Silicon electro-optic modulators based on microscopic photonic structures: from principles to advanced modulation formats

This paper reviews the progress of electro-optic modulators composed of silicon-based microscopic photonic structures. The basic principles, device structures, and advanced modulation capability of different geometric types are detailed for micro-ring modulators, photonic crystal modulators, and other related modulators. We illustrate the device operation mechanism with a focus on its photonic aspect and discuss their impacts on the modulator speed, power consumption, and thermal stabilities. The cavity enhancement and slow light effect significantly reduce the device footprint and power consumption, with the trade-off of limited operation wavelength range. Other emerging microscopic photonic structure-based silicon modulators for advanced modulation formats exhibit promising performance for further optimizations. Finally, we discuss the existing challenges and further directions of microscopic photonic structure-based silicon modulators for pertinent applications.