JPH073700B2 - Optical head device - Google Patents

Description

The present invention relates to an optical head device, and more particularly to a configuration of an optical system element of an optical head device for reading / writing a signal from an optical disc which is an optical information recording medium. It is a thing.

[Prior Art] FIG. 11 shows a conventional optical head device. In the figure, (1) is a light source such as a semiconductor laser, (2) is a light flux emitted from the light source (1), Reference numeral 3) is a diffraction grating for separating the outgoing light beam (2) into three light beams, (4) is a Harm prism (operating as a beam splitter) for separating the irradiation light beam (5) and the reflected light beam (6), (7) Is a condenser lens for converging the irradiation light beam (5) on the information track (13) of the disc-shaped information recording medium (disk) (12) as a light spot (14). The information recording medium (12) is placed in the vicinity of the focal point of the condenser lens (7) and a motor (not shown)
It is driven to rotate.

The light spot (14) is actually composed of three light spots (14a), (14b) and (14c) as shown in FIG. 12 (b), and the information track (13) is a pit (15). And land (16).

The luminous flux reflected by the information recording medium (12) is
After passing through the condenser lens (7) again, it passes through the half prism (4) and becomes a reflected light beam (6) toward the photodetector (19) side.

(17) is a concave lens that reduces the convergence angle of the reflected light beam (6) to increase the magnification of the reflected light beam, and (18) is a cylindrical concave lens that produces astigmatism in the light beam that has passed through the concave lens (17). ) And (18) are the optical system for detecting the focus shift (focusing sensor).

Reference numeral (19) is a photodetector, which is composed of a four-division photodetector (19a) and both-side photodetectors (19b) and (19c) as shown in FIG. 12 (a). The four-division photodetector (19a) divided into four in the center is arranged so that the lens center line of the cylindrical concave lens (18) is inclined by 45 ° with respect to the division line.

In FIG. 12 (a), (20a), (20b), and (20c) are a 4-resolution photodetector (19a) and a double-sided photodetector (19), respectively.
b), the luminous flux on (19c).

(21) is a double-sided photodetector (19b), a differential amplifier for operating and amplifying the outputs of (19c), (22) is an output of the differential amplifier (21),
(23) is a differential amplifier that differentially amplifies the output of adjacent detectors by making the photodetectors arranged at diagonal positions of the four-division photodetector (19a) common to each other, and (24) is differential The output of the amplifier (23), (25) is an adder for obtaining the sum output of the four-division photodetector (19a), and (26) is the output of the adder (25) for the disk (12).
This is the reproduced signal output.

Next, the operation will be described. The reproduction information read by the light spot (14a) is read by the adder (25) as an electric signal (2
6) and then processed by a processing means (not shown) to be converted into a TV signal, an audio signal or the like.

In the information recording medium (12), the center of rotation and the center of the disc do not normally coincide with each other due to a mounting error or the like. Therefore, the track shift occurs due to the rotation.

Therefore, in order to correctly read information by making the center of the track coincide with the center of the light spot (14a), the outputs of the two-sided photodetectors (19b) and (19c) are used as is known. That is, the luminous flux (20b) on both side photodetectors (19b) and (19c)
b) and (20c) correspond to side beams on the disc, that is, the light spots (14b) and (14c), and the line connecting the centers of these light spots (14b) and (14c) is the information track (13). ) Is arranged to be slightly inclined with respect to the direction.
Therefore, both sides of the photodetector (19) with respect to the deviation of the information track (13) and the central beam, that is, the light spot (14a).
b), the intensities of the luminous fluxes (20b) and (20c) on (19c) become unbalanced, and the differential output (22) becomes an output proportional to the track shift.

By applying this output to a tracking actuator (not shown) that moves the condenser lens (7) in a direction perpendicular to the information track (13) so as to form a negative feedback system, a light spot (14a) is formed. It can be continuously focused on the information track.

In this way, the three luminous fluxes (14a), (14
b) and (14c) are formed, and the method of detecting the track deviation from the difference in the intensities of the light beams (14b) and (14c) on both sides is called the twin spot method, and is described in, for example, Japanese Patent Publication No. 53-13123. Has been done.

Moreover, the disk surface is not flat, and surface wobbling occurs due to rotation. Next, the correction method will be described.

