Many fiber-optic sensors for measuring temperatures are based on fiber Bragg gratings (FBGs)., the wavelength of peak reflectivity. The first part of this article discussed general issues of sensing of physical parameters. This article provides a comprehensive overview of optical temperature sensors, which utilize optical technology, particularly fiber optics, for temperature measurements. Fiber-Bragg-Gratings (FBGs) are used for spot sensing, whereas Rayleigh, Brillouin and Raman scattering are used for distributed sensing in long fibers. At the beginning of this era, optical devices such as laser, photodetectors and the.