Coupling between two parallel long-period fibre gratings

The authors demonstrate both theoretically and experimentally that light coupling can take place effectively between two parallel identical long-period optical fibre gratings. In principle, a high coupling efficiency (up to a few tens percent) is possible by using proper grating designs and an index-matching external medium. This coupling mechanism shows great promise for the development of all-fibre optical devices, such as add/drop multiplexers and tunable couplers.