JP2002074732A - Optical pickup device and laser diode chip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device for which miniaturization is achieved by simplifying the device structure for using plural laser beams of different wavelengths and also to provide a laser diode chip. SOLUTION: The optical pickup device is provided, on the base plate, with at least two light-emitting parts for emitting laser beams having different wavelengths and an elliptical cross section. The device is also equipped with a means for emitting, selectively in the same direction, a laser beam from at least either one of the two light-emitting parts, and with an optical system that guides the laser beam emitted from the light emitting means to the recording face of a recording medium and that also guides the laser beam reflected on the recording face to a photodetecting means. At least two light-emitting parts are arranged on the base plate in such a manner that the major axes of the elliptical cross section of the outgoing laser beams are not parallel to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device which emits a plurality of laser beams having different wavelengths to read information from a plurality of recording media of different types, and a laser diode chip for the optical pickup device.

[0002]

2. Description of the Related Art In general, a semiconductor laser device is used as a light source of an optical pickup device for reproducing an optical disk such as a CD or a DVD. In order to reproduce the disc satisfactorily, the semiconductor laser device differs in the emission wavelength and the numerical aperture (NA) of the objective lens between the CD reproduction and the DVD reproduction.
A is 0.6, and the wavelength is 780 nm for CD.
And NA is 0.45.

In order to reproduce different types of discs such as CDs and DVDs with one player, 650 nm
An optical pickup device incorporating a light source having two wavelengths of / 780 nm has been studied. FIG. 1 shows an example of such an optical pickup device. The optical pickup device shown in FIG.
Laser element 1 that emits a laser beam having a wavelength of 650 nm
And a laser element 2 that emits a laser beam having a wavelength of 780 nm, a combining prism 3, a half mirror 4, a collimator lens 5, and an objective lens 6 are sequentially arranged. Further, on another optical axis branched from the half mirror 4, a cylindrical lens (not shown) and a photodetector 7 are arranged. In this configuration, the combining prism 3
In both cases, the light emitted from the laser element is transmitted to the disk 8 along the optical axis Y after passing through the combining prism 3 because the optical system from the optical disk to the disk 8 is shared by the CD and the DVD. It is being led. The objective lens 6 used here is a bifocal lens, and can obtain mutually different focal positions according to the two wavelengths. Thereby, it is possible to suppress the spherical aberration caused by the difference in the thickness of the surface substrate between the CD and the DVD.

[0004]

However, in the above-described configuration, the number of components is large and the price is expensive, such as the necessity of a synthetic prism. Further, it is necessary to perform alignment between the two laser elements and the combining prism, which complicates the configuration and makes the adjustment difficult. In view of the above problems, an object of the present invention is to provide an optical pickup device and a laser diode chip capable of simplifying the device configuration when using a plurality of laser beams having different wavelengths and achieving downsizing. is there.

[0005]

An optical pickup device according to the present invention has at least two light emitting portions for emitting laser beams having an elliptical cross section at different wavelengths on a substrate. A light emitting means for selectively emitting a laser beam from one of the light emitting portions in the same emission direction, and a laser beam emitted from the light emitting means being guided to a recording surface of the recording medium and reflected by the recording surface of the recording medium An optical system for guiding the laser beam to the light detecting means,
, Wherein at least two light-emitting portions are arranged on the substrate such that the major axes of the elliptical cross sections of the emitted laser beams are not parallel to each other.

