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The optical interconnect refers to any system of transmitting signals from one part of an integrated circuit to another using light and are highly being used in applications, such as telecommunication and data communication, and further providing connectivity solutions in the end-user industries, such as military and aerospace and automotive.
One major motivation for this transition comes from an important trend in the microelectronics industry which aims to increase the parallelism in computation by multithreading, by building large-scale multichip systems, and, more recently, by increasing the number of cores on a single chip. As users continue to demand greater computing performance, chip designers plan to increase this number to tens or even hundreds of cores. This multicore approach, however, only makes sense if each core can receive and transmit large messages from all other cores on the chip simultaneously. The individual cores located on today’s multicore microprocessors communicate with one another over millions of tiny copper wires.
However, this copper wiring would simply use up too much power and be incapable of transmitting the enormous amount of information required to enable massively multicore processors. In electrical interconnects, nonlinear signals (e.g., digital signals) are transmitted by copper wires conventionally, and these electrical wires all have resistance and capacitance which severely limits the rise time of signals when the dimension of the wires are scaled-down.
The performance of such high-performance chips is then not only limited by the amount of transistors but also limited by the amount of signals that can be transferred between cores or to another chip nearby. This communication/interconnect bottleneck becomes more severe when the number of cores on a single chip increases. The International Technology Roadmap for Semiconductors (ITRS) has highlighted interconnect scaling as a problem for the semiconductor industry.
An alternative solution to this problem has been proposed that interconnects the computing cores using pulses of light in an on-chip optical network based on silicon nanophotonic ICs. Optical solution are used to transmit signals through long distances to substitute interconnection between dies within the integrated circuit(IC) package. In integrated circuits optical interconnects refer to any system of transmitting signals from one part of an integrated circuit to another using light.
Optical interconnects emerged as a promising alternative that offers high throughput, low latency, and reduced power consumption. Just as telecommunications carriers replaced copper wires with optical fiber to exploit the fiber’s speed and capacity advantage over copper, researchers anticipate that Si nanophotonics, especially chip-scale optical components based on photonic crystal technology, will potentially enable production-capable data transmission at faster speeds than metallic interconnects on a chip-sized scale.
Particularly in telecommunications, it was an obvious and essential step from electrical to optical interconnects to cope with the ever-growing demand for higher bandwidths, transfer speeds, and the necessity to handle large volumes of data between data centers around the world.
Applications
One of the major applications of optical interconnectivity is within data communication networks which include datacenter networks, wireless access networks, and wired access networks. Current data center networks, which are based on electronic packet switches, experiences an exponential increase in network traffic due to cloud computing development.
Today, data traffic is still growing dramatically, e.g., through a tremendous increase in cloud computing, 5G, video services or internet-of-things applications, to name but a few. Optical interconnects are an attractive solution for increasing bandwidth while reducing density and power consumption in high performance data communication systems.
Integrated optical interconnects are anticipated to provide solutions for the ever-growing demand for low-cost, power-efficient, high-bandwidth interconnects. Initially these needs are most acute in data centers for communication between servers, but optical interconnects are poised to also provide solutions for even shorter-reach communication links such as chip to chip as well as processor to memory. While data communications applications are driving significant investment, there is a wide range of other applications of integrated photonics that take advantage of this investment to enable many future technologies, particularly in sensing.
Optical interconnects will play an increasing role in future intelligent networks. Transport of information over distances as small as centimeters benefits from the multiterabit capacity of optical fibers when the data rates exceed 10 Gb s−1 and the total throughput of a processor exceeds l Tb s−1. At present, directly modulated VCSEL arrays, parallel fiber ribbons, and detector arrays are being applied to optical backplane capacity problems. In the future, additional higher functionality is expected to emerge for optical interconnects, including features such as cross-connect switches and data packet routing in the optical domain
Fiber-optic solutions
The optical interconnect between different hardware from short to very long distances is mostly based on optical fibers. Bundled as cables, they bridge up to thousands of miles in telecommunications, or just hundreds of yards in a computer network within a building.
