JPS5848236A - Optical head - Google Patents

Abstract

PURPOSE:To detect assuredly the out-of-focus, by providing a light transmission limiting membe at the front or rear stage of an extracting member that extracts the reflected light given from an image forming layer in order to cut off the higher order terms of a Fourier pattern opposite to a pattern on the image 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 the higher order terms of a Fourier pattern are cut off by a light transmission limiting member 27 for the light 11. Then the light 11 is formed into an image on a 2-split photodetector 26 through a light extracting member (knife edge) 23 set at the position out of the optical path and a lens 24. Then the out- of-focus is detected by detecting the shift of a beam spot by photodetecting cells 26a and 26b. The effect of diffraction due to the fine recessed and projected surface of the layer 4 is reduced since the higher order terms of the Fourier pattern are cut off. Thus the out-of-focus can be assuredly detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a device that irradiates an information storage medium, such as an optical disc or a video disc, with a focused radar beam, and performs reproduction or recording/reproduction in which at least information can be read. Concerning optics that can be applied to equipment.

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 disc or a V-dio disc. The method is to detect defocusing of the laser beam on the information forming layer, which is a recording layer or a light reflecting layer, and to move and focus the objective lens based on this detection signal.

Conventionally, a typical method for detecting the defocus of radar light on an information formation layer as a recording layer or a light reflection layer is to reflect it from the information formation layer of an information storage medium and pass it through an objective lens. 9. A detection system optical lens consisting of a convex lens and a light detection section in which the detection section is divided concentrically into a plurality of parts are sequentially arranged on the reflected optical path of the laser light, and the suit size of the radar light when the light detector is irradiated is determined. f (area)
There is a way to detect the number.

However, the information forming layer as a recording layer or a light reflecting layer of an information recording medium has a low l! If there are minute irregularities on the surface, diffraction occurs in the laser light reflected from the surface, and a diffraction pattern appears in the spot ( ) on the photodetector.

Strictly speaking, this diffraction/4 turn is generally not symmetrical.

Therefore, due to the influence of this diffraction pattern, it may be detected that the focal point is deviated.

The present invention has been made based on the above circumstances, and its object is to provide an information forming layer as a recording layer or a light reflecting layer of an information storage medium.

8I for fine irregularities such as the tiger and king guide on the surface.
It is an object of the present invention to provide an optical head which is not easily affected by distortion, is capable of reliably detecting out-of-focus, and is capable of stably adjusting the out-of-focus.

The present invention will be described below with reference to an embodiment shown in Figures tIIc1 to 4. Figure 1 shows an information storage/reproduction device using an optical disk or a video disk as an information storage medium, a semiconductor radar as an optical device, and a PK. In the storage medium, the sBζot+nit storage medium 10 is moved to the storage medium 1 side, and the moving mechanism moves the information storage medium 1 in the raw direction (first direction).
It is an optical head that can freely reciprocate in the front and rear directions (in the figure).

The information storage medium 1 is formed into a disk shape, and has one side K.
C without E brass layer forms information as a light reflecting layer! The two transparent substrates 5.5 on which m4 are formed are attached to the information forming layer 4.4.
The inner and outer spaces 4-w-tl, so that the information forming layers 4, 4 are inwardly and a space is formed between mutually opposing surfaces of the information forming layers 4, 4.
The information forming layer 4 is formed by pasting with the outer spacer 1 interposed therebetween, and the information forming layer 4 is formed at nine locations with the F described later.
The king guide also has a rotary center hole (not shown) formed in its center.

The medium drive device 2 that rotationally drives the information storage medium 1 includes a rotating shaft 8 that is integrated with one drive shaft (not shown).
A rotary support body 9-, which is fitted onto the rotary shaft 8 and has a horizontal support surface perpendicular to the axis of the drive shaft 8 and supports the lower surface of the center of the information storage medium 1, and an upper end of the rotary shaft 8. It has a presser 10 that is attached to the section. Then, the rotational center hole of the information storage medium 1 is fitted into the rotation shaft 8 to perform radial positioning, and the rotational support 9 and the presser foot 10 sandwich the center of the information storage medium 1 so that the information storage medium 1 can be rotated in the planar direction. It is configured to restrict movement.

