Abstract:
An optical system for accessing a storage medium. The system combines two kinds of laser diode, abandons some unnecessary optical elements used in the prior art, and further uses a Penta prism to fold the optical path. Moreover, the optical system uses a CZBO prism to locate the two laser diodes abreast of each other. Thus, the space of the optical system is reduced, and the optical system is more compact.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to an optical system for accessing a storage medium.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 1 schematically shows a conventional optical pickup head for accessing a compact disc (CD) and a digital versatile disc (DVD). The conventional optical pickup head  10  has two laser diodes  1   a ,  1   b  emitting two beams with different wavelengths, two holographic optical elements (HOE)  2   a ,  2   b , a beam splitter  3 , a collimating lens  4 , a mirror  5 , and an objective lens  6 .  
           [0005]    As shown in FIG. 1, the conventional optical pickup head has two optical paths L 1 , L 2 , wherein one optical path L 1  starts from the laser diode  1   a  to the DVD, and the other optical path L 2  starts from the laser diode  1   b  to the CD. The laser diode  1   a  emits a beam with a wavelength of 650 nm, and the beam passing the HOE  2   a  is incident on the beam splitter  3 . The beam passes through the beam splitter  3  and is incident on the collimating lens  4 . Thus, the collimating lens  4  emits a collimated beam, and the collimated beam is reflected by the mirror  5 . The collimated beam reflected by the mirror  5  is projected on the DVD  7  by the objective lens  6 . Further, the DVD  7  emits a signal beam, and the signal beam following the foregoing optical path enters a detector (not shown) adjacent to the laser diode  1   a , whereby the detector converts the signal beam reflected from the DVD  7  to an electric signal.  
           [0006]    Referring to FIG. 1, another laser diode  1   b  emits a beam with a wavelength of 780 nm, and the beam passing the HOE  2   b  is incident on the beam splitter  3 . The beam splitter  3  reflects the beam from the HOE  2   b , and then the beam is incident on the collimating lens  4 . The collimating lens  4  emits a collimated beam, and then the collimated beam is reflected by the mirror  5 . The collimated beam reflected by the mirror  5  is projected on the CD  7  by the objective lens  6 . Further, the CD  7  emits another signal beam, and then the signal beam following the foregoing optical path enters another detector (not shown) adjacent to the laser diode  1   b , whereby the detector converts the signal beam reflected from the CD  7  to an electric signal.  
           [0007]    However, the lengths of the two optical paths in the conventional optical pickup head are too long. Referring to FIG. 1, the optical path L 1  has a length of 22.732 mm.  
         SUMMARY OF THE INVENTION  
         [0008]    To solve the above problems, it is an object of the present invention to provide an optical system for accessing a storage medium, whereby the optical system for accessing a storage medium abandons some unnecessary optical elements used in the prior art. Thus, the optical system for accessing a storage medium is more compact.  
           [0009]    According to the object, the invention provides an optical system for accessing a storage medium, which includes a laser diode, a holographic optical element, a beam splitter, a right-angle prism and an objective lens.  
           [0010]    According to the object, the invention provides another optical system for accessing a storage medium, which includes a laser diode, a Carl Zeiss Binocular-Ocular prism (CZBO prism), a Penta prism, a right-angle prism and an objective lens.  
           [0011]    According to the object, the invention provides another optical system for accessing a storage medium, which includes a laser diode, a CZBO prism, a Penta prism and an objective lens.  
           [0012]    A feature of the invention is that the light beam traveling in the Penta prism generates multi-reflections therein.  
           [0013]    Another feature of the invention is that one of the surfaces constructing the right angle of the right-angle prism is a spherical surface, so as to emit a collimated beam from the right-angle prism.  
           [0014]    Another feature of the invention is that one of the surfaces constructing the right angle of the right-angle prism is an aspherical surface, so as to emit a collimated beam from the right-angle prism.  
           [0015]    Another feature of the invention is that the emitting surface of the Penta prism is a spherical surface, so as to emit a collimated beam from the Penta prism.  
           [0016]    Another feature of the invention is that the emitting surface of the Penta prism is an aspherical surface, so as to emit a collimated beam from the Penta prism.  
           [0017]    Another feature of the invention is that the CZBO prism and two laser diodes emitting different wavelengths are packaged together, whereby the optical system for accessing a storage medium uses the CZBO prism and the two laser diodes are positioned abreast of each other.  
           [0018]    The invention has an advantage of shrinking the space of the optical system for accessing a storage medium, wherein the optical path of the beam is folded several times within the Penta prism.  
