JP2003272218A - Optical pickup device and optical reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably and satisfactorily reproduce a signal recorded on two types of optical recording media (for example, a CD and a DVD) which have protective layers different in thickness and different information recording density and use laser beams for recording/reproduction different in wavelength by using a common optical system for a dual-wavelength light source having two laser beam emitting parts incorporated in one package and an objective lens at each wavelength. <P>SOLUTION: The objective lens 16 which condenses the laser beam emitted from the dual-wavelength laser beam source 11 on the information recording surfaces of the optical recording media 1a and 1b and forms reading spots, includes a lens having positive power and a hologram with a shape of a concentric orbicular zone, and corrects a spherical aberration caused by the thickness of the protective layer of each optical recording medium 1a and 1b. A conjugate adjustment is carried out so that read light from each disk 1a and 1b focuses on each light receiving part 18a and 18b of a photodetector 18 with a sensor lens 17, and astigmatism is given to the read light. An astigmatism method is used for a focal error detection. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has different protective layer thicknesses and information recording densities, such as CD (Compact Disc) and DVD (Digital Versatile Disc), and different wavelengths of laser light used for recording and reproduction. Signals recorded on multiple types of optical recording media (optical disks)
An optical pickup device using a light source module in which two laser light emitting portions for short wavelength and long wavelength are incorporated in one package and reproducing by using a common optical system for each wavelength including an objective lens. And an optical reproducing device provided with the same.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 2000-207766 discloses a plurality of light sources having different wavelengths and a plurality of light receiving portions for individually receiving the respective return lights emitted from the plurality of light sources and reflected by an optical recording medium. An optical pickup device including a photodetector having a pattern formed on the same substrate, and an optical system sharing an optical path from a plurality of light sources to the photodetector, and an optical reproducing device including the optical pickup device are described.

In the above-mentioned publication, a plurality of light receiving section patterns are formed on the same substrate, and each light receiving section pattern has a high precision relative positional accuracy, so that the light receiving sections are emitted from a plurality of light sources having different wavelengths. It becomes possible to guide each return light reflected by the optical recording medium to the light receiving portion pattern with high accuracy, and it is possible to obtain a high quality reproduction signal or recording signal for different types of optical recording media. Is listed. Further, the above-mentioned 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.

Further, in Japanese Patent Laid-Open No. 2000-81566, it is possible to record / reproduce a plurality of types of optical recording media having different protective layers such as DVD and CD-R with a single objective lens, which has a high light utilization efficiency. An objective lens for an optical head is described. This objective lens is a resin single lens whose both surfaces are aspherical surfaces, and a diffractive lens structure is formed on one lens surface as a ring-shaped pattern centered on the optical axis.
The diffractive lens structure has wavelength dependence so that diffracted light of the same order by light fluxes of at least two different wavelengths forms good wavefronts for at least two types of optical disks having different protective layer thicknesses. There is.

For example, by using a two-wavelength semiconductor laser in which two light sources are formed on the same semiconductor substrate, the distance 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 systems of light receiving sections (light receiving section patterns) corresponding to each light source are formed on the same semiconductor substrate, the distance between the respective light receiving sections is increased. It can be kept accurate. Furthermore, by using the objective lens described in the above publication, spherical aberration and the like can be corrected for each of the optical recording media having different protective layer thicknesses.

[0006]

Therefore, data is recorded on a plurality of types of optical recording media such as CDs and DVDs having different thicknesses of protective layers and recording densities of information and different wavelengths of laser light used for recording and reproduction. 2 signals with different wavelengths
An optical pickup device that uses a light source module in which two laser light emitting units are incorporated into one package and uses a common optical system for each wavelength, including an objective lens, enables stable and excellent reproduction at low manufacturing cost. Practical application is desired.

An object of the present invention is to stably and satisfactorily reproduce signals recorded on a plurality of types of optical recording media having different thicknesses of protective layers and different information recording densities and different wavelengths of laser light used for recording and reproduction. It is to provide an optical pickup device at a low manufacturing cost.

[0008]

The above object is to provide a first light emitting portion for emitting a first laser light having a relatively short wavelength and a second light emitting portion for emitting a second laser light having a relatively long wavelength. A light source of the optical recording medium, a two-wavelength laser light source in which a light emitting unit of the above is incorporated in one package, a lens having a positive power, and a concentric annular zone hologram. An objective lens that condenses a recording surface to form a reading spot, a photodetector that receives the first or second laser light and converts it into an electrical signal corresponding to the intensity of the light beam, and the objective lens An optical system for guiding the first or second laser light emitted from the dual wavelength laser light source to the information recording surface of the optical recording medium, and a light beam reflected by the optical recording medium including the objective lens for the optical beam. With an optical system leading to the detector Is achieved by an optical pickup apparatus characterized and.

As a result, signals recorded on a plurality of types of optical recording media (optical disks) having different thicknesses of protective layers and recording densities of information and different wavelengths of laser light used for recording / reproducing are stably and satisfactorily reproduced. The optical pickup device made possible can be manufactured at low cost.

In the above-mentioned optical pickup device of the present invention, the objective lens uses the first laser beam to record a signal recorded on a first optical recording medium having a relatively thin first protective layer. When reproducing using light, the spherical aberration of the first laser light that occurs depending on the thickness of the first protective layer is corrected, and a second thick protective layer is formed. Spherical aberration of the second laser light that occurs depending on the thickness of the second protective layer when a signal recorded on the recorded second optical recording medium is reproduced using the second laser light. Is corrected.

