The nanostructurization of fiber core is a new method to modify optical properties of the fiber using standard stack-and-draw fiber manufacturing technology. This method allows to design and develop large mode area single mode active fibers using optimized gradient refractive index profiles by means of nano-structure composed of two or more types of glass. The distribution of discrete glass areas with feature size smaller than λ/5 results in continuous-like refractive index profiles. The nanostructurization has been successfully used by our group for development of microoptical components like single parabolic or axicon lenses, an array of lenses, recently applied as Shack-Hartmann sensor, or nonlinear components like vortex. We also used that method for developing passive optical fibers.
In this paper we present studies on the novel fiber for laser application with nanostructure core of uniform refractive index distribution. The fiber core consisted of two phosphate glasses, one glass undoped and the other glass doped with ytterbium, with percentage content of 57/43 respectively. They were matched with rheological properties, but differed with refractive indices of Δn = 0.001. We calculated the binary pattern composed of two types of nanorods which corresponded to uniform refractive index distribution. The average refractive index value was precisely selected to support single-mode operation in the fiber structure. If you used only doped glass in the standard fiber with similar dimensions you would obtain multimode fiber. The same undoped glass used in nanostructure core was also used for the cladding around the fiber core. For the fiber development we used doped phosphate glass with Yb2O3 concentration of 6 mol% (15.69×1020 Yb3+ cm-3) with the peak emission cross section of 1.45×10-20 cm2 and the luminescence lifetime of the Yb3+ ions of 0.6 ms.
The final fiber was manufactured with double-clad structure. The nanostructured core was 19 µm, and the internal cladding was 59 µm in diameter. The overall diameter of the fiber was 241 µm. The external cladding was created as an air-cladding with high numerical aperture suitable for efficient pumping. We put that fiber into the laser setup and for the fiber length of 15 cm we achieved 63 % of slope efficiency in relation to the launched power, which is comparable to our lately reported achievements. The maximum output power was 10.3 W and the threshold was 3 W. The output was single-mode with very good quality with numerical aperture of about 0.04. The spectrum of the laser wavelength was 18 nm (1012-1030 nm) without implementation of any diffraction elements.
The nanostructurization method allows to break the limits of classical manufacturing methods and opens new opportunities in precise shaping of the refractive index distribution, providing the development possibility of many theoretical studies. We believe that new approach may also lead to develop all-solid very large mode area active fibers and it can be easily applied to silica technology.
This work was supported by the project TEAM TECH /2016-1/1 operated within the Foundation for Polish Science Team Programme co-financed by the European Regional Development Fund under Smart Growth Operational Programme (SG OP), Priority Axis IV
We demonstrate the 3%mol ytterbium doped phosphate glass air-clad photonic crystal fibre (PCF) laser of 43 cm length
in single-mode operation. The fabrication and testing of the fibre laser is introduced. The laser generates from the 12 μm
core of photonic microstructure at wavelength of 1030 nm. Near 4-W output power and 14.6% slope efficiency against
the launched pump power is demonstrated in preliminary characterization.
Double-clad photonic crystal fibre structure for laser applications is demonstrated. The double-clad structure of the fibre has the air-cladding with glass bridges of waists less than 500nm. The fibre was produced with phosphate glass and the core region was doped with ytterbium. The fibre was investigated and we found it to be monomode for generation wavelength of 1008nm. Whole fibre producing process including doped and undoped glass manufacturing and fibre drawing was held in Institute of Electronic Materials Technology.
We present experimental realization of elliptical-hole rectangular lattice photonic crystal fibres fabricated from multi-component glass. The photonic cladding has a lattice constant 2.17 μ and 3.72 μ for main axis, respectively and elliptical holes with ellipticity 2.14. The rectangular lattice is chosen to obtain two-fold geometry and to increase the global asymmetry of photonic structure, which enhance birefringence of fibre. Rectangular lattice allows also a better control of elliptical air holes uniformity during fabricating process. Fabricated fibres have a cladding with a rectangular cross-section. It allows for easy identification of the fibre's principal axes and orientation of the fibre with respect to directional measured perturbation like axial stress, bending force in sensor applications. Using a full vector plane-wave expansion method an influence of structure parameters such as ellipticity of air holes and aspect ratio of rectangular lattice on birefringence and modal properties of the fibres are studied. Potential applications of the fibres are discussed.
A range of integrated fiber optic structures - lightguides, image guides, multicapillary arrays, microstructured (photonic) fibers - manufactured in the Institute of Electronic Materials Technology (ITME) is described. All these structures are made of multicomponent glasses (a part of them melted in ITME). They can be manufactured in similar multistep process that involves drawing glass or lightguide rods and tubes preparing glass performs, stacking a bundle with rods and (or) tubes, drawing multifiber or multicapillary performs. Structure formation, technological process, characterization and applications of different integrated structures are presented.
A square lattice photonic crystal fiber is described. The square lattice structures were fabricated, characterized and their polarization properties were investigated. The polarization properties of the fibers were not as strong as those reported previously in highly birefringent PCF, but these structures have considerable potential for high birefringence.
The use of piezoelectric transducer and acoustooptically induced waves were proposed for mode field excitation on a single-mode microbend fiber taper structure. As the result the in-line fiber attenuator was proposed tuned easily by the transducer low power drive voltage which was fully telecommunication compatible. The tuning range was up to 13 dB and the excess losses not exceeded 0.3 dB typically.