Abstract:
An optical head has a near-field light generating element generating near-field light; and a beam shaper which shapes an incident beam into a substantially toroidal beam and directs the shaped beam to said near-field light generating element. According to the optical head having the above-described structure, the incident light is shaped into a substantially toroidal beam without being intercepted, incident on the zonal part of the near-field light generating element, and condensed to a minute spot. That is, only the light of the high numerical aperture part is used with efficiency, and the light can be condensed to a minute spot.

Description:
RELATED APPLICATION 
     This application is based on application No. 2000-39522 filed in Japan, the content of which is hereby incorporated by reference. 
     1. Field of the Invention 
     The present invention relates to an optical head, particularly, an optical head for performing recording, reproduction and erasure by use of near-field light, and an optical recording and reproducing apparatus having the optical head. 
     2. Description of the Prior Art 
     In recent years, to realize high density recording by using light, a solid immersion technology has been proposed. This technology is to form a minute light spot of not more than 100 nm by reducing the wavelength of light by disposing a high refractive index material between an objective lens and a record medium. As the high refractive index material, although liquid (oil or water) is frequently used in the field of high resolution microscopes, in the field of optical recording, a solid immersion lens or a solid immersion mirror is used to form an optical head. 
     In such an optical head, a solid immersion lens or a solid immersion mirror is disposed at a distance shorter than the wavelength of light from the surface of the record medium so that the numerical aperture (NA) of light condensation is large, that is, the spot of light condensation is small, thereby realizing high density recording. 
     In this type of optical head, when some configurations of solid immersion mirrors are used, it is desirable to use only the zonal part of the incident beam without using the central part thereof. Moreover, there are cases where it is desirable to use only light of the high numerical aperture part in order that the spot of light condensation is small on the solid immersion lens or the solid immersion mirror. To obtain such incident light, it is considered to intercept the central part of the beam. However, this reduces the efficiency of use of light, which leads to reduction in the efficiency of recording and the like and reduction in speed. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved optical head and optical recording and reproducing apparatus. 
     Another object of the present invention is to provide an optical head and an optical recording and reproducing apparatus in which the efficiency of use of light is increased to solve the problems of reduction in the efficiency of recording and the like and reduction in speed. 
     The above-mentioned objects are achieved by an optical head comprises a near-field light generating element which generates near-field light; and a beam splitter which splits an incident light into a plurality of beams and directs the split beams to said near-field light generating element. 
     According to the optical head having the above-described structure, the light emitted from the light source portion is split into a plurality of beams, incident on the zonal part of the near-field light generating element, and condensed inside the element. Consequently, the light emitted from the light source portion is effectively used without being intercepted, and the light can be condensed to a minute spot, that is, the numerical aperture can be increased. 
     Moreover, an optical head of another structure comprises a near-field light generating element which generates near-field light; and a beam shaper which shapes an incident beam into a substantially toroidal beam and directs the shaped beam to said near-field light generating element. 
     According to the optical head having the above-described structure, the light emitted from the light source portion is shaped into a substantially toroidal beam without being intercepted, incident on the zonal part of the near-field light generating element, and condensed to a minute spot. That is, only the light of the high numerical aperture part is used with efficiency, and the light can be condensed to a minute spot. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of this invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which: 
     FIG. 1 schematically shows the structure of an optical recording and reproducing apparatus according to an embodiment of the present invention; 
     FIG. 2 is an explanatory view showing operation of a solid immersion mirror; 
     FIG. 3 is an explanatory view showing operation of a solid immersion lens; 
     FIG. 4 is an explanatory view showing a first example of beam shaper; 
     FIG. 5 is an explanatory view showing a second example of the beam shaper; 
     FIG. 6 is an explanatory view showing a third example of the beam shaper; 
     FIG. 7 is an explanatory view showing a fourth example of the beam shaper; 
     FIG. 8 is an explanatory view showing a fifth example of the beam shaper; 
     FIG. 9 is an explanatory view showing a sixth example of the beam shaper; 
     FIG. 10 is an explanatory view showing a seventh example of the beam shaper; 
     FIG. 11 is an explanatory view showing an eighth example of the beam shaped; 
     FIG. 12 is an explanatory view showing an example of beam splitter; and 
     FIG. 13 is an explanatory view showing the condition of light application to the solid immersion mirror by the beam splitter. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the optical head and the optical recording and reproducing apparatus according to the present invention will be described with reference to the attached drawings. 
     Optical Recording and Reproducing Apparatus, Referring FIG. 1 
     FIG. 1 shows an optical recording and reproducing apparatus  1  according to an embodiment of the present invention. The apparatus  1  mainly includes a light source portion  2 , a plane mirror  5  and an optical head  10 . The light source portion  2  is a known one comprising a laser diode  3  as a light source and a collimator lens  4 . The optical head  10  comprises a beam shaper  11  and a solid immersion mirror  12 . 