In the above optical pickup device of the present invention, the photodetector includes a first-system light receiving portion for receiving the first laser light and a second light receiving portion for receiving the second laser light.
And a light receiving unit of a system.

In the above-mentioned optical pickup device of the present invention, the full width at half maximum of the emission characteristic of the first laser light emitted from the first light emitting portion is set to θ1, and the light emitted from the second light emitting portion is emitted. When the full width at half maximum of the radiation characteristic of the second laser light is θ2, θ1> θ2. As a result, it becomes possible to form a light spot closer to the diffraction limit of light on the first recording medium (for example, DVD) having a higher information recording density.

In the above optical pickup device of the present invention, the objective lens is focus-controlled by an astigmatism method. In the above optical pickup device of the present invention, the photodetector has an astigmatic difference value α on the light receiving unit of the first system or on the light receiving unit of the second system used for the astigmatism method. , When the distance between the light receiving unit of the first system and the light receiving unit of the second system is LB,
The light receiving unit interval LB is characterized in being set in a range of 4 to 7 times the square root of the astigmatic difference amount α (4α ^1/2 <LB <7α ^1/2 ).

If the astigmatic difference amount α is set to a large value, it is necessary to increase the size of the light receiving element, and the distance LB between the light receiving portions becomes wide. For this reason, it becomes impossible to set the interval between the respective light receiving units corresponding to the interval between the respective light emitting units. Astigmatic difference α
If is set to a small value, the range for detecting the defocus on the optical recording medium (optical disk) becomes narrow, and the control operation of the focus servo tends to become unstable.

In the above optical pickup device of the present invention, the objective lens and the first optical recording medium when reproducing the signal recorded on the first optical recording medium by using the first laser beam The distance (working distance) is D1, and the distance between the objective lens and the second optical recording medium when the signal recorded on the second optical recording medium is reproduced using the second laser light. Is defined as D2, D1> D2.

In the above optical pickup device of the present invention, an optical system for guiding the first or second laser light to the information recording surface of the optical recording medium, and a light beam reflected by the optical recording medium for the photodetector. The optical position of the light beam reflected by the optical recording medium on the optical path of the optical system that guides the light beam reflected by the optical recording medium to the light receiving element, which is not shared with the optical system leading to the optical recording medium. It is characterized in that a reflected light focusing position adjusting unit for adjusting the focus is provided.

An optical reproducing apparatus according to the present invention comprises the optical pickup apparatus according to the present invention. As a result, it is possible to economically provide an optical reproducing device that can stably and satisfactorily reproduce signals recorded on a plurality of types of optical recording media (optical disks).

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 the optical pickup device according to the present embodiment. The optical pickup device 10 according to the present embodiment includes various digital versatile
It is adapted to support different types of optical recording media such as a disc (DVD-ROM, DVD-RAM, etc.) 1a and a compact disc (CD) 1b. The optical pickup device 10 includes a two-wavelength semiconductor laser (laser diode: LD) 11, a retardation plate 12, and diffraction gratings 13a and 13b sequentially arranged from the two-wavelength semiconductor laser 11 side.
, Beam splitter 14, collimator lens 15
And a raising mirror (not shown) and the objective lens 16
And a sensor lens 17 and a photodetector (PD-IC: photodiode integrated circuit) 18.

The two-wavelength semiconductor laser 11 includes a first light emitting portion which emits a first laser light beam having a relatively short wavelength and a second light emitting portion which emits a second laser light beam having a relatively long wavelength. A two-wavelength laser light source is incorporated in one package to generate a laser beam having a wavelength of 655 nm for DVD reproduction and a laser beam having a wavelength of 785 nm for CD reproduction. The optical output of the two-wavelength semiconductor laser 11 is in the reproduction class (for example, 5 mW). A semiconductor substrate (semiconductor laser body) of the two-wavelength semiconductor laser 11 is sealed in a housing (case) made of metal or the like, and each laser beam is emitted from a laser window portion provided in the housing. .
The back monitor (not shown) detects the light output amount of the two-wavelength semiconductor laser 11, and the power supplied to the semiconductor laser is feedback-controlled to automatically control the light output amount (APC:
Automatic power control).

FIG. 2 is a diagram showing a schematic structure of a two-wavelength semiconductor laser 11 which constitutes a light source and a radiation characteristic of a laser light beam, and FIG. 2A is a perspective view showing a schematic structure of the two-wavelength semiconductor laser. 2 (b) is an explanatory view showing the emission characteristic of the two-wavelength semiconductor laser, and FIG. 2 (c) is a graph showing the full width at half maximum angle of the emission characteristic of the light beam. FIG. 2A and FIG. 2B show only the main body of the semiconductor laser, excluding the casing that seals the semiconductor substrate. Semiconductor laser 11
Is a semiconductor substrate 1 made of, for example, gallium arsenide (GaAs)
Waveguide (first waveguide) 11 for wavelength 655 nm on 1a
b and wavelength 785 nm waveguide (second waveguide) 11
c are formed at a predetermined interval (for example, 110 μm), and the ends of the waveguides are the light emitting points 11d and 11e. Laser light having a wavelength of 655 nm is emitted from the first light emitting point (DVD light emitting point) 11d, and the second light emitting point (C
Laser light having a wavelength of 785 nm is emitted from the D emission point) 11e. Reference numeral LA is each light emitting point 11d of the two light sources,
The interval is 11e. 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 the photolithography process, the interval LA is formed with high accuracy and the manufacturing error is small.

