JPH0440290Y2 - - Google Patents

Description

[Detailed explanation of the idea] (b) Industrial application fields The present invention relates to a semiconductor laser device.

(b) Prior Art Currently, semiconductor laser chips are used as light sources in optical pickup devices that are used for optical fibers (disks on which information is optically readably recorded).

As an optical pickup device, one having the structure shown in FIG. 3 is known (for example, see Japanese Utility Model Application No. 75342/1983). In the figure, a laser beam emitted from a semiconductor laser 1 is diffracted by a diffraction grating 2, and becomes three beams P ₀ (main beam), P ₁ , and P ₂ (auxiliary beams), and a beam splitter ( The transmitted light and the reflected light have the same ratio or different ratios) 3 and enter the disk D through the objective lens 4. The beam reflected by disk D becomes reflected light P′ ₀ , P′ ₁ , P′ ₂ and returns along the original optical path in the opposite direction (auxiliary beams P ₁ and P ₂ are not perpendicular to the disk but slightly The light enters at an angle, but since this angle is extremely small, it can be considered that the reflected lights P' ₁ and P' ₂ essentially return along their original optical paths.) The beam passes through the objective lens 4 and reaches the beam splitter 3. The reflected beams (P' ₀ , P' ₁ , P' ₂ ) reflected by the beam splitter 3 reach the photo sensor 7 via the concave lens 5 and the cylindrical lens 6 . Photo sensor 7 is the reflected main beam
It is composed of a sensor 7c that receives _P'0 , a sensor 7a that receives reflected auxiliary beam _P'1 , and a sensor 7b that receives reflected auxiliary beam _P'2 . It is already known that an information signal and a focus error signal can be obtained from the sensor 7c, and that a radial error signal can be obtained as the difference in output between the sensors 7a and 7b.

Now, FIG. 4 shows changes in the radial error signal RE in a conventional pickup device.
The DC component of the radial error signal RE fluctuates in response to one rotation of the disk, and this fluctuation increases as the surface runout of the disk increases. When performing special disc playback such as searching for songs recorded on a disc, the DC component of the radial error signal RE, DC
The permissible range of variation is as follows, where A is the variation amplitude of the DC component and REp-p is the amplitude of the radial error signal.
It is necessary to satisfy A/REp-p≦0.2. Conventional pickup devices do not necessarily satisfy the above conditions.

The reason for the above-mentioned fluctuation in the DC component of the radial error signal is that the perpendicularity of the optical axis of the beam output from the pickup device to the disk changes over one rotation period depending on the surface runout of the disk, especially in the tangential direction of the disk. It is thought that this is because the degree of light interference that occurs between the beam necessary for signal reproduction and the unnecessary beam (stray light) changes in accordance with the change in verticality. This point will be explained in more detail below with reference to FIG.

In FIG. 5, reference numeral 8 indicates a semiconductor laser chip, and this chip 8 is fixed to a chip mount (submount) 9 by brazing or conductive adhesive. The laser beam P ₀ emitted from the radiation point 0 of the chip 8 is transformed into a main beam P ₀ that travels straight (does not undergo diffraction) due to the diffraction grating 2.
The beam is split into auxiliary beams P ₁ and P ₂ (±first-order diffracted light) generated by diffraction and directed toward the disk. A portion of the beams (P ₀ ', P ₁ ', P ₂ ') reflected by the disk returns to the diffraction grating 2 (the portion transmitted through the beam splitter 3 shown in FIG. 3). These beams pass through the diffraction grating 2 and head towards the laser chip 8 side. Among these beams, the beam [P ₀ ′ (+1), P ₂ ′ (0)] that follows the optical path of
It is reflected at the point and returns along the original optical path X. [The optical path You can think of it as returning along the optical path of
This reflected return light (stray light) causes interference with the beam P' ₂ , and the beam P ₂ ' subjected to such interference is directed toward the photo sensor 7b, causing fluctuations in the DC component of the output signal Sb of the photo sensor 7b ( (See Figure 6).
In Fig. θ, the horizontal axis θ indicates the angle that the optical axis of the objective lens makes in the tangential direction with respect to the perpendicular line to the disk surface, and the output signal
One wavelength of Sb is approximately 1.3 degrees.

