JPH0750032A - Optical head device and optical information device - Google Patents

Abstract

PURPOSE:To obtain an optical head, which has a high utilization efficiency of light and less return light into a light source and can obtain the stable signals without the occurrence of unwanted diffracted light. CONSTITUTION:A polarized anisotropic hologram 173 and a 1/4 wavelength plate 15 are arranged in the vicinity of an objective lens 4. Thus, the utilization efficiency of light becomes high, returning light into a light source is less, unwanted diffracted light does not occur and the effective diameter of the hologram 173 becomes large. Therefore, the allowable error in assembling can be made large. A unitary body is formed of the hologram 173 and the objective lens 4. Therefore, a servo signal is not deteriorated even if the objective lens 4 is moved by tracking following.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for recording / reproducing or erasing information to / from an information storage medium such as an optical storage medium such as an optical disk or an optical card or a magneto-optical storage medium. The present invention relates to an optical information device including a head device.

[0002]

2. Description of the Related Art In the field of optical memory technology, an optical disk having a pit-shaped pattern is used as a high density and large capacity information storage medium. In recent years, this optical memory technology has been put into practical use while expanding its applications with digital audio discs, video discs, document file discs, and even data files.

Recording / reproducing information on / from an optical disk
It is performed using a light beam focused on a minute spot. In order to record / reproduce such information with high reliability, the configuration of the optical system is important. Optical head device,
It is the main part of the optical system. The basic functions of the optical head device are roughly classified into focusing for forming a minute light spot at the diffraction limit, focus control and tracking control of the light beam, and detection of a pit signal. These functions are realized by a combination of various optical systems and photoelectric conversion detection methods according to the purpose and application.

In recent years, an optical head device using a hologram is being developed in order to make the optical head device smaller and thinner. Focusing on the fact that the hologram is a thin and lightweight planar element, the inventors of the present invention invented an optical head device in which a hologram and an objective lens are integrated (Japanese Patent Application Laid-Open No. 4-204).
No. 212730). Below, this optical head device,
This will be described with reference to FIGS. 14 to 19.

In FIG. 14, 1 is a blazed hologram, and 2 is a light source such as a semiconductor laser. The feature of this optical head device is that the blazed hologram 1 is installed close to the objective lens 4. The operation will be described below.

Light beam 3 (laser light) emitted from a light source
After passing through the blazed hologram 1, the light enters the objective lens 4 and is condensed on the recording medium 5. Recording medium 5
The light beam reflected by the laser beam retraces the original optical path and enters the blazed hologram 1 again. The light beam reflected from the recording medium 5 is diffracted by the blazed hologram 1 to generate + 1st order diffracted light 6. The photodetector 7 is
The first-order diffracted light 6 is received and an electric signal corresponding to the light intensity is output. The servo signal and the information signal are obtained by calculating the output of the photodetector 7.

If the hologram 1 is not blazed, as shown in FIG. 15, in the outward path from the light source 2 to the recording medium 5, unnecessary diffracted light generated from the hologram 1 (for example, in the outward path- After the first-order diffracted light 8) is reflected by the information recording medium 5, for example, the 0-th order diffracted light 81 on the return path
Will be incident on the photodetector 7. The hologram 1 is arranged near the objective lens 4, and the photodetector 7 and the light source 2 are arranged.
Although the and are arranged close to each other, the amount of unnecessary light that becomes noise to the servo signal and the information signal and is incident on the photodetector 7 is significantly reduced.

16 (a), 16 (b) and 16 (c) show an example of the manufacturing process of the blazed hologram 102. As shown in FIG. After etching the hatched portion shown in FIG.
The hatched portion shown in FIG. 16C is etched. next,
As shown in FIG. 16C, the hatched portion is further etched to produce a blazed hologram.

As a focus servo signal detection method, for example, a spot size detection method (SSD) is used.
Method) is used. As disclosed in Japanese Patent Application Laid-Open No. 2-185722, the SSD method can remarkably reduce the assembly tolerance of the optical head device and can stably obtain the servo signal even with respect to the wavelength variation.

In order to implement the SSD method, the + 1st-order diffracted light on the backward path of the hologram is designed to be two types of spherical waves having different curvatures. Each spherical wave is designed to have a focus on the front side e and the rear side f of the photodetector surface. FIG. 17
As shown in (a) to (c), the return +1 diffracted light 14
1 and 142 are received by the 6-division photodetector 71.

In FIGS. 17A to 17C, the left part is composed of three opto-electric converters S10, S20 and S30 which receive the +1 diffracted light 141, and the right part is the +1 diffracted light. It is formed of three opto-electrical converters S40, S50 and S60 which receive 142. Here, FIG. 17B shows the just focus state, and FIGS. 17A and 17C show the defocus state. The focus error signal FE is: FE = (S10 + S30-S20)-(S40 + S60-S50). ． ． It is obtained by the calculation of (Equation 1).

Even when the SSD method is used, the hologram 10
If 4 is blazed, the light utilization efficiency can be improved and the S / N ratio can be improved. FIG. 18 shows S
This is an example of realizing a blazed hologram for the SD method.
In FIG. 18, the area A 151 generates a spherical wave having a focus on the front side of the photodetector, and the area B 152 generates a spherical wave having a focus on the rear side of the photodetector. The far field pattern of the wavefront diffracted from the hologram pattern as shown in FIG. 18 is partially cut off as shown in FIG. 17 reflecting the fact that the hologram pattern is divided, but this does not affect the focus servo signal.

Further, as shown in FIG. 19, diffraction areas 153 and 154 are provided on the hologram so that a change in the light amount distribution on the hologram due to a change in the relative position between the focused spot on the information recording medium 5 and the track groove causes a tracking error. Signal TE
Are taking out as. The tracking error signal detecting diffracted light 163 from the diffraction areas 153 and 154 is received by the tracking error signal detecting photodetector 72, and the tracking error signal TE can be obtained by the following calculation.

