JP2008047237A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup which can form an appropriate spot on the label surface. <P>SOLUTION: When radiating a light flux to the label surface of an optical disk, a first lens L1 of a beam expander EXP is moved in the direction of the optical axis depending on the SUM signal or FE signal from the light receiving surface PDa-PDd of an optical detector PD. Thus, the light flux can be radiated to the label surface in the optimal spot diameter or in the optimal light intensity, and for example, clearer characters and images can be formed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device capable of forming an image on a label surface of an optical disc.

  In recent years, optical discs such as CDs and DVDs have become widespread as information recording media. The CD includes a reproduction-only CD-ROM, a recordable CD-R, a rewritable CD-RW, and the like. As the DVD, a reproduction-only DVD-ROM, a recordable DVD-R, and a rewritable DVD- There are RAM, DVD-RW, and the like. A recordable optical disk, that is, a recordable or rewritable optical disk has an information recording layer, and the recording capacity of the information recording layer is, for example, about 700 MB for a CD-R and about 4.7 GB for a DVD-R or the like. .

  Particularly in recent optical pickup devices, the reproduction of information recorded on an optical disk and the shortening of the wavelength of a laser light source used as a light source for recording information on the optical disk have progressed, for example, a blue-violet semiconductor laser, Laser light sources with wavelengths of 400 to 420 nm, such as blue SHG lasers that perform wavelength conversion of infrared semiconductor lasers using second harmonics, are being put into practical use. When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used, it is possible to record information of 15 to 20 GB on an optical disk having a diameter of 12 cm. When the NA of the objective lens is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, an optical disk and a magneto-optical disk using a blue-violet laser light source are collectively referred to as a “high density optical disk”.

By the way, a user writes a character, an image, or the like indicating the content on a label surface opposite to the information recording layer side of the optical disc and saves it. On the other hand, an optical disc and an optical pickup device have been developed that can record characters and images desired by a user on a label surface using laser light (see Patent Document 1).
JP 2005-346746 A

  However, according to the optical pickup device disclosed in Patent Document 1, laser light for recording an optical disk is focused on a label surface using an objective lens, and characters and images are formed there. The structure of the optical pickup device can be simplified. However, since a light source, an objective lens, and the like that irradiate laser light are also used for information recording / reproduction, it is not necessarily suitable for forming an image on a label surface. In particular, the diameter of the condensed spot at the time of recording / reproducing in the information pit is about several μm, whereas it is desirable to have a spot diameter of about several tens of μm when characters or images are formed on the label surface. There is a problem of how to perform such focusing control.

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an optical pickup device capable of forming an appropriate spot on a label surface.

The optical pickup device according to claim 1 includes a light source and a condensing optical system including a coupling lens and an objective lens, and transmits a light beam emitted from the light source via the condensing optical system. An optical pickup device that records and / or reproduces information by focusing on an information recording surface of an information recording medium,
A light detector that receives the light beam reflected from the label surface of the optical information recording medium at the light receiving surface and generates an electrical signal;
When irradiating a light beam on the label surface of the optical information recording medium, the coupling lens is displaced to a predetermined position in the optical axis direction different from the position where information is recorded and / or reproduced on the information recording surface. The objective lens is caused to perform a focusing operation in accordance with an electric signal from the light receiving surface.

  According to the present invention, when irradiating the label surface of the optical information recording medium with a light beam, the coupling lens has an optical axis different from a position at which information is recorded and / or reproduced on the information recording surface. Since the objective lens is moved to a predetermined position in the direction and the objective lens is subjected to a focusing operation in accordance with an electric signal from the light receiving surface, it is possible to irradiate the label surface with the optimum spot diameter or the optimum light intensity. And images can be formed. As the “predetermined position”, a position obtained by simulation or experiment can be used, or a position obtained by actually performing test writing on the label surface can be used. As an example of trial writing, first, recording is performed by irradiating laser light with one pulse or multiple pulses while changing the position of the coupling lens and performing a focusing operation on the label surface of the rotating optical disk. Can be considered. After trial writing, the reflectance of the recorded part is measured by monitoring reflected light from the label surface, for example, after one round (or after a plurality of rounds). If the measured length of the recording portion in the circumferential direction is within a predetermined range, it can be determined that the position of the coupling lens at the time of test writing is appropriate. If it is determined to be inappropriate, the trial lens may be written after changing the position of the coupling lens again. Once the optimum coupling lens position is obtained in this way, the optimum label surface recording conditions can be obtained by performing trial writing while sequentially changing the rotation speed and laser emission intensity of the optical disc in the same procedure. Can do.

