Erbium-doped lithium niobate waveguide devices

Recently, there has been a growing interest in erbium-doped optically pumped amplifiers and lasers in LiNbO₃. They operate in the wavelength range 1.52 μm<λ<1.62 μm, and are for that reason most attractive for fiber optical communication. LiNbO₃ has excellent electro- and acoustooptical properties allowing not only the development of modelocked, Q-switched and tunable lasers, but also of amplifying tunable filters, of loss compensating spectrum analyzers and of amplifying modulators. A whole range of new waveguide devices can be developed by combining optical amplification with nonlinear, electro- or acoustooptically controlled functions in the same structure. There are different methods to fabricate erbium-doped waveguides in LiNbO₃. The most versatile, reliable and simplest technique proved to be erbium-diffusion-doping of the surface of optical grade LiNbO₃ wafers followed by waveguide fabrication using standard titanium-indiffusion (or proton-exchange)