Abstract

We describe a ball lens assembly, which functions as a broadly tunable bandpass filter and polarizer with imaging capabilities. The physical basis is resonant tunneling of light through an air gap between two half-ball lenses symmetrically coated by few-layer (${\rm Si}/{\rm SiO}_2$ or ${\rm Ta}_2{\rm O}_5/{\rm SiO}_2$) admittance matching stacks. Tuning is achieved by simultaneous adjustments of the incident angle and the air gap thickness. Individual filters with operational ranges spanning visible (${\sim} {400 {-} 700}\;{\rm nm}$) and near-infrared (${\sim} {1000 {-} 1800}\;{\rm nm}$) wavelengths were assembled using 10 mm diameter lenses. We show that these filters, configured as a stand-alone scanning spectrometer, can provide a resolving power ${\sim} {100}$ and $ f $-number ${\sim} {2.5}$ for a fiber-compatible input aperture ${\lt} {15}\;\unicode{x00B5}{\rm m}$ in diameter. We also demonstrate that, with supplementary optics, the tunable ball filter might be used to implement a compact hyperspectral imaging system.

© 2020 Optical Society of America

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