Servo Beam Research Articles

Ultra-narrow interval angular control signal for holographic data storage system

A precise and fast method for controlling the reference-beam angle of an angular-multiplexed holographic data storage system (HDSS)—to achieve larger capacity and faster data-transfer rate—is proposed. The reference beam is first controlled by a galvanometer mirror (GM) with an “angular control signal (ACS)” applied to its zero-cross angle (which differs by a certain offset angle from the target angle). The offset angle is then eliminated by referring to the output from a rotary encoder inside the GM, and the optimum angle for the reference beam is obtained. Next, a servo beam is used for the ACS, and the ACS value is obtained as a differential signal between the beam intensities of the diffracted reference beam and the diffracted servo beam. The servo beam is orthogonally polarized in regard to the reference beam and has a slightly different incident angle. A reference-beam angular error lower than 3.3 mdeg was confirmed in simulations and experiments.

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

We propose a new servo technique for controlling the reference beam angle in angular multiplexing holographic memory to attain higher capacity and higher speed data archiving. An orthogonally polarized beam with an incident angle slightly different from that of the reference beam is newly applied to the optics. The control signal for the servo is generated as the difference between the diffracted light intensities of these two beams from a hologram. The incident angle difference between the beams to the medium was optimized as sufficient properties of the control signal were obtained. The high accuracy of the control signal with an angle error lower than 1.5 mdeg was successfully confirmed in the simulations and experiments.

Dynamic Characteristic Analysis of CNC Turret Punch Servo Beam

This paper resolved CNC turret punch cause vibration phenomenon in the course of processing sheet,analysis of its dynamic characteristics of the beam servo feed mechanism, using the method of constrained modal analysis.Through the establishment of finite element model exactly for the servo beam and setting the boundary elastic restraint stiffness, solving the natural frequencies and mode shapes of the servo beam under boundary constraints and loading conditions. Constraints modal analysis results are consistent with experimental monitoring results of CNC turret punch servo beam. This modeling methodology and results of the analysis has a high practical value for CNC turret punch dynamic characteristics analysis and structural optimization design.

Research on the Design of an Optical Information Storage Sensing System Using a Diffractive Optical Element

This paper introduces a compact optical information storage sensing system. Applications of this system include longitudinal surface plasmon resonance detection of gold nanorods with a single femtosecond laser in three-dimensional space as well as data storage. A diffractive optical element (DOE) is applied in the system to separate the recording-reading beam from the servo beam. This allows us to apply a single laser and one objective lens in a single optical path for the servo beam and the recording-reading beam. The optical system has a linear region of 8 λ, which is compatible with current DVD servo modules. The wavefront error of the optical system is below 0.03 λrms. The minimum grating period of the DOE is 13.4 μm, and the depth of the DOE is 1.2 μm, which makes fabrication of it possible. The DOE is also designed to conveniently control the layer-selection process, as there is a linear correlation between the displacement of the DOE and the layer-selection distance. The displacement of DOE is in the range of 0–6.045 mm when the thickness of the layer-selection is 0.3 mm. Experiments were performed and the results have been verified.

Optical design of a single-sided microholographic data-storage system using a diffractiveoptical element and a blue laser

We introduce a compact optical design for a single-sided microholographic data-storagesystem, using a diffractive optical element (DOE) and a blue laser diode. The diffractiveoptical element is used to separate the disc-focusing servo beam from the reference beam ina single optical path to create a compact optical system. In conventional systems,three beam paths are generally required for the reference beam, signal beam anddisc-focusing beam. Our design employs a single optical path for all three beams,utilizing a DOE. The total capacity of a 12 cm disc with a medium thickness of 400 µm is 1.09 terabytes, using a blue laser and an objective lens with anumerical aperture of 0.85. Optical aberrations are suppressed below0.01 λrms on all layers (47 layers) and the disc tilt margin is calculated based on tiltcompensation by the objective lens. The final design has a disc tilt margin of ± 0.1° and thus can endure very severe disc tilt.

P-OPT-05 EVALUATION OF SERVO METHOD DESIGNED FOR THE HOLOGRAPHIC DATA STORAGE SYSTEM(Optical Storage/Optical Devices for Storage,Technical Program of Poster Session)

Servo control system developed for holographic data storage system(HDSS) can be said as two types. The first type uses servo layer on the media and red laser for tracking and focusing servo control similar to conventional ODD, and the other type uses analyzed data of captured image. CISD(Center for Information Storage Device) in Yonsei University studied about servo control system of HDSS and developed another type of servo method using servo beam servo track writing method. In this paper, optical and mechanical characteristics of servo system developed by CISD are analyzed, and feasibility of the servo system is evaluated.

Real time servo control of the holographic data storage system with an additional servo beam

Holographic data storage is a next generation data storage device, which has high storage density, high data transfer rate and short access time. The device is very sensitive to disturbances due to its enormous storage density. In the disk type holographic data storage device deviation occurs successionally on the position of the data as the disk rotates. Therefore the spot where the probe beam is illuminated should directly be corrected in order to exactly retrieve the desired data. In this paper we suggest a method using an additional beam containing a servo pattern in order to detect the deviation of the media. We also propose a real time servo control method to compensate the affect of the unpredicted disturbance.