The reflected light flux (6) is magnified by the concave lens (17),
Astigmatism is formed by the cylindrical concave lens (18) and is guided to the photodetector (19).

As shown in FIG. 13, the direction of the ellipse differs by 90 degrees depending on the direction of deviation from the focal point of the objective lens of the information recording medium (12). At that time, the output (24) of the differential amplifier with respect to the focus shift changes as shown in FIG.

Therefore, if the focusing actuator that moves the condenser lens (7) in the optical axis direction is operated by the output, the focus shift of the condenser lens can be constantly corrected by a known method. As described above, Japanese Patent Publication No. 53-39123 discloses a method (astigmatism method) of applying astigmatism to the reflected light beam (6) from the disk (12) and detecting the focus shift from the change in the shape of the light beam. .

Here, the example in which the cylindrical concave lens (18) is located between the concave lens (17) and the photodetector (19) is shown, but the same principle can be applied even if the cylindrical concave lens (18) is in front of the concave lens (17). The focus shift can be detected at.

Here, the enlarging action of the concave lens (17) is used to increase the mutual spacing of the three light beams (20a), (20b), (20c) on the photodetector (19). That is, three spots (14a), (14
Regarding the intervals of b) and (14c), if this is set too large, the information track (13) and the light spots (14a) and (14b) are spiral or concentric. , (14c) There is a problem that the permissible width of the angle set value becomes small. Therefore, the three-beam interval on the information recording medium (12) cannot be unduly large, and for example, in the optical pickup for CD (compact disc player), the upper limit is about 22 μm.

On the other hand, if the center distance between the four-division photodetector (19a) and the two-sided photodetectors (19b) and (19c) is too small, the positioning accuracy of the detector with respect to the reflected light beam (6) becomes strict. It is desirable to be wide. Therefore, it is necessary to widen the three-beam interval of the reflected light beam (6), and the concave lens (17) is used.

The conventional device is described in detail in a document (Kondo et al., "MLP-2 type optical pickup for compact disc player", Mitsubishi Electric Technical Report vol, 58, No. 11, 1984).

[Problems to be Solved by the Invention] Since the conventional optical head device is configured as described above, the diffraction grating (3), the half prism (4) that functions as a beam splitter, the cylindrical lens (18), and the like. There is a problem in that it is necessary to properly position the individual parts and fix them on a mount (not shown), which takes time and effort for assembly. Further, since each component has a single function, it has been a factor of increasing the cost of the device.

The present invention has been made to solve such problems, and has one function such as a diffraction grating, a half prism operating as a beam splitter, and a lens functioning as an optical system for a focusing sensor placed in the reflection optical path. The present invention provides an optical head device that can be realized with the optical components described above, and can reduce the cost and the assembly time of the device.

[Means for Solving Problems] An optical head device according to a first aspect of the present invention includes a light source that emits a light beam for forming a light spot on an information recording medium via a light converging means, A light detector having two light receiving regions for focus shift control and track shift control, which is arranged in proximity to the light source, and a pair of first and second surfaces facing each other, and the light source and the information recording. An integrated optical element block arranged between the medium and a first surface of the optical element block near the light source, the light flux emitted from the light source is divided into a central light flux and a plurality of light fluxes on both sides. A second diffraction grating region of the optical element block, which is close to the information recording medium, is formed by forming a first diffraction grating region for separating and transmitting and a simple transmitting region for simply transmitting the reflected light flux from the information recording medium. On the surface of the first diffraction grating region Formed on the first surface by transmitting the light flux from the area and guiding it to the light converging means and spatially branching the light flux reflected from the information recording medium with the light flux from the first diffraction grating region. It is characterized in that a second diffraction grating region for guiding the divided light flux to a light flux for generating a defocus signal is formed in the simple transmission area.

