Whole-taper light delivery/collection
The ideal choice is to use the same fiber specs for both the Lambda fiber and the patch cord. Using a patch cord with larger NA and /or larger core than the Lambda fiber is also acceptable, as the effective emission/colection length (i.e. the active lenght) will be the preserved, although there will a significant light power loss at the patch cord-to-ferrule connection.
Site-selective light delivery/collection
Please refer to equipment documentation for the correct choice of patch cords.