Investigation of Ionizing-Radiation-Induced Photodarkening in Rare-Earth-Doped Optical Fiber Amplifier Materials

Persistent Link:
http://hdl.handle.net/10150/311557
Title:
Investigation of Ionizing-Radiation-Induced Photodarkening in Rare-Earth-Doped Optical Fiber Amplifier Materials
Author:
Fox, Brian Philip
Issue Date:
2013
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Motivated by an increasing demand for functionality and reliability of systems operating in harsh, ionizing-radiation environments, the core of the present research is an investigation of the response of rare-earth-doped, aluminosilicate fibers to ionizing radiation. These rare-earth-doped fibers, consisting of fibers doped with ions of erbium (Er³⁺) and ytterbium (Yb³⁺) designed for use in amplifier systems, reveal average specific losses in response to ⁶⁰Co gamma radiation to be in the range of 0.0285 - 0.193 dB/(m•krad(Si)) at wavelengths from 1300 nm to 1400 nm. An ionizing dose rate dependence was identified in which high dose rates of approximately 40 rad(Si)/s invariably lead to higher induced losses than lower dose rates of approximately 14 rad(Si)/s, indicating the possibility of complex radiation-related phenomena underlying the observed absorption. Data clearly show that Er³⁺-doped fibers are more sensitive to ionizing-radiation in comparison to Yb³⁺-doped fibers, while Er³⁺/Yb³⁺ co-doped fibers are found to be the least sensitive to radiation of all the fibers examined. Evidence of color center formation associated with the dopant aluminum is found in results of visible spectroscopy conducted on gamma-irradiated preform samples and on fibers flown in low-Earth orbit. Near infrared spectroscopic data is consistent with absorption derived from this dopant as well, with the interpretation of band-tailing from the visible portion of the spectrum. Evidence of the formation of a defect intrinsic to the silicate host matrix, the Non-Bridging Oxygen Hole Center (NBOHC), is also found following ionizing radiation of the optical fiber preforms. Since the observed ionizing-radiation-induced absorption is concentrated in the visible portion of the spectrum, the performance of actively operated rare-earth-doped amplifiers is largely impacted by the pump wavelength, which is located at higher energies within the near-infrared portion of the spectrum and therefore closer to the visible portion of the spectrum than the lasing wavelength. Experimental results stemming from rare-earth-doped amplifiers operated under ionizing radiation substantiate the importance of the pumping wavelength, and suggest the presence of cascaded pump photon absorption processes. Based on these results, pumping at longer wavelengths is advised to reduce the effect of color center absorption on this crucial aspect of active fiber amplifier operation.
Type:
text; Electronic Dissertation
Keywords:
gamma radiation; radiation effects; radiation-induced photodarkening; rare-earth-doped fibers; space radiation; Electrical & Computer Engineering; fiber amplifiers
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Electrical & Computer Engineering
Degree Grantor:
University of Arizona
Advisor:
Potter, Kelly S.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleInvestigation of Ionizing-Radiation-Induced Photodarkening in Rare-Earth-Doped Optical Fiber Amplifier Materialsen_US
dc.creatorFox, Brian Philipen_US
dc.contributor.authorFox, Brian Philipen_US
dc.date.issued2013-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractMotivated by an increasing demand for functionality and reliability of systems operating in harsh, ionizing-radiation environments, the core of the present research is an investigation of the response of rare-earth-doped, aluminosilicate fibers to ionizing radiation. These rare-earth-doped fibers, consisting of fibers doped with ions of erbium (Er³⁺) and ytterbium (Yb³⁺) designed for use in amplifier systems, reveal average specific losses in response to ⁶⁰Co gamma radiation to be in the range of 0.0285 - 0.193 dB/(m•krad(Si)) at wavelengths from 1300 nm to 1400 nm. An ionizing dose rate dependence was identified in which high dose rates of approximately 40 rad(Si)/s invariably lead to higher induced losses than lower dose rates of approximately 14 rad(Si)/s, indicating the possibility of complex radiation-related phenomena underlying the observed absorption. Data clearly show that Er³⁺-doped fibers are more sensitive to ionizing-radiation in comparison to Yb³⁺-doped fibers, while Er³⁺/Yb³⁺ co-doped fibers are found to be the least sensitive to radiation of all the fibers examined. Evidence of color center formation associated with the dopant aluminum is found in results of visible spectroscopy conducted on gamma-irradiated preform samples and on fibers flown in low-Earth orbit. Near infrared spectroscopic data is consistent with absorption derived from this dopant as well, with the interpretation of band-tailing from the visible portion of the spectrum. Evidence of the formation of a defect intrinsic to the silicate host matrix, the Non-Bridging Oxygen Hole Center (NBOHC), is also found following ionizing radiation of the optical fiber preforms. Since the observed ionizing-radiation-induced absorption is concentrated in the visible portion of the spectrum, the performance of actively operated rare-earth-doped amplifiers is largely impacted by the pump wavelength, which is located at higher energies within the near-infrared portion of the spectrum and therefore closer to the visible portion of the spectrum than the lasing wavelength. Experimental results stemming from rare-earth-doped amplifiers operated under ionizing radiation substantiate the importance of the pumping wavelength, and suggest the presence of cascaded pump photon absorption processes. Based on these results, pumping at longer wavelengths is advised to reduce the effect of color center absorption on this crucial aspect of active fiber amplifier operation.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectgamma radiationen_US
dc.subjectradiation effectsen_US
dc.subjectradiation-induced photodarkeningen_US
dc.subjectrare-earth-doped fibersen_US
dc.subjectspace radiationen_US
dc.subjectElectrical & Computer Engineeringen_US
dc.subjectfiber amplifiersen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineElectrical & Computer Engineeringen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorPotter, Kelly S.en_US
dc.contributor.committeememberPotter, Kelly S.en_US
dc.contributor.committeememberParks, Harold G.en_US
dc.contributor.committeememberRoveda, Janet M.en_US
dc.contributor.committeememberPotter, Barrett G.en_US
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