JPH1092040A - Magnetic recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a tracking error signal having high modulation degree and a good S/N ratio by forming the aperture of a converging optical system to be a reflection body and a rectangular shape parallel in the direction of a periodic physical change. SOLUTION: The aperture 2 of a converging optical system is formed to be a rectangular shape in the direction of a periodic physical change formed in a recording medium 4 and a beam width is made almost the same as a track width. When the maximum modulation degree of a circular aperture is compared with that of a rectangular aperture, the maximum modulation degree of the rectangular aperture is larger than that of the circular aperture. In such an aperture, when the angle R is made on the four corners, since beam intensity distribution becomes close to the beam intensity distribution of the circular aperture, the modulation degree is decreased. Consequently, the aperture is made a rectangle for making the modulation degree maximum. Since the aperture area is increased larger than 25% compared with a circular aperture and the output from a photodetector 15 is increased in proprtion to it, the S/N ratio is made higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field capable of stably detecting a high-accuracy tracking error signal and accurately recording, reproducing, or erasing data on a disk-shaped storage medium such as a fixed magnetic disk or a floppy disk. It relates to a recording device (IPC G11B 11/10).

[0002]

2. Description of the Related Art Conventionally, in a magnetic disk system for recording information on a magnetic storage medium, a track pitch is 2 bits.
Compared to about 00 μm, which is much larger than about 1.6 μm on an optical storage medium, rough track positioning was mechanically performed using a stepping motor or the like. However, in recent years, a track pitch of several μm to several tens of μm has been desired in order to realize a high capacity. In this case, a more accurate track positioning mechanism than in the past is required.

FIG. 8 shows an example of a conventional magnetic recording apparatus for detecting a tracking error signal using light. 8, reference numeral 1 denotes a semiconductor laser light source (hereinafter, referred to as a light source) that emits a linearly polarized divergent beam (hereinafter, referred to as a beam) 70. Reference numeral 16 denotes a diffraction beam that receives the beam 70 emitted from the light source 1 and branches into a plurality of beams. Element, 17 is diffraction element 1
The objective lens 21 receives the beam 70 transmitted through the objective lens 6 and condenses it on the magnetic storage medium 4, 21 is a support for supporting the objective lens 17, 15 is reflected and diffracted by the magnetic storage medium 4, and And a light detector 61 which receives the beam 70 branched by the diffraction element 16 and outputs an electric signal corresponding to the amount of received light. A photodetector 61 processes the electric signal output from the photodetector 15 to process a tracking error signal. , A base including a tracking error signal detecting optical system and a magnetic head 14 for recording and reproducing information, and a magnetic storage 91 for receiving a tracking error signal output from the signal processing unit 61. The drive unit adjusts a relative position between the medium 4 and the base 13.

Here, a finite system lens is used as the objective lens 17. In general, the peripheral portion of the lens surface is preferably not used because the light passing therethrough is affected by aberration and has an adverse optical effect on the shape of the condensed beam. In the vicinity of the light source 1 side of the objective lens 17, a circular opening 20 whose diameter is set smaller than the effective diameter of the objective lens 17
Are formed. At this time, the numerical aperture NA of the objective lens 17 is the diameter of the aperture 20, the light source 1, the aperture 20, and the lens 1.
7. Determined by the position of each magnetic storage medium 4 in the Z direction. The objective lens 17 is made of an injection-molded resin material, and has a variation in focal length due to molding errors. Therefore, by adjusting the position of the support 21 that supports the objective lens 17 in the Z direction, the focal position can be changed.
Exactly as above.

The diffraction element 16 has a region 16A formed on a surface near the light source 1 and a region 16B formed on a surface on the opposite side. Then, the divergent beam of linearly polarized light emitted from the light source 1 enters the region 16A of the diffraction element 16 and is branched into three beams of 0th-order diffracted light and ± 1st-order diffracted light, and the three beams generated in the region 16A Is the area 1
At 6B, the beam is further split into a plurality of beams. In the optical path from the light source 1 to the objective lens 17, the grating pitch of the region 16B is designed such that only the zero-order diffracted light of the diffracted light generated in the region 16B enters the opening of the objective lens 17. Further, the light is reflected and diffracted by the magnetic storage medium 4,
The beam 70 incident on the region 16B of the diffraction element 16 is split into a plurality of diffracted lights, of which ± 1st-order diffracted lights 71, 7
Only 2 is received by the photodetector 15.

FIG. 9 shows the relationship between a magnetic storage medium and a focused beam in a conventional magnetic recording apparatus. In the magnetic storage medium 4, discrete guide grooves are formed in the middle of adjacent tracks (areas where information is recorded or reproduced by the magnetic head 14). In addition, a tracking error signal and a synchronization signal synchronized with the rotation of the magnetic storage medium 4 can be optically detected. In FIG. 9, Tn-1, T
n, Tn + 1... are tracks, and Gn-1, Gn, G
n + 1... are guide grooves. Track pitch pt is 20
μm, and the width of the guide groove is set to 2 μm. These guide grooves are formed intermittently in the circumferential direction in order to obtain a rotation synchronization signal of the magnetic storage medium 4.
The circumferential pitch pt ′ is 720 rpm for the magnetic storage medium 4.
Is set so that the synchronization signal frequency obtained by the guide groove traversing the beam 70 in the circumferential direction becomes 20 kHz. Image side numerical aperture NA of objective lens 17
Is given by (Equation 1), where λ is the wavelength of the beam 70 emitted from the light source 1.
About 9 to 1.1 is selected. k = 1, λ = 0.79 μm
In this case, NA = 0.04.

[0007]

(Equation 1)

[0008] Of the beam 70, 70A is the diffraction element 16
0th-order diffracted light generated in the region 16A, 70B, 70C
Denotes ± 1st-order diffracted light generated in the area 16A of the diffraction element 16. The three beams 70A to 70C are arranged at intervals of pt / 4 with respect to the guide groove on the magnetic storage medium 4. FIGS. 10A and 10B show grating patterns of a diffraction element in a conventional magnetic recording apparatus.
(C) shows the relationship between the photodetector and the beam. FIG.
(A), (b), the region 16A of the diffraction element 16;
The grid patterns formed in the area 16A are patterns having the same pitch, and the grid pattern of the area 16A and the area 1
6B is orthogonal to the lattice pattern. The lattice pitch of the region 16A is 10 μm, and the lattice pitch of the region 16B is 3 μm. In FIG. 10C, the ± first-order diffracted lights 71 and 72 received by the photodetector 15 are composed of three beams 71A to 71C and 72A to 72C, respectively. The photodetector 15 has six light receiving sections 15A to 15F.
The beam 71A is the light receiving section 15B, the beam 71B is the light receiving section 15A, and the beam 71C is the light receiving section 15C.
The beam 72A is received by the light receiving unit 15E, the beam 72B is received by the light receiving unit 15D, and the beam 72C is received by the light receiving unit 15F.

In FIG. 10C, the light source 1 is
It is arranged on a photodetector 15 obtained by etching a silicon substrate. Further, a mirror 150 is formed on the silicon substrate, and the beam 70 emitted from the light source 1 in the Y direction is reflected by the mirror 150, and the X-Y on which the light receiving units 15A to 15F of the photodetector 15 are formed. The light is emitted in the Z-axis direction perpendicular to the plane.

FIG. 11 shows a circuit configuration of a signal processing section in a conventional magnetic recording apparatus. Light receiving section 15 of photodetector 15
A, 15B, 15C (or 15D, 15E, 15F)
Are connected to the IV conversion units 355, 354, and 353, respectively. Thereby, the light receiving unit 15 of the photodetector 15
A, 15B, 15C (or 15D, 15E, 15F)
Are output from the IV converter 35, respectively.
5, 354 and 353 convert the signals into voltage signals. When the magnetic storage medium 4 is rotating, the IV conversion unit 355,
The voltage signal v5 (or v
6, v7) is a synchronization signal of 20 kHz as shown in FIG. At this time, the maximum value v5 ″ of v5 is an output value in a state where there is no guide groove in the beam, and the minimum value v5 ′ of v5 is an output value in a state where the magnetic storage medium 4 rotates and the beam hits the guide groove. When the beam center coincides with the center of the guide groove in the X direction, | v5 ″ −v5 ′ | takes the maximum value.

When the beam 70 is displaced in proportion to the time t while the magnetic storage medium 4 is rotating, v5 (or v6, v7) becomes as shown in FIG.
Hz synchronous signal minimum value envelope v5 '(or v
6 ', v7') when the beam 70 has a displacement x from the center of the guide groove (e.g., Gn) of the magnetic storage medium 4, respectively, is approximately represented by the following (Equation 2) to (Equation 4). Waveform.

