Demonstration of a photonic integrated circuit for quantitative phase imaging

Quantitative phase imaging (QPI) is an optical microscopy method that has been developed over nearly a century to rapidly visualize and analyze transparent or weakly scattering objects in view of biological, medical, or material science applications. The bulky nature of the most performant QPI techniques in terms of phase noise limits their large-scale deployment. In this context, the beam shaping properties of photonic chips, combined with their intrinsic compact size and low cost, could be beneficial. Here, we demonstrate the implementation of QPI with a photonic integrated circuit (PIC) used as an add-on to a standard wide-field microscope. Combining a 50 mm x 50 mm footprint PIC as a secondary coherent illuminating light source with an imaging microscope objective of numerical aperture 0.45 and implementing a phase retrieval approach based on the Kramers-Kronig relations, we achieve a phase noise of 5.5 mrad and a diffraction limited spatial resolution of 400 nm. As a result, we retrieve quantitative phase images of Escherichia coli bacteria cells and monolayers of graphene patches from which we determine a graphene monolayer thickness of 0.45 f 0.15 nm. The current phase noise level is more than five times lower than that obtained with other state-of-the-art QPI techniques using coherent light sources and comparable to their counterparts based on incoherent light sources. The PIC-based QPI technique opens new avenues for low-phase noise, miniature, robust, and cost-effective quantitative phase microscopy. (c) 2024 Chinese Laser Press