Search

Phase is an important characteristic of electromagnetic waves. It is well known that a beam with a helical wave front characterized by a phase of \begin{document}$\exp({\rm{i}}l\theta )$\end{document} (which depends on azimuthal angle \begin{document}$\theta$\end{document} and topological charge l), has a momentum component along the azimuthal direction, resulting in an orbital angular momentum of per photon along the beam axis. Owing to its fascinating properties, the beam has received a great deal of attention and has provided novel applications in manipulation of particles or atoms, optical communication, optical data storage. In order to meet the needs of various applications, techniques for efficiently generating optical beams carrying orbital angular momentum are always required. Current schemes for generating the beams carrying orbital angular momentum include computer-generated holograms, spiral phase plates, spatial light modulators, and silicon integrated optical vortex emitters. Among the usual methods to produce helical beams, the traditional spiral phase plate is an optical device that utilizes the progressive increasing of height of a dielectric material along an azimuthal direction to produce a vortex beam for beam phase modulation with a high conversion efficiency. However, it is difficult to regulate the topological charge l of the outgoing beam through the superposition of the phase plates due to the special geometric feature. In this paper, the flat spiral phase plate is designed by compressing the height of traditional spiral phase plate, and inducing the refractive index to increase in the azimuthal direction based on coordinate transformation. By means of theoretical analysis and numerical simulation, it is found that the flat spiral phase plate can produce high quality vortex beams just as the traditional spiral phase plate can do. Particularly, the height of the flat spiral phase plate and the topological charge l carried by the vortex beams can be arbitrarily adjusted according to the refractive index selection of the dielectric material. In order to meet the needs of practical applications, the vortex beams with different topological charges can be obtained by stacking multiple layers of flat spiral phase plates. The flat spiral phase plate has broad potential applications in the fields of optical transmission and optical communication.

The new deal of China can be generalized as follows. A theme, sustained development; two motifs, harmonious society and scientific outlook on development; four focal points, the building of a new socialist countryside, the rising of the region, developing a circular economy, as well as the innovation for science and technology; a guarantee, reform. The building of a new socialist countryside marks the beginning of Chinese Roosevelt New Deal. To implement the policy of government intervention at present will avert from economic crisis that is resulted from the process of industrialization. The age of stimulating economic growth by ultra-low cost in the east has come to an end. The key to continuing the dream of world factory in China lies in the central region that can cope with the industrial transfer from the eastern region. In the new round of reform debuting, two kinds of tendencies should be against. One is the tendency of questioning the direction of the reform. The other is sanctifying the reform. Only in this way can it be guaranteed that we will intensify the development of reform in the right direction, so as to provide strong guarantee for the New Deal of China. Compared with the policy of reform and opening-up that changes the Chinese economy from the state of poverty and ignorance into the miracle of China, the Chinese New Deal will give great impetus to turning the economic development from the model of high speed into the pattern of high quality, comprehensive, balanced and sustainable. It is estimated that this Chinese New Deal will yield results around 2020, at the time of which the target of building a new socialistic countryside will be realized by and large, China will enter the late stage of industrialization, and the overall economic strength of China will rank in the first three places in the world