JPS6038740A - Optical head for photothermic magnetic recording medium - Google Patents

Abstract

PURPOSE:To attain a small and simple structure of the titled optical head by receiving two divided luminous fluxes by a photodetector after transmitting them through polarizing plates respectively to perform the focusing control with the differential signal of those luminous fluxes and then perform the tracking control by detecting the change of an optical distribution in the direction orthogonal to a signal track. CONSTITUTION:A light splitter 22 contains transmitting parts 18 and 18A and a reflecting part 19 for a luminous flux 20. The reflected luminous flux given from a recording medium 16 is divided into two parts by the splitter 22 and transmits through polarizing plates 70 and 71 to reach 2-split photodetectors 23 and 24 respectively. A differential signal between (A+B) and (C+D) obtained from photodetecting elements A and B and C and D of both detectors 23 and 24 is transmitted through a frequency discriminator to extract a low frequency component. Thus the focusing control is performed. While the differential is obtained between electric signals (A+C) and (B+D), and the change of an optical distribution in the direction orthogonal to a signal track is detected to perform the tracking control.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to the structure of an optical head for a photothermal magnetic recording medium, and in particular, the present invention relates to the structure of an optical head for a photothermal magnetic recording medium. Alternatively, an optical head for a photothermal magnetic recording medium that detects a relative positional deviation with the optical head due to a change in shape and performs focusing control (automatic focus control) or tracking control (automatic tracking control) based on the detected electrical signal. Regarding structure.

[Prior art]

Specific examples of recording media in which recording or reproduction is performed by condensing a minute spot of light include those on which signals such as video and audio are recorded in advance, such as video discs and audio discs, as well as those on which signals such as video and audio are recorded in advance. There are recording materials for Gobo AW, magneto-optical recording materials, etc., which have a recording material whose sparsity changes with the thermal energy caused by the recording material.

The former recording medium is used only for 11th graders, but the latter recording medium allows the user to record signals, and the magneto-optical recording medium allows signals to be erased. It has the convenience of being able to record and play back repeatedly.

When recording and reproducing signals by imaging a minute light spot on the recording body while running such a recording body due to rotational vibration, etc., the recording body is subject to longitudinal vibration due to surface runout, etc. and lateral displacement occur, and a relative positional change occurs between the optical head that images the optical slit (optical slit) and the recording medium. As a result, the irradiation position of the spot whose size has changed on the recording medium deviates from the signal pulse, and the output signal and the recorded trace become unclear.

In order to solve these problems, a photoelectric detector receives the reflected light from the recording medium, detects the relative positional deviation between the optical head and the recording medium based on changes in the intensity and shape of the light beam, and detects focus errors. A signal or a tracking error signal is fed back to the optical head or a part of the optical head components, and based on this feedback, positional deviations such as the distance and lateral displacement between the two are corrected.

An example of the structure of such a conventional optical head will be explained with reference to FIG.

In FIG. 1, a condensing lens 2 for condensing a light spot onto a recording medium 1 is mounted movably in the optical axis direction by a driving means 3. As shown in FIG. Reference numeral 4 is a rotating mirror (bipotting mirror) for polarizing the luminous flux, and reference numeral 5 is a 1/
4 wavelength plate, 6 is a collimator lens, 7 is a polarizing beam sinter, 1 is a light source such as a semiconductor laser,
Reference numeral 9 indicates a cylindrical lens, and reference numeral 10 indicates a four-part photodetector.

The light beam emitted from the light source 8 becomes a parallel light beam after passing through the polarization beam notter 7. In this case, the polarization plane of the light beam emitted from the light source 8 is adjusted to be parallel to the plane of the paper, and the polarization beam sinter 7 passes the light beam with such a polarization plane almost without loss. let The parallel light flux becomes a circularly or elliptically polarized light flux by passing through the quarter-wave plate 5, and is then reflected by a pivoting mirror (rotating mirror) 4 that can be rotated around a supporting axis.
The condensing lens 2 condenses the light onto the υ recording medium 1 as a minute spot.

On the other hand, the reflected light beam from the recording medium 1 passes through the condenser lens 2 and the rotary mirror 4 and reaches the quarter-wave plate 5 .