TE = S70-S80. ． ． (Equation 2) With such a configuration, the following effects are obtained. (1) By blazing the hologram, the diffraction efficiency of the 0th-order diffracted light on the outward path and the + 1st-order diffracted light on the return path is increased, so that the light utilization efficiency is improved and the S / N ratio of the servo signal and the information signal is improved. . (2) By the optimal design of the cross-sectional shape of the blazed hologram, the amount of diffracted light other than the 0th order diffracted light that is generated in the outward optical path from the light source to the information recording medium is suppressed on the photodetector. By doing so, it is possible to suppress the deterioration of the information signal and the focus servo signal without increasing the diffraction angle to prevent unnecessary diffracted light from entering the photodetector. Therefore, if the optical head device is configured using this blazed hologram, it is possible to simultaneously arrange the photodetector and the light source in close proximity and to increase the effective diameter R1 of the blazed hologram 1 at the time of assembly. The position tolerance at can be relaxed. (3) By using the configuration in which the blazed hologram is integrated with the objective lens, the diffracted light in the outward path generated from the hologram does not move on the photodetector regardless of the movement of the objective lens due to tracking tracking. Therefore, a stable focus error signal can be obtained in parallel with the tracking following. Further, since the hologram is blazed, the diffraction efficiency of unnecessary diffracted light such as −1st order diffracted light on the outward path is smaller than the diffraction efficiency of + 1st order diffracted light on the return path and 0th order diffracted light on the outward path. Degradation of the servo signal and the information signal due to unnecessary diffracted light such as −1st order diffracted light on the outward path is significantly reduced. Therefore, very stable servo and information reading can be realized. (4) By using the SSD method as the focus servo signal detection method, an optical head device with a larger assembly tolerance can be configured. Further, by dividing the hologram pattern and generating spherical waves having different curvatures from the two types of regions as + 1st order diffracted light in the return path, it is possible to easily realize the blazing of the hologram and the SSD method at the same time. Therefore, it is possible to remarkably reduce the assembly tolerance of the optical head device, and at the same time, to construct an optical head device that can obtain a signal with a very good S / N ratio.

[0015]

However, according to the above configuration, there are the following problems. (1) By optimizing the blaze shape, the diffraction efficiency of unnecessary diffracted light such as −1st order diffracted light on the outward path can be made smaller than the diffraction efficiency of + 1st order diffracted light on the return path and 0th order diffracted light on the outward path. is not. There is room for obtaining higher-quality servo signals and information signals by reducing unnecessary diffraction efficiency and bringing it closer to zero. In particular, in optical head devices such as higher density optical discs, compared to currently commercialized compact discs, unnecessary diffraction efficiency is further reduced to approach 0, and thus higher quality servo signals and information signals are obtained. It is important to get (2) Although the light use efficiency is improved by the blazing, the light use efficiency is 20% at most in the process in which the light beam passes through the hologram on the outward path and the return path. There is room for further increasing the noise margin of the detection signal by further increasing the light utilization efficiency. (3) The diffraction efficiency of diffracted light of each order is the same on the outward path and the return path. Since it is necessary to increase the diffraction efficiency (transmittance) of the 0th-order diffracted light (transmitted light) in the outward path, the diffraction efficiency of the 0th-order diffracted light is increased in the return path, and return light to the light source exists. For example, if the diffraction efficiency of the 0th-order diffracted light is 30%, the amount of returned light is 30% × 30% = 9%. When a semiconductor laser is used as the light source, the amount of this returning light may increase laser noise.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical head device having high light utilization efficiency.

Another object of the present invention is to provide an optical head device in which light returning to the light source is small and unnecessary diffracted light is less likely to occur.

Still another object of the present invention is to provide an optical head device which can obtain a stable signal.

Still another object of the present invention is to provide an optical information device provided with such an optical head device.

[0020]

The optical head device of the present invention comprises a light source for emitting a light beam, an objective lens for converging the light beam on an information recording medium, and the light reflected by the information recording medium. A hologram for receiving a beam and forming diffracted light of the light beam, the hologram having a second polarization state different from the first polarization state as compared to the light beam in the first polarization state. Light including a hologram having polarization anisotropy that diffracts more strongly, and a plurality of photodetectors that receive a part of the diffracted light and output a photocurrent according to the intensity of the part of the diffracted light. An optical head device comprising a detector, the device being an optical means arranged between the information recording medium and a hologram, the polarization of the light beam reflected by the information recording medium. Optical means for changing the state to the second polarization state is further provided. , The hologram, the distance between the hologram and the objective lens is arranged to be shorter than the distance between the hologram and the photodetector, the object is achieved.

It is preferable that the relative positional relationship between the hologram and the objective lens is fixed.

In the embodiment, the first polarization state is a linear polarization state in which the polarization direction is parallel to the first direction, and the second polarization state is the polarization direction in which the polarization direction is perpendicular to the first direction. It is in a linearly polarized state.

In an embodiment, the optical element is a quarter-wave plate which converts the first polarization state into a rotational polarization state and converts the rotational polarization state into the second polarization state. .

In an embodiment, the light source emits light in the first polarization state. It may further include other optical means for making the light emitted from the light source the first polarization state.

In the embodiment, the light source is a semiconductor laser. In an embodiment, the hologram has a lithium niobate substrate, a proton exchange layer periodically formed on the surface of the substrate, and a groove formed on the proton exchange layer.

It is preferable that the relative positional relationship among the hologram, the objective lens, and the optical element is fixed.

The diffracted light formed by the hologram is
It may include a spherical wave having a focus on the front side of the detection surface of the photodetector and a spherical wave having a focus on the rear side of the detection surface.

The hologram surface of the hologram includes a divided region H1 and a region H2, and the plurality of photodetector portions are provided in the photodetector region P1 provided on the detection surface.
And a photodetector region P2, and the photodetector region P2
1 receives the diffracted light diffracted by the divided area H1 of the hologram, and outputs an output signal E according to the intensity of the diffracted light.
1, the photodetector region P2 receives the diffracted light diffracted by the divided region H2 of the hologram, outputs an output signal E2 in accordance with the intensity of the diffracted light, and outputs the output signal E1 and the output signal E1. A tracking error signal may be obtained based on the output signal E2.

The hologram surface of the hologram includes a divided region H1 and a region H2, and the plurality of photodetector portions are provided in the photodetector region P1 provided on the detection surface.
And a photodetector region P2, and the photodetector region P2
1 receives the diffracted light diffracted by the divided area H1 of the hologram, and outputs an output signal E according to the intensity of the diffracted light.
1, the photodetector region P2 receives the diffracted light diffracted by the divided region H2 of the hologram, outputs an output signal E2 in accordance with the intensity of the diffracted light, and outputs the output signal E1 and the output signal E1. A signal indicating the amount of shift of the pit position with respect to the track center of the information recording medium may be obtained based on the output signal E2.

The divided area H1 and the divided area H2 on the hologram surface are symmetrical with respect to an axis of interest therebetween, and the axis of symmetry and the direction of the light beam from the light source to the mirror are both It is preferable that they are aligned with the track direction of the information recording medium.

Further, a substrate integrally supporting the plurality of photodetection portions is provided, and the substrate has a recessed portion having a bottom surface and a sidewall inclined surface, and the bottom surface of the recessed portion has the recessed portion. A light source may be provided, and a mirror that reflects a light beam emitted from the light source in a direction perpendicular to the surface of the substrate may be provided on the sidewall inclined surface of the recess.

