Silicon-on-Insulator In-Plane Gires–Tournois Interferometers

Gires–Tournois interferometers (GTIs) based on deep-etched silicon-air Bragg mirrors and on optical quality dicing of silicon are reported. Broadband reflectivity of the deep-etched Bragg mirrors allows operation on a wavelength range exceeding the C Band window. The waveguided in-plane configuration of the devices allows interferometer lengths that are not typically achievable on chips using out-of-plane designs (e.g., $L>1~{\rm mm}$ for a 25-GHz free spectral range). Optical characterization of GTIs having two different free spectral ranges (i.e., 25 and 100 GHz) yield off-resonance insertion losses below 2 dB and polarization-dependant losses (PDL) below 1 dB. Insertion losses and PDL are, however, more important near the resonance wavelengths, reaching, respectively, 15 and 5 dB. Calculations show that the reported devices could be useful for Michelson-GTI bandpass filters, such as optical interleavers.