[0012]

(Equation 2)

[0013]

(Equation 3)

[0014]

(Equation 4)

In the above (Equation 2) to (Equation 4), A1
A3 is an amplitude, and B1 to B3 are DC components. Where v
The ratio of the amplitude to the DC component of 5 ′ to v7 ′, that is, A
1 / B1 (or A2 / B2, A3 / B3) is called a modulation degree MOD. As shown in FIG. 11, the IV converters 353 and 354 include variable gain amplifiers 476 and 476, respectively.
77 and an envelope detection unit 356, 357, and is connected to the differential operation unit 374. Thereby, the voltage signals v5, v6 output from the IV conversion units 353, 354
Are adjusted so that the maximum amplitudes (A1 + B1 shown in FIG. 13) of the synchronization signals are equalized by the variable gain amplifiers 476 and 477, respectively, and then the envelope detectors 356 and 357 detect the displacement signals v5 ′ and v6 ′. The operation calculation is performed by the differential calculation unit 374, and the result is output as the voltage signal v8. Also, I-
The voltage signal v5 output from the V conversion units 354 and 355,
v7 is adjusted by the variable gain amplifiers 478 and 479 so that the maximum amplitudes of the synchronization signals are equal to each other, and after the displacement detectors 358 and 359 detect the displacement signals v5 ′ and v7 ′, the differential calculator 375 The differential operation is performed, and the voltage signal v9
Is output as The voltage signals v8 and v9 output from the differential operation units 374 and 375 are as follows (Equation 5),
It becomes a sine wave whose phase differs by π / 2 as represented by (Equation 6).

[0016]

(Equation 5)

[0017]

(Equation 6)

In the above (Equation 5) and (Equation 6), A4 is the amplitude. The differential operation units 374 and 375 are connected to the differential operation unit 433 via the variable gain amplifying units 474 and 475, respectively.
It is connected to the. Thereby, the differential operation units 374, 3
The voltage signals v8 and v9 output from 75 are adjusted to desired amplitudes by the variable gain amplifiers 474 and 475, respectively, added by the calculation unit 433, and output as the voltage signal v10. The voltage signal v10 has a waveform represented by the following (Formula 7), and is output from the output terminal 403 as a tracking error signal.

[0019]

(Equation 7)

In the above (Equation 7), K3 and K4 are the gains of the variable gain amplifiers 474 and 475, respectively, and Φ1 is-
π / 4. The tracking error signal v10 has a gain K
3. By appropriately selecting K4, a signal having an arbitrary phase and amplitude can be obtained. The range indicated by 65 is actually processed by a digital processor, and the envelope detectors 356 to 359 detect the envelope after A / D conversion (not shown) of the input analog voltage value. Digital output. The maximum input value at the time of A / D conversion is the maximum amplitude (A1 + B1 in FIG. 6) of the synchronization signal after being adjusted to be equal in the variable gain amplifier. Therefore, v5 ′ to v7 ′ output from the envelope detection units 356 to 359.
Assuming that the number of bits is n, the digital information amount N is represented by Expression 8 from the modulation degree MOD described above.

[0021]

(Equation 8)

In the case of 8 bits, the digital information amount N is MO
N = 256 if D = 1, but N if MOD is 0.7
= 210, the quantization error increases due to the decrease in the amount of digital information, and the tracking error increases. It is also clear from the above description that the optical and electrical noises have a low modulation factor MOD and a low signal-to-noise ratio, thereby increasing tracking errors.

Next, the tracking operation in the magnetic recording apparatus configured as described above will be described. 8, a linearly polarized divergent beam 7 emitted from the light source 1 is shown.
The 0 is incident on the region 16A of the diffraction element 16 and is split into three beams of 0-order diffracted light and ± 1st-order diffracted light. Area 1
The three beams generated in 6A are further split into a plurality of beams in the area 16B, but only the zero-order diffracted light of the diffracted light generated in the area 16B enters the opening of the objective lens 17. The three diffracted lights 70A to 70C are condensed on the magnetic storage medium 4 by the objective lens 17 (FIG. 9). The beam 70A reflected and diffracted by the magnetic storage medium 4
70C passes through the objective lens 17 again, and
6 and is split into a plurality of diffracted lights.
The ± 1st-order diffracted light 71A-
Only 71C and 72A to 72C are the light receiving portions 1 of the photodetector 15.
The light is received by 5A to 15F (see FIG. 10C). The light receiving units 15A to 15F of the photodetector 15 output an electric signal corresponding to the amount of received light of each beam to the signal processing unit 61.
(FIG. 11). This electric signal is sent to a signal processing unit 61.
And is output to the drive unit 91 as a tracking error signal. Drive unit 91 that has received a tracking error signal
Adjusts the relative position between the base 13 including the optical system and the magnetic head 14 and the magnetic storage medium 4. As a result, tracking is performed on a desired track.

