Abstract:
An optical pickup includes a light source which emits light, a grating which separates a portion of the light emitted from the light source, a reflecting member which reflects another portion of the light emitted from the light source, a monitoring photodetector disposed on a traveling path of the light reflected from the reflecting member and which measures the reflected light, an optical path changer which changes an optical path of the light separated by the grating, an objective lens light which condenses the light the optical path of which is changed onto a disc, and a signal detecting photodetector which receives the light reflected from the disc.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 2002-63845, filed on Oct. 18, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical pickup having an improved structure such that optical noise due to reflection of light by a signal detecting photodetector is not received by a monitoring photodetector, thereby enabling the monitoring photodetector to accurately determine the power of recording light, and an optical recording and/or reproducing apparatus using the same. 
     2. Description of the Related Art 
     Generally, optical pickups are used in optical recording and/or reproducing apparatuses for recording onto and/or reproducing information from optical recording media, such as, for example, optical discs. An optical pickup irradiates light onto a recording surface of an optical disc and receives light reflected from the optical disc while moving along a radial direction of the optical disc so that information is recorded onto and/or reproduced from the optical disc. 
     In a conventional optical pickup shown in  FIG. 1 , a portion of light emitted from a light source  103  is reflected by a beam splitter  107 , and the remainder of the light is transmitted by the beam splitter  107 . The light reflected from the beam splitter  107  passes through a collimating lens  110  and becomes parallel light. Thereafter, the parallel light passes through an objective lens  113  and is condensed on a disc  115 . 
     The light reflected from the disc  115  passes through the objective lens  113 , the collimating lens  110 , and the beam splitter  107  and is received by a signal detecting photodetector  120 . A light signal received by the signal detecting photodetector  120  is converted into an electric signal so that a signal recorded on the disc  115  is reproduced. 
     Meanwhile, a grating  105  is provided between the light source  103  and the beam splitter  107 . The light emitted from the light source  103  is separated into three beams by the grating  105 , and a tracking error signal is detected by a three-beam method using the three beams. 
     An astigmatic lens  118  is provided between the beam splitter  107  and the signal detecting photodetector  120 . In the astigmatic lens  118 , a curvature of a lens surface is not uniform, and a curvature in a longitudinal direction and a curvature in a transversal direction of the lens surface are different from each other, thereby generating astigmatism. The astigmatic lens  118  and the collimating lens  110  decrease a size of light beams received by the signal detecting photodetector  120 . Further, the astigmatic lens  119  is inclined oppositely to the inclination of the beam splitter  107 , in order to removed coma aberration generated in light passed through the beam splitter  107 . A focusing error signal of the disc  115  is detected by an astigmatic method using astigmatism generated by the astigmatic lens  118 . 
     Light emitted from the light source  103  and then transmitted by the beam splitter  107  is received by a monitoring photodetector  109  so that an amount of light emitted from the light source  103  is measured. Typically, about 91% or more of light emitted from the light source  103 , for example, a laser diode, is reflected by the beam splitter  107 , and the remainder of the light, that is, about 8-9% of the light is transmitted by the beam splitter  107  and detected by the monitoring photodetector  109 . 
     The monitoring photodetector  109  is generally used in an optical pickup for a recording apparatus and operates as a light receiving element for monitoring recording light of a light source. That is, the monitoring photodetector  109  measures an amount of light emitted from the light source and, with this measurement, power of light used for recording information on a disc is controlled. Thus, if light other than the light emitted from the light source is received by the monitoring photodetector  109 , the control of the power of the recording light is affected, resulting in a reduction in the performance of the recording and/or reproducing of the optical pickup. 
     When light reflected from the disc  115  is received by the signal detecting photodetector  120 , a portion of the received light is reflected from a surface of the signal detecting photodetector  120 . The light reflected from the signal detecting photodetector  120  is reflected from the beam splitter  107  and is received by the monitoring photodetector  109 . The light reflected form the signal detecting photodetector  120  is referred to as feedback optical noise. The monitoring photodetector  109  cannot accurately measure an amount of recording light when feedback optical noise is present. 
