KR930002162B1 - Tracking error detecting apparatus for an optical head - Google Patents

Abstract

No content.

Description

Tracking error detection device of optical head

1 and 2 are front views showing a semiconductor laser device of each embodiment of the tracking error detecting apparatus of the optical head according to the present invention.

3 is a weak ship arrangement diagram showing a tracking error detection device of a conventional optical head.

4 and 5 are front views showing an example of a semiconductor laser element in a conventional tracking error detecting apparatus for an optical head.

6 is a waveform diagram.

7 is a diagram provided in the description of the interference.

* Explanation of symbols for main parts of the drawings

Optical head 1: semiconductor laser device

1: Laser beam output section 1: Active layer

2: collimator lens 3: diffraction grating

4: beam splitter 5: objective lens

6: optical recording medium.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an optical head tracking error detection device which is most suitable for an optical recording device, a reproducing device and a recording and reproducing device.

The technical background and its problems will first be described with reference to FIG. 3, for a conventional tracking error detecting apparatus for an optical head. OH denotes the optical head as a whole. (1) is a semiconductor laser element (laser diode), and the diverging laser beam L having an ellipse in cross section emitted from the laser beam exit end surface 1A side thereof is a collimator lens (sometimes not necessary) (2). 2) is incident on the diffraction grating (grating) 3 after being incident to the flat beam. Zero-order beams (Lo) and ± first-order beams (L ₊₁ , L _-1 ) emitted from the diffraction grating (3, only the + 2nd phase and the beams below -2nd order) are unpolarized beam splitters (Hypermirror) (in the case of the deflection beam splitter, a quarter wave plate is provided between the objective lens 5) (4), the light is incident on the objective lens 5, and focused. The zeroth order beam (Lo) and the first order beam (L ₊₁ , L _-1 ) are incident on the recording surface of the optical recording medium (including the magneto-optical recording medium) 6 at a predetermined interval (for example, 10 μm). Lose.

The zero-order beam Lo and the ± first-order beam L _{+ 1} , L- ₁ reflected by the optical recording medium 6 pass through the objective lens 5, and then enter the beam splitter 4, A part thereof is reflected by the reflecting surface 4a and is incident on the photodetector 7. The photodetector 7 is configured as three photodetectors in which the zeroth order beam Lo and the ± first order beams L _{+ 1} and L- ₁ are respectively incident. Thus, the difference between the pair of photodetection outputs in the pair of photodetectors into which the ± first order beams are incident, respectively, results in a tracking state on the recording surface of the optical recording medium 6 of the zero order beam Lo. A tracking error signal is obtained. Further, in the incident photodetector of the 0th order beam, a reproduction signal, a focus error signal, and the like are obtained.

Next, an example of the semiconductor laser device 1 will be described with reference to FIG. This semiconductor laser device 1 is usually fixed on a heat sink 8 made of copper or the like serving as one electrode. Referring to the structure of the semiconductor laser device 1 from the upper layer to the lower layer in the drawing, (1a) is an electrode layer, (1b) is an n-GaAs layer (gas layer), and (1C) is an n-yAlyAs layer (clad). Layer), (1d) is a Ga _1- xAzAs layer (active layer), (1e) is a p-Ga _1- yAlyAs layer (clad layer) 1f is a p-GaAs layer. Thus, the laser beam L described above is emitted from the active layer 1d. When the laser beam exit end face (cleft face) 1A of the semiconductor laser device 1 is faced in front, its width is 100 to 300 µm, its height (thickness) is 80 to 100 µm, and its depth is 200 to 300 µm. The height at the top surface of the heat sink 8 of the active layer 1 is several μm.

However, if the tangential skew angle with respect to the recording surface of the optical recording medium 6 of the zero order beam Lo changes, the tracking error signal also changes periodically accordingly, so that an accurate tracking error could not be detected.

The present inventors have found the cause and found the following. The zeroth order beam Lo and the ± first order beams L _{+ 1} and L- ₁ reflected by the optical recording medium 6 pass through the objective lens 5, and then the reflective surface 4a of the beam splitter 4 In addition to reflecting from the beam, the beam passes through the beam splitter 4, enters the diffraction grating 3, and generates a distinct 0th order beam and a ± 1st order beam corresponding to the collimator lens 2, respectively. Pass through to the semiconductor laser device (1). The beam amount of the beam directed to the semiconductor laser device 1 is large when a non-polarization beam splitter is used, and rarely when a polarizing beam splitter is used. In this case, the center beam La directed to the semiconductor laser element 1 and both of them are located in accordance with the position of the laser beam emission end surface 1A of the semiconductor laser element 1 and the relative rotation angle of the diffraction grating 3. The arrangement of both beams Lb and Lc is such that the center beam La is located in the active layer 1d on the laser beam exit cross-section 1A so that both beams Lb and Lc pass through the position of the center beam La. In the case of being positioned up and down in a straight line orthogonal to the active layer 1d, the case where the center beam La and the two side beams Lb and Lc are located together on the active layer 1, and the center beam La And a straight line connecting both beams Lb and Lc may come to an arbitrary angular position in the middle of the two cases. Therefore, these center beams La and both beams Lb and Lc have 0th-order beams Lo and ± 1st-order beams L _{+ 1} and L- ₁ re-diffracted by the diffraction grating 3. They are also mixed and overlapped.

