JP2859456B2 - Signal detection system of magneto-optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detection system of a magneto-optical disk drive for detecting a tracking error signal, a focusing error signal, and a magneto-optical recording signal based on light reflected from a magneto- optical disk.

[0002]

2. Description of the Related Art FIG. 6 shows an optical system of a conventional magneto-optical disk drive. The optical system includes a light emitting system including a semiconductor laser 1, a collimator lens 2, a shaping prism 3, and a compound prism 4 having two half mirror surfaces 4a and 4b, and a condenser lens 5, a cylindrical lens 6, and a servo sensor 7a. Error signal detection system, condenser lens 5, λ /
2 plates 8, polarizing beam splitter 9, data sensors 7b, 7c
And a magneto-optical recording signal detection system.

The light beam emitted from the semiconductor laser 1 passes through the half mirror surfaces 4a and 4b of the composite prism 4 and travels to the magneto-optical disk. Then, the reflected light from the optical disk is reflected by each half mirror surface and reaches each sensor.

[0004]

In a magneto-optical disk drive, a light beam from a disk is received and a focusing error signal, a tracking error signal, and a magneto-optical recording signal are received.
At least three signals of the signal must be detected.
The above-described conventional optical disk device is provided with one light receiving element for detecting an error signal and two light receiving elements for detecting a magneto-optical recording signal .

However, if a dedicated element is provided for detecting an error signal, there is a problem that the number of light receiving elements increases and the optical system becomes complicated.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and provides a detection system of a magneto-optical disk drive capable of detecting an error signal and a magneto-optical recording signal with a common light receiving element. The purpose is to:

[0007]

In order to achieve the above object, a signal detection system of a magneto-optical disc apparatus according to the present invention converts a light beam reflected by a magneto-optical disc into a P-polarized component and an S-polarized light.
A polarization separating unit for separating the light into a polarized light component; and two light receiving elements for receiving the separated polarized light components. These two light receiving elements detect the error signals of focusing and tracking, and perform magneto-optical detection. Can also be used for recording signal detection
Each of the light receiving elements is configured to be operated by a push-pull method.
First order diffracted light in spot to detect racking error
Symmetrically spaced apart from each other
Two tracking error light receivers and
It is designed to fill the area between the light receiving sections for racking error.
Centered light receiving area and focussing by astigmatism method
For detecting a tracking error,
For detecting four focusing errors provided outside
And a light receiving unit .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

[0009]

Embodiment 1 FIGS. 1 to 3 show Embodiment 1 in which the present invention is applied to an information recording / reproducing apparatus for a magneto-optical disk.

As shown in FIG. 1, the optical system of this device includes a light source unit 10, an objective optical system 20, a half mirror prism 33, and a signal detection optical system 40. Light source unit 1
Reference numeral 0 denotes a semiconductor laser 11 that generates a divergent light beam, a collimator lens 12 that converts the divergent light beam into a parallel light beam, and two anamorphic prisms 1 that shape the cross section of the light beam.
3, 14 and a mirror 15 for generating a parallel beam having a circular cross section.

The objective optical system 20 includes an objective lens 21 for condensing a beam on a signal recording surface of the magneto-optical disk MOD,
And a mirror 22. Objective lens 21 and mirror 2
2 is provided in a head (not shown) that slides in the radial direction x of the magneto-optical disk MOD. Also,
The objective lens 21 is provided on an actuator provided in the head, and is driven in the optical axis direction z and the disk radial direction x.

A part of the light beam from the light source unit 10 is reflected by the half mirror prism 33 and is condensed by the condenser lens 34 on the light receiving element 35 for automatic output adjustment of the semiconductor laser. On the other hand, the light beam reflected from the disk is reflected by the half mirror prism 33, the polarization direction is rotated by 45 ° by the λ / 2 plate 32, and is incident on the prism block 44 having the polarization separation surface via the condenser lens 43. I do.

The P-polarized light component transmitted through the prism block 44 is condensed on the light receiving element 46a as shown in FIG.
The polarized light component is condensed on the light receiving element 46b via the cylindrical lens 45.

