Dynamic Tuning of Optical Waveguides with Electrowetting Pumps
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Dynamic Tuning of Optical Waveguides with Electrowetting Pumps
Francesco Cattaneo, Peter Mach, Jennifer Hsieh, Tom Krupenkin, Shu Yang, John A. Rogers Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, U.S.A. ABSTRACT This paper reviews some of our recent work on a new class of photonic component that uses electrowetting pumps and microfluidic channels for dynamic tuning of the characteristics of optical waveguides. These pumps exploit the ability to alter the contact angle of conductive liquids situated on top of a dielectric layer with appropriately patterned underlying electrodes. By applying different voltages to opposite sides of a conductive fluid plug, the contact angle imbalance created between the ends of the liquid drives fluid motion toward the higher field regions [1]. In our design, this electrically controlled, fully reversible motion of fluids contained within recirculating channels is used to alter the effective indices of waveguide modes of three different types of optical fiber structures: fiber Bragg and long period gratings and etched or tapered fiber. Our systems operate non-mechanically and have excellent optical performance, including low insertion and polarization-dependent losses. These characteristics suggest a promising potential for electrowetting-based microfluidic tuning of optical fiber devices and other photonic components.
INTRODUCTION Tunable optical fiber devices can be useful for many important operations in optical communication systems: dynamic chromatic dispersion compensation, programmable adding and dropping of wavelength channels, dynamic gain equalization, etc. Most of the existing technologies use thermo-optic or strain effects in the silica of the fiber; representative examples can be found in [2] and [3]. Recently, a microfluidic approach was demonstrated for dynamic tuning the transmission characteristic of optical fiber [4-6]. These techniques increase the range and type of tunability that is possible in these systems. They can be easily combined with the more traditional techniques to enable complex and multifunctional tuning. For example, thermal pressure pumping and thermo-optic tuning of microfluidic plugs in ‘holey’ fiber yield fully tunable wide and narrow band all-fiber filters [4]. In this paper, we review a design for electrowetting-based devices that offers many important advantages: optical and switching characteristics in a low cost, system that is compatible with use in fiber arrays, planar waveguides and other small-scale optical systems. We describe the device design and fabrication and demostrate its use with conventional etched fibers, Bragg gratings and long period gratings to produce tunable broadband and narrow fiber filters.
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EXPERIMENTAL The fluidic components described here involve an optical fiber that lies in a straight section of a fluidic channel in an oval “racetrack” configuration. An electrowetting pump dynamically controls the position of a fluidic plug relative to a fiber section whose optical properties ar
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