     Conventionally, in order to cut off the feedback optical noise, as shown in  FIG. 2 , the signal detecting photodetector  120  is inclined at an angle of about 2.5°. Light reflected from the inclined signal detecting photodetector  120  travels along an optical path different from that of the signal detecting photodetector  120  which is disposed flat (i.e., normal to the incident light) as shown in  FIG. 1 . Light reflected from the signal detecting photodetector  120  is not incident on the monitoring photodetector  109  due to the inclination of the signal detecting photodetector  120 . Specifically, as indicated with dotted lines in  FIG. 2 , the light reflected from the signal detecting photodetector  120  is reflected from the beam splitter  107  and is not incident on the monitoring photodetector  109 . That is, since the light reflected from the beam splitter  107  is not incident on the monitoring photodetector  109 , the feedback optical noise can be cut off. However, a portion of the light reflected from the signal detecting photodetector  120  is transmitted inside the beam splitter  107 , is reflected inside from the beams splitter  107 , and is incident on the monitoring photodetector  109 . Consequently, the feedback optical noise is not cut off completely. In  FIG. 2 , the light transmitted inside the beam splitter  107  is indicated with solid lines. 
     In the conventional method for cutting off the feedback optical noise, in addition to the above problem, since the signal detecting photodetector  120  is inclined to cut off the feedback optical noise incident on the monitoring photodetector  109 , a shape of light beams incident on the signal detecting photodetector  120  is circular so that unbalance in a servo signal may be generated. Further, the monitoring photodetector  109  must be shifted to cut off the feedback optical noise incident on the monitoring photodetector  109  according to an angle of the inclination of the signal detecting photodetector  120 . However, the monitoring photodetector  109  is much too small, and thus, it is very difficult to precisely manage an amount of shifting of the monitoring photodetector  109 . 
     In order for light reflected from the signal detecting photodetector  120  and then reflected from the beam splitter  107  to not be incident on the monitoring photodetector  109 , a nonreflecting coating may be applied on a reflecting surface  107   a  of the beam splitter  107 . However, since a complete nonreflecting coating is difficult to make, the feedback optical noise incident on the monitoring photodetector  109  is difficult to cut off completely. Consequently, the recording performance of the optical pickup due to the feedback optical noise remains affected. Accordingly, adequate measures for completely cutting off the feedback optical noise reflected from the signal detecting photodetector  120  are required. 
     SUMMARY OF THE INVENTION 
     The present invention provides an optical pickup for cutting off optical noise by disposing a monitoring photodetector at a position such that light reflected from a signal detecting photodetector does not reach the monitoring photodetector, and an optical recording and/or reproducing apparatus using the same. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     According to an aspect of the present invention, there is provided an optical pickup including: a light source which emits light; a grating which separates a portion of the light emitted from the light source; a reflecting member which reflects another portion of the light emitted from the light source; a monitoring photodetector disposed on a traveling path of the light reflected from the reflecting member and which measures the reflected light; an optical path changer which changes an optical path of the light separated by the grating; an objective lens which condenses the light the optical path of which is changed onto a disc; and a signal detecting photodetector which receives the light reflected from the disc. 
     The reflecting member may be disposed on an optical path of light traveling outside an effective aperture of the grating to reflect ineffective light of light emitted from the light source. 
     According to another aspect of the present invention, there is provided an optical pickup, in which a portion of light emitted from a light source is condensed onto a disc by an objective lens so that information is recorded on the disc, and light reflected from the disc is received by a signal detecting photodetector so that focusing servo and tracking servo operations are performable. The optical pickup includes: a grating which separates the light emitted from the light source which passes through an effective aperture thereof; and a monitoring photodetector disposed on an optical path of at least a portion of the light traveling outside of the effective aperture and which measures a power of the at least a portion of the light traveling outside of the effective aperture. 
