Abstract: An optical fiber which comprises a coating layer disposed outside a bare optical fiber having a core and a cladding and a grating formed in the core of the exposed bare optical fiber by removing the coating layer and its manufacturing method. The optical fiber is provided with a re-coating layer disposed in the exposed bare optical fiber.

Abstract: A method is presented for writing a permanent spatially periodic phase-matching second-order non-linearity grating in an optical waveguide. Single frequency exciting radiation is launched in a pair of guided modes of the waveguide in the presence of an external DC electric field applied in a direction transverse to the waveguide. The exciting radiation may be either co-propagating or counter-propagating. The above method may be refined by performing it once for an estimated value of exciting radiation frequency, testing the waveguide to determine error in the chosen estimate, erasing the grating and re-performing the method using a corrected value for the frequency of the exciting radiation.