JPS5848240A - Optical head - Google Patents

Abstract

PURPOSE:To realize the stable and simultaneous detection for both the out-of- focus and a shifted tracking, by detecting the difference signal of two sets of photodetecting cells which is formed with an oval beam spot on a 4-split photodetector, when the beam waist position coincides with the position of an information forming layer. CONSTITUTION:The laser light 11 is condensed on an information forming layer 4 via a coupling lens 13, a polarized beam splitter 15, a lambda/4 plate 16 and an objective lens 17. The reflected light travels backward to pass through the splitter 15 and forms an oval beam spot 11a on a 4-split photodetector 26 via a light shielding plate 23 set at the position out of the optical axis, a spherical lens 24a and a cylindrical lens 24b. Then the difference output is detected between two sets of photodetecting cells 26a/26b and 26c/26d, and the shifting direction of the beam spot is detected in terms of the direction of an arrow A and its orthogonal direction. In such way, the stable and simultaneous detection is possible for both the out-of-focus and a shifted tracking.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reproducing or reading information by irradiating an information storage medium such as an optical disk or a digital disk with a focused laser beam. The present invention relates to an optical head that can be applied to recording/reproducing devices and the like.

In general, the focus is adjusted so that the beam waist (the narrowest part) of the condensed radar light comes to the recording layer or information forming layer as a light reflective layer of an information storage medium such as an optical disc or video disc. One way to do this is to detect the defocusing of the laser beam on the information forming layer, which is a recording layer or a light reflecting layer, and then move the objective lens to focus based on the detection signal. .

Conventionally, a typical method for detecting the defocusing of radar light on an information formation layer as a recording layer or a linear light reflection layer is to reflect it from the information formation layer of an information storage medium and pass it through an objective lens. A detection system optical lens consisting of a convex lens and a photodetector in which the detection section is divided concentrically into a plurality of parts are sequentially arranged on the reflected optical path of the radar light that has passed, and the radar light when the photodetector is irradiated is Light suit size (area)
There is a way to detect this.

However, if there are minute irregularities on the surface of the recording layer of the information recording medium or the information forming layer as the light reflecting layer, the radar light reflected from the irregularities will be diffracted, causing the light to be reflected on the photodetector. A diffraction Δ turn appears in the switch. Strictly'! Moreover, these diffraction-arm turns are generally not symmetrical.

Therefore, it may be erroneously detected that multiple focal points are buried under the influence of this diffraction AI ethanon.

Then, as shown in Fig. 1(f))(c), there is an optical path asymmetrically located in the middle of the reflected optical path C of the light beam reflected from the information forming layer a and passed through the objective lens b. A photodetector having a light extracting member (N7W5P) d, a lens, and two photodetection cells f'e1g is provided, and the photodetector OWr is connected as in the conventional method. ,) Rather than detecting defocus by size, defocus is detected by the movement of the beams (in the direction of arrow j) on the photodetector, making it less susceptible to diffraction. Now I can think of what I did.

However, even if we try to make the size of the beam 4 sufficiently small compared to the gap k in the photodetector, it will not be made sufficiently small due to the effects of spherical aberration of the lens, etc., and the beam size will become smaller as shown in Figure 2. The influence of the shadow 1 of the diffraction Δ turn or the imaging Δ turn within the 4-point amount causes the focus to be lost.On the other hand, the conventional method for detecting the center and king deviations is to split the reflected light into two and use an optical system for detecting the focus deviation. The present invention solves the problem of detection using an optical system separate from the optical system, which requires a complicated structure, is heavy, and increases the cost. This was developed based on the above circumstances, and its purpose is to be able to simultaneously detect focus embedding and track deviation with a single photodetector, and to obtain extremely stable detection of both To and Hi. This is an attempt to provide a new perspective to optics.

The present invention will be described below with reference to an embodiment shown in FIGS. Figure 3 shows an optical disk or a video disk as an information storage medium, a semiconductor radar as an optical disk, and a semiconductor radar as an optical disk.
The information recording/reproducing device used in the card is shown. In the figure, 1 is a 6 information storage medium which is rotationally driven by a medium drive device 2, and 3.
is an optical head that faces one side of the information storage medium 10 and is capable of reciprocating in the radial direction of the information storage medium 1 (back and forth in FIG. 3) by a moving mechanism (not shown).

