Inverse-designed 3D laser nanoprinted phase masks to extend the depth of field of imaging systems

TL;DR

This paper presents an inverse-designed 3D laser nanoprinted phase mask that significantly extends the depth of field in optical microscopes, enabling multiplane imaging without sacrificing resolution.

Contribution

It introduces a novel inverse design approach combined with advanced fabrication techniques to create phase masks that enhance depth of field in microscopy.

Findings

Extends depth of field by approximately four times

Achieves high fabrication accuracy with two-photon laser nanoprinting

Enables multiplane imaging beyond original microscope capabilities

Abstract

In optical imaging, achieving high resolution often comes at the expense of a shallow depth of field. This means that when using a standard microscope, any minor movement of the object along the optical axis can cause the image to become blurry. To address this issue, we exploit inverse design techniques to optimise a phase mask which, when inserted into a standard microscope, extends the depth of field by a factor of approximately four without compromising the microscope's resolution. Differentiable Fourier optics simulations allow us to rapidly iterate towards an optimised design in a hybrid fashion, starting with gradient-free Bayesian optimisation and proceeding to a local gradient-based optimisation. To fabricate the device, a commercial two-photon 3D laser nanoprinter is used, in combination with a two-step pre-compensation routine, providing high fabrication speed and much better than subwavelength accuracy. We find excellent agreement between our numerical predictions and the measurements upon integrating the phase mask into a microscope and optically characterising selected samples. The phase mask enables us to conduct simultaneous multiplane imaging of objects separated by distances that cannot be achieved with the original microscope.