WO2011021458A1 - Semiconductor laser, method for manufacturing same, optical module, and optical transmission system - Google Patents

Semiconductor laser, method for manufacturing same, optical module, and optical transmission system Download PDF

Info

Publication number
WO2011021458A1
WO2011021458A1 PCT/JP2010/062078 JP2010062078W WO2011021458A1 WO 2011021458 A1 WO2011021458 A1 WO 2011021458A1 JP 2010062078 W JP2010062078 W JP 2010062078W WO 2011021458 A1 WO2011021458 A1 WO 2011021458A1
Authority
WO
WIPO (PCT)
Prior art keywords
layer
diffraction grating
quantum dots
semiconductor laser
quantum dot
Prior art date
Application number
PCT/JP2010/062078
Other languages
French (fr)
Japanese (ja)
Inventor
西研一
近藤勇人
田中有
Original Assignee
株式会社Ｑｄレーザ
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社Ｑｄレーザ filed Critical 株式会社Ｑｄレーザ
Publication of WO2011021458A1 publication Critical patent/WO2011021458A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • H01S5/1231—Grating growth or overgrowth details
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/341—Structures having reduced dimensionality, e.g. quantum wires
    • H01S5/3412—Structures having reduced dimensionality, e.g. quantum wires quantum box or quantum dash

Definitions

  • 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.
  • a semiconductor laser that emits a laser beam having a single wavelength is required.
  • a distributed feedback semiconductor laser hereinafter referred to as DFB
  • DFB distributed feedback semiconductor laser
  • 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.
  • 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.
  • the gain is basically uniform in the waveguide direction.
  • 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.
  • 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 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 diffraction grating layer may be formed below the quantum dot active layer.
  • the layer immediately below the quantum dot may have a configuration corresponding to the periodic configuration of the 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 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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. 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
  • 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.
  • 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
  • FIG. 1B is a schematic cross-sectional view in the direction perpendicular to the laser light emission direction.
  • 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.
  • 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.
  • FIG. 1 demonstrates the case where the dot layer 34 is laminated
  • FIG. 2 is a schematic cross-sectional view for explaining the dot layer 34 in detail.
  • 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.
  • 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.
  • FIG. 3A to FIG. 4B are schematic cross-sectional views in the direction parallel to the laser light emission direction
  • FIG. 4C is a schematic cross-sectional view in the direction perpendicular to the laser light emission direction.
  • the lower cladding layer 12 made of an n-type Al 0.4 Ga 0.6 As layer
  • the first layer 26 made of an n-type GaAs layer included in the diffraction grating layer 14 is sequentially deposited.
  • 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.
  • 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 thickness of, for example, 80 nm at a low growth temperature (for example, about 500 ° C.) at which surface flattening is difficult to occur.
  • 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.
  • 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.
  • the quantum dots 38 are preferably grown at 540 ° C.
  • the quantum dots 38 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.
  • 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.
  • 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.
  • a first dot layer 34 having a plurality of quantum dots 38 in the base layer 36 is formed.
  • 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.
  • 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.
  • the region 42 in which the density of the quantum dots 38 is sparse and the dense region 40 on the recess 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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).
  • 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.
  • the quantum dots 38 are made of InAs.
  • the quantum dots 38 are preferably a semiconductor layer containing As (for example, a group III-V compound semiconductor layer containing As) such as InAs or InGaAs.
  • the first layer 26 is an n-type GaAs layer and the second layer 28 is an n-type AlGaAs layer.
  • 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.
  • the first layer 26 is etched to form the diffraction grating 30, and then the second layer 28 is deposited.
  • 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.
  • 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.
  • region 42 are repeated periodically was demonstrated.
  • 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.
  • 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.
  • the first conductivity type is n-type and the second conductivity type is p-type.
  • 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. 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.
  • 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.
  • 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.

Landscapes

  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Nanotechnology (AREA)
  • Chemical & Material Sciences (AREA)
  • Biophysics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Semiconductor Lasers (AREA)
  • Optical Couplings Of Light Guides (AREA)

Abstract

Disclosed is a semiconductor laser provided with a quantum dot active layer (16) which comprises a plurality of quantum dots (38) and in which a region (40) with a high density of quantum dots (38)and a region (42) with a low density thereof are periodically repeated, a diffraction grating layer (14) which is formed on the upper side or lower side of the quantum dot active layer (16) and comprises a diffraction grating (30) consisting of periodic projections and depressions, a lower cladding layer (12) having a first conductivity type (n type), and an upper cladding layer (18) having a second conductivity type (p type) that is a conductivity type reverse to the first conductivity type, the lower cladding layer and the upper classing layer being formed so as to sandwich the quantum dot active layer (16) and the diffraction grating layer (14) therebetween in a vertical direction.