The optical head device according to the second aspect of the present invention is
A light source which emits a light beam for forming a light spot on an information recording medium through a light converging means, and a light which has two light receiving regions for focus shift control and track shift control and is arranged in proximity to the light source. A detector and a pair of opposing first and second
And an integrated optical element block disposed between the light source and the information recording medium, and the first surface of the optical element block near the light source emits light from the light source. The optical element block is formed with two types of areas, a diffraction grating area that separates the light flux into a central light flux and a plurality of light fluxes on both sides and transmits the light flux, and a simple transmission area that simply transmits the reflected light flux from the information recording medium. Of the second surface near the information recording medium, the light flux from the diffraction grating region is transmitted and guided to the light converging means, and the light flux reflected from the information recording medium is emitted from the light source. A two-division diffraction grating which is divided into two as a pair of light beams with the substantially center of the transmitting region as a boundary and which is spatially branched from the light beam from the diffraction grating region and is guided to the simple transmission region. Formed a region And it is characterized in and.

[Operation] With the optical head device according to the first aspect of the present invention,
Positioning of the simple transmission region and each of the diffraction grating regions is performed by using the first surface of the diffraction grating region and the simple transmission region and the second surface of the diffraction grating region as opposing faces of the integrated optical element block. Therefore, unnecessary re-diffracted light generated by re-transmission of the reflected light beam from the information recording medium through the first diffraction grating region does not enter the photodetector.

Further, according to the optical head device of the second aspect of the present invention, the reflected light flux from the information recording medium is spatially divided into two light fluxes and divided into two light fluxes, and the two-division diffraction for guiding to the photodetector. By forming the grating area on the second surface of the integrated optical element block and forming the diffraction grating area and the simple transmission area on the first surface, the positioning of the boundary of the two-divided diffraction grating area with respect to the incident light flux is surely performed. It can be realized.

[Embodiment] A first embodiment of the present invention is shown in FIG. In the figure,
The members (1) to (10) are the same as the conventional example. (30) is an optical element block made of a transparent medium introduced by the present invention, for example, a material such as optical glass or optical plastic, and comprises a first surface (35) on the light source (1) side and a condenser lens (7). ) Side second surface (36). Reference numeral (31) is a first diffraction grating formed on a part of the first surface (35) of the optical element block (30), and the first diffraction grating is a laser beam emitted from the light source (1). Is separated into three light fluxes of 0th-order diffracted light and ± 1st-order diffracted light.

Reference numeral (32) is a second diffraction grating formed on the second surface (36) of the optical element block (30). The second diffraction grating diffracts the light emitted from the light source (1) (2). It has the shape of an interference fringe with the light flux (6) to be separated. In addition, the second diffraction grating (32) has a fringe locus configuration that gives astigmatism in the first embodiment, and this is realized by making the fringe locus such that the grating interval changes substantially linearly. is doing.

Further, (33) is a non-reflection coating region, and the reflected light beam separated by the second diffraction grating is allowed to pass through this region and is made incident on the photodetector (19).

Next, the operation of the first embodiment will be described.

Light flux (2) emitted from a light source (semiconductor laser) (1)
Is a zero-order light or ± first-order light due to the diffraction grating (31) formed on the first surface (35) of the optical element block (30) made of a transparent medium (optical glass, optical plastic, etc.). The light is diffracted and separated into a light beam, and in this state the second diffraction grating (3
The light enters the condenser lens (7) as 0th-order transmitted diffracted light. After passing through the condenser lens (7), this light flux is condensed on the information recording surface of the optical disc (12) as three light spots (14a), (14b), and (14c).
These three focused spots correspond to the 0th and ± 1st order diffracted lights diffracted and separated by the first diffraction grating (31) formed in the optical path of the outgoing light (2).

Next, the light flux reflected by the optical disk (12) again passes through the condenser lens (7) and enters the second diffraction grating (32), and is reflected by the semiconductor laser as a reflected light flux (6) of the first-order transmitted diffracted light. After being separated from the emitted light (2), it is transmitted through the antireflection coating region (33) and is incident on the photodetector (19). The fringe locus of the second diffraction grating is created so that the reflected light beam (6) is diffracted and separated from the emitted light (2) from the semiconductor laser. At the same time, in the present embodiment, the reflected light beam (6) is generated. ) Has astigmatism, and has a wavefront that forms a circle of least confusion at the position of the photodetector (19).

Thus, the luminous fluxes (20a), (20b), (20c) irradiated on the photodetector (19) are as shown in FIG. 1 (b). In the figure, (19a) is an optical disc (12).
A four-division photodetector that receives a light beam (20a) corresponding to the upper center spot (14a), and is composed of four-divided elements A to D as shown in the figure.

