Systems and methods are provided for storing a mark-up language file and delivering the file from a network server to a user’s computer via a packet switched data network using a hyper-text transfer protocol. A main beam and sub-beams generated by the one-plane, two-wavelength diffraction grating and reflected from the surface of an optical disc are incident on corresponding light receiving elements among which the one to receive the main beam and those to receive the sub-beams are relatively shifted in a linear-speed direction of the optical disc. A cost advantaged manufacturing method is provided.