Abstract:
A dual optical pick-up head for accessing CD, CD-R and DVD discs is provided. The provided dual optical pick-up head uses an objective lens and a laser source for DVD discs, and uses another objective lens and another laser source for CD and CD-R discs. Spirit of the invention is that both objective lenses are located in the same lenses holder which connect to a guide rod, and the lenses hold moves only along a radius of the corresponding disc. Moreover, the laser beam produced by any laser source is transmitted through corresponding objective lens to a disc, and the reflected laser beam is transmitted through corresponding objective lens to a PDIC and then a spot is formed and detected. Hence, the location of each objective lens must satiate the requirement that any spot that corresponds to a specific track of disc does not mix with other spots that correspond to other track of disc.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    This application is a continuous-in-part of the original application Ser. No. as 09/325,380, which filed Jun. 4 1999. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a dual optical pick-up head that is capable of accessing both CD (compact disc) disc and DVD (digital versatile disc) discs. More particularly, the present invention relates to a dual optical pick-up head that not only employs two objective lenses and one actuator but also rids the requirement to switch position of objective lenses while different discs are detected.  
         DESCRIPTION OF THE PRIOR ART  
         [0003]    The DVD is an optical disc that is capable of recording a large amount of digital information. Its recording scheme allows the recording of digital information, such as video, computer information or the like on a disc having the same diameter as the CD, at a recording density of six to eight times as high as the CD. No matter how, although the storage amount of DVD disc is larger than CD disc, CD disc is more widespread used in many fields than DVD disc. Thus, it is common commercial benefit that a DVD player uses a dual optical pick-up head not only work with DVD discs but also compatibly work with traditional CD discs.  
           [0004]    Evidently, when picking up data from a DVD disc the dual optical pick-up head works with a shorter focal length of objective lens and a shorter wavelength laser beam. Moreover, when picking up data from a CD disc the dual optical pick-up head works with a larger focal lengths and a larger wavelength laser beam. Therefore, the dual optical pick-up head should be capable to work with different wavelength lasers and different focal-length objective lenses.  
           [0005]    In order to solve such a problem, one conventional method uses two objective lenses for both DVD and CD separated where two lenses are switched in accordance with the type of disc. Another conventional method uses a correcting lens that is inserted into a collimator portion, thereby correcting the aberration due to the disc. The other conventional method uses a two-focal objective lens such as holographic optical element (HOE) as an objective lens. A further conventional method uses a liquid crystal (LCD) shutter to modulate laser beam. Among these conventional methods, two methods are more popular than others and are explained in posterior paragraphs.  
           [0006]    [0006]FIG. 1A and FIG. 1B show the mechanism of the dual optical pick-up head with the usage of the two-focal point objective lens. When CD disc  10  is accessed and 780-nm wavelength laser beam  11  is incident, as shown in FIG. 1A, laser beam  11  transmits through two-focal point objective lens  12  and is focused on CD disc  10 . Similarly, when DVD disc  13  is accessed and 650-nm wavelength laser beam  14  is incident, as shown in FIG. 1B, laser beam  14  transmits through two-focal point objective lens  12  and is focused on DVD disc  13 . Obviously, the optical performance of the two-focal point objective lens  12  is complicated, and then the structure is complex and the cost is expensive.  
           [0007]    [0007]FIG. 2A and FIG. 2B show the mechanism of the dual optical pick-up head with the usage two objective lenses. When CD disc  23  is accessed and 780-nm wavelength laser beam  24  is incident, as shown in FIG. 2A, switching machine  22  puts CD objective lens  20  into path of 780-nm wavelength laser beam  24  and then 780-nm laser wavelength beam  24  is focused on CD disc  23 . Similarly, when DVD disc  26  is accessed and 650-nm wavelength laser beam  25  is incident, as shown in FIG. 2B, switching machine  22  put DVD objective lens  21  into path of 650-nm wavelength laser beam  25  and then 650-nm laser beam  25  is focused on DVD disc  26 . Evidently, the path of 780-nm wavelength laser beam  24  is equal to the path of 650-nm wavelength laser beam  25 . Therefore, the positions of both CD objective lenses  20  and DVD objective lens  21  are switched to put required objective lens into the path of laser beam  24 / 25  while different discs  23 / 26  is detected. Clearly, the case requires complicated switching machine  22  that occupies a large space is necessary to switch objective lens, and then it is not suitable for a compact dual optical pick-up head.  
           [0008]    Besides, in the method of using a LCD shutter, the polarization of the laser beam and location of LCD must be properly arranged, then the design is difficult to actualize. Furthermore, the LCD needs additional driving circuit to maintain shutter effect.  
           [0009]    According to previous discussion, although several conventional ways are presented to compass the subject, none of them efficient and compact enough. Therefore, it is necessary to develop an economical dual optical pick-up head for accessing both CD and DVD discs.  
         SUMMARY OF THE INVENTION  
         [0010]    One main object of the invention is to propose a dual optical pick-up head that can detect DVD discs and CD discs with one actuator and two objective lenses, especially to propose a dual optical pick-up head without the necessarily of a switching machine to switch these objective lenses while different discs are detected.  
           [0011]    In comparison with conventional dual optical pick-up head with two objective lenses, a significant character of the proposed dual optical pick-up head is that these objective lenses do not have to switch their position while different discs are detected.  
           [0012]    Therefore, the position that laser beam project into disc does not have to be located in a radius of disc that is parallel to the guide rod. Hence, the location of these two objective lenses is elastic and the configuration of the proposed dual optical pick-up head is convertible. Besides, because there is no requirement to use two-focal objective lens then the structure and fabrication of the proposed dual optical pick-up head is simplified and compact.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    Other objects, features, and advantages of the invention will become apparent from the following detailed description of preferred embodiments, with reference to the accompanying drawing in which:  
         [0014]    [0014]FIG. 1A and FIG. 1B illustrate an example of accessing both CD and DVD discs according to a conventional technique;  
         [0015]    [0015]FIG. 2A and FIG. 2B illustrate another example of accessing both DVD and CD discs according to another conventional technique;  
         [0016]    [0016]FIG. 3A to FIG. 3D illustrate a preferred embodiment of the invention; and  
         [0017]    [0017]FIG. 4A to FIG. 4C illustrate how projection that laser beam projects on photo-detector integrated circuit is varied. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    [0018]FIG. 3A to FIG. 3D schematically illustrate a preferred embodiment of the invention. Obviously, the proposed dual optical pick-up head at least has first objective lens  31 , second objective lens  32 , objective lenses holder  33 , guide rod  34 , first light assembly  35  and second light assembly  36 .  
         [0019]    The basic mechanism of the embodiment could be explained by referring to FIG. 3A and FIG. 3B, where first objective lens  31  and second objective lens  32  are located separated and are located with lenses holder  33  Herein, it should be noted that the shape, the distribution, and the connection of both these lenses  31 / 32  and lenses holder  33  in FIG. 3A to FIG. 3B only is an example of this invention, this invention is not limited by the details of these figures.  
         [0020]    When disc  30  is a DVD disc, first light beam  301  is incident, as shown in FIG. 3A, and is transmits through first objective lens  31  and focused on disc  30  (DVD disc). Similarly, when disc  30  is a CD disc, second light beam  302  is incident, as shown in FIG. 3B, and is transmits through second objective lens  32  and focused on disc  30  (CD disc). Indisputably, the invention uses two separate objective lenses  31 / 32  to detect different kind disc (DVD/CD) separately, thus, the structure and cost of each objective lenses  31 / 32  are simply and cheap, and it is not necessary to switch the location of the objective lenses  31 / 32  while different kind discs  30  are detected. Further, owing to objective lenses  31 / 32  must be moved to detect different tracks of the detected disc  30 , the invention only requires that the distances between each objective lens  31 / 32  and disc  30  is fixed and requires that objective lenses  31 / 32  essentially do not move along the tangent direction of disc  30 .  
