Abstract:
An optical head for performing optical data operations relative to a medium includes a slider body and at least one lens. Positioned between the slider body and the lens is an aperture stop for blocking the transmittance of light. The aperture stop includes an opaque layer that circumscribes a transparent region.

Description:
REFERENCE TO CO-PENDING APPLICATION 
     This application claims priority benefits from U.S. provisional patent application No. 60/059,469 entitled “APERTURE STOP FOR A FLYING OPTICAL HEAD” filed on Sep. 22, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to optical heads. In particular, the present invention relates to flying optical heads. 
     Optical data storage systems access data by focusing a laser beam or other light source onto a data surface of a medium and analyzing the light reflected from or transmitted through the medium. In general, data is stored in optical storage systems in the form of marks carried on the surface of the medium which are detected using a reflected laser light. 
     Compact discs, which are widely used to store computer programs, music and video, are one type of optical data storage system. Typically, compact discs are permanently recorded during manufacture by etching the surface of the compact disc. Another type of optical system is a write once read many (WORM) system in which a user may permanently write information onto a blank disc. Other types of systems are erasable, such as phase change and magneto-optic (M-O) systems. Phase change systems detect data by sensing a change in reflectivity. M-O systems read data by measuring the rotation of the incident light polarization due to the magnetic state of the storage medium. 
     The above systems require a beam of light to be focused on to a data surface of a disc. Storage density is determined not only by the size of the markings on the data surface, but also by the size of the beam focused on the surface (i.e., resolution). In general, the optics used to focus the beam on the surface can be divided into two groups: those with flying heads and those without flying heads. In those systems that do not use a flying head, a portion of the optics system typically moves radially over the disc to follow tracks on the disc. The moving portion of the optics is supported by a physical structure that extends over the disc. In systems with flying heads, the optics within the head are actually supported by a thin layer of fluid, typically air, that rotates with the disc. By flying on this thin layer of fluid, the optics of the head are positioned extremely close to the surface. 
     In both systems an objective lens is used to focus the light into a spot on the disc. In a system with a flying head, the objective lens is used in conjunction with a solid-immersion-lens or SIL. The objective lens focuses the beam into the SIL and the SIL reduces the beam spot size by virtue of wavelength reduction which occurs when light passes through optically dense media. Because it is on a flying head, the SIL is positioned very close to the data surface so that light from the SIL couples to the disc surface via evanescent waves. 
     In both optical systems, as light passes through the objective lens a portion of the light forms fringe fields around the perimeter of the otherwise focused beam. In systems where the objective lens and SIL do not fly over the medium, such as most compact discs, the objective lens is large enough that these fringe fields can be eliminated by coating the outer perimeter of the objective lens with a material that reflects or absorbs light. Alternatively, a separate piece may be inserted above the objective lens to block this extraneous light. 
     The coating method described above cannot be used with flying optical heads because the objective lens used in flying heads is too small and its hemispherical shape makes it difficult to properly align a mask for depositing material on the lens. Similarly, a separate piece cannot be added to the flying head to block the extraneous light because such a piece would add too much weight to the head. 
     SUMMARY OF THE INVENTION 
     An optical head for performing optical data operations relative to a medium includes a slider body and at least one lens. Positioned between the slider body and the lens is an aperture stop for blocking the transmittance of light. The aperture stop includes an opaque layer that circumscribes a transparent region. 
     In preferred embodiments, the aperture stop is deposited directly on the slider body through photolithography methods. The clear slider body allows the aperture stop to be aligned with a feature formed on the opposite side of the slider body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an optical system of the present invention. 
     FIG. 2 is a schematic diagram of the optics in the optical system of FIG.  1 . 
     FIG. 3 is a side view of the optical head of FIG.  1 . 
     FIG. 4 is an enlarged side view of a portion of the head of FIG.  3 . 
     FIG. 5 is a top view of the head of FIG.  1 . 
     FIGS.  6 ( 1 ) through  6 ( 8 ) are side views of the head of FIG. 1 during different steps of manufacturing the head. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a side view of an optical storage system  98  of the present invention. An optical module  108 , which includes a laser, creates a light beam  116  that is directed through an enclosed optical path  112  extending laterally from optical module  108 . Light beam  116  reflects off a bending mirror  114  toward an optical head  100 , which focuses the beam into a small spot on a disc  118 . Disc  118  spins about a central axis  120 , continuously bringing new data regions underneath the spot of light produced by optical head  100 . The light incident on disc  118  is reflected back through enclosed optical path  112  and is analyzed by a control module attached to optical module  108 . Through this process, optical storage system  98  retrieves information stored on disc  118 . 
     Optical head  100  is supported by a suspension assembly  102  that is supported by an arm  104 . Arm  104 , optical module  108 , and enclosed optical path  112  are all supported by a spindle  106 , which rotates about a central axis  110 . As spindle  106  rotates, head  100  moves to different radial positions across disc  118  and enclosed optical path  112  rotates to remain aligned with optical head  100 . 
