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Application and introduction of fiber laser

  04 Jun , 2020         Chris         7950

Fiber Laser refers to the element with rare earth doped glass Fiber as the gain medium of the Laser, Fiber Laser can be developed on the basis of the optical Fiber amplifier: within the optical Fiber under the action of the pump are high power density

Fiber Laser:

Fiber Laser refers to the element with rare earth doped glass Fiber as the gain medium of the Laser, Fiber Laser can be developed on the basis of the optical Fiber amplifier: within the optical Fiber under the action of the pump are high power density, causing the Laser working substances of Laser level "population inversion", as appropriate to join the positive feedback loop (a cavity) can form a Laser oscillation output.

Fiber laser application range is very wide, including fiber optic communications, laser space distance communication, industry, shipbuilding, automobile manufacturing, laser engraving, laser marking laser cutting, printing, metal, nonmetal drilling in rollers/cutting/welding, brazing welding, water quenching, cladding, and depth), military defense security, medical equipment, large infrastructure, as other laser pump sources are used, and so on.

Fiber laser refers to the laser which USES glass fiber doped with rare earth elements as gain medium. Fiber laser can be developed on the basis of fiber amplifier.Under the action of pump light, it is easy to increase the power density in the fiber, resulting in "particle number inversion" of the laser energy level of the laser working material. When a positive feedback loop (forming a resonator) is properly added, the laser oscillation output can be formed.


Structure:

The generation of laser signal requires three basic conditions: particle number inversion, optical feedback and reaching the laser threshold. Therefore, the laser is composed of three parts: working material, pump source and resonator.The basic structure of the fiber laser is as follows.The purpose of pumping light is to use it as external energy to reverse the number of particles in the gain medium, which is the pump source.The optical resonator consists of two mirrors that allow the photons to be fed back and amplified in the working medium.The pumped light is absorbed into the gain fiber, and then the number of energy level particles in the gain medium is reversed. When the gain in the resonator cavity is higher than the loss, laser oscillation will be formed between the two mirrors and the laser signal output will be generated.


Features:

(1) good beam quality.

The waveguide structure of optical fiber determines that the fiber laser is easy to obtain the single transverse mode output, and is less affected by external factors, which can realize the high brightness laser output.

(2) high efficiency.

Optical fiber laser can achieve high efficiency of light-to-light conversion by selecting the semiconductor laser whose emission wavelength is matched with the absorption characteristics of doped rare earth elements as the pump source.For ytterbium-doped high-power fiber lasers, 915 or 975 nanometer semiconductor lasers are generally selected. With a long fluorescence life, they can store energy effectively to achieve high-power operation.The overall electro-optic efficiency of commercial fiber laser is up to 25%, which is conducive to cost reduction and energy saving and environmental protection.

(3) good heat dissipation characteristics.

Optical fiber laser USES long and thin doped rare earth element fiber as laser gain medium, and its surface area and volume ratio are very large.About 1000 times that of solid block laser, it has natural advantages in heat dissipation capacity.In the case of medium and low power, there is no need for special cooling of optical fiber. In the case of high power, water cooling is adopted to dissipate heat, which can also effectively avoid the beam quality and efficiency decline caused by thermal effect commonly seen in solid-state lasers.

(4) compact structure and high reliability.

Because the fiber laser USES the small and soft fiber as the laser gain medium, it is advantageous to compress the volume and save the cost.Pump sources are used are also small volume, easy to modular semiconductor laser, commercial product can generally be tail fiber output, combined with optical fiber Bragg grating, packtized devices, as long as these devices are welding can be realized all packtized, immune to environmental disturbance ability is high, has the very high stability, and can save time and cost of maintenance.


Classification:

First, according to the type of fiber material classification

1. Crystal fiber laser.Working material is laser crystal fiber, mainly ruby single crystal fiber laser and nd3+ : YAG single crystal fiber laser.

2. Nonlinear optical fiber laser.There are mainly stimulated Raman scattering fiber laser and stimulated brillouin scattering fiber laser.

3. Rare earth doped fiber laser.Fiber optic matrix material is glass, doped into the fiber rare-earth element ions to activate, and made of fiber laser.

4. Plastic fiber laser.The fiber laser is made by adding laser dye into the plastic fiber core or cladding.

Ii. Gain media are classified as follows:

1. Crystal fiber laser.Working material is laser crystal fiber, mainly ruby single crystal fiber laser and Nd3+:YAG single crystal fiber laser.

