JP2003318489A - Semiconductor laser device - Google Patents

Abstract

(57) Abstract: Provided is a semiconductor laser device which can obtain laser light having a desired luminance and which can be used for a long time and has low power consumption. A light emitting layer having a pn junction is sandwiched between a pair of mirror layers, and a power is applied to the light emitting layer to generate light in the light emitting layer. A semiconductor laser device that resonates and amplifies two light beams having different wavelengths between the mirror layers 4 and emits the two resonated and amplified laser beams from one side of the mirror layer 4. The device 2 has a mirror layer 4 from which laser light is emitted.
The semiconductor laser device is configured so as to have a photodiode 5 that transmits one laser beam and absorbs the other laser beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device preferably used as a light source for optical communication.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser device has been used as a light source for optical communication.

As such a conventional semiconductor laser device,
For example, a light emitting layer made of a compound semiconductor such as GaAs having a pn junction is sandwiched by a pair of mirror layers formed by alternately laminating two types of compound semiconductors such as AlAs and GaAs. It is known that a resonator is provided, and electric power is applied to the light emitting layer to generate light in the light emitting layer to cause resonance / amplification of the light between a pair of mirror layers, and the laser which has been subjected to the resonance / amplification. By emitting light from one side of the mirror layer, it functions as a semiconductor laser device.

Above such a semiconductor laser device,
A photodiode is provided to detect the light intensity of the laser light, the photodiode absorbs a portion of the laser light to monitor the intensity, and the intensity is applied to the light emitting layer based on the obtained intensity information. The intensity of the laser beam is set by adjusting the power.

[0005]

However, in the above-mentioned conventional semiconductor laser device, when the intensity of the laser beam is monitored by the photo diode on the mirror layer, a part of the laser beam is absorbed by the photodiode. Therefore, the intensity of the laser light emitted to the outside is reduced by that amount.Therefore, even if the power applied to the light emitting layer is adjusted based on the intensity information obtained from the photodiode, the intensity of the laser light is reduced. Had a drawback that it was difficult to set the desired value.

Further, in order to eliminate the above-mentioned drawbacks, in order to compensate for the decrease in the light intensity absorbed by the photodiode, a power higher than usual is applied to the light emitting layer to set the laser light to a desired intensity. Can be considered,
In such a case, the semiconductor laser device consumes a large amount of power, and the load on the light emitting layer is large, so that the crystallinity of the light emitting layer is deteriorated and the light emission life of the semiconductor laser device is shortened. Had.

The present invention has been devised in view of the above-mentioned drawbacks, and an object thereof is to obtain a semiconductor laser device having a desired brightness and capable of being used for a long period of time with low power consumption. To provide.

[0008]

A semiconductor laser device of the present invention comprises a resonator in which a light emitting layer having a pn junction is sandwiched by a pair of mirror layers, and electric power is applied to the light emitting layer to emit light. A semiconductor laser device that generates light inside a pair of mirror layers, resonates and amplifies two lights having different wavelengths, and emits the two resonance and amplified laser beams from one side of the mirror layer. The resonator is characterized in that it has a photodiode, which transmits one laser beam and absorbs the other laser beam, on a mirror layer from which the laser beam is emitted. .

Further, in the semiconductor laser device of the present invention, the intensities of the two laser beams gradually increase with an increase in the power applied to the light emitting layer while maintaining a substantially constant correlation between the respective emission intensities. And the intensity of the other laser beam is 5% to 70% of the intensity of the one laser beam.

Further, in the semiconductor laser device of the present invention, the intensity of the other laser beam absorbed and detected by the photodiode is monitored, and the power applied to the light emitting layer is adjusted based on the obtained intensity information. It is characterized by.

