Fiber Laser Pump Source

Abstract: According to the special structure of fiber laser, different types of fiber laser pump sources are proposed, and the criteria for selecting pump source and its corresponding efficiency are given.

The main components of the laser are the resonant cavity, the pump source and the working substance. The pump source is the excitation source that causes the laser working medium to reach the population inversion. The process of particles from the ground state to the high energy level is called the pumping process. Common pumping methods include electric pumping, chemical pumping, optical pumping, and pneumatic pumping, while optical pumping and electric pumping are the most widely used methods. Gas lasers often use an electric pumping method as an excitation source, and optical pumping methods are widely used in solid and liquid lasers. Optical pumping uses a beam of light to illuminate the working substance so that the particles in the working substance absorb the energy of the photon and are excited to a high energy level. The LD pump source has many advantages such as high efficiency, low noise, stable frequency, long life and compact structure, and is often used as a pump source for solid-state lasers.

The working material of the fiber laser is generally doped fiber, and the feedback cavity is generally a fiber grating, a fiber end face, a ring mirror, etc.; the optical pumping mode is adopted to facilitate coupling the pump light into the fiber, and the fiber core itself is extremely fine, so that It is easier to form the accumulation of the number of upper level particles.

The essence of a fiber laser is a wavelength converter that converts the pump wavelength into light of a specific wavelength and outputs it as a laser. From the physics point of view, the principle of generating light amplification is to provide the working substance with light of its absorbable wavelength, so that the working substance can effectively absorb energy and be activated. Therefore, depending on the dopant material, the corresponding absorption wavelength is also different, and the requirements for the wavelength of the pump light are different. For example, the wavelength of the pump light of the erbium-doped fiber is 800 nm, 980 nm, 530 nm, etc., and the laser wavelength is 900 nm, 1060 nm, 1350 nm, etc.; the wavelength of the pump light of the erbium-doped fiber is 800 nm, 980 nm, 1480 nm, etc., and the laser wavelength is generated. 1550nm.

The choice of pump source for fiber lasers requires reference to the following standards:

(1) High pump efficiency. Pump efficiency directly affects pump power. The higher the pump power, the larger the tuning range;

The excited state absorption rate (ESA) is as small as possible. The ESA is usually measured by the value, which is the excited state absorption cross section, which is the ground state absorption cross section. For example, the wavelength of the pump light of the erbium-doped fiber is 532 nm, 980 nm, and 1480 nm. A YAG frequency-doubled solid-state laser can be used to generate a 532 nm laser, but the YAG frequency-doubled solid-state laser is bulky and inconvenient to put on the market. The pump laser with a wavelength of 980 nm and 1480 nm can be used with a high power LD. Its small size and high efficiency make it an ideal pump source. The pump source of the fiber laser can be a conventional solid-state laser, or a high-power multi-mode single-junction diode laser module or a diode array. For a diode array, end-pumping is commonly used to inject light into the fiber cladding. High-power diode arrays excite high-power lasers with an average run time of up to 104h. It has strict requirements for water-cooled, pulsed mode. For a single-junction diode optical pumping device, water cooling is not required and it is easier to couple into a double-clad fiber with high efficiency. The single-junction diode optical pumping unit has the same high output power as the array module and has a longer run time (up to 2 x 105h).

The research of fiber lasers has only developed single-clad fiber lasers in the initial stage, which is often used in the field of communication. However, single-clad fiber lasers are low-power lasers, which cannot meet the requirements of medical laser and machining. This is because strong pump light produces severe nonlinear effects when coupled into a very fine core, reducing conversion efficiency. Due to the limitations of pump light, fiber lasers can only be used in low power fields for a long time. Until the original single-mode fiber is replaced by a double-clad fiber, the high-efficiency conversion of the pump light to the diffraction limit is realized. The fiber laser finally has a place in the field of high-power lasers, and the double-clad fiber is introduced into the fiber. In the field of lasers, the limitation of fiber laser selection for pump sources is ended. The characteristics of pump sources are still very demanded by fiber lasers. The efficiency, size and lifetime of pump sources directly affect the light output of the entire laser.