JP3831689B2 - Optical pickup device and optical reproducing device including the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a plurality of types of optical recording, such as CD (compact disc) and DVD (digital versatile disc), which have different protective layer thicknesses and different information recording densities and different laser light wavelengths for reproduction. An optical system that uses a light source module in which two laser light emitting parts for a short wavelength and a long wavelength are incorporated in one package for a signal recorded on a medium (optical disk) and includes an objective lens for each wavelength. TECHNICAL FIELD The present invention relates to an optical pickup device that can be reproduced by using an optical pickup device, and an optical reproduction device including the same.
[0002]
[Prior art]
Japanese Patent Application Laid-Open No. 2000-207766 discloses a plurality of light sources having different wavelengths and a plurality of light receiving part patterns for individually receiving each return light emitted from the plurality of light sources and reflected by the optical recording medium. An optical pickup device including a photodetector formed in the above and an optical system sharing an optical path from a plurality of light sources to the photodetector, and an optical reproducing device including the same are described.
[0003]
In the above publication, by forming a plurality of light receiving part patterns on the same substrate, each light receiving part pattern has a high relative positional accuracy, so that it is emitted from a plurality of light sources having different wavelengths and is recorded on an optical recording medium. It is described that each return light reflected by the light can be guided to the light receiving part pattern with high accuracy, and high quality reproduction signals and recording signals can be obtained for different types of optical recording media. ing. Further, the above publication describes that if a plurality of light sources are formed on the same semiconductor substrate, the intervals between the light sources can be positioned with high accuracy.
[0004]
Japanese Patent Laid-Open No. 2000-81566 discloses an optical head with high light utilization efficiency that enables recording and reproduction of a plurality of types of optical recording media having different protective layers such as DVD and CD-R with a single objective lens. An objective lens is described. This objective lens is a resin single lens whose both surfaces are aspherical, and a diffractive lens structure is formed on one lens surface as a ring-shaped pattern with the optical axis as the center. The diffractive lens structure has wavelength dependency so that diffracted light of the same order by light beams of at least two different wavelengths forms a good wavefront for at least two types of optical discs having different protective layer thicknesses. Yes.
[0005]
For example, by using a two-wavelength semiconductor laser in which two light sources are formed on the same semiconductor substrate, the interval between the light sources can be maintained with high accuracy. Further, by using a light receiving element (photodiode integrated circuit: PD-IC) in which two light receiving portions (light receiving portion patterns) corresponding to each light source are formed on the same semiconductor substrate, the interval between the light receiving portions can be reduced. High accuracy can be maintained. Furthermore, by using the objective lens described in the above publication, spherical aberration and the like can be removed for each of the optical recording media having different protective layer thicknesses.
[0006]
[Problems to be solved by the invention]
Therefore, for example, signals recorded on a plurality of types of optical recording media having different protective layer thicknesses and different information recording densities, such as CD and DVD, and different wavelengths of laser light used for recording and reproduction can be reproduced stably and satisfactorily. It is desired to put an optical pickup device that can be used into practical use at a low manufacturing cost. In addition, a light source module in which two laser light emitting portions having different wavelengths are incorporated into one package is used, and recording is performed on a plurality of types of optical recording media using an optical system common to each wavelength including an objective lens. It is desired to put an optical pickup device that can reproduce signals stably and satisfactorily into practical use at a low manufacturing cost.
[0007]
However, when a common optical system is used for each wavelength including the objective lens, only one of the two light emitting units having different wavelengths can be arranged on the optical axis. That is, the other light emitting unit is disposed outside the optical axis. For this reason, the problem that either one aberration will become large arises. Further, the objective lens can be formed so as to remove the coma aberration with respect to one of the two types of optical recording media. However, in order to remove the coma aberration for both optical recording media, it is necessary to switch between two objective lenses formed to remove the coma aberration for either one of the optical recording media. is there. For this reason, the mechanism of an optical pick-up apparatus becomes complicated, and the problem that manufacturing cost will increase arises.
[0008]
An object of the present invention is to provide an optical pickup that can stably and satisfactorily reproduce signals recorded on a plurality of types of optical recording media having different protective layer thicknesses and information recording densities and different wavelengths of laser light used for reproduction. The present invention is to provide an apparatus and an optical regenerator provided with the apparatus at a low manufacturing cost.
[0009]
[Means for Solving the Problems]
The above-described object includes: first and second light emitting units that emit two lights having different wavelengths; a collimator lens that shapes light from the first and second light emitting units into parallel light bundles; and the collimator lens. An objective lens that condenses the light on either the first or the second optical recording medium and the reflected light from either the first or the second optical recording medium, and the intensity of the reflected light An optical pickup device having a light receiving unit for converting into an electrical signal corresponding to the first light emitting unit, wherein the second light emitting unit is disposed in the vicinity of a focal point of the collimator lens, and the objective lens is disposed from the first light emitting unit. This is achieved by an optical pickup device characterized by substantially satisfying the sine condition for the light of
[0010]
In the optical pickup device of the present invention, the light emitted from the first and second light emitting units is a divergent light beam.
[0011]
In the optical pickup device of the present invention, the objective lens is characterized in that a working distance in the first optical recording medium is different from a working distance in the second optical recording medium.
[0012]
In the optical pickup device of the present invention, the second light emitting unit is disposed at a position offset from the vicinity of the focal point of the collimator lens by a predetermined offset amount corresponding to the posture characteristic of the objective lens. Features.
[0013]
In the optical pickup device of the present invention, the first and second light emitting units are attached so that their positions can be adjusted in a plane substantially perpendicular to the optical axis of the collimator lens.
[0014]
In the optical pickup device of the present invention, the first optical recording medium is one of a DVD system or a CD system, and the second optical recording medium is the other of the DVD system or the CD system. .
