Briefly describe the core principles of fiber laserFiber laser uses glass fiber doped with rare earth elements as the gain medium, forming particle number inversion under the action of pump light, and coupled with a resonant cavity to provide optical feedback, ultimately achieving stable laser oscillation output. It is a representative of third-generation laser technology that combines high beam quality and high conversion efficiency.
1. The core function and working process of a resonatorThe resonator is the core structure that forms laser oscillation. It constructs a closed optical feedback loop, allowing photons to amplify back and forth within the cavity until the total loss is overcome to form a strong laser that can be output.
1.1In a typical ytterbium doped fiber laser, the resonator is composed of a pair of fiber Bragg gratings:High reflectivity grating: With a reflectivity of over 99% for the target laser wavelength, it is almost a total reflection mirror that completely reflects the light back to the gain fiberOutput coupled grating: Retain 10%~50% reflectivity to maintain intracavity oscillation, and the remaining transmitted output can be used for laser
1.2Complete workflow:Pump light is injected into the gain fiber through a beamformer to excite ytterbium ions and generate spontaneous emission; Only photons with wavelengths that match the grating are reflected by the two end gratings, and continuously amplified by stimulated radiation during the back and forth process inside the cavity. After the light intensity saturates, stable laser light is emitted from the output coupling end.
2. Pattern filtering mechanismThis mechanism is used to suppress high-order transverse modes, retaining only the fundamental mode to achieve high beam quality (M² close to 1) output, relying on dual paths to achieve:
2.1The waveguide constraint of double clad gain fiber: the core diameter is only 10-20 μ m, belonging to single-mode or few mode waveguide, and only the fundamental mode can achieve low loss and stable transmission; The outer large-sized cladding is responsible for transmitting multi-mode pump light to ensure pump efficiency
2.2Gain competition screening: The fundamental mode optical field is completely concentrated in the center of the ytterbium doped fiber core, with the highest overlap with the gain medium, and the amplification gain obtained is much higher than that of higher-order modes distributed at the edge of the fiber core; By intentionally bending the fiber, additional high-order mode leakage losses are introduced, ultimately completely suppressing high-order modes and achieving pure fundamental mode output.
Media Contact
Company Name: Beijing Rofea Optoelectronics Co., Ltd.
Email: Send Email
Country: China
Website: https://www.bjrofoc.com/
