JPH0519971Y2 - - Google Patents

Description

[Detailed Description of the Invention] The semiconductor laser device of the present invention will be explained in the following order.

A. Field of industrial application B. Outline of the invention C. Background art [Figures 5 and 6] D. Problems of the background technology [Figures 7 to 9] E. Means for solving the problems F. Effect G. Implementation Examples [Figs. 1 to 4] a First example [Fig. 1] b Second example [Fig. 2] c Third example [Fig. 3] d Fourth example [Fig. Figure 4] H Effects of the invention (A Field of industrial application) Regarding the semiconductor laser device of the present invention, especially the three-beam tracking type optical recording device, optical reproducing device, or optical recording/reproducing device constituting the optical recording/reproducing device. A novel semiconductor laser which, when used as a light source in a head, makes it possible to obtain a tracking error signal that is independent of changes in the tangential skew angle of the zero-order beam with respect to an optical recording medium. This is what we are trying to provide.

(B Overview of the invention) The present invention is a semiconductor laser chip that is made by bonding a semiconductor laser chip to a heat sink and is used as a light source in a three-beam tracking optical recording device, optical reproducing device, or optical head of an optical recording and reproducing device. In a laser device, in order to obtain a tracking error signal that is independent of changes in the tangential skew angle of the zero-order beam with respect to the optical recording medium, a heat sink and a laser beam emitting side of the semiconductor laser chip are provided. By making the feedback beam incidence part of the end face of the laser beam a surface that cannot reflect the feedback beam incident therein in the laser beam emission direction, interference by the feedback beam can be prevented, and as a result, interference of the zero-order beam with respect to the recording medium can be prevented. This is intended to prevent the tracking error signal from depending on the tangential skew angle.

(C. Background Art) [FIGS. 5 and 6] First, referring to FIG. 5, a conventional optical head using a semiconductor laser as a light source and a tracking error detection method will be described.

Reference numeral 1 denotes a semiconductor laser (laser diode), and a laser beam with an elliptical cross section emitted from the laser beam emitting end face 1A side of this laser beam is made incident on a collimator lens (sometimes not needed) 2 to become a parallel beam, and is diffracted. The light is made incident on a grating 3. 0 emitted from the diffraction grating 3
The next beam L ₀ and the ±1st order beams L ₊₁ , L _-1 (beams of +2nd order or higher and -2nd order or lower are ignored) pass through a non-polarizing beam splitter (half-mirror) 4, and then pass through an objective lens 5. The focused zero-order beam L ₀ and ±first-order beam L ₊₁ ,
L _-1 is an optical recording medium (including magneto-optical recording medium)
The light is incident on the recording surface of No. 6 at a predetermined interval (for example, 10 μm). In addition, the beam splitter 4
When using a polarized beam splitter instead of non-polarized light, it is necessary to arrange a quarter-wave plate between the polarized beam splitter and the diffraction grating 3.

The 0th-order beam L ₀ and the ±1st-order beams L ₊₁ and L _-1 reflected by the optical recording medium 6 pass through the objective lens 5 and are made to enter the beam splitter 4, and a part of them is incident on the entrance surface 4a. The light is reflected by the light beam and is incident on the photodetector 7. This photodetector 7 is a zero-order beam
It is composed of three photodetectors into which L ₀ and ±1st-order beams L ₊₁ and L _-1 are respectively incident. By detecting the difference between the pair of photodetection outputs from the pair of photodetectors into which the ±1st order beams are incident, the tracking state of the 0th order beam _L0 on the recording surface of the optical recording medium 6 is determined. A corresponding tracking error signal is obtained. In addition, from the photodetector section into which the zero-order beam is incident, a reproduced signal,
Obtain focus error signal etc.

Next, an example 1 of the semiconductor laser will be explained with reference to FIG. 6. This semiconductor laser 1 is chip-shaped and 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 1 will be explained from top layer to bottom layer. 1a is an electrode layer, 1b is an n-type GaAs layer (substrate layer), and 1c is an n-type GaAs layer (substrate layer).
1d is a GaAlAs layer (active layer), 1e is a P-type GaAs layer (cladding layer),
1f is a P-type GaAs layer. And active layer 1
d, the above-mentioned laser beam L is emitted especially from the central part. If the laser beam emitting end face (cleavage plane) 1A of this semiconductor laser 1 is the front, its width is
The thickness is 100 to 300 μm, the height (thickness) is 80 to 100 μm, and the depth is 200 to 300 μm. The height of the active layer 1d from the top surface of the heat sink 8 is several μm.

