  The on-chip measurement of polarization states plays an increasingly crucial
role in modern sensing and imaging applications. While high-performance
monolithic linearly polarized photodetectors have been extensively studied,
integrated circularly polarized light (CPL) photodetectors are still hindered
by inadequate discrimination capability. In this study, we employ achiral
all-dielectric nanostructures to develop a broadband CPL photodetector with an
impressive discrimination ratio of ~107 at the wavelength of 405 nm,
significantly surpassing its counterparts by two orders of magnitude. Our
device shows outstanding CPL discrimination capability across the visible band
without requiring intensity calibration. Its function mechanism is based on the
CPL-dependent near-field modes within achiral structures: under left or right
CPL illumination, distinct near-field modes are excited, resulting in
asymmetric irradiation of the two electrodes and generating a photovoltage with
directions determined by the chirality of the incident light field. The
proposed design strategy facilitates the realization of ultra-compact CPL
detection across diverse materials, structures, and spectral ranges, presenting
a novel avenue for achieving high-performance monolithic CPL detection.
