WO1986002191A1

WO1986002191A1 - Apparatus for detecting tracking error of an optical head

Info

Publication number: WO1986002191A1
Application number: PCT/JP1985/000547
Authority: WO
Inventors: Kenji Shintani; Takatoshi Yamada; Atsushi Fukumoto; Kiyoshi Ohsato
Original assignee: Sony Corporation
Priority date: 1984-10-04
Filing date: 1985-10-03
Publication date: 1986-04-10
Also published as: JP2575099B2; JPS6187225A; AU4963585A

Abstract

An apparatus for detecting tracking errors of an optical head, wherein a laser beam from a semiconductor laser element (1) is permitted to be incident upon a diffraction grating (3), a zero-order beam and ↓∃ primary beams from the diffraction grating (3) are permitted to be incident upon an object glass (5) via a beam splitter (4), the zero-order beam and ↓∃ primary beams that fall focused on an optical recording medium (6) are that are reflected thereby, pass through the object glass (5), are further reflected by the reflecting surface of the beam splitter (4), and are permitted to be incident on a light detector (7) which produces a pair of outputs corresponding to ↓∃ primary beams, in order to obtain a tracking error signal of the zero-order beam which corresponds to the tracking condition on the optical recording medium (6) based upon the difference between the above-mentioned pair of outputs. In this apparatus, provision is made of a light attenuating means in an optical path between the semiconductor laster element (1) and the optical recording medium (6), in order to attenuate the laser beam reflected by the beam emitting end face (1A) of the semiconductor laser element (1), the reflected beam being produced by the beam which returns from the optical recording medium (6). This makes it possible to reduce disturbance to the tracking error signals caused by the change in the tangential skew angle of the optical recording medium (6).

Description

Specification

Title of the invention Optical head tracking error detection device

Technical field

The present invention relates to an optical head tracking error detecting device suitable for application to an optical recording device, a reproducing device, and a recording / reproducing device.

Background art

First, a conventional optical head tracking error detecting device will be described with reference to FIG. OH indicates the optical head as a whole. (1) is a semiconductor laser device (laser diode), which emits a divergent laser beam L having an elliptical cross section, emitted from the laser beam emitting end face (1A) side, through a collimator lens (unnecessary). (In some cases.) After being incident on (2) to form a parallel beam, it is incident on a diffraction grating (grating). 0th order beam L emitted from diffraction grating). And ± 1st order beams L ₊₁ , L -1 (+ 2nd order, — beams below 2nd order are ignored) 'is a non-polarizing beam splitter (half mirror) (for a polarizing beam splitter) (In this case, a 1/4 wavelength plate is provided between the objective lens (5).) After passing through ( ⁴ ), the light is made to enter the objective lens (5) and is focused. L. The ± 1st-order beams L _{+ 1} > L-i are made to enter the recording surface of an optical recording medium (including a magneto-optical recording medium) (6) at a predetermined interval (for example, 10 / m). Zero-order beam L reflected by the optical recording medium ( ⁶ ). After passing through the +/- primary beam L + 1 and L through the objective lens, the beam is made incident on the beam splitter (4), and a part of the beam is reflected by the reflection surface (4a>) and the photodetector ( The photodetector) is composed of three photodetectors into which the zero-order beam L. and the ± first-order beams L _{+ 1} and L-i are separately incident. By taking the difference between the pair of photodetection outputs from the pair of photodetectors where the ± primary beams are respectively incident, the 0th-order beam L 0 on the recording surface of the optical recording medium ( ⁶ ) is obtained. Toratsuki A tracking error signal corresponding to the tracking state is obtained. Also, a reproduced signal, a focused signal, and the like are obtained from the photodetector on which the zero-order beam is incident.

Next, an example of the semiconductor laser device (1) will be described with reference to FIG. The semiconductor laser device (1) is usually fixed on a heat sink (8) made of copper or the like which also serves as one electrode. The structure of the semiconductor laser device ω will be described from the upper layer to the lower layer in the figure as follows.

(La) is the electrode layer, (lb) is n-GaAs layer (base layer), (lc) is n- G _ai -yAlyAs' layer (H la head layer), (Id) is Gai -XAlxAs layer (active (Le) is the p-Gai-yAiyAs layer (cladding layer), and (If) is the p-Ga layer. Then, the above-described laser beam L is emitted from the active layer (Id). When the laser beam emitting end face (cleavage plane) (IA) of this semiconductor laser device (1) is set to the front, the semiconductor laser device (1) has a width of 100 to 300 m and a height (thickness) of 100 to 300 m. 80 ~ 丄 00 <um, depth 200-300 m. The height of the active layer (Id) from the top surface of the heat sink (S) is several _m .