Description

半導体レーザ及びその製造方法、光モジュール、光伝送システムSemiconductor laser and method for manufacturing the same, optical module, and optical transmission system
　本発明は、半導体レーザ及びその製造方法、並びに、その半導体レーザを含む光モジュール及び光伝送システムに関し、特に、量子ドットを活性層に有する半導体レーザ及びその製造方法、並びに、その半導体レーザを含む光モジュール及び光伝送システムに関する。 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.
　光ファイバの分散による伝送信号劣化を低減するため、単一波長のレーザ光が出射される半導体レーザが求められている。このような半導体レーザとして、活性層で生成された光を、周期的な凹凸からなる回折格子でのブラッグ反射を利用して、動的単一モードを実現する分布帰還型半導体レーザ（以下、ＤＦＢレーザ）が知られている（例えば、特許文献１、２及び３）。 In order to reduce transmission signal deterioration due to dispersion of optical fibers, a semiconductor laser that emits a laser beam 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).
特開２０００－３５７８４１号公報JP 2000-357841 A 特開平１－２３１３８９号公報JP-A-1-231389 特開２００７－２９９７９１号公報JP 2007-299791 A
　ＤＦＢレーザにおける回折格子は、光が伝搬される導波方向で周期的に屈折率が変化した構造を有している。このような構造の場合、端面反射率等の影響により、ストップバンド両側の波長でレーザ光が発振する可能性があり、シングルモード発振歩留まりが低下してしまう場合がある。 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.
　例えば、量子井戸構造を用いたＤＦＢレーザの場合では、利得は導波方向に基本的に均一である。このため、シングルモード性は、回折格子による屈折率の周期的変化だけで実現されるため、端面反射率等の影響により、シングルモード発振歩留まりが低下してしまう場合がある。 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.
　本発明は、高いシングルモード歩留まりを実現することが可能な半導体レーザ及びその製造方法並びにその半導体レーザを含む光モジュール及び光伝送システムを提供することを目的とする。 It is an object of the present invention to provide a semiconductor laser capable of realizing a high single mode yield, a method for manufacturing the same, an optical module including the semiconductor laser, and an optical transmission system.
　本発明は、複数の量子ドットを有し、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層と、前記量子ドット活性層の上側又は下側に形成され、周期的な凹凸からなる回折格子を有する回折格子層と、前記量子ドット活性層と前記回折格子層とを上下方向から挟み込むように形成された第１導電型を有する下部クラッド層と前記第１導電型と反対の導電型の第２導電型を有する上部クラッド層と、を具備することを特徴とする半導体レーザである。本発明によれば、回折格子による屈折率の周期的変化と、利得の周期的変化と、を有する半導体レーザを得ることができ、高いシングルモード発振歩留まりを実現することができる。 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.
　上記構成において、前記量子ドットの密度が密な領域と疎な領域との周期は、前記回折格子の凹凸の周期の自然数倍である構成とすることができる。この構成によれば、高いシングルモード歩留まりを得ることができる。 In the above configuration, the period between the dense region and the sparse region of the quantum dots may be a natural number times the period of the unevenness of the diffraction grating. According to this configuration, a high single mode yield can be obtained.
　上記構成において、前記回折格子層は、前記量子ドット活性層の下側に形成されている構成とすることができる。 In the above configuration, the diffraction grating layer may be formed below the quantum dot active layer.
　上記構成において、前記量子ドットの直下の層は、前記回折格子の周期的な凹凸に対応した凹凸を有している構成とすることができる。この構成によれば、量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層を容易に得ることができる。 In the above configuration, the layer immediately below the quantum dot may have a configuration corresponding to the periodic configuration of the 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.
　上記構成において、前記量子ドットの密度が密な領域は、前記回折格子の凹凸の凹部上方及び／又は凸部上方に形成されている構成とすることができる。この構成によれば、高いシングルモード歩留まりを得ることができる。 In the above configuration, the dense region of the quantum dots can be formed above the concave and / or convex portions of the diffraction grating. According to this configuration, a high single mode yield can be obtained.
　上記構成において、前記量子ドットの密度が密な領域は、前記回折格子の凹凸の凹部と凸部との間の上方に形成されている構成とすることができる。この構成によれば、高いシングルモード歩留まりを得ることができる。 In the above configuration, the dense region of the quantum dots may be formed above the concave and convex portions of the diffraction grating. According to this configuration, a high single mode yield can be obtained.
　上記構成において、前記量子ドット活性層は、水平方向に設けられた前記複数の量子ドットと前記複数の量子ドットを覆うように設けられたベース層とで構成されるドット層が複数積層されていて、複数積層された前記ドット層のうち少なくとも１層のドット層について、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返されている構成とすることができる。 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.
