Cost-effective neutral density filters from polydimethylsiloxane

A neutral density filter (ND) is one of the basic and important optical components used in optical and photographic systems for controlling intensity of light at all wavelengths. It is typically fabricated by coating appropriate thin films on glass or plastic substrates through an expensive time-consuming and power-hungry thin-film coating system. In this work, we show for the first time how very low-cost NDs can be implemented on a well-known Polydimethylsiloxane (PDMS) material widely used in microfluidic applications. PDMS-based NDs with 10-80% transmission and a broad wavelength operation in a visible spectrum are highlighted.