Microwaves interact with optical photons on a chip to change their frequency
Light frequency is changed in a controllable manner on a photonic chip containing lithium niobate components.
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS; Cambridge, MA) and from Stanford University (Palo Alto, CA) have developed a new integrated photonics platform that can store light and electrically control its frequency in an integrated circuit.1
The platform could have a range of applications including photonic quantum information processing, optical signal processing, and microwave photonics.
"This is the first time that microwaves have been used to shift the frequency of light in a programmable manner on a chip," says Mian Zhang, a former postdoctoral fellow in applied physics at SEAS, now CEO of Harvard-spawned startup HyperLight Corporation. "Many quantum photonic and classical optics applications require shifting of optical frequencies, which has been difficult. We show that not only can we change the frequency in a controllable manner, but using this new ability we can also store and retrieve light on demand, which has not been possible before."
Microwave signals are ubiquitous in wireless communications, but researchers thought they interact too weakly with optical photons. That was before SEAS researchers, led by Marko Loncar, developed a technique to fabricate high-performance optical microstructures using the nonlinear optical material lithium niobate.
Loncar and his team previously demonstrated that they can propagate light through lithium niobate nanowaveguides with very little loss and control light intensity with on-chip lithium niobate modulators. In the latest research, they combined and further developed these technologies to build a molecule-like system and used this new platform to precisely control the frequency and phase of light on a chip.
"The unique properties of lithium niobate, with its low optical loss and strong electro-optic nonlinearity, give us dynamic control of light in a programmable electro-optic system," says Cheng Wang, who is now an assistant professor at City University of Hong Kong. "This could lead to the development of programmable filters for optical and microwave signal processing and will find applications in radio astronomy, radar technology, and more."
Next, the researchers aim to develop even lower-loss optical waveguides and microwave circuits using the same architecture to enable even higher efficiencies and, ultimately, achieve a quantum link between microwave and optical photons.
"The energies of microwave and optical photons differ by five orders of magnitude, but our system could possibly bridge this gap with almost 100% efficiency, one photon at a time," says Loncar, senior author of the paper. "This would enable the realization of a quantum cloud – a distributed network of quantum computers connected via secure optical communication channels."
1. Mian Zhang et al., Nature Photonics (2018); https://doi.org/10.1038/s41566-018-0317-y