| Summary: | 博士 === 國立臺灣大學 === 光電工程學研究所 === 103 === Broadband light sources are the key components in applications such as the high-capacity optical communication and the optical coherence tomography. In this dissertation, broadband photonic devices based on glass-clad fibers with single-crystalline cores were demonstrated. The cores of crystal fibers were grown with the laser-heated pedestal growth (LHPG) method, and then cladded with glass using the co-drawing LHPG process.
High-brightness broadband light source was presented with the Pyrex-clad Ce3+:YAG crystal fiber pumped with a blue laser diode. By optimizing the annealing conditions, the quantum yield under low pump power was estimated to be 95%. A 19.9-mW fluorescence output from the crystal fiber core with a 25-μm diameter was achieved with a 1.4-W pump power, and the corresponding radiance was 30.3 W mm-2 sr-1. This high-brightness broadband light source is useful for the optical coherence tomography.
Hemispherical external-cavity Cr4+:YAG double-clad crystal fiber lasers have been demonstrated with a 17.3% slope efficiency and a 56-mW threshold pump power. A simulation program with distributed model for the crystal fiber laser and amplifier was developed. The propagation loss extracted by fitting the laser performances with different output couplers was 0.01 dB/cm. Performance of the Cr4+:YAG crystal fiber amplifiers were also simulated, and a 22.7-dB gain at 1431 nm can be achieved with a 10-cm crystal fiber with enhanced concentration.
Broadband tunable laser from 1353 to 1509 nm was demonstrated with the Cr4+:YAG double-clad crystal fiber. The laser output wavelength was tuned by rotating a single-plate birefringent filter within the collimated external cavity. The laser threshold was 70 mW in the presence of the birefringent filter. The wavelength tuning was discrete due to the interference between the transverse modes.
High-index-glass-clad crystal fibers have been developed for decreasing the number of transverse modes and reducing the propagation loss. Few-mode pure YAG crystal fibers cladded with N-SF57 and N-LaSF9 glasses were successfully fabricated. Finally, we also proposed designs of N-LaSF9-clad and N-LaSF41-clad Cr4+:YAG crystal fibers which can achieve single-mode guiding over the wavelength range from 1 to 1.7 μm.
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