This book highlights the new technologies and applications presented at the 2021 International Conference on Precision Instruments and Optical Engineering held in Chengdu, China from 25 to 27 August 2021. The conference aimed to provide a platform for researchers and professionals to share research findings, discuss cutting-edge technologies, promote collaborations and fuel the industrial transition of new technologies. The invited and contributed papers covered recent developments in optoelectronic devices, nanophotonic research, optoelectronic materials, precision instruments, intelligent instruments, laser technology, optical spectroscopy and other optical engineering topics. The book is intended for researchers, engineers and advanced students interested in precision instruments and optical engineering and their applications in diverse fields.