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| Identifier |
000456647 |
| Title |
Light localization and diagnostics in micro-structured optical fibers |
| Alternative Title |
Διατάξεις εγκλωβισμού και διασποράς του φωτός σε μικρό-δομημένες οπτικές ίνες |
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Author
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Κόρακας, Νικόλαος
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Thesis advisor
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Καφεσάκη, Μαρία
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Reviewer
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Πισσαδάκης, Σταύρος
Πετεκίδης, Γεώργιος
Χαραλαμπίδης, Δημήτριος
Ριζιώτης, Χρήστος
Μητράκη, Άννα
Κομίνης, Ιωάννης
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| Abstract |
Whispering gallery mode (WGMs) resonances are useful for various applications due to their unique characteristics, such as high Q-factor and sensitivity to changes in refractive index. This thesis explores the potential of utilizing whispering gallery mode resonances to study amorphous materials such as ion-rich glass and silk fibroin protein and to correlate the behavior of the spectral resonances with their specific optical and mechanical properties.
▪ Whispering gallery mode resonances in thermally polarized glass hetero-fibers with radial symmetry are studied for the first time. In comparison to the spectral behavior of the fibers in their pristine state, the TE and TM polarized responses go through a spectral "cleaning" process; higher-order radial modes are suppressed or eliminated because of radially oriented thermal poling. The thermally poled hetero-fiber WGM cavities have been rigorously simulated utilizing the finite element method. The calculated modal eigenstates and transmission spectra have affirmed the mode selection mechanism introduced by the azimuthally symmetric thermal polling procedure. To reveal the spatial profile of the structural and optical changes introduced to the thermally poled hetero-fibers and correlate them with the WGM spectral measurements, second-harmonic generation (SHG) microscopy, energy dispersive x-ray spectroscopy (EDX), and micro-Raman (μRaman) measurements were carried out.
▪ During this research, cylindrical resonators made of silk fibroin were developed and attached to silica glass microfibers. For modal excitation, we employ a technique known as evanescent coupling, which uses optical fiber tapers. In addition, we investigate and analyze the optical birefringence properties of these resonators in the 1.5-micrometer spectral band. Through thermal annealing, silk fibroin undergoes a unique structural transformation from Silk I (amorphous) to Silk II (semi-crystalline). The increase of nano- crystalline sheet structures in Silk II is accompanied by several modifications to this biomaterial's physical (wettability) and optical (birefringence) properties. The photoelasticity of amorphous (Silk I) and semicrystalline Silk (Silk II) is attributed to the emergence of the β-sheet conformations that dominate the Silk II structure. Photo-elastic experiments are performed, tracing the TE and TM shifts of the whispering gallery mode resonances upon applying an axial strain. The strain optical coefficient K’ for Silk I fibroin was found to be 0.059±0.004, with the corresponding value for Silk II being 0.129±0.004.
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| Language |
English |
| Subject |
Optical cavities |
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Photoelasticity of silk fibroin |
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Thermal poling of glass |
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Whispering gallery modes |
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Θερμική πόλωση υάλου |
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Οπτικά αντήχεια |
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Φωτοελαστικότητα πρωτεϊνης μεταξιού |
| Issue date |
2023-07-19 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Materials Science and Technology--Doctoral theses
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Type of Work--Doctoral theses
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| Permanent Link |
https://elocus.lib.uoc.gr//dlib/0/e/1/metadata-dlib-1687776952-61702-16058.tkl
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| Views |
918 |
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