Optical coupling method utilizing a lensed fiber integrated with a long-period fiber grating

A novel optical coupling scheme that uses a lensed fiber integrated with a long-period fiber grating (LPFG) is proposed. Two experiments are performed to demonstrate the validity of such a scheme in single-mode-fiber-single-mode-fiber (SMF-to-SMF) and laser-diode-single-mode-fiber (LD-to-SMF) coupling setups. The measured results show that for an appropriate lens radius the addition of a LPFG will lead to a higher coupling efficiency over a longer range of working distance than without the LPFG. Coupling efficiencies of approximately 78% and 35% are achieved for corresponding working distances of approximately 250 and 110 microm, 1-dB longitudinal tolerances of approximately 40 and 26 microm, and 1-dB transverse tolerances of approximately 7.6 and 2.6 microm for SMF-to-SMF and LD-to-SMF, respectively.