Laser light emitted from each of the light emitting points 11d and 11e is emitted to the outside of the housing through a laser window formed in the housing (not shown). The two-wavelength semiconductor laser 11 has a wavelength of 6
A laser beam of 55 nm (for DVD) is oscillated in a self-excited oscillation mode, and a laser beam of wavelength 785 nm (for CD) is oscillated in a gain guide type multimode. The two-wavelength semiconductor laser 11 may be one that oscillates laser light of each wavelength in a single mode.

As shown in FIG. 2B, the wavelength 655n emitted from the first light emitting point (DVD light emitting point) 11d.
The full width at half maximum θ1 of the emission characteristic of the laser light beam of m (for DVD) is the half value of the emission characteristic of the laser light beam of wavelength 785 nm (for CD) emitted from the second emission point (emission point for CD) 11e. It is made larger than the full width angle θ2.
Here, the full width at half maximum θ (θ1, θ2) of the radiation characteristic is
As shown in FIG. 2C, the light intensity has a maximum value Imax of 1
The angle range is / 2. In this embodiment, the wavelength 6
The full width at half maximum angle θ1 of the radiation characteristic of the 55 nm (for DVD) laser light beam is set to 30 degrees to 35 degrees, and the wavelength is set to 785.
The full width at half maximum angle θ2 of the radiation characteristic of the laser light beam of nm (for CD) is set to about 25 degrees.

The phase difference plate 12 shown in FIG. 1 is a quarter-wave plate, and the phase difference plate 12 converts a linearly polarized light beam into circularly polarized light. Generally, circularly polarized light is desirable for high-speed DVD reproduction. In the present embodiment, as the retardation plate 12, a thin glass plate to which a functional film is attached is used. The retardation plate 12 is installed so that its optical axis is inclined by 45 degrees with respect to the polarization plane of linearly polarized light.

The diffraction grating 13a is, for example, the semiconductor laser 1
The grating surface for DVD is formed on the surface on the 1st side, and the diffraction grating 13
In b, a CD grating surface is formed on the surface on the beam splitter 14 side. The split light amount ratio in the diffraction gratings 13a and 13b is, for example, 1 (+ 1st order light) for both DVD and CD:
6 (0th order light): 1 (-1st order light). The grid pitch is
For example, 21.2 μm on the DVD side and 31.0 μm on the CD side
Is. The DVD grating surface should not diffract at the CD wavelength (785 nm), and the CD grating surface should be at the DVD wavelength (65 nm).
5 nm) has wavelength selectivity so as not to diffract. This exclusive action (wavelength selectivity) is realized by making the groove depth deeper than that of an ordinary diffraction grating and by adopting a grating shape in which the duty ratio of the grating interval is deviated from 0.5.

The beam splitter 14 is the semiconductor laser 1
The light beam from the first side is reflected toward the optical recording medium, and the reflected light from the optical recording medium is transmitted to the photodetector 18 side, which has a so-called half mirror function. In FIG. 1, a cubic beam splitter 14 is illustrated.

The collimator lens 15 converts the bundle of divergent rays from the semiconductor laser 11 which is a light source into a bundle of parallel rays and guides it to the objective lens 16, and also converts the bundle of parallel rays from the objective lens 16 into a bundle of focused rays. It leads to the photodetector 18. In this embodiment, a plastic injection molded product is used, and a collimator lens whose both surfaces are aspherical is used.

The raising mirror (not shown) reflects the parallel light flux from the collimator lens 15 toward the objective lens 16 and reflects the parallel light flux from the objective lens 16 toward the collimator lens 15 side. is there. In this embodiment, a flat mirror is used as the rising mirror. The bending angle (reflection angle) is 90 degrees.

FIG. 3 is a structural diagram of the objective lens.
3A shows a front view, and FIG. 3B shows a side view. FIG. 3 (c) shows a partially enlarged view of FIG. 3 (b). In FIG. 3B, each disc (optical recording medium) 1
Side surfaces of a and 1b are also shown together. Note that FIG. 3 (b)
In the above, reference numeral Ka is a DVD information recording surface, and reference numeral Kb is a CD information recording surface. The symbol ta is the thickness of the DVD (t
a = 0.6 mm), symbol tb is the thickness of the CD (tb = 1.
2 mm).

The objective lens 16 has a lens having a positive power and a concentric annular zone hologram for converging the first or second laser beam on the information recording surface of the optical recording medium to form a reading spot. It constitutes the objective lens.

Optical pickup device 1 according to the present embodiment
In 0, a double focus diffraction type objective lens is used as the objective lens 16. The objective lens (double focus diffractive objective lens) 16 is manufactured by injection molding an optical plastic material. As shown in FIG. 3B, the objective lens 16
Is formed with aspherical surfaces on both sides. As shown in FIG. 3A, a large number of concentric ring zones 1 are formed on the lens surface having a large curvature (on the side of the rising mirror, that is, on the side opposite to the optical recording medium).
A 6c-shaped holographic diffraction grating (hologram) is formed. As shown in FIG. 3C, the concentric ring zones are formed in a sawtooth cross-sectional shape to improve the diffraction efficiency. As shown in FIG. 3A, the central area of the objective lens 16 is a combined CD / DVD area 16a, and the area on the outer peripheral side thereof is a DVD dedicated area 16b. Objective lens 16
Outputs a light beam for DVD (wavelength 655 nm) to DVD1
a for the CD (wavelength 785n
The light beam m) is focused on the information recording surface Kb of the CD 1b.

