Optical characterisation of long-period grating using liquid droplets on an electrowetting-on-dielectric platform

The use of digital electrowetting as a means of characterising and modifying the optical transmission properties of long-period gratings (LPGs) fabricated in boron-doped germanosilicate single-mode fibre is described. An electrowetting-based platform has been designed to move fluid droplets, of about 2 μl volume, along the main axis of the LPG fibre. The droplets make contact with the cladding over the grating region of the fibre. Optical measurements are presented illustrating the tuning of the optical resonance wavelength of an LPG as the droplet advances stepwise along the fibre cladding under electrowetting-based actuation, and the increase of 53% in the LPG tuning range achieved by side polishing the grating section of the fibre.