JPS63292432A - Optical pickup device - Google Patents

Abstract

PURPOSE:To correctly separate an incident beam and a reflected beam by providing a total reflection optical element and having a dielectric film on the whole surface of a glass substrate, on an optical path of a light beam genera tion source and a photodetecting part and an objective lens. CONSTITUTION:A reflected laser light beam from a disk D passes through an objective lens 6 and converted to a parallel luminous flux, and made incident on a total reflection prism 21. In the total reflection prism 21, the reflected laser light beam in the optical axis direction Ib is brought to a total reflection by a surface 22a side on which a dielectric film 23 is provided and which has an incident angle of 45 deg., the optical axis direction is denoted as Ia, and also, a P polarization component and an S polarization component of an orthogonal polarization component come to further have a phase difference by pi/2, and said beam is converted to a linearly polarized light from a circularly polarized light and made incident on a polarized light beam splitter 3 through a collimator lens 4, separated from the laser light beam from a beam generation source 1 reflected by an analyzer surface 3a and led to a photodetecting part 8.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Field of industrial application B. Overview of the invention C. Prior art D. Problem to be solved by the invention E. Means for solving the problem F. Effect G. Example G-1 Overall configuration (Figure 1) G-2 Total reflection prism (Figs. 2 and 3) G-3 modification (Fig. 4) H Effect of the invention A Industrial application field The present invention allows a light beam to enter a recording medium through an objective lens, and The present invention relates to an optical pickup device that guides a reflected light beam from a photodetector to a photodetector and obtains a reading output of information recorded on a recording medium from the photodetector.

B. Summary of the Invention The present invention focuses a light beam from a light beam generation source onto a recording medium through an objective lens, guides the reflected light beam from the recording medium to a photodetection section through the objective lens, and directs the reflected light beam from the photodetection section from the photodetection section. In an optical pickup device that obtains a read information signal for information recorded on a recording medium based on a detection output of the optical pickup device, a polarizing beam splitter is provided on an optical path between a light beam generation source, a light detection unit, and an objective lens; A dielectric film is provided on one surface of a glass substrate, and a light beam emitted from a light beam generation source and passed through a polarizing beam splitter is incident on the glass substrate from a first direction, and the surface on which the dielectric film is provided is incident on the glass substrate from a first direction. At the same time, the reflected light beam from the objective lens is incident on the glass substrate from the second direction and is totally reflected on the side where the dielectric film is provided. By disposing a total reflection optical element that is guided to the polarizing beam splitter, an independent quarter-wave plate is not required, and the cost can be reduced. In the splitter, a light beam emitted from a light beam generation source and incident on an objective lens and a reflected light beam passing through the objective lens are appropriately separated.

C. Conventional technology In an optical disc player used to reproduce information recorded on a disc as an information recording medium, there is a system for reading recorded information from spiral or concentric recording tracks formed on the disc. An optical pickup device that constitutes an optical system is provided.

In an example of such an optical pick amplifier device, as shown in a simplified manner in FIG. In the radial direction (
(direction indicated by arrow A). Then, the laser light beam emitted from the semiconductor laser 1 enters the grating plate 2 and is diffracted by the grating plate 2 into three laser light beams (in FIG. 5, these are shown for the sake of simplicity). (three laser light beams are shown by one solid line), each laser light beam is incident on the polarizing beam splinter 3 and its analyzer surface 3
After passing through a, the light enters the collimator lens 4. The three laser beams incident on the collimator lens 4 are collimated by the collimator lens 4, and then 1/4
The light passes through the wavelength plate 5, enters the objective lens 6, is focused by the objective lens 6, and is made incident on the disk D. At that time, the three laser beams each
The center beam and the beams on both sides sandwiching the center beam are used for reading information recorded on the disk D and detecting the focus state on the recording surface of the disk D, and the beams on both sides are used for reading the information recorded on the disk D and detecting the focus state on the recording surface of the disk D. It is assumed that this is used to detect the tracking state of the central beam with respect to the recording track formed at D. The three laser beams incident on the disk D are each reflected while being modulated by the recording tracks formed on the disk D, and are turned into reflected laser beams.

Each of the three reflected laser beams from disk D is
It returns through the objective lens 6, is made into a parallel beam, and is again 17
It passes through a four-wavelength plate 5. In this way, the laser light beam emitted from the semiconductor laser 1 is divided into three laser light beams, each of which passes through the 174-wavelength plate 5 back and forth, and each of the three reflected laser light beams obtained has 174 wavelengths. Board 5
By passing twice, the polarization direction of each of the three laser beams incident on the disk D passing through the polarization beam splinter 3 is rotated by π/2.

The three reflected laser light beams whose polarization directions have been rotated by π/2 are incident on the collimator lens 4 , where the beams are converged and then incident on the polarizing beam splitter 3 . Then, each light is reflected by the analyzer surface 3a of the polarizing beam splitter 3, and the optical axis direction is changed, and the light is guided to the photodetector 8 through the light receiving lens 7. In the photodetector 8, 3
An information detection output signal corresponding to the information recorded on the recording trunk of the disc D and a focus state detection output signal corresponding to the focus state are obtained based on the central beam of the reflected laser light beams of the book, and A tracking state detection output signal corresponding to the tracking state is obtained based on the beams on both sides.

D Problems to be Solved by the Invention However, in the conventionally proposed optical pickup device as described above, the laser beam emitted from the semiconductor laser 1 and made incident on the disk D through the objective lens 6; The reflected laser beam that returns from the disk D through the objective lens 6 and is guided to the photodetector 8 is separated by the polarizing beam splitter 3. Therefore, in addition to the polarizing beam splitter 3, a relatively expensive The 174-wavelength plate 5, which is assumed to be a 174-wavelength plate, thereby divides the reflected laser light beam from the disk D that is incident on the polarization beam splitter 3 into the laser light beam that passes through the polarization beam splitter 3 and is incident on the disk D. It is used so that the polarization direction is rotated by π/2, and therefore, there is a disadvantage that the cost tends to increase.

In view of these points, the present invention makes a light beam from a light beam generation source enter a recording medium such as a disk through an objective lens in a focused state, and guides a reflected light beam that returns from the recording medium through the objective lens to a photodetector. In order to obtain a detection output according to the information recorded on the recording medium in the photodetection section, the optical path configuration can be such that the optical components used are relatively inexpensive, reducing costs. It is an object of the present invention to provide an optical pickup device that can achieve the following objectives.

E. Means for Solving the Problems In order to achieve the above-mentioned object, an optical pickup device according to the present invention includes a light beam generation source, a light beam from the light beam generation source that is incident on a recording medium in a focused state, and an objective lens that receives the reflected light beam from the recording medium;
A polarizing beam splitter that separates a light beam emitted from a light beam generation source and incident on an objective lens and a reflected light beam that passes through the objective lens, and a photodetector that detects the reflected light beam emitted from the polarizing beam splitter, moreover,
It has a glass substrate and a dielectric film provided on one surface of the glass substrate, and a light beam emitted from a light beam generation source and passed through a polarizing beam splitter is incident on the glass substrate from a first direction, and the dielectric film is formed on one surface of the glass substrate. It is assumed that the light beam is totally reflected on the side where the dielectric film is provided and guided to the objective lens, and the reflected light beam that passes through the objective lens is incident on the glass substrate from the second direction, and the dielectric film is provided. A total reflection optical element is provided that causes total reflection on the surface side and guides the beam to a polarizing beam splitter.

F Effect In the optical pickup device according to the present invention configured as described above, the light beam from the light beam generation source passes through the polarizing beam splitter and then passes through the glass substrate in the total reflection optical element as linearly polarized light from the first direction. It is made to be incident on. The light beam from this light beam source is
In the total reflection optical element, the light is totally reflected on the side of the glass substrate on which the dielectric film is provided, and becomes circularly polarized or elliptically polarized light, which is guided to the objective lens through the glass substrate, where it is focused and recorded. It is made incident on the medium.

