We all know that fiber lasers are widely used in daily life, so do you know what are the main devices inside? Where can it be mainly used? Let's take a look at it together

Generally speaking, the most critical parts of a fiber laser are pump source, gain fiber, fiber Bragg grating (FBG), isolator, coupler and output fiber. These things seem to be piecemeal, but each one is quite critical, and no one can do without it.

The pump source is equivalent to the "heart" of the whole laser, which provides energy for the system. At present, high-power semiconductor laser diodes are commonly used, and the wavelength is generally in the range of 915nm or 976nm. Its stability is very important, even if the current fluctuates a little, the output power will fluctuate with it, which is particularly prone to problems.

Let's talk about the gain fiber, which is actually an optical fiber doped with rare earth elements (such as erbium, ytterbium and thulium), and this part is the place where it "shines". The wavelength of light emitted by different doping materials is also different. For example, erbium-doped fiber is generally at 1550nm, which is used in communication systems. Yb-doped fiber is at 1064nm, which is a common band in industrial processing. The length, doping concentration and cladding structure of optical fiber must be matched, otherwise the efficiency will not go up and even self-excited oscillation will occur.

Fiber Bragg Grating (FBG) is a reflection grating engraved in optical fiber, which is used to build a resonant cavity. The reflectivity and central wavelength of FBG are just matched with the gain fiber. If this place is not well designed, the output spectrum will be chaotic, and the power will be meaningless.

The function of isolator is also very critical. Although it is inconspicuous, it can prevent light from reflecting back into the gain medium. Many lasers are unstable in power or easy to damage tubes, and the reflected light is often not handled well. Before, a customer connected the laser to the cutting head. As a result, the reflective material (such as copper plate) was cut without an isolator. After several reflections, the LD was directly burned.

Couplers and output optical fibers are mainly responsible for combining and outputting energy. Some systems use multi-pump beam combination. If this coupler is not well designed, the loss will be great.

In the field of communication, this is mainly a low-power erbium-doped fiber laser, which is used for optical communication amplification. Its stability and wavelength accuracy are particularly high. There are also some sensing applications, such as fiber optic gyroscopes, temperature or strain sensors, which also use fiber lasers.

In addition, there are many uses in medical treatment and scientific research, such as ytterbium fiber laser for tissue cutting and thulium fiber laser for minimally invasive surgery. The wavelength of this kind of laser is near the absorption peak of human tissue, with concentrated energy and little damage to tissue.

The core of fiber laser is an "efficient and stable energy conversion system". As long as each device is selected correctly and matched well, it can continuously output stable laser, and it is easy to use. Conversely, even if only one pump LD is aged or the reflectivity of grating is a little off, it may lead to power drift or even collapse of the whole system.