JPS5870431A - Optical head - Google Patents

Abstract

PURPOSE:To reduce influence exerted on an error signal due to unevenness of an information forming layer, by providing a member for shielding the light of a higher order term against a pattern on the information forming layer, before or behind a member for extracting an asymmetrical light with respect to an optical axis of a light beam. CONSTITUTION:Light reflected by an information forming layer 4 of an optical disk passes through light shielding plates 28, 23, a spherical lens 24a and a cylindrical lens 24b, and forms a beam spot 11a' in a photodetector 26. The light shielding plate 28 shields a higher order term of a Fourier pattern against a pattern on the information forming layer 4, therefore, influence due to fine unevenness of a tracking guide, etc. is reduced. A focus error signal is detected by a difference between a photodetector 26a and 26b, and a tracking error signal is detected by a difference between 26c and 26d, by movement of a shadow 30 of a track.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a reproducing or recording/reproducing device capable of at least reading information by irradiating a focused laser beam onto an information storage medium such as an optical disk or a pidyo disk. This invention relates to an applicable optical head.

Generally, the focus is adjusted so that the beam waist (the narrowest part) of the focused laser beam is on the recording layer or the information formation layer as a light reflection layer of an information storage medium such as an optical disk or video disk. As a method, all defocusing of the laser beam on the information forming layer as a recording layer or a light reflecting layer is detected, and the objective lens is moved and brought into focus based on this detection signal.

Conventionally, a typical method for completely detecting the defocusing of laser light in the recording layer or the information forming layer as a light reflecting layer is to reflect it from the information forming layer of the information storage medium and use the objective lens. Detection system consisting of an optical lens and a detection unit consisting of a convex lens, for example, a photodetector divided concentrically into a plurality of parts is sequentially arranged, and the laser when the photodetector is irradiated. There is a method to detect the spot size (area) of light.

However, if there are fine irregularities on the surface of the recording layer or the information forming layer as a light reflecting layer of the information storage medium, the laser beam reflected from the irregularities will be diffracted, causing the spot on the photodetector to be distorted. A diffraction pattern appears. Strictly speaking, this diffraction pattern is generally not symmetrical.

Therefore, due to the influence of this diffraction pattern, it may be mistakenly detected as being out of focus.

Therefore, as shown in FIG. Light extraction member (knife wedge) d Luns e1 and two light detection cells f.

G? c photodetector h? Instead of detecting defocus by the spot size at the photodetector as in the past, we detect the movement of the beam spot l on the photodetector (
In the direction of arrow J), the detection of out-of-focus state was made less susceptible to the influence of ellipse diffraction, and a female crab was conceived.

However, the size of the beam spot i is
5 Even if we try to make the gap sufficiently smaller than the gap k in h, it will be made sufficiently small due to the effects of the spherical aberration of the lens e, etc. As shown in Figure 2, the shadow l of the diffraction pattern or imaging pattern in the beam spot j. There are problems such as defocusing may be disturbed due to the influence of

On the other hand, the conventional method for detecting tracking deviation is to split the reflected light into two and use an optical system on the other side of the optical system for detecting defocus to detect it, which makes the structure of the optical head complicated and large. It also has problems in that it is heavy and expensive.

The present invention has been made based on the above-mentioned circumstances, and its purpose is to simultaneously detect defocus and track deviation with one photodetector, and to provide a tracking guide on the surface of the information forming layer. It is possible to reliably detect the focal point by taking into account the effects of diffraction caused by the minute irregularities of the light, allowing for stable focusing adjustment!
It is intended to provide all heads.

Hereinafter, one embodiment of the present invention shown in FIGS. 3 to 10 will be fully referred to.
f, and explain. FIG. 3 shows an information recording/reproducing device used as an optical disk or video disk all-information storage medium and a # conductor laser all-optical head. , 3 is an optical head that faces one side of the information storage medium 1 and is capable of reciprocating in the radial direction of the information storage medium 1 (the overlapping direction in FIG. 3) by a head moving mechanism (not shown).

The information storage medium 1 is formed into a disk shape, and the piece 1
2 transparent substrates 5, 5 on which an information forming layer 4 as a recording layer or a light reflecting layer is formed;
．． inner and outer spacers 6, so that the inner and outer spacers 4 are on the inside of each other and a space is formed between the mutually opposing surfaces of the information forming layers 4, 4;
A tracking guide, which will be described later, is formed at the location where the information forming layer 4 is formed, and a rotation center hole (not shown) is formed at the center thereof. has been done.

