JPS61233439A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a differential detection type optical pickup device which has the satisfactory S/N with a compact design and low cost by putting two optical dividers having diffraction structures superposedly. CONSTITUTION:The luminous flux reflected from a recording medium 45 is transmitted through an objective lens 46 and divided into the diffracted light 47 and the transmitted light by the 1st diffraction structure. The rays of light 47 pass through a polarizing plate 49 while having the total reflection on both sides of the 1st optical divider 43 and reaches an optical sensor 50. While the transmitted light is made incident on the 2nd diffraction structure and this diffracted light 48 passes through the plate 49 and reaches the sensor 50. A low refraction layer 44 having a refraction index lower than the base of the optical divider between the 1st and 2nd optical divider 43 and 42. At the same time, a phase control film 51 is provided on the reflecting surface of diffracted light of the divider 42 or 43. Thus a 180 deg. phase difference is obtained by the film 51 between the P and S polarization components of a reflection mode. Then the polarization surface of the diffracted luminous flux is turned by 90 deg.. As a result, a 90 deg. polarization surface is obtained between the diffracted luminous fluxes 48 and 47.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical pickup device that detects or records information by irradiating the information recording surface of an information carrier with light, and particularly relates to an optical pickup device that is small, low cost, and has high speed. This invention relates to an optical pickup device capable of generating /N signals.

[Prior art]

2. Description of the Related Art In recent years, research and development of reversible optical disc recording media and optical disc recording and reproducing devices using the media has been actively conducted. One such optical disk recording medium is a magneto-optical recording medium.

Signal reproduction from a magneto-optical recording medium (hereinafter simply referred to as a recording medium) is performed using a magneto-optical effect called the Kerr effect or Faraday effect.

That is, the reflected light or transmitted light from the recording medium is slightly rotated from the polarization plane when it is incident on the recording medium, and the rotational component is converted into intensity modulation using a polarizing plate or the like to perform signal detection.

Since the rotation angle of this plane of polarization is approximately 1°, the detected signal component is minute, and several improvements have been made to the optical pickup device for signal detection.

FIG. 8 shows a schematic diagram of a conventionally used optical pickup device. In the figure, a light beam emitted from a semiconductor radar 1 (hereinafter simply referred to as LD) is converted into a parallel light beam by a collimator lens 2. The parallel light beam then passes through a beam sinter 3 and is focused by an objective lens 4 onto a spot of approximately 1 μm in diameter on a recording medium 5.

The light beam reflected from the recording medium 5 undergoes polarization plane modulation due to the Kerr effect and Faraday effect, and passes through the objective lens 4 again.
The beam splitter 3 separates the beam from the incident light beam. The separated luminous flux is partially reflected by the second beam sinter 6, passes through the lens system 7, and enters the υ optical sensor 8.

The lens system 7 is constituted by a known system, such as an astigmatism system, a Naifezi system, or a Foucault prism system, and provides information on the distance between the recording medium 5 and the objective lens 4, that is, an AP error signal.

Also, a deviation from the information track, that is, an AT error signal, can also be obtained using the well-known pushinable method or the like. These error signals are fed back to an objective lens drive system (generally referred to as an actuator), not shown, to accurately track at an accurate focal position and to detect or record signals.

The remaining light flux passing through the second beam splitter 6 is
The beam passes through the wave plate 9 and is split into two directions by the polarizing beam sinter 10. When the optical crystal axis of the Iso wave plate 9 is arranged at an angle of 22.5 degrees with respect to the polarization axis of the incident light beam, the amount of light divided into two by the polarizing beam splitter 10 is equal.
This is equivalent to arranging polarizing plates such that each light beam has a transmission axis of 45° and -45°. The two divided light beams are each focused on a signal detection sensor 13.14 by a sensor focusing lens 11.12, and by differentiating the electrical signals from the signal detection sensor 13.14 (differential detection), a recording medium is detected. 5 can be detected.

The advantages of this differential detection method will be explained below.

