JPH0773499A - Optical head - Google Patents

Abstract

PURPOSE:To relax the mounting precision and to reduce the secular change by using two diffraction gratings, reducing the deviation in a light spot due to the fluctuation in a diffraction angle when a wavelength is fluctuated, making angle between a grating vector direction and a direction of a light receiving element division line nearly 45 degree and reducing the moving amount of the light spot. CONSTITUTION:An outgoing light from a laser 8 is transmitted through a hologram 12, and generates a zero-order light beam, and arrives at an optical disk 11 surface through a collimater lens 9 and an objective lens 10. The reflected light generates a diffraction light Ka by the hologram 12, and generates the diffraction light Kb by the hologram 13, and is received by a photodetector 14 with a bisected light receiving surface. Then, in the diffraction light Kb, the diffraction angle due to the fluctuation in the wavelength is canceled, and the fluctuation in the light spot on the element 14 is reduced. Since the angle between the grating vector direction V of the holograms 12, 13 and the direction X of the division line D of the photodetector 14 is 45 degree, even when the hologram 12 is rotated by DELTAtheta, the moving amount of the light spot P is only DELTAL=r.tanDELTAtheta/2<1/2> on the element 14. Thus, since the positional deviation of the light point is reduced even when the hologram 12 is deviated to some extent, the mounting is facilitated, and the secular change is reduced, too.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording, reproducing and erasing information by using reflected light from an optical information recording medium.

[0002]

2. Description of the Related Art FIG. 14 shows the structure of a conventional optical information recording / reproducing apparatus. The light 2 emitted from the light source 1 enters the surface of the diffraction grating 3a of the diffractive element 3 and is split into three beams of 0th-order light 4a and ± 1st-order lights 4b and 4c. These three beams pass through the surface of the holographic grating 3b of the diffractive element 3, are condensed by an objective lens (not shown), and are irradiated onto the surface of an optical disc (not shown). Of the reflected light from the optical disk, the 0th order light reads information, the ± 1st order light detects the track state, returns to the diffractive element 3 again, is diffracted by the holographic grating 3b, and is beam 4a. _1, 4b _1, 4c ₁ and 2 of the beam 4a _2, 4b _2, 4c ₂
It is split into a set of beams. The beams split into these two sets are guided to a light receiving element 5 having six light receiving surfaces a, b, c, d, e, and f.

FIGS. 15A and 15B show the state of the beam spot on the surface of the light receiving element 5. FIG. 15A shows the optical disk close, FIG. 15B shows the optical disk in focus, and FIG. 15C shows the optical disk. This is the beam state when it is far away. In this case, based on the signal values detected on the six light receiving surfaces a, b, c, d, e, f, the focus error signal F by the wedge prism method is used.
o, the track error signal Tr by the three-beam method, and the information signal RF can be obtained. Each signal value can be represented as follows: Fo = (a + d)-(b + c) Tr = e-f Rf = a + b + c + d. By thus placing the light source 1 and the light receiving element 5 in the same plane, it is possible to detect each signal value and perform focus servo, tracking servo, and information reproduction, so that the apparatus can be downsized. In addition, it is possible to perform stable signal detection at low cost.

[0004]

As described above, in the conventional example, the deviation of the light spot on the light receiving element caused by the wavelength variation is set so that the dividing line direction of the light receiving element and the direction of the light spot deviation are substantially the same direction. In other words, in other words, the dividing line direction of the light receiving element and the direction of the grating vector of the diffraction grating are made substantially the same direction, so that no offset occurs in the focus error signal Fo.

FIG. 16 shows the dividing line direction X of the light receiving element 6,
The conventional example is arranged so that the grating vector direction V of the diffraction grating 7 is substantially parallel. Normally,
In an element in which the light source (LD) and the light receiving element 6 (PD) are packaged, since the light receiving element 6 is fixed in advance, the alignment of the light spot P on the surface of the light receiving element 6 is performed by the diffraction grating. The position of the spot is moved by rotating 7 by Δθ. In this way, in the configuration in which the grating vector direction V and the dividing line direction X of the light receiving element 6 are arranged substantially parallel to each other, when the diffraction grating 7 is rotated by Δθ, the movement amount ΔLo of the light spot P becomes ΔLo = r · tan Δθ (1) However, r moves in the direction Y perpendicular to the parting line on the surface of the light receiving element 6 by the optical path length. In this way, Δθ is finely adjusted to move and adjust the light spot P so as to be divided into two equal parts along the dividing line.
The focus offset is reduced.

As a result, the signal can be stably detected even when the wavelength variation occurs, but when the diffraction grating 7 is assembled, the dividing line D of the light receiving element 6 is aligned so as to come to the central position of the light spot P. Therefore, since the diffraction grating 7 is rotated and the light spot P is moved for adjustment, extremely high precision is required for the assembly of the diffraction grating 7. Therefore, if the diffraction grating 7 is slightly rotated, the light spot P moves in a direction substantially perpendicular to the dividing line D of the light receiving element 6 and a large offset occurs.
As a result, a rotational adjustment deviation during assembly or a rotational deviation due to a change over time causes a large focus offset.

[0007]

According to a first aspect of the present invention, the light emitted from the laser light source is collimated by a collimator lens, and the collimated light is condensed by an objective lens to form a plane on the optical information recording medium. In an optical head for recording, reproducing, erasing information by irradiating the optical information on the optical head, the reflected light from the optical information recording medium is branched on an optical path between the laser light source and the optical information recording medium. A first diffraction grating for generating diffracted light is arranged, and a second diffracted light having the same grating vector direction as that of the first diffraction grating is generated on the optical path of the first diffracted light branched by the first diffraction grating. A two-diffraction grating is arranged, and a light-reception having a dividing line forming a direction of about 45 ° with the grating vector directions of the first and second diffraction gratings is provided on the optical path of the second diffracted light generated by the second diffraction grating. Special feature that the element is arranged Light head to be.

According to a second aspect of the present invention, in the first aspect of the invention, at least one of the first and second diffraction gratings has polarization efficiency in its diffraction efficiency.

According to the third aspect of the present invention, the light emitted from the laser light source is collimated by the collimator lens, and the collimated light is condensed by the objective lens and irradiated onto the surface of the optical information recording medium. In an optical head for recording, reproducing, erasing, etc., reflected light from the optical information recording medium is branched on the optical path between the laser light source and the optical information recording medium to generate at least two diffracted lights. A diffraction grating is provided, and at least two light receiving elements having a dividing line which receives the diffracted light from the diffraction grating and forms a direction of about 45 ° with the grating vector direction of the diffraction grating are provided.

According to a fourth aspect of the present invention, in the third aspect of the invention, the diffraction efficiency of the diffraction grating has polarization dependency.

According to the fifth aspect of the present invention, the light emitted from the laser light source is collimated by the collimator lens, the collimated light is condensed by the objective lens, and the collimated light is irradiated onto the surface of the optical information recording medium. In an optical head for recording, reproducing, erasing, etc., a polarizing film and a diffraction grating for branching reflected light from the optical information recording medium are provided on an optical path between the laser light source and the optical information recording medium. A polarization diffracting member formed integrally is disposed, and at least two light receiving elements having a dividing line which receives the diffracted light from the polarization diffracting member and forms a direction of about 45 ° with the grating vector direction of the diffraction grating. Was arranged.

[0012]

In the invention according to claim 1, the first and second aspects are provided.
By using the two diffraction gratings described above, it is possible to extremely reduce the deviation of the light spot due to the fluctuation of the diffraction angle when the wavelength is changed, and the grating vector direction and the direction of the dividing line of the light receiving element are set to about 45 °. This makes it possible to suppress the amount of movement of the light spot with respect to the direction of the dividing line on the light receiving element to be small even if the diffraction grating is largely rotated.

According to the second aspect of the present invention, since the diffraction efficiency of the diffraction grating has polarization dependency, the light utilization efficiency is improved, which makes it possible to use a low output semiconductor laser.

In the third aspect of the present invention, the diffracted light (± first-order light) from one diffraction grating is detected using two light receiving elements, respectively, so that the light spot shift due to the wavelength fluctuation is detected on the signal. It becomes possible to cancel, and by setting the grating vector direction and the dividing line direction of the light receiving element to be approximately 45 °, even if the diffraction grating is largely rotated, the light spot of the light spot in the direction of the dividing line on the light receiving element is It is possible to keep the amount of movement small.

According to the invention described in claim 4, the light utilization efficiency is improved, and it becomes possible to use a semiconductor laser having a low output.

In the invention described in claim 5, the light utilization efficiency is improved, a low output semiconductor laser can be used, and the irradiation light to the optical information recording medium fluctuates even when the diffraction grating is adjusted. There is nothing to do.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the invention according to claim 1 is shown in FIGS.
It will be described based on. First, the overall configuration of this device will be described with reference to FIG. Here, light emitted from a semiconductor laser 8 (LD) as a laser light source is collimated by a collimator lens 9, and the collimated light is condensed by an objective lens 10 on the surface of an optical disc 11 as an optical information recording medium. In the optical head that records, reproduces, and erases information by irradiating the semiconductor laser 8 and the optical disk 11
A hologram 12 as a first diffraction grating for branching the reflected light from the optical disk 11 to generate the first diffracted light Ka is disposed on the optical path between the first diffracted light and the first diffracted light branched by the hologram 12. The hologram 12 on the optical path of Ka
And a hologram 13 as a second diffraction grating for generating the second diffracted light Kb having the same grating vector direction. In addition, here, as shown in FIG.
On the optical path of the second diffracted light Kb generated by
The light receiving element 14 having the dividing line D that forms the direction X of approximately 45 ° with the lattice vector direction V of 2 and 13 is arranged.

In such a structure, the operation of the structure shown in FIG. 1 will be described. The light emitted from the semiconductor laser 8 passes through the hologram 12 to obtain the 0th order light, becomes parallel light by the collimator lens 9, is condensed by the objective lens 10, and is irradiated onto the surface of the optical disk 11. After the disc information is read, the reflected light from the optical disc 11 follows the opposite path and is diffracted by the hologram 12 to obtain the first diffracted light Ka. The first diffracted light Ka enters the hologram 13 and is diffracted again to obtain a second diffracted light Kb. The second diffracted light Kb is received by the light receiving element 14 having a light receiving surface divided into two. Therefore, in the light diffracted twice in this way (second diffracted light Kb), the fluctuation of the diffraction angle due to the fluctuation of the wavelength is canceled out, so that the light spot on the light receiving element 14 is changed as shown in FIG. Fluctuations are small. Figure 3
(B) shows a comparison of how the diffracted light diffracted by the conventional hologram 15 changes the light spot position on the surface of the light receiving element 16 due to wavelength fluctuation (± Δλ). As can be seen from this, the amount of fluctuation of the light spot on the light receiving surface is smaller when the light diffracted twice is detected.

Further, in this embodiment, as shown in FIG. 2, the hologram vector directions V of the holograms 12 and 13 and the direction X of the dividing line D of the light receiving element 14 are arranged at 45 °. Therefore, even if the hologram 12 is rotated by Δθ as shown in FIG. 4, the movement amount ΔL of the light spot P moves only on the surface of the light receiving element 14 by ΔL = r · tan Δθ / √2 (2). I understand.
As can be seen by comparing the value of the expression (2) with the value of the conventional expression (1), it can be said that the spot position deviation is small even if the hologram 12 is slightly deviated. As a result, the adjustment at the time of assembling is eased and it becomes stable with respect to the change with time.

As mentioned above, the two holograms 12, 1
By using No. 3, it is possible to make extremely small the deviation of the light spot due to the variation of the diffraction angle when the wavelength varies. Further, by setting the lattice vector direction V and the direction X of the dividing line D of the light receiving element 14 to be approximately 45 °, the hologram 12,
Even if 13 is rotated greatly, the dividing line D on the light receiving element 14
The movement amount of the light spot P with respect to the direction X can be suppressed to be small. Therefore, from the above, it is possible to realize an optical head that is easily finely adjusted and that operates in a stable state with respect to a change over time.

Next, an embodiment of the invention described in claim 2 will be described with reference to FIGS. 5 and 6A to 6C. In addition,
A description of the same parts as those of the invention described in claim 1 will be omitted, and the same reference numerals will be used for the same parts.

In the optical head according to the first aspect of the present invention, the diffraction efficiency of at least one of the first and second diffraction gratings has polarization dependency. Further, here, as shown in FIG. 5, a 1/4 is provided on the optical path between the collimator lens 9 and the objective lens 10.
The wave plate 17 is provided. Hereinafter, specific examples in which the diffraction efficiencies of the first diffraction grating (hologram 12) and the second diffraction grating (hologram 13) have polarization dependency will be described with reference to FIGS.
Based on.