The polarization direction of the laser beam reflected by the magneto-optical disk MOD is rotated by the magnetic Kerr effect in accordance with the magnetization direction of the disk at the position where the spot is formed.
This is rotated 45 ° to separate it into P and S components, and the recording signal is read from the difference in intensity.

Next, the arrangement of the light receiving area on the light receiving element and the calculation of each signal will be described. The first and second light receiving elements are the same element, and their light receiving areas are arranged as shown in FIG. In other words, these light receiving elements are two tracking error light receiving sections E and F which are spaced apart from each other and are symmetrically provided at positions mainly receiving the first-order diffracted light in the spot for tracking error detection by the push-pull method. And a central light receiving unit G provided to fill the area between the tracking error light receiving units, and four focusing error detection units provided outside the tracking error light receiving unit for detecting a focusing error by the astigmatism method. Light receiving units A, B, C, and D.

Here, signals output from the respective areas of the first light receiving element 46a are represented by area names A, B, C, D, E, F, and G, and the signals are output from the same area of the second light receiving element 46b. Output signals are A ', B', C ',
When represented by D ', E', F ', G', the focusing error signal FE,
The tracking error signal TE and the magneto-optical recording / reproduction signal MO
Each is obtained by the following calculations. FE = (A + C)-(B + D) TE = E-F MO = (A + B + C + D + E + F + G)-(A '+ B' + C '+ D' + E '+ F' + G ')

Next, the setting of the light receiving area on the light receiving element will be described. When an error signal and a magneto-optical recording signal are detected by two light receiving elements in the above-described optical system, a method in which one light receiving element is a quadrangle element shaped like a cross and the other element is an undivided element Can be considered. In this case, the focusing error signal is the difference between the output sums of the light receiving units located at diagonal positions of the four-divided element, and the tracking error signal is divided into two parts by a boundary line corresponding to the disk tangential direction of the four-divided element. Area output sum difference, magneto-optical recording signal
The signal is obtained as the difference between the sum of the outputs of all the regions of the 4-split element and the output of the non-split element.

[0018] However, the four-split element is suitable for detecting a focusing error signal by the astigmatism method, but is not optimal for detecting a tracking error signal by the push-pull method. In order to detect the tracking error signal, a pattern mainly receiving the first-order diffracted light of the spot formed on the light receiving element, that is, a pattern in the E and F regions in FIG. 3 is desirable.

In order to detect a track error, E, F
If the area of A, B, C, D is provided outside the area,
Both track and focus error signals can be accurately detected. However, since the area of the gap between E and F becomes a dead zone, a portion having the highest energy at the center of the spot is wasted, and the signal level when detecting the magneto-optical recording signal is reduced.

In any case, since the light receiving area of the split type light receiving element is smaller than that of the non-divided light receiving element by the dead zone, the output of both light receiving elements differs from the output when the magneto-optical recording signal is detected. And it is difficult to make adjustments for electrical balance.

In this embodiment, in order to solve the above-mentioned problems, firstly, light receiving areas E and F having an optimum shape for detecting a track error are set, and outside the light receiving areas A and F for detecting a focus error. B, C, and D are set, and an intermediate light receiving area G is set between the areas E and F. With such a configuration, the error signal is accurately detected, and the amount of light attenuated when the magneto-optical recording signal is detected is smaller than that of the non-divided light receiving element.

Further, since the light receiving regions of the two light receiving elements have the same pattern, the influence of the dead zone is common, and the magneto-optical recording signal can be calculated by the same design circuit.
The electrical balance of each polarization component can be easily obtained.

FIG. 4 shows a modification of the above embodiment. In the example of FIG. 4, the light beams separated into the P-polarized light component and the S-polarized light component by the prism block 44 are condensed on the light receiving elements 46a and 46b via the cylindrical lenses 45a and 45b, respectively.

