JPS63228432A - Two-beam type optical pick-up - Google Patents

Abstract

PURPOSE:To cause a focus position dislocation and the deterioration of a focus beam diameter to be hard to occur, to be high in the operation reliability of a tracking control and a focusing control and light in weight and small in size by using a grating lens optical system to be hard to be influenced by the change of an oscillation wavelength and have a small aberration. CONSTITUTION:When a beam 110 is contacted by the angle inclined to a light axis A from a first semiconductor laser 101 to a first area 11A of a first grating lens 11 of a grating lens system, the beam is bent so as to cross symmetrical to the axis and made incident on a first area 12A1 of a second grating lens 12. The beam is further bent by the second grating lens 12 and converged to one point O on an optical disk 107. The space frequency of first and second grating lenses 11 and 12 is designed so that the laser beam from the semiconductor laser 101 can pass through the light path. A beam 112 made incident from the slanting onto the point O is bent completely symmetrical to the axis to the outgoing beam 110 and made incident on a second area 11B1 of the first grating lens 11.

Description

[Detailed Description of the Invention] [Summary] A combination of two grating lenses: a first grating lens that crosses an incident laser beam axially symmetrically, and a second grating lens that converges this crossed beam onto an optical disk. In the newly developed grating lens system, which is able to achieve a good beam spot with little aberration and stable focusing performance without deviation, without being affected by wavelength fluctuations of the incident laser beam, The first grating lens is divided into a plurality of regions having different spatial frequencies by a plane including the optical axis, and the two laser beams are made to enter the grating lens system through the respective first regions of the first grating lens, and The two signal lights reflected from the optical disk travel backwards in an axially symmetrical manner within the grating lens system, pass through the respective second regions of the first grating lens, and are emitted from the grating lens system. The grating lens focuses the signal light on a different position than the forward path.Therefore, this signal light is separated into two beams using, for example, a half mirror, and one of the beams is guided to a focusing photodetector and the other to a tracking photodetector. As a result, it is possible to realize an optical disk pickup device with high detection accuracy and reliability, which reduces the focal position shift and the deterioration of the focal beam diameter due to changes in the wavelength of the light source laser.

[Industrial application field]

The present invention relates to an optical pickup, and particularly to a pickup device for magneto-optical and write-once optical disks using a grating lens system.

[Conventional technology]

In write-once optical disk devices that allow information to be written by the user of the optical disk, after information is recorded on the disk in the form of pits, it is necessary to read the information to confirm whether it was written correctly. However, research is being conducted on a two-beam optical head in which the read beam is placed near the write beam spot so that there is no need to wait for the disk to rotate once.

On the other hand, in response to demands for smaller and lighter optical disk devices and shorter access times, there is a desire for optical heads to be significantly smaller, lighter, and lower in price.

In order to satisfy such demands, the development of optical pickups using hologram elements has been progressing in recent years, and Applicant Motose previously proposed a new two-beam system using hologram lenses in Japanese Patent Application No. 61-43702. An optical pickup was proposed.

As shown in FIG. 13, this two-beam optical pickup corrects aberrations of laser beams 110 and 111 from two semiconductor lasers 101 and 102, respectively, and extends a predetermined distance ( d) includes two hologram lenses 103 and 104 for focusing on two focusing positions IPt and Pz, respectively, which are separated by an amount of distance zp1. p! The reflected light beams 112 and 113 are received by the hologram lenses 104 and 103 opposite to each other, and are guided to the respective detectors 105 and 106.

Laser light 110 from semiconductor laser 101 is focused by hologram lens 103 onto a focus position P1 on optical disk medium surface 107 .

Then, reflected light 112 from there is received by the other hologram lens 104 and guided to the detector 105. Conversely, the laser beam 111 from the semiconductor laser 102 is focused at the hologram lens 104 at a focal position P! The reflected light 113 is received by the opposite hologram lens 103 and guided to the detector 106.

At this time, since the wavelengths of the respective laser beams 110 and 111 are different, the respective reflected beams 112 and 113 are reflected from each semiconductor laser 102.
It does not return to the position 101, but is guided to each of the adjacent detectors 105 and 106.

