(N+1)X1 PUMP & SIGNAL SIDE-PUMP COMBINER

WHAT IS A PUMP AND SIGNAL COMBINER

A pump and signal combiner is an optical component that has two interfaces. The first interface is specifically designed to connect a specific type of active fiber directly by using the fusion-splicing technique. The second interface of the combiner features multiple input multi-mode fibers that can be connected to fiber-coupled pump laser diodes. Figure 1 shows a schematic diagram of a high-power fiber laser engine structure, where the green part is the pump and signal combiner. An (N+1)×1 pump and signal combiner has the ability to integrate N separate pump lasers into a single fiber and create a high-power pump laser source.

WHAT ARE THE DIFFERENT BETWEEN SIDE-PUMP COMBINERS AND END-PUMP COMBINERS

Consider all-fiber construction, several power combiner schemes have been develop and classified into two methods: side-pump method, the fusion area in side face of signal fiber; and end-pump method, the fusion area in end face of signal fiber. As shown in Figure 2 and Figure 3, the schematic diagrams of a side-pump combiner and an end-pump combiner illustrate the different fusion areas.

Figure 2. The schematic diagrams of a side-pump combiner

Figure 3. The schematic diagrams of an end-pump combiner



HOW IS SIDE-PUMP COMBINERS DENOTED?

We used to denote a side-pump fiber combiner as (N+1)×1 , where (N+1)×1 can combine or couple N pump lasers with 1 signal fiber into one fiber. Figure 4 shows a schematic diagrams of the relative positions of the pump fiber and the signal fiber in several side-pump combiners. In most cases of side-pump combiners, the signal fiber and the output fiber are the same fiber.



HOW IS END PUMP COMBINERS DENOTED?

We used to denote an end-pump fiber combiner as N×1, where N×1 refers to combining or coupling N pump lasers into one fiber. Figure 5 shows a schematic diagrams of a 7×1 end-pump fiber combiner. In an end pump combiner, the signal fiber and the output fiber can be different fibers.

Figure 5. A schematic diagrams of 7×1 end-pump combiner.



ADVANTAGES OF END-PUMP COMBINERS

End-pump combiners offer high transmission efficiency. Moreover, the ability to use different fibers for the signal and output fibers in end-pump combiners allows for satisfying specific environmental requirements.



ADVANTAGES OF SIDE-PUMP COMBINERS

Side-pump combiners offer two advantages:

  1. Side-pump combiners utilize the side of the signal fiber as the coupling surface, which differs from the coupling conditions of the end-pump combiners. The employed process technology enables good optical isolation.
  2. In most cases, the signal fiber and output fiber in side-pump combiners are the same fiber, ensuring material consistency during beam transmission. This consistency results in good signal insertion loss and beam quality(M2).

In summary, side-pump combiners provide excellent optical isolation, signal insertion loss, and beam quality, making them advantageous for the laser processing industry.



PARAMETERS OF SIDE-PUMP COMBINERS

When using side-pump combiners, there are several parameters to consider, including:

  1. Pump efficiency: The definition is the ratio of output power to input power (coupling efficiency) of the side-pump combiner, usually expressed as a percentage (%) . The formula definition is defined as follows (P1 ⁄ P0)×100% , where P0 and P1 are total input power and total output power of the side-pump combiner, respectively.
  2. Signal insertion loss: The definition is the signal power loss caused by the side-pump combiner. The formula is defined as follows -10log10(P1 ⁄ P0) , where P0 represents the signal power without the side-pump combiner, and P1 the signal power with the side-pump combiner, and usually expressed in dB.
  3. Beam quality (M2): The definition is the characteristics of the laser beam output by the side-pump combiner and generally expressed in terms of m square M2, where M2 indicate the degree of similarity between the beam and the lowest-order Gaussian beam. When the value of M2 is closer to 1, it means that the beam resembles the lowest-order Gaussian beam more closely.
  4. Pump power handling: pump power handling refers to the highest input power that each pump source can withstand without encountering any instability or damage.
  5. Laser power handling: laser power handling is defined as the maximum stable output power that a combiner can handle.
  6. Return loss: The definition is the ratio of light reflected back into the input path due to scattering and reflection from optical surfaces and expressed in dB. The formula is defined as follows 10log10 PR ⁄ P0 , where P0 is total input power from all pump light sources and PR is the reflected power during transmission. Figure 6 below shows a schematic dia gram of the return loss.

  7. Environmental parameters include:
    1. Operating Temperature: The allowable temperature range of the local ambient environment in which the optical component can operate safely.
    2. Storage Temperature: The allowable temperature range of the local ambient environment in which the optical component can be stored without being damaged.
    3. Operating Humidity: The allowable humidity range of the local ambient environment in which the optical component can operate safely.
  8. Package Dimensions: Package dimension refers to the size dimensions of this component.



APPLICATION OF PUMP AND SIGNAL COMBINERS

Pump and signal combiners are widely used in amplifiers and fiber laser engines, with the primary purpose of coupling pump light sources to the signal fiber to increase the output optical power of the laser. Figure 9 below shows a schematic diagram of the fiber laser engine structure produced by PCT (Photonicore Technologies), which utilizes two (6+1)×1 pump and signal combiners. Figure 12 shows an actual product photo of the pump and signal combiners produced by PCT (PhotoniCore Technologies).