A laser diode chip according to the present invention is a laser diode chip for an optical pickup device having at least two light emitting portions for emitting laser beams having elliptical cross sections at different wavelengths in the same emission direction on a substrate. Wherein the at least two light emitting units are arranged on the substrate such that the major axes of the elliptical cross sections of the emitted laser beams are not parallel to each other.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. FIG. 2 shows an optical system of the optical pickup device according to the present invention. This optical pickup device has a semiconductor laser element 11 that emits two types of laser beams having different wavelengths. In the optical pickup device, a laser beam emitted from a semiconductor laser element 11 reaches a half mirror (beam splitter) 13 via a grating 12. The grating 12 is provided to separate the laser beam into a plurality of light beams (zero-order light, ± first-order light). The 0th order light is for focus servo, and the ± 1st order light is 3
For tracking servo of beam method. The half mirror 13 reflects the laser beam at an angle of about 90 degrees with respect to the incidence of the laser beam. The direction of the reflected laser beam is in the direction of the optical disk 17 as a recording medium, and a collimator lens 14 and an objective lens 15 are arranged between the half mirror 13 and the optical disk 17.

The laser beam reflected by the half mirror 13 is configured to reach the disk 17 via the collimator lens 14 and the objective lens 15 in order. The collimator lens 14 converts the laser beam from the half mirror 13 into parallel light and supplies it to the objective lens 15. The objective lens 15 is a bifocal lens, and converges a parallel laser beam on the recording surface of the disk 17. A DVD and a CD (including a CD-R) are used as the disk 17, and one of the disks is mounted on a turntable (not shown).

The laser beam reflected by the recording surface of the disk 17 is converted into a parallel laser beam by the objective lens 15,
After being converted into a laser beam converged by the collimator lens 14, the laser beam passes through the half mirror 13 after being slightly refracted.
The laser beam that has passed through the half mirror 13 is
8. FIG. 3 shows a cross section of a chip of the semiconductor laser device 11. As shown in FIG. 3, the semiconductor laser element 11 is of a monolithic type, and has a first light emitting portion 3 having a first light emitting point A1 for emitting a first laser beam having a wavelength of 650 nm on a single Si substrate 30.
1 and a second laser emitting a second laser beam having a wavelength of 780 nm.
A second light emitting section 32 having a light emitting point A2 is formed. The light emitting surface of the first light emitting unit 31 having the light emitting point A1 and the light emitting surface of the second light emitting unit 32 having the light emitting point A2 face the same emission direction.

When the light emitting direction sides of the light emitting points A1 and A2 of the substrate 30 are set to the front, the front has a flat plate shape on the right side and a trapezoidal shape on the left side. The trapezoidal shape is the substrate 3
0 has an inclined surface at an angle of 45 degrees from the left side slightly from the center of the front. The first light emitting part 31 is formed in a flat plate-shaped part, and the second light emitting part 32 is formed on the inclined surface of the trapezoidal part.

The first light emitting section 31 and the second light emitting section 32 have a laminated structure as described later. On the surface of the substrate 30 opposite to the surface on which the first light emitting unit 31 and the second light emitting unit 32 are formed, a back electrode 34 serving as a common electrode for both light emitting units 31 and 32 is provided.
have. The first light emitting unit 31 is sequentially n
AlGalnP cladding layer 41, strained quantum well active layer 4
2, p-type AlGalnP cladding layer 43, n-type GaAs
It has a layer 44, a p-type GaAs layer 45, and an electrode 46. The cross section of the cladding layer 43 has a trapezoidal central portion. An n-type GaAs layer 44 is formed so as to cover the cladding layer 43 except for the trapezoidal top surface. A p-type GalnP layer 47 is formed on the trapezoidal top surface. The first light emitting point A1 is located in the strained quantum well active layer 42.

The second light emitting section 32 has a so-called double hetero structure, in which a pair of n-type AlGaAs buried layers 51 and 52 are arranged on the substrate 30 with a predetermined gap, and each of the pair of n-type AlGaAs buried layers 51 and 52 is provided. One of the electrodes 55 is provided on top of the other through insulating layers 53 and 54. On the substrate 30 between the buried layers 51 and 52, an n-type AlGaAs cladding layer 56, an undoped GaAs active layer 57, and a p-type AlGaAs cladding layer 58 are sequentially laminated. The cladding layer 58 is in contact with the electrode 55.
The second light emitting point A2 is located on the active layer 57. First emission point A
The distance between the optical axis from 1 and the optical axis from the second light emitting point A2 is, for example, 100 μm.

