Abstract
Phase-sensitive photonic devices fabricated in silicon-on-insulator platform can have their response significantly modified by wafer height fluctuations. In this letter, we demonstrate a novel metrology technique for measuring on-chip thickness variations using long integrated chirped Bragg gratings. Thickness variations are recovered from the measurement of the complex transmission and reflection spectra using an inverse scattering algorithm. With 1-cm long sidewall gratings on 1.2- $\mu \text{m}$ wide waveguides, we measure waveguide height variations with nanometer-scale precision and tens of micrometer of longitudinal resolution. The results are confirmed by atomic force microscopy measurements.
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