Optical structures and method for producing tunable waveguide lasers (202). In one embodiment, a waveguide is defined within a glass substrate doped with a rare-earth element or elements by ion diffusion. Feedback elements such as mirrors (240) or reflection gratings (230) in the waveguide further define a laser-resonator cavity so that laser light is output from the waveguide when pumped optically or otherwise. Means are disclosed for varying the wavelengths reflected by the reflection gratings and varying the effective length of the resonator cavity to thereby tune the laser to a selected wavelength. Apparatus and method for integrating rare-earth doped lasers and optics on glass substrates. The invention includes a laser component formed from a glass substrate doped with an optically active lanthanides species with a plurality of waveguides defined by channels within the substrate. The laser component may constitute a monolithic array of individual waveguides in which the waveguides of the array form laser resonator cavities with differing resonance characteristics. The channels defining the waveguides are created by exposing a surface of the substrate to an ion-exchange solvent through a mask layer having a plurality of line apertures corresponding to the channels which are to be formed.