Passive and active optical waveguides in LiF thin films

Lithium fluoride thin films represent an innovative material for integrated optics. Passive waveguides may be produced by using a LiF/NaF two-layer structure deposited on any substrate material. On the other hand, low-energy electron beam irradiation of LiF polycrystalline films gives rise to the efficient formation of laser active lattice defects showing intense photoluminescence and sizable optical gain in the visible spectral range from green to red at room temperature. This irradiation at the same time induces an increase of the real part of the refractive index, thus allowing one to exploit electron lithography techniques to directly write integrated optical amplifiers and lasers in LiF films. Experimental results of the characterization of both passive and active waveguides are reported, demonstrating the feasibility of more complex circuits in this material.