Hitless tunable WDM transmitter using Si photonic crystal optical modulators.

We have developed compact Si Mach-Zehnder modulators that are assisted by wideband low-dispersion slow light in lattice-shifted photonic crystal waveguides. We have also developed Si triangular-shaped coupled-microring multiplexers that allow a box-like spectrum, a wide free spectral range, and an efficient thermal tuning. In this study, we integrated three sets of these devices in a small footprint of 2.0 × 0.7 mm(2) and achieved their 25 Gbps/ch operation as a wavelength division multiplexing transmitter. Moreover, we demonstrated hitless wavelength tuning using thermo-optic switches loaded in the bus waveguide.