The semiconductor laser elements 11 are fixed to an insulating submount, and they are covered with a casing member 11a as shown in FIG. The semiconductor laser element 11 transmits a first laser beam and a second laser beam to a laser driving unit.
(Not shown) to selectively emit in response to a control signal. Although the two beams are not emitted at the same time, the central axis of the first laser beam and the central axis of the second laser beam are substantially parallel. The cross-sectional shapes of the emitted first and second laser beams are elliptical as shown by the broken lines in FIG. In the present application, the central axis of the laser beam is
This is a line passing through the center of distribution of light intensity in the cross section of the laser beam.

As shown in FIG. 4, the light receiving surface of the photodetector 18 is composed of three square areas T1, M, and T2, which are arranged in a line on the same plane in that order. Area M
Is located between the regions T1 and T2, and is divided into four parts in a cross. Each divided surface is formed by the light receiving elements 18a to 18d. The light receiving surfaces of the light receiving elements 18a and 18d are symmetrical with respect to the split intersection, and the light receiving surfaces of the light receiving elements 18b and 18c are symmetrical with respect to the split intersection. The areas T1 and T2 are tracking areas of the three-beam method, and are formed by the light receiving elements 18e and 18f.

In the optical system of the optical pickup device according to the present invention shown in FIG. 2, when the disk 17 is a DVD, the semiconductor laser element 11 is selectively driven by the laser drive unit so that the semiconductor laser element 11 has a first laser beam having a wavelength of 650 nm. Fire. The zero-order light of the first laser beam passes through the grating 12 as it is and reaches the half mirror 13. The 0th-order light of the first laser beam reflected by the half mirror 13 reaches the disk 17 via the collimator lens 14 and the objective lens 15.

FIG. 5 shows a carriage 2 which carries the pickup device and moves in the radial direction of the disk in the disk player equipped with such a pickup device according to the present invention.
FIG. 3 is a view of the shape of a cross section S of a first laser beam output from a disk viewed from a disk 17 side. Let X be a straight line connecting the rotation center point A of the turntable 21 supporting the disk 17 to the center axis B of the first laser beam, and let Y be a straight line passing through the center axis B in the track tangent direction perpendicular to the straight line L1. . The cross-sectional shape of the first laser beam is an ellipse, and the major axis of the ellipse is inclined by +45 degrees with respect to the straight line X. That is, the spot light by the first laser beam is formed on the track of the disk 17 at an angle of 45 degrees with respect to the disk radial direction.

The 0th-order light of the first laser beam reflected by the recording surface of the disk 17 passes through an objective lens 15, a collimator lens 14, and a half mirror 13 to a photodetector 18.
To the area M of the light receiving surface of Light receiving elements 18a to 18d
, A read signal RF, a tracking error signal TE, and a focus error signal FE are generated. The output signals of the light receiving elements 18a to 18d are sequentially represented by a
Ｄd, the read signal RF is RF = a + b + c + d, and the tracking error signal TE is calculated by the phase difference method as TE = (a ′ + d ′) − (b ′ + c ′). Note that a ', b', c ', and d' are signals calculated by comparing the phases of the signals a, b, c, and d and the read signal RF.

The focus error signal FE is calculated by the astigmatism method as FE = (a + d)-(b + c). These read signal RF, focus error signal FE, and tracking error signal TE are generated by an arithmetic circuit (not shown).

When the disk 17 is a CD, the semiconductor laser element 1 is selectively driven by the laser drive circuit described above.
1 emits a second laser beam having a wavelength of 780 nm. When the second laser beam reaches the grating 12,
± 1st-order light of the second laser beam is generated by the diffraction effect of the grating 12. The ± first-order light is used as a sub-beam for tracking in the three-beam method.