FIG. 9 schematically shows the signal amplitude components that are split between the wave plate 9 and the polarizing beam splitter 10 and reach the sensors 13 and 14. In the figure, when the vertical axis is the polarization direction of the incident light beam, the plane of polarization of the light beam reflected from the recording medium 5 is rotated to θ or partially depending on the direction (upward or downward) of the magnetic domain of the magneto-optical pattern. ■The combination of the wavelength plate 9 and the polarizing beam splitter 10 is equivalent to a system in which polarizing plates are arranged with the transmission axis tilted by ±45°, so the virtual transmission axis X,! The difference S1 and 81' between the projection components on the dotted line axes tilted by ±45°, respectively, becomes the signal amplitude component.

At the rotation angle θ and partly due to the magneto-optical pattern,
! Maroji Nasha on +11, signal detection sensor 13°14
Figure 10(a) shows the change in signal strength of the signal received by the
As shown in (b), the phases of the divided light beams are shifted by 1800.

Although the phase of the magneto-optical signal is reversed as described above, normally the noise component (the noise from the recording medium 5, the fluctuation noise of the LDI light, etc.) rides on these signals, and these noise components are in phase.

Therefore, if the signals obtained from the sensors 13 and 14 are differentiated, the signal components will strengthen each other and the noise component will be reduced.If the optical system is arranged correctly, S12
and S·12 are equal, and the noise amplitudes are also equal, so the signal is doubled and the noise is O. (Illustrated in FIG. 10(C)) As described above, the differential detection method as shown in FIG. 8 has the advantage of being able to detect signals with a good S/N ratio.

However, the optical pickup device as described above has a large number of parts, which is disadvantageous in terms of miniaturization and cost reduction. Therefore, the present applicant proposed an optical pickup device that uses a diffractive structure as a means to realize miniaturization and cost reduction. (Patent application 59-132293.59-132294.
59-138369.59 The outline thereof will be explained below.

FIG. 11 shows a schematic diagram of a light splitter used in the above optical pickup device, and FIG. 10(a) shows a light splitter having a holographically created diffraction structure.

In the figure, interference fringes are recorded on a photosensitive layer 16 coated on a transparent substrate 15 using, for example, an Ar radar. After that, a second transparent plate 17 for a cover is attached to form a thin (approximately 2 m) light splitter. A portion of the light beam 18 incident on this light splitter is diffracted by the interference fringes recorded on the photosensitive layer 16 as diffracted light 19, and the light beam 18 is completely diffracted at the interface between the first transparent substrate 15 and the second transparent substrate 17 and air. While being reflected, it is guided to an optical sensor (not shown). Also, the remaining luminous flux 2
0 travels straight as a 0th-order diffracted light beam 20. By designing the pitch, inclination, etc. of the interference fringes, it is possible to convert most of the incident light into diffracted light 19 and collect the light beam, and it is also possible to provide polarization characteristics.

FIG. 11(b) shows a light splitter manufactured by another manufacturing method. This light splitter is made by forming sawtooth-like uneven portions 24 on the surface of a transparent substrate 21 made of, for example, PMMA (polymethyl methacrylate) using a method such as combrella silane or laser cutting from a mold cut with a diamond cutter. It is made by doing.

A reflective film 22 having desired reflective properties is deposited on the serrated portion 24 of the tube, and then the transparent plate 23 of the cylinder 2 is bonded with an adhesive having almost the same optical refractive index as the transparent substrate 21 and the transparent plate 23. Create a light splitter. Even in such a light splitter, the incident light flux exhibits the same behavior as in the light splitter shown in FIG. 10(&).

The lattice structure of the light splitter has a curved structure as shown in FIG. 12. For example, in the figure, the grid structure is divided into three parts so that the center of the own vehicle is approximately at the position of the light sensors 25, 26, and 27. There is.

FIG. 13 shows a schematic diagram of an optical pickup device using a light splitter having a grating structure as described above.

The area 28 shown in FIG. 12 divides the peripheral luminous flux, and as shown in FIG. 13, the change in the distance between the objective lens 31 and the recording medium 32 is used as the movement of the divided luminous flux in the arrow A-A direction (shown in FIG. 12) to provide information. Convert.

