JPS5990237A - Optical head - Google Patents

Abstract

PURPOSE:To detect stably and reliably an out-of-focus state by arranging a converging means which converges reflected light from a recording medium and a light extracting means which extracts light asymmetrically, to satisfy a specific condition. CONSTITUTION:Parallel light is converged to the recording medium 14 through an objective (converging means) 40 and its reflected light is converged to a photodetector 58 through the objective 40, a light shield plate (light extracting member) 52', and a projection lens 54. An out-of-focus state is detected by the movement of the light spot. In this case, x<=f0+f<2>0/[2deltatf+(F-f0)] is satisfied, where f0 is the focal length of the objective 40, (x) and F are the distance from the farther principal point of the objective 40 from the recording medium to the light shield plate 52' and the distance from the closer point to a convergence point, and deltatf is the permissible amount of shifting the light reflecting layer of the recording medium 14 from the focus of projected light from the objective 40; and deltatf is set to 2.0mum to detect an out-of-focus state stably and reliably.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is applicable to information storage such as a CD (computer disc) for DAD, a video disc, an image file, a still image file, a COM (computer output memory), etc. 1. It is possible to obtain at least l'i' + information by irradiating the medium with focused light.
The present invention relates to an optical head used in a recording/L+recording device 1j6.

[Technical background of the invention and points j, l, between] Recently, the first
As shown in (a), (b), and (c), in the middle of the reflected optical path C of the 13t beam that has been reflected from the IR information forming layer a' and passed through the objective lens b', there is a .i'-I and asymmetrically extracted light extraction part (shielding plate such as a knife wedge) d8, lens e1 and two y (detection cells f, gt and photodetector hl) 19t of photodetector
By detecting the defocus t(t,!) as the movement of the beam spot t·i on the photodetector (in the direction of arrow j), we can calculate the defocus by the spot size t(t,!). I came up with the idea of something that would be less likely to be exposed to colored tubes.

In addition, as shown by the line 2), when the focus is on, there is a ``()'' and a gully, and the objective lens b' and 1
1r information formation layer a' approaches the main valve 111 of upper 11j1
Beams 71 for cell g? TS)l is hit and negative (M
In addition, the objective lens b' and the information forming layer a' are
)1. Beam spot i on photodetection cell f according to the following rule
1. If it hits and a positive signal is obtained. It has become so.

However, as shown by the two-dot chain line in FIG. 13 cambium a'
There is a serious problem in that the same negative signal is output when the two are too close to each other. Therefore, since it would be difficult in terms of characteristics to reverse the image even if the image is slightly out of focus, it is necessary to provide a relatively large amount of correction that can be made even if the image is out of focus.

This problem is not limited to the above-mentioned optical system, but also occurs in optical systems such as those shown in FIGS. 3 and 4 that use an aperture, slit, prism, mirror, photodetector, etc. instead of a knife nip. In FIG. 3, d2irlA, d2' and d2' are transparent parts. It's on the side, d in Figure 4.
3 is pipe rhythm.

[Purpose of the invention]

The present invention has been made based on the above-mentioned Hi, and its purpose is to provide an optical head that can detect out-of-focus more stably and with good reliability <1j. 1. ν It consists in offering.

[Summary of the invention]

The present invention includes a light collecting means that collects light reflected from an information storage medium that stores information, a light collecting means that passes through the collecting means, and
'f? :, is provided in the middle of the optical path of the light, and opposite to this optical axis [
At 7, a light extraction part scoop that extracts light asymmetrically and a photodetector that detects the light extracted by this light extraction part are installed.
C, the focal length of the light condensing means is set to fo, and the focal length of the light condensing means is focused from the principal point on the side closer to the IH information storage medium to y (the distance in S roll call is F1, which is far from the information recording medium of the above mentioned light condensing means). The distance from the principal point of the side to the above-mentioned light extraction part is X1 (creation from the above-mentioned objective lens). When f slip shore is δtf,
Sales item f: It is customary to set it so that it is satisfied.

