JPH09330531A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device, which can achieve the compact configuration, light weight and the simplification of the adjusting work of an optical element at the time of mounting, by using the complex optical element having the optical action of a 1/4 wavelength substrate. SOLUTION: In a complex optical element 10, a slant deposition film 11 is formed on a light passing surface 121 positioned on the upper surface of a polarization beam splitter 12. This slant deposition film 11 is the film, on which the inorganic material such as Ta2 , O5 , WO3 , Bi2 O3 , TiO2 or the like is deposited from the slant direction for the normal direction H of the light passing surface 121 and has the double refraction action. Therefore, this device using the complex optical element 10 constitutes the device, wherein the different 1/4 wavelength plate is omitted substantially. Thus, this device has the compact configuration and the light weight by that amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for recording / reproducing information on / from an optical recording medium. More specifically, it relates to an optical pickup device using a composite optical element in which a quarter-wave plate and other optical elements are integrated.

[0002]

2. Description of the Related Art In an optical pickup device for reproducing recorded information from an optical recording medium such as a compact disk (CD), a laser beam emitted from a light source and reflected light from the optical recording medium are used efficiently. Various optical elements have been devised such that the polarization planes of the laser beam and the reflected light are changed, or only the light having a predetermined polarization plane is transmitted. For example, in the optical pickup device 50 shown in FIG. 5, the lens 22, the mirror 23, the polarization beam splitter 54, the quarter wavelength plate 55, and the objective lens 26 are arranged on the optical path from the semiconductor laser 21 to the optical recording medium 27. Then, the laser beam emitted from the semiconductor laser 21 through these optical elements is focused on the optical recording medium 27. The reflected light from the optical recording medium 27 is incident on the polarization beam splitter 54 via the objective lens 26 and the quarter-wave plate 55. During this period, the laser light passes through the quarter-wave plate 55 twice, so that λ / 2
The plane of polarization rotates by π / 2 as if it had passed through the plate once. Therefore, all the reflected light from the optical recording medium 27 is reflected by the polarization beam splitter 54, and the photodetector 2
The light is received at 8.

In constructing such an optical pickup device 50, conventionally, a single crystal of quartz having birefringence, which is formed into a thin plate and is attached to a glass substrate, is used as a quarter wavelength plate 55. .

[0004]

However, as in the conventional case, a quarter of a crystal single crystal is attached to a glass substrate.
Since the wave plate 55 itself has a considerable thickness and weight, there is a problem in that the optical pickup device 50 cannot be made smaller and lighter. Further, when mounting the quarter-wave plate 55 and the polarization beam splitter 54 on the optical pickup device 50, it is necessary to adjust the mounting states of these optical elements according to the polarization direction of the laser. There is a problem that it takes time and effort.

[0005] In view of the above problems, an object of the present invention is to provide:
An object of the present invention is to provide an optical pickup device that can reduce the size and weight and can simplify the adjustment work of an optical element at the time of mounting by using a composite optical element having an optical function of a quarter-wave plate. .

[0006]

In order to solve the above problems, the present invention has at least a light source and a photodetector for detecting light emitted from the light source and reflected from an optical recording medium, On the optical path from the light source to the photodetector, a first optical element having an optical function as a quarter-wave plate and a second optical element having an optical function different from the first optical element. In the optical pickup device in which and are arranged, the first optical element is composed of a vapor deposition film that has a birefringence effect by vapor deposition from an oblique direction with respect to the light passage surface of the second optical element. It is characterized by being.

In the present invention, tantalum pentoxide (Ta ₂ O ₅ ), tungsten oxide (WO ₃ ), and bismuth trioxide (Bi ₂ O) are obliquely provided with respect to the light passage surface of the second optical element.
₃ ), titanium oxide (TiO ₂ ) or the like is vapor-deposited, the oblique vapor deposition film has an optical function as a quarter-wave plate.
That is, only by forming such an oblique vapor deposition film on the light passage surface of the second optical element, 1 /
A first optical element having an optical function as a four-wave plate can be added. Therefore, it is not only necessary to mount two optical elements on the optical pickup device,
Since it is not necessary to use a four-wave plate, the optical pickup device of the present invention is small and lightweight.

