JP2007208062A - Semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Fabry-Perot type semiconductor laser element having a narrow oscillating-spectrum width. <P>SOLUTION: The Fabry-Perot type semiconductor laser element 10 has an active layer 17, and a clad layer 13 having a refractive index lower than the one of the active layer. A light absorbing layer 14 is interposed between the active layer and the clad layer, and a separating layer 15 is interposed between the light absorbing layer and the active layer. The light absorbing layer has a fundamental-absorbing-edge wavelength shorter than the light-emitting peak-wavelength of the active layer, and has a band-gap energy smaller than that of the clad layer. The separating layer has a band-gap energy larger than those of the light absorbing layer and the active layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor laser element suitable for optical communication.

  In an optical communication application (for example, optical communication in a band of 1.25 μm to 1.65 μm) in which chromatic dispersion has a great influence, it is usually not a Fabry-Perot (FP) type semiconductor laser element but a distributed feedback (DFB) type. A semiconductor laser element is used. Since the DFB laser element oscillates in a single longitudinal mode and has a narrow spectrum width, it is possible to suppress the collapse of the signal light waveform due to wavelength dispersion.

  However, since the DFB laser element has a diffraction grating provided inside the laser element and realizes a single longitudinal mode oscillation by the diffraction wavelength, the manufacturing process is complicated, the yield is low, and the manufacturing cost is lower than that of the FP laser element. Is expensive.

  On the other hand, the FP laser element can be manufactured at a lower cost than the DFB laser element, but it oscillates in a multi-longitudinal mode, so that the oscillation spectrum width becomes wide. For this reason, when the FP laser element is used as a light source for signal light, the waveform of the signal light collapses due to wavelength dispersion during optical fiber transmission, and it is difficult to transmit the signal light well.

  Therefore, an object of the present invention is to provide a Fabry-Perot type semiconductor laser device having a narrow oscillation spectrum width.

  A Fabry-Perot type semiconductor laser device according to the present invention includes an active layer, a cladding layer having a refractive index lower than that of the active layer, a light absorption layer disposed between the active layer and the cladding layer, a light absorption layer, and an active layer. A separation layer disposed between the layers and a substrate on which the active layer, the cladding layer, the light absorption layer, and the separation layer are mounted are provided. The light absorption layer is made of a semiconductor having a fundamental absorption edge wavelength shorter than the emission peak wavelength in the active layer and a band gap energy smaller than that of the cladding layer. The separation layer has a larger band gap energy than each of the light absorption layer and the active layer.

  In general, a semiconductor efficiently absorbs light having a wavelength shorter than the fundamental absorption edge wavelength. As described above, the fundamental absorption edge wavelength of the semiconductor constituting the light absorption layer is shorter than the emission peak wavelength in the active layer. For this reason, the light absorption layer reduces the light intensity in a wavelength region shorter than the peak wavelength without reducing the peak light intensity in the oscillation spectrum of the semiconductor laser element. Since the conventional Fabry-Perot laser has a relatively strong emission intensity in a short wavelength region, its oscillation spectrum width is wide. On the other hand, according to the present invention, since the light absorption layer reduces the light intensity in a wavelength region shorter than the emission peak wavelength, the oscillation spectrum width can be narrowed without reducing the peak light intensity.

  Since the light absorption layer has a smaller band gap energy than the cladding layer, it does not hinder the injection of carriers into the active layer. Thereby, a favorable light emitting operation of the semiconductor laser element can be ensured.

  Since the separation layer has a band gap energy larger than that of the active layer, it prevents injection of carriers from the active layer to the light absorption layer. Thereby, the light emission in a light absorption layer can be suppressed and absorption efficiency can be improved.

  The active layer may have a quantum well structure in which quantum well layers and barrier layers having band gap energy larger than the quantum well layers are alternately arranged. In order to prevent carrier injection from the active layer to the light absorption layer, the separation layer preferably has a larger band gap energy than the barrier layer.

