The invention relates to a line for processing an optical fiber having first and second ends, the line comprising a support for receiving a reel with the fiber wounded thereon; a de-winder for unwinding the fiber without substantial rotation of the reel; and a processing station for receiving the optical fiber from said de-winder to perform a processing on a portion of the optical fiber. The invention also relates to a method for writing a grating on a fiber having first and second ends, the fiber being wounded on a first reel and being capable of being wounded on a second reel, the method comprising connecting the first end of the fiber to a circulator; connecting said circulator to a source of light and to a first measurement means; de-winding the fiber from the first reel without rotation of the reel; writing a grating on the fiber with a source of radiation; and measuring reflection spectra of the grating with said first measurement means. The method also comprises winding the fiber on the second reel without rotation of the reel.