     According to yet another aspect of the present invention, there is provided an optical recording and/or reproducing apparatus including: a spindle motor which rotates a disc; an optical pickup which is movably disposed in a radial direction of the disc and records information onto and/or reproduces information from the disc; a driving unit which drives the spindle motor and the optical pickup; and a controller which controls focusing servo operations and tracking servo operations of the optical pickup. The optical pickup includes: a light source which emits light; a grating which separates a portion of the light emitted from the light source; a monitoring photodetector disposed on an optical path of light traveling outside of an effective aperture of the grating and which monitors a power of the light incident thereon; an optical path changer which changes an optical path of the light passed through the grating; an objective lens light which condenses light reflected from the optical path changer on a disc; and a signal detecting photodetector which receives the light reflected from the disc. 
     According to yet another aspect of the present invention, there is provided an optical recording and/or reproducing apparatus including: a spindle motor which rotates a disc; an optical pickup which is movably disposed in a radial direction of the disc and records information onto and/or reproduces information from the disc; a driving unit which drives the spindle motor and the optical pickup; and a controller which controls focusing servo operations and tracking servo operations of the optical pickup. The optical pickup includes a light source which emits light, a grating which separates a portion of the light emitted from the light source, a reflecting member which reflects another portion of the light emitted from the light source, a monitoring photodetector disposed on a traveling path of the light reflected from the reflecting member and which measures the reflected light, an optical path changer which changes an optical path of the light separated by the grating, an objective lens light which condenses the light the optical path of which is changed onto a disc, and a signal detecting photodetector which receives the light reflected from the disc. 
     According to yet another aspect of the present invention, there is provided a method of recording to and/or reproducing from an optical disc, including: emitting light; separating a portion of the emitted light; reflecting another portion of the light emitted from the light source which is not separated in the separating; measuring the light reflected by the reflecting; changing an optical path of the light separated by the separating; condenses the light changed by the changing onto a disc; and receiving the condensed light after the condensed light is reflected from the disc. 
     According to yet another aspect of the present invention, there is provided a method of recording onto and/or reproducing from an optical disc using an optical pickup in which a portion of light emitted from a light source is condensed on a disc by an objective lens so that information is recorded on the disc, and light reflected from the disc is received by a signal detecting photodetector so that focusing servo and tracking servo operations are performable. The method includes: separating light emitted from the light source which passes through an effective aperture; and measuring at least a portion of the light traveling outside of the effective aperture of the grating and which measures a power of the at least a portion of the light traveling outside of the effective aperture. 
     According to yet another aspect of the present invention, there is provided an optical pickup including: a light source which emits light; an optical path changer which changes an optical path of a portion of the light so as to direct the light toward an optical disc; a monitoring photodetector disposed between the light source and the optical path changer and which detects another portion of the light; and a signal detecting photodetector which receives the light reflected from the disc. Optical noise reflected from a signal detecting photodetector is not read by the monitoring photodetector. 
     According to yet another aspect of the present invention, there is provided an optical pickup including: a light source which emits light; an optical path changer which changes an optical path of a portion of the light so as to direct the light toward an optical disc; a monitoring photodetector disposed one of between the light source and the optical path changer and on an optical path of light reflected by a reflecting member disposed between the light source and the optical path changer and which detects another portion of the light; and a signal detecting photodetector which receives the light reflected from the disc. Optical noise reflected from a signal detecting photodetector is not read by the monitoring photodetector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments taken in conjunction with the accompanying drawings in which: 
         FIG. 1  shows a conventional optical pickup; 
         FIG. 2  shows an optical path of light reflected from a signal detecting photodetector when the signal detecting photodetector of  FIG. 1  is inclined at an angle in order to cut off optical noise incident on a monitoring photodetector in the conventional optical pickup of  FIG. 1 ; 
         FIG. 3  is a schematic structure view of an optical pickup for cutting off optical noise according to a first embodiment of the present invention; 
         FIG. 4  shows an optical pickup for cutting off optical noise according to a second embodiment of the present invention; and 
         FIG. 5  schematically shows an optical recording and/or reproducing apparatus using an optical pickup shown in  FIGS. 3 and 4  according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     Referring to  FIG. 3 , an optical pickup according to a first embodiment of the present invention includes a light source  10 , a grating  13  for separating light emitted from the light source  10  into three beams, and an optical path changer  17  for changing an optical path of light by transmitting or reflecting light passed through the grating  13 . Further, a monitoring photodetector  11  is disposed on an optical path of light traveling outside an effective aperture of the grating  13  between the light source  10  and the optical path changer  17 . 
