JPH11134700A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head of an optical recording device capable of making it thin. SOLUTION: An optical path converting means (the first surface of a first transparent base 9) 14, a first grating element 5 and a second grating element 6 are arranged in the optical path from a light source 1 to an optical disk 11. A transmitted light beam from the light source 1 is made incident on the optical path converting means 14 through a collimator lens 3, totally reflected and made incident on the first grating element 5. A diffracted light beam is made incident on the second grating element 6 and converged on a recording medium by an objective lens. A diffracted light beam from the first grating element 5 and a diffracted light beam from the second grating element 6 are made to be generated in the direction mutually canceling the fluctuation of wavelengths.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for an optical recording / reproducing apparatus, and more particularly to an optical head which can be made thin.

[0002]

2. Description of the Related Art An optical head is an important component for reading a signal from an optical recording medium such as an optical disk such as a compact disk (CD) or a DVD, or an optical card memory. The optical head uses not only a signal detection function but also a focus servo, to extract signals from the optical recording medium.
It is necessary to provide a control mechanism such as a tracking servo.

FIG. 24 shows a typical conventional optical head. As shown in FIG. 24, a laser beam 2 emitted from a semiconductor laser 1 as a light source is converted into a parallel beam by a collimator lens 3, and after passing through a focus / track error signal detecting element 8 constituted by a hologram element,
The optical axis is bent by 90 ° by the rising mirror 20 and enters the objective lens 4. The laser light 2 condensed on the optical disk 11 by the objective lens 4 is reflected and folds the optical path, becomes parallel light by the objective lens 4,
Focus / reflected by the rising mirror 20
The light enters the track error signal detection element 8. focus/
The laser beam 2 incident on the track error signal detecting element 8 is
There, the light is split into two and focused on the photodetectors 13a and 13b. Thus, the reproduction signal and the focus error signal and the track error signal, which are the servo signals, are read.

[0004]

As shown in FIG. 24,
The height of the optical head is WD (working distance), the thickness of the objective lens 4, the space from the lower part of the objective lens 4 to the upper part of the rising mirror 20, the rising mirror 2
It is represented by the sum of heights lz of 0.

When an optical head is to be thinned, W
The minimum value of the sum of D, the lens thickness, and the space is almost determined by the type of the optical disk 11. For example, D
In the case of VD, WD, lens thickness and space are each set to 1.
Be estimated to 1mm and the minimum value, the height lz of the rising mirror 20, must be greater than the beam diameter w _1, for example, 3mm is needed. Therefore, in this case, the height of the optical head is 6.3 mm even when estimated to the minimum value, and it is difficult to further reduce the thickness.

The present invention has been made to solve the above-mentioned problems in the prior art, and has as its object to provide an optical head that can be made thinner.

[0007]

In order to achieve the above object, a first configuration of an optical head according to the present invention comprises first and second gratings arranged in order in an optical path from a light source to an objective lens. And an optical path conversion means disposed between the optical path between the light source and the first grating element or between the optical path between the second grating element and the objective lens. According to the configuration of the optical head, the optical distance between the first grating element and the second grating element can be reduced, so that the lateral shift of the optical axis due to the wavelength variation of the light source is reduced. be able to. As a result, it is possible to reduce the lateral shift of the optical axis from the center of the objective lens, and to form a good circular condensed spot.

In the first configuration of the optical head according to the present invention, an optical path changing means is disposed between an optical path between the light source and the first grating element, and the light emitted from the light source is converted into the optical path changing means. Through the first grating element, the diffracted light from the first grating element enters the second grating element, and the second grating element
It is preferable that the diffracted light from the grating element enters the objective lens and is focused on the recording medium. According to this preferred example, it is possible to bend light toward the objective lens side by using the second grating element, and to realize a thin optical head.

In this case, the first grating element is a reflection type element, and the optical path conversion means is a first transparent base having a first surface, and the first grating element and the optical path conversion element are connected to each other. The means may be configured such that an angle between an optical axis of light emitted from the light source and a normal to the first surface is equal to or greater than a critical angle, and a second angle from the normal to the first surface and the first grating element. Are arranged so that the angle of the diffracted light to the grating element with respect to the optical axis is equal to or less than the critical angle, and the light emitted from the light source is reflected by the first surface and is reflected by the first surface.
It is preferable that the diffracted light reflected from the first grating element is transmitted through the first surface and is incident on the second grating element.
According to this preferred example, the optical axis of the light emitted from the light source can be shifted in the direction of the recording medium, so that the thickness of the optical head can be reduced. In this case, the first transparent substrate is a triangular prism having a slope, a bottom surface, and a side surface. The slope surface serves as a first surface, and a first grating element is provided on the bottom surface. It is preferable that the light is incident on the first transparent substrate from the side surface. Further, in this case, the second grating element is a transmissive element, and the second grating element is further provided with a second transparent substrate formed on the upper surface, and the second grating element is provided on the first surface of the first transparent substrate. Preferably, a multilayer film is formed, and the first transparent substrate and the second transparent substrate are integrated via the multilayer film. Further, the second grating element is a transmissive element, and further includes a second transparent base on which the second grating element is formed on the upper surface, wherein the first transparent base and the second transparent base are connected to each other. Preferably, an air gap is interposed therebetween. Further, the second grating element is a transmission type element,
A second grating element formed on an upper surface of the second grating element;
It is preferable that the transparent substrate is further provided, and the second transparent substrate is a triangular prism. Further, the second grating element is a reflection type element, and further includes a second transparent substrate having the second grating element formed on the bottom surface, and a multilayer film is formed on the first surface of the first transparent substrate. Preferably, the first transparent substrate and the second transparent substrate are integrated via the multilayer film, and the first and second grating elements are preferably arranged on the same plane. According to this preferred example, the manufacture of the first and second grating elements becomes easy.

In this case, the first angle of incidence from the optical path conversion means to the first grating element with respect to the normal to the first grating element is the normal to the first grating element. Is larger than the emission angle of the diffracted light from the first grating element with respect to
The second incident angle with respect to the grating element of the second grating element with respect to the normal to the second grating element is the second incident angle.
It is preferable that the output angle of the diffracted light from the second grating element with respect to the normal to the grating element is larger than that of the second grating element. According to this preferred example, beam shaping can be performed to improve light use efficiency. In this case, it is further preferable that the emission angle of the diffracted light from the first and second grating elements is approximately 0 °. According to this preferred example, beam shaping can be performed efficiently. Further, a first transparent base and a second transparent base on which a second grating element is formed on an upper surface or a lower surface are further provided, and the first transparent base and the second transparent base are the first transparent base. It is preferable that they are integrated via a grating element. Further, the first and second incident angles are 4
It is preferably between 5 ° and 60 °. According to this preferred example, beam shaping can be performed effectively, and the light use efficiency can be improved.

Further, in the first configuration of the optical head according to the present invention, the amount of change in the wavelength of the optical axis of the diffracted light from the first grating element is changed by the light of the diffracted light from the second grating element. Preferably, the change in axis is at least partially offset from each other. According to this preferred example, when semiconductor laser light is used as light emitted from the light source, inclination of the optical axis can be prevented even if the wavelength of the emitted light changes due to a change in environmental temperature.

In the first configuration of the optical head according to the present invention, it is preferable that the first grating element and the second grating element are linear gratings having the same cycle and a uniform cycle. According to this preferred example, the influence of wavelength fluctuation can be completely eliminated.

In the first configuration of the optical head according to the present invention, it is preferable that the first grating element and the second grating element are volume holograms having a periodic structure of a refractive index distribution. According to this preferred example, even if the diffraction angle is large (for example, 45 °), a high diffraction efficiency of 90% or more can be realized. In this case, it is preferable that the polarization of the light incident on the volume hologram is S-polarized light in both the forward path and the return path. According to this preferred example, the production of the volume hologram is facilitated and the light use efficiency is improved. In this case, a polarization focus / track error signal detection element is further provided, and the amplitude of the refractive index change amount of the volume hologram is obtained by multiplying the primary diffraction efficiency of the S-polarized light by the primary diffraction efficiency of the P-polarized light. Is preferably set to a maximum value. According to this preferred example, the overall light use efficiency can be improved.

Further, in the first configuration of the optical head of the present invention, the focus / track error signal detecting element having the polarization property and the 1/4 provided in the optical path from the second grating element to the objective lens are provided. Preferably, a wave plate is further provided. According to this preferred example, the outgoing light from the light source is S-polarized, so that the light passes through the polarization focus / track error signal detection element on the outward path with almost no loss. Then, by reciprocating through the 波長 wavelength plate, on the return path, the light incident on the focus / track error signal detection element becomes P-polarized light and is effectively diffracted on the photodetector.

