VERSATEST-I, a versatile polychromatic dynamic testbed for optical disks

A polychromatic versatile dynamic testbed for the evaluation of optical disks is presented. The system can be used for all wavelengths from 400 to 690(780) nm, allowing any laser source in this range - especially the new blue laser diodes - to be utilized for read-write-erase experiments. In addition, the system allows testing of disk with substrate thicknesses ranging from 0 to 1.7 mm. The polarization of the system can easily be changed from linear to circular at the disk surface, so the use of both magneto-optical (MO) and phase-change disks (PD) is possible, in addition to read-only disks (CD, DVD). A variable leaky polarizing beam splitter has been specially designed for this tester. This device allows to continuously adjust the ratio between the s- and p- polarized components for the reflected beam reaching the detectors, enabling the optimization of the signal-to-noise ratio while adjusting the relative amounts of the two components of polarization at the detectors. The astigmatic method is used for focus control and the push-pull method is used for track control (other focusing and tracking schemes like DPD are under preparation). In a optional setup, the RF data signal and the focus and track servo signals can be derived from the same high speed quad detectors, allowing the use of the full optical power returning of the disk for all these purposes. So the astigmatic FES, the push-pull TES, the differential magneto-optical readout signal and the conventional sum signal for phase-change readout as well as the differential edge-signal for mark-edge detection are obtained. In this paper, we are presenting the basic functions of VERSATEST-I as well as future enhancements for latest optical data storage technology. Additionally typical test results on magneto-optical disks and phase-change disks (DVD-RAM 5.2GB) are reported.