  According to a second aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the objective lens is caused to perform a focusing operation based on a total amount of electric signals from the photodetector (for example, a SUM signal described later). Features. In addition, if the photodetector for information recording and / or reproduction is also used as the photodetector, the cost of the optical pickup device can be reduced, but a dedicated photodetector may be provided separately.

  According to a third aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the photodetector has a plurality of light receiving surfaces, and a difference between electrical signals from each of the plurality of light receiving surfaces (for example, an FE signal described later) ), The objective lens is subjected to a focusing operation. The difference between the electrical signals from the plurality of light receiving surfaces does not include a tracking push-pull signal or the like.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to any one of the first to third aspects, wherein the optical surface of any one of the optical elements of the condensing optical system is located at a predetermined distance from the optical axis. Is provided with an aperture restriction region for restricting the aperture, and when the light beam is irradiated onto the label surface of the optical information recording medium, the light beam emitted from the objective lens through an optical surface other than the aperture restriction region A spot that forms an image on the label surface is formed by superimposing the light beam that has passed through the aperture limiting region and emitted from the objective lens.

  In an optical pickup device capable of recording and / or reproducing information interchangeably with different optical information recording media, a diffraction structure may be provided in the optical system. In order to overcome the difference in numerical aperture NA when using interchangeably, such a diffractive structure flares a light beam that passes outside the numerical aperture NA (here, the aperture limiting region) when using an optical disc lower than a high-density optical disc, for example. In many cases, it has an aperture limiting function for emitting light. However, when the same objective lens is used to irradiate the label surface with a light beam, if the light beam that has passed through the aperture restriction region can be used to form characters or images on the label surface, the light can be effectively used. It will be.

  That is, according to the present invention, when a light beam is irradiated onto the label surface of the optical information recording medium, the light beam that has passed through an optical surface other than the aperture restriction region and is emitted from the objective lens, and the aperture restriction region are passed. By superimposing the light beam emitted from the objective lens, a spot for forming an image is formed on the label surface, so that the light intensity of the light beam for forming characters and images can be improved. Letters and images can be formed. The aperture restriction region is not limited to the objective lens, and may be provided in any one of the optical elements of the condensing optical system.

  The optical pickup device according to claim 5 is the invention according to any one of claims 1 to 4, wherein the coupling lens performs recording and / or reproduction of information with respect to an optical information recording medium. It has a function of correcting spherical aberration by displacing in the optical axis direction.

  ADVANTAGE OF THE INVENTION According to this invention, the optical pick-up apparatus which can form an appropriate spot on a label surface can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of an optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. Here, the first optical information recording medium is BD, the second optical information recording medium is DVD, and the third optical information recording medium is CD. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 is used for a blue-violet semiconductor laser LD1 (first light source) and a DVD that emits a 408 nm blue-violet laser beam (first beam) when recording / reproducing information on a BD. A red semiconductor laser LD2 (second light source) that emits light and emits a 658 nm laser beam (second beam) when information is recorded / reproduced with respect to the light source packages LDP and CD formed in one package. An infrared semiconductor laser LD3 (third light source) that emits a 785 nm laser beam (third beam) when recording / reproducing information and a photodetector that receives a reflected beam from the information recording surface RL3 of the CD Common detector PD1 for hololasers HL, BD and DVD composed of PD2 (may have a plurality of light receiving parts for BD and DVD), one group structure Single-lens objective lens (objective optical element) OL made of polyolefin plastic, 2-axis actuator AC1, 1-axis actuator AC2, and a single-axis actuator arranged in a common optical path through which the first to third light beams pass in common A beam expander (coupling lens) EXP composed of a first lens L1 and a second lens L2 that can be shifted in the optical axis direction from AC2, a first polarizing beam splitter BS1, a second polarizing beam splitter BS2, λ / 4 wavelength plate QWP, sensor lens SEN for adding astigmatism to the reflected light beam from the information recording surface RL1, the first light beam and the second light beam arranged in the optical path through which the first light beam and the second light beam pass. A first collimator COL1 that converts a light beam into a parallel light beam, and disposed in an optical path through which only the third light beam passes, the third light beam is converted into a parallel light beam. And a second collimator COL2 for conversion into In addition to the blue-violet semiconductor laser LD1 described above, a blue-violet SHG laser can also be used as a light source for BD. The coupling lens through which the first light beam passes, that is, the first collimator COL1, preferably has a diffractive structure having a function of correcting chromatic aberration on the optical surface. The light source package LDP and the holo laser HL constitute a light source. The first collimator COL1, the second collimator COL2, the beam expander EXP, and the objective lens OL constitute a condensing optical system. By displacing the first lens L1 of the beam expander EXP, it is possible to correct spherical aberration when using different optical disks. The coupling lens is not limited to a beam expander, and includes all lenses that change the optical magnification of the emission system from the light source to the information recording surface of the optical disk, such as a collimating lens and a zoom lens.

