Off-axis metalens avoiding aberrations and spectral line curvature for spectral analysis

Miniature spectrometers play an important role in a variety of fields, including environmental monitoring, biomedical diagnostics, and industrial quality control. For these applications, achieving high spectral resolution across broad wavelength ranges is important. This study presents an off-axis metalens that overcomes the key limitations of miniaturized spectrometers by simultaneously achieving broadband and high spectral resolution. Based on a systematic study of the influence of focal length, numerical aperture (NA), and off-axis angle on the spectral resolution, we optimized these three parameters and fabricated an off-axis metalens with a NA of 0.04, an off-axis angle of 5.71°, and an aperture of 1.6 mm. Experimental results demonstrate that the off-axis metalens effectively eliminates both aberrations and spectral line curvature in broadband spectral analysis. It achieves a reciprocal linear dispersion of 3.3 × 10^-2 nm/μm, enabling nanometer spectral resolution across the 500-750 nm wavelength range. The proposed off-axis metalens addresses key challenges in metalens-based spectrometers, such as aberrations and spectral line curvature, thereby enabling practical applications in portable high-precision spectral analysis systems.