Research Report on the Realization of Blue-Ultraviolet Light Mode-Locking by Polariton Waveguides

In the field of modern optoelectronics, continuous advancements in laser technology have greatly propelled the development of information technology, biomedicine, and industrial processing, among other sectors. Mode-locked laser technology, in particular, with its ultra-short pulses and high repetition rates, has demonstrated significant application value in areas such as precision measurement and high-speed communication. However, traditional mode-locked lasers based on quantum wells or nonlinear material effects usually suffer from pulse width and working temperature limitations. Hence, researchers are dedicated to exploring the potential for higher-performance laser sources within new material systems and device structures.

Recently, research teams from institutions such as the Laboratoire Charles Coulomb, L2C at the University of Montpellier, the Center for Nanosciences and Nanotechnologies, CNRS at Paris-Saclay University, Sorbonne Université, and others have published an important research paper titled “Waveguide Polariton Mode-Locking to Realize Blue-Ultraviolet Light.” This paper comprehensively describes a new type of mode-locked microlaser based on GaN waveguides, which operates at room temperature within the blue-ultraviolet light spectrum. It has a high repetition rate of up to 300 GHz, with individual pulse lengths of only 100 femtoseconds. The paper thoroughly introduces the self-phase modulation mechanism of the polariton-polariton interaction within the mode-locked polariton laser and, in conjunction with simulated results, confirms the precise characteristics of the mode-locking behavior. This article was written by H. Souissi, M. Gromovyi, and others, and was published in volume 11, issue 7 of the Optica journal by the Optica Publishing Group.

Research Background and Significance

Polaritons are quasi-particles achieved through strong coupling, composed of excitons (electron-hole pairs) in semiconductor quantum wells and photons in microcavities. Due to their half-particle, half-photon nature, polariton microlasers have significantly lower effective mass than excitons and exhibit strong nonlinear interactions. These characteristics make them an ideal choice for realizing low-threshold, ultra-short pulse mode-locked microlasers.

Research Content and Methodology

The research team utilized a 60-micrometer-long waveguide structure based on gallium nitride (GaN) and added Bragg reflectors on both sides to form a multimode horizontal microcavity. Through a combination of theoretical analysis and experimental investigation, the team discovered that interactions between polaritons could achieve self-phase modulation of modes, thereby compensating for mode dispersion and achieving mode-locking. Experimental results showed that the polariton microlaser could generate pulses as short as 100 femtoseconds at room temperature, with a repetition rate of 300 GHz. Additionally, numerical simulations further confirmed the mode-locking behavior observed in the experiments by varying parameters such as gain bandwidth and saturation density.

Research Findings

The study indicates that the mode-locked microlaser based on polaritons exhibits characteristics of ultra-fast pulses and high repetition frequency when operating in the blue-ultraviolet light spectrum. It possesses a certain degree of temperature independence, and under certain parameter settings, the mode-locking behavior and pulse morphology are irrespective of the pump length. The pulse width is commensurate with the actual size of the mode-locked microlaser device, demonstrating the potential to reduce the length and energy scale of nonlinear optical devices in the field of polaritonics while increasing operational frequencies.

Research Conclusions

This work has proven the feasibility of utilizing polariton nonlinearity in wide-bandgap semiconductors, laying a solid foundation for the future application of polaritonics in integrated optoelectronics. The compatibility of the GaN-based active layer with conventional electrical schemes paves the way for the realization of integrated ultraviolet microlasers.

This research not only proposes a novel type of polariton-based mode-locked microlaser theoretically but also successfully realizes its room temperature operation experimentally, opening new directions for the future development of the optoelectronics field.