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Fiber-Based Polarization Beam Combiners/Splitters, 3 PM Ports
Thorlabs' Polarization-Maintaining Fiber-Based Polarization Beam Combiners (PBC) or Splitters are designed to either combine two orthogonal polarizations into a single fiber or split a single input into its orthogonal linear polarizations through two fiber outputs. The devices on this page feature two legs of polarization-maintaining fiber on one side of a calcite prism and one leg of polarization-maintaining fiber on the other. The legs on the side with the two PM fibers have the slow axis of the fiber aligned for maximum transmission of one polarization state.
In the polarization-maintaining PBC, all three legs contain PM fiber. If a polarized beam is aligned to the slow axis of the fiber on port 3, as represented by the yellow arrows in the diagram on the right, then this beam will be deviated by the prism so that it emerges from port 1 with the polarization aligned to the slow axis. Conversely, if the beam entering port 3 is aligned with the fast axis of the fiber, as represented by the green arrows in the diagram on the right, then the light will be deviated by the prism such that it emerges from port 2 with the light aligned to the slow axis. Note that the slow axes of the fibers on port 1 and port 2 are orthogonal to each other to match the polarization emitted by the calcite prism. If the polarization incident on port 3 is at an angle with respect to the axes, the output at ports 1 and 2 will vary depending on the angle of the incident polarization state.
This PM PBC can also be used in reverse: light incident on port 1 along the slow axis will exit from port 3 aligned to the slow axis, and light incident at port 2 with the polarization aligned to the slow axis will exit from port 3 with the polarization aligned to the fast axis. Light incident at ports 1 and 2 aligned to the fast axis of the fibers will refract differently through the prism and will not exit port 3.
These polarization beam combiners are frequently utilized to combine the light from two pump lasers into a single fiber to increase the input into an erbium-doped fiber amplifier or Raman amplifier.
Alternative PBC Options