Er-doped integrated optical devices in LiNbO3

The state-of-the-art of Er-doped integrated optical devices in LiNbO₃ is reviewed starting with a brief discussion of the technology of Er-indiffusion. This technique yields high-quality waveguides and allows a selective surface doping necessary to develop optical circuits of higher complexity. Doped waveguides have been used as single- and double-pass optical amplifiers for the wavelength range 1530 nm<λ<1610 nm. If incorporated in conventional, lossy devices loss-compensating or even amplifying devices can be fabricated. Examples are an electrooptically scanned Ti:Er:LiNbO₃ waveguide resonator used as an optical spectrum analyzer and an acoustooptically tunable filter used as a tunable narrowband amplifier. Different types of Ti:Er:LiNbO₃ waveguide lasers are presented. Among them are free running Fabry-Perot lasers for six different wavelengths with a continuous-wave (CW)-output power up to 63 mW. Tunable lasers could be demonstrated by the intracavity integration of an acoustooptical amplifying wavelength filter yielding a tuning range up to 31 nm. With intracavity electrooptic phase modulation modelocked laser operation has been obtained with pulse repetition frequencies up to 10 GHz; pulses of only a few ps width could be generated. With intracavity amplitude modulation Q-switched laser operation has been achieved leading to the emission of pulses of up to 2.4 W peak power (0.18 μJ) at 2 kHz repetition frequency. Distributed Bragg reflector (DBR) lasers of emission linewidth ⩽8 kHz have been developed using a dry-etched surface grating as one of the mirrors of the laser resonator. Finally, as an example for a monolithic integration of lasers and extracavity devices on the same substrate, a DBR-laser/modulator combination is presented