Two transparent substrates 5.5 each having an information forming layer 4 as a recording layer or a light reflecting layer formed on one side thereof are placed in a state where the information forming layers 4, 4 are inside each other and the information forming layer 4 is placed on one side.
, 4 are bonded together with the inner and outer spacers 6 and the outer and outer spacers 1 interposed so that a space is formed between the inner surfaces. In front of the truck jig guide, which will be described later, is formed a rotating groove (not shown) in the center thereof.

The medium drive device 2 that rotationally drives the information storage medium 1 includes a rotation shaft e integrated with a drive shaft of a motor (not shown);
A rotary support 9 is fitted onto the rotary shaft 8 and has a horizontal support surface perpendicular to the axial center line of the drive shaft 8 and supports the central portion of the information storage medium 1; It has a presser 10 attached to the upper end. Then, when the information storage unit 10 rotation center hole is fitted to the rotation shaft 8 and radial positioning is performed, the center portion of the information storage medium 1 is held between the rotation support 9 and the presser 10. It has a structure that regulates movement in the plane direction.

Further, the optical head S has the following configuration.

That is, multi-conductor radar oscillation @1 that oscillates a laser beam 11 as a linear beam in the optical head J in the horizontal direction.
1 is provided, this semiconductor laser oscillator 110
A cutter lens 13 and a splitter 15 are arranged in sequence in the machine direction. Furthermore, above the polarizing beam sinter 15, objective lenses 5rs and 5rs are sequentially arranged.

Below the polarizing beam splitter 15, a half-light beam 18 is placed at an angle of 45 degrees to split the light that has passed through the polarizing beam splitter 1j into two and read it with an optical system 1p and a focal point. ) U, it is displayed so as to be distributed to the optical system 20 for detecting displacement. The reading system 1# is shown as having a half 21 and a reading photodetector 22.

In addition, the optical system 2a for detecting focus filling/travel and deviation is used as a light extracting member that extracts only a part of the light located at a position KTo shifted from the center of the optical axis, which is sequentially arranged below the half focus tool 18. A light shielding plate 23 consisting of a knife wedge, a detection system optical lens, Iei4h.

14b The photodetector 2 is configured to have an optical detection hot water outlet 26 in the lateral direction of the electric detector 2j1 and the photodetector 25.
# indicates the lens 2 for the information forming layer 4 when the position of the information forming layer 4 and the position of the beam waist of the condensed radar light 11 match as shown in FIG.
If the optical crystal is provided at the image formation position of 4&, then - and 4 and 5th
As shown in the figure, align the center with the generatrix of the reflected light, directly below it is the first photodetection cell xg, directly above it is the second photodetection cell pit, and on the left side is the third photodetection cell 26. The configuration is such that a fourth photodetection cell sea is placed on the right side.・In addition, 21 is objective lens J! 11 in the vertical direction (that is, the direction toward and away from the bottom surface of the information storage medium 1) is a lens drive device such as a coil type focus motor.

On the other hand, the detection system optical lens 24 & is a spherical lens-1 detection system optical lens [1 is not a cylindrical lens, the direction of the generatrix of the cylindrical lens a4bo is perpendicular to the direction of movement (direction of arrow) when the focal point is buried, It is parallel to the track deviation direction (arrow 1 direction) and the photodetector 2
The position # is placed at the imaging position with respect to the information forming layer 4 of the information storage medium 10. By doing so, in the direction perpendicular to the detection direction, 11% of the Radhe light traces a trajectory as shown in FIG. As shown in FIG. 5, "y)Jfa' has an elliptical shape whose major axis is in a direction perpendicular to the moving direction (direction of the arrow) of the beams /,)11&' at the time of out-of-focus detection.

On the other hand, there exists a position P 11 away from the photodetector j shown in FIG. On the photodetector j#, as shown in FIG. 5, a diffraction noturn J0 of a tiger, a gold, and a dazzle on the information forming layer 4 is observed.

Thus, the nine radar light 11 oscillated from the semiconductor radar oscillation @11 is turned into parallel light by the cylinder lens 13, and then polarized upward by the polarizing C-musderitter 1s. The polarized light passes through the V4 plate 16, and the linearly polarized light becomes circularly polarized light.
The FK light is focused on the information forming layer 4 as a recording layer or a light reflecting layer on the multi-information storage medium 1.

At this time, when the information forming layer 4 is a recording layer, by setting the irradiation energy to a predetermined value or more, the information forming layer 4 undergoes state changes such as the formation of ffi. At the beginning, information is recorded.

