No abstract

No abstract

No abstract

Abstmt-A new tracking technology for achieving high track density over 10 k tracks-peFinch ("PI) is developed ' l h key technologies am incorporated One is the application of optical ask technology to a magnetic dsk to obtain a high quality sew0 signal with a trackwidth 1.5 to 2 pm. "he other is the installation of a dusl-stage actvator wing a piezoelecMc device for the fine Pctustor to gain higher sew0 p e r l o m c e in a bandwidth gmaterthan 1 k I k "his paperdescribes the design of the optical servo system for the track pitch 1.5 ~rm, 17 k "PI, and experimental ~esults includng a comparison of magnetic heads. INIXODUCIIONFuture disk storage must be of larger capacity, have smaller drive units, higher recording density and faster access.To satisfy these requirements for high recording densityespecially track density, there are some key technologies.These include a narrow trackwidth magnetic head, a high quality servo signal, and improved mechanical system performance. This paper describes experiments on an optical tracking method using a laser diode. PRINCIPII OF SERVO SIGNAL DEECT'IONIt is well known that lasers can be significantly affected by external optical feedback. This occurs when a portion of the laser's output is fed back into the laser due to an external reflecting surface. This effect is great, especially in the semiconductor laser, because of high laser gain and the tendency to couple with extemal optical feedback. Though this behavior is avoided in the field of the optical communication as the feedback causes oscillation mode change and subsequent noise, the use of such feedback has been proposed for optical recording heads[l], [2]. In our method of magnetic disk head-tracking, the laser diode (LD) and photo detector are directly attached to the magnetic head slider without using an optical system such as a lens. As shown in Fig. 1, R2 is the reflectivity of the output surface of the laser light, R1 is that of the rear surface of the LD, and R3 is that of outside reflectors which are equivalent to the surface of the disk. This can be thought of as a coupled compound resonance system with the resonator of the LD composed of reflectivity RI and R2, and the other resonator composed of R3 and R2. Servo data formed on the disk 502 KandaGu, Tsuchiura, Ibaraki 300, Japan Laser Photo-detector Slider diode \ Magnetic head UFig. 1 Shucture of the optical sew0 head whae the laser diode is attached on the slider with its active layer parallel to the track line and apart from the disk surface.surface as a pattern is read by detecting the change in reflectivity caused by the coupling mentioned before. The principle of pattern detection is explained by the current to light output curve (L-I curve) shown in Fig. 2. Curve 'b' is a typical state without extemal feedback, and 'a' is with feedback. As for the signal, in a certain bias current Io over the threshold current of the laser output, at least two levels of H and L are detected depending on the resonant condition.Additionally, it can be determined whether it...

The random phase shifter method for Fourier transformed holograms is discussed. It is shown that by adopting the random phase shifters of the phase quantization levels beyond 2 (4, for example), the effectiveness becomes about twice that of 2, and that the reduction of the effectiveness by the coincidence between a pattern of the information and a phase shifter can be withdrawn under the probability of 10(-10). Hologram memories of information storage density of 10(5) bits/mm(2) and 2.0 x 10(3) characters/ mm(2) are demonstrated.