　上記構成において、前記量子ドット活性層は、水平方向に設けられた前記複数の量子ドットと前記複数の量子ドットを覆うように設けられたベース層とで構成されるドット層が複数積層されていて、複数積層された全ての前記ドット層について、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返されている構成とすることができる。この構成によれば、より高いシングルモード歩留まりを実現することができる。 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.
　本発明は、第１導電型を有する下部クラッド層を形成する工程と、前記下部クラッド層上に、周期的な凹凸からなる回折格子を有する回折格子層を形成する工程と、前記回折格子層上に、複数の量子ドットを有し、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層を形成する工程と、前記量子ドット活性層上に、前記第１導電型と反対の導電型の第２導電型を有する上部クラッド層を形成する工程と、を有することを特徴とする半導体レーザの製造方法である。本発明によれば、回折格子による屈折率の周期的変化と、利得の周期的変化と、を有する半導体レーザを得ることができ、高いシングルモード歩留まりを実現することができる。 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.
　上記構成において、前記量子ドットの直下の層を、前記回折格子の凹凸に対応した凹凸を有する構造とする工程を有し、前記量子ドット活性層を形成する工程は、前記量子ドット直下の層の凹凸を利用して、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層を形成する構成とすることができる。この構成によれば、量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層を容易に形成することができる。 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.
　上記構成において、前記量子ドット活性層を形成する工程は、前記量子ドットの密度が密な領域が前記回折格子の凹凸の凹部上方及び／又は凸部上方に形成されるように、前記量子ドット活性層を形成する工程である構成とすることができる。この構成によれば、高いシングルモード歩留まりを得ることができる。 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.
　上記構成において、前記量子ドット活性層を形成する工程は、前記量子ドットの密度が密な領域が前記回折格子の凹凸の凹部と凸部と間の上方に形成されるように、前記量子ドット活性層を形成する工程である構成とすることができる。この構成によれば、高いシングルモード歩留まりを得ることができる。 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.
　本発明は、上記半導体レーザを含むことを特徴とする光モジュールである。本発明によれば、高いシングルモード歩留まりを実現できる光モジュールを得ることができる。 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.
　本発明は、上記半導体レーザを含むことを特徴とする光伝送システムである。本発明によれば、高いシングルモード歩留まりの実現が可能な光伝送システムを得ることができる。 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.
　本発明によれば、回折格子による屈折率の周期的変化と、利得の周期的変化と、を有する半導体レーザを得ることができ、高いシングルモード歩留まりを実現することができる。 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.
図１（ａ）及び図１（ｂ）は、実施例１に係る量子ドットレーザの断面模式図である。FIGS. 1A and 1B are schematic cross-sectional views of the quantum dot laser according to the first embodiment. 図２は、ドット層を説明するための断面模式図である。FIG. 2 is a schematic cross-sectional view for explaining the dot layer. 図３（ａ）から図３（ｃ）は、実施例１に係る量子ドットレーザの製造方法を示した断面模式図（その１）である。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. 図４（ａ）から図４（ｃ）は、実施例１に係る量子ドットレーザの製造方法を示した断面模式図（その２）である。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. 図５は、量子ドット密度の密な領域が回折格子の凹部と凸部との間の斜面上方に形成されている場合を説明する断面模式図である。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. 図６は、量子ドット密度の密な領域が回折格子の凸部上方に形成されている場合を説明する断面模式図である。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. 図７は、実施例１の変形例に係る量子ドットレーザの断面模式図である。FIG. 7 is a schematic cross-sectional view of a quantum dot laser according to a modification of the first embodiment. 図８は、実施例２に係る光モジュールのブロック図である。FIG. 8 is a block diagram of an optical module according to the second embodiment. 図９は、実施例３に係る光伝送システムのブロック図である。FIG. 9 is a block diagram of an optical transmission system according to the third embodiment.
　以下、図面を参照して、本発明の実施例を説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
　図１は、実施例１に係る量子ドットレーザ１００の断面模式図である。図１（ａ）は、レーザ光の出射方向に水平方向の断面模式図であり、図１（ｂ）は、レーザ光の出射方向に垂直方向の断面模式図である。図１（ａ）のように、量子ドットレーザ１００は、ｎ型ＧａＡｓ基板１０表面上に、ｎ型Ａｌ０．４Ｇａ０．６Ａｓ層からなる下部クラッド層１２、回折格子層１４、量子ドット活性層１６、ｐ型ＡｌＧａＡｓ層からなる上部クラッド層１８、及びｐ型ＧａＡｓ層からなるコンタクト層２０が順次積層されている。 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.
　回折格子層１４は、ｎ型ＧａＡｓ層からなる第１の層２６とｎ型Ａｌ０．２Ｇａ０．８Ａｓ層からなる第２の層２８とを含む。なお、第２の層２８は、ＩｎＧａＰ層である場合でもよい。第１の層２６はクラッド層としての機能を有し、第２の層２８は光ガイド層としての機能を有する。第１の層２６と第２の層２８との間に、量子ドット活性層１６で生成された光が伝搬する導波方向に、周期的な凹凸からなる屈折率変調型の回折格子３０が形成されている。回折格子層１４の上面（即ち、第２の層２８の上面）には、回折格子３０の周期的な凹凸に対応した凹凸３２が形成されている。つまり、凹凸３２も周期的に形成されている。 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.
