The core structure of a single-mode fiber laser

The core structure of a single-mode fiber laser

The outstanding performance of single-mode fiber laser stems from their precise internal structure design. The efficient collaborative operation among all components is the foundation for achieving stable and high-quality laser output.

For instance, a 976nm laser with a relatively high electro-optical conversion efficiency is used to charge the doped fiber, and then a 1064nm seed light with good beam quality is used to guide the charged doped fiber to release a 1064nm laser with higher energy. The higher the required 1064nm laser energy, the more power and quantity of the pump source are demanded.

Detailed explanation of key components

The pump source is the energy source of the laser, usually a semiconductor laser diode, whose emission wavelength matches the absorption peak of the gain medium (for example, a ytterbium-doped fiber corresponds to a wavelength of 915nm or 976nm). Single-mode laser require the pump light source to also have high spatial coherence. Therefore, single-mode fiber-coupled laser diodes are often used to ensure that the pump light can be efficiently injected into the fine single-mode fiber core.

2. Gain fibers are the core medium for laser generation and are usually quartz glass fibers doped with rare earth elements. Common doped ions include ytterbium (Yb³⁺), erbium (Er³⁺), thulium (Tm³⁺), etc., which correspond to different output wavelength bands (such as 1064nm, 1550nm, 2μm, etc.). The length of the gain fiber needs to be precisely designed to ensure full absorption of the pump light while maintaining high-efficiency opto-optical conversion.

3. The most common implementation form of a resonant cavity is the fiber Bragg grating pair. A grating is formed by exposing optical fibers to ultraviolet laser interference fringes, causing a permanent periodic change in the refractive index of their core regions. By controlling the period and length of the grating, the central wavelength and bandwidth of its reflection can be precisely controlled. This fully fiberized resonant cavity structure does not require discrete components such as optical lenses, significantly enhancing the stability and anti-interference capability of the system.

4. The beam collimation output system is usually located behind the output end grating. Its function is to convert the divergent laser emitted from the optical fiber into collimated parallel light or further focus it onto the working surface. This system usually includes self-focusing lenses or micro-miniature lens groups and adopts a precise mechanical structure to ensure alignment accuracy. High-quality optical design can effectively reduce aberrations and ensure that the output beam maintains an excellent Gaussian distribution.