           [0019]    The invention has another advantage of adjusting the optical system for accessing a storage medium easier by abandoning some unnecessary optical elements.  
           [0020]    The invention has further advantage of shrinking the space of the optical system for accessing a storage medium, whereby when the optical system uses the CZBO prism, the two laser diodes emitting different wavelengths are positioned abreast of each other. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    This and other objects and features of the invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the drawings, in which:  
         [0022]    [0022]FIG. 1 schematically shows a conventional optical pickup head for accessing a compact disc (CD) and a digital versatile disc (DVD);  
         [0023]    [0023]FIG. 2 schematically shows an optical system for accessing a storage medium according to the first embodiment of the invention;  
         [0024]    [0024]FIG. 3A is a side view of the first embodiment of the invention and schematically shows the ray tracing therein;  
         [0025]    [0025]FIG. 3B is a three-dimensional view of the first embodiment of the invention and schematically shows the ray tracing therein;  
         [0026]    [0026]FIG. 4 schematically shows an optical system for accessing a storage medium according to the second embodiment of the invention;  
         [0027]    [0027]FIG. 5A is a three-dimensional view of the second embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium;  
         [0028]    [0028]FIG. 5B is a vertical view of the second embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium;  
         [0029]    [0029]FIG. 5C is another three-dimensional view of the second embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium;  
         [0030]    [0030]FIG. 5D is another vertical view of the second embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium;  
         [0031]    [0031]FIG. 6 schematically shows an optical system for accessing a storage medium according to the third embodiment of the invention;  
         [0032]    [0032]FIG. 7A is a three-dimensional view of the third embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium;  
         [0033]    [0033]FIG. 7B is a vertical view of the third embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium;  
         [0034]    [0034]FIG. 7C is another three-dimensional view of the third embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium;  
         [0035]    [0035]FIG. 7D is another vertical view of the third embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    First Embodiment  
         [0037]    [0037]FIG. 2 schematically shows an optical system for accessing a storage medium according to the first embodiment of the invention. In the first embodiment of the invention, the optical system for accessing a storage medium includes a first laser diode  20   a , a second laser diode  20   b , a first holographic optical element (HOE)  30   a , a second HOE  30   b , a beam splitter  40 , a right-angle prism  50  and an objective lens  60 . At least one surface  50   a  or  50   b  constructing the right angle of the right-angle prism is a spherical or aspherical convex surface and has a collimating function. Thus, the beam emitted from the right-angle prism  50  is collimated and incident on the objective lens  60 .  
         [0038]    [0038]FIG. 3A is a side view of the first embodiment of the invention and schematically shows the ray tracing therein. As shown in FIG. 3A, a beam with a wavelength of 650 nm emitted from the first laser diode  20   a  is incident on the first HOE  30   a . After passing the first HOE  30   a , the beam is incident on the beam splitter  40 . After passing the beam splitter  40 , the beam is incident on the right-angle prism  50 . The right-angle prism  50  deviates the beam normal to the incident surface  50   b  by 90°, that is to say, the beam is internally reflected. At least one of the two surfaces  50   a ,  50   b  constructing the right angle of the right-angle prism is a convex surface  55 , such as a spherical convex surface or an aspherical convex surface. Thus, a collimated beam is emitted from the right-angle prism  50 , and then the collimated beam from the right-angle prism  50  is projected on the storage medium  70 , such as a digital versatile disc (DVD) by the objective lens  60 . Next, the DVD  7  emits a signal beam, and then the signal beam following the foregoing optical path enters a detector (not shown) adjacent to the first laser diode  20   a , whereby the detector converts the signal beam reflected from the DVD  70  to an electric signal.  
         [0039]    [0039]FIG. 3B is a three-dimensional view of the first embodiment of the invention and schematically shows the ray tracing therein. As shown in FIG. 3B, a beam with a wavelength of 780 nm emitted from the second laser diode  20   b  is incident on the second HOE  30   b . After passing the second HOE  30   b , the beam is incident on the beam splitter  40 , and the beam splitter  40  deviates the beam normal to the incident surface by 90° and emits the beam again. The beam emitted from the beam splitter  40  is incident on the right-angle prism  50 . The right-angle prism  50  deviates the beam normal to the incident surface  50   b  by 90°, that is to say, the beam is internally reflected. A collimated beam is emitted from the right-angle prism  50 , and then the collimated beam from the right-angle prism  50  is projected on the storage medium  70 , such as a compact disc (CD) by the objective lens  60 . Next, the CD  70  emits another signal beam, and then the signal beam following the foregoing optical path enters a detector (not shown) adjacent to the second laser diode  20   b , whereby the detector converts the signal beam reflected from the CD  70  to an electric signal.  