[Example of actual invention]

An embodiment of the present invention will now be described with reference to FIGS. 5 to 16. FIG. 5 schematically shows an information recording and reproducing apparatus (f:lit) to which the "f:lit" head of the present invention is applied, and 2 in the figure is an optical disk as an information recording medium.
This optical disc 2 includes a pair of disc-shaped transparent plates 4.6.
'f) The inner and outer spacers 8.10f are bonded to each other, and a light reflecting layer 12.14 as an information recording layer is formed by vapor deposition on each inner surface of the transparent delta 4.6. I'm No L. Each of the light reflecting layers 12 and 14 is provided with a helical tracking guide 16 (see FIG. 6).
is formed, and information is recorded in the form of bits on this tracking guide 16. A hole is bored in the center of the optical disk 2, and when the optical disk 2 is placed on a turntable (not shown), the center spindle 2o of the turntable is inserted into the hole of the optical disk 2, and the turntable and the optical disk 2 are inserted into the hole. The rotation centers of the two are aligned. The center spindle 20 of the turntable is provided with a chuck device i' (22), and this chuck device ffff, 22 fixes the disc 2 on the turntable. The turntable is rotatably supported by a support base (not shown) and driven by a 24K drive motor.
The second one is rotatable at a constant rate.

Size/ko, 26VJ, optical head, this is knee r
・By actuator 28 or rotating arm)゛C-
A 1/-de device 30 for generating a (-1,1)-beam is provided within the optical head 26, which is movable in the radial direction of the disk 20.

-7, When importing information to the original disk 2,
)11 The light intensity changes according to the power of 11-information.
114 JI, the laser beam is emitted 4L from the laser device 30, and the 46 information is read from the optical disk 2 1?1
1, a laser beam with a constant brightness it is 1
It is generated from 1 to 30. Laser device 3
The laser beam generated from 0 is emitted by a concave l/lens 32, a convex lens, and a convex lens. 4 is converted into a parallel beam of light and directed to a polarizing beam splitter 36. The parallel laser beam &:t reflected by the polarizing beam splitter 36 passes through the 1/4 wavelength plate 38 to the objective lens 40, and is directed to the light reflective layer 14 of the optical disc 2 by this objective lens 40. It's focused.

The objective lens 40 is supported by a voice coil 42 so that the light beam can be moved in the 1t11 direction.
is positioned at a predetermined position, the beam waist of the focused laser beam emitted from the objective 1/lens 40 is projected onto the surface of the light reflective layer 14, and the minimum beam density d? A cut is formed on the surface of the light reflecting layer 4. In this state, the objective lens 40 can be kept in focus, and the objective lens 40 can be kept in focus.
Reading and reading become the oil. 46 reports in 1! (When reading information, the tracking guide (pre-group) 16 of the light reflection layer 14 is formed by the light intensity modulated 1/-the beam), and when reading the information,
A laser beam with constant light intensity is used for tracking and
Strong light absorption +r+ by the bit formed in the guide 16
It is reflected by ta-a.

The divergent beam reflected from the optical disk 20 and the light reflection layer 14 is converted into a parallel beam by the objective lens 40 when focused, and the 0.1/4 wavelength plate 38 is 1i1J passed;-teiiwa, j,) "0 Beano splitter, 'fA8 goes to 76. The laser beam is ]/4θU
1.24g<3. s f by passing 17-
The Beam &:L (!*^Light beam splitter 36
The plane of polarization is rotated by 9 degrees compared to when it is reflected by /ζ, resulting in this 901 shape. Awns,
This polarizing beam splitter 36 will be traced 74. I jut')'tLbeano splitter)'
0 passed 1, / - the b 1.11, divided into 12 systems by the half mirror block 44] 6, one of which is convex 46 - so (6J exit 48, 48B
1 in 407 and 48! (i shot)7. Ru. The first signal detected by the detector 48 is recorded on the optical disk 2, includes a signal processor 1, and is sent to the signal processing device 1, 50V, and then digitally transmitted.・It is converted into data and the tracking number is 2 (÷5OA and the total number 44 5013 (7 is the output).Half mirror block 4411'l: Therefore, divided il,
The other laser beam
; 4 Ibarade fili 4 Tsukasa) 52, only the component jj (1; +2!
The light is reflected by the light and enters the second photodetector 58.

Here, the light shielding plate 52 is a prism.

The force may be composed of an aperture, slit, knife, edge, etc. Further, the nof mirror block 44, the shielding °0 plate 52, and the projection lens 54 are in close contact with each other. The signal detected by the second source detection bell t58 is processed by the focus signal generator 60.
No. 2451 is particularly effective for the voice coil drive circuit 62. The voice fill back circuit driving circuit 62 drives the voice coil 42 in accordance with the focus confidence to maintain the object lens 40 in focus. Note that when tracing the tracking guide 16 formed on the light reflection layer 14 of the -yt nib disk 2 to the stop 6 (++'), the G4 're from the second photodetector 48 is The linear actuator 28 may be fully activated by processing k, or the objective lens 40 may be moved in the direction of the rj force, or a galvano mirror (not shown) may be activated.