     The laser beam L emitted from the laser diode  3  is collimated by the collimator lens  4  and reflected at the mirror  5  to be directed to the optical head  10 . Then, the laser beam L is shaped into a toroidal beam L 1  by the beam shaper  11 , incident on the solid immersion mirror  12 , condensed on the bottom surface of the mirror  12  and oozes out as near-field light. The near-field light is applied to an optical record medium  18 . 
     The optical record medium  18  is a known one having a recording layer and a protective layer formed on the surface thereof. The optical record medium  18  is clamped to the rotation shaft of a spindle motor  19  and rotated about a shaft center C at a predetermined speed. The optical head  10  moves along the radius of the optical record medium  18  at a constant speed to perform recording, reproduction or erasure on the entire surface of the recording layer. 
     The structure and operation of the beam shaper  11  and the solid immersion mirror  12  will be described below. The beam shaper  11  and the solid immersion mirror  12  may be replaced by beam splitter  13  and a solid immersion lens  14  described below. 
     Solid Immersion Mirror, Referring to FIG. 2 
     FIG. 2 shows the solid immersion mirror  12  for generating near-field light. The solid immersion mirror  12  is made of a high refractive index material, and comprises a first surface (top surface) being plane and a second surface (bottom surface) being spherical or a spherical. A reflecting film  12   a  is formed in the center of the incident surface, and a reflecting film  12   b  is formed in the peripheral zonal part of the bottom surface. 
     On the top surface of the solid immersion mirror  12 , the toroidal beam L 1  shaped by the beam shaper  11  is incident. The beam L 1  is reflected at the reflecting film  12   b  to be converged, further reflected at the reflecting film  12   a  to be condensed to a minute spot at the center of the bottom surface, and oozes out as near-field light. 
     Solid Immersion Lens, Referring to FIG. 3 
     FIG. 3 shows the solid immersion lens  14  for generating near-field light like the solid immersion mirror  12 . The solid immersion lens  14  is also made of a high refractive index material, and comprises a first surface (incident surface) being hemispherical (the first surface may be hyperhemisperical) and a second surface (bottom surface, exit surface) being plane. Immediately above the solid immersion lens  14 , a condenser lens  15  is disposed. 
     Various modes are present in which a laser beam is made incident on such immersion lens  14 . In this example, when the toroidal beam L 1  shaped by the beam shaper  11  is made incident through the condenser lens  15 , the beam L 1  is refracted to be converged, condensed to a minute spot at the center of the bottom surface, and oozes out as near-field light. The reason why the beam L 1  being toroidal is made incident is that a minute light condensation spot can be formed by using light of the high numerical aperture part. 
     First Example of Beam Shaper, Referring to FIG. 4 
     This beam shaper  11  comprises a first axicon lens  21  and a second axicon lens  22  coaxially disposed so that convex conical surfaces  21   a  and  22   a  thereof are opposed to each other. The parallel laser beam L being incident on the first axicon lens  21  so that the axis thereof coincides with the optical axis of the lens  21  is refracted at the conical surface  21   a , intersects at the axis center and is ten shaped into a radially spreading beam being toroidal in cross section. Then, the beam L is incident on the second axicon lens  22  to be refracted at the conical surface  22   a , shaped into the parallel tubular beam L 1  being toroidal in cross section, and incident on the zonal part of the top surface of the solid immersion minor  12 . 
     Second Example of Beam Shaper, Referring to FIG. 5 
     This beam shaper  11  uses reflection, and comprises a mirror  41  having a conical reflecting surface  41   a  and a ring-shaped mirror  42  having a conical reflecting surface  42   a  on the inner surface thereof. The parallel laser beam L being incident on the mirror  41  through the central opening of the ring-shaped mirror  42  is reflected at the reflecting surfaces  41   a  and  42   a , shaped into the parallel tubular beam L 1  being toroidal in cross section, and incident on the zonal part of the top surface of the immersion mirror  12 . 
     Third Example of Beam Shaper, Referring to FIG. 6 
     This beam shaper  11  uses a single lens  25  to shape the laser beam L into the toroidal beam L 1 . The lens  25  is formed as a double cone prism having convex conical surfaces  25   a  and  25   b  at the top and bottom. The parallel laser beam L is refracted at each of the conical surfaces  25   a  and  25   b , shaped into the parallel tubular beam L 1  being toroidal in cross section, and incident on the zonal part of the top surface of the solid immersion mirror  12 . 
     Fourth Example of Beam Shaper, Referring to FIG. 7 
     This beam shaper  11  uses a single lens  26  to shape the laser beam L into the toroidal beam L 1  like the third example. The lens  26  is formed as a double cone prism having a concave conical surface  26   a  at the top and a convex conical surface  26   b  at the bottom. The parallel laser beam L is refracted at each of the conical surfaces  26   a  and  26   b , shaped into the parallel tubular beam L 1  beingtoroidal in cross section, and incident on the zonal part of the top surface of the solid immersion mirror  12 . 