FIG. 6A shows an example in which only the first diffraction grating has polarization dependency. When the reflected light from the optical disk 11 is incident on the hologram 12 having polarization dependency, about 100% is diffracted to become the first diffracted light Ka, and about 100% of the first diffracted light Ka is incident on the hologram 13. About 30% is diffracted by the second diffracted light Kb.
And is guided to the light receiving element 14. In this case, since the hologram 13 has no polarization dependency, the transmitted light T is generated, and the light utilization efficiency on the surface of the light receiving element 14 is about 25%.
If the transmitted light T is guided to the light receiving element 14a and detected as an information signal and the focus error signal Fo is detected by the second diffracted light Kb, there is no problem in terms of detection sensitivity.

FIG. 6B shows an example in which the first diffraction grating and the second diffraction grating have polarization dependence. The light reflected from the optical disk 11 is a hologram 12 having polarization dependence.
When about 100% of the first diffracted light Ka is diffracted into the first diffracted light Ka, and about 100% of the first diffracted light Ka enters the hologram 13 having polarization dependence, about 100% thereof is diffracted into the first diffracted light Ka. 2 Diffracted light Kb becomes light receiving element 1
Guided to 4. As a result, the light utilization efficiency on the surface of the light receiving element 14 is about 90%, and the light utilization efficiency can be significantly improved.

FIG. 6C shows an example in which only the second diffraction grating has polarization dependency. When the reflected light from the optical disk 11 enters the hologram 12, about 30% is diffracted to become the first diffracted light Ka, and about 30% of the first diffracted light Ka enters the hologram 13 having polarization dependence. About 100% of the light is diffracted to become the second diffracted light Kb, which is guided to the light receiving element 14. As a result, the light use efficiency on the surface of the light receiving element 14 is about 25%, but it is easy to manufacture a diffraction grating without polarization dependence, which may be low in light use efficiency to some extent, and is advantageous in that it has high mass productivity. is there.

As described above, by making the diffraction efficiencies of both diffraction gratings (holograms 12 and 13) polarization dependent, it is possible to greatly improve the light utilization efficiency in the form of an optical isolator. As a result, the laser power of the semiconductor laser 8 can be used efficiently, and a high-performance optical head can be realized at low cost. Further, also in the case of this embodiment, the adjustment at the time of assembling is eased, and the stable operation can be performed even with a change with time.

Next, an embodiment of the invention described in claim 3 will be described with reference to FIGS. The description of the same parts as those of the first and second aspects of the present invention will be omitted,
The same reference numerals are used for the same portions.

In the optical head shown in FIG. 7, the optical disk 11 is placed on the optical path between the semiconductor laser 8 and the optical disk 11.
Diffraction grating that splits the reflected light from to generate at least two diffracted lights, here two diffracted lights (± first-order light) K
Split holograms 18a and 18b are provided as diffraction gratings for generating c and Kd. Also, as shown in FIG.
Diffracted lights Kc and Kd from the divided holograms 18a and 18b
Is incident and has at least two light receiving elements having a dividing line D that makes a direction X of approximately 45 ° with the lattice vector direction V of the divided holograms 18a and 18b, in this case, the light receiving surfaces a and b.
And light receiving element 20 having light receiving surfaces c and d
And.

In such a structure, the optical disk 11
The reflected light from is incident on the divided holograms 18a and 18b to generate diffracted light of the + 1st order light Kc and the -1st order light Kd. The + 1st order light Kc is received by the light receiving element 19, and the -1st order light K is received. The light is received by the element 20. FIG. 8 shows the direction X of the dividing line D of the light receiving elements 19 and 20 with respect to the lattice vector direction V.
Shows the situation when the angle is about 45 °. In the embodiments of claims 1 and 2 described above, the case where only the + 1st order diffracted light is received is described.
Here, two diffracted lights Kc and Kd from the same plane are received separately.