In the first configuration of the optical head according to the present invention, it is preferable that the diffraction angles of the first and second grating elements are 45 ° or more. According to this preferred example, the optical head can be made extremely thin.

In the first configuration of the optical head according to the present invention, it is preferable that the first and second grating elements are provided on the same transparent substrate. Also,
In this case, it is preferable that the first and second grating elements are provided on the same surface of the same transparent substrate.
In this case, it is preferable that the first and second grating elements are further provided on the surface of the same transparent substrate. Further, it is preferable that a triangular prism is disposed on the transparent substrate with the bottom surface facing the first grating element, and the inclined surface of the triangular prism is an optical path conversion unit.
Further, it is preferable that a reflection plate is provided on the back surface side of the transparent substrate via an air layer, and that the refracted light from the transparent substrate to the air layer is reflected by the reflection plate and enters the second grating element. According to this preferred example, laser light transmitted through the first grating element and incident on the transparent base is refracted at the boundary between the transparent base and the air layer, reflected by the reflector, and reflected by the second grating element. Since the light can be incident, the total thickness of the transparent substrate, the air layer, and the reflection plate can be set small. As a result, the thickness of the optical head can be reduced.

In the first configuration of the optical head according to the present invention, it is preferable that the second grating element is an optical element that converts parallel light into divergent light or converts divergent light into parallel light. According to this preferred example, when a two-wavelength configuration is formed by using one collimator lens and one objective lens, both the optical disk having a thick protective layer such as a CD and the thin optical disk such as a DVD can be used. Both light beams of corresponding wavelengths can be favorably focused on the pit surface without aberration.

Further, in the first configuration of the optical head according to the present invention, the first and second grating elements include:
It is preferable that each volume hologram is composed of a plurality of layers corresponding to different wavelengths. According to this preferred example, a plurality of types of optical disks corresponding to different wavelengths can be used. Further, in this case, it is preferable that the thickness of each of the plurality of layers of the volume hologram differs according to the wavelength. According to this preferred example,
The tolerance of the diffraction efficiency for each wavelength can be set optimally according to the optical disc corresponding to it. In this case, it is further preferable that the thickness of each of the plurality of layers of the volume hologram is substantially proportional to the wavelength. According to this preferred example, the tolerance of the diffraction efficiency for each wavelength can be made equal. In this case, the multi-layer volume hologram is
It is preferable that the fringes of the periodic structures of the respective refractive index distributions have different inclination angles. According to this preferred example,
Since the generation of unnecessary diffracted light in the layer not corresponding to each wavelength can be reduced, the light use efficiency is improved. In this case, the multi-layer volume hologram is
It is preferable that the fringes of the periodic structure of each refractive index distribution have the same inclination angle. According to this preferred example, the inclination of the optical axis at each wavelength of the diffracted light from the first grating element to the second grating element can be made equal. Further, in this case, the different wavelengths are two wavelengths λ ₁ and λ ₂ , and the first and second grating elements are obtained from two-layer volume holograms corresponding to the two wavelengths λ ₁ and λ ₂ , respectively. And the two wavelengths λ ₁ and λ ₂ are 0.60 μm ≦ λ ₁ ≦ 0.68 μm,
It is preferable that 0.76 μm ≦ λ ₂ ≦ 0.87 μm. According to this preferred example, unnecessary diffraction light at other wavelengths in the first and second grating elements having a two-layer structure is reduced, and, for example, a DVD, a CD-R, and a CD can be read well. Can be. Also, in this case, the different wavelengths are three wavelengths λ ₁ , λ ₂ , λ ₃ ,
First and second grating elements, each of said three wavelengths lambda _1, lambda _2, made from the volume hologram of three layers corresponding to lambda _3, the three wavelengths lambda _1, lambda _2, lambda ₃ is
0.38 μm ≦ λ ₁ ≦ 0.52 μm, 0.60 μm ≦ λ
₂ ≦ 0.68 μm, 0.76 μm ≦ λ ₃ ≦ 0.87 μm
It is preferred that According to this preferred example, unnecessary diffracted light at other wavelengths in the first and second grating elements having a three-layer structure is reduced, and for example, a high-density disc of 10 GB or more, DVD, DVD-R, CD , CD
Many optical disks such as -R can be read well.

In a second configuration of the optical head according to the present invention, the light source emits a light beam in a first direction, and a first deflecting unit deflects the light beam in the first direction in a second direction. When,
A second deflecting means for deflecting the light beam deflected by the first deflecting means in a third direction; and an objective lens for converging the light beam deflected by the second deflecting means on an optical recording medium. The third direction is substantially perpendicular to the recording surface of the optical recording medium, and the dimension of the second deflecting means in the third direction is the dimension of the light flux in the first direction in the third direction. It is characterized by being smaller than. According to the second configuration of the optical head, the light beam emitted from the light source can be deflected obliquely downward (second direction) by the first deflecting means. The incident angle can be inclined from the y-axis direction. As a result, the height occupying the lower part of the objective lens is reduced, and the height of the optical head can be reduced.

Further, in the second configuration of the optical head according to the present invention, it is preferable that the first deflecting means is a triangular prism. In the second configuration of the optical head according to the present invention, it is preferable that the second deflecting means is a reflective grating element.

Further, in the second configuration of the optical head of the present invention, it is preferable that the second deflecting means is a mirror.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment> First, an optical head according to a first embodiment of the present invention will be described in detail with reference to FIGS.

FIG. 1 is a side view showing a basic configuration of an optical head and a state of light propagation according to a first embodiment of the present invention.
FIG. 2 is a plan view showing (a) a first or second grating element in the optical head according to the embodiment;
(B): Side view showing the configuration of the central portion and details of the first and second grating elements. FIG. 3 shows the first-order diffraction efficiency and refraction of the first and second grating elements in the optical head of the embodiment. A diagram showing a relationship between the rate change amount and the amplitude Δn,
FIG. 4 is a side view showing how the diffracted light from the first and second grating elements behaves when the wavelength of the incident light fluctuates in the optical head of the embodiment.

As shown in FIG. 1, in the optical head according to the present embodiment, a light source 1 controls a recording medium such as DVD or C
D in the optical path to the optical disk 11 such as
4, a first grating element 5, and a second grating element 6. Light source 1 and photodetector 1
3a and 13b are integrated in the light source / photodetector unit 17.

A laser beam 2 of, for example, S-polarized light (the electric field direction of the light is in the x-axis direction), for example, having a wavelength λ = 0.655 μm, emitted in the y-axis direction from the semiconductor laser as the light source 1
Is, for example, a beam diameter of 2.
The light becomes parallel light of 8 mm, passes through the focus / track error signal detection element 8 (using the 0th-order diffracted light), and enters the optical path conversion unit 14. -Z
The laser light 2 totally reflected in the axial direction enters the first grating element 5. Then, for example, the angle θ ₁ = 45
The first-order diffracted light reflected and diffracted at an angle passes through the optical path changing means 14 and enters the second grating element 6. Next, for example, the first-order diffracted light diffracted in the z-axis direction at an angle θ ₂ = 45 ° is collected on the optical disk 11 by the objective lens 4.

The laser beam 2 reflected by the optical disk 11 is turned back in the opposite direction, passes through the objective lens 4, the second grating element 6, the first grating element 5, and the optical path changing means 14 in this order, and returns to the -y axis. The optical path is directed in the direction, divided by the focus / track error signal detection element 8 (using the first-order diffracted light), and
b.

In the present embodiment, as the first transparent base 9, a triangle formed by an angle between the inclined surface (first surface) and the bottom surface, for example, P ₁ = 45 ° and a height of 3.2 mm. A prism (for example, made of glass, resin, or the like) is used, a first grating element 5 is formed on the bottom surface of the first transparent base 9, and an inclined surface (first surface) is used as an optical path conversion unit 14. . The second grating element 6 has a thickness (height) of 1.7 mm and an inverted trapezoidal cross section having an inclined surface with P ₂ = 45 °, for example.
(For example, made of glass, resin, etc.). The first transparent substrate 9 and the second transparent substrate 10 are integrated by joining their slopes via the multilayer film 12. In this case, the first transparent substrate 9
And the bottom surface of the second transparent substrate 10 are located on the same plane.

The focus / track error signal detecting element 8 is composed of, for example, a resin substrate or a glass substrate and a hologram element formed on the surface thereof, and is integrated with the side surface of the first transparent base 9. Have been.

