JPH0512747A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To record and reproduce an information signal with symmetrical variation in characteristic regardless of a direction of defocusing and without any deterioration in characteristic such as C/N even if a beam spot becomes elliptic. CONSTITUTION:The plane containing the normal of the light splitting surface 4 of a beam splitter 3 which splits reflected light from a magnetooptic disk 6 and the optical axis of parallel light which is made incident on the light splitting surface is set in parallel or perpendicularly to the track direction of the magnetooptic disk 6, and a semiconductor laser 1 is set perpendicularly to or in parallel to the plane containing the normal of the light splitting surface and the optical axis of the parallel light. The characteristic of a magnetooptic signal, etc., varies symmetrically to make servocontrol hard to free and also decrease read errors of the information signal. Further, the information signal can be led without any loss and characteristics such as the C/N do not deteriorate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for optically recording / reproducing information using a magneto-optical disk as an information recording medium.

[0002]

2. Description of the Related Art In an optical information recording / reproducing apparatus, a semiconductor laser is used as a light source, and light emitted from the semiconductor laser is applied to a magneto-optical disk to reflect and reflect the magneto-optical disk.
Due to the effect of the effect, the light rotated in the direction in which the vibration direction of the light is different depending on the direction of the magnetization on the magneto-optical disk is detected by the photodetector to reproduce the information (conventional example 1). The outline of this device will be further described with reference to FIG. 6. A semiconductor laser (LD) 51
The light emitted from the collimator lens 52 is converted into parallel light, and further transmitted through the polarizing film 54 of the beam splitter 53,
It passes through the objective lens 55 and reaches the magneto-optical disk 56. The light flux reflected by the magneto-optical disk 56 is again returned to the objective lens 55.
To reach the polarizing film 54 of the beam splitter 53. The light flux is reflected by the polarizing film 54 toward the photodetector 57, passes through the analyzer 58, and then enters the photodetector 57 to detect a magneto-optical signal.
The polarization film 54 of the beam splitter 53 has a P-polarized reflectance.
30%, S-polarized light reflectance is 100%, and phase difference of reflected light is 0 deg.

(1), (2), which are displayed in FIG.
(3) is a coordinate for explaining the polarization state. LD51
To the magneto-optical disk 56, using the coordinates of (1),
As shown in FIG. 7A, the polarization direction of the semiconductor laser 51 coincides with the X axis. Light passing through the collimator lens 52, the polarizing film 54 of the beam splitter 53 and entering the magneto-optical disk 56 has an intensity of 70% due to the influence of the polarizing film 54 as shown in FIG. 7B. , The polarization direction coincides with the X axis. Next, the light reflected from the magneto-optical disk 56 is the beam splitter.
The coordinates in FIG. 6 (2) are used until reaching the polarizing film 54 of 53. The reflected light from the magneto-optical disc 56 is
Due to the effect of the reflectance and the Kerr effect on the magneto-optical disk 56, the light is rotated in the directions of Θ _k and -Θ _k depending on the direction of magnetization on the magneto-optical disk 56, and the polarization state shown in FIG. 7C is obtained. Next, the beam splitter 53
6 (3) is used for the light after being reflected by the polarizing film 54 of FIG. The light reflected toward the photodetector 57 is reflected by the polarizing film 54.
Due to the influence of, the intensity is linearly polarized and the intensity in the P polarized direction only is 30%.
(FIG. 7D). After that, the light passes through the analyzer 58 and enters the photodetector 57, and the magneto-optical signal is detected.

FIG. 8 shows a beam spot on the magneto-optical disk. The LD used in the magneto-optical disk device has an astigmatic difference (LD ass), and the light emission angle is parallel to and perpendicular to the bonding surface of the LD chip crystal (hereinafter, simply referred to as parallel direction and vertical direction). It is known that it is different from that of (as shown in FIG. 9). Therefore, when the aperture is limited by the objective lens or the collimator lens, the vertical direction in which the NA is substantially large due to the influence of the light emission angle is narrowed in the focused state as shown in FIG. 8A as compared with the parallel direction. It becomes a beam spot. Further, when the magneto-optical disk and the objective lens are moved away from the focused state (+ defocus) and approached (-defocus) due to the influence of the LD astigmatism,
The beam spot becomes elliptical and the major axis directions of the elliptical spot coincide with the track direction and the radial direction, respectively. FIG. 8B shows a + defocus state, and FIG. 8C shows a −defocus state.

Next, FIG. 10 shows a general compact disc reading optical system (conventional example 2). LD
The light emitted from 51 is 3 beams due to the grating 59.
It is converted into a beam, is reflected in the optical disc direction by the polarizing film 61 formed on the parallel plate 60, passes through the objective lens 55, and reaches the optical disc 62. The luminous flux reflected by the optical disc 62 is
After passing through the objective lens 55 again, the parallel plate 60, the concave lens 63 that is tilted with respect to the optical axis, and enters the photodetector 57 to detect an information signal. The polarizing film 61 formed on the parallel plate 60 is a half film having a P-polarized reflectance of 50% and an S-polarized reflectance of 50%.

The coordinates in FIG. 10 are coordinates for explaining the polarization state. The polarization direction of the light from the LD 51 coincides with the X axis as shown in FIG. Further, the entire pickup is rotated around the optical axis of the objective lens so that the polarization direction of the incident light with respect to the pit arrangement direction on the optical disk 62, the LD ass, the parallel direction, or the vertical direction is approximately 45 °. Therefore, as shown in FIG. 12, the shape of the beam spot on the magneto-optical disk 62 is the same as that of the conventional example 1 at the time of focusing and in the defocus state, but the direction of the major axis of the spot ellipse. Is inclined at 45 ° to the pit direction. Figure 12B
Shows a + defocus state, and FIG. 12C shows a-defocus state.

As a specific example of irradiating a beam spot with a tilt angle on a pit train on an optical disk as described above, the one disclosed in Japanese Patent Laid-Open No. 61-196435. There is. It is said that this makes it possible to reduce interference with adjacent tracks, increase tolerance to inclination in the track direction or tangential direction, and reduce the crosstalk amount as an output characteristic.

[0008]

However, the conventional example 1 has the following problems. Generally, when injection-molded plastic such as polycarbonate resin is used for the substrate of the magneto-optical disk, it has a fast axis in the disk radial direction or in the direction along the tangent line of the groove as shown in FIG. It is known to have birefringence (reference: POLYMERS I
N INFORMATION STORAGE TECHNOLOGY, Page 207 ~ 215,
Edited by KLMlttal, Publisher: Plenum Publishing C
orporation, 1989, America).

In this case, unless the polarization direction of the incident light on the magneto-optical disk (parallel to the joining surface of the LD chip) is parallel or perpendicular to the group, it is reflected from the magneto-optical disk due to the effect of birefringence. The light becomes elliptical and the C / N of the reproduced signal deteriorates. Therefore, the polarization direction of the light incident on the magneto-optical disk is selected to be parallel or perpendicular to the track direction. However, when the polarization direction of the light incident on the magneto-optical disk is set as described above, the LD ass and the track direction coincide with each other, and the + defocus state of the objective lens or
-In the defocus state, the long axis direction when the beam spot is deformed is parallel or perpendicular to the track direction, and each characteristic such as track error signal amplitude, jitter, and magneto-optical signal amplitude is in the + defocus state. And-it becomes asymmetric in the defocus state.

That is, each of the above characteristics changes extremely in either the + defocus-direction or the -defocus-direction. Then, the beam spot becomes the default due to the temperature change of the defect disk and the surrounding environment.
In the case of the waste state, the servo easily comes off or the reading error of the information signal increases. Further, either inter-track interference or inter-code interference in the defocus state will increase.

Further, LD ass and collimator lens N
A and the third-order Zernikea's aberration coefficient of the propagating light wavefront is as follows: Third-order Zernikea's aberration coefficient of the propagating wavefront = NA ² / 4λ × L
There is a relationship of D as (λ: LD wavelength). Write-once (WORM) and rewritable optical discs are better than read-only (ROM) optical discs.
It is necessary to increase the collimator lens NA in order to reduce the beam spot diameter on the optical disk and to secure the light efficiency. Therefore, it becomes easy to be affected by the LD ass from the above relational expression.

