokan, Sundarrajan.

Subjects/Keywords: Bragg Grating; Photosensitivity; Germanosilicate Fibers; Fiber Bragg Gratings; Fiber Bragg Grating Sensors; Anomolous Thermal Dynamics; Nano-Indentation; Pre-strained Gratings; Germania; Fabry-Perot Filter; Germano-silicate Optical Fiber; FBG Sensors; Instrumentation

Record DetailsSimilar RecordsGoogle PlusoneFacebookTwitterCiteULikeMendeleyreddit

APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Rahman, A. (2009). Germanosilicate Fibers And Bragg Gratings : Newer Efforts In Understanding Photosensitivity And Novel Methods For Strain-Temperature Discrimination. (Thesis). Indian Institute of Science. Retrieved from http://hdl.handle.net/2005/948

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Rahman, Aashia. “Germanosilicate Fibers And Bragg Gratings : Newer Efforts In Understanding Photosensitivity And Novel Methods For Strain-Temperature Discrimination.” 2009. Thesis, Indian Institute of Science. Accessed January 22, 2020. http://hdl.handle.net/2005/948.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Rahman, Aashia. “Germanosilicate Fibers And Bragg Gratings : Newer Efforts In Understanding Photosensitivity And Novel Methods For Strain-Temperature Discrimination.” 2009. Web. 22 Jan 2020.

Vancouver:

Rahman A. Germanosilicate Fibers And Bragg Gratings : Newer Efforts In Understanding Photosensitivity And Novel Methods For Strain-Temperature Discrimination. [Internet] [Thesis]. Indian Institute of Science; 2009. [cited 2020 Jan 22]. Available from: http://hdl.handle.net/2005/948.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Rahman A. Germanosilicate Fibers And Bragg Gratings : Newer Efforts In Understanding Photosensitivity And Novel Methods For Strain-Temperature Discrimination. [Thesis]. Indian Institute of Science; 2009. Available from: http://hdl.handle.net/2005/948

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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