The one-stage master oscillator power amplifier (MOPA) is an efficient way to acquire high-power narrow-linewidth fiber lasers (NLFLs), which have wide usage in beam combination and detection. However, stimulated Raman scattering (SRS) is still one of the main obstacles for further power scaling. In this paper, we set up a counter-pumping kW-level narrowlinewidth one-stage MOPA fiber laser system and tried to use a chirped and tilted fiber Bragg grating (CTFBG) as a broadband rejection filter to suppress the Raman stokes light in the output laser. We finally acquired a 2.5 kW output with 3 dB linewidth of about 0.87 nm, and the SRS isolation ratio is ~42 dB on the spectrum, which is 12.7 dB higher compared with the situation without CTFBG.
In this paper, we design and fabricate a series of single-mode scale gratings based Fabry Perot (FP) by using excimer laser and chirped phase mask, then use it to measure the reflectivity of weak reflection gratings on large-mode-area doubleclad (LMA-DC) fibers. Experimental results show that the Bragg resonance reflectivity of the LMA-DC weak reflection grating is between 1.19% and 1.49%. The method of measuring weak reflection grating reflectivity based on scale grating is convenient, efficient, and the accuracy is greatly improved.
In this paper, we used a femtosecond laser direct writing system to fabricate all-fiber structure Fabry-Perot (FP) cavities based on fiber Bragg gratings (FBGs) on single-mode fibers, which was used as a scale for weak reflectivity measurement of output-coupling FBGs (OC-FBGs). By this method, the intensity of the Bragg resonance reflectivity peak of OC-FBG can be measured to be as low as ~1%. Compared with the traditional method based on the transmission spectrum, this method is much higher measurement accuracy.
In this paper, we propose a novel method of weak reflectivity measurement of FBGs by grating scale. We design and manufacture a series of scale gratings in single-mode fiber using excimer laser and phase mask. The weak reflectivity of measured grating could be achieved by comparing the peak reflection resonance with that of scale gratings. Experimental results show that the reflectivity measurement method based on grating scale is simple and quick, and it does not depend on the transmission spectrum of grating and could effectively avoids the influence of higher-order modes. In the future, by improving grating manufacture technology, it is expected that the reflectivity can be measured more accurately.
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