Radiation Tolerant Superfluorescent Fiber Sources for High Performance Fiber Optic Gyroscopes in Space Environment
Date Issued
2012
Date
2012
Author(s)
Peng, Tz-Shiuan
Abstract
This dissertation solves the most important problem for a high performance interferometric fiber optic gyroscope (IFOG) in space applications. It reports the radiation effects of erbium doped fibers (EDFs), proposes the photo-annealing method to rapidly recover the radiation induced attenuation (RIA) of EDFs, and proposes the reflectivity tuning technique to totally eliminate the radiation-induced mean-wavelength drifts of the superfluorescent fiber sources (SFSs), thus a high performance, radiation hardened IFOG can be realized in the future.
The RIA of an optical fiber results from the radiolytic electrons or holes trapped by defect sites in the glass matrix of the fiber''s core. Doping material in the fiber''s core always increases the RIA sensitivity of the optical fiber, so an EDF has much higher RIA sensitivity than a pure silica core fiber. The RIA of EDF was mainly due to other dopants, e.g. aluminum and germanium. The RIA dependence on dose was always well fitted by a power law function. A linear dependence of RIA sensitivity on the Al3+ concentration was found and it had a slope of 0.24 dB/m/krad/mole% when the Al3+ concentration was from 1.1 M% to 4.2 M%.
The 532-nm photo-annealing showed excellent annealing efficiency, and it could nearly diminish the RIA of EDFs in the wavelength range from 900 nm to 1700 nm. The simulation study estimated the RIA of irradiated EDFs in space could be as low as 0.002 dB/m by using the 532-nm photo-annealing technique. In addition, by employing reflectivity tuning method, the SFS could maintain the same mean-wavelength during irradiation, and have a broad linewidth of 34 nm. Combining these two techniques in an SFS, even under irradiation of 200 krad, the mean-wavelength could be stabilized and the output power could be higher than 40 mW. Such a radiation-tolerant SFS had improved performance and was better than those in the previous reports. In addition, the performance of this radiation-tolerant SFS was also better than that of superluminescent diode (SLD). A radiation-hardened IFOG with navigation grade is possible by using the proposed radiation-tolerant SFS. Furthermore, if the dependence of coil''s RIA on dose rate could be well extrapolated by using the modified power law for the low dose rate in space, a radiation-hardened IFOG with high performance could be realized.
Subjects
superfluorescent fiber sourece
radiation hardening
fiber optic gyroscope
space photonics
Type
thesis
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