DIY hyperspectral imaging via polarization-induced spectral filters

Our approach produces tunable spectral filters from a stack of waveplates and polarizers to create a vivid array of transmission spectra that allow us to reconstruct the spectra of incoming light. Here we visualize a beam of light as a “bundle” of fibers, each with its own wavelength (color), amplitude (diameter), and polarization state (ellipse/line in the cutaway). Incoming light (a) passes through the first linear polarizer (b), which transmits only the polarization component of each fiber aligned with its transmission axis (c). Then, the light passes through the waveplate (d), which causes a wavelength- and orientation-dependent phase shift – linear polarization is transformed into another polarization state, generally elliptical polarization (e). In this illustration, long wavelengths are affected least strongly and short wavelengths affected most strongly. Lastly, the light passes through the second linear polarizer (f), or “analyzer”, which again transmits only the polarization component aligned with its transmission axis. The compound effect of the optical elements together is wavelength-dependent transmission (g).

Abstract

We propose a novel design for a do-it-yourself hyperspectral imaging system which operates by taking multiple photographs through tunable, polarization-induced, spectral filters. Prior approaches in this do-it-yourself arena achieve hyperspectral imaging by selecting from a discrete set of spectra baked into existing products. In contrast, our approach is capable of generating a continuous family of broadband transmission spectra by simple rotations of stacked polarizers and waveplates. This greatly expands the potential range of representable spectra from a fixed-dimensional to an arbitrary-dimensional space. We analyze the theoretical spectral gamut of our approach and demonstrate its viability for spectral surface reflectance reconstruction both in simulation and with a low-cost physical prototype. Our prototype demonstrates that our approach can achieve comparable quality to prior work at reduced cost, while the new design space holds ample opportunity for increased quality and flexibility with professional manufacturing.

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Acknowledgements

This work was generously supported by NSF award 1844538, and a Neukom Institute CompX faculty grant.

Cite

@inproceedings{salesin22DIY,
    author    = {Salesin, Katherine and Seyb, Dario and Friday, Sarah and Jarosz, Wojciech},
    title     = {{DIY} hyperspectral imaging via polarization-induced spectral filters},
    booktitle = {International Conference on Computational Photography (ICCP)},
    year      = {2022},
    month     = aug,
    doi       = {10/jgzs},
    keywords  = {birefringence, computational imaging}
}