A coated optical fiber can have a primary coating and a secondary coating, where the primary coating can have good microbending resistance and is obtained by curing a composition having a high cure speed. In one example, a coated optical fiber can include as optical fiber, a primary coating and a secondary coating. The optical fiber can have an attenuation increase of less than 0.650 dB/km at 1550 nm, with the primary coating having a modulus retention ratio of at least 0.5, a glass transition temperature of -35.degree. C., and where the primary coating is obtained by curing a primary coating composition having a cure dose to attain 95% of the maximum attainable modulus of less than 0.65 J/cm.sup.2.