Si photonic integrated chips (Si-PIC) (1)

Si photonic integrated chips (Si-PIC)

Silicon (Si) has an indirect bandgap of approximately 1.12 eV. As a result, it has low transmittance in the visible light region and higher transmittance in the infrared region. Silicon absorbs light with wavelengths shorter than visible light (approximately less than 1.1 μm) effectively. Silicon's refractive index is about 3.5, which means that light refracts significantly when passing through silicon, allowing it to confine light strongly in a small space. This property is important for miniaturizing and densely integrating chips in optical device design. Silicon also has high thermal conductivity, which makes it resistant to temperature changes and allows it to operate stably in high-temperature environments. Additionally, through manufacturing processes similar to CMOS, both electronic circuits and optical circuits can be integrated onto the same chip.

The Silicon Photonics Chip (Si Photonics Chip) refers to a semiconductor chip that utilizes silicon-based optical technology to generate, manipulate, and detect optical signals. This technology leverages light (photons) instead of traditional electronic circuits to transmit and process data, offering advantages such as high-speed communication, low power consumption, and miniaturization. Si Photonics Chips are notable for their compatibility with existing CMOS (Complementary Metal-Oxide-Semiconductor) technology, as they utilize silicon semiconductor manufacturing processes, enabling cost-effective mass production. Below, we will provide a detailed explanation of the structure, operating principles, key components, advantages, and application areas of Si Photonics Chips.

Optical circuit structure

A Silicon Photonics Chip uses a Silicon-on-Insulator (SOI) wafer as the base material. An SOI wafer consists of a silicon substrate with an insulating layer (SiO₂) and a thin silicon layer on top, making it suitable for effectively confining and propagating light. The chip consists of the following key components:

• Waveguide: The path for transmitting light, which confines light using the high refractive index of silicon and the low refractive index of the surrounding insulating layer.

• Optical Modulator: Converts electrical signals into optical signals or adjusts the characteristics of optical signals.

• Photodetector: Converts received optical signals into electrical signals.

• Light Source: Typically, silicon has difficulty emitting light directly (due to its indirect bandgap properties), so external lasers or III-V group semiconductors (e.g., InP) are integrated and used.

• Coupler and Filter: Distributes optical signals or selectively processes light of specific wavelengths.

These components are all integrated into a single chip on the silicon substrate, and electrical connections are included for interaction with electronic circuits.

<Silicon-on-Insulator (SOI) wafer>

<Schematic of a photonic integrated circuit showing various optical components (not to scale), source: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics>