  Quantitative phase imaging (QPI) is a valuable label-free modality that has
gained significant interest due to its wide potentials, from basic biology to
clinical applications. Most existing QPI systems measure microscopic objects
via interferometry or nonlinear iterative phase reconstructions from intensity
measurements. However, all imaging systems compromise spatial resolution for
field of view and vice versa, i.e., suffer from a limited space bandwidth
product. Current solutions to this problem involve computational phase
retrieval algorithms, which are time-consuming and often suffer from
convergence problems. In this article, we presented synthetic aperture
interference light (SAIL) microscopy as a novel modality for high-resolution,
wide field of view QPI. The proposed approach employs low-coherence
interferometry to directly measure the optical phase delay under different
illumination angles and produces large space-bandwidth product (SBP) label-free
imaging. We validate the performance of SAIL on standard samples and illustrate
the biomedical applications on various specimens: pathology slides, entire
insects, and dynamic live cells in large cultures. The reconstructed images
have a synthetic numeric aperture of 0.45, and a field of view of 2.6 x 2.6
mm2. Due to its direct measurement of the phase information, SAIL microscopy
does not require long computational time, eliminates data redundancy, and
always converges.
