JP2000322761A - Optical signal detector and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable plural kinds of optical disks to be reproduced by dividing an optical flux reflected by a disk groove into plural optical fluxes by a diffraction grating element and performing adding/subtracting operations on electrical signals from these optical fluxes. SOLUTION: A confocal system is constituted by the light emitting point of plural semiconductor laser light sources and the light receiving point of plural photodetectors. The light emitted from a semiconductor laser 1, 2 is converged on an optical disk, and the light detected by a disk groove is divided into plural light fluxes when passing through a second diffraction grating element 23 and is detected by the photodetectors. In this case, no light spot moves on the light receiving point of the photodetectors even by the change in the optical system on the way, with the stability of the system maintained for reading optical disk signals for each of the plural light sources by the semiconductor lasers 1, 2. Further, adding and subtracting operations are performed for the plural electrical signals detected by the photodetectors, reading out focus control signals, tracking control signals and the information recorded on the disk grooves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pickup for an optical disk, and more particularly, to a light source for an optical pickup and an optical signal detecting device.

[0002]

2. Description of the Related Art In recent years, the density of optical discs and the wavelength of semiconductor lasers have been shortened, and a DVD optical disc standard combining these has been formulated. One year later, a RAM standard that allows not only reproduction but also recording was established. So D
It is desired to play both VD-ROM disks and DVD-RAM disks.

On the other hand, in order to expand the market within the conventional CD standard, disk devices that can not only read a signal from a conventional CD disk but also record have been marketed. Among them, CD-R discs that can be recorded only once are widely used in the market because they can be manufactured at very low cost and have a high reflectance from the disc and can be easily reproduced by a conventional CD player. . However, this CD-R disc is 70-degree to a conventional laser beam having a wavelength of 800 nm for CD reproduction.
% Or more, but the DVD standard wavelength 660 nm
With respect to the laser light, the disk reflectance is reduced to about several percent, and it is impossible to read a signal stably with the laser light having a wavelength of 660 nm. For this reason, recent DVD players are not only compatible with CD-ROMs but also with laser wavelengths of 660 nm and 800 nm for compatibility with CD-Rs.
It has become necessary to construct an optical pickup incorporating the two semiconductor lasers.

[0004]

However, the incorporation of two lasers into one DVD optical pickup does not merely have the problem of increasing the number of components.
Furthermore, as the volume occupied by the optical pickup increases, DVD-ROM, DVD-RAM, CD, CD-R
Also, the generation of a control signal for reading various kinds of disks satisfactorily and the accompanying various adjustments become difficult. Therefore, various measures have been taken to solve these problems, but specific examples and remaining problems will be specifically described with reference to the example of FIG.

In the optical pickup shown in FIG. 8, two lasers are arranged in one package, and signal detection is performed in combination with the astigmatism detection method. Two types of semiconductor lasers 1 and 2 having a wavelength of 660 nm for DVD reproduction and a wavelength of 800 nm for CD reproduction are respectively mounted on the stem 51 at right angles. First D
When reproducing a VD disk, the semiconductor laser 1 for a wavelength of 660 nm is emitted. The emitted laser beam is bent at a right angle by the half mirror 52. The bent light is converted into a parallel light beam by the collimator lens 53, collected by the objective lens 54, and collected on the DVD disk signal surface 55. The reflected light is modulated by the disc pit groove. After the reflected light passes through the objective lens 54 and the condenser lens 53 again, a part of the reflected light returns to the laser by the half mirror 52, and a part of the reflected light passes through the Wollaston prism 60. The mounting direction of the DVD semiconductor laser 1 is determined so that the laser light having a wavelength of 660 nm has a polarization plane that is not bent by the Wollaston prism 60. Therefore, the reflected light flux of the DVD reading semiconductor laser light from the disk travels straight through the Wollaston prism 60 and is guided to the photodetector 61. In the case of this optical pickup, the focus signal for reading the disk uses the astigmatism method, so that the focus signal, tracking signal, and RF signal are detected from the photodetector 61 divided into four parts. FIG.
Shows the surface of the photodetector of the astigmatism detection method in this example.

