A fiber laser system comprising at least one waveguide configured with: - an active Nd-doped fiber and a coreless passive pump delivery fiber optically connected to one another and extending along substantially parallel axis, the active and passive fibers (24, 28) having respective axially extending central regions (38, 44), which are coupled to one another to define a structure wherin the active fiber is provided with a core configured with an axial double bottleneck- shaped cross-section, the double bottleneck-shaped cross-section having the core central region flanked by core end regions, wherein an area of the core central region is larger than an area of the core end regions, - and the passive pump delivery fiber having an axial dumbbell-shaped cross-section, wherein the dumbbell-shaped cross-section has the central region and spaced end regions which flank the central region, the central region of the passive pump delivery fiber being configured with an area smaller than an area of the spaced end regions, - the central regions (38, 44) of the respective active and passive pump delivery fibers (24, 28) being configured to provide for such a pump light absorption rate in a portion of the core extending along the central region of the active fiber that the latter has a shortest possible length which allows for a desired gain of signal light at a working wavelength while limiting a gain of the signal light at a parasitic wavelength to a preset threshold, wherein the Nd ion are introduced into the core at a given concentration selected to provide the active fiber with the desired gain at the working wavelength and the preset gain at the parasitic wavelength, - wherein the fiber laser system further comprises a protective fiber coating surrounding the central regions (38, 44) of respective active and passive pump delivery fibers (24, 28), - and wherein a maximum coefficient k at which a total clad area of the central regions (38, 44) of the respective active and passive pump delivery fibers (24, 28) may be reduced is k= [ NA af / NA pump] 2 wherein NA af = [√n clad 2 - n coat 2] 2 is a numerical aperture of the active fiber with n clad and n coat being respective indices of refraction of cladding and coating of the active fiber, and NA pump is a numerical aperture of pump emission. - an active Nd-doped fiber and a coreless passive pump delivery fiber optically connected to one another and extending along substantially parallel axis, the active and passive fibers (24, 28) having respective axially extending central regions (38, 44), which are coupled to one another to define a structure wherin the active fiber is provided with a core configured with an axial double bottleneck- shaped cross-section, the double bottleneck-shaped cross-section having the core central region flanked by core end regions, wherein an area of the core central region is larger than an area of the core end regions, - and the passive pump delivery fiber having an axial dumbbell-shaped cross-section, wherein the dumbbell-shaped cross-section has the central region and spaced end regions which flank the central region, the central region of the passive pump delivery fiber being configured with an area smaller than an area of the spaced end regions, - the central regions (38, 44) of the respective active and passive pump delivery fibers (24, 28) being configured to provide for such a pump light absorption rate in a portion of the core extending along the central region of the active fiber that the latter has a shortest possible length which allows for a desired gain of signal light at a working wavelength while limiting a gain of the signal light at a parasitic wavelength to a preset threshold, wherein the Nd ion are introduced into the core at a given concentration selected to provide the active fiber with the desired gain at the working wavelength and the preset gain at the parasitic wavelength, - wherein the fiber laser system further comprises a protective fiber coating surrounding the central regions (38, 44) of respective active and passive pump delivery fibers (24, 28), - and wherein a maximum coefficient k at which a total clad area of the central regions (38, 44) of the respective active and passive pump delivery fibers (24, 28) may be reduced is k= [ NA af / NA pump] 2 wherein NA af = [√n clad 2 - n coat 2] 2 is a numerical aperture of the active fiber with n clad and n coat being respective indices of refraction of cladding and coating of the active fiber, and NA pump is a numerical aperture of pump emission.