  The clad layer may be made of an n-type semiconductor. In this case, the light absorption layer is disposed in a region where electrons are injected toward the active layer. For this reason, in the vicinity of the top of the valence band of the light absorption layer, there are almost no holes and electrons are likely to exist. Light absorption occurs when electrons in the valence band transition to a vacant level of the conductor. Therefore, electrons are likely to exist near the top of the valence band, so that the absorption efficiency of the light absorption layer is increased. Thereby, the oscillation spectrum width of the semiconductor laser element can be further reduced.

  The thickness of the separation layer is preferably 20 nm or less. By suppressing the thickness of the separation layer, carriers are efficiently injected into the active layer. Thereby, it is possible to ensure a more favorable light emitting operation of the semiconductor laser element.

  The light absorption layer may be a quantum well layer. In this case, the semiconductor laser device further includes two barrier layers each having a band gap energy larger than that of the light absorption layer, with the light absorption layer being sandwiched in contact with the light absorption layer. One of these barrier layers may be the above clad layer, and the other may be the above separation layer.

  Since the light absorption layer is a quantum well layer, the rise of the absorption spectrum of the light absorption layer becomes steep due to the quantum effect. As a result, it is possible to further narrow the oscillation spectrum width without reducing the peak light intensity of the semiconductor laser element.

  The light absorption layer may have a smaller lattice constant than the substrate. In this case, tensile strain can be generated in the light absorption layer. This tensile strain increases the absorption efficiency of TM mode light in the vicinity of the fundamental absorption edge wavelength. For a semiconductor laser element in which the short wavelength region of the oscillation spectrum is enhanced by the contribution of TM mode light, the oscillation spectrum width can be narrowed efficiently by using a light absorbing layer having tensile strain.

  According to the present invention, a Fabry-Perot type semiconductor laser device having a narrow oscillation spectrum width can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

First Embodiment FIG. 1 is a schematic cross-sectional view showing a semiconductor laser device according to a first embodiment. The semiconductor laser element 10 is a Fabry-Perot (hereinafter “FP”) type, and includes a lower clad layer 13, a light absorption layer 14, a separation layer 15, a lower guide layer 16, and an active layer sequentially stacked on the upper surface of a substrate 12. It has a layer 17, an upper guide layer 18 and an upper cladding layer 19. Each of these layers is made of a compound semiconductor. The substrate 12 and the lower cladding layer 13 may be integrated. In this case, the substrate 12 and the lower clad layer 13 constitute one base material made of a single semiconductor, and the surface layer of the base material functions as the lower clad layer 13.

  A striped anode 20 is provided on the upper clad layer 19. The entire lower surface of the substrate 12 is covered with the cathode 22. Both end faces of the laser element 10 are mirror surfaces and constitute a laser resonator. By injecting a current into the active layer 17 through the anode 20 and the cathode 22, the laser element 10 causes laser oscillation and outputs laser light from one end face thereof.

  The active layer 17 has a higher refractive index than each of the lower guide layer 16 and the upper guide layer 18. The guide layers 16 and 18 both have a higher refractive index than each of the lower cladding layer 13 and the upper cladding layer 19. These layers form an optical waveguide that guides light generated in the active layer 17.

  FIG. 2 is an energy band diagram of the laser element 10. In FIG. 2, reference numeral 26 indicates a conduction band, reference numeral 27 indicates a valence band, black circles indicate electrons, and white circles indicate holes. Reference numerals 35 and 36 denote directions of electrons and holes injected into the laser element 10, respectively. Reference numeral 37 denotes electron transition due to light absorption of the light absorption layer 14, and reference numeral 38 denotes electron transition due to stimulated emission in the active layer 17.

  The light absorption layer 14 has a larger band gap energy than the active layer 17. As a result, the fundamental absorption edge wavelength of the light absorption layer 14 becomes shorter than the emission peak wavelength in the active layer 17. The light absorption layer 14 efficiently absorbs light having a wavelength shorter than the fundamental absorption edge wavelength.

