Researchers from the University of Maryland and the Army Research Laboratory have fabricated microscopic structures on the surface of ultrathin glass fibres that precisely control light as it travels through the fibre. The platform, dubbed surface nanoscale axial photonics (SNAP), could help signals move more smoothly along high-speed optical cables, which carry data in the form of light through pure silica glass.
Modern optical communications depend on fibres that are as defect-free as possible, because imperfections scatter light, distort the signal and cause data loss. The SNAP approach addresses this by creating microresonators, small structures that shape how light propagates. Dashiell Vitullo, who developed SNAP at the Army Research Laboratory, explained that the team shapes the surface of low-cost optical fibres at the nanoscale to control whispering gallery modes at the glass–air interface. He said the academic partners recognized the platform as an ideal tool for topological photonics because of its exceptional fabrication precision and ultralow signal loss.
Using this platform, the team investigated topological lattices of SNAP microresonators and explored novel topological heterojunctions. Topological light states are notable for their natural immunity to physical imperfections. Vitullo said the work helps researchers understand how to steer light reliably even when a system degrades, which he described as a critical step toward robust communication and sensing networks for the military.
To make the devices, the researchers used ultraprecise lasers to write nanoscale variations in the effective radius of the glass–air interface. A single fibre can host many microresonators, and they can be post-processed with laser heat to reshape the surface bumps with sub-angstrom precision. By contrast, photonic integrated circuits made by planar lithography typically need active tuning to compensate for nanometre-scale fabrication errors, a process that is highly energy intensive.
The SNAP microresonators showed propagation losses of less than 0.001 dB/cm, compared with an average of 0.01 dB/cm for photonic integrated circuits. The researchers chained together 21 microresonators to form an optical highway that steers light around obstacles, preventing scattering and maintaining transmission quality. The highway contained multiple interfaces between microresonators with different fabrication patterns, and understanding whether light stopped or passed smoothly at each boundary required new mathematical models. That understanding gave the team control over the signal and provided physics insights that could inform faster and more efficient optical cables.
Vitullo said SNAP offers a cost-effective, ultraprecise platform for photonic analogue Hamiltonian simulation. Traditional photonic chips can require researchers to measure and sort through many nonfunctional devices because of imperfect fabrication yield, whereas SNAP devices can be characterized and locally adjusted after fabrication. The microresonators also support multiple axial modes that provide built-in parameter sweeps, so a single inexpensive fibre device can do the work of many separate test structures.
The researchers are now looking at nonlinear optical behaviours, where light could be used to create synthetic dimensions that let them manipulate several aspects of light at once. In principle, this could increase the amount of data carried in an optical signal without changing the size of the fibre. Vitullo also suggested that such optics could help pave the way for quantum navigation sensors that do not rely on GPS.
The present work demonstrated one-dimensional models. The team plans to explore two-dimensional or higher-dimensional models, potentially by using cavity-enhanced nonlinear-optical effects to couple light between resonant frequency modes. Vitullo said scaling to higher dimensions is key to building practical photonic analogue simulators capable of modelling complex quantum systems that overwhelm conventional computers. The research is published in Nature Communications.
Source: physicsworld.com
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