Multimode Fiber Cables MMC

1. To prevent damage to the sensitive fiber end-face, always insert the fiber connector`s ferrule at an angle, with the connector key properly aligned to the receptacle notch.
2. When the ferrule tip is safely located in the inner cylinder of the receptacle, align the connector to the receptacle axis and carefully introduce the connector into the fiber coupler.
3. Then, orient the connector key in a way that it is pressed gently onto the right-hand side of the receptacle notch ("right-hand orientation rule").
4. Gently screw on the connector cap nut onto the receptacle until it is finger-tight.
5. Gently tighten the fiber grub screw to reduce the free play of the ferrule in the receptacle.

When the ferrule tip is safely located in the inner cylinder of the receptacle, align the connector to the receptacle axis and carefully introduce the connector into the fiber coupler. 

Then, orient the connector key in a way that it is pressed gently onto the right-hand side of the receptacle notch.

The tightened grub screw and the "right-hand orientation rule" for the connector, ensure a high reproducibility in mode field position and angle, which is especially important for attaching and reattaching polarization-maintaining fibers reproducibly.

Yes, you can- without any problem. Simply adhere to the "right-hand orientation rule".

Generally, with any FC PC or FC APC type connector there is a freeplay when inserting the fiber into the fiber coupler. The free play in between the connector ferrule and receptacle is only a few microns, but necessary for inserting the ferrule without force. There is a difference between the receptable and key width for wide key (2.14 mm) and narrow key (2.0 mm) fibers. If you follow the so-called "right-hand orientation rule" you can reproducibly attach and reattach even PM fibers with narrow key receptacle to fiber couplers with wide key receptacle without difficulty.

"Right-hand orientation rule":

When the ferrule tip is safely located in the inner cylinder of the receptacle, align the connector to the receptacle axis and carefully introduce the connector into the fiber coupler. Then, orient the connector key in a way that it is pressed gently onto the right-hand side of the receptacle notch. The tightened grub screw and the "right-hand orientation rule" for the connector, ensure a high reproducibility in mode field position and angle, which is especially important for attaching and reattaching polarization-maintaining fibers reproducibly.

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 “super-Gaussian” 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, “super-Gaussian” beam profile exiting the multimode fiber.