Design enhances power scalability and selectivity of orbital-angular-momentum light

Some helical light fields can carry orbital angular momentum, which makes them potentially appealing for several optical devices, such as super-high-resolution microscopy and laser machining. However, these applications require such light to be pure, power-scalable and able to select specific wavelengths on demand.

A paper in APL Photonics has introduced a method of generating power-scalable orbital-angular-momentum light at different wavelengths. This technique, which the authors demonstrated both theoretically and experimentally, relies on the mixing of four orbital-angular-momentum-carrying wave modes to improve their device’s wavelength selectivity and power efficiency over conventional means.

The authors’ experimental setup included lasers whose output were modulated into orbital-angular-momentum and spin-orbital-momentum light. This modulated light was inputted into an optical fiber, which contained a ring that could stably guide orbital-angular-momentum-carrying light over long distances. The resulting fiber output was characterized for its purity and behavior using different analyzers.

By testing multiple combinations of energy states, the authors showed their device matched theoretical predictions and increased the number of degrees of freedom by which desirable results could be obtained. Notably, the authors showed that these processes, unlike previous attempts, were power-scalable, demonstrating a pure L=9 orbital-angular-momentum state with about 2.8 kilowatts generated at 888.8 nanometers.

Co-author Xiao Liu said the authors plan to continue improving their device.

“We aim to optimize our system better to understand and push to the limits of the highest FWM (four-wave mixing) efficiency,” Liu said. “We are also interested in breaking the bandwidth restrictions of inter-modal FWM processes.”

Source: “Nonlinear four-wave mixing with enhanced diversity and selectivity via spin and orbital angular momentum conservation,” by X. Liu, E. N. Christensen, K. Rottwitt, and S. Ramachandran, APL Photonics (2020). The article can be accessed at https://doi.org/10.1063/1.5130715 .