Development of long-period fiber grating coupling devices.

A long-period fiber grating (LPFG) formed in a single-mode fiber is considered as an effective device to tap light from the core of fiber. This light-tapping property of the LPFG allows a new class of wavelength-selective optical couplers to be realized by using the configuration of parallel LPFGs. Over the years a number of four-port and six-port LPFG couplers with peak coupling efficiencies greater than 80% have been demonstrated. To further increase the functionality of LPFG couplers and facilitate device packaging and integration, long-period grating couplers formed in planar waveguides have also been proposed, and the preliminary results are promising. A review of these coupling devices is presented.