Andrew Corselli
Researchers have used the centuries-old idea of pinhole imaging to create a high-performance mid-infrared imaging system without lenses. The new camera can capture extremely clear pictures over a large range of distances and in low light, making it useful for situations that are challenging for traditional cameras.
"Many useful signals are in the mid-infrared, such as heat and molecular fingerprints, but cameras working at these wavelengths are often noisy, expensive, or require cooling," said Research Team Leader Heping Zeng from East China Normal University. "Moreover, traditional lens-based setups have a limited depth of field and need careful design to minimize optical distortions. We developed a high-sensitivity, lens-free approach that delivers a much larger depth of field and field of view than other systems."
In Optica, the researchers describe how they use light to form a tiny "optical pinhole" inside a nonlinear crystal, which also turns the infrared image into a visible one. Using this setup, they acquired clear mid-infrared images with a depth of field of over 35 cm and a field of view of more than 6 cm. They were also able to use the system to acquire 3D images.
"This approach can enhance night-time safety, industrial quality control, and environmental monitoring," said Research Team Member Kun Huang from East China Normal University. "And because it uses simpler optics and standard silicon sensors, it could eventually make infrared imaging systems more affordable, portable, and energy efficient. It can even be applied with other spectral bands such as the far-infrared or terahertz wavelengths, where lenses are hard to make or perform poorly."
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Huang.
Tech Briefs: What was the biggest technical challenge you faced while developing this lens-free system?
Huang: The biggest challenge was to make a system that can "see" mid-infrared light clearly without using any lenses. Mid-infrared light carries valuable chemical and thermal information, but it’s difficult to detect because sensors are noisy and optical components are limited. We had to precisely synchronize ultrashort laser pulses and design a nonlinear crystal that could act as both a light converter and a virtual aperture. Balancing these optical conditions — so that we could get clear, stable, and sensitive imaging — was technically demanding and required a lot of optimizations.
Tech Briefs: Can you please explain in simple terms how it works?
Huang: It’s a bit like bringing the ancient pinhole camera back to life — but for invisible infrared light. In a normal pinhole camera, light passes through a small hole to form an image. In our system, that hole isn’t physical — it’s made of light inside a special crystal. The crystal not only acts as the pinhole but also changes the color of mid-infrared light into visible light, so a regular camera can capture it. Because this pinhole is optical and tunable, we can image scenes over a very large depth range and in low-light conditions, without using any lenses.
Tech Briefs: Do you have any set plans for further research?
Huang: Yes, we do. Our next steps focus on three main directions:
- Improving conversion efficiency and sensitivity — by refining the laser parameters and using advanced nonlinear materials to make the upconversion process more efficient.
- Adding dynamic control — we plan to introduce spatial light modulators to reshape the optical pinhole in real time, allowing the system to adapt automatically to different imaging scenarios.
- Making the system more compact — the current setup is still a proof-of-concept that relies on a complex laser system. With progress in integrated light sources and new materials, we aim to build a smaller, more practical version for real-world use.
Tech Briefs: Is there anything else you’d like to add that I didn’t touch upon?
Huang: Yes. This work is special because it bridges fundamental optics and real-world applications. It revives one of the oldest imaging ideas — pinhole imaging, first described by the Chinese philosopher Mozi in 4th century BC — and brings it into the modern era of infrared photonics. The concept not only satisfies scientific curiosity about new ways to form images, but also has clear value for industrial inspection, night vision, and environmental monitoring. We see it as both a tribute to optical history and a step toward the future of intelligent imaging systems.
Tech Briefs: Do you have any advice for researchers aiming to bring their ideas to fruition?
Huang: Stay observant and open-minded. Many ordinary or long-known phenomena may hold new potential when revisited with modern technologies and fresh thinking. Sometimes, even an ancient idea — when combined with today’s scientific tools — can lead to real breakthroughs in unexpected fields.