         [0040]    In the first embodiment of the invention, the right-angle prism  50  has replaced the collimating lens  4  and the mirror  5  used in the prior art. The right-angle prism  50  deviates the beam by 90° and emits a collimated beam by a spherical convex surface or an aspherical convex surface constructing the right angle thereof. In the first embodiment of the invention, the optical path length from the first laser diode  20   a  to the DVD  70  is 19.919 mm. Compared with the prior art, the optical path length shortens 2.813 mm.  
         [0041]    Second Embodiment  
         [0042]    [0042]FIG. 4 schematically shows an optical system for accessing a storage medium according to the second embodiment of the invention. In the second embodiment of the invention, the optical system for accessing a storage medium includes a first laser diode  20   a , a second laser diode  20   b , a Carl Zeiss Binocular-Ocular prism (CZBO prism)  80 , a Penta prism  90 , a right-angle prism  50  and an objective lens  60 . At least one surface  50   a  or  50   b  constructing the right angle of the right-angle prism  50  is a spherical or aspherical convex surface and has a collimating function. Thus, the beam emitted from the right-angle prism  50  is collimated and incident on the objective lens  60 .  
         [0043]    [0043]FIG. 5A is a three-dimensional view of the second embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium, and FIG. 5B is a vertical view of the second embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium. As shown in FIGS.  5 A and  5 B, a beam with a wavelength of 650 nm emitted from the first laser diode  20   a  is incident on the CZBO prism  80 . Two internal reflections take place to redirect the beam in the CZBO prism  80 . After passing the CZBO prism  80 , the beam is incident on the Penta prism  90 . The Penta prism  90  deviates the beam by 90° and emits the beam, wherein two of its surfaces must be silvered. After emitting the beam, the beam is incident on the right-angle prism  50 . The right-angle prism  50  deviates the beam normal to the incident surface  50   b  by 90°, that is to say, the beam is internally reflected. At least one of the two surfaces  50   a ,  50   b  constructing the right angle of the right-angle prism is a convex surface  55 , such as a spherical convex surface or an aspherical convex surface. Thus, a collimated beam is emitted from the right-angle prism  50 , and then the collimated beam from the right-angle prism  50  is projected on the storage medium  70 , such as a digital versatile disc (DVD) by the objective lens  60 . Next, the DVD  70  emits a signal beam, and then the signal beam following the foregoing optical path enters a detector (not shown) adjacent to the first laser diode  20   a , whereby the detector converts the signal beam reflected from the DVD  70  to an electric signal.  
         [0044]    [0044]FIG. 5C is another three-dimensional view of the second embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium; and FIG. 5D is another vertical view of the second embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium. As shown in FIGS. 5C and 5D, a beam with a wavelength of 780 nm emitted from the second laser diode  20   b  is incident on the CZBO prism  80 . In the CZBO prism  80 , the beam passes the OPL (optical path length) compensator  84  and the rhomboidal prism  82  in sequence, whereby one internal reflection and one mirror reflection take place to redirect the beam in the CZBO prism  80 . After passing the CZBO prism  80 , the beam is incident on the Penta prism  90 . The Penta prism  90  deviates the beam by 90° and emits the beam, wherein two of its surfaces must be silvered. After emitting the beam, the beam is incident on the right-angle prism  50 . The right-angle prism  50  deviates the beam normal to the incident surface  50   b  by 90°, that is to say, the beam is internally reflected. At least one of the two surfaces  50   a ,  50   b  constructing the right angle of the right-angle prism is a convex surface  55 , such as a spherical convex surface or an aspherical convex surface. Thus, a collimated beam is emitted from the right-angle prism  50 , and then the collimated beam from the right-angle prism  50  is projected on the storage medium  70 , such as a compact disc (CD) by the objective lens  60 . Next, the CD  70  emits a signal beam, and then the signal beam following the foregoing optical path enters a detector (not shown) adjacent to the second laser diode  20   b , whereby the detector converts the signal beam reflected from the CD  70  to an electric signal.  
