We present a low-cost, reconfigurable, parallel optofluidic switch that exploits the optical and magnetic properties of water-based ferrofluid. Each switch is composed of an integrated waveguide orthogonally crossing a microfluidic channel containing high-index oil and a ferrofluid plug. The switch is turned ON or OFF by movement of the ferrofluid plug. In contrast to conventional integrated switches, ferrofluid plugs act as switching mechanisms that are portable and reconfigurable. Switches are demonstrated in parallel geometries for single and multimode waveguides. Possible applications include optofluidic memory, multiplexed sensing for lab-on-chip, or frequency-encoded laser excitation.
We present a portable optofluidic switch using a ferrofluid plug in a commercially produced microfluidic chip with waveguides added via femtosecond laser micromachining (FLM). FLM enabled the one-step fabrication of highly reproducible, perfectly aligned integrated waveguides orthogonally crossing an existing microfluidic channel. In the "ON" state for each output, the ferrofluid plug is outside the intersection and input light arrives at the output with relatively small loss. In the "OFF" state, the plug is inside the intersection and the input light is absorbed. The same plug is used to turn ON and OFF several parallel waveguides with contrast ratios of 22 dB or better. In addition, the plug is driven periodically using an electromagnet combined with a permanent magnet for frequency-dependent characterization. Photodiode data show high contrast up to 50 Hz and linear frequency response up to 1 KHz.
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