[0015]
The above-mentioned object is achieved by an optical reproducing apparatus comprising the optical pickup device of the present invention.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
An optical pickup device and an optical reproducing device according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic structural diagram of an optical pickup device according to the present embodiment. The optical pickup device 10 according to the present embodiment can cope with different types of optical recording media such as various digital versatile discs (DVD-ROM, DVD-RAM, etc.) 1a and compact disc (CD, etc.) 1b. It has become. The optical pickup device 10 includes a two-wavelength semiconductor laser (laser diode: LD) 11, a phase difference plate 12, diffraction gratings 13a and 13b arranged in this order from the two-wavelength semiconductor laser 11 side, a beam splitter 14, and a collimator lens. 15, a rising mirror (not shown), an objective lens 16, a sensor lens 17, and a photodetector (PD-IC: photodiode integrated circuit) 18.
[0017]
The two-wavelength semiconductor laser 11 includes a first light emitting unit that generates a first laser beam having a relatively short wavelength and a second light emitting unit that generates a second laser beam having a relatively long wavelength. A two-wavelength laser light source incorporated in one package is configured. The two-wavelength laser light source can generate a laser beam with a wavelength of 655 nm for DVD reproduction and a laser beam with a wavelength of 785 nm for CD reproduction. The optical output of the two-wavelength semiconductor laser 11 is a reproduction class (for example, 5 mW). In the two-wavelength semiconductor laser 11, a semiconductor substrate (semiconductor laser body) is sealed in a metal case or the like (case), and each laser beam is emitted from a laser window provided in the case. . The light output amount of the two-wavelength semiconductor laser 11 is detected by a back monitor (not shown), and the light output amount is automatically controlled (APC: automatic power control) by feedback control of the power supplied to the semiconductor laser. Yes.
[0018]
FIG. 2 is a diagram showing a schematic structure of the two-wavelength semiconductor laser 11 constituting the light source and a radiation characteristic of the laser beam. FIG. 2A is a perspective view showing a schematic structure of the two-wavelength semiconductor laser, and FIG. ) Is an explanatory diagram showing the radiation characteristics of the two-wavelength semiconductor laser, and FIG. 2C is a graph showing the full width at half maximum of the radiation characteristics of the light beam. 2 (a) and 2 (b) show only the main body of the semiconductor laser, excluding the housing for sealing the semiconductor substrate. In the semiconductor laser 11, for example, a waveguide for wavelength 655 nm (first waveguide) 11b and a waveguide for wavelength 785 nm (second waveguide) 11c are formed on a semiconductor substrate 11a made of gallium arsenide (GaAs) at a predetermined interval ( For example, the end portion of each waveguide is the light emitting points 11d and 11e. Laser light with a wavelength of 655 nm is emitted from the first light emission point (DVD light emission point) 11d, and laser light with a wavelength of 785 nm is emitted from the second light emission point (CD light emission point) 11e. A symbol LA is an interval between the light emitting points 11d and 11e of the two light sources. In the present embodiment, the distance LA between the light emitting points 11d and 11e of the two light sources is 110 μm. Since the semiconductor laser 11 is manufactured by a photolithography process, the interval LA is formed with high accuracy and manufacturing errors are small.
[0019]
The housing of the semiconductor laser 11 can be adjusted in position so that the light emitting points 11e and 11f move in a plane perpendicular to the optical axis after being attached to the optical pickup device. FIG. 3 shows the arrangement of the light emitting points 11 d and 11 e and the collimator lens 15. In FIG. 3, the phase difference plate 12, the diffraction gratings 13a and 13b, and the beam splitter 14 are not shown. As shown in FIG. 3, the light emitting point 11 e is disposed near the focal point (optical axis) of the collimator lens 15. Here, “arranged in the vicinity of the focal point” means that the light emitting point 11e is closer to the focal point than the light emitting point 11d. The light emitting point 11d is disposed on a virtual plane 70 including the focal point of the collimator lens 15 and perpendicular to the optical axis (view angle ψ ≠ 0 °). Since the position of the semiconductor laser 11 can be adjusted after the housing of the semiconductor laser 11 is attached to the optical pickup device, the light emitting points 11d and 11e can be easily arranged at the optimum positions.
[0020]
Laser light emitted from each of the light emitting points 11d and 11e is emitted from the laser window formed in the housing (not shown) to the outside of the housing. The two-wavelength semiconductor laser 11 oscillates a laser beam having a wavelength of 655 nm (for DVD) in a self-excited oscillation mode, and oscillates a laser beam having a wavelength of 785 nm (for CD) in a gain guide type multimode. The two-wavelength semiconductor laser 11 may oscillate laser light of each wavelength in a single mode.
[0021]
As shown in FIG. 2B, the full width at half maximum θ1 of the radiation characteristic of the laser beam with the wavelength of 655 nm emitted from the first light emitting point 11d is the laser with the wavelength of 785 nm emitted from the second light emitting point 11e. The full width at half maximum θ2 of the radiation characteristic of the light beam is made larger. Here, the full width at half maximum angle θ (θ1, θ2) of the radiation characteristic is an angle range in which the light intensity is ½ of the maximum value Imax, as shown in FIG. In the present embodiment, the full width at half maximum θ1 of the radiation characteristic of the laser beam with the wavelength of 655 nm is set to 30 degrees to 35 degrees, and the full width at half maximum θ2 of the radiation characteristic of the laser beam with the wavelength of 785 nm is set to about 25 degrees. is doing.
[0022]
The retardation plate 12 shown in FIG. 1 is a quarter wavelength plate. The phase difference plate 12 converts the linearly polarized light beam into circularly polarized light. In general, circularly polarized light is desirable for high-speed playback of DVDs. In the present embodiment, a retardation plate 12 in which a functional film is attached to a thin glass plate is used. The phase difference plate 12 is installed such that the optical axis is inclined by 45 degrees with respect to the polarization plane of linearly polarized light.
