Spectrum evolution of Rayleigh backscattering in one-dimensional waveguide

 
Rayleigh scattering, as a representative of distributed optical feedback, has a better linewidth compression effect in the field of narrow linewidth lasers, which has been experimentally proved. However, up to now, the linewidth compression mechanism especially for the frequency evolution mechanism of laser in Rayleigh scattering medium structure has not been systematically investigated. The research group of Prof. Tao Zhu from the College of Opto-electronic Engineering, Chongqing University mainly engages in the fields of controllable laser and precision measurement technology in recent years. After successful investigation of Rayleigh backscattering (RBS) in different types of optical fibers in their previous work, the RBS has been successfully applied to optical fiber lasers and semiconductor lasers to realize the deep linewidth compression. In order to further reveal the evolution characteristics in frequency domain starting from the source, they demonstrates the dynamic characteristics of the spectrum evolution (SpE) of Rayleigh scattering in a one-dimensional waveguide based on the quantum theory and establish a corresponding SpE-model. By means of simulation, the evolution law which represents the dynamic process of the spectrum linewidth at a state of continuous scattering is revealed, which is consistent with our previous experimental observation. Moreover, an approximate theoretical prediction of the existing relationship between the spectrum linewidth of RBS source and the transmission length in ODW is proposed.

 
 
Spectrum analysis of Rayleigh backscattering in an ODW and spectrum evolution curve.

    The research group of Prof. Zhu reports the investigation of the spectrum evolution of Rayleigh scattering in one-dimensional waveguide. Rayleigh scattering has been tremendously investigated in many fundamental researches attributing to its potential application. However, the spectrum characteristics are not investigated systematically in the aforementioned study, which is an essential characteristic for Rayleigh scattering. After successful investigation of the RBS in different types of optical fibers in their previous work, the RBS acting as an effective linewidth compression mechanism has been successfully applied to fiber lasers and semiconductor lasers attributing to its narrowband-pass filtering characteristic. However, it is still a challenge and almost unexplored topic to understand the dynamic characteristics of sSpE of laser in Rayleigh scattering medium structure and the linewidth compression mechanism. In order to answer these questions, they demonstrate the dynamic characteristics of SpE in an ODW based on the quantum theory. They establish a SpE-model of RBS source in ODW and simulate the dynamic process of the SpE in the continuous scattering. An approximate theoretical prediction for the relationship between the spectrum linewidth of the scatting source and the transmission length is proposed based on theoretical assumption. Also, a theoretical model of the micro-cavity structure employed to realize the effective linewidth compression is proposed. This investigation provides a reference value and a theoretical support for a better understanding of the deep compression of laser linewidth, which is also of great significance to the design and fabrication of micro-cavity structure for realizing the deep compression of laser linewidth.

About the Group 
The research group of Prof. Zhu from the College of Opto-electronic Engineering, Chongqing University mainly engages in the fields of controllable laser and precision measurement. In this research fields, many original works including the tunable mechanism of laser frequency-domain linewidth and time-domain pulse-width, control core devices, time/frequency-domain controllable laser system and application of precision measurement have been carried out, and a full-chain achievement has been formed from basic research to technology application. The controllable laser and precise measurement system based on the independent  core technology has been applied in the fields of health and safety monitoring, aerospace, Southern Power grid, national coal and so on. And it will continue to develop high-performance controllable light source and precise measurement system to serve the national construction. Prof. Zhu is the head of a research team which consists of two professors, one researcher, one associate professor, four lecturers and two postdoctoral students. He is a recipient of the first prize of natural science of the ministry of education, the first prize of scientific and technological progress of Sichuan province, second prize of technological invention of Chongqing and second prize of Natural Science of Chongqing. Presently, he presides more than 10 research funds including National Outstanding Youth Fund, the Key Project of Natural Science Foundation of China,the key research and development project of Ministry of Science and Technology etc. He has authored/co-authored over 200 academic papers in important journals (such as Optics Letters, Optics Express) with more than 4000 Google Scholar citations (h index 34). He is a recipient of over 20 authorized invention patents with 6 transferred and a monograph entitled "Principles and Applications of Fiber Bragg Grating" cooperatively.

Article
Li F H, Lan T Y, Huang L G, Ikechukwu I P, Liu W M et al. Spectrum evolution of Rayleigh scattering in one-dimensional waveguide. Opto-Electron Adv 2, 190012 (2019).
DOI:10.29026/oea.2019.190012