- Also, the medium drive device 2 that rotationally drives the information storage medium 1 includes a rotating shaft 8 that is integral with the drive shaft of a motor (not shown), and a rotating shaft 8 that is fitted onto the rotating shaft 8 and is aligned with the axis of the driving shaft 8. The rotating support 9 has a right-angled horizontal support surface and supports the central lower surface of the information storage medium 1, and a presser 10 is attached to the upper end of the rotating shaft 8. Then, the information storage medium 10 is fitted into the rotation shaft 8 in the rotation center hole to perform radial positioning, and the center portion of the information storage medium 1 is held between the rotation support 9 and the presser 10 to fully move the information storage medium 1 in the plane direction. Further, the optical head 3 has the following construction.

That is, inside the optical head 3 is a semiconductor laser oscillator 1 that oscillates laser light 11 as a light beam in the entire horizontal direction.
A coupling lens 13 and a polarizing beam splitter 15 are arranged in this order in the lateral direction of this semiconductor laser oscillator 12. Further, above the polarizing beam splitter 15, a λ/4 plate 16 and an objective lens 17 are arranged in this order. A half mirror 18 is placed below the polarizing beam splitter 15 at an angle of 45 degrees, and the beam passes through the polarizing beam splitter 15 completely, splitting it into two parts, and connecting it to the reading optical system 19 and defocusing/tracking. The light is distributed to the optical system 20 for detecting deviation. The reading optical system 19 has lenses 21 and a reading photodetector 22 arranged in sequence in the lateral direction of the half mirror 18.

゛In addition, the optical system 20 for detecting defocus/track deviation is
Only a part of the light located at a position shifted from the center of the optical axis sequentially arranged below the half mirror 18: A light shielding plate 23 made of a knife wedge as a light extracting member, a spherical lens 24a, and a cylindrical lens 24b A detection system optical lens consisting of a mirror 25. A photodetector 26q is provided in the lateral direction of the mirror 25, and furthermore, the light passing range is completely restricted in the front stage of the light shielding plate 23 to shield higher-order terms of the Fourier pattern for the pattern on the information forming layer 4. It has a structure in which a light passage restricting member 27 is arranged.

Further, the light passage restricting member 22 is composed of an fc light shielding plate 28 having a light transmitting portion (Srin) 28a', r, and has an aperture restriction in the defocus detection direction parallel to the generatrix of the cylindrical lens 24b. , the structure has no aperture limit in the track deviation detection direction perpendicular to the generatrix of the cylindrical lens 24b. The above photodetector 2
Reference numeral 6 denotes a lens 2 for the information forming layer 4 when the position where the information forming layer 4 exists and the position of the beam waist of the focused laser beam 11 match as shown in FIG. 4(A).
4a, and the center is aligned with the optical axis of the reflected light as shown in FIG. 26b
The structure is such that 83 photodetection cells 26c1 are placed on the left side, and a fourth photodetection cell 26df is placed on the right side.

Note that 29 is a lens drive device such as a voice coil type focus motor that moves the objective lens 17 in the vertical direction (that is, in the direction toward and away from the bottom surface of the information storage medium 1).

On the other hand, the cylindrical lens 24b of the detection system optical lens
The direction of the generatrix is parallel to the direction of movement at the time of defocus (direction of arrow B) and perpendicular to the direction of track deviation (direction of arrow B). placed in an imaging position relative to layer 4; By doing so, the laser beam 11a has a full width trajectory as shown in FIG. 4(B) in a direction that is at an angle to the defocus detection direction, and the beam spot 11a' on the photodetector 26 is as shown in FIG. Beam spot 11 when defocusing is detected as shown in
It has an elliptical shape whose major axis is in the direction perpendicular to the direction of movement of a' (direction of arrow A). On the other hand, when viewed from the track deviation detection direction, the image forming point for the information forming layer 4 is as shown in FIG.
Exists at a position [P] away from the photodetector 26 indicated by
On the photodetector 26, a visiting pattern 3o of the tracking guide on the information forming layer 4 is detected as shown in FIG.

Thus, the laser beam 11 oscillated from the semiconductor laser oscillator 12 is turned into parallel light by the coupling lens 13, and then polarized upward by the polarizing beam splinter 15. This polarized light passes through λ/4 &16'c, so that the linearly polarized light becomes circularly polarized light, and then the objective lens 17
The light is focused on the information forming layer 4 as a recording layer or a light reflecting layer on the information storage medium 1.

At this time, if the information forming layer 4 is a recording layer, the irradiation energy of the laser beam 1)? When the value exceeds a predetermined value, a state change such as the formation of pits (holes) occurs in the area information forming layer 4, and a sentimental poem is recorded.

