Patent Publication Number: US-2006002275-A1

Title: Optical head

Description:
FIELD OF THE INVENTION  
      The present invention relates to an optical head and particularly to an optical head that has dual optical paths.  
     BACKGROUND OF THE INVENTION  
      Using an optical head to access data on an optical recording medium is a technique known in the art. While the storage capacity and density of the optical recording medium has increased gradually, the structure of the optical head has also improved. One of the advanced features is that the wavelength of laser light to access the optical recording medium becomes shorter, and the numerical aperture (NA) of the objective lens gradually increases (i.e. the converging focal point of the laser light to access the optical recording medium becomes smaller, its size is in direct proportion with the wavelength of the laser light, but is in inverse proportion with the NA of the objective lens) to respond to the increasing storage capacity and density of the optical recording medium.  
      The new type of optical head has to be inversely compatible. Namely, it must be able to access new types of optical recording media and also has to access the older types of optical recording media. Hence the new type of optical head has to equip with a read/write mechanism for laser light of different wavelengths. As a result, optical recording media capable of storing data of two different densities have been developed. For instance, now many optical heads can read/write a Compact Disk (CD) and a Digital Versatile Disk (DVD).  
      One example is U.S. Pat. No. 5,446,565, which discloses a dual focal points converging objective lens that can form different NA of the objective lens. When a laser light generation unit generates laser light, which travels to a holographic optical element (HOE), the laser light forms diffraction because of the HOE, and the converging objective lens focuses the light on an optical recording medium. Using the characteristics of the HOE that can form two diffraction angles, and is coupled with the converging objective lens, the laser light may be converged to different foal points (the data surface of the optical recording medium that has different data storage densities) to access the optical recording medium that has two different data storage densities. However, the HOE is more expensive in fabrication.  
      Based on cost consideration, employing two light sources and two objective lenses is a more economic choice. Korea patent No. 00255233 discloses a technique that uses laser light of two different wavelengths to couple with different lenses to provide different focal points and read optical spots of different diameters. The optical head allows laser lights of different wavelengths generated by two laser light generation units to travel their own optical paths to reach the converging objective lens. And according to different NA of the objective lens corresponding to the laser light of different wavelengths, different sizes of focal points are formed. After reflected by the optical recording medium, each travels back to its own photo detector, thereby can access the optical recording medium that has two different data storage densities. But the dual optical paths system significantly increases the size of the whole device. This is against the prevailing requirements of 3C products.  
     SUMMARY OF THE INVENTION  
      In view of the aforesaid disadvantages occurring to conventional techniques, the primary object of the present is to provide an optical head that has dual optical paths to access data on an optical recording medium, having two different data storage densities and reducing the size of the optical head.  
      The optical head that has dual optical paths according to the invention aims to read/write an optical recording medium that has different data storage densities. It consists of two sets of optical path systems. Each optical path system includes a laser light generation unit, a light guiding unit, a converging objective lens and a photo detector. The two laser light generation units generate laser lights of different wavelengths. The light guiding unit is located on the optical path of the laser light generation unit to direct the laser light generated by the laser light generation unit to travel, and pass through the converging objective lens, and focus on the data side of the optical recording medium. The focused laser light is reflected on the optical recording medium and carries optical data signals recorded on the data side, and returns to the light guiding unit along the optical path, to be received by the photo detector for transforming to corresponding electric signals. The optical paths of the two optical path systems are crossed to shrink the total size of the optical head.  
      The present invention further includes an optical head, which has an actuator for holding the two optical path systems. It includes an objective lens holding seat, a focus coil, a track coil, a magnetic path device and a plurality of metal wires. The converging objective lenses of the two optical path systems are located on the topside of the objective lens holding seat. The focus coil is located on the objective lens holding seat and has the inductive magnetic direction coincided with the focusing direction of the converging objective lens. The track coil is located on the objective lens holding seat and has the inductive magnetic direction normal to the focusing direction to serve as the track direction. The magnetic path device generates a magnetic field in a direction parallel with the inductive magnetic field of the track coil and normal to inductive magnetic field direction of the focus coil. The metal wires aim to brace the objective lens holding seat and enable the objective lens holding seat to be movable in the focusing direction and the track direction.  
      The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic view of an embodiment of the present invention.  
       FIG. 2  is a schematic view of an embodiment of the actuator of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The optical head of multiple wavelengths according to the present invention aims to access data on an optical recording medium that has different data storage densities. Refer to  FIG. 1  for an embodiment of the invention. It includes a first optical path system  110  and a second optical path system  120  that are crossed to reduce the size of the optical head.  
      The first optical path system  110  and the second optical path system  120  include respectively a laser light generation unit, a light guiding unit, a converging objective lens (not shown in the drawing) and a photo detector  130 . The laser light generation unit includes a laser diode  111  and a diffraction grating  112 . The laser diode  11  emits a linear polarized laser light. The diffraction grating  112  changes the emitted laser light into a laser light for reading and tracking.  
