Time-gating technique converts near-infrared to visible light for clearer imaging through tissue and fog

University of Rochester researchers have demonstrated an imaging system that converts near-infrared light into visible light using a time-gating technique, enabling clearer images through scattering environments such as biological tissue and fog. The work, led by the laboratory of optics professor Robert Boyd, was published in Nature Communications.

Near-infrared imaging is widely used in biomedical diagnostics and autonomous vehicle LiDAR because it penetrates scattering media better than visible light. However, photons still deviate from their paths in dense tissue or fog, degrading image quality, and conventional near-infrared detectors rely on expensive materials that limit adoption.

The new system uses a thin film of indium tin oxide as an optical gate. Ultrafast light bursts open the gate for roughly one picosecond — the time light takes to travel a distance comparable to the size of a period at the end of a sentence — allowing only the earliest-arriving, least-scattered near-infrared photons to pass. Those photons are converted to visible light, which inexpensive silicon-based detectors can then capture.

Lead author Yang Xu, a recent Ph.D. graduate, described the gate as functioning like a camera shutter controlled by light rather than mechanics. By rejecting later-arriving scattered photons, the technique preserves spatial information that would otherwise be lost.

In a companion study published in Light: Science & Applications, the Rochester team collaborated with researchers at UCLA to combine the time-gating approach with machine learning. The artificial intelligence component reconstructs a larger target area from the limited field of view captured by the ultrafast gate, dramatically expanding the usable imaging region.

The researchers say the technology could improve cancer detection in biomedical imaging and enhance LiDAR performance for self-driving cars operating in fog or other adverse conditions. The system's reliance on silicon detectors rather than exotic materials also promises lower cost and broader accessibility.

Both studies involved contributions from optics alumna Saumya Choudhary and physics doctoral student Long Nguyen. The findings represent more than a decade of refinement of time-gating methods in Boyd's laboratory.