Several articles suggest, in a MOPA configuration high power fiber laser, the SRS can be mitigated by increasing the bandwidth of the OC FBG. How to determine the optimized bandwidth of such FBG? Does the bandwidth of the HR FBG is also related? What is the relationship between the bandwidths of the FBGs and the amount of Raman output?
For example, we saw an SRS peak by using a 1.6nm OC. In order to reduce the SRS effect we inserted a 3nm bandwidth OC instead of the 1.6nm. Instead of a reduction in Raman, we observed multiple Raman peaks with the 3nm with a lot of back reflection.
More details of the example should be provided. One of the key parameters are the bandwidth of the HR FBG. It is predicated that the bandwidth of the HR FBG is related to SRS in [General analysis of SRS-limited high-power fiber lasers and design strategy]. The bandwidth of the FBGs should be matched.
Vincent Lecoeuche Rumao Tao One of the articles is [General analysis of SRS-limited high-power fiber lasers and design strategy]. They also suggest to have HR FBG and OC FBG identical. In our setup, we keep the HR FBG constant (5nm) and changed the OC FBG. If the HR FBG also has to be changed, how to determine the matched pairs?
Did you measure the temporal characteristics of the laser? Normally, Increasing OC bandwidth will decrease power spectral density of laser, so the Raman threshold can be raised in amplifiers. But, in some case, the increased OC bandwidth may enhance noise feedback in the oscillator, which can cause temporal fluctuations. In turn, the temporal noise will lower SRS threshold.
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