The light flux that has passed through this 174-wavelength plate 5 has its polarization plane perpendicular to the direction of incidence, and most of the #1 light flux is reflected by the polarizing beam splitter 7 and is reflected by the cylindrical lens 9.
is incident on the photodetector 10 divided into four parts at d. In this case, the reflected light forms a light beam with an astigmatism distribution shape on the photodetector 10 by an astigmatism generating optical system composed of a collimator lens 6 and a cylindrical lens 9. Therefore,
Focus of the spot on the recording medium 1 depending on its distribution state.
state can be detected.

FIGS. 2(4), (B), and (C) are diagrams illustrating the state of light distribution on the photodetector 10 in various focusing states of the spot, and FIG. FIG. 2(B) illustrates the light distribution in the focused state, and FIG. 2(C>) illustrates the light distribution in the rear bin state.

Each photoelectric element of the 4-split photodetector lO is shown in Figure 2 (5) ~
As shown in (C), (A, B, C, D), the output value of (A-)-C)-(B+D) is detected based on the amount of light received by each element, and the output value is negative. , zero, or positive, it can be determined whether the state is p-front focus, in-focus, or rear-focus. In addition, by feeding back to the Igk operating device 3 via an electric processing system having a dyne of this output value kM, correction of distance fluctuations between the condenser lens and the recording medium 1, that is, automatic focusing control (focusing control) is performed. )It can be performed.

Automatic tracking control (auto tracking) for correctly tracking the signal track of the recording medium is performed in the following manner.

That is, the track direction is indicated by a broken line, and the photodetector lO
FIG. 2 (
As shown in b), the track direction is arranged along the dividing line of the 4-split photodetector 10. In this way, if the light spot deviates from the signal track due to the eccentricity of the recording medium 1, the intensity distribution of the light beam will be shifted in the left-right direction as shown in FIG. A track deviation signal is obtained as a change in the output value of B+C). After electrically processing this signal, it is applied to the drive system of the rotating mirror 4, and auto-tracking becomes possible.

That is, if the focal length of the condensing lens ((f) is shown in Figure 3, when the rotary mirror 4 is rotated by an angle of 0, the spot on the recording medium l will move laterally by 2fθ. Therefore, When the reflected light flux passes through the condenser lens 2, rotating mirror 4, and cylindrical lens 9 and reaches the 4-split photodetector 10, its optical axis is shifted, and the light distribution on the photodetector 10 is
As shown in Figure (B), it moves in the horizontal direction from the circle indicated by a chain line to the circle indicated by a broken line. In this case, (
If the light distribution is symmetrical to the origin and moves along the dividing line, the output value of C)-(B+D) will change only slightly due to fluctuations in the output value of the tracking signal. However, since it is actually a cylindrical optical system, it is extremely difficult to make its movement and shape ideal, and changes in the output value of the tracking signal do not affect the output value of the focusing signal. Therefore, it is necessary to suppress the movement of the light flux caused by the tracking operation to the extent that it does not affect the focus signal.
It is also necessary to limit the soaking control range.

As is clear from the above explanation, in the conventional optical head shown in FIGS. 1 to 3, the positioning of the four-split photodetector 10 and the cylindrical lens 9 in the generatrix direction is strictly performed. Therefore, there is a disadvantage that it is time consuming and costly when assembling the optical head. Furthermore, when the rotating mirror 4 is rotated during the tracking operation, this affects the focus signal, and there is a drawback that the focus control cannot be performed accurately.

As a conventional technique to solve such drawbacks, for example, the Foucault method (Naifezi method) is used to generate a focus signal [
At the same time, the photodetector is arranged conjugately with the light source (Fig. 3 (4)
) A method has been proposed to remove the deviation of the luminous flux at the time of tracking by adjusting the position 11), but such a method has the disadvantage that the luminous flux is blocked by the knife in the optical path, resulting in a large loss of light quantity. There is.

These drawbacks are not limited to recording media such as video discs and digital audio discs in which images and backdoor signals are recorded in advance and the user only plays back the signals, as well as recording media that change with light or thermal energy caused by light. The same applies to recording bodies that have layers and allow the user to perform both signal reproduction and signal recording.

