JP2004178763A - Pickup device and disk device using this pickup device - Google Patents

Abstract

A sub-beam reflected by a sub-beam generated by a diffraction grating does not cause unnecessary reflection at a mirror portion of a chip end face of a semiconductor laser by setting an angle between a surface of the diffraction grating and an optical axis to a predetermined value. And a disk device using the pickup device.
A chip end face provided inside a semiconductor laser for emitting a light beam toward an information recording medium, and a diffraction grating for splitting the light beam emitted from the chip end face into a main beam and two sub-beams 8 and an objective lens 11 for condensing each light beam split by the diffraction grating 8 on a predetermined recording surface of the information recording medium, and each light beam condensed by the objective lens 11 is used for information recording. After being reflected by the medium, the diffraction grating 8 is tilted by a predetermined amount so that the chip end surface 202 is not irradiated.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a CD (Compact Disk), a CD (Compact Disk) -R (Recordable) / RW (ReWritable), a DVD (Digital Versatile Disk) -ROM (Read Only Memory), and a DVD (Digital Radio (DRAM)). The present invention relates to a pickup device for recording or reproducing information on or from an optical disk such as an access memory, and a disk device using such a pickup device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, in the field of recording media, DVDs have been developed that have the same size as the diameter (12 cm) of a conventional CD on which audio or digital data is recorded, and yet are capable of high-density recording. Since the DVD has a high recording density, laser light having a wavelength (for example, 650 nm) shorter than the wavelength (for example, 780 nm) of light for reading data of the CD is required.
[0003]
As a disk device, a device capable of recording and reproducing both a CD system and a DVD system is desired. Thus, as a pickup device using a light emitting element (laser element) that emits a laser beam of a predetermined wavelength, a first light source for CD (780 nm wavelength) and a second light source for DVD (650 nm wavelength) Have been developed.
[0004]
By the way, when recording or reproducing information by irradiating a laser beam using a light source as in the above-described pickup device, after the laser beam from the light source is radiated to the information recording surface of the disc via the diffraction grating, In some cases, the reflected light from the information recording surface returns to the light source again (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP-A-61-150391 (page 4, FIG. 2, FIG. 3)
[0006]
[Problems to be solved by the invention]
As described above, when the laser light emitted from the light source is reflected on the information recording surface of the disk and the reflected light returns to the light source, noise is likely to occur, and the S / N of the reproduced signal is deteriorated. There was a problem that occurred.
[0007]
The present invention has been made to solve such a problem, and by setting the angle between the surface of the diffraction grating and the optical axis to a predetermined value, the disk reflected light of the sub-beam generated by the diffraction grating can be used for the semiconductor laser. It is an object of the present invention to realize a pickup device capable of obtaining good tracking error signal characteristics without causing unnecessary reflection at a mirror portion of a chip end surface, and a disk device using the pickup device.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a laser chip end face which is provided inside a semiconductor laser and emits a light beam toward an information recording medium, and comprises a light beam emitted from the laser chip end face. A diffraction grating for splitting the light beam and two sub-beams, and light collecting means for condensing each light beam split by the diffraction grating on a predetermined recording surface of the information recording medium; After the respective light beams condensed by the means are reflected by the information recording medium, the diffraction grating is tilted by a predetermined amount so as not to be irradiated on the end face of the laser chip.
[0009]
According to the above configuration, since the return light from the disk is not irradiated on the chip end surface of the semiconductor laser, a good tracking signal can be obtained.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view showing the configuration of a pickup device described in this embodiment. A pickup device for reproducing information from a read-only optical disk will be described as an example.
[0011]
In FIG. 1, a semiconductor laser 6 serving as a light source for emitting a light beam, and a collimator lens 7, a diffraction grating 8, and a collimator lens disposed between the semiconductor laser 6 and the optical disk 5 with their optical axes aligned with each other. There is an objective lens 11, and a non-polarizing beam splitter (BS) 9 is provided between the collimator lens 7 and the diffraction grating 8. A rising mirror 10 for bending the optical path by 90 degrees is provided between the collimator lens 7 and the BS 9. Further, the pickup device 101 includes a photodetector 14 that receives light reflected from the optical disk 5. As shown in FIG. 2, the photodetector 14 includes a main beam detector 26A that receives a main beam located at the center of the three divided light beams, and two sub beams that are located on both sides of the main beam. A first sub-beam detector 26B and a second sub-beam detector 26C are provided. The first and second sub-beam detectors 26B and 26C are disposed on both sides of the main-beam detector 26A with the main-beam detector 26A interposed therebetween.
