Light propagation studies on laser modified waveguides using scanning near-field optical microscopy

By means of direct laser writing on Al, a new method to locally modify optical waveguides is proposed. This technique has been applied to silicon nitride waveguides, allowing modifications of the optical propagation along the guide. To study the formed structures, a scanning near-field optical microscope (SNOM) has been used. The laser modifications locally changes the optical properties of the waveguide. The change in the effective refractive index is attributed to a TE to TM mode conversion. Thus, the laser modification might be a new way to fabricate optical mode converters.