-4) In the information forming layer, the four reflected lights are changed from circularly polarized light to linearly polarized light by the V4 plate 1σ, and this light travels straight through the polarizing beam splitter 15 and exits downward, and is transmitted to the 8th plane. Passed 18 and filled the focus/Tora.

It is guided to an optical system 20 for detecting displacement. Therefore, as will be described later, detection is made based on the difference in the amount of light detected by the laser beam 26 on the information forming layer 4 at @1 to the fourth photodetection cells 111 to Xta.

In other words, as shown in Fig. 3, a portion of the light that is asymmetrical with respect to the optical axis, that is, located at a position shifted from the center of the optical axis, is located in the middle of the reflected optical path after passing through the one-polarized beam λ splitter J-8. After extracting only 11a through a light shielding plate 2J as a light extraction member and passing it through the detection system optical lenses z4m and 24b,
When the direction is changed by the ζ-25 so that it can be placed on the photodetector 2#, - When the focus of the radar light 11 on the information forming layer 4 is filled, the light reflected by the ζ-25 is photodetected. Figure 6 shows how the container 26 moves vertically from its center position.
, (b) 1. (c) This will be explained with reference to the principle diagram shown in k.

That is, as shown in FIG. 6(f), when the radar beam 11t) is focused on the information forming layer 4, the reflected light that has passed through the objective beam *Kd and e11 is parallel to the optical axis. The light beam 11a' that has passed through the light shielding plate 23 is located at the center of the photodetector 26. However, as shown in FIG. 6(b), if the information forming layer 4 and the objective lens 11 are too close to each other and cannot be focused, the reflected light passing through the objective lens 11 gradually moves away from the optical axis. As it spreads outward,
Light passing through light shielding plate 2J (11*O1'-musd'y)
11 On the second detection cell 2σb provided above the center position of a'q, there is also an information forming layer 4 and an objective lens 1r as shown in FIG. If it is too far away and cannot be focused, the reflected light passing through the objective lens 11 will be focused inward so as to gradually approach the optical axis. tsu) 1
1 There are many marks on the first detection cell 2σb provided below the center position of a'a.
When the distance from M 4 h n, vyx, 2 is kept constant and in focus, the first photodetection cell 26
The amount of light detected by & and the second photodetection cell xgb is almost zero or at the same level as the tortoise, and when the information forming layer 4 and the objective lens 11 are close to each other and the focal point is blurred, If the output level of the second photodetection cell 2ib on the upper side is higher than the output level of the first photodetection cell '26b on the lower side, or conversely, if the output level of the second photodetection cell 2ib on the lower side is too far away and the focus is blurred, the output level of the second photodetection cell 2ib on the lower side The output level of the photodetection cell 26m increases.

At this time, the photodetector 2# is installed at an optical imaging position with respect to the information forming layer 4 when the position where the information forming layer 4 exists and the position of the beam waist of the condensed radar light 11 match. Therefore, the information storage medium 1 or the objective lens, e
17 is tilted and the angle of the high-brightness portion of the light that passes through the objective lens 11 is shifted, the position of the light hitting the photodetector 26 will not shift. If the beams 'y)JJa' are placed offset from the camera 26, the beams 'y)JJa' will spread, resulting in a shift in the angle of the high-brightness part. Because it shifts, it looks like Beams 4. To J
J&'The position of the turtle may be mistakenly detected as having shifted.

On the other hand, as shown in FIG.
is input to the drive circuit 33 via the lens drive circuit 21.
The objective lens ' and leIF are moved in the direction of focus through the lens.

In this way, the focus blemishes caused by ridges or the like on the information storage medium 1 are automatically corrected.

Note that the information formed in the information forming layer 4 with the uneven shape can be read using the polarizing beam splitter 1.
5, and the light reflected by the half mirror 18 is passed through the lens 1.
1 to the reading photodetector 22.

