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 Δ
λ
and
N
output waveguides with channel spacing of Δ
λ
. 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 Δ
λ
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 mm
²
. 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 (PD
λ
) 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.