JPH02110987A - Multi-wavelength semiconductor laser - Google Patents

Abstract

PURPOSE:To enable the same semiconductor laser to project laser rays of different wavelengths by a method wherein a required quantum level is selected from two or more quantum levels provided to the quantum well structure of an active layer and a loss characteristic is so controlled as to enable a laser oscillation to start at the required quantum level. CONSTITUTION:The following are successively laminated on an n-GaAs substrate 7 provided with a plane: an n-GaAs buffer layer 8; an n-AlGaAs clad layer 9; an n-AlGaAsSC (Separate Confinement) layer 10 whose Al composition decrease in a quadratic functional manner in a thicknesswise direction; a GaAs single quantum well type(SQW) layer 11; a p-AlGaAsSC (Separate Confinement) layer 12 whose Al composition increases in a quadratic functional manner in a thicknesswise direction; a p-AlGaAs clad layer 13; and a p-GaAs cap layer 15. The GaAs SQW layer 11 is composed of a well whose composition is GaAs and barriers, provided on both its sides, whose composition is Ga0.7Al0.3As and has two quantum levels, n=1 and n=2. If an oscillation starts when n is equal to one, laser rays 870nm in wavelength are projected, and laser rays 810nm in wavelength are projected when n is two. And, a loss characteristic is controlled through the injection of a current taking advantage of the reduction of a waveguide path in refractive index just under an electrode due to a plasma effect of injected carriers.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a multi-wavelength semiconductor laser capable of emitting laser beams of different wavelengths from one element, and particularly to a multi-wavelength semiconductor laser capable of emitting laser beams of different wavelengths from one element, and in particular, a multi-wavelength semiconductor laser capable of emitting laser beams of different wavelengths from one element. This invention relates to a multi-wavelength semiconductor laser that can be changed as desired.

[Conventional technology]

Conventionally, a semiconductor laser element capable of emitting multiple laser beams of two or more wavelengths from one element has a structure in which multiple active layers with different compositions are arranged so that the emitted laser wavelengths are different: distribution Feedback type (Distri
butted feed back (DBR) semiconductor laser, or distributed reflection type (Dis-tribute
d BraggReflector, IIBR) By arranging a plurality of semiconductor lasers on the same substrate and making the pitch of the diffraction grating of each laser structure different, the Bragg wavelength corresponding to the pitch of each diffraction grating is made different, and each laser structure There are known devices having a configuration in which the wavelengths of the emitted light are made different.

Furthermore, in recent years, as a method to further change the oscillation wavelength, a quantum well structure is used in the active layer, and the 12-well structure is set deeper than usual, creating a structure with two or more quantum levels. In addition, a method is being used to selectively select an oscillation wavelength that corresponds to two or more quantum levels by controlling the internal loss in the laser cavity by changing the width of the active stripe region and the cavity length. .

[Problem to be solved by the invention]

However, conventional multi-wavelength semiconductor lasers using a quantum well structure in the active layer have the following problems.

For example, in a configuration in which a quantum well layer with two or more quantum levels is used as the active layer and the width of the active stripe region is varied to control the wavelength, the shape of the near-field pattern is determined by the width of the active stripe region. It is difficult to oscillate a laser beam having the same optical characteristics from a single element because the optical characteristics such as optical characteristics and astigmatism change.

On the other hand, in a configuration in which a quantum well layer with two or more quantum levels is used as the active layer and the internal loss characteristics of the resonator are changed by changing the resonator length, if the end face formation method by normal cleavage is used, It is not possible to form a monolithic structure in which a plurality of semiconductor lasers emitting a plurality of laser beams having different wavelengths are integrated into one element.

In addition, in conventional multi-wavelength semiconductor lasers, two
Since the emission positions of the above laser beams are different, in order to align each laser beam irradiation position or laser beam imaging position,
A separate optical system is required for this purpose.

The present invention was devised in view of the problems with conventional multi-wavelength semiconductor lasers as described above, and it is a laser diode with different wavelengths that has good optical properties such as astigmatism and near-field pattern with little variation. An object of the present invention is to provide a multi-wavelength semiconductor laser capable of emitting laser light from the same emitting site.