According to the semiconductor laser device of the present invention, the intensities have a substantially constant correlation with each other and the wavelengths are different from each other.
Two laser beams are emitted from the mirror layer forming the resonator, and one laser beam used as a main light source such as a light source for optical communication is transmitted on the mirror layer from which the laser beams are emitted, and Providing a photodiode that absorbs the other laser beam used as a monitoring light source for obtaining the intensity information of the one laser beam, and to the light emitting layer based on the intensity information of the other laser beam obtained by the photodiode By adjusting the applied power of
One of the laser beams can be set to have a desired intensity. Therefore, the problem that most of the laser light used as the main light source is absorbed by the photodiode and the intensity thereof is lowered is effectively prevented, and a high-performance semiconductor capable of obtaining laser light emitting at a desired brightness. A laser device is realized.

Further, in this case, one of the laser beams passes through the photodiode, and its intensity is hardly reduced. Therefore, in order to compensate for the intensity reduction of the one laser beam, a power larger than usual is emitted from the light emitting layer. Therefore, the power consumption of the semiconductor laser device can be kept small, and the load on the light emitting layer can be minimized to keep the crystallinity of the light emitting layer in a good state. There is also an advantage that can be used for a long time.

Further, according to the semiconductor laser device of the present invention, since the photodiode is formed directly on the mirror layer from which laser light is emitted, it is emitted from the mirror layer. Most of the laser light of (1) is incident on the photodiode, and the light detection accuracy of the photodiode can be further improved.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention. In the figure, 1 is a single crystal substrate, 2 is a resonator, 3 is a light emitting layer, 4 is a mirror layer, and 5 is a photodiode. .

The single crystal substrate 1 is formed of a compound semiconductor such as GaAs into various shapes such as a circular shape, a triangular shape, and a quadrangular shape, and a resonator 2 and electrodes (not shown) are provided on the upper surface thereof. , Which functions as a support base material for supporting these.

When such a single crystal substrate 1 is made of GaAs, for example, a GaAs ingot (lump) formed by a conventionally well-known vertical Bridgman method (VB method) or the like is sliced into a predetermined thickness, and this is sliced. It is manufactured by polishing the surface.

The resonator 2 provided on the upper surface of the single crystal substrate 1 has a structure in which a light emitting layer 3 having a pn junction is sandwiched between a pair of mirror layers 4.

The light emitting layer 3 is made of In _a Al _b Ga _{1 -ab} A
s _c P _d N _1-cd (where a, b, c, d are 0 ≦ a ≦ 1, 0
≦ b ≦ 1, 0 ≦ c ≦ 1, 0 ≦ d ≦ 1, 0 ≦ a + b ≦ 1,
(A value satisfying 0 ≦ c + d ≦ 1) has a pn junction formed by sequentially stacking a p-type semiconductor layer and an n-type semiconductor layer made of a GaAs-based single crystal thin film, and the light-emitting layer 3 is illustrated. When a predetermined electric power is applied through the non-electrode, holes are injected into the n-type semiconductor layer and electrons are injected into the p-type semiconductor layer, respectively, and both are recombined in the vicinity of the pn junction, whereby the light emitting layer 3 Emits light, the emitted light is resonated and amplified inside the light emitting layer 3, and the laser light is emitted to the outside.

Further, the light emitting layer 3 is set so that the film thickness (t) thereof satisfies the relationship of the following formula, whereby light resonated and amplified inside the light emitting layer has two different wavelengths. Laser light L ₁ , L ₂ (wavelength of laser light L ₁ is λ ₁ ,
The wavelength of the laser beam L ₂ is λ ₂ . However, λ ₁ > λ ₂ ). For example, when the light emitting layer 3 is made of GaAs (the refractive index of GaAs is n = 3.53), and the thickness (t) is set to about 0.84 μm, l = 7 and k = 1.
^{_{As, λ 1 = 850 × 10 -}} 9 m, λ 2 = 744 × 10 -
Two laser beams L ₁ and L ₂ having a wavelength of ⁹ m are emitted from the light emitting layer 3
It will be resonated and amplified inside.

