Fabrication of focus-variable fluidic microlens using single casting

An elastomeric microfluidic lens of variable focal length was fabricated by single casting from a microfabricated mold. The lens is a poly(dimethylsiloxane) (PDMS) microfluidic chamber covered with a thin membrane. By introducing fluid inside, the pressure varied in the microfluidic chamber, which produced a shift in the microlens focal plane resulting in a change in the back focal length of the lens. Hot pressing was used to fabricate the microfluidic chamber and membrane in a single body. The fabrication processes are simple, avoid handling difficulties of the thin membrane, and provide uniform thickness of the membrane, which essentially affect lens performance. The optical properties of the lens such as lens shape, back focal length, and numerical aperture were calculated and measured at various lens geometries and applied pressures. The back focal length of the lens changed approximately from 30 to 5 mm. The relationships of the optical properties, namely, back focal length and numerical aperture, with applied pressure were studied and verified using optical image tests. The variable focal length of the microfluidic lens is critical to increase the efficiency of light detection in optical or biophotonic applications.