2r (the optical system for detecting the time of focus shown in Figure 5 is
To simplify the diagram and add an explanation, the trajectory of the laser beam related to focus detection is shown in Figure 7 (A), (B), and
It is arranged as shown in c). 1- Nawachi, objective lens 4
When o is in focus, the beam waist is projected onto the light reflecting layer 14'', and the minimum beam is reflected. That is, the beam waist spot 64 is located on the light reflecting layer 14.
formed on top. Normally, the laser beam that enters the objective lens 4° from the laser device 3o is a parallel beam of light, so the beat waist is formed on the focal point of the objective lens 4o. However, when the objective lens is set at 4°, the l/-re' device f
! 1: ? The laser that enters the beam from zero emits a little f.
When the lk h lamp is convergent, the beam waist is formed near the focal point of the objective lens 4o. Figure 5,
8. Light 'I'' shown in Figures 6 and 7 (a), (b) e→
In the case of a thread, the light-receiving surface &;L of the )°0 detector 58 is located at the imaging plane of its beam waist spot 64 in the focused state. Therefore, during focusing, an image of the beam waist spot 64 is formed at the center of the light receiving surface of the photodetector 58. That is, as shown in Figure 7 (a).
As shown in V, the beam waist spot 64 is located on the light reflecting layer 1.
40 is formed at 21, and the light reflecting layer 14 reflects no. 1. The laser beam is converted into a parallel beam by the objective lens 4o and directed toward the light shielding plate 52. Only the light component in the narrow region t ii+) is extracted and focused by the projection lens 54 to form a minimum beam waist spot image on the photodetector 58. Next, when the objective lens 4o approaches the light reflecting layer 14, the beam waist is
As shown in Figure 7 (b), the laser beam is reflected by the light reflecting layer 4. That is, the beam waist is caused by light reflection 1tm 141filK from the objective lens 4o. In such an out-of-focus state, the beam waist occurs within the focal length of the common objective lens 4o, so if we assume that the beam waist is The 1/-the beam (reflected by the reflective layer I4 and ejected from the objective lens 4o) is converted into a diverging laser beam i'1. by the objective lens 4°.

524 pieces of light shielding plates, 1tr3 (, ta1) - Since the beam component is similarly divergent, even if this laser beam component is focused by the projection lens 54, the photodetector,
The light is not converged to the minimum on the light receiving surface of the photodetector 58, but is focused on a point farther away than the photodetector 58. Therefore, the laser beam component from the center of the °C plane received by the photodetector 58 towards the two hands is 4Q /IJ (I), and the beam component above the photodetector 58 is 4Q /IJ? A turn larger than 1!4 degrees is formed. Furthermore, when the objective 1/lens 4o is separated from the light reflecting layer 14 as shown in the 71st lens 10→, after forming the beat... cloth l-, the laser beam is
The reflective layer 14 causes reflection. When the camera is out of focus like this,
Normally, the focal length of the objective lens 4o is I −r;
Since the shape 1+'y, iJ) exists between 4, the objective lens 40
However, the reflected laser beam directed toward the light shielding plate 52 has poor convergence. Therefore, the light shielding plate 52 can be passed through 1154.
1 degree and the 1 nose beam component is further converged by the L1 projection 1/ lens 54 to form a convergence point.
The light is projected onto the receiving surface of the single device 58. As a result, y(:
On the light-receiving surface of the detector 58, IP turns, which are larger than the images of the beat and waist spots, are formed downward from the center.