  The lower cladding layer 13 adjacent to the light absorption layer 14 has a higher band gap energy than the light absorption layer 14. Further, the separation layer 15 adjacent to the light absorption layer 14 has a higher band gap energy than each of the light absorption layer 14 and the active layer 17.

  Below, the advantage of this embodiment is demonstrated, comparing with the conventional FP semiconductor laser element. FIG. 3 is an energy band diagram of a conventional FP laser element. This laser element has a structure in which the light absorption layer 14 and the separation layer 15 are removed from the laser element 10 described above.

  FIG. 4 shows the gain spectrum and the oscillation spectrum for both the conventional and the FP laser elements of this embodiment. Here, (a) and (b) show the gain spectrum 41 and oscillation spectrum 45 of the conventional FP laser element, respectively, and (c) and (d) show the gain spectrum 41 of the FP laser element 10 of the present embodiment. And the oscillation spectrum 46 are shown. In (c), an absorption spectrum 42 of the light absorption layer 14 is also shown.

  As shown in FIG. 4A, the gain spectrum 41 of the FP laser element is asymmetric with respect to 1.3 μm, which is the emission peak wavelength showing the highest gain. This is because the state density shape and the distribution shape of carriers in the active layer 17 are asymmetric with respect to the energy level corresponding to 1.3 μm. Reflecting such a gain spectrum, as shown in FIG. 4B, the envelope of the conventional oscillation spectrum 45 is asymmetric with respect to the emission peak wavelength (the wavelength showing the highest light intensity in the oscillation spectrum). Have a different shape. This envelope shows a relatively high light intensity at a wavelength shorter than the emission peak wavelength. For this reason, the conventional FP laser element has a wide oscillation spectrum width δλ. In the present embodiment, the oscillation spectrum width δλ means the width of the envelope of the oscillation spectrum at an intensity that is 20 dB lower than the maximum intensity of the oscillation spectrum.

  On the other hand, in the FP laser 10 of the present embodiment, the light absorption layer 14 absorbs light having a wavelength shorter than the emission peak wavelength. As shown in FIG. 4C, the light absorption layer 14 has an absorption spectrum 42 in which the amount of absorption greatly increases from the emission peak wavelength of 1.3 μm toward the lower wavelength side. This suppresses stimulated emission at a wavelength shorter than the emission peak wavelength. Since the fundamental absorption edge wavelength of the light absorption layer 14 is shorter than the emission peak wavelength, the light absorption layer 14 hardly suppresses stimulated emission at the emission peak wavelength. As a result, as shown in FIG. 4D, the oscillation spectrum width δλ can be narrowed without reducing the peak light intensity.

  Since the light absorption layer 14 has a shorter band gap energy than the lower cladding layer 13, the light absorption layer 14 does not hinder the injection of electrons from the lower cladding layer 13 to the active layer 17. Thereby, the favorable light emission operation | movement of the semiconductor laser element 10 is securable.

  Since the separation layer 15 has a larger band gap energy than the light absorption layer 14, the separation layer 15 becomes a barrier against the injected electrons. However, if the thickness of the separation layer 15 is suppressed, a sufficient amount of injected electrons for causing laser oscillation passes through the separation layer 15 and reaches the active layer 17. The thickness of the separation layer 15 is preferably 20 nm or less. In this case, electrons can be efficiently injected into the active layer 17 to ensure a good light emitting operation of the semiconductor laser element 10.

  Since the separation layer 15 has a larger band gap energy than the active layer 17, it prevents the injection of holes from the active layer 17 to the light absorption layer 14. When holes are injected into the light absorption layer 14, light emission is likely to occur due to transition of electrons in the conduction band to the holes. This reduces the absorption efficiency of the light absorption layer 14. On the other hand, in this embodiment, since the separation layer 15 prevents the injection of holes into the light absorption layer 14, light emission in the light absorption layer 14 is suppressed, the absorption efficiency is increased, and as a result, the oscillation spectrum width is further increased. It can be narrowed.

