Tapered optical fiber addresses problem posed by Brillouin scattering

When optical beams, consisting of photons, journey by way of fibers, they trigger vibrations that generate acoustic waves, consisting of phonons. The phenomenon, referred to as Brillouin scattering, has been harnessed by researchers to optomechanically “couple” acoustic waves with gentle waves. This coupling permits info carried by photons to be transduced, or transformed, to the phonons, which journey practically one million instances extra slowly than gentle waves.

Opto-acoustic coupling has enabled researchers to learn and manipulate the transduced info extra simply. To date, nevertheless, most of the Brillouin scattering methods researchers have used depend on customary fiber geometries that trigger acoustic waves to die out rapidly, limiting the efficacy of the coupling.

Now, utilizing an optical fiber with a micron-sized waist, University of Rochester researchers have demonstrated the best way to couple propagating optical waves and long-lived acoustic waves, with sturdy optical-acoustic interactions.

“This is a unique and desirable combination that has not previously been achieved,” says Wendao Xu, a Ph.D. candidate within the analysis group of William Renninger, assistant professor at Rochester’s Institute of Optics. Xu is the lead creator of a paper in Optica describing the breakthrough.

The breakthrough allows info carried by a lightweight pulse to be quickly saved in slowly propagating acoustic waves lengthy sufficient for a second pulse of sunshine to “read” the data. The achievement might have functions for gentle storage, radio-frequency photonics filtering, and optical delay traces.

The analysis acquired Best Presentation Award on the WOMBAT 2022 Workshop on Optomechanics and Brillouin Scattering on the Max Planck Institute for the Science of Light, the place it was offered by co-author Arjun Iyer, additionally a Ph.D. candidate in Renninger’s lab.

“Wendao, Arjun, and our collaborators at the University of Tokyo did a great job in demonstrating the promise of this new platform and we are all excited as we begin focusing on next generation devices and real-world applications,” Renninger says.

Brillouin scattering in optical fibers: Overcoming challenges

“The amplitude of the acoustic wave keeps decreasing as it travels,” Xu explains. “Basically, all the high-impact Brillouin scattering that people are dealing with right now produce strong interactions, but the acoustic waves are high in frequency, in the gigahertz range. The higher the frequency, the shorter the wave can actually travel before it dies out.”

Xu’s tapered optical fiber system achieves each sturdy interactions and longer acoustic lifetimes. It consists of a multi-mode glass fiber with the cladding (coating) eliminated. By heating the middle of the fiber and concurrently making use of mechanical stress to stretch the fiber at each ends, Xu and his collaborators produced a tightly confined, symmetrical “waist” within the fiber.

This waist offers “an ideal optomechanical overlap yielding the strongest Brillouin coupling strengths observed to date from a fiber taper, and comparable to the largest optomechanical coupling strength for any system,” the paper notes.

Moreover, the lifetime of the phonons that the system generates—about 2 microseconds—is lengthy sufficient that info carried by a lightweight pulse might be quickly saved on this slowly propagating acoustic wave for a comparatively lengthy time frame, earlier than a second pulse of light reads the data.

A tapered optical fiber system

According to Iyer, Xu’s achievement is twofold. “One is the system, the tapered fiber device, which supports an acoustic wave family that people didn’t pay a lot of attention to previously,” he says. “The other is the process itself, using an interaction between two different optical spatial modes to get what we wanted.”

The course of—together with the physics concerned in reaching sturdy interactions with lengthy phonon lifetimes—might be tailored and utilized instantly to enhance present applied sciences, he says. For instance, detecting and filtering out undesirable radio frequencies in photonic filters, or producing fiber-optic transmission delays to compensate for delay variations in optical fiber techniques.

The tapered fiber system, however, whereas helpful for analysis, is probably going too fragile for actual world functions outdoors the lab, Iyer says. “These are micron-sized filaments of glass that are just hanging there,” he says.

However, the researchers are already exploring methods to package deal the system for actual world functions, Iyer says.