Comparison Study of Multi-Slot Designs in Epsilon-Near-Zero Waveguide-Based Electro-Optical Modulators

We present a systematical comparative research on the modulation performance and the optimization of the multi-slot waveguide modulator at the telecom wavelength of 1.55 μm. It is found that the existence of epsilon-near-zero indium tin oxide slots in modulators can enhance the optical confinement, thus yielding a high extinction ratio (ER) and low insertion loss. Among the designed four types of slot modulators, the single-slot modulator exhibits the widest modulation bandwidth of 78.75 GHz and lowest energy consumption of 1.15 pJ/bit, while the dual-slot one shows the moderate performance. For the more-slot designs, the tri-slot has the advantages of a maximum figure of merit of ∼106, and the quadri-slot one has the highest ER of 1.38 dB/μm. By integrating the multi-slot modulator on the silicon waveguide, the quadri-slot modulator waveguide exhibits broad optical bandwidth of 83 nm from 1479 to 1560 nm and large modulation depth (∼18.3 dB). The performance of four types of slot modulators can be further improved from different aspects by the optimization of their geometric parameters. The results of this work could be useful in the design and selection of high performance on-chip modulators for optical communications and ultrafast data processing.