Preparation of Narrow Linewidth and High Debye Factor Single Photon Source Femtosecond Laser in AlN Crystals

Preparation of Narrow Linewidth and High Debye Factor Single Photon Source Femtosecond Laser in AlN Crystals

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At present, people have used AlN to prepare high Q-value resonant cavities and low loss waveguides. It has also been reported to be a single photon source that can operate at room temperature in AlN crystals. However, as a light source in quantum integrated optical circuits, there are still challenges: firstly, the optical properties of the single photon source in AlN are poor, exhibiting high background fluorescence, with zero phonon lines accounting for a low proportion of the entire spectral emission (Debye factor is very low, only 3%), and the emission linewidth is also relatively large. To achieve coupling with resonant cavities and optical waveguides, it is necessary to accurately control the position of a single photon source. How to achieve a single photon source with a narrow linewidth, high Debye factor, and precise and controllable position in AlN is an urgent issue in the development of optical quantum integration platforms for AlN.

1. Study on High Performance Single Photon Source Prepared in AlN by Femtosecond Laser

Recently, a research team has used femtosecond laser to prepare a color center light source for single photon emission. In high-quality AlN single crystals, the nonlinear interaction between femtosecond laser pulses and materials is utilized to achieve processing beyond the diffraction optical limit. Induce the formation of quantum defects at the laser focal point, generate color centers, and introduce new luminescent color center energy levels into the bandgap.

Fig. 1 Schematic diagram and spectral and quantum emission characteristics testing of a single photon source in femtosecond laser preparation of aluminum nitride

Fig. 1 Schematic diagram and spectral and quantum emission characteristics testing of a single photon source in femtosecond laser preparation of aluminum nitride

Experiments have shown that single photon source localization can be achieved on AlN single crystal substrates, and the processing yield of luminescent color centers can reach over 50%. Interestingly, the single photon source line prepared by femtosecond laser has a narrow width, a very pure spectrum, and very low background fluorescence, exhibiting a single sharp emission peak and very weak phonon sidebands. After calculation, the Debye factor of the single photon source can reach over 65%. By monitoring its spectral changes and single photon counting, it was found that the laser prepared single photon source maintains high stability under long-term optical excitation. In addition, the research team also conducted first principles calculations on the types of color centers prepared and proposed that oxygen related defects may be the type of single photon source emitted by these color centers.

Fig. 2 Optical characteristics of a single photon source processed by femtosecond laser

Fig. 2 Optical characteristics of a single photon source processed by femtosecond laser

2. Prospectof Single Photon Source in AlN Single Crystal

The research team used femtosecond laser to position and prepare a high-performance single photon source (narrow linewidth, high Debye factor, high stability at room temperature) on an AlN single crystal substrate, with a yield of over 50%. The study demonstrate that AlN crystals can achieve stable and high-quality room temperature single photon emission, showing the enormous potential of the next generation of quantum photon chips and providing a reliable preparation technology for single photon sources for the development of integrated quantum platforms based on aluminum nitride.

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