This book offers a concise yet comprehensive overview of optical phenomena, various types of optical fibers, and fiber-optic sensing systems. It delves into the different laser sources utilized in sensors and explores the development of innovative mechanisms related to fiber-optic sensors. The content includes detailed discussions on a range of laser and fiber-based devices, supported by mathematical simulations for sensor development, as well as performance measurements of the latest advancements in sensor technology. Additionally, this book examines the unique properties of photonic crystal fibers (PCFs), their diverse applications in PCF-based sensors, and cutting-edge topics such as surface plasmon resonance and hybrid plasmonic waveguides. Key features:• Covers the breadth of optical sensing topics, including laser-based sensing. • Presents various types of lasers, including next-generation semiconductor lasers used for medical applications. • Discusses techniques for temperature sensors using laser and fiber optics. • Reviews techniques with photonic crystal fiber (PCF) on the applications in sensing different parameters and current technologies. • Explores surface plasmon resonance and hybrid plasmonic waveguide. This book is aimed at researchers and graduate students in optics, sensors, and optoelectronics.