Each disc (optical recording medium) 1a, 1b is
The information recording surfaces Ka and Kb are protected by a protective film made of polycarbonate or the like. The thickness of the protective film (corresponding to the thickness of the optical recording medium) varies depending on the type of the optical recording medium. Since the spherical aberration of incident light changes depending on the thickness of the protective film,
The amount of spherical aberration also differs depending on the type of optical recording medium. Therefore, the double focus diffraction objective lens 16 is used to correct the difference in spherical aberration due to the type of the optical recording medium.

The objective lens 16 is held on an actuator assembly (actuator assembly) not shown so as to be movable in the focus direction and the tracking direction (radial direction of the optical recording medium). Then, the position of the objective lens 16 is controlled by the focus servo control and the tracking servo control, and the spot of the light beam can be made to follow the reading point on the optical recording medium.

The sensor lens 17 is an important member in the optical pickup device 10 according to the present embodiment, and the sensor lens 17 realizes the following five functions. First of all, the sensor lens 17 includes a light source (object point) and light receiving portions (image points) 18a and 18b of the photodetector 18.
The focus offset is adjusted by adjusting (conjugate adjustment) so that and become substantially conjugate. Secondly, astigmatism is applied to the light beam (reading light) for detecting the focus (focus) by the astigmatism method. Thirdly, the inconvenient astigmatism generated in the beam splitter 14 is removed. Fourth, the spot on the photodetector 18 is enlarged, and the position adjustment accuracy of the photodetector 18 is relaxed to about ± 5 μm to facilitate the position adjustment of the photodetector 18. Fifthly, the inconvenient coma aberration generated in the beam splitter 14 is removed. By removing the inconvenient coma aberration, the quality of the DVD-RAM reproduction signal can be improved.

FIG. 4 shows an example of the structure of the sensor lens 17, FIG. 4 (a) is a front view, FIG. 4 (b) is one side sectional view, and FIG. 4 (c) is the other side sectional view. 4 (d) is FIG.
4A is a sectional view taken along the line AA ′ of FIG. 4A, and FIG. 4E is a sectional view taken along the line BB ′ of FIG. The sensor lens 17 has the following configuration in order to realize the above various functions. As shown in FIG. 4B, the surface of the sensor lens 17 on the beam splitter 14 side is a concave lens 17b for lowering the NA (numerical aperture of the lens) on the photodetector 18 side to facilitate conjugate adjustment. There is.

The surface of the sensor lens 17 on the photodetector 18 side is a cylindrical concave lens 17a. The cylindrical concave lens 17a functions as an astigmatism generation element. The direction of the cylindrical surface of the cylindrical concave lens 17a takes into consideration the direction of astigmatism required for the astigmatism method and the direction of astigmatism necessary for correction of astigmatism when the beam splitter 14 is a parallel plate. Will be decided.

The sensor lens 17 is made of optical plastic by injection molding, and the position adjusting pin hole 17c and the position adjusting guide are also integrally formed.

Generally, when a transparent parallel plate, a lens, or the like is arranged obliquely with respect to the optical axis in the optical path of a bundle of focused rays, coma occurs. If there is coma, the push-pull balance will be lost when the signal is reproduced by the push-pull method or the like described later. Therefore, as shown in FIG. 4E, the sensor lens 17 is arranged so as to cancel the generated coma aberration.
The lens surface is tilted with respect to the optical axis to remove coma.

As shown in FIG. 1, a photodetector (PD-IC) 18 including a light receiving element is used for reflecting light (D-D) from the DVD 1a.
A light receiving portion 18a for VD) and a light receiving portion 18b for reflected light (for CD) from the compact disc 1b are provided. Reference numeral LB in the drawing indicates the distance between the light receiving portions 18a and 18b. The interval LB between the light receiving portions 18a and 18b is set to the light emitting points 11d and 1
It is set wider than the interval LA of 1e. More specifically, the distance LB between the light receiving portions 18a and 18b is set to the light emitting point 1
The distance LA between 1d and 11e is 1.1 to 1.6 times. That is, β = 1.1 to 1.6 in the relation of LA = (1 / β) · LB.

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 (PD: photo diode part or photo detect part). Then, the current signal generated in the light receiving section is converted into a voltage signal, a predetermined calculation is performed, and various signals (reproduction signal (R
F signal), a focus error signal, a tracking error signal, and the like). In the present embodiment, the light receiving section and the arithmetic section (IC section)
Is composed of a monolithic IC, and this monolithic IC is enclosed in, for example, a 14-pin COB (chip on board) package.

FIG. 5 is a diagram showing a light receiving element pattern configuration of the light receiving portion of the photodetector. Photodetector (PD-IC) 18
Includes a DVD light receiving portion 18a and a CD light receiving portion 18b. Reference numeral LB in FIG. 5 indicates 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 distance LB is set to 152 μm. Therefore, the distance LB (152 μm) between the light receiving portions is about 1.38 times the distance LA (110 μm) between the light emitting points. In other words, β = 1.38 in the relation of LA = (1 / β) · LB.

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, d which are divided into four in a square shape.

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, e which are divided into four in a square shape.
3 and e4. The first sub-beam light receiving element pattern portion 18a2 includes the main beam light receiving element pattern portion 1
8a1 is arranged slightly offset to the left in the drawing. Second sub-beam light receiving element pattern portion 18a3
Has four sub-beam light receiving element patterns f1, f2, f3, f4 divided into four in the shape of a square. The second sub-beam light-receiving element pattern portion 18a3 is arranged slightly offset to the right 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.

Further, the main beam light receiving element pattern portion 18a1 of the DVD light receiving portion 18a is the CD light receiving portion 18a.
The main beam light receiving element pattern portion 18b1 of b is slightly displaced downward in the drawing.

