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“Up-Converting” Short-Infrared Light Frequency to Visible Range

Researchers at the Indian Institute of Science (IISc) have created a device to increase, or “up-convert,” the frequency of short infrared light to the visible range. The results of this study are published in Laser & Photonics Reviews.

“Up-Converting” Short-Infrared Light Frequency to Visible Range
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. Image Credit: Jyothsna KM

Only a limited range of frequencies, known as the visible spectrum, are visible to the human eye; red light is the lowest of these frequencies. Red and infrared light have different frequencies; infrared light is invisible to humans.

Light upconversion has several uses, particularly in optical communications and defense. To accomplish this upconversion and widefield imaging capacity, the IISc team first designed what they refer to as a non-linear optical mirror stack using a 2D material. The stack is composed of a silicon dioxide layer stacked between two layers of multilayered gallium selenide adhered to the top of a gold reflective surface.

Traditional infrared imaging employs exotic low-energy bandgap semiconductors or microbolometer arrays, typically detecting heat or absorption signals from the studied object. Infrared imaging and sensing have many applications, including astronomy and chemistry. For example, when infrared light is transmitted through a gas, scientists may use the light's modifications to determine the gas's unique qualities. Such sensing is not always achievable with visible light.

However, existing infrared sensors are heavy and inefficient. Due to their defense applications, they are also subject to export restrictions. Hence, there is an urgent need to design indigenous and efficient equipment.

The IISc team’s solution includes feeding an input infrared signal and a pump beam onto a mirror stack. The nonlinear optical characteristics of the stack’s material cause frequency mixing, resulting in an output beam with higher (up-converted) frequency while maintaining the rest of the attributes.

Using this technology, researchers could convert infrared light with a wavelength of roughly 1550 nm to visible light at 622 nm. The output light wave can be detected with 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.

Varun Raghunathan, Study Corresponding Author and Associate Professor, Department of Electrical Communication Engineering, Indian Institute of Science

He stated that the advantage of utilizing gallium selenide is its high optical nonlinearity, which allows a single photon of infrared light and a single photon of the pump beam to combine to produce a single photon of light with an up-converted frequency. Even with a thin 45 nm layer of gallium selenide, the team was able to accomplish up-conversion.

Its modest size makes it less expensive than standard systems that employ centimeter-sized crystals. Its performance was also determined to be similar to the most advanced up-conversion imaging systems available today.

Jyothsna K Manattayil, a Ph.D. student at ECE and first author, demonstrated how they employed a particle swarm optimization approach to speed up the computation of the required layer thickness. The wavelengths that can travel through gallium selenide and be up-converted vary according to thickness, implying that the material thickness needs to be adjusted based on the application.

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. We saw that the performance didn’t drop for a wide range of infrared wavelengths, from 1400 nm to 1700 nm.

Jyothsna K Manattayil, Study First Author and Ph.D. Student, Department of Electrical Communication Engineering, Indian Institute of Science

In the future, the researchers hope to expand their work to up-convert longer wavelength light. They are also experimenting with other stack designs to increase the device’s efficiency.

Raghunathan concluded, “There is a lot of interest worldwide in doing infrared imaging without using infrared sensors. Our work could be a game-changer for those applications.

Journal Reference:

Manattayil, J. K., et. al. (2024) 2D Material Based Nonlinear Optical Mirror for Widefield Up-Conversion Imaging from Near Infrared to Visible Wavelengths. Laser & Photonics Reviews. doi:10.1002/lpor.202400374

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