In the first embodiment, astigmatism imparted to the disc reflected light by the second diffraction grating (32) is the deformation of the light beam (20a) when the light spot on the optical disc (12) is out of focus. The focal line direction is given so as to be in the x and y directions as indicated by the broken line in the figure.
(A + C) -for the current output by the ~ D element
By performing the calculation of (B + D), it is possible to detect the focus shift by the astigmatism method.

In addition, the luminous fluxes (20b) and (20c) correspond to the spots (14b) and (14C) on both sides of the disc, and the outputs of the two side photodetectors (19b) and (19c) are differentiated as in the conventional example. By performing the calculation, it is possible to detect the track shift according to the principle of the twin spot method. The first surface (35) of the optical element block (30) is also provided with a non-reflection coating on a region (33) (enclosed by a broken line) through which the reflected light beam (6) diffracted and separated is transmitted, This increases the amount of light incident on the photodetector (19). Anti-reflective coating area (33)
Is not limited to this, and there is no problem even if it is formed over the entire surface of the first surface (35). Further, when the intensity of the light emitted from the light source (1) is sufficiently high, the antireflection coating may not be applied.

Next, the first diffraction grating (31) and the second diffraction grating (32)
The points to be noted in forming The second diffraction grating has the following two functions as described above.

(1) Spatial separation of the luminous flux (2) emitted from the semiconductor laser and the reflected luminous flux (6) which is the first-order diffracted light (function of the beam splitter in the conventional example).

(2) To add astigmatism to the diffracted separated light for detecting the focus shift (function of the cylindrical lens of the focusing sensor optical system in the conventional example).

In the above-mentioned function (1), in particular, a circle (2s) representing the transmission positions of the light beams (2) and (6) on the first surface (35),
It is important that (6s) do not overlap. And (6s)
Must be outside the area where the first diffraction grating (31) is formed. If (6s) enters the area of the first diffraction grating (31), the light beam incident on the photodetector (19) is diffracted,
This is an obstacle to correct reading of information.

Next, a second embodiment of the present invention will be described with reference to FIG. The second embodiment differs from the first embodiment in the following points.

(1) The division line direction of the 4-division photodetector (19a) is rotated by 45 ° as compared with FIG. 1, and is in the x and y directions shown.

(2) In forming the fringe locus of the second diffraction grating (32),
When the focused light beam on the optical disc (12) is out of focus, the focal line direction of the light beam on the four-division photodetector (19a) is x,
It is considered that the direction is 45 ° with the y direction. That is, when the fringe locus of the second diffraction grating (32) is provided, the direction of the astigmatism of the reflected light beam (6) is larger than that of the first embodiment.
The wavefront rotated by 45 ° is assumed.

Also in the second embodiment, the four-divided elements A, B,
By focusing the output of C and D by (A + C)-(B + D), the focus shift of the light flux on the disc can be detected, and the twin side photodetectors (19c) and (19b) are used for the twin. Track deviation can be detected by the principle of the spot method. However,
In the second embodiment, the dividing line of the detector (19a) is x,
Since the lens is oriented in the y direction, when the condenser lens (7) is displaced in the x direction by an actuator (not shown) to add a track as is known, deterioration of the focus shift detection characteristic (offset of the focusing sensor) Occurrence) becomes smaller. This is because the light beam (20a) on the four-division photodetector (19a) moves in the x-direction substantially in proportion to the movement of the condenser lens (7) in the x-direction. This is due to the fact that the detection output to (A + C)-(B + D) does not change during focusing (as shown in JP-B-53-37722).

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, the fringe locus of the second diffraction grating (32) is rotated by 45 ° around the Z axis as compared with the first embodiment. The direction of the dividing line of the 4-division photodetector (19a) is rotated by 45 °. Further, the relative position of the photodetector (19) with respect to the light source (1) is rotated by 45 ° around the central luminous flux (Z direction) of the emitted light of the light source (1). The division line directions of the four-division photodetector (19a) can be set to the x and y directions only by rotating the locus of the diffraction grating (32) similar to that of the embodiment by 45 °. Therefore, as in the second embodiment, x by the tracking actuator of the condenser lens (7)
It is possible to solve the problem of characteristic deterioration at the time of detecting the focus shift due to the movement in the direction.