As a method for solving such a problem, a λ / 2 plate is inserted between the objective lens and the beam splitter, and only the polarization direction of the LD is LD around the optical axis of the objective lens.
There is a method of rotating it independently of the ass direction. That is, the LD ass direction is set to 45 ° with respect to the track direction, and the asymmetry of each characteristic in the + defocus state and the −defocus state is eliminated with only the polarization direction as the track direction. However, since this method uses λ / 2,
There is a problem that alignment of the fast axis or the slow axis is required and a phase difference error is generated, resulting in an increase in man-hours for assembling the apparatus, deterioration of characteristics, and an increase in cost.

Further, the conventional example 2 has the following problems. Beacon in Defocused State in Conventional Example 1
In order to eliminate the asymmetry of the mu spot, it is conceivable to apply a general compact disc reading optical system as shown in Conventional Example 2 to the magneto-optical signal detection based on the magneto-optical disc. In this case, the analyzer used in the conventional example 1 is inserted between the parallel plate and the detector, and the phase difference of the transmitted light is set to 0 without changing the spectral ratio of the characteristics of the polarizing film formed on the parallel plate.
It will be deg. By doing so, the asymmetry of the beam spot in the defocusing state as shown in Conventional Example 1 is eliminated, but the spectral ratio of the polarizing film 61 (FIG. 10) is 50% for both P-polarized light and S-polarized light. Since it becomes transparent and the information signal component (P-polarized component) is also halved, there is a problem that the characteristics such as C / N deteriorate.

The present invention is proposed in order to solve the above-mentioned problems, and has a simple structure, and the characteristics such as the track error signal amplitude, the jitter, and the magneto-optical signal are symmetrical regardless of the direction of the defocus. It is an object of the present invention to provide an optical information recording / reproducing device that changes and characteristics such as C / N do not deteriorate.

[0015]

In order to achieve the above object, the present invention provides a semiconductor laser, a collimator lens for collimating the light emitted from the semiconductor laser, and a collimator lens for collimating the collimated light. Optical having an objective lens for forming an image on a magnetic disk, a beam splitter for separating the reflected light from the magneto-optical disk from the optical paths of the collimator lens and the objective lens, and a light detecting means for receiving the separated light. In the optical information recording / reproducing apparatus, the beam splitting surface of the beam splitter is inclined with respect to the optical axis of the parallel light, and at least the S polarization reflectance or the P polarization reflectance or the S polarization transmittance is formed on the light splitting surface. Alternatively, a polarizing film having a P-polarized light transmittance of 100% is formed, and a surface including the normal line of the light separation surface and the optical axis of parallel light is formed to be parallel or perpendicular to the track direction of the magneto-optical disk, The semiconductor laser is connected to the crystal. The optical information recording / reproducing device is characterized in that the joining direction of the mating surfaces is formed so as not to be perpendicular or parallel to the surface including the normal line of the light separating surface and the optical axis of the parallel light.

[0016]

With this structure, even if the beam spot on the optical disk is elliptical, the track error is eliminated regardless of the direction of the defocus without complicating the structure.
It is possible to record and reproduce information signals in which characteristics such as signal amplitude change symmetrically and characteristics such as C / N do not deteriorate.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an outline of an apparatus according to the present invention. A collimator lens 2 is provided in a traveling direction of light emitted from a semiconductor laser (hereinafter abbreviated as LD) 1, and light converted into parallel light by the collimator lens 2 is provided in the traveling direction thereof. It enters the beam splitter 3. The incident light is polarized by the polarizing film 4 formed on the beam splitter 3.
, And then through the objective lens 5 to reach the magneto-optical disk 6. A part of the light incident on the beam splitter 3 is reflected, and the photodetector 7 used to keep the amount of light emitted from the objective lens 5 constant.
Is received by.

