Rare-earth doped planar waveguide lasers

Rare-earth doped planar waveguide lasers have been realised in many host materials, using a range of waveguide fabrication techniques. Laser action has been obtained in ion-implanted Nd-doped crystals such as YAG, YAP, LiNbO3, & BGO, in proton-exchanged and titanium indiffused waveguides in Nd- and Er-doped LiNbO3, in Nd- and Er-doped silica waveguides on silicon, in Nd-doped sputtered glass waveguides, and in ion-exchanged Nd-doped glass waveguides. Each of these materials systems has specific advantages either as a laser host, or because of the potential for increased functionality through use of electro-optic effects, for example. Recent advances in this technology exploit the advantages that planar devices have over fibre devices. In particular, acousto-optic, electro-optic, or thermo-optic modulators may readily be monolithically integrated, complex multiple cavity devices may be defined photolithographically, there is access to the waveguides for surface interactions, and waveguide geometries may be changed along the device for efficient interfacing to external components and optimisation of individual devices. Recently, an FM mode-locked waveguide laser in Nd-doped LiNbO3 with an integral modulator), and a waveguide laser in LiNbO3 with locally diffused erbium have been demonstrated. The particular importance of the latter development is that passive waveguide components may be realised on the same substrate as those with gain