Phase Sensitivity Characterization of a Photonic Integrated Circuit for Sub-nm Profilometry

In this work, we present the development of a pho-tonic integrated circuit (PIC)-based profilometer on the indium phosphide platform. Here, we focus on the phase sensitivity and resolution that can be achieved with an on-chip Mach-Zehnder interferometer, which forms the core phase-sensing element of a profilometer. Our measurements demonstrate an attainable phase resolution of 0.020 degrees, corresponding to an axial resolution well below 0.1 nm in a profilometer context, highlighting the potential of integrated phase sensors for high-precision metrology. The proposed PIC could be integrated into a probe head, which offers a scalable and compact solution for advanced in-line and in-process metrology.