JPH10320811A - Efficiency controlled diffraction grating and optical pickup having the diffraction grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a complex grating pattern such as a grating lens by forming a first transparent electrode, a grating layer and an insulating layer on a transparent substrate, forming a post layer on a portion of the insulating layer and forming a second electrode which functions as a reflection mirror. SOLUTION: The efficiency controlled diffraction grating is made by piling up a first transparent electrode 22, a grating layer 23 which has repeated grating patterns with reflection and transparent sections, an insulation layer 24, a post layer 25 located at an edge section and a second electrode 26, which also works as a reflection mirror, on a transparent substrate 21. By controlling the voltage applied between the electrodes 22 and 26, the gap between the electrode 26 and the layer 23 is varied and the efficiency of a first order diffraction is controlled. Thus, the layer 23 is fixed the electrode function is eliminated from the construction, the diffraction grating having various grating patterns is formed and the durability is made superior.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an efficiency control diffraction grating for changing the efficiency of a diffraction grating, and to an optical pickup device provided with the efficiency control diffraction grating for recording and reproducing an optical disk.

[0002]

2. Description of the Related Art Conventionally, as an element for modulating the intensity of light, an efficiency control diffraction grating utilizing the diffraction effect of light has been proposed, for example, in the article by O. Solgaard et al., "Deformable grating optical modulator"(""). Deformable Gratin
g Optical Modulator "/ Optics Letters / Vol.17, N
o.9 / May 1, 1992). This efficiency control diffraction grating can be miniaturized and can be manufactured by an IC process, so that there is an advantage that it can be mass-produced collectively.

[0003] This efficiency control diffraction grating will be described with reference to FIG. The efficiency control diffraction grating includes a silicon substrate 41 and spacers 42 formed on a peripheral region of the silicon substrate 41.
(Silicon oxide film) and a grating composed of a plurality of fine dielectric beams 43 (silicon-rich silicon nitride film) supported at both ends by spacers. On the upper surface of the grating, a reflection film 44 that also functions as an electrode is provided.

FIG. 9A shows a reflection film 44 and a silicon substrate 4.
1 shows a state where no voltage is applied.
In this state, the light incident on the efficiency control diffraction grating is directly reflected and returned. However, when a voltage is applied between the reflective film 44 and the silicon substrate 41, an electrostatic force acts between the two, and the grating 43 is curved as shown in FIG. 41 comes into contact with the upper surface. At this time, since the distance between the reflective film on the upper surface of the grating 43 and the reflective film on the upper surface of the silicon substrate 41 changes, diffracted light is generated. By controlling the applied voltage, the diffraction efficiency can be changed.

The present invention also relates to an optical pickup device for recording and reproducing two types of optical disks having different thicknesses. In addition to the conventional optical disc standard represented by CD, a new standard of high-density optical disc called DVD has been born. The thickness of the DVD disk substrate is 0.6 mm, which is half the thickness of the conventional CD of 1.2 mm. According to the DVD standard, the wavelength of the light source to be used is changed from 780 nm to 650 nm in addition to the change in the thickness of the disk substrate.
, The NA of the objective lens has been changed from 0.45 to 0.6.

[0006] On the other hand, an optical pickup device for recording / reproducing an optical disk can usually deal only with an optical disk having a specific thickness. In other words, recording and reproduction cannot be performed on an optical disc whose substrate thickness is outside the specified range (about ± 0.1 mm or more) because aberrations such as spherical aberration occur.
A normal optical pickup device could not record and reproduce both a CD and a DVD. Various methods have been proposed to solve this problem. As one of them, the one disclosed in Japanese Patent No. 2532818 will be described with reference to FIG.

In this optical pickup device, a combination of a refraction type objective lens 45 and a hologram lens 46 including a concentric lattice pattern is used, and the lattice pattern of the hologram lens 46 depends on the difference in the thickness of the disk substrate. It is designed to compensate for the generated spherical aberration. At the time of recording / reproduction of a DVD, as shown in FIG.
The light is focused to the diffraction limit on 7. When playing a CD,
As shown in FIG. 0 (b), the first-order diffracted light of the hologram lens 46 is focused on the CD 48 to the diffraction limit. In this manner, the optical pickup device of FIG. 10 can perform recording / reproduction on two types of optical disks having different substrate thicknesses.

In addition, a method has been proposed in which two types of objective lenses are prepared for CD and DVD, and these are mechanically switched, and a method of reducing the spherical aberration by limiting the aperture at the time of CD reproduction is proposed. I have.