The above-mentioned change in the trajectory of the 1/- laser, that is, the change in the trajectory of the light beam, is caused by the following change in Yakiniku optical direction. rutfJh
s'f! :Koshichi ga r heart. The optical AJ system of the objective 1/lens 40 can be expressed as shown in FIG. Here, fo is the focal length of the objective 1/lens 40, and δ is the focal length of the objective 1/lens 40 from in-focus to out-of-focus, that is, the focal length of the optical disc 2. #The dynamic pressure is 1η11, and the trajectory shown by the -C solid line in FIG. Light rMl+ s passes through a point '4' mf+ at a distance of 1)^[1 from q, showing what is focused.2
When in focus, as shown in FIG. 7(a), δ=0, and when out of focus, as shown in FIG. However, since the beam waist is formed by being reflected by the light reflecting layer 14, the beam waist l- is twice as close to the objective lens 40. (If it is close, δ (0) Also, the out-of-focus 11 shown in FIG. Since the laser beam is retracted from the light reflective layer 14 after forming the beam waist I~ by a distance h from the objective 1/lens 40 by δ, substantially the light reflective layer 14
It is the same as if a beam waist was formed behind the beam waist, and the beam waist is 1li from the objective 1/ns by 2δ.
It will take 1'1. When focusing, the beam waist is at the focal position 1i' of the objective 1/lens 40? When it is formed at f, the optical disc 2 moves by δ! rill L
If V(-, then the distance between the beam waist and the principal surface of the objective lens 40 as shown in FIG. 8 is (f, +2δ
). If we consider the beam waist as a light point, the angles βol☆ and β in Fig. 8 are expressed as (1) and (1).
2) It is shown by the formula.

Also, from the lens imaging formula, Therefore, β, -βo + b o / f.

jJ'z Figure 9 shows the trajectory of the light Pi1 in the -)Y: system of the projection lens 54, and it is treated as if the projection lens 54 consists of a pair of interlocking lenses 54-1 and 54-2. .

Here, the lenses 54-1 and 54-2 each have a focal length f
l r f2, and a light plate 52 is located at a distance a from the main surface of the objective lens 40.
), main surface of riJ 'l'yJ+/ns 40 mustard only 1
(17. The main surface of the lens 54-1 is placed in A, and furthermore, the main surface of the lens 54-2 is placed between the soil surface of this lens 54-■ and It is determined that 11v is obtained when the detector and receiver 5'C of E8 are arranged at a distance of t. thing 1/ns 40 and 11-
The boarding area J1 shows the surface of the light beam 52 of the board 52, which is separated by y from the light beam 111153.

b'L meat: iy+, i, -t11self (3) formula'T: i
'? I will be forgotten.

y = ho-aβ weight ■ ==ho(la)...(
3) fo + fo2/2δ Jinkov, F(δ) = (fo + f(1/2δ)
)-1 is the equation (3), which is the following equation:
Ru.

y−ho (1−aF(δ)) =−(4
)? 11′tsu-C1...(5) bO-1-・F(δ) Hill 7C% Motonadasu! is the principal surface of the lens 54-1, '+f
The digit h1 from above the optical axis 53 is expressed by equation (6).

h + = 'j (L-a) β.

Find the angle β2 in the same way as the formula
(Represented by the force formula.

...(Power gland, 0-line light 1IllI53 passing over the main surface of the lens 54-2 in a downward manner, position h2 and incident angle β3 from above is incident on the light-receiving surface of the photodetector 58. The position h3 from the optical axis 53, that is, the deviation, V, 1 is (8] to (10), respectively.
It is expressed by the formula.

h2=h, -HI3...(δ) and h3=h2(LH)β38158The optical system shown in FIG. 9 and FIG. , detection ÷ 1; ; The light beam on 58 is h3-
Since it is focused to 0, under this condition,
F((1)=0, 102V↓, expressed by the following formula.

Furthermore, since only the light passing through the optical axis 53 is extracted by the light shielding plate 52, it is yNO. Therefore, if we simplify this equation -ζ and equation (10), we can obtain equation (13) or equation (I4). 4) It will be done.

Or, if δ is sufficiently small (δ<<fo2), kl, (a
Since fo)
The lateral magnification m of the beam waist image formed on the light receiving surface of
is expressed in the -F expression fIfi1.

Ru.

m = -β0/β3 (inverted image) Here, I0 at δ = 0 is 10, so in equation (12), (l"If I2 is eliminated from I1 equation, this equation can be changed to t, , f, To find the solution for 1:, the length of -
)'f; Academic T&J:
m-β0/β3)lfl is expressed by the following formula.

So, when I tried hard to find f2 from equation (12), I found (?
(21) 2 and (22)
The formula is obtained.

h 3-shi, + 2my δ
... (
)2)y However, (a f o )<< fo2/2δth! l
jJ's) ゛(, In the academic system, if the projection l/lens 54 is a single lens and the power is f2-■, then f, =/-
and m = f H/ f 6, and in the optical system shown in Figure 8, the beam waist is
(assumed to be formed at the focus of 0) 8, divergence or 1
When a focused laser beam is incident on the objective lens 40, the beam waist is formed offset by b from the focal point. U(-, considering the entire optical system as one lens, 2δ=2δ' plus, and similar cutting-(? to (-
If so, the deviation (ih3) can be found.