Furthermore, the optics section 3 has the following configuration.

That is, a semiconductor radar oscillator 1 which oscillates a radar beam 11 as a part of the optical beam in the horizontal direction is installed in the optical door 3.
2 is provided. This semiconductor radar oscillator 1
In the lateral direction of 2, a heating element f13 and a polarizing beam splitter 15 are sequentially arranged. Further, above the polarizing beam splitter 15, a λ/4 plate 1# and an objective lens 11 are sequentially arranged. Further, a half mirror 18 is located below the polarizing beam sinter 15.
Polarized beam sgritter placed at an angle of 1 degree
The light passing through the optical system 5 is divided into two parts and distributed to a reading optical system 1# and a focal point detection optical system 20. The reading optical system 19 has a lens f21 and a reading photodetector 22 arranged in sequence in the lateral direction of the half mirror 18.

Further, the defocus detection optical system 20 includes a half mirror 11
80 Downward KJ
In the horizontal direction of the mirror 26 and the mirror 25, the vertical direction 2
Divided first and second photodetection self 6 m, 21
1b, and further includes a wrapping light plate 23.
The structure is such that a light passage restricting member (1) is placed in front of the information forming layer (4) to limit the light passage range and block higher-order terms of 7-lienoturns for d-tar/ on the information forming layer (4).

Further, the light passage restricting member 21 has a hole 2# as a light-transmitting part.
The size of the hole 28a as the light-transmitting part is determined by the measurement result of measuring the proportion of the focus error signal, and the size of the hole 28a as the light-transmitting part is determined to be a size that allows good signal characteristics to be obtained, that is, a reflection It is set to 0.4 to 0.95 parts of the beam size fa in the middle of the optical path.

Further, the photodetector 26 detects the lens l? 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. ! It is provided at the optical connection position of No. 4.

In addition, a lens such as an image coil type focus motor that moves the 2# objective lens xr in the vertical direction (that is, in the direction toward and away from the bottom of the information storage medium 1) is installed.

However, the nine radar beams 11 oscillated from the semiconductor radar oscillator 12 are turned into parallel beams by the pulling lens 11, and then polarized? - Musdeli is polarized upwards at 15. This polarized light passes through the λ/4 plate 1#, where the linearly polarized light becomes circularly polarized light, and then the objective lens flf
(1) 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 radar light 11 should be set to a predetermined value or more to prevent changes in the information forming layer 4 such as the formation of holes. This happens when information is memorized.

On the other hand, the reflected light from the information forming layer 4 is changed from circularly polarized light to linearly polarized light by /λA7 plate 1#, and this light beam is expanded and polarized! The beam passes straight through the litter 15 and exits downward, passes through a half mirror 18, and is guided to a detection optical system 20. ζζ, as described later, the radar light 11b on the information forming layer 4
The focus is filled with the first and second photodetection cells 26 of the photodetector 2C.
It is detected by the difference in the amount of light detected at m and 16b. That is, as shown in FIG. 1, a portion of the light 1' that passes through the polarizing beam splitter 15 and 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 optical path reflected by the nine fireflies.
Only 1 m of the light shielding plate 23 is extracted as a light extraction member,
After passing through the detection system optical lens 24, the direction is changed by the ζ sheath 25 so that it hits the photodetection cell x6.In this case, the direction in which the focus of the radar light 11 on the information forming layer 4 is arranged (vertical direction)
Move to.

ζ' will be explained with reference to the principle diagrams shown in FIGS. 0, (b), and G-1. That is, when the laser beam 11 is focused on the information forming layer 4 as shown in FIG. The light that passed through 11&e)♂-Musxl
- and 11m' are located at the border between the first photodetection cell 26a and the second photodetection cell 26b. If the information forming layer 4 and the objective lens 11 are too close to each other and cannot be brought into focus, as shown in Figure 2), the reflected light passing through the objective lens 11 will gradually move away from the optical axis As it spreads outward, the vaginal light 1 [
Beam of light 11a passing through z3 -y ) 11 m'
This applies to the first detection cell 26a located above. On the other hand, if the information forming layer 4 and the objective lens 11 are too far apart and cannot be brought into focus, as shown in FIG. The light 11*O beam suit 111' that has passed through the light shielding plate jJ is focused inward so as to gradually approach the light beam and is in a good condition.
It will remain on the detection cell 261I.

