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 image-stabilizing technique and several servo mechanisms.
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 1mm thickness polymer media, corresponding to 6.22 pixels/μm2 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.
We have studied high-density magneto-optical recording using a Domain Wall Displacement Detection medium with a 664-nm wavelength laser diode and a 0.60-NA objective lens. Employing a wide-land structured disk and 16 - 17 modulation code, large recording/readout tolerances were obtained with a linear recording density of 0.11 micrometers /bit and an user data-transfer rate of 21 Mbit/sec. Furthermore, the feasibility of higher user data-transfer rate up to 50 Mbit/sec was studied.
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.
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.
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.
The transition jitters of a double-masked rear aperture detection (D-RAD) readout were calculated as a function of defocusing, disk tilt, and recording mark width. The modeling results successfully explain our experimental results. Large jitter tolerances and a low byte error rate were obtained using 0.3 micrometers bit length recording.
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.
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