(D Problems in Background Art) [Figures 7 to 9] By the way, the optical recording medium 6 of the zero-order beam L ₀
When the tangential skew angle with respect to the recording surface changes, the tracking error signal also changes periodically, making it impossible to accurately detect the tracking error.

When we investigated the cause, we found the following. The 0th-order beam L ₀ and the ±1st-order beams L ₊₁ and L _-1 reflected by the optical recording medium 6 pass through the objective lens 5 and then pass through the reflecting surface 4 of the beam splitter 4.
The beam is not only reflected at a, but also passes through the beam splitter 4 and enters the diffraction grating 3. Then, zero-order beams and ±first-order beams are generated corresponding to each incident beam, which pass through the collimator lens 2 and head toward the semiconductor laser 1 . The amount of beam directed toward the semiconductor laser 1 is large when a non-polarizing beam splitter is used, and small when a polarizing beam splitter is used. In this case, the incident position of the central beam 1a on the semiconductor laser 1 and the incident positions of the both side beams Lb and Lc located on both sides thereof are determined according to the relative rotational angle position of the laser beam emission end face 1A of the semiconductor laser 1 with respect to the diffraction grating 3. The positional relationship with
There are three types of positional relationships. The first one is such that the incident position of the central beam La is located on the active layer 1d on the laser beam output end surface 1a, and the beams Lb and
This is a case where Lc passes through the position of the central beam La and is incident on a portion located above and below the central beam 1a on a straight line orthogonal to the active layer 1d. Also, the second one has a central beam La and both side beams Lb,
Lc are both located on the active layer 1d, and the third one is a central beam La and both side beams Lb, Lc
The straight line connecting the incident positions of is a certain angle between the above two cases. And these central beams La
And both side beams Lb, Lc are ±1 with the primary beam L ₀
The secondary beams L ₊₁ and L _-1 are re-diffracted by the diffraction grating 3 and are mixed and superimposed.

By the way, in the case of the first positional relationship, both beams 1b and 1c are incident on the surface of the heat sink 8, and one, that is, the lower beam 1c, and the other, that is,
The upper beam Ib enters the beam emitting end face 1A of the semiconductor laser 1. Since the reflectance of this end surface 1A is larger than the reflectance of the surface of the heat sink 8, the explanation will focus first on the beam reflected at the heat sink emitting end surface 1A. The return beam reflected by the end face 1A passes through the above-mentioned optical path and enters the photodetector 7, where it interferes with the +1st or -1st order beam. Therefore, the intensity of the +1st or -1st order beam incident on the photodetector 7 changes depending on the tangential skew angle of the 0th order beam L ₀ with respect to the recording surface of the optical recording medium 6, resulting in a tracking error. The signal changes periodically depending on its skew angle. FIG. 8 shows the tangential deviation of the zero-order beam L0 with respect to the recording surface when one of the beams Lb and Lc on both sides is incident on the laser beam emission end face _1A of the semiconductor laser 1, and the other Lc is incident on the heat sink 8. FIG. 3 is a curve diagram showing an ideal relationship between the U angle α° and the level of the tracking error signal Se. As can be seen from this figure, the level of the tracking error signal Se changes at a cycle of every λ/2 with respect to the wavelength λ of the laser beam according to a change in the skew angle α°. Specifically, as |a| increases, the level of the tracking error signal Se decreases. Incidentally, when the beams Lb and Lc on both sides are incident on the laser beam output end face 1A, the amplitude of the waveform is twice that at the center _L0 , and the phase is also different from that shown in FIG.

Next, the interference when the beam Lb on one side is incident on the laser beam exit surface 1A and the beam Lc on the other side is incident on the heat sink 8 will be explained with reference to FIG. Note that the illustration of the lens system is omitted in this figure. In this figure, the output end face 1
In A, a normal state is shown by a broken line, and a general state tilted from the normal state is shown by a solid line. Further, the normal state of the optical recording medium 6 is shown by a broken line, and the general state tilted from the normal state is shown by a solid line.

The zero-order beam L ₀ is perpendicular to the laser beam emission end face 1A and (the recording surface of) the optical medium 6 in the normal state. In FIG. 9 or the following equations (1) to (6), θ is the angle of the +1st order beam L ₊₁ with respect to the 0th order beam _L0 , and _l1 is the phase length between the laser emission end face 1A and the diffraction grating 3. , l ₂ is the phase length between the diffraction grating 3 and the optical recording medium 6 (recording surface thereof), Δl ₁ and Δl ₂ are the zero-order beams for the phase lengths l ₁ and l ₂
is the phase difference between L ₀ and +1 beam L ₊₁ . Δl ₃ ,
Δl ₄ is the skew phase of the optical recording medium 6 and the laser beam output end face 1A, g is the phase difference between the 0th-order beam L ₀ and the +1st-order beam L ₊₁ in the diffraction grating 3, and i ₀ and i ₁ are the diffraction 0th order beam in grating 3, +1
The transmittance of the secondary beam, t is the transmittance of the half mirror 4, and r and f are the reflectances on the recording surface of the optical recording medium 6 and on the laser beam output end surface 1A.