By the way, recording bodies (photothermal magnetic recording bodies) having a recording material layer that changes with the thermal energy of the light and capable of both recording and reproduction, such as MnB i+ GdTbFe HTbFe
+TbDyFe + MnCuB1 + GdTbF
A system using eCo etc. has been proposed and is under development. The recording process for such a photothermal magnetic recording medium will be explained below with reference to FIG.

In FIG. 4(A), a light beam 61 condensed onto a recording medium 62 by a condensing lens 60 causes a local temperature of the recording medium 62 to rise. At this time, the coercive force of the photothermal magnetic recording medium changes with temperature as shown in FIG. 4(B). That is, Fig. 4 (B
), if we take the temperature on the horizontal axis and the coercive force of the photothermal magnetic recording medium on the vertical axis, as is clear from this graph, the coercive force decreases as the temperature of the recording medium increases, and at the Curie temperature Tc, the coercive force decreases. IIc becomes zero.

Then, the temperature of the recording medium rises to the temperature To, and the coercive force increases to H(
If the strength of the surrounding magnetic flux loop or the magnetic field He applied from the outside as shown by the broken line in Fig. 4 (5) is greater than the coercive force HO, then the coercive force HO in Fig. 4 (Q As shown in the figure, the direction of the magnetic field in the magnetic domains that initially had an upward magnetic field in the drawing is reversed downward.Therefore, depending on the vertical direction of the magnetic field in each magnetic domain, information signals can be recorded on the recording medium. can do.

On the other hand, the reproduction of written information is achieved by the Kerr effect or F
This can be done by using the optical effect known as the araday effect.

Next, the Kerr effect will be explained with reference to FIG. 5(4).

The Kerr effect is a phenomenon that occurs when a light beam is reflected from a magnetic medium, and the polarization plane 63 of the light beam upon incidence is rotated by an angle .theta., as shown by reference numeral 64.65 in the drawing. The direction of rotation of this plane of polarization is clockwise or counterclockwise with the magnetic domain facing upward or downward. Therefore, by inserting a polarizing plate into the reflected light beam, the rotation of the polarization plane can be extracted as a change in light intensity.

Therefore, the direction of the transmission axis of the polarizing plate is set at 6 in FIG. 5(B).
If the polarization plane of the incident light beam is tilted by an angle ψ as shown in Figure 6, the intensity change IAC of the light obtained in this case is given by the following equation (1), and a signal with an intensity proportional to the angle θK is obtained. It will be done.

i AC electric♂(ψ−θK) −cos”(ψ+θK)=
2ψ龜20K...(1) Therefore, signal recording can be performed by changing the light source to brightness or darkness according to the signal, and signal reproduction can be performed by recording a constant light amount (light amount below the sensitivity of the recording medium). This can be done by irradiating the medium and detecting the reflected light.

As mentioned above, even when used in such a photothermal magnetic recording medium, the conventional optical head requires strict alignment of the four-split photodetector 10 and the cylindrical lens 9 in the generatrix direction. The drawback is that it takes a lot of time to assemble the optical head and increases manufacturing costs. In addition, there is also the disadvantage that shaking the rotary mirror 4 while performing a tracking operation also affects the focus signal, making focusing control inaccurate.

〔the purpose〕

The purpose of the present invention is to eliminate the disadvantages of the conventional light for photothermal magnetic recording media as described above, to eliminate the influence of tracking operation on focusing control, and to provide a compact, simple, and inexpensive structure. An object of the present invention is to provide an optical head for a photothermal magnetic recording medium that can be manufactured.

A feature of the present invention is that each of the first and second beams obtained by dividing the reflected light is received by a photodetector after passing through a polarizing plate, and a difference signal of the electrical signals is generated. The above objective is achieved by performing focusing control using the low frequency component t passed through a frequency separator, and tracking control using the electrical signal obtained by detecting changes in the light distribution in the direction perpendicular to the signal track. That's true.

[Explanation of Examples]

The present invention will be described in detail below with reference to FIGS. 6 to 12.

FIG. 6 (4) is a diagram showing the principle of the overall structure of the optical head for photothermal magnetic recording medium according to the present invention, in which a light beam emitted from a light source 12 such as a semiconductor radar is transmitted to a polarizing beam sinter 13. The light is reflected and focused by the condenser lens 15 onto the recording medium 16 as a minute light spot. The light beam reflected by the recording medium 16 passes through the condenser lens 15 and the polarizing beam slittor 13ft again, is split into two by the light splitter 22, and then passes through the respective polarizing plates 70 and 71. The flames reach the two-split photodetector 23,24.

