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 μm2 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 μm2. 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.