Nano-pixel polarization rotator for a photonic integrated breath sensor

In response to the global aging population, a photonic-integrated-circuit sensor is investigated for the detection of disease markers within human breath content. The device relies on cavity-ring-down spectroscopy with an amplifying medium and loop feedback to secure sufficient sensitivity down to ppm-order concentration detection. This configuration, however, might cause unwanted oscillation, and the polarization rotation method has been proposed to prevent this issue. We have researched a waveguide-based polarization rotator using nano-pixels. The device consists of two regions: (1) From TE00 mode TE10 modes conversion and (2) TE10 to TM00 modes conversion. As the intermediary TE10 mode quality is key to realizing polarization rotation performance, the purpose of this study is to realize high-quality TE10 by employing the mean-squared-error criterion for waveguide design optimization. A finite-difference time-domain simulation with this method reveals a TE10 mode with 1% accuracy that results in a polarization extinction ratio improved from 4.3 to 8.6 dB.