Asia-Pacific Optical Sensors Conference: focus issue introduction.

This feature issue of Optics Express contains 17 articles expanding on recent advances in optical sensors presented at the eighth Asia-Pacific Optical Sensors Conference (APOS 2019) held in Auckland, New Zealand, from November 19 to 22, 2019. These articles span sensing for real-time positioning, refractive indices, strain, gas, and temperature using a variety of methods including photoacoustic computed tomography, coherent optical frequency-modulated continuous-wave interferometry, enhanced Bragg gratings, and phase-sensitive optical frequency-domain reflectometry.