Programming Light on a Chip

A new integrated photonics platform that can store light and electrically control its frequency in an integrated circuit. (Source: Loncar Lab, Harvard SEAS)

Researchers from the Harvard John A. Paulson School of Engi­neering and Applied Sciences SEAS have developed a new inte­grated photonics platform that can store light and elec­trically control its frequency in an inte­grated circuit. The platform draws inspi­ration from atomic systems and could have a wide 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,” said 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 photons. That was before SEAS researchers, led by Marko Loncar, the Tiantsai Lin Professor of Electrical Engi­neering, developed a technique to fabricate high-perfor­mance optical micro­structures using lithium niobate, a material with powerful electro-optic pro­perties. 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,” said Cheng Wang, 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 percent effi­ciency, one photon at a time,” said Loncar. “This would enable the reali­zation of a quantum cloud – a dis­tributed network of quantum computers connected via secure optical communi­cation channels.” (Source: SEAS)

Reference: M. Zhang et al.: Electronically programmable photonic molecule, Nat. Phot. 13, 36 (2018); DOI: 10.1038/s41566-018-0317-y

Link: Laboratory for Nanoscale Optics, John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, USA

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