According to the team, the method could lead to faster, more powerful, and more efficient optical chips, which in turn could transform optical communications and optical signal processing.
"We have built integrated nanophotonic devices with the smallest footprint and largest operating bandwidth ever," assistant professor Nanfang Yu says.
The optical power of light waves propagating along waveguides is confined within the core of the waveguide – researchers can only access the guided waves via the small evanescent ‘tails’ that exist near the waveguide surface.
The guided waves are hard to manipulate and so photonic integrated devices are often large, taking up space and limiting the device integration density of a chip.
To reduce device size, the research team developed miniature optical nano-antennas that pull light from inside the waveguide core, modify the light's properties, and release light back into the waveguides.
The densely packed array of nano-antennas can achieve functions such as waveguide mode conversion within a propagation distance no more than twice the wavelength.
"This is a breakthrough considering that conventional approaches to realise waveguide mode conversion require devices with a length that is tens of hundreds of times the wavelength," Yu says. "We've been able to reduce the size of the device by a factor of 10 to 100."
The team created waveguide mode converters that can convert a certain waveguide mode to another waveguide mode; these are key enablers of mode-division multiplexing.
"Our waveguide mode converters could enable the creation of much more capacitive information pathways," Yu explains.
The researchers are exploring converting waves propagating in waveguides into strong surface waves, which could eventually be used for on-chip chemical and biological sensing.