     FIG. 2 is a schematic diagram of the optics in optical system  98  of FIG.  1 . Within optical module  108 , a laser diode  130  generates a light that passes through a beam splitter  132  and a relay lens  134 , reflects off a galvo mirror  136 , is collimated by an imaging lens  138 , reflects off bending mirror  114 , and is focused onto optical disc  118  by optical head  100 . The light reflects off optical disc  118 , returns through head  100 , reflects off bending mirror  114 , passes through imaging lens  138 , reflects off galvo mirror  136 , passes through relay lens  134 , is reflected by beam splitter  132 , passes through a Wollaston prism  140 , and comes to focus either before or after a detector plane  142 . In preferred embodiments, galvo mirror  136  is capable of being deflected by an electric current in order to change the position of the light spot on the disc. This provides fine positioning control of the light spot making it possible to move the spot of light across several tracks on the disc without moving optical head  100 . 
     FIG. 3 is a side view of optical head  100  of FIG.  1 . Light  116  enters an objective lens  150  that is supported by a standoff  152  on a transparent slider body  154 . Light  116  is focused by objective lens  150  through a cap lens  156  that is bonded to slider body  154  by an adhesive. Together, cap lens  156 , the adhesive, and slider body  154  form a solid immersion lens. Beneath the perimeter of cap lens  156  is an opaque layer forming an aperture stop  158 . The opaque layer of aperture stop  158  surrounds a transparent region that permits light  116  to pass into and through slider body  154 . Objective lens  150 , cap lens  156 , and aperture stop  158  operate together to form a small light spot at the bottom surface of slider body  154 . Aperture stop  158  prevents extraneous light at the perimeter of objective lens  150  from passing through slider body  154 , thereby improving the resolution of the spot. 
     FIG. 4 is an enlarged view of a portion of aperture stop  158  and cap lens  156 . As shown in FIG. 4, aperture stop  158  is preferably formed from a layer of material deposited directly on slider body  154 . In addition, cap lens  156  is bonded to slider body  154  and aperture stop  150  by an adhesive layer  160 . It should be noted that the thickness of adhesive layer  160  affects the absorption and reflectance of light that is incident on aperture stop  158 . It is preferred that the absorption of light be maximized and that the reflectance of light be minimized for light that is incident on aperture stop  158 . In preferred embodiments, where aperture stop  158  was formed from chromium, reflectance was minimized for an adhesive layer of  450  nanometers measured from the top of aperture stop  158  to the bottom of cap lens  156 . 
     FIG. 5 is a top view of optical head  100  showing objective lens  150 , aperture stop  158  and slider body  154 . FIG. 5 also shows a topography feature  162  that extends from the bottom of and is formed as a single piece of material with slider body  154 . Topography feature  162  is centered within aperture stop  158  and objective lens  150 , and is preferably used as a reference point for positioning the masks to produce aperture stop  158  on slider body  154 . The outer perimeter of aperture stop  158  may then be used to position standoff  152  relative to the center of aperture stop  158 . In that position, standoff  152  provides an excellent starting location for positioning objective lens  150 . The exact placement of objective lens  150  is achieved by passing a light beam through optical head  100  and moving the objective lens until the spot at the bottom of the slider is optimized. Aperture stop  158  quickens this process by significantly degrading the spot when the objective lens is off-center relative to the center of aperture stop  158 . 
     FIGS.  6 ( 1 ) through  6 ( 8 ) show different stages of optical head  100  during the process of manufacturing the head. In the first stage shown in FIG.  6 ( 1 ), slider body  154  is coated with an opaque layer of material  170 , which is preferably an optically reflective material such as chromium. Preferably, the layer of chromium is 1000 angstroms thick. In FIG.  6 ( 2 ), the second step of the method involves coating opaque layer  170  with a photoresist  172 . In FIG.  6 ( 3 ), photoresist  172  has been patterned using a shadow mask and has been developed to remove unwanted photoresist material leaving patterned ring  174  on opaque layer  170 . The portions of opaque layer  170  that are not protected by protective ring  174  are removed leaving aperture stop  158  covered by protective ring  174  as shown in FIG.  6 ( 4 ). In FIG.  6 ( 5 ) protective ring  174  has been removed leaving aperture stop  158  exposed. 
     FIG.  6 ( 6 ), adhesive  160  is applied to aperture stop  158  and the portion of slider body  154  located within the center of aperture stop  158 . Cap lens  156  is applied on top of adhesive  160  and is thus bonded to slider body  154  and aperture stop  158 . In FIG.  6 ( 7 ), standoff  152 , which is in the form of a ring, is aligned with the outer perimeter of aperture stop  158  and is bonded to slider body  154 . In the final step of the process, shown in FIG.  6 ( 8 ), object lens  150  is mounted on standoff  152 , and centered on the center of aperture stop  158  to optimize the light spot formed at the bottom of slider body  154 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.