JP4956325B2 - Optical pickup - Google Patents

Description

  The present invention relates to an optical pickup that irradiates a recording layer of an optical disc with laser light for information recording or information reading.

  Optical pickups used in various optical disk drive devices for reading optical information recorded on an optical disk such as a CD (Compact Disc) and a DVD (Digital Versatile Disc) and writing optical information on the optical disk are generally The laser light emitted from the laser light source is configured to converge on the recording layer of the optical recording medium.

  By the way, the size of each pit recorded on the recording layer of the optical disc is in the wavelength order of the laser beam used for the optical disc in order to maximize the recording density of the optical disc. Therefore, for the imaging performance of the objective lens used in such an optical pickup, it is required that the spherical aberration is well corrected.

  Such spherical aberration occurs when the thickness of the cover layer from the surface of the optical disk to the recording layer (that is, the distance from the disk surface to the recording layer) varies from a predetermined value. Therefore, in an optical disc having a plurality of recording layers in multiple layers, the apparent cover layer thickness from the surface differs for each recording layer, so that the optical pickup performs focusing of the objective lens. When switching the recording layer to be recorded or read out, even if the spherical aberration is corrected for one of the recording layers, the spherical aberration occurs for the other recording layer. An example of such a two-layer recording type optical disc is a Blu-ray disc.

  On the other hand, spherical aberration occurs even when the state of the laser light incident on the objective lens (degree of convergence or divergence) changes. Therefore, in the conventional optical pickup, the collimating lens is moved in accordance with the change in the thickness of the cover layer (apparent) in order to correct the spherical aberration due to the change in the thickness of the cover layer up to the recording layer. Thus, a configuration has been adopted in which the state of the laser light incident on the objective lens is changed, thereby correcting the spherical aberration in each recording layer.

  On the other hand, a feedback control mechanism called APC (Auto Power Control) is generally added to laser equipment to keep the amount of laser light emitted from the laser light source constant regardless of individual differences in the laser light source. Has been. That is, a part of the laser light emitted from the laser light source is separated by a beam splitter, the light amount is measured by the light receiving element, and the power supplied to the laser light source is adjusted so that the measured value matches the target value. The amount of laser light actually emitted from the laser light source is kept constant.

The beam splitter that separates the laser light for APC is arranged between the laser light source and the collimating lens so that the amount of light received by the light receiving element is not affected by the movement of the collimating lens described above. It is common.
JP 2005-327395 A

  However, depending on the effective diameter of the objective lens itself and the shape of the lens frame, there is a limit to the diameter of the light beam that can be incident on the objective lens. Therefore, when the collimating lens moves as described above, the amount of laser light reaching the recording layer of the optical disk changes (when reading information, it is reflected by the recording layer and received by the light receiving element for reading information). The amount of reflected light also changes).

  As described above, since the APC is configured to operate independently of the movement of the collimating lens for correcting the spherical aberration, the laser light emitted from the laser light source regardless of the movement of the collimating lens. It is only controlled to keep the light quantity of the laser beam constant, and it is impossible to correct the decrease in the incident light quantity of the laser beam to the recording layer due to the movement of the collimating lens.

  Therefore, the present invention has been devised in view of the above problems in the conventional optical pickup, and even if the collimator lens is moved for correcting the spherical aberration, the laser beam incident on the recording layer of the optical disc is devised. It is an object to provide a pickup that can keep the amount of light constant.

The present invention employs the following means in order to solve the above problems. In other words, the optical pickup according to the present invention is an optical pickup that irradiates an optical disc with laser light emitted from a laser light source, and the laser light emitted from the laser light source when in a predetermined position. A collimating lens for converting into parallel light; a collimating lens actuator for holding the collimating lens movably from the predetermined position along the optical path of the laser light; and an objective lens for converging the light transmitted through the collimating lens; A beam splitter that is provided between the laser light source and the collimating lens, guides the laser light emitted from the light source toward the objective lens, and separates a part thereof, and is separated by the beam splitter Condensing lens for converging laser light, and laser light condensed by the condensing lens The driving power is supplied to the light receiving element that receives and photoelectrically converts the laser light source, and the driving power is large so that the light amount of the laser light received by the light receiving element matches a predetermined target value. A control circuit that adjusts the height of the laser beam and restricts the beam diameter of the laser light incident on the light receiving element, and in conjunction with the movement of the collimating lens, the collimating lens is closer to the laser light source than the predetermined position. Reduces the beam diameter of the laser beam incident on the light receiving element than when the collimating lens is at the predetermined position, and when the collimating lens is closer to the objective lens than the predetermined position, lens and a diaphragm mechanism for expanding the beam diameter of the laser beam incident on the light receiving element than when in said predetermined position, comprising the And wherein the door.

