As the two most representative operation modes in an optical imaging system, bright-field imaging and phase contrast imaging can extract different morphological information on an object. Developing a miniature and low-cost system capable of switching between these two imaging modes is thus very attractive for a number of applications, such as biomedical imaging. Here, we propose and demonstrate that a Fourier transform setup incorporating an all-dielectric metasurface can perform a two-dimensional spatial differentiation operation and thus achieve isotropic edge detection. In addition, the metasurface can provide two spin-dependent, uncorrelated phase profiles across the entire visible spectrum. Therefore, based on the spin-state of incident light, the system can be used for either diffraction-limited bright-field imaging or isotropic edge-enhanced phase contrast imaging. Combined with the advantages of planar architecture and ultrathin thickness of the metasurface, we envision this approach may open new vistas in the very interdisciplinary field of imaging and microscopy.
Keywords: Metasurface; edge detection; orbital angular momentum; phase contrast imaging.