The angle between the optical axis of the laser beam 2 emitted from the light source 1 and the normal of the slope (optical path changing means) 14 of the first transparent base 9 is a critical angle (for example, the first transparent base 9 When the refractive index is 1.5, the angle is set to 41.8 ° or more, for example, 45 °, and the normal of the slope (optical path conversion means) 14 of the first transparent base 9 and the first grating The angle between the optical axis of the diffracted light from the element 5 and the second grating element 6 is set to an angle smaller than the critical angle, for example, 0 °. This makes it possible to shift the optical axis of the laser light 2 emitted from the light source 1 indicated by the broken line in the z-axis direction, that is, in the direction of the optical disk 11 (in FIG. 1, the laser light emitted from the light source 1). (2) A configuration in which the optical axis of 2 is set near the surface of the second transparent substrate 10). As a result, for example, an optical head having a total height of 5.0 mm can be realized, and the thickness can be significantly reduced as compared with a conventional optical head (with a total height of 6.3 mm). In particular, by setting the diffraction angles θ ₁ and θ ₂ to 45 ° or more, the overall height of the optical head can be set to 5 mm or less, and ultra-thinness can be achieved.

In this embodiment, as the first and second grating elements 5 and 6, for example, a linear grating having a uniform period of Λ = 0.57 μm as shown in FIG. Is used. In particular, the first
A reflection type volume hologram is used as the grating element 5, and a transmission type volume hologram is used as the second grating element 6.

As shown in FIG. 2B, these volume holograms are formed by using, for example, a photopolymer.
Known Ar laser light (for example, wavelength λ = 0.5145)
μm or 0.488 μm) to form a sinusoidal periodic structure having a refractive index distribution by a two-beam interference method. By using volume holograms as the first and second grating elements 5 and 6, for example, 45
Even with a large diffraction angle such as °, a high diffraction efficiency of, for example, 90% or more can be realized. The material of the volume hologram is not necessarily limited to a photosensitive resin such as a photopolymer, but may be gelatin or Fe-doped L having a photorefractive effect.
iNbO ₃ , BiTiO ₃ or the like may be used.

The first grating element 5 has a structure in which the refractive index distribution layer 15 has a thickness of, for example, L = 7 μm, and a reflective film 16 of, for example, Al or Au is deposited on the surface thereof. refractive index distribution (amplitude Δn of the refractive index change amount, for example, 0.04) is the fringe 18a of the periodic structure of the upper is inclined in the -y-axis direction (an inclination angle phi ₁ is
Half the value of the diffraction angle, for example 22.5 °). This allows
The laser beam 2 vertically incident on the first grating element 5 is obliquely 45 ° (θ ₁ = 45 °) by Bragg diffraction.
°) as primary diffracted light. The first grating element 5 has a diffraction angle of, for example, 45 °. When the diffraction angle exceeds the critical angle, the reflective film 16 may not be provided. The second grating element 6 has the same period and thickness as the refractive index distribution layer 15 of the first grating element 5, but has no reflective film deposited thereon, and the fringe 18b of the refractive index distribution has Are inclined in the y-axis direction (the inclination angle φ ₂ is, for example, 22.5 °).

By setting the inclination angles of the fringes of the first grating element 5 and the second grating element 6 in the opposite directions, the light emitted from the light source 1 in the y-axis direction can be converted into the light emitted in the z-axis direction. Can be efficiently deflected. In addition, when the semiconductor laser light is used, the wavelength of the emitted light changes by about ± 10 nm due to the change of the environmental temperature. In the present embodiment, the wavelength of the optical axis of the diffracted light from the first grating element 5 is changed. The change is at least partially offset from the change in the optical axis of the diffracted light from the second grating element 6. As a result, the light is emitted vertically irrespective of the wavelength, and the influence of the wavelength fluctuation of the light source 1 is canceled.

Next, the behavior of a light wave when a wavelength fluctuation occurs will be specifically described with reference to FIG. Light source 1
When there is no fluctuation in the wavelength (Δλ = 0), the laser beam 2 incident in the y-axis direction is diffracted by the first and second grating elements 5 and 6 as shown in the figure, as shown by the solid lines ( Both diffraction angles will be described as the same θ), z
It is emitted in the axial direction (vertical). The direction in which the wavelength becomes longer (Δ
(λ> 0), the diffraction angle is increased by Δθ + in the first grating element 5 as shown by the broken line, but the incident angle is also increased by Δθ + in the second grating element 6 as shown by the broken line. Therefore, the resulting diffracted light is also emitted in the z-axis direction (vertical emission), and the optical axis does not tilt due to wavelength fluctuation. On the other hand, when the wavelength fluctuates in the direction of shortening (Δλ <0), as shown by the two-dot chain line, the diffraction angle in the first grating element 5 is reduced by Δθ−, but in the second grating element 6 Since the incident angle is also reduced by Δθ-, the resulting diffracted light is also emitted in the z-axis direction (vertical emission), and the optical axis is not tilted due to wavelength fluctuation. In particular, when the periods of the first and second grating elements 5 and 6 are completely matched, the influence of the wavelength fluctuation completely disappears, but even if they are slightly different, they tend to cancel each other.

The optical path from the light source 1 to the objective lens 4
In the first grating element 5 and the second grating element
In this configuration, the first elements are arranged in order, so that the first gray
Between the switching element 5 and the second grating element 6
Can be reduced in optical distance. As a result, light
Lateral shift s of the optical axis due to wavelength variation of source 1₁, S _Two
Can be reduced. As a result, the objective lens 4
Reduce the lateral shift of the optical axis from the center
A circular light spot can be formed.

In the present embodiment, a volume hologram having a periodic structure of a sinusoidal refractive index distribution is used as the first and second grating elements 5 and 6, but as shown in FIG. The next diffraction efficiency depends on the polarization direction of the incident light depending on the amplitude Δn of the refractive index change amount.
It turns out to behave differently. FIG. 3 (a),
(B) and (c) show diffraction angles θ of 45 ° and 55, respectively.
° and 65 ° indicate the first-order diffraction efficiency. Note that the solid line is S-polarized light, and the broken line is P-polarized light (the electric field
Wavelength λ = 0.655 μm,
The thickness L was 7 μm, the average refractive index n of the volume hologram was 1.5, and the inclination angle φ of the fringe was θ / 2.

As shown in FIG. 3, when the diffraction angle θ is large, using the S-polarized light as the incident light can realize a first-order diffraction efficiency of 100% with a small refractive index change amplitude Δn (P The opposite is true for polarized light), and as the diffraction angle θ increases,
The optical head tends to be thinner. When the S-polarized light is used, when the diffraction angle θ increases, 1
The value of the amplitude Δn of the amount of change in the refractive index at which the next diffraction efficiency becomes 100% becomes smaller (the opposite is true for P-polarized light). Since the volume hologram can be easily manufactured when the amplitude Δn of the amount of change in the refractive index is small, the volume hologram can be easily manufactured by making the polarization of the light into the S-polarized light in both the forward path and the return path in the optical head of the present invention. At the same time, the light use efficiency is improved. However, operation is possible with P-polarized light.

In this embodiment, the case where a volume hologram having a refractive index distribution is used as the first and second grating elements 5 and 6 has been described as an example, but a surface relief type grating is used. But operation is possible. However, in that case, it is difficult to achieve both a large diffraction angle and high diffraction efficiency.

In the present embodiment, the first transparent substrate 9 and the second transparent substrate 10 are joined and integrated via the multilayer film 12, but are not necessarily limited to this configuration. Not the first, for example, as shown in FIG.
The operation can be performed only by providing the air gap 23 between the transparent substrate 9 and the second transparent substrate 10d. However, FIG.
As shown in FIG. 1, a first transparent substrate 9 and a second transparent substrate 10
It is more preferable that the multilayer film 12 is interposed between the first and second layers because the structure is stabilized.

In the present embodiment, the transparent substrate 10 having an inverted trapezoidal cross section is used as the second transparent substrate, but the present invention is not necessarily limited to this configuration. The second transparent substrate may have any shape as long as it can secure the optical path of the laser beam 2 and has a surface on which the second grating element 6 can be formed on the objective lens 4 side. As shown in FIG. 5, a triangular prism similar to the first transparent substrate 9 can be used.

Further, according to the present embodiment, the optical axis of the laser beam 2 emitted from the light source 1 can be shifted in the z-axis direction, that is, in the direction of the optical disk 11, so that as shown in FIG. In addition, between the second grating element 6 and the optical disk 11a, there are provided a plurality of objective lenses 4a which are lenses having a high NA of, for example, 0.7 to 0.9,
4b can be arranged, and as a result, both a reduction in the thickness of the optical head and an increase in the density of the optical disk 11a can be achieved.