　量子ドット活性層１６は、２層のドット層３４を含む。なお、図１では、ドット層３４が２層積層されている場合について説明するが、２層の場合に限らず、複数層積層されている場合でもよい。図２は、ドット層３４について詳しく説明するための断面模式図である。図２のように、ドット層３４は、ＧａＡｓからなるベース層３６内にＩｎＡｓからなる複数の量子ドット３８を有する。即ち、複数の量子ドット３８は、基板１０表面に水平な方向に設けられていて、ベース層３６は複数の量子ドット３８を覆うように設けられている。第１層目のドット層３４（下側のドット層３４）の量子ドット３８が直接形成されている、量子ドット３８直下のベース層３６は、膜厚が薄いため、回折格子層１４上面の凹凸３２に対応した凹凸を有している。量子ドット３８は、光の伝搬方向である導波方向に一様に形成されてなく、図１のように、量子ドット３８の密度が密な領域４０と疎な領域４２とが、導波方向で周期的に繰り返されている。量子ドット３８の密度が密な領域４０は、例えば、回折格子３０の周期的な凹凸の凹部上方に形成され、量子ドット３８の密度が疎な領域４２は、例えば、回折格子３０の周期的な凹凸の凸部上方に形成されている。 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.
　図１（ｂ）のように、上部クラッド層１８とコンタクト層２０は孤立したリッジ部１９を有する。つまり、量子ドットレーザ１００は、リッジ構造を有している。コンタクト層２０上面にはｐ電極２２が形成され、ｎ型ＧａＡｓ基板１０裏面にはｎ電極２４が形成されている。 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.
　次に、図３（ａ）から図４（ｃ）を用い、実施例１に係る量子ドットレーザ１００の製造方法を説明する。図３（ａ）から図４（ｂ）は、レーザ光の出射方向に平行方向の断面模式図であり、図４（ｃ）は、レーザ光の出射方向に垂直方向の断面模式図である。図３（ａ）のように、ｎ型ＧａＡｓ基板１０の表面上に、例えば、ＭＢＥ（Molecular Beam Epitaxy）法を用い、ｎ型Ａｌ０．４Ｇａ０．６Ａｓ層からなる下部クラッド層１２と、回折格子層１４に含まれるｎ型ＧａＡｓ層からなる第１の層２６とを順次堆積する。続いて、第１の層２６をエッチングして、周期的な凹凸からなる回折格子３０を形成する。回折格子３０の凹凸は、例えば５０ｎｍである。 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.
　図３（ｂ）のように、第１の層２６の上面に、例えば、ＭＢＥ法を用いて、ｎ型ＧａＡｓ層を薄く堆積した後、回折格子層１４に含まれるｎ型Ａｌ０．２Ｇａ０．８Ａｓ層からなる第２の層２８を堆積する。第２の層２８は、表面平坦化の生じ難い低温の成長温度（例えば、５００℃程度）で、例えば８０ｎｍの膜厚に成長させる。このように、第２の層２８の堆積膜厚や堆積条件を調整して、第２の層２８の上面に、回折格子３０の周期的な凹凸に対応した凹凸３２が形成されるように、第２の層２８を堆積する。これにより、第１の層２６と第２の層２８とを含み、第１の層２６と第２の層２８との間に周期的な凹凸からなる屈折率変調型の回折格子３０を有する回折格子層１４が形成される。 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 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.
　図３（ｃ）のように、回折格子層１４の上面に、例えば、ＭＢＥ法を用いて、ドット層３４を形成する。具体的には、まず、例えば、ＭＢＥ法を用いて、ベース層３６となるＧａＡｓ層を薄く堆積し、その後、ＩｎＡｓである量子ドット３８を成長させる。回折格子層１４上面に形成されたＧａＡｓ層は薄いため、回折格子層１４上面の凹凸３２に対応する凹凸を有する。そして、量子ドット３８となるＩｎＡｓを、通常よりも高い成長温度で成長させる。成長温度は、例えば、５１０℃以上５５０℃以下である場合が好ましい。より具体的には、例えば、通常の成長温度が５００℃である場合は、５４０℃で量子ドット３８を成長させることが好ましい。また、例えば、ドット層３４の下層（ＡｌＧａＡｓ層やＧａＡｓ層）の成長温度よりも高い成長温度でＩｎＡｓからなる量子ドット３８を成長させる場合が好ましい。高い成長温度で量子ドット３８を成長させることで、回折格子層１４の凹凸３２の凸部上方に成長されるＡｓは高温の影響で飛び易く、吸着し難くなる。このため、凹凸３２の凸部上方は量子ドット３８の密度が疎な領域４２となり、凹部上方は量子ドット３８の密度が密な領域４０となる。つまり、回折格子３０の凹凸の凸部上方は量子ドット３８の密度が疎な領域４２となり、凹部上方は密な領域４０となる。 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.
　次いで、例えば、ＭＢＥ法により、量子ドット３８を覆うように、ベース層３６となるＧａＡｓ層を堆積する。これにより、ベース層３６内に複数の量子ドット３８を有する第１層目のドット層３４が形成される。なお、ベース層３６の堆積膜厚や堆積条件を調整して、第１層目のドット層３４の上面に、回折格子層１４の凹凸３２に対応した凹凸が形成されるように、第１層目のドット層３４を形成する場合が好ましい。 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.
　図４（ａ）のように、上記に説明したドット層３４の形成を、所望の回数、例えば更に１回行い、第２層目のドット層３４を形成し、２層のドット層３４を含む量子ドット活性層１６を形成する。このとき、第１層目のドット層３４の上面に凹凸が形成されていることで、第２層目のドット層３４の量子ドット３８を、高い成長温度で成長させると、凹凸の凸部上に量子ドット３８の密度が疎な領域４２を、凹部上には密な領域４０を形成することができる。即ち、第２層目のドット層３４も、第１層目のドット層３４と同様に、回折格子３０の凹凸の凹部上方は量子ドット３８の密度が密な領域４０となり、凸部上方は疎な領域４２となる。 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.
　図４（ｂ）及び図４（ｃ）のように、量子ドット活性層１６の上面に、例えば、ＭＢＥ法を用いて、上部クラッド層１８とコンタクト層２０とを堆積する。次いで、上部クラッド層１８とコンタクト層２０とをエッチングして、孤立したリッジ部１９を形成する。最後に、コンタクト層２０上にｐ電極２２を、基板１０の下面にｎ電極２４を形成する。これにより、図１に係る量子ドットレーザ１００が完成する。 4B and 4C, the upper cladding layer 18 and the contact layer 20 are deposited on the upper 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.
　以上説明したように、実施例１に係る量子ドットレーザ１００によれば、図１のように、周期的な凹凸からなる回折格子３０を有する回折格子層１４が、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返された量子ドット活性層１６の下側に形成されている。回折格子層１４と量子ドット活性層１６との上下方向（基板１０の表面に垂直な方向）には、回折格子層１４と量子ドット活性層１６とを挟み込むように、下部クラッド層１２と上部クラッド層１８とが形成されている。回折格子３０の周期的な凹凸は導波方向に形成され、量子ドット３８の密度の密な領域４０と疎な領域４２との周期的な変化も導波方向に形成されている。 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 irregularities has a high density of quantum dots 38. 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.