2. Nonlinear optical fiber laser.There are mainly stimulated Raman scattering fiber laser and stimulated brillouin scattering fiber laser.

3. Rare earth doped fiber laser.The fiber is activated by doping rare earth element ions into the fiber (Nd3+, Er3+, Yb3+, Tm3+, etc., and the matrix can be quartz glass, zirconium fluoride glass, single crystal) to make the fiber laser.

4. Plastic fiber laser.The fiber laser is made by adding laser dye into the plastic fiber core or cladding.

Three, according to the resonant cavity structure classification

It is divided into f-p cavity, ring cavity, ring reflector fiber resonator cavity, "8" shaped cavity, DBR fiber laser, DFB fiber laser and so on.

Four, according to the fiber structure classification

It is divided into single cladding fiber laser, double cladding fiber laser, photonic crystal fiber laser and special fiber laser.

Classification by output laser characteristics

Divided into continuous fiber laser and pulse fiber laser, pulse fiber laser according to its pulse forming principle can be divided into Q modulated fiber laser (pulse width is ns magnitude) and mode-locked fiber laser (pulse width is ps or fs magnitude).

 


Advantage:

As the representative of the third generation laser technology, fiber laser has the following advantages:

(1) low manufacturing cost of glass fiber, mature technology and advantages of miniaturization and intensification brought by optical fiber's windings;

(2) the glass fiber does not need the same strict phase matching as the crystal for the incident pump light, which is due to the wide absorption band caused by the non-uniform broadening caused by the Stark splitting of the glass matrix;

(3) glass material has extremely low volumetric area ratio, fast heat dissipation and low loss, so the conversion efficiency is high and the laser threshold is low;

(4) multiple output laser wavelengths: this is because rare earth ion energy levels are very rich and rare earth ion types are numerous;

(5) tunability: due to the wide rare earth ion level and the wide fluorescence spectrum of glass fiber.

(6) since there is no optical lens in the resonant cavity of the fiber laser, it has the advantages of free adjustment, free maintenance and high stability, which is incomparable to the traditional laser.

(7) fiber optic export enables the laser to be easily qualified for various multi-dimensional processing applications in arbitrary space, making the design of mechanical system very simple.

(8) capable of harsh working environment, with high tolerance for dust, shock, impact, humidity and temperature.

(9) do not need thermoelectric refrigeration and water cooling, only simple air cooling.

(10) high electro-optical efficiency: the comprehensive electro-optical efficiency is as high as more than 20%, which can greatly save the power consumption during work and the operation cost.

(11) the high power, commercial fiber laser is 6 kw.


Application:

1. Marking application

Pulse fiber laser with good beam quality, reliability, and the longest free maintenance time, with the highest overall electro-optic conversion efficiency, pulse repetition frequency, the smallest volume, don't need to water the simplest and the most flexible way of use, the lowest operating cost makes it in high speed, high precision laser engraving the only choice.

A fiber-optic laser marking system may consist of one or two fiber-optic lasers with a power of 25 watts, one or two scanning heads used to direct light to the workpiece, and an industrial computer that controls the scanning head.This design is more than four times more efficient than using a 50W laser beam split between two scan heads.The maximum marking range of the system is 175mm*295mm, the spot size is 35um, and the absolute positioning accuracy in the full marking range is +/-100um.The focusing spot at a working distance of 100um can be as small as 15um.

2. Application of material processing

The material treatment of fiber laser is based on the heat treatment process where the material absorbs the laser energy.Laser light energy of about 1um is easily absorbed by metal, plastic and ceramic materials.

3. Application of material bending

Fiber laser molding or bending is a technique used to change the curvature of a metal plate or hard ceramic.Centralized heating and rapid self-cooling lead to malleable deformation in the laser-heated region, which permanently changes the curvature of the target workpiece.It has been found that laser microbending is far more precise than other methods, and it is an ideal method for microelectronics manufacturing.

4. Application of laser cutting

With the increasing power of fiber laser, fiber laser has been applied in industrial cutting.For example, stainless steel arterial tubes are microcut by a fast chopper continuous fiber laser.Because of its high beam quality, fiber lasers can achieve very small focusing diameters and the resulting small slit widths that are refreshing standards in the medical device industry.

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