Coupling Method Between Laser and Optical Fiber

Coupling Method Between Laser and Optical Fiber

Laser and fiber coupling is also called fiber-coupled laser, which is used for PCB plate making, LDI exposure, fluorescence excitation, biological detection, welding, 3D printing and other purposes. The coupling methods of semiconductor lasers and optical fibers can be divided into two categories: direct coupling and optical lens group coupling.

The following is a detailed introduction to these two different coupling methods:

1. Direct coupling method

A. Fiber direct coupling: 

This method is to align the output end of the laser directly with the input end of the fiber core. Usually, a precise alignment device is required to ensure the precise alignment between the two. It is suitable for low-power lasers and shorter coupling distances.

Advantages: simple structure, small size, and low cost.

Disadvantages: alignment is difficult, the coupling efficiency is greatly affected by the alignment accuracy and laser wavelength, and it is easily affected by mechanical vibration and temperature changes.

B. Direct coupling of optical fiber microlens: 

A microlens is integrated at the end of the optical fiber to focus the output beam of the laser into the core of the optical fiber. The microlens can be a spherical lens or an aspherical lens, which effectively optimizes the beam quality and improves the coupling efficiency, such as directly coupling the laser diode to the pigtail output.

Advantages: The coupling efficiency is improved and the alignment accuracy requirements are relatively low.

Disadvantages: The manufacturing cost of the microlens optical fiber is high and may introduce additional optical losses.

2. Optical lens group coupling method

A. Single lens coupling: 

Use a single lens to focus the laser beam to the input end of the optical fiber.

The choice of lens (such as focal length, numerical aperture) has an important influence on the coupling efficiency.

Advantages: The structure is relatively simple and easy to implement.

Disadvantages: The coupling efficiency may not be as good as that of the multi-lens system, and the optical quality requirements of the lens are higher.

B. Double-lens coupling (4f system):

The 4f optical system consists of two lenses. The first lens focuses the laser beam to an intermediate image plane, and the second lens focuses the beam of this image plane to the input end of the optical fiber. This configuration can provide higher coupling efficiency and better compression of the laser beam, which is suitable for some industrial lasers for engraving and cutting.

Advantages: high coupling efficiency, good laser beam quality, good spot compression effect, and relatively easy system alignment.

Disadvantages: increased system complexity and relatively high cost.

3. Multi-lens coupling:

Use multiple lens combinations to optimize the transmission and coupling of laser beams, which can include polarization, collimation, compression lens arrays and other optical elements such as beam shapers, wavefront correctors, etc.

Advantages: A highly optimized coupled fiber system can be designed as needed, suitable for demanding applications.

Disadvantages: The system is complex, costly, and difficult to design and align.

When choosing a coupling method, you can make your selection based on the laser power, laser wavelength, fiber core diameter, coupling efficiency, power stability, output method, and economic requirements of the fiber-coupled laser. If you have any other questions, please feel free to communicate with us.