In this way, each optical path is separated in space and time, so there is no need for a polarizing beam splitter or a λ/4 plate as in the past, making it possible to significantly reduce the weight and size of the optical pickup.

[Problem that the invention seeks to solve]

However, in a hologram, the diffraction angle changes as the wavelength changes, so in a hologram that has a lens effect (hologram lens), the wavelength of the light source is λ. In the case of an in-line hologram lens, when it changes from λ to λ (λ.
As shown in the figure, aberrations occur as the focal length (position in the optical axis direction) changes, and in the case of an off-axis hologram lens, as shown in Figure 15, aberrations occur as the focal length (position in the optical axis direction) changes.
In addition to the occurrence of aberrations, the focal position is deviated from the optical axis.

Semiconductor lasers used in optical pickups exhibit ±± within the ambient temperature range (0 to 50°C) due to temperature changes, changes in driving methods, or variations in center oscillation wavelength due to individual differences.
This is accompanied by a change in the oscillation wavelength of about 12 nm or more. In other words, it can be considered that the oscillation wavelength of a laser is virtually constantly changing.When such a change in the oscillation wavelength of a semiconductor laser occurs, the above-mentioned problem occurs in an optical pickup using a hologram, and the beam spot deteriorates. This makes it difficult to read and write information on the optical signal. The off-axis hologram lens shown in FIG. 15 is particularly susceptible to changes in the wavelength of the semiconductor laser.

By the way, the applicant of this application previously filed Japanese Patent Application No. 61-22087.
In the specification of No. 0, a grating lens optical system that can always obtain a good beam spot free of aberrations without being influenced by the above-mentioned wavelength fluctuations of incident light and has accurate and stable focusing performance. proposed a system.

The present invention solves the above problems by using this grating lens optical system, and satisfies the requirements of light weight, small size, and low aperture, while also achieving high precision that is not easily affected by wavelength fluctuations, and high stability. The purpose is to provide an optical pink-up device.

[Means for solving problems]

According to the present invention, two laser beams having different wavelengths from two semiconductor lasers are respectively focused on different positions on an optical signal recording medium, and each reflected beam is received. In a two-beam optical pickup that records and reads information by A second grating lens that focuses the light onto one point on the optical signal recording medium is arranged on the optical axis, and the first grating lens is divided into at least two regions having different spatial frequencies by a plane including the optical axis. The two laser beams pass through the respective first regions of the first grating lens and are converged onto the optical signal recording medium by the second grating lens, and the two signal beams reflected by the optical signal recording medium are converged onto the optical signal recording medium. A structural feature is that the light beams are axially symmetrically intersected by the two grating lenses and guided to the photodetector through the respective second regions of the first grating lenses.

[For production]

The diverging light of the semiconductor laser enters the first grating lens, is diffracted by the first grating lens so as to cross the optical axis symmetrically, and enters the second grating lens, after which it is reflected onto the optical disk by the second grating lens. Focuses light without aberration. As will be described later, this grating lens system focuses light onto the optical disk without aberration even if the oscillation wavelength of the semiconductor laser varies by at least ±12 nm from the center.

In this grating lens system, the diverging light from the semiconductor laser is incident on the first region of the first grating lens, and is diffracted in an axially symmetrical direction according to the spatial frequency of the first region of the first grating lens. The light enters the grating lens No. 2, is diffracted according to its spatial frequency, and is focused onto the optical disk. At this time, the incident optical axis is inclined with respect to the plane of the optical disc. The reflected signal light from the optical disk follows a different path from the incident light (axis-symmetrical position y1), enters the second grating lens, is diffracted in an axially symmetrical direction according to its spatial frequency, and passes through the first grating lens. 2, is diffracted according to its spatial frequency, and is incident on a photodetector. At this time, if the spatial frequency distributions of the first and second N regions of the first grating lens are equal, the signal light returns to the semiconductor laser and signal detection cannot be performed, but the spatial frequency distribution of the second region is different from that of the first region. It is guided by a photodetector.