According to this configuration, not only the magneto-optical recording signal MO but also each of the error signals FE and TE can be detected by using signals from the two light receiving elements as described below. FE = {(A + C)-(B + D)} + {(A '+ C')-(B '+ D')} TE = (E-F) + (E '-F') MO = (A + B + C + D + E + F + G)-(A '+ B' + C '+ D' + E '+ F' + G ') The error signals FE and TE are calculated by adding The amplitude is approximately doubled, and the detection accuracy can be improved.

[0025]

Embodiment 2 FIG. 5 shows Embodiment 2 of the present invention.

This device has the same light source unit 1 as in the first embodiment.
0, an objective optical system 20, and a half mirror prism 33. A part of the light beam from the light source unit is reflected on the half mirror surface and condensed on the light receiving element 35 for APC via the condenser lens 34. The light beam reflected by the magneto-optical disk OMD is reflected by the half mirror surface, passes through the λ / 2 plate 32, and enters the prism block 44 having a polarization separation surface via the condenser lens 43.

The light beams separated into the P-polarized light component and the S-polarized light component by the prism block 44 are passed through the cylindrical lenses 45a and 45b, respectively, to the light receiving elements 46a and 46b.
Focus on 6b. In this example, the cylindrical lenses are provided such that the generatrix directions are orthogonal to each other.

The light receiving amount range of the light receiving element is the same as that shown in FIG. 3, and the calculation method for error detection is as follows. FE = {(A + C) − (B + D)} − ｛(A ′ + C ′)
− (B ′ + D ′)｝ TE = (E−F) + (F′−E ′) MO = (A + B + C + D + E + F + G) − (A ′ + B ′)
+ C '+ D' + E '+ F' + G ')

If the light beam incident on the disc contains a wavefront aberration, an abnormal intensity distribution occurs in the spot on the light receiving element when the track is traversed, and a so-called F / T crosstalk noise is included in the focusing error signal. May ride. However, the intensity distribution abnormality that occurs on each light receiving element has a 180 ° rotational symmetry with respect to the intersection of the x and y axes on the light receiving element because the cylindrical lenses are symmetrically arranged. For this reason, the noise components included in the output of each light receiving element are output as opposite phases, and can be canceled by taking the sum of them.

As described above, according to the present invention,
The error signal and the magneto-optical recording signal can both be detected by the two light receiving elements, and the effect of the dead zone of the light receiving elements is made common by using the same pattern of light receiving elements,
It is possible to easily balance the light reception signals of the P and S polarization components , and to accurately detect an error signal,
Light at the time of magneto-optical signal detection compared to non-separable light receiving element
The amount attenuation can also be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical system of a magneto-optical disk device according to a first embodiment.

FIG. 2 is a plan view of a light receiving unit shown in FIG.

FIG. 3 is an explanatory diagram showing a pattern of a light receiving region of a light receiving element.

FIG. 4 is a plan view of a light receiving unit according to a modification.

FIG. 5 is a perspective view of an optical system of the magneto-optical disk device according to the second embodiment.

FIG. 6 is a plan view of an optical system of a conventional magneto-optical disk device.

[Explanation of symbols]

 11 Semiconductor laser MOD magneto-optical disk 44 Polarization separation prism 46a, 46b Light receiving element

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 7/095 G11B 7/095 A

Claims (1)

(57) [Claims] 1. A polarized light separating means for separating a light beam reflected by a magneto-optical disk into a P-polarized light component and an S-polarized light component, and two light receiving elements for receiving each of the separated polarized light components. The two light-receiving elements are used to detect focusing and tracking error signals and to detect magneto-optical recording signals.
Each light receiving element can be used for tracking by the push-pull method.
Primarily diffracted light in the spot for error detection
Symmetrically spaced apart from each other at the light receiving position
Tracking error receiver and this tracking
Inside the space between the light receiving parts for error
Central photodetector and focusing error detection by astigmatism method
Out of the light receiving section for tracking error.
And the four focusing error detection light-receiving units
Signal detection of magneto-optical disc device characterized by comprising
system.