Patent Publication Number: US-2005117486-A1

Title: Optical pickup unit and optical disk unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-400796, filed Nov. 28, 2003, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to the configuration of a photoreceptor device which is provided in an optical pickup of an optical disk unit and which directly detects light quantity of laser light from a light emitting device. More specifically, the invention relates to an optical disk unit using a monitor unit integrally formed of a laser-light reflection/refraction mechanism, photoreceptor device, and circuit device by using a transparent resin.  
      2. Description of the Related Art  
      Generally, as a method of controlling the intensity of laser emanation light, an optical disk unit employs a method using an APC (auto power controller) circuit. The APC circuit detects laser emanation light, and inputs a front monitor signal which is proportional to a detection amount of the laser light. In this case, a front monitor to be built in an optical pickup should be provided separately from a photodetector which receives reflected light of the laser light from an optical disk. This makes it difficult to miniaturize the optical pickup. As techniques for compactly mounting the front monitor, related techniques as described below is known.  
      Jpn. Pat. Appln. KOKAI Publication No. 2002-352458 discloses an optical head which takes off part of laser light having just been emitted from a photodiode via an optical fiber and which controls a front monitor to detect the part of laser light. The front monitor in this case can be relatively compactly mounted.  
      However, the prior art disclosed in Jpn. Pat. Appln. KOKAI Publication has problems in that, for example, wiring of the optical fiber is intricate, as it requires high precision. In addition, the optical fiber lacks the strength against mechanical shocks, and can cause significant influence on the magnitude of a detection signal depending on the mounting state.  
     BRIEF SUMMARY OF THE INVENTION  
      An embodiment according to the invention is an optical pickup unit comprises a light emitting device which emits laser light; and a monitor unit formed of a transparent resin, which integrally forms a photoreceptor device which receives the laser light and a circuit device connected to the photoreceptor device. A part of the transparent resin of the monitor unit is disposed in a part of an optical path of the laser light; the transparent resin causes part of the laser light to be reflected or refracted for supply to the photoreceptor device; the photoreceptor device outputs a detection signal corresponding to the part of the laser light; and upon receipt of the detection signal from the photoreceptor device, the circuit device performs a signal process and produces an output. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       FIG. 1  is a cross-sectional view showing an example of the configuration of a monitor unit in an optical pickup unit according to the present invention;  
       FIG. 2  is a block diagram showing an example of the configuration of an optical disk unit using the optical pickup unit according to the invention;  
       FIG. 3  is an explanatory view showing an example of the interior configuration of the optical pickup unit according to the invention;  
       FIG. 4  is an explanatory view showing an example of the configuration of an APC circuit of the optical disk unit according to the invention;  
       FIG. 5  is a solid diagram showing an example of the configuration of the monitor unit according to the invention; and  
       FIG. 6  is a cross-sectional view showing another example configuration of a monitor unit in the optical pickup unit according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Embodiments according to the present invention will be described below with reference to the drawings.  
      &lt;Optical Disk Unit According to the Invention&gt; 
      Examples of optical disk units according to the invention will be described hereunder with reference to the drawings.  
      (Configuration)  
      Referring to  FIG. 2 , the optical disk unit has an optical disk motor  12  which supports and drives an optical disk D to rotate at a predetermined speed rate; an optical pickup unit  14  which emits an optical beam to the optical disk D and detects reflected light; an RF amp (amplifier)  16  which is supplied with a detected signal and which generates a servo-control signal; a signal processing circuit  18  and a laser output determination circuit  21  which are each supplied with an RF signal. In addition, the optical disk unit has an interface  31  which exchanges data with the outside; and a buffer memory  30  which is connected to the interface  31  to temporarily store, for example, supplied data or playback data having been read by the optical pickup unit  14 .  
      The optical disk unit further has an encode processing circuit  28  which is connected to the buffer memory  30  and the interface  31  to encode supplied data; and a laser emission driver  20  which is supplied with an output encoded by the encode processing circuit  28 . The laser emission driver  20  produces a laser emission drive signal d under control of a control signal received from the laser output determination circuit  21  connected to a system controller  10  which manage the total system operation. Thereby, the laser light corresponding to the RF signal, which is supplied from the RF amplifier  16 , is generated through the optical pickup unit  14 . The system controller  10  is connected to the above-described individual portions to control operations thereof. As described below in detail, the system controller  10  includes a correction amount determination section. This determination section performs a detection process and a determination process for a correction process which is performed by a write APC circuit  11 . The detection process detects an error amount corresponding to wringing and waveform abnormality or corruption, and the determination process determines a correction signal corresponding to the error amount.  