Therefore, the light emitted from the second region of the first grating lens is divided into two by a half mirror or the like, and the reflected light (or transmitted light) is guided to a focusing photodetector to perform focusing control. An optical pickup can be realized by guiding light (light) to a tracking detector and performing tracking control.

As will be described later, the grating lens system is not easily affected by wavelength fluctuations of the laser beam, and can focus on one point on the optical disk within a certain wavelength range (for example, 830±12n...).

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the configuration of the grating lens system, which plays an important role in the present invention, will be briefly explained with reference to FIGS. 16 and 17. The detailed structure of this grating lens system is disclosed in the above-mentioned Japanese Patent Application No. 61-220870.

In FIG. 16, the grating lens system includes 11th and 12th in-line type grating lenses 11 and 12.
are arranged on the same optical axis (dotted chain line), and a spherical wave diverging from a point P (coherent light source) on the optical axis is diffracted toward the optical axis side by the first grating lens 11, and once connected to the optical axis. After crossing, the second grating lens 12 focuses the light on a predetermined point Q on the optical axis.

The first grating lens 11 has a predetermined spatial frequency distribution that is rotationally symmetrical with respect to the optical axis, so that diffracted lights from any two points that are symmetrical with respect to the optical axis intersect on the optical axis. . Further, the second grating lens 12 has a predetermined spatial frequency distribution that is rotationally symmetrical with respect to the optical axis, so that the crossed diffracted lights are focused on one point Q on the optical axis.

In the above configuration, mutually different wavelengths λ0. Consider two paths of light λ (λ0<λ). First, light with a wavelength λ is diffracted by a first in-line grating lens at a larger angle than light with a wavelength λ0, and after both of these diffracted lights intersect with the optical axis, they are passed through a second in-line grating lens. reach above the lens. The distance from the optical axis of the arrival point of these lights is that the light with wavelength λ is farther from the 0th order than the light with wavelength λ0.These lights are diffracted by the second in-line grating lens, but this At this time, the light with wavelength λ is diffracted at a larger angle than the light with wavelength λ0, so the distance between the two lights gradually narrows, and eventually they intersect at one point. Therefore, by providing the two in-line grating lenses with a predetermined spatial frequency distribution, the point where the two lights intersect can be placed at a designated point on the optical axis.

The above can be said about the light incident on any point of the first in-line grating lens, and since the above spatial frequency distribution is rotationally symmetric with respect to the optical axis, the wavelength of the incident diverging spherical wave light is Even if the light changes, it will be focused on the predetermined point on the optical axis, and therefore no aberrations or focal position shifts will occur.

Next, a specific method for determining the spatial frequency distribution of the grating lens tt, 12 will be described below in (i) to (iv) using FIG. 17. Note that the distance between the point P and the first grating lens 11 is 11, the distance between the two grating lenses 11 and 12 is d1, and the distance between the grating lens 12 and point Q is z2.

(1) First, consider a ray of wavelength λO that is emitted from point P and reaches point R1 at the outermost periphery of grating lens 11.

This light beam is diffracted at point R1, reaches point rl (=0) at the center of grating lens 12, and is further diffracted there, reaching point Q (solid line a in FIG. 17).

Then, by assuming the above-mentioned optical path (P→R1→r1→Q), the spatial frequencies Fl, f at points R1, rl are
l is determined.

(ii) Next, consider the case where the wavelength changes from λ0 to λ (>λ0). A ray of wavelength λ that has traveled from point P to point R1 is diffracted at point R1 at a larger angle than when the wavelength is λ0, and is diffracted at point r on grating lens 12.
2 (dashed line b).

Here, the spatial frequency 12 at point r2 is determined from the condition that the light is focused on point Q even when the wavelength is λ.

(iii) Returning to the case where the wavelength is λ0, it is possible to find out from which point on the grating lens 11 the light ray that is diffracted at point r2 and reaches point Q comes from (solid line c
). If the point on the grating lens 11 is R2, then from the condition that the diffracted light at point R2 reaches point P,
Spatial frequency F2 at point R2 is determined.

