The Facile Implementation of Soft/Tunable Multiband Optical Filters by Stacking Vertical Silicon Nanowire Arrays for Smart Sensing

Abstract

Multiple band optical filters for optical smart sensing, which is simultaneous multispectral detection of objects, are intensively used in many applications, such as remote monitoring, biomedical imaging, wearable optical sensors, and wireless communication. Typically, periodically stacked dielectric layers are used in multiple band optical filters. However, the use of dielectrics inevitably results in rigidity and inflexibility, which is not suitable for advanced smart optical sensors fabricated on flexible substrates. Therefore, herein, a strategy to implement soft/tunable multiband optical filters made from silicon nanowire array-based stackable optical filters (Si NW-SOFs) composed of polymeric membranes containing vertical silicon nanowire arrays that filter light from visible to nearinfrared regions with a narrow bandwidth is proposed. Theoretical and experimental results indicate wavelength selectivity by geometrical parameters (e.g.,diameter, period, and height) and the absence of optical disturbance between the layers in the integrated states. Therefore, multiband optical filters with single- to triple-band stops are easily created by changing Si NW-SOFs. Finally, imaging demonstrations that involve the filtering of monochromatic light sources of three wavelengths (i.e., red, green, and blue) and fluorescent biological tissues show the practical multiple band characteristics of Si NW-SOFs.