In the above three embodiments, the astigmatism method is used as the focus shift detection (focusing sensor), and the twin spot method is used as the track shift detection (tracking sensor). However, the optical element block (30) of the present invention can use the twin spot method as the tracking sensor and can be combined with other various methods as the focusing sensor. This can be achieved by changing the second diffraction grating (32) to be suitable for other focusing sensor system. In the following fourth and fifth embodiments, an example of combining with another focusing sensor will be described.

FIG. 4 shows a fourth embodiment of the present invention, and a known Foucault method is adopted as the focusing sensor. In this example, the second diffraction grating (32) is linearly divided into two parts with the center of the circular region of the part through which the light flux (2) emitted from the light source (1) passes, as the both sides of the division line. Two sets of lattice loci (32a) and (32a ') are formed in the. Therefore, the disc reflected light becomes the reflected light flux (6) of the first-order diffracted light by the second diffraction grating (32), but the regions (32a), (32a ')
The diffracted light becomes two sets of light beams (6a) and (6a ') spatially separated from each other. The photodetector (19) is placed at the focal point of the reflected light beams (6a) and (6a '),
The spot has a luminous flux (2
0a), (20b), (20c), (20a '), (20b'), (20
c '), and the light beams (20a), (20b), (20c) are the focal points of the reflected light beam (6a), while the light beams (20a'), (20c)
b ') and (20c') are three light fluxes that can be formed as condensing points of the reflected light flux (6a '). Also, (20a) and (20a ') correspond to the central spot (14a) on the disc, and (20b),
(20b ') and (20c), (20c') correspond to the double-sided spots (14b) and (14c) on the disc, respectively.

In this case, the tracking sensor output is {(19c) + (19c ')}-{(19b) + (19
b ′)}. Next, the operation of the Foucault focusing sensor will be described with reference to FIG.

Fig. 5 shows the photodetector (19a) for the focusing sensor,
It is a drawing in which only (19a ′) is extracted, and (a), (b), and (c) in the drawing sequentially show a focusing shift in a direction in which the condenser lens (7) and the optical disk (12) are close to each other. Light beam (20a) on the photodetectors (19a) and (19a ') when (7) and (12) are out of focus.
The spot shape changes of a) and (20a ') are shown.

In this way, the spot shape changes depending on the focusing misalignment direction of the disc, so that four detector elements A,
Focus misalignment can be detected by performing an operation of (A + C)-(B + D) for B, C, and D. In the second diffraction grating (32), the second surface formed by the point light sources having the wavelength of the semiconductor laser disposed at each of the condensing point (20a) and the emission point (1 ') of the light source (1) ( 36) The interference fringe locus on 36) is used as the locus of the diffraction grating region (32a), and the semiconductor laser which is the light source (1) is arranged at the condensing point (20a ') and the emission point (1') of the light source (1). Second formed by a point light source having a wavelength
The fringe locus on the plane (36) may be used as the fringe locus of the diffraction grating region (32a ').

Next, a fifth embodiment of the present invention will be described with reference to FIG.

In the fifth embodiment, the second diffraction gratings (32a '), (32) are separated by the central light flux of the outgoing light flux (2) of the light source (1).
a) is divided into two areas. The light detector (19)
As shown by the broken line (100) in the lower part of the figure, (19a),
(19b), (19c), (19a '), (19b'), (19c ')
And each of (19a) and (19a ') has a three-divided structure.

FIG. 7 is a view of FIG. 6 viewed in the z and y planes, and in FIG. 7B, a view of the second diffraction grating (32) particularly in the x and y planes is extracted. Is shown. As shown in the figure, the second diffraction grating (32) is a pair of diffraction grating regions (32a), (32a ') divided by a straight line (50) passing through the central ray (2') of the emission (2) of the semiconductor laser. Consists of an optical disc (1
The light beams reflected by 2) and diffracted by the diffraction grating regions (32a) and (32a ') are spatially separated and condensed at converging points f ₁ and f ₂ before and after the photodetector (19). . Note that (19) is two converging points f ₁ with respect to the traveling direction of the diffracted and separated light beam (6),
It is located approximately in the middle of f ₂ . The light flux on the detector is the sixth
As shown in the figure (b), corresponding to three spots (14a), (14b), (14c) on the disc, (20a), (20
a ') and (20b), (20b'), (20c), and (20c '). That is, the set of (20a) to (20c) and the set of (20a ') to (2
The group of 0c ') is spatially separated by (32a) and (32a'). The tracking sensor output is {(19c) + (19c ')}-{(19
b) + (19b ')}.