The luminous flux irradiated on the magneto-optical disk 6 and reflected there passes through the objective lens 5 again and reaches the polarizing film 4 of the beam splitter 3. The light that has reached the polarizing film 4 is reflected in the direction of the photodetector 8, passes through the analyzer 9, and then is received by the photodetector 8 to detect a magneto-optical signal. In addition, the characteristic of the polarizing film 4 is a P-polarized reflectance of 30.
%, S-polarized light reflectance is 100%, and the phase difference of reflected light is 0 deg. The coordinates (1) to (3) in FIG. 1 are for explaining the polarization state, but the polarization direction of the emitted light from LD1 is 45 ° with respect to the X axis at coordinates (1). There is.

Next, each polarization state of the device shown in FIG. 1 will be described. The LD1 to the magneto-optical disk 6 will be described with reference to the coordinates in FIG. 1 (1). The polarization direction of the emitted light from the LD1 is 45 ° with respect to the X axis as described above (FIG. 2A). Of the light incident on the polarizing film 4 of the beam splitter 3, 100% of the S-polarized component is reflected and 70% of the P-polarized component is transmitted, so that the polarizing film 4 of the beam splitter 3 is transmitted. The light that is transmitted through and is applied to the magneto-optical disk 6 becomes linearly polarized light having an intensity of 35% and aligned with the X axis as shown in FIG. 2B.

The polarization state until the light beam reflected from the magneto-optical disk 6 reaches the polarizing film 4 of the beam splitter 3 is
Explaining with reference to the coordinates in FIG. 1 (2), the optical axis is rotated in the direction of Θ _k or −Θ _k depending on the direction of magnetization on the magneto-optical disk 6 due to the reflectivity of the magneto-optical disk 6 and the effect of the car. The polarization state is as shown in 2C. Beam splitter 3
The polarization state of light from being reflected by the polarizing film 4 to reaching the photodetector 8 will be described with reference to the coordinates in FIG. 1 (3). The magneto-optical signal component (information signal) is the S polarization component. Since it is 100% reflected by the polarizing film 4, the magneto-optical signal component is incident on the analyzer 9 in a polarized state as shown in FIG. 2D without being lost, and the photo-detector 8 detects the magneto-optical signal.

Next, the beam spot image on the magneto-optical disk will be described with reference to FIG. As described above, it is known that the LD used in the magneto-optical disk device has an astigmatic difference, and the light emission angle differs between the parallel direction and the vertical direction with respect to the bonding surface of the LD chip crystal. Therefore, when the aperture is limited by the objective lens or the collimator lens, the vertical direction in which the NA is substantially large due to the influence of the light emission angle is narrowed in the focused state as shown in FIG. 3A as compared with the parallel direction. Bee
It becomes a must spot. Moreover, since the polarization direction of the light emitted from the LD1 is 45 ° with respect to the X axis of the coordinates shown in FIG. 1 (1), the magneto-optical disk and the objective lens are out of focus due to the influence of LD ass. In the state of moving away (+ defocus) and the state of moving away (-defocus), the beam spot becomes elliptic and the directions of the major axes of the elliptical spot form 45 ° with respect to the track direction (Fig. 3B, C). Note that FIG.
B shows a + defocus state, and FIG. 3C shows a-defocus state.

As described above, according to this embodiment, in the + defocus state and the −defocus state, the direction of the ellipse of the beam spot on the magneto-optical disk is 45 ° with respect to the track. Can be formed into Therefore, the amount of change in characteristics such as the track error signal amplitude becomes symmetrical. That is,
Even if the beam spot on the magneto-optical disk is in the defocused state due to the temperature change of the defect disk or the surrounding environment, the characteristics do not change extremely in either the + or-defocus state. , The servo is hard to come off, and the reading error of the magneto-optical signal (information signal) is reduced. Further, the magneto-optical signal (information signal) can be guided to the analyzer and the photodetector without loss, and the characteristics such as C / N are not deteriorated.

