Phase-shifting apodizer for next-generation DVD

The next generation digital versatile disk (DVD) which uses blue laser will have a capacity of 13 Gbytes to 15 Gbytes. Compared with the current DVD, the wavelength will be shorter and the NA will be higher. But with the increase of NA and decrease of wavelength, the depth of focus (DOF) decreases rapidly, which makes it hard to track by the servo-system. In this paper, we propose to use an optimized three-portion phase-shifting apodizer to increase the depth of focus and at the same time minimize the spot size, which makes the DOF of next generation DVD comparable to current DVD. The simulation results show that an optical system with this apodizer also has a good defocusing characteristic.