Further, the reflected light beam from the recording medium returns through the objective lens and is made incident on the glass substrate of the total reflection optical element from the second direction as circularly polarized light or elliptically polarized light. The reflected light beam is then totally reflected on the surface side of the glass substrate in which the dielectric film is provided in the total reflection optical element, and the polarization direction is π with respect to the light beam from the light beam generation source.
The linearly polarized light is rotated by /2 and is made incident on the polarizing beam splitter via the glass substrate. The polarization direction of the reflected light beam incident on this polarizing beam splitter is rotated by π/2 with respect to the light beam from the light beam generating source. It is separated from the beam and guided to the photodetector. As a result, a detection output corresponding to the information recorded on the recording medium, that is, an information reading output is obtained from the photodetector.

In this way, an independent one, which is relatively expensive,
Based on an optical path configuration that does not use a 74-wavelength plate and consists of relatively inexpensive components, a polarizing beam splitter separates the light beam emitted from the light beam source and incident on the objective lens, and the reflected light that passes through the objective lens. The beam is properly separated, and as a result, an information reading output having a good signal-to-noise ratio can be obtained from the photodetector.

G Example c-i Overall configuration (FIG. 1) FIG. 1 shows an example of an optical pickup device according to the present invention.

Like the optical pickup device shown in FIG. 5, this example is used to reproduce information recorded on a disk D, and is assembled to form one optical block 20. It has an optical path configuration that allows it to move along the radial direction (direction shown by arrow A) of the disk D on which a spiral recording track is formed.

In this optical path configuration, the laser beam emitted from the semiconductor laser 1 is diffracted by the grating plate 2 into three laser beams, similar to the case of the optical pickup device shown in FIG. (1st
In the figure, for simplicity, these three laser beams are shown as one solid line), each laser beam passes through the analyzer surface 3a of the polarization beam splinter 3,
The laser beam enters a collimator lens 4 that converts the laser beam into a parallel beam. The three laser beams collimated by the collimator lens 4 enter the total reflection prism 21, which is a total reflection optical element, are totally reflected by the total reflection prism 21, and are guided to the objective lens 6. , and is made incident on the disk D while being focused by the objective lens 6. In this case as well, the three laser beams that are focused by the objective lens 6 and made incident on the disk D are placed in a relationship such that they form a central beam and beams on both sides sandwiching it, with the central beam hitting the disk D. It is used to read recorded information and detect the focus state on the recording surface of the disc D, and the beams on both sides are used to detect the tracking state of the center beam with respect to the recording track formed on the disc D. be done.

The three laser beams incident on the disk D are each modulated by the recording trunk formed on the disk D and then reflected to become reflected laser beams. Each of the reflected laser light beams returns via the objective lens 6, becomes a parallel light beam, and enters the total reflection prism 21. Then, each reflected laser light beam is again totally reflected by the total reflection prism 21 and guided to the collimator lens 4, where it is converged into a beam of light and made to enter the polarizing beam splitter 3.

In this way, the beam is totally reflected by the total reflection prism 21 and passed through the collimator lens 4 to the polarization beam splinter 3.
It is assumed that the polarization direction of the reflected laser beam that is incident on the laser beam is rotated by π/2 with respect to the laser beam that is incident on the total reflection prism 21 from the semiconductor laser 1 via the polarization beam splinter 3. Therefore, each of the reflected laser light beams incident on the polarizing beam splitter 3 is reflected by the horizontal photon surface 3a of the polarizing beam splitter 3, and is made to enter the total reflection prism 21 from the semiconductor laser 1 via the polarizing beam splitter 3. It is separated from the laser light beam and guided to the photodetector 8 through the light receiving lens 7.

In the photodetector 8, an information reading output and a focus state detection output signal corresponding to the focus state are obtained based on the central beam of the three reflected laser light beams, and tracking state detection is performed based on the beams on both sides. An output signal is obtained.