      The light guiding unit is located on the optical path of the laser light generation unit, for direct traveling of the laser light generated by the laser light generation unit and passing through the converging objective lens and focusing on the data side of the optical recording medium. The focused laser light is reflected and returns to the light guiding unit along the optical path to be received by the photo detector  130  for transforming the optical data signals to corresponding electric signals. As shown in  FIG. 1 , the light guiding unit includes a beam-splitter  121 , a collimator  122  and a folding mirror  123 . The beam-splitter  121  first reflects the laser light generated by the laser light generation unit. The laser light passes through the collimator  122  to become parallel light, then reaches the folding mirror  123  to be directed to the converging objective lens  124 . The laser light is converged by the converging objective lens  124  and focuses on the data side of the optical recording medium. The focused laser light is reflected on the optical recording medium, and passes along the optical path to the folding mirror  123 , the collimator  122  and the beam-splitter  121 , and finally is received by the photo detector  130 . In this embodiment, a concave lens  131  is provided and located on the optical path before the laser light reaches the photo detector  130  to amend the optical signal quality reflected by the optical disk. By means of such a construction, the first optical path system  110  and the second optical path system  120  can read the optical recording medium that has two different data densities. The two optical paths cross at about 30 to 150 degrees to enable the whole space to be fully utilized.  
      For a data writing process on the optical recording medium, the optical path of the incident laser light and the reflection laser light is the same as the one of data reading previously discussed. The difference is that, in the writing process, a function generator is used to regulate the driving circuit of the laser light generation unit, so that the energy of laser light may be altered as desired. Through a photothermal effect, a physical change occurs to the material of the optical recording medium. According to the energy of the laser light, pits that represent the data of “0” or “1” are formed on the data storage surface of the optical recording medium. To make the optical head reading the data smoothly, the optical head actuator should be able to perform a parallel focus to allow the laser light passing through the objective lens, to focus accurately on the data recording layer of the disk. A parallel tracking characteristic is needed to keep the focal point in the center of the data track of the data recording layer of the data recording medium.  
      The optical head according to the invention further includes an actuator for holding the two optical path systems. Refer to  FIG. 2  for an embodiment of the actuator of the invention. It includes a magnetic path device which includes of an objective lens holding seat  200 , a focus coil  240 , a track coil  230 , a yoke  210  and a magnet  220 , four metal wires  241 , a damper holding dock  250  and a circuit board  260 . The objective lenses  201  and  202  of the two optical path systems are located on the top side of the objective lens holding seat  200  in two openings formed thereon. The objective lens holding seat  200  has a plurality of first lugs  204  and second lugs  203  extended from a lateral side. Each of the first lugs  204  has a conical opening, to allow one metal wire  241  to pass through. The second lugs  203  are in contact with a distal end of the focus coil  240  or the track coil  230 , to facilitate soldering of the coil and the metal wire  241 . Thereby, the metal wires  241  can support the objective lens holding seat  200  and enable the objective lens holding seat  200  to be movable in focusing direction and track direction. The focus coil  240  is located on the objective lens holding seat  200  and has the inductive magnetic field direction coinciding with the focusing direction of the converging objective lenses  201  and  202 . The track coil  230  is located on the objective lens holding seat  200  and has the inductive magnetic field direction normal to the focusing direction, to serve as the track direction.  
      The magnetic path device aims to generate a magnetic field. The direction of the magnetic field is parallel with the inductive magnetic field direction of the track coil and normal to the inductive magnetic field direction of the focus coil. In the embodiment shown in  FIG. 2 , the magnetic path device includes the yoke  210 , and the magnet  220  attached to the yoke  210 . The yoke  210  has one or more sidewalls  211  and one or more inner walls  213 , corresponding to the sidewalls  211 . The magnet  220  is attached to the side wall  211 . The magnet  220 , sidewall  211 , inner wall  213  and the bottom of the yoke  210  that is clamped between the side wall  211  and the inner wall  213  jointly form the magnetic path set forth above. The sidewall  211  has two flanges  212  extended from two sides towards the magnet. The flanges  212  have a bending angle of about 10 to 120 degrees to direct the magnetic field linedistribution of the magnetic field. The yoke  210  has an arched bottom extending outwards for adjusting the inclination angle during installation. There is a damper holding dock  250  fastened to the yoke through a screw  214  such, that the damper holding dock  250  is turning about the screw  214  relative to the yoke  210  to adjust the inclination angle of the actuator during installation of the optical system. The circuit board  260  is coupled to the surface of the damper holding dock  250 . The metal wires  241  are connected to the circuit board  260 , to establish electric connection with the exterior. An upper lid  270  is provided to protect the movable elements against external impact and prevent the movable elements from moving outside the allowable range.  
      While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments, which do not depart from the spirit and scope of the invention.