  As shown in FIG. 2, in the objective lens OL according to the present embodiment, a central region CN including the optical axis on the aspherical optical surface on the light source side, a peripheral region MD disposed around the central region CN, and a periphery thereof Are formed concentrically with the optical axis as the center. Note that a diffractive structure to be described later is formed in the central region CN, the peripheral region MD, and the outermost peripheral region OT.

  When recording / reproducing information with respect to the BD in the optical pickup device PU1, the position of the first lens L1 in the optical axis direction so that the first light beam is emitted from the beam expander EXP in a parallel light beam state. Is adjusted by the single-axis actuator AC2, and the blue-violet semiconductor laser LD1 is caused to emit light. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is reflected by the first polarization beam splitter BS1 and then converted into a parallel light beam by the collimator COL1 as depicted by the solid line in FIG. The diameter is expanded by EXP, passes through the λ / 4 wave plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and enters the objective lens OL in the state of parallel light, and then passes through the protective substrate PL1 of the BD from there. This is a spot formed on the recording surface RL1. A focused spot is formed on the information recording surface RL1 of the BD by the light beam that has passed through the central area CN, the peripheral area MD, the most peripheral area OT, and the optical surface on the optical disc side of the objective lens OL. The objective lens OL is driven for focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective lens OL, the λ / 4 wave plate QWP, the beam expander EXP, and the second polarization beam splitter BS2, and then converted into a converged light beam by the first collimator COL1. Then, after passing through the first polarizing beam splitter BS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD1. And the information recorded on BD can be read using the output signal of photodetector PD1.

  Further, when information is recorded / reproduced with respect to the DVD in the optical pickup device PU1, the optical axis direction of the first lens L1 is emitted so that the second light flux is emitted from the beam expander EXP in the state of a parallel light flux. Is adjusted by the single-axis actuator AC2, and then the red semiconductor laser LD2 is caused to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the first polarization beam splitter BS1 and then converted into a parallel light beam by the collimator COL1, as depicted by the dotted line in FIG. 1, and the beam expander EXP. The diameter of the light beam passes through the λ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and enters the objective lens OL in the state of parallel light, and from there, the information is recorded through the protective substrate PL2 of the DVD. This is a spot formed on the surface RL2. A focused spot, that is, a spot center portion is formed on the information recording surface RL2 of the DVD by the light flux that has passed through the central area CN, the peripheral area MD, and the optical surface on the optical disc side of the objective lens OL. The light flux that has passed through the outermost peripheral region OT is flared to form a spot peripheral portion. The objective lens OL is driven for focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective lens OL, the λ / 4 wave plate QWP, the beam expander EXP, and the second polarizing beam splitter BS2, and then converted into a converged light beam by the first collimator COL1. Then, after passing through the first polarizing beam splitter BS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD1. And the information recorded on DVD can be read using the output signal of photodetector PD1.

