Waveguide-based technique for wafer-level measurement of phase and group effective refractive indices

A novel optical technique for multipoint on-wafer testing is reported. The technique exploits an integrated optical waveguide named point reflector optical waveguide (PROW) carrying multiple sensing probes based on lumped reflectors. PROW can be placed on the wafer along the desired paths, is compatible with chips tiling, requires a very small dedicated area and is here exploited to map the on-wafer distribution of the phase and group effective indices with an accuracy down to 10-3. The technique is useful to retrieve and map the variations of the physical and geometrical properties of the waveguides (e.g., width and core material composition) on the investigated wafer area. The potential of the PROW is here demonstrated on a InP wafer but can be readily extended to other platforms.