As shown in FIG. 6(B), the light splitter 22 has light flux transmission parts 18, 18A and a light flux reflection part 19, and the light flux 2o is distributed with respect to the light splitter 22 as shown in the figure. .

Further, the direction of the signal track of the recording body 16 is T-T in the figure.
' is set in the direction shown. Note that the light beam reflecting section 19 is not limited to a total reflection mirror, and may be constructed as appropriate.
8 and 18A can also be configured by replacing them with each other. ◎Figures 6 (C) and (B) show the relationship between the luminous flux distribution on the two-split photodetector 23 and 24, the dividing line of the light receiving element, and the signal track direction. FIG. The light distribution on the two-split photodetector 23, as shown in FIG. The line 21 is arranged so that the light distribution is directed towards the light receiving elements A and BVC4 as shown in the figure, and is arranged in a direction that coincides with the signal track direction T-T'.On the other hand,
The light distribution on the two-split photodetector 24, as shown in FIG. 6(b), has a capsule-like cross-sectional shape because it is the reflected light from the reflection section 19 of the light splitter 22. Parting line 21 in this case
and the signal track direction T-T' are the same as in the case of Ω in FIG.

When the light-year system described above in FIG. 23.
Reach 24. In this case, the light distribution on the light splitter 22 is as shown in FIG.
Each light receiving element A.

Based on electrical signals according to the amount of light received by B, C, and D (A
+B) -(C+D) The output value is calculated and the output is set as the signal level at the time of focusing. For example, when the recording medium 16 suffers vertical vibration such as surface vibration, the center point of FIG. 6 (A) occurs. When moving to the 16' position shown by the line, the reflected light beam becomes as shown by the broken line in the figure.In this case, one of the detectors 23
As the field of view to the other detector 24 decreases, the amount of light to the other detector 24 increases, and therefore the output f of (A+B)-(C+D) decreases.

On the contrary, when the recording body 16 moves in the direction opposite to the direction indicated by the broken line, (A + B) - (C + D)
The output value of increases. In this way, each two-split photodetector 23
．． A focus error signal is obtained by calculating the output value of the gap (A+B) - (C+D) based on the electrical signals corresponding to the amount of light received by each of the 24 light receiving elements A, B, C, and D. The focus state can be detected based on the optical system shown in FIG. 6. Next, correction of the spot deviation from the signal track by the optical system shown in FIG. This can be done according to the principles described with reference to the figures. FIG. 7 shows a case where the signal tracks of the recording medium are formed by grooves.

In Fig. 7, the upper column shows the light-receiving surface of each of the two-split photodetectors 23 and 24, the middle column shows the light intensity distribution on the detectors fabricated in these far fields, and the lower column shows the light beam 4? The relative positional relationship between the cut and the signal trunk is shown respectively.

Fig. 7 (■) shows these states when the light spot is on the signal track, and Fig. 7 (B) shows the state in which the light spot is shifted to the left. (C> is light;
J? This is a diagram showing the respective states when (g) is shifted to the right. As is clear from the figure, the light intensity distribution on the photodetectors 23 and 24 changes as shown in the respective middle columns depending on the positional relationship between the light spot and the signal track. Since these changes are already well known, they will not be described specifically. Therefore, depending on the light intensity of the light receiving element of each photodetector, (A+C) - (B+
By calculating the output value of D), this can be used as a tracking signal.

Furthermore, if no track is formed by the groove, no optical change can be obtained from the groove, so each photodetector 23, 24 is placed at the imaging plane of the recording medium, that is, at the position indicated by numerals 72, 73 in FIG. 6. It is also possible to perform tracking control by detecting changes in the optical plane intensity as shown in the middle column of FIG. 7 due to the movement of the signal pattern image.