         [0045]    In the second embodiment of the invention, the right-angle prism  50  has replaced the collimating lens  4  and the mirror  5  used in the prior art, the CZBO prism  80  has replaced the beam splitter  3  used in the prior art, and the Penta prism  90  folds the optical path. The two laser diodes  20   a ,  20   b  are positioned abreast by utilizing the CZBO prism  80 , and packaged with the CZBO prism  80 . The Penta prism  90  reflects the beam twice and shrinks the space of the optical system. Moreover, the right-angle prism  50  deviates the beam by 90° and emits a collimated beam by a spherical convex surface or an aspherical convex surface constructing the right angle thereof.  
         [0046]    In the second embodiment of the invention, the optical system for accessing a storage medium has a length of 7.587 mm, a width of 5.743 mm and a height of 6.186 mm.  
         [0047]    Third Embodiment  
         [0048]    [0048]FIG. 6 schematically shows an optical system for accessing a storage medium according to the third embodiment of the invention. In the third embodiment of the invention, the optical system for accessing a storage medium includes a first laser diode  20   a , a second laser diode  20   b , a Carl Zeiss Binocular-Ocular prism (CZBO prism)  80 , a Penta prism  90 , and an objective lens  60 . At least one emitting surface of the Penta prism  90  is an aspherical surface, so as to emit a collimated beam from the Penta prism  90 . Thus, the beam emitted from the Penta prism  90  is collimated and incident on the objective lens  60 . The CZBO prism  80  has two rhomboidal prisms  81 ,  82 , a right-angle prism  83  and an OPL (optical path length) compensator  84 .  
         [0049]    [0049]FIG. 7A is a three-dimensional view of the third embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium, and FIG. 7B is a vertical view of the second embodiment of the invention and schematically shows the ray tracing from the first laser diode to the storage medium. As shown in FIGS. 7A and 7B, a beam with a wavelength of 650 nm emitted from the first laser diode  20   a  is incident on the CZBO prism  80 . Two internal reflections take place to redirect the beam in the CZBO prism  80 . After passing the CZBO prism  80 , the beam is incident on the Penta prism  90 . The Penta prism  90  deviates the beam by 90° and emits the collimated beam, wherein two of its surfaces must be silvered. After emitting the collimated beam from the Penta prism  90 , the collimated beam is projected on the storage medium  70 , such as a digital versatile disc (DVD) by the objective lens  60 . Next, the DVD  70  emits a signal beam, and then the signal beam following the foregoing optical path enters a detector (not shown) adjacent to the first laser diode  20   a , whereby the detector converts the signal beam reflected from the DVD  70  to an electric signal.  
         [0050]    [0050]FIG. 7C is another three-dimensional view of the third embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium; and FIG. 7D is another vertical view of the third embodiment of the invention and schematically shows the ray tracing from the second laser diode to the storage medium. As shown in FIGS. 7C and 7D, a beam with a wavelength of 780 nm emitted from the second laser diode  20   b  is incident on the CZBO prism  80 . In the CZBO prism  80 , the beam passes the OPL (optical path length) compensator  84  and the rhomboidal prism  82  in sequence, whereby one internal reflection and one mirror reflection take place to redirect the beam in the CZBO prism  80 . After passing the CZBO prism  80 , the beam is incident on the Penta prism  90 . The Penta prism  90  deviates the beam by 90° and emits the collimated beam, wherein two of its surfaces must be silvered. After emitting the collimated beam from the Penta prism  90 , the collimated beam is projected on the storage medium  70 , such as a compact disc (CD) by the objective lens  60 . Next, the CD  70  emits a signal beam, and then the signal beam following the foregoing optical path enters a detector (not shown) adjacent to the second laser diode  20   b , whereby the detector converts the signal beam reflected from the CD  70  to an electric signal.  
         [0051]    In the third embodiment of the invention, the CZBO prism  80  has replaced the beam splitter  3  used in the prior art, and the Penta prism  90  folds the optical path and has replaced the collimating lens  4  and the mirror used in the prior art. The two laser diodes  20   a ,  20   b  are positioned abreast by utilizing the CZBO prism  80 , and packaged with the CZBO prism  80 . The Penta prism  90  reflects the beam twice and shrinks space of the optical system. Furthermore, the Penta prism  90  deviates the beam by 90° and emits a collimated beam by a spherical convex surface or an aspherical convex surface.  
         [0052]    In the third embodiment of the invention, the optical system for accessing a storage medium has a length of 9.493 mm, and a height of 7.429 mm.  
         [0053]    While the preferred embodiment of the present invention has been described, it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims.