Resonant and slow-light 2×2 switches enabled by nanobeams and grating-coupled waveguides

Abstract

This paper reviews recent experimental and theoretical progress on 2 × 2 crossbar switches that operate within a narrow band of wavelengths (Δλ ∼ 0.5 nm) in a manner similar to that of 4-port reconfigurable add-drop multiplexers (ROADMs). The waveguided integrated-photonic devices discussed here can be actuated by thermo-optic (TO) or electro-optic (EO) means, the latter offering ultralow switching energy of 1 fJ/bit or less. The main switch architectures are the Mach-Zehnder interferometer (MZI) and the 2-waveguide (WG) contra-directional coupler with asymmetric WGs. Our 2 × 2 MZI's employ a pair of 1D photonic-crystal connecting arms — WGs with airhole or Bragg-grating lattices. Those WGs are (1) nanobeams that provide transmission over a Lorentzian resonance profile or (2) bandedge slow-light (SL) grating-WGs that give a step-like T/R spectrum with reflection at wavelengths below the edge and transmission above the edge. The grating-assisted asymmetric contra-directional coupler (ACDC) is resonant at the phase-matching wavelength between its two super modes. Reflection into the input is avoided using a A/4 phase shifting segment between two grating sections. This ACDC sends a reflected wave instead into the drop port. We discuss two NB devices, one SL device and three ACDC devices. In each case, the TO- or EO-induced wavelength shift of the resonance or step is Δλ s ∼ 0.8-nm, obtained by engineering the lattice and mode parameters. Our 2 × 2 s have great potential for creating N × N fabrics in WDM systems.