On the other hand, when reproducing a CD disk, the wavelength 8
The 00 nm semiconductor laser 2 emits light. Since the semiconductor laser 2 is mounted at a right angle on the stem 51,
The polarization plane of the laser beam having a wavelength of 800 nm is 66 for DVD.
It is orthogonal to the plane of polarization of the laser beam of 0 nm. This wavelength 80
The laser beam of 0 nm is also applied to the disc through the half mirror, the collimator lens, and the objective lens, similarly to the light of the DVD wavelength of 660 nm. In this case, the disc to be reproduced is, of course, the CD disc 56 having a base material thickness of 1.2 mm. The reflected light from the CD disk 56 passes through the objective lens 54 and the condenser lens 53 and then returns to the laser by the half mirror 52 as in the case of reproducing the DVD disk. The light reaches the prism 61. Here, in the case of a light beam having a wavelength of 800 nm, the beam is bent by the Wollaston prism 60 because the polarization plane is orthogonal to the light beam having a wavelength of 660 nm for the above-described reason. The bent light beam has a wavelength of 660 nm on the photodetector 61.
Is coincident with the position 62 to be irradiated. That is, the Wollaston prism 60 corrects an initial set position error of the DVD and CD semiconductor lasers.

Accordingly, in the adjustment of the optical pickup having such an optical system, first, the X, Y, Z positions of the photodetector 61 shown in FIG. The position of the DVD laser is adjusted.

Next, a description will be given of the optimum adjustment at the time of reproducing a CD. It is apparent that there is no adjusting means at all at the time of reproducing a CD. That is, after the DVD has been optimally adjusted, each component is required to have the necessary accuracy so that the CD simply becomes an optimal situation based on the setting accuracy and mechanical accuracy of each component. Let's consider the degree to which these parts are required. FIG. 9 shows the optimum position 62 at which the surface of the photodetector 61 and the light beam reflected from the disk should strike. This focus control signal detection method is a method called astigmatism method. When the objective lens is in focus on the disk, the reflected light beam from the disk is narrowed down, and a circular state is formed at the intersection of the photodetector quadrants. (Position 62). On the other hand, if the distance between the objective lens and the disk 54 is too close or too far from the focal length, the light spot on the photodetector will be at the position 63,
It changes like 64. Therefore, in the case of this type of focus detection, it is extremely sensitive to a light spot position shift in the x and y directions. Therefore, in the state of the focal point, the allowable deviation amount from the dividing line must be usually 10 μm or less.
Therefore, in order to reduce the error of the lateral displacement, it is necessary to increase the focus detection magnification in this method. Usually, a detection optical system having a lateral magnification of 10 times or more is configured. This means that if the lateral position of the semiconductor laser and the angle of the half mirror 52 slightly change, a significant movement of the light spot on the photodetector occurs. First, even if an angle shift into the objective lens on the outward path occurs only from the semiconductor laser, a positional error of the semiconductor laser can be tolerated by only 1 μm. This means that if there is any error in other components, no error in the semiconductor laser is allowed or it cannot be assembled.

Also, the setting accuracy of the half mirror 52 becomes very strict. For example, in the case of this example, if the focal length of the collimator lens is 20 mm, an accuracy of 10 μm or less is required, so that the detection system needs to be 5 milliradians or less. Therefore, the beam tilt allowed on the objective lens side is 0.5 milliradians, so that the variation in the emission angle of the laser is within 0.3 °, and even if only the allowable angle shift due to the temperature of the half mirror is assigned, it is 0.3 °. Become. Normally, the variation of the laser emission angle is about 2 to 3 ° due to the variation of fusion precision, cleavage plane precision and the like, and 0.3 °.
Is an extremely difficult precision for mass production.

[0010] From such a viewpoint, two packages are included in one package.
The method of arranging a laser and performing signal detection in combination with the astigmatism detection method is simple in structure, but the accuracy required for each element is too strict. For this reason, it has not been mass-produced to integrate the two lasers and to simplify the optical pickup fundamentally by using this configuration. Further, in the astigmatism focus signal detection method used in this example, the CD-
Although it can be easily combined with the three-beam tracking method required for R reproduction, there is a problem that a groove crossing signal is mixed into a focus signal which is a problem during DVD-RAM reproduction. Further, it is difficult to secure a stable push-pull signal required for DVD-RAM reproduction. As described above, for complete compatibility between a CD and a DVD, it is necessary to reproduce each disk with light having a wavelength of 800 nm and a wavelength of 660 nm. However, it is necessary to employ an optical system suitable for each reproduction in the optical pickup for this, and it is difficult to simplify the optical configuration and adjustment, and it is difficult to mass-produce.

[0011] The object of the present invention has been made in view of such circumstances.
An object of the present invention is to provide a small-sized two-wavelength semiconductor laser type optical signal detecting device and an optical pickup in one package which are capable of reproducing a plurality of types of optical disks and have high reliability.