The CD light receiving portion 18b includes a main beam light receiving element pattern portion 18b1, a first sub beam light receiving element pattern portion 18b2, and a second sub beam light receiving element pattern portion 18b3. The main beam light receiving element pattern portion 18b1 has four main beam light receiving element patterns A, B, C, D divided into four in a square shape.

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 which are vertically divided into two. The sub beam light receiving element pattern E1 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 E2 on the far side. First sub-beam light receiving element pattern portion 18b
Reference numeral 2 is arranged so as to be slightly displaced to the left in the drawing with respect to the main beam light receiving element pattern portion 18b1.

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 which are vertically divided into two. 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. Second sub-beam light receiving element pattern portion 18b
3 is arranged to be slightly shifted to the right in the drawing with respect to the main beam light receiving element pattern portion 18b1. In addition,
In the present embodiment, the division interval of each light receiving element pattern in each light receiving element pattern portion is about 4 μm.

FIG. 6 is an explanatory diagram of the operation mode of the photodetector (PD-IC). FIG. 6 shows types of optical recording media (discs) (DVD-ROM, DVD-RAM, CD-ROM, and CD-RW), a light-receiving element used for reproduction, a focus error detection method, and a tracking error detection method. The relationship between and is shown in a tabular form. Incidentally, in FIG. 6, a light receiving element used for reproduction is shown by adding a circle mark representing a light beam spot.

When reproducing a DVD-ROM, a DVD
Main beam receiving element patterns a, b, c,
Only d is used. Focus error detection (FES) is performed using the astigmatism method. Each light receiving element pattern a, b,
If the outputs of c and d are Va, Vb, Vc, and Vd, respectively, the focus error detection output FES by the astigmatism method is expressed by the following equation. FES = (Va + Vc)-(Vb + Vd)

In reproducing the DVD-ROM, the tracking error detection (RES) is performed by using the phase difference method. The phase difference method detects a tracking error by utilizing the fact that, when a track shift occurs, not only amplitude modulation by pits but also transfer bias can be detected. If only the DVD-ROM is reproduced, the sub-beam is not necessary, so the diffraction grating 13
a and 13b are unnecessary.

When reproducing a DVD-RAM, a DVD
Use all the light receiving element patterns of the light receiving section. Focus error detection (FES) is performed using the differential astigmatism method. In the DVD-RAM, the land and the groove formed on the disk surface have the same width, and a groove crossing noise is generated in the normal astigmatism method. Since this groove crossing noise has the opposite phase between the main beam and the sub beam, the groove crossing 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. The outputs of the respective light receiving element patterns a to d, e1 to e4, f1 to f4 are respectively Va to Vd, Ve1 to Ve4 and Vf1 to V.
If f4, the 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)}

When the DVD-RAM is reproduced, the tracking error (RES) is detected by using the differential push-pull method. Since the DVD-RAM has a land-groove structure, the 3-beam method cannot be applied. Further, the DVD-RAM requires push-pull output in order to reproduce the address information (CAPA) recorded by the zigzag embossed pits. On the other hand, the simple push-pull method is easy to adjust because the tracking error is detected only by the main beam, but the radial shift characteristic is poor. 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 are offset by the radial shift, the push-pull output waveform of the sub-beam is inverted upside down and the in-phase 2 By adding the signals, a good tracking error output with an improved radial shift characteristic can be obtained. In the differential push-pull method (DPP), it is a prerequisite that each sub beam is deviated from the main beam by ± 1/2 cycle of one track pitch.

When reproducing a CD-ROM and a CD-RW, the light receiving element patterns A, B, and
C, D, E1, E2, F1 and F2 are used. Focus error detection (FES) is performed using the astigmatism method. The output of each light receiving element pattern A, B, C, D is VA,
Assuming 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)

Tracking error detection (RES) at the time of reproducing the CD-ROM and the CD-RW is performed by using the three-beam method. The three-beam method is widely used as a tracking detection method for CDs (compact discs). The sub-beams are arranged so as to be offset from the main track by 1/4 pitch of the track pitch. The output of each light receiving element pattern E1, E2, F1, F2 is VE
1, VE2, VF1, VF2, the tracking error detection output (RES) by the three-beam method is expressed by the following equation. FES = (VE1 + VE2)-(VF1 + VF2)

In the three-beam method, the light receiving element pattern portion of the first sub beam does not have to be divided into two sub beam light receiving element patterns E1 and E2. The sub beam light receiving element patterns F1 and F2 may not be divided into two.

FIG. 7 is an explanatory diagram of the astigmatic difference used in the astigmatism method. In FIG. 7, the beam splitter 14 provided between the collimator lens 15 and the sensor lens 17 is omitted. When the astigmatic difference amount α is set to be small, the range for detecting the defocus on the optical recording medium (optical disk) becomes narrow, and the operation of the focus servo control tends to become unstable. If the astigmatic difference amount α is set to a large value, it is necessary to increase the size of the light receiving element, which makes it impossible to dispose the light receiving portions apart from each other.

As described above, the optical pickup device 10 according to the present embodiment uses the astigmatism method for detecting the focus error signal (focus error signal). The photodetector includes a first light receiving section corresponding to a first light emitting section that generates a first laser beam having a relatively short wavelength, and a second laser beam generating a second laser beam that has a relatively long wavelength. The second light receiving unit corresponding to the two light emitting units. The first used in this astigmatism method
When the value of the astigmatic difference on the light receiving unit of the system or the light receiving unit of the second system is α and the interval between the light receiving unit of the first system and the light receiving unit of the second system is LB, the light receiving unit interval LB is a range of 4 to 7 times the square root of the astigmatic difference amount α (4α ^1/2 <LB <7
Set to α ^1/2 ). By setting the relationship between the light receiving unit distance LB and the astigmatic difference amount α within the above range, it is possible to accurately detect the focus error.

