Columbia University engineers report development of the first magnet-free non-reciprocal circulator on a silicon chip that operates at millimeter-wave frequencies (frequencies near and above 30 GHz).
Signal transmission in most devices is characterized by reciprocity -- signals travel in the same manner in forward and reverse directions. Circulators and other nonreciprocal devices allow forward and reverse signals to traverse different paths and therefore be separated. Nonreciprocal devices have been built from special magnetic materials that make them bulky, expensive and not suitable for consumer wireless electronics.
The new mode for nonreciprocal transmission of waves is based on synchronized high-speed transistor switches that route forward and reverse waves differently. Think of two trains approaching each other at super-high speeds that are detoured at the last moment to avoid colliding.
The advance enables circulators to be built in conventional semiconductor chips and operate at millimeter-wave frequencies, supporting full-duplex or two-way wireless. Virtually all electronic devices currently operate in half-duplex mode at lower radio-frequencies (below 6 GHz) and devices are rapidly running out of bandwidth. Full-duplex communications, in which a transmitter and a receiver of a transceiver operate simultaneously on the same frequency channel, permits doubling of data capacity within existing bandwidth. New bandwidth that is not currently in use is rendered available by operating at millimeter wave frequencies of 30 GHz and above.
“This mm-wave circulator enables mm-wave wireless full-duplex communications, and this could revolutionize emerging 5G cellular networks, wireless links for virtual reality, and automotive radar,” said Harish Krishnaswamy, associate professor of electrical engineering.
The circulator can benefit autonomous driving technology, as self-driving cars require low-cost fully-integrated millimeter-wave radars. It could also be used to build millimeter-wave full-duplex wireless links for virtual reality headsets, which currently rely on a wired connection or tether to the computing device.