Then, by detecting the movement of these light beams with the two-split optical sensor 25,
g) Obtain the signal. Further, if the direction of the information track of the recording medium 32 is the direction of the arrow T-T and the area of the diffraction structure is divided into 29.30 areas parallel to this direction, as is well known, the area of 29.30 of the diffraction structure is tracked. Since the amount of arriving light differs depending on the deviation, AT (aut) is determined by taking the difference between the outputs of the optical sensors 26 and 27 that detect the light beam diffracted from each area.

tracking) signal can be obtained. It is also possible to detect a signal of the recorded information from the sum of the optical sensors 26, 27 or from the sum of the optical sensors 25, 26.27.

That is, when targeting a magneto-optical recording medium, as shown in FIG. 13, an LD 33, a frimeter lens 34, an objective lens 31, a light splitter 35, a polarizing plate 36 attached to the right end surface of the light splitter, A low-cost Pizquaf device can be constructed using an optical sensor of 25°9.6.27.

However, in this conventional configuration, differential detection of signals for the purpose of noise removal as shown in FIG. 8 cannot be performed, and there is a disadvantage when considering the S/N ratio of the signal.

[Purpose of the invention]

An object of the present invention is to further improve the above-mentioned compact and low-cost optical pickup device, and to provide an optical pickup device that can perform differential signal detection and improve signal S/N.

[Summary of the invention]

The purpose of the above is to have a first light splitter and a second light splitter each having a diffraction structure, to irradiate the information recording surface with light emitted from the light source, and to separate the information from the information recording surface. means for guiding the reflected light to the first light splitter, the reflected light is incident on the first light splitter to generate a first diffracted light, and the light transmitted through the first light splitter is transmitted to the first light splitter. generating a second diffracted light by making it incident on a second light splitter; and means for relatively rotating the plane of polarization of the first diffracted light and the plane of polarization of the second diffracted light by approximately 90'; Said first
This is achieved by an optical pickup device characterized by having means for guiding the diffracted light and the second diffracted light to a light receiving section of a photodetector.

〔Example〕

FIG. 1 is a diagram showing a schematic configuration diagram of an optical pickup device of the present invention. In the figure, the light beam emitted from the LD 40 becomes a parallel light beam at a collimator lens 41, and is transmitted through a light splitter 42 having a second diffraction structure. Thereafter, the light beam passes through a light splitter 43 having a first diffraction structure, and is directed onto a recording medium 45 by an objective lens 46. Collect the light with a cut.

The light beam reflected from the recording medium 45 is directed back to the objective lens 4.
6 is split into diffracted light 47 and transmitted light by the first diffraction structure. The diffracted light 47 is totally reflected on the upper and lower surfaces of the first light splitter 43 and passes through the polarizing plate 49 to the light sensor 5.
Reach 0. On the other hand, the transmitted light enters the second diffraction structure, and the diffracted light 48 similarly passes through the polarizing plate 49 and reaches the light sensor 50. (Here, the light splitter into which the reflected light from the recording medium 45 first enters is referred to as the first light splitter.)
It is more convenient for assembly, etc., if the light splitter 42 and the first light splitter 43 are integrated, but at this time, in order to ensure that the diffracted light is totally reflected, there is a A low refractive layer 44 is provided by an adhesive having a refractive index lower than that of the base of the light splitter or by separately depositing a dielectric film. Alternatively, a similar effect can be obtained by providing a highly reflective film layer.

Further, a phase adjustment film 51 is provided on either the diffracted light reflecting surface of the second light splitter 42 or the first light splitter 43. (FIG. 1 shows an example in which it is provided on the lower surface of the first light splitter 43.) This phase adjustment film 51 allows the phase difference between the P polarized light component and the S polarized light component at the time of reflection to be 1800 degrees, and the diffracted light beam is Rotate the plane of polarization by 90°. Therefore, the diffracted light beam 48
The polarization planes of the diffracted light beams 47 and 47 make an angle of 90° to each other. Furthermore, the same effect can be obtained by using a wave plate made of crystal or the like instead of the phase adjustment film 51.

