A circuit that lets a radio send and receive data simultaneously over the same frequency could supercharge wireless data transfer. The circuit makes it possible for a radio to send and receive signals on the same channel simultaneously – something known as “full-duplex” communications. That should translate to a doubling of the rate at which information can be moved around wirelessly.
Today’s radios must send and receive at different times to avoid drowning out incoming signals with their own transmissions. As a smartphone accesses the Internet via a cell tower, for example, its radio flips back and forth between sending and receiving, similar way to the way two people having a conversation take turns to speak and listen.
Circuit implementation of the non-reciprocal coupled-resonator loop at radio frequencies.
The new circuit design avoids magnets, and uses only conventional circuit components. “It’s very cheap, compact, and light,” says Andrea Alù, the associate professor who led the work. “It’s ideal for a cell phone.”
The two-centimeter-wide device could easily be miniaturized and added to existing devices with little modification to the design. “This is just a standalone piece of hardware you put behind your antenna.”
Alù’s circulator design looks, and functions, like a traffic circle with three “roads,” in the form of wires, leading into it. Signals can travel into, or out of, the circle via any of those wires. But components called resonators spaced around that circle force signals to travel around it only in a clockwise direction.
Alù says that his circulator can easily be adjusted to work at a wide range of frequencies, and that he is exploring options for commercializing the design. The circuit could, for instance, help simplify and improve technology being tested by some U.S. and European cellular carriers that uses a combination of software and hardware to allow full-duplex radio links
Magnetic-free non-reciprocity with angular-momentum biasing
Non-reciprocal components, which are essential to many modern communication systems, are almost exclusively based on magneto-optical materials, severely limiting their applicability. A practical and inexpensive route to magnetic-free non-reciprocity could revolutionize radio-frequency and nanophotonic communication networks. Angular-momentum biasing was recently proposed as a means of realizing isolation for sound waves travelling in a rotating medium, and envisaged as a path towards compact, linear integrated non-reciprocal electromagnetic components. Inspired by this concept, here we demonstrate a subwavelength, linear radio-frequency non-reciprocal circulator free from magnetic materials and bias. The scheme is based on the parametric modulation of three identical, strongly and symmetrically coupled resonators. Their resonant frequencies are modulated by external signals with the same amplitude and a relative phase difference of 120°, imparting an effective electronic angular momentum to the system. We observe giant non-reciprocity, with up to six orders of magnitude difference in transmission for opposite directions. Furthermore, the device topology is tunable in real time, and can be directly embedded in a conventional integrated circuit.
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