Ion-exchanged tapered-waveguide laser in neodymium-doped BK7 glass

We report what is to our knowledge the first operation of a planar dielectric tapered-waveguide laser. The waveguide laser is fabricated by potassium-ion exchange in Nd(3+) -doped BK7 glass and consists of a single-mode channel waveguide of a few micrometers' width followed by a linear taper up to a broad region with a width of ~180microm . A slope efficiency of 42% is found both in the tapers and in standard channel waveguides fabricated upon the same substrate, indicating that the tapers and the channels have similar internal losses; hence the low-loss nature of the tapered beam expansion. The output from either end of the tapered structure is found to be nearly diffraction limited.