A two-photon vision-based retinal display for augmented reality applications

Seeing the Unseen: Next-Generation AR Goggles Based on Two-Photon Vision

A decade ago, Polish physicists from Nicolaus Copernicus University in Toruń and the International Centre for Eye Research (ICTER) were the first in the world to discover two-photon vision - a phenomenon allowing humans to perceive short pulses of infrared radiation. This discovery was remarkable because infrared light generally falls outside the human eye's visible spectrum. Today, scientists are identifying practical applications for two-photon vision, with one promising avenue being advanced smart glasses designed for military and medical deployment. Prototype development is currently underway at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS), led by Katarzyna Komar, PhD Eng., a co-discoverer of the phenomenon. The project is funded under the Proof of Concept action by the European Funds for a Modern Economy 2021 - 2027 (FENG) program and implemented by the Foundation for Polish Science (FNP).

The light-sensitive component of the human eye responsible for vision is the retina. It comprises roughly 120 million rods and 6 million cones - specialized cells containing visual pigments. These pigments absorb light photons, triggering a cascade of chemical reactions that generate an electrical signal processed by the brain into an image. Human visual pigments absorb photons and respond to electromagnetic waves spanning approximately 380 nm to 780 nm (from violet to red). Wavelengths outside this range, such as infrared (above 780 nm) or ultraviolet (below 380 nm), remain invisible without specialized equipment.

Because infrared photons have longer wavelengths, their individual energy is insufficient to excite visual pigment molecules in the eye. However, when two infrared photons strike the retina simultaneously, they "join forces" and are absorbed together by the visual pigments, triggering the same reaction cascade as a single photon of visible light.

"In essence, the brain is tricked into assuming a single photon of visible light was absorbed by the retina. In reality, it absorbed two infrared photons, each carrying half the energy. This is the foundation of two-photon vision, enabling us to perceive short-pulse laser beams in the near-infrared spectrum (ranging from 800 nm to 1300 nm). These beams are perceived as distinct colors, corresponding approximately to half their actual wavelength," explains Katarzyna Komar, PhD Eng.

Leveraging this two-photon mechanism, Dr. Komar plans to build augmented reality (AR) glasses that expand the human visual spectrum into the near-infrared. "In many professional settings, having supplementary information overlaid directly onto the visual field - without glancing at an external display - is invaluable. Such augmented reality capabilities hold clear utility in medicine, defense, and education. The primary challenge lies in miniaturization, as existing setups for investigating two-photon vision are large optical table assemblies. Despite this ambitious goal, we successfully built a next-generation AR glasses prototype within a single year," states Katarzyna Komar, PhD Eng.

Katarzyna Komar, PhD Eng., graduated with a degree in technical physics from Gdańsk University of Technology and earned her PhD in technical sciences at the Institute of Fluid-Flow Machinery of the Polish Academy of Sciences. Early in her career, she applied laser spectroscopy techniques to cultural heritage diagnostics. Since 2011, she has been affiliated with the Institute of Physics at Nicolaus Copernicus University in Toruń, and since 2020, also with the International Centre for Eye Research in Warsaw. For over a decade, her research focus has centered on functional and structural ocular imaging. She specializes in designing optical systems and psychophysical methods to investigate two-photon vision and integrate them with eye-imaging technologies. Throughout her career, she has participated in numerous national and international research initiatives and completed scientific visits and fellowships at Case Western Reserve University (Cleveland, USA), the University of California, Irvine (USA), Heidelberg University (Germany), and the University of Murcia (Spain). From 2017 to 2022, she led an NCN OPUS grant dedicated to two-photon vision. She currently leads another NCN OPUS grant aiming to quantify the sensitivity of specific retinal photoreceptor types to two-photon vision, paving the way for two-photon photometry. This research is conducted at the International Centre for Eye Research (ICTER), a unit of IPC PAS.