°)에 대한 트랙킹에러 신호(Se)의 레벨 변화의 주기성을 표시한다. 또한, 실제로는, │

│ 가 증대함에 따라서, 트랙킹에러신호(Se)의 레벨은 감쇠한다. 또한, 양쪽비임(Lb, Lc) 공레이저비임 출사단면(1A)에 입사하는 경우는, 제6도에 대응하는 파형의 진폭이 제6도의 그것의 2배로 되어, 위상은 제6도와 다르다.However, when at least one of both beams Lb and Lc enters the surface of the heat sink 8, since the surface is rough surface, the beam is diffusely reflected there, so there is no problem, but both beams Lb and Lc When at least one of the incident portions enters the laser beam exit end face 1A of the semiconductor laser device 1, the end face 1A has a good reflectance (for example, 10%), so that the end face 1A reflects the end face 1A. The light enters the photodetector 7 after passing through the optical path, causing interference with the +1 order or -1 beam. For this reason, the intensity of the + 1st or -1st order beam incident on the photodetector 7 changes according to the tangential skew angle with respect to the recording surface of the optical recording medium 6 of the 0th order beam Lo, and thus the tracking error. The signal changes periodically with its skew angle. 6 shows that one side Lb of both beams Lb and Lc enters the laser beam light emitting end surface 1A of the semiconductor laser element 1, and the other side Lc enters the heat sink 8. In this case, the tangential skew angle with respect to the recording surface of the optical recording medium 6 of the zeroth order beam Lo

Indicates the periodicity of the level change of the tracking error signal Se. Also, in practice, │

As it increases, the level of the tracking error signal Se decreases. In addition, in the case where the beams are incident on the both-beams Lb and Lc co-laser beam exit end face 1A, the amplitude of the waveform corresponding to FIG. 6 is twice that of FIG. 6, and the phase is different from FIG.

Next, one side Lb of both beams Lb and Lc enters the laser beam exit end surface 1A of the semiconductor laser element 1, and the other side Lc enters the heat sink 8. Will be described with reference to FIG. 7 (not shown in the lens system). In FIG. 7, 1A indicated by a solid line indicates a general case inclined with respect to the laser beam exit cross section or the exit cross section 1A of a normal position indicated by a broken line, and is also indicated by a solid line. Denoted at 6 is an optical recording medium or a case inclined with respect to the optical recording medium 6 at a normal position indicated by broken lines. The zero-order beam Lo is perpendicular to the laser beam exit cross section 1A at the normal position and to the recording surface of the optical recording medium 6 at the normal position. θ is the angle to the 0th order beam Lo of the + 1st order beam L ₊₁ . l ₁ is the optical path distance l ₂ between the laser beam exit section 1A and the diffraction grating 3 is the optical path distance between the diffraction grating 3 and the recording surface of the optical block medium 6. 4l ₁ and 4l ₂ are optical path differences between the 0th order beam Lo and the + 1st order beam L _{+ 1 for the} optical path distances 1 ₁ and 1 ₂ , respectively. 4l ₃ and 4l ₄ are optical path differences due to the skew of the optical beam medium laser beam exit section 1A due to the skew of the optical recording medium 6, respectively.

In addition, g is taken as an optical path difference between the 0th order beam Lo and the + 1st order beam L ₊ 1 in the diffraction grating 3. i ₀ and i ₁ are the diffraction gratings 3, respectively, for the 0th-order beam, + 1st-order beam, and t is the transmittance (r, f) of the half mirror 4, respectively. Is the reflectance on the laser beam exit surface 1A on the recording surface.

Thus, the complex amplitude of light at the point A on the recording surface of the optical recording medium 6 into which the + 1st order beam L ₊₁ is incident is considered to be divided into the following four cases.

(1) a ₁ : When incident to the direct point (A) of the + 1st order beam (L _{+ 1} ).

(2) a ₂ : The zero-order beam obtained by reflecting from the optical recording medium 6 of the zero-order beam Lo and entering the diffraction grating 3 again is reflected from the laser beam exit section 1A, and the diffraction grating again This is the case where the + 1st beam obtained by incidence into (3) enters point A.

(3) a ₃ : The + 1st order beam obtained by reflecting the 0th order beam Lo from the optical recording medium 6 and entering the diffraction grating 3 again reflects from the laser beam exit cross section 1A, and again The case where the zero-order beam obtained by incidence into the diffraction grating 3 is incident on the point A.

₍₄₎ a 4: reflected by the + first order beam (L _{+ 1)} The optical recording medium 6, the zero order beam is again incident obtained hameuroseo the diffraction grating 3 is reflected by the laser beam emitting end face (1A) This is the case where the 0th order beam obtained by incidence into the diffraction grating 3 again enters the point A.

Next, a ₁ to a ₄ are represented by formulas.

