Inside the world’s largest data center, the Citadel by Switch. Source: TechVision
Optical communication has been around for millennia, while the earliest electrical device created to do so was the photophone, invented in 1880. Fast forward to the present, the potential of optics and photonics for communication is rapidly expanding and will be the foundation of future communication systems. This article provides an overview of the data communications applications where integrated photonics will make a significant impact in the coming decades.
The combined storage capacities of all the data centers of the world surpass 13 Exabytes. For context, 1 Exabyte is roughly equal to 1 billion Gigabytes. This number is only set to grow as new possibilities open up in the world of Artificial Intelligence (AI), the Internet of Things (IoT), and Big data.
As the amount of data transfer increases, the conventional copper cables used for interconnecting the servers tend to bottleneck the bandwidth of the entire system. Typically, a copper cable hits its limits within a few Gbps, whereas the limits of an optic fiber are purely theoretical.
This is the reason why making use of Integrated Photonics and optic fibers present as the best way to combat the bottleneck. The crazy hundreds of GBps or TBps transfer speed and ultra-low latencies required in the data centers are realizable with PICs. But the applications of PICs are not just limited to that. Instead of simply replacing all the copper wires with optic cables, silicon photonics can be used to make onboard components like high-bandwidth transmitters and receivers.
PICs can be used for anything from enabling communication between two chips on a Printed Circuit Board (PCB) to long-haul communications for data center interconnects. The possibilities are endless. A significant improvement in the performance of data centers can be achieved by using optic fiber communication and PICs in data centers.
Another issue that needs our attention is the increasing energy demand of the data centers. Data centers are estimated to consume more than 3% of the world’s total electricity, which seems relatively small, but with the voracious demand for connected devices, cloud computing, and systems, the potential for this to exponentially jump is viable.
Cooling systems alone account for the highest energy consumption within the data centers. Compared to conventional electronics, systems that are powered by photonics generate a lot less heat. Hence, PICs don’t require any dedicated cooling systems; and not having dedicated cooling systems eventually reduce the overall electricity consumption. 
Fiber-optic communication is probably among the earliest applications of photonics. The technology works on the principle of total internal reflection. First, the data at the source is encoded into optical signals. These signals are sent via an optic fiber to the receiver, where the signals are converted back to their original forms. The signals are reflected multiple times internally in the core of the communication link before finally reaching the destination.
Optic fiber is the fastest mode of wired communication known yet. The first optic fiber communication systems were developed by German physicist Manfred Börner back in the year 1965. It was then the idea of reducing the attenuation of optic fibers below 20 dB/Km seemed possible. In the decades that followed, developments in optic fibers led to a drastic reduction in the attenuation levels, and optic fibers with attenuation of under 4 dB/Km were made available. This reduced the number of repeaters required between a link, ultimately bringing down the cost of the setup.
Even though the initial establishment of optic fiber communication seemed higher at first, over the long run, the technology emerged as an affordable alternative to conventional copper wires. This caught the interest of telecom companies that started adopting it for long-range communication. Today, the technology has become the most widely accepted mode of wired communication between cities, states, and nations.
The world is shifting from vehicles that run on fossil fuels to electric and hybrid vehicles. While Electric Vehicles (EVs) are completely powered by electricity, hybrid vehicles can smartly switch between petrol/diesel and electricity.
But a truly smart EV is much more than just a vehicle powered by electricity. It is a complete package of Advanced Driver Assistance Systems (ADAS) enhancing the traveling experience. There is a lot of real-time computing occurring, and with self-driving vehicles, the amount of computing and communication speed required is even higher.
The collection (and processing) of data from all the sensors in the electric vehicle can be done faster with integrated photonics. Check out our previous article, The Road Ahead for Integrated Photonics in Automotive, for more on the topic.
5G networking services have recently picked up pace in different parts of the world, and we’re yet to hit its limits. The next generation of mobile networks is anticipated to be rolled out by the end of this decade, and integrated photonics has the potential to play a key role in the development of this technology. 
6G could be based on photonics defined radio.  This will bring the benefits of optics to mobile communication. We are still not sure how fast the future network will be, but if speculations are to be believed, the speeds could touch a whopping 1 TBps mark. The technology might even bring free-space optical communication to the table. 3D holographic videos, 8K streaming, AR/VR, cloud gaming, smart vehicles, and cities are just some areas where 6G is set to bring big changes.
There are some significant hurdles to cross when it comes to making photonic communication a widely implemented technology. Dispersion is one such problem that arises due to imperfections in the design of optic fibers (birefringence). This affects long-distance photonic communication. Optical systems also suffer from harsh crosstalk. Then there are unwanted signals in a communication channel (as in a telephone, radio, or computer) caused by transference of energy from another circuit. Another scalability problem stems from the acute shortage of skilled engineers and technicians in the photonics industry. As a result of all the challenges, the scaling of integrated photonics has been almost 10x slower than conventional electronic ICs. 
In this article, we discussed the basic principles of PIC-based communication and explained the various applications of the technology. We also listed some of the challenges that researchers face today when working with PICs.
It is necessary to understand that this is just a beginning for integrated photonics, much like how the period of the 1960s and 1970s was for electronics. The next decade is crucial for the research and development of integrated photonics, and its use in applications such as data centers not only provides benefits for speed but can help deliver a more energy-efficient future.
About the sponsor: PhotonDelta
PhotonDelta is a growth accelerator for the Dutch integrated photonics industry. PhotonDelta works with partners across the industry, including universities, startups, and established foundries, to develop a solid industry growth strategy and funding opportunities that will enable the integrated photonics industry to reach its potential. PhotonDelta has developed several roadmaps that outline growth paths for Integrated Photonic technologies, including automotive and biosensing. They are currently working on a data and communications roadmap that we will outline in our next article. You can register now for the launch of the roadmap here.
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