[0012]

According to the present invention, there is provided an optical signal detecting apparatus comprising: a plurality of semiconductor lasers oscillating at different wavelengths; a plurality of light detecting elements; and a light beam emitted from the plurality of semiconductor lasers. And one diffraction grating element through which light incident on the plurality of photodetectors passes. The firing points of the semiconductor lasers and the signal detection points of the photodetectors are arranged to form a confocal system. The diffraction grating element divides an incident light beam into a plurality of light beams, and the light detection element includes a plurality of regions for detecting the plurality of divided light beams. The emitted light beam of the semiconductor laser is focused on the desk,
When the light beam reflected from the disk groove passes through the diffraction grating element, the reflected light beam is split into a plurality of light beams by the diffraction grating element, and the light beams irradiate the light detecting element. By performing addition and subtraction operations using electric signals from these light beams, a conjugate spot size detection method focus control signal, phase difference tracking control signal, push-pull tracking signal,
The information recorded in the disk groove can be read out as an electric signal by obtaining a three-beam tracking signal or the like.

Preferably, in the optical signal detecting device, the diffraction grating element has two planes.
A first diffraction grating that divides the emitted light beam of the semiconductor laser into three is formed on one of the surfaces near the semiconductor laser emission surface. In addition, a second diffraction grating is formed on another surface far from the semiconductor laser emission surface, and the emission surfaces of the plurality of semiconductor lasers and the photodetector are arranged at substantially the same distance from the second diffraction grating. You. At least one of the oscillation wavelengths of the plurality of semiconductor lasers is adjusted by the second diffraction grating.
One of the first-order diffracted light and the -1st-order diffracted light forms a light beam condensed in front of the light detection element, and the other first-order diffracted light forms a light beam condensed at a position behind the light detection element. Form. Preferably, in the optical signal detection device, the plurality of regions of the photodetector generate a tracking control signal in a three-beam system, a phase difference system, and a push-pull system by adding and subtracting the output of each region of the photodetector. Divided as possible. Preferably, in this optical signal detection device, the first diffraction grating diffracts the wavelength of light emitted from one of the plurality of semiconductor lasers, and adjusts the wavelength of light emitted from the other semiconductor laser. It does not diffract or remarkably weakly diffracts wavelengths. Preferably, in this optical signal detection device, the second diffraction grating further separates the light beam reflected from the disk into two. Preferably, in this optical signal detection device, the first diffraction grating is made of an isotropic material that diffracts regardless of the polarization plane direction of the light beam, and the second diffraction grating is formed on the polarization plane of the emitted light of the semiconductor laser. It does not diffract, but diffracts on the plane of polarization orthogonal to the plane of polarization of the emitted light of the semiconductor laser.
An optical pickup device according to the present invention includes the optical signal detection device described above, and a light beam emitted from a semiconductor laser of the optical signal detection device is focused on a desk, and a light beam reflected from a disk is incident on the optical signal detection device. An optical system for reading signals on an optical disk;

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup and an optical signal detecting device according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same reference symbols indicate the same or equivalent ones. The principle of the optical signal detection device of the present invention is as follows. The optical signal detection device includes a plurality of semiconductor lasers 1 and 2 that emit light having different wavelengths and a plurality of photodetectors 6 and 7, and a light beam emitted from the semiconductor laser passes through the same diffraction grating element 23. A plurality of semiconductor lasers 1 and 2 and a plurality of photodetectors 6 and 7 are arranged on the same silicon substrate, and a light emitting point of the plurality of semiconductor laser light sources and a plurality of light receiving points of the plurality of photodetectors form a confocal system. Constitute. Light emitted from the semiconductor lasers 1 and 2 is focused on an optical disk. The light reflected by the disk groove of the optical disk is split into a plurality of light beams by the diffraction grating element when passing through the diffraction grating element 23, and the light beams irradiate one or more light detectors, and the light detectors 6, 7 At this time, since the light spot on the light receiving point of the photodetector does not move due to the fluctuation of the optical system in the middle, the optical disk signal is read for each of the plurality of light sources 1 and 2 by the semiconductor laser. Keep the stability of the optical system.

Further, by performing addition and subtraction operations on electric signals of a plurality of light beams detected by the photodetectors 6 and 7, a focus control signal for reading a signal on a disk, a tracking control signal, and The information recorded in the disk groove is read out as an electric signal. The focus control signal necessary for reading the disc signal is DVD-
A spot size detection method in which the tracking signal is less mixed in the RAM reproduction is configured. Further, a phase difference tracking signal required for DVD-ROM reproduction, a push-pull signal required for RAM reproduction, and a three-beam tracking control signal required for CD-R reproduction, which were difficult to combine with the tracking signal method, It is easily obtained by giving the signal detection diffraction grating 23 a two-divided action together with the conventional lens action.

