Versatile optical frontends for multicolor fluorescence imaging with miniaturized lensless sensors

Lensless imaging enables exceptionally compact fluorescence sensors, advancing applications in in vivo imaging and low-cost, point-of-care diagnostics. These sensors require a filter to block the excitation light while passing the weak fluorescent emissions. However, conventional thin-film interference filters are sensitive to angle of incidence (AOI), complicating their use in lensless systems. Here, we thoroughly analyze and optimize a technique using a fiber optic plate (FOP) to absorb off-axis light that would bleed through the interference filter and improve image resolution. Through simulations, we show that the numerical aperture (NA) of the FOP drives inherent design tradeoffs: collection efficiency improves rapidly with a higher NA, but at the cost of resolution, increased device thickness, and fluorescence excitation efficiency. To illustrate these tradeoffs, we optimize two optical frontend designs using FOPs with full-width at half maximums of 8.3° and 45.7°. Implementing these designs, we show that to maintain performance across all AOIs, filters must be coated on both sides of the FOP to mitigate internal scattering effects. In imaging experiments, the 520-µm-thick high-NA design collects 59× more light, but its resolution degrades rapidly with increased working distances. Alternatively, the low-NA design is capable of three-color fluorescence imaging with at least 110-µm resolution at a 1-mm working distance. Overall, we demonstrate a versatile optical frontend that is adaptable to a range of applications using different fluorophores, illumination configurations, and lensless imaging techniques.