Broadband and low-loss mode scramblers using CO-laser inscribed long-period gratings.

We demonstrate broadband and low-loss three-mode and six-mode scramblers employing CO-laser inscribed long-period gratings (LPGs) for space-division multiplexing. Step-index (SI) few-mode fibers are used to avoid mode coupling to the cladding modes. We characterize the mode scramblers using a swept-wavelength interferometer. Mode-dependent loss (MDL) and modal transfer matrices over the C+L band are presented. Demonstrated LPGs with negligible MDL and low insertion loss contributed to high-performance CO-laser inscription. The total MDLs induced by the SI fiber with LPGs in three-mode and six-mode scramblers are measured to be 2 and 4 dB, respectively.