(iv) Consider the case where the wavelength becomes λ again, and consider (ii)
), the point r3 on the grating lens 12 is
(not shown) and its spatial frequency f3 is determined. Then, the wavelength is returned to λ0, and the point R3 (not shown) on the grating lens 11 and its spatial frequency F3 are determined in the same manner as in (iii) above. In this way, point Rn (n=1.
2, 3. ...) reaches the center of the grating lens 11 by repeating the steps (11) and (iii) above to determine the radial spatial frequency distribution in the grating lenses 11 and 12. In addition,
The diameter of the second grating lens 12 is determined at the position of point rn.

By determining the spatial frequency distribution of the grating lenses 11 and 12 as described above, even if the light emitted from the point P has a wavelength λ different from the reference wavelength λ0, it can be transmitted to the point Q without aberration. can be focused on.

The present invention realizes an optical pickup device using the grating lens optical system as described above, and the present invention will be described in detail with reference to FIG. 1 and subsequent figures, taking an optical disk as an example of an optical signal recording medium.

According to the present invention, for each beam 110, 111 (FIG. 13), the first grating lens 11 is divided into two by a plane including the optical axis, as shown in FIG. 1.2. This will be explained in detail with reference to FIG. 3.4. In FIG. 3, the first grating lens 11 and the second grating lens 12 have two regions 11A1, 11B1, 12A1, 12 with different diffraction angles, that is, different spatial frequencies.
It is divided into B. In addition, the second grating lens 1
2, the first and second regions 12A1 and 12B+ are arranged in the first and second regions 12A1 and 12B+ for convenience in accordance with the first grating lens 11. This is divided into a second area, and this first area. Second area 12A1.12
B, may have the same spatial frequency. That is, the second grating lens 12 does not necessarily need to be divided into two regions (the reason for this will be described later).

When the beam 110 is applied from the first semiconductor laser 101 to the first region 11A of the first grating lens 11 of the grating lens system configured in this way at an angle oblique to the optical axis Z (FIG. 3), The beam is bent to intersect axially symmetrically and enters the first region 12A+ of the second grating lens 12. This beam is further bent by the second grating lens 12 and converged to a point 0 on the optical disk 107. The spatial frequencies of the first and second grating lenses 11 and 12 are designed so that the laser beam from the semiconductor laser 101 follows the above-mentioned optical path. The beam 112 obliquely incident on point 0 is reflected there in an axially symmetrical direction and enters the second region 12B1 of the second grating lens 12.

Then, it is bent completely axially symmetrically with respect to the forward beam 110, and the second region 11B+ of the first grating lens 11 is
incident on .

Here, the first region 11 of the first grating lens 11
When A+ and the second region 11B+ have the same spatial frequency, the second region 11B of the first grating lens 11
The reflected beam (signal light) 112 incident on the semiconductor laser 101 returns to the semiconductor laser 101, and the signal light cannot be detected. Therefore, the second region 11 of the first grating lens 11
B is the first N area 11A.

It is designed to have different spatial frequencies. As a result, the second region 11 of the first grating lens 11
The signal light 112 incident on B1 is projected onto the photodetector 105 at a different position from the semiconductor laser 101. 1st
The spatial frequency of the second N region of the grating lens 11 is determined according to the position of the photodetector 105.

As is clear from the above description, in the second grating lens 12, the outgoing beam 11o and the reflected beam 11
Therefore, the first and second areas of the second grating lens 12 are aligned with the first grating lens, and the part through which the outgoing beam 110 passes is the first area, and the reflected beam 112 is completely axially symmetrical. Although the portion through which the light passes through is named the second region, the same grating lens having exactly the same spatial frequency may be used.