Therefore, when the distance between the information forming layer 4 and the objective lens 11 is kept constant and the focus is on, the first,
Second photodetection cell 2#a.

The amounts of light detected by the first light detection cell 2611 are both zero or at the same level, and when the information forming layer 4 and the objective lens fir approach each other and defocus occurs, the output level of the first light detection cell 26a is large; On the other hand, when the focus is blurred due to distance, the output level of the second photodetection cell J6b increases.

At this time, the photodetector 26 is provided at an optical imaging position for the information forming layer 4 when the position where the information forming layer 4 is present and the position of the V-waist of the focused laser beam 11 match. , information storage medium 1 or objective lens 1
Even if lens 1 is tilted and a high-brightness portion of the light passing through objective lens flr is angularly shifted, there is no possibility that the position of light hitting photodetector 2# will shift. Note that if it is possible to shift the optical imaging position and the photodetector 26, the beam
y) If JJ&' widens and the angle of the high-brightness part shifts, even if the focus is on, the position of the high-brightness part will shift, making it look like Ze-mus 4. G11
The position of m' itself may be misaligned and may be erroneously detected as being good.

On the other hand, as shown in FIG.
The output signals of 1g and 26b are input to the drive circuit jIK via the difference amplification circuit S#, and the objective lens e11 is moved in the direction of focus via the 2:e drive circuit 2#.

In this way, the focus burying caused by the distortion of the information storage medium 1 is automatically corrected.

Note that the reflected light 11 from the information forming layer 4 is reflected by the objective lens 1.
'After the IO, it is divided into the frequency components of the parable turn. That is, the Δ-turn shape on the information forming layer 4 shown in FIG. 4 0 has a lower frequency closer to the optical axis, and goes outward as shown in FIG. It is divided into peripheral frequency components so that the frequency becomes higher in sequence.

On the other hand, when the ζ0 reflected light 11 passes through the light track plate ZaO light-transmitting part IIIa as the light passage restricting member 21, it is affected by the higher-order terms of Fouri and Notaturn, that is, the Takaoka liquid as shown in FIG. 4 (portion S). When exposed to light and reconnected, the information formation layer 4 is exposed to light (Fig. 4 (() K) as shown in Fig.
(shown) has rounded corners/4 turns. Therefore, the □rm spot 111 on the photodetector 26
Image formation z in ′? The amount of focus error signal due to the effect of turning can be reduced.

Furthermore, by arranging the light passage restricting member 21, the actual beam size of the radar light 11& passing through the detection system optical lens f24 can be reduced (len y!). :1
By reducing the proportion of spherical aberration caused by 4, the movement of the beams I and I1m' on the photodetector 26 can be reliably detected.

Furthermore, the light that passes through the outside of the objective lens 11 or is diffracted by surrounding structures or devices may travel in an unexpected direction (for example, to the outside), and this may cause the optical lens of the detection system to travel in an unexpected direction (for example, to the outside). 24
After passing, this light causes an error signal to be generated on the photodetector 26, but by arranging the light passage restricting member 21, these lights are blocked and do not have any adverse effects.

On the other hand, in order to read the information formed in the information forming layer 4flC' (holes) or uneven shapes, the polarized beam splitter passes through the polarization beam splitter 15, and the half 1? -III, the forward light is guided to the photodetector zzPc for reading through the lens e21.

In the above-mentioned embodiment, a knife was used as a light extraction member for extracting only a part of the light located nine positions off the optical axis. Furthermore, it is also possible to arrange a lens, a prism, etc. at a position offset from the center of the optical axis of the reflected optical path so as to extract only a portion of the O light located at a position offset from the optical axis.

Furthermore, although the light passage restricting member 21 is arranged before the light extracting member 23, the present invention is not limited to this).
or between the detection system optical lens 24 and the photodetector 26
It may be placed between the information forming layer 4 and the information forming layer 4, as long as it is sufficiently far away from the information forming layer 4.