Here, the complex amplitude of the incident light at point A on the recording surface of the optical recording medium 6 where the +1st-order beam L ₊₁ is incident is expressed in the following four cases (1) to (4) (a ₁ to a ₄ ) Think about it separately.

(1) a ₁ : The complex amplitude of the incident light when the +1st order beam L+ ₁ is directly incident on point A. (2) a ₂ : The 0th order beam _L0 is reflected by the optical recording medium 6 and passes through the diffraction grating again. 3, the zero-order beam obtained by entering the laser beam emitting end surface 1A
Complex amplitude of the incident light when the +1st-order beam obtained by reflecting at the diffraction grating 3 and entering the diffraction grating 3 again enters the point A (3) a ₃ :0th-order beam L ₀ is the optical recording medium 6 and enters the diffraction grating 3 again, the +1st order beam obtained is reflected at the laser beam output end face 1
Complex amplitude of the incident light when the 0th-order beam obtained by reflecting at point A and entering the diffraction grating 3 again enters point A (4) a ₄ :+1st-order beam L ₊₁ is the optical The 0th-order beam obtained by being reflected by the recording medium 6 and incident on the diffraction grating 3 again is reflected by the laser beam output end face 1A, and the 0th-order beam obtained by being incident on the diffraction grating 3 again. Complex amplitude of the incident light when the beam is incident on point A Next, a ₁ to _{a 4} are expressed as a ₁ = i ₁ t・esp {j (l ₁ + g + l ₂ + Δl ₂ + Δl ₃ )}
...(1) a ₂ = i ₀ ² i ₁ t ³ rf・esp [j{3 (l ₁ + l ₂ ) + g + Δl ₂ +
Δl ₃ }] ...(2) a ₃ = i ₀ ² i ₁ t ³ rf・exp[j{3(l ₁ +l ₂ )+g+2Δl ₁
+
Δl ₂ +Δl ₃ +2Δl ₄ }] …(3) a ₄ =i ₀ ² i ₁ t ³ rf・exp[j{3(l ₁ +l ₂ )+g+3(Δ
l ₂
+Δl ₃ ) +2Δl ₁ +2Δl ₄ }] ...(4) To simplify the calculation, if the coherence length of the laser beam is set to 2(l ₁ +l ₂ ) or less, the light intensity Ia at point A is given by the following formula. expressed.

Ia＝｜a ₁ ｜ ² +｜a ₂ +a ₃ +a ₄ ｜ ² =i ₁ ² t ² [1+i ₀ ⁴ t ⁴
r ² f ² {3+2cos2(Δl ₁ +Δl ₄ )+2cos2(Δl ₁ +Δl ₄
+Δl ₂ +Δl ₃ )+2cos2(Δl ₂ +Δl ₃ }]...(5) In addition, when both beams Lb and Lc are incident on the laser beam output end face 1A, the +1st order beam
When L ₊₁ is incident on point A on the recording surface of optical recording medium 6, and -1st order beam L _-1 is incident on point B which is symmetrical with respect to 0th order beam _L0 , the light at point A is The intensity Ia is as shown in equation (5) above, but the intensity Ib of the light at point B
is expressed by the following equation.

Ib＝i ₁ ² t ² [1 + i ₀ ⁴ t ⁴ r ² f ² {3 + 2 cos2 (Δl ₁ − Δl ₄
)＋
2cos2(Δl ₁ −Δl ₄ +Δl ₂ −Δl ₃ )+2cos2(Δl ₂ −
Δl ₃ )}] ...(6) In this way, at least one of the beams Lb and Lc on both sides enters the beam output end face 1A, and as a result, it is reflected at the end face 1A and enters the photodetector 7. Interference occurs with the +1st order or -1st order beam. Therefore, the intensity of the +1st or -1st order beam incident on the photodetector 7 changes depending on the change in the tangential skew angle of the 0th order beam with respect to the optical recording medium. In other words, the level of the tracking error signal depends not only on the tracking state;
It also changes due to changes in the tangential skew angle.

Therefore, attempts have been made to cut out the portion of the end surface of the semiconductor laser 1 into which the upper feedback beam Lb is incident, to prevent the upper feedback beam Lb from being returned to the original optical path of the optical head. However, the above-mentioned problems were still not completely solved.
This is because, although the reflectance of the heat sink 8 is lower than that of the end face 1a of the semiconductor laser 1, a portion of the lower feedback beam that returns onto the heat sink is reflected back to the original optical path of the optical head. This is because that.

Therefore, as a result of searching for ways to further prevent the feedback beam from being reflected in the laser beam emission direction, the present invention was born.

Therefore, the present invention has been devised to completely eliminate the interference caused by the return beam incident on the heat sink.

(E. Means for Solving Problems) In order to solve the above problems, the present invention incorporates a semiconductor laser chip on the bonding surface of the heat sink 8.
is bonded to the heat sink 8 and the end face of the laser beam output side of the semiconductor laser chip 1, and a feedback beam Lb whose incident part is focused by a diffraction grating is formed.
A surface 9 on which the feedback beams Lc are incident, and which cannot reflect the feedback beams in the laser beam emission direction, at least on the portions of the semiconductor laser chip 1 and the heat sink 8 on which the feedback beams Lb and Lc are incident;
10 and 12 are formed.

(F Effect) According to the present invention, the feedback beam incident on the heat sink and the semiconductor laser chip does not return to the original optical path of the optical head, so there is interference caused by the feedback beam incident on the heat sink and the semiconductor laser chip. This can completely prevent the tracking error signal from changing, and further reduce the dependence of the tracking error signal on changes in the tangential skew angle of the zero-order beam with respect to the recording medium.

Since the end face of the heat sink on the laser beam output side may be formed at right angles to the bonding surface of the semiconductor laser chip, the present invention uses a heat sink whose end face on the laser beam output side is at an acute angle with respect to the bonding surface. This makes it easier to assemble the heat sink to the semiconductor laser device than in the case where the heat sink is attached to the semiconductor laser device. In addition, it is only necessary to locally form a surface that prevents reflection in the laser beam emission direction only on the part of the end face on the laser beam emission side of the heat sink where the return beam enters, so it is possible to use a simple method such as stamping. Interference can be prevented.

(G Embodiment) [FIGS. 1 to 4] The semiconductor laser device of the present invention will be described below according to the embodiment shown in the accompanying drawings.

(a First Embodiment) [FIG. 1] FIG. 1 shows an example of the implementation of the semiconductor laser device of the present invention. A feedback beam incident portion above the laser beam emitting end face 1A of the semiconductor laser chip 1 is notched. 9 is the notch. or,
The return beam incidence section on the lower side of the heat sink 8 is formed into an inclined surface. 10 is its slope,
In this embodiment, it is inclined toward the back side from the bottom to the top.

According to such a semiconductor laser device, the upper and lower feedback beams returned to the semiconductor laser device side
Lb and Lc are incident on the notch 9 and the inclined surface 10. The upper beam b is diffusely reflected by the notch 9. This is because the notch 9 is formed by photo-etching the semiconductor substrate, and its surface is not a cleaved surface like the laser beam emitting end surface 1A, so it is not a mirror surface but a rough surface, and is therefore diffusely reflected. It is. However, since the surface of the notch 9 is naturally inclined due to sand etching, the direction of the diffusely reflected beam having the strongest luminous intensity distribution is in a direction different from the laser beam emission direction of the semiconductor laser device.

Therefore, the upper beam incident on the upper input section
Lb almost never returns to the original optical path of the optical head.

Further, the lower return beam Lc is reflected by the inclined surface 10 of the heat sink 8 in a direction completely different from the direction of incidence. Therefore, the lower beam Lc also does not return to the original optical path of the optical head.

Therefore, the upper beam Lb and the lower beam Lc pass through the original optical path of the optical head and become the +1st order beam and -1st order beam.
The problem of interference with the primary beam can be solved, and it is possible to prevent the tracking error signal from changing due to a change in the tangential skew angle of the zero-order beam with respect to the optical recording medium.

(b Second Embodiment) [FIG. 2] FIG. 2 shows another embodiment of the semiconductor laser device of the present invention. In this embodiment, the return beam incidence part has an obliquely upward inclined surface 10 and an obliquely downward inclined surface 10, and 11 is the ridge line thereof. According to such an embodiment, when the lower beam Lc is located where the ridgeline 11 crosses the beam Lc, a part of the beam is reflected diagonally upward and a part of the beam is reflected diagonally downward. be done. Note that this embodiment is the same as the first embodiment in that a notch 9 is provided in the semiconductor laser chip 1 to prevent the upper feedback beam Lb from being reflected in the laser beam emission direction.

(c Third Embodiment) [FIG. 3] FIG. 3 shows still another embodiment of the semiconductor laser device of the present invention. In this embodiment, two inclined surfaces 10 are provided at the return beam incidence part of the heat sink 8.
10 is formed to face obliquely to the side, and the lower return beam Lc is reflected not to the front side but to the diagonally side, diagonally left side.

In this case, the two slopes 1
A vertical ridgeline 11 formed between 0 and 10
can be used as an index for positioning (particularly horizontal positioning) during bonding of the semiconductor laser chip 2.

Incidentally, the inclined surface 10 in each of the embodiments shown in FIGS. 1 to 3 can be easily formed by stamping or the like.

This embodiment is the same as the first and second embodiments in that a notch 9 is provided in the semiconductor laser chip 1 to prevent the upper feedback beam Lb from being reflected in the laser beam emission direction.

(d Fourth Embodiment) [FIG. 4] FIG. 4 shows still another embodiment of the semiconductor laser device of the present invention. This example is the lower beam
The Lc entrance part 1 is made to have a very rough surface 12 so that the reflectance of the surface is extremely small.
Even in this case, the amount of the lower beam Lc returning to the original optical path of the optical head is very small, and no interference can occur.

Further, the same effect can be obtained by making the incident part of the lower beam Lc a surface having light absorbing properties.

Note that this embodiment is the same as the first, second and third embodiments in that a notch 9 is provided in the semiconductor laser chip 1 to prevent the upper feedback beam Lb from being reflected in the laser beam emission direction.

As described above, the semiconductor laser device of the present invention can be implemented in various ways. The semiconductor laser device of the present invention can also be applied to a type of semiconductor laser device in which a semiconductor laser chip is bonded to a part of a semiconductor pellet on which a photodiode for monitoring laser light is formed, and the semiconductor pellet is bonded to a heat sink. .

(H. Effect of the invention) As described above, according to the semiconductor laser device of the invention, the feedback beam incident on the heat sink and the feedback beam incidence part of the semiconductor laser chip does not return to the original optical path of the optical head. It is possible to completely prevent interference caused by the feedback beam incident on the heat sink and semiconductor laser chip.
Furthermore, the dependence of the tracking error signal on changes in the tangential skew angle of the zero-order beam with respect to the recording medium can be further reduced.

Since the end face of the heat sink on the laser beam output side may be formed at right angles to the bonding surface of the semiconductor laser chip, the present invention uses a heat sink whose end face on the laser beam output side is at an acute angle with respect to the bonding surface. It is easier to assemble the heat sink to the semiconductor laser device than in the case where the heat sink is attached to the semiconductor laser device. In addition, it is only necessary to locally form a surface that prevents reflection in the laser beam emission direction only on the part of the end face on the laser beam emission side of the heat sink where the return beam enters, so it is possible to use a simple method such as stamping. Interference can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the first embodiment of the semiconductor laser device of the present invention, FIG. 2 is a perspective view showing the second embodiment, and FIGS. 3A and 3B show the third embodiment. FIG. 4 is a perspective view showing a fourth embodiment of the semiconductor laser device of the present invention, and FIG.
Figures 9 to 9 are for explaining the background art and its problems. Figure 5 is a layout diagram showing the outline of an optical head, and Figures 6 and 7 are semiconductors used in the optical head. Front view showing an example of a laser, No. 8
The figure is a curve diagram showing changes in the level of the tracking error signal with respect to changes in the tangential skew angle, and FIG. 9 is a diagram used to explain interference. Explanation of symbols, Lb, Lc... Return beam, 1...
Semiconductor laser chip, 8...Heat sink, 9,
10, 11, 12... Surfaces that cannot reflect the return beams Lb, Lc in the laser beam emission direction.

Claims (1)

[Claim for Utility Model Registration] The semiconductor laser chip 1 is bonded to the bonding surface of the heat sink 8, and the return beams Lb, Lc whose incident portions are focused by a diffraction grating are formed on the laser beam output side end faces of the heat sink 8 and the semiconductor laser chip 1. At least on the semiconductor laser chip 1 and the heat sink 8, surfaces 9, 10, and 12 that cannot reflect the feedback beams in the laser beam emission direction are formed on the portions of the semiconductor laser chip 1 and the heat sink 8 where the feedback beams Lb and Lc are incident. A semiconductor laser device characterized by: