With so many recent developments in silicon-based optoelectronics and fiber optic systems, it seems silicon will be the element not just associated with the technological developments of the past, but also those of the future.
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Of all the elements in the Periodic Table, silicon has become the one most closely associated with technology and technical developments. Probably the most famous application of silicon is its role as a semiconductor in electronic products, which is how it came to lend its name to one of the world centers for technological development: Silicon Valley.
The development of silicon-based transistors revolutionized computing and the ability to achieve more and more computational power has revolutionized many scientific fields in terms of the possibilities of the scale, accuracy, and level of detail that can be achieved in computational models. However, with a move towards exascale computing as the next generation in high-performance computing power, conventional electronics is facing a number of challenges.
One of the biggest problems for exascale computers is the huge amounts of data being generated need to be transferred. For large-scale computing facilities, hundreds of separate nodes all need to communicate and swap information to try and parallelize large-scale computations. Achieving this is where silicon may yet save the day again through the development of silicon-based optoelectronics for facilitating data transfer at the speed of light.
Optoelectronics is the light-based analog to electronics. Rather than relying on the control and transport of electrons to make circuits and carry information, optoelectronics systems use packets of light energy known as photons.
Current technologies making use of optoelectronics already include fiber optic communications, light-emitting diodes, many types of sensors, and photovoltaic devices like solar cells. Optoelectronic devices do not suffer from many of the limitations faced by conventional electronic circuits such as extensive problems with heat load making miniaturization beyond a certain scale challenging and limited data transfer and communication speeds.
As silicon was already being widely used in electronics, making optoelectronic devices from the same material was a natural progression. Fortunately, silicon has many desirable optical properties that make it an ideal candidate in optoelectronic devices, including a high refractive index and being easy to machine.
Silicon is the material that has dominated the creation of fiber optics for the telecommunications industry. Silicon-based fiber optic cables (normally silicon dioxide) are also commonly used in many laser and spectroscopy applications. Now, the ability of silicon to be used to both manipulate electrons and photons is being pushed to develop fiber optic devices and data links that will allow for record volumes of data transfer. Finding more efficient ways to transfer large bandwidths of information through fiber optic cables is a very important development as the data demands of Internet traffic and network use seem to be endlessly increasing.
Recent developments have made creating optical fibers with a pure silicon core much easier and more reliable through chemical vapor deposition processes. Most traditional optical fibers are still based on silica but have a glass core that is wrapped in a cladding made from a slightly different material.
Now, there are manufacturing processes capable of growing hundreds of meter-long silicon cores for optical fibers that have micrometer diameters. While fiber optics may be the tool of choice for telecommunications, growing fibers of high quality is still a highly technical and challenging process, demanding very high-purity silicon as well as clean manufacturing conditions.
The advantage of being able to create pure silicon cores is that it would allow for even better transmission efficiencies in many different wavelength regions. Highly crystalline silicon should be capable of transmitting infrared and terahertz radiation with very high efficiency and allow for the fiber optic to carry more power without causing any damage to the fiber itself.
Another avenue of development for silicon optoelectronics is not just finding ways to make pure silicon components but combining silicon with other types of materials that have desirable electronic and optoelectronic properties to create integrated circuits. Many 2D materials such as graphene and black phosphorous have very interesting properties, such as very high absorption cross sections when the materials are still only one atom thick.
The high cross-section makes them very efficient at absorbing light which could then be converted to other applications. With the excellent transmission properties of silicon in the infrared region, the 2D material layer could then be combined with a silicon waveguide to create a highly efficient optoelectronic device.
While the zero bandgaps in graphene limits some of its applications, black phosphorous has a bandgap that can be scaled with the number of layers of the material used and has excellent carrier mobility and unique anisotropy values. The hope is that combining the properties of silicon with 2D materials will facilitate the creation of highly effective and sensitive nanosensors for light or even more complex optical processes such as amplification or the generation of mid-infrared light on a chip.
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References and Further Reading
de la Iglesia, D., Garcia-Remesal, M., de la Calle, G., Kulikowski, C., Sanz, F., & Maojo, V. (2013). The impact of computer science in molecular medicine: Enabling high-throughput research. Current topics in medicinal chemistry, 13(5), 526-575. https://doi.org/10.2174/1568026611313050002
Goto, S., McGuire, D. K., & Goto, S. (2022). The Future Role of High-Performance Computing in Cardiovascular Medicine and Science-Impact of Multi-Dimensional Data Analysis. Journal of atherosclerosis and thrombosis, 29(5), 559-562. https://doi.org/10.5551/jat.RV17062
Heldens, S., Hijma, P., Werkhoven, B. Van, Maassen, J., Belloum, A. S. Z., & Van Nieuwpoort, R. V. (2020). The Landscape of Exascale Research: A Data-Driven Literature Analysis. ACM Computing Surveys, 53(2). https://doi.org/10.1145/3372390
Bernabé, S., Wilmart, Q., Hasharoni, K., Hassan, K., Thonnart, Y., Tissier, P., Désières, Y., Olivier, S., Tekin, T., & Szelag, B. (2021). Silicon photonics for terabit/s communication in data centers and exascale computers. Solid-State Electronics, 179(July 2020). https://doi.org/10.1016/j.sse.2020.107928
Gao, D., & Zhou, Z. (2022). Silicon-based optoelectronics: progress towards large scale optoelectronic integration and applications. Frontiers of Optoelectronics, 15(1), 2–3. https://doi.org/10.1007/s12200-022-00030-7
Peacock, A. C., Gibson, U. J., & Ballato, J. (2016). Silicon optical fibres–past, present, and future. Advances in Physics: X, 1(1), 114–127. https://doi.org/10.1080/23746149.2016.1146085
Kudinova, M., Bouwmans, G., Vanvincq, O., Habert, R., Plus, S., Bernard, R., Baudelle, K., Cassez, A., Chazallon, B., Marinova, M., Nuns, N., & Bigot, L. (2021). Two-step manufacturing of hundreds of meter-long silicon micrometer-size core optical fibers with less than 0.2 dB/cm background losses. APL Photonics, 6(2), 0–7. https://doi.org/10.1063/5.0028195
Youngblood, N., & Li, M. (2017). Integration of 2D materials on a silicon photonics platform for optoelectronics applications. Nanophotonics, 6(6), 1205–1218. https://doi.org/10.1515/nanoph-2016-0155