JPH0244553A - Magento-optical recording and reproducing method - Google Patents

Abstract

PURPOSE:To execute focus control with high accuracy by detecting a focus error signal on the basis of the reflected light of a beam, whose intensity is strong, out of plural beams to be condensed and to irradiate a magneto-optical disk. CONSTITUTION:The reflected light by spots 18a and 18b, which are reflected from a magneto-optical disk 17, is reflected by a beam splitter 15 and separated to a reflected light and a proceeding light by a knife edge prism 21. The two proceeding beams are rotated by 45 deg. with a lambda/2 board 25 and separated to P-polarizing component and an S-polarizing component by a Wollaston prism 26. Then, the beams are incident to a photodetecting element 28 for focus error signal and magnetic signal detection totally as four spots 27a1, 27a2, 27b1 and 27b2. This spot 27a2 is caused by the reflected light of the beam for recording, whose intensity is strong, out of the two beams, with which the disk 17 is irradiated. Then, by using this spot, an error can be made minimum in the focus error detection.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention emits a plurality of beams from a semiconductor laser as a single light source, focuses them onto the same track of a magneto-optical disk using the same objective lens, and adjusts the recording mode. The present invention relates to a magneto-optical recording and reproducing method using a multi-beam optical pickup, in which information is sometimes recorded with a leading beam and information immediately after recording is reproduced with a trailing beam.

Conventional technology In recent years, the beam from a semiconductor laser has been narrowed down to a minute spot using an objective lens, and information has been recorded/reproduced or recorded/reproduced/
Optical discs that can be erased are attracting attention. This is because optical disks have a large capacity and a low cost per bit.
This is because the disk has advantages such as being removable and easy to handle.

However, it has the disadvantage that access time is longer than conventional magnetic disks. That is, when recording on an optical disc, when there is a command, the spot is first accessed and positioned at the desired address.

Next, recording is performed, and after the recording is completed, confirmation reproduction is performed to confirm the written information. As described above, since the optical disc has two recording modes: recorder confirmation playback, it takes a lot of time.

In order to solve these drawbacks, a multi-beam optical pickup device has been proposed. That is, a plurality of beams are focused one after the other on the same track, recording is performed using one of the preceding beams, and information is confirmed and reproduced RAW (read-after-write) using the other beam that follows. This method has the advantage that recording and reproduction can be performed simultaneously during one rotation, and the time required for recording mode processing can be shortened. This is reported, for example, in the document ``Prototype of 3.5-inch compact magneto-optical disk device'', Proceedings of the 1986 Institute of Electronics, Information and Communication Engineers Spring National Conference. That is, override and RAW are essential technical issues in achieving high speed and high performance of magneto-optical disks.

A conventional example of such a multi-beam optical pickup device will be explained with reference to FIG. First, two light emitting points 1a, lb
Two laser beams emitted at different emission angles from an array-shaped semiconductor laser (or two-wavelength hybrid laser array) (2) are collimated by the same coupling lens 2, transmitted through the beam splitter 3, and then deflected The light is reflected approximately 90' by the prism 4 and goes toward the magneto-optical disk 5 side. At this time, the light is focused onto the magneto-optical disk 5 by the same objective lens 6, and is irradiated on the magneto-optical disk 5 one after the other as two spots 7a and 7b on the same track.

Here, the leading spot 7a is for recording, and an air-levitating magnetic head 8 is used which is modulated according to recorded information during recording.
Recording is performed in response to a magnetic field generated by

The trailing spot 7b is for reproduction or confirmation reproduction.

In addition, the reflected light from these spots 7a and 7b reflected from the magneto-optical disk 5 passes through the objective lens 6 and the deflection prism 4 again, is reflected by the beam splitter 3, and is separated from the incident light. By passing through the filter 9, only one of the two reflected lights is directed to the signal detection system 10, where it is used for detection of a magneto-optical signal, a focus error signal, and a tracking error signal.

Problems to be Solved by the Invention However, such a conventional multi-beam optical pickup device uses a semiconductor laser array or a plurality of semiconductor lasers as the light source 1, and images are formed on a disk through the same objective lens. In devices that obtain multiple spots, the relative positional relationship of the spots on the disk is determined entirely by the characteristics of the semiconductor laser (chip spacing, wavelength, etc.), so the focus of the spots can be controlled with high precision using multiple light beams. It's difficult to do. Further, semiconductor lasers having multiple light emitting points have drawbacks such as being expensive.

That is, (1) When a semiconductor laser array is used as the light source, the distance between the spots 7a and 7b on the magneto-optical disk 5 is uniquely determined by the distance between the light emitting points.

In other words, the distance between the light emitting points cannot be narrowed beyond a certain level because the temperature rise between the chips of the semiconductor laser affects each other, causing variations in the emission wavelength and output. Therefore, the minimum value of the spot interval on the magneto-optical disk 5 is determined by the characteristics of the semiconductor laser. Furthermore, in order to suppress variations in the spot spacing on the magneto-optical disk 5, it is necessary to measure the chip spacing of the semiconductor laser chips, which further increases costs.

(2) When the light source is a semiconductor laser array, the focal positions of the two spots 7a and 7b on the magneto-optical disk 5 will differ depending on the light emitting point position of the semiconductor laser array. That is, when mounting the semiconductor laser l on the magneto-optical disk 5, if the position is tilted from the position where the chip end face of the semiconductor laser 1 is perpendicular to the normal position (optical axis of the coupling lens 2 to the objective lens 6). The deviation of the in-focus position in the optical axis direction becomes magnified. Therefore, in order to satisfy the deviation tolerance of the focusing positions of the two spots 7a and 7b, the semiconductor laser 1 must be mounted with great precision at the corners. In addition, if the corners of this installation become large, the spot spacing will also change.

(2) In the case of a semiconductor laser using a hybrid laser array with independent light emitting points, the focusing positions of the two spots 7a and 7b on the magneto-optical disk 5 differ depending on the positions of the light emitting points 1a and lb. As a result, 2 on the magneto-optical disk 5
In order to suppress variations in the focusing positions of the two spots 7a and 7b to below a permissible value, it is necessary to suppress variations in the distance between the semiconductor laser chips in the optical axis direction as much as possible, which leads to increased costs. Further, as in the case (2) described above, mounting of the semiconductor laser also causes a shift in the position of the light emitting point in the optical axis direction, so assembly requires strict adjustment.

■ As the wavelength of the semiconductor laser changes, the refractive index of the lens also changes. Assuming that the speed of light is ν (constant) and the C1 frequency, there is a relationship n=c/λν between the wavelength λ and the refractive index n. This means that the larger the wavelength, the smaller the refractive index.

On the other hand, semiconductor lasers generally have a characteristic that as the power increases, the wavelength increases (for example, a relationship of several nm nm7l0). Here, in the semiconductor laser with multiple light emitting points that we are currently focusing on, these two light emitting points do not emit light with the same output, so each light emission wavelength is different, and the refractive index of the lens for each wavelength is different. changes, and the in-focus positions of the two spots 7a and 7b on the magneto-optical disk 5 are shifted. The direction of deviation is both directions described in ■■.

In particular, in the case of a two-wavelength hybrid laser array, this tendency is more pronounced because the two wavelengths are originally different, such as 780 nm and 830 nm.

Here, it is possible to use an achromatic lens to cancel the wavelength fluctuation, but achromatic lens is not possible with a single lens such as an aspherical lens, which leads to an increase in the size and cost of the optical pickup.

Means for solving the problem A plurality of beams are formed from a beam emitted from a semiconductor laser as a single light source, and these beams are focused onto the same track of a magneto-optical disk by the same objective lens.
In a magneto-optical recording and reproducing method in which a leading beam records information in a recording mode and a trailing beam reproduces information immediately after recording, the one with the stronger intensity among a plurality of beams focused and irradiated onto the magneto-optical disk. A focus error signal is detected based on the reflected light of the beam.

The multiple spots obtained on the magneto-optical disk are formed by separating one beam emitted from a single light source, a semiconductor laser, so the optical axis direction of these spots on the magneto-optical disk is The light condensing positions will be the same.

Therefore, the focus error signal can be detected using any one of the plurality of beams reflected from the magneto-optical disk. At this time, since detection is performed using the one with the stronger intensity, it is possible to detect a focus error signal with a minimum error, and the focus of a plurality of beams can be controlled with high precision.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 6. First, a single chip semiconductor laser 11 is used as a light source.
is provided. One laser beam emitted from this semiconductor laser 11 is collimated by a coupling lens 12, beam-shaped by a beam shaping prism 13, and then enters a Wollaston prism 14. At this time, the polarization plane of the laser beam emitted from the semiconductor laser 11 is tilted by an angle θ in a plane perpendicular to the plane of the paper in FIG. Both polarized light components will be incident. Therefore, by passing through the Wollaston prism 14, the light is separated into two beams: a beam containing only the P-polarized light component and a beam containing only the S-polarized light component. 2 separated like this
The intensity ratio of the two beams can be arbitrarily changed by changing the angle θ of the plane of polarization of the laser beam incident on the Wollaston prism 14.

After passing through the same beam splitter 15, the two beams separated by the Wollaston prism 14 are placed one after the other as two minute spots 18a and 18b on the same track of the magneto-optical disk 17 by the same objective lens 16. The light is focused and formed. Here is the advance spot 18a
is for recording (override), and during recording, recording is performed by receiving a magnetic field from an air-levitating magnetic head 19 that is modulated according to recorded information. The trailing spot 18b is for reproduction or confirmation reproduction.

Then, the reflected light from these spots 18a and 18b reflected from the magneto-optical disk 17 is again reflected by the objective lens 1.
6, is reflected by the beam splitter 15, is separated from the incident light, and heads toward the detection optical system. First, the light travels while being converged by the detection lens 20, and is separated into reflected light and straight light by the Knifezi prism 21. The two beams reflected by the Knifezi prism 21 enter the light receiving element 24 for track signal detection as elliptical spots 23a and 23b through the cylindrical lens 22. Here, this light-receiving element 23 is divided into four parts as shown in FIG. Top and bottom of 23b (in Figure 2)
The tracking error signal ΔT is calculated by the push-pull method that takes the difference between
Detect.

On the other hand, the two beams traveling straight through the Naifezi prism 21 have their polarization planes rotated by 45 degrees by the λ/2 plate 25, and then are each polarized by the Wollaston prism 26, which is orthogonal to the beam separation direction by the Wollaston prism 14. Separated into polarized light component and S-polarized light component, total of 4 spots 2
7 a,, 27a,, 27 b,, 27
It enters the light receiving element 28 for detecting a focus error signal and a magneto-optical signal as b□.

This light-receiving element 28 is located at the third point in the direction of arrow B in FIG.
As shown in the figure, it is divided into eight parts.

Based on the detection signal of the light receiving element 28, a focus error signal ΔF and a magneto-optical signal M/○ are detected.

Here, the signal of the four divided areas in the light receiving element 24 is expressed as E-
Assuming that the signals of the 8 divided areas of the H1 light receiving element 28 are from ■ to P, the information about the recording/erasing spot 18a is as follows: ΔT=E−F ΔF= (M+N)−(0+P) or ΔF=M− It can be detected as 〇 or ΔF=N-P M10= (M10)-(N+P). On the other hand, information regarding the spot 18b for reproduction (confirmation reproduction) is as follows: ΔT=G−H ΔF=(I+J)−(K+L) or ΔF=I−K or ΔF=J−L M10=(I+K)−(J+L ) can be detected as

Here, two spots l8 on the magneto-optical disk 17
a and 18b are formed by separating one beam emitted from the semiconductor laser 11, and the focusing positions of the two spots 18a and 18b on the magneto-optical disk 17 in the optical axis direction are equal. Become. That is, the signal regarding the focus error will be the same for the two beams. Therefore, in order to detect the focus error signal ΔF, the above-mentioned ΔF= (M0N)-(0+P) or ΔF=M-0 or ΔF=N-P or ΔF= (I0J)-(K0+P) is required. It can be said that detection may be performed by any one of the following six types: L), ΔF=I−K, or ΔF=J−L.

Focus error signal Δ is determined based on which detection signal.
If F is detected, consider whether it is best.

First, the intensity ratio of the recording/erasing spot 18a and the reproducing spot 18b is set to 3:1, and the disk human incident light component incident on the magneto-optical disk 17 as shown in FIG. It is reflected by the magnetic disk 17 at a Kerr angle ek with the Kerr effect as shown in FIG.
Consider a case where the intensity ratio between the signal component X and the other component Y of the magneto-optical signal M10 is 110. In this case, four spots 27 a, 27 a on the light receiving element 28
2. The intensity ratio of 27b, 27b is (I+K):(J+L):(M+O):(N+P) Well 1
0:l:3+30. FIG. 5 shows such an intensity ratio relationship ((10), (1), (3), and (30) in FIG. 5 represent the ratio).

