The human eye can only perceive a limited range of light frequencies known as the visible spectrum. Infrared light, which falls below the frequency of red light, remains invisible to us. However, a team from the Indian Institute of Science (IISc) has now engineered a device capable of converting—or “up-converting”—infrared light into visible light.

Figure 1. The Proposed Method. (Credit: Jyothsna KM)

This technological advancement holds significant promise for fields like defense and optical communications. The IISc team has pioneered a method using a 2D material to create what they term a non-linear optical mirror stack. This innovative design not only achieves light up-conversion but also integrates widefield imaging. The stack is composed of multiple layers of gallium selenide on top of a reflective gold surface, with an intermediary silicon dioxide layer.

Figure 1 shows From Left to Right: Schematic of the nonlinear optical mirror used for up-conversion imaging. Energy diagram showing the sum frequency generation process used for up-conversion. Representative up-converted images of IISc logo and spokes where the object pattern at 1550 nm is upconverted to 622 nm wavelength [2].

Traditional infrared imaging relies on specialized low-energy bandgap semiconductors or micro-bolometer arrays, which detect heat or absorption patterns. These methods are indispensable in disciplines ranging from astronomy to chemistry. For instance, infrared light can reveal unique characteristics of gases when they alter its properties. Yet, current infrared sensors are often bulky, inefficient, and restricted in trade due to defense applications, highlighting the need for efficient and indigenous solutions [1].

The IISc approach involves projecting an input infrared signal and a pump beam onto the mirror stack. Thanks to the stack’s nonlinear optical characteristics, the light frequencies mix, producing an up-converted output beam with the same properties as the original. This technique successfully converted infrared light at a wavelength of 1550 nm to visible light at 622 nm, which can be captured using conventional silicon-based cameras.

“This process is coherent – the properties of the input beam are preserved at the output. This means that if one imprints a particular pattern in the input infrared frequency, it automatically gets transferred to the new output frequency,” explains Varun Raghunathan, Associate Professor in the Department of Electrical Communication Engineering (ECE) and the study’s corresponding author, published in Laser & Photonics Reviews.

Gallium selenide was chosen for its high optical nonlinearity, enabling single photons of infrared and pump light to combine and produce a single photon with a higher frequency. Remarkably, this up-conversion was achieved with a thin 45 nm layer of gallium selenide, making it more cost-effective than traditional centimeter-sized crystal-based devices. Despite its compact size, the performance matched existing state-of-the-art systems.

First author and ECE PhD student, Jyothsna K Manattayil, notes that the team utilized a particle swarm optimization algorithm to fine-tune the thickness of the layers, which determines the range of wavelengths that can be up-converted. “In our experiments, we have used infrared light of 1550 nm and a pump beam of 1040 nm. But that doesn’t mean that it won’t work for other wavelengths,” she says. “We saw that the performance didn’t drop for a wide range of infrared wavelengths, from 1400 nm to 1700 nm.”

Looking ahead, the researchers aim to adapt their technology to up-convert longer wavelengths and are exploring new stack configurations to boost efficiency.

“There is a lot of interest worldwide in doing infrared imaging without using infrared sensors. Our work could be a gamechanger for those applications,” says Raghunathan.

Source: Indian Institute of Science (IISc)

References:

1. https://www.newindianexpress.com/states/karnataka/2024/Jun/21/iisc-fabricates-device-to-convert-infrared-light-into-the-visible-range
2. https://www.eurekalert.org/news-releases/1048811

Cite this article:

Hana M (2024), IISc Researchers Develop Breakthrough Infrared-to-Visible Light Conversion Device, AnaTechmaz, pp. 1042