Researchers from China's Dalian University of Technology, University of Hong Kong and HKU-SIRI have achieved low-threshold, wide-wavelength tunable single-mode laser emission in the near-infrared (NIR) by combining phase-change perovskite with the traditional vertical-cavity surface-emitting laser (VCSEL) structure.
Schematic of a tunable microlaser based on phase-change perovskite gain medium, sandwiched between Au mirror and DBR reflector sitting on a quartz glass substrate, pumped by blue-violet laser (λ = 405 nm) and emitting a tunable beam in the near-IR from 790.7 nm to 799.5 nm. Image from: Opto-Electronic Advances
As an important light source, lasers are widely used in many fields such as communications, medical treatment, display technology and scientific research. However, the continuous advancement of technology means higher requirements from the performance of lasers, especially in terms of integration and tunability. Traditional lasers typically rely on fixed gain media and external microcavity structures (such as Fabry-Perot cavities, photonic crystals, whispering galleries, etc.). Although these structures can achieve efficient laser emission, their operating wavelengths are often fixed, which makes it difficult to meet the needs of modern science and technology for tunability. Therefore, the development of a laser that can achieve low-threshold laser emission and is tunable over a wide wavelength range has become one of the current research focuses.
Halide perovskite semiconductor materials boast high dielectric constants, high photoluminescence quantum yields, tunable band gaps and narrow radiation spectra, and are considered to be ideal gain media for realizing low-cost, high-performance lasers.
Since the first optical pumping laser of halide perovskite was realized in 2014, researchers have successfully constructed perovskite lasers such as distributed feedback (DFB) lasers and vertical cavity surface emitting lasers (VCSELs) using various external microcavity structures. These lasers have made significant progress in controlling laser wavelength and beam shape, but they are still limited to fixed wavelength operation mode and cannot meet the needs of tunable lasers.
Halide perovskites not only have excellent optical properties, but also can achieve crystal phase transition through changes in temperature, pressure or chemical composition, thereby causing significant changes in refractive index, making them ideal candidate materials for realizing tunable lasers. Despite this, the potential of halide perovskites as phase-change tunable laser gain media has not yet been fully developed.
The team's recent work addresses this matter. They developed a tunable vertical cavity surface emitting laser (VCSEL) employing a tunable gain medium of halide phase-change perovskites-specifically MAPbI3 perovskite, sandwiched between two highly reflective mirrors composed of bottom-distributed Bragg reflectors (DBRs). This VCSEL possesses single-mode lasing emission with a low threshold of 23.5 μJ cm−2 under 160 K, attributed to strong optical confinement in the high-quality (Q) cavity. Upon the phase change of MAPbI3 perovskite, both its gain and dielectric constant changes dramatically, enabling a wide (Δλ >9 nm) and temperature-sensitive (0.30 nm K−1 rate) spectral tunability of lasing mode in the near-infrared (N-IR) region.
The laser displays excellent stability, demonstrating an 80% lifetime of >2.4×107 pulses excitation.
The next step for the team is to optimize the phase-change perovskite layer to achieve temperature-tunable lasers at room temperature. This work not only promotes the development of tunable perovskite VCSELs but also provides inspiration for the next generation of stable electrically injected perovskite lasers.
