One-Way Electronic Devices Double the Data Capacity of Wireless Networks
Researchers from Columbia University in New York City are the first team to construct non-reciprocal devices on a compact chip aimed to double the data capacity of current wireless networks.
The Principles of Reciprocity
Reciprocity is a theorem that is used to describe specific trade-offs in social psychology, electromagnetism, optics, and electrical networks. In relation to electrical networks, reciprocity is used to describe signal waves traveling in the same manner, in forward and reverse directions.
In 1948, researchers were attempting to create an ideal gyrator, a passive network element that violates the principles of reciprocity. That study paved the way for future engineers to create a gyrator that could potentially allow particles to travel in one fluid direction.
Routing waves in the same direction would break the principles of reciprocity. The non-reciprocal occurrence would result in one-way components such as circulators and isolators that are used in two-way communication.
This would double the data capacity of current wireless networks. The problem with components like gyrators is that they are bulky and expensive. There needs to be a more elegant design that can disrupt reciprocity at a smaller size and half the cost.
Microphotograph of the Columbia Engineering single-chip circulator with watt-level power handling. Image used courtesy of Columbia University
The Study: Breaking the Laws of Reciprocity
Over the last four years, Harish Krishnaswamy, an electrical engineering professor at Columbia University in the City of New York has led a team of researchers to conduct studies on utilizing non-reciprocity in wireless applications. In 2017, Krishnaswamy and his team were able to demonstrate the non-reciprocal transmission of waves.
Now in 2020, the team was able to fabricate a new compact chip that performed 25 times better than before and can handle several watts of power. This will be the foundation of potential innovation for 5G networks, autonomous vehicles, quantum computers, and virtual reality (VR).
Their new fabricated chip became a leading performer in a DARPA SPAR (Signal Processing at RF) program that focuses on miniaturizing devices to improve performance metrics. Power handling is one of the most important metrics for circulators and isolators.
Krishnaswamy’s new chip is able to transmit signals while still experiencing several watts of power. “For these circulators to be used in practical applications, they need to be able to handle watts of power without breaking a sweat,” stated Krishnaswamy.
Non-Reciprocal Devices For Automotive and VR Applications
Looking at automotive applications, autonomous vehicles require low-cost, fully integrated radars that work alongside ultra-sound and camera-based sensors. These devices need to work in all weather conditions and during all times of the day.
These radars inherently need to be full-duplex; a duplex radar enables simultaneous transmission and reception but at two separate frequencies. Krishnaswamy’s team discovered that a full-duplex, closed-loop design would achieve non-reciprocal circulation.
The circulator could also be used to build millimeter-wave (mm-wave) full-duplex wireless links for VR headsets. Virtual reality currently relies on a wired connection or tether to a computing device. A large amount of data is received and transmitted during the use of wireless VR, which requires low latency, bi-directional communication, thus making components of a non-reciprocity ideal.
A figure demonstrating non-reciprocity based on active transistors or nonlinearity. Information provided by Aravind Nagulu, Negar Reiskarimian, and Harish Krishnaswamy. Image used courtesy of Columbia University
Non-Reciprocal Devices To Redefine 5G and Quantum Computing
Defying the principles of reciprocity will allow the development of high-power transmitters for communication applications and full-duplex wireless radios. Wireless, full-duplex communication allows transmitters and receivers to communicate with each other through the same antenna without interference. And thanks to the power metrics of the circulator, these non-reciprocal components will be suitable for cellphone transmitters that have an output of a single watt of power.
Future studies will be done to capitalize on the development of this new compact chip that will deal with quantum computing. Quantum computers use components like circulators and isolators to read qubits without disturbing them. Magnetic circulators and isolators are currently used in cryogenic quantum computers.
However, they are not ideal due to their large size and cost. Krishnaswamy, along with his colleagues, plan to use superconducting Josephson Junctions, which is used to make a qubit, to realize chip-scale cryogenic circulators that can be directly integrated with qubits. Avoiding traditional magnetic circulators and isolators will present a smaller and cost-effective solution.
Krishnaswamy and his team at Columbia University have figured out how to build one-way devices on a compact chip, defying the principles of reciprocity. This development can lead to the creation of high-power transmitters for communication as well as transform VR, automotive, and quantum applications.