On the other hand, the reflected light from the information forming layer 4 changes from circularly polarized light to line-side light at the λ/4 plate 16, and this light travels straight through the polarizing beam splitter 15, exits downward, and passes through the half mirror 18. It is guided to an optical system 20 for defocusing and tracking deviation detection. Here, as will be described later, the defocus and track deviation of the laser beam 11 on the information forming layer 4 are detected by the difference in the amount of light detected by the first to fourth photodetection cells 26a to 26d of the photodetector 26. be done.

That is, as shown in FIG.
Part 1 of the light is asymmetrical with respect to the optical axis, that is, it is located at a position shifted from the center of the optical axis, in the middle of the reflected optical path after passing through the 5 beams.
1& is extracted from the light shielding plate 23 as a member for extracting all light, and after passing through the detection system optical lenses 24a and 24bf, the direction is changed by the mirror 25 and the light is applied to the photodetector 26, when the light on the information forming layer 4 is When the laser beam 11 is defocused, the light reflected by the mirror 25 moves vertically from the center position of the photodetector 26. This principle is shown in FIGS. 6(a), (b), and (c). This will be explained with reference to the figures. That is, when the laser beam 11 is focused on the information forming layer 4 as shown in FIG. A beam spot 11a' of the transmitted light 11a is located at the center of the photodetector 26. However, as shown in FIG. 6 (b), when the information forming layer 4 and the objective lens 17 are too close to each other and cannot be focused, the reflected light passing through the objective lens 17 gradually moves away from the optical axis↓ A beam spot 11a' of the light 11a that spreads outward and passes through the light shielding plates 23 hits a second detection cell 26b provided above the center position. Also, on the contrary, Figure 6 0
), when the information forming layer 4 and the objective lens 17 are too far apart and cannot be focused, the reflected light passing through the objective lens 17 is focused inward so as to gradually approach the optical axis. Beam spot 1 of light 11a passing through light shielding plate 23
1a' mostly hits the first detection cell 26a'r- provided below the center position area.

Therefore, when the distance between the information forming layer 4 and the objective lens 17 is kept constant and the focus is on, the amounts of light detected by the first photodetection cell 26a and the second photodetection cell 26b are both the same. When the information formation layer 4 and the objective lens 17 are close to each other and defocus occurs, the output level of the upper second photodetection cell 26b or the output level of the lower first photodetection cell becomes almost zero or the same level. Thicker than the output level of 26b,
1*, on the other hand, if the focus is far away and defocus occurs, the lower first
The output level of the photodetection cell 26a increases.

At this time, the photodetector 26 was installed at an optical imaging position with respect to the information forming layer 4 when the position where the information forming layer 4 existed and the position of the beam waist of the focused laser beam 1 coincided. , information storage medium 1 or objective lens 1
Even if the angle of the high-brightness portion of the light passing through the objective lens 17 is shifted due to tilting of the lens 7, the position of the light hitting the photodetector 26 will not shift. Note that if the optical imaging position and the photodetector 26 are arranged with a shift, the beam spot 11a' will spread, and if an angular shift occurs in the high-luminance part due to obscurity, the beam spot 11a' will become in focus. However, since the position of the high brightness part shifts, it seems as if beam spot 1
1a' itself may be erroneously detected as being out of position.

On the other hand, as shown in FIG. 7, the output signals of the first photodetection cell 26a and the second photodetection cell 26b are inputted to the drive circuit 32 via the difference amplification circuit 31, and are inputted to the drive circuit 32 via the lens drive circuit 29. The objective lens 17 is moved in the direction in which the object is in focus. In this way, the loss of focus due to the undulation of the information storage medium 1 is automatically corrected. Note that the reflected light 1 from the information forming layer 4 No is objective lens 17
After that, the pattern is divided into frequency components. That is, the pattern shape on the information forming layer 4 shown in FIG. 8(a) is as shown in FIG.

The device shown in (2) and (2) divides the signal into frequency components such that the one closer to the optical axis has a lower frequency and the frequency becomes higher as it goes outward.

On the other hand, in the gap where this reflected light 111 passes through the light shielding plate 28 as the light passage restricting member 27, higher-order terms of the Fourier pattern, that is, high-frequency components as shown in FIG. When the image is refocused, the pattern on the information forming layer 4 (shown in FIG. 8(a)) becomes a rounded pattern with no corner, as shown in FIG. 8(c). , the amount of focus error signal due to the influence of the imaging pattern within the beano spot 11a' on the photodetector 26 can be reduced.

