JP2011044539A - Semiconductor laser and method for manufacturing the same, optical module, and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser and a method for manufacturing the same that attain a high single-mode yield, to provide an optical module, and to provide an optical transmission system. <P>SOLUTION: The semiconductor laser includes a quantum dot active layer 16 which has a plurality of quantum dots 38 such that a region 40 of high density of quantum dots 38 and a region 42 of low density are periodically repeated, a diffraction grating layer 14 formed above or below the quantum dot active layer 16 and having a diffraction grating 30 formed of periodic unevenness, a lower clad layer 12 of a first conductivity type (n type) formed to sandwich the quantum dot active layer 16 and diffraction grating layer 14 from up/down directions, and an upper clad layer 18 of a second conductivity type (p type) opposite to the first conductivity type. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor laser and a manufacturing method thereof, and an optical module and an optical transmission system including the semiconductor laser, and more particularly, a semiconductor laser having a quantum dot in an active layer, a manufacturing method thereof, and an optical including the semiconductor laser. The present invention relates to a module and an optical transmission system.

  In order to reduce transmission signal degradation due to dispersion of an optical fiber, a semiconductor laser that emits laser light having a single wavelength is required. As such a semiconductor laser, a distributed feedback semiconductor laser (hereinafter referred to as DFB) that realizes a dynamic single mode by using light generated in an active layer and Bragg reflection at a diffraction grating having periodic unevenness. Laser) is known (for example, Patent Documents 1, 2, and 3).

JP 2000-357841 A JP-A-1-231389 JP 2007-299791 A

  The diffraction grating in the DFB laser has a structure in which the refractive index periodically changes in the waveguide direction in which light propagates. In such a structure, the laser light may oscillate at wavelengths on both sides of the stop band due to the influence of the end face reflectance and the like, and the single mode oscillation yield may be reduced.

  For example, in the case of a DFB laser using a quantum well structure, the gain is basically uniform in the waveguide direction. For this reason, the single mode property is realized only by the periodic change of the refractive index by the diffraction grating, and therefore the single mode oscillation yield may be lowered due to the influence of the end face reflectivity and the like.

  It is an object of the present invention to provide a semiconductor laser capable of realizing a high single mode yield, a manufacturing method thereof, an optical module including the semiconductor laser, and an optical transmission system.

  The present invention includes a quantum dot active layer having a plurality of quantum dots, wherein the quantum dots are densely and sparsely periodically repeated, and above or below the quantum dot active layer. A diffraction grating layer having a diffraction grating formed of periodic unevenness, a lower cladding layer having a first conductivity type formed so as to sandwich the quantum dot active layer and the diffraction grating layer from above and below, and And an upper cladding layer having a second conductivity type opposite to the first conductivity type. According to the present invention, a semiconductor laser having a periodic change in refractive index and a periodic change in gain due to a diffraction grating can be obtained, and a high single mode oscillation yield can be realized.

  The said structure WHEREIN: The period of the area | region where the density of the said quantum dot is dense can be set as the structure which is a natural number multiple of the period of the unevenness | corrugation of the said diffraction grating. According to this configuration, a high single mode yield can be obtained.

  The said structure WHEREIN: The said diffraction grating layer can be set as the structure currently formed under the said quantum dot active layer.

  The said structure WHEREIN: The layer immediately under the said quantum dot can be set as the structure which has the unevenness | corrugation corresponding to the periodic unevenness | corrugation of the said diffraction grating. According to this configuration, it is possible to easily obtain a quantum dot active layer in which a quantum dot density region and a sparse region are periodically repeated.

  The said structure WHEREIN: The area | region where the density of the said quantum dot is dense can be set as the structure currently formed above the recessed part and / or convex part of the unevenness | corrugation of the said diffraction grating. According to this configuration, a high single mode yield can be obtained.

  The said structure WHEREIN: The area | region where the density of the said quantum dot is dense can be set as the structure currently formed between the recessed part and the convex part of the unevenness | corrugation of the said diffraction grating. According to this configuration, a high single mode yield can be obtained.

