Abstract: Microstructured optical fiber for transmitting optical signals comprised of light, the optical fiber including a core region and a cladding region surrounding the core region, the cladding region including at least one annular region having an index of refraction lower than that of the remainder of the cladding. The optical fiber provides an absolute SBS threshold in dBm greater than about 9.3+10log[(1?e?(0.19)(50)/4.343)/(1?e?(?)(L)/4.343)], wherein L is the length in km and ? is the attenuation in dB/km at 1550 nm, and a fiber cutoff wavelength of less than 1400 nm.