Spectroscopy using tunable liquid crystal Fourier filters

Fourier multispectral filtering is an attractive means to acquire an approximation of full spectral signal with very few measurements. In our previous work, we demonstrated this technique using photodetectors fabricated in-house using a single dielectric thin film as a Fabry-Perot sinusoidal filter. The main disadvantage of such filters is the design trade-off between the oscillation amplitude and the purity of the sinusoidal transmission spectrum. In this work we demonstrate a more attractive technique using liquid crystals (LCs). The birefringence response of the LCs naturally lends itself to a nearly perfect sinusoidal transmission function with high contrast, ideally oscillating between a transmission of 0% and 100%. Furthermore, the period of oscillations can be controlled by the applied voltage, making it possible to continuously tune the transmission spectrum and acquire a high resolution spectrum of the target signal. Our design consists of 16 custom photodetectors integrated with individually-addressable LC pixels. The whole system can be integrated onto a single-chip and enable high resolution spectroscopy capability in portable electronics.