Tracking servo method using reflective optical filter for holographic data storage system

Holographic data storage system is one of the next-generation data storage systems and is characterized by its high storage density and fast data transfer rate. However, holographic data storage systems are very sensitive to disturbances that affect the position of the media. Therefore, tracking servo control is needed to ensure a good performance of the system even if disturbances occur, such as eccentricity of the disk and external shock. In our previous researches on tracking servo methods, we used additional beams or recorded servo track images with data pages to record additional gratings with data pages. Therefore, the recording density may be reduced and the system may be complicated. In addition, the performance of the system may be compromised by cross-talk noise caused between the reference beams and additional beams. In this paper, we propose a tracking servo method using the residual beam, which is reflected by the reflective optical filter. This method does not require recording supplementary gratings or use additional beams, and only needs to record data pages. The residual beam is retrieved with desired retrieved beam by the reference beam and wasted during the retrieving process. We first constructed a holographic data storage system and designed a reflective optical filter to detect tracking error signals. After detecting the tracking error signals, a tracking servo controller using a lead-lag compensator was incorporated to reduce the tracking error signals. The performance of the designed controller was verified by simulated and experimental results. Finally, the performance of the tracking servo method was investigated by comparing the retrieved data images.