The above is performed in exactly the same manner for the second beam 111 from the second semiconductor laser 102. That is, as shown in FIG. 5, the first grating lens 11 is aligned with the optical axis Z(
3) into first and second regions 11Ax and liBg having different spatial frequencies, and accordingly, the second grating lens 12 is also nominally divided into first and second regions 12Az, 12Bt. divided into The signal light 113 reflected at point 0' of the optical disk 107 is provided at a different position from the second semiconductor laser 102 by the second region 11Bt of the first grating lens 11 via the second region 11Bg of the second grating lens 12. The purpose is to cause the second photodetector and the beam 112 to follow different paths for beam convergence and signal light detection.

As can be seen from the above description, the subscript A corresponds to the outgoing beam, and the subscript B corresponds to the reflected beam.

Furthermore, the subscript 1 corresponds to the first grating lens 11 and the subscript 2 corresponds to the second grating lens 12, respectively. Therefore, for example, IIA+ indicates the first region through which the beam 110 passes through the first grating lens 11.

FIG. 1.2 shows the basic configuration of the present invention based on the above basic concept.

FIG. 1 shows the configuration for forward beams 110 and 111 from two semiconductor lasers 101 and 102, and
The figure shows reflected beams 112 and 11 from an optical disk 107.
The configuration for 3 is shown.

In general, the method for writing and reading information onto and from an optical disk using a two-beam optical pickup is to use a wavelength of λ1.
Write and erase with the first beam of λ2, and read and reproduce with the second beam of wavelength λ2 after a distance d in the track direction)
and check whether writing was performed correctly. In the case of only reading, any wavelength can be used. Therefore, in Fig. 1, the horizontal direction (
X direction) is the track groove direction, the first beam 110
When the focused point on the optical disk for the second beam 111 is set to 0, the focused point on the optical disk for the second beam 111 is designed to be a point O' which is shifted from O by d in the track direction.

d is generally d=10-20 μm.

Therefore, the first and second regions 11A of the first grating lens 11 for the first beam 110 (λ1).

For the division center passing through the optical axis 2 of 11B1 (corresponding to 0),
The division center passing through the optical axis 2' of the first and second regions of the first grating lens 11 for the second beam 111 (λ)
0') is shifted by d in the track direction (X direction) of the optical disc. This positional relationship seen in a plan view is shown in FIG. In FIG. 6, the first and second regions 11At and 11B for the second beam 111 are arranged orthogonally to the first and second regions 11A1 and 11B+ for the first beam iio, but this It is sufficient if the dividing centers 0 and 0' are shifted by d in the track direction (X direction), and it is not necessarily necessary to make them orthogonal.

The above-mentioned displacement arrangement in the track direction is exactly the same for the second grating lens 12.

During actual manufacturing, the first grating lens 11
The four regions 11A1, 11B, 11Az, and 118g may be formed in the arrangement shown in FIG.
I, IIA! , 11Bt may be arranged on the same plane as shown. Second
The same applies to the grating lens 12. 1st
region 11/'1, 12A1, and second region 11B1,
The spatial frequency of 12B+ is designed with a center wavelength of 830 nm, for example, and the first region 11A2, 12A2 and the second region
For example, the spatial frequency of region 11B t, 12A, z is 7
It is designed with B0nm as the center wavelength.

Note that the first beam 110. and the second beam have the same wavelength, the first region 11A for the first beam 110.

The spatial frequencies of the second region 11A2 for the first beam 110 and the second region 11A2 for the first beam 111 may be the same, and similarly, the spatial frequencies of the second region 11B for the first beam 110 and the second region 11B2 for the second beam 111 may be the same. .

In FIG. 1, a first diverging light 110 (λ1) from a first semiconductor laser 101 is incident on a first N region 11A1 of a first grating lens 11 at a predetermined angle, and is diffracted in an axially symmetrical direction according to its spatial frequency. The light enters the first region 12A of the grating lens 112. Thereafter, the light is diffracted according to the spatial frequency of the first region 12A of the second grating lens 12 and focused on the first focal point 0 of the optical disk 107. Indeed, the second semiconductor laser 102 also
The diverging light 111 (λ2) is the first grating lens 11
The first area 1IAt of.

The light passes through the first region 12At of the second grating lens 12 and is focused on the second focal point O' of the optical disk 107.

