Tolerance of 3 beam cross-talk canceller

The next-generation digital versatile disc (DVD) is required to have a capacity of 15 Gbytes so that it can store high-definition television signals for two hours or longer. To achieve the capacity, we developed a 3 beam cross-talk canceller (CTC) which uses two sub-beams positioned on adjacent tracks to cancel cross-talk components. The sub-beam positions are varied due to a grating adjustment error, a radial deviation of a track and a wavelength change of a laser diode. Since the sub-beam offset deteriorates signals reproduced from the adjacent tracks, it might degrade a performance of the CTC system. The tolerance of the CTC system against the sub-beam offset should be discussed for practical use. We measured the performance of the CTC system when the sub-beam positions were shifted. As a result, we confirmed that the CTC system has sufficient margin against the sub-beam offset.