G-2 Total reflection prism (Figures 2 and 3) The total reflection prism 21 described above consists of a glass prism base 22 and its surface 22.
A and a dielectric film 23 provided at a. Then, the total reflection prism 2 passes through the collimator lens 4.
1 and the reflected laser beam that passes through the objective lens 6 and enters the total reflection prism 21 is totally reflected on the surface 22a of the glass prism base 22 on which the dielectric film 23 is provided.

As shown in FIGS. 2 and 3, the glass prism base 22 receives the laser beam incident from the collimator lens 4 and is totally reflected on the surface 22a side so that the laser beam enters the glass prism base 22.
Common optical axis direction 1 with the reflected laser beam emitted to
The light beam exiting surface 22b is perpendicular to a, and the laser beam that is totally reflected on the surface 22a side and exits to the objective lens 6 and the reflected laser beam that enters from the objective lens 6 are aligned in the common optical axis direction Ib. It has an orthogonal light beam exit surface 22c. Further, the surface 22a of the glass prism base 22 on which the dielectric film 23 is provided is within the virtual plane 22d that includes both the optical axis directions 1a and Ib described above [L is the optical axis direction 1a]. The inclined surface forms an angle of 45 degrees with respect to each of Ib and Ib.

The dielectric film 23 provided on the surface 22a of the glass prism base 220 is formed, for example, by vacuum deposition.

Based on this configuration, a beam 1 in the optical axis direction is emitted from the semiconductor laser 1, passes through the grating plate 2 and the polarizing beam splinter 3, and is converted into a parallel beam by the collimator lens 4.
A laser light beam having a linearly polarized state enters the glass prism base 22 from the light beam exit surface 22b perpendicular to the optical axis direction 1a. This light beam person exit surface 2
The polarization direction a of the laser beam incident from 2b is set at 45 degrees with respect to the above-mentioned virtual plane 22d.

The laser beam that has entered the glass prism base 22 through the light beam exit surface 22b in this way has an incident angle of 45 degrees with respect to the surface 22a of the glass prism base 22, and its polarization direction α is imaginary. It is made to form an angle of 45 degrees with respect to the surface 22d, and is totally reflected on the surface 22a side of the glass prism base 22 where the dielectric film 23 is provided, and has the optical axis direction 1b. The P polarization component and the S polarization component, which are orthogonal polarization components, are π/
The linearly polarized light is converted into circularly polarized light, and is emitted from the light beam output surface 22C to the objective lens 6. At this time, there is a π
In order to generate a phase difference of /2, the refractive index of the glass prism base 22 and the thickness and refractive index of the dielectric film 23 are selected. For example, the refractive index of the glass prism base 22 is approximately 1.51. Further, the thickness of the dielectric film 23 is about 0.3 μm, and the refractive index is about 2.2 to 2.3.

Then, the circularly polarized laser beam enters the disk D through the objective lens 6, is reflected by the disk D, and becomes a reflected laser beam that passes through the objective lens 6 and enters the total reflection prism 21. Become. Therefore, in the total reflection prism 21, the reflected laser light beam having the optical axis direction Ib, which has been made into a parallel beam through the objective lens 6, is circularly polarized and is perpendicular to the optical axis direction 1b. The light enters the glass prism base 22 from 22c. The reflected laser light beam incident on the glass prism base 22 from the light beam output surface 22c in this way also
The glass prism base 22 has an incident angle of
is totally reflected on the surface 22a side where the dielectric film 23 is provided, and has an optical axis direction 1a, and
The P-polarized light component and the S-polarized light component are further set to have a phase difference of π/2, and are converted from circularly polarized light to linearly polarized light.
emit to. This light beam person exit surface 22. The reflected laser light beam emitted from b has a phase difference π between the P polarization component and the S polarization component compared to the laser light beam entering the glass prism base 22 from the light beam exit surface 22b. , Therefore, the polarization direction β is rotated by π/2 with respect to the above-mentioned polarization direction α.