Further, when two separate optical elements are mounted on the optical pickup device, it is necessary to adjust the mounting state for each of them, whereas in the optical pickup device of the present invention, two optical elements are mounted. Since the mounting state of the element can be adjusted at once, the adjustment work can be simplified.

In the optical pickup device of the present invention, the second optical element is, for example, a hologram optical element,
It is a polarization beam splitter, a reflection mirror, or an objective lens. For example, in an optical pickup device for an optical recording medium such as a CD, a polarization beam splitter and a quarter wave plate which are separately configured are conventionally used, but the polarization beam splitter is used as a second optical element. If the above-mentioned oblique vapor deposition film is formed on the light passage surface, 1
It is possible to obtain a polarization beam splitter (composite optical element) to which a / 4 wavelength plate is added. Therefore, even when the polarization beam splitter and the quarter-wave plate are mounted on the optical pickup device, the polarization beam splitter to which the quarter-wave plate is added may be mounted, so that the size and weight of the optical pickup device can be reduced. Can be realized. Moreover, in the optical pickup device, when the mounting state of the quarter-wave plate or the polarization beam splitter is aligned with the polarization plane of the laser in the polarization direction of the laser, it is only necessary to adjust the polarization beam splitter (composite optical element). The adjustment work can be simplified.

In the optical pickup device of the present invention, from the viewpoint of improving the light utilization efficiency, the light passage surface on the first optical element side, the light passage surface on the second optical element side, or the first optical element side. It is preferable to form an antireflection film on at least one of the boundary surfaces between the optical element and the second optical element.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical pickup device according to the present invention will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 is a diagram showing a schematic configuration of an optical pickup device according to the present invention.

In FIG. 1, an optical pickup device 20 of this example is an optical pickup device for an optical recording medium such as a CD, and collects a laser beam emitted from a semiconductor laser 21 which is a light source on an optical recording medium 27. It can be divided into a forward path for performing the operation and a return path for guiding the reflected light from the optical recording medium 27 to a photodetector 28 such as a photodiode for photodetection.

On the outward path, a lens 22, a mirror 23, a composite optical element 10, and an objective lens 26 are arranged in this order from the semiconductor laser 21 toward the optical recording medium 27.
Here, the composite optical element 10 is a vapor deposition film 1 having an optical function as a polarization beam splitter 12 and a quarter-wave plate.
And 1. Therefore, when the laser beam emitted from the semiconductor laser 21 passes through the polarization beam splitter 12 of the composite optical element 10 and then passes through the oblique vapor deposition film 11 having an optical function as a quarter wavelength plate, Almost all of the light is converted from linearly polarized light into circularly polarized light by the composite optical element 10, and then is condensed on the optical recording medium 27 via the objective lens 26. The focused laser beam is reflected while being subjected to intensity modulation based on the data recorded on the optical recording medium 27, and is guided to the return path.

On the return path, the objective lens 26 and the composite optical element 10 are arranged in this order toward the photodetector 28. The reflected light from the optical recording medium 27 is reflected by the objective lens 26.
It is incident on the composite optical element 10 via. Composite optical element 1
Almost all of the reflected light incident on 0 is converted from circularly polarized light to linearly polarized light when passing through the obliquely evaporated film 11 having an optical function as a quarter-wave plate. During this time, the laser beam has passed twice through the obliquely vapor-deposited film 11 having an optical function as a quarter-wave plate, so that the plane of polarization of this linearly polarized light is the polarization of the laser beam emitted from the semiconductor laser 21. It is offset by 90 ° from the surface. For this reason,
Almost all of the linearly polarized light is reflected by the optical function of the polarization beam splitter 12 of the composite optical element 10 and guided to the photodetector 28. Therefore, the data recorded on the optical recording medium 27 can be reproduced based on the detection result of the photodetector 28.

(Structure of Composite Optical Element) A composite optical element used in the optical pickup device to which the present invention is applied will be described with reference to FIG.

FIG. 2A is an explanatory view showing the composite optical element of this example, and FIG. 2B is an explanatory view schematically showing the structure of the obliquely deposited film formed on this composite optical element.