<Second Embodiment> Next, a second embodiment of the present invention will be described.
The optical head according to the second embodiment will be described with reference to FIGS. 7 and 8, focusing on differences from the first embodiment.

FIG. 7 is a side view showing the basic structure of an optical head and the state of light propagation according to a second embodiment of the present invention. FIG. 8 is a view showing the first and second optical heads according to the second embodiment.
FIG. 6 is a diagram showing a relationship between the first-order diffraction efficiency of the grating element and the amplitude Δn of the amount of change in the refractive index.

As shown in FIG. 7, in the present embodiment, a polarizing focus / track error signal detecting element 8a is provided in the optical path from the collimating lens 3 to the optical path converting means 14, and the second Grating element 6
A quarter-wave plate 7 is provided in the optical path from to the objective lens 4. The polarization focus / track error signal detection element 8a is formed by forming a hologram element using, for example, LiNbO ₃ as a substrate. Is a hologram. Therefore, compared to the optical head of the first embodiment formed on a normal substrate that is not polarized,
The light use efficiency is improved more than twice. The second transparent substrate 10a is formed such that the right side surface is parallel to the left side surface (for example, obliquely at 45 °), and the entire cross-sectional shape is a parallelogram. By forming the second transparent base 10a in such a shape, a large number of pieces can be cut out from a large glass substrate by simply cutting in a diagonal direction. Costs can be reduced.

As shown in FIG. 7, the laser light 2 emitted from the light source 1 is, for example, S-polarized light.
The laser beam 2 is transmitted through the polarization focus / track error signal detection element 8a with almost no loss. And the second
Quarter wave plate 7 formed on the grating element 6 of FIG.
Is reciprocated, the laser beam 2 incident on the focus / track error signal detection element 8a becomes P-polarized light on the return path and is effectively diffracted onto the photodetectors 13a and 13b. As the 波長 wavelength plate 7, a material exhibiting birefringence such as quartz can be used. For example, if an obliquely deposited film such as Ta ₂ O ₅ is used, its thickness may be several μm.
The thickness can be reduced.

Focus / track error signal detecting element 8
a, the arrangement of the quarter-wave plate 7 is, in principle, the light source 1, the focus / track error signal detecting element 8a, 1 /
It is sufficient that the optical order of the four-wavelength plate 7 and the optical disk 11 is satisfied, but it is better not to dispose the focus / track error signal detection element 8a in the optical path from the second grating element 6 to the objective lens 4. It is desirable in terms of thinning. Further, when the quarter-wave plate 7 is arranged in the optical path from the light source 1 to the first grating element 5, the light incident on the first and second grating elements 5, 6 becomes circularly polarized light, Since it is necessary to consider the influence of the phase shift due to the polarization, the design of the first and second grating elements 5 and 6 is particularly complicated. Therefore, the design can be simplified by disposing the quarter-wave plate 7 in the optical path from the second grating element 6 to the objective lens.

In the present embodiment, for example, S-polarized light is incident on the first and second grating elements 5 and 6 on the outward path, and P-polarized light is incident on the backward path.
As shown by the arrows in FIG. 8, the value of the amplitude Δn of the refractive index variation of the volume hologram, the product of the first-order diffraction efficiency eta _P to the primary diffraction efficiency eta _S and P-polarized light with respect to S-polarized light eta _S · eta
By setting _P to a maximum value, overall light use efficiency can be improved.

[0048] Incidentally, the value of [Delta] n, the product of the first-order diffraction efficiency eta _P to the primary diffraction efficiency eta _S and P-polarized light with respect to S-polarized light eta _S ·
By setting the value of η _P to the maximum value, in addition to the first-order diffracted light, some 0th-order diffracted light that is transmitted and reflected as it is is generated. First, since the 0th-order diffracted light from the first grating element 5 on the outward path is emitted right above in the z-axis direction, it becomes a critical angle or more with respect to the optical path conversion unit 14. Therefore, the light cannot be transmitted and is reflected in the −y-axis direction, and does not reach the photodetector 13. Further, the 0th-order diffracted light from the second grating element 6 on the outward path is emitted upward and to the right and does not return, so there is no influence. Next, since the 0th-order diffracted light from the second grating element 6 on the return path is emitted immediately below in the −z-axis direction, the 0th-order diffracted light cannot pass through the optical path conversion unit 14. Furthermore, the 0th-order diffracted light from the first grating element 5 on the return path is emitted to the upper left, and does not reach the photodetector 13.

That is, in the optical head according to the present embodiment, the optical path changing means 14 plays a role of a dam that transmits only the first-order diffracted light by using the critical angle.
It is possible to detect a reproduced signal with good N.

<Third Embodiment> Next, a third embodiment of the present invention will be described.
The optical head according to the third embodiment will be described with reference to FIG. 9 focusing on the differences from the first embodiment.

FIG. 9 is a side view showing a basic configuration of an optical head and a state of light propagation according to a third embodiment of the present invention. As shown in FIG. 9, in the present embodiment, the second grating element 6a is a reflective element, and this second grating element 6a is formed on the bottom surface of the second transparent base 10. I have. The laser beam 2 diffracted from the first grating element 5 at an angle of θ ₁
The light is totally reflected once on the upper surface of the transparent substrate 10 and enters the second grating element 6a. With such a configuration, the surface of the second transparent base 10 facing the lower part of the objective lens 4 is, for example, only a glass surface, and it is easy to wipe off dust and dirt. Even if the second grating element 6a is in contact with the transparent substrate 10, the damage to the second grating element 6a is small.

The first and second transparent substrates 9 and 10 are arranged such that their back surfaces are on the same surface.
The first and second grating elements 5, 6a are arranged on the same plane. With such an arrangement,
The manufacture of the first and second grating elements 5, 6a is facilitated. The first and second grating elements 5 and 6a have substantially the same structure as the first grating element shown in FIG. Since the first and second grating elements 5 and 6a have the same structure in which the reflective film is formed on the upper surface of the refractive index distribution layer, the first and second grating elements 5 and 6a are similarly distorted when a disturbance such as a temperature change occurs. For this reason, the symmetrical shape has the effect of canceling out each other, and is characterized by being strong against disturbance. Note that the first grating element 5 and the second grating element 6a have fringes whose inclinations are opposite to the z-axis direction. The first grating element 5 has a diffraction angle of, for example, 45 °. When the diffraction angle exceeds the critical angle, the reflective film 16 may not be provided.

Further, by making the second grating element 6a a reflection type element, it is possible to increase the space from the first transparent base 9 to the objective lens 4, so that the objective lens 4 is controlled. Mounting of an actuator (not shown) is facilitated.

In this embodiment, the first transparent base 9 made of a triangular prism and the second transparent base 9 having an inverted trapezoidal cross section are used.
The first and second grating elements 5 are formed by joining the slopes of the transparent base 10 so that the back surfaces of the first and second transparent bases 9 and 10 are on the same plane.
Although 6a is arranged on the same surface (back surface), it is not necessarily limited to this configuration. For example, as shown in FIG. 10, a plate-shaped second transparent base 10e is used as the second transparent base, and a substantially left half of the upper surface of the second transparent base 10e is formed of a first triangular prism. Transparent substrate 9
And the first and second grating elements 5 on the back surface of the second transparent substrate 10e.
The same effect can be obtained by arranging 6a. In addition, by forming the second transparent base 10e in such a shape, a large number of pieces can be cut out from a large glass substrate only by cutting in the vertical direction, so that mass productivity is improved. The cost can be reduced.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.
The optical head according to the second embodiment will be described with reference to FIGS. 11 and 12, focusing on differences from the first embodiment.

FIG. 11A is a side view showing a basic structure of an optical head and a state of light propagation according to a fourth embodiment of the present invention, FIG. 11B is a plan view thereof, and FIG. FIG. 6 is a side view showing the configuration of a central portion and details of first and second grating elements in the optical head according to the embodiment.

