Metalens-based imaging spectrometer for confocal endoscopy imaging.

Current confocal endoscopy techniques have difficulties in achieving high spectral resolution imaging of lesion cell in vivo, which significantly hinders the early accurate diagnosis. In this paper, a novel, to our knowledge, metalens-based imaging spectrometer (MLIS) with the capability of obtaining both a high resolution and a high dispersion linearity in a compact structure for confocal endoscopy imaging, is proposed. First, the ratio of the focal length to dispersion width of the MLIS is studied to achieve both high dispersion linearity and high spatial resolution imaging. Then, to realize a high spectral resolution, how the phase distribution of the dispersive metalens affects the dispersion width of the system is analytically studied. Moreover, the polynomial terms of the phase distribution are further studied to balance the astigmatism and coma aberration of MLIS. Accordingly, an MLIS with only 6mm×2.4mm diameter in volume in the wavelength band from 780 to 860 nm, achieving both a high dispersion linearity and a high spectral resolution of 0.4 nm, is proposed. It paves the way for developing an MLIS with high resolution and high dispersion linearity for lesion cell diagnosis in vivo.