Now, let us consider a case where the focus error signal Fo is detected using this apparatus. Light receiving surface a to d
The focus error signal Fo corresponding to can be detected by the same principle as the Foucault method by the formula: Fo = (a + c)-(b + d) (3). FIGS. 9A to 9C are the same as FIGS.
Each corresponds to the environmental condition of (c). Further, here, the following features are provided. That is, when the light spot P is displaced due to the variation of the diffraction angle due to the wavelength variation (λ ₀ ± Δλ), for example, when the diffraction angle becomes small, the light spot P on one of the light receiving elements 19 as shown in FIG. Moves to the light receiving surface a side, and the light spot P on the other light receiving element 20 moves to the light receiving surface d side. In this case, since the diffracted lights Kc and Kd from the same hologram 18a are used, the spot variation amount is the same, and thus the signal disturbance due to the spot variation is canceled. Therefore, from the above, it is possible to eliminate the occurrence of offset in the focus error signal Fo due to the canceling action between the signals even if the spot shift occurs due to the wavelength variation. Moreover, in this case, since the lattice vector direction V and the direction X of the dividing line D of the light receiving elements 19 and 20 form approximately 45 °, the adjustment accuracy of the holograms 18a and 18b is relaxed, and thus the change over time is prevented. However, it is possible to realize an optical head that can perform stable operation.

Further, in the present embodiment, the adjustment accuracy as described above is relaxed and stable with respect to changes over time, but
When the light receiving elements 19 and 20 are assembled in the initial stage and both of the light receiving elements 19 and 20 are not arranged at the proper positions, even if the holograms 18a and 18b are rotationally adjusted, the two light spots P Simultaneously center the light receiving element 1
In some cases, it may not be possible to match the positions of the dividing lines D of 9 and 20. Therefore, in such a case, only one of the light spots P is used to align its center with the position of the dividing line D, and then one light spot P such as the well-known knife edge method is used for focusing. The error signal Fo is detected. The light receiving element 19 shown in FIG. 11A is used as a focus error signal detecting element, and the light receiving element 20 shown in FIG. 11B is used as an offset adjusting light receiving element.
As a result, if the focus error signal Fo is detected only by the light receiving element 19 and the light spot P is deviated by the light receiving element 20, the focus error signal Fo is: Fo = (ab) + G (cd). (4) G: can be detected as a gain constant, which can reduce the focus offset due to spot variation.

Next, an embodiment of the invention described in claim 4 will be described. The description of the same parts as those in the first to third aspects of the present invention will be omitted, and the same reference numerals will be used for the same parts.

Here, in the optical head according to the third aspect of the invention, the divided holograms 18a, 1 which are diffraction gratings are used.
It is characterized in that the diffraction efficiency of 8b has a new polarization dependence. Also here, as in the embodiment described in claim 2, the divided holograms 18a and 18b are provided with such polarization dependence, and the quarter wavelength plate 17 is arranged in the optical path, whereby the specific example (FIG. As described in 6 (a) to 6 (c)), the light utilization efficiency can be further improved, and since the low-power semiconductor laser 8 can be used, the cost of the device can be reduced. .

Next, an embodiment of the invention described in claim 5 will be described with reference to FIGS. 12 and 13. It should be noted that the description of the same parts as those of the above-described inventions according to claims 1 to 4 is omitted, and the same reference numerals are used for the same parts.

Here, in the optical head shown in FIG. 12, on the optical path between the semiconductor laser 8 and the optical disk 11, a polarizing film 21 and reflection as a diffraction grating for branching the reflected light from the optical disk 11 are provided. The type diffraction grating 22 and the prism 23 are integrally provided on the prism 23. In this case, the polarization film 21, the reflection type diffraction grating 22 and the prism 23 constitute a polarization diffraction member 24. Further, as shown in FIG. 13, the diffracted lights Ke and Kf from the polarization diffraction member 24 are incident and also have a dividing line D that forms a direction X substantially 45 ° with the grating vector direction V of the reflection type diffraction grating 22. At least two light receiving elements, here, a light receiving element 25 having light receiving surfaces a and b and a light receiving element 26 having light receiving surfaces c and d are provided.