[0023]
In the diffraction grating 13a, for example, a grating surface for DVD is formed on the surface on the semiconductor laser 11 side, and in the diffraction grating 13b, a grating surface for CD is formed on the surface on the beam splitter 14 side. The divided light quantity ratio in the diffraction gratings 13a and 13b is, for example, 1 (+ 1st order light): 6 (0th order light): 1 (-1st order light) for both DVD / CD. The grating pitch is, for example, 21.2 μm on the DVD side and 31.0 μm on the CD side. The DVD grating surface is given wavelength selectivity so that it is not diffracted at the CD wavelength (785 nm), and the CD grating surface is not diffracted at the DVD wavelength (655 nm). This exclusive action (wavelength selectivity) is realized by making the groove depth deeper than that of a normal diffraction grating and making the grating shape with the duty ratio of the grating interval shifted from 0.5.
[0024]
The beam splitter 14 reflects the light beam from the semiconductor laser 11 side toward the optical recording medium, and transmits the reflected light from the optical recording medium to the photodetector 18 side, and has a so-called half mirror function. is doing. FIG. 1 illustrates a cube-shaped beam splitter 14.
[0025]
The collimator lens 15 converts a divergent light beam from the semiconductor laser 11 as a light source into a parallel light beam and guides it to the objective lens 16, and converts the parallel light beam from the objective lens 16 into a focused light beam to detect the light. 18 leads to. In the present embodiment, a collimator lens is used which is a plastic injection molded product and both surfaces are aspherical.
[0026]
The raising mirror (not shown) reflects the parallel light beam from the collimator lens 15 toward the objective lens 16 and reflects the parallel light beam from the objective lens 16 toward the collimator lens 15. In this embodiment, a planar mirror is used as the rising mirror. The bending angle (reflection angle) is 90 degrees.
[0027]
4A and 4B are structural diagrams of the objective lens, in which FIG. 4A shows a front view and FIG. 4B shows a side view. FIG. 4 (c) shows a partially enlarged view of FIG. 4 (b). In FIG. 4B, the side surfaces of the respective disks (optical recording media) 1a and 1b are also shown. In FIG. 4B, the symbol Ka is the information recording surface of the DVD, and the symbol Kb is the information recording surface of the CD. The symbol ta represents the thickness of the DVD (ta = 0.6 mm), and the symbol tb represents the thickness of the CD (tb = 1.2 mm).
[0028]
The objective lens 16 includes an objective lens having a positive power lens and a concentric ring-shaped hologram for condensing the first or second laser light on the information recording surface of the optical recording medium to form a reading spot. It is composed.
[0029]
In the optical pickup device 10 according to the present embodiment, a double focus diffractive objective lens is used as the objective lens 16. The objective lens (double focus diffraction objective lens) 16 is manufactured by injection molding of an optical plastic material. As shown in FIG. 4B, both sides of the objective lens 16 are aspheric. As shown in FIG. 4A, a large number of concentric annular zone 16c holographic diffraction gratings (holograms) are formed on the lens surface having a large curvature (on the rising mirror side, that is, on the side opposite to the optical recording medium). Has been. As shown in FIG. 4C, the concentric ring zone is formed in a sawtooth cross-sectional shape, thereby improving the diffraction efficiency. As shown in FIG. 4A, the central area of the objective lens 16 is a CD / DVD combined area 16a, and the outer peripheral area is a DVD dedicated area 16b. The objective lens 16 focuses the light beam for DVD (wavelength 655 nm) on the information recording surface Ka of the DVD 1a and the light beam for CD (wavelength 785 nm) on the information recording surface Kb of the CD 1b.
[0030]
The objective lens 16 is formed so as to satisfy the sine condition with respect to the DVD light beam. FIG. 5 is an explanatory diagram of the sine condition. As shown in FIG. 5, an object point O (light source) is arranged on one side of the convex lens 72 on the optical axis. Light rays emitted from the object point O are transmitted through the convex lens 72 to form an image point O ′. If the distance between the object point O and the lens 72 is a, and the distance between the convex lens 72 and the image point O ′ is b, the image magnification β1 = b / a. Here, the angle between the light axis diverging from the object point O and the optical axis of the convex lens 72 is u1, and the angle between the light axis focused on the image point O ′ is u2. The sine condition violation amount Sc at this time is Sc = (sin (u1)) / (sin (u2)) − β1. If the sine condition is satisfied, the sine condition violation amount Sc of all the light beams emitted from the object point O and transmitted through the convex lens 72 becomes zero. Further, if the sine condition is satisfied, the aberration (axis) of the light beam that diverges from the off-axis object point O1 (off-axis object point) and converges at the off-axis image point O1 ′ (off-axis image point). (External aberration) is minimized.
[0031]
Each disk (optical recording medium) 1a, 1b protects the information recording surfaces Ka, Kb with a protective layer made of polycarbonate or the like. The thickness of the protective layer (which roughly corresponds to the thickness of the optical recording medium) varies depending on the type of optical recording medium. Since the spherical aberration of incident light changes depending on the thickness of the protective layer, the amount of spherical aberration varies depending on the type of optical recording medium. Therefore, by using the double focus diffractive objective lens 16, the difference in spherical aberration due to the type of optical recording medium is corrected.
[0032]
The objective lens 16 is held on an actuator assembly (actuator assembly) 80 so as to be movable in the focus direction and the tracking direction (radial direction of the optical recording medium). FIG. 6 is a structural diagram of the actuator assembly 80. As shown in FIG. 6, the actuator assembly 80 includes a frame 83, a holder 81 that holds the objective lens 16, and a wire 82 that holds the holder 81 movably with respect to the frame 83. Focus servo control and tracking servo control are performed by a combination of a magnetic circuit (not shown) and a drive coil to control the position of the objective lens 16 so that the spot of the light beam can follow the reading point on the optical recording medium. It has become.
[0033]
FIG. 7 is a diagram showing a working distance between the objective lens and the optical recording medium, and FIG. 7A shows an optical recording medium (DVD) 1a reproduced using a laser beam having a short wavelength and the objective lens 16. FIG. 7B shows the working distance D2 between the optical recording medium (CD) 1b to be reproduced using a laser beam having a long wavelength and the objective lens 16. FIG.
