Better than a lens? Increasing the signal-to-noise ratio through pupil splitting

Abstract

Incoherent imaging via an unmodified full pupil seemingly yields the maximum achievable signal-to-noise ratio (SNR) with respect to a fixed photon budget. Such photon-limited SNR is critical in many imaging scenarios, for example, in the case of fluorescence microscopy. In this work, we propose a general method that achieves a better SNR for transmitting high spatial frequency information through an optical imaging system, without the need to capture more photons. This is achieved by splitting the pupil of an incoherent imaging system such that two sub-images are simultaneously acquired and computationally recombined. We compared the theoretical performance of split pupil imaging to the non-split scenario and implement the splitting using a tilted elliptical mirror covering ≈50% of the pupil, placed at the back-focal-plane (BFP) of a fluorescence widefield microscope. Additionally, the proposed system exhibits an extended-depth-of-field (EDoF), utilized further to assign some of the measured (in-focus) signal to different axial planes of the reconstructed sample, through thick slice deconvolution. Our proposed method can be modified to tailor SNR enhancements to specific metrology tasks or to exploit other properties (e.g., spectral or polarization information) for SNR enhancement with impact on future imaging schemes.