         [0021]    Both first objective lens  31  and second objective lens  32  are located in objective lenses holder  33  without any machine to switch position of both objective lenses  31 / 32 . Thus, both objective lens  31 / 32  are moved with objective lenses holder  33 , neither first objective lens  31  not second objective lens  32  would be moved inside objective lenses holder  33 . In other words, both objective lenses  31 / 32  are fixed in objective lenses holder  33 . Further, guide rod  34  is used to move objective lenses holder  33 , first light assembly  35  and second light assembly  36 . However, it should be emphasized that guide rod  34  is essentially parallel to the detected disc  30 , thus, the distance between both objective lens  31 . 32  and disc  30  essential is fixed, and also is independent on the movement of guide rod  34 . Further, the number of guide rod  34  is not limited, the shape and the construction of guide rod  34  also are not limited.  
         [0022]    Moreover, numerical aperture of first objective lens usually is about 0.60 and numerical aperture of said second objective lens usually is about 0.4 to 0.5. Besides, first light assembly  35  comprises first laser source  351 , first beam splitter  352 , first collimator  353  and first photo detector integrated circuit (PDIC)  354 . Second light assembly  36  comprises second laser source  361 , second beam splitter  362 , second collimator  363  and second photo-detector integrated circuit  364 .  
         [0023]    It should be noted that first objective lens  31  and first light assembly  35  are used to access DVD disc; second objective lens  32  and second light assembly  36  are used to access CD disc. Moreover, in the embodiment, The position that first laser beam project on disc  30  does not locate in a radius that is parallel to guide rod  34 , but the position that second laser beam project on disc  30  does locate in a radius that is parallel to guide rod  34 . However, the invention never limits the project location of both laser beams.  
         [0024]    When disc  30  is a DVD disc, first laser source  351  produces first laser beam which transmits through first beam splitter  352 , first collimator  353 , first objective lens  31  in sequence and then is focused on disc  30 . Therewith first laser beam is reflected by disc  30  and reflected first laser beam transmits through first objective lens  31 , first collimator  353 , first beam splitter  352  in sequence and then is detected by first photo detector integrated circuit  354 .  
         [0025]    In comparison, if disc  30  is a CD disc, second laser source  361  produces second laser beam which transmits through second beam splitter  362 , second collimator  363 , second objective lens  32  in sequence and is focused on disc  30 . Next, second laser beam is reflected by disc  30  and reflected second laser beam transmits through second objective lens  32 , second collimator  363  and second beam splitter  362  in sequence, and then is detected by second photo-detector integrated circuit  364 .  
         [0026]    When different tracks of disc  30  are accessed, first objective lens  31 , first light assembly  35 , second objective lens  32  and second light assembly  36  all are moved by guide rod  34 , where the moving direction is parallel to a radius of disc  30 . FIG. 3C illustrates a specific case that the innermost track of disc is accessed and FIG. 3D illustrates another specific case that the outermost track of disc is accessed.  
         [0027]    According to FIG. 3A through FIG. 3D, it is apparent that second laser beam is always incident to second objective lens  32  by a direction which is vertical to moving direction of objective lenses holder  33 . In comparison, first laser beam is incident to first objective lens  31  by a direction that always is not parallel to tangent direction of disc  30 . Wherein, the degree of the angle that between the direction that first laser beam is incident to first objective lens  31 , and the tangent direction of a point of disc  30  that first laser beam is projected on it is varied. Furthermore, the degree of the angle is gradually increased from the innermost track of disc  30  to outermost track of disc  30 . When first objective lens  31  locates in a first position that corresponds to the innermost track of disc  30 , the degree of the angle is {circumflex over (−)}1; when first objective lens  31  locates in a second position that corresponds to the outermost track of disc  30 , the degree of the angle is(D  2 . Obviously, the values of both {circumflex over (−)} 1 and {circumflex over (−)} 2 depend on the configuration of the dual optical pick-up head, and should be carefully controlled to ensure the correct access of disc  30 .  