[0034]
In the optical pickup device 10 according to the present embodiment, when the first optical recording medium (DVD) 1a is reproduced using the first laser beam having a relatively short wavelength, the protective layer is thin and the information recording density is high. A second optical recording medium having a thick protective layer and a low information recording density using a second laser beam having a relatively long wavelength for the distance (working distance) D1 between the objective lens 16 and the first optical recording medium 1a. The distance (working distance) D2 between the objective lens 16 and the second optical recording medium 1b when reproducing the medium (CD) 1b is set longer. The working distances D1 and D2 are distances (intervals) from the top surface of the objective lens 16 on the optical recording medium side to the surface facing the objective lens 16 of the optical recording medium.
[0035]
Therefore, the holder 81 in FIG. 6 moves in the direction of the double arrow shown in FIG. 6 so that a predetermined working distance can be obtained according to the type of the optical recording medium 1a, 1b to be reproduced. At this time, since one end side of the wire 82 is fixed to the frame 83, the objective lens 16 '' when reproducing the CD 1b is connected to one end side of the wire 82 with respect to the objective lens 16 'when reproducing the DVD 1a. Lower and tilt. For this reason, as shown in FIG. 3, the light emitting point 11e for CD has a predetermined offset amount from the focal point of the collimator lens 15 corresponding to the tilted state (posture characteristic) of the objective lenses 16 ′ and 16 ″. It can be placed at an offset position.
[0036]
7 shows an example in which the optical recording media 1a and 1b are arranged so that the distances between the information recording surfaces of the optical recording media 1a and 1b and the objective lens 16 are equal. FIG. As shown, the optical recording media 1a and 1b may be arranged such that the distance between the information recording surface and the objective lens 16 is different for each of the optical recording media 1a and 1b.
[0037]
Returning to FIG. 1, the sensor lens 17 is an important member in the optical pickup device 10 according to this embodiment, and the sensor lens 17 implements the following five functions. First, the sensor lens 17 is adjusted (conjugate adjustment) so that the light source (object point) and the light receiving portions (image points) 18a and 18b of the photodetector 18 are substantially conjugate to adjust the focus offset. Do. Second, astigmatism is imparted to the light beam (reading light) for focus detection by the astigmatism method. Third, inconvenient astigmatism generated in the beam splitter 14 is removed. Fourth, the spot on the photodetector 18 is enlarged, the position adjustment accuracy of the photodetector 18 is relaxed to about ± 5 μm, and the position adjustment of the photodetector 18 is facilitated. Fifth, inconvenient coma aberration generated in the beam splitter 14 is removed. By removing inconvenient coma aberration, the quality of the DVD-RAM playback signal can be improved.
[0038]
FIG. 8 shows an example of the structure of the sensor lens 17. FIG. 8 (a) is a front view, FIG. 8 (b) is one side sectional view, FIG. 8 (c) is the other side sectional view, and FIG. ) Is a cross-sectional view taken along line AA ′ of FIG. 8A, and FIG. 8E is a cross-sectional view taken along line BB ′ of FIG. 8A. The sensor lens 17 has the following configuration in order to realize the various functions described above. As shown in FIG. 8B, the surface of the sensor lens 17 on the beam splitter 14 side is a concave lens 17b to reduce the NA (lens numerical aperture) on the photodetector 18 side to facilitate conjugate adjustment. Yes.
[0039]
The surface of the sensor lens 17 on the side of the photodetector 18 is a cylindrical concave lens 17a. The cylindrical concave lens 17a functions as an astigmatism generating element. The direction of the cylindrical surface of the cylindrical concave lens 17a takes into account the direction of astigmatism necessary for the astigmatism method and the direction of astigmatism necessary for astigmatism correction when the beam splitter 14 has a parallel plate shape. Determined.
[0040]
The sensor lens 17 is made of optical plastic by injection molding, and the position adjustment pin hole 17c and the position adjustment guide are also integrally molded.
[0041]
In general, coma aberration occurs when a transparent parallel plate, a lens, or the like is disposed obliquely with respect to the optical axis in the optical path of the convergent beam. If there is coma, the push-pull balance will be lost when the signal is reproduced by the push-pull method described later. Therefore, as shown in FIG. 8E, the coma aberration is removed by inclining the lens surface of the sensor lens 17 with respect to the optical axis so as to cancel the generated coma aberration.
[0042]
As shown in FIG. 1, a photodetector (PD-IC) 18 including a light receiving element includes a light receiving portion 18a for reflected light (for DVD) from a DVD 1a and a light receiving portion 18b for reflected light from a CD 1b (for CD). With. Reference sign LB in the figure is the interval between the light receiving portions 18a and 18b. The interval LB between the light receiving portions 18a and 18b is set wider than the interval LA between the light emitting points 11d and 11e. More specifically, the interval LB between the light receiving portions 18a and 18b is set to about 1.1 to 1.6 times the interval LA between the light emitting points 11d and 11e. That is, β = 1.1 to 1.6 in the relationship LA = (1 / β) · LB.
[0043]
The photodetector (PD-IC) 18 receives a main beam and a sub beam and converts them into current signals corresponding to the main beam and the sub beam, respectively, and a light receiving unit (PD: a photodiode unit or a photo detector unit). A calculation unit (IC unit) that generates and outputs various signals (reproduction signal (RF signal), focus error signal, tracking error signal, etc.) by converting a current signal generated in the unit into a voltage signal and performing a predetermined calculation; have. In the present embodiment, the light receiving unit and the calculation unit (IC unit) are configured by a monolithic IC, and the monolithic IC is enclosed in, for example, a 14-pin COB (chip-on-board) package.
[0044]
FIG. 9 is a diagram showing a light receiving element pattern configuration of the light receiving portion of the photodetector. The photodetector (PD-IC) 18 includes a DVD light receiving portion 18a and a CD light receiving portion 18b. The symbol LB in FIG. 9 is the distance between the center point of the DVD light receiving portion 18a and the center point of the CD light receiving portion 18b. In the present embodiment, the interval LB is 152 μm. Therefore, the distance LB (152 μm) between the light receiving parts is about 1.38 times the distance LA (110 μm) between the light emitting points. In other words, β = 1.38 in the relationship LA = (1 / β) · LB.