Here, four spots 27 a,, 27 a,,
Regarding the positional relationship between 27b and 27b, the spot interval in the vertical direction in FIG. Since the separation angle is determined, for example, the apex angle of the prism can be devised)
. On the other hand, although the left and right spot spacing in FIG. Spot spacing on the disk 17,
Limited by the size of the optical pickup. Therefore, by setting the focus error signal ΔF to the one with the largest intensity difference between the left and right spots, the error in focus error signal detection can be minimized.

In this embodiment, ΔF=N due to spot 27a2
It is better to detect it as -P. This spot 27a2 is caused by the reflected light of a recording beam with high intensity among the two beams irradiated onto the magneto-optical disk 17, and
This recording beam is reflected from the magneto-optical disk 17 and separated into a P-polarized component and an S-polarized component by the Wollaston prism 26, and the beam is composed of the polarized component light with the stronger intensity. be.

That is, when considering the above-mentioned intensity distribution on the light receiving element 28, it can be shown as shown in FIG.

Under the situation described in 2, for example, the focus error signal ΔF is expressed as ΔF = (M 0 N) - (0 + P) or ΔF = M - 0 or ΔF = (I 0 J) - (K + L) or ΔF = J - L. If it is detected in either, the M and L regions are affected by the neighboring spots, so it is not possible to accurately detect the focus error signal ΔF by detecting these components including the M and L components.

In this respect, among the four spots, there is almost no influence from the neighboring spots, as can be seen from Figure 6, I, K, and N.
and spots 27b1 and 27a2 incident on P.

Among these, the spot 27a2 has a strong intensity and the intensity ratio with the neighboring spot is 1=30, so the spot 27a2
It is less affected than by the b1 side. Therefore, if the focus error signal ΔF is detected using ΔF=N−P, detection can be performed with the smallest error.

In addition, instead of dividing the light reception detection area in the light receiving element 28 into 8 parts as shown in FIG. 3, as shown in FIG. , 0 portions may be collectively designated as M, the N portion may be divided into two as Nl and N2, and the P portion may be divided into two as PL and P2.

In this case, ΔF = (PL + P2) - (Nl + N2) M10 = M
(N1+N2+PL+P2) Playback signal immediately after recording (
Verification signal)=I-J.

In this embodiment, the Knifezi method has been described as a method for detecting the focus error signal, but other methods such as the astigmatism method, the concentric circle method, etc. may also be used.

Further, if the tracking error signal is not required due to sample servo or the like, the light receiving element 24 for detecting the tracking error signal may of course be omitted.

Effects of the Invention Since the present invention is configured as described above, the plurality of spots obtained on the magneto-optical disk are formed by separating one beam emitted from a semiconductor laser as a single light source. Since the focusing positions of these spots in the optical axis direction on the magneto-optical disk are the same, the focus error signal can be detected by any one of the plurality of beams reflected from the magneto-optical disk. Since the one with the stronger intensity is used for detection, it is possible to detect a focus error signal with a minimum error, and to control the focus of a plurality of beams with high precision.

・・・Magneto-optical disk applicant Co., Ltd. Rico

[Brief explanation of the drawing]

FIG. 1 is a schematic front view of an optical system showing an embodiment of the present invention;
Figure 2 is a plan view of the light-receiving element as viewed from arrow A, Figure 3 is a side view of the other light-receiving element as viewed from arrow B, Figure 4 is a vector diagram of the polarization components of incident/reflected light, and Figure 5 is the received light. FIG. 6 is an explanatory diagram showing the intensity ratio in the element, FIG. 6 is an explanatory diagram of the light-receiving element also showing the intensity distribution, FIG. 7 is a side view showing a modified example of the light-receiving element, and FIG.
The figure is a front view showing a conventional optical system. 11... Semiconductor laser, 16... Objective lens, 17
Figures (a) (b)]

Claims (1)

[Claims] 1. A plurality of beams are formed from a beam emitted from a semiconductor laser as a single light source, and these beams are focused onto the same track of a magneto-optical disk by the same objective lens to record. In a magneto-optical recording and reproducing method in which a leading beam records information and a trailing beam reproduces information immediately after recording in the mode, the magneto-optical disk is condensed and irradiated with the one with the stronger intensity among the plurality of beams focused and irradiated onto the magneto-optical disk. A magneto-optical recording and reproducing method characterized by detecting a focus error signal based on reflected light of a beam. 2. According to claim 1, the focus error signal is detected based on the polarized component light having the stronger intensity after separating the reflected light from the magneto-optical disk into P-polarized component light and S-polarized component light. magneto-optical recording and reproducing method.