As shown in FIG. 2A, in the composite optical element 10 of this example, the polarization beam splitter 12 (second optical element) functions as a quarter-wave plate (first optical element). It has been added. In FIG. 2A, when the polarization beam splitter 12 is represented by a prismatic optical element, the lower surface, the upper surface, and the side surface thereof are respectively light passing surfaces 122,
The polarization splitting film 120 is formed so as to form 121 and 123.

In this example, of the light passage surfaces 122, 121, 123 of the polarization beam splitter 12, the light passage surface 121 on the upper surface side has an oblique vapor deposition functioning as a quarter-wave plate (first optical element). The film 11 is formed.

As shown in FIG. 2 (b), the obliquely vapor-deposited film 11 forms a predetermined angle with respect to the light-passing surface 121 of the polarization beam splitter 12 with respect to the normal direction H thereof in the direction of arrow A. It is a vapor deposition film composed of an inorganic substance such as tantalum pentoxide, tungsten oxide, bismuth trioxide, titanium oxide, etc. Since the obliquely evaporated film 11 thus formed has a birefringence effect, in this example, the angle formed by the normal direction H and the evaporation direction A, that is, the normal direction H
And the crystal axis of the obliquely deposited film 11 is, for example, θ =
The angle is set to 70 ° and the film thickness is adjusted so that the obliquely vapor-deposited film 11 has an optical function as a quarter wavelength plate. At this time, the crystal optical axis of the vapor deposition film 11 is formed at 45 ° with respect to the polarization direction of light.

In the composite optical element 10 thus constructed, in the polarization beam splitter 12, when linearly polarized light having a polarization plane in a predetermined direction enters from the light passage surface 122 located on the lower surface side, the polarization beam splitter 12 Splitter 1
2 transmits almost all the light and emits it from the light passage surface 121 located on the upper surface side. However, the light polarized in the direction perpendicular to this direction is not reflected by the polarization beam splitter 1.
When incident from the light passing surface 121 located on the upper surface side of 2,
Almost all of this light is reflected by the polarization separation film 120 and is emitted from the light passage surface 123 located on the side surface thereof.

In the obliquely vapor-deposited film 11 having a function as a quarter-wave plate, for example, when linearly polarized light passes, one polarized component is delayed by one quarter wavelength with respect to the other, and circularly polarized light is emitted. Is converted to. Conversely, when circularly polarized light passes through the obliquely evaporated film 11, it becomes linearly polarized light.

As described above, the composite optical element 10 of this example is
Although it is one optical element, it has a function that has both an optical action as a quarter-wave plate and an optical action as a polarization beam splitter.

Further, in this example, in order to improve the light utilization efficiency, the surface of the obliquely vapor-deposited film 11 constituting the composite optical element 10 and the light passage surface 1 of the polarization beam splitter 12 are formed.
An antireflection film may be formed on the boundary surface (light passage surface 121) of the polarized beam splitter 12 and the obliquely evaporated film 11, 22, 123.

Thus, the optical pickup device 2 of this example
0, the composite optical element 10 is arranged in such a manner that the light passing surface 121 of the polarization beam splitter 12 is Ta ₂ O ₅ , W ₂ from an oblique direction.
Inorganic substances such as O ₃ , Bi ₂ O ₃ and TiO ₂ are vapor-deposited, and the oblique vapor-deposited film 11 is used as it is as a quarter-wave plate.
It is cheaper than a four-wave plate. In addition, the composite optical element 1
Compared with a combination of a separate 1/4 wave plate and a polarization beam splitter, 0 can substantially omit the 1/4 wave plate, and is small and lightweight. Therefore, the optical pickup device 20 of this example is small and lightweight because the quarter-wave plate is substantially omitted.

Further, in the optical pickup device 20 of this example, it is not necessary to individually adjust the mounting states of the polarization beam splitter and λ / 4 so as to match the polarization direction of the laser beam, and the composite optical element 10 as a whole is The mounting state may be adjusted so as to match the polarization direction of the laser beam. Therefore, in the optical pickup device 20 of this example, the adjustment work is easy.

