A method for manufacturing an optical grating on a length of optical fiber having input and output ends. Guided light is conducted into the input end of the fiber and light reflected back from the output end is measured with an optical sensor. An optical grating is formed in the fiber between the input and output ends and guided light is conducted into the input end of the fiber and light reflected back from the grating is measured with an optical sensor. Measured light is compared to determine a percentage of guided light reflected back from the grating.