[0020]

[Equation 1]

Since it is easy to form the layer 3, it is preferable to set l to a natural number satisfying the relational expression of "l ≧ 4" and k to 1 or 2. Is the other laser beam L ₂
Is set to 5% to 70% of the intensity of _one laser beam L ₁ , and these intensities have a substantially constant correlation with each other as the power applied to the light emitting layer 3 increases. It has a characteristic that the laser light L ₁ gradually increases while keeping the same, and the laser light L _{1 which} is _one of the light sources is transmitted through a photodiode 5 described later and is used as a main light source used for optical communication or the like.
Part of the other laser beam L ₂ is absorbed by the photodiode 5 and its intensity is monitored.

The light emitting layer 3 is formed, for example, by a well-known MOCVD method (Metal Organic Chemical Vapor Deposit).
ion) method or the like, and a GaAs-based single crystal thin film such as AlGaAs is sequentially epitaxially grown on the upper surface of the mirror layer 4 on the single crystal substrate 1 side to have a predetermined thickness.

Further, a pair of mirrors sandwiching the light emitting layer 3 is provided.
Layer 4 is made of two types of single crystals such as GaAs and AlGaAs
Thin films were alternately laminated periodically (20 to 30 cycles)
It has a structure, and the wavelength between these pair of mirror layers 4 is
Two laser beams L with different₁, L₂Resonance and amplification
Both, the two laser beams L that are resonated and amplified₁, L ₂To
It has the function of emitting light from one side of the mirror layer 4.

The pair of mirror layers 4 may be formed, for example, by the well-known MOCVD (Metal Organic Chemical Vapor) method.
Deposition) method is adopted, and GaAs and AlGaA
Each mirror layer 4 is formed to a thickness of 0.5 μm to 2.0 μm by alternately epitaxially growing a single crystal thin film of s on the single crystal substrate 1 or the light emitting layer 3, and the resonator 2 is Mirror layer 4 from which laser light is emitted
Has a photodiode 5 on a part of its upper surface.

The photodiode 5 is, for example, AlG.
It has a structure in which a p-type semiconductor layer and an n-type semiconductor layer made of a single crystal thin film such as aAs or InGaAs are sequentially stacked, and when the above-mentioned two laser beams L ₁ and L ₂ are incident therein, One laser beam L ₁ is transmitted and the other laser beam L ₂ is absorbed, and the absorbed laser beam L ₂ generates electrons and holes near the pn junction, and the electrons are n-type semiconductor layers. Then, holes are respectively injected into the p-type semiconductor layer, and these are extracted as an electric signal through an electrode (not shown) to monitor the intensity of the other laser beam L ₂ .

On the other hand, as described above, the two laser beams L ₁ and L ₂ emitted from one side of the pair of mirror layers 4 are
Since their intensities have a substantially constant correlation with each other,
Other and the intensity information of the laser beam L _2, which was monitored by the photodiode 5, can be calculated one of the intensity of the laser light L ₁ from the conversion table shown in FIG. 2, one of the intensity of the laser beam L ₁ I understand. For example, when the intensity of the other laser beam L ₂ monitored by the photodiode 5 is 1.5 mW, the intensity of the _one laser beam L ₁ is 3.0 mW from the conversion table shown in FIG.
It can be seen that it is. At this time, if the desired intensity of _one laser beam L ₁ is 6.0 mW, it can be seen from the conversion table that the other laser beam L ₂ should be emitted with an intensity of 3.0 mW. The power applied to 3 is 1
It should be adjusted to 3.5 mW.

In this way, the photodiode 5 can
The other laser light L that has been annealed ₂Based on the strength information of
By adjusting the power applied to the light emitting layer 3,
Laser light L₁Can be set to the desired strength
Therefore, the one laser light L used as the main light source₁
Is absorbed by the photodiode 5
Laser light that emits light with the desired brightness.
High-performance semiconductor laser device capable of achieving
Be done.

