Silicon Photonics Modulators and Photodetectors for Next-Generation CPO and Optical I/O

This article focuses on recent advancements in high-speed electro-optical modulators and photodetectors for next-generation co-packaged optics (CPO) and optical I/O (OIO), specifically targeting 400Gbps per lane transmission. The discussion covers several types of modulators, including Si ring and disk modulators, electro-absorption modulators (EAMs) in Ge(Si), and those integrated with InP-on-Si.

Key developments discussed in the paper include:

1. GeSi Franz-Keldish (FK) Electro-Absorption Modulators (EAMs): These modulators exhibit high modulation bandwidth (over 100GHz) and have demonstrated the potential for 400G/lane data transmission in PAM-4 intensity-modulated direct-detection (IMDD) links. The modulator operates with an extinction ratio of around 4 dB and insertion losses ranging from 4 to 8 dB.

2. GeSi Quantum-Confined Stark Effect (QCSE) EAMs: These modulators use the QCSE effect to enable low-loss, high-efficiency operation in the O-band. They are still undergoing optimization to reduce excessive insertion loss and improve power efficiency.

3. InP-on-Si QCSE EAMs: Combining the benefits of III-V materials with Si integration, these modulators show promising performance with a bandwidth of over 80GHz and insertion losses of less than 7 dB. These are positioned as strong candidates for high-performance 400G/lane CPO implementations.

4. Si Ring and Disk Modulators: Silicon-based modulators such as rings (RM) and disks (DM) are being developed for both 200G and 400G lane rates, with an emphasis on minimizing power consumption while achieving high efficiency. The paper highlights the development of a disk modulator with a thermal tuning efficiency exceeding 100GHz/mW, capable of supporting high-density wavelength division multiplexing (DWDM) optical links.

5. Ge-on-Si Photodetectors: The article also discusses the development of high-performance Ge-on-Si photodetectors that meet the demands of next-generation CPO links, achieving bandwidth greater than 100GHz, low dark current, and low parasitic capacitance. These devices are integral for future optical receivers used in high-speed optical interconnects.

The overall aim of the research is to address the scalability challenges posed by growing data demands, particularly in AI training and inference, by improving the efficiency and integration of optical modulators and photodetectors within compact, high-performance systems for optical I/O. The successful integration of these devices could play a critical role in enabling the next generation of high-speed optical communication systems.