Fiber polarization controller

Fiber polarization controller (FPC) developed as an open source alternative for commercial ones. Thanks to the user-specified fiber-loop diameter, it allows printing the FPC for a given wavelength, with single-paddle operation very close to free-space quarter- or half-wave plate. Neodymium magnets on the base bottom tightly hold the FPC to an optical table. For nonmagnetic surfaces or long-term setups, multiple cutouts on each side of the FPC provide excellent mounting points to an optical table or breadboard. Additionally, printing with different colors allows for color-code your polarization control setup.

The loop diameter has been calibrated through direct polarization measurement @1555nm with SMF-28, see graph. 

The OpenSCAD model allows for adjusting many parameters of the FPC, such that, e.g., two-paddle config or imperial mounting spacing is possible.

Complete assembly of a single FPC (with default settings) requires

• 3D printed parts:
  • base
  • 2 base end covers
  • 3 paddles
  • 2 QWP paddle covers
  • 1 HWP paddle cover
  • 2 holders A1 and A2 each,
  • single holders B1, B2, C1, and C2
  • 2 smoothers
  • 3 cylindrical magnets - diameter 10mm and max thickness 2.5mm
• other
  • 8 screws M4 length 12mm
  • 3 screws M4 length 6mm
  • 11 nuts M4

I recommend printing the FPC with PETG since PLA is too rigid. I didn't try hotter plastics like ABS. Set thin layers for the paddles to keep the rotation cylinder more cylindrical (but 0.15 is enough). Use two colors for paddle covers to highlight the text. The best way to print holders is on their side, see photo. 

The only parts requiring postprocessing are the paddles - for these, cut off the rectangle brim and linear support along the whole rotation cylinder, shown in the photo. You can also do sanding or some whittling.

Assembly: The loops configuration should be 2-4-2 in the case of SMF-28 for the C-band (1550nm). Magnets should be placed in the three cutouts in the base - you can use superglue for mounting; for advanced users, I recommend tweaking the model to achieve a good press fit. The order of holders is shown in one of the photos. By tightening holder screws, you can change the pressure applied to paddles and, by such, change their rotation friction. Additional smoothers can be mounted with a triangular locking mechanism for taping the fiber to smooth height transition (FPC ←→ optical table).

Attached are G-codes for MK3S PETG with all recommendations mentioned above.