Dutta, Debjit (2021) Development of chromium doped nanoengineered YAS glass based optical fibers with and without rare-earths for use as a saturable absorber to make pulse fiber laser along with broadband sources. PhD thesis, CSIR CGCRI and Jadavpur University.

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Abstract

The demand of high bandwidth in optical communications as well as increasing need for tunable fiber laser source and laser cavity components like fiber saturable absorber for allfiber application lead to search for new materials that can serve for said purposes and besides provide other applications like fiber dosimetry. In this dissertation, chromium especially in +4 state in glass core of preform has been fabricated (using MCVD solution doping method) and drawn to fiber to investigate their different properties. Although chromium in different crystal hosts and in some kind of glasses is known to posses desired properties but those are not reported in case of fiber-based system. Nevertheless, the development of such Cr-doped fiber is challenging because of multiple bottlenecks such as chromium evaporation problem, stabilization of Cr+4, achieving nano-phase separated core etc. Accordingly, various material characterization techniques viz. Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, X-Ray Diffraction, Electron Probe Micro Analysis etc. are used to optimize different process parameters to achieve the desire target. Nano-engineering of core glass in terms of nano-phase separation has been administrated by thermal annealing and investigated using optical and material characterizations. The compositional variations and microscopic study between the phases in phase separated core glass was carried out by spot energy dispersive X-ray in conjunction with TEM. Other fabrication method like powder-in-tube (PIT) was also tried using wet chemical method for synthesis of YAG crystal powder followed by fiber implementation and respective characterizations. Some representative fabricated yttria-alumino-silicate (YAS) based fibers were set for experiment. Presence of different oxidation states including the desired +4 state is inferred from absorption spectra and emission spectra at NIR region with proper excitation wavelength. Fluorescence lifetime, photo-bleaching and Raman spectra are also investigated besides study on influence of divalent alkaline earth ions towards retention of Cr+4 ion in ultimate fiber core. The fibers were also set for the experiment regarding the electron irradiation effect resulting characteristic induced absorption and its posterior optical bleaching property (at 633/1070 nm wavelengths) has been investigated. In this experiment we also established that the desired properties of fibers are depends on Cr+4 ion whose amount in turn determined on 9 some divalent alkaline earth ions (Mg here). The study indicates the potentiality of the fabricated fibers in dosimetric application. Another important feature, saturable absorption, has been studied at 1.55 μm and 2 μm region for some representative fabricated fibers. Incorporating them in different laser cavities (EDFL and TDFL) show pulsed laser output, even nanosecond pulse (EDFL produces 432 ns pulse width, while TDFL produces 59 ns pulse width) also achieved. Effect of chromium codoping on rare-earths like erbium (Er) doped fiber has also been studied due to the overlapping fluorescence band of both ions expecting improvement in erbium lasing. The fabricated fibers were compared with pure erbium doped fiber shows improvement in terms of the ratio of bleached to residual resonant absorption and net-gain to small signal absorption emerges as useful for core pumping NIR applications. Besides, reduced up-conversion phenomena and long NIR fluorescence lifetimes put positive remark on the fabricated fibers.

Item Type:	Thesis (PhD)
Additional Information:	Supervisor: Dr. Mukul Chandra Paul
Subjects:	Engineering Materials
Divisions:	Fiber Optics and Photonics
Depositing User:	Ms Upasana Sahu
Date Deposited:	28 May 2024 07:27
Last Modified:	28 May 2024 07:27
URI:	http://cgcri.csircentral.net/id/eprint/5722

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