[0045]
The DVD light receiving portion 18a includes a main beam light receiving element pattern portion 18a1, a first sub beam light receiving element pattern portion 18a2, and a second sub beam light receiving element pattern portion 18a3. The main beam light receiving element pattern portion 18a1 has four main beam light receiving element patterns a, b, c, and d that are divided into four in a square shape.
[0046]
The first sub beam light receiving element pattern portion 18a2 of the DVD light receiving portion 18a has four sub beam light receiving element patterns e1, e2, e3, and e4 divided into four in a square shape. The first sub-beam light receiving element pattern portion 18a2 is arranged slightly shifted in the left direction in the drawing with respect to the main beam light receiving element pattern portion 18a1. The second sub-beam light receiving element pattern portion 18a3 has four sub-beam light receiving element patterns f1, f2, f3, and f4 divided into four in a square shape. The second sub-beam light receiving element pattern portion 18a3 is arranged slightly shifted in the right direction in the drawing with respect to the main beam light receiving element pattern portion 18a1. In the present embodiment, the division interval of each light receiving element pattern in each light receiving element pattern portion is about 4 μm.
[0047]
Further, the main beam light receiving element pattern portion 18a1 of the DVD light receiving portion 18a is arranged slightly shifted in the downward direction in the figure with respect to the main beam light receiving element pattern portion 18b1 of the CD light receiving portion 18b.
[0048]
The CD light-receiving part 18b includes a main beam light-receiving element pattern part 18b1, a first sub-beam light-receiving element pattern part 18b2, and a second sub-beam light-receiving element pattern part 18b3. The main beam light receiving element pattern portion 18b1 has four main beam light receiving element patterns A, B, C, and D that are divided into four in a square shape.
[0049]
The first sub-beam light-receiving element pattern portion 18b2 of the CD light-receiving portion 18b has sub-beam light-receiving element patterns E1 and E2 that are divided into two in the illustrated vertical direction. The sub beam light receiving element pattern E1 on the side closer to the main beam light receiving element pattern portion 18b1 is set to have a larger area than the sub beam light receiving element pattern E2 on the far side. The first sub beam light receiving element pattern portion 18b2 is arranged slightly shifted in the left direction in the drawing with respect to the main beam light receiving element pattern portion 18b1.
[0050]
The second sub-beam light-receiving element pattern portion 18b3 of the CD light-receiving portion 18b has sub-beam light-receiving element patterns F1 and F2 that are divided into two in the illustrated vertical direction. The sub beam light receiving element pattern F2 on the side closer to the main beam light receiving element pattern portion 18b1 has a larger area than the sub beam light receiving element pattern F2 on the far side. The second sub beam light receiving element pattern portion 18b3 is arranged slightly shifted in the right direction in the drawing with respect to the main beam light receiving element pattern portion 18b1. In the present embodiment, the division interval of each light receiving element pattern in each light receiving element pattern portion is about 4 μm.
[0051]
FIG. 10 is an explanatory diagram of the operation mode of the photodetector (PD-IC). FIG. 10 shows types of optical recording media (discs) (DVD-ROM, DVD-RAM, CD-ROM, and CD-RW), light receiving elements used for reproduction, focus error detection method, and tracking error detection method. Is shown in tabular form. In FIG. 10, a light receiving element used for reproduction is shown by adding a circle representing a light beam spot.
[0052]
When reproducing a DVD-ROM, only the main beam light receiving element patterns a, b, c, d of the light receiving part for DVD are used. Focus error detection (FES) is performed using the astigmatism method. Assuming that the outputs of the respective light receiving element patterns a, b, c, and d are Va, Vb, Vc, and Vd, the focus error detection output FES by the astigmatism method is expressed by the following equation.
FES = (Va + Vc) − (Vb + Vd)
[0053]
When reproducing a DVD-ROM, tracking error detection (RES) is performed using a phase difference method. The phase difference method detects a tracking error by utilizing the fact that a transport deviation can be detected in addition to amplitude modulation by a pit when a track deviation occurs. Note that when reproducing only a DVD-ROM, the sub-beams are unnecessary, so that the diffraction gratings 13a and 13b are unnecessary.
[0054]
When reproducing a DVD-RAM, all the light receiving element patterns of the DVD light receiving unit are used. Focus error detection (FES) is performed using a differential astigmatism method. In the DVD-RAM, lands and grooves formed on the disk surface have the same width, and a groove asymmetry noise is generated in a normal astigmatism method. Since the cross-groove noise has an opposite phase between the main beam and the sub-beam, the cross-groove noise can be removed by adding the detection output by the main beam and the detection output by the sub-beam. Therefore, astigmatism detection is performed using both the main beam and the sub beam. Assuming that the outputs of the light receiving element patterns a to d, e1 to e4, and f1 to f4 are Va to Vd, Ve1 to Ve4, and Vf1 to Vf4, focus error detection output DAD-FES by the differential astigmatism method (DAD). Is expressed by the following equation. In the following equation, k is a coefficient.
DAD-FES = {(Va + Vc)-(Vb + Vd)} + k {(Vf1 + Vf3 + Ve1 + Ve3)-(Vf2 + Vf4 + Ve2 + Ve4)}
[0055]
The tracking error (RES) is detected using the differential push-pull method when reproducing the DVD-RAM. Since the DVD-RAM has a land-groove structure, the three-beam method cannot be applied. Further, the DVD-RAM needs a push-pull output to reproduce the address information (CAPA) recorded by the staggered emboss pits. On the other hand, the simple push-pull method is easy to adjust because it detects a tracking error with only the main beam, but has a poor radial shift characteristic. In the differential push-pull method (DPP), even if the push-pull output of the main beam and the push-pull output of the sub beam cause an offset due to a shift in the radial direction, the push-pull output waveform of the sub beam is inverted up and down, and the in-phase 2 By adding the signals, a good tracking error output with improved radial shift characteristics can be obtained. In the differential push-pull method (DPP), it is a precondition that each sub beam is shifted by ± 1/2 period of 1 track pitch with respect to the main beam.