[0024]

As described above, in the conventional magnetic recording apparatus, since the beam shape focused on the magnetic storage medium is circular, the degree of modulation does not rise above a certain value. In addition, there is a problem that the signal-to-noise ratio of the tracking error signal is poor and the tracking operation becomes unstable.

When the shape of the focused beam is circular, the objective lens 1
7 has a relationship as shown in FIG. 7A between the image-side numerical aperture NA and the modulation degree MOD, and the modulation degree MOD increases in proportion to the NA when the NA is equal to or smaller than the value obtained by (Equation 1). However, when NA exceeds this value, the rate of increase of the modulation factor MOD decreases. On the other hand, it is desirable that the tracking error signal is a sine wave. However, if the NA exceeds the value obtained by (Equation 1), the beam diameter focused on the magnetic storage medium becomes smaller than the track pitch, so that the tracking error signal becomes The shape changes from a sine wave to a distorted shape, and a phase error increases, thereby causing a tracking position shift.

An object of the present invention is to provide a magnetic recording apparatus capable of detecting a tracking error signal having a high degree of modulation and a good signal-to-noise ratio in order to solve the above-mentioned problems in the prior art.

[0027]

In order to solve the above-mentioned problems, a magnetic recording apparatus according to the present invention comprises a recording medium on which a periodic physical change giving a change in reflectance is formed, and a light source for emitting a light beam. And a condensing optical system that receives the beam emitted from the light source and condenses it on the disk-shaped storage medium; and a beam that is reflected and diffracted by the recording medium and transmitted again through the opening of the condensing optical system. Receiving light, outputting a signal corresponding to the amount of received light, signal processing means for processing a signal output from the light detection means to output a tracking error signal, and output from the signal processing means. A magnetic device comprising: a driving unit that receives a tracking error signal and positions a beam on a desired track; and a magnetic head that records information on the recording medium or reproduces or erases information on the recording medium. A recording apparatus, wherein an opening of the light-collecting optical system is formed in a rectangular shape parallel to a direction of a periodic physical change formed in the recording medium, and a beam width is set substantially equal to a track width. It is possible to detect a tracking error signal having a higher degree of modulation and a better signal-to-noise ratio than a conventional circular aperture.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic recording apparatus according to a first aspect of the present invention includes a recording medium on which a periodic physical change giving a change in reflectance is formed, a light source for emitting a light beam, and a light source. A condensing optical system for receiving the emitted beam and condensing it on the disk-shaped storage medium; and receiving and receiving the beam reflected and diffracted by the recording medium and transmitted again through the opening of the condensing optical system. Light detection means for outputting a signal corresponding to the amount;
Signal processing means for processing a signal output from the light detection means to output a tracking error signal; and driving means for receiving a tracking error signal output from the signal processing means and positioning a beam on a desired track. And a magnetic head for recording information on the recording medium, or reproducing or erasing information on the recording medium, wherein an opening of the condensing optical system is formed in the recording medium. It is characterized in that it has a rectangular shape parallel to the direction of the periodic physical change, and that the beam width is set to be approximately equal to the track width. As a result, a tracking error signal having a good signal-to-noise ratio and a small phase distortion can be obtained.

Next, in a magnetic recording apparatus according to a second aspect of the present invention, in the first aspect, the position of the objective lens for focusing the beam emitted from the light source on the recording medium is adjusted in the optical axis direction. In addition to the above, an aperture for determining the numerical aperture of the condensing optical system is arranged between the recording medium and the objective lens, and the distance between the recording medium and the recording medium is constant. Since the image-side numerical aperture is kept constant irrespective of the adjustment position of the objective lens, there is no decrease in the modulation degree due to the lens position adjustment, and a tracking error signal with a good signal-to-noise ratio is detected. You can do it. (Embodiment 1) An embodiment of the present invention described in claim 1 of the present invention will be described below with reference to FIGS.

