fiber liekkitm yb1200-20/125dc liekkitm yb1200-20/125dc-pm optical peak cladding absorption at 976 nm (nominal) db/m 29 30 cladding absorption at 920 nm db/m 6.8 ± 1.7 7.1 ± 1.7 core numerical aperature 0.08 ± 0.01 0.08 ± 0.01 birefringence > 8.0e-05 geometrical and mechanical core diameter μm 20 ± 2 20 ± 2 core concentricity error μm < 1.5 0.46 > 0.46 proof test kpsi > 100 > 100