[0012]
The main beam detector 26A is equally divided into four sensing regions 41A to 41D by two dividing lines L1 and L2 orthogonal to each other at the center. The line width of the dividing lines L1 and L2 is 5 to 10 μm, and the light incident on the dividing lines L1 and L2 is not converted into an electric signal by the photodetector 14. Therefore, the four sensing areas 41A to 41D in the main beam detector 26A are The light received independently of each other is converted into an electric signal.
[0013]
The light beam emitted from the semiconductor laser 6 is incident on the diffraction grating 8, and is divided into a main beam 27A, a first sub beam 27B, and a second sub beam 27C and transmitted. The diffraction grating 8 is not parallel to the optical axis of the light beam emitted from the semiconductor laser 6 and has a slight angle, more specifically, an angle of about 1 to 4 degrees.
[0014]
Each light beam divided into three by the diffraction grating 8 is reflected by the beam splitter 9 and its optical path is changed by 90 degrees. The beam splitter 9 is a non-polarization type, and reflects about half of the incident light beam and reflects about the other half.
[0015]
Further, the light beam reflected by the beam splitter 9 is reflected by the rising mirror 10 and the optical path is changed by 90 degrees. The light beam reflected by the rising mirror 10 is incident on the collimator lens 7, where each beam is converted from divergent light into parallel light and transmitted. The light beam transmitted through the collimator lens 7 enters the objective lens 11, where it is converged and focused on a predetermined information recording surface of the optical disk 5. Since the light beam incident on the objective lens 11 is composed of three light beams, three condensed spots are formed on the information recording surface.
[0016]
The three light beams reflected by the optical disk 5 reach the objective lens 11 again. Each light beam transmitted through the objective lens 11 reaches the collimator lens 7, where it is converted from a parallel light beam into convergent light again, and reaches the rising mirror 10 and the beam splitter 9. Approximately half of the three light beams that have entered the beam splitter 9 are transmitted and reach the photodetector 14, while the other approximately half are reflected and proceed to the semiconductor laser 6 side.
[0017]
Since the diffraction grating 8 has a slight angle, the reflected light that has proceeded to the semiconductor laser 6 is prevented from hitting an end face of a later-described laser chip in the semiconductor laser 6.
[0018]
Each light beam that has reached the photodetector 14 irradiates a main beam detector 26A, a first sub-beam detector 26B, and a second sub-beam detector 26C in the photodetector 14 as condensed spots. Here, since the normal line of the beam splitter 9 is not parallel to the optical axis but at an angle (here, for example, 45 degrees), when a light beam in a converged state is transmitted, a so-called astigmatism is generated. Aberration occurs.
[0019]
Since the main beam detector 26A is equally divided into four divided areas into four sensitive areas 41A to 41D, the focusing control of the objective lens 11 is performed based on the amount of the main beam applied to each of these areas. Assuming that the photoelectric conversion outputs obtained in the four sensing areas 41A to 41D are I1, I2, I3, and I4, respectively, a so-called focus error signal FES indicating the amount of defocus on the information recording surface of the optical disk 5 is expressed by the following equation 1. can get.
[0020]
(Equation 1) FES = (I1 + I3)-(I2 + I4)
This pickup device is configured to detect a focusing error by a so-called astigmatism method and perform focus control. That is, when the converged main beam reflected from the optical disk 5 is transmitted through the parallel plate beam splitter 9, astigmatism occurs in principle. Utilizing this effect, a focusing error signal is obtained by the arithmetic processing of the electric signal of (Equation 1). The details are as described in the document "Compact disk reader" (Heitaro Nakajima, Hiroshi Ogawa: Ohmsha).
[0021]
On the other hand, the first side beam 27B and the second side 27C are incident on the first sub-beam detector 26B and the second sub-beam detector 26C of the photodetector 14, respectively. Assuming that the photoelectric conversion outputs obtained by the first sub-beam detector 26B and the second sub-beam detector 26C are I5 and I6, respectively, a tracking error signal which is a track deviation of the main beam from the recording track on the information recording surface of the optical disk 5 TES is obtained by the following equation (2).
[0022]
(Equation 2) TES = I5-I6
This pickup device is configured to perform tracking control by detecting a tracking error by a so-called three-beam method, and to perform focus control by detecting a focusing error by an astigmatism method. The generation of the tracking error signal is well known, and its details are described in the document "Compact Disc Reader" (Heitaro Nakajima, Hiroshi Ogawa: Ohmsha), and the description thereof is omitted here.
