Simulation of germanium nanobeam electro-optical 2 × 2 switches and 1 × 1 modulators for the 2 to 5 µm infrared region

nanobeams (NBs) operating at 2 to 5 µm wavelengths. The wavelength of operation can be extended to 15 µm by mounting the Ge channel waveguides on a bulk Si chip. Electrons and holes are injected into the intrinsic Ge NB cavity center via thin P- and N- doped Ge wings on the NB (a lateral PIN diode at ~0.5 V forward bias). Simulations of the carrier-induced resonance-wavelength shift-and-damping in a 1 × 1 modulator show 6 dB of extinction at ~60 fJ/bit over the mid infrared. The NB's active length is λ-scale. The cavity uses tapered-diameter air holes. Intensity modulation at ~1 Gb/s appears feasible. High-performance 2 × 2 switching is predicted by embedding one NB in each arm of a Mach-Zehnder device. The resonance of each identical NB is shifted by the same Δλ via carrier injection. Calculations show very low insertion loss and crosstalk in both the cross and bar states; however, the cross-to-bar energy, around 8 pJ/bit, is much higher than that in the 2 × 2 version that employs PN-junction carrier depletion.