In fiber based Fabry-P\'{e}rot Cavities (FFPCs), limited spatial mode
matching between the cavity mode and input/output modes has been the main
hindrance for many applications. We have demonstrated a versatile mode matching
method for FFPCs. Our novel design employs an assembly of a graded-index and
large core multimode fiber directly spliced to a single mode fiber. This
all-fiber assembly transforms the propagating mode of the single mode fiber to
match with the mode of a FFPC. As a result, we have measured a mode matching of
90\% for a cavity length of ∼400 μm. This is a significant
improvement compared to conventional FFPCs coupled with just a single mode
fiber, especially at long cavity lengths. Adjusting the parameters of the
assembly, the fundamental cavity mode can be matched with the mode of almost
any single mode fiber, making this approach highly versatile and integrable.Comment: 6 pages, 5 figures, articl