Monolithically Integrated Silicon Photonic Spectrometer for Arbitrarily Polarized Light

On-chip spectrometers offer great opportunity for developing wearable monitoring devices, industrial remote sensing systems, and agricultural evaluation. In practical application scenarios, the spectrometer is imperative to be highly integrated and capable of processing light signals with randomly polarized states in the environment. Here, we propose and demonstrate a monolithically integrated silicon photonic spectrometer with a compact footprint of 0.24 × 1.0 mm2 for arbitrarily polarized light for the first time. The spectrometer couples the light with uncertain polarization states to the TE0 modes guided in two separated waveguides using a polarization splitter rotator. These two TE0 modes are then filtered and received with a very concise configuration by utilizing the unique bidirectionality of a tunable adiabatic elliptical-microring with the maximized free spectral range and a monolithically integrated Ge/Si photodetector (PD). Measurement results show the present spectrometer achieves a broad operation window of 36.5 nm as well as a high resolution of 0.2 nm. The lowest detectable power is characterized experimentally, demonstrating the capability to detect the spectra with a low peak power of −55 dBm and distinguish a peak power difference as high as 45 dB with the integrated Ge/Si PD. As a result, the broadband complex spectra reconstruction with arbitrary polarization states demonstrates our spectrometer is featuring monolithic integration and polarization-insensitive operation.