We report an optofluidics-based variable optical attenuator (VOA) employing a tapered side-polished single-mode optical fiber attached to an electrowetting-on-dielectric (EWOD) platform. The side polishing of the fiber cladding gives access to the evanescent field of the guided mode, while the EWOD platform electrically controls the stepwise translation of a liquid droplet along the variable thickness polished cladding of the fiber. The penetration of the evanescent field into the droplet leads to tunneling of optical power from the fiber core to the droplet, from where it is radiatively lost. As a result of the variable cladding thickness, the position of the droplet along the length of the polished fiber determines the degree of penetration of the evanescent field into the droplet. The droplet position can be electrically changed; thus, controlling the optical power loss from the fiber. This approach has been used to demonstrate an optofluidic continuous-fiber VOA typically providing up to 26 dB of broadband attenuation in the 1550-nm transmission window, with a wavelength dependent loss less than 1.1 dB. In this paper, we present the theoretical modeling and experimental characterization of the system, discussing the influence of the design parameters on the performance of this VOA.
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