Energy-Efficient Frequency Comb Could Be Used for Quantum Encryption

A new design for a frequency comb that requires 1000 times less power than traditional combs uses organic molecules to generate combs in ultrahigh-quality (ultrahigh-Q) factor microcavities.

This is an image of an organic-molecule-enhanced frequency comb. A single input laser (left) enters the spherical frequency comb generator that includes a single layer of organic molecules (4-diethylamino[styryl]pyridinium, DASP). The light orbits inside the sphere over 10,000 times in a few nanoseconds, interacting with the molecules during each orbit and resulting in the generation of the frequency comb. Courtesy of Vinh Diep and Alexa Hudnut.

A University of Southern California (USC) research team has demonstrated a materials-driven strategy to generate low-threshold frequency combs in organic-silica hybrid microcavities. To verify its approach, the team used a self-assembly method to graft small molecules with large Kerr coefficients on the surface of optical resonators.

As a result of the precision of the monolayer formation, the ultrahigh-Q values of the devices were minimally affected. The large Kerr coefficients of the molecular monolayers significantly increased the overall nonlinearity of the device, improving optical parametric oscillation generation over nonfunctionalized devices by three orders of magnitude. The functionalized microcavities demonstrated high-efficiency parametric oscillation in the NIR and generated primary frequency combs with 0.88-milliwatt thresholds.

Professor Andrea Armani said, “Organic optical materials have already transformed the electronics industry, leading to lighter, lower-power TVs and cellphone displays, but previous attempts to directly interface these materials with lasers stumbled. We solved the interface challenge. Because our approach can be applied to a wide range of organic materials and laser types, the future possibilities are very exciting.”

The reduced size and power requirements for the USC team’s frequency comb design could be particularly useful for advancing data encryption technology.

The team further believes that its strategy could provide a universal approach for optimizing integrated photonic devices with novel functionalities. The process that enables the comb to be generated is distinctly different in the two material classes. The combination of highly nonlinear organic molecules with integrated nanophotonics could open the door to a wide range of organic-hybrid photonic technologies for frequency combs, ultrafast optical modulations, all-optical switching and quantum information processing.

The research was published in Science Advances (doi: 10.1126/sciadv.aao4507).