light transmission in the fiber laser

Light conduction through optical fibers has permanently changed many areas of life. They make decisive contributions, particularly in telecommunications, process technology, fiber optic sensor technology, spectroscopy and medical diagnostics. Another important area is laser technology, in which fiber laser are increasingly replacing other types of laser. Due to their versatility and efficiency, they have become an indispensable tool in numerous industries.

light transmission in fibers

Typical optical fibers consist of a core surrounded by a cladding with a lower refractive index. Total internal reflection guides the light in the coreThis enables low-loss transmission over long distances. Laser technology also makes use of a special property of fibers: Doped quartz fiber cores can amplify light and serve as an active laser medium.

The most common dopants and their typical emission lines are:

• Erbium: 1550 nm
• ytterbium: 1030 nm
• neodymium: 1064 nm
• thulium: 1500 nm

Double-cladding fibers are used to efficiently pump the light into the doped fibers. The pump light runs in an additional cladding around the core and ensures a long interaction path. This technology is a decisive step in the further development of laser technology.

How fiber lasers work

A conventional solid-state laser consists of a pump diode, laser crystal and mirror resonator. In the fiber laser, a doped fiber replaces the laser crystal, and so-called fiber Bragg gratings (FBGs) replace the mirrors. These gratings selectively reflect the desired laser wavelength in the core fiber and offer several advantages:

• High stability, since no adjustment of the mirrors is required.
• High efficiencybecause up to 70 % of the pump light is converted into laser light.
• High gainThis is made possible by the long interaction distance along the fiber.

Fiber amplifiers and their performance

Fiber lasers often use a combination of seed lasers and fiber amplifiers, such as EDFAs (erbium-doped fiber amplifiers) or YDFAs (ytterbium-doped fiber amplifiers). These amplifiers amplify the laser signal in stages and allow flexible adaptation to different applications.

The maximum power is limited by the damage threshold of the power amplifier fiber:

• single-mode fibers: up to 10 kW
• multimode fibers: up to 50 kW

To avoid feedback, Faraday isolators are used to increase the stability of the system.

high-power and low-power lasers

Fiber lasers can be divided into high-power and low-power lasers:

• low-power lasers are used in biotechnology and telecommunications. Frequency-doubled fiber lasers from MBP Communications generate wavelengths in the visible range that are ideal for fluorescence microscopy and flow cytometry. These lasers provide precise excitation for various fluorescent markers.
• high-power laser are mainly used in material processing. Applications include the cutting and welding of metals. One notable example is the fiber laser from IPG with a beam power of 18 kW.

Pulsed fiber lasers and MOPA technology

Pulsed fiber lasers are used for applications that require short light pulses. The MOPA technology (Master Oscillator Power Amplifier) offers considerable advantages. A seed laser defines the pulse duration, while the fiber amplifiers amplify the energy without changing the pulse duration. This results in precise and repeatable pulses, which are particularly advantageous in material processing and medical applications.

Limitations of Fiber Lasers

Despite their many advantages, fiber lasers require careful design in order to work reliably:

• Destruction threshold of the power amplifierHigh laser power can damage the fiber.
• ASE (Attenuated Spontaneous Emission)Leads to undesirable radiation effects.
• Nonlinear effectsPhenomena such as stimulated Raman and Brillouin scattering can impair efficiency.

However, many of these challenges can be successfully overcome by taking appropriate measures such as optimizing the materials and system parameters.

Future Prospects of Fiber Lasers

The continuous development of fiber laser technology is producing ever more powerful and efficient systems. Advances in miniaturization are enabling the use of compact lasers in new sectors such as environmental technology and medical technology. With the integration of artificial intelligence and machine learning, future fiber lasers could offer even more precise and efficient applications.

Conclusion

fiber laser have established themselves as indispensable tools in numerous industries. Their efficiency, versatility and performance make them the preferred choice for applications in materials processing, biotechnology and telecommunications. With ongoing research and technological innovation, fiber lasers will continue to push the boundaries of what is possible and open up new fields of application.