[Means for solving problems]

The multi-wavelength semiconductor laser of the present invention is a semiconductor laser having an active layer having a quantum well structure having two or more t' quantum levels, and a resonator for oscillating light generated in the active layer. It is characterized by comprising means for controlling loss characteristics within the resonator (loss characteristic control means).

That is, in the multi-wavelength semiconductor laser of the present invention, a quantum level necessary for oscillation at a desired wavelength is selected from a plurality of quantum levels of the quantum well structure of the active layer, and the loss characteristics of the resonator are selected. By controlling the loss characteristic control means to enable oscillation at the quantum level determined by the semiconductor laser, laser beams of different wavelengths can be emitted from the same semiconductor laser.

Therefore, according to the multi-wavelength semiconductor laser of the present invention, laser beams of different wavelengths with the same emission spot size can be selectively obtained from the same emission position, so when used for optical communication, optical disks, etc., it is possible to form an image. This has the advantage that the optical system used for this purpose is simple.

Moreover, the optical characteristics such as astigmatism and near-field pattern of each emitted laser beam are good and uniform, and the thickness of each layer and the size of the ridge structure can be changed as appropriate. [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Note that each layer constituting the laser element of the present invention can be formed using materials and methods commonly used in this field, and the thickness of each layer and the size of the ridge structure can be changed as appropriate.

Embodiment 1 FIG. 1 is a perspective view of a main part of an example of a multi-wavelength semiconductor laser of the present invention, and FIG. 2 is a partial cross-sectional view taken along line AB in FIG. 1.

The semiconductor laser of this example is an n-G laser diode with a (100) plane.
n-GaA on aAs substrate 7 (thickness: ~350 q)
s buffer layer 8 (thickness: 0.5 pm), n-
AlGaAs cladding layer 9 (thickness: 1.5 p), A
To the n-A IGa 8s in which the composition of 2 decreases quadratically in the film thickness direction (:(Separate Con
finement) layer 10 (thickness: 0.2 gIn), G
aAs single quantum well type (Single Quantum
Well, 5QW) layer 11 (thickness: ~0.01.),
A p-AlGaAs SC layer 12 (thickness: 0.2
gm), a p-AlGaAs cladding layer 13 (thickness within the ridge structure: 1-5 μm), and a p-GaAs cap layer 15 are sequentially laminated.

In addition, in this example, current confinement and light confinement are performed by a ridge structure (height: 2 to 1.8 μs, width: ~2.5 μs), and this ridge structure is located between the active region and a pair of reflective surfaces. It constitutes an active stripe region (2-300 mm long) with a resonator arranged with a leading waveguide.

This ridge structure is created by sequentially laminating the above-mentioned layers and then etching the ridge structure so that the portion that will become the ridge structure remains in a stripe shape to form a ridge portion.
Formation of insulating film 23 (thickness: 0.2p), then Au
';'It is formed by performing the film formation of 1ii2.3.

Note that the Au electrodes are connected to the n-GaAs substrate 7 and the p-GaAs substrate 7, respectively.
- Alloyed with GaAs cap layer 15.

The GaAs SQW layer 11 has a well composition of GaAs,
Well width is 100 people, barrier composition on both sides is Gao7
Alo: Consists of +As. As a result,
It has two quantum levels, n=1 and n・2. When oscillation occurs at the n=1 quantum level, a laser beam is emitted at a wavelength of 870 nm, and oscillation occurs at the n・2 quantum level. At this time, a laser beam is emitted with a wavelength of 81 Or+m.

On the other hand, a current source 4 and a current source 5 are connected to the electrode 2 and the electric current Fi3, respectively, so that current can be applied to these electrodes separately. The current source 4 is for supplying current for laser oscillation, and the current source 5 is a current source for wavelength selection, and includes the electrode 3, a portion of the common electrode 6 corresponding to the voltage 1ji3, and the current source 5. This portion forms the loss characteristic control means in the present invention.

The principle by which wavelength selection can be performed using the current source 5 will be explained below.

