Modal content in hypocycloid Kagomé hollow core photonic crystal fibers

The modal content of 7 and 19 cell Kagomé anti resonant hollow core fibers (K-ARF) with hypocycloid core surrounds is experimentally investigated through the spectral and spatial (S²) imaging technique. It is observed that the 7 and 19 cell K-ARF reported here, support 4 and 7 LP mode groups respectively, however the observation that K-ARF support few mode groups is likely to be ubiquitous to 7 and 19 cell K-ARFs. The transmission loss of the higher order modes (HOMs) was measured via S² and a cutback method. In the 7 cell K-ARF it is found that the LP₁₁ and LP₂₁ modes have approximately 3.6 and 5.7 times the loss of the fundamental mode (FM), respectively. In the 19 cell it is found that the LP₁₁ mode has approximately 2.57 times the loss of the FM, while the LP₀₂ mode has approximately 2.62 times the loss of the FM. Additionally, bend loss in these fibers is studied for the first time using S² to reveal the effect of bend on modal content. Our measurements demonstrate that K-ARFs support a few mode groups and indicate that the differential loss of the HOMs is not substantially higher than that of the FM, and that bending the fiber does not induce significant inter modal coupling. A study of three different input beam coupling configurations demonstrates increased HOM excitation at output and a non-Gaussian profile of the output beam if poor mode field matching is achieved.