  In the above configuration, the quantum dot active layer includes a plurality of dot layers each including a plurality of quantum dots provided in a horizontal direction and a base layer provided so as to cover the plurality of quantum dots. The at least one dot layer among the plurality of dot layers stacked may be configured such that a dense region and a sparse region of the quantum dots are periodically repeated.

  In the above configuration, the quantum dot active layer includes a plurality of dot layers each including a plurality of quantum dots provided in a horizontal direction and a base layer provided so as to cover the plurality of quantum dots. For all the dot layers that are stacked, a region where the density of the quantum dots is dense and a region where the quantum dots are dense may be periodically repeated. According to this configuration, a higher single mode yield can be realized.

  The present invention includes a step of forming a lower cladding layer having a first conductivity type, a step of forming a diffraction grating layer having a diffraction grating composed of periodic irregularities on the lower cladding layer, and A step of forming a quantum dot active layer having a plurality of quantum dots, wherein the quantum dots have a dense density and a sparse area periodically repeated, and on the quantum dot active layer, And a step of forming an upper cladding layer having a second conductivity type opposite to the first conductivity type. According to the present invention, a semiconductor laser having a periodic change in refractive index and a periodic change in gain due to a diffraction grating can be obtained, and a high single mode yield can be realized.

  In the above-described configuration, the layer immediately below the quantum dots has a step having a structure corresponding to the unevenness of the diffraction grating, and the step of forming the quantum dot active layer includes the step of forming a layer directly below the quantum dots. By using the unevenness, it is possible to form a quantum dot active layer in which a dense region and a sparse region of the quantum dots are periodically repeated. According to this configuration, it is possible to easily form a quantum dot active layer in which a quantum dot density region and a sparse region are periodically repeated.

  In the above-described configuration, the step of forming the quantum dot active layer includes the step of forming the quantum dot active layer so that a dense region of the quantum dots is formed above the concave and / or convex portions of the diffraction grating. It can be set as the structure which is the process of forming a layer. According to this configuration, a high single mode yield can be obtained.

  In the above configuration, the step of forming the quantum dot active layer includes the step of forming the quantum dot active layer so that a dense region of the quantum dots is formed between the concave and convex portions of the diffraction grating. It can be set as the structure which is the process of forming a layer. According to this configuration, a high single mode yield can be obtained.

  The present invention is an optical module including the semiconductor laser. According to the present invention, an optical module capable of realizing a high single mode yield can be obtained.

  The present invention is an optical transmission system including the semiconductor laser. According to the present invention, an optical transmission system capable of realizing a high single-mode yield can be obtained.

  According to the present invention, a semiconductor laser having a periodic change in refractive index and a periodic change in gain due to a diffraction grating can be obtained, and a high single mode yield can be realized.

FIGS. 1A and 1B are schematic cross-sectional views of the quantum dot laser according to the first embodiment. FIG. 2 is a schematic cross-sectional view for explaining the dot layer. FIG. 3A to FIG. 3C are schematic cross-sectional views (part 1) illustrating the method for manufacturing the quantum dot laser according to the first embodiment. FIG. 4A to FIG. 4C are schematic cross-sectional views (part 2) illustrating the method of manufacturing the quantum dot laser according to the first embodiment. FIG. 5 is a schematic cross-sectional view illustrating a case where a dense region of quantum dots is formed above the slope between the concave and convex portions of the diffraction grating. FIG. 6 is a schematic cross-sectional view illustrating a case where a dense region of quantum dot density is formed above the convex portion of the diffraction grating. FIG. 7 is a schematic cross-sectional view of a quantum dot laser according to a modification of the first embodiment. FIG. 8 is a block diagram of an optical module according to the second embodiment. FIG. 9 is a block diagram of an optical transmission system according to the third embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of a quantum dot laser 100 according to the first embodiment. FIG. 1A is a schematic cross-sectional view in the horizontal direction in the laser light emission direction, and FIG. 1B is a schematic cross-sectional view in the direction perpendicular to the laser light emission direction. As shown in FIG. 1A, the quantum dot laser 100 includes a lower cladding layer 12, a diffraction grating layer 14, and quantum dots formed on an n-type Al _0.4 Ga _0.6 As layer on the surface of an n-type GaAs substrate 10. An active layer 16, an upper cladding layer 18 made of a p-type AlGaAs layer, and a contact layer 20 made of a p-type GaAs layer are sequentially stacked.