         [0028]    Because the reflected first laser beam does not be parallel to tangent direction of disc  30  in first objective lens  31 , the projection that reflected first laser beam projects in first PDIC  352  is moveable. When different tracks of disc  30  are accessed, as shown in FIG. 4B to FIB.  4 C, not only first objective lens  31  is moved in a interval that between the first position and the second position, but also the angle that between the incident direction of first laser beam and tangent direction of disc  30  is varied in another interval that between {circumflex over (−)} 1 and {circumflex over (−)} 2. Moreover, the variation of the angle is proportional to the moving distance of first objective lens  31 , and the proportional relation comprises linear direct proportional relation. Of course, projection  40  that first laser beam projects on first PDIC  354  also is moved in a homologous range, and homologous range also is proportional to the moving distance of first objective lens  31 . Thus, it is important that projection  40  of reflected first laser beam from any track should not be mix with projections  40  of reflected first laser beam which from other tracks, otherwise it is impossible to correctly access disc  30 . In other words, the value of {circumflex over (−)} 1 and value of {circumflex over (−)} 2 must satisfy the requirement that projection  40  of reflected first laser beam from any track should not be mix with projections  40  of reflected first laser beam which from other track.  
         [0029]    [0029]FIG. 4A to FIG. 4C illustrate how projection  40  that first laser beam projects in first photo detector integrated circuit  354  is varied. Moreover, in the provided embodiment the type of first PDIC  354  is choused to such that there are four projections  40  correspond to one reflected first laser beam in first PDIC  354  at same time. First, if location of first objective lens  31  is corresponding to a radius of disc  30  which is parallel to moving direction of objective lenses holder  33 , as second objective lens  32  of the provided embodiment, then projection  40  are formed in both x-axis and y-axis of first PDIC  354 , as shown in FIG. 4A.  
         [0030]    No matter how, in the provided embodiment first object lens  31  does not correspond to such a radius of disc  30 , and the angle that between the incident direction of first laser beam and the tangent direction is varied in a range from {circumflex over (−)} 1 to {circumflex over (−)} 2. Thus, projection  40  of first laser beam does not locate in both axes of first PDIC  354 . When the innermost track of disc is accessed, degree of the angle that between the incident direction of first laser beam and the tangent direction is {circumflex over (−)} 1, and projection  40  on first PDIC  354  is counterclockwise moved with same angle {circumflex over (−)} 1, as shown in FIG. 4B. Thereafter, when the outermost track is accessed, degree of the angle that between the incident direction of first laser beam and the tangent direction is {circumflex over (−)} 2, and projection  40  of first laser beam is counterclockwise moved with same angle {circumflex over (−)} 2, as shown in FIG. 4C.  
         [0031]    Consequently, it is important that {circumflex over (−)} 2 is enough small such that projection  40  of first laser beam never overrun either x-axis or y-axis of first PDIC  354  to insure that projection  40  of first laser beam which from any specific track of disc  30  is not confused with the projection of first laser beam that from other track of disc  30 .  
         [0032]    Hence, the configuration of first laser source  351 , first beam splitter  352 , first collimator  353 , first photo-detector integrated circuit  354  and first objective lens  31  is restricted by the requirement that projection  40  of first laser beam which from a specific track should not be mixed with projections  40  of first laser beam which from any other tracks.  
         [0033]    While in the previous embodiment the location of CD objective lens (second objective lens  32 ) is corresponding to a radius of disc  30  that always is parallel to guide rod  34  and the location of DVD objective lens (first objective lens  31 ) is located in another radius of disc  30  that always is not parallel to guide rod  30 . It is obviously that the mechanism of the invention is not restricted by the provided embodiment. By contrast, both CD objective lens (second objective lens  32 ) and DVD objective lens (first objective lens  31 ) can be locate in any position. Therefore, the only restriction of the structure of proposed dual optical pick-up head is that both projection  40  of first laser beam form a specific track of disc  30  can not be mixed with other projection  40  of first laser beam that form other track of disc  30 . And projection that second laser beam projects on second PDIC  364  form a specific track of disc  30  also can not be mixed with other projection of second laser beam that form other track of disc  30 .  
         [0034]    According to previous discussion, the location of first objective lens  31 , second objective lens  32 , first light assembly  35  and second light assembly  36  are elastic, and then the configuration of the proposed dual optical pick-up head is convertible. Moreover, because there is no requirement to use two-focal objective lens, the structure and fabrication of the proposed dual optical pick-up head is simple and compact.  
         [0035]    While the invention has been described by way of example and in terms of preferred embodiment, the invention is not limited there to. To the contrary, it is intended to cover various modifications, procedures and products, and the scope of the appended claims therefore should be accorded to the broadest interpretation so as to encompass all such modifications and similar arrangement, procedures and products.