[0009] The present invention also relates to an optical pickup device for recording and reproducing data on and from an optical disk having different tracking control methods.

At present, a three-beam method is mainly used as a tracking control method for a CD. In this method, two sub-beams are newly generated using a diffraction grating so that the sub-beams are arranged in front of and behind the main beam for signal reading on the optical disc, and this arrangement is slightly inclined with respect to the track row. By doing so, when the main beam spot deviates from the track, a light amount difference is generated in the reflected light of the two sub-beams from the optical disk, and a radial error signal is obtained from the difference.

On the other hand, D which has a higher density than CD
In VD, the track pitch is narrower than in CD. Therefore, if recording and reproduction of CD and DVD are to be performed using the same optical pickup device and the three-beam method as the tracking control method, the position of the sub-beam is changed to the CD.
In the case of adjusting for DVD, the sub-beam is applied to the adjacent track at the time of recording / reproducing the DVD, and when the adjustment is made for DVD, the radial error signal at the time of reproducing the CD becomes weak.

In order to overcome this problem, tracking control is performed by a method generally called a phase difference detection method when recording and reproducing a DVD. This is a one-beam tracking control method utilizing the fact that, when the spot 49 is shifted from the center of the pit 50 to the left and right as shown in FIG. The reflected light 51 from the disk shown in FIG.
By processing the result, a radial error signal is obtained. In this phase difference detection method, when the pit depth deviates from λ / 4, a radial offset occurs. Therefore, in order to perform tracking control of a CD and a DVD having different pit depths by the phase difference detection method, it is more complicated. Processing is required. For this reason, in many cases, a method of detecting a radial error signal by a three-beam method during CD reproduction and detecting a radial error signal by a phase difference detection method during DVD reproduction is adopted.

[0013]

Since the conventional efficiency control diffraction grating has a structure in which the beams are driven up and down, both ends of the beams must be supported. For example, a grating in which the beams are arranged in parallel. Only a pattern was formed, and a diffraction grating having a complicated shape such as a concentric grating pattern could not be formed. In addition, if a diffraction grating with a fine grating pitch and a shallow groove depth is required, the beam to be driven becomes narrower, so higher manufacturing accuracy is required, and it is difficult to form all beams precisely and drive accurately. Become. In addition, durability decreases.

Further, the conventional optical pickup device for recording and reproducing two types of optical disks having different thicknesses has a problem that the light use efficiency is low because the light is always divided into two. The light use efficiency is, for example, 30 at the time of CD reproduction.
%, And 70% during DVD playback. Since the light use efficiency is low, the output power of the semiconductor laser must be increased,
The burden on the semiconductor laser will increase. Particularly, at the time of recording, a large irradiation power is required, and therefore, improvement in light use efficiency has been desired.

In other methods, the objective lens switching method is a mechanical mechanism and therefore lacks reliability.
It is difficult to miniaturize. In the aperture limiting method, there is a problem that the reproduction signal quality is deteriorated because the residual aberration is large.

In a conventional CD / DVD compatible reproduction optical pickup provided with a three-beam generation grating for CD reproduction, an unnecessary sub-beam is generated at the time of DVD reproduction, and the light use efficiency at the time of DVD reproduction is reduced. There was a problem of doing it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it has been proposed to manufacture an efficiency control diffraction grating capable of forming a complicated grating pattern such as a grating lens, and to use the efficiency control diffraction grating. High light use efficiency,
It is an object of the present invention to provide a CD- and DVD-compatible playback optical pickup device excellent in reliability and signal quality.

[0018]

An efficiency control diffraction grating according to the present invention comprises a transparent substrate, a transparent first electrode formed on the transparent substrate, and a transparent electrode formed on the first electrode and arranged alternately. A grating layer composed of a reflecting portion and a transmitting portion, an insulating layer formed on the grating layer, a post layer formed on a part of the insulating layer, and supported by the post layer. And a second electrode that also functions as a reflection mirror. The grating layer and the second electrode are adjusted by adjusting a voltage applied between the first electrode and the second electrode. And thereby controlling the diffraction efficiency of light incident through the transparent substrate,
Thereby, the above object is achieved.

Preferably, the wavelength of the light in air is λ.
_0, and when the refractive index of the insulating layer is n, the thickness d2 of the thickness d1 and the post layer of insulating layers, respectively, lambda ₀ / 4n, represented by an odd multiple of lambda _0/4 .

The efficiency control diffraction grating may further include an anti-reflection film formed on at least one of the surface of the transparent substrate on which the light is incident and the insulating layer.

