Abstract

During the last six years, intense research on single-mode rare-earth doped fiber lasers and amplifiers has led to the development of a range of active devices, in particular the Er³⁺-doped fiber amplifiers with application for optical telecommunications at 1.5 to 1.6 µm. Integrated optics may offer an alternative way for realizing such single-mode waveguide active devices with potential advantages over fibers,such as a more compact size, the feasibility of Q-switching, frequency doubling and the possibility of processing many devices on a single substrate. It also offers possibilities for new monolithic laser or amplifier components combining the medium’s gain and the large range of integrated optical functions already demonstrated. It may include coupled cavity, Q-switched, mode-locked or frequency doubled lasers and amplified optical integrated circuits with no insertion losses. The possibility of ion-doping of standard integrated-optic waveguides has recently allowed the demonstration of Nd- and Er-doped single-mode channel waveguide lasers in single crystal Ti:LiNbO₃ waveguides^[1'^3] and various glass waveguides^[4-7]. Waveguide lasers have a number of useful applications including amplification of high speed modulated signals, optical generation and manipulation of microwave signals(e.g.,injection locking for phased-array antennas), all-optical repeaters for long distance communication, optical interconnection and coherent communication. However,due to the intrinsic limitations of LiNb0₃ and glass, the above mentioned applications are strictly limited. First,glass waveguides are not electrooptic, therefore, an active device cannot be made using these substrates. Second, LiNb0₃ waveguides have significant walk-off between the refractive indices of microwave and optical waves. Consequently, the modulation speed of the EO modulator, which serves as the input signal generator for the waveguide amplifier, is limited to -40 GHz. Third, the waveguide fabrication methods on LiNbO₃ and glass substrates are not universal. They are not transferable to other substrates. For instance,Si and GaAs are the most frequently used substrates for optoelectronics. LiNbO₃ and glass waveguide lasers

© 1993 Optical Society of America