As shown in FIG. 11, the optical system of this embodiment
The head has a two-wavelength configuration. That is, for DVD
For example, wavelength λ₁= 0.655 μm semiconductor laser
The light source 1a and, for example, wavelengths for CD-Rs and CDs
λ_Two= 0.795 μm semiconductor laser light source 1b
Have been. The light sources 1a and 1b are respectively
It is built in the output module 17a, 17b. Ma
In addition, as shown in FIG.
The switching elements 5b and 6b also have a configuration corresponding to two wavelengths. sand
That is, for example, Al, Au
Of a two-layer structure having a reflective film 16 such as
Element 5b is formed to form a two-layer structure.
The refractive index distribution layers 5c and 5d corresponding to the respective wavelengths are
Each of the thickness and the period varies according to the wavelength.
You. For example, the thickness is L₁= 7 μm, L _Two= 8.5 μm
Yes, the cycle is Λ₁= 0.57 μm, Λ_Two= 0.69 μm
It is. The thickness of the refractive index distribution layers 5c and 5d is substantially
If set to a proportional value, diffraction for each wavelength
Efficiency tolerances can be made equal. Refractive index distribution
The fringes 18c and 18d having the periodic structure of
It is inclined in the y-axis direction, and the inclination angle is the same for both.
Is set to 22.5 °, which is half the diffraction angle
I have.

Similarly, the second grating element 6b also has a two-layer structure of the refractive index distribution layers 6c and 6d, and the refractive index distribution layer 6c has a refractive index distribution layer 5c and a refractive index distribution layer 6d.
Are the same as the refractive index distribution layer 5d and the specifications other than the inclination angles or the inclination directions of the fringes 18e and 18f. Fringe 1
The inclination angles of 8e and 18f are half of the diffraction angle, for example, 2
It is set to 2.5 °.

By setting the angle of inclination of the fringe 18 having a two-layer structure in each grating element to the same angle, the first grating element 5b and the second
The inclination of the optical axis at each wavelength of the diffracted light to the grating element 6b can be made the same.

Laser light 2a having a wavelength λ ₁ = 0.655 μm
, The refractive index distribution layers 5c and 6c diffract light by Bragg diffraction. For example, the wavelength λ ₂ =
With respect to a laser beam having another wavelength such as 0.795 μm, the laser beam does not satisfy the Bragg diffraction condition and almost transmits the laser beam. Similarly, a laser beam 2b having a wavelength λ ₂ = 0.795 μm
, The refractive index distribution layers 5d and 6d diffract light by Bragg diffraction. For example, the wavelength λ ₁ =
With respect to a laser beam having another wavelength such as 0.655 μm, the laser beam does not satisfy the Bragg diffraction condition and functions to transmit almost.

The angle of the fringe 18 having a two-layer structure in each grating element is made slightly different, for example, from about 1 ° to about 5 °, so that unnecessary diffracted light is generated in a layer that does not correspond to each wavelength. Can be reduced.
That is, for example, referring to the first grating element 5b, the refractive index distribution layer 5c is a layer for the wavelength lambda _1, since the light passes through the other of the refractive index distribution layer 5d,
A small amount of light is diffracted by this layer. At this time, the inclination angle of the fringe 18d in the refractive index distribution layer 5d is determined by the inclination angle of the fringe 18c in the refractive index distribution layer 5c.
If slightly different, the condition tends to further deviate from the Bragg diffraction condition, so that the generation of unnecessary diffracted light is drastically reduced, and the light use efficiency is improved.

As shown in FIG. 11, the optical head according to the present embodiment is provided with a beam splitter 19 in the optical path so that the laser light 2a emitted from each of the light sources 1a and 1b,
2b is incident on the same collimator lens 3. The distance from the collimator lens 3 to the light source 1b is set to, for example, 5 mm shorter than the distance from the collimator lens 3 to the light source 1a. Thus, among the laser beam passing through the collimator lens 3, the beam corresponding to the wavelength lambda ₁ becomes parallel light beam corresponding to the wavelength lambda ₂ are a little with a slope of about up to 1.2 ° Divergent light. As a result, the focal position for the wavelength λ ₂ becomes larger in the z-axis direction than the focal position for the wavelength λ ₁ , and the optical disc 11 a
b.

Further, a doughnut-shaped multilayer film having wavelength selectivity that allows only light of wavelength λ ₁ to pass therethrough is formed around the second grating element 6 b, and a wavelength λ ₂ incident on the objective lens 4 is formed. The aperture of the light is restricted. Thus, the numerical aperture NA of the light having the wavelength λ _{2 is} substantially reduced.

Two wavelengths λ₁, Λ_TwoWith 0.60 μm ≦ λ₁
≦ 0.68 μm, 0.76 μm ≦ λ _Two≤0.87μm
If set, the first and second grating elements having a two-layer structure
Reduction of unnecessary diffracted light at other wavelengths in the elements 5b and 6b
For example, DVD, CD-R and CD discs
Can be read well.

In the present embodiment, the first transparent substrate 9 and the second transparent substrate 10 are joined and integrated via the multilayer film 12, but are not necessarily limited to this configuration. Instead, for example, as shown in FIGS. 13 and 14, the operation can be performed only by providing the air gap 23 between the first transparent base 9 and the second transparent base 10d. However, as shown in FIGS. 11 and 12, it is more preferable that the multilayer film 12 is interposed between the first transparent substrate 9 and the second transparent substrate 10 because the structure is stable.

In the present embodiment, the transparent substrate 10 having an inverted trapezoidal cross section is used as the second transparent substrate, but the present invention is not necessarily limited to this configuration. The second transparent substrate may have any shape as long as it can secure the optical path of the laser beam 2 and has a surface on which the second grating element 6 can be formed on the objective lens 4 side. 13, as shown in FIG. 14, a second transparent base 10d made of a triangular prism can be used similarly to the first transparent base 9.

In the present embodiment, of the refractive index distribution layers 5c and 5d constituting the first grating element 5b having the two-layer structure, the refractive index distribution layer 5d having a large period is the first transparent base 9 , But is not necessarily limited to this configuration. For example, FIG.
As shown in the figure, the first grating element 5 having a two-layer structure
Of the refractive index distribution layers 5c and 5d constituting b, the refractive index distribution layer 5c having a small period may be formed in contact with the first transparent base 9 (the same configuration as the second grating element 6b). If such a configuration is adopted, the first grating element 5b and the second grating element 6b can be manufactured in the same process, so that the manufacture of the first and second grating elements 5b, 6b is facilitated. .

In this embodiment, the inclination angles of the fringes 18e and 18f of the refractive index distribution layers 6c and 6d constituting the second grating element 6b having a two-layer structure are set to the same angle. It is not necessarily limited to this configuration. For example, as shown in FIG. 14, the inclination angle of the fringe 18g of the refractive index distribution layer 6f closer to the objective lens 4 among the refractive index distribution layers 6c and 6f constituting the second grating element 6e having a two-layer structure. Is gradually larger than the inclination angle of the fringe 18e of the refractive index distribution layer 6c toward the right side (for example, + 1 ° at the rightmost part with respect to the center of the refractive index distribution layer 6f), and the left side of the refractive index distribution layer 6c is The following effects can be obtained by setting the angle to be gradually smaller than the inclination angle of the fringe 18e (for example, -1 ° at the leftmost portion with respect to the center of the refractive index distribution layer 6f). That is, the second grating element 6f
, The Bragg condition is satisfied over the entire surface, and the diffraction efficiency around the second grating element 6f does not decrease, so that high efficiency can be obtained. In this case, FIG.
As shown in FIG. 3, by setting the distance from the collimator lens 3 to the light source 1a and the distance from the collimator lens 3 to the light source 1b to be the same, the beams corresponding to the wavelengths λ ₁ and λ ₂ are both parallel light. It is necessary to be.

Further, in the present embodiment, a case corresponding to two wavelengths has been described as an example. However, the present invention is not necessarily limited to this case, and a structure corresponding to three or more wavelengths is also possible. is there. In this case, the first and second grating elements are composed of a plurality of layers of volume holograms corresponding to the respective wavelengths. According to this configuration, a plurality of types of optical disks corresponding to different wavelengths can be used. In this case, it is preferable that the thickness of each of the plurality of layers of the volume hologram differs according to the wavelength. According to this preferred configuration, the allowable error of the diffraction efficiency with respect to each wavelength can be set optimally according to the optical disc corresponding thereto.

For example, if the corresponding wavelengths are three wavelengths λ ₁ , λ ₂ ,
and lambda _3, the first and the second grating element, respectively, lambda _1, lambda _2, constituted by a volume hologram three layers corresponding to lambda _3, the lambda _1, lambda _2, lambda _3, 0.38 .mu.m ≦
λ ₁ ≦ 0.52 μm, 0.60 μm ≦ λ ₂ ≦ 0.68 μ
m, 0.76 μm ≦ λ ₃ ≦ 0.87 μm,
Unnecessary diffracted light at other wavelengths in the first and second grating elements having a three-layer structure is reduced, for example, a high-density optical disk of 10 GB or more, DVD, DVD-R, C
Many optical disks such as D and CD-R can be read well.