  According to the present invention configured as described above, when the collimating lens is moved by the collimating lens actuator in order to correct the spherical aberration in accordance with the thickness of the cover layer according to the type of the optical disc, it enters the objective lens. The ratio of the amount of light incident on the optical disc D of the total amount of laser light changes as the beam diameter of the laser beam changes. However, the aperture mechanism operates in conjunction with the movement of the collimating lens, and the beam splitter and collecting The beam diameter of the APC laser beam incident on the light receiving element through the optical lens is changed. As a result, the ratio of the amount of light incident on the light receiving element to the total amount of laser light incident on the collimating lens via the beam splitter changes, and the control device performs feedback control by APC based on the amount of light received by the light receiving element. As a result, the amount of laser light emitted from the laser light source changes. That is, when the collimating lens approaches the laser light source and the ratio of the amount of light incident on the optical disk out of the total amount of laser light decreases, the beam diameter of the laser light incident on the light receiving element is reduced by the aperture mechanism. Therefore, the control circuit increases the power supplied to the laser light source so that the amount of laser light emitted from the laser light source increases. As a result, the amount of decrease in the ratio of the amount of light incident on the optical disc D out of the total amount of laser light is corrected, and the amount of light incident on the optical disc is kept substantially constant. On the other hand, when the ratio of the amount of light incident on the optical disc D out of the total amount of laser light increases as the collimating lens approaches the objective lens, the beam diameter of the laser light incident on the light receiving element is enlarged by the aperture mechanism. Therefore, the control circuit reduces the power supplied to the laser light source so that the amount of laser light emitted from the laser light source is reduced. As a result, the increase in the ratio of the amount of light incident on the optical disk out of the total amount of laser light is corrected, and the amount of light incident on the optical disk is kept substantially constant.

  In the present invention, the diaphragm mechanism only needs to be capable of expanding and reducing the beam diameter of the laser light incident on the light receiving element in conjunction with the movement of the collimating lens. For example, a plurality of diaphragm blades are centered from the outer edge of the laser light. A so-called iris diaphragm that moves evenly toward the center may be linked to the movement of the collimating lens and operated, or it is inserted into the optical path of the laser beam from the side by rotating one diaphragm blade. A slit-like aperture whose width gradually increases from the end close to the collimating lens to the other end is formed in the region intersecting the laser light on the plate that moves integrally with the collimating lens. An aperture plate may be used.

  According to the optical pickup of the present invention configured as described above, the amount of laser light incident on the recording layer of the optical disk can be kept constant even when the collimating lens is moved for spherical aberration correction.

  Embodiments of an optical pickup according to the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of an optical disc drive apparatus according to an embodiment of the present invention. As shown in FIG. 1, this optical disc drive apparatus includes a thin box-shaped casing 1 incorporated in a casing of a personal computer, a video recorder, etc. (not shown), and a tray 2 that can be advanced and retracted from the casing 1. Is made up of. A spindle 3 and a carriage 4 are incorporated in the tray 2. In this embodiment, a Blu-ray disc is loaded in the optical disc drive device as an optical disc.

  In the optical disk drive apparatus shown in FIG. 1, on the upper surface of the tray 2, there is formed a disk mounting portion 2a that is recessed in accordance with the circular outer edge of the optical disk so that the optical disk D can be mounted and rotated. ing. A spindle 3 is embedded in the center of the disk mounting portion 2a. The spindle 3 is rotated by a direct drive motor having a built-in shaft that is inserted into a hole formed in the center of the optical disc D and clamps the tip. As a result, the spindle 3 can rotate the optical disk D.

  The carriage 4 incorporates an optical pickup, and is slidably held by two rails 5 and 6 in a notch 2b formed on the bottom surface of the disk mounting portion 2a. A window 4 d for exposing the objective lens 7 included in the optical pickup is formed in the upper surface of the carriage 4, and a cavity for accommodating the optical pickup is formed inside the carriage 4.

  2 shows an optical configuration of each optical component constituting the optical pickup built in the carriage 4 (however, the illustration of the reflecting member such as a reflecting mirror and the refractive member such as a prism is omitted, and the optical path is linearized. And a block configuration of the control circuit.