Next, the detection principle of the focusing sensor is detected by an optical detector (19
a), 8th drawn by extracting the light spot on (19a ')
It will be described with reference to the drawings. 8 (a) and 8 (b) show the case where the light spots on the disc are out of focus in the direction close to the condenser lens (7), and FIG. FIGS. 8D and 8E show changes in the light spot on the detector when a focus shift occurs in the far direction.

As shown in FIG. 8 (c), at the time of focusing, the light beam shapes on the photodetectors (19a) and (19a ') are semicircular and of equal size. Further, the amounts of light incident on the detectors denoted by the elements A and B, and A ′ and B ′ are the same. And
S ₁ = A- for the photoelectric conversion outputs of the elements A, B, C
When the calculation of (B + C), S ₂ = A ′ − (B ′ + C ′) is performed, the change of S ₁ and S ₂ with respect to the focus shift is shown in FIG.
It becomes like (g). Furthermore, regarding S ₁ and S ₂ (S ₁ −S ₂ )
It is understood that when the differential calculation is performed, a focus shift detection output (so-called S-shaped curve) as shown in FIG. 6H is obtained, and the amount and direction of the focus shift can be detected and output. The present applicant has already disclosed a focusing sensor having the same principle as that of the present invention in JP-A-60-059545.

Next, a method of forming the locus of the second diffraction grating (32) will be described. As is apparent from FIG. 7, since the light beam f ₁ diffracted by the diffraction grating region (32a) is focused and the light beam diffracted by the diffraction grating region (32a ′) is focused on f ₂ , The fringe locus of 32a) is an interference fringe formed on the second surface (36) by the point source of the wavelength of the semiconductor laser placed at each of the emission point (1 ') and the point f ₁ of the light source (1). It may be a locus. Also, (32
Similarly, the fringe locus of a ′) is also formed on the second surface (36) by the point sources of the wavelength of the semiconductor laser placed at each of the emission point (1 ′) and the point f ₂ of the semiconductor laser (1). The generated interference fringe locus may be used.

FIG. 9 shows a sixth embodiment of the present invention, which is a modification of the focusing sensor system similar to FIG. 6 which is the fifth embodiment. In the fifth embodiment, the reflected light beam (6) which is the first-order diffracted light is diffracted and separated in the y direction, but in the present embodiment, it is separated in the x direction. The second diffraction grating (32) has two diffraction grating regions (32a) (32a) on the left and right with a straight line (50) in the x direction intersecting the central ray of the emitted light beam (2) of the semiconductor laser (1) as a boundary. 32a '), and the light beams diffracted in each area are collected before and after the detector (19).
Lattice trajectories are provided to focus light on f ₁ and f ₂ .

As shown in FIG. 9 (b), the optical spot (14a) on the disc is (20a), (20a '), (14b) is (20b),
(14c) corresponds to (20b ') and (20c'). The tracking sensor output is obtained by the differential calculation of (19b) and (19c) (twin spot method).

Further, the photodetectors (19a) and (19a ') are each divided into three by a dividing line along the x direction as shown in the drawing, and each element is divided by A, B, C, A', B as shown in the drawing. If ′ and C ′, then S ₁ = A− (B + C) and S ₂ = A ′ as in the fifth embodiment.
The focusing sensor output is obtained by the differential (S ₁ -S ₂ ) calculation of the calculations S ₁ and S ₂ of − (B ′ + C ′). In this embodiment, the direction of the dividing lines of the photodetectors (19a) and (19a ') is in the x direction, which coincides with the diffraction direction of the diffraction grating regions (32a) and (32a'). Even if the semiconductor laser of (1) causes a wavelength change due to a change in ambient temperature, a change in drive current, etc., the light beams (20a) and (20a ') on the photodetector are in the direction (x direction) along the dividing line. The advantage is that the deterioration of the detection characteristics of the focusing sensor can be virtually ignored. The same effect is exerted also in the configuration example of FIG. 4 showing the fourth embodiment.