<Fifth Embodiment> Next, a fifth embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on differences from the second embodiment.

FIG. 15 is a side view showing a basic structure of an optical head and a state of light propagation according to a fifth embodiment of the present invention. The optical system of the optical head according to the first to fourth embodiments has a configuration without beam shaping, whereas the optical system of the optical head according to the present embodiment has a configuration having a beam shaping function. .

The first grating element 5a is a transmissive element, and the first incident angle θ from the optical path changing means 14 to the first grating element 5a with respect to the normal to the first grating element 5a. ₁ is larger than the emission angle of the diffracted light from the first grating element 5a with respect to the normal to the first grating element 5a, and the second angle from the first grating element 5a to the second grating element 6 The second incident angle θ ₂ with respect to the normal to the grating element 6 is larger than the emission angle of the diffracted light from the second grating element 6 with respect to the normal to the second grating element 6. It has a configuration. In FIG. 15, the output angles of the diffracted light from the first and second grating elements 5a and 6 are 0 °. The first transparent base 9 sandwiches (via) the first grating element 5a with the second transparent base 10b on which the second grating element 6 is formed, and
It is integrated.

The laser light 2 emitted from the light source 1 is converted into parallel light by the collimator lens 3, and its beam diameter in the z-axis direction is w ₁ and its beam diameter in the x-axis direction is w ₃ (not shown).
Assuming that the beam diameter in the y-axis direction after emission from the second grating element 6 is w ₂ (the beam diameter in the x-axis direction remains w ₃ ), w ₂ / w ₁ > 1.

Generally, the light emitted from the semiconductor laser light source 1 is an elliptical beam, and it is necessary to shape the elliptical beam into a circular beam in order to increase the light use efficiency.

In the optical head of this embodiment, the laser
Since the polarization of the laser beam 2 is P-polarized,
A long beam is emitted from the light source 1. This beam is the optical path
It is bent in the -z-axis direction by the conversion means 14, and the first
For example, θ₁= 45 ° angle
Incident on the first grating element 5a.
Next-order diffracted light is emitted vertically. The beam diameter of the light at that time
Is w₁/ Cosθ₁It is expanded to. In addition, the first group
First-order diffraction emitted perpendicular to the rating element 5a
The light is totally reflected on the bottom surface of the second transparent substrate 10b,
For example, θ_TwoAt an angle of 45 °
Incident, first-order diffraction on second grating element 6
Light exits vertically. The beam diameter of the light at that time is w_Two
= W₁/ (Cos θ₁・ Cos θ_Two). An example
For example, θ₁= Θ_Two= 45 °, w _Two= 2w₁Becomes
It is twice as large. Also, θ₁= Θ_Two= 52 °
And w_Two= 2.6w₁And the ellipse emitted from the light source 1
The beam can be shaped almost perfectly circular.
θ₁, Θ_Two= ~ 52 ° is most desirable,₁= Θ
_Two= Setting from ~ 45 ° to ~ 60 ° effectively beam
Shaping can be performed to improve light use efficiency. Special
First, as shown in FIG.
Angle of the diffracted light from the element 5a, 6
Thus, beam shaping can be performed efficiently.

<Sixth Embodiment> Next, a sixth embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on the differences from the fifth embodiment.

FIG. 16 is a side view showing a basic structure of an optical head and a state of light propagation according to a sixth embodiment of the present invention. As shown in FIG. 16, in the optical head of the present embodiment, the optical axis from the light source 1 to the optical path changing means 14 is slightly inclined from the y-axis direction to the z-axis direction, for example, about 5 °. In response, the light source / photodetector unit 1
7, the collimator lens 3, and the focus / track error signal detecting element 8 are also inclined, and are configured to adjust the angle of the optical path conversion means 14 so as to reflect right below in the -z axis direction. With this arrangement, the light source
By effectively utilizing the space under the photodetector unit 17,
Since the space between the optical disk 11 and the optical components 3, 17 and the like can be increased, a margin is provided in the arrangement, and the arrangement and adjustment become easy.

<Seventh Embodiment> Next, a seventh embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on the differences from the fifth embodiment.

FIG. 17 is a side view showing a basic structure of an optical head and a state of light propagation according to a seventh embodiment of the present invention. As shown in FIG. 17, in the optical head of the present embodiment, as the second grating element 6a,
A reflective element is used, and the second grating element 6a is provided on the back surface of the second transparent base 10b. The multilayer film 12 is formed on the upper surface of the second transparent base 10b.
a is formed, and a 波長 wavelength plate 7 is provided on the upper surface of the multilayer film 12a.

By using the reflective element for the second grating element 6a, it is possible to increase the space from the first transparent base 9 to the objective lens 4, and to use an actuator (not shown) for controlling the objective lens 4. Is easy to install. The multilayer film 12a separates the light so as not to be affected by the ４ wavelength plate 7 when the light is totally reflected in the second transparent substrate 10b.

<Eighth Embodiment> Next, an eighth embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on the differences from the seventh embodiment.

FIG. 18 is a side view showing a basic structure of an optical head and a state of light propagation according to an eighth embodiment of the present invention. As shown in FIG. 18, in the optical head of the present embodiment, as the first grating element 5e,
A reflective element is used, and the first grating element 5e is provided on the slope of the second transparent base 10c. On the left upper surface of the second transparent substrate 10c, the multilayer film 1 is formed.
A first transparent base 9 is provided via 2a.

Since the first grating element 5e is a reflection type element, the first grating element 5e
Need not be provided between the first transparent substrate 9 and the second transparent substrate 10c, the structure is stabilized and the assembly is facilitated.

<Ninth Embodiment> Next, a ninth embodiment of the present invention will be described.
The optical head according to the embodiment is described with reference to FIG.
The following description focuses on the differences from the first embodiment.

FIG. 19 is a side view showing a basic configuration of an optical head and a state of light propagation according to a ninth embodiment of the present invention. As shown in FIG. 19, in the present embodiment, a flat second transparent substrate 10 is used as the second transparent substrate.
The first and second grating elements 5a and 6 are formed on the surface of the second transparent base 10e. Here, the first and second grating elements 5
Both a and 6 are transmissive elements. On the second transparent substrate 10e, a first prism formed of a triangular prism with its bottom surface facing the first grating element 5a.
Of the first transparent substrate 9 is disposed.
Are the optical path conversion means 14.

The laser light 2 converted into parallel light by the collimating lens 3 is totally reflected in the −z-axis direction by the optical path changing means 14, passes through the first grating element 5 a, and enters the second transparent base 10 e. I do. Then, the laser beam 2 incident on the second transparent base 10e is totally reflected once on the bottom surface of the second transparent base 10e, and is incident on the second grating element 6.

As described above, by using the flat second transparent substrate 10e as the second transparent substrate, it is possible to collectively cut a large number from a large glass substrate simply by cutting in the vertical direction. Therefore, the mass productivity is improved and the cost can be reduced. The first and second grating elements are both transmission type elements.
The use of the second grating elements 5a and 6 causes the same distortion when a disturbance such as a temperature change occurs. For this reason, the symmetrical shape has the effect of canceling out each other, and is characterized by being strong against disturbance. In addition, the first and second grating elements 5a and 6 are
The first and second grating elements 5a and 6 can be easily manufactured by forming them on the same surface of e.

<Tenth Embodiment> Next, an optical head according to a tenth embodiment of the present invention will be described with reference to FIG. 20, focusing on differences from the ninth embodiment.

FIG. 20 is a side view showing the basic structure of an optical head and the state of light propagation in a tenth embodiment of the present invention. As shown in FIG. 20, in the optical head of the present embodiment, a reflection plate 24 is provided on the back surface side of the flat second transparent substrate 10e via an air layer.

The laser light 2 converted into parallel light by the collimating lens 3 is totally reflected in the -z-axis direction by the optical path changing means 14, passes through the first grating element 5a, and enters the second transparent base 10e. I do. The refracted light from the second transparent substrate 10e to the air layer is reflected by the reflector 24 and enters the second grating element 6.

As described above, the reflection plate 24 is provided on the back surface side of the second transparent substrate 10e via the air layer,
The laser beam 2 that passes through the first grating element 5a and enters the second transparent base 10e is applied to the second transparent base 1
0e and the air layer, the light can be refracted at the boundary between the second transparent substrate 10e, the air layer, and the reflection plate 24.
Can be set to be smaller than the thickness of the second transparent substrate 10e in the ninth embodiment. As a result, it is possible to make the optical head thinner than the optical head of the ninth embodiment.

