High-speed reference-beam-angle control technique for holographic memory drive

Abstract

We developed a holographic memory drive for next-generation optical memory. In this study, we present the key technology for achieving a high-speed transfer rate for reproduction, that is, a high-speed control technique for the reference beam angle. In reproduction in a holographic memory drive, there is the issue that the optimum reference beam angle during reproduction varies owing to distortion of the medium. The distortion is caused by, for example, temperature variation, beam irradiation, and moisture absorption. Therefore, a reference-beam-angle control technique to position the reference beam at the optimum angle is crucial. We developed a new optical system that generates an angle-error-signal to detect the optimum reference beam angle. To achieve the high-speed control technique using the new optical system, we developed a new control technique called adaptive final-state control (AFSC) that adds a second control input to the first one derived from conventional final-state control (FSC) at the time of angle-error-signal detection. We established an actual experimental system employing AFSC to achieve moving control between each page (Page Seek) within 300 µs. In sequential multiple Page Seeks, we were able to realize positioning to the optimum angles of the reference beam that maximize the diffracted beam intensity. We expect that applying the new control technique to the holographic memory drive will enable a giga-bit/s-class transfer rate.

High-speed focus servo control system using Nyquist aperture mounted on a triaxial actuator for holographic disc drive system

“…Therefore, we developed a high-speed reference beam angle control mechanism in order to access a reproduced data page quickly and precisely. 27 As a result, we demonstrated multiple sequential moving control processes between each page within 300 μs∕page with less than AE3.0 m deg in an actual experimental system. To realize fast access times between books, it is necessary to control the relative position shift between a target hologram and an optical system (hereafter called an optical unit) of the HDSS.…”

Practical angular-multiplexing holographic data storage system with 2 terabyte capacity and 1 gigabit transfer rate

“…The servo system for the reference beam angle consists of an optical error detecting system generating an angle servo signal from the diffracted beams not used for data reproduction and a two-degree-of-freedom control system using a combination of feedforward and feedback control. 33,34) Figure 11 shows a schematic view of the optical error detecting system. The reference beam angle, in other words, the incident angle on the disc, is controlled by a galvano mirror.…”

Highly accurate servo control of reference beam angle in holographic memory with polarized servo beam

“…In addition, the reference beam angle is controlled with a 2-degrees-of- freedom control system to realize high-speed and highprecision control. 36) When the target page is sufficiently detected with the camera, the galvo mirror is moved forward to reproduce the next page and the drive repeats the same sequence as explained above. The influence of disc vibration is vanishingly small in this sequence, because each page is read in a very short time interval in our system and the disc vibration can virtually be ignored in this time interval.…”

“…We can reproduce hologram images without the SNR deterioration that is induced with intentional displacement. 36)…”