Abstract:
High density near field optical recording/reproducing device, including a light source for emitting a bean of light, a converging lens for converging the light emitted from the light source, and a near filed light generating part formed of a material of which light transmittance is varied with light temperature sectors, thereby overcoming a limit of resolution coming from diffraction, whereby increasing a recording density, significantly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high density near field optical recording/reproducing device which can increase a recording density significantly by overcoming a limit of light diffraction. 
     2. Background of the Related Art 
     In general, the optical data storage technology has been developed significantly centered on CD and DVD technologies, particularly the realization of a semiconductor blue laser, which permits 3 to 4 times of a recording density increase, makes a large capacity optical recording technology available. However, to meet current demands both for information on image of a higher resolution and a small sized, light weight, but large capacity information storage, which is essential for personal information terminal, a leap of increase of information recording density is required. As a technical response to the demands, even though improvements in the recording density of magnetic information recording device, such as hard disk used as supplementary recording device for a computer, the magnetic information recording device has difficulty in increasing the recording density compared to an optical recording medium which uses a concentrated laser beam in nature. 
     Theoretically, the optical recording technology has a limit of recording density dependent on a wavelength of a laser beam used for recording/reproduction of a data. In the optical recording technology, a minimum length of one bit of data mark can be expressed as the following equation.        d   =     λ     (     2      NA     )                              
     Where, λ denotes a wavelength of the laser beam, which is approx. 650 nm in a case of a semiconductor red laser beam, and approx. 410 nm in a case of a semiconductor blue laser beam. ‘NA’ denotes a numerical aperture, which is approx. 0.5˜0.7 for a general optical system lens. Therefore, a minimum pitch of data tracks which can be distinguished is in a range of a wavelength, which is a limit of size reduction permitted by an increased recording density, that is caused by diffraction of the laser beam. A technology spot lighted to overcome the limit is the near field optical recording technology. In the near field optical recording technology, a light transmissive probe is put near to a beam of light within a wavelength, and input/output of the light through the probe is made possible, for overcoming a spatial resolution limit from the wavelength. As a method for realizing the near field optical recording technology, there is the SIL(Solid Immersion Lens) method of the Terastor in the USA that comes closest to practical use up to now, in which an NA value is increased by using an SIL, which reduces a focus point size of a laser beam used for recording/reproduction, that improves the spatial resolution limit caused by diffraction of light. This method is favorable in view of putting into practical use in that a related art optical recording/reproducing method using a lens system can be utilized. However, even if the SIL is employed, the limitation of the NA value is still a limit in improving the recording density. Other than this method, even though there is the NSOM(Near-Field Scanning Optical Microscopy) in which an optical fiber probe tip is put near to a beam within a wavelength of a recording/reproducing light, the NSOM has not been used for an information recording device because of technical difficulties, such as difficulty in continuously maintaining a distance between the optical fiber probe tip and a disc within a range of the near field, a low data recording/reproducing rate, and the like. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a near field optical recording/reproducing device that substantially obviates one or more and disadvantages of the related art. 
     An object of the present invention is to provide a near field optical recording/reproducing device which can improve a recording density by using a near field optical recording technology. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the near field optical recording/reproducing device includes a light source for emitting a bean of light, a converging lens for converging the light emitted from the light source, and a near filed light generating part formed of a material of which light transmittance is varied with light temperature sectors. 
     The near field optical recording/reproducing device further includes a mirror for reflecting the light emitted from the light source toward the converging lens, a package housing for protecting the converging lens and the near field light generating part, and a supporter for supporting the mirror and the package housing. 
     The near field optical recording/reproducing device further includes a piece of optical fiber, or lens between the light source and the mirror for providing the light from the light source to the mirror. 
     The near field light generating part is formed of any one selected from VO 2 , Sb, and AgOx. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention: 
     In the drawings: 
     FIG. 1 illustrates a near field optical recording/reproducing device having a thermal aperture in accordance with a preferred embodiment of the present invention, schematically; 
     FIG. 2 illustrates a section of an optical pick up head in FIG. 1; 
     FIG. 3 illustrates a principle of generating the thermal aperture in the near field light generator in FIG. 2; and, 
     FIG. 4 illustrates a principle of near field light generation and information recording/reproduction by means of the thermal aperture. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The present invention suggests a high density information storage which is realized by combining a near field generated by using a thermal aperture formed of a material having a transmittance varied with temperature sectors, realization of a data mark of a size below a wavelength of an input laser beam by using the near field, and positional adjustment of data track pitches by means of a cantilever connected to a fine adjustment actuator. FIG. 1 illustrates a near field optical recording/reproducing device having a thermal aperture in accordance with a preferred embodiment of the present invention, and FIG. 2 illustrates a section of an optical pick up head in FIG.  1 . 