Preferably, the pattern of the grating layer has a concentric elliptical shape or a concentric circular shape, whereby the efficiency control diffraction grating functions as a grating lens.

An optical pickup device according to the present invention comprises: a light source;
A condensing optical system for condensing light from the light source on an optical disc, and receiving the light reflected by the optical disc;
A photodetector for converting the signal into an electric signal; and the efficiency control diffraction grating is provided on an optical path of the condensing optical system, thereby achieving the above object.

The optical pickup device may include a polarizing beam splitter that transmits only light of a predetermined polarization state, and a 1/4 light beam disposed between the polarizing beam splitter and the efficiency control diffraction grating in an optical path of the light. And a wave plate. In this case, the polarizing beam splitter and the quarter-wave plate transmit the light through the polarizing beam splitter, pass through the quarter-wave plate, enter the efficiency control diffraction grating, and The light reflected by the diffraction grating
The light beam passes through the ４ wavelength plate again, enters the polarization beam splitter, and is reflected by the polarization beam splitter to be guided to the condensing optical system.

Preferably, the combination of the condensing optical system and the efficiency control diffraction grating forms an optical system having two focal points, and the zero-order diffracted light generated by the efficiency control diffraction grating has different thicknesses. And the first-order diffracted light is focused on the other information surface of the two types of optical disks.

Preferably, the voltage applied between the first electrode and the second electrode of the efficiency control diffraction grating is controlled so that the diffraction efficiency of the diffracted light to be focused on the optical disk is maximized. And thereby maximize light utilization efficiency.

The optical pickup device may further include a diffraction grating having a variable diffraction efficiency for dividing the light from the light source into a plurality of lights.

Another optical pickup device of the present invention comprises a light source, an element for dividing a light beam from the light source into a plurality of light beams, and a condensing optical system for condensing the plurality of light beams on an optical disk. A light detector for receiving the plurality of light beams reflected by the optical disk and converting the light beams into an electric signal, wherein the element is the efficiency control diffraction grating, thereby achieving the above object.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram schematically showing the configuration of the first embodiment of the optical pickup device of the present invention.

The optical pickup device 10 according to the first embodiment
Numeral 0 denotes a semiconductor laser 1 as a light source, a rising prism 3, an efficiency control diffraction grating 4 bonded and fixed to an inclined surface of the rising prism 3, an objective lens 5, a photodetector 7,
And a hologram 2 for guiding the reflected light from the optical disk 6 to the photodetector 7.

The light 10 emitted from the semiconductor laser 1 is
The light enters the rising prism 3 and is guided to the efficiency control diffraction grating 4. The efficiency control diffraction grating 4 is a reflection type diffraction grating in which a concentric elliptical grating pattern is engraved, and generates zero-order diffraction light and first-order diffraction light. Each diffracted light is
The light enters the objective lens 5 and is condensed on the optical disk 6. At this time, the 0th-order diffracted light forms a condensed spot 11 of the diffraction limit on the optical disk 6 having the substrate thickness t1, and the 1st-order diffracted light is The shape of the objective lens 5 and the grating pattern of the efficiency control diffraction grating 4 are designed so as to form a diffraction-limited focused spot 12 on the optical disk 6 at t2.

The efficiency control diffraction grating 4 can change the step of the uneven portion of the diffraction grating by controlling the applied voltage, thereby controlling the efficiency of the first-order diffraction. The structure and operation of the efficiency control diffraction grating 4 of the present embodiment will be described in detail with reference to FIG. FIG. 2 (a)
Indicates a state where no voltage is applied, and (b) indicates a state where a voltage is applied. FIG. 2C shows a state where the grating pattern of the efficiency control diffraction grating 4 is viewed from the front.

The efficiency control diffraction grating 4 comprises a transparent first electrode 22 and a grating layer 2 on a transparent substrate 21 such as glass.
3, the insulating layer 24, the post layer 25, and the second electrode 26 are sequentially stacked. The second electrode 26 also serves as a reflection mirror. Also, the grating layer 2
The lattice pattern of No. 3 is a repetition of a reflection part and a transmission part. The reflecting portion of the grating layer 23 and the reflecting mirror 2
6 constitutes a reflective diffraction grating. Also, the insulating layer 2
The layer thickness d ₁ of 4 is set to be an odd multiple of λ ₀ / 4n, where n is the refractive index of the insulating layer 24 and λ ₀ is the wavelength of light to be used in the air. Layer thickness d _{2 of} layer 25
It is set to be an odd multiple of λ _0/4.

