Compact and Energy-Efficient Forward-Biased PN Silicon Mach-Zehnder Modulator

A compact device model along with simulations and an experimental analysis of a forward-biased PN junction-based silicon Mach-Zehnder modulator (MZM) with a phase-shifter length of 0.5 mm is presented. By placing the PN junction to a certain off-center such that 72% of the waveguide is p-doped, the refractive index swing at a given drive voltage swing is increased by 2% compared to the symmetric layout. The effects of the phase shifters' length mismatch and asymmetric splitting on the modulation efficiency and extinction ratio of the modulator are simulated and compared with experimental results. Without any pre-emphasis or post-processing, a high-speed operation up to 15 Gb/s using a non-return-to-zero modulation format is demonstrated. A modulation efficiency ({{\boldsymbol{V}}_{\boldsymbol{\pi}}}{\boldsymbol{L}}) as low as 0.07 V × cm is verified and power consumption of 0.88 mW/Gb/s is recorded while a high extinction ratio of 33 dB is experimentally demonstrated. Compared to previously reported forward-biased silicon integrated modulators, without active tuning of the power splitting ratio between the arms, the extinction ratio is 10 dB higher. This MZM along with its compact structure is also sufficiently energy-efficient due to its low power consumption. Thus, it can be suitable for applications like analog signal processing and high-order amplitude modulation transmissions.