A Polarization-Insensitive High-Resolution Micro-Spectrometer Using (N + 3) × (N + 3) Arrayed Waveguide Grating On SOI Platform

Ultra-compact on-chip spectrometers with high resolution and large bandwidth play a crucial role in miniaturized spectroscopic analysis systems. Here we present a novel polarization-insensitive micro-spectrometer with high resolution and large bandwidth based on a (N + 3) × (N + 3) arrayed waveguide grating (AWG) on silicon-on-insulator (SOI) platform. The proposed AWG can be viewed as two same 3 × N AWGs with each one having three input waveguides with channel spacing of 4/3 Δλ and N output waveguides with channel spacing of Δλ. The three input waveguides are time division multiplexed, i.e., they are excited one by one in sequence. As a result, combining all spectral responses of each input, a micro-spectrometer with channel wavelength spacing enhanced to one-third Δλ and channel number enlarged to 3 × (N – 2) is achieved, only using N output channels. The polarization diversity scheme is utilized to address the polarization sensitive issue of silicon nano-waveguide, i.e., the AWG operates at a counter-propagating manner to process each polarization, respectively. In experiment, we demonstrate a micro-spectrometer with 81 channels and channel wavelength spacing of 0.4 nm by employing a 32 × 32 AWG on the SOI platform. The footprint of the fabricated micro-spectrometer is only 1.1 × 2.35 mm2. Experimental results show that the spectrometer has on-chip losses ranging from –5.8 to –2.5 dB, noise level of better than 17 dB, polarization dependent wavelength shift (PDλ) of less than 0.07 nm and polarization dependent loss (PDL) of less than 1.5 dB, for all 81 wavelength channels. The resolution of the micro-spectrometer is mainly dependent on the 3-dB bandwidth of each channel and is simulated to be ∼0.65 nm. The proposed ultracompact and polarization insensitive high-resolution on-chip spectrometer provides a very promising approach for achieving miniaturized spectrometer-on-a-chip with good performance for applications such as in fiber Bragg grating (FBG) sensor readout unit and optical waveguide sensor systems.