...(2.1) Here, if a = O, t o-1-b >> 2δ is C;l:.

Totoru.

Next, Figure 1O shows the relationship between the focal length detection signal Y and the focus height X, and Figure 11 shows the relationship between the focus height detection signal Y and the focus height detection signal Y for the focus height B+XK. photodetector 5
8 shows the relationship between the sum Z of the detected light h'L. All of these are graphs based on Equation (24). Focused fishmeal lI9: (X = 00 place) The focus angle detection Iris No.・Focus report X is δif or δ1
When the number 1 becomes n, it becomes 80% of the saturated signal product, and δpf
The dimension is saturated at δpn. However, the first ()
In Fig. 11 (1), the focus is saturated and the focus of the time is 2.
When the focus is focused on the pregnant woman, the beam at the second photodetector 58 expands and becomes δof
Otherwise, at δOn, 19 points of the T beams protrude from the second photodetector 58. Therefore, if the focus becomes further below δOf or δOn, the sum of the focus I, the detection signal Y, and the detected light signal Z decreases by the amount that the beam spot 64 protrudes from the C detector 58 at t1'↓2. (-However, the objective lens 40 and the light reflective layer 14
[If the beam spot is too far away, the beam spot will be as shown by the button line in Fig. 7 (C)] °C: The center line will be about 9 degrees above the detector 58. δt in Figure 10
f (\1 volume of the light reflecting layer 14 from the focal point of the emitted light from the objective lens 40)tjii-) than the objective lens 40.
When 5N1 is low, the objective lens ゛4 L) and -)f: reflective layer (information forming layer) 14 are close together; In this case, as the curves in Figures 1 () and 11, 3 fll is a type of /l
'l(Q, is shown. 1- That is, the 111
iXli (knife edge end face or aperture,
l around the slit? When the fla part) is located at the center of the optical axis of the optical system q', the characteristic of the curve A ('I'fd: is shown).

-Also, the shading plate 52 is off from the center of the optical axis 53, and furthermore, the shading plate 52 obstructs the optical path. 7'L bottom' + 1 letter jl::1 If completed, 1 leg B,
-The light passing through the center of the light 'full 53 is the light shielding plate 52.
In the case where the optical path is reduced by 42 and it is not possible to reach the photodetector 58 of 42, the corresponding characteristic of curve C is shown. The graph in Fig. 11 is obtained by taking the absolute unity of the focal point detection coefficient of the l-1LLiO2 curve except for the vicinity of the in-focus position. is I: 1 line, C < force. Also, in Figure 11, the focused fish
Near i, the beam spot on the second photodetector 58 falls within the light-insensitive region between the photon IUJ and the photodetector. Since there is a lot of Fi-, the amount of flow is reduced, so the detection light J'1'U
, the total 11th Z becomes smaller.

Next, the 12th is the 1st, the 13th (as in ¥1, the objective lens 4 is
From the rear principal point of 0 to the knife nip 5λ252
The total distance X+ to the point 4 from which a part of the laser beam R153 consisting of 'Y' and the light plate Y is extracted is the total distance X.

Let X' be Xl &: J: Find the relationship between x' and δtf yl is condensing light. In the case of Figure 12, C (
) into the formula hl = f) + a = 0 + L = x, 〇-y (l-fo + fo2/2δtf'x = f
6 +fo2/2δtf 13th If r>1, h2=0+a for equation (8)
= 0 and L −1−H= x/, −yl (
]-H/f, )-[x'(,1-11/f + )
-1-L2/f + ], since normally f1>H, the relationship X>X' holds true for identity.

In FIG. 10, if the directivity of δtf is too small, the out-of-focus detection -I, i'F4 will be inverted]2 even if the focus is slightly out of focus.

Next, let's check the maximum allowable amount for defocus.

