Resolution-improved Fourier ptychographic microscopy using high-numerical-aperture condenser

High-resolution (HR) and wide field-of-view (FOV) microscopic imaging plays a central role in diverse applications such as high-throughput screening and digital pathology. However, for bright-field microscopy system, high-resolution and wide field-of-view (FOV) always could not be achieved simultaneously, limiting its applications which require large space-bandwidth-product (SBP). Various super-resolution techniques have been proposed to break this limitation, such as on-chip sub-pixel scanning methods, structured illumination microscopy, and Fourier ptychographic microscopy (FPM). Among these super-resolution techniques, FPM became increasingly popular recently since it can combine the numerical apertures (NAs) of the objective lens and the illumination light to form a larger synthetic system NA without sacrificing the FOV. Thus, the resolution-FOV tradeoff can be effectively decoupled in FPM. In addition, it is also very convenient to build an FPM system by simply replacing the illumination system of a bright-field microscope with a commercial programmable LED board. Lately, a lot of efforts have been made to improve the accuracy and efficiency of FPM, however, to date, the effective imaging NA achievable with a typical FPM system is still limited to the range of 0.4-0.7. Here, we build an FPM platform using an oil-immersion condenser to boost the resolution of a bright-field microscopy system and significantly increase its SBP. This FPM system involves a 10X0.4NA objective lens and a 1.2NA oil-immersion condenser to synthesize a system NA of 1.6. We confirmed the accuracy of this technique by achieving a half-pitch resolution of 154 nm at a wavelength of 435 nm with a FOV of 2.34 mm(2), corresponding to an SBP of 98.5 megapixels (similar to 50 times higher than that of the conventional incoherent microscope with the same resolution). We also demonstrated the effectiveness of this approach by imaging various biological samples, such as human blood smears. Our work indicates that FPM is an attractive method which could broadly benefit wide-field imaging applications that demand large SBP, and it still has a great potential to achieve much larger SBP of bright-field microscopes.