RESUMEN
An air-core fiber imposed by torsion is investigated in this paper. We refer to this kind of fiber as twisted air-core fiber (TAF). It has been demonstrated that the eigenstates of the TAF consist of guided optical vortex waves with different propagation constants of a different effective index. With the increase of the twist rate, TAF could separate the OAM modes which are near degenerate or degenerate in the air-core fiber. The separation of OAM modes in TAF is conductive to ultralong distance propagation with low crosstalk. TAF could be considered as an ideal candidate fiber for OAM based optical communication. Moreover, we investigated the twisted air-core photonic crystal fiber (TAPCF) which can improve the relative energy distribution of the OAM modes. Compared with TAF, more energy is located in the ring shaped core, which is conductive to ultralong distance propagation. TAF and TAPCF are of potential interest for increasing channel capacity in optical telecommunications, and the result is also of interest to the photonic crystal community.
RESUMEN
We proposed an approach for creating three-dimensional (3D) multifocal perfect vortices arrays by using a high numerical aperture objective. The position, orbital angular momentum states, number and diameter of the perfect vortices can be freely modulated by a special designed hybrid phase plate (HPP). HPP could be calculated by 3D phase shifting expression which is derived from Fourier transform theory of the Debye diffraction integral. Furthermore, we developed a novel pixel checkerboard method for adding phase information into the HPP. The segmentation of HPP is related to vortex quality and intensity uniformity. This method could fully use each pixel to modulate the light, since the spatial light modulator has to be used. Small size lattices could generate high quality and uniform intensity vortex arrays in tight focusing region, which may have potential applications in coupling, optical coding and decoding.
RESUMEN
Ammonia is a promising fuel with high energy density, accessible storage, and no CO2 production by combustion, but its combustion produces the pollutant NO. In this study, a Bunsen burner experimental bench was selected to investigate the concentration of NO generated by ammonia combustion at different initial oxygen concentrations. Further, the reaction pathways of NO were analyzed in depth, and sensitivity analysis was performed. The results show that the Konnov mechanism has an excellent predictive effect on NO generated by ammonia combustion. In the ammonia-premixed laminar flame at atmospheric pressure, the NO concentration peaked at an equivalence ratio of 0.9. The high initial oxygen concentration enhanced the combustion of ammonia-premixed flame and increased the conversion of NH3 to NO. NO was not only a product but a contribution to the combustion of NH3. As the equivalence ratio increases, NH2 consumes a large amount of NO and reduces NO production. The high initial oxygen concentration enhanced NO production, and the effect was more pronounced at low equivalents. The study results provide theoretical guidance for the utilization of ammonia combustion and pollutant reduction and help to drive the process of ammonia combustion toward practicality.