light source for daily use converts infrared light into blue light for sterilization and disinfection | Research & Technology | June 2021

OSAKA, Japan, June 25, 2021 – A microcavity device that converts infrared (IR) radiation into blue light could enable safe daily use of deep ultraviolet light (DUV) for disinfection and sterilization.

The device was developed by a research group at Osaka University and was built without a reverse polarity structure. The lack of dependence on birefringence or periodically polarized inverted structure extends flexibility in the selection of device structures and materials – giving researchers more flexibility in the selection of structures and materials for length conversion d wave to be converted into DUV light.

Digital camera image of second harmonic blue light emission with a wavelength of 428 nm using an IR cut filter. Courtesy of Osaka University.

A DUV wavelength range of 220-230nm is desirable if DUV light is to be used safely as a disinfectant. Although wavelength conversion offers a potential solution to achieve this unrealized wavelength, conventional ferroelectric wavelength conversion materials cannot be used, due to the absorption edge.

To realize a DUV light for bactericidal use, the researchers constructed a monolithic second harmonic generation (SHG) microcavity device using a low birefringence paraelectric material and a dielectric material. They used two distributed Bragg High Reflectivity (DBR) reflectors to double the frequency of light entering the device. The DBRs enhanced the intensity of a fundamental wave in the microcavity. Counter-propagating SHG waves were generated efficiently in a very short region close to a coherence length.

As a first step towards the practical application of their approach, the researchers constructed a gallium nitride (GaN) microcavity device using microfabrication technology, including dry etching and anisotropic wet etching for vertical DBR sidewalls. and smooth. When they demonstrated the wavelength conversion in the GaN microcavity, they observed a 428nm blue SHG wave in the absence of a reverse polarity structure.

Schematic of a GaN monolithic microcavity SHG device on an Si plinth structure. Courtesy of Osaka University.

Nitride semiconductors such as GaN and aluminum nitride (AIN) have relatively high optical nonlinearity, making them suitable for use in wavelength conversion devices; AlN is particularly suitable for DUV wavelength conversion devices, due to its transparency up to 210 nm. However, making structures with periodically reversed polarity, such as structures in conventional ferroelectric wavelength converting devices, has proven difficult using these materials.

“Our device can be adapted to use a wider range of materials,” Prof. Masahiro Uemukai said. “They can be applied to the emission of deep ultraviolet light or even to the generation of broadband photon pairs.”

The researchers hope that their flexible approach to wavelength conversion will facilitate the construction of future nonlinear optical devices.

The research was published in Applied Physics Express (www.doi.org/10.35848/1882-0786/abff9e).