Abstract
Suppression of stimulated Raman scattering (SRS) by means of chirped and tilted fiber Bragg gratings (CTFBGs) has become a key topic. However, research on high-power systems is still lacking due to two problems. Firstly, after the inscription, there are a large number of hydroxyl compounds and hydrogen molecules in CTFBGs that cause significant heating due to their strong infrared absorption. Secondly, CTFBGs can couple Stokes light from the core to the cladding and the coating, which causes serious heating in the coating of the CTFBG. Aimed at overcoming these bottlenecks, a process that combines constant-low-temperature and variable-high-temperature annealing is used to reduce the thermal slope of the CTFBG. Also, a segmented-corrosion cladding power stripping technology is used on the CTFBG to remove the Stokes light which is coupled to the cladding, which solves the problem of overheating in the coating of the CTFBG. Thereby, a CTFBG with both a kilowatt-level power-carrying load and the ability to suppress SRS in a fiber laser has been developed. Further, we establish a kW-level CW oscillator to test the CTFBG. Experimental results demonstrate that the power-carrying load of the CTFBG is close to 1 kW, the thermal slope is lower than $0.015\,^{\circ }\text{C}/\text{W}$, and the SRS suppression ratio is nearly 23 dB.
Highlights
Fiber lasers have been widely used in many fields, including industrial processing[1, 2], biomedicine[3, 4] and communication[5], due to their compact structure, high efficiency and high spatial beam quality[6]
The chirped and tilted fiber Bragg gratings (CTFBGs) is inserted between the cladding power stripper (CPS) and a quartz block of high power (QBH), and the temperature of the CTFBG is monitored in real time by an infrared thermal imager
Aimed at providing a high-power CTFBG, a process that combines constant-low-temperature and variable-hightemperature annealing is used to reduce the thermal slope of the CTFBG
Summary
Fiber lasers have been widely used in many fields, including industrial processing[1, 2], biomedicine[3, 4] and communication[5], due to their compact structure, high efficiency and high spatial beam quality[6]. 20/400 photosensitive fiber in 2018[14], and applied it in the seed of a master oscillator power amplifier (MOPA) structure fiber laser with a 4.2 kW output power in 2019 to suppress the SRS in a 100 W-level seed[15] They did not consider the power-carrying load of the CTFBG in the case of high power. A large number of hydroxyl compounds are generated in the CTFBGs after the inscription, while there are still a large number of unreacted hydrogen molecules in the CTFBG These materials cause significant heating in the high-power case due to strong infrared absorption, which greatly limits the power-carrying load of CTFBGs. Secondly, CTFBGs can couple Stokes light from the core to the cladding and coating, which will cause serious heating in the coating of the CTFBG in the incident direction of the laser at high power. To the best of our knowledge, this is the first time that a CTFBG has been applied to a kW-level fiber laser system to suppress the SRS
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