     A laser diode may be used, for example, as the light source  10 . The light source  10  emits divergent light, and a portion of light emitted therefrom travels toward a disc  25  after passing through an effective aperture of the grating  13 . The remainder of the light which does not pass through a range of the effective aperture of the grating  13  is ineffective light which does not contribute to recording information on the disc  25 . In order to monitor power of recording light using the ineffective light, the monitoring photodetector  11  is disposed on a traveling path of the ineffective light traveling outside the effective aperture of the grating  13 . 
     Although the monitoring photodetector  11  is shown disposed adjacent to a sidewall of the grating  13  in  FIG. 3 , it is to be understood that the monitoring photodetector  11  may be disposed at any position between the light source  10  and the optical path changer  17 . Reference numeral  14  denotes a stop for cutting off light passing through a lateral portion of the grating  13 . 
     The optical pickup according to the first embodiment of the present invention further includes an optical path changer  17 , an objective lens  23  for condensing light traveling along the optical path changed by the optical path changer  17  on the disc  25 , and a signal detecting photodetector  30  for receiving light reflected from the disc  25  and then passed through then the objective lens  23  and the optical path changer  17 . A collimating lens  20  is disposed on an optical path between the objective lens  23  and the optical path changer  17  and makes incident light into parallel light. An astigmatic lens  27  is disposed on an optical path between the optical path changer  17  and the signal detecting photodetector  30 . 
     Light passed through the grating  13  is transmitted through or reflected by the optical path changer  17  so that an optical path of the light is changed. The light traveling along the optical path changed by the optical path changer  17  is condensed on the disc  25  by the objective lens  23 . Thereafter, light reflected from the disc  25  passes through then the objective lens  23  and the optical path changer  17  and is incident on the signal detecting photodetector  30 . Information recorded on the disc  25  is reproduced on focusing servo and tracking servo are performed using a photoelectric transformation signal generated by the signal detecting photodetector  30 . At this time, even if a portion of the light incident on the signal detecting photodetector  30  is reflected, the reflected light is not incident on the monitoring photodetector  11 . 
     The optical path changer  17 , for example, may be a beam splitter which reflects or transmits incident light by a ratio according to a reflective coating of the beam splitter, or a polarized beam splitter which reflects or transmits incident light according to a polarization direction of the incident light. 
     An optical pickup according to a second embodiment of the present invention, as shown in  FIG. 4 , includes a light source  10 , a grating  13 , and an optical path changer  17 . Further, a reflecting member  15  is disposed between the light source  10  and the optical path changer  17 , and a monitoring photodetector  12  is disposed on a traveling path of light reflected from the reflecting member  15 . In  FIG. 4 , the same reference numerals as those in  FIG. 3  represent the same elements, and thus their descriptions will be omitted. 
     The reflecting member  15  is disposed on an optical path of light emitted from the light source  10  and then traveling outside an effective aperture of the grating  13 . When the reflecting member  15  is disposed in this manner, it uses ineffective light of light emitted from the light source  10  as described in the first embodiment of the present invention. The reflective member may be, for example, a mirror. A portion of light emitted from the light source  10  travels toward a disc  25  after passing through the effective aperture of the grating  13 , and the remainder of the light is reflected from the reflecting member  15  and incident on the monitoring photodetector  12 . Power of recording light for recording information on the disc  25  is controlled using a signal detected by the monitoring photodetector  12 . 
     The reflecting member  15  is provided around the grating  13 . Particularly, the reflecting member  15  is disposed on the traveling path of light traveling outside the effective aperture of the grating  13  so that power of recording light is monitored using ineffective light which is not used for recording information, thereby increasing an optical efficiency of the optical pickup. 
