Polarization-independent arrayed waveguide grating spectrometer on the silicon-nitride platform

In this work, we present a polarization-independent arrayed waveguide grating (AWG) spectrometer. By splitting the two orthogonal polarization portions in the fiber system, then processing and merging these two portions with an on-chip multi-input AWG, we can demultiplex an arbitrary polarized signal. Under the case where the powers of two orthogonal polarizations are close (50% TE/50% TM), the spectrometer divides the signal into eight channels with an insertion loss of 2.2 dB and a resolving power of 2800. The polarization-dependent loss (PDL) is 1.21 dB and the polarization-dependent wavelength shift (PDWS) is 0.29 nm. We also discuss the relationship between the channel profile and the input waveguide separation. By varying the TE/TM ratio, our spectrometer demonstrates its polarization insensitivity with a stable throughput of around 60%.