The diffraction grating layer 14 includes a first layer 26 made of an n-type GaAs layer and a second layer 28 made of an n-type Al _0.2 Ga _0.8 As layer. The second layer 28 may be an InGaP layer. The first layer 26 has a function as a cladding layer, and the second layer 28 has a function as a light guide layer. Between the first layer 26 and the second layer 28, a refractive index modulation type diffraction grating 30 formed of periodic irregularities is formed in the waveguide direction in which the light generated in the quantum dot active layer 16 propagates. Has been. Irregularities 32 corresponding to the periodic irregularities of the diffraction grating 30 are formed on the upper surface of the diffraction grating layer 14 (that is, the upper surface of the second layer 28). That is, the irregularities 32 are also periodically formed.

  The quantum dot active layer 16 includes two dot layers 34. In addition, although FIG. 1 demonstrates the case where the dot layer 34 is laminated | stacked two layers, it is not restricted to the case of two layers, The case where it laminates two or more layers may be sufficient. FIG. 2 is a schematic cross-sectional view for explaining the dot layer 34 in detail. As shown in FIG. 2, the dot layer 34 has a plurality of quantum dots 38 made of InAs in a base layer 36 made of GaAs. That is, the plurality of quantum dots 38 are provided in a horizontal direction on the surface of the substrate 10, and the base layer 36 is provided so as to cover the plurality of quantum dots 38. The base layer 36 directly below the quantum dots 38, in which the quantum dots 38 of the first dot layer 34 (lower dot layer 34) are directly formed, has a thin film thickness. It has unevenness corresponding to 32. The quantum dots 38 are not uniformly formed in the waveguide direction, which is the light propagation direction. As shown in FIG. 1, the quantum dots 38 have a dense region 40 and a sparse region 42 in the waveguide direction. Is repeated periodically. The region 40 where the density of the quantum dots 38 is dense is formed, for example, above the concave portion of the periodic unevenness of the diffraction grating 30, and the region 42 where the density of the quantum dots 38 is sparse is, for example, the periodic region of the diffraction grating 30. It is formed above the concave and convex portions.

  As shown in FIG. 1B, the upper cladding layer 18 and the contact layer 20 have an isolated ridge portion 19. That is, the quantum dot laser 100 has a ridge structure. A p-electrode 22 is formed on the upper surface of the contact layer 20, and an n-electrode 24 is formed on the back surface of the n-type GaAs substrate 10.

Next, a method for manufacturing the quantum dot laser 100 according to the first embodiment will be described with reference to FIGS. FIG. 3A to FIG. 4B are schematic cross-sectional views in the direction parallel to the laser light emission direction, and FIG. 4C is a schematic cross-sectional view in the direction perpendicular to the laser light emission direction. As shown in FIG. 3A, on the surface of the n-type GaAs substrate 10, for example, using the MBE (Molecular Beam Epitaxy) method, the lower cladding layer 12 made of an n-type Al _0.4 Ga _0.6 As layer and Then, the first layer 26 made of an n-type GaAs layer included in the diffraction grating layer 14 is sequentially deposited. Subsequently, the first layer 26 is etched to form a diffraction grating 30 having periodic unevenness. The unevenness of the diffraction grating 30 is, for example, 50 nm.

As shown in FIG. 3B, after the n-type GaAs layer is thinly deposited on the upper surface of the first layer 26 by using, for example, the MBE method, the n-type Al _0.2 Ga contained in the diffraction grating layer 14 is deposited. _A second layer 28 consisting of a _0.8 As layer is deposited. The second layer 28 is grown to a film thickness of, for example, 80 nm at a low growth temperature (for example, about 500 ° C.) at which surface flattening is difficult to occur. In this way, by adjusting the deposition thickness and deposition conditions of the second layer 28, the irregularities 32 corresponding to the periodic irregularities of the diffraction grating 30 are formed on the upper surface of the second layer 28. A second layer 28 is deposited. Accordingly, the diffraction including the refractive index modulation type diffraction grating 30 including the first layer 26 and the second layer 28, and having the periodic unevenness between the first layer 26 and the second layer 28. A lattice layer 14 is formed.

