Direct measurement of tunable optical delays on chip analogue to electromagnetically induced transparency

Direct time-domain measurement of tunable optical delay in a silicon resonating structure is presented. The structure is composed by a double-ring resonator, whose spectrum has a narrow transparency peak with low group velocity analogous to that in electromagnetically induced transparency. Effective group indices from 90 to 290 are obtained by tuning the resonator thermally. The measurements agree well with the theoretical analysis.