The apparatus includes a beam splitter, which transmits the light in the first polarization state and reflects the light in the second polarization state, between the light source and the hologram. A part of the light beam reflected by the information storage medium may be diffracted by the hologram and then guided to the photodetector via the beam splitter.

The optical information device of the present invention comprises a storage medium driving means for driving the information storage medium, an optical head device, and an optical head driving means for adjusting the positional relationship between the information storage medium and the optical head device. An optical information device comprising: a light source for emitting a light beam, an objective lens for converging the light beam onto an information recording medium, and the light beam reflected by the information recording medium. Which is a hologram for receiving light and forming diffracted light of the light beam, and comparing the light beam in the second polarization state different from the first polarization state with respect to the light beam in the first polarization state. A hologram having polarization anisotropy that strongly diffracts, and receives a part of the diffracted light,
A photodetector including a plurality of photodetectors for outputting a photocurrent according to the intensity of the part of the diffracted light; and an optical means arranged between the information recording medium and the hologram, Optical means for changing the polarization state of the light beam reflected by the information recording medium to the second polarization state, and the hologram has a distance between the hologram and the objective lens from that of the hologram. It is arranged so as to be shorter than the distance from the photodetector, and the relative positional relationship between the hologram and the objective lens is fixed and fixed, whereby the above object is achieved.

[0034]

By using the above means, (1) since the polarization anisotropic hologram and the optical element (1/4 wavelength plate) for changing the polarization state are used in combination, unnecessary diffraction does not occur in the outward path, In the return path, diffracted light for obtaining a servo signal or the like is generated. Therefore, there is no noise due to unnecessary diffracted light, and a signal with a very high S / N ratio can be obtained. (2) Since a polarization anisotropic hologram and an optical element (1/4 wavelength plate) that changes the polarization state are used in combination, unnecessary diffraction does not occur in the outward path, and a servo signal or the like is obtained in the return path. Generates diffracted light. Therefore, since the light utilization efficiency is high and the signal amplitude is large, the S /
A signal with a high N ratio can be obtained. (3) Since it is possible to obtain a high extinction ratio, it is possible to obtain a signal with a very high S / N ratio, in particular, in addition to high light utilization efficiency and a large signal amplitude, and no noise due to unnecessary diffracted light. When you can Furthermore, since the 1st-order diffraction efficiency on the return path can be increased and the 0th-order diffraction efficiency (transmittance) can be made almost 0, the amount of light returned to the light source can be made almost 0. Therefore, when a semiconductor laser is used as the light source, it is possible to avoid the generation of noise due to the returning light.

[0035]

【Example】

(Embodiment 1) An optical head device according to the present invention will be described below with reference to the drawings. Note that the directions of the xyz axes in FIG. 1 are as shown in FIG. 3, FIG. 4B, FIG. 5 to FIG. 7, FIG.
Coincides with the direction of the xyz axis of.

As shown in FIG. 1, the optical head device of this embodiment focuses a light source (semiconductor laser) 2 for emitting a light beam (laser light) 3 and the light beam 3 on an information recording medium 5. The objective lens 4, the polarization anisotropic hologram 173 that receives the light beam 3 reflected by the information recording medium 5 and forms the diffracted light of the light beam 3, and a part of the diffracted light (6 and 6).
7), and a photodetector including a plurality of photodetectors 74a and 74b that outputs a photocurrent according to the intensity thereof.

The polarization anisotropic hologram 173 of this embodiment.
As will be described later, compared to a light beam linearly polarized in a certain direction (first direction), a direction perpendicular to that direction (second
Light that is linearly polarized in (direction) is diffracted more. More specifically, this polarization anisotropic hologram 173 receives the light beam 3 emitted from the light source 2, and receives the information recording medium 5
The light beam 3 is adjusted so as not to be substantially diffracted when transmitted in the direction of. However, the polarization anisotropic hologram 173 is adjusted so that the light beam 3 reflected by the information recording medium 5 is diffracted when the light beam is transmitted toward the light source 2. In this sense, the polarization anisotropic hologram 173 also has a function as a polarization separation element. Various information can be obtained by detecting the diffracted light generated by the diffraction of the polarization anisotropic hologram 173 using the photodetectors 74a and 74b.

Incidentally, this polarization anisotropic hologram 173
Is preferably provided closer to the objective lens 4 than the intermediate point between the objective lens 4 and the photodetectors 74a and 74b. The reason will be described later. In this embodiment, the distance between the polarization anisotropic hologram 173 and the objective lens 4 is 3 m.
In contrast to m, the distance between the polarization anisotropic hologram 173 and the photodetector 74a is 20 mm.

The hologram 173 having the above-mentioned polarization anisotropy
In addition to the above, the optical head device according to the present embodiment further includes optical means (1/4 wavelength plate 1) for adjusting the polarization state of the light beam.
5). The quarter-wave plate 15 is arranged between the information recording medium 5 and the polarization anisotropic hologram 173, more specifically, between the objective lens 4 and the polarization anisotropic hologram 173.

The objective lens 4, the polarization anisotropic hologram 173, and the quarter-wave plate 15 are integrally held by the holding member 13, and the driving means 110 directly drives the holding member 13. The objective lens 4
The positional relationship between and the information recording medium 5 is adjusted. Photo detector 7
The outputs of 4a and 74b are sent to a known control circuit (not shown) to control the driving of the driving means.

Hereinafter, each part of the optical head device of this embodiment will be described.
This will be described in more detail. First, the light beam 3 emitted from the light source (semiconductor laser) 2 is substantially linearly polarized in a direction parallel to the active layer (not shown). The light beam 3 having such a polarization state is generated by the polarization anisotropic holograms 173 and 1
After passing through the quarter wave plate 15, the light enters the objective lens 4 and is condensed on the information recording medium 5 (outward path). In this way, the light beam 3 is linearly polarized when emitted from the light source 2, but becomes circularly polarized by passing through the quarter-wave plate 15. If there is enough light, instead of using a semiconductor laser that emits linearly polarized light in a specific direction as a light source, use a light source that emits light with multiple polarization components, and A polarization filter that selectively transmits only linearly polarized light in a predetermined direction may be inserted between the sex hologram 173 and the polarization component other than a specific polarization component may be cut. Alternatively, the polarization plane of the linearly polarized light beam 3 emitted from the light source 2 may be rotated by a necessary angle and then incident on the hologram 173.

The polarization direction of the light beam 3 upon entering the polarization anisotropic hologram 173 is set such that the light beam 3 is not substantially diffracted by the polarization anisotropic hologram 173. This point will be described in detail when the polarization anisotropic hologram 173 is described.

The optical beam reflected by the information recording medium 5 is
The original optical path is traced in reverse, and the light is again transmitted through the quarter-wave plate 15, and then enters the polarization anisotropic hologram 173. The light beam returns to linearly polarized light by passing through the quarter-wave plate 15. The polarization direction at this time is perpendicular to the polarization direction immediately after being emitted from the light source. The polarization anisotropic hologram 173 diffracts the light transmitted through the objective lens 4. As a result, of the backward diffracted lights formed by the polarization anisotropic hologram 173, the + 1st-order diffracted lights 6 and −1
The second-order diffracted light 67 is detected by the photodetectors 74a and 74b.
Incident on each. Photodetector 74a and photodetector 74
b is the + 1st order diffracted light 6 and the −1st order diffracted light 67, respectively.
The electric signal is output according to the intensity of the. Photo detector 74
The servo signal and the information signal are obtained by calculating the outputs of a and b.

According to this embodiment, since the polarization anisotropic hologram 173 and the quarter wavelength plate 15 are used in combination, at least the following effects can be obtained.

(1) In the outward path of the light beam, unnecessary diffraction by the polarization anisotropic hologram does not occur, and in the return path, diffracted light for forming a servo signal or the like is obtained from the polarization anisotropic hologram. be able to. As a result, noise due to unnecessary diffracted light does not occur, and a signal with a high S / N ratio can be obtained. In addition, the utilization efficiency of light is high and the signal amplitude is large. For optical discs having a higher density than commercialized compact discs, it is strongly demanded to further reduce the diffraction efficiency of unnecessary diffracted light to approach zero. According to this embodiment, it is possible to obtain a servo signal or information signal of sufficiently high quality that satisfies the demand.

(2) According to this embodiment, the first-order diffraction efficiency in the returning path of the light beam is improved, and the zero-order diffraction efficiency (transmittance) becomes almost zero. Therefore, the amount of light returned to the light source 2 can be made almost zero. When a semiconductor laser is used as the light source 2, the return light makes the oscillation mode of the semiconductor laser unstable and causes noise. However, according to this embodiment, it is possible to avoid the generation of noise due to the returning light.

The main constituent elements of the optical head device of this embodiment and the signal detection method will be described in detail below.

Polarization Anisotropy Hologram FIG. 2 shows a polarization anisotropic hologram 17 used in this embodiment.
It is a figure which shows the detail of 3. Note that the directions of the xyz coordinate axes in FIG. 2 do not match the directions of the coordinate axes in FIG. 1 and other drawings.

In this polarization anisotropic hologram 173, a proton exchange layer (depth dp) 41 is periodically formed on the surface of the x-plane lithium niobate substrate 40, and then only the surface of the proton exchange layer 41 is selectively formed. By etching, thereby forming the groove 42.

If the refractive index of the lithium niobate substrate 40 for ordinary light is no, the refractive index for extraordinary light is ne, the refractive index of the proton exchange layer 41 for ordinary light is nop, and the refractive index for extraordinary light is nep, then ordinary light and extraordinary light are assumed. Refractive Index of Proton Exchange Layer 41 to Lithium Niobate Substrate 40
The refractive index differences Δno and Δne are respectively given by the following equations.

Δno = nop-no (Equation 3) Δne = nep-ne (Equation 4) The refractive index for light having a wavelength of 0.78 μm is as follows between the proton exchange layer 41 and the lithium niobate substrate 40. Have a relationship.

Δno = −0.04 Δne = 0.145 The polarization anisotropic hologram used in this embodiment utilizes the difference in refractive index difference between ordinary light and extraordinary light. The groove 42 formed on the surface of the proton exchange layer 41 has a function of canceling a change in the refractive index of extraordinary light. In other words, there is no optical path difference for extraordinary light.

The function of the polarization anisotropic hologram 173 will be described below. First, consider a case where ordinary light (light having an electric field vector parallel to the y-axis direction of the crystal) is incident on the polarization anisotropic hologram 173. Based on the phase of light that does not pass through the proton exchange layer 41, that is, only passes through the lithium niobate substrate 40, the proton exchange layer 41 and the groove 4 are formed.
Since the refractive index of 2 is smaller than that of the lithium niobate substrate 40, the light passing through this region has a phase lead.
The amount of phase change Δφo is given by the following equation when the phase lead is expressed as negative and the phase delay is expressed as positive.

Δφo = (2π / λ) (Δno · dp + Δnoa · da) (Formula 5) where λ is the wavelength of the incident light, and Δnoa is the difference between the ordinary refractive index no of the substrate and the refractive index of air 1, It is given by the following formula.

Δnoa = 1-no (Equation 6) On the other hand, anomalous light (crystal z
Consider a case where light having an electric field vector parallel to the axial direction is incident. Since the refractive index of the groove 42, which is based on the light that does not pass through the proton exchange layer 41, that is, the light that passes through only the lithium niobate substrate 40, is smaller than the refractive index of the lithium niobate substrate 40, the light passing through this region has a phase difference. Progress occurs. On the other hand, since the refractive index of the proton exchange layer 41 is larger than that of the lithium niobate substrate 40, the light passing through this region has a phase delay and cancels the advance of the phase by the groove 42. The phase change amount Δφe is given by the following equation, where the phase lead is expressed as negative and the delay is expressed as positive.

Δφe = (2π / λ) (Δne · dp + Δnea · da) (Equation 7) where λ is the wavelength of the incident light and Δnea is the difference between the extraordinary refractive index ne of the substrate and the refractive index of air 1. , Is given by the following equation.

Δnea = 1-ne (Equation 8) Thus, the polarization anisotropic hologram 173 has a function of diffracting ordinary light and not diffracting extraordinary light. That is (Equation 7)
The depth dp of the proton exchange layer 41 and the depth da of the groove 42 are appropriately selected so that the phase difference Δφe of the extraordinary light given by is not an integer multiple of 2π and only the ordinary light is the phase difference Δφo. It is a thing. In particular, the extinction ratio becomes maximum when Δφo is an odd multiple of π. If this condition is expressed by an equation, (2π / λ) (Δno · dp + Δnoa · da) = − (2n + 1) π (Equation 9) (2π / λ) (Δne · dp + Δnea · da) = 2mπ (Equation 10) . Here, n and m are arbitrary integers. Especially n =
In the case of 0 and m = 0, da = (λ / 2) {Δne / (ΔnoΔnea−ΔneΔnoa)} (Formula 11) dp = (λ / 2) {Δnea / (ΔneΔnoa−ΔnoΔnea)} (Formula 12) For example, in order to realize a polarization separation element for light having a wavelength of 0.78 μm, the depth da of the groove 42 is set to 0.25 μm and the depth dp of the proton exchange layer 41 is set to 2 according to (Equation 11) and (Equation 12). It may be set to 0.000 μm.

As is clear from the above description, when the polarization direction of the light beam 3 emitted from the light source 2 is set to be the direction of extraordinary light with respect to the polarization anisotropic hologram 173, diffraction does not occur in the outward path. In the return path, the polarization direction is rotated by 90 ° and becomes ordinary light, so that diffraction occurs.

Since the proton exchange region 41 is manufactured by the diffusion process, it is difficult to set the lattice pitch to 10 μm or less. However, in this embodiment, the polarization anisotropic hologram 173 is arranged in the vicinity of the objective lens, that is, at a position distant from the photodetectors 74a and 74b. Therefore, it is not necessary to design the grating pitch to be 10 μm or less,
The polarization anisotropic hologram 173 having the required function can be easily manufactured. As a result, a high extinction ratio can be obtained, and the light utilization efficiency is improved. In addition, the signal amplitude is large and there is no noise due to unnecessary diffracted light, and a signal with a very high S / N ratio can be obtained. The distance between the polarization anisotropic hologram 173 and the objective lens is 1
It is preferably 5 mm or less. More preferably, this distance should be 8 mm or less in order to reduce the thickness of the optical head when the objective lens 4 and the hologram 173 are integrated.

By disposing the polarization anisotropic hologram 173 near the objective lens, the effective diameter R1 of the polarization anisotropic hologram 173 can be increased even in the finite optical system. For this reason, the tolerance of the position of the polarization anisotropic hologram 173 at the time of assembling the optical head device can be relaxed, and the assembling cost of the optical head device can be reduced.

The polarization anisotropic hologram may be other than the one using the lithium niobate substrate.
For example, a liquid crystal cell may be used.

Holding Member 13 It is preferable that the polarization anisotropic hologram 173, the quarter-wave plate 15 and the objective lens 4 are integrally held by the holding member 13 and have a constant relative positional relationship. With such a configuration, even if the objective lens 4 moves for tracking control, the polarization anisotropic hologram 17
The optical beam reflected by the information recording medium 5 hardly moves on the polarization anisotropic hologram 173. Therefore, despite the movement of the objective lens 4,
The signal obtained from the photodetector 7 does not deteriorate. This effect will be described in more detail later.

Structure of Photodetector and Light Source FIG. 3 shows an example of the structure of the photodetector and light source of FIG. The element shown in FIG. 3 is a hybrid element in which the photodetector 74a, the photodetector 74b, and the light source 2 are integrally arranged on one photodetector substrate. More specifically,
A recess (notch) is provided between the photodetector 74a and the photodetector 74b, and the light source 2 is provided on the bottom surface of the recess.
However, a mirror 7a is provided on the side wall inclined surface of the recess. The mirror 7a changes the direction of the laser light emitted from the light source 2 to a predetermined direction.

By adopting such a configuration, the photodetector 74a and the photodetector 74b of this embodiment are integrated on one photodetector substrate by using the semiconductor integrated circuit manufacturing technology. Can be formed. By using the integrated circuit manufacturing technology, the relative position of the photodetector 74a and the photodetector 74b is set to a design value with high accuracy on the order of μm.

Each constituent element of the hybrid device shown in FIG.
It is electrically connected to an external circuit by wiring. In this embodiment, all the connection directions are along the xy plane of FIG.
Since each connection wire is brought close to each component along a common direction, automatic assembly is facilitated. Further, since the reference line at the time of assembly need only be provided on the xy plane, the relative positions of the photodetectors 74a, 74b and the light source 2 can be easily determined with high accuracy.

Focus Servo Signal Detection Method Next, a focus servo signal detection method in this embodiment will be described.

As shown in FIG. 4A, the surface of the polarization anisotropic hologram (173) of this embodiment on which the hologram pattern 150 is formed is divided into a plurality of regions 153, 154 and 155. There is. The divided area 155 is a diffracted light generation area for detecting a focus error signal.

In this embodiment, the spot size detection method (SS
Method D) is used. According to the SSD method, Japanese Patent Laid-Open No. 2-185
As disclosed in Japanese Patent No. 722, the assembling tolerance of the optical head device can be remarkably alleviated, and the servo signal can be stably obtained against the wavelength fluctuation. SS
The D method uses diffracted light having a focus in front of or behind the reference surface.

The diffracted light generating region 155 for detecting the focus error signal is formed so as to form two diffracted lights having different focal positions by using an off-axis Fresnel zone plate or interference fringes of two spherical waves having different focal positions. Can be designed. In FIG. 4B, reference planes (photodetectors 74a and 74a
Diffracted light having a focus at positions (a and b) in front of and behind the detection surface b) is shown. FIG. 5 shows a state on the photodetector of the diffracted light formed by the diffracted light generation region 155 for focus error signal detection designed as described above. FIG. 5B shows the diffracted light on the photodetector during just focus, and FIGS. 5A and 5C show the diffracted light on the photodetector during defocus. .

The focus error signal FE is expressed by the following equation. FE = (S1 + S3-S2)-(S4 + S6-S5). ． ． (Equation 13) If the polarization anisotropic hologram 173, the quarter-wave plate 15 and the objective lens 4 are held by the holding member 13 while maintaining a constant relative position, for example, the information recording medium will move even if the objective lens 4 moves. The light beam reflected from No. 5 hardly moves on the polarization anisotropic hologram 173. This is because the polarization anisotropic hologram 173 moves together with the objective lens 4. As a result, despite the movement of the objective lens 4, the diffracted light on the photodetector 74 does not move, and the signal obtained from the photodetector 74 does not deteriorate. Therefore, the focus error signal can be stably obtained.

Tracking Error Signal The divided areas 153 and 154 shown in FIG. 4A are diffracted light generating areas for tracking error signal detection. FIG. 6 is a diagram for explaining the functions of the diffraction areas 153 and 154. When the relative position of the focused spot on the information recording medium 5 and the track groove changes, the light amount distribution of the reflected light on the polarization anisotropic hologram changes. According to the configuration shown in FIG. 6, this change in the light amount distribution can be extracted as the tracking error signal TE. Hereinafter, a method of detecting the tracking error signal will be described with reference to FIG.

The Y direction in FIG. 6 coincides with the track direction of the information recording medium 5, the so-called tangential direction. The light (diffracted light for tracking error signal detection) 163 diffracted by the diffraction areas 153 and 154 is received by the photodetector 72 for tracking error signal detection (FIGS. 6 and 7), and the tracking error signal TE is calculated by the following calculation. Form.