In each of the above embodiments, an example of a combination of the astigmatism method, the Foucault method, and the C-SSD method as the focusing sensor in the optical system using the twin spot method as the tracking sensor is shown. A combination with a sensor is also possible, in short, a diffraction grating for generating three beams is formed on a part of the first surface (35), that is, a part through which the emitted light of the semiconductor laser is transmitted, and the second surface (36 ), The transmitted zero-order light is transmitted to the condenser lens side for the light directed to the disc side, and 1 for the reflected light from the disc.
It is the gist of the invention to create a diffraction grating that separates the emitted light of the semiconductor laser as the secondary diffracted light and processes the light flux for the focusing sensor.

Further, although the light source (1) and the photodetector (19) are described as being spatially separated, the diffraction angle by the second diffraction grating (32) is small and the amount of separation from the emitted light beam (2) is small. When the size is small, the light source (1) and the photodetector (19) may be arranged in the same package (60) as shown in FIG. 10, and in that case, the next time the wavelength change of the light source (1) occurs. Since the change in the diffraction angle of the folded light is small, it is possible to maintain good focusing sensor characteristics even when the wavelength changes. Needless to say, applicable information media include various types such as a write-once type, a magneto-optical type, and a phase change type, in addition to the information-recorded information having a read-write concavo-convex shape.

[Effects of the Invention] As described above in detail, according to the optical head device of the first invention of the present invention, the light beam for forming the light spot on the information recording medium is formed through the condensing means. Light source,
A light detector having two light receiving regions for focus shift control and track shift control, which is arranged in proximity to the light source, and a pair of first and second surfaces facing each other, and the light source and the information recording. An integrated optical element block arranged between the medium and a first surface of the optical element block near the light source, the light flux emitted from the light source is divided into a central light flux and a plurality of light fluxes on both sides. A second diffraction grating region of the optical element block, which is close to the information recording medium, is formed by forming two types of regions, that is, a first diffraction grating region that is separated and transmitted and a simple transmission region that simply transmits the reflected light flux from the information recording medium. On the surface, the first
The light flux from the diffraction grating area is guided to the light converging means, and the light flux reflected from the information recording medium is spatially branched from the light flux from the first diffraction grating area. Since the second diffraction grating region for guiding the branched light flux to the light flux for generating the defocus signal is formed on the simple transmission area formed on the surface, the simple transmission area formed on the first surface is formed. Since the relative positioning between the first diffraction grating area and the first and second diffraction grating areas can be performed very accurately, the reflected light beam from the information recording medium re-transmits through the first diffraction grating area. There is an effect that unnecessary re-diffracted light that does not enter the photodetector, and the disturbance of the information reproduction characteristic does not occur.

According to the optical head device of the second aspect of the present invention, the light source for emitting the light beam for forming the light spot on the information recording medium via the light converging means, the focus deviation control and the track deviation. A photodetector having two light receiving regions for control and arranged in the vicinity of the light source, and a pair of first and second surfaces facing each other, and arranged between the light source and the information recording medium. An integrated optical element block, and a first surface near the light source of the optical element block is provided with a light beam emitted from the light source, which is divided into a central light flux and a plurality of light fluxes on both sides to be transmitted. Two types of areas, a diffraction grating area and a simple transmission area for simply transmitting the reflected light flux from the information recording medium, are formed, and the diffraction grating is formed on the second surface of the optical element block near the information recording medium. The luminous flux from the area is transmitted to The light flux reflected from the information recording medium is split into two as a pair of light fluxes with the center of the region through which the light flux emitted from the light source is transmitted as a boundary, and the split light flux is divided into the diffraction gratings. Since the two-divided diffraction grating region is spatially branched from the light flux from the region and guided to the simple transmission region, in addition to the effect of the first invention, positioning of the boundary of the two-division diffraction grating region with respect to the incident light flux is performed. Can be performed very accurately, so that a reliable defocus signal can be easily obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical head according to an embodiment of the present invention,
2 to 10 are views showing another embodiment of the present invention, and FIG.
The figure shows a conventional optical head device, and FIGS. 12 to 14 are diagrams for explaining the principle of the conventional optical head device. In the figure, (1) is a light source such as a semiconductor laser, (7) is a condenser lens, (12) is an optical disk, (19) is a photodetector,
(30) is an optical element block, (31) is the first diffraction grating,
(32) is the second diffraction grating (35) is the first surface, and (36) is the second surface. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (15)

