We propose a germanium-on-silicon photodetector with a bilateral mode-evolution-based coupler. Based on the double-sided mode-evolution, the light illuminates the whole Ge absorption region uniformly, which alleviates the space-charge effects and decreases the saturation effects. The simulated results show 53% more photocurrent generation and more than 19 times the opto-electrical bandwidth than conventional butt-coupled photodetectors under high-power illumination. In addition, an equivalent circuit model is presented to investigate the limiting factors of bandwidth. A genetic algorithm is used to extract the parameter values of components in an equivalent circuit by fitting the simulated two-port S22 parameter. The results show significant improvement in high-power and high-speed performance compared with conventional butt-coupled detectors.
Ge/Si separate absorption, charge, and multiplication avalanche photodiodes (SACM APDs) coupled with waveguides have shown significant potential as high-sensitivity, low-noise, and high-speed photodetectors for optical communications. In this study, we present a waveguide-integrated Ge/Si SACM APD fabricated on an eight-inch silicon photonics platform. The device exhibits a primary responsivity of 0.68 A/W at the unit gain voltage of 6 V for the O-band (1310 nm) wavelength, with a 10 μm-long and 1 μm-wide Ge layer. Additionally, the device demonstrates a 3 dB bandwidth of 25.7 GHz, with an input optical power of −16.8 dBm. The largest gain bandwidth product (GBP) is 247 GHz at a gain of 9.64 and a bias voltage of 15.7 V. The eye diagram is open at the bias voltage of 16 V, with a capacity to receive 28 Gbps of data. This APD shows potential for application in high-speed data transmission systems.
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