The second laser beam that has passed through the grating 12 as described above is reflected by the half mirror 13 and then reaches the disk 17 via the collimator lens 14 and the objective lens 15. FIG. 6 is a view of the cross section S of the second laser beam (main beam) output from the carriage 22 of the pickup device as viewed from the disk 17 side in a disc play equipped with such a pickup device according to the present invention. Similarly to FIG. 5, a straight line connecting the rotation axis A of the turntable 21 supporting the disk 17 to the center axis B of the second laser beam is defined as X, and the center axis B is defined as a track tangent direction perpendicular to the straight line L1. The straight line that passes is Y. The shape of the cross section S of the second laser beam is an ellipse, and the major axis of the ellipse coincides with the straight line Y, and the ellipse cross section S has no inclination. That is, the spot light of the second laser beam is applied to the tracks of the disk 17 with the disk radial direction as the short axis and the track tangential direction as the long axis.

Each secondary light beam of the second laser beam reflected by the recording surface of the disk 17 is passed through an objective lens 15, a collimator lens 14, and a half mirror 13 to a photodetector 18.
Reach the regions T1, M, and T2 of the light receiving surface of. That is,
The main beam of the second laser beam forms a spot light in the region M, and the sub beam for tracking forms a spot light in the regions T1 and T2.

A read signal RF and a focus error signal FE are generated according to each output signal of the light receiving elements 18a to 18d. Further, a tracking error signal TE is generated according to each output signal of the light receiving elements 18e and 18f. Assuming that the output signals of the light receiving elements 18a to 18f are a to f in that order, the read signal RF is RF = a + b + c + d, and the tracking error signal TE is calculated by the three-beam method as TE = ef.

The focus error signal FE is calculated by the astigmatism method as FE = (a + d)-(b + c). In the Gaussian distribution of the elliptical beam, as shown in FIG. 7, the range having the intensity equal to or more than the predetermined intensity from the center intensity is widened in the long-axis direction cross section, and as shown in FIG. A range having an intensity equal to or more than a predetermined intensity from the center intensity becomes narrow. Then, the objective lens 15 for that narrow the beam as the rim intensity of Gaussian distribution (intensity near the lens opening) is large, the beam collected by the size W _L in the longitudinal cross-section is smaller than the beam size W _S in the short axis cross-section Become. That is, by passing through the objective lens 15, the major axis direction of the cross section of the elliptical beam is rotated by 90 degrees.

Generally, in an optical pickup device,
When the major axis of the elliptical beam is perpendicular to the tangent direction of the track, the spot on the disk has the major axis of the ellipse parallel to the tangential direction of the track for the above-described reason. As a result, the crosstalk from the adjacent track decreases and the jitter component of the read signal increases, but the level of the high frequency component of the RF signal decreases due to the poor resolution of the pit detection. On the other hand, when the short axis of the elliptical beam and the tangential direction of the track are perpendicular to each other, the spot on the disk has the short axis of the ellipse parallel to the tangential direction of the track. As a result, the jitter component due to crosstalk is reduced, but the resolution is improved and the high frequency component level of the RF signal is increased.

In the optical pickup device of the present invention described above, when the disk 17 is a DVD of high-density recording, the track-to-track distance is small and the pits are small. And the straight line in the tangential direction of the track are tilted by 45 degrees, making it less susceptible to the crosstalk from the adjacent track, preventing an increase in the jitter component of the read signal, and at the same time, extremely deteriorating the resolution. Can be prevented.

When the disk 17 is a CD, the CD has a wider track interval than a DVD and is hardly affected by crosstalk. Therefore, the major axis of the elliptical beam and the straight line in the tangential direction of the track are made parallel. Good resolution is ensured by making the short axis of the elliptical beam perpendicular to the straight line in the tangential direction of the track. Further, in the above-described embodiment, the case where the present invention is applied to the infinite optical system using the collimator lens 14 has been described, but the present invention can also be applied to a finite optical system.