  As shown in FIG. 3C, the dot layer 34 is formed on the upper surface of the diffraction grating layer 14 by using, for example, the MBE method. Specifically, first, for example, by using the MBE method, a GaAs layer serving as the base layer 36 is thinly deposited, and thereafter, quantum dots 38 that are InAs are grown. Since the GaAs layer formed on the upper surface of the diffraction grating layer 14 is thin, it has irregularities corresponding to the irregularities 32 on the upper surface of the diffraction grating layer 14. Then, InAs to be the quantum dots 38 is grown at a growth temperature higher than usual. The growth temperature is preferably, for example, 510 ° C. or higher and 550 ° C. or lower. More specifically, for example, when the normal growth temperature is 500 ° C., the quantum dots 38 are preferably grown at 540 ° C. For example, it is preferable to grow the quantum dots 38 made of InAs at a growth temperature higher than the growth temperature of the lower layer (AlGaAs layer or GaAs layer) of the dot layer 34. By growing the quantum dots 38 at a high growth temperature, As grown above the convex portions of the concavo-convex 32 of the diffraction grating layer 14 is likely to fly under the influence of the high temperature and difficult to be adsorbed. For this reason, the upper part of the projections and depressions 32 of the unevenness 32 becomes a region 42 where the density of quantum dots 38 is sparse, and the upper part of the recesses becomes a region 40 where the density of quantum dots 38 is dense. That is, above the concave and convex portions of the diffraction grating 30 is a region 42 where the density of the quantum dots 38 is sparse, and above the concave portion is a dense region 40.

  Next, a GaAs layer serving as the base layer 36 is deposited so as to cover the quantum dots 38 by, for example, the MBE method. As a result, a first dot layer 34 having a plurality of quantum dots 38 in the base layer 36 is formed. It should be noted that the first layer is formed so that the unevenness corresponding to the unevenness 32 of the diffraction grating layer 14 is formed on the upper surface of the first dot layer 34 by adjusting the deposited film thickness and deposition conditions of the base layer 36. It is preferable to form the dot layer 34 of the eye.

  As shown in FIG. 4A, the dot layer 34 described above is formed a desired number of times, for example, once, to form a second dot layer 34, which includes two dot layers 34. The quantum dot active layer 16 is formed. At this time, since the unevenness is formed on the upper surface of the first dot layer 34, when the quantum dots 38 of the second dot layer 34 are grown at a high growth temperature, In addition, it is possible to form the region 42 in which the density of the quantum dots 38 is sparse and the dense region 40 on the recess. That is, in the second dot layer 34, similarly to the first dot layer 34, the density of quantum dots 38 is high in the upper portion of the concave portion of the diffraction grating 30, and the upper portion of the convex portion is sparse. The region 42 becomes a large area.

  As shown in FIGS. 4B and 4C, the upper cladding layer 18 and the contact layer 20 are deposited on the top surface of the quantum dot active layer 16 by using, for example, the MBE method. Next, the upper cladding layer 18 and the contact layer 20 are etched to form an isolated ridge portion 19. Finally, a p-electrode 22 is formed on the contact layer 20 and an n-electrode 24 is formed on the lower surface of the substrate 10. Thereby, the quantum dot laser 100 according to FIG. 1 is completed.

  As described above, according to the quantum dot laser 100 according to the first embodiment, as shown in FIG. 1, the diffraction grating layer 14 having the diffraction grating 30 composed of periodic unevenness has a dense quantum dot 38 density. A region 40 and a sparse region 42 are formed below the quantum dot active layer 16 that is periodically repeated. In the vertical direction of the diffraction grating layer 14 and the quantum dot active layer 16 (direction perpendicular to the surface of the substrate 10), the lower cladding layer 12 and the upper cladding so as to sandwich the diffraction grating layer 14 and the quantum dot active layer 16 therebetween. Layer 18 is formed. The periodic unevenness of the diffraction grating 30 is formed in the waveguide direction, and the periodic change between the dense region 40 and the sparse region 42 of the quantum dots 38 is also formed in the waveguide direction.

