Large-mode-area active optical fiber and preparation method thereof

Abstract

The invention provides a large-mode-area active optical fiber, which comprises a fiber core, a first cladding, a second cladding and a third cladding, wherein the first cladding, the second cladding and the third cladding sequentially encircle the periphery of the fiber core; the effective refractive index of the second cladding is lower than the effective refractive indexes of the first claddingand the fiber core; a pump core area encircles the outer side of the third cladding; an external cladding encircles the outer side of the pump core area and comprises a layer of air vent holes or capillary bars doped with quartz glass; and the effective refractive index of the external cladding is lower than that of the pump core area. On the premise of ensuring a large mode area of the active optical fiber, the optical fiber suppresses amplified spontaneous radiation, improves the stability of the optical fiber, and ensures the quality of light beam. The invention also provides a preparationmethod of the active optical fiber. By adopting a liquid phase multi-point doping mode of gas-phase aluminum doping and rare-earth ions, continuous doping for many times can be flexibly controlled and realized, the size of a rare-earth doped core bar is greatly increased, and uniform doping of the rare-earth ions and aluminum is simultaneously realized.

Description

technical field [0001] The invention relates to an active optical fiber and a preparation method thereof, in particular to an active optical fiber with large mode field and high beam quality and a preparation method thereof. Background technique [0002] As the main gain medium, active fiber plays a vital role in fiber lasers and amplifiers. The development and progress of active fibers directly promote the progress of fiber lasers and amplifiers. [0003] From the original core-pumped fiber laser, due to the limitation of pump power, after Snitzer et al. proposed a double-clad laser fiber in 1988, cladding-based pump lasers have developed rapidly, and countries around the world have successively realized single-fiber output The power exceeds the kW level, but as the output power continues to increase, the problems of the active fiber itself are becoming more and more obvious, and the impact on the performance of the laser is becoming more and more serious. [0004] Therefo...

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Problems solved by technology

[0007] Chinese patent announcement number CN101038353B proposes a high-power double-clad pumped single-mode output multi-core fiber and its manufacturing method, using a multi-core structure to disperse the power density, but because of multiple active cores, if you want to achieve Both the near-field and far-field output are the same spot, and it is difficult to control the same mode process

Chinese patent CN1260588C is a method and equipment for expanding the mode field of optical fiber applied by Sumitomo of Japan. It mainly uses a heater to heat the fiber to realize the diffusion of dopants to expand the mode field. Fiber and the device using it, these two patents have achieved a certain mode field expansion, but there are great limitations in the use of kilowatt-level high-power fiber lasers

[0009] At the same time, although the optical fiber has a large surface area / volume ratio, when the output laser power reaches thousands of watts, the heat caused by the high pump light power will also become a serious problem, and the uneven temperature distribution in the optical fiber will cause the core to refract The change of the thermal effect of the rate is different, forming a thermal lens effect similar to that of a solid-state laser, and causing gravity or expansion, and destroying the low-refractive index coating of the outer cladding, thereby reducing the life of the fiber

Heat at a higher temperature will cause brittle cracks in the optical fiber, etc., reducing the efficiency of the laser or even destroying the entire laser

[0010] In addition, the active fiber as a gain fiber is amplified while the signal is amplified, and the spontaneous emission is also continuously amplified during the transmission process, forming amplified spontaneous emission (ASE), and in the large mode field active fiber, the increased mode The field area will inevitably make the refractive index difference between the modes smaller, and the reduction of the refractive index difference between the modes will cause a mode to be coupled into an adjacent high-order mode due to an external disturbance, making the mode unstable, that is, mode distortion and Mode coupling, so the stability of the mode is also a technical problem currently existing in large mode field active fibers

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