JP3344084B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device used for an optical information recording device for recording, reproducing or erasing information by irradiating light.

[0002]

2. Description of the Related Art An optical head is used for a video tape system using a conventional magnetic head, a converged light beam is irradiated on a recording medium on which information is recorded, and light reflected from the recording medium is detected and recorded. Recently, an optical disk system for reproducing information content of a medium as video or sound has become remarkably widespread. As a recording medium, a compact disk is well known in the audio field, and a laser disk is well known in the video field, and an optical pickup device using an optical semiconductor device as an optical head is used to read information from the optical disk. The optical recording / reproducing technology using these optical semiconductors is being developed as a technology that plays a key role in a so-called multimedia, which is a center of the advanced information society, as it can be applied to data storage in a large computer network or a personal computer.

Hereinafter, a conventional optical pickup device will be described. FIG. 3 is a configuration diagram of a conventional optical pickup device.

In FIG. 3, reference numeral 1 denotes a semiconductor laser device;
Is a light receiving element, 3 is a diffraction grating, 4 is a hologram, 5 is a lens, 6 is a recording medium on which information is recorded, 7a is a light beam emitted from the semiconductor laser element 1, and 7b is a divided light divided by the diffraction grating 3. A beam 8 is a signal light beam reflected from the recording medium 6.

In the conventional optical pickup device configured as described above, the semiconductor laser device 1 of a single laser beam is used.
Is used, and the light beam 7a emitted from the semiconductor laser device 1 becomes a light beam 7b divided into three by the diffraction grating 3, and reaches the recording medium 6 through the lens 5. Pits and the like for recording information are formed on the recording medium 6. The optical path of the signal light beam 8 reflected from the recording medium 6 is largely changed by the hologram 4 and enters the light receiving element 2. As described above, the conventional optical pickup device converts the signal light beam 8 incident on the light receiving element 2 into an electric signal and reads information.

Next, a semiconductor laser device used in a conventional optical pickup device will be described. FIG. 4 is a sectional view of a main part of the semiconductor laser device. As shown in FIG. 4, a clad layer 22 made of n-type GaAlAs is formed on an n-type GaAs substrate 21, and an active layer 23 made of GaAlAs is formed thereon. An optical guide layer 24 made of p-type GaAlAs is formed on the active layer 23, and has a striped window 25 a thereon.
A current blocking layer 25 of type GaAs is formed. On top of this, a cladding layer 26 made of p-type GaAlAs is formed to fill the window 25a, and furthermore, p-type GaAs
Is formed.

[0007]

However, in the above-mentioned conventional configuration, since a single-beam semiconductor laser device is used, a diffraction grating for splitting a beam is required, and furthermore, a semiconductor laser device and a hologram are required. There was a problem that three diffraction gratings had to be aligned.

Generally, in an optical pickup device, about 1% of the output from the semiconductor laser element returns to the semiconductor laser element again due to a manufacturing error of the optical system or birefringence in the recording medium. Fluctuates to generate noise, and the S / N ratio during reproduction is reduced. In order to solve this problem, a method has been adopted in which a high-frequency current is superimposed on a DC current for driving a semiconductor laser device to cause multi-mode oscillation and reduce coherence to control noise, thereby improving the effect. However, there is a problem that the circuit configuration becomes complicated even with a single-beam semiconductor laser device.

Attempts have been made to use a semiconductor laser device which oscillates a multi-beam in order to simplify the optical system by omitting a diffraction grating for splitting a light beam. In the element, the phase of the high-frequency current flowing through each light-emitting point is different even if the amplitude is the same, and there is a problem that the circuit configuration becomes complicated to solve the point.

An object of the present invention is to provide an optical pickup device which uses a semiconductor element which oscillates three beams with high reliability and a low operating current value and does not require a diffraction grating. Aim.

[0011]

Means for Solving the Problems A semiconductor laser device of the present invention to achieve this object, Ga _1-x Al _x As active
One conductive layer on at least one side of the main surface of the layer (0 ≦ x ≦ 1)
Ga _1-y3 Al _y3 As clad layer (x <y3 <1) and
And a Ga ₁ -z Al _z As current blocking layer (y3
<Z ≦ 1) is formed, and the active layer and the cladding layer
Between the active layer side and Ga _1-y1 Al _y1 As.
A first light guide layer, Ga _1-y2 Al _y2 As (x <y2 <y
1 <y3), a second light guide layer is sequentially provided.
A plurality of stripe-shaped grooves are formed in the current block layer.
The current blower so as to fill the stripe-shaped groove.
A lock layer is formed .

[0012]

With this configuration, it is possible to realize a semiconductor laser device that can operate at a low current, is highly reliable, and can stably emit three beams. That is, in the semiconductor laser device according to the configuration of the present invention, A
Oscillation in a single transverse mode because the lAs mixed crystal ratio is set higher than the AlAs mixed crystal ratio in the cladding layer, and low current operation is possible because there is no light absorption by the current block layer of laser light. It is.

[0013]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an optical pickup device according to the present embodiment.

In FIG. 1, the same portions as those in the conventional example shown in FIG. 3 are denoted by the same reference numerals, and the description thereof will be omitted. Only different points will be described. Reference numeral 11 denotes a semiconductor laser device that oscillates three light beams 12a. As described above, since the semiconductor laser element 11 can oscillate three light beams 12a, the diffraction grating 3 required in the conventional example shown in FIG. 3 becomes unnecessary.

The three light beams 12a emitted from the semiconductor laser element 11 pass through the lens 5 to become irradiation light 12b, which is irradiated on the recording medium 6. The signal light 12c reflected from the recording medium 6 and the optical path of which is changed by the hologram 4 enters the light receiving element 2, where it is converted into an electric signal and processed. At this time, the semiconductor laser element 11 oscillates in multiple modes from the point of spectrum, has low coherence with the reflected light returning to the semiconductor laser element, and has low noise characteristics.

Next, a semiconductor laser device used in the optical pickup device according to the present embodiment will be described. FIG. 2 is a sectional view of a main part of the semiconductor laser device.

As shown in FIG. 2, an n-type GaAs substrate 3
1, a first cladding layer 32 made of n-type Ga _0.4 Al _0.6 As, an active layer 33 made of Ga _0.85 Al _0.15 As, p
A first light guide layer 34 of Ga _0.5 Al _0.5 As type,
A second optical guide layer 35 made of p-type Ga _0.8 Al _0.2 As is formed, and n-type Ga is provided in a region other than the windows 36a, 36b, and 36c serving as current channels for current confinement.
_A current block layer 36 made of _0.4 Al _0.6 As is formed. On these, a second cladding layer 37 made of p-type Ga _0.5 Al _0.5 As and a contact layer 38 made of p-type GaAs are formed.

Here, in order to obtain stable single transverse mode oscillation, the AlAs mixed crystal ratio of the current blocking layer 36 is set higher than the AlAs mixed crystal ratio of the second cladding layer 37. If the current blocking layer 36 has an AlAs mixed crystal ratio of
If it is the same as 7, there is a decrease in the refractive index in the stripe due to the plasma effect, and it becomes an anti-guide waveguide,
A single transverse mode oscillation cannot be obtained. Further, when the AlAs mixed crystal ratio of the current blocking layer 36 is lower than that of the second cladding layer 37, the transverse mode becomes completely unstable. In the present embodiment, as shown in FIG. 2, the AlAs mixed crystal ratio of the current blocking layer 36 is set to 0.1 higher than the AlAs mixed crystal ratio of the second cladding layer 37 to 0.6.

In this structure, the current injected from the contact layer 38 is confined in the windows 36a, 36b, and 36c, and laser oscillation in the 780 nm band occurs in the lower active layer 33. Here, the AlAs mixed crystal ratio of the first optical guide layer 34 is sufficiently higher than the AlAs mixed crystal ratio of the active layer 33, and carriers are effectively confined in the active layer 33. 780n
In order to obtain m-band laser oscillation, the AlAs mixed crystal ratio must be 0.45 or more, and is set to 0.5 in this embodiment. Regrowth is performed by the second light guide layer 35 having a low AlAs mixed crystal ratio.
There is no problem of surface oxidation at all.
The AlAs mixed crystal ratio of the second light guide layer 35 is desirably 0.3 or less, which facilitates regrowth, and is transparent to the laser oscillation wavelength. In this embodiment, it is 0.2. Further, the film thickness is desirably 0.05 μm or less which does not significantly affect the light distribution, and is 0.03 μm in this embodiment.
And Further, since the forbidden band width of current blocking layer 36 is larger than the forbidden band width of active layer 33, current blocking layer 3
6, a semiconductor laser device with a low operating current and a small waveguide loss can be obtained. Low-current operation leads to a reduction in the amount of heat generated, so that long life characteristics can be obtained. Further, in this structure, since there is no light absorption by the current blocking layer 36, the laser beam spreads to the lower portion of the current blocking layer 36, the spectrum tends to be multimode, and a low-noise laser can be easily obtained. The oscillation wavelength of the semiconductor laser device can be changed by changing the AlAs mixed crystal ratio.

As described above, in the present embodiment, three windows 36 are provided.
By using a semiconductor laser device having a, 36b, and 36c and capable of emitting three light beams, an optical pickup device that does not require a diffraction grating can be configured.

[0021]

As described above, the present invention uses a multi-mode, low-current operation, and low-noise three-beam semiconductor laser device realized by appropriately selecting the composition and the mixed crystal ratio of each layer of the semiconductor laser device. An excellent optical pickup device in which the diffraction grating is omitted and the optical system is simplified can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of a semiconductor laser device used in an optical pickup device according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of a conventional optical pickup device.

FIG. 4 is a sectional view of a main part of a semiconductor laser device used in a conventional optical pickup device.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser element 2 light receiving element 3 diffraction grating 4 hologram 5 lens 6 recording medium 7a light beam 7b divided light beam 8 signal light beam 11 semiconductor laser element 12a light beam 12b irradiation light 12c signal light 21 n-type GaAs substrate 22 cladding layer 23 Active layer 24 Light guide layer 25a Striped window 25 Current block layer 26 Cladding layer 27 Contact layer 31 n-type GaAs substrate 32 First clad layer 33 Active layer 34 First light guide layer 35 Second light guide layer 36a, 36b, 36c window 36 current blocking layer 37 second cladding layer 38 contact layer

Claims (2)

(57) [Claims] 1. A Ga _1-x Al _x As active layer (0 ≦ x ≦ 1)
Ga _{1-y 3} Al of one conductivity type is provided on at least one side of the main surface of
_{y 3} As clad layer (x <y 3 <1) and G of opposite conductivity type
a _1-z Al _z As current blocking layer (y 3 <z ≦ 1) is formed, between the active layer and the cladding layer, said active
First light guide made of Ga _1-y1 Al _y1 As from the layer side
A second light guide layer made of Ga _{1 -y 2} Al _{y 2} As (x < _{y 2} <y 1 <y 3 ) is sequentially provided, and a plurality of stripe-shaped grooves are formed in the current block layer ; Stra
The current blocking layer is formed to fill the groove
Semiconductor laser device. 2. The method according to claim 1, wherein the second light guide layer has a thickness of 0.05 μm.
2. The semiconductor laser device according to claim 1 , wherein m is equal to or less than m.