Further, in this case, one of the laser beams L ₁ is transmitted through the photodiode 5 and its intensity hardly decreases. Therefore, in order to make up for the intensity reduction of the laser beam L _1, a larger power than usual is used. Is not required to be applied to the light emitting layer 3, so that the power consumption of the semiconductor laser device can be kept small, and the load on the light emitting layer 3 can be minimized so that the crystallinity of the light emitting layer 3 is good. Therefore, there is an advantage that the semiconductor laser device can be used for a long period of time.

Further, since the photodiode 5 is formed so as to be directly attached to the upper surface of the mirror layer 4 from which the laser beams L ₁ and L ₂ are emitted, the photodiode 5 is emitted from the mirror layer 4. Most of the other laser beam L ₂ is incident on the photodiode 5, and the light detection accuracy of the photodiode 5 can be further improved.

The photodiode 5 absorbs the other laser beam (wavelength λ ₂ ) of the two laser beams L ₁ and L ₂ and transmits _one laser beam (wavelength λ ₁ ). In order to achieve the above, in the graph showing the relationship between the wavelength λ of the laser light absorbed by the photodiode 5 and the absorption coefficient α of the photodiode 5, by adjusting the material forming the photodiode 5, wavelength lambda _x in the discontinuous become regions may be set so as to be positioned between the wavelength lambda ₂ of the laser beam L ₂ to absorption wavelength lambda ₁ and the laser light L ₁ to be transmitted (see FIG. 3), For example, if the photodiode 5 is Al _x Ga _1-x As (0 <x <
1), the wavelength λ _{1 of one} laser beam L ₁ is 8
50 × 10 ^-9 m, the wavelength lambda ₂ of the other laser beam L ₂ is 744
When ^{x10 −9} m, the wavelength λ _x is adjusted to the wavelength λ ₁ and the wavelength λ by adjusting x in the range of 0.05 ≦ x ≦ 0.20.
Set between ₂ In this case, the larger than 0.20 the value of x, the wavelength lambda _x is smaller than the wavelength lambda _2, the absorption coefficient of the photodiode 5 at a wavelength lambda ₂ alpha
Becomes extremely small, and it becomes difficult for the photodiode 5 to absorb the other laser beam L ₂ . On the other hand, when less than 0.05 the value of x, the wavelength lambda _x is greater than the wavelength lambda _1, the absorption coefficient of the photodiode 5 alpha becomes extremely large at the wavelength lambda _1, the other only the laser beam L ₂ Of course, the one laser beam L ₁ is also absorbed, and the intensity of the _one laser beam L ₁ is reduced. Therefore, when the photodiode 5 is made of Al _x Ga _{1 -x} As (0 <x <1), the wavelength λ _{1 of the one} laser beam L ₁ to be transmitted is 850.
× 10 ^-9 m, when other wavelength lambda ₂ of the laser beam L ₂ to be absorbed is 744 × 10 ^-9 m, 0.05 ≦ a x x ≦ 0.
It is preferable to adjust the range to 20. When such a photodiode 5 is made of AlGaAs, for example, a conventionally well-known MOCVD method (Metal Organic Chemical) is used.
Vapor Deposition) method or the like is employed, and a single crystal thin film made of AlGaAs is sequentially epitaxially grown on the upper surface of the mirror layer 4 to have a thickness of 2 μm to 10 μm.

Thus, in the semiconductor laser device described above, electric power is applied to the light emitting layer 3 to generate light in the light emitting layer 3, and two laser beams L ₁ and L having different wavelengths are generated between the pair of mirror layers 4. ₂ resonates and amplifies the
The amplified two laser beams L ₁ and L ₂ are emitted from one side of the pair of mirror layers 4 to function as a semiconductor laser device.

The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above embodiment, the single crystal substrate 1 is made of GaAs, but instead of this, the single crystal substrate is made of Si, GaP, GaN, GaSb, I.
It may be formed of another compound semiconductor such as nP or InAs.