In FIG. 1, the basic configuration is the same as the configuration shown in FIG. 8 of the conventional embodiment, and the same portions are denoted by the same reference numerals and description thereof will be omitted. The points different from the conventional example are as follows. That is, in the above-described conventional example, the circular opening 20 whose diameter is set to be smaller than the diameter of the objective lens 17 is formed near the light source 1 side of the objective lens 17; The aperture 2 is formed in a rectangular shape parallel to the direction of the periodic physical change formed in the reflector, and has a diagonal length smaller than the diameter of the objective lens 17. The reason why an optical system that focuses a beam transmitted through such a rectangular aperture on a reflector can obtain a higher degree of modulation than an optical system that focuses a beam transmitted through a circular aperture on a reflector. This will be described below.

The light intensity distribution of the beam focused on the reflector by the present focusing optical system can be approximated as Fraunhofer diffraction. In the case of a circular aperture having a radius a, the light intensity I ′ of the focused beam is expressed by ( Equation 9) is given. Here, J1 is the first
Seed Bessel function, k is a wave number given by k = 2π / λ,
λ is the wavelength, w is the radius from the beam center on the reflector,
I'0 is the maximum value of I 'at w = 0.

[0032]

(Equation 9)

On the other hand, the width in the x direction is 2a, and the width in the y direction is 2
The light intensity I of the condensed beam due to the rectangular aperture b is (Equation 10)
Given by Here, p and q are distances in the x and y directions from the beam center on the reflector, respectively, and I0 is p = 0 and q = 0.
Is the maximum value of I.

[0034]

(Equation 10)

FIGS. 2 (a) and 2 (b) show the relative intensities of the condensed beams on the reflector given by (Equation 9) and (Equation 10) in contour maps, respectively. When analyzing an electric signal obtained by reflecting and diffracting a beam on a magnetic storage medium on which a guide groove is formed, the Y of the guide groove is compared with the beam diameter.
Since the length in the direction is sufficiently large, the relative relationship between the intensity distribution in the X direction obtained by integrating the beam intensity in the Y direction and the guide groove may be seen. FIGS. 3A, 3B, and 3C show a beam with a circular aperture, and FIGS. 4A, 4B, and 3C show beams integrated in the Y direction when the beam diameter is changed for a rectangular aperture. 4 shows a positional relationship of a guide groove with respect to intensity and beam intensity. 3 and 4 show a state in which the beam is located between the adjacent guide grooves, and the electric signal at this time is represented by (Equation 2) and x = p
v = −A1 + B1 obtained by substituting t / 2. Here, v is a difference between an electric signal in a state where the guide groove is not applied to the beam at all and an electric signal obtained by reflecting and diffracting the beam with the guide groove applied thereto. It is considered that the beam intensity distribution curve corresponds to the area s of the guide groove width portion as shown by the hatched portions s1 to s6 in FIG. Further, as described above, the modulation degree MOD is MOD =
Since this is given by A1 / B1, this and v = −A1
MOD = (1-v / B1) ∝ (1-s / B from + B1)
1), the larger the area s is, the greater the modulation MO
It can be seen that MOD is higher when D is lower and s is lower.

As shown in FIG. 3A, when the beam diameter is large, the area s1 is large and the modulation MOD is low. FIG. 3B shows the case where the beam diameter is substantially equal to the pitch pt of the guide groove, but the area s2 is smaller than s1 in FIG. 3A, and the modulation MOD is relatively high. The NA obtained by (Equation 1) is a value at which the beam diameter becomes the state shown in FIG. When the beam diameter is as shown in FIGS. 3A and 3B, the phase waveform obtained when the beam is displaced with respect to the guide groove is a sine wave that can be approximated by (Equation 2). It is a close shape. When the beam diameter is further reduced as compared with FIG. 3B, s3 is further reduced as shown in FIG. 3C, and the modulation degree MOD can be increased. Such a beam diameter cannot be set because the shape becomes distorted, the phase error increases, and the tracking position shifts. FIG. 7A shows the relationship between the modulation factor MOD and the phase error with respect to the image-side numerical aperture NA in the case of the circular aperture described above, and X1, X
2 and X3 correspond to FIGS. 3A, 3B, and 3C, respectively.

When the phase error is equal to or less than a predetermined value, the maximum modulation obtained in the case of a circular aperture is the value of X2 in consideration of the predetermined phase error, and the modulation MOD at this time is 1-
s2 / B1. On the other hand, when the beam diameter of the rectangular aperture is large, the hatched portion s4 is large and the modulation factor MOD is low as in the case of the circular aperture as shown in FIG. 4A, but the beam diameter is almost as shown in FIG. When the pitch is equal to the guide groove pitch pt, the beam intensity distribution differs from the circular aperture, and the intensity is almost 0 at the portion x, so that the hatched portion s4 is close to 0 and the modulation factor MOD is very high. The modulation MOD at this time is 1-s5 / B1. Also in the case of a rectangular aperture, when the beam diameter becomes smaller than the state shown in FIG. 4B, the phase waveform is distorted from a sine wave. FIG. 4 (c)
As shown in the figure, the hatched portion s6 is larger than s5 in FIG.

FIG. 7B shows the relationship between the modulation MOD and the phase error with respect to the image-side numerical aperture NA in the case of a rectangular aperture.
And Y1, Y2, and Y3 are respectively shown in FIG.
(B) and (c). As is clear from the above description, the modulation degree MOD tends to increase as the beam diameter is reduced by increasing the image-side numerical aperture NA in both the circular aperture and the rectangular aperture.
Is increased, there is a maximum limit of the modulation factor MOD that is limited because the phase waveform obtained by displacing the beam from the guide groove is distorted from a sine wave to cause a tracking position shift. When the maximum modulation is compared between the circular aperture and the rectangular aperture, s2> s5 due to the difference in the beam intensity distribution, so that the maximum modulation of the rectangular aperture is greater than the maximum modulation of the circular aperture.

On the other hand, from the above theory, as shown in FIG. 5, if the width Wy in the Y direction of the opening 19 is sufficiently longer than the width Wx in the X direction, it can be estimated that the same effect can be obtained even if the opening 19 is not rectangular. Due to the restrictions on miniaturization and thinning required for magnetic recording devices, the lens size is at most an effective diameter Φ2
mm is allowed, and the use of the peripheral portion of the lens is affected by aberrations. Therefore, it is preferable to avoid the optical performance as much as possible. As a result, Wx is only about 1 mm at most. Since Wy is also about 0.8 mm, in such an opening size, if the corners R are formed at the four corners of the opening, the beam intensity distribution approaches the intensity distribution of the circular opening, so that the modulation degree decreases. Therefore, in order to increase the degree of modulation to the maximum, the opening needs to be rectangular.

Further, the rectangular aperture increases the aperture area by 25% or more compared to the circular aperture.
5 also has the advantage that the signal-to-noise ratio is further increased since the output from 5 increases in proportion thereto. (Embodiment 2) Next, an embodiment of the invention described in claim 2 of the present invention will be described with reference to FIG.

6A and 6B, the basic configuration of the magnetic recording apparatus is the same as that of the first embodiment shown in FIG. The difference from the first embodiment is that in order to keep the image-side numerical aperture NA constant regardless of the adjustment position of the objective lens 17, the aperture 2 is located between the lens 17 and the magnetic storage medium 4, This is a point provided so that the distance is constant.

In FIG. 8 showing a conventional example, an objective lens 1 is shown.
7 so that the focal position of the aperture 7 coincides with the magnetic storage medium 4.
When the objective lens 17 is moved together with the support 21 on which 0 is formed, the image-side numerical aperture NA changes so that the lens 17 becomes smaller as the distance from the magnetic storage medium 4 increases.
As described above, when the image-side numerical aperture NA decreases, the modulation degree MOD
Therefore, the maximum degree of modulation cannot always be obtained depending on the focal length variation of the objective lens 17.

In the present invention, the rectangular opening 2 is provided at an intermediate position between the objective lens 17 and the magnetic storage medium 4, so that the distance between the rectangular opening 2 and the magnetic storage medium 4 is constant regardless of the position of the objective lens 17 in the Z direction. It has become. That is, since the rectangular opening 2 is provided in the base 13, the distance between the rectangular opening 2 and the recording medium 4 is constant even if the objective lens 17 moves.

With the above-described configuration, the image-side numerical aperture NA is constant regardless of the position of the objective lens 17 for focus position adjustment, so that the modulation factor MOD does not change. It is possible to obtain.

[0045]

As described above, according to the magnetic recording apparatus of the present invention, the aperture of the focusing optical system is formed in a rectangular shape parallel to the direction of the periodic physical change formed in the reflector. Accordingly, it is possible to detect a tracking error signal having a higher degree of modulation and a better signal-to-noise ratio than a conventional circular aperture.

In a magnetic recording apparatus in which the position of the objective lens can be adjusted in the direction of the optical axis, an opening for determining the numerical aperture of the condensing optical system is arranged between the disk-shaped storage medium and the objective lens. In addition, since the distance from the disk-shaped storage medium is constant, the image-side numerical aperture is constant regardless of the adjustment position of the objective lens, so that the maximum modulation degree can always be obtained, and the signal-to-noise ratio is good. It is possible to obtain a proper tracking signal.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a magnetic recording device according to a first embodiment of the present invention.

2A is a diagram showing the intensity distribution of a condensed beam by a conventional circular aperture; FIG. 2B is a diagram showing the intensity distribution of a condensed beam by a rectangular aperture in the first embodiment of the present invention;

FIG. 3 is a diagram showing the influence of a guide groove on the intensity distribution of a condensed beam by a conventional circular aperture.

FIG. 4 is a diagram showing the influence of a guide groove on the intensity distribution of a focused beam due to a rectangular aperture according to the first embodiment of the present invention.

FIG. 5 is a diagram showing theoretically possible openings according to the first embodiment of the present invention;

FIG. 6 is a configuration diagram showing a magnetic recording device according to a second embodiment of the present invention.

7A is a diagram showing a relationship between a numerical aperture and a modulation factor and a phase error due to a conventional circular aperture. FIG. 7B is a diagram showing a relationship between a numerical aperture and a modulation factor and a phase error due to a rectangular aperture according to the embodiment of the present invention. Figure

FIG. 8 is a configuration diagram showing a magnetic recording device according to a conventional embodiment.

FIG. 9 is a diagram showing a relationship between a magnetic storage medium and a focused beam;

10A and 10B are diagrams showing a grating pattern of a conventional diffraction element. FIG. 10C is a diagram showing a relationship between a conventional photodetector and a beam.

FIG. 11 is a circuit configuration diagram showing a signal processing unit of the magnetic recording device.

FIG. 12 is a signal waveform diagram in a tracking signal processing unit of the magnetic recording device.

FIG. 13 is a signal waveform diagram in a tracking signal processing unit when a beam of a magnetic recording device is displaced.

[Explanation of symbols]

Reference Signs List 1 semiconductor laser light source 2 opening 4 magnetic storage medium 13 base 14 magnetic head 15 photodetector 15A to 15F light receiving unit 16 diffractive element 17 objective lens 19, 20 opening 21 support body 61 signal processing unit 65 digital processor 70 to 74, 71A ~ 71C, 73A ~ 73C, 74A
~ 74C beam 91 drive unit 353-355 current-voltage (IV) conversion unit 356-359 envelope detection unit 374,375 differential operation unit 403 output terminal

Claims (2)

[Claims] 1. A disk-shaped recording medium on which a periodic physical change giving a change in reflectivity is formed, a light source for emitting a light beam, and a beam received from the light source, collected on the storage medium A condensing optical system that emits light, a light detecting unit that receives a beam that is reflected and diffracted by the recording medium and transmits again through the opening of the condensing optical system, and outputs a signal corresponding to a received light amount; A signal processing unit that processes a signal output from the detection unit to output a tracking error signal, and a driving unit that receives the tracking error signal output from the signal processing unit and performs beam positioning on a desired track. A magnetic recording device comprising: a magnetic head that records information on the recording medium or reproduces or erases information on the recording medium, wherein an opening of the condensing optical system is formed in the recording medium. And forming parallel rectangular in the direction of cyclic physical change, a magnetic recording apparatus characterized by taking equal beam width approximately the track width. 2. An objective lens for condensing a beam emitted from the light source on the recording medium, the position of which can be adjusted in an optical axis direction, and an aperture for determining a numerical aperture of the condensing optical system is provided. 2. The magnetic recording apparatus according to claim 1, wherein the magnetic recording apparatus is arranged between a recording medium and the objective lens and has a constant distance from the recording medium.