     Referring to FIGS. 1 and 2, the near field optical recording/reproducing device includes a cantilever  1  connected to an actuator for fine adjustment of position, a laser diode integrated on the cantilever  1 , a mirror mount  11  connected to the cantilever  1 , a 45° mirror  15  on the mirror mount  11 , a converging lens  12 , and a package housing  16  for protecting a near field light generating part  13  of a thin film for generating a thermal aperture. And, there is a piece of optical fiber  14  or lens(not shown) positioned between the laser diode and the 45° mirror  15 . The laser beam from the laser diode is incident to the 45° mirror  15  through the optical fiber  14  or the lens, reflected at the 45° mirror  15 , converged by the converging lens  12 , and transmits the near field light generating part  13 . Then, the laser beam, transmitted through the near field light generating part  13 , is incident to the optical disk  2  of a phase change material, and makes information recording/reproduction thereon/therefrom. The near field light generating part  13  is formed of a material having a transmittance varied with temperature sectors of the laser beam, such as VO 2 , or Sb thin film, and AgOx. The VO 2  thin film is involved in metal-insulator transition at a temperature ranging 60 ˜70° C. at a temperature below which the VO 2  thin film transmits no light, and above which the VO 2  thin film transmits lights.(Hiroyuki Abe et al, Jpn. J. Appl. Phys. vol. 36, pp. 165-169, 1997). And, the Sb thin film has a light transmittance enhanced at approx. 200° C.(J. Tominaga et al, Applied Physics Letters, vol. 73, no. 15, p2078). 
     A principle for forming a thermal aperture  17  in the near field light generating part  13  by using an optical property of such a material will be explained with reference to FIG.  3 . 
     Referring to FIG. 3, upon directing a laser beam onto the near field light generating part  13 , an optical intensity distribution of the laser beam causes a temperature distribution of a surface onto which the laser beam directed. In this instance, only a portion of the near field light generating part  13  centered on a light axis(as much as a diameter ‘d’ in FIG. 3) having a threshold temperature Tc at which the transmittance alters is altered transparent because, as explained, transmission of the laser beam through the near field light generating part  13  is dependent on a temperature of the thin film of the near field light generating part  13 . The laser beam transmitted through the transparent portion of the neat field light generating part  13  has a size which can be reduced below the limitation of ‘D’ of a beam spot size the related art optical system can realizes. As shown in FIG. 4, the laser beam reduced by the thermal aperture  17  of the near field light generating part  13  becomes a near field light  18 , and is directed onto a phase change thin film  22  on the surface of the disk substrate  21 , to write or read one bit of information  23 . In this instance, the near field light  18  can be generated only when a gap ‘g’ between the near field light generating part  13  and the surface of the disk  2  should be maintained to be below a wavelength of the incident light. Accordingly, in order to maintain the gap ‘g’ to be below a wavelength of the incident laser beam, the aerodynamic levitation is used. 
     A method for recording/reproducing information of the aforementioned near field light recording/reproducing device of the present invention will be explained. 
     First, referring to FIG. 1, in order to write information on a desired position of the disk  2 , a fine movement of the optical pick-up head shown in FIG. 2 is made by using the cantilever  1  connected to the actuator. Then, once the optical pick-up is fixed to the desired position, a laser beam is generated at the laser diode, incident to the 45° mirror  15  through the optical fiber  14  or the lens, reflected at the mirror  15 , and converged by the converging lens  12  onto the near field light generating part  13 . As shown in FIG. 3, of portions of the laser beam incident to the near field light generating part  13 , only the portion of the laser beam incident to a portion of the near field light generating part  13  having a temperature higher than the threshold temperature Tc transmits the thermal aperture, and generates a near filed light  18 . The near field light  18  is incident to a phase change thin film formed on the surface of the disk substrate  21 , to write one bit of information in a high density. Then, by making a fine adjustment of the actuator, to move the pick-up to a desired position, information can be written, continuously. The minimum resolution in the present invention which is dependent on a controllable minimum distance of the fine adjustment actuator is controllable to be below 0.1 μm. Since a method for reproducing information is the same with the method for recording information, the method for reproducing information will be omitted. 
     As has been explained, the near field optical recording/reproducing device of the present invention can overcome a limitation of resolution coming from an optical diffraction to increase a recording density significantly, by combining a near field generated by using a thermal aperture formed of a material having a transmittance varied with temperature sectors, realization of a data mark of a size below a wavelength of an input laser beam by using the near field, and positional adjustment of data track pitches by means of a cantilever connected to a fine adjustment actuator. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the near field optical recording/reproducing device of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.