VERSATILE POLYCHROMATIC DYNAMIC TESTBED FOR OPTICAL DISKS

A dynamic testbed for the evaluation of optical has been designed and constructed. The system is achromatic within the wavelength range 440- 690 nm, allowing any light source in this range to be utilized for rea d-write-erase experiments. In addition, the system accepts disks with substrate thicknesses ranging from 0 to 1.7 mm. The polarization handl ing capabilities of the testbed are such that, with the turn of a knob , one can generate either linearly polarized or circularly polarized l ight at the disk surface. This feature permits the testing of both mag neto-optical and phase-change disks, in addition to compact disks and digital versatile disks, without any modifications to the system. A le aky polarizing beam splitter (LPBS) has been specially designed and bu ilt for this tester. The LPBS allows continuous adjustment of the rati o between p- and s-polarized components of the reflected beam that rea ch the detectors. This feature is especially useful for magneto-optica l disks, where one can achieve an optimum signal-to-noise ratio by adj usting the relative amounts of the two components of polarization at t he detection module. Focus-error detection is based on the astigmatic method, and the primary track-error detection scheme is the push-pull method, although other focusing and tracking schemes may also be imple mented. The rf data signal and focusing and tracking servo signals are all derived for the same detectors, thus allowing the optical power r eturning from the disk to be used in its entirety for these multiple p urpose. The detection channel consists of two high-speed quad detector s mounted on the two arms of a differential detection module. By combi ning the various outputs of these detectors it is possible to generate the astigmatic focus-error signal, the push-pull track-error signal, the differential magneto-optical readout signal, the conventional sum signal for phase-change disk readout, and the differential edge-signal for mark-edge detection on various types of optical media. (C) 1997 O ptical Society of America.