Significance The advent of next-generation information technology has spurred rapid advancements in fields like big data, cloud computing, and artificial intelligence, resulting in an exponential increase in global data volumes. However, traditional electrical analog and digital communication techniques face limitations such as bandwidth constraints, rising power consumption, severe crosstalk, and significant transmission losses when dealing with such vast data amounts. These challenges pose significant hurdles in designing electronic chips used in communication systems. Optical communication, relying primarily on fiber-optical technology, has emerged as a critical component in data centers and ultralong-distance signal transmission networks due to its inherent advantages: vast bandwidth, high-capacity transmission, minimal losses, and reduced crosstalk. In recent years, breakthroughs in optoelectronic integration technology have enabled the miniaturization and multifunctionality of traditional fiber-optical communication systems. This trend has catalyzed a surge in manufacturing, packaging, and IP development of chips tailored specifically for optical communication, marking a dynamic growth trajectory in this field. Silicon photonics technology aims to integrate optoelectronic devices onto a silicon platform, constructing comprehensive optoelectronic systems that enable intricate functionalities. This technology boasts numerous advantages, including an abundant supply of raw materials, compatibility with CMOS manufacturing processes, mature and highly reliable processing techniques, as well as a diverse array of functionalities for both active and passive systems. Consequently, it serves as a pivotal approach for miniaturizing and boosting the multifunctionality of optical communication systems. Silicon-based electro-optical modulators play a crucial role in converting signals between the electrical and optical domains, occupying a central position in information transmission and processing. Exploring the latest developments in silicon-based modulators and alongside analyzing structural designs, methodologies, strengths, and weaknesses of various modulator types are imperative for guiding researchers in devising devices that exhibit superior performance and align better with practical application requirements. Therefore, conducting a comprehensive review and analysis of existing research on silicon-based modulators is necessary and holds great importance. Progress Silicon-based modulators are generally classified into two categories: pure silicon modulators and silicon-based heterogeneous integration modulators. Among pure silicon modulators, we specifically discuss the silicon Mach. Zehnder modulator (MZM), silicon microring modulator (MRM), and silicon slow-light modulator. Firstly, we delve into the working principles and historical evolution of silicon MZMs, providing a thorough analysis of different structural designs and key performance metrics (Figs. 1-3). Currently, segmented MZMs utilizing lateral PN junction structures have achieved an impressive electro-optical bandwidth of 67 GHz, and a modulation efficiency of 3 V center dot cm. Nevertheless, the relatively large size of MZMs remains a challenge for integration. In contrast, silicon MRMs offer a more compact footprint and leverage a lumped electrode for wider bandwidths. Presently, MRMs have demonstrated electro-optical bandwidths surpassing 67 GHz and a modulation efficiency of 0.52 V center dot cm (Figs. 4 and 5). Nonetheless, silicon MRMs are notably susceptible to environmental disturbances and process variations, which hinder their practical deployment. On the other hand, silicon slow-light modulators exploit the slow-light effect to enhance modulation efficiency. Compared to MZMs, they achieve higher efficiency with a smaller form factor, boasting a large passband and superior thermal stability over MRMs. These modulators have achieved electro-optical bandwidths exceeding 110 GHz on a scale of hundred micrometers (Fig. 8), underscoring their promising potential for future advancements. For silicon-based heterogeneous integration modulators, we provide an analysis and summary encompassing four categories: silicon-based germanium modulators, silicon-based polymer hybrid modulators, silicon-based lithium niobate thin-film modulators, and silicon-based two-dimensional material modulators. Silicon-based germanium modulators incorporate germanium material onto a silicon substrate, utilizing the electro-absorption effect for modulation. These modulators have achieved an electro-optical bandwidth of 110 GHz with a modulation arm length of 20 mu m (Fig. 9). Silicon-based polymer hybrid modulators exploit the Pockels effect, enabling the fabrication of microring modulators with an electro-optical bandwidth of up to 176 GHz. Furthermore, these modulators exhibit excellent thermal stability (Fig. 10). Silicon-based lithium niobate thin-film modulators exploit the Pockels effect of lithium niobate material, resulting in modulators capable of exceeding 170 GHz electro-optical bandwidth (Fig. 11). There is also potential for achieving bandwidths exceeding 200 GHz in the future. Finally, silicon-based two-dimensional material modulators leverage the high electron mobility, wide operating bandwidth, and flexible integration capabilities of two-dimensional materials, achieving substantial progress in thermal-optical, electro-optical, and all-optical modulation (Fig. 12). Conclusions and Prospects Silicon-based modulators, essential for electro-optical conversion, are undergoing rapid development to meet the future demands of optical interconnects. The roadmap for silicon-based modulators focuses on achieving larger bandwidths and higher transmission rates, reducing losses, shrinking device sizes, strengthening system stability in packaging and integration, and enabling cost-effective mass production for practical applications. These improvements position silicon-based modulators as critical components in overcoming speed, bandwidth, power consumption, and size limitations in future optoelectronic information systems, cementing their pivotal role in advancing information technology.