  The region 40 where the density of the quantum dots 38 is dense has a higher gain than the sparse region 42. That is, the quantum dot laser 100 according to the first embodiment has a gain distribution in the waveguide direction. That is, it is possible to obtain a gain that periodically changes in the waveguide direction. Therefore, according to the quantum dot laser 100 according to the first embodiment, a dynamic single mode can be realized by both the periodic change of the refractive index by the diffraction grating 30 and the periodic change of the gain. Single mode yield can be obtained. For example, even when the quantum dot laser 100 is operated with a wide temperature range or high modulation, dynamic single mode characteristics can be realized, and single mode yield can be improved.

  As shown in FIG. 1, the region 40 in which the quantum dots 38 are dense is formed above the concave and convex portions of the diffraction grating 30 (that is, above the concave and convex portion 32 on the upper surface of the diffraction grating layer 14), and the sparse region 42 is the diffraction grating 30. The case where it is formed above the uneven | corrugated convex part of is preferable. That is, it is preferable that the period between the dense region 40 and the sparse region 42 of the quantum dots 38 is the same period (one period) as the unevenness period of the diffraction grating 30. As described above, when the period between the dense region 40 and the sparse region 42 of the quantum dots 38 is a natural number times the period of the unevenness of the diffraction grating 30, the refractive index is periodically changed by the diffraction grating 30. In addition, the dynamic single mode can be realized by both the periodic change of the gain, and a high single mode yield can be obtained.

  Therefore, for example, as shown in FIG. 5, the region 40 in which the density of the quantum dots 38 is dense is formed above the slope between the concave and convex portions of the diffraction grating 30 (that is, the concave portion of the concave and convex portion 32 of the diffraction grating layer 14). It may be formed on the upper surface of the slope between the projection and the projection. In this case, the period between the dense region 40 and the sparse region 42 of the quantum dots 38 is twice the period of the unevenness of the diffraction grating 30. Even in this case, a high single mode yield can be obtained.

As shown in FIG. 5, in order to form the region 40 in which the density of the quantum dots 38 is dense above the slope between the concave and convex portions of the diffraction grating 30, the InAs serving as the quantum dots 38 is made to be larger than usual. Grow at high As pressure. For example, the As pressure is preferably 8 × 10 ⁻⁶ Torr or more. More specifically, for example, when the normal As pressure is 5 × 10 ⁻⁶ Torr, it is preferable to grow the quantum dots 38 at 1 × 10 ⁻⁵ Torr which is about twice the As pressure. The quantum dots 38 are formed on the upper surface of the base layer 36 as shown in FIG. Since the base layer 36 on which the quantum dots 38 of the first dot layer 34 are directly formed is thin, the base layer 36 has irregularities corresponding to the irregularities 32 formed on the upper surface of the diffraction grating layer 14. That is, the base layer 36 immediately below the quantum dots 38 has a structure having unevenness corresponding to the periodic unevenness of the diffraction grating 30. Steps (stepped shape) are formed on the slope between the irregularities, and the step becomes smaller as the angle of the slope becomes steeper. When the As pressure is increased and the quantum dots 38 are grown, As is easily adsorbed on the step portion of the slope of the base layer 36, the density of the quantum dots 38 becomes dense in the portion where the slope angle is steep. Therefore, a region 40 in which the density of the quantum dots 38 is dense is formed above the slope between the concave and convex portions of the diffraction grating 30. Further, the plane orientation of GaAs that is the base layer 36 in the direction perpendicular to the slope between the irregularities is, for example, the (411) plane. Since whether quantum dots 38 are easily formed or difficult to form depends on the plane orientation, from the viewpoint that the quantum dots 38 are easily formed, a preferable surface of GaAs that is the base layer 36 in the direction perpendicular to the slope between the irregularities The azimuth other than the above is, for example, the (511) plane.

  Further, for example, as shown in FIG. 6, when the region 40 in which the density of the quantum dots 38 is dense is formed above the concavo-convex portion of the diffraction grating 30 (that is, above the concavo-convex portion 32 of the diffraction grating layer 14). But you can. In this case, the period between the dense region 40 and the sparse region 42 of the quantum dots 38 is the same as the period of the unevenness of the diffraction grating 30 (one time period). Even in this case, a high single mode yield can be obtained. Further, for example, when the region 40 where the density of the quantum dots 38 is dense is on both the upper and lower concave portions of the diffraction grating 30, or all of the slopes between the concave and convex portions and the convex and concave portions. High single mode yields can be obtained even when above.