[0023]
In the pickup device having the above-described configuration, the light returning to the semiconductor laser 6 out of the reflected light from the optical disk 5 may cause the inconvenience described below due to the size and positional relationship of each optical element. Yes, and will be described in detail below.
[0024]
FIG. 3 is a configuration diagram showing a semiconductor laser, and FIG. 4 is an enlarged view of an LD chip mounted on the semiconductor laser. FIG. 5 shows a state in which the reflected light reflected from the disk travels to the semiconductor laser via the diffraction grating. FIG. 5A shows a state in which the surface of the diffraction grating is perpendicular to the optical axis of the light beam. (B) shows the case where the diffraction grating surface makes a slight angle from a state perpendicular to the optical axis of the light beam.
[0025]
In the semiconductor laser 6 shown in FIG. 3, the flange 210 is made of a heat conductive material and is for heat dissipation, and is for suppressing the lead wire 211. The reference surface 212 indicates a reference position when the LD chip (laser chip) 201 or the like is mounted. The window glass 213 protects the LD chip 201 and the like. The PD chip 214 detects the light intensity of the light beam irradiated opposite to the light beam emitted from the LD chip 201 toward the optical disk, and the detected light intensity is subjected to APC (Automatic power control). Is done.
[0026]
An LD chip 201 shown in FIG. 4 is disposed on an insulating submount 215 and has an end face 202 at a position where the LD chip 201 is irradiated with a light beam. The light beam is emitted from the end face 202. The end surface 202 is a mirror surface, which is made by utilizing the cleavage property of a crystal corresponding to the substrate of the LD chip 201. Further, since the end surface 202 is a mirror surface, light incident on the end surface 202 for some reason is reflected by the end surface 202.
[0027]
The light reflected from the optical disk 5 and returned to the semiconductor laser 6 passes through the diffraction grating 8 before reaching the semiconductor laser 6. In the outward light path, the light beam emitted from the semiconductor laser 6 is divided into three by the diffraction grating 8 as described above, but in the return light path, after these three light beams Through the diffraction grating 8, the light beam is again split into three light beams. These three light beams return to different parts in the semiconductor laser 6. The design point of the diffraction grating 8 is how to set the diffraction angle of the ± 1st-order diffracted light and the light amount ratio of the ± 1st-order diffracted light to the 0th-order light.
[0028]
At this time, as shown in FIG. 5A, the first sub-beam 27B and / or the second sub-beam 27C are placed on the end face 202 of the LD chip 201 due to the relationship between the diffraction angle and the distance between the diffraction grating 8 and the semiconductor laser 6. May reach. In such a situation, the first sub-beam 27B and / or the second sub-beam 27C are reflected by the mirror end surface 202 and reach the optical disk 5 again. This sub-beam will be referred to herein as a chip end face reflected beam.
[0029]
After being reflected by the optical disk 5, the chip end face reflected beam is incident on the first sub-beam detector 26B and / or the second sub-beam detector 26C. Since the chip end face reflected beam does not always have the same phase relationship with the first and second sub-beams that first passed through the outward optical path, the resulting optical disc 5 is obtained by the first and second sub-beams by the outward optical path. A DC component is superimposed on a modulation signal based on the recorded information. An example of this is shown in FIG. FIG. 6A shows a tracking error signal when the return light is reflected by the chip end face, and it can be seen that the amplitude of the tracking error signal fluctuates greatly. This means that a DC component is also superimposed on the tracking error signal TES, and as a result, tracking servo cannot be applied based on this signal.
[0030]
Also, as shown in FIG. 5B, the normal line of the diffraction grating 8 is not parallel to the optical axis of the light beam emitted from the semiconductor laser 6, but forms a slight angle. Accordingly, even if the reflected light of the optical disk returning to the semiconductor laser 6 along the return optical path is divided into three by the diffraction grating 8, neither of the sub-beams reaches the end face 202. For this reason, the chip end face reflected beam shown in FIG. 5A is not generated, and a good tracking error signal TES as shown in FIG. 6B can be obtained, and stable tracking control can be performed.
[0031]
Note that the angle between the light beam emitted from the semiconductor laser 6 and the optical axis is not limited to 1 degree to 4 degrees, and the optical specifications of the diffraction grating 8, the semiconductor laser 6, and other optical elements. Needless to say, it may be determined as appropriate from the dimensions, shape, arrangement relationship between the optical elements, and the like. The point is to prevent the reflected light from the optical disk from hitting the end face 202 of the LD chip 201 in the semiconductor laser 6. In general, it can be set in the range of 1 to 4 degrees. Further, the place where the diffraction grating 8 is provided is not limited to immediately after the semiconductor laser 6, but may be before or immediately after the collimator lens 7 depending on the design of the optical system.