Second Embodiment FIG. 5 is an energy band diagram of a semiconductor laser device according to a second embodiment. The second embodiment has a structure in which the lower guide layer 16, the active layer 17, and the upper guide layer 18 in the laser device 10 of the first embodiment are replaced with an active layer 30 having a multiple quantum well structure. In the active layer 30, a plurality of quantum well layers 31 and a plurality of barrier layers 32 are alternately stacked. The barrier layer 32 has a larger band gap energy than the quantum well layer 31.

  The advantages described in the first embodiment can be obtained not only when the active layer is a bulk semiconductor but also when the active layer has a quantum well structure. The fundamental absorption edge wavelength of the light absorption layer 14 is shorter than the emission peak wavelength in the active layer 30. Therefore, since the light intensity in the wavelength region shorter than the emission peak wavelength is reduced by the light absorption layer 14, the oscillation spectrum width can be narrowed without reducing the peak light intensity as in the first embodiment. . Since the separation layer 15 has a band gap energy larger than that of the barrier layer 32, the injection of carriers from the active layer 30 to the light absorption layer 14 is prevented, thereby suppressing light emission of the light absorption layer 14. it can.

Third Embodiment FIG. 6 is an energy band diagram of a semiconductor laser device according to a third embodiment. The third embodiment is different from the second embodiment in that two light absorption layers 14 and two separation layers 15 are provided. Other configurations are the same as those of the second embodiment. By providing a plurality of light absorption layers 14, the light absorption efficiency can be increased and the oscillation spectrum width can be further narrowed.

Fourth Embodiment FIG. 7 is an energy band diagram of a semiconductor laser device according to a fourth embodiment. In the fourth embodiment, a lower SCH (Separated Confinement Heterostructure) layer 28 and an upper SCH layer 29 are provided above and below an active layer 30 having a multiple quantum well structure. The second embodiment is different from the second embodiment in that the second separation layer 15 and the second light absorption layer 14 are laminated thereon. Other configurations are the same as those of the second embodiment. Since the two light absorption layers 14 are disposed above and below the active layer 30, the light absorption efficiency can be increased and the oscillation spectrum width can be further narrowed.

  Since the second light absorption layer 14 has a band gap energy smaller than that of the upper cladding layer 19, the second light absorption layer 14 injects holes from the lower cladding layer 19 into the active layer 17. I do not disturb. Thereby, the favorable light emission operation | movement of the semiconductor laser element 10 is securable.

  Since the second separation layer 15 has a larger band gap energy than the second light absorption layer 14, the second separation layer 15 becomes a barrier against injected holes. However, if the thickness of the second separation layer 15 is suppressed, a sufficient amount of injected holes for causing laser oscillation passes through the second separation layer 15 and reaches the active layer 17. The thickness of the second separation layer 15 is preferably 20 nm or less. In this case, holes can be efficiently injected into the active layer 17 to ensure a good light emitting operation of the semiconductor laser element 10.

  Since the second separation layer 15 has a larger band gap energy than the active layer 17, it prevents the injection of electrons from the active layer 17 to the second light absorption layer 14. When electrons are injected into the second light absorption layer 14, light emission is likely to occur due to transition of the electrons from the conduction band to the valence band. This reduces the absorption efficiency of the second light absorption layer 14. However, in the present embodiment, since the second separation layer 15 prevents the injection of electrons into the second light absorption layer 14, the light emission in the second light absorption layer 14 is suppressed, and the absorption efficiency is increased. As a result, the oscillation spectrum width can be further reduced.

