Ahmed Kandeel

We present an RF equivalent circuit model for GeSi quantum confined stark effect (QCSE) electro-absorption modulator (EAM) integrated in a 300 mm Si photonics platform. The model incorporates two key components: the first captures the contributions from interconnects and bondpads, while the second represents the electrical and optical characteristics of the modulator. The model is validated by fitting it to measured S₁₁ parameters across various EAM lengths under different bias conditions. The derived circuit parameters are subsequently employed to simulate the electro-optic S₂₁ response, successfully estimating the EAM 3dB bandwidth in a good agreement with the measured small-signal modulation response. Additionally, deeper insights about the physical interpretation of the S₁₁ data are obtained by converting the S₁₁ to the impedance (Z) domain. Our model facilitates the analysis of EAM performance under high-speed operation, identifying the limiting factors for further speed enhancement.

We report the recent progress of waveguide-coupled O-band GeSi quantum confined stark effect electroabsorption modulators, monolithically integrated in a Si photonics platform on 300 mm Silicon-on-insulator wafers with 220 nm thick Si top layer. A wafer-scale analysis of static insertion loss (IL) and extinction ratio (ER) is presented, showing IL down to 7.5 dB with ER of 5 dB for a 36.8 µm long device, at drive voltages of 2 V peak-to-peak. Modulation bandwidths beyond 50 GHz are demonstrated, with an extracted junction capacitance of 57 fF and series resistance of 8.3 Ω. Finally, open eye diagrams are demonstrated for non-return-to-zero on-off keying (NRZ-OOK) modulation for data rates from 40 Gb/s up to 64 Gb/s, with dynamic extinction ratio of 2.5 dB, at 1320 nm wavelength.

We present an elegant and effective approach for the design of adiabatic waveguide couplers tailored for the heterogeneous integration of photonic building blocks. This method empowers users to incorporate the shortest taper(s) in their designs, while upholding optimal coupling efficiency. The technique assesses mode overlap between a minimum of two waveguides within the cross-section of any heterogeneous material stack, determining the necessary waveguide cross-sectional dimension to achieve optimal coupling efficiency. Two illustrative design applications are showcased and compared to a linear, concave, and convex taper for reference: a SiN-to-polymer structure exhibiting a 40% coupling improvement and a Si-to-GeSi structure having a 2.2 up to 5 times shorter length.