OPTOELECTRONICS An introduction to Silicon Photonics

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Silicon photonics is a hybrid technology between semiconductors and optical elements. This optoelectronic integration of silicon substrate and optical devices is a new domain that may empower power electronics and various other fields. This article gives an introduction to silicon photonics and its future.

What is silicon photonics?

Silicon photonics is a study and an emerging technology in industrial electronics that fabricates microphotonic components on silicon wafers using a special type of fabrication process called SOI CMOS. The resultant device is an integration of semiconductors and optics. Silicon photonics can build photonic integrated circuits (PICs), and optical devices like detectors, couplers, waveguides, and many more.

Abbreviated as ‘SiPh’, silicon photonics has been a subject of research in universities and institutions since the early 2000s. In 2015, foundries and big tech in semiconductor design and fabrication started researching the subject. Soon silicon photonic devices were brought from the books to the physical world and commercialized. As of 2022, the valuation of the silicon photonics industry stands at USD1.29 billion.

Silicon photonics manufacturing process

The special type of microfabrication process to produce silicon photonic integrated circuits is called Silicon-on-Insulator Complementary Metal-Oxide-Semiconductor “SOI CMOS”. Standard 200 nm and 300 nm CMOS manufacturing processes use silicon on an insulator (SOI) wafer to construct hybrid devices of semiconductors and photonics. The insulating material can be silica or silicon dioxide for making SOI wafers that support the functioning of such devices. Indium Phosphide, a direct band gap material, is also used to manufacture photonic integrated circuits.

Working principles of Silicon Photonics

In any form of optoelectronic device, photons (E = hv) are used for transmission, processing, detection, and reception. The information signal is imposed on optical energy for communication. The resulting photonic integrated circuit (from silicon photonics) utilizes silicon to act as an optical medium to transmit and receive photons. The propagation of light through the silicon photonic chip is a function of the relationship between optical phenomena and electric field and inter-particle interaction between photons and semiconductor material.

The usage of a silicon-insulator interface in the wafer of a photonic integrated circuit provides total internal reflection for improved performance. Simply put, photons governed by material properties and nonlinear optical behavior pass through the micro-optical components embedded in the chip to perform target chip operation. As a result, most silicon photonic devices have bidirectional capabilities to convert electrical energy into optical energy and vice versa, making them serve multiple applications.

Features

• Silicon photonic integrated circuits offer prototyping and can have high yield, reliability, and low manufacturing cost.

• Silicon photonic devices have reduced parasitic capacitance for improved efficiency.

• Silicon photonics are functional in the mid-range infrared and ultraviolet spectrum of light.

• Silicon phonics offer wavelengths from 1.55 up to 4 nm.

• Silicon photonic-based fiber optics offer a higher data rate compared to normal fiber optics.

• Silicon photonics are better contenders to make optical interconnects in semiconductors and waveguides.

Limitations

• Silicon photonic devices have modulational instability at low powers, hence they can be efficient for power electronic systems.

• The resultant output beam of an optical device built from silicon photonics can be redshifted or blueshifted.

• Signal loss can occur beyond 1.55 nm wavelength.

• Silicon photonic devices for UV spectrum are unreliable when compared to mid-range infrared spectrum.

• The manufacturing process can be lengthy and costly as microprecision and SOI are required.

What role can silicon photonics play in power electronics?

As discussed above, silicon photonics is academically a research field and commercially an emerging technology. Silicon photonics have major applications in fiber optics, telecommunications, and data centers. Some small-growing applications are augmented reality, artificial intelligence, optical processing, and quantum computing.

Power electronics is an integral part of all these fields as high-power devices are required for transmission, reception, and processing. Hence, silicon photonics serve many power electronic applications for improving the overall performance of various systems. These are the most important applications of silicon photonics in power electronics:

• High power waveguides: Silicon photonics can build waveguides for power electronics devices. Laser diodes and various other power devices build waveguides on silicon substrates to direct beams of light, perform optical amplification, and many more functions.

• Increased efficiency: Silicon photonics opens up new possibilities in optical communication and signal processing, which are an important portion of any power system. As a result, silicon photonics can improve the efficiency and performance of power electronics systems.

• High data rate: Power electronic devices are used in long-distance communication for data transmission and reception. Hence, data centers of telecommunication networks deploy multi-million silicon photonic chips and use optical interconnects to achieve an overall higher data rate and bandwidth.

• Sensing and measurement: Power electronic systems use optoelectronic devices to sense, measure, and control physical parameters such as distance, speed, temperature, pressure, and voltage. Silicon photonics can build modulated lasers, interferometers, LIDARs, and detectors for effective sensing.

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