Atmospheric transmission characteristics of vortex beams

 

Along with the advancement of the era of information, the Internet industry has been developed rapidly. Therefore, larger information capacity and faster transmission speed have become important development directions of the communication industry today. Currently, channel multiplexing methods such as frequency division multiplexing, time division multiplexing, wavelength division multiplexing, and polarization division multiplexing are usually used to improve the spectral efficiency and channel capacity of communication systems. These technologies have played a major role in the development history of space optical communications. However, with the explosive growth of traffic, these traditional multiplexing methods can no longer provide enough signal capacity and spectral efficiency. In the field of space optical communication, traditional modulation and multiplexing technology is difficult to meet the demand of high channel capacity and high-frequency spectral efficiency communication system. Therefore, a new multiplexing technology is urgently needed to reform the space optical communication system.

The vortex beam with orbital angular momentum provides a completely new dimension for channel multiplexing and provides the possibility for the realization of communication systems with higher channel capacity and spectral efficiency. In theory, the orbital angular momentum of a single-wavelength vortex beam may be infinite and orthogonal to the vortex beams with other orbital angular momentum. In addition, the orbital angular momentum of the vortex beam is independent of the wavelength and polarization. Therefore, the orbital angular momentum multiplexing technology of the vortex beam can be combined with traditional multiplexing technologies such as wavelength division multiplexing and polarization division multiplexing, which greatly improves the communication capacity of the system.

However, all the beams used in space optical communication are inevitably disturbed by atmospheric turbulence, as is the vortex beam. The most representative effect is the mode crosstalk of vortex beam. Thus, in order to provide a theoretical basis for the future development of space optical communication systems based on vortex beams, the atmospheric transmission characteristics of vortex beam should be characterized systematically.

The research team of Shen Feng (Researcher) in the Institute of Optics and Electronics, Chinese Academy of Sciences has proposed an analytical theoretical model based on the topological charge detection probability to study the atmospheric transmission characteristics of vortex beams. Take the typical vortex beam: Laguerre-Gaussian vortex as an example, by studying the variation of the rotation coherence function of the vortex beam during the transmission in atmospheric turbulence, the crosstalk between the orbital angular momentum modes of the vortex beam transmitted in atmospheric turbulence has been summarized. By using the topological charge detection probability of the vortex beam to describe the crosstalk law, an analytical expression for the topological charge detection probability has been derived.

Through further analysis of the analytical theoretical model, the distribution of the angular momentum mode in the vortex beam passed through turbulence has been studied, and the results has been compared with the numerical simulation results of the vortex beam passing through the atmospheric random phase screen, and the derivation has been verified. The analytical theoretical model can be used to further study the interaction between atmospheric turbulence and vortex beams. This analytical theoretical model provides a theoretical basis for selecting the appropriate topological charge interval and beam waist to reduce the bit error rate caused by crosstalk in a spatial optical communication system based on a vortex beam.


Figure 1 When the topological charge l=1, atmospheric refractive index structure constant Cn2 =5×10-14 m-2/3, transmission distance z = 1 km, simulation and theoretical detection probability of topological charge in vortex beam

 

Figure 2 The crosstalk of vortex beam with after turbulent atmosphere with adjacent topological charges
as a function of coherence parameter  ζ 

About The Group

The research team of Shen Feng (Researcher) in the Institute of Optics and Electronics Chinese Academy of Sciences has been engaged in the research of optical engineering system theory and technology. Their research fields are laser transmission, transformation and control technology, laser coherent beam combining technology, and micro-optical wavefront measurement technology. In recent years, they have focused on the technical research on the generation, transmission and detection of vortex beams, and have formed a dynamic research team. Researcher Shen Feng, the person in charge of the project, is responsible for completing a number of national high-tech projects. He is currently working on major projects. In recent years, he has won 1 the first prize of National Science and Technology, 1 outstanding science and technology award of Chinese academy of sciences, 3 Science and Technology Progress First Award, published more than 30 academic papers, and authorized 5 invention patents.

Article

Zhang Lihong, Shen Feng, Lan Bin. Characteristic analysis of orbital angular momentum of vortex beam propagating in atmospheric turbulent[J]. Opto-Electronic Engineering, 2020, 47(4): 190272.

DOI:10.12086/oee.2020.190272