Definition: Optical pumping refers to the process of electronically exciting a medium with light or populating certain electronic levels. When you optically pump a medium, it means to inject light to excite the medium or some of its constituents into usually higher energy levels.

Meaning of Optical Pumping in the Context of Lasers

When optical pumping is used in the context of lasers or laser amplifiers, you are required to achieve a population inversion in the gain medium and hence, to obtain optical amplification through stimulated emission for some range of optical frequencies.

Use of Optical Pumping in Different Types of Lasers

Various types of lasers can be optically pumped. High-power fiber lasers and amplifiers also use optical pumping. One can inject pump and signal light into rare-earth doped double-clad fibers used for those fiber lasers and amplifiers. It is typically done for laser and amplifier devices in the research stage.

When it comes to industrial lasers, they are based on an all-fiber setup, where fiber-coupled pump laser diodes are connected to the active fiber via some passive transport fibers. It helps avoid any air spaces in the path. In addition to those simple transport fibers, which are usually multimode fibers, you also need fiber-optical pump combiners, also called pump and PM signal combiners.

What is a pump and signal combiner?

A Pump and Signal Combiner is a special type of coupler that can combine N pump lasers and 1 signal channel over one fiber and create a high-power pump laser source, that can further be used in different industries, such as medical, military, industrial, etc.

The use of pump and signal combiners in fiber lasers allow for better stability and robustness of devices.

Some versions of pump and signal combiners can handle power levels of multiple kilowatts. Devices used in this context have the following interfaces:

  • On one side, you will find a fiber that is directly connected to a certain type of active fiber, usually by fusion splicing. In some cases, between these two fibers, there is also an additional passive fiber to include fiber Bragg grating if it cannot be included in the active fiber.
  • On the other side, the combiner has several input multimode fibers that can be connected to fiber-coupled pump laser diodes. In addition, there is often another fiber, usually a single-mode fiber or a few-mode fiber, through which one can inject or extract signal light. In a fiber laser, though there is no need to inject signal light, you need to extract the signal light from one end.

Most often, pump and signal combiners come with a heat sink that helps avoid excessive heating due to dissipated power.

Use of Optical Pumping in Fiber Amplifiers – EDFAs

In addition to industrial high-power fiber lasers, high-power pump signal combiners are also widely used for erbium-doped fiber amplifiers (EDFAs) in optical fiber communications. While low-power EDFAs work with simple dichroic fiber combiners based on SM fibers, high-power EDFAs based on double-clad fibers based on MM fibers need multimode pump-and-signal combiners.

DK Photonics offers pump and signal combiners with different specifications for pumping high-power fiber lasers and fiber amplifiers. For any queries on pump and signal combiners, please contact DK Photonics.