Design and fabrication of a novel evanescent germanium electro-absorption (EA) modulator

An electro-absorption (EA) modulator holds distinct advantages over the silicon Mach-Zehnder interferometer (MZI) modulator by having lower energy consumption, a smaller footprint on-chip, and a potentially higher modulation speed. These are crucial for efficient encoding of optical signals in silicon photonics circuits. Furthermore, the development of a Group IV-based (i.e. silicon- or germanium-based) EA modulator allows compatibility with standard complementary metal-oxide-semiconductor (CMOS) processing. In this work, we demonstrate a novel evanescent germanium (Ge) EA modulator structure. A lateral electric field is employed in the Ge rib to enhance absorption via the Frank-Keldysh effect. This shifts the absorption edge significantly with applied bias for wavelengths beyond 1600 nm. A peak extinction ratio of ~15 dB at 1600 nm could be achieved for a <3 V dynamic voltage swing from a 20 μm modulator. The impact of device dimensions and design structure on optical modulation and insertion loss are also investigated. In addition, monolithic integration of waveguided Ge-based modulator and photodetector can be simplified with our proposed EA modulator structure. The results from this work can make a low power and high speed Ge-based EA modulator viable for future silicon photonics applications.