Fifth Embodiment FIG. 8 is an energy band diagram of a semiconductor laser device according to a fifth embodiment. The fifth embodiment is different from the fourth embodiment in that the light absorption layer 14 and the separation layer 15 are provided only on the electron injection side of the active layer 30. Other configurations are the same as those of the fourth embodiment.

  The light absorption layer 14 is disposed in a region where electrons are injected toward the active layer 30. For this reason, in the vicinity of the top of the valence band of the light absorption layer 14, holes are almost eliminated and electrons are likely to exist. Light absorption occurs when electrons in the valence band transition to a vacant level of the conductor. Therefore, electrons are likely to be present near the top of the valence band, so that the absorption efficiency by the light absorption layer 14 is increased. For this reason, even if only the single light absorption layer 14 is provided, the oscillation spectrum width is sufficiently narrowed.

Sixth Embodiment FIG. 9 is an energy band diagram of a semiconductor laser device according to a sixth embodiment. The sixth embodiment is different from the fifth embodiment in that a carrier stop layer 48 is inserted between the upper SCH layer 29 and the upper cladding layer 19. Other configurations are the same as those of the sixth embodiment. The carrier stop layer 48 has a larger band gap energy than each of the upper SCH layer 29 and the upper cladding layer 19. The carrier stop layer 48 can suppress carrier overflow.

Seventh Embodiment Hereinafter, a semiconductor laser device according to a seventh embodiment will be described. The seventh embodiment has a configuration in which the light absorption layer 14 in the first embodiment is not a bulk semiconductor but a quantum well layer. Other configurations are the same as those of the first embodiment.

  In order to make the light absorption layer 14 a quantum well layer, the thickness of the light absorption layer 14 is preferably 20 nm or less. The lower cladding layer 13 and the separation layer 15 sandwich the light absorption layer 14 while being in contact with the light absorption layer 14, and each has a larger band gap energy than the light absorption layer 14. Therefore, the lower cladding layer 13 and the separation layer 15 function as a barrier layer for the light absorption layer 14 that is a quantum well layer. The light absorption layer 14 may be composed of a plurality of quantum well layers.

  FIG. 10 is a diagram showing a gain spectrum, an absorption spectrum, and an oscillation spectrum of the semiconductor laser device according to this embodiment. Here, (a) shows the gain spectrum 41 and the absorption spectrum 43, and (b) shows the oscillation spectrum 47. As shown in (a), the rising of the absorption spectrum 43 is steep due to the quantum effect of the light absorption layer 14. Thereby, stimulated emission at a wavelength lower than the emission peak wavelength can be efficiently suppressed, and the oscillation spectrum width δλ can be further narrowed without reducing the peak light intensity.

Eighth Embodiment Hereinafter, a semiconductor laser device according to an eighth embodiment will be described. The eighth embodiment has a configuration in which the light absorption layer 14 in the first embodiment is a tensile strain layer. Other configurations are the same as those of the first embodiment.

  In order to apply tensile strain to the light absorption layer 14, in this embodiment, the lattice constant of the light absorption layer 14 is smaller than the lattice constants of the substrate 12, the lower cladding layer 13, and the separation layer 15. That is, the optical absorption layer 14 is tensile strained by the substrate 12, the lower cladding layer 13 and the separation layer 15.

  Since the substrate 12 is thicker than the lower clad layer 13 and the separation layer 15, the contribution to applying tensile strain to the light absorption layer 14 is high. Therefore, if the light absorption layer 14 has a lattice constant sufficiently smaller than that of the substrate 12, tensile strain can be applied to the light absorption layer 14 regardless of the lattice constants of the lower cladding layer 13 and the separation layer 15. It is.

  The tensile strain generated in the light absorption layer 14 increases the absorption efficiency of the TM mode light in the vicinity of the fundamental absorption edge wavelength of the light absorption layer 14. Therefore, for the semiconductor laser element in which the short wavelength region of the oscillation spectrum is enhanced by the contribution of the TM mode light, the oscillation spectrum width can be narrowed efficiently by using the light absorption layer 14 having tensile strain.