      The optical disk unit has a focus servo amp driver  23  and a tracking servo amp driver  25 . The focus servo amp driver  23  operates to enable focus control of the optical pickup unit  14  upon receipt of the focus error signal, which is the servo-control signal, generated by the RF amp  16 . The tracking servo amp driver  25  operates to enable tracking control of the optical pickup unit  14  upon receipt of the track error signal, which is the servo-control signal, received from the RF amp  16 .  
      Additionally, with reference to  FIG. 3 , the optical pickup unit  14  of the optical disk unit according to the invention has an actuator  39  having an objective lens  42 . In the actuator  39 , a track-direction actuator drive coil  40  and a focus-direction actuator drive coil  41  are provided. In the present case, a tracking control signal C T  and focus control signal C F  are supplied, respectively, from the focus servo amp driver  23  and tracking servo amp driver  25  described above, whereby servo control is enabled.  
      The optical pickup unit  14  performs both emission and photoreception in accordance with operations of a beamsplitter  37  and the like. Laser light emitted from a photodiode  35  in correspondence to the drive signal d of the laser emission driver  20  passes through a lens  36  and the beamsplitter  37 . Then, the laser light is focused by the objective lens  42  through, for example, a one-quarter (¼) waveplate  38 , and is irradiated onto a predetermined region of the optical disk D. Further, reflected light from the optical disk D is expanded by the objective lens  42 , is split by the beamsplitter  37  to the side of a focusing lens  34 , and further, is supplied to a photodetector  32 . The photodetector  32  supplies a detection signal S. The tracking error signal and the focus error signal are supplied to the tracking servo amp driver  25  and the focus servo amp driver  23 , respectively. Further, the detection signal S for generating a replay signal is supplied to the signal processing circuit  18 .  
      The optical disk unit according to the invention has a write APC (auto power controller) circuit  11  which receives a front monitor signal M from a front monitor  33  of the optical pickup unit  14  and which supplies to the laser emission driver  20  an appropriate control signal C corresponding to the front monitor signal M whereby to perform control of the laser emission driver  20 . In particular, the write APC circuit  11  performs output control of laser light in the event of a write to the optical disk D.  
      As shown in  FIG. 4 , the write APC circuit  11  has a gain amp  51  and a sampling hold circuit  52 . The gain amp  51  receives the front monitor signal M from the front monitor  33  of the optical pickup unit  14  and a voltage VR indicative of a control target value. The sampling hold circuit  52  is supplied with an output of the gain amp  51 .  
      (Basic Operation)  
      In the optical disk unit having the configuration described above, an optical-disk replay process is performed as follows. Under the control of the system controller  10 , the optical disk D rotated by the optical disk motor  12  at a predetermined speed rate generates laser light corresponding to the laser emission driver  20  set by the laser output determination circuit  21 . Reflected light of the laser light is detected by the optical pickup unit  14 , and a detection signal corresponding to the reflected light is output. The detection signal is supplied to the RF amp  16 , and the RF signal output therefrom is supplied to the signal processing circuit  18  and the laser output determination circuit  21 . Concurrently, a focus error signal and tracking error signal generated in the RF amp  16  are supplied to the focus servo amp driver  23  and tracking servo amp driver  25 , respectively. In the signal processing circuit  18 , the RF signal is decoded, and a decoded signal is temporarily stored into the buffer memory  30  or is output to the outside through the interface  31 . In addition, the system controller  10  generates a control signal for controlling the rotation of the optical disk motor  12 , thereby controlling the rotation of the optical disk motor  12 .  
      Further, in the optical disk unit thus configured, an optical-disk record process is performed as follows. Under the control of the system controller  10 , data supplied through, for example, the interface  31 , is temporarily stored into the buffer memory  30  and is thereafter supplied to the encode processing circuit  28 . In this manner, the data is encoded and output. Corresponding to the encoded output and the output of the laser output determination circuit  21 , a driver output of the laser emission driver  20  is supplied to the optical pickup unit  14 . In the optical pickup unit  14 , laser light corresponding to the driver output of the laser emission driver  20  is emitted from the mounted photodiode  35  and is irradiated onto a storage area of the optical disk D rotated by the optical disk motor  12  at a predetermined speed rate, whereby the record process is performed.  
      &lt;Monitor Unit Included in the Optical Pickup Unit According to the Invention&gt; 
      A monitor unit according to the invention, which is included in the optical pickup unit  14  according to the invention, will be described in detail below with reference to the drawings. Referring to  FIG. 1 , a monitor unit  33 - 1  according to the invention has a photoreceptor device  33  formed of a photodiode or the like; and a circuit device  33 - 2  including, for example, an amp circuit which amplifies a low output signal of the photoreceptor device  33  and which supplies the signal to, for example, a backstage control circuit. The photoreceptor device  33  and the circuit device  33 - 2  are integrally formed by using a transparent resin such as a polycarbonate.  
