Abstract
Being one of the most proven fiber optic devices, the fiber Bragg grating has developed continually to extend its applications, particularly in extreme environments. Accompanying the growth of Type-IIa Bragg gratings in some active fibers, a new resonance appears at the shorter wavelength. This new type of grating was named “secondary Bragg grating” (SBG). This paper describes the formation and applications of the SBGs. The formation of the SBG is attributed to the intracore Talbot-type-fringes as a result of multi-order diffractions of the inscribing beams. The SBG presents a variety of interesting characteristics, including dip merge, high-temperature resistance, distinct temperature response, and the strong higher-order harmonic reflection. These features enable its promising applications in fiber lasers and fiber sensing technology.
Highlights
Fiber Bragg gratings (FBG) are one of the most well-known optical fiber devices due to their compact size, narrow bandwidth, immunity to electromagnetic interference, and their inherent multiplexing capability [1]
Depending on the high temperature resistance of Type-IIa grating, those thermally-triggered distributed Bragg reflector (DBR) fiber lasers can be potentially used as high-temperature alarms, of whose warning temperature can be flexibly managed through setting the pump power [27]
By a large amount of the cumulative fluence, which is needed which is needed in Type-IIa FBG inscription, the weaker periodical modulation would result in the in Type-IIa FBG inscription, the weaker periodical modulation would result in the generating of the generating of the secondary Bragg grating” (SBG)
Summary
Fiber Bragg gratings (FBG) are one of the most well-known optical fiber devices due to their compact size, narrow bandwidth, immunity to electromagnetic interference, and their inherent multiplexing capability [1]. FBGs have been exploited as distributed reflectors in fiber lasers, spectral filters for wavelength-division-multiplexing (WDM) applications, microwave photonic signal processing, and dispersion compensators in optical telecommunications. They are important photonic sensors, which are capable of measuring temperature [2], strain [3], bending [4], vibration [5], acoustic waves [6], refractive index [7] and, recently, even biomolecules [8]. The Type-IIa FBG can work at temperatures up to 800 ◦ C It has attracted increasing attention since a new mechanism in photosensitivity needs to be clarified for the negative index changes. We describe our recent works on SBGs, including the investigation of their formation mechanism, and the applications in high-temperature-resistant fiber grating lasers, thermally-triggered fiber grating lasers, and the higher harmonic grating fiber lasers
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