When no voltage is applied to the first electrode 22 and the second electrode 26 (when the applied voltage is 0 V), FIG.
As shown in (a), the step between the reflection portion of the grating layer 23 and the reflection mirror 26 is an integral multiple of λ / 2 (where λ is the wavelength in the medium). Therefore, no first-order or higher order diffracted light is generated, and the efficiency control diffraction grating 4 functions as a reflection mirror.

On the other hand, when a positive voltage is applied to the first electrode 22 and the second electrode 26, the first electrode 22 and the second electrode 26 form a capacitor including the air layer and the insulating layer 24, and The electrode 22 is charged with a positive charge, and the second electrode 26 is charged with a negative charge. Since an electrostatic attractive force acts between the electric charges, the second electrode 26 is attracted until it contacts the insulating layer 24 as shown in FIG. At this time, the step between the reflection portion of the grating layer 23 and the reflection mirror 26 is an odd multiple of λ / 4. At this time, since the phase difference between the reflected light from the reflecting portion of the grating layer 23 and the reflected light from the reflecting mirror 26 is π, the first-order diffraction efficiency is maximized, and the order of the light incident on the efficiency control diffraction grating 4 is about 40% of first-order diffracted light is obtained.

FIG. 2C is a view of the efficiency control diffraction grating 4 as viewed from the front. In this figure, the second electrode 26 is omitted. As the grating pattern of the grating layer 23, for example, a concentric elliptical shape as shown in FIG. The post layer 25 is disposed so as to surround a portion where the transmission part of the lattice pattern exists.

Next, an optical system of an optical pickup device using the efficiency control diffraction grating 4 will be described with reference to FIG. FIG. 3A shows a mechanism for recording / reproducing a DVD having a thin substrate, and FIG. 3B shows a mechanism for recording / reproducing a CD having a thick substrate.

At the time of recording / reproducing a DVD, no voltage is applied to the efficiency control diffraction grating 4. Therefore, no first-order diffracted light is generated, and the efficiency control diffraction grating 4 functions as a reflection mirror. The light reflected by the efficiency control diffraction grating 4 is
The light is focused on the DVD 6 by the objective lens 5. Since the objective lens 5 is designed to minimize aberration in this optical system, it is possible to form a diffraction-limited condensed spot on the DVD 6.

In this optical system, the efficiency control diffraction grating 4
Is 100%, the light use efficiency is extremely high. Therefore, it is possible to reduce the power consumption of the light source and extend the life of the light source. Further, it is easier to secure the irradiation power at the time of recording as compared with a conventional optical pickup device combining a refraction type objective lens and a hologram lens.

Next, the case of recording and reproducing a CD will be described. When a voltage is applied to the efficiency control diffraction grating 4, as described above, the first-order diffracted light of up to 41% is generated. At the time of reproducing a CD, since the grating pattern of the efficiency control diffraction grating 4 is designed so that aberration is minimized by the combination of the efficiency control diffraction grating 4 and the objective lens 5, the generated first-order diffracted light passes through the objective lens 5. Thus, a diffraction-limited light-converged spot is formed on the CD.

The light condensed on the CD or DVD in this way is diffracted by the pit train on the disk.
Is reflected. The reflected light from the disk enters the hologram 2 along a path reverse to the outward path, where it is diffracted and guided to the photodetector 7. A reproduction signal and a servo error signal are detected from this light by the photodetector 7.

As described above, the optical pickup device of the present embodiment using the efficiency control diffraction grating 4 has a higher optical power than a conventional optical pickup device combining a refraction type objective lens and a hologram lens with fixed diffraction efficiency. Use efficiency can be improved. Specifically, the light use efficiency of the bifocal lens in the conventional optical pickup device is DVD
It is 70% during reproduction and 30% during CD reproduction, whereas the optical pickup device of the present embodiment uses a DVD.
It can be 100% during reproduction and 40% during CD reproduction.

Next, a second embodiment of the optical pickup device of the present invention will be described.

FIG. 4 shows an optical pickup device 2 according to this embodiment.
00 is shown. The optical pickup device 200 includes a semiconductor laser 1 as a light source, a collimator 8, an efficiency control diffraction grating 4, an objective lens 5, a photodetector 7, and a hologram 2 for guiding reflected light from the optical disk 6 to the photodetector 7. When,
It consists of. The efficiency control diffraction grating 4 is formed on a transparent flat substrate, and is disposed at an angle of 45 ° with respect to the optical path so that it can also serve as a rising mirror.