However, when the beam waist position of the radar beam 11 matches the position of the information forming layer 4, the beam 111' on the photodetector 1# is focused on the detection photodetection cell Jlta. , jgb is arranged in an elliptical shape with its long axis in the direction perpendicular to the array direction, the beam spot y) 11 m' is the distance between the lower 10th photodetector cell 26a and the upper 2nd photodetector cell 3111. Opposed to the gear 31, the photodetection cell 16 corresponds to the total ratio of photoelectric beams irradiating the photodetection cells 26a to zeta 111'.
The proportion of the area corresponding to m and 16b is much smaller than that of the round beam shown in FIG. Therefore, the diffraction pattern or imaging within the beams fy) 11 m' - the shadow of Cape Navel SO (as shown in Figure 5)
In addition, the focal point will not be adversely affected by the foliage.
(The pattern is shown in Fig. 6), eAs it is now, it will protrude greatly toward the upper photodetection cell 26'bTo or the lower photodetection cell xttb, so the out-of-focus detection sensitivity will decrease. Never happened.

Further, a tracking guide (as shown in the figure) is formed in advance in the information storage medium 1 in a spiral shape. In order to achieve higher density in the information storage medium 1, it is necessary to narrow the track pitch. Mechanical control of the actuator that controls the position of the optical head 3 to control the optical head 3 to reach a predetermined track position during writing or reading is insufficient in reliability;
The compatibility of the information storage medium 1 is poor from the perspective of the device,'C.
In contrast, if a tracking guide is provided on the information storage medium 1, it will detect the position of the optical head 30 in the radial direction on the information storage medium 1 and feed back the correction to the actuator. This can increase reliability for tracking.

The tracking guide is formed by forming grooves with a width smaller than the beam waist size of the laser beam 11 focused on the information forming layer 4 in a grove shape like a normal record board. As will be described later, if the center of the focused laser beam 11 deviates from the center of the groove, this can be optically detected due to the diffraction phenomenon of the reflected light.

In addition, the optical axis used for defocus detection is deflected in the length direction of the king guide with respect to the optical axis of the objective lens 11 for extracting the light JJa whose center is shifted. It is formed so as to extract the light JJa at the position O. Then, the radar beam for reproduction or linear recording and reproduction is aligned with the optical axis of the objective lens 11, and the focused laser beam is sandwiched between the incident laser beam for detection and the focused beam for detection. The straight line connecting them is parallel to the length direction of the tiger and king guides.

Therefore, as shown in FIG. 8, the length direction of the shadow SO of the reflection fM4fi-y or the four-turn diffraction of the tracking guide reflected on the photodetector 26 is the beam spot y.
) J 1 m' along the moving direction (the true direction of the arrow) on the photodetector 26.

Therefore, the optical head I is in the radial direction of the information storage medium l,
In other words, when moving in the direction across the tracking guide, the shadow J0 of the imaging pattern or diffraction pattern of the tracking guide on the photodetector (arrow true direction)
It will move in the direction K perpendicular to (the direction indicated by the arrow).

Therefore, the length direction of the shadow SO is perpendicular to the direction of movement of the light for out-of-focus detection on the photodetector 26 (the true direction of the arrow), and the shadow 3Q may be parallel to the direction of the arrow A. When the shadow 30 moves in the direction, the outer tWA difference signal appears as if the focus is disturbed.
The output from the table never appears.

On the other hand, when no track deviation occurs, as shown in FIG. The third photodetection cell 26 is located on the left side of the beam at the center of IJ a'.
It is located on the right side of the photoelectric signal amount from Φ. The amount of photoelectric signals from the fourth photodetection cell 26d becomes equal. In addition, if a track misalignment occurs and the center of the light shifts to the right side of the track, or if the center of the light stays on the left side of the track, please refer to Figure 8). Shadow 30 is V
-Mussu, ) J J a' is shifted to the right side or to the company friend side, and the photoelectric signal amount from the 30th photodetection cell l11m on the left side and the photoelectric signal from the 4th photodetection cell 2641 on the right side. There will be a difference in quantity. Then, as shown in FIG. 9, the output signals of the left photodetection cell 2 and the right photodetection cell sea are inputted to the actuator drive circuit 35 via the difference amplification circuit 34, and are input to the linear actuator S6.
The objective lens 1el'l is then moved to a position where the misalignment is corrected.
' At this time, the direction of change on photodetector 2# due to the shift and the direction of change due to defocus are orthogonal;
Peemes out of focus? .

) 11 a' moves on the detector 2#, and the main discrepancy detection system is not affected by this. In the above-mentioned embodiment, the detector 2# is moved over the optical axis. It is also possible to use an illumination plate with a light extraction part that extracts only the light from the area, and furthermore, it is possible to use an illumination plate that has a light extraction part that extracts only the light from the area. Rhythm elements may be arranged to extract only a portion of the light located at a position offset from the optical axis.