  Further, when information is recorded / reproduced with respect to the CD in the optical pickup device PU1, the first lens L1 is set so that the third light beam is emitted from the beam expander EXP in the state of weakly divergent light beam or parallel light beam. After the position in the optical axis direction is adjusted by the uniaxial actuator AC2, the infrared semiconductor laser LD3 is caused to emit light. The divergent light beam emitted from the infrared semiconductor laser LD3 is converted into a parallel light beam by the second collimator COL2, as illustrated in FIG. Thereafter, the light is reflected by the second polarizing beam splitter BS2 and is changed to a weakly divergent light beam by the beam expander EXP, or is expanded in diameter while being a parallel light beam, and then passes through the λ / 4 wavelength plate QWP to reach the objective lens OL. After entering in the state of weak finite diverging light or parallel light, it becomes a spot formed on the information recording surface RL3 from there through the protective substrate PL3 of the CD. A focused spot, that is, a spot center portion is formed on the information recording surface RL3 of the CD by the light beam that has passed through the central region CN of the objective lens OL and the optical surface on the optical disc side. The light flux that has passed through the most peripheral area OT and the peripheral area MD is flared to form a spot peripheral portion. The objective lens OL is driven for focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof.

  The reflected light flux modulated by the information pits on the information recording surface RL3 is again transmitted through the objective lens OL, the λ / 4 wavelength plate QWP, and the beam expander EXP, and then reflected by the second polarization beam splitter BS2, and is reflected by the second collimator COL2. Converted to convergent luminous flux. Then, it converges on the photodetector PD2. And the information recorded on CD can be read using the output signal of photodetector PD2.

  When the first light beam emitted from the blue-violet semiconductor laser LD1 enters the objective optical element OL, the first diffractive structure in the central region CN, the second diffractive structure in the peripheral region MD, and the third diffractive structure in the most peripheral region OT. Can appropriately correct the spherical aberration of the first light flux and appropriately record and / or reproduce information on the BD having the thickness t1 of the protective substrate. Further, when the second light beam emitted from the red semiconductor laser LD2 is incident on the objective lens OL, the first diffractive structure in the central region CN and the second diffractive structure in the peripheral region MD are the thicknesses of the protective substrates of the BD and DVD. The spherical aberration of the second light beam generated due to the difference in thickness and the difference in wavelength between the first light beam and the second light beam is appropriately corrected, and the most peripheral area OT causes the second light beam to flare on the information recording surface of the DVD. Therefore, it is possible to appropriately record and / or reproduce information on a DVD having a protective substrate thickness t2. Further, when the third light beam emitted from the infrared semiconductor laser LD3 is incident on the objective optical element OL, the first diffractive structure in the central region CN is different in the thickness difference between the BD and CD protective substrates and the first light beam. The spherical aberration of the third light beam generated due to the difference between the wavelength of the third light beam and the third light beam is appropriately corrected, and the second diffractive structure of the peripheral region MD and the outermost peripheral region are transferred to the third light beam on the information recording surface of the CD. Due to the flare, information can be recorded and / or reproduced appropriately for a CD having a protective substrate thickness t3. Further, since the first diffraction structure in the central region CN has a good diffraction efficiency of the third light beam used for recording / reproduction, it is possible to obtain a light amount of the third light beam sufficient for recording / reproduction. In addition, the second diffractive structure of the peripheral region MD has a spherochromatism (chromatic spherical aberration) when the wavelength of the first light flux and the second light flux deviates from the reference wavelength due to a laser manufacturing error or the like. ) Or a spherical aberration that occurs with a temperature change when a temperature change occurs.

  FIG. 3 is a diagram schematically showing the light receiving surface of the photodetector PD2 (or PD1). In the photodetector PD2, four square light receiving portions PDa to PDd arranged in a square shape are arranged counterclockwise in this order. Here, the electrical signal output by the light receiving unit PDa according to the amount of light received is A, the electrical signal output by the light receiving unit PDb is B, the electrical signal output by the light receiving unit PDc is output by the C, and the light receiving unit PDd outputs the electrical signal. Let D be the electrical signal.

  Here, the SUM signal obtained by processing the electrical signal of the photodetector PD2 is SUM = A + B + C + D, and the FE signal is also FE = (A + C) − (B + D). FIG. 4 is a graph showing the SUM signal and the FE signal with the signal intensity on the vertical axis and the focusing position on the horizontal axis.

  When recording and / or reproducing information on a CD as described above, the light beam reflected from the information recording surface of the CD passes through the objective lens OL and enters the photodetector PD. As shown in the spot SP1, the optimum focusing position is assumed to be circular and distributed to each of the light receiving portions PDa to PDd by ¼ circle. In such a case, the FE signal is zero.

  On the other hand, in the state where the light receiving portions PDa and PDc are irradiated with a large amount of light flux as in the spot SP2 indicated by the dotted line in FIG. 3, the FE signal becomes FE> 0, and the optimum focusing position is reached. The objective lens OL is driven to be focused so that FE = 0.

  Further, as in the spot SP3 indicated by the one-dot chain line in FIG. 3, when a large amount of light is irradiated on each of the light receiving portions PDb and PDc, the FE signal becomes FE <0, and the FE signal is under the optimum focusing position. The objective lens OL is driven to focus so that FE = 0.

  Next, image formation on the label surface will be described. The problem here is the position at which the optical system should be set when the label surface of the optical disk is set toward the objective lens. When the light beam reflected from the optical disk passes through the objective lens OL and enters the photodetector PD, the inventor does not necessarily have the diameter and light amount of the spot irradiated on the label surface even when the FE signal is zero. I found it not optimal.

  FIGS. 5A to 7A correspond to the reflected light beam from the label surface when the focusing operation of the objective lens is performed in a state where the first lens L1 of the beam expander EXP is set at a predetermined position. It is a graph of a SUM signal and an FE signal. 5 (a) to 7 (a), the vertical axis represents the output signal of the photodetector, the horizontal axis represents the position of the objective lens in the optical axis direction, and the origin is in a state of minimum spherical aberration on the label surface. . 5 (b) to 7 (b) show the state in which the objective lens is displaced relative to the label surface at the position (FP) where the FE signal becomes zero in FIGS. 5 (a) to 7 (a). It is explanatory drawing for demonstrating spot light intensity distribution on a label surface.

  First, at the time of label surface recording, as shown in FIGS. 5A to 7A, when the coupling lens is displaced, the peak value of the SUM signal or the zero point of the FE signal approaches the origin on the graph. But it doesn't overlap. This is because the condensing optical system including the coupling lens and the objective lens is designed optimally for recording and / or reproducing information on the information recording surface of the optical disc.

  On the other hand, for label surface recording, it is not always appropriate to reduce the focused spot to the minimum diameter. This is because if the recorded point is too small, it may not be suitable for forming an image. Therefore, it is necessary to form a focused spot in a defocused state to some extent on the label surface. Therefore, the position at which the objective lens is driven to focus is a problem.

  Therefore, according to the present embodiment, first, the coupling lens is displaced to a predetermined position in the optical axis direction (such as obtained in advance through experiments and simulations). As a result, the focus servo position of the objective lens shifts in a direction in which the aberration of the exit spot of the objective lens is reduced. As a result, compared with the case where the coupling lens is not displaced, the condensing spot on the label surface. As a result, the light utilization efficiency during recording increases. In other words, when the coupling lens is not displaced, the condensing spot on the label surface becomes wide, and the energy density for recording becomes particularly low around the spot, so that the image may be blurred.

  Further, the objective lens is moved to a position where the FE signal becomes zero (distance β from the origin in FIGS. 5A to 7A), or a position where the SUM signal peaks (FIGS. 5A to 7A). To control the focusing drive to a distance α) from the origin. At this time, depending on the position of the coupling lens, various light intensity distributions as shown in FIGS. 5B to 7B can be obtained. However, the optimum light intensity distribution (optimum depending on the characters, symbols, and images to be drawn is used. It is preferable to select the position of the coupling lens so that the diameter of the spot and the amount of light are small. Note that the objective lens may be controlled to be a value using the values α and β (for example, a position of (α + β) / 2).

  When forming an image on the label surface of the optical disc, the optical pickup device PU1 displaces the first lens L1 of the beam expander EXP to the semiconductor laser side as described above, and then uses the label surface of the optical disc as an objective. After setting toward the lens side and adjusting the position of the first lens L1 in the optical axis direction by the uniaxial actuator AC2, the infrared semiconductor laser LD3 is caused to emit light. The divergent light beam emitted from the infrared semiconductor laser LD3 is converted into a parallel light beam by the second collimator COL2, as illustrated in FIG. Thereafter, the light is reflected by the second polarizing beam splitter BS2 and is changed to a weakly divergent light beam by the beam expander EXP, or is expanded in diameter while being a parallel light beam, and then passes through the λ / 4 wavelength plate QWP to reach the objective lens OL. After entering in the state of weak finite divergent light or parallel light, the label surface is irradiated from there and becomes a spot formed on the label surface. In the present embodiment, the light beam that has passed through the peripheral area MD and the most peripheral area OT (here, the aperture restriction area) of the objective lens OL does not become flare light, but the central area CN (here, areas other than the aperture restriction area). ) And superimposed on the light beam that becomes a condensing spot on the label surface, it is possible to form a spot with higher light intensity in addition to the light beam that has passed through the central region CN. A desired image can be formed by repeatedly turning the spot on and off while rotating the optical disk.