At this point, when the tangential skew angle of the Qth-order beam L. with respect to the recording surface of the optical recording medium (6) changes, the trasso King error—the symbol is periodically changed accordingly. And it was not possible to detect an accurate tracking.

The present inventors have investigated the cause and found the following. Optical recording medium (6) 0 order beam reflected by the L 0 and ± 1-order beam L _+1, after L is passing through the objective lenses), reflected by the reflecting surface of the beam Splitter ⁽⁴⁾ (4a) In addition to passing through the beam splitter (4) and entering the diffraction grating (3), a special zero-order beam

Beam and ± first-order beams are generated and pass through the collimator lens ( ² ) to the semiconductor laser device (1). The beam amount of the beam going to this semiconductor laser element-(1) can be reduced by using an unpolarized beam splitter. Most are less when using a polarizing beam splitter. In this case, as shown in FIG. 7, according to the relative rotation angle position between the laser beam emitting end face (1A) of the semiconductor laser element (1) and the diffraction grating (3), the semiconductor laser element (1) The arrangement of the center beam L a toward the beam and the two side beams L b and L c located on both sides of the center beam La are such that the center beam La is located on the active layer (Id) on the laser beam emitting end face (U), respectively. The two-sided beams Lb and Lc pass through the position of the center beam La and are positioned vertically on a straight line perpendicular to the active layer (Id), and when the center beam La and the two-sided beams Lb and Lc are Both cases are located on the active layer (Id), and a straight line connecting the center beam La and the side beams Lb and Lc is located at an arbitrary angular position between the above two cases. Note that the center beam La and both-side beams Lb> Lc are such that the 0th-order beam _Lc and the ± 1st-order beams L _{+ 1} , L in FIG. 5 are re-diffracted by the diffraction grating ( ³ ) and mixed. Are superimposed.

By the way, when at least one of the two-sided beams Lb> Lc is incident on the surface of the heat sink ( ⁸ ), the surface is rough and the beam is diffusely reflected there. Although there is no problem, when at least one of the two-sided beams Lb and Lc is incident on the laser beam emitting end face () of the semiconductor laser device (1), this end face (U) has a good reflectance (for example, 10 %), The light is reflected from this surface (1A), passes through the optical path described above, and enters the photodetector), causing interference with the +1 order or -1 beam. Therefore, the zero-order beam L. According to the tangential skew angle with respect to the recording surface of the optical recording medium (6), the intensity of the eleventh or primary beam incident on the photodetector (7) changes, and the tracking error is caused. The signal changes periodically according to its skew angle.

FIG. 8 shows a case where one of the two side beams Lb and Lc enters the laser beam emitting end face (U) of the semiconductor laser device (1) and the other Lc enters the heat sink). 0th order beam L. Optical recording media (6) 5 shows the periodicity of the level change of the tracking error signal Se with respect to the tangential skew angle of the recording surface. In practice, as IαI increases, the level of the tracking error signal S e attenuates.简, both side beams Lb, Lc Both laser beams. Outgoing end face (When incident on 10, the amplitude of the waveform corresponding to Fig. 8 is twice that of Fig. 8, and the phase is the same as Fig. 8. Is different.

Next, when one of the two side beams Lb and Lc is incident on the laser beam emitting surface (U) of the semiconductor laser device (1), and on the other hand, c is incident on the heat sink (8). The interference will be described with reference to FIG. 9 (illustration of the lens system is omitted). In Fig. 9, (1A) shown by the solid line is the laser beam emission end face, but the general case where it is inclined with respect to the emission surface (U) at the regular position shown by the broken line. Is shown. Also, (6) indicated by a solid line indicates an optical recording medium, which is inclined with respect to the optical recording medium ( ⁶ ) at a regular position indicated by a broken line. 0th order beam L. Is perpendicular to the laser beam emission surface (1 A) at the regular position and the recording surface of the optical recording medium (6) at the regular position. 0 is the angle of the first-order beam L with respect to the zero-order beam L o. Is the optical path length between the laser beam output surface (1A) and the diffraction grating), and & 2 is the optical path length between the plane-folded grating) and the recording surface of the optical recording medium (6). ", Delta & 2 are each optical path县£ i, is an optical path difference between the zero-order beam L. and + 1-order beam L ₊₁ against the & 2. Δ ί ₃厶₄ are each an optical recording medium (6 ) Is the optical path difference due to the skew, and the optical path difference due to the skew at the laser beam emitting end face (1A).