The light passage restriction is 8", and all 5 materials and 27 are used.
Spherical lens 24a'< By reducing the substantial beam size of the passing laser light 11FL ↓ spherical m) By reducing the proportion of spherical aberration caused by the lens 24a, the beam spot 11a' on the photodetector 26 is This makes it possible to reliably detect the movement of the beam spot 11a'. Furthermore, light that passes outside the objective lens 12 or is diffracted by peripheral edges may travel in an unexpected direction (for example, to the outside), and after passing through the spherical lens 24a, the light is detected by the photodetector 26-H. However, by arranging the light passage restricting member 27, these lights are blocked and do not have any adverse effects.

On the other hand, the light shielding plate 23 for extracting the light 11af located off the center of the optical axis used for defocus detection is used to extract the light 11af located at a position offset in the length direction of the tracking guide with respect to the optical axis of the objective lens 17. 11af is designed to be extracted. Then, the laser beam for reproduction or recording/reproduction is aligned with the optical axis of the objective lens 17, and the incident laser beam for defocus detection is made into an incident laser beam for defocus detection in a state where the laser beam is sandwiched. The return laser beam is located, and the straight line connecting them is parallel to the length direction of the lagging guide.

Therefore, the length direction of the shadow 3o of the imaging pattern or diffraction pattern of the tracking guide reflected on the L-uniphotodetector 26 shown in FIG. 9 is the beam spot 11a.
The optical head 3 moves in the radial direction of the information storage medium 1,
That is, when the beam spot 11a moves in the direction across the tracking guide, the shadow 3 of the imaging pattern or the diffraction pattern of the tracking guide on the photodetector 26. )
It will move in the direction perpendicular to (direction of arrow B).

Therefore, the length direction of the shadow 3o is perpendicular to the direction of movement of the light for defocus detection on the photodetector 26 (direction of arrow A), and the shadow 30 moves in a direction parallel to the direction of arrow A. The photodetector 26 does not output a disturbance error signal as if the movement of the shadow 3o had disturbed the focus, which would occur in the case where the shadow 3o moves.

When no track deviation occurs, the shadow 3o of the imaging pattern or diffraction pattern of the tracking guide 29 hits the center in the width direction of the photodetector 26, as shown in FIG. 9(A). 11a', and is located on the right side of the photoelectric signal amount from the third photodetection cell 26c located on the left side. The amount of photoelectric signals from the fourth photodetection cell 26d becomes equal. Also, track misalignment may occur, causing the center of the light to shift to the right side of the track, or
Or, if the center of the light hits the left side of the track, the shadow 30 is shifted to the right or left of the center position of the beam spot 11a', as shown by 0 in FIG. 9 (b),
A difference occurs between the amount of photoelectric signals from the third photodetection cell 26c on the left [IIi and the amount of photoelectric signals from the fourth photodetection cell 26d on the right. As shown in FIG. 10, the output signals of the photoelectric cell 26c on the left side and the photodetection cell 26d on the right side are inputted to an actuator drive circuit 35 via a differential amplification circuit 34, and then sent to an objective signal via a linear actuator 36. The lens 17 will be moved to the position where the track deviation is fully corrected. At this time, since the direction of change on the photodetector 26 due to the track deviation and the direction of change due to defocus are orthogonal,
Even if the beam spot 11a' moves completely on the detector 26 due to defocusing, the track deviation detection system is not affected by it at all.

Further, since the light shielding plate 28 having the slit 28a serving as the light passage restricting member 27 has no aperture limit in the track deviation detection direction, a sufficiently large track deviation detection signal can be obtained without completely losing the amount of the track deviation detection signal.

Note that the information formed in the information forming layer 4 by pits (holes) or uneven shapes is read using the polarizing beam splitter 15.
The original gold lens 21 is reflected by the half mirror 18.
This is done by guiding the light to the photodetector 22 for reading.

In the above-mentioned embodiment, the light shielding plate 23 made of a knife wedge was used as a light extracting member provided at the rest of the reflected optical path and extracting light asymmetrically with respect to the optical axis.
Not limited to this, for example, light shielding plates other than knife wedges,
Optical prisms, optical lenses, light reflectors, slits, apertures, etc. may also be used.

In addition, although the light passage restricting member 27 is arranged before the light extraction member 23, the present invention is not limited to this.
or between the detection system optical lens 24 and the photodetector 26
The information forming layer 4 may be arranged between the information forming layer 4 and
It is fine as long as the position is close enough to the target.

