Active Core
To manufacture the laser generating active core material a common method is the Chemical Vapor Deposition (CVD) inside a substrate tube.
Fiber Pumping
The fiber pumping of an active laser fiber consists of three parts. The pump source, the pump fibers to feed the pump light to the active fiber and the pump cladding of active fiber. Depending on the power level the system is targeting, there are different options.
Power Level
Medium Power Laser Systems
For medium-power laser systems, a pure quartz glass fiber with a fluorinated plastic cladding, a so-called plastic clad silica (PCS) fiber, is sufficient in most cases to guide the pump light from the laser diodes to the pump cladding. The advantages of these fibers are a higher numerical aperture (NA) and lower manufacturing costs. They are made from a rod of pure synthetic fused silica and coated with a fluorinated polymer. The same polymer can be used for the pump cladding of the active fiber. Another possibility is that the pump cladding is produced by overlaying the active core with a synthetic fused silica tube with a second highly fluorinated fused silica layer.
High Power Laser Systems
For high power systems the solution with a fluorinated polymer is usually not sufficient. For high power systems therefore common all silica solutions are the standard. Here the cladding of the pump layer is created by a highly fluorine doped fused silica layer. The maximum achievable NA is 0.3 by our sophisticated Plasma Outside Deposition (POD) process. We can apply this process on your own core rod or supply jacket tubes already consisting of the pump and cladding layer as jacketing tube for your core rods.
Find more information on our Cladding Service
For the pump fibers to connect your pump source with the active fiber for high power systems all silica fibers can be used.
Efficiency
To increase the efficiency of the active fiber pumping a common method is to use unsymmetric pump claddings. The broken symmetry causes a mode mixing of the pump light and suppresses helix modes of the pump light. We can offer shaped pure silica tubes if you use a fluorinated polymer to guide your pump light and offer all silica solutions as well with a shaped interface between the fused silica pump layer and the fluorine doped fused silica cladding layer and a round outer shape to jacket your active core rods to increase the pump efficiency of your laser system.
Fiber Coupling
To achieve high power laser systems, it is common to combine several pump fibers into one active fiber or to combine several lasers generating active fibers into one delivery fiber. Heraeus Conamic is suppling capillaries for this application. Depending on your system configuration different material grades are available.
Application | Material grade | Advantages |
Medium power plastic clad silica (PCS) pump fiber | F300 | Pure silica, tight tolerance capillaries |
Medium power plastic clad silica (PCS) pump fiber | F320 | Lower refractive index (NA ~0.1) and viscosity compared to F300 |
High power all silica pump fibers and feed fibers | Highly Fluorine Doped TNU | Very low refractive index (NA 0.22) and viscosity |
Transmission Fiber
The transmission fiber connects your laser system with the workstation where the laser is used. Damage threshold and lowest attenuation are key criteria for the selection of core material and fiber design. Depending on the wavelength you want to use the fiber designs can be optimized by core material, numerical aperture, layer thickness and structure or by adjusting the core shape.
Fiber Termination
In high power laser systems at the end face of the feed fiber the fused silica bonding is exposed to air and therefore the damage threshold conditions are different compared to the bulk material. This can cause damages to the fiber end face in high power laser systems due to the high energy density at the surface. These surface defects can be solved by splicing a so-called end cap or end block to the end face of the fiber. This end cap has a larger diameter than the fiber.
The laser is still focused on the fiber end, but the interface is now fused silica / fused silica and therefore the damage threshold is the same as in the bulk material. The interface fused silica / air is now at the end face of the attached fused silica block. Due to the beam expansion, the cross section and therefore the energy density at this interface fused silica / air is now reduced and the end face is protected. Additionally, this end cap can be covered by an anti-reflective coating which increases the efficiency of your system.