The diffraction grating element for signal detection has two planes. A first diffraction grating for dividing an emitted light beam of the semiconductor laser into three is formed on a surface near the semiconductor laser emission surface of the two surfaces. The first diffraction grating is
The semiconductor laser has a characteristic of diffracting the wavelength of the light emitted from one of the plurality of semiconductor lasers and not diffracting the wavelength of the light emitted by the other semiconductor lasers, or having extremely weak diffraction. Preferably, the first diffraction grating is made of an isotropic material that diffracts regardless of the direction of the polarization plane of the light beam, and the second diffraction grating formed on a surface far from the semiconductor laser emission surface is a semiconductor. It has the effect of diffracting the plane of polarization of the semiconductor laser output light without diffracting it on the plane of polarization of the laser output light.

A second diffraction grating 23 formed on the other one of the two surfaces (a surface farther from the semiconductor laser emission surface) has the above-mentioned lens function and simultaneously transmits a reflected light beam from a disk. It also has the effect of separating into two. The second diffraction grating 23 has a plurality of semiconductor laser emitting surfaces and the photodetector substantially equidistant from each other, and has a second diffraction grating with respect to at least one of the oscillation wavelengths of the plurality of semiconductor lasers. Either the + 1st-order diffracted light or the -1st-order diffracted light by 23 forms a light beam condensed in front of the photodetector, and the other first-order diffracted light converges at a position behind the photodetector. To form Second diffraction grating 23
Due to this lens action, for example, the + 1st-order diffracted light 24a
If the focal point (front focal point 24b) is in front of the photodetector, the -1st-order diffracted light 25a of the conjugate light beam has a focal point (back focal point 25b) behind the photodetector (see FIG. 5). in this way,
Distance AB from the position B of the signal detection diffraction grating 23 to the light emitting point A of the semiconductor laser for at least one oscillating light of the plurality of laser light sources 1 and 2 and the light receiving surface C from the position B of the diffraction grating 23 , C ′ are set equal, so that the distance between the light receiving surface C ′ and the front focal point 24b is exactly the same as the distance between the light receiving surface C and the rear focal point 25b. In addition, the equivalence of the distance between the focal point and the light receiving surface can be maintained even if the wavelength varies. Therefore, a so-called conjugate spot size detection focus signal detection method is configured. If the luminous flux systems on the photodetector of the + 1st-order diffracted light beam and the -1st-order diffracted light beam are the same size, the shape of the + 1st-order diffracted light photodetector is also -1st-order diffracted light so that the electric signal output becomes zero The photodetector shape is also divided into three parts, and these electric signals are added and subtracted. If the electric signal output is zero, it is detected that the distance between the disk and the objective lens is the focal length. As described above, the conjugate spot size focus detection method is stable with respect to wavelength fluctuation, and also has a partial photodetector shape for lasers of other wavelengths, in particular, a line of a three-segment detector constituting focus detection. The detection is made possible by changing the width division amount and suppressing the occurrence of the focus offset amount due to the wavelength difference.

Further, since the optimum tracking method is different between CD reproduction and DVD reproduction, the pitch of the signal detection diffraction grating is changed left and right with respect to the signal track direction (see FIG. 7), so that the + 1st-order diffracted light beam can be obtained. -1
The secondary diffracted light beams are further separated left and right with respect to the track direction. By separating this diffracted light beam in the signal track direction, it is possible to use the conventional three-beam tracking method for CD reproduction, and to use the focus detection unit photodetector for DVD reproduction. It is possible to detect a phase difference tracking signal and a push-pull signal suitable for DVD-RAM reproduction from the division at the center simply by dividing a part in the tracking direction.

FIG. 1 shows an optical pickup according to an embodiment of the present invention. This optical pickup comprises two types of semiconductor lasers 1 and 2 having a wavelength of 660 nm for DVD reproduction and a wavelength of 800 nm for CD reproduction and a plurality of photodetectors 6 and 7 in one package.
Are used on the same silicon substrate. The light detection element 30 further includes a diffraction grating. The diffraction grating element has two planes, and one of the two planes near the semiconductor laser emission plane has a first three-beam plane. Is formed on the other surface far from the semiconductor laser emission surface.
3 is formed. Control signals necessary for reproduction are transmitted to the diffraction grating 23.
Detected after dividing by. In this diffraction grating 23, the positions of the light sources 1 and 2 and the distances to the signal detectors 6 and 7 are set to be equal for one wavelength. The focus signal is made compatible with the conjugate spot size method and the wavelength difference is made compatible by changing the detector width.
In addition, since the diffraction grating 23 divides the spot into two in the track direction, various control signals can be easily obtained by combining the two divisions and the three divisions of focus signal detection by the spot size detection (CSD) method. .