In FIG. 2, the focused light from the first semiconductor laser 101 is obliquely incident on the first focal point 0 of the optical disk 107 as described above, and is reflected there to become reflected signal light 112.

The signal light follows a separate path that is axially symmetrical to the focused light, enters the second region 12B1 of the second grating lens, is diffracted in an axially symmetrical direction according to its spatial frequency, and enters the second region 11B of the first grating lens 11. The light is diffracted according to its spatial frequency and guided to the first photodetector 105.

Focused light 111 (λ2) from the second semiconductor laser 102 is reflected by the second focal point 0' of the optical disk 107 and becomes reflected signal light 113. The signal light 113 enters the second region 12B2 of the second grating lens, is diffracted in an axially symmetrical direction according to its spatial frequency, enters the second region 11Bg of the first grating lens 11, is diffracted according to its spatial frequency, and becomes a second region 12B2. guided to a photodetector 106.

Next, specific tracking error and focus error detection will be explained.

Although the wavelength of the beam from the semiconductor laser changes virtually constantly, aberrations caused by wavelength changes can be absorbed as described above by using a grating lens system.

As is well known in the optical disk device, if there is a difference in the intensity of reflected light from the pits on the optical disk 107 and the intensity of reflected light from the lands, the intensity of the interfered total reflected light is weakened according to the degree of the difference. Utilizing the phenomenon that the intensity of reflected light is not weakened because there is no such interference in land areas without pits, the presence or absence of pits can be detected by detecting the intensity of reflected light using a beam spot focused close to the diffraction limit. , thus detecting the optical signal.

FIG. 7 shows a signal detection method during information reproduction (second semiconductor laser 102). The diffracted light (signal light) 113 diffracted by the second region 11B of the first grating lens 11 is so-called polarized light having polarization characteristics. The light passes through a beam splinter hologram (PBS hologram) 27, where the magneto-optical signal is converted into a light amount difference signal.

That is, the PBS hologram 27 limits the amount of transmitted light according to its diffraction angle, guides only the transmitted light to a photodetector, and detects the magneto-optical signal based on the difference in light amount, that is, the strength of the light amount.

The transmitted light (error detection light) of the PBS hologram 27 is separated into two by a half mirror 29, one of which, for example, the transmitted light, is guided to a focusing photodetector 37, and the other, for example, the reflected light, is guided to a tracking photodetector. Leads to 39.

The focusing photodetector 37 and the tracking photodetector 39 are composed of, for example, a two-split or four-split photodetector composed of a split-type PIN photodiode, which is known per se.

The presence or absence of pits on the optical disc, ie, channel pit signals, is identified by the strength or weakness of the outputs of these split photodetectors.

FIG. 8(1) shows an example of the arrangement of the two-split photodetector forming the tracking photodetector 39.

For example, in a magneto-optical disk, tracking is performed by a guide groove of the optical disk. The split planes of the two-split photodiodes 39a and 39b constituting the tracking photodetector 39 are located parallel to the guide groove of the optical disc 107, that is, the track direction (X direction).

In FIG. 8(1), when the beam focused on the magneto-optical disk 107 is located at the center of the guide groove,
As shown in (a) of ), the beam spot is located at the center of the dividing plane of the photodiodes 39a and 39b. Furthermore, (b
) indicates the case where the beam shifts to the right side (y direction) of the guide groove; in this case, the amount of light received by one of the photodiodes 39b becomes partially dark, and conversely, the beam shifts to the right side of the guide groove (-
(y direction), the amount of light received by the other photodiode 39a becomes partially dark as shown in FIG. Incidentally, since the laser beams are made to intersect axially symmetrically within the grating lens system, the dark portion due to the positional deviation of the aberration beam is inverted and transferred to the photodiode 39a.

It appears near the dividing plane of 39b. The tracking error detection method shown in FIG. 2 utilizes a push-pull method that detects the difference in the amount of light between the photodiodes 39a and 39b.

FIG. 8(2) shows an example of the arrangement of four-split photodetectors constituting the focusing photodetector 37. The four-division photodetector 37 has a light receiving area divided into four PIN photodiodes 37a and 37b.