[Embodiment 2] FIG. 3 is a composite optical system using an objective lens as a second optical element forming a first optical element (oblique vapor deposition film) having an optical function as a quarter-wave plate. It is explanatory drawing which shows an element. In the composite optical element shown in FIG. 3, the oblique vapor deposition film formed on each light passage surface is the same as the oblique vapor deposition film 11 described in Example 1 with reference to FIG. Common parts are given the same reference numerals, and detailed description thereof will be omitted.

First, as shown in FIG. 3, the composite optical element 1
0a has the oblique vapor deposition film 11 formed on the light passage surface 131 having the larger radius of curvature, of the two light passage surfaces 131 and 132 of the objective lens 13 (convex lens) which is the second optical element. . The vapor-deposited film 11 is formed of Ta ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , TiO, as in the composite optical element according to the first embodiment.
An inorganic substance such as _{2 is} vapor-deposited from an oblique direction and has an optical function as a quarter wavelength plate (first optical element).

The composite optical element 10a thus constructed
In addition, even if the inorganic substance such as Ta ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and TiO ₂ is vapor-deposited on the light passage surface 131 of the objective lens 13 from the oblique direction, the objective lens 13 has an optical function as a convex lens. Since it can have an optical function as a quarter-wave plate, it is cheaper than manufacturing an objective lens and a quarter-wave plate in which a single crystal of quartz is attached to a glass substrate. In addition, the composite optical element 10a
Is used, the quarter wave plate is substantially omitted. That is, as seen from the conventional optical pickup device shown in FIG. 5, the quarter-wave plate 55 and the objective lens 26 are replaced with the composite optical element 10a of the present example.
Therefore, the optical pickup device using the composite optical element 10a is small and lightweight. Further, in the optical pickup device using the composite optical element 10a of this example, it is not necessary to individually adjust the mounting state of the objective lens and λ / 4 so as to match the polarization direction of the laser beam, and the composite optical element 1
The mounting state of 0a may be adjusted so as to match the polarization direction of the laser beam. Therefore, in the optical pickup device using the composite optical element 10a, the adjustment work can be simplified.

Also in this example, in order to improve the light utilization efficiency, the surface of the obliquely deposited film 11 constituting the composite optical element 10a, the light passing surface 132 of the objective lens 13, or the obliquely deposited film 11 and the objective. An antireflection film may be formed on the boundary surface (light passage surface 131) with the lens 13.

[Embodiment 3] FIG. 4 shows a composite using a hologram optical element as a second optical element forming a first optical element (oblique vapor deposition film) having an optical function as a quarter-wave plate. It is explanatory drawing which shows an optical element. In the composite optical element shown in FIG. 4 as well, the obliquely evaporated film formed on the light passage surface is the same as the obliquely evaporated film 11 described in Example 1 with reference to FIG. Detailed description thereof will be omitted.

As shown in FIG. 4, in the composite optical element 10b, the hologram optical element 14 is used as the second optical element, and of the light passage surfaces 141, 142, the flat light passage surface 141 is obliquely vapor-deposited. A film 11 is formed. Similar to the composite optical element 10 according to the example 1, the obliquely vapor-deposited film 11 has an inorganic substance such as Ta ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , and TiO ₂ vapor-deposited from an oblique direction, and has an approximately ¼ wavelength plate. (First
Optical element) has an optical function.

The composite optical element 10b thus constructed
In the case of Ta, the light passing surface 141 is obliquely attached to Ta.
_The hologram optical element 14 can have an optical function as a quarter-wave plate only by depositing an inorganic substance such as ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , or TiO ₂ . Therefore, 1 /
In an optical pickup device using a four-wave plate and a holographic optical element having a polarization property, when a different diffraction is performed between a forward path and a backward path of a laser beam, a quarter-wave plate and a hologram optical element which are separately configured. Since it is not necessary to use a device, the quarter wave plate can be substantially omitted.

That is, in the optical pickup device 20a shown in FIG. 4B, the composite optical element 10b is arranged between the semiconductor laser 21 as a light source and the reflection mirror 23 with the vapor deposition film 11 side facing the reflection mirror 23 side. Are arranged. However, the film thickness of the vapor deposition film 11 is set so as to deviate by 90 ° from the polarization plane of the laser beam emitted from the semiconductor laser 21 when the laser beam passes twice. Therefore, the laser beam emitted from the semiconductor laser 21 enters the reflection mirror 23 without being diffracted, and the reflected light from the optical recording medium 27 passes through the vapor deposition film 11 and the polarization plane of the laser beam emitted from the semiconductor laser 21. Since it is deviated by 90 ° compared to, the holographic optical element diffracts the ± first-order light and guides it to the two photodetectors 28.