[0056]
When reproducing the CD-ROM and CD-RW, the respective light receiving element patterns A, B, C, D, E1, E2, F1, and F2 of the CD light receiving unit are used. Focus error detection (FES) is performed using the astigmatism method. Assuming that the outputs of the light receiving element patterns A, B, C, and D are VA, VB, VC, and VD, the focus error detection output FES by the astigmatism method is expressed by the following equation.
FES = (VA + VC) − (VB + VD)
[0057]
When reproducing CD-ROM and CD-RW, tracking error detection (RES) is performed using a three-beam method. The three-beam method is widely used as a CD tracking detection method. Each sub-beam is arranged so as to be shifted from the main track by a quarter of the track pitch. When the outputs of the light receiving element patterns E1, E2, F1, and F2 are VE1, VE2, VF1, and VF2, respectively, tracking error detection output (RES) by the three beam method is expressed by the following equation.
FES = (VE1 + VE2) − (VF1 + VF2)
[0058]
In the three-beam method, the light receiving element pattern portion of the first sub beam may not be divided into two sub beam light receiving element patterns E1 and E2, and similarly, the light receiving element pattern portion of the second sub beam may be divided into each sub beam light receiving element. There is no need to divide the pattern into F1 and F2.
[0059]
As shown in FIG. 1, a linearly polarized light beam (laser light) emitted from a two-wavelength semiconductor laser 11 is converted into circularly polarized light by a phase difference plate 12 and then incident on diffraction gratings 13a and 13b for tracking. The two sub-beams (+ 1st order light and −1st order light) and the main beam (0th order light) for RF detection and focusing are incident on the beam splitter 14. About half the amount of light of each of the main beam and each sub beam incident on the beam splitter 14 is reflected by the beam splitter 14, the traveling direction is bent 90 degrees, and the light is emitted to the collimator lens 15 side. The light beam incident on the collimator lens 15 is a divergent beam.
[0060]
The collimator lens 15 converts the light beam (divergent light beam) incident from the beam splitter 14 side into a parallel light beam. The light beam (parallel beam bundle) emitted from the collimator lens 15 is changed in a direction substantially perpendicular to the disk surfaces (recording surfaces) of the optical recording media 1a and 1b by a rising mirror (not shown). Then, the light is incident on the objective lens 16, and is focused on the information recording surfaces of the optical recording media 1 a and 1 b as spot light by the objective lens 16.
[0061]
The reflected light reflected by each of the optical recording media 1a and 1b reaches the beam splitter 14 in the order of the objective lens 16, the rising mirror (not shown), and the collimator lens 15, and approximately half the amount of light passes through the beam splitter 14. To do. The light transmitted through the beam splitter 14 reaches the photodetector (PD-IC) 18 through the sensor lens 17 and is converted into an electric signal by the photodetector (PD-IC) 18.
[0062]
In the present embodiment, the optical system that guides the light beam emitted from the light source 11 to the optical recording medium includes a phase difference plate 12, diffraction gratings 13a and 13b, a beam splitter 14, a collimator lens 15, a rising mirror (not shown), and an objective. And a lens 16. The optical system that guides the light beam reflected by the optical recording medium to the light receiving element 18 includes an objective lens 16, a rising mirror (not shown), a collimator lens 15, a beam splitter 14, and a sensor lens 17. The beam splitter 14, the collimator lens 15, the rising mirror (not shown), and the objective lens 16 serve as a shared portion (common optical path) in both the optical systems. The phase difference plate 12 and the diffraction gratings 13a and 13b are exclusively used for light projection and are not shared. Further, the optical path (optical system) from the beam splitter 14 to the photodetector (PD-IC) 18 is dedicated to light reception and is also a non-shared part. The optical pickup device 10 according to the present embodiment is reflected by the optical recording medium on the optical path of the optical system dedicated to light reception (specifically, the optical path from the beam splitter 14 to the photodetector 18) in the non-shared portion. A sensor lens 17 is provided as a reflected light focusing position adjusting unit for optically adjusting the focusing position of the light beam.
[0063]
Further, a sensor lens 17 interposed between the beam splitter 14 and the photodetector (PD-IC) 18 (in other words, provided in the front stage of the photodetector (PD-IC) 18) is an optical recording medium. Astigmatism is generated in the reflected light (readout light) from the light, and the reflected light (readout light) is enlarged at a predetermined optical system magnification to form an image on each of the light receiving portions 18a and 18b. The sensor lens 17 constituting the reflected light focusing position adjusting unit may be constituted by a hologram or the like that generates a lens action having a negative refractive index.
[0064]
Further, the sensor lens 17 is mounted in an optical pickup housing (not shown) so as to be movable in the optical axis direction. Then, by moving the sensor lens 17 in the optical axis direction, an adjustment mechanism that realizes a conjugate relationship between the two-wavelength laser light source (each light emitting point 11d, 11e) and the light receiving element (each light receiving unit 18a, 18b) is configured. It should be noted that the sensor lens 17 has an adhesive or the like after the position of the sensor lens 17 is adjusted so that the reflected light (reading light) from the optical recording medium is focused on the light receiving portions 18a and 18b of the photodetector 18. Is used to bond and fix in an optical pickup housing (not shown).
[0065]
By adjusting the position of the sensor lens 17 in the optical axis direction, the optical system magnification when reproducing the signals recorded on the optical recording media 1a and 1b changes, but recording on the optical recording media using one of the light sources. The optical system magnification when reproducing the recorded signal is equal to the optical system magnification when reproducing the signal recorded on the optical recording medium using the other light source. That is, the optical system magnification when the DVD 1a is reproduced using the first light source (wavelength 655 nm) and the optical system magnification when the CD 1b is reproduced using the second light source (wavelength 785 nm) are the same value.