Further, although the light shielding plate 28 having the slits 28aq is used as the light passage restricting member 27, the present invention is not limited to this, and the structure may have an aperture restriction in the defocus detection direction and not have an aperture restriction in the track deviation detection direction. Good.

In addition, it goes without saying that the present invention can be modified in various ways without departing from the gist of the invention.

As explained above, the present invention is directed to extracting a light sound asymmetrical with respect to the optical axis of a light beam that is reflected from a recording layer of an information storage medium or an information formation layer as a light reflection layer and completely passes through an objective lens. Tracking is achieved by detecting the direction of movement of the beam spot on the detector, detecting the defocus of the light beam on the information forming layer, and detecting the entire direction of movement of the imaging pattern or diffraction pattern within the beam spot. An optical device that detects all deviations, and is characterized by providing a light passage restricting member that emits kB of light of a higher-order term of the Fourier pattern with respect to the pattern on the information forming layer before or after the light extraction member. -\It's in Rad.

Therefore, defocus and track misalignment can be detected with one photodetector. Compared to the conventional method, which uses separate optical system sounds, two laser beams are used for detection. Since there is no need for means for separating the optical system, the optical system can be easily assembled, the structure is simple, the optical head can be made smaller, lighter, and less costly, and reliability against failures is increased. Furthermore, a light passage restricting member that restricts the entire light passage range was installed to completely block light from the local area of the Fourier pattern for the patternin on the information forming layer, so when the image is fully focused again, it will have a rounded shape with no corners. This has the effect of reducing the amount of focus error signals due to the influence of the imaging pattern within the beam spot on the photodetector.

In addition, the light passage restriction section has an aperture restriction in the defocus detection direction and no aperture restriction in the track deviation detection direction, so while the defocus detection sensitivity is fully increased, the tracking deviation detection sensitivity is reduced. It has the effect that it never happens.

[Brief explanation of drawings]

In Figure 1 (a), (b), and H, are the focal points lost due to the movement of the beam spot? FIG. 2 is an explanatory diagram showing the basic principle of detection, FIG. 2 is an explanatory diagram showing the state of the beam spot on the photovoltaic device, and FIG. 3 is a schematic configuration diagram of an information recording/reproducing apparatus to which all embodiments of the present invention are applied. , FIGS. 4(a) and 4(b) are explanatory diagrams showing the principle of forming an elliptical beam spot in the same embodiment, and FIG.
The figure is an explanatory diagram showing the state of the beam spot formed on the photodetector, and Figures 6 (A), (B), and H are for explaining the principle of defocus detection according to an embodiment of the present invention. Fig. 7 is an explanatory diagram showing the drive system for automatic blurring adjustment>1.
Figure 8 (a), (mouth 1), (mouth 2), (mouth,). G"3 is an explanation for showing the pattern on the information forming layer, the frequency component of this pattern, and the pattern shape on the photodetector. Figures 9 (a), (b), and (c) are the same implementation. An explanatory diagram showing the state of an imaging pattern or a diffraction pattern of a tracking guide on a photodetector in an example,
FIG. 1() is an explanatory diagram showing a drive system for automatic tracking deviation adjustment. 1... Information storage medium, 3... Optical q head, 4...-
Note @ Information forming layer as a layer or light reflecting layer, 1 no...
Light beam (laser light), 17...Objective lens, 20
. . . Optical system for out-of-focus detection, 23 .
6d... Light detection cell, 27... Light passage restriction member. Applicant's agent Patent attorney Takehiko E 3 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 8 Figure 11) 1 1 1 1 (3)-11--□□----- - 1 1 1 1 1 Figure 9 (c) 6d

Claims (2)

[Claims] (1) Extract the light that is asymmetrical with respect to the optical axis of the light beam that has been reflected from the recording layer or the information formation layer as a light reflection layer of the information storage medium and passed through the objective lens, and extract the light that is asymmetrical with respect to the optical axis of the light beam that is reflected from the information formation layer as the recording layer or light reflection layer of the information storage medium, and extract the light that is asymmetric with respect to the optical axis. It detects all the moving directions of the spot, and detects all the defocusing of the light beam with respect to the information forming layer, as well as detects all the moving directions of the imaging pattern or diffraction pattern within the beam spot. An optical head characterized in that a light passage restricting member is provided at the front or rear stage of the light extracting member for blocking optical sound of higher-order terms of the Fourier pattern with respect to the pattern on the information forming layer. (2) The optical head according to claim 1, wherein the light passage restricting member has an aperture restriction in the defocus detection direction and does not have an aperture restriction in the track deviation detection direction.