Laminated proximity field optical head and optical information r

Details Laminated proximity field optical head and optical information r Laminated proximity field optical head and optical information r

1997-09-05

1999-08-31

Hindi, Nabil

Dynamic information storage or retrieval

Specific detail of information handling portion of system

Radiation beam modification of or by storage medium

369109, G11B 700

Patent

active

059462817

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to an optical disk apparatus and an optical information processing device using such an apparatus.


BACKGROUND ART

Attention has been paid so far to an optical disk apparatus as a replaceable medium of a large capacity. However, due to recent progress in the rapid realization of a large capacity magnetic disk apparatus, recording density is almost equal to 1 Gbits/inch.sup.2. It seems almost certain that in a few years, the optical disk apparatus will be overtaken by a magnetic disk apparatus in terms of the recording density because of a difference in the progressing speed of the realization of the large capacity. A size of a recording mark in the optical disk apparatus is expressed by the following expression 2. ##EQU1## where, .gamma. denotes a wavelength of a laser beam which is used for recording and reproducing, and NA is a numerical aperture which is expressed by NA=sin.theta. by using an angle .theta. between an optical axis and an optical axis of a light beam which has a maximum angle with the optical axis in a light that is converged by a lens. Therefore, the realization of a high density of the optical disk apparatus has progressed from four directions of a technique for forming a micro information recording mark and a technique for accurately reproducing an information recording mark smaller than a diameter of a light spot, by using the realization of a short wavelength of a semiconductor laser beam and the realization of a high NA of a condenser lens as centers. As for the first approach, in recent years, there are epoch-making advancements such as continuous oscillation at room temperature of a green laser by a semiconductor of the II-VI groups, production of a blue light emitting diode by a semiconductor of the III-V groups of the gallium nitrogen system, and the like. As for the third and fourth approaches as well, the progress is steadily being performed. However, even if they are integrated, it is presumed that the recording density can be improved by at most about one order of magnitude. A fundamental cause is because the light cannot be reduced than a wavelength of light due to a diffraction phenomenon of the light.
As a method of improving the recording density by two orders of magnitude as compared to the present situation by breaking such a limitation, attention is paid to an optical recording and reproducing method using a proximity field (evanescent field). For instance, as disclosed in Applied Physics Lettes, Vol. 61, No. 2, pp. 142-144, 1992, there has been reported an example in which a probe constructed in a manner such that a tip of an optical fiber is worked into a conical shape and regions other than a region of tens of nm of the tip are covered by a metal coating film is manufactured, the probe is mounted in a precision actuator which uses a piezoelectric element, a position is controlled, and a recording mark having a diameter of 60 nm is recorded and reproduced onto/from a multilayer film of platinum/cobalt. In case of the above example, the recording density reaches 45 Gbits/inch.sup.2 and can be increased to about 50 times as high as the present one. More recently, in Applied Physics Lettes, Vol. 65, No. 4, pp. 388-390, 1994, there has been reported an example in which, by effectively raising the numerical aperture NA by using a solid immersion lens (hereinafter, abbreviated to SIL) shown in FIG. 2, 40 Gbits/inch.sup.2 can be accomplished in principle.


DISCLOSURE OF INVENTION

The above conventional example, however, has the following problems.
First, in the first example using the optical probe, it can be pointed out that a signal level is low.
In the above first conventional example, a detecting power is only about 100 nW which is extremely small and it is not on the level which can be used in the optical disk apparatus. To improve it, for example, in Applied Physics Lettes, Vol 63, No. 26, pp. 3550-3552, 1993, an output of 0.3 mW can be obtained for a gold reflecting film by an input of 45 mW by using a fiber laser of Nd dop

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Applied Physics Letters, vol. 61, No. 2, 1992, "Near-field magneto-optics and high density data storage", Betzig et al, pp. 142-144.
Applied Physics Letters, vol. 65, No. 4, 1994, "Near-field optical data storage using a solid immersion lens", B.D. Terris et al, pp. 389-390.
Applied Physics Letters, vol. 63, No. 26, "Fiber laser probe for near-field scanning optical microscopy", Betzig et al, pp. 3550-3552.

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