Then, the reflected laser beam emitted from the light beam output surface 22b to the collimator lens 4 enters the polarizing beam splitter 3 via the collimator lens 4, and thereby becomes polarized via the collimator lens 4 as described above. The polarization direction of the reflected laser beam incident on the beam splitter 3 is rotated by π/2 with respect to the laser beam incident on the total reflection prism 21 from the semiconductor laser 1 via the polarizing beam splitter 3. °
The situation is as follows.

G-3 Modified Example (FIG. 4) In the above example, the surface 2 on which the dielectric film 23 is provided is incident on the glass prism base 22 of the total reflection prism 21.
The laser beam that is totally reflected on the 2a side is assumed to have a phase difference of π/2 between its P-polarized light component and S-polarized light component, and is changed from linearly polarized light to circularly polarized light, or from circularly polarized light to linearly polarized light. However, unlike that, the laser beam that enters the glass prism base 22 of the total reflection prism 21 and is totally reflected on the surface 22a side where the dielectric film 23 is provided is The polarized light component and the S-polarized light component may have a predetermined phase difference other than π/2, thereby converting linearly polarized light into elliptically polarized light, or from elliptically polarized light to linearly polarized light. .

Moreover, instead of the total reflection prism 21 in the above example,
As shown in FIG. 4, a total reflection mirror 31 composed of a plate glass substrate 32 and a dielectric film 33 provided on one surface 32a of the plate glass substrate 32 is connected to a polarizing beam splitter 3 and an objective lens 6. It may also be used as a total reflection optical element placed between the two.

Effects of the Invention H As is clear from the above explanation, the optical pickup device according to the present invention makes the light beam from the light beam generation source enter the recording medium such as a disk in a focused state through the objective lens, and The reflected light beam that returns from the source through the objective lens is separated from the light beam directed from the light beam generation source toward the recording medium by a polarizing beam splitter, and is guided to the photodetection section. To obtain the information reading output, which is the detection output, a total reflection optical element is placed on the optical path between the polarizing beam splitter and the objective lens, and an independent 174-wave plate, which is relatively expensive, is used. Based on the optical path configuration, a state is obtained in the polarizing beam splitter in which the light beam emitted from the light beam generation source and incident on the objective lens is properly separated from the light beam reflected after passing through the objective lens. It turns out. Therefore, it is possible to significantly reduce the cost required for the optical path configuration, and moreover,
Information reading output with a good signal-to-noise ratio can be obtained from the photodetector.

[Brief explanation of the drawing]

FIG. 1 is a simplified configuration diagram showing an example of an optical pickup device according to the present invention, and FIGS. 2 and 3 are perspective views for explaining a total reflection prism used in the example shown in FIG. Figure 4 is a side view showing a total reflection mirror that can be used in place of the total reflection prism in the example shown in Figure 1. Figure 5 is a simplified example of a conventionally proposed optical pickup device. FIG. In the figure, 1 is a semiconductor laser, 3 is a polarizing beam splitter,
4 is a collimator lens, 6 is an objective lens, 8 is a photodetector, 20 is an optical block, 21 is a total reflection prism, 22 is a glass prism base, 23 and 33 are dielectric films, 31 is a total reflection mirror, 32 is a third Figure 1 Figure 4

Claims (1)

[Scope of Claims] A light beam generation source; an objective lens that makes the light beam from the light beam generation source enter a recording medium in a focused state and receives the reflected light beam from the recording medium; and the light beam generation source. a polarizing beam splitter for separating a light beam incident on the objective lens from a light beam reflected from the objective lens; a glass base and a dielectric film provided on one surface of the glass base; A light beam emitted from a light beam generation source and passed through the polarizing beam splitter is incident on the glass substrate from a first direction, is totally reflected on the surface side where the dielectric film is provided, and is reflected by the objective lens. At the same time, the reflected light beam that has passed through the objective lens is incident on the glass substrate from a second direction different from the first direction, and the reflected light beam is completely incident on the surface side where the dielectric film is provided. An optical pickup device comprising: a total reflection optical element that is reflected and guided to the polarization beam splitter; and a photodetector that detects the reflected light beam emitted from the polarization beam splitter.