In the Pu5h-Full method, which detects track deviation by using the sub-first fold pattern of reflected light from the tracking guide 16 of the condensed laser beam, the track deviation detection signal does not appear if the focus is significantly out of focus. Figure 14 (
A) ~ (Y) and @15 Figure (A) ~ ((C) is the 16th
In the figure, when a laser spot crosses the groove (pre-group (height λ/8)) in the direction of arrow Q that continuously extends in a spiral shape as a tracking guide, the tracking deviation is detected for each groove. showing a signal. Then, I shifted my focus in each direction.
Each drawing shows the state of the haiku when the track slippage is detected. In this drawing, S is the distance i′L of the light reflecting layer 14 from the focal point of the generated light from the objective lens 40,
Shine from objective i l/lens 40 1IFill f: Set as positive. Also, the upper curve is tracking
:3 DTP 07200 mV/div,)5
(l A % T 'Jllll's curve is total i and rock (F3B) - Tal 20 (1rnV/old V,) 50
B Y, H are shown, the zero point is 2 div from the top,
The value below stiffness is positive. Normally 3.0μ from this point
If m1 is at most 5() μm or more in focus, Pu5h
-Pu1l Law Chi: ・It can be seen that the 50A cannot detect the tiger and the deviation (In addition, the Shin B,
5 The smoother the QA waveform, the larger the amplitude, the better. ).

'-1 In addition, when recording is performed by making holes in the reflective layer 14 of the 111 information storage medium and causing rapid state changes,
When defocus occurs and the spot on the reflective layer 14 becomes large, recording becomes difficult.

The spot size at in the reflective layer 14 at the time of focus is nt=
Assume that it is given by 0.82λ/NA...C2'n (where λ is the wavelength of the laser and NA is the numerical aperture of 1°). In addition, the intensity distribution at this time is similar to the Gaussian base distribution, and ≠ + collar ÷ 1 -, and the half-child of the ring zone where the strong IAf at the beam waist is 1/e2 of the center strong III is C0. In this case, the radius of ma, which is 2' shifted from there, is ω
(Z') , -1-that is 2' Riff 1 (When 1 point is loose, this lJl spot center! 1ili Ijk' I
A little bit of ash will be removed. 8 [:Rukayo 1 ka j anti-1 generation A) b
Compensation (11j firefly lm1n and 1 - now λ = (1,83ttm, NA = 0.6, I
mjn=0.7 and "= 0.811 stone m λ=0.831rm + N A=0.5 r lm1
When n = 0.7, the focal length frj is approximately 05 to 2.0 μm.

According to this, the allowable focusing cap is roughly 2.0 μm.
It becomes the rank. Therefore, δtf needs to be 20 μm or more. Further, δtf is required to be 20 μm even if the automatic focusing is not performed properly. Therefore, in the case of the optical system shown in FIGS. 12 and 13, x'(x < f
o +fo'/2δtf, where δtf needs to be 2.0 μm or 20 μm.

In the case of an optical system in which the distance from the front principal point of the objective lens 40 to the focal point in the direction of the information storage medium is not fo but F=fo+b, the distance of 2δtf is 2δtf + b = 2δtr
→−(Ffo) enters x'(x < f 6 +fo2
/2δtf+(F fo), where δtf is 2. Ot
tm or 20/4m. Now (F fo)-b(
In the case of O, it is necessary that
tf is large @(direct). In this case, only 2δtf
+(F-fo) is -1-2.0μm or +20μm
It is necessary that it be more than that. The light is reflected by the light reflecting layer (or recording layer) 14 of the recording medium, and the light after passing through the objective lens 40 has the property of being focused and divergent.

Therefore, as long as the focus is not significantly blurred, the light shielding plate 52
No. 19 "The collection) is not 0. In this case, the objective lens 4
The focus is changed at the point where yC that has passed 0 becomes parallel, and the focus is detected until there is a 2.011m shift/angle to the awn.1-1
Since the moon does not reverse, 2δtf (F-fo) ≧ 20μm
And so.

In Figures 12 and 13, a knife nip 62'' ma-slit or an aperture 52' is used as the part 4+ for extracting a portion of the laser beam 4, but other devices include a prism, a mirror, and a fume detector.

The present invention is applicable even when using ground glass, lenses, hard-hole materials, etc., as described by Kei et al.
1. Ru.

i fr-gp, l 21! i, 113 Figure TTI:
When fi4La, 5Y [B0 detector 58 is placed at the 1P light point (imaging point) in the force direction of the small instrument 58 1'! I do, but that's about it.
N+: , shifted by 1 degree]' (The present invention is also applied to 4 students in the 1st academic system.