FIG. 8 is a diagram showing the working distance between the objective lens and the optical recording medium, and FIG. 8 (a) is an optical recording medium (DVD) 1a for reproducing using a laser beam having a short wavelength and the objective lens. 16 shows a working distance D1 between the optical recording medium and the optical recording medium (CD), which is reproduced by using a laser beam having a long wavelength.
The working distance D2 between 1b and the objective lens 16 is shown.

Optical pickup device 1 according to the present embodiment
At 0, the first optical recording medium (D) having a thin protective layer and a high information recording density by using the first laser beam having a relatively short wavelength is used.
(VD) 1a When reproducing, the distance (working distance) D1 between the objective lens 16 and the first optical recording medium 1a is increased by using a second laser beam having a relatively long wavelength to record information with a thick protective layer. The distance (working distance) D2 between the objective lens 16 and the second optical recording medium 1b when reproducing the second optical recording medium (CD) 1b having a low density is set to be larger. 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 of the optical recording medium facing the objective lens 16.

Although FIG. 8 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 in b), the optical recording mediums 1a and 1b may be arranged such that the distance between the information recording surface and the objective lens 16 is different for each optical recording medium 1a and 1b.

As shown in FIG. 1, a two-wavelength semiconductor laser 1
The linearly polarized light beam (laser light) emitted from 1 is
After being converted into circularly polarized light by the phase plate 12, the diffraction grating 13
Two sub-beams for tracking (+ 1st-order light and -1st-order light) and a main beam for RF detection and focusing (0th-order light) are incident on the beamsplitter 1 a and 13b.
It is incident on 4. The light beams of about half the amount of light of each of the main beam and each of the sub-beams that have entered the beam splitter 14 are reflected by the beam splitter 14, the traveling direction thereof is bent by 90 degrees, and emitted to the collimator lens 15 side. The light beam incident on the collimator lens 15 is a divergent ray bundle.

The collimator lens 15 converts the light beam (divergent ray bundle) incident from the beam splitter 14 side into a parallel ray bundle. The light beam (parallel light flux) emitted from the collimator lens 15 is directed to the optical recording medium (each disc 1 by a raising mirror not shown).
a, 1b) is changed to a direction substantially orthogonal to the disc surface (recording surface) and is incident on the objective lens 16,
At 6, the light beam becomes a focused light beam, and the information recording surface of each of the optical recording media 1a and 1b is irradiated as spot light.

The reflected light reflected by each disk (optical recording medium) 1a, 1b reaches the beam splitter 14 in the order of the objective lens 16, the raising mirror (not shown), and the collimator lens 15, and the light of about half the amount of light is emitted. Is the beam splitter 14
Through. The light transmitted through the beam splitter 14 reaches the photodetector (PD-IC) 18 via the sensor lens 17, and is converted into an electric signal by the photodetector (PD-IC) 18.

In this embodiment, the optical system for guiding the light beam emitted from the light source 11 to the optical recording medium is the retardation plate 1.
2, the diffraction gratings 13a and 13b, the beam splitter 14, the collimator lens 15, the raising mirror (not shown), and the objective lens 16. The optical system for guiding 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), and a collimator lens 1.
5, the beam splitter 14, and the sensor lens 17. Then, the beam splitter 14, the collimator lens 15, the raising mirror (not shown), and the objective lens 16 serve as a common portion (common optical path) in both the optical systems. The phase difference plate 12 and the diffraction gratings 13a and 13b are dedicated to projecting light and are non-shared portions. 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 portion. The optical pickup device 10 according to the present embodiment is reflected by the optical recording medium in the optical path of the optical system dedicated to light reception in the non-shared portion (specifically, the optical path from the beam splitter 14 to the photodetector 18). A sensor lens 17 is provided as a reflected light focusing position adjusting section for optically adjusting the focusing position of the light beam.

Further, the sensor lens 17 provided between the beam splitter 14 and the photodetector (PD-IC) 18 (in other words, provided in the preceding stage of the photodetector (PD-IC) 18), Astigmatism is generated in the reflected light (readout light) from the optical recording medium, and the reflected light (readout light) is magnified by a predetermined optical system magnification to obtain each light receiving unit 18
An image is formed on a and 18b. The sensor lens 17 forming the reflected light focusing position adjusting section may be formed of a hologram having a negative refractive index and generating a lens action.

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, the two-wavelength laser light source (each light emitting point 11
d, 11e) and the light receiving element (each of the light receiving portions 18a, 18b) constitute an adjusting mechanism for realizing the conjugate relationship. The sensor lens 17 reflects light (read light) from the optical recording medium.
After the position of the sensor lens 17 is adjusted so as to focus on the light receiving portions 18a and 18b of the photodetector 18, it is adhesively fixed in an unillustrated optical pickup housing using an adhesive or the like.

By adjusting the position of the sensor lens 17 in the optical axis direction, the optical system magnification in reproducing the signal recorded on the optical recording medium changes, but recording on the optical recording medium using one light source. The optical system magnification in reproducing the reproduced signal is equal to the optical system magnification in reproducing the signal recorded on the optical recording medium using the other light source. That is, using the first light source (wavelength 655 nm), the DVD 1a
Magnification and second light source (wavelength 785n
m) is the same as the optical system magnification when the compact disc 1b is reproduced.

