Vacuum feed-through
Multi-The fiber cable with vacuum feed-through made by Schäfter+Kirchhoff is equipped with a multimode fiber cable for type MMC-S-VIS/NIR-100-NA022. The feed-through is suitable for vacuums down to 10-7 mbar and is supplied with a screw-type flange with thread type M12 x 0.75 mm (nickel silver). It is sealed by a Viton O-ring sealing.
End-to-end fiber cable
The vacuum feed-through is supplied with a non-exchangable, continous, end-to-end fiber cable. That means there is no additional fiber connection (mating) at the vacuum flange.
The benefit is no additional coupling losses due to mating.
Multimode fiber cable
On the vacuum side, the fiber cable is equipped with Ø 900 μm buffer made of Hytrel. The part of the fiber cable outside the vacuum, has a Ø 3 mm cable with Kevlar strain-relief with bend protection both at the fiber connector and the flange.
V-SF-MMC-S-VIS/NIR-100-NA022-18-30/120
The beam profile exiting a multimode fiber is strongly dependent on how the light interacts within the fiber and is often very different from that of a single-mode fiber - it might even change with time and fiber position. For a good, symmetric, and âsuper-Gaussianâ distribution of light exiting the multimode fiber (aside from laser speckle), it is important that mode mixing has occurred within the fiber or that multiple modes have been excited from the start when coupling in.
For example, if you couple light into the fiber from a single-mode laser source, only a few modes will be excited. If you then change the fiber position or touch the fiber, the ex-fiber beam profile can change rapidly over time because different modes are excited that may not have a symmetric, Gaussian-like output (e.g. donut modes).
To avoid this, you can either make the multimode fiber longer (to increase mode mixing as it passes through the fiber) or coil the fiber with a smaller bend radius to increase mode mixing. You can also choose a smaller focal length to have a larger light cone when coupling into the fiber, which in turn excites more modes. Often a combination of these three strategies will result in a stable, âsuper-Gaussianâ beam profile exiting the multimode fiber.
Polarization-maintaining fiber cables
for coupling into single-mode and polarization-maintaining fiber cables
for collimating radiation exiting an optical fiber or as an incoupler