Since the reflection type diffraction grating 22 is not polarization dependent by separately forming the polarization film 21 having polarization characteristics in this way, it is not necessary to use a diffraction grating such as an LN crystal or a deep groove grating. As a result, it is possible to provide a device that is easy to manufacture and has high mass productivity, and it is possible to improve the light utilization efficiency and use the low-power semiconductor laser 8 to reduce the cost. Further, in the embodiments described in claims 1 and 2, when the glass substrates of the holograms 12 and 13 are inclined with respect to the optical axis,
Although the light irradiated to the optical disk 11 is tilted as the rotation is adjusted, the polarization film 21 is already fixed when the reflection type diffraction grating 22 is rotationally adjusted as in the present embodiment. The light emitted to the optical disk 11 is not affected at the time of adjustment, and thus the accuracy of assembly adjustment can be relaxed. The focus error signal Fo here can be obtained by Fo = (a + c)-(b + d) (5). Also in this case, the focus offset due to the spot variation can be reduced as in the case of the third embodiment.

[0037]

According to the first aspect of the present invention, the light emitted from the laser light source is collimated by the collimator lens, and the collimated light is condensed by the objective lens and irradiated onto the surface of the optical information recording medium. In an optical head for recording, reproducing, erasing information, etc. by means of the above, reflected light from the optical information recording medium is branched on the optical path between the laser light source and the optical information recording medium to generate a first diffracted light. And a second diffraction grating for generating a second diffracted light having the same grating vector direction as that of the first diffracted light on the optical path of the first diffracted light branched by the first diffracted grating. A light-receiving element having a dividing line that forms an angle of about 45 ° with the grating vector directions of the first and second diffraction gratings is provided on the optical path of the second diffracted light generated by the second diffraction grating. I did so, 2
By using two diffraction gratings, the deviation of the light spot due to the fluctuation of the diffraction angle at the time of wavelength fluctuation can be made extremely small, and by making the grating vector direction and the direction of the dividing line of the light receiving element approximately 45 °, the diffraction grating The amount of movement of the light spot with respect to the direction of the dividing line on the light receiving element can be suppressed to a small amount even if the optical axis is rotated by a large amount, which makes it possible to easily perform fine adjustment and to provide an optical head that is stable over time. Is something that can be done.

According to a second aspect of the present invention, in the first aspect of the invention, at least one of the first and second diffraction gratings has a polarization dependency of diffraction efficiency. It is possible to improve the light utilization efficiency and use a low-power semiconductor laser, which can reduce the cost of the device.

According to the third aspect of the invention, the light emitted from the laser light source is collimated by the collimator lens, and the collimated light is condensed by the objective lens and irradiated onto the surface of the optical information recording medium. In an optical head for recording, reproducing, erasing, etc., reflected light from the optical information recording medium is branched on the optical path between the laser light source and the optical information recording medium to generate at least two diffracted lights. Since the diffraction grating is arranged and the diffracted light from the diffraction grating is incident, and at least two light receiving elements having a dividing line forming a direction of about 45 ° with the grating vector direction of the diffraction grating are arranged, By detecting (± first-order light) using two light-receiving elements, it is possible to cancel the light spot shift due to wavelength variation on the signal, and also to divide the grating vector direction and the light-receiving element. By setting the dividing line direction at about 45 °, the amount of movement of the light spot with respect to the direction of the dividing line on the light receiving element can be suppressed to a small amount even if the diffraction grating is rotated by a large amount. It is possible to provide an optical head that is stable against changes.

According to a fourth aspect of the invention, in the invention of the third aspect, the diffraction efficiency of the diffraction grating has polarization dependency, so that the light utilization efficiency is improved and a low output semiconductor laser is used. Therefore, the cost of the device can be reduced.

According to a fifth aspect of the present invention, the light emitted from the laser light source is collimated by a collimator lens, the collimated light is condensed by an objective lens, and the collimated light is irradiated onto the surface of the optical information recording medium. In an optical head for recording, reproducing, erasing, etc., a polarizing film and a diffraction grating for branching reflected light from the optical information recording medium are provided on an optical path between the laser light source and the optical information recording medium. A polarization diffracting member formed integrally is disposed, and at least two light receiving elements having a dividing line which receives the diffracted light from the polarization diffracting member and forms a direction of about 45 ° with the grating vector direction of the diffraction grating. Since the above is provided, it is possible to improve the light utilization efficiency and use a low-power semiconductor laser, so that the cost of the device can be reduced, and the optical information can be recorded even when the diffraction grating is adjusted. Does not vary the irradiation light to the medium, it is capable of performing stable adjustment.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of an optical head according to an embodiment of the invention described in claim 1.