As shown in FIG. 8(1)(a), the four-split photodetector 37 includes photodiodes 37a, 37b', 37c, and 37d in the focused state.
The punch is placed so that the beam spot hits the center of the punch. When the optical disc 10 approaches the second grating lens 12 from the in-focus position, the spot of the signal light on the 4-split photodetector 37 becomes a horizontally long ellipse as shown in FIG. 8(1)(b), and vice versa. As it moves away, it becomes a vertically long ellipse as shown in (c).

Therefore, the four regions 37a of the four-division photodetector 37.

The difference in optical output between 37b, 37c, and 37d, i.e. (
If you measure II + 12) - (13 + I4), it will be 0" when the optical disc is in focus, <Q when the optical disc approaches, and > 0 when it moves away. Therefore, this error signal (It - [2
) -(13+14) becomes 0 by controlling the optical system up and down with an actuator (not shown) to perform focusing. This focusing control is based on an astigmatism method that utilizes astigmatism caused by the half mirror 29.

FIG. 9 shows another embodiment of the signal detection method during information reproduction. In this embodiment, the reflected light from the half mirror 29 is used as focusing detection light, and the transmitted light from the half mirror 29 is used as focusing detection light. Further, the tracking detector 39 uses a two-split photodetector and uses the push-pull method as in the case of FIG. FIG. 10 (1) shows on-track, and FIG. 10 (b) and (C) show cases where the beam is shifted in the -y direction and the y direction, respectively. In this case as well, the dividing line is placed parallel to the track. FIG. 10(2) shows the light distribution in the focusing photodetector 37. In this second embodiment, focusing is performed using a known knife method using a knife 36. (a) of FIG. 10(2) shows on-focus, and (b).

(C) shows when the disk is close and when it is far. The edge of the knife 36 is arranged, for example, on the X axis. The focusing photodetector 37 is of a two-part type, and is installed so that the dividing line is parallel to the knife.

FIG. 11 shows a signal detection method when erasing information recording (using the first semiconductor laser 101). In the case of a two-beam type optical pickup, it is said that tracking alone is sufficient for signal detection when recording and erasing information. Therefore, the light emitted from the second region 11B1 of the first grating lens 11 (
It is not necessary to divide the signal light (signal light) 112 into two by a half mirror, and it is sufficient to directly guide the signal light to the tracking photodetector 37'. Therefore, in this case, the tracking photodetector 37'
corresponds to the photodetector 105 shown in FIG. The tracking photodetector 37' is composed of a two-split photodetector in exactly the same way as the tracking photodetector 37 shown in FIG.
Therefore, the light distribution is exactly the same as that shown in FIG. 10 (1).

FIG. 12 shows an example of a specific structure of an optical pickup according to the present invention. In this embodiment, the first grating lens 11 and the second grating lens 12 are disposed orthogonally, and a bending mirror 51 is interposed therebetween, thereby making the entire device thinner.

Note that T indicates track T on the optical disk 107.

The adjustment of the optical system when a focusing error or tracking error is detected by the focusing photodetector or the tracking photodetector can be done, for example, by moving the entire optical system to the optical disc 107 using an appropriate actuator (not shown). This can be done by moving it in a predetermined direction relative to the object.

In each of the embodiments described above, the three photodetectors are not limited to the above-mentioned single photodiode, and the one divided into two and one is not limited to the photodiode divided into four, but it is of course possible to use other photodetectors.

[Effects of the Invention] As described above, according to the present invention, by using a grating lens optical system that is less susceptible to changes in the oscillation wavelength and has fewer aberrations, it is possible to achieve tracking that is less likely to cause focal position shift and deterioration of the focal beam diameter. It is possible to realize a high-performance two-beam optical pickup device that is lightweight, compact, and inexpensive and has high operation reliability for control and focusing control.