In the case of reproducing a DVD, a light beam having a wavelength of 660 nm emitted from the photodetector 30 is collimated by a collimator lens 53.
The light beam is turned into a parallel light beam by the light beam bending mirror 40 and changes its direction at a right angle. The light beam is converged by the objective lens 54 on the converged light beam 57 for DVD and condensed on the signal surface 55 of the DVD disk. The reflected light is modulated by the disc pit groove. The reflected light passes through the objective lens 54 again, becomes a parallel light flux, changes its direction at a right angle by the light beam bending mirror 40, passes through the condenser lens 53, and then passes to the photodetectors 6 and 7 in the photodetector 30. Guided and converted to electrical signals.
Note that the beam position correcting diffraction grating 41 is provided in the light beam bending mirror 40 and corrects the beam position. In the case of CD reproduction, a wavelength of 800 nm emitted from the light detection element 30
Is similarly condensed on the signal surface 56 of the CD into the condensed light beam 58 for CD. The reflected light from the CD is similarly guided to the photodetectors 6 and 7 in the photodetector 30 and is converted into an electric signal.

Regarding the photodetector and signal detection of the present invention,
This will be described in more detail below. Here, FIG. 2 shows a side surface of the optical signal detection device, FIG. 3 shows an upper surface of a silicon substrate portion of the optical signal detection device, and FIG. 4 is an enlarged view of the silicon substrate region 6 of FIG. FIG. 5 is an enlarged view of the area 20 in FIG. Semiconductor laser 1 that emits light with a wavelength of 660 nm
A semiconductor laser 2 that emits light having a wavelength of 800 nm is mounted on a silicon substrate 3. For CD playback,
A laser 2 having a wavelength of 800 nm is emitted. The emitted laser light is bent by the rising mirror 4 and passes through the three-beam diffraction grating 21. In the present embodiment, the diffraction grating 2
No. 1 does not diffract light having a wavelength of 800 nm, and has a wavelength of 6 nm.
It is the depth at which diffraction occurs for light of 60 nm. As an example of this condition, when the refractive index n of the glass is 1.5 and the depth of the diffraction grating is 1.3 μm, the phase difference with respect to the diffraction grating is 2π for a wavelength of 660 nm, and no diffracted light is generated, and the wavelength is 800 nm. For this light, a diffracted light is generated because the phase difference becomes small. Under this condition, the + 1st order diffracted light and-
The efficiency of the first-order diffracted light is about 12%, which is the optimum condition for obtaining a three-beam tracking signal in CD reproduction.

On the other hand, light having a wavelength of 660 nm for DVD reproduction is not diffracted and passes through the diffraction grating 23 for signal detection. In the case of the present embodiment, as the diffraction grating 23 for signal detection, polarized light that diffracts 30% with respect to the plane of polarization of the emitted light beam of the semiconductor laser and 70% with respect to the light beam having an orthogonal plane of polarization. Use a hologram. For this reason, 70
% Passed and the remaining 30% were diffracted. The reason for using such a polarization hologram is that when a disk to be read has large birefringence, when a polarization hologram of complete extinction is used, the reflected light beam from the disk is not diffracted by the diffraction element for signal detection and the signal cannot be read. That's why. In order to read a signal even from such a birefringent disc, it is necessary to generate diffracted light even in such a situation. Accordingly, the hologram diffracts 30% of the light beam emitted from the semiconductor laser. Therefore, this 30% is a loss of light amount on the outward path.

The light that has passed through the signal detection diffraction grating 23 is
Next, the light passes through the wave plate 30. In the case of the present embodiment, the wavelength plate 30 is a / λ plate for light having a wavelength of 660 nm, and is equivalent to a λλ plate. Accordingly, the polarization plane directions of the light having the wavelength of 660 nm are orthogonal to each other by passing through the outward return path. On the other hand, the present wave plate 30 has a wavelength of 80.
Since the light having a wavelength of 0 nm is a λ plate, the polarization direction does not change even when the light passes through the forward path and the backward path, and the polarized light of the 660 nm wavelength light beam is converted into circularly polarized light. The luminous flux passing through the wave plate 30 is converted into parallel light by the collimator lens 53,
The light is sent to the objective lens 54 and is focused on the disk signal surface 56 by the objective lens 54.