<Eleventh Embodiment> Next, an optical head according to an eleventh embodiment of the present invention will be described with reference to FIG.

In the first to tenth embodiments, the case where the optical path changing means is disposed between the light paths of the light source and the first grating element has been described as an example. However, the present invention is not limited to this, and a configuration in which an optical path conversion unit is disposed between the optical paths of the second grating element and the objective lens may be used.

FIG. 21 is a side view showing the basic structure of an optical head having this structure and how light propagates. As shown in FIG. 21, in the optical head of the present embodiment, an optical disk 1 such as a DVD or a CD as a recording medium is
In the optical path up to 1, a first grating element 5f,
The second grating element 6f and the optical path changing means 20 are arranged. Light source 1 and photodetectors 13a, 13b
Are integrated in the light source / photodetector unit 17. Here, the first and second grating elements 5f,
6f is a transmissive element.

Between the optical path between the light source 1 and the first grating element 5f, a collimating lens 3 for converting the laser light 2 emitted from the light source 1 in the y-axis direction into parallel light, and a focus / track error signal detecting element 8 And are arranged. Here, the focus / track error signal detecting element 8 is composed of, for example, a resin substrate or a glass substrate and a hologram element formed on the surface thereof, and is integrated with the surface of the first grating element 5f. I have. The second grating element 6f is arranged in parallel with the first grating element 5f and shifted in the -z-axis direction. The optical path changing means 20 composed of a rising mirror is disposed at an angle of 45 ° with respect to the second grating element 6f.
Is reflected in the z-axis direction and guided to the objective lens 4.

For example, the wavelength λ = 0.65 of S-polarized light emitted from the semiconductor laser as the light source 1 in the y-axis direction, for example.
The 5 μm laser light 2 is converted into parallel light having a beam diameter of 2.8 mm by the collimating lens 3,
Transmission through the track error signal detection element 8 (using the 0th-order diffracted light)
Then, the light enters the first grating element 5f. Thereafter, for example, the first-order diffracted light transmitted and diffracted at an angle of 45 ° is:
The light is incident on the second grating element 6f at an angle of 45 °. Next, for example, the first-order diffracted light diffracted in the y-axis direction at an angle of 45 ° is reflected in the z-axis direction by the optical path conversion unit 20 and is collected on the optical disc 11 by the objective lens 4.

The laser light 2 reflected by the optical disk 11 is turned back in the opposite direction, passes through the objective lens 4, the optical path changing means 20, the second grating element 6f, and the first grating element 5f in this order, and returns to the -y axis. The optical path is directed in the direction, divided by the focus / track error signal detection element 8 (using the first-order diffracted light), and
3b.

According to the configuration of the optical head of the present embodiment, the optical axis of the laser beam 2 emitted from the light source 1 can be shifted in the −z-axis direction, that is, in the direction opposite to the optical disk 11. As a result, it is possible to increase the installation space for the objective lens 4 and to easily attach an actuator (not shown) for controlling the objective lens 4.

<Twelfth Embodiment> An optical head according to a twelfth embodiment of the present invention will be described with reference to FIG.

FIG. 22 is a side view showing the basic structure of an optical head and light propagation in a twelfth embodiment of the present invention. As shown in FIG. 22, the optical head according to the present embodiment includes a light source 1 that emits a light beam 2 in a first direction (y-axis direction) and a light beam 2 in the first direction in a second direction (obliquely). A first deflecting unit 21 such as a prism, for example, which deflects to the lower left), and a light beam 2 deflected by the first deflecting unit 21
A second deflecting means 22a such as a mirror, for example, and an objective lens 4 for converging the light flux 2 deflected by the second deflecting means 22a on the optical disk 11. I have it. Third direction is substantially perpendicular to the recording surface of the optical disk 11, the third dimension lz the second deflection means 22a, from the dimensions w ₁ of the light beam 2 in the first direction the third direction Is also small. First deflecting means 2
As 1, for example, a triangular prism is used,
In the optical path from the light source 1 to the first deflecting means 21, a collimator lens 3 and a focus / track error signal detecting element 8 are further provided.

In the configuration of the conventional optical head, w ₁ ≦ lz
However, in the optical head of this embodiment, the laser light 2 emitted from the light source 1 is deflected obliquely downward (second direction) by the first deflecting means 21. Therefore, the angle of incidence on the second deflecting means 22a can be inclined from the y-axis direction, the height lz occupying the lower part of the objective lens 4 is reduced (w ₁ > lz), and the height of the optical head is reduced. Can be reduced.

<Thirteenth Embodiment> An optical head according to a thirteenth embodiment of the present invention will be described with reference to FIG. 23, focusing on differences from the twelfth embodiment.

FIG. 23 is a side view showing a basic structure of an optical head and a state of light propagation according to a thirteenth embodiment of the present invention. As shown in FIG. 23, in the optical head of the present embodiment, a reflective grating element is used as the second deflecting means 22b, and the second deflecting means 22b is parallel to the optical disc 11 (y (Parallel to the axial direction). By providing the second deflecting means 22b in parallel with the optical disk 11, the second deflecting means 2b is provided.
The thickness lz in the z direction of 2b is set to a minimum value, for example, 0.3 mm
Can be made thinner than the optical head of the ninth embodiment.

The optical heads according to the first to thirteenth embodiments of the present invention have been described above. In addition to the optical heads according to these embodiments, optical heads obtained by combining the configurations of the respective optical heads are also included. Of course, it is possible and has the same effect. Note that the objective lens and the collimator lens used in the description of the embodiments are named for convenience, and are the same as generally used lenses.

[0106]

As described above, according to the present invention,
It is possible to realize a thin optical head.

[Brief description of the drawings]

FIG. 1 is a side view showing a basic configuration of an optical head and a state of light propagation according to a first embodiment of the present invention.

FIG. 2A is a plan view showing a first or second grating element in the optical head according to the first embodiment of the present invention, and FIG. 2B is an optical head according to the first embodiment of the present invention; FIG. 3 is a side view showing a configuration of a central portion and details of first and second grating elements in FIG.

FIG. 3 is a diagram showing a relationship between first-order diffraction efficiencies of first and second grating elements in the optical head according to the first embodiment of the present invention and an amplitude Δn of a refractive index change amount.

FIG. 4 is a side view illustrating the behavior of diffracted light from the first and second grating elements when the wavelength of incident light fluctuates in the optical head according to the first embodiment of the present invention.

FIG. 5 is a side view showing a basic configuration of another optical head and a state of light propagation according to the first embodiment of the present invention.

FIG. 6 is a side view showing a basic configuration of still another optical head and a state of light propagation according to the first embodiment of the present invention.

FIG. 7 is a side view showing a basic configuration of an optical head and a state of light propagation according to a second embodiment of the present invention.

FIG. 8 is a diagram illustrating a relationship between first-order diffraction efficiencies of first and second grating elements and an amplitude Δn of a refractive index change amount in an optical head according to a second embodiment of the present invention.

FIG. 9 is a side view showing a basic configuration of an optical head and a state of light propagation according to a third embodiment of the present invention.

FIG. 10 is a side view showing a basic configuration of another optical head and a state of light propagation according to a third embodiment of the present invention.

FIG. 11A is a side view showing a basic configuration of an optical head and a state of light propagation according to a fourth embodiment of the present invention;
(B) is a plan view thereof.

FIG. 12 is a side view showing a configuration of a central portion and details of first and second grating elements in an optical head according to a fourth embodiment of the present invention.

FIG. 13A is a side view showing a basic configuration of another optical head and a state of light propagation according to a fourth embodiment of the present invention, and FIG. 13B is a plan view thereof.

FIG. 14 is a side view showing a configuration of a central portion and details of first and second grating elements in another optical head according to the fourth embodiment of the present invention.

FIG. 15 is a side view showing a basic configuration of an optical head and a state of light propagation according to a fifth embodiment of the present invention.

FIG. 16 is a side view showing a basic configuration of an optical head and a state of light propagation according to a sixth embodiment of the present invention.

FIG. 17 is a side view showing a basic configuration of an optical head and a state of light propagation according to a seventh embodiment of the present invention.

FIG. 18 is a side view showing a basic configuration of an optical head and a state of light propagation according to an eighth embodiment of the present invention.

FIG. 19 is a side view showing a basic configuration of an optical head and a state of light propagation according to a ninth embodiment of the present invention.

FIG. 20 is a side view showing a basic configuration of an optical head and a state of light propagation according to a tenth embodiment of the present invention.

FIG. 21 is a side view showing a basic configuration of an optical head and a state of light propagation in an eleventh embodiment of the present invention.

