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Definition
Silicon photonics (SiPh) is a material platform from which photonic integrated circuits (PICs) can be made. It uses silicon on insulator (SOI) wafers as the semiconductor substrate material and most of the standard CMOS manufacturing processes can be applied.
Advantages and Challenges of Silicon Photonics
PICs enable, extend, and increase data transmission. PICs may consume less power and generate less heat than conventional electronic circuits, offering the promise of energy-efficient bandwidth scaling. SiPh is compatible with CMOS (electronic) fabrication, which allows SiPh PICs to be manufactured using established foundry infrastructure. Given the physics of photonics, older CMOS nodes can be perfectly suitable to pattern and fabricate the photonic devices and circuits.
Waveguides, the interconnects between photonic devices in the circuit, are made from a silicon core and come in different style: like a rib or strip and have the oxide from the SOI substrate as bottom cladding and air or another layer of silicon oxide as top cladding. The light is transported in these waveguides and given the material properties of the silicon only infrared signals can be transported without significant losses. Nowadays, silicon photonics PIC processes often include additional waveguides build from silicon nitride as the core material, this opens the ability to carry wavelengths over a wider range, including visible light.
Light sources (lasers, the “power supply” of photonic circuits and systems) are today impossible to manufacture in silicon due to the indirect bandgap of the material (a horizontal shift between the valence and conduction band of the material). For light to be generated, a material needs to have a direct bandgap. Therefore, other materials with a direct bandgap (III-V materials), such as Indium Phosphide (InP), are most commonly used to create semiconductor lasers for the wavelengths used in tele and datacom (1550 and 1310nm). Various techniques exist to integrate III-V materials and or complete lasers in the SiPh wafer (chip) to drive the photonic components within the photonic circuit.
How Photonic and Electronic Circuits Complement Each Other
PICs cannot do without “normal” or Electronic ICs to form a complete solution serving an application. In an optical pluggable transceiver, one needs the circuitry to drive the modulator and amplify the signals from the photodetector, and additional digital electronics signal processing is often required. Silicon photonics fabrication processes can vary from one foundry to another and include electrical devices. If that is the case we speak about monolithic silicon photonics, allowing designers to design both electrical and optical functions in one and the same chip, instead of designing two (or more) chips that need to be combined in a package. As always with product development, decision making about what technology to select for a particular application comes with cost, performance, time to market considerations and partnering early with a potential foundry and packaging provider will help making the right trade-off analysis.
SiPh is increasingly used in optical datacom, sensing, biomedical, automotive, astronomy, aerospace, AR/VR and AI applications. An example of an automotive application is integrated LiDAR chips for autonomous vehicles.
Synopsys supports the industry by providing a unique and complete end-to-end design solution for silicon photonics, covering electronics and photonics. Synopsys is working closely with all major foundries to support the development of silicon photonics manufacturing, PDKs and tool enablement.