Analysis of output polarization state of non-polarization-maintaining fiber laser

1 Introduction 　　Using Jones matrix theory, a simplified analysis model of polarization characteristics of non-polarization-maintaining fiber grating ring laser is established. Through experimental verification, the analysis results using this model are consistent with the experimental results. Analysis shows that lasers made of non-polarization-maintaining fibers can get a relatively stable power output, but the polarization state is disordered; and simply adding a polarizer will deteriorate the stability of the laser's output power, and the polarization characteristics are also not good. To improve. To use non-polarization-maintaining fiber to achieve single-polarization output, special polarization control measures must be taken for the laser.　　 Fiber laser (fiber laser cutting machine) has attracted the attention of researchers due to its good compatibility with fiber, high power and other advantages. Fiber lasers with different structures and characteristics are constantly being reported. Although the polarization characteristics of lasers are not required in the fields of instrument testing, laser processing, etc., there are still many application fields such as optical fiber communication external modulation, fiber optic gyroscopes, sensing, etc., which have strict requirements on the polarization characteristics of lasers, requiring it to have a single polarization. Output. Using polarization-maintaining fiber to make lasers is the easiest way to achieve single-polarization output. However, due to the high price of polarization-maintaining doped fiber, its application is strictly limited. People have been exploring the use of ordinary doped fibers to achieve single-polarization output, and various structures have been proposed, but there are very few theoretical analyses on the polarization characteristics of fiber lasers. This paper uses Jones matrix theory to establish a simplified model for analyzing the polarization characteristics of fiber ring lasers using non-polarization-maintaining fibers and fiber grating frequency selection.　　2Theoretical analysis 　　Using fiber grating as a frequency-selective element is a typical structure of fiber lasers. The Jones matrix theory is used to analyze the polarization characteristics of fiber grating ring cavity lasers. Lasers using other frequency-selective elements can also use similar analysis methods.　　 Due to the all-fiber structure of the fiber grating laser, when considering its polarization characteristics, the wavelength division multiplexer (WDM), circulator and coupler used therein are all polarization independent, while the doped fiber is non-polarization maintaining.