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Photonics

New light conversion

Miniaturization on a microchip that transforms a type of electromagnetic radiation into two distinct frequencies could reduce the size of laser devices

Brazilian and American physicists have developed a much smaller version of a light source that converts a type of radiation into two distinct frequencies (colors) of the electromagnetic spectrum. Built on a silicon photonic chip that uses light instead of electrons to process information, this so-called optical parametric oscillator measures just 0.14 millimeters. Hundreds of times smaller than its commercial counterparts, the minuscule oscillator is capable of transforming a beam of near-infrared radiation—a wavelength that is not observable with the naked eye—into visible light and frequencies used in telecommunications.

Controlling this conversion allows scientists to produce light at highly specific wavelengths for specific purposes, such as industrial applications, research in quantum computing, and the study of interactions between matter and various frequencies of electromagnetic radiation. The latter, known as spectroscopy, is used to analyze the color emitted by materials, to infer what elements they are made up of and how they are structurally arranged. The technique has a range of uses, from determining the composition of the atmosphere to identifying contaminants diluted in a glass of water.

Due to its small dimensions, the oscillator, developed in partnership by the Institute of Physics (IF) at the University of São Paulo (USP) and Columbia and Cornell universities in New York, USA, can be used to make smaller devices that could be integrated into computer equipment, according to its creators. “Our device can be installed on a circuit board or as part of a hybrid system involving electronics and photonics,” says physicist Marcelo Martinelli of IF-USP, one of the authors of the paper published in the scientific journal Optica in March.

In Brazil, the study is funded by FAPESP, the Brazilian National Council for Scientific and Technological Development (CNPq), and the Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES). “The article is the first major result of our research with silicon chips,” says another author of the paper, physicist Paulo Nussenzveig, also from IF-USP.

The transformation of a beam of light into two other types of electromagnetic radiation usually involves relatively large laser devices installed in research laboratories, which use optical parametric oscillators to generate light in different bands of the electromagnetic spectrum. These oscillators usually measure between 5 and 20 centimeters—between 350 and 1,400 times larger than the new device. The microchip-mounted oscillator developed by the Brazilian and American team works as a microresonator or an optical cavity—a closed circuit composed of an integrated optical fiber that can amplify and convert a laser signal into other frequencies, depending on its geometric layout and other parameters. The chip was produced in the USA, but the experiment was carried out in Brazil.

“We designed microresonators in the form of a ring, within which light circulates through guides made of silicon nitride [Si3N4] coupled with a silicon oxide substrate [SiO2],” explains physicist Renato Domeneguetti, lead author of the article, who worked on the research as part of his doctorate, defended at IF-USP in 2018. “Our device may be of interest for applications in communication and quantum computing. There are many companies and academic research groups currently working on similar devices.” It is possible, for example, that the light particles in the two distinct beams of electromagnetic radiation generated by the photonic chip have some level of quantum correlation, a property that theoretically can be exploited to encode and retrieve information.

According to Martinelli, the combination of microelectronics and photonics on the same chip could reduce energy loss and prevent a computer circuit board from heating up. Currently, computers operate based on the properties of electrons (hence the term microelectronics). In the world of photonics, light is responsible for processing information, like with fiber optic cables. Although it uses less energy than electronics, photonics is still expensive and there is still the challenge of more accurately controlling the properties of light.

Project
Exploring quantum information with atoms, crystals, and chips (no. 15/18834-0); Grant Mechanism Thematic Project; Principal Investigator Marcelo Martinelli (USP); Investment R$3,366,437.68.

Scientific article
DOMENEGUETTI, R. R. et al. Parametric sideband generation in CMOS-compatible oscillators from visible to telecom wavelengths. Optica. Vol. 8, no. 3. Mar. 2021.

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