Here, considering the light intensity of the beam after diffraction, the light intensity ratio of the 0th-order diffracted light (light that does not undergo diffraction) and the ±1st-order diffracted light is 1:1/3 to 1/8, so 2
Light that has been diffracted more than once has a small light intensity level, and there is no need to consider interference. In FIG. 5, the beam P ₀ '(+1) is the +1st-order diffracted light of the reflected light P ₀ ' from the disk, and since it has undergone only one diffraction, the beam P 0 '(+1) has no effect on the interference.
P ₂ ′(0) is the 0th-order light of the reflected light P _{2 ′} of the first-order diffracted light P ₂ generated when the laser light P 0 passes through the diffraction grating ₂ from bottom to top in FIG. [In other words, when passing through the diffraction grating 2 from top to bottom, it is light that travels straight without undergoing diffraction], so similarly 1
It is only subjected to the second diffraction, which affects the interference.

Note that the beams [P ₀ '(-1) (first order light of beam P ₀ ') and P ₁ '(0) (0th order light of beam P ₁ ')] heading toward optical path Y undergo one diffraction. However, since the received beam does not enter the laser chip 8 as shown in FIG. 5, no interference occurs with the beam P ₁ '. Therefore, as shown in FIG. 6, fluctuations in the DC component of the output signal Sa of the photo sensor 7a receiving the beam P ₁ ' are reduced.

According to the above explanation, beam P ₂ ′(0) of optical path
and P ₀ '(+1) is reflected by the radiation surface N of the laser chip 8, and the reflected light is a radial error signal [the difference between the output signals Sa and Sb of the photo sensors 7a and 7b]
It can be seen that this is the cause of fluctuations in the DC component of

Therefore, in order to prevent reflection on the radiation surface N of the laser chip 8, a structure was proposed in which a film 22 made of a low light reflection material is provided on the radiation surface N as shown in FIG.
It has been proposed in No. 60-157604, etc.

In Fig. 7, 11 is a stem made of Cu, and 12 is a stem made of Cu.
The heat sink is made of Si single crystal, and the heat sink is thermally and electrically fixed to one main surface of the stem. Reference numeral 13 denotes a semiconductor laser chip, and this chip has a first semiconductor laser chip made of p-type Ga1-XA1XAS (0<X<1) on one main surface of a p-type GaAS substrate 14.
Grad layer 15, non-doped Ga1-YA1YAS (0
≦Y<X) active layer 16, n-type Ga1-
Second grading layer 17 made of XAlxAS and n-type
The cap layer 18 made of GaAS is sequentially laminated, and the end face that becomes the radiation surface N is formed by cleavage, and a protective film 19 made of SiO ₂ or the like is formed on the cleavage surface. The thicknesses of the substrate and each layer 15 to 18 are 90 μm, 2 μm, 0.1 μm, and 0.1 μm, respectively.
They are 1.5μm and 2μm. Reference numeral 22 denotes a film formed on the radiation surface N excluding the radiation point O, and the film is made of a low light reflection material such as black silicone resin. 20,
21 are the other main surface of the substrate 14 and the cap layer 18, respectively.
The automic first and second electrodes 23 formed on the surfaces connect the first electrodes 20 to the heat sink 1.
2 is a conductive adhesive for adhering to the surface.

According to such a configuration, the return light shown in FIG.
When P ₂ ′ (0) and P ₀ ′ (+1) are incident on the radiation surface N of the laser chip 8, most of them are absorbed by the anti-reflection film 22, and even if some are reflected, they are diffusely reflected, and the amount that returns along the optical path X is becomes extremely small. Therefore, the returned light P ₀ ′(0) is reflected at the radiation surface N, diffracted by the diffraction grating 2, and then the light [P _{0 ′} (0)
The first-order diffracted light of the light reflected by the radiation surface] only interferes with P ₂ ', and the fluctuation in the output signal Sb of the photo sensor 7b is significantly reduced as shown in FIG.

(c) Problems to be solved by the invention However, in such a configuration, the production yield is poor because the film 22 must be attached manually while looking at a microscope, etc. Also, since the film 22 is made of resin, There were problems in that it was prone to peeling and evaporation at high temperatures, and lacked reliability.

(d) Means for solving the problems The present invention was devised in view of the above points, and its features include a semiconductor laser chip having a pair of resonator surfaces, and a semiconductor laser chip having a pair of resonator surfaces; A metal block whose surface is blackened with metal and a groove is formed on a surface perpendicular to the blackened surface,
The semiconductor laser chip is arranged in the groove of the metal block so that its emission point is located above a plane perpendicular to the blackened surface of the block.

(E) Effect This configuration suppresses fluctuations in the DC component of the radial error signal.

(F) Embodiment FIG. 1 shows an embodiment of the present invention, where 31 is a block made of copper, for example, and 32 is one main surface 31 of the block.
This is a black layer formed on the block a, and the layer can be formed by chrome plating or oxidation of the block surface. 33 is a groove, and the groove is located on the main surface 31.
It is formed on a surface 31b perpendicular to a. Incidentally, such groove portion 33 can be formed with high accuracy by, for example, laser processing. 34 is a laser chip, and the laser chip is fixed to the bottom surface of the groove 33 with a conductive adhesive 35 or the like. Incidentally, such a laser chip 34 is the seventh laser chip.
Since it is the same as that explained in the figures, the same parts are given the same numbers and the explanation will be omitted.

In such a configuration, the height h of the radiation point O of the laser chip 34 with respect to the surface 31b is 50 μm, and the height h of the radiation point O of the laser chip 34 from the surface of the black layer 32 is
When the groove portion 33 is formed so that the distance from the groove portion 33 to the groove portion 33 is 50 μm to 150 μm, since the vertical light spread angle θ of the output light of a normal semiconductor laser is 20° to 40°, such output light will be directed to the groove portion 33. It is not blocked by the side wall 33a.

Furthermore, since most of the returned lights P ₂ '(0) and P ₀ '(+1) are absorbed by the black layer 32 of the block 31, the amount of them returning along the optical path X becomes extremely small. Therefore, as with the conventional configuration, fluctuations in the output signal of the photo sensor 7 are significantly reduced.

Furthermore, in such a configuration, a black layer 3 that absorbs returning light is provided.
Since 2 is made of chromium or copper oxide, it does not peel off or evaporate even at high temperatures.

Figure 2 shows a laser chip with an oscillation wavelength of 7900 Å.
Life test results of this example device using a VSIS type laser (A in the figure) and life test results of a conventional device whose radiation surface was coated with black silicone resin (B in the figure)
shows. Furthermore, this life test was conducted in an atmosphere of 60℃.
This study investigated the change in drive current over time during continuous oscillation of 4mW.

As is clear from FIG. 2, in the conventional device, the drive current increases rapidly after 7,000 hours, whereas in the device of this embodiment, no change is observed in the drive current even after 10,000 hours.

(g) Effects of the invention As is clear from the above explanation, the present invention is based on a method in which a semiconductor laser chip is placed in a groove of a metal block so that its emission point is located above a surface perpendicular to the blackened surface of the block. Since most of the returned light is absorbed by the blackened surface, fluctuations in the output signal of the photo sensor are significantly reduced. In addition, since the blackened surface for absorbing the returned light is formed on the surface of the block, the formation process is simpler than before, and since this blackened surface is blackened with metal, , its lifespan is long;
A highly reliable semiconductor laser device can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is a characteristic diagram showing life characteristics, Fig. 3 is a diagram showing a conventional pickup device, and Fig. 4 is a diagram showing a radial error signal of the conventional device. , FIG. 5 is a diagram explaining the principle of interference, FIG. 6 is a diagram showing changes in the output signal of the photo sensor of the conventional device, FIG. 7 is a sectional view showing the improved conventional device, and FIG. 8 FIG. 2 is a diagram showing changes in the output of a photo sensor. 31...Block, 32...Black layer, 33...
Groove, 34... semiconductor laser chip.

Claims (1)

[Claims for Utility Model Registration] A semiconductor laser chip having a pair of resonator surfaces; a metal block having one main surface blackened with metal and a groove formed in a surface perpendicular to the blackened surface; A semiconductor laser device, characterized in that the semiconductor laser chip is disposed in a groove of the metal block such that its radiation point is located above a surface perpendicular to the blackened surface of the block.