Demonstration of in-depth analysis of silicon photonics circuits using OFDR: waveguides with grating couplers

Optical frequency domain reflectometry (OFDR) is a powerful technique to investigate backscatter in waveguides. However, its use in Si photonics circuits has so far been limited to measuring the propagation loss and group index of a waveguide. We demonstrate that the transmittance (T) and reflectance (R) of elemental devices comprising a Si photonics circuit can be determined by OFDR. An analysis of Si wire waveguides with grating couplers (GCs) is described in detail. The wavelength dependence of T and R of the GCs were determined by using a backscatter model incorporating time-equivalent multiple-reflection paths and were well reproduced by a numerical simulation.