Key Components

In order for this technology to become space flight ready there is a need to comprise characterization methods and achieve an understanding of the failure and degradation modes of optical fiber lasers from a component perspective.  Towards that goal several available designs are being studied to identify the most common components used.

 

Amplifier Laser Fiber:

Most rare earth doped fiber lasers and amplifiers consist of either Erbium or Erbium/Ytterbium fiber with fewer consisting of Ytterbium.  Erbium based fiber lasers are more closely related to typical fiber communications wavelengths in that they emit near around 1550 nm while Ytterbium type fiber lasers emit near 1060 nm making them more closely related to Lidar applications or free space communications where diffraction limited beams are necessary.  For applications that require wavelengths in the UV range either type of fiber laser can be utilized by frequency conversion using nonlinear crystals. 

 

General Components:

For applications that require shorter wavelengths (visible or UV), the larger the output power of the amplification stage to the nonlinear crystals the more likely crystals can be used that not require additional thermal control for frequency conversion to those wavelengths.  Fiber lasers can also include fiber bragg gratings for control of narrow linewidths.  Other passive optical components are used in a variety of designs.  In many designs, single mode doped laser fiber is used with double cladding to protect the fiber from optical damage but also to allow coupling from multimode pump sources.  The ability to couple multimode sources allows for higher pump powers.  In more recent state of the art designs under development, multimode rare earth doped optical fiber is being utilized to overcome problems with creating enough gain in the amplification stage in addition to the advantages of coupling greater power.

 

Pumping methods:

There are several methods of coupling pump laser diodes to the amplification fiber and a wide variety of pump diodes available at select wavelengths.  In many cases wavelength division multiplexing couplers are used for pumping laser diodes into the amplification fiber.  Less common are side pumping methods in which part of the fiber is etched in a manner than allows for pump light to enter the fiber through the cladding or in such way to allow for the ends of the amplification fiber to be available to the other components in the system.  The pump diode wavelengths are chosen based on which rare earth doped fiber is selected for the amplification stage.  The idea is to pump with the highest power, laser diode available for maximum efficiency to the output power.  Pump diodes range from simple laser diode modules to bar diodes and arrays.  Pump laser diode wavelengths are typically near or in close range to 808 nm, 980 nm, 1064 nm, and 1480 nm.