FIG. 2 is a schematic diagram showing an arrangement relationship between a hologram and a light receiving element.

FIG. 3 is a view showing a state of a light spot fluctuation due to a wavelength fluctuation, (a) is a side view in the case of the present invention,
(B) is a side view in the case of the conventional example.

FIG. 4 is a schematic diagram showing a method of aligning a light spot.

FIG. 5 is a perspective view showing a configuration of an optical head according to an embodiment of the invention as set forth in claim 2.

6A is a side view when only the first diffraction grating has polarization dependence, FIG. 6B is a side view when the first and second diffraction gratings have polarization dependence, and FIG. 4] is a side view in the case where only the second diffraction grating has polarization dependency.

FIG. 7 is a perspective view showing a configuration of an optical head which is an embodiment of the invention as set forth in claim 3;

FIG. 8 is a schematic diagram showing an arrangement relationship between a hologram and a light receiving element.

FIG. 9 is a schematic diagram showing a light spot state during defocusing.

FIG. 10 is a schematic diagram showing a state of a light spot when a wavelength changes.

FIG. 11 is a schematic diagram showing a state during offset adjustment.

FIG. 12 is a plan view showing a configuration of an optical head according to an embodiment of the invention as set forth in claim 5;

FIG. 13 is a schematic diagram showing an arrangement relationship between a reflection type diffraction grating and a light receiving element.

FIG. 14 is a perspective view showing a configuration of a conventional optical information recording / reproducing apparatus.

FIG. 15 is a schematic diagram showing a state of a light spot on a light receiving element surface.

FIG. 16 is a schematic diagram showing a conventional light spot alignment method.

[Explanation of symbols]

 8 Laser Light Source 9 Collimator Lens 10 Objective Lens 12 First Diffraction Grating 13 Second Diffraction Grating 14 Light-Receiving Element 18a, 18b Diffraction Grating 19, 20 Light-Receiving Element 21 Polarizing Film 22 Diffraction Grating 24 Polarizing Diffraction Member Ka First Diffracting Light Kb Second Diffracted light

Claims (5)

[Claims] 1. Recording, reproduction, and erasing of information by collimating light emitted from a laser light source by a collimator lens, condensing the collimated light by an objective lens, and irradiating the collimated light onto the surface of an optical information recording medium. In the optical head for
A first diffraction grating that branches reflected light from the optical information recording medium to generate first diffracted light is disposed on an optical path between the laser light source and the optical information recording medium, and the first diffraction grating is provided. A second diffraction grating for generating a second diffracted light having the same grating vector direction as that of the first diffracted light is arranged on the optical path of the first diffracted light branched by the second diffracted light generated by the second diffracted grating. An optical head, characterized in that a light receiving element having a dividing line forming a direction of approximately 45 ° with the grating vector directions of the first and second diffraction gratings is arranged on the optical path of light. 2. The optical head according to claim 1, wherein at least one diffraction grating of the first and second diffraction gratings has polarization dependency on diffraction efficiency. 3. Recording, reproduction, and erasing of information by collimating light emitted from a laser light source by a collimator lens, condensing the collimated light by an objective lens and irradiating the collimated light onto the surface of an optical information recording medium. In the optical head for
A diffraction grating for branching the reflected light from the optical information recording medium to generate at least two diffracted light is disposed on the optical path between the laser light source and the optical information recording medium, and the diffraction from the diffraction grating is provided. An optical head characterized in that at least two light receiving elements having a dividing line which is incident on light and forms a direction of about 45 ° with a grating vector direction of the diffraction grating are arranged. 4. The optical head according to claim 3, wherein the diffraction efficiency of the diffraction grating has polarization dependency. 5. Recording, reproduction, and erasing of information by collimating light emitted from a laser light source by a collimator lens, condensing the collimated light by an objective lens and irradiating the collimated light on the surface of an optical information recording medium. In the optical head for
A polarization diffractive member, in which a polarizing film and a diffraction grating for branching reflected light from the optical information recording medium are integrally formed, is arranged on an optical path between the laser light source and the optical information recording medium. An optical head characterized in that at least two light-receiving elements are arranged which have a dividing line which receives the diffracted light from the polarization diffractive member and forms a direction of about 45 ° with the grating vector direction of the diffraction grating.