Optical, measuring, signaling and checking apparatus and instruments in the nature of optical telecommunication hardware, namely optical filter for wavelength division multiplexing, optical switches, fiber optic components, namely fiber Bragg gratings for optical processing, fiber lasers that act as optical sources in optical telecommunication systems; optical measuring, signaling and checking apparatus and instruments, namely optical light guides, namely waveguides in the optical domain, optical fibers, optical fiber lasers, optical fiber gratings in the nature of a component that is based on a periodic variation of the refractive index in optical light guides and used in optical telecommunication for equalization of optical amplifiers and used in optical sensing as a sensor element, optical fiber sensors used as thermometers and/or strain sensors for wavelength response to changes in temperature and strain; optical filters and optical fiber components used in telecommunications and optical sensing, namely fiber Bragg grating, fiber based WDM network, fiber coupled optical isolator, fiber attenuator