6 and 7 above, and a method similar to this for detecting the focusakunda signal in the configuration and arrangement of the optical head of the present invention is described in Japanese Patent Publication No. 53-4.
No. 3302. However, in this prior art, the setting is such that focusing occurs when the difference between the two photodetectors on New Year's Day is zero. Therefore, even if only the focusing signal detection method is compared, in such conventional technology, it is necessary to equally divide the amount of light to each photodetector, and the tolerance of the area ratio of the non-reflective part and the reflective part of the light splitter is limited. (+: There is a problem that it must be kept extremely small. This has the disadvantage of making it difficult to manufacture and increasing the cost. Also, strict accuracy is required for the positional index of the light splitter, making it difficult to manufacture and assemble. In addition, as mentioned above, this conventional technology does not have a tracking signal detection means, and is extremely inadequate as an optical head for an optical information recording medium.In contrast, as shown in FIGS. In the embodiment shown in FIG. 7, the reflective surface of the light splitter is on a stripe as shown in FIG. Advantageous effects can be achieved.

That is, when tracking is performed by moving the condensing lens 15 in a direction perpendicular to the track based on a tracking signal, the light splitter 22 is
However, according to this embodiment, as shown in FIG. 8, even if the light flux moves from the position of the solid line to the position of the broken line, the movement of the light flux occurs in the reflection surface stripe direction and the signal track direction T.
-T' and the position correction direction of the condensing lens 15 are placed in the positional relationship as explained in FIG. Even if the focus signal is detected by (A + B) - (C + D
), the tracking operation has no effect on the focus signal unless the light beam jumps out of each photodetector. Therefore, tracking signal detection and focus signal detection can be performed under desired conditions without any restrictions, the accuracy of these detection signals can be increased, and highly reliable control can be easily realized. I can do it.

As described above, according to the optical system of the present invention explained with reference to FIGS. 6 and 7, automatic focus control (autofocus)
and automatic signal track following control (auto tracking)
An optical head for a photothermal magnetic recording medium is obtained which can easily perform the above operations with high accuracy.

FIG. 9 is a diagram showing another embodiment of the optical head for a photothermal magnetic recording medium of the present invention, and in particular is a diagram illustrating a configuration arrangement that allows miniaturization.

In FIG. 9, the light flux from the light source 3o is a polarized beam f! The light is reflected by the J-shaped star 31 and focused by the condenser lens 33 onto the recording medium 34 as a minute light spot. The reflected light flux passes through the condensing lens 33 and is passed through the polarizing beam snoritzer.
31f, transparent. A light splitting element 35 such as a prism is integrally provided on the end face (outgoing end face) of this polarizing beam series filter 31. (having a function) 35 changes the traveling direction, and the remaining light beam remains in the original traveling direction and passes through the polarizing beam splitter 31. These light beams (the first light beam and the second light beam) whose traveling directions are changed by a small angle pass through separate polarizing plates 75 and 76, respectively, and then enter one four-split photodetector 36.

As described above, in this embodiment, the polarizing beam splitter 31 and the light splitter 35 are integrated as shown in FIG. 9 (BJ), thereby realizing miniaturization of the optical head. The device 36 is a four-split photodetector as shown in FIG. 9(C), and the luminous flux distribution (
The relative positional relationship between the diagonally shaded portion), the track direction T-T', and the dividing line between each light receiving element is as shown in the figure.

Each of the polarizing plates 75, 76 shown in FIG. 9) has its transmission axis at the angle ψ shown in FIG.
ψ).

The signal obtained when the transmission axis of one polarizing plate 75 is arranged at the angle ψ as described above is given by the following equation, taking into account the bias component.

I75 = I (1(as"ψ+CQS"(ψ-θK
)−−2(ψ1θK))=Io (2+ 2cos
2ψjuku2ψself20K] ... (2) Also, when the other polarizing plate 7-6 is placed on the transmission axis t (9o0-ψ), the signal obtained when all bias components are taken into consideration is expressed by the following equation (3
) is given by

l76=I'6(cas"(90° 9')+cos"
(90'-ψ+θx) 005"(90'-ψ-θK)
)=I'o[22cas2 ψ−th2 ψ5in2
θK ] ... (3) In each of the above formulas, Io and ■
I is the amount of light after dividing the luminous flux.

If the gains when obtaining signals through full photoelectric conversion of these amounts of light are respectively G and G', the electric signals V75 and V76 obtained for each of the above amounts of light are given by the following equations (4) and (5). .