Next, a second embodiment of the present invention will be described. In this embodiment, the optical system constituting the device is the same as that in the first embodiment, but in this embodiment, the polarization direction of the emitted light from the LD is 30 with respect to the X axis in the coordinates of FIG. 1 (1). I am trying to achieve FIG. 4 shows the polarization state. The shape of the beam spot on the magneto-optical disk is as shown in FIGS. A indicates the in-focus state, and B and C indicate the + defocus state and the −defocus state. In these defocus states, the direction of the major axis of the ellipse is relative to the track. It is symmetrically inclined in the direction of 30 °.

Since the P-polarized light component incident on the beam splitter is larger than the S-polarized light component because of the above-described configuration (P-polarized light component 87%, S-polarized light component 13%), the beam
The amount of light that passes through the splitter is 61%, which improves the efficiency of use of the LD radiation. In the present embodiment, the polarization direction is set to 30 ° with respect to the X-axis, but the angle is not limited to this, and an arbitrary angle of 45 ° or less may be set. However, the asymmetry of each characteristic in the defocus state increases as it deviates from 45 °, so LD
It is necessary to select it in consideration of the use efficiency of the radiated light from.

The present invention is not limited to the above embodiment, but various modifications and variations are possible. For example, in the present invention, in the layout of the device, the characteristics of the polarizing film are S-polarized reflectance of 100% and P-polarized reflectance of 30%.
The layout may be 100%. In this case, in order to improve the use efficiency of the LD, it is necessary to make the S-polarized component incident on the beam splitter larger than the P-polarized component, and therefore, for example, 60 ° with respect to the X-axis in the coordinates in FIG. 1 (1). The polarization direction may be such that

[0026]

As described above, according to the present invention, the beam spot of the optical disk becomes elliptic in the defocus state due to the influence of the LD astigmatism and the light amount distribution with a simple structure without providing a new optical element. However, the characteristics of the track error signal amplitude, the jitter, the magneto-optical signal amplitude, etc. change symmetrically regardless of the direction of the defocus when the in-focus state is reached, making it difficult for the servo to come off and the information signal. Misreading is also reduced.
Furthermore, since the information signal can be guided to the photodetector without loss, information can be recorded and reproduced without deteriorating the C / N.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a polarization state in the above device.

FIG. 3 is an explanatory view of a beam spot shape on a magneto-optical disk in the above device.

FIG. 4 is an explanatory diagram of a polarization state of an LD according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram of a beam spot shape on the magneto-optical disk in the second embodiment.

FIG. 6 is a schematic diagram of an apparatus according to Conventional Example 1.

FIG. 7 is an explanatory diagram of a polarization state in the above device.

FIG. 8 is an explanatory view of a beam spot shape on a magneto-optical disk in the above device.

FIG. 9 is an explanatory diagram showing a light intensity distribution of an LD.

FIG. 10 is a schematic diagram of an apparatus according to Conventional Example 2.

FIG. 11 is an explanatory diagram of a polarization state of an LD in the above device.

FIG. 12 is an explanatory diagram of a beam spot shape on a magneto-optical disk in the above device.

FIG. 13 is an explanatory diagram of a magneto-optical disk.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser (LD) 2 Collimator lens 3 Beam splitter 4 Polarizing film 5 Objective lens 6 Magneto-optical disk 7 Photodetector 8 Photodetector 9 Analyzer

Claims (1)

Claim: What is claimed is: 1. A semiconductor laser, a collimator lens for collimating light emitted from the semiconductor laser into parallel light, and an objective lens for focusing the parallel light on a magneto-optical disk. In an optical information recording / reproducing apparatus having a beam splitter for separating reflected light from a magneto-optical disk from an optical path of a collimator lens and an objective lens, and a light detecting means for receiving the separated light, a beam is provided. The light splitting surface of the splitter is formed to be inclined with respect to the optical axis of the parallel light, and the light splitting surface has at least S-polarized reflectance or P-polarized reflectance, or S-polarized transmittance or P-polarized transmittance of 100%. A film is formed so that the plane including the normal line of the light separation surface and the optical axis of the parallel light is parallel or perpendicular to the track direction of the magneto-optical disk, and the semiconductor laser is the bonding surface of the crystal. Is the normal of the light splitting surface An optical information recording / reproducing apparatus, which is formed so as not to be perpendicular or parallel to a surface including an optical axis of parallel light.