SILICON PHOTONICS Photonic integrated circuits might replace silicon chips in data centers

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Photonic integrated circuits (PICs), also known as photonic chips, are a subject of research for many enterprises. In photonic chips, light does all the “work” of current. Light performs computing and signal processing faster than conventional chips. Emerging startups are developing efficient photonic chips to replace traditional silicon-based electronic integrated circuits (EICs) in data centers.

IBM’s demonstration of the 1 nm chip has proved that Moore’s law isn’t dead yet. The chips are getting smaller and smaller. The AI of today runs on advanced nodes, including 3nm, 5nm chips, and 7nm chips. 2nm and 1nm chips are anticipated for exceptional AI performance. As the process node shrinks, the chip becomes power-hungry. Data centers, on average, consume more than 1.5% of global electricity and deal with 200 billion terabytes of data.

The present can be promising, but everything comes to an end. In the future, a hard limit will put an end to the number of transistors companies can place in a standard-sized chip. Quantum tunneling becomes a problem. It gives rise to leakage currents, which further make insulation difficult with smaller gate sizes [pitches]. The efficiency of computers and IT won’t scale. Photonic integrated circuits might beat Moore’s law.

What are photonic integrated circuits?

Just as the name suggests, photonic integrated circuits process, detect, and route photons [light pulses] by integrating micro-optical components on a single chip for high-speed and lossless communication.

Simply, PICs use a laser source to inject and process light, just as electronic chips inject and process electric current. Instead of electric current, light drives the components on and off. Light carries and distributes information. The fabrication process of a photonic chip is quite similar to that of a silicon chip, but miniaturized optical components are used.

The light enters the chip through the external or bonded chiplet laser. The coupler injects the light into the chip. Similar to metallic traces on silicon chips, optical waveguides enable light to travel throughout the chip. The optical modulator uses electrical signals to encode the information on the optical signal. Modulated signals exit the chip via the output coupler and photodiodes.

PICs can be made from the following:

• Silicon can enable the manufacturing of energy-efficient, high-speed, robust, and scalable PICs. It comes under the field of silicon photonics, where microphotonic components are fabricated onto a silicon substrate using a manufacturing process known as SOI CMOS. SOI stands for silicon-on-insulator. We described silicon photonics in our detailed article. Silicon photonics is a preferable solution for PIC manufacturing.

• Silicon nitride (SiN) can operate over a wider range of wavelengths.

• Group III-V semiconductors, such as indium phosphide and gallium arsenide, can make highly efficient PICs. However, the manufacturing process lacks compatibility with the CMOS process.

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Why photonic integrated circuits in data centers?

Photonic integrated circuits can function as AI accelerator chips. Electronic silicon-based chips consume extensive power when deployed as accelerators in advanced and complex AI and ML workloads.

Faster chips: Photonic integrated circuits use light to transmit and receive the signal. Light is made from photons, which are the fastest particles or perhaps waves in the universe. However, photons on chips travel at lower speeds, but very slightly faster than electrons. As a consequence, photonic chips can deliver and receive data at higher speeds.

Massive bandwidth: Photons carry more information per second than electrons. The bandwidth allotted to optics is unregulated and unlicensed. The visible spectrum is in the range of 400 to 700 nm, the infrared spectrum ranges from 750 nm to 1 mm, and the UV spectrum ranges from 100 nm to 400 nm. All of them fall under the scope of photonic chips.

The bandwidth range is [Theoretically] PetaHertz, which might fulfil the bandwidth needs of hyperscalers and AI factories. Commercial PICs can operate in the infrared domain due to minimal loss in silicon and multiple degrees of freedom for multiplexing.

Low-resistance path: Electrons are negatively charged. They collide with other atoms and impurities, facing resistance. As a result, they attenuate, and signals can be lost. Photons don’t have an electrical charge, making them free of resistance from other particles. They are fundamentally “transparent” to whichever medium they’re moving in. The problem of quantum tunneling no longer persists.

Low crosstalk: Different signals travelling through adjacent wires, cables, and devices interfere with each other. Unwanted energy transfer results in signal quality degradation, logical failure, and faulty chip operations. Photons from adjacent channels just pass through each other unaffected. Chip failure modes are effectively reduced.

Control of cooling units: Heating is an effect of current. As more current passes through the chip, it heats up, requiring extra cooling. Photons don’t heat up. As a result, photonic integrated circuits offer better thermal performance. PICs target sub-picojoule energy per bit, lowering thermal footprint. The reduced need for large-scale cooling units, essentially in data centers, can lower both CapEx and OpEx.

Low noise: At room temperature 26 degrees Celsius, thermal energy is smaller than infrared photon energy. Thermal fluctuations, generated by other semiconductor materials in the system, cannot produce optical noise. Weaker interaction results in lower power dissipation. Optical signals remain more efficient than copper at comparable rates.

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Photonic chips are being developed by Intel Photonics, Lightintelligence (California), Lightmatter (Shanghai), Ayar Labs (San Jose), Broadcom, Cisco Acacia, and many more. Telecom or Datacom PICs are commercial products. Data center-level PICs and co-packaged optics are in development and pilot deployment phases. The industry, including hyperscalers, data centers, and AI factories, awaits widespread adoption.

References

https://www.synopsys.com/glossary/what-is-a-photonic-integrated-circuit.html#1

https://lightmatter.co/knowledge-hub/what-is-a-photonic-integrated-circuit/

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