Large-field-of-view narrowband light collection enabled by metasurfaces

The narrow bandpass filters are essential in a wide range of applications and systems, including Raman spectroscopy, fluorescence imaging, microscopy, LiDAR, and optical communications. However, strong angular dispersion of thin-film filters typically causes a blue shift in the transmission spectrum at oblique incidence, thereby limiting the usable field of view (FOV). To mitigate this limitation, we augment such thin-film filters with engineered metasurfaces that provide flexible capabilities for wavefront manipulation. We demonstrate that integrating gradient-phase metasurfaces with a narrowband filter significantly enhances angular tolerance and broadens the effective FOV (∼120^∘), while preserving the filter's narrow spectral bandwidth (fractional bandwidth of ∼1% at green). Moreover, thanks to the ultrathin form factor of the metasurface, the proposed configuration achieves a significantly smaller device footprint compared to conventional refractive solutions.