[0066]
When the light emitting point 11d for DVD is disposed outside the optical axis of the collimator lens 15, the parallel light beam emitted from the collimator lens 15 is inclined with respect to the optical axis of the collimator lens 15 (view angle ψ ≠ 0). Become. However, since the objective lens 16 satisfies the sine condition with respect to the DVD light beam, the occurrence of aberration can be suppressed, and a good light spot can be formed on the information recording surfaces of the optical recording media 1a and 1b. . FIG. 11 is a graph showing the relationship between the angle of view ψ of the parallel light beam incident on the collimator lens 15 and the generated aberration. The horizontal axis represents the angle of view ψ, and the vertical axis represents the aberration. A line a indicates a case where the sine condition is not satisfied (Sc ≠ 0), and a line b indicates a case where the sine condition is satisfied (Sc = 0). When the sine condition is not satisfied, coma and astigmatism are generated based on the angle of view ψ. On the other hand, no coma occurs when the sine condition is satisfied. For this reason, as shown in FIG. 11, when the sine condition is satisfied, the occurrence of aberration can be suppressed as compared to the case where the sine condition is not satisfied.
[0067]
As described above, in the optical pickup device 10 according to the present embodiment, the CD light emitting unit 11e is offset corresponding to the position near the focal point of the collimator lens 15 or the attitude characteristic of the objective lens 16 from the focal point of the collimator lens 15. It is arranged at the position. The objective lens 16 is formed and arranged so as to satisfy the sine condition with respect to the DVD light beam. Thereby, even when reproducing the signal recorded on the information recording surface of any optical recording medium, the occurrence of aberration can be suppressed as much as possible. Furthermore, since it is not necessary to provide two objective lenses formed so as to remove coma aberration on one of the optical recording media, the mechanism of the optical pickup device is not complicated, and the manufacturing cost is reduced. Can be suppressed.
[0068]
The light emitting point 11d for DVD is arranged at a position near the focal point of the collimator lens 15 or at a position offset from the focal point of the collimator lens 15 in accordance with the posture characteristic of the objective lens 16, and the objective lens 16 is arranged for the CD. You may form so that a sine condition may be satisfied with respect to a light beam.
[0069]
Then, by configuring the optical reproducing device using the optical pickup device 10 according to the present embodiment, an optical reproducing device corresponding to different types of optical recording media can be economically provided.
[0070]
FIG. 12 shows a schematic configuration of an optical reproducing device 50 equipped with the optical pickup device 10 according to the present embodiment. As shown in FIG. 12, the optical reproducing apparatus 50 includes a spindle motor 52 for rotating the optical recording medium 100, an optical pickup apparatus 10 for irradiating the optical recording medium 100 with a laser beam and receiving reflected light, and a spindle. A controller 54 that controls the operation of the motor 52 and the optical pickup device 10, a laser drive circuit 55 that supplies a laser drive signal to the optical pickup device 10, and a lens drive circuit 56 that supplies a lens drive signal to the optical pickup device 10. I have.
[0071]
The controller 54 includes a focus servo tracking circuit 57, a tracking servo tracking circuit 58, and a laser control circuit 59. When the focus servo tracking circuit 57 is activated, the recording surface of the rotating optical recording medium 100 is focused. When the tracking servo tracking circuit 58 is activated, the eccentric signal of the optical recording medium 100 is detected. The laser beam spot automatically follows the track. The focus servo tracking circuit 57 and the tracking servo tracking circuit 58 are respectively provided with an auto gain control function for automatically adjusting the focus gain and an auto gain control function for automatically adjusting the tracking gain. The laser control circuit 59 is a circuit that generates a laser drive signal supplied from the laser drive circuit 55, and generates an appropriate laser drive signal based on the recording condition setting information recorded on the optical recording medium 100. I do.
[0072]
The focus servo tracking circuit 57, the tracking servo tracking circuit 58, and the laser control circuit 59 do not need to be circuits incorporated in the controller 54, and may be separate components from the controller 54. Furthermore, these need not be physical circuits, and may be software executed in the controller 54.
The optical reproducing device 50 may be included in an optical recording / reproducing device having a recording function or may be a reproduction-only device that does not have a recording function.
[0073]
FIG. 13 is a schematic structural diagram of another optical pickup device according to this embodiment. In the optical pickup device 20 shown in FIG. 13, the optical axis of the light beam emitted from the two-wavelength semiconductor laser 21 is orthogonal to the optical axis of the reflected light from the objective lens 26 to the photodetector (PD-IC) 28. The optical pickup device 20 is further downsized by reducing the size of the optical pickup device 20 in the width direction (the direction perpendicular to the optical axis of the reflected light).
[0074]
The configuration and operation of the optical pickup device 20 are basically the same as those of the optical pickup device 10 shown in FIG. In FIG. 13, in order to prevent the laser light emitted from the two-wavelength semiconductor laser 21 from being reflected by the phase difference plate 22 and partially returning to the laser 21, the phase difference plate 22 is inclined. The symbol LA is the distance between the first light emitting point 21d and the second light emitting point 21e. Reference symbol LB represents the interval between the light receiving portions.
[0075]
In the optical pickup device 20, a parallel plate-shaped base material is used as the beam splitter 24. A half mirror film is formed on one surface (surface on the two-wavelength semiconductor laser 21 side) 24 a of the beam splitter 24. Further, a harmful antireflection film is formed on the other surface (the surface on the photodetector 28 side) 24b of the beam splitter plate 24.
[0076]
The light beam emitted from the two-wavelength semiconductor laser 21 is incident on one surface 24 a of the beam splitter plate 24 via the phase difference plate 22 and diffraction gratings 23 a and 23 b, and a part of the light beam is reflected by the beam splitter 24. The light beam reflected by the beam splitter 24 is converted into a parallel light beam by a collimator lens 25, bent by a rising mirror (not shown) in the direction perpendicular to the paper surface, and focused by an objective lens (double focus diffractive objective lens) 26. Then, an information recording surface of an optical recording medium (not shown) is irradiated as a light spot.
[0077]
The reflected light beam reflected by the optical recording medium (not shown) reaches the beam splitter 24 via the objective lens 26, the rising mirror (not shown), and the collimator lens 25, and part of the reflected light beam is transmitted through the beam splitter 24. The reflected light beam transmitted through the beam splitter 24 is incident on the light receiving portions 28a and 28b of the photodetector (PD-IC) 28 via the sensor lens 27, and the intensity of the reflected light beam is detected by the light receiving portions 28a and 28b. Is done.
