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.
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