Let there be light


HorizonLight is a pretty amazing thing. The eclectic exhibit of colors that dazzles us comes from the magic of light. The visible light that our eyes can see is an electromagnetic radiation with wavelengths ranging from 400 to 700 nanometers (nm). Different colors have different wavelengths (source: NASA). When light is incident on any object, the surface of the object reflects some colors and absorbs the rest. As we know from physics, our eyes only perceive the reflected colors. The color of an object is not an inherent property of that object. The aurora borealis, the colorful Great Barrier Reef, the rainbows, starry and moonlit nights, green woods, the white Antarctic, the sunrise and the fireflies are just a few of mother nature’s magnificent showcases of light.

Light has played a significant role in communication technologies. Modern-day telecommunications are unimaginable without optical fiber communication technologies. Light signals of wavelengths ranging from 1260 to 1675 nm have been used for transmitting information using a single mode fiber (SMF). These wavelengths, which are invisible to the human eye, are confined in the fiber by total internal reflection. A single mode fiber is the type of fiber that allows only one mode of light ray. Readers might be familiar with wavelength division multiplexing (WDM) and more advanced dense wavelength division multiplexing (DWDM). These technologies multiplex multiple optical signals, each representing a data stream, onto a single fiber. With DWDM, it is possible to achieve a 40 Gbps or even higher data link.

Regardless of the human eye’s ability to see light, we can understand that light is very important in our life. The bandwidth available from a single optical fiber is 100 THz (terahertz) or 100,000 GHz (gigahertz), whereas the spectrum used by wireless communications goes from 1 MHz (megahertz) to nearly 5 MHz (source: “Broadband facts, fiction and urban myths”). As a result, a single optical fiber can carry 20,000 times more information than the entire radio frequency spectrum. Now that we have seen how optics is benefitting telecommunications, let’s have a look at how it is going to revolutionize next-generation computing.

In December 2012, IBM announced a commercially viable and cheap electronic-photonic optical chip. This breakthrough technology, called “silicon nanophotonics,” is capable of using light instead of electrical signals to carry information for future computing systems (source: IBM press release). This is Big Blue’s response to the challenges that have arisen from big data. Light can carry information by allowing a greater bandwidth and faster speed than an electrical wire. Thus this new technology will be able to move data faster between computer chips in servers, cloud data centers, large data centers and supercomputers by using optical signals and creating information superhighways. Thus it alleviates the bottleneck of congested data traffic and expensive traditional interconnects.

IBM silicon nanophotonics chip

Figure 1: Cross-sectional view of IBM silicon nanophotonics chip

Different optical components are integrated side-by-side with electrical components on this silicon nanophotonics chip in a standard 90 nm semiconductor fabrication. Integrated circuits (IC) allow integration of billions of transistors in microprocessors. Similarly, IBM’s industry-first breakthrough technology will allow shrinking of optical components into a smaller form factor. A variety of nanophotonics components, like modulators, germanium  photodetectors and ultra-compact wavelength division multiplexers will be placed alongside high-performance analog and digital complementary metal-oxide semiconductor (CMOS) circuitry (source: Silicon Integrated Nanophotonics).

Inside of IBM Silicon Nanophotonics chip

Figure 2: Information superhighways inside an IBM Silicon Nanophotonics chip

Figures 1 and 2 show the cross-sectional and angled view of the IBM silicon nanophotonics chip. In figure 1, the red feature on the left side of the cube is a photodetector, and the blue feature on the right side is a modulator. As I explained above, these nanophotonics components are fabricated side-by-side with silicon transistors (red sparks on the far right of the cube) on a standard 90 nm semiconductor fabrication. Nine levels of yellow metal wires connect nanophotonics circuits and silicon transistors.

In figure 2, we can see blue optical waveguides transmitting high-speed optical signals and yellow copper wires carrying high-speed electrical signals. This new integrated chip demonstrates transceivers to exceed a 25 Gbps data rate. Furthermore, a number of parallel optical data streams can be multiplexed into a single fiber using on-chip ultra-compact WDM devices. It is possible to achieve a data transfer rate of a terabyte per second or more, using WDM technologies to transfer data between distant parts of computing systems and to tackle the performance requirements of future optical communications needed in large data centers.

This new technology is based on IBM’s proof of concept from 2010. The most important thing is that optical components can be integrated alongside CMOS electrical circuitry using the existing fabrication process. Thus, it will provide a significant cost reduction.

These days, especially in this era of cloud computing, a single request from a user can invoke multiple servers within the same or different racks of the same or geographically separate data centers, storages and so on. One request does not involve just one processor. In today’s computing systems, processor power is not the limiting factor. Hundreds of processors are interconnected by means of copper wires in a big data center or in a supercomputer. Copper interconnects the limit maximum data transfer rate between processors and memory, and thus creates a bottleneck to process the massive amount of data being generated. We experience data congestion and latency despite having superfast microprocessors. Furthermore, these interconnects are expensive and not scalable.

The processors inside the integrated chip use electrical signals. But the chip, with help of its nanophotonics components, converts electrical signal into optical signal and gets the data ready for transmission. When the data arrives at another silicon nanophotonics chip, optical signal is converted into electrical signal. Optical signal can travel much faster than electrons in electrical wire and go a larger distance without attenuation and deterioration of signal quality. Thus this technology can seamlessly interconnect various components of large computing systems, whether a few centimeters or a few kilometers apart from each other.

Digital data is growing at a staggering rate. IBM’s new silicon nanophotonics chip will provide an information superhighway to transfer data at a terabit per second (Tbps) or more to undertake big data challenges. This chip ushers in a new optical technology to meet the performance requirements of future computing. In the future it is going to be the de facto standard for cloud computing, supercomputers and anything related to processing big data. The day is coming when lights will solve the bottlenecks in large computing systems. So, let there be light.

Shamim Hossain is an experienced technical team leader and project manager leading a number of complex and global projects with involvement in the full project lifecycle ranging from planning, analysis, design, test and build through to deployment. He is an IBM Certified Cloud Solution Advisor and Cloud Solution Architect. You can reach him on Twitter @shamimshossain.

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