Electro-optic focusing system for a high-density optical disk

We have developed an electro-optic cell as a fine-adjustment focusing system for an optical disk. The cell is fabricated from transparent lead lanthanum zirconate titanate ceramic and has concentric-patterned indium tin oxide electrodes. The electro-optic cell can generate a relative phase shift in the pupil function. We have confirmed, theoretically and experimentally, that the phase shift induces a change in focal position that is as much as twice the focal depth without degrading the region near the main lobe of the point-spread function.