  The optical components constituting the optical pickup are a laser light source 8, a beam splitter 9, a collimator lens 10, an objective lens 7, a condenser lens 11, an APC light receiving element 12, a sensor lens 13, and a reproducing light receiving element 14. .

  The laser light source 8 is supplied with driving power from a control block 15 to be described later, so that the laser light in the wavelength band conforming to the standard of the optical disc D held by the clamp 3 with a light amount corresponding to the magnitude of the driving power. ,

  The beam splitter 9 is a prism (polarizing beam splitter) that is disposed in the optical path of laser light emitted as divergent light from the laser light source 8 and has a separation surface 9a inclined by 45 degrees with respect to the optical path. In other words, the separation surface 9 a of the beam splitter 9 reflects a portion of the laser light emitted from the laser light source 8 toward the condenser lens 11 and most of the remaining portion toward the collimator lens 10. To Penetrate. Further, when the reflected light obtained by modulating the laser light incident on the recording layer R of the optical disk D by the information recorded on the recording layer R returns, most of the separation surface 9a faces the sensor lens 13. Reflect.

  The collimating lens 10 is a positive lens that is held by a collimating lens actuator 16 so that its optical axis is directed in the direction toward the light emitting point of the laser light source 8, and emits a beam emitted from the laser light source 8 when in the reference position. The laser light transmitted through the splitter 9 is refracted so as to be converted from divergent light to parallel light. The collimator lens actuator 16 is a known mechanism that moves the collimator lens 10 in the direction of the optical axis in accordance with a control signal from the control block 15. For example, a linear motor is used as the drive source.

  The objective lens 7 is a condensing lens (positive lens) that focuses the laser light transmitted through the collimating lens 10 onto the recording layer R of the optical disc D. The objective lens 7 is a positive plastic single lens made in accordance with the Blu-ray Disc standard, and is directed and held by the objective lens actuator 17 so that its optical axis is coaxial with the collimating lens 10. ing. In response to a control signal from the control block 15, the objective lens actuator 17 moves the objective lens 7 in the optical axis direction (focusing direction) and the tracking direction (radial direction of the optical disc D held by the clamp 3 described above). Each can be moved within a certain range.

  On the other hand, the sensor lens 13 receives reflected light that is reflected by the laser light incident on the optical disc D by the objective lens 7 while being modulated according to the information recorded on the recording layer R of the optical disc D. 7. The light enters through the collimating lens 10 and the separation surface 9a of the beam splitter 9. The sensor lens 13 further converges the reflected light and converges on the light receiving surface of the reproduction signal light receiving element 14.

  As is well known, the light receiving surface of the reproduction signal light receiving element 14 is divided around the optical axis of the sensor lens 13, and detects the amount of reflected light incident on each of the divided areas. In addition, the value of the incident light quantity detected in each area in this way is calculated by a control block 15 to be described later, whereby a reproduction signal indicating information recorded on the recording layer R of the optical disc D, an objective lens The focus signal indicating the deviation between the convergence point of the laser beam converged by 7 and the recording layer R of the optical disc D, and the tracking error signal indicating the deviation between the convergence point and the track on the recording layer R are obtained.

  The condensing lens 11 is disposed so that the optical axis bent at the separation surface 9 a of the beam splitter 9 is coaxial with the optical axis of the collimating lens 10 and penetrates the light emitting point of the laser light source 8. Therefore, the laser light emitted as diverging light from the laser light source 8 and partially reflected by the separation surface 9 a of the beam splitter 9 enters the condenser lens 11. The condensing lens 11 converges the incident laser light and converges on the light receiving surface of the APC light receiving element 12 (corresponding to a light receiving element that receives and photoelectrically converts the laser light condensed by the condensing lens).

  The APC light receiving element 12 sequentially measures the amount of laser light incident on the light receiving surface and notifies the control block 15 of the light. The control block 15 has the APC function described above, and when supplying drive power to the laser light source 8 during recording and reading with respect to the optical disc D, the light quantity (modulation) measured by the APC light receiving element. In this case, the light amount (peak value) of the laser light emitted from the laser light source 8 is kept constant by performing feedback control so that the peak value thereof matches a predetermined target value.