The light reflected from the disk surface passes through the objective lens 54 again and becomes parallel light. This light passes through the collimator lens 53 and again passes through the wavelength plate 23, and as described above, the light having the wavelength of 660 nm is converted into a light beam having a polarization plane orthogonal to the laser emission light. Next, this light passes through the diffraction grating 23 for signal detection.
Uses a polarization hologram having the above-mentioned characteristics, so that it diffracts 30% for light having a wavelength of 800 nm and 70% for light having a wavelength of 660 nm. FIG. 7 shows an enlarged view of the diffraction grating for signal detection. further,
This polarization hologram has a weak lens power and is designed to divide a passing light beam into two in the radial direction. Therefore, as shown schematically in FIG. 7, the diffraction grating pitch is slightly different between the right region 23a and the left region 23b. The light beams 24a and 24b diffracted by passing through the signal detection hologram pass by the three-beam diffraction grating 21, so that the return-path diffraction light is not affected by the diffraction grating.

FIG. 3 shows an arrangement of spots projected on the photodetectors 6 and 7, and FIG. Area 7
However, the signal state on the disk surface on each spot is point-symmetric with respect to the center of the light beam for the reason described later. In FIG. 4, spots 8a, 8b, 9, and 10 represent spots of light having a wavelength of 800 nm projected during CD reproduction, and spots 13a and 13
“b” indicates a spot of light having a wavelength of 660 nm projected during DVD reproduction. As described above, the light having the wavelength of 800 nm is divided into three optical paths on the outward path by the three-beam diffraction grating, and is divided by the detection light division hologram on the return path, so that three spots appear in the vertical direction. On the other hand, the wavelength 660
In the case of the light of nm, since it is not divided by the three-beam diffraction grating on the outward path, there is only left and right divisions by the detection hologram.

Now, there is only a three-beam method as a stable tracking method at the time of CD-R reproduction. On the other hand, in the case of DVD, since the track pitch is narrowed to 0.75 μm, a good tracking signal cannot be detected by the three-beam method. Therefore, in the case of DVD, a phase difference tracking method is usually used. On the other hand, DVD-RAM
In order to reproduce the data, a push-pull method is used as a tracking method. In addition, since a continuous groove is used as a signal recording groove in a DVD-RAM disk, an astigmatism method in which tracking signals are frequently mixed is useless as a focus method, and an SSD (spot size detection method) focus in which mixing is small is used. It is necessary to configure a signal detection method. In addition, there is a wavelength difference of about 1.2 times between the two wavelengths of 660 nm and 800 nm, and there is a difficult problem that an SSD focus signal detection method can simultaneously obtain good focus signals for these wavelengths. .

For this reason, as a result of various studies to be very simple and satisfy all conditions, in this embodiment, in order to obtain good focus signal detection for two wavelengths, light having a wavelength of 660 nm is used. Conjugation type spot size detection focus method by making the distance from the point where any diffracted light beam of 800 nm light hits the photodetector to the hologram for detection signal equal to the distance from the diffraction grating for signal detection to the light source Is adopted. In the case of the present embodiment, as shown in FIG.
The distance between the light emitting point A of the light source 1 and the center point B of the diffraction grating for signal detection, the + 1st-order diffracted light beam and the -1st-order diffracted light beam of the diffraction grating having a wavelength of 660 nm and the diffraction grating center point B on the photodetector. The position of the signal detection diffraction grating was determined so that the distance between the center positions C and C ′ was equal. In this configuration, light having a wavelength of 800 nm is diffracted more strongly than light having a wavelength of 660 nm by about 1.2 times the wavelength difference. Therefore, for light having a wavelength of 800 nm, the distance between the light source and the signal detection diffraction grating is not equal to the distance between the signal detection diffraction grating and the center position of the diffracted light beam on the light detection surface. In order to maintain the same distance with respect to this 800 nm wavelength light, it is necessary to increase the distance between the signal detection diffraction grating and the light source. That is, it is necessary to increase the position of the signal detection diffraction grating 23. In other words, this is equivalent to the hologram slipping below the optimum distance. Therefore, in this case, a focus offset occurs. To correct this, the line width of the three divisions, particularly the center line width, may be corrected to be thin. The state of the photodetector at this time is indicated by a dotted line 1.
4a and 14b (FIG. 4). Conversely, the wavelength is 800 nm
The position of the laser 2 may be farther from the rising mirror 4 than the position of the laser 1 having a wavelength of 660 nm. With these measures, the amount of offset generation for two wavelengths can be solved.

