Reconfigurable diffraction gratings based on elastomeric microfluidic devices

This paper describes the fabrication and operating principles of a reconfig urable diffraction grating based on a microfluidic device. The device consi sts of an array of microscopic channels (50 mu m wide and 20 mu m deep) def ined by the conformal contact between a transparent elastomeric material th at has an embossed surface relief and a flat glass substrate. The microchan nels can be filled reversibly with fluids (gas, aqueous solutions, or organ ic solutions). The difference in index of refraction between the fluid in t he array of microchannels and the structural elastomeric solid generates a difference in,the phase of the light passing through the device; absorption by the fluid changes the amplitude of the light. Both of these effects giv e rise to diffraction. The gratings are reconfigured by pumping liquids wit h different indices of refraction and optical densities through the microch annels. In these experiments, the devices exhibited maximum depths of modul ation of similar to 20 dB and switching times of similar to 50 ms; the volu me of liquid sampled by the incident light was about 8 nl. The potential ap plication of these devices as sensing elements in micro total analysis syst ems (mu TAS) and as actuators is evaluated. (C) 1998 Elsevier Science S.A. All rights reserved.