For the sake of simplicity, if the coherence distance of the laser beam is 2 (l ₁ + l ₂ ) or less, the light intensity I _A at the point A is expressed as follows.

In addition, when both the beams Lb and Lc enter the laser beam exit end face 1A, the + 1st beam L ₊₁ is the point A on the recording surface of the optical recording medium 6. When incident to and the -first beam L _-1 enters the point B which is symmetrical with respect to the 0-th order beam Lo, the light intensity I _A of the point _A is as follows (5). . The intensity of light I _{B at} point B is expressed as

SUMMARY OF THE INVENTION An object of the present invention is to propose that in the above-described optical tracking error detecting apparatus, a false-free tracking error signal that varies according to a change in the tangential skew angle with respect to the optical recording medium of the zero-order beam of the optical head can be obtained. .

SUMMARY OF THE INVENTION The present invention relates to a semiconductor laser device, a diffraction grating into which a laser beam is incident on the semiconductor laser, a beam splitter through which a zero-order beam and a ± first-order beam emitted from the diffraction grating pass, and the beam. The 0th and ± 1st beams emitted from the splitter are focused and incident on the optical recording medium, and the 0th and ± 1st beams reflected by the optical recording medium pass through the objective lens. After reflecting back from the opposite side of the beam splitter, it has a photodetector which is incident, and the photodetector obtains a pair of photodetection outputs corresponding to ± 1st order beams, and the 0th order beams according to the difference of the pair of photodetector outputs. An optical head tracking error detecting device for obtaining a tracking error signal according to a tracking state on an optical recording medium, comprising: reflecting from an optical recording medium to an objective lens and a beam The shape of the laser beam exit cross section of the semiconductor laser device is selected so that the center beam passing through the liter and the diffraction grating and toward the semiconductor laser device and both beams on both sides do not enter the laser beam exit section of the semiconductor laser device. It is characterized in that formed by.

According to the present invention as described above, in such an optical tracking error detection device, it is possible to obtain a false tracking error signal which is changed by a change in the tangential skew angle with respect to the optical recording medium of the 0th order beam of the optical head. .

EXAMPLES Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1, but in FIG. 1, parts corresponding to those of FIGS. 3 to 7 are denoted by the same reference numerals and redundant description thereof will be omitted.

FIG. 1 is a case where the straight line connecting the center beam La and the both beams Lb and Lc directed to the semiconductor laser element 1 is substantially orthogonal to the active layer 1d of the semiconductor laser element 1.

In this embodiment, the thickness (height) of the semiconductor laser device 1 is made thin (low), for example, about 80 μm, so that the upper beam Lb in the drawing of both beams Lb and Lc is the laser beam exit cross-section ( Do not enter 1A). In the drawing, the lower beam Lc enters the heat sink 8 and is diffusely reflected there. In addition, the other structure is the same as FIG.

In this way, according to the tracking error detection device of the optical head, even if the beam reflected from the optical recording medium is directed to the semiconductor laser device 1 through the objective lens 5, the beam splitter 4 and the diffraction grating 3, Since there is no false reflected from the laser beam exit end face 1A, a false error tracking error signal that changes due to the change in the tangential skew angle with respect to the optical recording medium of the 0th order beam of the optical head OH can be obtained.

In addition, when the thickness of the semiconductor laser element 1 is reduced, when there is a problem in strength, as shown in FIG. 2, the groove 9 is formed in the center of the upper surface of the semiconductor laser element 1, The beam Lb of may not be incident on the laser beam exit section 1A.

If both beams Lb and Lc are likely to enter the laser beam exit end face 1A together, the width of the semiconductor laser element 1 should be folded or the grooves will be formed on both sides. Just do it.

It is also as described above when the arrangement of the beams is in the intermediate state described above.

According to the above-described effects of the present invention, in the tracking error detecting device of the optical head, a false error tracking error signal is obtained which varies according to the change in the tangential skew angle with respect to the optical recording medium of the zeroth order beam of the optical head. You can get what you can.

Claims (1)

A semiconductor laser element, a diffraction grating into which the laser beam is incident on the semiconductor laser element, a beam splitter through which the zero-order beam and the ± first-order beam emitted from the diffraction grating pass, and zero emitted from the beam splitter The objective lens and the primary beam are focused to be incident on the optical recording medium, and the reflected zeroth order beam and the ± first primary beam pass through the objective lens again. Reflecting on the opposite side of the beam splitter, and having a photodetector to be incident thereon, the photodetector obtains a pair of photodetection outputs corresponding to the ± first order beams and according to the difference of the pair of photodetector outputs An optical head tracking error detecting apparatus for obtaining a tracking error signal in accordance with a tracking state on an optical recording medium of a zero-order beam, the optical recording medium comprising: Reflecting, the center beam passing through the objective lens, the beam splitter and the diffraction grating toward the semiconductor laser device, and both beams of the two beams do not enter the laser beam of the semiconductor laser device. And a shape of a laser beam exit cross section of the semiconductor laser device, wherein the tracking error detection device of the optical head is formed.

Images