Abstract

A high-Q Mach–Zehnder interferometer (MZI)-coupled microring is presented for optical sensing with high sensitivity and a large measurement range. By optimizing the length difference between the two arms of the MZI coupler, the MZI-coupled microring with a high-Q factor and high extinction ratio is obtained. In the present example, the Q factor of the designed silicon-nanowire-based microring is as high as 1.8×105 when the silicon nanowire has a propagation loss L=2dBcm. Due to this high-Q factor, the sensitivity for the change Δn of the effective refractive index is about 105106 by measuring the shift of the resonant wavelength. Because of the wavelength dependence of the coupling ratio of the MZI coupler, it is possible to have only one resonant wavelength with a high extinction ratio in a very large wavelength span [i.e., the quasi-free spectral range of the MZI-coupler microring], which offers a very large measurement range covering the refractive index change of gas/liquid samples (e.g., 0Δn<0.48 in the present example).

© 2009 Optical Society of America

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