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What is Photonics-electronics convergence?

Technologies and the approach of integrating optical and electronic circuits very close together or as one unit, replacing electrical wiring with light. The aim is to cut power by extending optical links from between equipment to between boards and between chips. The Japanese term (kōden yūgō) is widely used in Japan.

Japanese name: 光電融合

Photonics-electronics convergence appears in 2 practice questions across 1 topic, including Silicon photonics.

Field: Silicon photonics

Why bring optics close to electronics

Electrical wiring loses more as signals get faster and distances longer, and the circuits that compensate consume power. Loss in optical fibers and waveguides is nearly independent of distance at data-center scales, and wavelength multiplexing puts many signals on one fiber. On the other hand, sending data optically requires electrical-optical conversion, which also costs power. Photonics-electronics convergence brings optical components right next to electronic circuits to eliminate long electrical wiring and reduce conversion power, shortening the distance at which optics becomes the better choice.

Optics reaching ever shorter distances

Optical links have spread from long-haul communication to links between equipment in a data center and between boards in a rack. The next steps are co-packaged optics (CPO), which places optical transceivers in the same package as a switch IC, and optical I/O near the chip, linking chips directly with light. Within its IOWN initiative, NTT has presented a plan to use photonics-electronics convergence devices to extend optical links step by step from between data centers to between boards, between chips and eventually within chips (as of the mid-2020s).

Enabling technologies

At the center is silicon photonics, which integrates optical waveguides, modulators and photodetectors using the same manufacturing technology as CMOS. Because silicon is poor at emitting light, lasers made of compound semiconductors such as InP are bonded on, or light is supplied from outside. Stacking optical chips with electronic chips such as drivers and TIAs for short connections, and assembly technology that attaches many fibers with high precision, are also essential.

Challenges

Optical components are temperature sensitive and must be kept stable next to hot processors. Laser reliability, pre-assembly testing of parts that cannot be replaced, and the cost and yield of fiber attachment are further issues. Unless electrical-optical conversion becomes efficient enough, electrical wiring remains better over very short distances. How far optics can replace wiring depends on improving conversion efficiency and packaging cost.

Try it: questions about Photonics-electronics convergence

In photonics-electronics convergence, what is the main aim of placing optical transceivers right next to electronic circuits?

  1. ATo eliminate long electrical wiring, reducing loss and power, and shorten the distance at which optical transmission becomes advantageous
  2. BTo make optical components easy to unplug and replace from the front panel
  3. CTo eliminate electrical-optical conversion and perform all computation with light alone
Show answer and explanation

Answer: A. To eliminate long electrical wiring, reducing loss and power, and shorten the distance at which optical transmission becomes advantageous

Electrical wiring loses more as signals get faster and distances longer, and the circuits that compensate consume power. Optical loss is nearly independent of distance at data-center scales, but electrical-optical conversion costs power. Photonics-electronics convergence places optical components right next to electronic circuits to eliminate long electrical wiring and reduce conversion power, shortening the distance at which optics becomes the better choice. CPO is a representative form, and later steps aim to make links between and within chips optical.

Even as photonics-electronics convergence advances, why is electrical wiring expected to remain in use for very short links such as those inside a chip?

  1. ALight has higher propagation loss over shorter distances
  2. BOptical fibers and waveguides cannot be cut or made short
  3. COptical transmission requires electrical-optical conversion, whose power and latency can exceed the loss of a short electrical wire
Show answer and explanation

Answer: C. Optical transmission requires electrical-optical conversion, whose power and latency can exceed the loss of a short electrical wire

Sending a signal optically requires converting electricity to light at the transmitter (modulation) and back at the receiver (detection and amplification), each adding power and latency. Electrical wiring loss grows with distance, so optics wins over long distances, but over very short distances the conversion overhead can be larger. The goal of photonics-electronics convergence is to raise conversion efficiency and shorten the distance at which optics pays off.

FAQ

What is the difference between photonics-electronics convergence and silicon photonics?

Silicon photonics is the technology for making optical circuits with silicon manufacturing processes. Photonics-electronics convergence refers to the broader approach of using such technologies to combine optical and electronic circuits closely and replace electrical wiring with light.

How is it related to CPO?

CPO, which places optical transceivers in the same package as a switch IC and shortens the electrical path to a few millimeters, is one representative form of photonics-electronics convergence. Later steps aim to make links between and within chips optical.

Is it a common English term?

It is a translation of a term widely used in Japan; NTT writes it as Photonics-Electronics Convergence (PEC). In English-speaking contexts, similar work is often described by specific technology names such as co-packaged optics or optical I/O.

Photonics-electronics convergence in the explanations

Questions that mention Photonics-electronics convergence (2)

  1. In photonics-electronics convergence, what is the main aim of placing optical transceivers right next to electronic circuits?
  2. Even as photonics-electronics convergence advances, why is electrical wiring expected to remain in use for very short links such as those inside a chip?

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Related terms

CPO (co-packaged optics) C-band Chromatic dispersion Edge coupler Extinction ratio Grating coupler Mach-Zehnder modulator O-band Plasma dispersion effect Propagation loss

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