Waves — whether they are light waves, sound waves, or any other kind — travel in the same manner in forward and reverse directions. This is known as the principle of reciprocity. If waves could be routed in one direction only — breaking reciprocity — many applications could be transformed by enabling “one-way” components such as circulators and isolators that enable two-way communication, which could double the data capacity of today's wireless networks. These components are essential to quantum computers that read a qubit without disturbing it. They are also critical to radar systems in self-driving cars or those used by the military.
Researchers have built a high-performance non-reciprocal device on a compact chip with a performance 25 times better than previous work. Power handling is one of the most important metrics for these circulators; the new chip can handle several watts of power — enough for cellphone transmitters that put out a watt or so of power.
Traditional “one-way” devices are built using magnetic materials, such as ferrites, but these materials cannot be integrated into modern semiconductor fabrication processes because they are too bulky and expensive. While creating non-reciprocal components without the use of magnetic materials has a long history, advancements in semiconductor technology have brought it to the forefront.
The original discovery was made while trying to build a different kind of device called a duplexer, which enables simultaneous transmission and reception but at two separate frequencies. In experiments with the circuit, it was connected in a loop, exhibiting the non-reciprocal circulation behavior.