Silicon-wire-based ultrasmall lattice filters with wide free spectral ranges

Using silicon-on-insulator-based silicon-wire waveguides with submicrometer cross sections, we constructed ultrasmall channel-dropping lattice filters for $1.5‐\mathit{\mu }\mathrm{m}$ infrared systems. The waveguide’s low-loss bends with $2.5‐\mathit{\mu }\mathrm{m}$ radius reduce the total length of the filter to less than $100 \mathit{\mu }\mathrm{m}$ and enlarge the free spectral range to more than 80 nm. The measured spectra show fine channel-dropping characteristics, and the results agree well with numerical predictions. Moreover, we have succeeded in tuning the dropping wavelength by adjusting the lengths of the delay lines.