Also, g is the 0th-order beam L in the diffraction grating. And + the phase difference between the primary beams L _{+ i} . i. , Ii are the transmittances of the 0th-order beam and the + 1st-order beam in the diffraction grating (3), t is the transmittance of the half mirror (4), and r and f are the transmittances of the optical recording medium (6). The reflectivity on the recording surface and on the laser beam emitting end surface (U). Thus, the complex amplitude of light at the point A on the recording surface of the optical recording medium (6) on which the + 1st-order beam L _{+ 1} is incident is divided into the following four cases.

(1) ai + primary beam L ₊₁ is directly incident on point A.

(2) a 20th order beam L. Is reflected by the optical recording medium (6) and re-enters the diffraction grating), the 0th-order beam obtained is reflected by the laser beam exit end face (1A) and re-enters the grating (3) This is the case where the + first-order beam obtained at this point enters point A.

(3) a 0th order beam L. Is reflected by the optical recording medium (6) and re-enters the diffraction grating), the + primary beam is reflected by the laser beam exit surface (U), and is again reflected by the grating (3). This is the case where the 0th-order bead obtained by incidence enters point A.

(4) The a + 1 primary beam L _{+ 1} is reflected by the optical recording medium, and the 0th-order beam obtained by re-entering the diffraction grating ( ³ ) is reflected by the laser beam exit surface (U) In this case, the zero-order beam obtained by re-entering the folded grating (3) enters point A.

Then shows a a 1 ~ a ₄ in the formula.

al = i 1 texp {j (& i + g + ί 2 + m J2 ₂

+ 1)} (1) a 2 iiit ³ rf · exp C j {3 (H i + i ₂ ) + g

+ A & 2 + Δ 3}] (2)

―One ί 2

^{1 0 it 3 rf - exp (} j {3 (& i + 8. 2) + g

+ 2 & ί + A & 2 + m £ 3 + 2 Δ £ 4}] (3) a 4 = i I iit ³ rf-exp [j {3 (& i + & ₂ ) + g

+ 3 (Δ £ 2 + Δ jg 3) + 2 m 1 + 2 Δ jg 4})

(Four) For simplicity of calculation, if the coherence length of the laser beam is 2 (ϋ1 + & 2) or less, the light intensity IA at point A is expressed as

I A = a + a 2 + a + a 4

= i [l + it ⁴ r ² f ² {3 + 2 cos 2 (Δ £.! + A £ 4) + 2 cos 2 (Δ 5 i + Δ ί 4 + Δ £ a + m) + 2 cos 2 (m ^ 2 + m 3)}] · · · (5) When both beams L b and L c are incident on the laser beam exit end face (1A), the + primary beam L "is optically recorded. incident on a point a on the recording surface of the medium ^(6), - primary beam if L is incident on the zero-order beam L ₀ symmetric point with respect to B, the intensity I _a of the light from the point a) formula As described above, the light intensity IB of the point B is expressed by the following equation.

IB = i I t ² ί ϊ + i ⁴ r ² f ² (3 + 2cos 2 (A & i

-Δ jg 4) + 2 cos 2 (m i m 4 + A £ 2 m 3) + 2 cos 2 (m £ 2-Δ £ ₃ )}] · · · · (6) It is an object of the present invention to propose a tracking error 'detection device capable of obtaining a tracking error signal in which disturbance due to a change in a tangential skew angle with respect to an optical recording medium is reduced.

Disclosure of the invention

The present invention relates to a semiconductor laser device, a diffraction grating to which a laser beam (having a wavelength of より) from the semiconductor laser device is incident, and a 0-order beam and a soil primary beam emitted from the diffraction grating. The beam splitter to be fixed, the zero-order beam and the soil primary beam emitted from the beam splitter are focused and focused by the objective lens to be incident on the optical recording medium, and reflected by the optical recording medium. The 0th-order beam and the 1st-order beam pass through the objective lens and are reflected by the reflecting surface of the beam splitter. A pair of photodetection outputs corresponding to ± primary beams from the photodetector, and based on the difference between the pair of photodetection outputs, the 0th-order beam on the optical recording medium. In a tracking error detection device of an optical head that obtains a tracking error signal according to a tracking state, light is attenuated in an optical path between a semiconductor laser element and an optical recording medium. Means to attenuate the reflected beam of the return beam from the optical recording medium due to the laser beam emitting end face of the semiconductor laser element, and to disturb the tracking error signal due to the fluctuation of the tangential skew angle of the optical recording medium. Is to be reduced.