It goes without saying that various other modifications can be made without departing from the gist of the present invention.

As explained above, this actual line is the light that is reflected from the O information forming layer as the recording layer or linear light reflection layer of the information storage medium and passes through the objective lens. A light extraction member that extracts the light asymmetrically with respect to the axis and a photodetector that detects the light extracted by the light extraction member are provided, and the C-mus 4 detects the extracted light on the photodetector. ．． When the movement of the light beam is detected, the focus of the light beam on the information forming layer is detected, and a light passage restricting member for restricting the light passage range is provided before or after the light extracting member. The present invention is characterized in that the optical system is provided so as to shield a higher-order 0 term of a Fourier-arm turn with respect to an arm-turn on the information forming layer. Therefore, as in the past,
Compared to methods that detect defocus based on changes in the information storage medium, the surface of the information storage medium recording layer or the information forming layer as a light reflecting layer is less susceptible to the effects of diffraction caused by minute irregularities and can reliably detect defocus. can do. In addition, rounding, which only requires alignment of the photodetector in the direction of light movement, greatly facilitates adjustment when assembling the optical system. Since the optical system is very forgiving, it loses stability when the entire optical system shifts due to heat, etc. Furthermore, since the light passage restricting member that controls the light passage range was set to block the higher-order 0 term of the Fourier mother turn for the /parameter turn on the information forming layer, when the image is refocused, the angle It has the effect of reducing the appearance of focus error signals due to the influence of the constriction and arm turns in the O beam slit on the photodetector.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic configuration diagram of an information recording/reproducing apparatus to which an embodiment of the present invention is applied, and FIG. A rounded explanatory diagram illustrating the principle of defocus detection according to an embodiment of the invention, FIG. 3 is an explanatory diagram showing a drive system for automatic defocus adjustment, and FIG. 4 N),
fO), f-1 is No! on the information formation layer! Turn, ζoia
frequency components of the turn, and 't' on the photodetector t)
It is an explanatory view for showing a jl turn shape. 1--information storage medium, J--optics, 4--information forming layer as recording layer or light-reflecting layer, 11...
Light beam (radical light), 1r...objective lens, 20
... optical system for out-of-focus detection, 23... light extraction member (!I light plate), j #-... photodetector, 21... light passage restriction member. ApplicationﾾRepresentative Patent Attorney Takehiko Suzue Figure 1 Figure 4 Figure 11 1 1 1 Commissioner of the Japan Patent Office Kazuo Wakasugi 1, Indication of Case Patent Application No. 146541/1982 2, Title of Invention Optical Head 3, Amendment Relationship with the case of a person who does The phrase “shown in Figure 4 (mouth, ), (mouth, ), (mouth,)” should be corrected to “shown in Figure 4 (mouth J, (/1, -)”. (2) Similarly, in Figure 12 In the first line from the bottom of the page, "(口,)" should be corrected to "ni)". (31 Similarly, in the first line of page 13, "Fig. 4 09" should be changed to "Fig. )". (4) Similarly, in the first line from the bottom of page 16, "Fig. 4 (Il(o> , (/1 is
, (c4.←1°), (E)”. (5) In Figure 4 of the drawings, the symbol “(口,), (口,)
, (口, ), (c)" should be corrected to "r (CFJ, (/1, ni), -" as shown in the attached drawing). Figure 4 1 1

Claims (3)

[Claims] (1) A light extraction member that extracts the light beam asymmetrically with respect to the optical axis in the middle of the reflected optical path of the light beam 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 k; A photodetector is provided to detect the light extracted by the light extraction member, and by detecting the movement of the extracted light on the photodetector, the light V to the information forming layer is detected. - A light passage restricting member is provided at the rear stage of the light extracting member 011JR to restrict the light passage range, and is used to detect the defocusing of the information forming layer. An optical head characterized in that a higher-order term of a Δ turn is shielded from light. (2) The optical head according to claim 1, wherein the light passage restricting member comprises a light shielding plate having a light-transmitting portion. (3) The optical spatula P according to claim 2, characterized in that the size t of the transparent part is set to 0.4 to 0.95 times the beam size f4 in the middle of the reflected optical path.