  The reflected light beam reflected from the label surface is transmitted again through the objective lens OL, the λ / 4 wavelength plate QWP, the beam expander EXP, and the second polarizing beam splitter BS2, and then converged into a first light beam by the first collimator COL1. After passing through the polarization beam splitter BS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD1. Then, using the SUM signal or the FE signal from the photodetector PD1, the objective lens OL can be focused and tracked to form a clear image.

  For example, the red semiconductor laser LD2 may be used to form an image on the label surface, or when the label surface is formed with a photosensitive layer whose color changes according to the wavelength, the blue-violet semiconductor laser LD1 A cyan component is formed using the light beam, a magenta component is formed using the light beam of the red semiconductor laser LD2, and a yellow component is formed using the infrared semiconductor laser LD3, thereby forming a full-color image on the label surface. You can also

  FIG. 8 is a graph in which the SUM signal and the FE signal are obtained by simulation without displacing the first lens L1 of the beam expander EXP from the position at the time of recording and / or reproducing information with respect to the CD. FIG. 9 shows the spot light PL on the label surface with the focus servo on without displacing the first lens L1 of the beam expander EXP from the position when recording and / or reproducing information on the CD. FIG.

  FIG. 10 shows a simulation of the SUM signal and the FE signal in a state where the first lens L1 of the beam expander EXP is displaced from the position at the time of recording and / or reproducing information to the CD to the 1.5 mm light source side. It is the calculated | required graph. As is clear from the graph of FIG. 8, it can be seen that the peak value of the SUM signal and the zero point of the FE signal have moved to the under side. FIG. 11 shows a state where the first lens L1 of the beam expander EXP is displaced from the position at the time of recording and / or reproducing information on the CD to the 1.5 mm light source side and the focus servo is turned on. It is a simulation figure which shows the spot light PL on a label surface. As apparent from the comparison with FIG. 9, it can be seen that the spot diameter is reduced and the light density is increased.

  In FIG. 12, the SUM signal and the FE signal are obtained by simulation in a state where the first lens L1 of the beam expander EXP is displaced to the 3 mm light source side from the position when recording and / or reproducing information with respect to the CD. It is a graph. 8 and 10, it is clear that the peak value of the SUM signal and the zero point of the FE signal have moved further to the under side. FIG. 13 shows a label surface in a state in which the focus servo is in the state where the first lens L1 of the beam expander EXP is displaced to the 3 mm light source side from the position when recording and / or reproducing information on the CD. It is a simulation figure which shows the upper spot light PL. As apparent from the comparison with FIGS. 9 and 11, it can be seen that the spot diameter is further reduced and the light density is increased. The spots shown in FIGS. 9, 11, and 13 may be appropriately selected according to the photosensitive characteristics of the label surface.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, the present invention may be an optical pickup device compatible with HD DVD / DVD / CD, an optical pickup device compatible with BD / DVD, or an optical pickup device compatible with HD DVD / DVD. There may be.