  According to the manufacturing method of the quantum dot laser 100 according to the first embodiment, the diffraction grating layer 14 having the diffraction grating 30 composed of periodic irregularities is formed on the lower cladding layer 12 as shown in FIG. Then, as shown in FIGS. 3C and 4A, a plurality of quantum dots 38 are provided on the diffraction grating layer 14, and a region 40 in which the density of the quantum dots 38 is dense and a region 42 in which the quantum dots 38 are sparse are formed. A periodically repeated quantum dot active layer 16 is formed. Thereby, the quantum dot laser 100 which has both the periodic change of the refractive index by the diffraction grating 30 and the periodic change of a gain can be obtained. That is, the quantum dot laser 100 that can realize a high single mode yield can be obtained.

  Further, as shown in FIG. 3B, the diffraction grating layer 14 is formed so that the irregularities 32 corresponding to the periodic irregularities of the diffraction grating 30 are formed on the upper surface. Then, as shown in FIG. 3C, after depositing a thin GaAs layer having irregularities corresponding to the irregularities 32, the growth temperature is raised and InAs is grown, so A region 40 in which the density of the quantum dots 38 is dense is formed above the concave and convex portions of the diffraction grating 30. In this manner, the layer immediately below the quantum dots 38 (in the first embodiment, the base layer 36 made of a GaAs layer) has a structure having unevenness corresponding to the periodic unevenness of the diffraction grating 30, and the layer immediately below the quantum dots 38. It is preferable to form the quantum dot active layer 16 in which the dense regions 40 and the sparse regions 42 of the quantum dots 38 are periodically repeated by using the unevenness. Thereby, the structure where the density 40 of the quantum dots 38 and the sparse area 42 change in the same period as the period of the unevenness of the diffraction grating 30 can be easily formed without increasing the number of manufacturing steps. be able to.

  It is preferable that the unevenness of the layer immediately below the quantum dots 38 has a maximum angle of 4 degrees or more with respect to the horizontal direction of the surface of the substrate 10. Thereby, the growth temperature or the As pressure is increased, and the quantum dots 38 made of InAs are grown, so that the quantum dots 38 are formed above the concave and convex portions of the diffraction grating 30 and above the inclined surface between the concave and convex portions. The region 40 having a high density can be easily formed.

  FIG. 7 is a schematic cross-sectional view in the horizontal direction of the laser beam emission direction of the quantum dot laser 110 according to a modification of the first embodiment. As shown in FIG. 7, in the quantum dot laser 110 according to the modification of the first embodiment, the diffraction grating layer 14 is formed on the upper side of the quantum dot active layer 16, and the concave and convex period of the diffraction grating 30 and the quantum dots 38. The period of the dense area 40 and the sparse area 42 is the same period (1 time period). As described above, even when the diffraction grating layer 14 is formed on the upper side of the quantum dot active layer 16, the dynamic simple due to both the periodic change of the refractive index due to the diffraction grating 30 and the periodic change of the gain. Since one mode can be realized, a high single mode yield can be obtained.

  In the first embodiment, the case where the quantum dots 38 are made of InAs has been described as an example. As described with reference to FIG. 3C and FIG. 5, by growing the quantum dots 38 by increasing the growth temperature and As pressure in the MBE method, As is difficult to adsorb or is easily adsorbed to a specific place. Utilizing this property, a structure is formed in which the dense region 40 and the sparse region 42 of the quantum dots 38 are periodically repeated. Therefore, from such a viewpoint, the quantum dot 38 is preferably a semiconductor layer containing As (for example, a group III-V compound semiconductor layer containing As) such as InAs or InGaAs.

  In the first embodiment, the first layer 26 is an n-type GaAs layer and the second layer 28 is an n-type AlGaAs layer. However, the first layer 26 is an n-type AlGaAs layer or an InGaP layer. The second layer 28 may be an n-type GaAs layer. That is, it is sufficient if there is a difference in refractive index between the first layer 26 and the second layer 28, even if the refractive index of the first layer 26 is lower than the refractive index of the second layer 28. It can be expensive. However, as described in FIGS. 3A and 3B, the first layer 26 is etched to form the diffraction grating 30, and then the second layer 28 is deposited. When 26 is an AlGaAs layer, the surface may be oxidized. Therefore, it is preferable from the viewpoint of manufacturing that the first layer 26 is a GaAs layer and the second layer 28 is an AlGaAs layer.

