A new era for ultrafast photonics: two-dimensional mercury-acetylide frameworks for near-infrared nonlinear optics

In the increasingly digital world, the demand for faster, more efficient and miniaturised optical devices is ever-growing. From high-speed internet and secure quantum communications to advanced medical imaging and precision manufacturing, the backbone of these technologies is light, specifically how we can control and manipulate it at the nanoscale. Two-dimensional (2D) materials have emerged as a game-changer in this arena, offering unique properties that can be harnessed for ultrafast photonics and nonlinear optical applications. 

However, the search for materials that combine stability, tunability and high performance in the near-infrared (NIR) region, a crucial window for telecommunications and sensing, remains a significant challenge. Prof. Yuen Hong TSANG, Associate Head and Professor of the Department of Applied Physics at The Hong Kong Polytechnic University (PolyU), and his research team introduce a new class of 2D quantum materials, the mercury(II)-acetylide frameworks (Hg–H2TPP), which not only overcome many of the limitations of existing materials but also open up exciting possibilities for switchable nonlinear optics and ultrafast laser technologies.

By integrating heavy mercury(II) ions into a porphyrin-containing graphdiyne framework, the team has developed a material with remarkable optical properties, including strong and tuneable nonlinear absorption, rapid carrier dynamics and the ability to function as both a saturable absorber and an optical limiter. These features are critical for the development of advanced photonic devices such as Q-switched and mode-locked lasers, which are essential for telecommunications, high-precision measurements and quantum information processing. The research was published in Carbon. 
The study demonstrates that the newly synthesised Hg–H2TPP nanosheets possess a combination of properties highly desirable for advanced photonic applications. Most notably, the material exhibits both saturable absorption and reverse saturable absorption behaviours, with nonlinear absorption coefficients that can be tuned across a wide range. This switchable nonlinear response is crucial for enabling the material to function as both a saturable absorber and an optical limiter, depending on the incident light intensity. 

This study marks a significant advance in the field of quantum materials and nonlinear optics. By engineering a D-π-A-structured 2D mercury(II)-acetylide framework, Prof. Tsang’s team has created a material that combines strong NIR absorption, tuneable nonlinear optical responses and ultrafast carrier dynamics, which are all essential ingredients for next-generation photonic devices. 

The ability to switch between saturable and reverse saturable absorption, coupled with the successful demonstration of both mode-locked and Q-switched lasers, underscores the potential of Hg–H2TPP for applications ranging from telecommunications and quantum information processing to biomedical imaging and laser-based manufacturing. 

The insights gained from this work not only advance our understanding of 2D quantum materials but also lay the groundwork for the development of practical, high-performance devices that will shape the future of quantum technology.

Source: Innovation Digest