[0032]
Furthermore, in the above description, the sub-beam generated by the diffraction grating 8 in the reflected light of the optical disk is configured to escape above the chip end face, but is configured to escape to the left and right sides of the chip end face. You can also.
[0033]
Next, a second embodiment will be described.
In the second embodiment, as in the first embodiment, the normal to the diffraction grating 8 is not parallel to the optical axis of the light beam emitted from the semiconductor laser, but forms a slight angle. In the second embodiment, a mechanism for changing the inclination of the diffraction grating is further provided. This will be described below.
[0034]
FIG. 7 shows a variable mechanism for varying the inclination of the diffraction grating according to the second embodiment of the present invention.
The diffraction grating 8 is joined on a metal leaf spring 110. An opening is provided at the center of the metal leaf spring 110, and does not block the light beam transmitted through the diffraction grating 8. A part of the metal leaf spring 110 has a constriction 111, and holes 112 and 113 are provided at both ends. The metal leaf spring 110 to which the diffraction grating 8 is joined is fixed to a diffraction grating holder 116 by holes 112 and screws 114.
[0035]
On the other hand, a spring 117 is provided between the other hole 113 and the diffraction grating holder 116, and the metal leaf spring 110 and the spring 117 are connected to the diffraction grating holder 116 by screws 115. With such a configuration, since the metal leaf spring 110 is constantly pressed by the spring 117, the amount of deflection of the metal leaf spring 110 can be changed depending on the degree of tightening of the screw 115. As a result, the angle of the diffraction grating 8 joined to the metal leaf spring 110 can be adjusted.
[0036]
Next, a specific adjustment method will be described.
FIG. 8 shows an adjustment method in which the variable mechanism is attached to an optical base to change the inclination of the diffraction grating.
As shown in FIG. 8, the diffraction grating holder 116 pre-assembled as described above is disposed in a hole 118 provided first in the optical base 15 for mounting each optical element. One end surface thereof is pressed by a leaf spring 119 fixed to the base 15. However, since the optical base 15 is not completely fixed but is pressed with a predetermined pressure, the optical base 15 can be rotated in the adjustment for rotating the optical base 15 described later.
[0037]
Further, the diffraction grating holder 116 has a groove 120 below the diffraction grating holder 116 so that the tip 122 of the adjustment pin 121 can be inserted in the adjustment for rotating the optical base 15 described later.
[0038]
After assembling as described above, it is observed by a predetermined process how the first sub-beam 27B and the second sub-beam 27C irradiate the information recording pit array of the optical disk 5. Next, the adjustment pin 121 shown in FIG. 9 is inserted from the bottom of the optical base 15. The tip 122 of the adjustment pin 121 is configured to enter the groove 120 below the diffraction grating holder 116. Further, the center of the tip 122 is off the center of the end face of the adjustment pin 121. For this reason, when the adjustment pin 121 is rotated by a certain rotation angle with the adjustment pin 121 inserted into the optical base 15, the tip 122 of the adjustment pin 121 comes into contact with the groove 120 of the diffraction grating holder 116, and the diffraction grating The holder 116 is rotated. As a result, at a certain rotation position of the adjustment pin 121, the first sub beam 27B and the second sub beam 27C can be arranged in a desired relationship with the information recording pit row of the optical disk 5.
[0039]
More specifically, with respect to the pit row irradiated by the main beam 27A, the first sub-beam 27B is displaced from the center of the pit to the inner side or the outer side by a quarter of the pit row interval, On the other hand, the second sub-beam 27C is displaced from the center of the pit to the outer peripheral side or the inner peripheral side by a quarter of the pit row interval.
[0040]
When such adjustment is completed, the process proceeds to the step of observing the pit crossing signal. When the screw 115 is rotated, the angle formed by the diffraction grating 8 with respect to the optical axis via the metal leaf spring 110 changes, thereby preventing the generation of a chip end face reflected beam. A state that is not affected by the swell can be realized.
[0041]
The present invention is not limited to the above-described embodiment, and can be variously modified in an implementation stage without departing from the scope of the invention.
[0042]
【The invention's effect】
As described above, by setting the angle between the surface of the diffraction grating and the optical axis to a predetermined value, the disk reflected light of the sub-beam generated by the diffraction grating causes unnecessary reflection on the mirror surface of the chip end surface of the semiconductor laser. Good tracking error signal characteristics can be obtained without causing any.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a pickup device according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a photodetector.
FIG. 3 is a configuration diagram showing a semiconductor laser.
FIG. 4 is an enlarged view of an LD chip mounted on a semiconductor laser.