As described above, except that the rising prism 3 is omitted, the optical pickup device 200 of the present embodiment is used.
Has a configuration similar to that of the optical pickup device 100 of the first embodiment, and also operates during DVD playback and CD playback according to the first embodiment.
It is almost the same as 00. Therefore, a detailed description of the configuration and operation is omitted.

The light emitted from the semiconductor laser 1 is converted into parallel light by the collimator 8 and guided to the efficiency control diffraction grating 4. The light diffracted and reflected by the efficiency control diffraction grating 4 rises, passes through the objective lens 5, and is condensed on the optical disk 6.

As described above, in the optical pickup device 200 of the present embodiment, a rising prism is not required, and a bonding step between the rising prism and the efficiency control diffraction grating is not required. For this reason, production costs can be reduced.

Next, a third embodiment of the optical pickup device of the present invention will be described.

FIG. 5 shows the configuration of the optical pickup device 300 of the present embodiment. The optical pickup device 300 includes a semiconductor laser 1 as a light source, a collimator 8, a polarization beam splitter 13, a quarter-wave plate 14, an efficiency control diffraction grating 4, an objective lens 5, a photodetector 7, an optical disc, And a hologram 2 for guiding the reflected light from 6 to a detector 7. The 波長 wavelength plate 14 and the efficiency control diffraction grating 4 are provided on one surface of the polarization beam splitter 13 in this order. Therefore, in the first and second embodiments, the efficiency control diffraction grating 4 is arranged to be inclined with respect to the optical axis, whereas in the present embodiment, the efficiency control diffraction grating 4 is perpendicular to the optical axis. Are located in Except for this point, also in this embodiment, the efficiency control diffraction grating 4 operates in the same manner as in the first and second embodiments. That is, no voltage is applied during DVD recording and reproduction, and the device functions as a reflection mirror. On the other hand, during CD reproduction, a voltage is applied to the efficiency control diffraction grating 4 so as to function as a reflection type diffraction grating.

The polarization direction of the linearly polarized light emitted from the semiconductor laser 1 is set so as to be completely transmitted through the polarization beam splitter 13. The optical axis of the １ ／ wavelength plate 14 is set so that the linearly polarized light becomes circularly polarized light after passing through the 波長 wavelength plate 14.

The optical pickup device 30 having such a configuration
At 0, the linearly polarized light emitted from the semiconductor laser 1 passes through the polarization beam splitter 13 and then passes through the quarter-wave plate 14 to become circularly polarized light and is guided to the efficiency control diffraction grating 4. The circularly polarized light diffracted and reflected by the efficiency control diffraction grating 4 passes through the quarter-wave plate 14 again and is changed to linearly polarized light. The polarization direction of this linearly polarized light is rotated by 90 ° as compared with the linearly polarized light immediately after emitting the semiconductor laser 1. For this reason, the light that has passed through the 波長 wavelength plate 14 is totally reflected by the polarization beam splitter 13, enters the objective lens 5, and is focused on the optical disk 6 by the objective lens 5.

In the present embodiment, the grating pattern of the efficiency control diffraction grating 4 is not concentric elliptical but concentric. By making the grating pattern concentric, it becomes easier to design the grating pattern of the efficiency control diffraction grating.

As described above, in the present embodiment, the efficiency control diffraction grating 4 is arranged perpendicular to the optical axis, so that light is incident on the diffraction grating 4 vertically. Therefore, by providing an antireflection film on the surface of the efficiency control diffraction grating 4 on the light incident side, the light use efficiency can be further improved.

Next, an optical pickup device according to a fourth embodiment of the present invention will be described.

FIGS. 6A and 6B are diagrams showing the configuration and operation of the optical pickup device 400 according to the fourth embodiment, wherein FIG. 6A shows the time of DVD recording and reproduction, and FIG. 6B shows the time of CD reproduction.

The optical pickup device 400 has a semiconductor laser 1 as a light source, a first efficiency control diffraction grating 15 for generating a sub-beam, a rising prism 3, and a second prism fixed to an inclined surface of the rising prism 3. A two-efficiency control diffraction grating 4, an objective lens 5, a photodetector 7, and a hologram 2 for guiding reflected light from the optical disk 6 to the photodetector 7,
It consists of. Thus, the optical pickup device 4
00 has a configuration similar to that of the optical pickup device 100 of the first embodiment except that the first efficiency control diffraction grating 15 is added. Therefore, description of the configuration and operation of the optical pickup device 400 will be omitted.

The first efficiency control diffraction grating 15 functions as a grating that splits one beam emitted from the semiconductor laser 1 to form a main beam and a sub beam. Like the efficiency control diffraction grating 4, the efficiency control diffraction grating 15 can change the diffraction efficiency by controlling the applied voltage, thereby adjusting the light amount of the sub beam.

