Ultrafast multivalley optical switching in germanium for high-speed computing and communications

Researchers demonstrate ultrafast transparency switching across multiple wavelengths using single laser excitation in germanium

2025-04-16

(Press-News.org)

Opaque materials can transmit light when excited by a high-intensity laser beam. This process, known as optical bleaching, induces a nonlinear effect that temporarily alters the properties of a material. Remarkably, when the laser is switched on and off at ultrahigh speeds, the effect can be dynamically controlled, opening new possibilities for advanced optical technologies.

Multicolored optical switching is an important phenomenon with potential applications in fields such as telecommunications and optical computing. However, most materials typically exhibit single-color optical nonlinearity under intense laser illumination, limiting their use in systems requiring multicolor or multiband switching capabilities. Currently, most optical switches are based on microelectromechanical systems, which require an electric voltage or current to operate, resulting in slow response times.

To address this gap, a group of researchers, led by Professor Junjun Jia from the Faculty of Science and Engineering at Waseda University, Japan, in collaboration with Professor Hui Ye and Dr. Hossam A. Almossalami from the College of Optical Science and Engineering at Zhejiang University, China, Professor Naoomi Yamada from the Department of Applied Chemistry at Chubu University, Japan, and Dr. Takashi Yagi from the National Institute of Advanced Industrial Science and Technology, Japan, investigated the multivalley optical switching phenomenon in germanium (Ge) films. They focused on how intense laser irradiation induces ultrafast optical switching across multiple wavelengths in Ge, a multivalley semiconductor. Their study demonstrated efficient multicolored optical switching using a single-color pulse laser, potentially overcoming the limitations of traditional single-color optical nonlinearities. Their research was published in Physical Review Applied on February 24, 2025.

By irradiating Ge with an intense pulse laser, the team achieved ultrafast switching between transparency and opacity across a wide wavelength range. Femtosecond time-resolved transient transmission measurements revealed ultrafast optical switching in both the Γ and L valleys, due to the existence of intravalley and intervalley scattering. "Our results confirm that intense laser irradiation in Ge films allows for ultrafast optical switching across multiple wavelengths, offering the possibility of controlling a material’s transparency and opening new doors for possible applications in optical communications, optical computing, and beyond,” explains Prof. Jia.

Such multivalley optical switching is found to strongly depend on the band structure of Ge. Experimental measurements suggest that the transient signal is highly dependent on the specific region of the band structure involved. For example, the transient transmission spectra reveal a split-off energy of 240 meV at the L high symmetric point. “Careful selection of probing energies, based on the band dispersion calculated with the HSE06 functional and spin-orbit coupling effects, allowed us to accurately capture the transient electronic occupation in both the Γ and L valleys,” says Prof. Jia. This allows the extraction of intervalley and intravalley scattering times in multivalley materials from transient measurements.

Overall, this study highlights the significant potential of Ge as a key material for advanced optical switching, with promising applications in high-speed data transmission and computing. By enabling control over transparency at multiple wavelengths using a single-color pulse laser, exciting possibilities open up for the development of ultrafast optical switches. “This finding is expected to address the growing demand for higher data rates and security in the face of increasing internet traffic, marking a key step forward in the advancement of ultrafast optical switching devices,” concludes Prof. Jia.

***

Reference

DOI: 10.1103/PhysRevApplied.23.024060

Authors: Junjun Jia1, Hossam A. Almossalami2, Hui Ye2, Naoomi Yamada3, Takashi Yagi4

Affiliations

1Global Center for Science and Engineering (GCSE), Faculty of Science and Engineering, Waseda University, Japan

2College of Optical Science and Engineering, Zhejiang University, China

3Department of Applied Chemistry, Chubu University, Japan

4National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Japan

About Waseda University
Located in the heart of Tokyo, Waseda University is a leading private research university that has long been dedicated to academic excellence, innovative research, and civic engagement at both the local and global levels since 1882. The University has produced many changemakers in its history, including nine prime ministers and many leaders in business, science and technology, literature, sports, and film. Waseda has strong collaborations with overseas research institutions and is committed to advancing cutting-edge research and developing leaders who can contribute to the resolution of complex, global social issues. The University has set a target of achieving a zero-carbon campus by 2032, in line with the Sustainable Development Goals (SDGs) adopted by the United Nations in 2015.

To learn more about Waseda University, visit https://www.waseda.jp/top/en

About Professor Junjun Jia
Junjun Jia is a Professor at the Faculty of Science and Engineering, Waseda University, Japan. He earned his Ph.D. from the University of Tokyo in 2021. His research focuses on the design and fabrication of functional solid-state materials, as well as the development of solid-state devices, including solid-state thermal circuital elements, acoustic wave-based devices, and nonequilibrium electronic devices. His interests include nonlinear optics, non-equilibrium physics, and excited electronic/phonon structure in solids materials. Dr. Jia has published extensively in peer-reviewed journals such as Advanced Functional Materials, Physical Review B, Physical Review Applied. He has received several awards, including the Waseda e-Teaching Award in 2022. He is a member of various committees, including the Materials Research Society of Japan.