As described above, the optical pickup device 20a using the composite optical element 10b is small and lightweight because the quarter wave plate is omitted. Further, in the optical pickup device 20a using the composite optical element 10b, it is not necessary to individually adjust the mounting states of the quarter-wave plate and the hologram optical element, and the mounting state of the composite optical element 10b can be changed in the polarization direction of the laser beam. You can adjust it to suit. Therefore, in the optical pickup device using the composite optical element 10b, the adjustment work can be simplified.

Also in this example, in order to improve the light utilization efficiency, the surface of the obliquely vapor-deposited film 11 forming the composite optical element 10b or the boundary surface between the obliquely vapor-deposited film 11 and the hologram optical element 14 (light An antireflection film may be formed on the passage surface 141).

[Other Embodiments] In an optical pickup device having a quarter-wave plate and a reflection mirror on the optical path from the light source to the photodetector, an oblique vapor deposition film is formed on the reflection surface (light passage surface) of the reflection mirror. You may form the quarter wave plate which becomes. In this case, in order to improve the light utilization efficiency, an antireflection film may be formed on the surface of the obliquely evaporated film or on the boundary surface between the obliquely evaporated film and the reflection mirror.

[0038]

As described above, in the optical pickup device of the present invention, the oblique vapor deposition film is formed on the light passage surface of the optical element so that the optical element functions as a quarter wavelength plate. It is characterized in that the added composite optical element is used. Therefore, it is not necessary to mount two optical elements on the optical pickup device, and it is not necessary to use a separate quarter-wave plate, so that the optical pickup device can be made smaller and lighter. it can. Also,
When two separate optical elements are mounted on the optical pickup device, the mounting state of each of them needs to be adjusted. On the other hand, in the optical pickup device to which the present invention is applied, the mounting state of the two optical elements is adjusted. Since the adjustment can be performed at once, the adjustment work can be simplified.

[Brief description of drawings]

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

FIG. 2A is a perspective view of a composite optical element used in an optical pickup device according to the present invention, in which a polarization beam splitter is provided with an optical function as a quarter-wave plate, and FIG. FIG. 4 is an explanatory view showing an enlarged structure of a vapor deposition film formed on a polarization beam splitter.

FIG. 3 is an explanatory diagram of a composite optical element used in the optical pickup device according to the present invention, in which an objective lens is provided with an optical function as a quarter-wave plate.

FIG. 4 is an explanatory diagram of a composite optical element used in the optical pickup device according to the present invention, in which a hologram optical element is provided with an optical function as a quarter wavelength plate.

FIG. 5 is a schematic configuration diagram of a conventional optical pickup device.

[Explanation of symbols]

 10, 10a, 10b Composite optical element 11 Evaporated film 12 Polarizing beam splitter 121, 131, 141 Light passing surface 13 Objective lens 14 Hologram optical element 20 Optical pickup device 21 Semiconductor laser 21 27 Optical recording medium 28 Photodetector

Claims (3)

[Claims] 1. A light source and at least a photodetector for detecting light emitted from the light source and reflected from an optical recording medium, and 1 is provided on an optical path from the light source to the photodetector. In an optical pickup device in which a first optical element having an optical function as a quarter-wave plate and a second optical element having an optical function different from that of the first optical element are arranged, the first optical element The optical pickup device is characterized in that the element is composed of a vapor deposition film having a birefringence effect by vapor deposition from an oblique direction with respect to the light passage surface of the second optical element. 2. The optical pickup device according to claim 1, wherein the second optical element is any one of a hologram optical element, a polarization beam splitter, a reflection mirror, and an objective lens. . 3. The light passing surface on the side of the first optical element, the light passing surface on the side of the second optical element, and the first optical element and the second optical element according to claim 1. An optical pickup device characterized in that an antireflection film is formed on any one of the boundary surfaces between and.