[0078]
By adjusting the position of the sensor lens 27 in the optical axis direction, a reflected light beam having a wavelength corresponding to each light receiving portion can be focused on each light receiving portion 28a, 28b. Thereby, conjugate adjustment of the light source-light receiving element is performed. Since the occurrence of the focus offset is eliminated, the signals recorded on any of the different types of optical recording media can be reproduced satisfactorily.
[0079]
By setting the interval LB of each light receiving portion to about 1.1 to 1.6 times the interval LA of each light emitting point, the overall size of the optical pickup device 20 is not increased so much, and the light source-light receiving element Can be easily adjusted. That is, conjugate adjustment can be performed without requiring high accuracy for the position adjustment of the sensor lens 27. Therefore, even when the position of the sensor lens 27 is automatically adjusted, high position control accuracy is not required, and a conjugate automatic adjustment device, a conjugate adjustment jig, and the like can be realized economically.
[0080]
【The invention's effect】
As described above, according to the present invention, recording is performed on a plurality of types of optical recording media such as CDs and DVDs having different protective layer thicknesses and different information recording densities and different laser light wavelengths for recording and reproduction. Therefore, an optical pickup device that can stably and satisfactorily reproduce the signal and an optical reproduction device including the same can be realized at a low manufacturing cost.
[Brief description of the drawings]
FIG. 1 is a schematic structural diagram of an optical pickup device according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a schematic structure of a two-wavelength semiconductor laser (laser diode) constituting a light source.
FIG. 3 is a diagram showing an arrangement of light emitting points and collimator lenses.
4A and 4B are structural views of an objective lens, in which FIG. 4A is a front view, FIG. 4B is a side view, and FIG. 4C is a partially enlarged view of FIG.
FIG. 5 is an explanatory diagram of a sine condition of a lens.
FIG. 6 is a structural diagram of an actuator assembly.
FIG. 7 is a diagram showing a working distance between the objective lens and the optical recording medium. FIG. 7A is a diagram showing a distance between the optical recording medium (DVD) reproduced using a laser beam having a short wavelength and the objective lens. FIG. 7B is a diagram showing the working distance between the optical recording medium (CD) to be reproduced using a laser beam having a long wavelength and the objective lens 16.
8A and 8B are structural views of the sensor lens, in which FIG. 8A is a front view, FIG. 8B is a side sectional view of one, FIG. 8C is the other side sectional view, and FIG. FIG. 8A is a cross-sectional view taken along the line AA ′ in FIG. 8A, and FIG. 8E is a cross-sectional view taken along the line BB ′ in FIG.
FIG. 9 is a diagram showing a light receiving element pattern configuration of a light receiving unit of a photodetector.
FIG. 10 is an explanatory diagram of an operation mode of a photodetector (PD-IC).
FIG. 11 is a graph showing the relationship between the angle of view ψ of a parallel light beam and the generated aberration.
FIG. 12 is a diagram showing a schematic configuration of an optical reproducing apparatus equipped with an optical pickup device according to an embodiment of the present invention.
FIG. 13 is a schematic structural diagram of another optical pickup device according to an embodiment of the present invention.
[Explanation of symbols]
1a Digital Versatile Disc (DVD)
1b Compact disc (CD)
10, 20 Optical pickup device
11, 21 Two-wavelength semiconductor laser (light source)
11d, 11e, 21d, 21e Light emitting point
12, 22 phase difference plate
13a, 13b, 23a, 23b diffraction grating
14, 24 Beam splitter (beam splitter plate)
15, 25 Collimator lens
16, 26 Objective lens (double focus diffractive objective lens)
17, 27 Sensor lens (reflected light focusing position adjusting means, lens having negative refractive index)
17a Cylindrical concave lens
17b concave lens
17c Position adjustment pin hole
18, 28 Photodetector (PD-IC)
18a, 28a Light receiving part for CD
18b, 28b DVD photo detector
18a1, 18b1 Main beam light receiving element pattern section
18a2, 18a3, 18b2, 18b3 Sub-beam light receiving element pattern portion
50 Optical regenerator
52 Spindle motor
54 controller
55 Laser drive circuit
56 Lens drive circuit
57 Focus servo tracking circuit
58 Tracking servo tracking circuit
59 Laser control circuit
70 virtual plane
72 Convex lens
80 Actuator assembly
81 holder
82 wires
83 frames
100 Optical recording medium
LA Luminescent point interval
LB Distance between light receiving parts
θ1, θ2 Full width at half maximum angle
ψ angle of view

Claims (6)

First and second light emitting units that emit two lights having different wavelengths, a collimator lens that shapes the light from the first and second light emitting units into a parallel light bundle, and the light from the collimator lens An objective lens that condenses light on either the first or second optical recording medium and reflected light from either the first or second optical recording medium, and receives an electric light corresponding to the intensity of the reflected light. An optical pickup device having a light receiving unit for converting into a signal,
The second light emitting unit is arranged at a position offset by a predetermined offset amount corresponding to the posture characteristic of the objective lens from the vicinity of the focal point of the collimator lens.
The objective lens substantially satisfies a sine condition with respect to light from the first light emitting unit. The optical pickup device according to claim 1,
The light picked up from the first and second light emitting units is a divergent light beam. The optical pickup device according to claim 1 or 2,
The optical pickup device, wherein the working distance of the objective lens in the first optical recording medium is different from the working distance in the second optical recording medium. In the optical pick-up device according to any one of claims 1 to 3,
The first and second light emitting units are attached so that their positions can be adjusted in a plane substantially perpendicular to the optical axis of the collimator lens.
An optical pickup device characterized by the above. In the optical pick-up device according to any one of claims 1 to 4,
The first optical recording medium is one of a DVD system or a CD system,
The second optical recording medium is the other of the DVD system or the CD system
An optical pickup device characterized by the above. An optical pickup device according to any one of claims 1 to 5 is provided.
An optical regenerator characterized by the above.

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