  In Example 1, as shown in FIG. 1, the quantum dot active layer 16 has two dot layers 34 stacked, and the two stacked dot layers 34 are regions where the density of quantum dots 38 is dense. The case where 40 and the sparse area | region 42 are repeated periodically was demonstrated. As described above, for all the dot layers 34 that are stacked, a higher single-mode oscillation yield is realized in the structure in which the dense regions 40 and the sparse regions 42 of the quantum dots 38 are periodically repeated. can do. In order to form all the dot layers 34 that are stacked in such a manner that the dense regions 40 and the sparse regions 42 of the quantum dots 38 are periodically repeated, as described in FIG. It is preferable to form irregularities on the upper surface of the lower dot layer 34.

  Further, for at least one dot layer 34 among the plurality of stacked dot layers 34, if the quantum dot 38 has a dense region 40 and a sparse region 42 that are periodically repeated, Single mode oscillation yield can be improved.

  In the first embodiment, the first conductivity type is n-type and the second conductivity type is p-type. However, the first conductivity type may be p-type and the second conductivity type may be n-type.

  Example 2 is an example of an optical module including the quantum dot laser 100 according to Example 1. FIG. FIG. 8 is a block diagram of an optical module 200 according to the second embodiment. As illustrated in FIG. 8, the optical module 200 includes the quantum dot laser 100 according to the first embodiment, a housing 120, and a lens 122. A quantum dot laser 100, a lens 122, and a single mode fiber 124 are fixed to the housing 120. Laser light 126 emitted from the quantum dot laser 100 is optically coupled to the tip of the single mode fiber 124 by a lens 122. As a result, the laser light 126 emitted from the quantum dot laser 100 is incident on the single mode fiber 124 and transmitted through the single mode fiber 124.

  Since the optical module 200 according to the second embodiment uses the quantum dot laser 100 according to the first embodiment, a dynamic single mode is realized by both a periodic change in refractive index and a periodic change in gain. Thus, an optical module capable of obtaining a high single mode yield can be obtained.

  Note that the optical module 200 according to the second embodiment has been illustrated with the quantum dot laser 100 according to the first embodiment as an example, but includes the quantum dot laser 110 according to the first modification of the first embodiment. It may be the case. Even in this case, an optical module capable of obtaining a high single mode yield can be obtained.

  The third embodiment is an example of an optical transmission system including the optical module 200 according to the second embodiment. FIG. 9 is a block diagram of an optical transmission system 300 according to the third embodiment. As illustrated in FIG. 9, the optical transmission system 300 according to the third embodiment includes a first device 210 and a second device 220. Each of the first device 210 and the second device 220 includes the optical module 200 according to the second embodiment that functions as a transmission unit, reception units 212 and 222, and control units 214 and 224. The optical module 200 converts transmission data signals from the control units 214 and 224 into light and emits laser light. The emitted laser light is incident on the single mode fiber 230. The receiving units 212 and 222 receive the laser beam transmitted through the single mode fiber 230 and output it to the control units 214 and 224 as reception data signals. Thereby, data communication can be performed between the first device 210 and the second device 220.

  According to the optical transmission system 300 according to the third embodiment, by using the optical module 200 according to the second embodiment (that is, using the quantum dot laser 100 according to the first embodiment), a high single mode yield is achieved. An optical transmission system that can be realized can be obtained.

  As shown in FIG. 9, an optical transmission system 300 that performs data communication using a single mode fiber 230 between a first device 210 and a second device 220 includes an FTTH (Fiber To The Home) and an optical communication backbone network. The case where it is used for is preferable. Alternatively, the first device 210 and the second device 220 may perform data communication by receiving laser light emitted into the space without using the single mode fiber 230. In this case, the first device 210 and the second device 220 may be personal computers, for example, and one of the first device 210 and the second device 220 is a personal computer and the other is a mobile phone. Further, it may be an electronic device such as a digital camera or a video camera, or a projector.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to such specific embodiments, and various modifications can be made within the scope of the gist of the present invention described in the claims.・ Change is possible.