　量子ドット３８の密度が密な領域４０は、疎な領域４２に比べて利得が高くなる。つまり、実施例１に係る量子ドットレーザ１００は、導波方向に利得の分布を有している。即ち、導波方向で周期的に変化した利得を得ることができる。したがって、実施例１に係る量子ドットレーザ１００によれば、回折格子３０による屈折率の周期的変化と、利得の周期的変化と、の両方により動的単一モードを実現することができ、高いシングルモード歩留まりを得ることができる。例えば、広い温度範囲や、高変調で量子ドットレーザ１００を動作させる場合においても、動的単一モード特性を実現でき、シングルモード歩留まりを向上させることができる。 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.
　図１のように、量子ドット３８の密度が密な領域４０は回折格子３０の凹凸の凹部上方（つまり、回折格子層１４上面の凹凸３２上方）に形成され、疎な領域４２は回折格子３０の凹凸の凸部上方に形成されている場合が好ましい。つまり、量子ドット３８の密度が密な領域４０と疎な領域４２との周期は、回折格子３０の凹凸の周期と同じ周期（１倍周期）となる場合が好ましい。このように、量子ドット３８の密度が密な領域４０と疎な領域４２との周期が、回折格子３０の凹凸の周期の自然数倍となる場合は、回折格子３０による屈折率の周期的変化と、利得の周期的変化と、の両方により動的単一モードを実現することができ、高いシングルモード歩留まりを得ることができる。 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.
　したがって、例えば、図５のように、量子ドット３８の密度が密な領域４０を、回折格子３０の凹凸の凹部と凸部との間の斜面上方（つまり、回折格子層１４の凹凸３２の凹部と凸部との間の斜面上方）に形成する場合でもよい。この場合は、量子ドット３８の密度が密な領域４０と疎な領域４２との周期は、回折格子３０の凹凸の周期の２倍周期となる。この場合でも、高いシングルモード歩留まりを得ることができる。 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.
　図５のように、回折格子３０の凹凸の凹部と凸部との間の斜面上方に、量子ドット３８の密度が密な領域４０を形成するには、量子ドット３８となるＩｎＡｓを、通常より高いＡｓ圧で成長させる。Ａｓ圧は、例えば、８×１０－６Ｔｏｒｒ以上である場合が好ましい。より具体的には、例えば、通常のＡｓ圧が５×１０－６Ｔｏｒｒである場合は、２倍程度のＡｓ圧である１×１０－５Ｔｏｒｒで量子ドット３８を成長させることが好ましい。量子ドット３８は、図２のように、ベース層３６上面に形成される。第１層目のドット層３４の量子ドット３８が直接形成されるベース層３６は膜厚が薄いため、回折格子層１４上面に形成された凹凸３２に対応した凹凸を有している。つまり、量子ドット３８直下のベース層３６は、回折格子３０の周期的な凹凸に対応した凹凸を有する構造をしている。凹凸間の斜面には、ステップ（段々形状）が形成されており、斜面の角度が急なほど、ステップはより小さくなる。Ａｓ圧を高くして量子ドット３８を成長させると、Ａｓはベース層３６の斜面のステップ部分に吸着され易くなるため、斜面の角度が急な部分は、量子ドット３８の密度が密になる。したがって、回折格子３０の凹凸の凹部と凸部との間の斜面上方に、量子ドット３８の密度が密な領域４０が形成される。また、凹凸間の斜面に垂直な方向におけるベース層３６であるＧａＡｓの面方位は、例えば、（４１１）面である。量子ドット３８が形成され易いか、形成され難いかは面方位によっても変わるため、量子ドット３８が形成され易いという観点から、凹凸間の斜面に垂直な方向におけるベース層３６であるＧａＡｓの好ましい面方位は、上記以外には、例えば、（５１１）面等である。 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. If the As pressure is increased and the quantum dots 38 are grown, As is easily adsorbed to 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 angle of the slope 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.
　また、例えば、図６のように、量子ドット３８の密度が密な領域４０を、回折格子３０の凹凸の凸部上方（つまり、回折格子層１４の凹凸３２の凸部上方）に形成する場合でもよい。この場合は、量子ドット３８の密度が密な領域４０と疎な領域４２との周期は、回折格子３０の凹凸の周期と同じ（１倍周期）となる。この場合でも、高いシングルモード歩留まりを得ることができる。さらに、例えば、量子ドット３８の密度が密な領域４０が、回折格子３０の凹凸の凹部上方と凸部上方との両方にある場合や、凹部と凸部と凹凸部の間の斜面との全ての上方にある場合でも、高いシングルモード歩留まりを得ることができる。 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.
　実施例１に係る量子ドットレーザ１００の製造方法によれば、図３（ｂ）のように、下部クラッド層１２上に周期的な凹凸からなる回折格子３０を有する回折格子層１４を形成する。そして、図３（ｃ）及び図４（ａ）のように、回折格子層１４上に、複数の量子ドット３８を有し、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返された量子ドット活性層１６を形成する。これにより、回折格子３０による屈折率の周期的変化と、利得の周期的変化と、の両方を有する量子ドットレーザ１００を得ることができる。つまり、高いシングルモード歩留まりを実現できる量子ドットレーザ１００を得ることができる。 According to the method of manufacturing 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.
　また、図３（ｂ）のように、回折格子３０の周期的な凹凸に対応した凹凸３２が上面に形成されるように回折格子層１４を形成する。そして、図３（ｃ）のように、凹凸３２に対応した凹凸を有する薄い膜厚のＧａＡｓ層を堆積した後、成長温度を高くしてＩｎＡｓを成長させることで、凹凸３２の凹部上方（つまり、回折格子３０の凹凸の凹部上方）に量子ドット３８の密度が密な領域４０を形成する。このように、量子ドット３８の直下の層（実施例１では、ＧａＡｓ層からなるベース層３６）を、回折格子３０の周期的な凹凸に対応した凹凸を有する構造とし、量子ドット３８直下の層の凹凸を利用して、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返された量子ドット活性層１６を形成することが好ましい。これにより、量子ドット３８の密度が密な領域４０と疎な領域４２とが、回折格子３０の凹凸の周期と同じ周期で変化する構造を、製造工数の増加を伴うことなく、容易に形成することができる。 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.
　量子ドット３８直下の層が有する凹凸は、基板１０表面の水平方向に対して最も大きくなる最大角度が４度以上である場合が好ましい。これにより、成長温度又はＡｓ圧を高くして、ＩｎＡｓからなる量子ドット３８を成長させることで、回折格子３０の凹凸の凹部上方や凹部と凸部との間の斜面上方に、量子ドット３８の密度が密な領域４０を容易に形成することができる。 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.
　図７は、実施例１の変形例に係る量子ドットレーザ１１０のレーザ光出射方向の水平方向における断面模式図である。図７のように、実施例１の変形例に係る量子ドットレーザ１１０は、回折格子層１４が、量子ドット活性層１６の上側に形成されていて、回折格子３０の凹凸の周期と量子ドット３８の密度が密な領域４０と疎な領域４２との周期とは同じ周期（１倍周期）である。このように、回折格子層１４が、量子ドット活性層１６の上側に形成されている場合でも、回折格子３０による屈折率の周期的変化と、利得の周期的変化と、の両方により動的単一モードを実現できるため、高いシングルモード歩留まりを得ることができる。 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.
