Raman suppression within the gain fiber of high-power fiber lasers

Abstract

We report the effective suppression of Raman emission in a monolithic ytterbium-doped fiber laser by the insertion of a chirped and tilted fiber Bragg grating (CTFBG) directly within the gain fiber of the laser. In comparison with a non-compensated filtered laser cavity for which the Raman threshold occurs at an output power of 1.54 kW, the insertion of a CTFBG within the gain medium leads to an increase in the Raman threshold by 260 W. We also demonstrate that the insertion of a CTFBG in between a laser cavity and a passive beam delivery fiber leads to an increase in the Raman threshold by 100 W with respect to the non-compensated case.

Fabrication of 2 kW-Level Chirped and Tilted Fiber Bragg Gratings and Mitigating Stimulated Raman Scattering in Long-Distance Delivery of High-Power Fiber Laser

“…The output powers reached 1438 W, 1529 W, 1408 W, and 1438 W, while the maximum Raman isolation ratio of −31.8 dB, −33.9 dB, −34.6 dB, and −36.7 dB were acquired in Setup I to Setup IV, respectively. Because the function of the CTFBG is filtering, the Raman suppress effects and the output power would change in different insertion positions of the CTFBG by retarding the accumulation of the SRS along the fiber to different degrees [18]. Therefore, a better insertion position could be obtained through the comparison experiments, as well as the chance of longer laser delivery distance.…”

“…However, for LPFGs, the instability resulting from cross-sensitivity is the most important fact limiting their applications [15]. In comparison, CTFBGs possess better stability and have been intensively studied in the past few years [16][17][18][19][20]. Although good SRS suppression have been obtained in many high-power fiber laser systems, in most cases CTFBGs were inserted between the seed and the amplification-stage in master oscillator power-amplifier (MOPA) systems [21,22], which is mainly limited by the power handling capacity.…”

Broadband, Continuous-Wave, Mid-Infrared Generation Based on TFBG Spectral Modulation

“…With the maturity of fiber grating inscription technology in recent years, it has been widely used in fiber optic communication [17,18] and fiber sensing [19][20][21], especially in the flatness of the gain and ASE suppression [22][23][24]. The TFBG is selected for the required flattening requirements and existing conditions.…”

Experimental Optimization of a High Power Fiber Laser With Raman Filter

“…Within those, stimulated Raman scattering (SRS) limits the power of HPFLs by shifting laser power by ∼13.2 THz towards longer wavelengths. Besides power depletion from the laser wavelength, the onset of SRS degrades the output beam quality and increases the risk of damaging pump lasers due to backward SRS [2]. Therefore, HPFL research is intensive towards means to suppress SRS and increase output power.…”

“…Chirped and tilted fiber Bragg gratings (CTFBG) are promising SRS filters because of their high intensity damage threshold as well as their low sensitivity to temperature, strain, and stress [3]. CTFBGs have demonstrated effective SRS suppression in kW HPFLs [2,4]. In this paper, we use a simple design of master-oscillator power amplifier (MOPA) to perform a systematic study of the impact of CTFBG insertion in a HPFL.…”