In situ loss measurement of direct UV-written waveguides using integrated Bragg gratings.

The propagation loss of a direct UV-written silica-on-silicon waveguide is measured using an elegant nondestructive method. The technique uses integrated Bragg grating structures, which are observed from opposing launch directions to obtain information about the optical power at different positions along the length of the waveguide. Critically, the technique is ratiometric and independent of coupling loss and grating variability. This high-precision measurement is suitable for low-loss planar waveguides. From this data, the propagation loss of the UV-written waveguides was observed to be 0.235+/-0.006 dB/cm.