Spin separation based on-chip optical polarimeter via inverse design.

Polarimetry has been demonstrated essential in various disciplines, such as optical communications, imaging, and astronomy. On-chip nanostructures for polarization measurements are most expected to replace the conventional bulk elements, and hence minimize the polarimeter for integrated applications. Some on-chip nanophotonic polarimeter via polarization detection has been implemented, in which the separation of two spin polarized states is needed. However, due to the relatively low coupling efficiency or complicated photonic silicon circuits, on-chip polarimetry using a single device still remains challenging. Here, we introduce and investigate an on-chip polarimeter with nanostructures using the inverse design method. The developed device shows the ability to detect the four polarization components of light, two of which are the spin polarizations, and the other two are the linear polarizations. The retrieved Stokes parameters with experimentally tested data are in close agreement with the numerical results. We also show the proof of concept demonstration for high-speed Stokes vector optical signals detection. In the high-speed communication experiment with data rate up to 16 GBd, the detected optical signals via polarization measurements at multiple wavelengths in the C-band were recovered with the bit error rate below the 20% forward error correction threshold. The proposed on-chip polarimeter shows promising performance both in Stokes polarimetry and high-speed optical communication applications.