The optical pickup device 40 having the above configuration
At 0, the light emitted from the semiconductor laser 1 is reflected by the first efficiency control diffraction grating 15, passes through the hologram 2, and enters the rising prism 3. The light that has passed through the rising prism 3 enters the second efficiency control diffraction grating 4,
Here, it is reflected and diffracted. The light diffracted and reflected by the second efficiency control diffraction grating 4 rises and is focused on the optical disk 6 via the objective lens 5. The light reflected by the optical disk 6 is transmitted to the objective lens 5 and the second efficiency control diffraction grating 4.
Passes through the hologram 2, where it is diffracted and guided to the photodetector 7. The light detector 7 generates an electric signal according to the received light.

The optical pickup device 400 detects a radial error signal by a phase difference detection method at the time of reproducing a DVD, and detects a radial error signal by a three-beam method at the time of reproducing a CD. Therefore, the first efficiency control diffraction grating 15
The voltage applied to is set to 0 at the time of DVD reproduction, and no diffracted light is generated. For this reason, at the time of DVD reproduction, the first efficiency control element 15 functions as a reflection mirror, and the loss of light can be extremely reduced. Further, the voltage applied to the second efficiency control diffraction grating 4 is also the same as in the first to third embodiments.
It is set to 0 during DVD playback, and the second efficiency control diffraction grating 4 also functions as a reflection mirror during DVD playback.

On the other hand, when reproducing a CD, as shown in FIG. 6B, a voltage is applied to the first efficiency control diffraction grating 15 to generate diffracted light. Two of them (for example, ± 1st-order diffracted light) are used as sub-beams for radial signal detection, and the 0th-order diffracted light is used as a main beam for signal reading. These three beams are used by the hologram element 2
Pass through the rising mirror 3 and enter the second efficiency control diffraction grating 4. As in the first embodiment, a voltage is applied to the second efficiency control diffraction grating 4 so as to function as a reflection type diffraction grating. Therefore, the three beams incident on the second efficiency control diffraction grating 4 are diffracted and reflected, respectively, and condensed on the CD surface by the objective lens 5. As described in the first embodiment, the grating pattern of the second efficiency control diffraction grating 4 is designed so that aberration is minimized by the combination of the objective lens 5 and the second efficiency control diffraction grating 4. For this reason, a diffraction-limited condensed spot is formed on the recording surface of the CD.

The three beams reflected by the CD are:
The hologram 2 arrives at the hologram 2 by following a path reverse to the outward path, where it is diffracted and guided to the photodetector 7. The photodetector 7 has 2
A radial error signal is detected from a difference between the light amounts of the sub beams, and a reproduction signal is detected from the main beam.

As described above, in the optical pickup device 400 of this embodiment, the diffraction efficiency of the three-beam forming grating can be changed. For this reason, D
The tracking control using the three-beam method is performed during CD reproduction without lowering the light use efficiency during VD reproduction,
At the time of VD reproduction, tracking control using the phase difference detection method can be performed.

Next, a method of manufacturing the efficiency control diffraction grating of the present invention will be described with reference to FIG.

First, as shown in FIG. 7A, a transparent conductive film used as the first electrode 22 is formed on a transparent glass substrate 21. ITO is well known as a material for the transparent conductive film. Subsequently, a metal layer used as the grating layer 23 is formed on the first electrode 22. As described above, since the efficiency control diffraction grating of the present invention functions as a reflection type diffraction grating, a material having a high reflectance such as aluminum or gold is used as a material of the metal layer. further,
A resist 27 for forming a mask used for etching the metal layer is applied on the metal layer.

Next, as shown in FIG. 7B, the resist 27 is exposed and developed to form a mask used for etching.

Next, as shown in FIG. 7C, the metal layer is etched to form a mask pattern on the grating layer 23.
Transfer to After that, the resist 27 is removed with a remover.

On the grating layer 23, FIG.
As shown in (d), an insulating layer 24 is formed. Insulating layer 2
As the material of No. 4, SiO ₂ or the like can be used.
Further, a post layer 25 is formed on the insulating layer 24. Since the post layer 25 has to be partially removed later by etching, a material which can be selectively etched with respect to the insulating layer 24 is used. Examples of the material include Si ₃ N ₄ . The thicknesses of the insulating layer 24 and the post layer 25 are set to the values specified above, respectively. For example, if the light source wavelength is 650 nm, the thickness of the insulating layer may be 488 nm, and the thickness of the post layer may be 557 nm.