V75=I75-G=I,)G・(2+2CfB2ψ1㎜2ψsin 2θx) =(4)V76=I76・G
'=I'oG' [4-)-ψ-5ln2ψ5ln20
:] −'(h)θKt Considering as a function of time,
Electrical value 4 given by these equations (4) and (5) If the outputs of V75 and V76 are shown as a graph, the first
It will look like Figure 0 and (B). In these graphs, the horizontal axis represents time, and the vertical axis represents electrical signals V75 and V.
76 voltage value 1 is shown.

In addition, in FIG. 10 (4), the amplitude a is I. G51n2
ψS stone 2 (equal to lx, bias component sum. GC7
+2cxs2ψ]. In addition, in FIG. 10(B), the amplitude a' is I'oGl+I+129×2θ, and the bias component b' is I′oGl+I+129×2θ. ” [22 min 2 ψ].

What should be noted here is that the sign of the signal amplitude is reversed between equation (4) and equation (5). Therefore, by calculating the difference (■) between these signals, the following equation (6) is obtained.

V=V75-v76=N I, G-I'6G') +H
cos2ψ(I.G+I'oG')+CIoG+I'
oG' ) gln2ψ2θK − (6) where, I
oG '''I'6G' When rψ=4°5 degrees, the difference V between these signals is expressed by the following equation (7).

V = 2I. G51n2θK'...(7) According to the signal difference (■) in equation (7), there is no bias component,
Moreover, only a signal component with double the signal amplitude compared to Equation (4) or Equation (5) is obtained.
The result will be as shown in Figure (C).

By erasing the bias component in this way, noise components that are not related to polarization, such as irregularities in the reflectance of the recording medium and fluctuations in the light intensity of the light source, can be removed due to their influence on the electrical signal. Signal regeneration can be performed.

Next, an example of an electrical processing system for obtaining the information signal S, the autofocus signal AF, and the autotracking signal AT will be explained with reference to FIG.
, B, C, and D are processed in the following manner. In addition to amplifying with an appropriate gain, the C+D signal amplifier 81 amplifies the signal with an appropriate gain. These signals are input to a differential amplifier 82 to take the difference, and then a frequency separator 83 separates the signal component band. By taking it out, an information signal S is obtained.

When obtaining the autofocus signal AF, the difference obtained by the differential amplifier 82 is guided to the frequency component separator 83, and the low frequency component is extracted by the frequency component separator 83 to obtain the autofocus signal AF. is obtained. Considering the surface accuracy and surface wobbling of the recording medium, this autofocus signal AF is normally obtained by extracting a frequency component of approximately 2 kHz or less.

When obtaining the auto-tracking signal AT, if a signal turn is imaged on the light-receiving surface of the photodetector, light-receiving elements A and B and light-receiving elements C and D detect the light on those surfaces. Since the distribution is reversed, (A+C) and C
An auto-tracking signal is obtained by extracting the optical component from the signal B±D) using a differential amplifier 84.

If there is a pregroove on the recording medium, (A-)-C)-(
A tracking signal can be obtained by detecting the direct output of (13+D). l
! Examples of single-layer captures of + include structures as shown in Figure 12 - Φ). In addition to the effects obtained by the embodiment described with reference to the figures, it is possible to achieve miniaturization of the optical head obtained by the embodiment shown in FIG.

The 121st prisoner is the first surface 52 of the polarizing beam splitter 50.
A structure is shown in which a reflecting mirror 51 (i-) is provided in a part of the area, and light splitting is performed by installing the reflecting mirror.

FIG. 12(B) shows a configuration in which a blazed diffraction grating 53'7 is provided on one surface 52 of the polarizing beam splitter 50, and light is split using this diffraction action r.

In FIG. 12(C), a holographic splitting element 54 is provided on one surface of a polarizing beam splitter 50 to perform light splitting. In this configuration, a fine-pitch diffraction grating 55 is provided on the end face of the light splitter 54, and the diffraction angle of the diffracted light is made sufficiently large to cause total reflection at the interface between the splitter 55 and the air. The end face) is configured to emit diffracted light.

) in FIG. 12 is one surface 5 of the polarizing beam splitter 50.
Light is divided by providing an element with a light condensing function, such as a half lens or a half 7-lens lens, on the lens 2.

By using the light division profits as shown in Sections 121-(D) above, the same effect as in the embodiment explained in FIGS. 6 and 7 or the embodiment explained in FIG. 9 can be obtained. By integrating the polarizing beam sinter and the light splitter, it is possible to achieve miniaturization of the optical head for photothermal magnetic recording media.