　実施例１では、量子ドット３８はＩｎＡｓからなる場合を例に説明した。図３（ｃ）や図５で説明したように、ＭＢＥ法での成長温度やＡｓ圧を高くして量子ドット３８を成長することで、Ａｓが特定の場所に吸着し難く又は吸着し易くなる性質を利用し、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返された構造を形成している。したがって、かかる観点から、量子ドット３８は、ＩｎＡｓやＩｎＧａＡｓのように、Ａｓを含む半導体層（例えば、Ａｓを含むＩＩＩ－Ｖ族化合物半導体層）である場合が好ましい。 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.
　実施例１では、第１の層２６がｎ型ＧａＡｓ層で第２の層２８がｎ型ＡｌＧａＡｓ層である場合を例に示したが、第１の層２６がｎ型ＡｌＧａＡｓ層やＩｎＧａＰ層で、第２の層２８がｎ型ＧａＡｓ層である場合でもよい。即ち、第１の層２６と第２の層２８との間で屈折率に差が生じる場合であればよく、第１の層２６の屈折率が第２の層２８の屈折率より低い場合でも、高い場合でもよい。しかしながら、図３（ａ）及び図３（ｂ）で説明したように、第１の層２６をエッチングして回折格子３０を形成した後、第２の層２８を堆積するため、第１の層２６がＡｌＧａＡｓ層である場合は、表面が酸化されてしまう場合がある。したがって、第１の層２６がＧａＡｓ層で第２の層２８がＡｌＧａＡｓ層である場合が、製造の観点から好ましい。 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.
　実施例１では、図１のように、量子ドット活性層１６は、ドット層３４が２層積層されていて、積層された２層のドット層３４は共に、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返されている場合を説明した。このように、複数積層された全てのドット層３４について、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返された構造の場合、より高いシングルモード発振歩留まりを実現することができる。複数積層された全てのドット層３４について、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返すように形成するには、図４（ａ）で述べたように、下層のドット層３４の上面に凹凸を形成する場合が好ましい。 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.
　また、複数積層されたドット層３４のうち少なくとも１層のドット層３４について、量子ドット３８の密度が密な領域４０と疎な領域４２とが周期的に繰り返された構造をしていれば、シングルモード発振歩留まりを改善することができる。 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.
　実施例１では、第１導電型としてｎ型、第２導電型としてｐ型を例に説明したが、第１導電型がｐ型、第２導電型がｎ型である場合でもよい。 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.
　実施例２は、実施例１に係る量子ドットレーザ１００を備える光モジュールの例である。図８は、実施例２に係る光モジュール２００のブロック図である。図８のように、光モジュール２００は、実施例１に係る量子ドットレーザ１００、筐体１２０、レンズ１２２を有している。筐体１２０には、量子ドットレーザ１００、レンズ１２２、及びシングルモードファイバ１２４が固定されている。量子ドットレーザ１００から出射されたレーザ光１２６は、レンズ１２２によりシングルモードファイバ１２４の先端に光結合されている。これにより、量子ドットレーザ１００から出射されたレーザ光１２６は、シングルモードファイバ１２４に入射され、シングルモードファイバ１２４内を伝送する。 Example 2 is an example of an optical module including the quantum dot laser 100 according to Example 1. 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.
　実施例２に係る光モジュール２００によれば、実施例１に係る量子ドットレーザ１００を用いているため、屈折率の周期的変化と利得の周期的変化との両方により動的単一モードを実現でき、高いシングルモード歩留まりを得ることが可能な光モジュールを得ることができる。 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.
　なお、実施例２に係る光モジュール２００は、実施例１に係る量子ドットレーザ１００を備えている場合を例に示したが、実施例１の変形例１に係る量子ドットレーザ１１０を備えている場合でもよい。この場合でも、高いシングルモード歩留まりを得ることが可能な光モジュールを得ることができる。 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.
　実施例３は、実施例２に係る光モジュール２００を備えた光伝送システムの例である。図９は、実施例３に係る光伝送システム３００のブロック図である。図９のように、実施例３に係る光伝送システム３００は、第１の装置２１０及び第２の装置２２０を有する。第１の装置２１０及び第２の装置２２０はそれぞれ、送信部として機能する実施例２に係る光モジュール２００、受信部２１２及び２２２、並びに制御部２１４及び２２４を有する。光モジュール２００は、制御部２１４及び２２４からの送信データ信号を光に変換してレーザ光を出射する。出射されたレーザ光はシングルモードファイバ２３０に入射される。受信部２１２及び２２２は、シングルモードファイバ２３０内を伝送してきたレーザ光を受光し、受信データ信号として制御部２１４及び２２４に出力する。これにより、第１の装置２１０と第２の装置２２０との間でデータ通信を行うことができる。 Example 3 is an example of an optical transmission system including the optical module 200 according to Example 2. 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.
　実施例３に係る光伝送システム３００によれば、実施例２に係る光モジュール２００を用いている（つまり、実施例１に係る量子ドットレーザ１００を用いている）ことで、高いシングルモード歩留まりを実現することが可能な光伝送システムを得ることができる。 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.
　図９のように、第１の装置２１０と第２の装置２２０との間でシングルモードファイバ２３０を用いてデータ通信を行う光伝送システム３００は、ＦＴＴＨ（Fiber To The Home）や光通信基幹網に用いられる場合が好ましい。また、シングルモードファイバ２３０を用いずに、第１の装置２１０と第２の装置２２０とが、空間に出射したレーザ光を受光することでデータ通信を行う場合でもよい。この場合、第１の装置２１０と第２の装置２２０とは、例えばパーソナルコンピュータとすることができ、また、第１の装置２１０及び第２の装置２２０の一方はパーソナルコンピュータとし、他方は携帯電話、デジタルカメラ、ビデオカメラ等の電子機器やプロジェクタとしてもよい。 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) or 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.
　以上、本発明の好ましい実施例について詳述したが、本発明は係る特定の実施例に限定されるものではなく、特許請求の範囲に記載された本発明の要旨の範囲内において、種々の変形・変更が可能である。 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.

