An optical element, such as a lightguide or an optical film, is formed with a predetermined, programmed pattern of optical structures. The method comprises entering a PTT communication mode and providing a PTT application, when a function key and an abbreviated number key for performing the PTT communication service are input to the portable terminal and performing the PTT communication service based on subscriber information of the PTT communication service corresponding to the input abbreviated numbers. The carrier tubes used to hold ink tubes are preferably closed, thus providing a secondary containment in the event of an ink leak. The support element comprises a third portion extending from the radially innermost end of the second portion and folded on the second portion itself so as to generate, in the folding area, a rounded edge cooperating with the annular seat of the elastically deformable element. A data transmission apparatus outputs an initialization pattern signal at turn-on of power or after reset, and the data reception apparatus establishes clock synchronization on the basis of the received initialization pattern signal and starts data reception after setting of evaluation levels to be used for threshold evaluation of signal levels.