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The whispering gallery mode (WGM) microcavity has been widely used for sensing and detection because of its high quality factor, small mode size, simple and diverse manufacturing process, and high sensitivity to the surrounding environment. Microsphere cavityand microdisk cavity are typical whispering gallery mode microcavities. However, the real controllable size of the on-chip three-dimensional microsphere cavity has rarely been reported because it is difficult to prepare by photolithography. At the same time, most of the current microsphere cavity are prepared by hot melting, which have the poor ability to control the size. In this article, we have mainly demonstrated the fabrication of a dye-doped polymer whispering gallery mode microsphere by femtosecond laser two-photon polymerization, which shows good surface smoothness with a fabrication spatial resolution beyond the diffraction limit. The microsphere cavity consists with commercial photoresist SU-8 as the cavity material and Rhodamine B as the gain medium. With the 532 nm pump, the RhB-doped SU-8 can emit fluorescence in the spectral range of 600–700 nm, and thus resonant whispering gallery laser modes in this spectral region can be eventually formed in the microsphere cavities. The microcavity shows excellent lasing performance with a quality factor of ~2000. Due to the special luminescence mechanism of organic dyes, the fluorescence spectrum of the dye drifts with the change of ambient temperature, and it will form a new resonance excitation with the eigenmode of the cavity. Within a certain temperature range (20 ℃－35 ℃), the wavelength of the main lasing peak is linearly related to temperature. The results shows that the organic dye doped micro-resonator has a unique laser mechanism which can be used to construct a new type of microlaser. Moreover, the tunable microsphere laser can be used as a temperature sensor after further optimized. We believe our work will provide a positive inspiration for the rational design of miniaturized lasers with ideal performance.

Sapphire has shown broad application prospects in military and medical fields, due to its high hardness, excellent corrosion resistance and high transmission in the infrared band. However, these characteristics have also brought about lots of difficulties in machining or chemical etching the material. Femtosecond laser processing with excellent characteristics including small heat-affected zones and high processing resolution ratio, has become an emerging field. Therefore, it has important application prospects and has found increasingly wide applications in the fields of material modification and high-quality fabrication of three-dimensional micro-nano structures and devices. In this paper, we propose a method in which femtosecond laser processing based on multi-photon absorption is used to process sapphire beyond the optical diffraction limit. In this work, femtosecond laser with a central wavelength of 343 nm is focused on the sapphire and the surface of sapphire is scanned with the high-precision piezoelectric positioning stages. Nano structures each with a width of about 61 nm are obtained, and the minimum space between the nano structures could be as short as about 142 nm. Further, the influences on the processing resolution from laser power and scanning speed are investigated and the generation mechanism for the nano-ripple structure is discussed. Finally, femtosecond laser processing on the sapphire with a resolution beyond the optical diffraction limit is achieved. This work provides a reference for processing the hard and brittle materials by femtosecond laser.

Organic solar cells based on small molecules and conjugated polymers are attracting much attention due to their merits of low costs, simple fabrication processes, light weights, and mechanical flexibilities. Metals are usually considered as promising candidates for the semi-transparent electrodes. In such devices, a strong microcavity resonance can be supported between the two electrodes, resulting in a narrowed bandwidth of light absorption, which, unfortunately, will lower the performances of organic solar cells since broadband absorption is always highly desired. To overcome this obstacle, people have proposed many designs such as using ultra-thin electrodes or using dielectric-metal hybrid electrodes. Although the light absorption bandwidth can be improved considerably, the absorption efficiency would be lowered due to the weakened microcavity resonance. This is a tough problem that always bothers both researchers and engineers. To solve this problem, we propose a light trapping scheme based on broadband hybrid modes due to the hybridization between microcavity resonance and antireflection resonance. By introducing a capping layer outside the device structure, antireflection resonance can be excited inside the capping layer and can then couple with the intrinsic microcavity resonance, inducing dual microcavity-antireflection resonance hybrid modes. The hybrid modes are of broadband and their resonant wavelengths can be easily designed by tuning the capping layer thickness and cavity length, since the capping layer thickness would affect the antireflection resonance while the cavity length would affect the microcavity resonance. By matching the resonance with the high absorption region of the active layer, the overall absorptivity of the proposed device can be greatly enhanced by~37% compared to the conventional microcavity based device where only one mode, that is, the microcavity resonance can be supported. Moreover, we compare our light trapping scheme with the surface plasmon-polaritons based scheme where surface waves are excited to help improve the light absorption. We find that the overall absorptivity of the proposed device cannot be further improved when we introduce grating structure into the device in order to excite surface plasmon-polaritons. This is mainly because the light absorption based on our hybrid mode scheme is already thorough so that the introduction of grating structure can only improve the light loss dissipated in the metal electrodes due to scatterings and diffractions by the gratings. Therefore, the proposed hybrid mode based scheme can be considered as a simple and effective light trapping scheme for organic solar cells and may find applications in both polymer and small molecular based organic solar cells.

SiO2 glass films doped with GeO2 were prepared by the flame hydrolysis deposition method, then annealed at 1200?C. After exposure to high pressure hydrogen, the as-deposited films were irradiated with excimer laser pulses operated at 248?nm. The induced refractive index change (the growth of index change was 0.33%) was measured by a spectroscopic ellipsometer. A waveguide array has been written in the film by irradiation through a phase mask.