      The configuration of the transparent resin in this case is disposed so as to acquire part of laser light of the photodiode  35  which is a light emitting device for emitting laser light L. Specifically, as shown in  FIG. 1 , the configuration is formed and disposed to have a part of the transparent resin which intersects with a part of an optical path L. Thereby, influence on the laser light L can be minimized, the area of the place for mounting the monitor unit  33 - 1  can be minimized, and the optical pickup unit  14  can be miniaturized overall. In this case, a reflecting mirror may be provided to guide the laser light to the photoreceptor device. In addition, it is preferable that the transparent resin in a region where reflection or refraction takes place be formed independently of an other transparent resins, and be later formed by being adhered with the other transparent resin.  
      In the configuration in which the photoreceptor device  33  and the circuit device  33 - 2  are integrally formed by using the transparent resin, the configuration has high mechanical strength and enables minimizing the load to be imposed on an assembly worker for the monitor unit  33 - 1 .  
      For example, the monitor unit  33 - 1  is disposed and adhered to a flexible substrate P on which the laser emission driver  20  shown in  FIG. 2  and the like are mounted. Thereby, mounting of the monitor unit  33 - 1  can be facilitated, and mechanical strength can be imparted. In addition, the electrical wiring enables amplified signals from the monitor unit  33 - 1  to be easily supplied to the flexible substrate P.  
      As shown in  FIG. 5  in detail, the monitor unit  33 - 1  is preferably formed such that the photoreceptor device  33  and the circuit device  33 - 2  are provided on a single semiconductor chip  33 - 3 , such as a silicon chip. This enables stabilizing electrical performance and reducing the number of assembly steps.  
      An optical pickup unit  14  shown in  FIG. 6  is configured such that the monitor unit  33 - 3  is mounted on the flexible substrate P, and a transparent resin  33 - 4  serving as a housing member of the optical pickup unit  14  is mounted in an optimal position with respect to a monitor unit  33 - 3  on the flexible substrate P. The transparent resin  33 - 4  serving as the housing member is mounted to intersect with a part of the optical path L of the laser light to thereby guide the part of the laser light to the photoreceptor device  33 . In this case, a reflecting mirror  43  may be provided. With the monitor unit  33 - 3  thus mounted, the configuration is formed such that the reflecting mirror  43  serving as the housing member of the optical pickup unit  14  is used, and space reduction for the monitor unit  33 - 3  is implemented. Thereby, the monitor unit, optical pickup unit, and optical disk unit using them can be provided that are entirely compact, excellent in mechanical strength, and excellent in stability, and assembly is facilitated.  
      As described above, in the optical pickup unit according to the invention, the monitor unit including the front monitor for detecting the light quantity of the laser light is formed in the manner that the photoreceptor device and the circuit device connected thereto are integrally formed by using the transparent resin. In addition, the part of the transparent resin of the monitor unit is disposed in the part of the optical path of the laser light, whereby the part of the laser light is reflected or refracted and thereby introduced into the photoreceptor device. Thereby, since the monitor unit can be disposed near the optical path of the laser light, the optical pickup unit can be miniaturized.  
      Since both the photoreceptor device and circuit device are integrally formed with the transparent resin, the monitor unit is excellent in mechanical strength. In addition, since the work of disposing the monitor unit is also performed such that, for example, the monitor unit is adhered to a predetermined position on the flexible substrate, the work can be easily and securely performed. Consequently, the optical pickup unit excellent in operational stability can be provided. Accordingly, the optical disk device is provided that is capable of stably performing light quantity control of laser light and performing a stabilized playback/record process.  
      According to the various embodiments described above, those concerned in the art will be able to implement the invention, and various other modified examples will easily occur to those skilled in the art. Further, it will be possible even for those not having sufficient inventive knowledge and skills to adapt the invention by way of various other embodiments, and the invention may be applied to various embodiments even without having inventive skills. Accordingly, the invention is not limited to the above-described embodiments as it covers a broad range of applications as long as they do not contradict the principles and novel features disclosed herein. For example, while the above-described embodiments are each provided with the front monitor unit for the DVD-dedicated light, the monitor may be disposed such that after DVD-dedicated light (wavelength: close to 650 nm) and CD-dedicated light (wavelength: close to 780 nm) have been synthesized using a DP, and part of the light in contact with an external side of the aperture of the objective lens is incident on a PD.