Introduction to fiber lasers

Introduction to Fiber Lasers

Optical fiber amplifiers developed using optical fibers doped with rare earth elements have brought revolutionary changes to the field of lightwave technology. Since any optical amplifier can form a laser with the proper feedback mechanism, fiber lasers can be developed on the basis of fiber amplifiers. The fiber lasers currently developed mainly use rare-earth element-doped fiber as the gain medium. Because the fiber core of the fiber laser is very thin, it is easy to form a high power density in the fiber under the action of the pump light, resulting in the "number inversion" of the laser energy level of the laser working material. Therefore, when a positive feedback loop (constituting a resonant cavity) is properly added, laser oscillation can be formed. In addition, because the fiber matrix has a wide fluorescence spectrum, fiber lasers can generally be made tunable, which is very suitable for WDM system applications.

We can classify fiber lasers from different angles. For example, according to the structure of the resonant cavity of the fiber laser, it can be divided into two categories: Fabry-Perot cavity and ring cavity. It can also be divided into single-wavelength and multi-wavelength according to the number of output wavelengths. For the characteristics of different types of fiber lasers, the following points should be considered: (1) The lower the threshold, the better; (2) The linearity between the output power and the pump optical power is better; (3) The output polarization state; (4) The mode structure ; (5) Energy conversion efficiency; (6) Laser operating wavelength, etc.

Compared with semiconductor lasers, the advantages of fiber lasers are mainly reflected in: fiber lasers are waveguide-type structures, capable of high-capacity pumping, high gain, high conversion efficiency, low threshold, good output beam quality, narrow line width, simple structure, High reliability, easy to realize and optical fiber coupling.

Compared with CO2 lasers, CO2 lasers are used in more stable, larger-format, and faster machine tools, while fiber lasers are mainly used for curved surfaces below 2mm. The main advantages of fiber lasers are: 1. The wavelengths of fiber lasers and CO2 lasers differ by an order of magnitude. CO2 lasers cannot be transmitted by optical fibers, while fiber lasers can be transmitted by optical fibers, which greatly increases the flexibility of processing; 2. The photoelectric conversion rate of fiber lasers is as high as more than 25%, while the photoelectric conversion rate of CO2 lasers is only about 10%. The advantages of fiber lasers in terms of electricity consumption and supporting cooling systems are quite obvious.