A Broadband Interferometric Sensor System for the Determination of Hard Disk Dynamic Properties

In order to evaluate the dynamic behavior of hard disk substrates made from aluminum and ceramic materials, we have developed a multi-probe optical sensor system that is used in conjunction with commercially available air-bearing spindle technology. The interferometric system uses erbium-doped fiber technology and digital demodulation to measure the instantaneous height of the disk surface from the end of one or more single-mode fiber probes. The ability to use multiple probes is useful to distinguish between mechanical properties of the disk and artifacts introduced by the clamping mechanism and spindle. Another advantage of the system is its potentially low cost, especially when multiple probes are required. We describe the main components of the system and present some preliminary results on substrates made of aluminum and of a proprietary ceramic material currently under development at Raychem.