Furthermore, a rock wave plate is provided between the second light splitter 42 and the first light splitter 43, so that the polarization planes of the light beams incident on the second diffraction structure and the first diffraction structure differ by 90'. You can also let

When the light beam from the LD 40 enters the light splitter 42 and 43, it is partially diffracted, but the direction of the diffraction is towards the optical sensor 5.
Since the direction is opposite to 0 and the diffraction structure has a curvature, even if the light reaches the light sensor 50 as a divergent light beam as stray light, the light has extremely low intensity and there is no problem.

Next, the reason why magneto-optical information signals can be obtained differentially in the above configuration will be explained.

FIG. 2 schematically shows the signal amplitude component, where X is the direction of the polarization plane of the light beam incident on the recording medium 45, and Y is the direction perpendicular thereto. The plane of polarization of the reflected light from the recording medium 45 is tilted at a slight angle θ due to the magneto-optic effect. This inclination may be upward or downward in the clockwise or counterclockwise direction (in θ or 10k), and the amount of inclination is approximately 1°. Now, the direction of the transmission axis of the polarizing plate 49 in FIG. 1 is tilted approximately 45 degrees from the X direction. In the example shown in FIG. 1, the diffracted light 48 is in the state shown in FIG. 2 (4), and the diffracted light 47 is in the state shown in FIG. 8 (B). Therefore, the intensity change of the light flux passing through the polarizing plate is 5s2=S't2=((45°−θk))2−(
cos (45°+θk))2, but Fig. 2(4)
, o3), the sizes of K are in a complementary table relationship. That is, the intensity modulation of the two beams transmitted through the polarizing plate 49 has a phase shift of 1800 degrees from each other.

As shown in FIG. 3(B), the optical sensor 50 has a light receiving section divided into a plurality of segments. For example, if a part of the optical sensor is divided into 8 parts as shown in the figure, and each diffraction structure of the light splitter 42 and 43 is divided into 3 parts as shown in FIG. 3 (4), each The signal output from each segment is IAI I! 11 Ice IDI III! , e
I, l I. can be obtained by the following calculation.

AP error signal IA, = (I□+IE) −(1, +I
, )AT error signal IAT= (IC+I,) −(I
, +IH) magneto-optical information signal l5=(I, +I, +I,
+I, )-(I, +I, +I, +IH) As an example of another combination, as shown in FIG.
2 is divided into 3 parts, light splitter 43 is not divided, optical sensor 50
If the five segments A-E are arranged as shown in Figure 4(B), then the AF error signal IAF=A
'B AT error signal IAT =IC-■D Magneto-optical information signal I, = (I, +Il+I, +ID)-
I.

It can be obtained with

Also, as shown in Figure 5, the light splitter 42 is a two-part light splitter 43.
If the optical sensor 50 is divided into two segments and the five segments A-H are arranged as shown in Fig. 5 (B), then AF error signal "AP" A-II AT error signal IAT" From '1 magneto-optical information signal l5=(IA-1-I,-)-I,)
−(I, +1.). Depending on the method of dividing the diffraction structure of the fine light splitter and the arrangement of the light receiving section of the optical sensor 50, several types of combinations are possible.

Furthermore, by incorporating the circuit and amplifier system for calculating each signal on the same chip as the light receiving section or in the optical sensor 50, signal detection that is resistant to disturbance noise becomes possible.

Furthermore, if the diffraction structure is formed by interference of the light beams from two point light sources, the light beams 47.48 in FIG. The separation of the two luminous fluxes becomes clear, and the groups A to D and the groups E to H of the sensor light-receiving parts can be brought close to each other, making it possible to downsize the sensor.

Furthermore, when implementing the optical pickup device having the configuration shown in FIG. 1, the light flux emitted from the light source passes through two light splitters 42 and 43, so a reduction in the amount of light reaching the recording medium may become a problem. obtain. When a magneto-optical recording medium is used, since recording is also performed, the problem of reduction in light amount must be considered in conjunction with the sensitivity of the medium.

FIG. 6 is a schematic diagram showing an optical pickup device that takes the above points into consideration. In the figure, the light beam from the LD 40 is passed through a collimator lens 41 into a collimated beam beam slitter 52 and an objective lens 46 to form a minute soot on a recording medium 45. The reflected light from the recording medium 45 passes through the objective lens 46 again, is split by the beam splitter 52, enters the light splitter 42, 43 having a diffraction structure, and similarly to the previous embodiment, various signals are sent to the optical sensor. Detected at 50.