TE = S7-S8. ． ． (Equation 14) Alternatively, TE = (S7 + S10)-(S8 + S9). ． ． (Equation 15) If the polarization anisotropic hologram 173, the quarter-wave plate 15 and the objective lens 4 are held by the holding member 13 while maintaining a constant relative position, for example, the information recording medium will move even if the objective lens 4 moves. The light beam reflected from No. 5 hardly moves on the polarization anisotropic hologram 173. This is because the polarization anisotropic hologram 173 moves together with the objective lens 4. As a result, the diffracted light on the photodetector 72 does not move despite the movement of the objective lens 4. Therefore, the diffracted light for tracking error signal detection can be obtained from a fixed position on the far field pattern of the light beam, and a stable tracking error signal can be obtained without offset.

A configuration example of the photodetector and the light source will be described in more detail with reference to FIGS. 3 and 8. FIG. 8 shows A of FIG.
It is a -B sectional view.

When the light beam 3 is reflected by the mirror portion 7a, as shown in FIG. 8, points C and D in FIG.
Diffract in a plane that passes through the points and is parallel to the paper surface of FIG. Therefore, as shown in the graph inserted in FIG. 8, the light amount of the light beam 3 changes along the Y direction. Therefore, for example, it is not preferable to divide the polarization anisotropic hologram pattern 150 as shown in FIG. 6 and obtain the tracking error signal by the difference in the diffracted light amount generated from each divided region. This is because the light amount distribution is disturbed along the Y direction, so that if the light beam 3 is split in this direction, imbalance of the light amount is likely to occur.

Therefore, when the tracking error signal is obtained by the difference in the amount of diffracted light generated from the divided regions 153 and 154 (push-pull method), it is preferable to divide in the X direction of FIGS. 3 and 6. In other words, the line dividing the divided areas 153 and 154 of FIG. 4 is preferably parallel to the Y direction. Furthermore, the track direction of the information recording medium 5, that is, the so-called tangential direction (Y direction) is made to coincide.

Here, the case where the signal TE is used as a tracking error signal has been described. However, it can also be carried as another type of signal. Figure 9
Shows schematically the information recording medium 5 on which the wobble signal is recorded. This information recording medium has pits 5e and 5
d and the like are shifted (wobbled) to the left and right with respect to the track center 5b, and the position of the pit expresses information (wobble signal). The wobble signal recorded on such an information recording medium 5 can be obtained in the same manner as when the above-mentioned signal TE is obtained.

Even when a wobble signal is reproduced from the information recording medium 5, the polarization anisotropic holograms 173, 1 /
The four-wave plate 15 and the objective lens 4 are attached to, for example, the holding member 13.
Therefore, it is preferable to hold it while maintaining a constant relative position. Then, even if the objective lens 4 moves, the optical beam reflected from the information recording medium 5 hardly moves on the polarization anisotropic hologram 173. This is because the polarization anisotropic hologram 173 moves together with the objective lens 4. As a result, the diffracted light on the photodetector 72 does not move despite the movement of the objective lens 4. Therefore, diffracted light for detecting a wobble signal can be obtained from a fixed position on the far field pattern of the light beam, and a stable wobble signal without offset can be obtained.

(Embodiment 2) Another optical head device of the present invention will be described with reference to FIG.

The photodetector 7 of this embodiment is similar to that shown in FIGS.
9 has the same structure as the photodetector 7 of FIG. The polarization anisotropic hologram pattern of the polarization anisotropic hologram 174 is
It has the same configuration as the pattern of the polarization anisotropic hologram 103 in FIG. Except for these points, the configuration of the present embodiment is similar to that of the embodiment of FIG.

In this embodiment, the photodetector 7 is arranged only on one side of the light source 2. Therefore, the hybrid element in which the light source 2 and the photodetector 7 are combined can be easily manufactured, and the manufacturing cost can be reduced.

(Embodiment 3) Another optical head device of the present invention will be described with reference to FIG.

In each of the above-mentioned embodiments, a so-called finite optical system is adopted. In this embodiment, as shown in FIG. 11, an infinite optical system using a collimating lens 1220 is adopted. The present embodiment has the same configuration as the embodiment of FIG. 1 in other points.

According to the present embodiment, the collimating lens 122
By using 0, the optical path length can be freely designed.

(Embodiment 4) Another optical head device of the present invention will be described with reference to FIG.

The light beam 3 (laser light) emitted from the light source (semiconductor laser) 2 is collimated by the collimator lens B (12).
By 2), it becomes almost parallel light. After that, the light beam 3
After passing through the beam splitter 36 and further entering the polarization anisotropic hologram 175, the quarter wavelength plate 15 and the objective lens 4, the light is condensed on the information recording medium 5.

The optical beam reflected by the information recording medium 5 and the diffracted light (not shown in the figure) diffracted by the polarization anisotropic hologram 175 are reflected by the beam splitter 36, and then collimated lens A ( 121)
It is incident on the photodetector 7. By calculating the output of the photodetector 7, the servo signal (focus error signal and tracking error signal) and the information signal can be obtained.

In this embodiment, the collimating lens B (12
By increasing the numerical aperture (NA) of 2), a larger amount of light of the light beam 3 can be guided into the effective aperture of the objective lens 4. Therefore, the light utilization efficiency can be further increased. In addition, the collimator lens A (12
The sensitivity of the focus error signal can be increased by decreasing the numerical aperture (NA) of 1) and increasing the vertical magnification with respect to the objective lens 4. Furthermore, the light source 2
It is easy to insert a beam shaping unit such as a wedge prism or an anamorphic lens between the collimating lens B (122) and the collimating lens B (122). By inserting such a means, it is possible to focus the focused spot on the information recording medium 5 smaller.