     The reflecting member  15  is disposed only in a portion of a peripheral portion of the grating  13 . The reflecting member  15  is disposed such that a portion of light reflected from the reflecting member  15  is incident on the monitoring photodetector  12 . In  FIG. 4 , light reflected from the reflecting member  15  and then incident on the monitoring photodetector  12  is indicated with dotted lines. 
     If the power of the recording light measured by the monitoring photodetector  12  is lower or higher than a reference power, the power of the light source  10  is controlled so that the power of the recording light is controlled to maintain a power required for recording information. 
     Light passed through the grating  13  is reflected from the optical path changer  17 , passes through the collimating lens  20  and the objective lens  23 , and is condensed on the disc  25  so that information is recorded on the disc  25 . Next, light reflected from the disc  25  passes through the objective lens  23 , the collimating lens  20 , and the optical path changer  17 , and is focused on a signal detecting photodetector  30 . 
     Focusing servo and tracking servo operations are performed using a light signal focused on a signal detecting photodetector  30 . At this time, even if a portion of the light incident on the signal detecting photodetector  30  is reflected, the reflected light is not incident on the monitoring photodetector  11 . 
     Referring to  FIG. 5 , an optical recording and/or reproducing apparatus using an optical pickup  50  according to an embodiment of the present invention is configured such that a spindle motor  40  for rotating a disc  25  is installed under a turntable  43 , the disc  25  is placed on the turntable  43 , and a clamp  45  for chucking the disc  25  via an interaction between the disc  25  and the turntable  43  is installed oppositely to the turntable  43 . When the disc  25  is rotated by the spindle motor  40 , the optical pickup  50  is installed movably in a radial direction of the disc  25  so that information is recorded on the disc  25  or the information recorded on the disc  25  is reproduced. 
     The spindle motor  40  and the optical pickup  50  are driven by a driving unit  53 . Focusing servo and tracking servo operations of the optical pickup  50  are controlled by a controller  55  so that information recording on and/or reproducing from the disc  25  are performed. 
     The optical pickup according to the first embodiment (refer to  FIG. 3 ) or the second embodiment (refer to  FIG. 4 ) of the present invention may be used as the optical pickup  50 . 
     In the optical pickup according to the first embodiment of the present invention, the monitoring photodetector  11  is provided on an optical path of light traveling outside the effective aperture of the grating  13  between the light source  10  and the optical path changer  17 . In the optical pickup according to the second embodiment of the present invention, the reflecting member  15  is provided on an optical path of light traveling outside the effective aperture of the grating  13  between the light source  10  and the optical path changer  17 , and the monitoring photodetector  12  is provided on a traveling path of light reflected from the reflecting member  15 . 
     In the optical pickup  50  according to the present invention, a photoelectric transformation signal generated in the signal detecting photodetector  30  is input to the controller  55  through the driving unit  53 . The driving unit  53  controls a rotation speed of the spindle motor  40 , amplifies the input photoelectric transformation signal, and drives the optical pickup  50 . The controller  55  sends focusing servo instructions and tracking servo instructions adjusted based on the photoelectric transformation signal input from the driving unit  53  to the driving unit  53  so that the focusing servo and the tracking servo are performed. 
     As described above, since a monitoring photodetector for monitoring power of recording light is disposed not to be affected by optical noise, accurate monitoring can be performed. 
     According to an optical pickup and an optical recording and/or reproducing apparatus using the same, since the monitoring photodetector is disposed between a light source and an optical path changer, optical noise reflected from a signal detecting photodetector does not affect the monitoring photodetector. Thus, power of recording light can be measured exactly, and also a recording performance of the optical pickup can be improved. 
     Further, since optical noise can be cut off completely by disposing the monitoring photodetector around a grating or having a reflecting member, the method of cutting off optical noise according to the present invention is simpler than a conventional method, thereby reducing manufacturing cost. Since the signal detecting photodetector does not need to be inclined at a predetermined angle, unbalance of a servo signal can be prevented. 
     Furthermore, since power of recording light is monitored using an effective light of light emitted from the light source which is not used for recording information on a disc, an optical efficiency of the optical pickup increases. 
     Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the disclosed embodiments. Rather, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.