Optical Fiber Laser principles and characteristics

Optical Fiber Laser principles and characteristics

I. Introduction

Fiber Laser (Fiber Laser) is a device that uses glass Fiber reinforced with rare earth elements as the gain medium to produce Laser output. The fiber laser can be developed based on the fiber amplifier. Because the fiber core in the fiber laser is very small, the internal power density of the fiber is high under the pump, in this way, the laser energy level is "inverse of the number of particles". On this basis, a resonator is formed through a positive feedback loop to form a laser oscillation at the output.

Ii. Structure

The structure of a fiber laser is similar to that of a traditional solid-state laser and a gas laser. It consists of three parts: the pump source, the gain medium, and the cavity, as shown in. Among them, the pump source is generally a high-power semiconductor laser, the gain medium is glass fiber mixed with rare earth elements, the cavity consists of a coupler or fiber grating.

Iii. Principles

In the middle, the pump light from the pump source is coupled into the gain medium through a mirror. Because the gain medium is a rare earth-doped optical fiber, the pump light is absorbed, the rare earth ions absorbing the photon energy have an energy level transition and realize the inversion of the number of particles. After the reversal, the particles pass through the cavity and transition from the excited state back to the ground state, releasing energy and forming a stable laser output.

Iv. Features

Feature 1: Because the diameter of the fiber core is small, the content of the fiber core is easy to form a high power density, therefore, the optical fiber laser has a high conversion efficiency, a low threshold value, a high gain, a narrow line width, and can be easily and efficiently connected to the current optical fiber communication system.

Feature 2: Because the optical fiber has good flexibility, the optical fiber laser is compact, cost-effective, and easier to integrate systems.

Feature 3: compared with traditional solid-state lasers and gas lasers, fiber laser features high energy conversion efficiency, compact structure, high reliability, and is suitable for mass production.

Feature 4: Compared with a semiconductor laser, an optical fiber laser has a good color, produces a small number of latencies and distortion during modulation, and has a low coupling loss with the optical fiber.

Compared with a semiconductor laser, the advantages of a fiber laser are mainly reflected in the fact that the fiber laser adopts a waveguide structure and can be used as a high-capacity pump, it features high gain, high conversion efficiency, low threshold, good output beam quality, narrow line width, simple structure, and high reliability, and is easy to achieve coupling with optical fiber.

We can classify the optical fiber lasers from different angles. For example, according to the structure adopted by the resonator of the optical fiber laser, it can be divided into two categories: Fabry-Perot cavity and annular cavity. It can also be divided into single wavelength and multi wavelength according to the number of output wavelength.

The following aspects should be taken into account for the characteristics of different types of Optical Fiber Lasers:

(1) The lower the threshold, the better;

(2) The linearity between the output power and the pumped optical power is better;

(3) output polarization state;

(4) mode structure;

(5) energy conversion efficiency;

(6) laser operating wavelength.