Further, instead of the beam splitter 36,
If the utilization efficiency of light is increased by using the polarization beam splitter, the amount of light returning to the light source 2 can be reduced. By doing so, even when a semiconductor laser is used as the light source 2, the effect of avoiding the generation of return light noise becomes more remarkable. With respect to this point, the inventors of the present application point out that, in Japanese Patent Laid-Open No. 63-241735, a polarization anisotropic hologram is inserted in the optical path system, whereby returning light noise can be reduced. According to the present invention, the polarization anisotropic hologram is inserted in a portion closer to the objective lens than the intermediate point between the lens and the photodetector, thereby increasing manufacturing and adjustment margins. By integrating, various problems can be solved as described above. That is, the polarization anisotropic hologram 175, the quarter-wave plate 15, and the objective lens 4 are provided, for example, by holding the fixed relative positions by the holding member 13, so that the objective lens 4 can be controlled for tracking control. , The polarization anisotropic hologram 175 moves as a unit, and the optical beam reflected from the information recording medium 5 hardly moves on the polarization anisotropic hologram 175. Therefore, despite the movement of the objective lens 4, the diffracted light on the photodetector 75 also does not move, and the signal obtained from the photodetector 75 does not deteriorate. Therefore, there is an effect that the focus error signal can be stably obtained. In addition, as shown in FIG.
4 is provided in the polarization anisotropic hologram pattern 150, and the change in the light amount distribution on the polarization anisotropic hologram due to the change in the relative position between the focused spot on the information recording medium 5 and the track groove is used as the tracking error signal TE. take out,
The polarization anisotropy hologram 175, the quarter-wave plate 15 and the objective lens 4 are provided so as to maintain a fixed relative position, so that the polarization anisotropy is maintained even if the objective lens 4 moves for tracking control. Since the hologram 175 moves as a unit and the optical beam reflected from the information recording medium 5 hardly moves on the polarization anisotropic hologram 175, a tracking error signal is detected from a fixed position on the far field pattern of the light beam. Can obtain the diffracted light for
There is an effect that there is no offset and a stable tracking error signal can be obtained.

(Embodiment 5) FIG. 13 shows an optical information device using the optical head device according to the present invention.

In FIG. 13, the information recording medium (optical disk) 5 is rotated by the information recording medium drive mechanism 405. The optical head device 311 is roughly moved by the optical head device driving device 312 to a track on the information recording medium 5 where desired information exists. The optical head device 31
Reference numeral 2 also indicates a focus error signal or a tracking error signal in correspondence with the positional relationship with the information recording medium 5.
Send to 03. In response to this signal, the electric circuit 403 sends a signal for finely moving the objective lens to the optical head device 311. By this signal, the optical head device 31
Reference numeral 1 performs focus servo and tracking servo on the information storage medium 5, and reads, writes, or erases information on the information recording medium 5.

The optical information device of this embodiment is the optical head device 3.
Since the optical head device capable of obtaining an information signal having a very good S / N ratio as described in the present invention is used as 11, there is an effect that information can be reproduced accurately and stably.

Further, since the optical head device of the present invention is small and lightweight, the optical information device of the present embodiment using this is also small and lightweight, and has the effect of short access time. Further, the optical head device of the present invention can detect a very stable servo signal. In particular, even if the position of the objective lens is different from the normal position, a stable servo signal without offset can be obtained, and therefore, there is an effect that information can be reproduced accurately and stably.

[0094]

As is clear from the above description,
According to the present invention, the following effects can be obtained. (1) Since the polarization anisotropic hologram and the optical means (1/4 wavelength plate) for changing the polarization state are used in combination, unnecessary diffraction does not occur in the forward path, and diffraction for obtaining a servo signal or the like in the return path. Emits light. Therefore, there is no noise due to unnecessary diffracted light, and a signal with a very high S / N ratio can be obtained. (2) Since the polarization anisotropic hologram and the optical means (1/4 wavelength plate) for changing the polarization state are used in combination, unnecessary diffraction does not occur in the outward path, and diffraction for obtaining a servo signal or the like in the return path. Emits light. Therefore, since the light utilization efficiency is high and the signal amplitude is large, the S / N ratio is very high.
A signal with a high ratio can be obtained. (3) Since the proton exchange region of the polarization anisotropic hologram is produced by the diffusion process, it is difficult to set the grating pitch to 10 μm or less. However, in the present invention, the polarization anisotropic hologram is provided in the vicinity of the objective lens, that is, to detect light. Since it is arranged at a position away from the vessel, the grating pitch can be designed to be 10 μm or more, a polarization anisotropic hologram can be easily produced, and a high extinction ratio can be obtained easily and at low cost. There is an effect. (4) Since it is possible to obtain a high extinction ratio, it is possible to obtain a signal with a very high S / N ratio, in particular, in addition to high light utilization efficiency and a large signal amplitude, and noise due to unnecessary diffracted light. There is an effect that can be. Furthermore, the 1st-order diffraction efficiency in the return path is increased, and the 0th-order diffraction efficiency (transmittance) is almost zero.
Therefore, the amount of light returned to the light source can be made almost zero. Therefore, when a semiconductor laser is used as the light source, it is possible to avoid the generation of noise due to the returning light. (5) Since the polarization anisotropic hologram is arranged near the objective lens, that is, at a position away from the photodetector, the effective diameter R1 of the polarization anisotropic hologram can be increased even in a finite optical system. There is an effect that the tolerance of the position of the polarization anisotropic hologram can be eased and the assembling cost of the optical head device can be reduced. (6) Even if the objective lens moves for tracking control, the polarization anisotropic hologram, the quarter-wave plate, and the objective lens are provided so as to be held at a fixed relative position by, for example, holding means. The polarization anisotropic hologram moves integrally, and the optical beam reflected from the information recording medium hardly moves on the polarization anisotropic hologram. Therefore, despite the movement of the objective lens, the diffracted light on the photodetector does not move, and the signal obtained from the photodetector does not deteriorate. Therefore, there is an effect that the focus error signal can be stably obtained. (7) By using the SSD method as the detection method of the focus servo signal, an optical head device having a larger assembly tolerance can be configured. (8) Even if the objective lens moves for tracking control, the polarization anisotropic hologram, the quarter-wave plate, and the objective lens are provided so as to hold a certain relative position by, for example, holding means. The polarization anisotropic hologram moves integrally, and the optical beam reflected from the information recording medium hardly moves on the polarization anisotropic hologram. Therefore, the tracking error signal (or wobble signal) starts from a certain position on the far field pattern of the light beam.
There is an effect that the diffracted light for detection can be obtained, there is no offset, and a stable tracking error signal or wobble signal can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an optical head device according to the present invention.

FIG. 2 is a partial sectional perspective view of a polarization anisotropic hologram used in an embodiment of the present invention.

FIG. 3 is a perspective view of a hybrid element of a photodetector and a light source used in an embodiment of the present invention.

FIG. 4A is a plane showing a hologram pattern of a polarization anisotropic hologram used in an embodiment of the present invention, and FIG. 4B is a schematic diagram showing a focal position of diffracted light.

5 (a), (b) and (c) are plan views showing the state of diffracted light on a photodetector.

FIG. 6 is a schematic perspective view showing a method for detecting a tracking error signal.

FIG. 7 is a plan view showing a state of diffracted light on a photodetector in another embodiment according to the present invention.

8 is a cross-sectional view taken along the line AB of FIG.

FIG. 9 is a schematic plan view of an information recording medium having wobble pits formed thereon.