Next, as shown in FIG. 7E, the central part of the post layer 25 is removed. This is performed by, for example, masking the peripheral portion with a resist and wet-etching the central portion where the lattice pattern is cut with hot phosphoric acid.

Next, as shown in FIG. 7F, the portion where the post layer 25 has been etched is filled with a sacrificial layer 28.
For the sacrificial layer 28, a material that can be selectively etched with respect to the insulating layer 24 and the post layer 25 is used. As a material,
Examples include SOG, resist, and aluminum. Then
The surface is chemically and mechanically polished with the sacrifice layer 28 being filled,
The surface is smoothed, and the upper surface of the sacrificial layer 28 is aligned with the upper surface of the post layer 25.

Next, as shown in FIG.
A second electrode 26 that also functions as a reflection mirror is formed on the post layer 8 and the post layer 25. For the second electrode 26, a metal material having resistance to etching of the sacrificial layer performed later is used. As a material, there is nickel or the like. The thickness of the nickel second electrode is about 8 μm if the post layer thickness is about 500 nm. As a result, with an applied voltage of several volts, 5
It can be displaced by about 00 nm.

Finally, as shown in FIG. 7H, the sacrificial layer 28 is removed. A hole is made in an unnecessary portion of the peripheral portion of the second electrode 26, and the sacrificial layer 28 below the second electrode 26 is removed by wet etching. The etchant is the sacrificial layer 28
Is KOH for SOG, an organic solvent for resist, and an alkaline solution for aluminum.

In the above-described method of manufacturing the efficiency control diffraction grating, each layer is formed by using a method such as sputtering, CVD, vapor deposition, and plating depending on the material.

Next, an efficiency control diffraction grating according to a fifth embodiment of the present invention will be described.

FIG. 8 shows the efficiency control diffraction grating 2 of this embodiment.
0 shows a cross-sectional configuration. The efficiency control diffraction grating 20 includes a first electrode 22, a grating layer 23,
An insulating layer 24, an antireflection film 29, a post layer 25, and a second electrode 26 are sequentially stacked on each other.
The antireflection film 30 is also provided on the surface on the side where the light is incident. The method of forming the efficiency control diffraction grating 20 is substantially the same as the step of forming each layer in the method of manufacturing the efficiency control diffraction grating described with reference to FIG. The difference is that the anti-reflection film 29 is formed beforehand, and that the anti-reflection film 30 is formed on the surface of the transparent substrate 21 opposite to the surface on which the reflection type diffraction grating is formed.

The provision of the antireflection films 29 and 30 can reduce reflections occurring at the interface between the insulating layer 24 and air or at the interface between the transparent substrate 21 and air. In particular, when light is incident perpendicularly on the efficiency control diffraction grating, the light use efficiency can be further improved.

[0076]

As described above, according to the efficiency control diffraction grating of the present invention, since diffraction gratings having various grating patterns can be formed, a grating lens or the like can be manufactured. In the past, there was a problem in durability because the thin beam was supported and driven at two points, but the present invention is excellent in durability because it is a structure that drives the entire reflecting mirror and supports the periphery thereof. .

Further, by using the efficiency control diffraction grating of the present invention, it is possible to perform recording and reproduction of two types of optical disks having different thicknesses. Efficiency control By controlling the voltage applied to the diffraction grating, it is possible to condense the light to the diffraction limit on a CD or DVD, and to increase the light use efficiency as compared with the case where a fixed efficiency hologram lens is used. Can be.

Further, by using the efficiency control diffraction grating of the present invention, it is possible to improve the light use efficiency of the optical pickup device using both the three-beam tracking control and the one-beam tracking control.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an optical pickup device according to an embodiment of the present invention.

2A and 2B are diagrams illustrating a structure of an efficiency control diffraction grating according to the present invention, in which FIG. 2A is a cross-sectional view in a state where no voltage is applied between electrodes, and FIG. It is a sectional view showing, and (c) is the figure which looked at the diffraction grating pattern from the front.

3A and 3B are diagrams showing an operation of the optical pickup device of FIG. 1, wherein FIG. 3A shows a state in which no voltage is applied to the efficiency control diffraction grating, and FIG. 3B shows a state in which a voltage is applied to the efficiency control diffraction grating. The state is shown.

FIG. 4 is a diagram illustrating a configuration of an optical pickup device according to another embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an optical pickup device according to still another embodiment of the present invention.

