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A unique coaxial optical system which enables us to record and retrieve the holographic data on a continuously rotating disc is proposed. The system supports an im age-stabilizing technique and several servo mechanisms. Keywords : Holographic data recording, optical system, image-stabilizing technique, servo mechanism. 1. INTRODUCTION Holographic data storage is an attractive candidate for next generation high-density optical memories. Among several holographic recording systems 1) , the combination of a coaxial recording method with a shift multiplexing technique is most promising because the optical system has a simple structure and simple co mponents such an optical disc pick-up. Also, holographic disc rotating at a constant velocity is similar to the optical disc. From these characteristics, one can expect to realize a very compact, inexpensive holographic disc drive. In order to perform shift multiplexing on a rotating disc, however, a short-pulse laser with considerable power at its peak must be used for recording/retrieving. Generally, a solid-state Q-switch laser is used for this application, but it is expensive and space-consuming.

We developed one dimensional data pattern hologram writer using GLV device as a spatial light modulator. The following advantages were expected: easier pixel matching, simpler signal processing, low height drive and high transfer rate. 171 angular multiplex recording holograms on a lmm thickness polymer media, corresponding to 6.22 pixels/μm 2 in density were demonstrated. With a Bit Error Rate (BER) of less than 2 x 10 -4 , 101 multiplexing holograms were successfully stored. Then, considerable error factors were discussed and solutions were given for higher multiplex recording.

A new class of super resolution method was proposed for magneto-optical recording by T. Shiratori et.al. The method called DWDD (Domain Wall Displacement Detection) is principled on momentary magnetic wall displacement during a read-out.

Land/groove recording in an MO system was demonstrated using MFM recording technology and a 690 nm wavelength diode laser. The CNR of 55 dB and cross-talk of about -35 dB were obtained at a 1.88 micrometers recorded mark length and a 0.7 micrometers yielded a 0.35 micrometers bit length and a 0.7 micrometers track pitch were 8.1% on land and 8.7% on groove. The disk tilt margins were radially +/- 0.42 deg and tangentially +/- 0.45 deg when reading out on land, and +/- 0.40 deg and +/- 0.44 deg on the groove. The recording power margins were estimated to be +/- 8.0% on land and +/- 9.0% on groove considering over-writability and cross-write characteristics.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

PSR (premastered optical disk by super-resolution) is a super-resolution technique used to increase the recording density of ROM optical disks. Our PSR system uses a novel disk with a nonlinear optical layer, a second-harmonic-generation green laser ((lambda) equals 532 nm), 0.52NA objective lens and eight-to-fourteen modulation coding. By using PSR, a high C/N ration of 51dB was obtained for a pit length of 0.2 micrometers which is beyond the conventional optical limit. Furthermore, we obtained a bit error rate of less than 10-5 for a linear density of 0.185 micrometers /bit and a track pitch of 0.8 micrometers , thus demonstrating the feasibility of our PSR system with six times the areal density compared to the current CD.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The transition jitters of a Double-masked Rear Aperture Detection (D-RAD) readout werecalculated as a function of defocusing, disk tilt and recording mark width. The modelling resultssuccessfully explain our experimental results. Large jitter tolerances and a low byte error rate were obtained using 0.3 tm bit length recording. 1. INTRODUCTIONMagnetically induced super resolution (MSR) in magneto-optical (MO) disks using exchange- coupled magnetic multi-layer film have been previously reported'6. A portion of the focused spot is optically masked for the readout of the MO signal. The effective spot size after masking is much smallerthan that of the focused spot. Therefore super-resolution is realized.Various types of the MSR methods have been developed to achieve super-resolution. Among thesemethods, D-RAD has an advantage as it achieves a higher linear-density readout, because the width of theeffective spot in the tangential direction is significantly reduced by double masks. Using this method the

The cut-off frequency was extended by a factor of more than two using a magneto-optical disk with thermally induced mask.

A super resolution has been achieved in the magneto-optical disk using an exchange-coupled multilayer film. Two types of magnetically induced super resolution, front aperture detection and rear aperture detection have been successfully investigated. A high C/N of more than 42 dB is obtained experimentally for a mark length of 0.3 micrometers which is much shorter than the resolution limit expected from the conventional diffraction theory.