FIG. 10 is a schematic sectional view of another optical head device according to the present invention.

FIG. 11 is a schematic cross-sectional view of still another optical head device according to the present invention.

FIG. 12 is a schematic sectional view of an optical head device according to a seventh embodiment of the present invention.

FIG. 13 is a schematic sectional view of an optical information device according to the present invention.

FIG. 14 is a schematic sectional view of a conventional optical head device.

FIG. 15 is a schematic sectional view of another conventional optical head device.

FIG. 16 is a schematic explanatory view showing an example of a manufacturing process of a blazed hologram.

FIG. 17 is a plan view showing a state of diffracted light on a photodetector in a conventional optical head device.

FIG. 18 is a plane showing a hologram pattern in a conventional optical head device.

FIG. 19 is a schematic perspective view of a main part of a conventional optical head device.

[Explanation of symbols]

 2 light source 3 light beam 4 objective lens 5 information recording medium 6 return path + 1st order diffracted light 61 forward path 0th order diffracted light 67 return path −1st order diffracted light 7, 74a, b photodetector 71 6-division photodetector 72 tracking error signal detection Photodetector 13 Holding means 14 Holding means for all optical system 15 Quarter wave plate 110 Driving means 173 Polarization anisotropic hologram

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroaki Yamamoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Makoto Kato, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. ( 72) Inventor Tetsuo Hosomi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (16)

[Claims] 1. A light source for emitting a light beam, an objective lens for converging the light beam on an information recording medium, a light beam reflected by the information recording medium, and diffracted light of the light beam. The first hologram
A hologram having polarization anisotropy that more strongly diffracts light in a second polarization state different from the first polarization state as compared with a light beam in a polarization state of And a photodetector including a plurality of photodetectors for receiving a part of the diffracted light and outputting a photocurrent in accordance with the intensity of the part of the diffracted light. The optical recording medium further comprises optical means arranged between the recording medium and the hologram for changing the polarization state of the light beam reflected by the information recording medium to the second polarization state, An optical head device in which a hologram is arranged such that a distance between the hologram and the objective lens is shorter than a distance between the hologram and the photodetector. 2. The optical head device according to claim 1, wherein the relative positional relationship between the hologram and the objective lens is fixed. 3. The first polarization state is a linear polarization state in which the polarization direction is parallel to the first direction, and the second polarization state is a linear polarization state in which the polarization direction is perpendicular to the first direction. The optical head device according to claim 1, which is in a state. 4. The optical element converts the first polarization state into a rotational polarization state and converts the rotational polarization state into the second polarization state.
The optical head device according to claim 3, wherein the optical head device is a quarter-wave plate that converts the polarized state of the light. 5. The optical head device according to claim 3, wherein the light source emits light in the first polarization state. 6. The optical system according to any one of claims 1 to 5, further comprising another optical means for changing the light emitted from the light source to the first polarization state.
The optical head device according to any one of 1. 7. The light source is a semiconductor laser.
The optical head device described in 1. 8. The hologram has a lithium niobate substrate, a proton exchange layer periodically formed on the surface of the substrate, and a groove formed on the proton exchange layer. The optical head device according to any one of 1. 9. The relative positional relationship between the hologram, the objective lens, and the optical element is fixed.
9. The optical head device according to any one of 1 to 8. 10. The diffracted light formed by the hologram includes a spherical wave having a focus on the front side of the detection surface of the photodetector and a spherical wave having a focus on the rear side of the detection surface. 9. The optical head device according to any one of 9 to 9. 11. A hologram surface of the hologram includes an area H1 and an area H2 which are divided, and the plurality of photodetector sections include a photodetector area P1 and a photodetector provided on the detection surface. The region P2 is included, and the photodetector region P1 is the divided region H1 of the hologram.
Receives the diffracted light diffracted by and outputs an output signal E1 according to the intensity of the diffracted light.
The tracking error signal is obtained based on the output signal E1 and the output signal E2, by receiving the diffracted light diffracted by the device, outputting an output signal E2 according to the intensity of the diffracted light. The optical head device described in 1. 12. The hologram surface of the hologram includes an area H1 and an area H2 that are divided, and the plurality of photodetector sections include a photodetector area P1 and a photodetector provided on the detection surface. The region P2 is included, and the photodetector region P1 is the divided region H1 of the hologram.
Receives the diffracted light diffracted by, and outputs an output signal E1 according to the intensity of the diffracted light, and the photodetector region P2 is the divided region H2 of the hologram.
Receives the diffracted light diffracted by and outputs an output signal E2 in accordance with the intensity of the diffracted light, and based on the output signal E1 and the output signal E2, the shift amount of the pit position with respect to the track center of the information recording medium. 11. The optical head device according to claim 1, which obtains a signal indicating 13. The apparatus further comprises a substrate that integrally supports the plurality of photodetection units, the substrate having a recessed portion having a bottom surface and a sidewall inclined surface, and the bottom surface of the recessed portion. 13. The light source is provided, and a mirror for reflecting a light beam emitted from the light source in a direction perpendicular to the surface of the substrate is provided on the side wall inclined surface of the recess. The optical head device described in 1. 14. The divided area H1 and the divided area H2 of the hologram surface are symmetrical with respect to an axis of interest therebetween, and the axis of symmetry and the direction of the light beam from the light source to the mirror are The optical head device according to claim 13, wherein both are aligned with the track direction of the information recording medium. 15. The apparatus comprises a beam splitter between the light source and the hologram, the beam splitter transmitting the light in the first polarization state and reflecting the light in the second polarization state. A part of the light beam reflected by the information storage medium is
The optical head device according to claim 1, wherein the optical head device is guided to the photodetector via the beam splitter after being diffracted by the hologram. 16. An optical information apparatus comprising: a storage medium drive means for driving an information storage medium; an optical head device; and an optical head drive means for adjusting the positional relationship between the information storage medium and the optical head device. Where the optical head device receives a light source that emits a light beam, an objective lens that converges the light beam on an information recording medium, the light beam reflected by the information recording medium, and the light beam A hologram for forming diffracted light of
A hologram having polarization anisotropy that more strongly diffracts light in a second polarization state different from the first polarization state as compared with a light beam in a polarization state of A photodetector including a plurality of photodetectors for receiving a part of the diffracted light and outputting a photocurrent according to the intensity of the part of the diffracted light; and an optical means arranged between the information recording medium and the hologram. And optical means for changing the polarization state of the light beam reflected by the information recording medium to the second polarization state, wherein the hologram is between the hologram and the objective lens. An optical information device, which is arranged such that a distance is shorter than a distance between the hologram and the photodetector, and a relative positional relationship between the hologram and the objective lens is fixed.