FIG. 6 is a diagram showing the configuration and operation of an optical pickup device according to still another embodiment of the present invention, and (a).
Shows the operation of the optical pickup device at the time of reproducing a DVD, and (b) shows the operation of the optical pickup device at the time of reproducing a CD.

FIG. 7 is a cross-sectional view showing a manufacturing process of the efficiency control diffraction grating of the present invention.

FIG. 8 is a sectional view of an efficiency control diffraction grating according to still another embodiment of the present invention.

FIG. 9 is a diagram illustrating the operation of a conventional efficiency control diffraction grating.

FIG. 10 is a diagram showing a configuration of a main part of a conventional optical pickup device for reproducing two types of optical disks having different thicknesses.

FIG. 11 is a diagram illustrating a phase difference detection tracking control method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Hologram 3 Rising prism 4 Efficiency control diffraction grating 5 Objective lens 6 Optical disk 7 Photodetector 8 Collimator 13 Polarization beam splitter 14 Quarter wave plate 15 3 Beam generation efficiency control diffraction grating 21 Transparent substrate 22 First Electrode 23 Grating layer 24 Insulating layer 25 Post layer 26 Second electrode 27 Resist 28 Sacrificial layer 29, 30 Antireflection film

Claims (10)

[Claims] 1. A grating layer comprising a transparent substrate, a transparent first electrode formed on the transparent substrate, and alternately arranged reflecting portions and transmitting portions formed on the first electrode. An insulating layer formed on the grating layer; a post layer formed on a part of the insulating layer; a post layer provided so as to be supported by the post layer, and functioning as a reflection mirror. Adjusting the voltage applied between the first electrode and the second electrode to change the distance between the grating layer and the second electrode, thereby changing the distance between the grating layer and the second electrode. An efficiency control diffraction grating that controls the diffraction efficiency of light incident through a transparent substrate. 2. When the wavelength of the light in air is λ ₀ and the refractive index of the insulating layer is n, the thickness d1 of the insulating layer
And the thickness d2 of the post layer, respectively, lambda _0/4
n, represented by an odd multiple of λ _0/4, efficiency control diffraction grating according to claim 1. 3. The efficiency control diffraction grating further comprises an antireflection film formed on at least one of a surface of the transparent substrate on which the light is incident and the insulating layer. 3. The efficiency control diffraction grating according to 2. 4. The efficiency control according to claim 1, wherein the pattern of the grating layer has a concentric elliptical shape or a concentric circular shape, whereby the efficiency control diffraction grating functions as a grating lens. Diffraction grating. 5. A light source, a light condensing optical system for condensing light from the light source on an optical disc, and a photodetector for receiving the light reflected by the optical disc and converting the light into an electric signal. An optical pickup device, further comprising the efficiency control diffraction grating according to any one of claims 1 to 4 provided on an optical path of the condensing optical system. 6. An optical pickup device, comprising: a polarizing beam splitter that transmits only light of a predetermined polarization state; and an optical pickup device disposed in an optical path of the light between the polarizing beam splitter and the efficiency control diffraction grating. And a 波長 wavelength plate, wherein the light passes through the polarizing beam splitter and
Passing through the wave plate and entering the efficiency control grating, being reflected by the efficiency control grating and passing through the quarter wave plate again to enter the polarizing beam splitter and reflected by the polarizing beam splitter. The optical pickup device according to claim 5, wherein the optical pickup device is guided to the condensing optical system by performing the operation. 7. The combination of the condensing optical system and the efficiency control diffraction grating constitutes an optical system having two focal points, and the 0th-order diffracted light generated by the efficiency control diffraction grating has different thicknesses. 7. The optical pickup device according to claim 5, wherein the optical pickup device converges on one information surface of the two types of optical disks and the first-order diffracted light converges on the other information surface of the two types of optical disks. 8. The voltage applied between the first electrode and the second electrode of the efficiency control diffraction grating is controlled such that the diffraction efficiency of the diffracted light to be focused on the optical disk is maximized. The optical pickup device according to claim 7, wherein the light use efficiency is maximized. 9. The optical pickup device according to claim 5, further comprising a diffraction grating having a variable diffraction efficiency for dividing light from the light source into a plurality of lights. An optical pickup device according to item 1. 10. A light source, an element for dividing a light beam from the light source into a plurality of light beams, a condensing optical system for condensing the plurality of light beams on an optical disk, and the plurality of light beams reflected by the optical disk And a photodetector that receives the light beam and converts the light beam into an electric signal, wherein the element is the efficiency control diffraction grating according to any one of claims 1 to 4. , Optical pickup device.