Simple working principle on optical fiber of fiber laser cutting machine

 Optical fiber of fiber laser cutting machine is a kind of medium-infrared band laser with fiber laser as the working material (gain medium). It can be divided into rare earth doped fiber laser, optical fiber nonlinear effect laser, single crystal fiber laser, fiber arc lasers,etc..based on the launching excitations. Among them, rare earth doped fiber lasers are very mature, such as doped erbium fiber amplifier (EDFA) has been widely used in optical fiber communication systems. High fiber lasers are mainly used in military (photoelectric confrontation, laser detection, laser communication, etc.), laser processing (laser marking, laser robot, laser micromachining, etc.), medical and other fields.

The fiber laser is made by SiO2 as the matrix material of glass solid fiber, which principle of light guide is to make use of the total reflection principle of the tube, that is, when the light is emitted from the optical density medium of high refractive index to the one of small refractive index with a angle larger than the critical angle, total reflection will appear and the incident light will be totally reflected to optical density medium of high refractive index. When the light is emitted from the optical density medium (that is, the refractive index of the light in the medium is large) to the interface of the optical sparse medium (i.e., the refractive index of the light is small in the medium), all of the light is reflected back into the original medium. There’s no light to penetrate the optical density medium which is of small refractive index.. Ordinary bare fiber is generally composed of a high refractive index glass core (diameter of 4 ~ 62.5μm), an intermediate low refractive index silicon glass cladding (core diameter 125μm) and an outermost reinforced resin coating. Fiber optic propagation mode can be divided into single-mode (SM) fiber and multi-mode (MM) fiber. Single-mode fiber core diameter, of smaller core diameter ( 4 ~ 12μm) can only spread one model of light and the mode dispersion is small. Multimode fiber core diameter which is thicker (diameter greater than 50μm) can spread a variety of modes of light while the intermodal dispersion is larger. According to the refractive distribution rate, optic fiber can be divided into step index (SI) fiber and graded index (GI) fiber.

Take rare earth doped fiber lasers for example, doped with rare earth particles as a gain medium, doped fibers are fixed between two mirrors forming a resonant cavity. The pump light is incident from the M1 into the fiber and then produces laser from M2. When the pump light passes through the fiber, it is absorbed by the rare earth ions in the fiber and the electrons are excited to a higher excitation level to achieve the population inversion of particles. The inversed particles are transferred from the high energy level to the ground state in the form of radiation to produce laser.