Claims (14)

  1. 　複数の量子ドットを有し、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層と、
    　前記量子ドット活性層の上側又は下側に形成され、周期的な凹凸からなる回折格子を有する回折格子層と、
    　前記量子ドット活性層と前記回折格子層とを上下方向から挟み込むように形成された第１導電型を有する下部クラッド層と前記第１導電型と反対の導電型の第２導電型を有する上部クラッド層と、
    　を具備することを特徴とする半導体レーザ。     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 side or the 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. 　前記量子ドットの密度が密な領域と疎な領域との周期は、前記回折格子の凹凸の周期の自然数倍であることを特徴とする請求項１記載の半導体レーザ。 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 unevenness of the diffraction grating.
  3. 　前記回折格子層は、前記量子ドット活性層の下側に形成されていることを特徴とする請求項１又は２記載の半導体レーザ。 3. The semiconductor laser according to claim 1, wherein the diffraction grating layer is formed below the quantum dot active layer.
  4. 　前記量子ドットの直下の層は、前記回折格子の周期的な凹凸に対応した凹凸を有していることを特徴とする請求項３記載の半導体レーザ。 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. 　前記量子ドットの密度が密な領域は、前記回折格子の凹凸の凹部上方及び／又は凸部上方に形成されていることを特徴とする請求項４記載の半導体レーザ。 5. The semiconductor laser according to claim 4, wherein the dense region of the quantum dots is formed above and / or below the concave and convex portions of the diffraction grating.
  6. 　前記量子ドットの密度が密な領域は、前記回折格子の凹凸の凹部と凸部との間の上方に形成されていることを特徴とする請求項４記載の半導体レーザ。 5. The semiconductor laser according to claim 4, wherein the region in which the density of the quantum dots is dense is formed above the concave and convex portions of the diffraction grating.
  7. 　前記量子ドット活性層は、水平方向に設けられた前記複数の量子ドットと前記複数の量子ドットを覆うように設けられたベース層とで構成されるドット層が複数積層されていて、複数積層された前記ドット層のうち少なくとも１層のドット層について、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返されていることを特徴とする請求項１から６のいずれか一項記載の半導体レーザ。 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.
  8. 　前記量子ドット活性層は、水平方向に設けられた前記複数の量子ドットと前記複数の量子ドットを覆うように設けられたベース層とで構成されるドット層が複数積層されていて、複数積層された全ての前記ドット層について、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返されていることを特徴とする請求項１から６のいずれか一項記載の半導体レーザ。 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.
  9. 　第１導電型を有する下部クラッド層を形成する工程と、
    　前記下部クラッド層上に、周期的な凹凸からなる回折格子を有する回折格子層を形成する工程と、
    　前記回折格子層上に、複数の量子ドットを有し、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層を形成する工程と、
    　前記量子ドット活性層上に、前記第１導電型と反対の導電型の第２導電型を有する上部クラッド層を形成する工程と、
    　を有することを特徴とする半導体レーザの製造方法。     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:
  10. 　前記量子ドットの直下の層を、前記回折格子の凹凸に対応した凹凸を有する構造とする工程を有し、
    　前記量子ドット活性層を形成する工程は、前記量子ドット直下の層の凹凸を利用して、前記量子ドットの密度が密な領域と疎な領域とが周期的に繰り返された量子ドット活性層を形成することを特徴とする請求項９記載の半導体レーザの製造方法。     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.
  11. 　前記量子ドット活性層を形成する工程は、前記量子ドットの密度が密な領域が前記回折格子の凹凸の凹部上方及び／又は凸部上方に形成されるように、前記量子ドット活性層を形成する工程であることを特徴とする請求項１０記載の半導体レーザの製造方法。 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.
  12. 　前記量子ドット活性層を形成する工程は、前記量子ドットの密度が密な領域が前記回折格子の凹凸の凹部と凸部と間の上方に形成されるように、前記量子ドット活性層を形成する工程であることを特徴とする請求項１０記載の半導体レーザの製造方法。 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.
  13. 　請求項１から８のいずれか一項記載の半導体レーザを含むことを特徴とする光モジュール。 An optical module comprising the semiconductor laser according to any one of claims 1 to 8.
  14. 　請求項１から８のいずれか一項記載の半導体レーザを含むことを特徴とする光伝送システム。 An optical transmission system comprising the semiconductor laser according to any one of claims 1 to 8.
PCT/JP2010/062078 2009-08-20 2010-07-16 Semiconductor laser, method for manufacturing same, optical module, and optical transmission system WO2011021458A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2009-190936 2009-08-20
JP2009190936A JP2011044539A (en) 2009-08-20 2009-08-20 Semiconductor laser and method for manufacturing the same, optical module, and optical transmission system