It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment which can record and / or reproduce | regenerate information appropriately with respect to BD, DVD, and CD which are different optical disks. It is sectional drawing of the objective lens OL concerning this Embodiment. It is a figure which shows typically the light-receiving surface of photodetector PD2 (or PD1). It is a graph which shows a SUM signal and an FE signal, with the signal intensity on the vertical axis and the focusing position on the horizontal axis. The figure which shows the graph (a) of the SUM signal and FE signal corresponding to the reflected light beam from a label surface, and light intensity distribution (b) when the optical axis direction position of the 1st lens L1 of the beam expander EXP is changed. is there. The figure which shows the graph (a) of the SUM signal and FE signal corresponding to the reflected light beam from a label surface, and light intensity distribution (b) when the optical axis direction position of the 1st lens L1 of the beam expander EXP is changed. is there. The figure which shows the graph (a) of the SUM signal and FE signal corresponding to the reflected light beam from a label surface, and light intensity distribution (b) when the optical axis direction position of the 1st lens L1 of the beam expander EXP is changed. is there. It is a simulation figure shown repeatedly. It is the graph which calculated | required the SUM signal and the FE signal by simulation, without displacing the 1st lens L1 of the beam expander EXP from the position at the time of recording and / or reproducing | regenerating information with respect to CD. FIG. 7 is a simulation diagram showing spot light PL on a label surface in a state where a focus servo is turned on without displacing the first lens L1 of the beam expander EXP from a position at the time of recording and / or reproducing information with respect to a CD. is there. A graph in which the SUM signal and the FE signal are obtained by simulation in a state where the first lens L1 of the beam expander EXP is displaced to the 1.5 mm light source side from the position at the time of recording and / or reproducing information on the CD. is there. On the label surface with the focus servo turned on with the first lens L1 of the beam expander EXP displaced from the position at the time of recording and / or reproducing information on the CD to the 1.5 mm light source side It is a simulation figure which shows the spot light PL. It is the graph which calculated | required the SUM signal and the FE signal by simulation in the state which displaced the 1st lens L1 of the beam expander EXP to the 3 mm light source side from the position at the time of recording and / or reproducing | regenerating information with respect to CD. Spot light on the label surface with the focus servo turned on with the first lens L1 of the beam expander EXP displaced from the position for recording and / or reproducing information to the CD to the 3 mm light source side It is a simulation figure which shows PL.

Explanation of symbols

AC1 2-axis actuator AC2 1-axis actuator BS1 1st polarization beam splitter BS2 2nd polarization beam splitter CN Central region COL1 1st collimator COL2 2nd collimator EXP Beam expander FL Flare light HL Holo laser L1 1st lens L2 2nd Lens LD1 Blue-violet semiconductor laser LD2 Red semiconductor laser LD3 Infrared semiconductor laser LDP Light source package MD Peripheral region OL Objective lens OT Most peripheral region PD1 First photodetector PD2 Second photodetectors PDa to PDd Light receiving surface PL Spot light PL1 Protective substrate PL2 Protective substrate PL3 Protective substrate PU1 Optical pickup device QWP λ / 4 wavelength plate RL1 Information recording surface RL2 Information recording surface RL3 Information recording surface SEN Sensor lens

Claims (5)

A light source and a condensing optical system including a coupling lens and an objective lens, and condenses the light beam emitted from the light source on the information recording surface of the optical information recording medium via the condensing optical system. An optical pickup device that records and / or reproduces information,
A light detector that receives the light beam reflected from the label surface of the optical information recording medium at the light receiving surface and generates an electrical signal;
When irradiating a light beam on the label surface of the optical information recording medium, the coupling lens is displaced to a predetermined position in the optical axis direction different from the position where information is recorded and / or reproduced on the information recording surface. And an optical pickup device that causes the objective lens to perform a focusing operation in accordance with an electrical signal from the light receiving surface.   The optical pickup device according to claim 1, wherein the objective lens is caused to perform a focusing operation based on a total amount of electric signals from the photodetector.   2. The optical pickup device according to claim 1, wherein the photodetector has a plurality of light receiving surfaces, and performs the focusing operation of the objective lens based on a difference between electrical signals from the plurality of light receiving surfaces. The optical surface of any one of the optical elements of the condensing optical system is provided with an aperture limiting region for performing aperture limitation at a position away from the optical axis by a predetermined distance,
When the light beam is irradiated onto the label surface of the optical information recording medium, the light beam that has passed through the optical surface other than the aperture restriction region and emitted from the objective lens, and the light beam that has passed through the aperture restriction region and emitted from the objective lens. 4. The optical pickup device according to claim 1, wherein a spot for forming an image is formed on the label surface by superimposing the collected light beam. The said coupling lens has a function which correct | amends spherical aberration by displacing to an optical axis direction, when recording and / or reproducing | regenerating information with respect to an optical information recording medium. 5. The optical pickup device according to any one of 4 above.

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