However, in the above implementation 1j, the L11 light shielding plate 52 was installed near the projection lens 540 and the objective lens 40, so there was a 1 volume shift 1.
3δLf'', H can be increased. In other words, in Figures 12 and 13, as mentioned above, when x)
becomes smaller, so if X=x' then V, 1'δlfx)
δtfx'. Therefore, if the overall size of the C head is the same in the arrangement shown in No. 121\l and the arrangement shown in Fig. 13, then x(x', δtfx > δtf
x', so h' [the amount of recess deviation δtf can be made much larger. Moreover, since the light-shielding plate is placed 1 inch in front of the projection lens, it is possible to achieve a more compact design.

〔Effect of the invention〕

An information storage W1 for storing 1111 information, a light condensing means for condensing light from the body 1, and a condensing means for condensing light from the body 1, passing through the light means, and provided in the middle of the path of the tape C. , the original payment Lll ftR4 which is extracted 5'i 'e asymmetrically with respect to this optical axis
tl and detect the light extracted by this light output port 1~
The focal length Pub of the light collecting means is fO, and the distance from the principal point of the IJI near the information storage medium of the light collecting means to the collecting point L is R1 on F1. , '+ collection jt means 11° 1 information from the principal point on the far side to the storage medium above) ``C without IJ, 1 person It 11 distance 1
iif be
When f is set, the conditions are set so that v1i force is 1-, so horizontal use of out-of-focus can be performed more stably and reliably.21 eJ' k! - It produces a certain effect.

Fig. 1 (a), (b), and (c) show the focusing and non-focusing of the first conventional C system. Explanation showing the trajectory (Fig. 1, Fig. 2 shows the change in state of the optical detector as the beam spot moves on the optical detector) (Fig. (c) Q1 2nd
Figure 4 shows the locus of 1/-the beam when the conventional optical system is in focus ``l, -J: hi and out of focus 04''. Figures 11 and 11 show the trajectory of the laser beam during focusing, and Figures 5 and 16 show one embodiment of the present invention, and Figure 5 shows the information recording internal generation device i'. 1 (+: Flock diagram shown, Figure 6 is a diagram showing the optical system shown in Figure 5, No. 71 ¥ 1 (A)
(b) (c) shows the trajectory of the laser beam that is round when in focus and out of focus.
! ;(lυThe trajectory of the ray that passes through the objective 1/lens shown in Fig. 6?: Diagram for solving the problem, No. 9 M &'J, g
i', Analyzing the locus of the line yr passing through the projection lens shown in Figure 6, the 7th ward 1, the 10th sag, the focal point is 9: and the relationship diagram between the focal point 1 digit detection Ig++, The 11th and 1 are detected by the focus amount and the focus if detection detector)'0
Relationship diagram with the sum of forces j, ε612 (shi(, F- and the 13th
The figure shows the distance from the focal point of the light emitted from the objective 1/lens (: tolerance deviation of the reflective layer and j/a from the objective lens):
l'l; Analyzing the relationship with the distance in & dimension / ζ-th figure, Figure 14 (a) ~ (yo) and Figure 15 (a) ~
(Force) is a figure showing the track misalignment detection Shingetsuo with respect to the amount of focus, and ν1 shows the optical system shown in Figure 16 and Figure 5.
It is.

40... Condensing means (objective lens), 52... Jade exit (shielding) °0 plate), 58... Second) Y4 (moxibustion device).

u'+h, 'It person's agent patent attorney fr:i i
t Takehiko Figure 10 Eclipse Figure 11 Figure 12 Figure 13 Figure 14 (Wa) (Yo) 239- (Power)

Claims (3)

[Claims] (1) Information f: A condensing means for condensing the ''lC reflected by the information storage medium described in 1.0, and a condensing means provided in the middle of the optical path of the light that passed through this condensing means, and a A light extraction part that extracts light asymmetrically through the light extraction part and a photodetector that detects the light extracted by the light extraction part paulownia.
The focal length of the light condensing means is f, 10'NL: collection) ゛CC
Several steps closer to the information storage medium (distance from the principal point of ill to the focal point 1 is F1) Information of the above light condensing means 6 distance k x z
When the n'1 displacement of the light reflecting layer on the information storage medium from the focal point of the light emitted from the objective lens is δtf, the condition is set so that the following conditions are added: 1-ru light q head. (2) The optical head according to claim 1, wherein F-fo≧00 and @ are 2δtf=2.0 μm. (3) F-fo (when 0, 2δtf-t-(F f
o)=2. (The optical head according to claim 1, wherein the diameter is 1 μm.