[Brief explanation of drawings]

1 and 2 are diagrams showing the basic configuration of a two-beam optical pickup device according to the present invention. FIG. 1 shows the case of beam convergence, FIG. 2 shows the case of signal light convergence, and FIG. The figures show the basic concept of the present invention, Figure 4 shows the basic configuration of the invention for the first beam, Figure 5 shows the basic configuration of the invention for the second beam, and Figure 6. is a diagram showing the geometric planar arrangement relationship between the two divided regions of the first beam and the second beam in the first grating lens, FIG. 7 is a diagram showing the signal detection method during information reproduction, and FIG. 7
FIG. 8 (2) is a diagram showing three types of beam detection states of the two-segment tracking photodetector shown in the figure. A diagram showing three types of beam detection states, FIG. 9 is a diagram similar to FIG. 7 showing another embodiment of the present invention, and FIG. 10 (1) is a diagram showing the two-split type tracking light shown in FIG. 9. Detector 3
FIG. 10 (2) is a diagram showing three types of beam detection states of the two-part focusing photodetector shown in FIG. 9. FIG. 11 is a diagram showing information writing, erasing, etc. FIG. 12 is an illustrative diagram showing an example of the specific structure of the optical pickup according to the present invention.
Figure 3 is a diagram showing the basic configuration of the two-beam hologram pickup disclosed in the applicant's previous application, Figure 14 is a diagram showing the focus shift of an in-line type hologram lens, and Figure 15 is a diagram showing the focus shift of an off-axis type hologram lens. A diagram showing
FIG. 16 is a diagram showing the basic configuration of a grating lens optical system used in the present invention, and FIG. 17 is a diagram explaining a method for determining the spatial frequency of the grating lens shown in FIG. 16. 11...first grating lens, 12...second
Grating lens, 37...Photodetector for focusing, 39...Photodetector for tracking, 101, 102...Semiconductor laser, 105, 10
6...Detector, 110, 111...Laser light, 1
12, 113...Reflected light, 11 A +, 11A
z...first area, 11B1, 118z...second area. Diagram showing the basic configuration of the present invention Diagram showing the basic configuration of the present invention (In the case of beam convergence) (In the case of signal light convergence) Figure 1 Figure 2 Figure 3 Figure 4 Basics of the present invention regarding the second beam Diagrams showing the configuration Figures 5 and 6 Diagrams showing the signal detection method during information reproduction Figure 7 Diagrams showing the (1) racking method (2) Focusing method Figure 8 Diagram showing the method Fig. 9 shows an example of the method Fig. 10 shows the signal detection method during information writing and erasing Fig. 11 shows the structure of the original Binocanog Fig. 12 shows the grating lens system Figure 16 shows the basic configuration of 1. Method for determining the spatial frequency of the second grating lens Figure 17 Diagram showing the principle of a conventional two-beam hologram pink amplifier Figure 13 Diagram showing the focal shift of the in-line hologram lens Figure 1
Figure 4 Diagram showing the focus shift of off-axis type hologram lens Figure 15

Claims (1)

[Claims] Two laser beams (110, 111) having different wavelengths from two semiconductor lasers (101, 102) are directed to different positions (O, O') on an optical signal recording medium (107). In a two-beam optical pickup that records and reads information by condensing light and receiving each reflected light (112, 113), each laser light (110, A first grating lens (11) that intersects the two gratings 111) axially symmetrically, and the diffracted light transmitted through the first grating lens is transferred to an optical signal recording medium (107).
A second grating lens (1
2) are arranged on the optical axis, and the first grating lens has at least two regions (11A_1, 11B_1, 11A_2, 1
1B_2), and the two laser beams are divided into the respective first areas (11A_1, 11A_1, 11A_2) of the first grating lens.
The two signal beams that have passed through _2) and been converged onto the optical signal recording medium by the second grating lens and reflected by the optical signal recording medium are axially symmetrically crossed by the second grating lens and are then converged onto the optical signal recording medium by the second grating lens, and are then converged onto the optical signal recording medium by the second grating lens. A two-beam optical pickup characterized in that the optical pickup is guided to a photodetector (37, 39, 37') through a second region (11B_1, 11B_2).