Silicon Photonics

- Overview

Silicon photonics (Si Ph) is the study of the optical properties of the group-IV semiconductor and the design and fabrication of devices for generating, manipulating and detecting light. Silicon is prevalent in photodetectors, solar cells in particular. However, its indirect band structure means that it is not a natural creator of light.

SiPh is a material platform that can fabricate photonic integrated circuits (PICs). It uses silicon-on-insulator (SOI) wafers as the semiconductor substrate material and can apply most standard CMOS manufacturing processes. 

PIC enables, expands and increases data transfer. PICs may consume less power and generate less heat than traditional electronic circuits, offering the promise of energy-efficient bandwidth expansion. SiPh is compatible with CMOS (electronics) fabrication, allowing SiPh PICs to be fabricated using established foundry infrastructure. Given the physics of photonics, older CMOS nodes can be well suited for patterning and fabricating photonic devices and circuits.

- Silicon Photonic Systems as the Optical Medium 

Silicon photonics (Si Ph) is the research and application of photonic systems using silicon as the optical medium. Silicon is often patterned into microphotonic components with sub-micron precision. They operate in the infrared, most commonly the 1.55-micron wavelength used by most fiber-optic telecommunications systems. Silicon is usually placed on top of a layer of silicon dioxide (by analogy with similar structures in microelectronics) called silicon-on-insulator (SOI).

- Silicon Photonics Devices

Silicon photonics (Si Ph) devices can be fabricated using existing semiconductor fabrication techniques, and since silicon is already used as the substrate for most integrated circuits, it is possible to create hybrid devices that integrate optical and electronic components onto a single microchip. As a result, many electronics manufacturers, including IBM and Intel, as well as academic research groups are actively working on silicon photonics as a means of following Moore's Law to provide faster speeds between and within microchips through the use of optical interconnects. data transmission. 

The propagation of light through silicon devices is governed by a series of nonlinear optical phenomena, including the Kerr effect, Raman effect, two-photon absorption, and interactions between photons and free charge carriers. The presence of nonlinearity is crucial because it allows light to interact with light, thus allowing applications such as wavelength conversion and all-optical signal routing in addition to the passive transmission of light.

- Silicon Waveguides

Silicon waveguides are also of great academic interest, due to their unique guiding properties, they can be used in communications, interconnects, biosensors, and they offer the possibility to support exotic nonlinear optical phenomena such as soliton propagation.

A waveguide is the interconnection between photonic devices in a circuit, made of a silicon core, with different styles: like ribs or strips, the oxide of the SOI substrate as the bottom cladding, and air or another layer of silicon oxide as the top cladding Light travels in these waveguides, and given the material properties of silicon, only infrared signals can travel without significant loss. Today, silicon photonic PIC processes often include additional waveguides built with silicon nitride as the core material, which opens up the ability to transmit wavelengths over a wider range, including visible light. 

Due to the material's indirect bandgap (the horizontal shift between a material's valence and conduction bands), light sources ("power sources" for lasers, photonic circuits and systems) cannot be fabricated in silicon today. In order to generate light, the material needs to have a direct band gap. Therefore, other materials with direct band gaps (III-V materials), such as indium phosphide (InP), are most commonly used in the fabrication of semiconductor lasers for long-range and data communications (1550 and 1310nm) wavelengths. Various techniques exist to integrate III-V materials and/or complete lasers into SiPh wafers (chips) to drive photonic components in photonic circuits.

 [More to come ...]