Coupling Loss From Free Space to Large Mode Area Photonic Crystal Fibers

Simulated and measured results are presented for the coupling loss from free space into a large mode area (LMA) photonic crystal fiber. The total measured loss (using bulk optics) for a signal (lambda = 1.55 mu m) going in and out of a 1-m-long fiber was -2.15 dB. It was also observed that the fiber is not that sensitive to lateral misalignment compared that to the conventional single-mode fiber. Due to the low loss, this type of fiber could be used to create long delays in optical true-time-delay engines based on the White cell concept and others. The above loss can be further reduced by using field lenses or lensed LMA. LMA fibers are excellent media to create long optical true time delays with only -2.15 dB/m coupling loss.