Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-03-20
2002-08-06
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
Reexamination Certificate
active
06429419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a near-field optical head and, more particularly to a near-field optical head capable of promoting high resolution and enhancing a mechanical strength by devising a structure of a head, facilitating fabrication thereof and realizing high scattering efficiency of an evanescent field.
2. Background Information
At present, there has widely used an information reproducing device of a reproduction exclusive type represented by a CD as well as a CD-ROM. According to the information reproducing device, information recorded on an optical disk is reproduced by using light. For example, in the case of a CD, a surface thereof is recorded with pits each having a size of substantially a wavelength of laser beam used in reproduction and a depth of substantially a quarter of the wavelength as recess and projection information and the interference phenomenon of light is utilized for reproducing the information. When a spot of laser beam is illuminated onto the pit, since the depth of the pit is a quarter of the wavelength, a difference of optical paths of reflected light reflected by a bottom face of the pit and reflected light reflected by the surface becomes a half of the wavelength of the illuminated laser beam. Therefore, the provided reflected light becomes weaker than that in the case of irradiating the spot of laser beam onto a surface at other than the pit. In this way, by detecting the intensity of the reflected light, presence or absence of the pit is determined to thereby achieve reproduction of information recorded on the optical disk.
In a system of irradiating the above-described laser beam and a system of detecting thereof, a lens optical system used in a conventional optical microscope is used, however, the spot size of the laser beam cannot be made equal to or smaller than a half of the wavelength owing to a diffraction limit of light. Meanwhile, in order to increase an information recording density of the optical disk, the size of the pit must be reduced and a track pitch must be narrowed. Accordingly, when an information recording unit is constituted by a size smaller than the wavelength of the laser beam, a conventional information reproducing apparatus cannot be used.
In view of such a problem, in recent years, there has been proposed an optical memory utilizing technologies of a near-field optical microscope. A near-field optical microscope uses a probe having a very small aperture of, for example, a diameter equal to or smaller than the wavelength of illuminated laser beam, for example, about one tenth of the wavelength and observes a very small surface structure and an optical characteristic distribution of a sample by utilizing near-field light (a nonpropagated component in light which exist in a region of optical wavelength or less from a surface of a substance: evanescent field). According to such a near-field optical microscope, by irradiating propagated light from a rear face of the sample, the near-field light is generated at the surface of the sample, the very small aperture of the probe and the surface of the sample are made to proximate to each other to a degree of the diameter of the very small aperture of the probe and the near-field light is scattered at the very small aperture by which the near-field light is taken out from the very small aperture as propagated light. The near-field light generated at the surface of the sample is accompanied by an intensity and a phase reflecting the very small structure and the optical characteristic distribution of the surface of the sample and by processing the taken-out propagated light by an optical detector, observation having a resolution which cannot be realized by a conventional optical microscope is made feasible.
Further, a system of using an AFM cantilever provided with a sharpening treatment at its front end has frequently been used. There have been described technologies of forming a light transmitting tip at a front end of an AFM cantilever in a literature “Hulst et al., Appl. Phys. Lett. (1993) Vol. 62, p461”, a literature “Hulst et al., SPIE (1992) Vol. 1639, p36”, Japanese Patent Laid-Open No. 160719/1994 and PCT International Application Publication WO95/03561. Further, there have been described technologies of forming an AFM cantilever by a tip which does not transmit light in a literature “Zenhausern et al., Appl. Phys. Lett. (1994) Vol. 65, p1623”, a literature “Bachelot et al., Ultramicroscopy (1995) Vol. 61, p111” and Proceedings of Near-field Optics Research Group (“A reflective type near-field optical microscope using a metal probe and observation of a semiconductor sample having a fine structure”, Proceedings of the 4th Symposium of Near-field Optics Research Group 1995, p53).
By applying the above-described near-field optical technologies to an optical memory, information can be detected from an optical disk constituted by an information recording unit of a wavelength of laser beam or smaller.
However, according to the above-described method of forming a very small aperture, formation of the very small aperture is difficult and a size capable of forming the aperture is provided with a limit and, accordingly, there poses a problem in which a resolution is difficult to be improved to several tens nm or smaller. Meanwhile, according to the above-described method of using an AFM cantilever, the front end is subjected to the sharpening treatment and therefore, the mechanical strength is weak and there poses a problem in which the reliability is low in using the AFM cantilever as a head. For example, the tip becomes liable to be damaged by the dust on a medium face or vibration of a medium. Further, many steps of a sharpening process are needed in forming the tip and assuming the case of forming the tip at a flying head, there poses a problem in which heights of the flying head and the front end of the tip are difficult to be matched. Further, a surface area of the tip is small and accordingly, there poses a problem in which the scattering efficiency of an evanescent field is lowered.
Hence, the invention has been carried out in view of the above-described drawbacks in the conventional art, and it is an object thereof to provide a near-field optical head capable of improving a resolution and enhancing a mechanical strength, facilitating fabrication thereof and having a high scattering efficiency of an evanescent field.
SUMMARY OF THE INVENTION
According to an aspect of the invention, there is provided a near-field optical head wherein in a near-field optical head for reproducing information recorded on a medium based on an intensity of scattered light of an evanescent field generated when a front end portion of a head is made proximate to the medium at an interval of a distance equal to or smaller than a wavelength of light therebetween and light is illuminated to the medium, the front end portion of the head is formed in a shape of an edge in which two planes intersect with each other.
According to another aspect of the invention, there is provided a near-field optical head wherein in a near-field optical head for reproducing information recorded on a medium based on an intensity of scattered light of an evanescent field generated when a front end portion of a head is made proximate to the medium at an interval of a distance equal to or smaller than a wavelength of light therebetween and light is illuminated to the medium, the front end portion of the head is formed in a shape of an edge in which two planes intersect with each other and a side thereof is microscopically provided with a radius of curvature.
According to another aspect of the invention, there is provided a near-field optical head wherein in a near-field optical head for reproducing information recorded on a medium based on an intensity of scattered light of an evanescent field generated when a front end portion of a head is made proximate to the medium at an interval of a distance equal to or smaller than a wavelength of light therebetween and light
Chiba Norio
Kasama Nobuyuki
Mitsuoka Yasuyuki
Nakajima Kunio
Niwa Takashi
Adams & Wilks
Kim Robert H.
Seiko Instruments Inc.
Thomas Courtney
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