Photonics: The Future of Electronics - Understanding the Advantages of Optical Systems

While there is no question that fibre optics are superior for data transmission, they are never found in consumer devices due to the lack of technologies surrounding optical systems. What challenges do modern electronics face, what advantages do optical fibres have over electricity, and what technologies do optical systems need?

What challenges do modern electronics face?

Since the development of the first transistor, engineers have been able to rely on the constant shrinking of semiconductors to develop new technologies. The first processors allowed for basic calculator systems to be manufactured, while the immediate next generation of processors (taking no more than a year or two) allowed for basic computers with programming capabilities to be manufactured. The next generation after that brought about graphical displays, allowing information to be represented in more human-readable formats, and the generation after that introduced more complex peripherals, which made computers far more practical for the average user.

But no matter the electronic device being developed, it is the shrinking of electronic components that has primarily fuelled technological developments. Shrinking components not only allows for more parts to be integrated into devices but also helps to improve performance in terms of efficiency and speed. For example, reducing the size of a transistor reduces the current it consumes, increases the rate at which it can switch, and even lowers the voltage at which it operates.

However, the atomic nature of the universe means that transistors have a minimum finite size, and once this figure is reached, technology will no longer be able to improve by simply reducing the size of transistors. While transistors can be made using individual atoms, such devices are unlikely to exist due to the technical difficulties faced with fabricating a trillion interconnected transistors. Instead, transistors will likely be manufactured with monolayers surrounded by bulk material, but no commercial transistor will ever be one atom for the gate, one atom for the drain, and one atom for the source.

But it is not just the size of transistors that engineers are starting to face challenges with; data transmission is another critical barrier limiting technological progress. For example, an extremely fast CPU will face bottlenecks if external memory devices are significantly slower, thus resulting in the CPU having to idle during data transfers.

Finally, trying to transfer data at high speed along wires and traces introduces all kinds of challenges that further limit bandwidth. For example, long lengths of wire can be highly susceptible to external electromagnetic interference (EMI), which worsens signal integrity. This can be overcome with the use of larger voltages and slower speeds, but the result of such actions is a reduction in bandwidth. Twisted pairs can help provide immunity to EMI, but this increases both the cost of cables and the complexity of transceivers.

What advantages do photonic optical systems present?

One area that shows real promise in providing continual technological advancements is photonics engineering, combining traditional electronics with optical systems. But what exactly is it about optical systems that make them highly advantageous?

When it comes to data transmission, no technology comes close to the bandwidth of optic cables. In fact, the bandwidth of fibre optic cables is so great that current technology hasn’t come close to fully utilising the available bandwidth. This was recently demonstrated when researchers transmitted the equivalent of all internet traffic through a single fibre optic cable.

The reason why fibre optics are so advantageous comes down to several reasons. The first is that the high frequency of light allows it to be modulated at extremely high frequencies. Considering that visible light has a frequency range of between 400THz and 700THz, this translates to potential data transmission rates of 400Tbps and 700Tbps, assuming that a single pulse of light can be sent as a single cycle of a wave.

The second reason why light offers significantly greater bandwidths comes down to the fact that a large number of frequencies (400THz to 700THz) results in the possibility for many different independent channels. As individual frequencies of light do not interfere with each other, it is possible to have a single fibre optic cable carry multiple frequencies of light simultaneously. So long as the receiving end of an optic cable has a prism or diffraction grating, these channels can be individually separated and sent to independent detectors. 

The third reason that makes optical systems highly advantageous comes down to the bidirectional nature of fibre optics. While electrical cables can only carry one signal at a time in one direction, fibre optics can transmit and receive on a single cable simultaneously. Two light beams travelling down a cable from opposite ends do not interfere with each other, and this not only increases the bandwidth of each cable but also reduces cable complexity.

Finally, a single cable can have two identical wavelengths of light sent down at opposite ends without the two interfering with each other. Thus, a pair of identical transceivers can be used at either end, simplifying design and increasing the bandwidth capabilities of the fibre optic cable. 

What technologies do optical systems need?

If optical technologies are to become commonplace in electronics, there are a few technologies that need to be developed. 

The first is the need for on-chip optical transceivers that integrate optical components directly onto chips. Currently, transceivers are mounted onto PCBs that sit outside of chips, resulting in an electrical connection between a chip and a fibre optic. Such a design limits the maximum bandwidth capabilities while adding to system complexity, and this makes using optical cables problematic. 

The second is that transceivers need to be vastly improved in performance. While optical cables provide many advantages, the electronics that support them are unable to fully utilise the speeds that optical cables can provide. This means that transceivers used with optical systems can often be slower than a differential pair over short distances. In order to make the most of optical systems, transceivers need to increase in speed, and this will require the exploration of new photonic semiconductors.

The third technology that is desperately needed is optical interposers and optical PCBs. If chips can be developed with integrated optical ports, the need for PCBs with integrated waveguides will become essential as it will allow chips to transmit data over PCBs via optical links. Not only would this help reduce system complexity (from the perspective of part count), but it will also allow extremely high-speed connections between photonic parts. For example, future CPUs may utilise an optical bus for RAM and network cards while using an electrical bus for slower peripherals. 

Overall, photonic technologies present an exciting opportunity for engineers, and there is no doubt that it will dominate the electronics market in the far future. But if we are to get photonics up and running, we need to start considering how we can integrate photonics into everyday devices and how to create the infrastructure necessary to support it.