In addition, in the arrangement of the embodiment shown in FIG. 9(A), the light source 3
In order to convert the diverging light from zero into parallel light, a collimator lens is provided between the light source 30 and the polarizing beam splitter 31, and another condensing lens is provided between the polarizing beam splitter 31 and the photodetector 36. In addition, a collimator lens may be provided between the polarizing beam snoritzer 31 and the condenser lens 33. With such an arrangement, it is possible to achieve substantially the same effects as in each of the embodiments described above.

According to the embodiments described above with reference to FIG. 6, FIG. 7, FIG. 9, and FIG. There is no need to adopt the method (setting the target value for all servos when the difference in light intensity is zero), and the cylindrical lens can also be removed, so the positional accuracy and dimensional accuracy of each element can be relatively relaxed. Can this reduce manufacturing costs? can be reduced.

Furthermore, in each of the above embodiments, the reflective portion and non-reflective portion of the photomolecular II device are formed into stripes as shown in FIG. 6(B), and the direction of the signal track T-T'i is set perpendicular to the stripe. Therefore, the influence of the tracking operation on the focus signal can be removed, and thereby autofocus and autotracking can be controlled easily and reliably.

Furthermore, according to the embodiments shown in FIGS. 9 and 12, the light splitting element is integrally provided on one end face of the polarizing beam splitter, which requires less space than when using an independent light splitter. This makes it possible to reduce the size of the optical head.

[Effects] As is clear from the above description, according to the present invention, it is possible to eliminate the influence of the tracking operation on the focus signal, and thereby each control of autofocus and autotracking can be performed easily and accurately. is possible,
Furthermore, an optical head for a photothermal magnetic recording medium can be obtained which does not require the positional accuracy and dimensional accuracy of each element to be as severe as conventional optical heads, thereby reducing manufacturing costs.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram illustrating the arrangement of the optical system of a conventional optical head, and Figs. Figures 3 (4) and (B) are explanatory diagrams illustrating the state of light flux movement due to tracking correction in a conventional optical head, and Figures 4 (4) to (C) are diagrams illustrating the movement of light flux to the photothermal magnetic recording medium. FIGS. 5(4) and (B) are explanatory diagrams showing the reproducing principle of a photothermal magnetic recording medium. FIGS. 7 (N to (C) are explanatory diagrams illustrating changes in light distribution on the photodetector surface due to tracking deviation;
The figure is an explanatory diagram illustrating a light splitter used in the optical head for a photothermal magnetic recording medium according to the present invention, and FIGS. 10 (5) to (CJ are graphs illustrating reproduced signals obtained in the optical head for a photothermal magnetic recording medium of the present invention, the first
Figure 1 is a diagram showing the use of the optical head for photothermal magnetic recording media of the present invention, and Figures 12 (4) to (c) are various types of optical splitters used in the optical head for photothermal magnetic recording media of the present invention. FIG. 2 is an explanatory diagram showing an example of the structure. 16.34... Photothermal magnetic recording medium, 15.33... Condenser lens, 13, 31.50... Polarizing beam splitter 122, 35... Light splitter, 70.71° 75.
76...Polarizing plate, 23,24.36...Photodetector,
83... Frequency separator, A, B, C, D... Light receiving element of photodetector, T-T'... Direction of signal track,
AF: autofocus signal, AT: autotracking signal. Figure 1 Figure 2 Figure 113 (B-Figure 4 (C) Figure 5 Figure 6 Figure 1 (B) (C) (D) T T T T'T'T' Figure 7 Figure 8 ■ ↑ 119 Figure 910 Figure 11 Figure 12

Claims (1)

[Claims] (1) Irradiate the recording medium with light focused by a condensing lens,
The light beam reflected from the recording medium is divided into a first beam and a second beam by a light splitting means.
The first and second beams are each passed through a polarizing plate and then received by a photodetector, and the difference signal between these electrical signals is passed through a frequency separator and the low frequency components are focused. The photothermal magnetic recording is characterized in that the photodetector detects changes in the original distribution of the first and second beams of the recording medium in the direction of signal trunk and direct burning, and the tracking control is performed using the electric signal. To body light. Do.