END

[Attachments] See images for this press release:

ELSE PRESS RELEASES FROM THIS DATE:

Simulating protein structures involved in memory formation

2025-04-16

Our brain’s remarkable ability to form and store memories has long fascinated scientists, yet most of the microscopic mechanisms behind memory and learning processes remain a mystery. Recent research points to the importance of biochemical reactions occurring at postsynaptic densities—specialized areas where neurons connect and communicate. These tiny junctions between brain cells are now thought to be crucial sites where proteins need to organize in specific ways to facilitate learning and memory formation. More specifically, a 2021 study revealed that memory-related proteins can bind together to form droplet-like structures ...

Forward genetics approach reveals the factor responsible for carbon trade-off in leaves

2025-04-16

Plants store carbon in two primary forms: starch and triacylglycerols (TAGs). Starch is mainly stored in chloroplasts in leaves, where it serves as a readily available energy source, while TAGs are stored in seeds for long-term energy storage. Past studies have shown that a carbon trade-off exists between these two storage forms, implying that an increase in the levels of one form often reduces the levels of the other. Interestingly, attempts to increase TAG in leaves have led to a decrease in the levels of starch, suggesting ...

The most distant twin of the Milky Way ever observed

2025-04-16

An international team led by the University of Geneva (UNIGE) has discovered the most distant spiral galaxy candidate known to date. This ultra-massive system existed just one billion years after the Big Bang and already shows a remarkably mature structure, with a central old bulge, a large star-forming disk, and well-defined spiral arms. The discovery was made using data from the James Webb Space Telescope (JWST) and offers important insights into how galaxies can form and evolve so rapidly in the early Universe. The ...

New method to deliver cell therapies in critically ill patients on external lung support

2025-04-16

A multidisciplinary clinical team led by Professor Bernat Soria from the Institute of Bioengineering at the Miguel Hernández University of Elche (UMH, Spain) has developed a new method to deliver cell therapies in patients on extracorporeal membrane oxygenation (ECMO), a life support system used in cases of severe lung failure. The advance has been published in Stem Cell Research & Therapy (Springer Nature Group). The team has opted not to patent the technique in order to encourage its use in public health systems ...

Climate-related trauma can have lasting effects on decision-making, study finds

2025-04-16

A new study from University of California San Diego suggests that climate trauma — such as experiencing a devastating wildfire — can have lasting effects on cognitive function. The research, which focused on survivors of the 2018 Camp Fire in Northern California, found that individuals directly exposed to the disaster had difficulty making decisions that prioritize long-term benefits. The findings were recently published in Scientific Reports, part of the Nature portfolio of journals. “Our previous research has shown that survivors of California’s 2018 Camp Fire experience prolonged symptoms ...

Your cells can hear

2025-04-16

Kyoto, Japan -- There's a sensation that you experience -- near a plane taking off or a speaker bank at a concert -- from a sound so total that you feel it in your very being. When this happens, not only do your brain and ears perceive it, but your cells may also. Technically speaking, sound is a simple phenomenon, consisting of compressional mechanical waves transmitted through substances, which exists universally in the non-equilibrated material world. Sound is also a vital source of environmental information for living beings, while its capacity to induce physiological responses at the cell ...

Farm robot autonomously navigates, harvests among raised beds

2025-04-16

Strawberry fields forever will exist for the in-demand fruit, but the laborers who do the backbreaking work of harvesting them might continue to dwindle. While raised, high-bed cultivation somewhat eases the manual labor, the need for robots to help harvest strawberries, tomatoes, and other such produce is apparent. As a first step, Osaka Metropolitan University Assistant Professor Takuya Fujinaga has developed an algorithm for robots to autonomously drive in two modes: moving to a pre-designated destination and moving alongside ...

The bear in the (court)room: who decides on removing grizzly bears from the endangered species list?

2025-04-16

By Dr Kelly Dunning The Endangered Species Act (ESA), now 50 years old, was once a rare beacon of bipartisan unity, signed into law by President Richard Nixon with near-unanimous political support. Its purpose was clear: protect imperiled species and enable their recovery using the best available science to do so. Yet, as our case study on the grizzly bear in the Greater Yellowstone Ecosystem reveals, wildlife management under the ESA has changed, becoming a political battleground where science is increasingly drowned out by partisan ideology, bureaucratic delays, power struggles, and competing political interests. ...

First study reveals neurotoxic potential of rose-scented citronellol at high exposure levels

2025-04-16

Citronellol, a rose-scented compound commonly found in cosmetics and household products, has long been considered safe. However, a Korean research team has, for the first time, identified its potential to cause neurotoxicity when excessively exposed. A collaborative research team led by Dr. Myung Ae Bae at the Korea Research Institute of Chemical Technology (KRICT) and Professors Hae-Chul Park and Suhyun Kim at Korea University has discovered that high concentrations of citronellol can trigger neurological and behavioral toxicity. The study, published in the Journal ...

For a while, crocodile

2025-04-16

Most people think of crocodylians as living fossils— stubbornly unchanged, prehistoric relics that have ruled the world’s swampiest corners for millions of years. But their evolutionary history tells a different story, according to new research led by the University of Central Oklahoma (UCO) and the University of Utah. Crocodylians are surviving members of a 230-million-year lineage called crocodylomorphs, a group that includes living crocodylians (i.e. crocodiles, alligators and gharials) and their many extinct ...