Further, although the description has been made regarding the case where the tracking i-guide is provided in advance, it is needless to say that the invention is not limited to this.
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 1 extracts the light that is reflected from the recording layer of the information storage medium or the information formation layer as a light reflection layer, passes through the objective lens, and is asymmetrical with respect to the optical axis of the Jiushang beam. In addition to detecting the moving direction of the beams f and g on the photodetector, the light V- to the information forming layer is detected.
・A system that detects the focus deviation of the beam and detects the center track shift by detecting the diffraction/middle-turn moving square within the beam suite.
When the beam waist position of the Rade light matches the position of the information forming layer above, the beam on the photodetector? The focal point of the photodetector has an elliptical shape with long sleeves in the direction perpendicular to the arrangement direction of the photodetector cells for detection, and the photodetector has at least four photodetection cells arranged diagonally. At least one of the focus detection and shift detection is inside the photodetector! The optical head is characterized in that the optical head performs the conversion using the difference signal of the photoelectric conversion signals from the photodetection cells facing each other with the center point as the boundary.

Therefore, since we have made it possible to detect focus embedding, traverse, and misalignment with a single photodetector, the radar is much easier to detect than conventional detection methods that use separate optical systems for each. To optical systems that do not require a means to separate light into two, easy to assemble an optical system, and have a simple structure,
This makes it possible to make the board smaller, lighter, and lower in terms of power consumption, and also increases reliability, which is less likely to occur due to failure.

In addition, the beam spot may have an elliptical shape with its long axis perpendicular to the arrangement direction of the photodetector cells for defocus detection. Since the movement is detected using the difference signal of the photoelectric conversion signal from (♂, G signal, etc.)
It is extremely unlikely to be affected by the Q-diffraction pattern of the light reflected from the ζ or the imaging pattern, and stable focusing control can be performed. Moreover, it appears that the defocus detection sensitivity is reduced compared to the conventional method.

In addition, since the direction of change due to track deviation is perpendicular to the direction of change due to focus blur and in the long axis direction of the beam spot on the photodetector, it is sufficient to detect focus blur without any negative effect. This has the effect that a signal with a tracking deviation can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the basic principle of detecting multifocal beams by the movement of fo (n re is beams &,). Fig. 2 is an explanatory diagram showing the state of beams on the optical analyzer. Figure, 3rd
The figures are a schematic configuration diagram of an information recording and reproducing apparatus to which embodiment 1 of the present invention is applied, FIG. 6 is an explanatory diagram showing the state of the beam suite formed on the photodetector, and FIGS. FIG. 7 is an explanatory diagram showing the drive system for automatic defocus adjustment, and FIGS. 91 is an explanatory diagram showing the state of the diffraction pattern, and No. 91 is an explanatory diagram showing the drive system for automatically adjusting the tiger and king deviations. 1.-Information storage medium, J-Optical, 4. Information forming layer as recording layer or light reflection layer, 11-.Optical V-
Person (radar light), 11 - objective lens, 2# - focal spot is detection optical system, 2J - light extraction member (3i! light plate), 1
4 m = spherical lens, j4b - cylindrical lens, zg -] detector, J6a to j#d - light detection ring. Applicant's representative Patent attorney Takehiko Suzue No. 2I, No. 3II

Claims (2)

[Claims] (1) Extract the light that is asymmetrical with respect to one optical axis of the beam that has been reflected from the information formation layer as the recording layer or light reflection layer of the information storage medium and passed through the objective lens, and detect this light on the photodetector. Beams. By detecting the movement and direction of the beam, the focusing of the beam on the information forming layer is detected, and the
) by detecting the direction of image formation/4 turns or diffraction/turns O. When the laser beam waist position coincides with the position of the layer, the beam on the photodetector is 4°. The focal point has an elliptical shape with its long axis perpendicular to the direction in which the detection photodetection cells are arranged, and the photodetector has at least four photodetection cells arranged diagonally. The optical head is characterized in that focus burying is performed using photoelectric conversion signals from photodetection cells facing each other with the center point in the one-line photodetector at least t out of the detection, traverse, and corner detection. . (2) Detecting defocusing using difference signals from a pair of photodetection cells that are positioned opposite to each other with the center point as a boundary among at least four photodetection cells arranged on each diagonal;
by the difference signal from the other photodetection cell located in the opposite position. The optical head according to claim 1, wherein the optical head detects a squirrel and a lean.