Nowadays, optical interconnects are standard in data centers and broadband telecommunication networks. Commonly, fiber-optic cables are physically connected to transceivers with integrated lasers and detectors. They are capable of both transmitting and receiving an optical signal. Transceivers are available with varying form factors, specifications, speeds, and protocols.
Choosing the right transceiver for your application mainly depends on the type of data to be transported, and what speed and distance is best suited. Typical application areas for fiber-optic communication are intra- and inter-datacenter interconnects, FTTx (the last mile to premises), metropolitan optical fiber networks that interconnect services beyond FTTx, submarine communications cables on the seabed for very long distances, and many more.
Free-space interconnection
Free-space optical interconnect is another option for optical telecommunication or network connections. Its application is rather limited to special use cases where optical fibers are not applicable or are too expensive.
In free-space optical interconnects, the light signal propagates free in the atmosphere, space, or vacuum instead of being coupled into an optical fiber cable. It is a straight point-to-point link as free-space transmission cannot be bent in direction like a fiber optical cable and it is generally collimated with lenses or mirrors. In terrestrial applications, it has a maximum range of up to around two miles. Limiting factors are the weather conditions which cause scattering and damping of the signal, environmental light, and atmospheric distortions.
Long-distance free-space optical interconnects were established in some non-commercial cases for ground-satellite links. Also, satellite-to-satellite communication was realized mainly for demonstration purpose. Both approaches are aimed to be commercialized in the future.
Optical Interconnect technology
The key technologies enabling optical interconnects, include photonic active and passive components, photonic integration and assembly technologies, and related systems.
Polymer optical waveguide technology can enable high volumes of optical interconnects to be integrated into racks and onto motherboards, in a manageable and cost-effective manner. The requirements of polymer optical waveguides for high performance computing applications can be demanding, and must meet low optical loss targets, long-term reliability, and current cost constraints. A wide variety of materials have been used as polymer optical waveguides over the past decade, but not all are able to meet these requirements.
The two leading material systems that can meet these demands are based on polynorbornene and silicone. Both material systems are matured and ready for commercialization, and the manufacturing technology to bring these polymer waveguide systems forward is in place. In this chapter, manufacturing and performance of both materials are discussed in detail.
Components for optical interconnects
Besides the actual optical interconnect technologies, it is crucial how data is transferred via the optical interconnects. Here, wavelength-division multiplexing is the common approach today. Optical filters are essential components to multiplex or de-multiplex wavelength signals in optical networks. Iridian offers a wide choice of high-quality telecom filters for example for CWDM, DWDM, FTTx, free space and more. Please contact us for custom requirements and quotes on our telecom filters.
New polymer materials make fabricating optical interconnects easier
Silicon photonics technology allows light-based components to be integrated onto a tiny chip. Although many of the basic building blocks of silicon photonic devices have been demonstrated, better methods are needed to fabricate the optical connections that link these components together to make more complex systems.
In the journal Optical Materials Express, the researchers report new polymer materials that feature a refractive index that can be adjusted with ultraviolet (UV) light and low optical losses. These materials allow a single-mode optical interconnect to be printed directly into a dry film material using a low cost, high throughput lithography system that is compatible with the CMOS manufacturing techniques used to make chip-based photonic components.
“This technology makes it more practical to fabricate optical interconnects, which can be used to make the Internet — especially the data centers that make it run — more efficient,” said Norwood. “Compared to their electronic counterparts, optical interconnects can increase data throughput while also generating less heat. This reduces power consumption and cooling requirements.”
Replacing wires with light
The research expands on a vinylthiophenol polymer material system known as S-BOC that the investigators developed previously. This material has a refractive index that can be modified using UV illumination. In the new work, the researchers partially fluorinated S-BOC to improve its light efficiency. The new material system, called FS-BOC, exhibits lower optical propagation losses than many other optical interconnect materials.
