Design and fabrication of 3μm silicon-on-insulator waveguide integrated Ge electro-absorption modulator

We present the design and fabrication of a waveguide-based Ge electro-absorption (EA) modulator integrated with a 3 µm silicon-on-isolator (SOI) waveguide. The proposed Ge EA modulator employs a butt-coupled horizontally-oriented p-i-n structure. The optical design achieves a low-loss transition from Ge to Si waveguides. The interaction between the optical mode of the waveguide and the bias induced electric field in the p-i-n structure was maximized to achieve high modulation efficiency. By balancing the trade-offs between the extinction ratio and the insertion loss of the device, an optimal working regime was identified. The measurement results from a fabricated device were used to verify the design. Under a -4Vpp reverse bias, the device demonstrates a total insertion loss (including the transition loss) of 2.7-5.2 dB and an extinction ratio of 4.9-8.2 dB over the wavelength range of 1610-1640 nm. Subtracting the contribution of the transition loss, the Δα/α value for the fabricated device was estimated to be between 2.2 and 3.2 with an electric field around 55 kV/cm.