In such an optical pickup device, since there is no light splitter 42 or 43 in the optical path from the LD 40 to the recording medium 45, the light from the LD 40 is recorded only by passing through one light splitter (beam splitter 51). It has the advantage of being able to enter the medium 45.

Further, as shown in FIG. 7, for example, a photosensitive material is coated on both sides of a substrate 60, two diffraction structures having different diffraction angles are holographically printed, and cover glasses 61 and 62 are pasted to increase weather resistance. When a splitter is used, the diffracted light beams 47 and 48 are separated and focused on the sensor surface. Therefore, it is possible to construct a light splitter that is thinner than that shown in FIG. 1, which has the advantage that the division interval of the light-receiving section can be made narrower, and the sensor can be miniaturized.

In the figure, the first light splitter is a transmission type diffraction grating, and the second light splitter is the same reflection type diffraction grating as used in the first embodiment.

In such an optical pickup device, the diffraction structure 63 and the substrate 60 constitute the light splitter 42, and the other diffraction structure 64 and the substrate 60 constitute the light splitter 43. Considering that the two light splitters are integrated, the structure and effects can be considered in the same way as in the above two embodiments.

〔Effect of the invention〕

As explained above, by stacking two light splitters with diffraction structures, it is possible to achieve small size, low cost, and S/N ratio.
A differential detection type optical pickup device with good performance can be provided.

According to this optical pickup device, in addition to the above effects,
It has the advantages of being able to reduce the number of parts, being integrated, which makes axis alignment easy and resistant to axis misalignment during use, and having a differential amplifier circuit built into the optical sensor, making it resistant to noise.

[Brief explanation of the drawing]

Figure 1 shows the optical pick-up arrangement of the present invention! This is a schematic diagram of a first embodiment of the apparatus, and FIGS. 6 and 7 are schematic diagrams showing a second embodiment and a third embodiment, respectively. FIG. 2 is a schematic diagram showing the signal amplitude component of the luminous flux. FIGS. 3, 4, and 5 are schematic diagrams showing examples of combinations of grating structures and optical sensors, respectively. FIG. 8 is a schematic diagram of a conventional differential detection type optical pickup device that does not use a diffraction structure, and FIGS. 9 and 10 are diagrams for explaining the differential detection method, respectively. FIG. 11 is a diagram showing an example of a light splitter having a diffraction structure, and FIGS. 12 and 13 are schematic diagrams of an optical pickup device using the light splitter shown in FIG. 11, respectively. 40: semiconductor radar, 41: collimator lens, 42:
Second light splitter, 43: First light splitter, 45: Recording medium,
46: Objective lens, 49: Polarizing plate, 50: Optical sensor,
51: Phase adjustment film. Agent Patent Attorney Jo Taira Yamashita Figure 1 Figure 2 Figure 3 (A) (B) Figure 411 Figure 5 Figure 91! I

Claims (4)

[Claims] (1) It has a first light splitter and a second light splitter each having a diffraction structure, irradiates the information recording surface with light emitted from the light source, and directs the reflected light from the information recording surface to the comprising a means for guiding the reflected light to a first light splitter, causing the reflected light to enter the first light splitter to generate a first diffracted light, and splitting the light transmitted through the first light splitter into the second light splitter. generating second diffracted light by making it incident on a container; and means for relatively rotating the plane of polarization of the first diffracted light and the plane of polarization of the second diffracted light by approximately 90 degrees; An optical pickup device comprising means for guiding light and the second diffracted light to a light receiving section of a photodetector. (2) The optical pickup device according to claim 1, wherein the first light splitter and the second light splitter are provided in an optical path from the light source to the information recording surface. (3) The optical pickup device according to claim 1, characterized in that the photodetector includes a plurality of light receiving sections, and has means for processing signals received by the light receiving sections by differential detection. . (4) The optical pickup device according to claim 1, wherein the first light splitter and the second light splitter are integrated.