[Claims] 1. A light source which emits a light beam for forming a light spot on an information recording medium through a light converging means, and two light receiving regions for focus shift control and track shift control. An optical element block having a pair of opposed first and second surfaces and an optical element block disposed between the light source and the information recording medium; On the first side of the block near the light source,
Two types of regions, a first diffraction grating region that separates and transmits the light beam emitted from the light source into a plurality of light beams of a central light beam and side light beams, and a simple transmission region that simply transmits the light beam reflected from the information recording medium. On the second surface of the optical element block near the information recording medium, the light flux from the first diffraction grating region is transmitted to be guided to the condensing means and is reflected from the information recording medium. The light flux is spatially branched from the light flux from the first diffraction grating area to be guided to a simple transmission area formed on the first surface, and the branched light flux is converted into a light flux for generating a defocus signal. An optical head device characterized in that a second diffraction grating region is formed. 2. The second diffraction grating region is an interference fringe locus of a light beam emitted from a light source and a light beam branched by the second diffraction grating region. 1
An optical head device according to the item. 3. The second diffraction grating region is configured so as to impart astigmatism to the light beam split by the second diffraction grating region. Optical head device. 4. The optical head device according to claim 1, wherein the second diffraction grating region has a fringe locus such that the grating spacing thereof changes substantially linearly. 5. The optical head device according to claim 1, wherein the optical element block is made of optical glass or optical plastic. 6. The optical head device according to claim 1, wherein a region including a simple transmission region on the first surface is provided with an antireflection coating. 7. A tracking actuator for moving the light spot following the information track by displacing the light converging means in a direction parallel to the surface of the information recording medium and substantially orthogonal to the information track of the information recording medium. However, at least one of the dividing lines for detecting the defocus signal formed in the area for defocus control of the photodetector,
The optical head device according to claim 1, wherein the optical head device is arranged along a moving direction of the light spot. 8. The optical head device according to claim 1, wherein the photodetector and the light source are arranged close to each other in the same package. 9. A light source that emits a light beam for forming a light spot on an information recording medium via a light converging means, and two light receiving regions for focus shift control and track shift control. An optical element block having a pair of opposed first and second surfaces and an optical element block disposed between the light source and the information recording medium; On the first side of the block near the light source,
Two types of areas are formed: a diffraction grating area that separates the light flux emitted from the light source into a plurality of light fluxes of a central light flux and both side light fluxes, and a simple transmission area that simply transmits the reflected light flux from the information recording medium. On the second surface of the optical element block near the information recording medium, the light flux from the diffraction grating region is transmitted and guided to the condensing means, and the light flux reflected from the information recording medium is transmitted to the light source. Is divided into two parts as a pair of light beams with the substantially center of the region through which the light beam emitted from is transmitted as a boundary, and the two divided light beams are spatially branched from the light beams from the diffraction grating region to form the simple transmission region. An optical head device characterized in that a two-division diffraction grating region for guiding is formed. 10. A diffraction pattern according to claim 9, wherein each of the two-divided diffraction grating regions has a substantially linear stripe locus.
An optical head device according to the item. 11. The tenth aspect of the present invention is characterized in that the substantially linear stripe loci formed in each of the two-division diffraction grating regions are made substantially orthogonal to the boundary line of the two-division diffraction grating regions. The optical head device described. 12. The two-division diffraction grating region is configured so that a pair of light beams divided by the two-division diffraction grating region are given different converging distances, respectively. The optical head device described. 13. The pair of light beams divided by the two-division diffraction grating region are provided with different focusing distances, respectively, and the photodetector is arranged at a substantially intermediate position between the two focusing points. The optical head device according to claim 12. 14. A diffractive separation of a pair of light beams divided by the two-division diffraction grating region in the direction of a dividing line for detecting a defocus signal formed in a light receiving region for defocus control of the photodetector. The optical head device according to claim 9, wherein the optical head device is aligned with the direction. 15. The optical head device according to claim 9, wherein the photodetector and the light source are arranged close to each other in the same package.