Optimal operation conditions for a push-pull dual-ring silicon modulator from a viewpoint of dispersion engineering and linearity

A silicon dual-ring modulator designed for chirp tuning in an intensity-modulated system is described and its performance is modelled. Previous experimental work using this device geometry partially demonstrates the advantages of the dual-ring approach. However, we provide here the first comprehensive theoretical treatment from which optimal operation parameters can be deduced. The device consists of two, over-coupled micro-ring resonators independently coupled to a MachZehnder interferometer and driven by a push-pull signal. Utilizing the interference effect provided by the Mach-Zehnder geometry, the device produces a large modulation depth and improved linearity, compared to single ring geometries, provided that the appropriate resonance detuning between the two micro-ring resonators and the correct phase condition are met. The differential drive configuration generates opposing signs of dispersion from the two rings leading to an adjustable modulation chirp that can be tuned into the negative or positive regime, or can be fixed at an essentially zero-chirp condition. System-level simulation is reported to validate the chirp tuning for a non-return-to-zero signal at a modulation rate of 28 Gb/s.