The wavelength of light emitted within the active layer can be specified by selecting a quantum level, and this selection of the quantum level can be performed by changing the amount of current injected into the active layer.

First, the amount of current necessary to obtain light emission at the quantum level n=1 is injected from the electrode 2. Furthermore, a current amount is injected from the current source 5 through the electrode 3 such that the waveguide directly under the electrode 3 becomes a gain region for the light emitted by the active layer directly under the electrode 2 .

The loss characteristics in the waveguide directly under the electrode 3 are controlled by injecting current from the electrode 3 by utilizing the fact that the refractive index of the waveguide directly under the electrode is reduced due to the plasma effect of the injected carriers.

By forming the gain region in this manner, oscillation occurs at a low oscillation threshold current.

That is, oscillation occurs at the n-1 quantum level without any current being injected until the quantum level n·2 is capable of oscillation, and therefore a laser beam with a wavelength of 870 nm is emitted.

On the other hand, when the current injected into the current source 5 is gradually reduced, the active layer directly under the electrode 3 becomes a loss region for the light emitted in the active layer directly under the electrode 111iI2.

Therefore, in order to cause laser oscillation, the current source 4
Therefore, it is necessary to increase the amount of current injected.

When the amount of current injected by the current source 4 reaches a certain level -F, oscillation at the quantum level n·2 becomes possible. Since the gain for light at quantum level n~2 is larger than the gain for light at quantum level n-1, when oscillation at n·2 becomes possible, laser light with a wavelength of 810r+o+ is emitted.

Embodiment 2 FIG. 3 is a plan view of the main parts of another embodiment of the multi-wavelength semiconductor laser of the present invention.

16 is the active stripe region of the semiconductor laser (length 2 to 3
oou), and the cross section of this CD portion is the same as that shown in FIG.

The ridge structure is provided with a so-called Maha-Zehnder interferometer type waveguide 18 (length: 1 mm) with two Y branches, and the wavelength control electrode 17 is connected to one side of the waveguide constituting the Maha-Zehnder interferometer. A high reflection film 19 (reflectance: 90% or more, so-called λ/4 alternating 4-layer film composed of Al2O3 and Si) is coated on the end face of the wafer placed directly above the surface, and these have the loss characteristic in the present invention. forming control means.

The principle by which wavelength selection can be performed in this embodiment will be explained below.

When no current is injected from the current source 20 through the electrode 17, there is no optical path difference between the two waveguides of the Mach-Zehnder interferometer 18, so when they merge at the Y branch 23,
Since the light waves with the same phase merge, the light emitted in the active stripe region I6 reaches the high reflection film 19 with almost no loss, is reflected, and passes through the Maha-Zehnder interferometer again to the active stripe region. Return to 16. Therefore, when a current is injected from the current source 21 into the active stripe region 16, the characteristics are similar to those of a laser coated with a highly reflective film, and oscillation occurs at a low injection current (approximately 30 mA). Therefore, oscillation occurs at the quantum level nJ, and the wavelength is 87
A laser beam λ of 0nn+ is emitted from the end face.

Further, a current (approximately 5
mA), the refractive index of the waveguide directly under the electrode decreases due to the plasma effect of the injected carriers. Therefore, when the phases are shifted and the lights merge at the Y branch 23, a loss of light occurs. Therefore, the amount of light reaching the high reflection film 19 is reduced. Further, the reflected light passes through the same Mach-Zehnder interferometer again and joins at the Y branch 22, but a loss occurs due to a phase shift caused by the injected current. For this reason, the light emitted in the active stripe region 16 has a small amount of light that returns through the Mach-Zehnder interferometer, so before laser oscillation occurs,
A high injection current amount (approximately 80 mA) is required. Therefore, it becomes a state of oscillation at quantum level n-2, and the wavelength is 810n.
m laser beams are now emitted.

Embodiment 3 FIG. 4 is a plan view of the main parts of another embodiment of the multi-wavelength semiconductor laser of the present invention.

24 is the active stripe region of the semiconductor laser (length: ~3
00JJJl), and this partial cross section at F is the same as the structure shown in FIG.