  An aperture plate 19 as an aperture mechanism is inserted on the optical path of the laser light between the condenser lens 11 and the APC light receiving element 12. The aperture plate 19 has a plate-like shape bent in an inverted L shape in the plane of FIG. 2, and the end of the shorter arm is fixed to the edge surface of the collimator lens 10, and the longer arm is The collimating lens 10 extends parallel to the optical axis, and the vicinity of the tip is inserted between the condenser lens 9 and the APC light receiving element 12. Therefore, when the collimating lens 10 is moved by the collimating lens actuator 16, the aperture plate 19 is also moved together. Note that the aperture plate 19 is always located between the condenser lens 11 and the APC light receiving element 12 regardless of where the collimator lens 10 moves within the range of movement by the collimator lens actuator 16. The length of the longer arm of 19 is set.

  It should be noted that the optical path of the laser light is within a range in which the intersection with the optical path of the laser light (the optical axis of the condensing lens 11) relatively moves with the movement of the aperture plate 19 itself on the aperture plate 19. On the other hand, a long hole-shaped aperture 19a that functions as a variable diaphragm is bored with its long axis direction parallel to the moving direction of the aperture plate 19 itself (the optical axis direction of the collimating lens 10). As shown in FIG. 3, the width of the aperture 19 is formed so as to be wider on the side far from the collimator lens 10 and narrower as it approaches the collimator lens 10.

  That is, when the collimator lens 10 approaches the objective lens 7 as shown in FIG. 4, the laser light emitted from the collimator lens 10 and incident on the objective lens 7 becomes convergent light. Accordingly, since the beam diameter when entering the objective lens 7 is reduced, the amount of vignetting caused by the limit of the effective diameter of the objective lens actuator 17 and the objective lens 7 itself is reduced. The ratio of the amount of light incident on the optical disc D to the amount of light increases. Therefore, in this case, in order to suppress the light amount of the laser light incident on the optical disc D to be a constant value, it is necessary to reduce the light amount of the laser light emitted from the laser light source 8 itself. For this purpose, the apparent light quantity measured by the APC light receiving element 12 may be increased. Therefore, in order to enlarge the beam diameter of the laser light incident on the APC light receiving element 12, the optical path of the laser light in the state in the aperture 19a The width of the intersecting portion (that is, the end on the side away from the collimator lens 10) is wide (see FIG. 5).

  On the other hand, as shown in FIG. 6, when the collimator lens 10 approaches the laser light source 8, the laser light emitted from the collimator lens 10 and incident on the objective lens 7 becomes divergent light. Therefore, since the beam diameter when entering the objective lens 7 becomes large, the luminous flux vignetted increases due to the limit of the effective diameter of the objective lens actuator 17 and the objective lens 7 itself, so that the laser beam emitted from the collimating lens 10 is increased. The ratio of the amount of light incident on the optical disc D to the amount of light becomes small. Therefore, in this case, in order to make the amount of laser light incident on the optical disk D constant, it is necessary to increase the amount of laser light emitted from the laser light source 8 itself. For this purpose, the apparent light quantity measured by the APC light receiving element 12 only needs to be reduced. Therefore, in order to reduce the beam diameter of the laser light incident on the APC light receiving element 12, the optical path of the laser light in the state in the aperture 19a The width of the intersecting portion (that is, the end close to the collimator lens 10) is narrow (see FIG. 7).

  Next, the control block 15 described above is further connected to a disk type determination unit 18. The disc type discriminating unit 18 detects whether the recording layer R of the optical disc D held by the clamp 3 is a single layer by detecting a difference for each disc format such as the reflectivity of the disc surface of the optical disc D. Determine if it is a layer. Then, the control block 15 is notified of the determined number of layers of the optical disc D. The control block 15 receives a write signal (a signal modulated by information to be recorded on the recording layer R of the optical disc D) from the outside through an interface circuit (not shown).

  The control block 15 sends the number of recording layers R of the optical disc D notified from the disc type discriminating unit 18 (and, if there are a plurality of recording layers, a recording layer R switching command from a processor (not shown)). ), In order to move the objective lens 7 to a position suitable for the position of the recording layer of the optical disk D held by the clamp 3, a control signal is supplied to the objective lens actuator 17, and the protective layer of the optical disk D is A control signal is supplied to the collimating lens actuator 16 in order to move the collimating lens 10 to a position where the spherical aberration due to the thickness can be corrected. For example, when the recording layer R of the optical disc D is a single layer or a plurality of layers but the recording layer R to be recorded or read is a shallow layer, in order to make convergent light enter the objective lens 7, The control block 15 brings the collimator lens 10 closer to the objective lens 7. On the other hand, when the recording layer of the optical disc D is a plurality of layers and the recording layer R to be recorded or read is a deep layer, the control block 15 includes a collimator so that parallel light or divergent light is incident on the objective lens 7. The lens 10 is brought closer to the laser light source 8.

