In the paper, we report on the development of a synthesis and melting method of phosphate glasses designed for active microstructured fiber manufacturing. Non-doped glass synthesized in a ...P₂O₅-Al₂O₃-BaO-ZnO-MgO-Na₂O oxide system served as the matrix material; meanwhile, the glass was doped with 6 mol% (18 wt%) of Yb₂O₃, as fiber core. The glasses were well-fitted in relation to optical (refractive index) and thermal proprieties (thermal expansion coefficient, rheology). The fiber with the Yb
-doped core, with a wide internal photonic microstructure for a laser pump, as well as with a high relative hole size in the photonic outer air-cladding, was produced. The laser built on the basis of this fiber enabled achieving 8.07 W of output power with 20.5% slope efficiency against the launched pump power, in single-mode operation
² = 1.59, from a 53 cm-long cavity.
We present the pedestal-free thulium doped silica fiber with a large nanostructured core optimized for fiber lasers. The fiber is composed of over 6 thousand thulium doped silica nanorods with a ...diameter of 71 nm each which form a nanostructured step-index core. We study the influence of non-continuous distribution in nanoscale active areas on gain, beam quality, and fiber laser performance. The proof-of-concept fiber is effectively single mode for wavelength above 1.8 µm. We demonstrate the performance of the fiber in a laser setup pumped at 792 nm. Single mode laser emission with a slope efficiency of 29% at quasi-continuous output power of 4 W with M
= 1.3 at the emission spectrum 1880-1925 nm is achieved.
A nanostructured core silica fiber with active and photosensitive areas implemented within the fiber core is demonstrated. The photosensitivity, active and passive properties of the fiber can be ...independently shaped with this new approach. We show that discrete local doping with active ions in form of nanorods allow to obtain effective laser action as in case of continuous distribution of the ions in the core. Co-existing discrete photosensitive nanostructure of germanium doped silica determine single-mode performance and allow inscription of highly efficient Bragg grating over the entire core area. Each nanostructure do not degrade performance of other one since physical interaction between active and photosensitive areas are removed. As a proof of concept, we have designed and fabricated the nanostructured, ytterbium single-mode silica fiber laser with the Bragg grating inscribed in the entire core area. We demonstrated fiber laser with good quality of generated laser beam (M
=1.1) with lasing efficiency of 44% and inscribed Bragg grating with 98.5% efficiency and -18 dB contrast.
We developed a passive silica based large mode area fiber with the nanostructured core with a diameter of 30 μm devoted to fiber Bragg grating inscription for application in an all-fiber laser ...cavity. The fiber is perfectly matched to the commercial active fiber with NA = 0.06 and core/cladding diameters 30/250 μm. Measured modal characteristics and bending loss of the fiber confirm single-mode operation for bending diameter of 8 cm with bending losses as low as 0.15 dB/m. Although the nanostructured fiber core is low germanium doped, we fabricated high reflectivity (98.5%) UV induced fiber Bragg grating (FBG) and verified its performance in fiber laser setup. The laser cavity formed with highly reflective FBG inscribed in the fiber and Fresnel reflection on the free end of active fiber results in lasing efficiency of 65.5%. The flexibility of the nanostructuring approach gives prospects for the development of free-form large mode area fibers for passive fiber components and matched with any type of active fibers.
We present the pedestal-free thulium doped silica fiber with a large nanostructured core optimized for fiber lasers. The fiber is composed of over 6 thousand thulium doped silica nanorods with a ...diameter of 71 nm each which form a nanostructured step-index core. We study the influence of non-continuous distribution in nanoscale active areas on gain, beam quality, and fiber laser performance. The proof-of-concept fiber is effectively single mode for wavelength above 1.8 µm. We demonstrate the performance of the fiber in a laser setup pumped at 792 nm. Single mode laser emission with a slope efficiency of 29% at quasi-continuous output power of 4 W with M2 = 1.3 at the emission spectrum 1880-1925 nm is achieved.
The power scaling of single mode fiber lasers and amplifiers, due to the wide area of applications, has been the subject of great interest for many years. Increasing the mode area seems to be the ...obvious way to scale up the output power level from the single emitter if you consider well-known limitations like nonlinear effects, material damage threshold or thermal lensing. The nanostructurization of the fiber core is a method to control precisely optical properties of the active fiber. This method allows to design and develop the fiber with the core of any arbitrary defined refractive index distribution, with precision not available with other known fiber technology. The nanostructurization also open up an opportunity to incorporate simultaneously various active and non-active glasses into the fiber core. Those advantages can be used to fabricate the new class of fibers for laser applications. Here we show ytterbium doped phosphate single-mode fiber with nanostructured core, which is the first proof-of-concept of active fiber with entirely nanostructured core area.
We present numerical studies on bend-induced effective single-mode large-mode area fibers with various refractive index profiles: step index, parabolic, and triangular and hyperbolic for laser ...applications. We report the fiber with effective mode area as large as 1530 μm 2 for 110-μm all-solid core diameter using triangular refractive index profile, in single-mode regime. We also report the fiber with parabolic refractive index profile, 70-μm core diameter with effective single-mode area of 1170 μm 2 . Development of novel active very large nanostructured core fiber with dedicated gradient index profile is discussed. Owning to nanostructurization, the extremely large core in the all-solid fiber can be obtained and used in a laser system to diminish undesirable nonlinear effects and increase the output power level with diffraction-limited beam quality. The nanostructurization method allows us to break the limits of classical manufacturing methods and opens new opportunities in precise shaping of the refractive index distribution.
We present the experimental verification of a new type of an active nanostructured fiber devoted to simultaneous laser emission at two wavelengths: 1040 nm and 1534 nm in the fundamental mode. The ...fiber core is formed with two types of nanorods made of a phosphate glass doped with either Yb 3+ or co-doped with Yb 3+ /Er 3+ ions, respectively. A distribution of the nanorods in the core allows to control relative gain and modal properties of the fiber at both wavelengths and to maintain the single mode performance with a high quality beam generated in a single fiber core. The double-cladding fiber structure allows efficient excitation with a single 975 nm diode pump laser. As a proof-of-concept we demonstrated an active fiber with 15 µm core diameter composed of 6649 nanorods with an individual diameter of 160 nm. The fiber was used in a laser setup. The laser operation was verified for simultaneous two-color laser generation at output power levels of 0.78 W and 0.42 W with slope efficiency of 23.0% and 9.8% at 1040 nm and 1534 nm, respectively.
We report development of ytterbium doped silica fiber with nanostructured core for laser applications. We study influence of non-continuous distributed Yb dopants on gain, beam quality, and fiber ...laser performance. The fiber core is composed of over 43 thousand nanorods with a central part doped with Yb. The diameter of each nanorod is 72 nm. With this method we obtained a flat refractive index profile with uniformity of 1.3 × 10
refractive index unit (RIU) despite the non-uniformity of 1.2 × 10
RIU in Yb doped preform rods used for the fiber development. We demonstrate a nanostructured core single-mode fiber laser with 61.8% of slope efficiency, and extremely low numerical aperture 0.027 of generated mode.
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