We demonstrate a dual-wavelength passively Q-switched Nd^（3＋）-doped glass fiber laser using a few-layer topological insulator Bi2Se3 as a saturable absorber（SA） for the first time, to the best of our knowledge. The laser resonator is a simple and compact linear cavity using two fiber end-facet mirrors. The SA is fabricated by Bi2Se3/polyvinyl alcohol composite film. By inserting the SA into the laser cavity, a stable Q-switching operation is achieved with the shortest pulse width and maximum pulse repetition rate of 601 ns and 205.2 kHz,respectively. The maximum average output power and maximum pulse energy obtained are about 6.6 mW and 38.8 nJ, respectively.
Optical security devices play an essential role in the fight against counterfeiting. In this paper, we study and design a pair of metal-dielectric optical filters based on metameric effect, which offer a hidden image effect by the color shift at a specific angle of observation. Compared with all-dielectric multilayer system, the metal-dielectric multilayer structure has larger color shift with varying incident angle, higher color saturation and fewer layers. Finally, the stacks with 5 layers and 7 layers are achieved, and the color difference index is only 0.71, which shows good metameric matching effect. Simultaneously, the sensitivity of filters to deposition errors is analyzed when the thickness deviation is ±2%, and the results show that the two filters have good manufacturability.
We report the fabrication and optical characterization of spherical whispering gallery mode(WGM) resonators made from ultraviolet(UV)-curable adhesive. The fabricated microspheres have good sphericity and surface smoothness, and can directly adhere to the tip of half-tapered fibers for easy manipulation. WGMs are e?ciently excited in the microsphere using an evanescent field of the tapered silica optical fibers. Resonances with quality factors of 1.3×10 5 are observed. The dependence of wavelength shifts of WGM resonances on the input light powers shows that the resonant wavelength of the proposed microsphere resonators can be tuned thermo-optically.