The spots 13a and 13b of the light having the wavelength of 660 nm projected at the time of reproducing the DVD have the area 11 as in the conventional case.
a, 11b, 12a, 12b, 16, 17, 18, 2
The light is divided into 0, 21 and 22 and detected by the photodetectors 6 and 7. Here, the shape of the + 1st-order light photodetector is -1 so that the electrical signal output becomes zero if the + 1st-order diffracted light beam and the -1st-order diffracted light beam have the same beam diameter on the photodetector. The shape of the photodetector for the next light is also divided into three regions 11a and 11b and regions 12a and 12b.
The outer part thereof is similarly formed in the regions 16, 17, 18 and the region 2
It is divided into 0, 21, and 22. A tracking control signal is generated by a three-beam system, a phase difference system, and a push-pull system by adding and subtracting the output signals of the respective regions of the photodetector.
In addition, the conjugate spot size detection focus signal can be expressed as (20 + 22 + 12b + 17 + 11a) − (16 + 18 +) by expressing the electric signal by the reference number of each detection area.
12a + 21 + 11b).

In the detection of the phase difference tracking during DVD reproduction, the phase difference can be detected by detecting the RF phase difference between the regions 12a and 12b shown in FIG. The spots on the photodetector generated by the detection hologram in the areas 6 and 7 are upside down, left and right. This will be described with reference to FIG. Signal detection diffraction grating 23
However, on a surface far from the laser output surface of the base material 22 having a parallel plane, an isotropic resin, a glass substrate, a surface of the base material 22, a resin having polarization anisotropy, and a single crystal substrate It is composed of an uneven or refractive index type diffraction grating. Moreover, the signal detection diffraction grating 23 is formed of a so-called off-axis Fresnel lens so as to have a weak lens function. Moreover, this lens is divided into two regions 23a and 23b at the center of the diffraction grating, and the Fresnel lens is designed so that the amount of axial deviation differs in each region. Signal detection diffraction grating 2 designed in this way
When light passes through No. 3, + 1st-order diffracted light 24a and -1st-order diffracted light 25a are generated. If the + 1st order diffracted light 24a is designed to have a convex lens effect, the -1st order light will be subjected to a concave lens effect. Therefore, the + 1st-order light is condensed 24b before the photodetector surface 6a, and the -1st-order light is condensed 25b deeper than the photodetector surface 7a. (If the focus of the detection hologram 23 is infinite, ie, there is no lens action, the light is converged on the equidistant surface 27 with the light source.)
The spots on the photodetector surface generated by the signal detection diffraction grating in the areas 6 and 7 are turned upside down and left and right. Therefore, the light spot included in the area 12b has the same signal as the light spot included in the area 13a. Therefore, in order to obtain the phase difference tracking signal, simply 12a-
13a. However, from the viewpoint of focus detection, the photodetector 13a is connected to another detector, and the phase difference may not be detected properly. Therefore, in this case, if the ratio is set to 12a-12b, a phase difference signal can be obtained successfully. In the present embodiment, it is possible to achieve both focus signal detection and phase difference tracking signal detection in a three-division conjugate spot size detection (CSD) method. In addition, from the same idea, the central light detection unit of the CSD method focus detection,
By separating them as shown by the regions 11a and 11b in FIG. 3, a push-pull signal required at the time of reproducing a DVD-RAM signal can be detected from 11b-11a.

When the phase difference signal is detected by this method, if the laser emission points 1a and 2a are not on the photodetector center line 5, the focus detection spot is also deviated from the center of the photodetector. Even if the focus detection spot is the same size spot, that is, the distance between the disc and the objective lens is at the in-focus position, the focus signal does not become zero, i.e., offset. Will have. For this reason, the generated offset is adjusted by rotating the signal detection diffraction grating to shift the spot position. In this case, when signals are detected as regions 12a and 12b for phase difference signal detection from 12a to 12b, the amount of spots included in these regions may be too small. In this case, the differential is obtained after adding the center signal, that is, (11a + 12
a)-(11b + 12b) may be used to detect the phase difference and the push-pull tracking signal. The reproduction signal of the CD is obtained as 20 + 21 + 22 + 18 + 17 + 16. On the other hand, the DVD playback signal is 20 + 21 + 22 + 18 + 17
+ 16 + 11a + 12a.