  Several examples of the semiconductor laser device according to the present invention will be given below.

First Example The first example has the same structure as that of the above-described second embodiment (see FIG. 5) and has a GaInAsP / GaInAsP quantum well having an oscillation wavelength band of 1.25 μm to 1.65 μm. Type semiconductor laser element. In the active layer 30, both the quantum well layer 31 and the barrier layer 32 are made of GaInAsP mixed crystal. The lattice strain of this quantum well layer 31 with respect to InP is a compressive strain of 0 to 1.5%. The substrate 12, the lower cladding layer 13 and the upper cladding layer 19 are made of InP. The light absorption layer 14 and the separation layer 15 are made of GaInAsP mixed crystal.

  The electron-hole transition energy Egw of the quantum well layer 31 is 0.745 eV to 0.99 eV. The energy Egl of the emission peak wavelength is in the vicinity of Egw and satisfies Egl ≧ Egw. The band gap energy Egb of the barrier layer 32 is 0.8 eV to 1.5 eV and satisfies Egb> Egl. The band gap energy Ega of the light absorption layer 14 satisfies Egb> Ega> Egl. The band gap energy Egs of the separation layer 15 satisfies Egs> Ega.

  The number of quantum well layers 31 is 5-15. The quantum well layer 31 has a thickness of 4 nm to 10 nm, and the barrier layer 32 has a thickness of 4 nm to 50 nm. The thickness of the light absorption layer 14 is 4 nm to 100 nm. If the light absorption layer 14 is sufficiently thin, the light absorption layer 14 becomes a quantum well layer.

Second Example The second example has the same structure as that of the above-described second embodiment (see FIG. 5), and has a GaInAsP / AlGaInAs quantum well having an oscillation wavelength band of 1.25 μm to 1.65 μm. Type semiconductor laser element. In the active layer 30, the quantum well layer 31 is made of a GaInAsP mixed crystal, and the barrier layer 32 is made of an AlGaInAs mixed crystal. The lattice strain of the quantum well layer 31 with respect to InP is a compressive strain of 0 to 2%. The substrate 12, the lower cladding layer 13 and the upper cladding layer 19 are made of InP. The light absorption layer 14 is made of a GaInAsP mixed crystal, and the separation layer 15 is made of an AlGaInAs mixed crystal.

  The electron-hole transition energy Egw of the quantum well layer 31 is 0.745 eV to 0.99 eV. The energy Egl of the laser emission peak wavelength is in the vicinity of Egw and satisfies Egl ≧ Egw. The band gap energy Egb of the barrier layer 32 is 0.8 eV to 1.5 eV, and satisfies Egb> Egl. The band gap energy Ega of the light absorption layer 14 satisfies Egb> Ega> Egl. The band gap energy Egs of the separation layer 15 satisfies Egs> Ega.

  The number of quantum well layers 31 is 5-15. The quantum well layer 31 has a thickness of 4 nm to 10 nm, and the barrier layer 32 has a thickness of 4 nm to 50 nm. The thickness of the light absorption layer 14 is 4 nm to 100 nm. If the light absorption layer 14 is sufficiently thin, the light absorption layer 14 becomes a quantum well layer.

Third Example The third example has the same structure as that of the above-described second embodiment (see FIG. 5), and has an oscillation wavelength band of 1.25 μm to 1.65 μm and is an AlGaInAs / AlGaInAs quantum well. Type semiconductor laser element. In the active layer 30, the quantum well layer 31 is made of an AlGaInAs mixed crystal, and the barrier layer 32 is made of an AlGaInAs mixed crystal. The lattice strain of the quantum well layer 31 with respect to InP is a compressive strain of 0 to 2%. The substrate 12, the lower cladding layer 13 and the upper cladding layer 19 are made of InP. The light absorption layer 14 and the separation layer 15 are made of an AlGaInAs mixed crystal.