     Fifth Example of Beam Shaper, Referring to FIG. 8 
     This beam shaper  11  also uses reflection, and comprises a single mizror  43  having conical reflecting surfaces  43   a  and  43   b . The parallel laser beam L being incident on the central part of the mirror  43  is reflected at the reflecting surfaces  43   a  and  43   b , shaped into the parallel tubular beam L 1  being toroidal in cross section, and incident on the zonal part of the top surface of the solid immersion mirror  12 . 
     In the fifth example, instead of the Fresnel lenses  31  and  32 , transmission-type diffraction optical elements using a hologram or the like and having similar functions to the Fresnel lenses  31  and  32  may be used. In the beam shaper  11  of the first to the fourth examples, the axicon lenses may be replaced by diffraction optical elements such as Fresnel lenses. 
     Sixth Example of Beam Shaper, Referring to FIG. 9 
     This beam shaper  11  uses reflection, and comprises a mirror  41  having a conical reflecting surface  41   a  and a ring-shaped mirror  42  having a conical reflecting surface  42   a  on the inner surface thereof. The parallel laser beam L being incident on the mirror  41  through the central opening of the ring-shaped mirror  42  is reflected at the reflecting surfaces  41   a  and  42   a , shaped into the parallel tubular beam L 1  beingtoroidal in cross section, and incident on the zonal part of the top surface of the solid immersion mirror  12 . 
     By forming the beam shaper  11  by use of reflection-type elements as described above, generation of chromatic aberration can be prevented. 
     Seventh Example of Beam Shaper, Referring to FIG. 10 
     This beam shaper  11  also uses reflection, and comprises a single mirror  43  having conical reflecting surfaces  43   a  and  43   b . The parallel laser beam L being incident on the central part of the mirror  43  is reflected at the reflecting surfaces  43   a  and  43   b , shaped into the parallel tubular beam L 1  beingtoroidal in cross section, and incident on the zonal part of the top surface of the solid immersion mirror  12 . 
     In the sixth and the seventh examples of the beam shaper  11 , the reflecting surfaces of the mirrors  41 ,  42  and  43  do not necessarily have the illustrated configurations but may be, for example, reflecting surfaces having a configuration of an aggregation of concentric cones like Fresnel lenses. Further, reflection-type diffraction optical elements using a hologram may be used. 
     Eighth Example of Beam Shaper, Referring to FIG. 11 
     This beam shaper  11  is formed integrally with the solid immersion mirror generating near-field light. Specifically, the mirror  43  shown in the seventh example and the solid immersion mirror  12  are cemented together. The conical space formed in the center is left hollow or filled with a different medium. The beam shaper  11  and the solid immersion lens may be integrated to form an optical head. 
     Beam Splitter, Referring to FIGS. 12 and 13 
     Next an example of the beam splitter  13  used instead of the beam shaper  11  will be described The beam splitter  13  comprises, as shown in FIG. 12, one plane parallel mirror  51  having a partially reflecting surface  51   a  and a totally reflecting surface  51   b.    
     Part of the parallel laser beam L emitted from the light source portion  2  is reflected at the partially reflecting surface  51   a  to be incident in a spot shape on a zonal part  12   c  of the solid immersion mirror  12  as a beam L 2 . Part of the laser beam L transmitted by the partially reflecting surface  51   a  is reflected at the totally reflecting surface  51   b  to be incident in a spot shape on the zonal part  12   c  of the solid immersion mirror  12  as a beam L 3 . 
     By using one plane parallel mirror  51  as described above, the laser beam L can be split into the two beams U and L 3  so as to be incident on the zonal part  12   c  of the solid immersion mirror  12 . Further, by adding another plane parallel mirror, as shown in FIG. 13, beams L 4  and L 5  can be made incident on the zonal part  12   c . The number of combinations of plane parallel mirrors may be three or more. 
     As the beam splitter  13 , various splitter may be used as well as a plane parallel minor. Moreover the beam splitter  13  and the solid immersion lens  14  may be combined to form an optical head. 
     Other Embodiments 
     The optical head and the optical recording and reproducing apparatus according to the present invention are not limited to the above-described embodiment, but various changes and modifications may be made without departing from the spirit and scope of the invention. 
     While the beam shaper is combined with a solid immersion mirror in the first to the eighth examples of the beam shaper, it may be combined with a solid immersion lens. Moreover, the optical recording and reproducing apparatus may be used as a master plate exposing apparatus manufacturing master plates of optical record media. 
     Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modification depart from the scope of the present invention, they should be construed as being included therein.