Preferably, in the optical signal detecting device, 3
A beam splitting diffraction grating and a signal detection diffraction grating that are integrally formed are used. Therefore, in this case, a wave plate is not required. In this case, the light use efficiency was poor,
There was no problem in DVD reproduction characteristics and CD reproduction characteristics.

Also, for a 0.6 mm layer as a disc, D
A VD signal is recorded, and a CD signal is recorded through the inner 0.6 mm layer.
Both semiconductor lasers for VD and CD were irradiated simultaneously. As a result, it was possible to reproduce DVDs and CDs favorably.

[0033]

By using the optical signal detection device according to the present invention, a laser light source having a wavelength of 800 nm and a D
An optical pickup with a 660 nm wavelength laser light source for VD reproduction, compact, stable at two wavelengths, excellent in mass productivity, inexpensive, and capable of CD-R reproduction has become possible. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a two-wavelength optical pickup.

FIG. 2 is a side view of a photodetector.

FIG. 3 is a top view of a silicon substrate portion of the photodetector.

FIG. 4 is an enlarged view of a silicon substrate region 6;

FIG. 5 is an enlarged view of a region 20 in FIG. 3;

FIG. 6 is an enlarged view of a 3-beam diffraction grating.

FIG. 7 is an enlarged view of a diffraction grating for signal detection.

FIG. 8 is a diagram showing a configuration of a conventional two-wavelength optical pickup.

FIG. 9 is a diagram for explaining a conventional astigmatism focus signal detection method.

[Explanation of symbols]

1,2 semiconductor laser, 6,7 photodetector,
21 first diffraction grating, 23 second diffraction grating,
Reference Signs List 30 optical signal detection device, 40 light beam bending mirror, 53 collimator lens, 54 objective lens.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tetsuo Hosomi 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 5D066 HA01 5D118 AA26 BA01 CA13 CA24 CB05 CD03 CF05 CF16 CG04 CG26 5D119 AA41 BA01 CA10 CA16 EA02 EC41 EC47 FA05 FA08 FA25 JA13 JA22 KA04 KA08 KA19 LB06

Claims (7)

[Claims] A plurality of semiconductor lasers that oscillate at different wavelengths, a plurality of photodetectors, and a light beam emitted from the plurality of semiconductor lasers passes therethrough.
A single diffraction grating element through which light incident on the plurality of photodetectors passes; and a firing point of the plurality of semiconductor lasers and a signal detection point of the plurality of photodetectors constitute a confocal system. The optical signal detection device is arranged, wherein the diffraction grating element divides an incident light beam into a plurality of light beams, and the light detection element includes a plurality of regions for detecting the plurality of divided light beams. 2. The optical signal detection device according to claim 1, wherein the diffraction grating element has two planes, and one of the two planes near the semiconductor laser emission plane has the semiconductor. A first diffraction grating that divides the emitted light beam of the laser into three is formed, and a second diffraction grating is formed on another surface far from the semiconductor laser emission surface, and the plurality of diffraction gratings are formed with respect to the second diffraction grating. The emission surface of the semiconductor laser and the photodetector are arranged at substantially equal distances, and at least one of the oscillation wavelengths of the plurality of semiconductor lasers has + 1st-order diffracted light and -1st-order diffracted light by the second diffraction grating. One of the folded lights forms a light beam condensed in front of the light detection element, and the other first-order diffracted light forms a light beam condensed at a position behind the light detection element. Optical signal detector. 3. The optical signal detection device according to claim 2, wherein the plurality of regions of the photodetector are provided with a tracking control signal of a three-beam system, a phase difference system, and a push-pull system. An optical signal detection device, which is divided so that it can be generated by adding and subtracting the output of each area. 4. The optical signal detection device according to claim 2, wherein the first diffraction grating diffracts a wavelength of light emitted by one of the plurality of semiconductor lasers;
An optical signal detection device having the characteristic of not diffracting or remarkably weakly diffracting the wavelength of light emitted from another semiconductor laser. 5. The optical signal detection device according to claim 2, wherein the second diffraction grating further separates the light beam reflected from the disk into two. 6. The optical signal detection device according to claim 2, wherein the first diffraction grating is made of an isotropic material that diffracts regardless of the polarization plane direction of the light beam, and the second diffraction grating is An optical signal detection device, wherein the optical signal detection device does not diffract a polarization plane of the semiconductor laser emission light, but diffracts a polarization plane orthogonal to the semiconductor laser emission light polarization plane. 7. An optical signal detecting device according to claim 1, wherein a light beam emitted from a semiconductor laser of said optical signal detecting device is focused on a desk and reflected from a disk. An optical system for causing a light beam to enter the optical signal detection device.