What Is a Fiber Combiner? (Important Components of Fiber Laser)

The optical fiber combiner is a kind of optical fiber connecting device.

Through the optical fiber precision fusion technology, the optical energy output by the transmitting optical fiber is coupled to the receiving optical fiber to the maximum extent, and the impact on the system caused by its intervention in the optical path is minimized.

The fiber combiner is an important component in the fiber laser system.

Its quality not only directly determines the power and beam quality of the fiber laser, but also an important guarantee for the safe and stable operation of the laser.

fiber combiner

Classification of optical fiber combiners

According to the functional classification, fiber combiners can be divided into two categories: power combiners and pump combiners.

(1) The pump combiner is mainly used to combine multiple pump beams into an optical fiber for output, which is mainly used to improve the pump power.

(2) The power combiner is used to combine multiple single-mode lasers into an optical fiber for output to improve the output power of the laser.

Pump Combiner

Power combiner

Power combiner

According to the classification of composition, the optical fiber combiner can be divided into two categories: N×1  optical fiber combiner without signal fiber and (N+1)×1 optical fiber combiner with signal fiber.

Different from N×1  fiber combiner, one fiber in the center of (N+1)×1 fiber combiner is signal fiber.

In the manufacturing process, N optical fibers must be closely and symmetrically arranged around the signal optical fibers, and the signal optical fibers in the middle are used for signal light input.

N×1 the combiner includes both power combiner and pump combiner.

The different functions depend on the model of N-channel input fiber.

If the n-channel fiber is single-mode fiber or large mode field fiber, it can be directly connected with n lasers to improve the output power of the laser, that is, the power combiner;

If the N-way fibers are multimode fibers, they are connected with N pump sources to improve the pump power of the laser, that is, the pump combiner.

N × 1 optical fiber combiner

N × 1 optical fiber combiner

(N+1) × 1 beam combiners are pump beam combiners, which are mainly used in optical fiber amplification systems.

The single-mode fiber in the middle of the combiner is the signal fiber for signal light transmission, and the N-channel multimode fiber surrounding it is the pump fiber for pump light transmission.

This combiner is usually used in MOPA structures.

(N+1) × 1 optical fiber combiner

(N+1) × 1 optical fiber combiner

Side pump combiner and end pump combiner

The center of the side pump combiner is a signal fiber, the core is a single-mode or quasi single-mode waveguide for laser transmission, and the six peripheral fibers are pump fibers for pump light transmission.

After the seven optical fibers are arranged in order, they are melted, drawn and welded with the output double clad optical fiber.

End pumped combiner fiber combiner

The difference between the side pump combiner and the end pump combiner is that the pump fiber of the side pump combiner is taped to the cladding of the signal fiber, while the signal fiber is not melted and tapered.

Therefore, the signal transmission of side pump combiner is superior to that of end pump combiner in principle.

Side pumped fiber combiner

Side pumped fiber combiner

Fabrication of beam combiner

The basic structure of the power combiner consists of three parts: input fiber, fused taper fiber bundle and output fiber.

Basic structure of power combiner

Basic structure of power combiner

First of all, in order to make the fiber bundle fuse and taper well with the output fiber, the cross-section of the fiber bundle must be circular, and the pump fibers are closely arranged in a certain geometric way, usually the fibers are closely arranged in a regular hexagon.

In the manufacturing process, the input fiber bundles are first assembled, then the input fiber bundles of the assembled bundles are fused and tapered to form a fused taper fiber bundle, and then the taper waist of the fused taper fiber bundle is cut and fused with the output fiber.

Finally, a suitable packaging and heat dissipation structure is designed to ensure that the beam combiner can work stably for a long time.

Usually, copper or aluminum with high thermal conductivity will be used as the shell for packaging and heat dissipation, and the water-cooling structure will be designed on the metal packaging if necessary.

Fiber laser realizes the connection of fiber devices by welding.

In order to achieve higher power, high-quality fiber fusion is very important.

In the process of welding fiber, inevitably there will be losses.

These losses will continuously accumulate light and heat during the operation of the laser, which may lead to the deterioration of beam quality or the damage of optical components.

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