Abstract

The thin-film active quasi-waveguide (Fig. 1) is a system which consists of a thin (up to several dozen wavelengths) active layer inserted between two passive dielectric media with refractive indexes higher than those of the active medium. Therefore this system has only leaky modes. In the active quasi-waveguide the role of mirrors of the ordinary resonator is carried out by the boundaries of the active layer with the coefficient of reflection determined by Fresnel's formulae. The order of interference determines the modes of quasi-waveguide radiation analogous to transverse modes of an ordinary laser. Each wavelength in modes is being radiated under a different angle; that is, the quasi-waveguide is an active dispersion system, which permits the generation wavelength to be tuned smoothly by turning only the external mirrors. The possibility of light generation in active quasi-waveguide is investigated in Ref. ¹. We have realized a double-frequency quasi-waveguide laser with independent frequency tuning in spatially separated laser beams using two external mirrors. Another important application of the quasi-waveguide is its operation as a thin-film amplifier. In this case radiation with divergence close to diffraction divergence was obtained for incident signal of arbitrary divergence. The signal was injected into the quasi­waveguide system both below and above threshold.

© 1994 IEEE