Ever needed to connect elements in your experimental setup with widely varying requirements regarding the numerical aperture (NA) or mode field diameter (MFD)? Perhaps your emitter has a very small area but then the FBG is written in a standard fiber and you really cannot afford those pesky power losses due to mode mismatch? We have a solution for you. Fibrain mode conversion patchcords can adjust the NA and MFD as you need it and they look just like a standard patchcord. The whole magic happens inside, from the user point of view they just need to use a standard fiber optic patchcord, with clearly marked connectors. The excess loss due to modal conversion is typically very low, while still maintaining strict single-mode regime. Almost any connector type and any fiber types combinations are possible. Just an example: it could be UHNA4/FC APC on one side, SM1950/E2000 UPC on the other side. Similarly, the length is customizable.