As described above, the optical pickup device 10 according to the present embodiment includes a light source that emits a plurality of lights having different wavelengths corresponding to different types of optical recording media and a plurality of light receiving devices that correspond to the respective recording media. And the sensor lens 17 is provided in front of the photodetector (PD-IC) 18 constituting the light receiving portion, while the distance LB between the light receiving portions is larger than the distance LA between the light emitting points. Therefore, by adjusting the position of the sensor lens 17 in the optical axis direction, the conjugate adjustment of the light source-light receiving element can be easily performed. As a result, a focus offset occurs in which light is not focused on the optical recording medium even though it is in focus, or conversely, a focus offset is in focus that is focused on the light receiving portion but not on the optical recording medium. It can be resolved. Therefore, it is possible to provide the optical pickup device in which the dimensional accuracy of the housing and the like is relaxed to a general tolerance and the good reproduction signal quality can be secured even when the mounting accuracy is relaxed.

By constructing an optical reproducing device using the optical pickup device 10 according to this embodiment, it is possible to economically provide an optical reproducing device corresponding to different types of optical recording media.

FIG. 9 shows a schematic structure of an optical reproducing device 50 equipped with the optical pickup device 10 according to the present embodiment. The optical reproducing device 50 includes a spindle motor 52 for rotating the optical recording medium 100 as shown in FIG.
An optical pickup device 10 that irradiates a laser beam on the optical recording medium 100 and receives the reflected light thereof, a controller 54 that controls the operations of the spindle motor 52 and the optical pickup device 10, and a laser drive signal are supplied to the optical pickup device 10. And a lens drive circuit 56 for supplying a lens drive signal to the optical pickup device 10.

The controller 54 includes a focus servo follow-up circuit 57, a tracking servo follow-up 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, and when the tracking servo tracking circuit 58 is activated,
The spot of the laser beam automatically follows the eccentric signal track of the optical recording medium 100. The focus servo follow-up circuit 57 and the tracking servo follow-up circuit 58 are respectively provided with an automatic gain control function for automatically adjusting the focus gain and an automatic gain control function for automatically adjusting the tracking gain. The laser control circuit 59 is a circuit for generating a laser drive signal supplied by 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.

The focus servo follow-up circuit 57, the tracking servo follow-up circuit 58, and the laser control circuit 59 do not have to be circuits incorporated in the controller 54, and may be parts separate from the controller 54. Furthermore, these do not have to be physical circuits and may be software executed in the controller 54. The optical reproducing device 50
Is included in an optical recording / reproducing device equipped with a recording function,
Alternatively, it may be a reproduction-only device having no recording function.

FIG. 10 is a schematic structural diagram of another optical pickup device according to the present embodiment. In the optical pickup device 20 shown in FIG. 10, 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. By tilting the optical pickup device 20 by a predetermined angle, the size of the optical pickup device 20 in the width direction (direction orthogonal to the optical axis of the reflected light) is reduced, and the optical pickup device 20 is further downsized.

The structure 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. 10, the phase difference plate 22 is tilted 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. Reference numeral LA is the first light emitting point 21d and the second light emitting point 21d.
Is the distance from the light emitting point 21e. Reference numeral LB is an interval between the respective light receiving units.

In this 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 (the surface on the side of the two-wavelength semiconductor laser 21) 24a 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.

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 the diffraction gratings 23 a and 23 b, and a part thereof is reflected by the beam splitter 24. To do. The light beam reflected by the beam splitter 24 is converted into a bundle of parallel rays 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 diffraction type objective lens) 26. Then, the information recording surface of the optical recording medium (not shown) is irradiated as a light spot.

The reflected light beam reflected by the optical recording medium (not shown), the objective lens 26, the raising mirror (not shown),
Beam splitter 24 via collimator lens 25
And part of the light passes through the beam splitter 24. The reflected light beam that has passed through the beam splitter 24 enters each light receiving portion 28a, 28b of the photodetector (PD-IC) 28 via the sensor lens 27, and the reflected light beam intensity is detected by each light receiving portion 28a, 28b. To be done.

By adjusting the position of the sensor lens 27 in the optical axis direction, the reflected light beam having the wavelength corresponding to each light receiving portion can be focused on each light receiving portion 28a, 28b.
As a result, the 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 well.

By setting the interval LB of each light receiving portion to be about 1.1 to 1.6 times the interval LA of each light emitting point, the light source can be provided without increasing the overall size of the optical pickup device 20. -The conjugate adjustment of the light receiving element can be easily performed. That is, the 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 the conjugate automatic adjustment device, the conjugate adjustment jig, and the like can be economically realized. Although the two-wavelength semiconductor laser housed in one package is used as the light source in the above embodiment, the present invention is not limited to this. For example, the present invention can be applied to each set of two wavelengths in an optical pickup device including a light source in which a semiconductor laser that emits light of three or more kinds of wavelengths is stored in one package.

[0079]

As described above, according to the present invention, a plurality of types of light, such as CD and DVD, having different thicknesses of protective layers and recording densities of information and different wavelengths of laser light used for recording / reproducing are used. A signal recorded on a recording medium (optical disc) is used by using a light source module in which two laser light emitting units having different wavelengths are incorporated in one package, and an optical system common to each wavelength including an objective lens, It is possible to provide an optical pickup device and an optical reproducing device capable of stable and excellent reproduction at low cost.

[Brief description of 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) which constitutes a light source.