Further, in the above embodiment, the semiconductor laser element is provided with two light emitting points having different emission wavelengths. However, the present invention is also applicable to a semiconductor laser element having three or more light emission points having different emission wavelengths. The invention can be applied.
Further, in the above-described embodiment, the slope of the substrate 30 on which the second light emitting unit 32 is disposed is inclined at 45 degrees with respect to the plane, but the angle is not limited to this. Further, the inclination of the cross section S of the first laser beam in FIG. 5 is not limited to 45 degrees.

[0028]

As described above, according to the present invention, the optical systems can be compactly arranged and arranged, so that the configuration of the optical pickup device can be simplified and the size can be reduced. Further, since the two light emitting units are arranged and formed on the substrate such that the major axes of the elliptical cross sections of the emitted laser beams are not parallel to each other, appropriate reading is performed according to the recording density of the recording medium. be able to.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of a conventional optical pickup device.

FIG. 2 is a diagram showing a configuration of an optical pickup device of the present invention.

FIG. 3 is a diagram showing a configuration of a semiconductor laser device in the device of FIG. 2;

FIG. 4 is a diagram showing a light receiving pattern of a photodetector in the apparatus of FIG.

FIG. 5 is a diagram showing the spot shape and direction of an irradiation laser beam on a DVD.

FIG. 6 is a diagram showing a spot shape and a direction of an irradiation laser beam on a CD.

FIG. 7 is a diagram showing a Gaussian distribution in a longitudinal section of an elliptical beam.

FIG. 8 is a diagram showing a Gaussian distribution in a short-axis direction cross section of an elliptical beam.

[Explanation of symbols]

 1,2,11 Semiconductor laser element 6,15 Objective lens 7,18 Photodetector 8,17 Optical disk 31 First light emitting unit 32 Second light emitting unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D119 AA01 AA03 AA41 BA01 BB01 BB04 EC45 EC47 FA05 FA08 LB04 5F073 AA74 AB27 AB29 BA05 BA06 CA05 CA14 CB04 EA04 FA01 FA11

Claims (6)

[Claims] 1. A substrate having at least two light emitting portions for emitting laser beams having an elliptical cross section at different wavelengths on a substrate, wherein at least one of the at least two light emitting portions is provided.
A light emitting unit that selectively emits a laser beam from the light emitting unit in the same emission direction, and guides the laser beam emitted from the light emitting unit to a recording surface of a recording medium and is reflected by the recording surface of the recording medium. An optical system for guiding the laser beam to light detection means, wherein the at least two light emitting units are arranged such that major axes of elliptical cross sections of the emitted laser beam are not parallel to each other. An optical pickup device disposed on the substrate. 2. A laser beam having a shorter wavelength among the laser beams emitted from the at least two light-emitting portions has a major axis of an elliptical cross section inclined with respect to a tangential direction of a recording track of the recording medium. Said at least two
The laser beam having a longer wavelength among the laser beams emitted from the two light-emitting portions is characterized in that the major axis of its elliptical cross section is parallel to the tangential direction of the recording track of the recording medium. The optical pickup device according to claim 1. 3. The recording medium irradiated with the shorter wavelength laser beam is a DVD, and the recording medium irradiated with the longer wavelength laser beam is a CD. Item 3. The optical pickup device according to Item 2. 4. A laser diode chip for an optical pickup device, wherein at least two light-emitting portions for emitting laser beams having elliptical cross-sections at different wavelengths in the same emission direction are formed on a substrate, A laser diode chip, wherein the two light emitting units are arranged on the substrate such that major axes of an elliptical cross section of the emitted laser beam are not parallel to each other. 5. The substrate has a flat portion and a slope portion following the flat portion, one of the at least two light emitting portions is formed on the flat portion, and the at least two light emitting portions are formed on the flat portion. The laser diode chip according to claim 4, wherein the other light emitting portion is formed on the slope portion. 6. The laser diode chip according to claim 5, wherein a wavelength of the laser beam emitted from the one light emitting unit is shorter than a wavelength of the laser beam emitted from the other light emitting unit.