25 is a directional coupler, and this coupling length is injected from an electrode disposed between two waveguides 31 and 32 (width: 3 μm, height 1 scale) constituting the directional coupler. The refractive index is controlled by using the change in refractive index caused by the electric current. 27 is a high reflective film coated on the end face (reflectance = 90% or more, A120
3-5i is a so-called λ/4 alternating four-layer film), 28 is a low reflection film coated on the end face (reflectance ゛: 5%, ^12
03λ/4 single layer film). The directional coupler 25 is set so that the coupling length and the directional coupler length are exactly the same when no current is injected by the current source 29. These directional coupler 25, reflective film 27.2
8 constitutes the loss characteristic control means in the present invention.

In this example, almost all of the light emitted from the active stripe region 24 reaches the high reflection film 27 and is reflected. On the other hand, when a current is applied from the current source 29, the directional coupler coupling length changes due to the refractive index change due to the injected current, and part of the light emitted from the active stripe region 24 reaches the low reflection film 28. It becomes like this.

As a result, as described above, the loss characteristics of the resonator are changed by changing the reflectance, and the quantum level is selected.
Any two wavelengths can be selectively obtained.

In the above configuration, each Om from the current source 29.30
A. When a current of 30 mA is injected, light with a wavelength of 870 nm is oscillated, and when currents of 5 mA and 80 mA are injected from the current source 29.30, respectively, the wavelength is 810 r.
++n light can be oscillated.

In the above examples, as the active layer! Although the SQW structure with two quantum levels in the claw quantum well was used, the present invention is not limited to this, and the present invention is not limited to this, but may also be applied to an MQW structure with two or more quantum levels, or to the patent application No. 62-0449.
As shown in 39, the same optical waveguide structure may have a plurality of light emitting layers having different emission wavelengths.

Furthermore, the structure of the multi-wavelength semiconductor laser of the present invention is not limited to that shown in the examples described above, and the oscillation wavelength from the same active drive region is changed by switching the loss characteristics of the resonator. It can take any structure as long as it can. For example, any structure that has current confinement and a good optical confinement structure, such as a buried heterostructure (BH structure), may be used.

〔Effect of the invention〕

As explained below, according to the present invention, a multi-laser beam that can emit a plurality of laser beams of different wavelengths having good and consistent optical characteristics such as astigmatism and a near-field pattern from the same emission site is provided. We can provide wavelength semiconductor lasers,
Laser beams of different wavelengths can be emitted from the same emission site, so when used as a laser light source for optical communication or optical disk playback devices, it simplifies the configuration of the optical system to image the laser beam at a desired position. becomes possible.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the main parts of an example of a multi-wavelength semiconductor laser according to the present invention, FIG. 2 is a partial sectional view taken along line A-B in FIG. 1, and FIGS. The top view of the principal part of another example of a wavelength semiconductor laser is shown. 7 Two semiconductor laser substrates Laser injection electrode Wavelength control electrode Laser injection current source Wavelength control current source Common electrode n-GaAs buffer layer 9: 10: I]: 12: 13: 14: 15: 16: 17: 18= 19: 20: 21: 22. 24: 25= 26= 27= 28: 29: n-AlGaAs cladding layer n-AlGaAs SC layer GaAs SQW layer GaAs SC layer p-A lGaAs cladding layer Sin insulating layer p-GaAs cap layer Active strip region wavelength control electrode Mach-Zehnder interferometer High reflection film Current source for wavelength control Laser injection current source 23: Y-branch active stripe region Directional coupler Wavelength control electrode High reflection film Low reflection film Wavelength control current source 30: Laser injection current source

Claims (1)

[Claims] 1) In a semiconductor laser having an active layer having a quantum well structure having two or more quantum levels and a resonator for oscillating light generated in the active layer, A multi-wavelength semiconductor laser characterized by having means for controlling loss characteristics of the laser. 2) Claim 1, wherein the active layer has a quantum well structure having two or more quantum levels in one quantum well.
The described multi-wavelength semiconductor laser. 3) The multi-wavelength semiconductor laser according to claim 1, wherein the active layer is constituted by two or more quantum wells having different quantum levels.