3A and 3B are structural views of an objective lens, FIG. 3A being a front view and FIG. 3B being a side view.

4A and 4B are structural views of a sensor lens, FIG. 4A is a front view, FIG. 4B is one side sectional view, FIG. 4C is the other side sectional view, and FIG. 4A is a sectional view taken along the line AA ′ of FIG. 4A, and FIG. 4E is a sectional view taken along the line BB ′ of FIG.

FIG. 5 is a diagram showing a light receiving element pattern configuration of a light receiving portion of a photodetector.

FIG. 6 is an explanatory diagram of an operation mode of a photodetector (PD-IC).

FIG. 7 is an explanatory diagram of an astigmatic difference used in the astigmatism method.

FIG. 8 is a diagram showing a working distance between an objective lens and an optical recording medium, and FIG. 8 (a) is a diagram between an optical recording medium (DVD) for reproducing using a laser beam having a short wavelength and an objective lens. 8B is a diagram showing a working distance between the objective lens 16 and an optical recording medium (CD) which is reproduced by using a laser beam having a long wavelength.

FIG. 9 is a diagram showing a schematic configuration of an optical reproducing device equipped with an optical pickup device according to an embodiment of the present invention.

FIG. 10 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 gratings 14, 24 Beam splitter (beam splitter plate) 15,25 Collimator lens 16,26 Objective lens (double focus diffraction type 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 adjusting pin holes 18, 28 Photodetector (PD-IC) 18a, 28a CD light receiving portion 18b, 28b DVD light receiving portion 18a1, 18b1 Main beam light receiving Element pattern parts 18a2, 18a3, 18b2, 18b3 Sub-beam light receiving element pattern parts 50 Optical reproduction device 52 Spindle motor 54 Controller 55 Laser drive circuit 56 Lens drive circuit 57 Focus servo follow-up circuit 58 Tracking servo follow-up circuit 59 Laser control circuit 100 Optical recording medium D1, D2 Working distance LA Distance between light emitting points LB Distance between light receiving parts α Astigmatic difference (amount of astigmatic difference) θ1, θ2 Full width half maximum angle

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5D118 AA26 BA01 BB01 BB07 CD02                       CF01                 5D119 AA40 AA41 BA01 BB01 BB04                       EA03 EC01 EC45 EC47 FA08                       JA43 JA47 KA04 LB12                 5D789 AA40 AA41 BA01 BB01 BB04                       EA03 EC01 EC45 EC47 FA08                       JA43 JA47 KA04 LB12

Claims (9)

[Claims] 1. A package comprising a first light emitting portion for emitting a first laser light having a relatively short wavelength and a second light emitting portion for emitting a second laser light having a relatively long wavelength. A two-wavelength laser light source, a lens having a positive power, and a concentric ring-shaped hologram, and the first or second laser light is focused on the information recording surface of the optical recording medium and read. An objective lens that forms a spot, a photodetector that receives the first or second laser light and converts it into an electric signal corresponding to the intensity of a light beam, and an emission from the two-wavelength laser light source that includes the objective lens An optical system for guiding the first or second laser light to the information recording surface of the optical recording medium, and an optical system for guiding the light beam reflected by the optical recording medium including the objective lens to the photodetector. Optical pick-up characterized by having Device. 2. The optical pickup device according to claim 1, wherein the objective lens outputs a signal recorded on a first optical recording medium having a relatively thin first protective layer. When reproducing using the first laser light, the spherical aberration of the first laser light that occurs depending on the thickness of the first protective layer is corrected, and the second thicker laser light is used. When a signal recorded on the second optical recording medium on which the second protective layer is formed is reproduced by using the second laser light, a second signal is generated depending on the thickness of the second protective layer. An optical pickup device, which corrects spherical aberration of laser light. 3. The optical pickup device according to claim 1, wherein the photodetector includes a first-system light receiving unit that receives the first laser light, and the second laser light. An optical pickup device comprising a second system light receiving section for receiving light. 4. The optical pickup device according to claim 1, wherein the full width at half maximum angle of the emission characteristic of the first laser light emitted from the first light emitting portion is θ1. And θ1> θ2, where θ2 is the full width at half maximum of the emission characteristic of the second laser light emitted from the second light emitting section. 5. The optical pickup device according to claim 1, wherein the objective lens is focus-controlled by an astigmatism method. 6. The optical pickup device according to claim 5, wherein the photodetector is provided on the light receiving unit of the first system or the light receiving unit of the second system used for the astigmatism method. When the value of the astigmatic difference is α and the distance between the light receiving unit of the first system and the light receiving unit of the second system is LB, 4α ^1/2 <LB <7α ^1/2 Optical pickup device. 7. The optical pickup device according to claim 1, wherein the signal recorded on the first optical recording medium is reproduced by using the first laser light. The objective lens and the first
The distance (working distance) from the optical recording medium is D1, and the objective lens and the second light are used when the signal recorded on the second optical recording medium is reproduced using the second laser light. An optical pickup device characterized in that D1> D2, where D2 is the distance from the recording medium. 8. The optical pickup device according to claim 1, wherein the optical system guides the first or second laser light to an information recording surface of the optical recording medium, The optical recording is performed in a non-shared portion with an optical system that guides the light beam reflected by the optical recording medium to the photodetector and on an optical path of the optical system that guides the light beam reflected by the optical recording medium to the light receiving element. An optical pickup device, comprising: a reflected light focusing position adjusting unit for optically adjusting a focusing position of a light beam reflected by a medium. 9. An optical reproducing apparatus comprising the optical pickup device according to claim 1. Description: