| Degradation of signal level, caused by transmission and distribution losses, is an important problem in integrated optoelectronics. While transmission loss can be reduced by minimizing waveguide length and/or by improving material quality, distribution loss is intrinsic to device design, as in the case of 1 x N splitters. Erbium-doped thin-film waveguides, suitable for monolithic integration with other guided-optic devices, are promising as loss-compensating devices for photonic integrated circuits and systems.; In this thesis, we have investigated the major challenges in developing Er-doped waveguide amplifiers: the requirement of higher Er concentrations, the development of a proper fabrication process for low-loss waveguides, and the limitations on the maximum-obtainable gain of Er-doped thin-film amplifiers. As a prototype example of photonic integrated circuits, we have developed Er-doped optical amplifiers that are monolithically integrated with 1 x 2 splitters. A novel fabrication process was developed and used in forming the Er-waveguide structure. The process does not require etching of an Er-doped film in defining the lateral dimension of a waveguide, but involves a collimated sputtering in conjunction with the use of a mesa-etched substrate or with a lift-off deposition process. A 2-cm-long amplifier shows a 1.54-μm signal enhancement of 12–14 dB with 980-nm pump power of 50 mW. This signal enhancement is sufficient to compensate for various losses (absorption, scattering, and coupling losses, and 1 x 2 splitter loss) of the amplifier/splitter module, thus resulting in zero insertion loss.; For applications to 1 x N splitters with larger N, it would be desirable to increase the waveguide length, thus increasing the maximum obtainable gain of optical amplifiers. This would require maximum coupling of pump power available from a laser diode chip. In this thesis we have proposed and developed a new pumping scheme that utilizes a flared-end waveguide structure in conjunction with a micro-optics for direct coupling of a diode laser beam onto a waveguide facet. Using this scheme, we have achieved a coupling efficiency of 20–40% with a maximum pump power coupling of ∼200 mW from a 1 Watt laser diode chip. This corresponds to 300–400% enhancement over the conventional end-coupling method, which involves using a single-mode-fiber pigtailed laser module. The Er-doped optical amplifiers with this new pumping scheme will be very useful for various photonic and integrated optoelectronic circuits/systems where distribution/propagation losses of optical signals need to be compensated. |
