Mid-infrared fiber lasers have shown out standing prospects in many fields, so mid-infrared fiber Bragg grating (FBG) as the most essential component in mid-infrared fiber laser oscillators has attracted much attention. Here, we fabricated mid-infrared FBGs on ZBLAN fibers operating nearby 2.8-2.9 μm by femtosecond laser direct inscription technique, and measured their transmission spectra by all-fiber measurement system, which lays the foundation of high-power all-fiber mid-infrared laser oscillators near 2.8 μm.
In this paper, we fabricate FBGs-based FPCs using femtosecond laser and the temperature characteristics is studied. The FBGs are inscribed by line-by-line scanning technique, by which the FBGs can be limited to a specific area in the fiber core region. Besides, the grating length, the grating position and the distance between two successive FBGs can be precisely controlled to adjust bandwidth and free spectral range. FP interference is obviously seen in reflection and transmission spectrum. Line-by-line inscribed FPC is a good candidate for sensing application.
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.
Chirped and tilted fiber Bragg gratings (CTFBGs) have attracted a lot of attention for stimulated Raman scattering (SRS) suppression in high-power fiber laser systems in past years. Here, we fabricate CTFBGs in large-mode-area double cladding fibers and demonstrate its application in a 2-kW fiber laser for SRS filtering at the system’s output. A maximum Raman suppression of about 17 dB is obtained at the central wavelength, and the insertion loss is smaller than 0.2 dB for signal laser. In addition, no obvious degradation of laser beam quality is observed. Better suppression effect could be achieved by broadening the rejection bandwidth of the CTFBGs in the future.
In this paper, mode distribution in large-mode-area (LMA) 25/400 fiber was investigated while attempts to recognize and sort different modes with their combination were carried out on a CNN net via Tensorflow. VGG16 model was chosen as the backbone net through several test to increase precision. The model was trained on a dataset including 6000 pictures in 15 categories. And the final accuracy was up to 0.98. It indicates that recognizing modes in high power fiber laser system based on a CNN net was a feasible plan in the mode control assignment.
Stimulated Brillouin scattering (SBS) is one of the mainly factors those limit the output power in narrow-linewidth highpower fiber laser systems. Here, we propose and demonstrate a novel method for the suppression of SBS in optical fibers using a tilted fiber Bragg grating (TFBG). With a TFBG being inserted between a single-mode fiber (SMF) amplifier and a 150-meter-length single-mode energy-transmitting fiber, not only the backward Stokes wave is rejected, but also an obvious increasing of the SBS threshold is observed with a value of 1.2 times that without the TFBG, which increases the effective laser output power by about 18 %. This work provides a new idea for SBS suppression in fiber. It is very useful for the further power scaling of high-power narrow bandwidth all-fiber lasers.
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