DESCRIPTION OF SYMBOLS 10 Substrate 12 Lower clad layer 14 Diffraction grating layer 16 Quantum dot active layer 18 Upper clad layer 19 Ridge part 20 Contact layer 22 P electrode 24 N electrode 26 First layer 28 Second layer 30 Diffraction grating 32 Concavity and convexity 34 Dot layer 36 Base layer 38 Quantum dot 40 Dense region 42 Sparse region 100 Quantum dot laser 110 Quantum dot laser 120 Case 122 Lens 124 Single mode fiber 126 Laser light 200 Optical module 212 Receiving unit 214 Control unit 222 Receiving unit 224 Control unit 230 Single Mode fiber 300 optical transmission system

Claims (14)

A quantum dot active layer having a plurality of quantum dots, wherein the quantum dots have a dense region and a sparse region periodically repeated;
A diffraction grating layer formed on the upper or lower side of the quantum dot active layer and having a diffraction grating composed of periodic irregularities;
A lower cladding layer having a first conductivity type formed so as to sandwich the quantum dot active layer and the diffraction grating layer from above and below, and an upper cladding having a second conductivity type opposite to the first conductivity type Layers,
A semiconductor laser comprising:   2. The semiconductor laser according to claim 1, wherein a period between the dense region and the sparse region of the quantum dots is a natural number times the period of the irregularities of the diffraction grating.   3. The semiconductor laser according to claim 1, wherein the diffraction grating layer is formed below the quantum dot active layer.   4. The semiconductor laser according to claim 3, wherein the layer immediately below the quantum dots has irregularities corresponding to the periodic irregularities of the diffraction grating.   5. The semiconductor laser according to claim 4, wherein the dense region of the quantum dots is formed above the concave and / or convex portions of the concave and convex portions of the diffraction grating.   5. The semiconductor laser according to claim 4, wherein the dense region of the quantum dots is formed between the concave and convex portions of the diffraction grating.   The quantum dot active layer includes a plurality of dot layers each including a plurality of quantum dots provided in a horizontal direction and a base layer provided so as to cover the plurality of quantum dots. In addition, for at least one dot layer among the dot layers, a dense region and a sparse region of the quantum dots are periodically repeated. The semiconductor laser described in the item.   The quantum dot active layer includes a plurality of dot layers each including a plurality of quantum dots provided in a horizontal direction and a base layer provided so as to cover the plurality of quantum dots. 7. The semiconductor laser according to claim 1, wherein, for all of the dot layers, a dense region and a sparse region of the quantum dots are periodically repeated. Forming a lower cladding layer having a first conductivity type;
Forming a diffraction grating layer having a diffraction grating composed of periodic irregularities on the lower cladding layer;
Forming a quantum dot active layer having a plurality of quantum dots on the diffraction grating layer, the quantum dots having a dense density and a sparse area periodically repeated;
Forming an upper clad layer having a second conductivity type opposite to the first conductivity type on the quantum dot active layer;
A method of manufacturing a semiconductor laser, comprising: The layer directly under the quantum dots has a step having a structure corresponding to the unevenness of the diffraction grating;
In the step of forming the quantum dot active layer, a quantum dot active layer in which a dense region and a sparse region of the quantum dot are periodically repeated is formed using the unevenness of the layer immediately below the quantum dot. 10. The method of manufacturing a semiconductor laser according to claim 9, wherein the semiconductor laser is formed.   In the step of forming the quantum dot active layer, the quantum dot active layer is formed such that a dense region of the quantum dots is formed above the concave and / or convex portions of the diffraction grating. The method of manufacturing a semiconductor laser according to claim 10, wherein the method is a process.   In the step of forming the quantum dot active layer, the quantum dot active layer is formed so that a dense region of the quantum dots is formed between the concave and convex portions of the diffraction grating. The method of manufacturing a semiconductor laser according to claim 10, wherein the method is a process.   An optical module comprising the semiconductor laser according to claim 1.   An optical transmission system comprising the semiconductor laser according to claim 1.

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