FIG. 5 is a diagram showing a state where reflected light reflected from a disk has advanced to a semiconductor laser via a diffraction grating.
6A is a diagram illustrating a tracking error signal when return light is reflected by a chip end surface, and FIG. 6B is a diagram illustrating a tracking error signal when return light is not reflected by a chip end surface.
FIG. 7 is a view showing a variable mechanism that varies the inclination of a diffraction grating according to a second embodiment of the present invention.
FIG. 8 is a diagram illustrating an adjustment method of attaching a variable mechanism to an optical base and varying the tilt of a diffraction grating.
FIG. 9 is a configuration diagram showing an adjustment pin.
[Explanation of symbols]
Reference Signs List 5 optical disk 6 semiconductor laser 7 collimator lens 8 diffraction grating 9 beam splitter 10 rising mirror 11 objective lens 14 photodetector 15 optical base 101 pickup device 110 leaf spring 111 constricted portions 112, 113 holes 114, 115 screws 116 diffraction grating holder 118 holes 120 Groove 121 Adjusting pin 122 Tip 201 LD chip 202 End face

Claims (10)

A laser chip end face that is provided inside the semiconductor laser and emits a light beam toward the information recording medium,
A diffraction grating that divides the light beam emitted from the laser chip end face into a main beam and two sub beams;
Light collecting means for condensing each light beam split by the diffraction grating on a predetermined recording surface of the information recording medium,
A pickup device, wherein the diffraction grating is tilted by a predetermined amount so that each of the light beams condensed by the light condensing means is reflected on the information recording medium and is not irradiated on the end face of the laser chip. 2. The pickup device according to claim 1, wherein the diffraction grating has a normal to a surface of the diffraction grating that is not parallel to an optical axis of the light beam emitted from an end face of the laser chip. 2. The pickup device according to claim 1, wherein the diffraction grating is inclined by 1 to 4 degrees with respect to the optical axis of the light beam. A laser chip end face that is provided inside the semiconductor laser and emits a light beam toward the information recording medium,
A diffraction grating that divides the light beam emitted from the laser chip end face into a main beam and two sub beams;
Light collecting means for condensing each light beam split by the diffraction grating on a predetermined recording surface of the information recording medium,
A pick-up device comprising: an adjusting unit for tilting the diffraction grating by a predetermined amount so that the respective light beams condensed by the condensing unit are reflected on the information recording medium and are not irradiated to the end face of the laser chip. . 5. The pickup device according to claim 4, wherein the adjustment unit adjusts the normal of the surface of the diffraction grating to be non-parallel to the optical axis of the light beam emitted from the end face of the laser chip. A laser chip end face that is provided inside the semiconductor laser and emits a light beam toward the information recording medium,
A diffraction grating that divides the light beam emitted from the laser chip end face into a main beam and two sub beams;
Condensing means for condensing each light beam split by the diffraction grating on a predetermined recording surface of the information recording medium,
Detection means for detecting the light intensity of each of the light beams condensed by the light condensing means,
Output means for outputting a signal for controlling the light condensing means in the tracking direction and the focusing direction based on the reflected light detected by the detection means, wherein each of the light beams condensed by the light condensing means is The disk device according to claim 1, wherein the diffraction grating is tilted by a predetermined amount so as not to irradiate the end face of the laser chip after being reflected by the information recording medium. 7. The disk device according to claim 6, wherein the diffraction grating has a normal to a surface of the diffraction grating that is non-parallel to an optical axis of the light beam emitted from an end face of the laser chip. 7. The disk drive according to claim 6, wherein the diffraction grating is inclined by 1 to 4 degrees with respect to the optical axis of the light beam. A laser chip end face that is provided inside the semiconductor laser and emits a light beam toward the information recording medium,
A diffraction grating that divides the light beam emitted from the laser chip end face into a main beam and two sub beams;
Condensing means for condensing each light beam split by the diffraction grating on a predetermined recording surface of the information recording medium,
Detection means for detecting the light intensity of each of the light beams condensed by the light condensing means,
Output means for outputting a signal for controlling the light condensing means in the tracking direction and the focusing direction based on the reflected light detected by the detection means, wherein each of the light beams condensed by the light condensing means is A disk device, comprising: adjusting means for tilting the diffraction grating by a predetermined amount so as not to irradiate the laser chip end face after being reflected by the information recording medium. 10. The disk device according to claim 9, wherein the adjusting unit adjusts a normal of a surface of the diffraction grating to be non-parallel to an optical axis of the light beam emitted from an end face of the laser chip.

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