At the IEEE International Solid-State Circuits Conference in February, Krishnaswamy's group unveiled a new device: the first magnet-free non-reciprocal circulator on a silicon chip that operates at millimeter-wave frequencies (frequencies near and above 30GHz). Following up on this work, in a paper (DOI 10.1038/s41467-017-00798-9) published in Nature Communications, the team demonstrated the physical principles behind the new device.
Most devices are reciprocal – signals travel in the same manner in forward and reverse directions. Nonreciprocal devices, such as circulators, on the other hand, allow forward and reverse signals to traverse different paths and therefore be separated. Traditionally, nonreciprocal devices have been built from special magnetic materials that make them bulky, expensive, and not suitable for consumer wireless electronics.
A new way to enable nonreciprocal transmission of waves was developed by the the research team that uses carefully synchronized high-speed transistor switches that route forward and reverse waves differently. In effect, it is similar to two trains approaching each other at super-high speeds that are detoured at the last moment so that they do not collide.