Further, in the above-described embodiment, when the light emitting layer 3, the mirror layer 4 and the photodiode 5 are formed, M
Although the OCVD method is adopted, other methods,
For example, it may be formed by the MBE (Molecular Beam Epitaxy) method or the like.

Further, in the above-mentioned embodiment, the photodiode 5 is attached to a part of the upper surface of the mirror layer 4, but instead of this, a photodiode 5'is provided as shown in FIG. The entire upper surface of the mirror layer 4 may be adhered. In this case, the other laser light L
₂ can be made incident on the photodiode 5'without leakage, and the photodetection accuracy of the photodiode 5'can be made extremely high. Therefore, it is preferable that the photodiode 5'be attached to the entire upper surface of the mirror layer 4.

[0036]

According to the semiconductor laser device of the present invention, two laser beams having intensities having a substantially constant correlation with each other and having different wavelengths are emitted from the mirror layer constituting the resonator, and the laser beams are emitted. On the mirror layer where light is emitted,
A photodiode that transmits one laser beam used as a main light source such as a light source for optical communication and absorbs the other laser beam used as a monitoring light source for obtaining intensity information of the one laser beam. One laser beam can be set to a desired intensity by providing the laser beam and adjusting the power applied to the light emitting layer based on the intensity information of the other laser beam obtained by the photodiode. Therefore, the problem that most of the laser light used as the main light source is absorbed by the photodiode and the intensity thereof is lowered is effectively prevented, and a high-performance semiconductor capable of obtaining laser light emitting at a desired brightness. A laser device is realized.

Further, in this case, one of the laser beams passes through the photodiode and its intensity is hardly reduced. Therefore, in order to make up for the intensity reduction of the one laser beam, a power larger than usual is applied to the light emitting layer. Therefore, the power consumption of the semiconductor laser device can be kept small, and the load on the light emitting layer can be minimized to keep the crystallinity of the light emitting layer in a good state. There is also an advantage that can be used for a long time.

Further, according to the semiconductor laser device of the present invention, since the photodiode is formed directly on the mirror layer from which laser light is emitted, the photodiode is emitted from the mirror layer. Most of the laser light of (1) is incident on the photodiode, and the light detection accuracy of the photodiode can be further improved.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between applied power and light intensity regarding two laser lights emitted from the semiconductor laser device of FIG.

FIG. 3 is a photodiode 5 of the semiconductor laser device of FIG.
7 is a graph showing the relationship between the wavelength of the laser light absorbed by the laser and the absorption coefficient of the photodiode 5.

FIG. 4 is a sectional view of a semiconductor laser device according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Single crystal substrate 2 ... Resonator 3 ... Light emitting layer 4 ... Mirror layer 5, 5 '... Photodiode

Claims (3)

[Claims] 1. A resonator comprising a light emitting layer having a pn junction sandwiched by a pair of mirror layers, wherein electric power is applied to the light emitting layer to generate light in the light emitting layer, and the light emitting layer is sandwiched between the pair of mirror layers. A semiconductor laser device that resonates / amplifies two lights having different wavelengths and emits the two resonated / amplified laser lights from one side of the mirror layer, wherein the resonator emits the laser light. A semiconductor laser device having a photodiode that transmits one laser beam and absorbs the other laser beam on the mirror layer to be formed. 2. The two laser beams have a characteristic that their intensities gradually increase with an increase in the power applied to the light emitting layer while maintaining a substantially constant correlation between their respective emission intensities.
The semiconductor laser device according to claim 1, wherein the intensity of the other laser beam is 5% to 70% of the intensity of the one laser beam. 3. The power applied to the light emitting layer is adjusted based on the intensity information obtained by monitoring the intensity of the other laser beam absorbed and detected by the photodiode. The semiconductor laser device according to claim 2.