BRIEF DESCRIPTION OF THE FIGURES

1 to 4 are cross-sectional views showing the optical attenuation means of each embodiment of the present invention. FIG. 5 is a schematic arrangement diagram showing a conventional optical head tracking error detecting device, and FIG. FIGS. 7 and 8 are front views showing an example of a semiconductor laser device in a conventional optical head tracking error detecting device, FIG. 8 is a waveform diagram, and FIG. FIG. BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of the present invention will be described below. The overall configuration example of the optical head tracking error detection device and the configuration example of the semiconductor laser device are described in FIGS. 5 and 6, respectively. Figures and explanations based on them are referred to, and duplicate explanations are omitted.

In the present invention, the optical path between the semiconductor laser device (1) and the optical recording medium (6) is provided with light attenuating means.

In the first embodiment, as shown in FIG. 1, the beam splitter ( ⁴ ) shown in FIG. 5 is used as an optical attenuator, and its transmittance is relatively small (for example, 25%). Are relatively selected as dogs (for example, 65%). In this case, the loss is 10%.

As is well known, a beam splitter (half mirror) is a triangular prism. Prism (4 t), (4 2) dielectric multilayer film between the (4 ₃₎ which was deposited form, its thickness, by controlling the number of layers or the like, controlling the transmittance及beauty reflectance can do.

In the second embodiment, as shown in FIG. 2, the diffraction grating (3) shown in FIG. 5 is used as light attenuation means! Therefore, the light absorption layer (3b) is formed on the surface opposite to the surface on which the groove (3a) is formed. A light reflecting layer may be used instead of the light absorbing layer (3b).

In the third embodiment, as shown in FIG. 3, the transmittance is reduced by using a neutral density (ND) filter (a light reflection filter is also possible) as the diffraction grating (3) itself. This is a case where it is used as a light attenuation means.

In the embodiment shown in FIG. 4, as shown in FIG. 4, an optical attenuator is used as a window (10) provided in a metal package (9) of the semiconductor laser device (1) shown in FIG. This is the case when the means is used.

In addition, a separate ND filter (a light reflection filter is also possible) may be provided in the optical path between the semiconductor laser element (1) and the optical recording medium (6) to serve as an optical attenuation means. If the ND filter is provided in the optical path between the semiconductor laser element (1) and the beam splitter (4), the optical path between the beam splitter ( ⁴ ) and the optical recording medium (6) is better. The intensity of the beam incident on the photodetector) can be made to be a dog as compared with that provided inside, and the output power of the semiconductor laser element (1) does not need to be increased accordingly.

By providing the light attenuating means as described above, it is possible to reduce the transmittance in the above formulas ( ⁶ ) and ( ⁶ ), whereby the light intensities I _A , I s Can be reduced. Since this reduces the amount of light incident on the photodetector, it is necessary to increase the output power of the semiconductor laser element (1).

Therefore, according to the optical head tracking error detecting device of the present invention, the semiconductor laser element of the return beam from the optical recording medium is provided. It is possible to attenuate the reflected beam from the laser beam emitting end face of the optical recording medium, and reduce disturbance to the tracking error signal due to the fluctuation of the tangential skew angle of the optical recording medium. .

Claims

The scope of the claims

A semiconductor laser device, a diffraction grating into which a laser beam from the semiconductor laser device is incident, a beam splitter through which a zero-order beam and a ± first-order beam emitted from the diffraction grating are passed, and the beam splitter An objective lens in which the zero-order beam and soil primary beam emitted from the foot are focused and made incident on the optical recording medium, and the zero-order beam and soil primary beam reflected by the optical recording medium A light detector that passes through the objective lens, is reflected by the reflection surface of the beam splitter, and then enters the light detector. The light detector detects a pair of light beams corresponding to the soil primary beam. A detection output is obtained, and a tracking error signal corresponding to a tracking state of the zero-order beam on the optical recording medium is obtained based on a difference between the pair of light detection outputs. In the tracking error detecting device for an optical head described above, light attenuating means is arranged in an optical path between the semiconductor laser element and the optical recording medium, and a return beam from the optical recording medium is provided. The beam reflected by the laser beam emitting end face of the semiconductor laser element is attenuated to reduce disturbances to the tracking error signal due to a change in the tangential skew angle of the optical recording medium. An optical head tracking error detection device.