Rare-earth-doped planar waveguide lasers

Research into active, rare-earth-doped planar waveguides is rapidly gathering pace. As with rare-earth-doped optical fibres, the small dimension of the waveguide region allows high gain to be achieved with very modest pump powers. Compared with fibres, the planar geometry potentially offers a number of additional benefits, such as a much higher degree of integration with access to properties available in crystals but not in glass, such as the possibilities of modulation and frequency conversion where the host medium is a nonlinear crystal. A wide variety of host media, in crystals and glasses is currently under investigation, along with a wide variety of techniques for waveguide fabrication and processing. A broad survey of this activity will be given, covering recent results and indicating some future directions