  The electron-hole transition energy of the quantum well layer 31 is 0.745 eV to 0.99 eV. The energy Egl of the laser emission peak wavelength is in the vicinity of Egw and satisfies Egl ≧ Egw. The band gap energy Egb of the barrier layer 32 is 0.8 eV to 1.5 eV, and satisfies Egb> Egl. The band gap energy Ega of the light absorption layer 14 satisfies Egb> Ega> Egl. The band gap energy Egs of the separation layer 15 satisfies Egs> Ega.

  The number of quantum well layers 31 is 5-15. The quantum well layer 31 has a thickness of 4 nm to 10 nm, and the barrier layer 32 has a thickness of 4 nm to 50 nm. The thickness of the light absorption layer 14 is 4 nm to 100 nm. If the light absorption layer 14 is sufficiently thin, the light absorption layer 14 becomes a quantum well layer.

  The present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

  In the seventh and eighth embodiments, the active layer is made of a bulk semiconductor. However, as in the second to sixth embodiments, the active layer may have a quantum well structure.

It is a schematic sectional drawing which shows a semiconductor laser element. It is an energy band figure of the semiconductor laser element concerning a 1st embodiment. It is an energy band figure of the conventional semiconductor laser element. It is a figure which shows the gain spectrum and oscillation spectrum of the past and 1st Embodiment. It is an energy band figure of the semiconductor laser element concerning a 2nd embodiment. It is an energy band figure of the semiconductor laser element concerning 3rd Embodiment. It is an energy band figure of the semiconductor laser element concerning 4th Embodiment. It is an energy band figure of the semiconductor laser element concerning 5th Embodiment. It is an energy band figure of the semiconductor laser element concerning 6th Embodiment. It is a figure which shows the gain spectrum of 7th Embodiment, an absorption spectrum, and an oscillation spectrum.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor laser element, 12 ... Substrate, 13 ... Lower clad layer, 14 ... Light absorption layer, 15 ... Separation layer, 16 ... Lower guide layer, 17 ... Active layer, 18 ... Upper guide layer, 19 ... Upper clad layer, DESCRIPTION OF SYMBOLS 20 ... Anode, 22 ... Cathode, 26 ... Conduction band, 27 ... Valence band, 28 ... Lower SCH layer, 29 ... Upper SCH layer, 30 ... Active layer, 31 ... Well layer, 32 ... Barrier layer, 41 ... Gain spectrum 42 and 43 ... absorption spectrum, 45-47 ... oscillation spectrum, 48 ... carrier stop layer.

Claims (6)

A Fabry-Perot type semiconductor laser device,
An active layer,
A cladding layer having a lower refractive index than the active layer;
A light absorption layer made of a semiconductor disposed between the active layer and the cladding layer and having a fundamental absorption edge wavelength shorter than an emission peak wavelength in the active layer and a band gap energy smaller than the cladding layer;
A separation layer disposed between the light absorption layer and the active layer and having a larger band gap energy than each of the light absorption layer and the active layer;
A substrate on which the active layer, the clad layer, the light absorption layer and the separation layer are mounted;
A semiconductor laser device comprising: The active layer has a quantum well structure in which quantum well layers and barrier layers having band gap energy larger than the quantum well layers are alternately arranged,
The separation layer has a larger band gap energy than the barrier layer;
The semiconductor laser device according to claim 1.   The semiconductor laser device according to claim 1, wherein the cladding layer is made of an n-type semiconductor.   The semiconductor laser element according to claim 1, wherein the separation layer has a thickness of 20 nm or less. The light absorbing layer is a quantum well layer;
5. The semiconductor laser device according to claim 1, further comprising two barrier layers sandwiching the light absorption layer in contact with the light absorption layer, each having a larger band gap energy than the light absorption layer.   The semiconductor laser device according to claim 1, wherein the light absorption layer has a lattice constant smaller than that of the substrate.

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