Pulses of light could encrypt data, protect cryptocurrencies

Technology News | January 12, 2018

By Rich Pell

The frequency comb is tiny compared to current traditional frequency combs that can be as large as a refrigerator. This tool that increases the potential applications of lasers by converting a single wavelength into multiple wavelengths, effectively creating tens to hundreds of lasers from a single laser. It would find applications in heatlhcare, IoT, mobile networks, cryptocurrencies and protecting thousands of miles of fiber optic cables under the oceans at risk of being hacked,

The small frequency comb was made possible by researchers Andrea M. Armani, Xiaoqin Shen, Rigoberto Castro Beltran, Vinh M. Diep, and Soheil Soltani – using a fundamentally different approach to invent a new method to create a frequency comb where current state-of-the-art materials such as silicon are replaced with carbon-based or organic molecules. Attaching only a single layer of a 25-atom organic molecule to the surface of a laser, frequency combs were demonstrated with 1000x reduction in power, making them ideal for mobile applications.

Professor Armani, the Ray Irani Chair in Engineering and Material Sciences at the USC Viterbi School of Engineering, likens the change from conventional silicon to organic materials as analogous to the change of “gas to electric.” At the most basic level, the process that enables the comb to be generated is distinctly different in the two material classes.

“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,” said Armani, “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.”

Optical encryption of data

The first applications of frequency combs focused on detecting trace amounts of chemicals and high precision time-keeping. However, recently, with the advent of crypto-currencies and IoT, quantum cryptography has come to the fore to solve ever demanding cybersecurity issues.

When a data signal is traveling to its destination, it is packaged like a letter in a locked envelope. Just like any lock, some are easier to crack than others, and current encryption efforts have focused on creating increasingly complex and dynamic locks. However, one fundamental limitation with many current approaches is that it is not possible to detect when an encryption has failed.

Quantum encryption presents an alternative approach. Not only can more complex keys be implemented, but intrusions are immediately apparent through changes in the transmitted data signal.

While many strategies are being pursued to enable quantum cryptography, one of the leading contenders is based on a phenomenon called photon entanglement. Entangled pairs of photons must be created at exactly the same time with exactly the same properties. Enter frequency combs, which are effectively entangled photon generators.

This is an illustartion 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 10,000x in a few nanoseconds, interacting with the molecules during each orbit and resulting in the generation of the frequency comb. Image courtesy of Vinh Diep and Alexa Hudnut.

The first step in forming the frequency comb occurs when the primary laser generates a secondary pair of wavelengths. However, because of energy conservation, one wavelength must have higher energy and one wavelength must have lower energy. Additionally, the energies must sum to be exactly equal to the primary laser, and the two new wavelengths must appear at exactly the same time. Thus, frequency comb generators can be viewed as entangled photon generators.

While reducing the size and power requirements of the frequency comb were key technical hurdles, there are many integration and manufacturing challenges remaining before quantum cryptography on portable platforms will be commonplace.

Armani, a faculty member in the new USC Michelson Center for Convergent Bioscience, indicated that in addition to the important role that quantum encryption could play in securing our healthcare information in the future, frequency combs are also being used to improve the detection of cancer biomarkers.

The full study “Low threshold parametric oscillation in organically modified microcavities” is available in Science Advances.

www.usc.edu