Optical servo writing

The present invention relates to a method for servo writing an optical or magneto-optical medium where a data path is defined by transmitting a laser beam onto the medium to change the crystalline structure at preselected portions. These portions can guide an optical head along the data path. Embodiments include using a far-field laser servo writer to transmit a laser beam in combination with a high numerical aperture, using a far-field laser servo writer to transmit a laser beam in combination with a solid immersion lens, using a near-field laser servo writer to emit a laser beam in combination with a solid immersion lens, creating a sub-wavelength aperture for emitting a laser beam onto the medium, lithographic and maskless lithographic techniques. The present invention also relates to a medium for the storage of data which has portions of its substrate with a different crystalline structure than the rest of the substrate of the medium, so that these portions of the substrate can serve as optically created servo fields for a tracking device.