FIG. 22 is a side view showing a basic configuration of an optical head and a state of light propagation according to a twelfth embodiment of the present invention.

FIG. 23 is a side view showing a basic configuration of an optical head and a state of light propagation in a thirteenth embodiment of the present invention.

FIG. 24 is a side view showing a configuration of a conventional optical head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Laser beam 3 Collimator lens 4 Objective lens 5 1st grating element 6 2nd grating element 7 1/4 wavelength plate 8 Focus / track error signal detection element 9 1st transparent base 10 2nd transparent base 11 Optical disc 12 Multilayer film 13 Photodetector 14 Optical path conversion means (first surface of first transparent base) 15 Refractive index distribution layer 16 Reflective film 17 Light source / photodetector unit 18 Fringe 19 Beam splitter 20 Start-up mirror (optical path conversion) Means) 21 First deflecting means 22 Second deflecting means 23 Air gap 24 Reflector

Claims (36)

[Claims] A first grating element disposed in an optical path from a light source to an objective lens, and an optical path between the light source and the first grating element or the second grating element. An optical path conversion means disposed between the optical path with the objective lens. 2. An optical path changing means is disposed between an optical path between a light source and a first grating element, and light emitted from the light source enters the first grating element via the optical path changing means, and Diffracted light from the first grating element is incident on the second grating element, and the second
2. The optical head according to claim 1, wherein the diffracted light from the grating element is incident on the objective lens and focused on the recording medium. 3. The change due to the wavelength change of the optical axis of the diffracted light from the first grating element is at least partially offset from the change in the optical axis of the diffracted light from the second grating element. Item 2. The optical head according to item 1. 4. The first grating element is a reflection type element, the optical path changing means is a first transparent base having a first surface, and the first grating element and the optical path changing means are provided by a light source. The angle between the optical axis of the outgoing light and the normal to the first surface is greater than or equal to the critical angle, and the angle between the normal to the first surface and the first grating element to the second grating element The light emitted from the light source is reflected by the first surface and enters the first grating element, and the first light is emitted from the light source. 3. The optical head according to claim 2, wherein the diffracted light reflected from the grating element is transmitted through the first surface and is incident on the second grating element. 5. The optical head according to claim 1, wherein the first grating element and the second grating element are linear gratings having the same period and a uniform period. 6. The optical head according to claim 1, wherein the first grating element and the second grating element are volume holograms having a periodic structure of a refractive index distribution. 7. The optical head according to claim 6, wherein the polarization of the light incident on the volume hologram is S-polarized light in both the forward path and the return path. 8. A polarization focus / track error signal detecting element is further provided, and the amplitude of the refractive index change amount of the volume hologram is maximized by the product of the first-order diffraction efficiency for S-polarized light and the first-order diffraction efficiency for P-polarized light. The optical head according to claim 6, wherein the optical head is set to the following value. 9. A first transparent substrate is a triangular prism having a slope, a bottom surface, and side surfaces, wherein the slope surface is a first surface, and a first grating element is provided on the bottom surface,
The optical head according to claim 4, wherein light emitted from a light source is incident on the first transparent base from the side surface. 10. The second grating element is a transmission type element, further comprising a second transparent substrate having the second grating element formed on an upper surface thereof, wherein a multilayer is provided on the first surface of the first transparent substrate. The optical head according to claim 9, wherein a film is formed, and the first transparent substrate and the second transparent substrate are integrated via the multilayer film. 11. The second grating element is a transmissive element, further comprising a second transparent substrate having the second grating element formed on an upper surface thereof, wherein the first transparent substrate and the second transparent substrate are provided. The optical head according to claim 9, wherein an air gap is interposed between the optical head and the base. 12. The second grating element is a transmissive element, further comprising a second transparent substrate having the second grating element formed on an upper surface thereof, wherein the second transparent substrate is a triangular prism. The optical head according to claim 9. 13. The optical device according to claim 1, further comprising a polarization focus / track error signal detection element, and a quarter-wave plate provided in an optical path from the second grating element to the objective lens. head. 14. The second grating element is a reflection-type element, further comprising a second transparent substrate having the second grating element formed on a bottom surface, and a multilayer on the first surface of the first transparent substrate. A film is formed, the first transparent substrate and the second transparent substrate are integrated via the multilayer film, and the first and second grating elements are arranged on the same plane. 10. The optical head according to 9. 15. The optical head according to claim 1, wherein the diffraction angles of the first and second grating elements are 45 ° or more. 16. The optical head according to claim 1, wherein the first and second grating elements are provided on the same transparent substrate. 17. The optical head according to claim 16, wherein the first and second grating elements are provided on the same surface of the same transparent substrate. 18. The optical head according to claim 17, wherein the first and second grating elements are provided on the same transparent substrate. 19. A triangular prism is arranged on a transparent substrate with a bottom surface facing the first grating element,
2. The slope of the triangular prism is an optical path changing means.
9. The optical head according to 8. 20. A reflection plate is provided on the rear surface side of the transparent substrate via an air layer, and refracted light from the transparent substrate to the air layer is reflected by the reflection plate and enters the second grating element. Item 19. The optical head according to Item 18. 21. The optical head according to claim 1, wherein the second grating element is an optical element that converts parallel light into divergent light or converts divergent light into parallel light. 22. The optical head according to claim 1, wherein each of the first and second grating elements comprises a plurality of layers of volume holograms corresponding to different wavelengths. 23. The volume hologram having a plurality of layers, each of which has a different thickness corresponding to a wavelength.
An optical head according to item 1. 24. The optical head according to claim 23, wherein the thickness of each of the plurality of volume holograms is substantially proportional to the wavelength. 25. The optical head according to claim 22, wherein the volume holograms having a plurality of layers have different fringe inclination angles of a periodic structure having respective refractive index distributions. 26. The optical head according to claim 22, wherein the plurality of volume holograms have the same fringe inclination angle in the periodic structure of the respective refractive index distributions. 27. The different wavelengths are two wavelengths λ ₁ and λ ₂ , and the first and second grating elements are respectively
The two wavelengths lambda _1, made from the volume hologram of the two layers corresponding to lambda _2, the two wavelengths lambda _1, lambda ₂ is, 0.60Myu
m ≦ λ ₁ ≦ 0.68 μm, 0.76 μm ≦ λ ₂ ≦ 0.8
The optical head according to claim 22, which is 7 µm. 28. The different wavelengths having three wavelengths λ ₁ , λ ₂ , λ
₃ , the first and second grating elements are each composed of a three-layer volume hologram corresponding to the three wavelengths λ ₁ , λ ₂ , λ ₃ , and the three wavelengths λ ₁ , λ ₂ ,
λ ₃ is 0.38 μm ≦ λ ₁ ≦ 0.52 μm, 0.60
μm ≦ λ ₂ ≦ 0.68 μm, 0.76 μm ≦ λ ₃ ≦ 0.
The optical head according to claim 22, which has a thickness of 87 µm. 29. A first angle of incidence from the optical path converting means to the first grating element based on a normal to the first grating element, wherein the first angle of incidence is based on a normal to the first grating element. A second angle of incidence, which is larger than the angle of emergence of the diffracted light from the first grating element and from the first grating element to the second grating element with respect to a normal to the second grating element. 3. The optical head according to claim 2, wherein the angle is larger than an emission angle of diffracted light from the second grating element with respect to a normal to the second grating element. 30. The optical head according to claim 29, wherein an outgoing angle of the diffracted light from the first and second grating elements is substantially 0 °. 31. A semiconductor device further comprising a first transparent substrate, and a second transparent substrate having a second grating element formed on an upper surface or a lower surface, wherein the first transparent substrate and the second transparent substrate are provided. 30. The optical head according to claim 29, wherein the optical head is integrated via a first grating element. 32. The first and second angles of incidence are between 45 ° and 6 °.
The optical head according to claim 29, wherein the angle is 0 °. 33. A light source that emits a light beam in a first direction;
A first deflecting unit for deflecting the light beam in the first direction in a second direction, a second deflecting unit for deflecting the light beam deflected by the first deflecting device in a third direction, An objective lens that converges the light beam deflected by the second deflecting means onto an optical recording medium, wherein the third direction is substantially perpendicular to the recording surface of the optical recording medium, and 3 is the third direction of the light flux in the first direction.
Optical head smaller than the dimension in the direction of. 34. The optical head according to claim 33, wherein the first deflecting means is a triangular prism. 35. The optical head according to claim 33, wherein the second deflecting means is a reflective grating element. 36. The optical head according to claim 33, wherein the second deflecting means is a mirror.