“With this material we can use a process that we call SmartPrint to directly write optical interconnections between different optical printed circuit board elements, such as ion-exchange (IOX) glass waveguides provided by our collaborator Lars Brusberg from Corning Incorporated,” said Norwood.
To perform the SmartPrint process, a FS-BOC film is applied directly to a photonic component. No mechanical alignment is needed because the optical interconnect is made using a maskless lithography system that calculates where the interconnect is required by looking at the components and then writing the optical interconnect into the polymer using photoexposure. No additional processing is necessary other than briefly heating the polymer film to 90 °C. Because the fabrication approach is maskless, writing patterns can be changed without making a new photomask.
Creating a connection
To demonstrate the new materials, the researchers deposited them directly onto ion-exchange glass waveguide arrays, which are commonly used for integrated photonic devices. They then printed the coupling features needed to allow light to travel out of one IOX waveguide, propagate into the newly fabricated polymer interconnect, and then enter a second IOX waveguide adjacent to the initial IOX waveguide.
According to the researchers, the polymer optical interconnects worked well and showed low propagation and coupling losses, which means very little light was lost as it traveled within the interconnect or between it and the other components.
The researchers are now working to improve the material’s refractive index contrast and performance at high temperatures. “A higher refractive index contrast would make the material more tolerant to manufacturing variations while high temperature performance is likely needed for the interconnect to withstand solder reflow processes, which take place above 200 °C,” said Norwood.
Optical Interconnect Market
The Optical Interconnect Market was valued at USD 8,919.8 million in 2020, and is expected to reach to USD 21,711.3 million by 2026, while registering a CAGR of about 13.29% during the forecast period (2021 – 2026).
Global data traffic has recently increased significantly. The modern Internet is about more than just connectivity. In the age of the COVID-19, the Internet has evolved into a reliable connection with lower latency, faster speed, and greater bandwidth. Consumers are spending more time online than usual in the aftermath of the recent pandemic outbreak. This has had a significant impact on Wi-Fi access points, causing congestion and increasing the burden on interconnecting points. As a result, businesses are rushing to buy optical interconnects in order to mitigate the impact on interconnects. This pandemic has increased demand for optical interconnect, and this trend is expected to continue in the near future. However, due to raw material shortages, production of all fibre optics-related products has dropped by 25% in this pandemic situation.
Based on applications, Data communications dominated the Optical Interconnect market with a share of 9.48% in 2021 and is also anticipated to witness significant growth during 2022-2027, owing to growth of cloud computing applications and rise in number of data centers. Optical interconnects are used as an attractive solution for accelerating bandwidth while reducing density and power consumption in high performance data communication systems, thus raising its adaptability.
As per IEEE Communications Society survey in 2019, optical networks could provide up to75% energy savings in the data centers. Large data centers has significant interest in disposition of optical interconnect due to its high bandwidth and low latency. Such factors can be considered vital in boosting the market growth of optical interconnects in the long run.
Data centre deployment is difficult because it frequently involves managing multiple hardware platforms and technologies. The integration of traditional servers, networking equipment, and storage resources must be meticulously planned, flawlessly executed, and meticulously maintained. The increased deployment of data centres will be a significant growth driver for the market.
Cost has always been a major impediment to the growth of the optical interconnects market around the world. The high costs associated with the application of optical interconnect technologies have hampered the commercialization of this technology. As a result, cost will continue to be a major impediment to market growth.
Key players are II-VI Incorporated, InnoLight Technology (Suzhou) Ltd., NVIDIA CorporationLumentum Operations LLC, Molex LLC, TE Connectivity, Amphenol Corporation, Broadcom Inc., Sumitomo Electric Industries, Ltd., Juniper Networks, Inc., Fujitsu Ltd.
References and Resources also include:
https://www.iridian.ca/learning_center/overview-optical-interconnect-technology/
https://www.sciencedaily.com/releases/2022/04/220413131210.htm