  As a result, as described above, the aperture plate 19 moves in accordance with the movement of the collimating lens 10, and the laser incident on the APC light receiving element 12 according to the degree of divergence or convergence of the laser light incident on the objective lens 7. The beam diameter of light changes. In this state, the control block 15 supplies drive power to the laser light source 8 while performing feedback control by APC. That is, at the time of recording, the control block 15 controls the power supplied to the laser light source 8 based on the recording signal while controlling the peak value of the light amount detected by the APC light receiving element 12 to coincide with a predetermined target value. Modulate. As a result, a laser beam having a constant peak value is incident on the recording layer R of the optical disc D, and information is recorded on the recording layer of the optical disc D according to the disc format of the optical disc D held by the clamp 3. Recorded in R. At the time of reading, the control block 15 causes the laser light source 8 to emit a constant amount of laser light while controlling the peak value of the amount of light detected by the APC light receiving element 12 to match a predetermined target value. . As a result, a laser beam having a certain intensity is incident on the recording layer R of the optical disc D, and the reflected light modulated according to the information recorded on the recording layer R is received by the reproducing light receiving element 14. Photoelectrically converted and input to the control block 15. As described above, the control unit block 15 generates a focusing error signal and a tracking error signal based on the signal input by the reproducing light receiving element 14, supplies the focusing error signal and the tracking error signal to the objective lens actuator 17, and generates a reproduction signal. , Output from an interface circuit (not shown) to the outside.

  As described above, according to the present embodiment, the collimator lens 10 is moved so as to correct the spherical aberration in accordance with the thickness of the protective layer of the optical disk D held by the clamp 3 and is incident on the objective lens 7. Even if the degree of light divergence or convergence is changed, the aperture plate 19 moves integrally with the collimator lens 10, so that the beam diameter of the APC laser light incident on the APC light receiving element 12 (that is, the collimator lens 10). The ratio of the amount of light detected by the APC light-receiving element 12 to the amount of laser light incident on the laser beam changes, and as a result, the amount of laser light itself emitted from the laser light source 8 changes. Thus, the amount of laser light incident on the recording layer R of the optical disc D is kept constant.

1 is an overall perspective view of an optical disk drive device according to Embodiment 1 of the present invention. The figure which shows the optical structure of the optical component which comprises an optical pick-up, and a circuit block Front view of the aperture plate in FIG. The figure which shows the state which the collimating lens approached the objective lens rather than the state of FIG. The figure which shows the state which the collimating lens approached the objective lens rather than the state of FIG. The figure which shows the state which the collimating lens approached the laser light source rather than the state of FIG. The figure which shows the state which the collimating lens approached the laser light source rather than the state of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 7 Objective lens 8 Laser light source 9 Beam splitter 10 Collimating lens 11 Condensing lens 12 Light receiving element for APC 15 Control block 16 Collimating lens actuator 19 Aperture plate 19a Aperture D Optical disc

Claims (2)

An optical pickup that irradiates an optical disc with laser light emitted from a laser light source,
The laser light source;
A collimating lens that converts laser light emitted from the laser light source into parallel light when in a predetermined position;
A collimating lens actuator that holds the collimating lens movably from the predetermined position along the optical path of the laser beam;
An objective lens for converging light transmitted through the collimator lens;
A beam splitter that is provided between the laser light source and the collimating lens, guides the laser light emitted from the light source toward the objective lens, and separates a part thereof;
A condenser lens for converging the laser beam separated by the beam splitter;
A light receiving element that receives and photoelectrically converts the laser light collected by the condenser lens;
A control circuit that supplies driving power to the laser light source and adjusts the magnitude of the driving power so that the amount of laser light received by the light receiving element matches a predetermined target value;
Thereby limiting the diameter of the laser beam incident on the light receiving element, in conjunction with movement of the collimating lens, when the collimating lens is close to the laser light source than the predetermined position, the collimating lens is the prescribed When the beam diameter of the laser beam incident on the light receiving element is reduced as compared to when the collimating lens is closer to the objective lens than the predetermined position, the collimating lens is located at the predetermined position. And an aperture mechanism for enlarging the beam diameter of the laser light incident on the light receiving element.   The diaphragm mechanism is a plate that moves integrally with the collimator, and the width of the plate that is close to the collimating lens is narrow in the region of the plate that intersects the laser light as the plate moves, and is close to the laser light source. 2. The optical pickup according to claim 1, wherein a slit-like aperture having a wide side is formed.