| Continued and rapid growth expounded by the bandwidth explosion in the area of dense-wavelength-division-multiplexed (DWDM) telecommunication and information networks, like the internet, has been and continues to be met by the global deployment of optical fiber. In turn, this has resulted in the unprecedented demand for the integrated-optical components used in these fiber networks. Of particular interest is devices fabricated in ferroelectrics, most notably lithium niobate (LiNbO3) and lithium tantalate (LiTaO 3). Although current demands are being met by LiNbO3, its brethren LiTaO 3exhibits a much higher threshold for optical damage, providing the opportunity to fabricate devices, such as lasers and modulators, with much higher output and throughput levels than currently obtainable with LiNbO3. In addition, LiTaO3 has a shorter wavelength ultra-violet (UV) absorption edge (280nm) than LiNbO3 (350nm), permitting nonlinear conversion by frequency doubling to shorter wavelengths with less absorption.; A number of obstacles, however, prevent the large-scale development of optical devices in LiTaO3. The various processes of waveguide formation have not been completely investigated or characterized. For instance, the annealed proton exchange (APE) technique is known to exhibit a number of anomalies which to date have not been understood, the most significant being the temporal instability of the waveguide index increment. Additionally, no work has been performed to characterize the impact of Er-indiffusion, necessary for the fabrication of 1.5mum lasers.; In this dissertation, the above issues are addressed. Conditions for the indiffusion of Er in LiTaO3 are identified. Fluorescence and Raman spectroscopy are used to identify energy transfer upconversion (ETU) between neighboring clusters of Er3+ ions as the dominant mechanism of upconversion, leading to increased photorefractivity, a gain-limiting factor for lasers. Upconversion is then decreased through a novel Li-treatment process to reduce clustering, with results showing a significant advantage over LiNbO 3. Additionally, the structural phase diagram for APE:LiTaO3 waveguides is constructed and used to explain the previously observed anomalies associated with this process in LiTaO3. The stability of waveguides fabricated by various techniques is also examined, resulting in the determination that instability does not depend on fabrication conditions, as it does in LiNbO3, but rather it is inherent to the crystal, the likely result of an immature growth process. Finally, to demonstrate the potential of LiTaO 3 and indicate the desire for higher quality crystals, a high-speed traveling-wave modulator is fabricated and its measured results compared to theory. This work hopefully will inspire crystal growth companies to arrive at a growth process which produces crystals with better crystal stoichiometry, desirable for improved device performance. |
