Optics (physics.optics)

Abstract: Holotomography, a three-dimensional quantitative phase imaging technique, presents an innovative, non-invasive approach to studying biological samples by exploiting the refractive index as an intrinsic imaging contrast. Despite offering label-free quantitative imaging capabilities, its potential in cell biology research has been stifled due to limitations in molecular specificity and axial resolution. Here, we propose and experimentally validate a solution to overcome these constraints by capitalizing on the intrinsic dynamic movements of subcellular organelles and biological molecules within living cells. Our findings elucidate that leveraging such sample motions enhances axial resolution. Furthermore, we demonstrate that the extraction of uncorrelated dynamic signals from refractive index distributions unveils a trove of previously unexplored dynamic imaging data. This enriched dataset paves the way for fresh insights into cellular morphologic dynamics and the metabolic shifts occurring in response to external stimuli. This promising development could broaden the utility of holotomography in cell biology.

Abstract: Numerical simulations have become a cornerstone technology in the development of nanophotonic devices. Specifically, 3D finite difference time domain (FDTD) simulations are a widely used due to their flexibility and powerful design capabilities. More recently, FDTD simulations in conjunction with a design methodology called inverse design has become a popular way to optimize device topology, reducing a device's footprint and increasing performance. We implement a commercial inverse design tool to generate complex grating couplers and explore a variety of grating coupler design methodologies. We compare the conventionally designed grating couplers to those generated by the inverse design tool. Finally, we discuss the limitations of the inverse design tool and how different design strategies for grating couplers affect inverse design performance, both in terms of computational cost and performance of the resulting device.