Publications (1)

Publication Number Publication Date
WO2011021458A1 true WO2011021458A1 (en) 2011-02-24

Family

ID=43606913

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2010/062078 WO2011021458A1 (en) 2009-08-20 2010-07-16 Semiconductor laser, method for manufacturing same, optical module, and optical transmission system

Country Status (2)

Country Link
JP (1) JP2011044539A (en)
WO (1) WO2011021458A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6298462B2 (en) 2013-06-05 2018-03-20 日東光器株式会社 An activity having nanodots (also referred to as “quantum dots”) on a mother crystal composed of zinc blende type (also referred to as cubic) AlyInxGa1-y-xN crystal (y ≧ 0, x> 0) grown on a Si substrate. Region and light emitting device using the same (LED and LD)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06112122A (en) * 1992-08-10 1994-04-22 Canon Inc Two-dimensional quantum device structure
WO2003073570A1 (en) * 2002-02-27 2003-09-04 National Institute Of Advanced Industrial Science And Technology Quantum nano-composite semiconductor laser and quantum nano-composite array
JP2006080122A (en) * 2004-09-07 2006-03-23 National Institute Of Advanced Industrial & Technology Quantum nano-structure semiconductor laser

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH06112122A (en) * 1992-08-10 1994-04-22 Canon Inc Two-dimensional quantum device structure
WO2003073570A1 (en) * 2002-02-27 2003-09-04 National Institute Of Advanced Industrial Science And Technology Quantum nano-composite semiconductor laser and quantum nano-composite array
JP2006080122A (en) * 2004-09-07 2006-03-23 National Institute Of Advanced Industrial & Technology Quantum nano-structure semiconductor laser

Also Published As

Publication number Publication date
JP2011044539A (en) 2011-03-03

Similar Documents

Publication Publication Date Title
US7596158B2 (en) Method and structure of germanium laser on silicon
US7535946B2 (en) Structure using photonic crystal and surface emitting laser
JP4977377B2 (en) Semiconductor light emitting device
US9960567B2 (en) Laser device integrated with semiconductor optical amplifier on silicon substrate
JP6487195B2 (en) Semiconductor optical integrated device, semiconductor optical integrated device manufacturing method, and optical module
JP2008277445A (en) Semiconductor laser and optical module
JPWO2011096040A1 (en) Semiconductor laser device, method for manufacturing semiconductor laser device, and optical module
US7483470B2 (en) Semiconductor laser capable of coupling with single mode optical fiber at high coupling efficiency
CN108603980B (en) Photonic integrated device with dielectric structure
JP2011513954A5 (en)
WO2007053431A2 (en) Method and structure of germanium laser on silicon
TW202315254A (en) A semiconductor laser diode including multiple junctions and grating layer
JP4006729B2 (en) Semiconductor light-emitting device using self-assembled quantum dots
JP3421999B2 (en) Optical functional device, optical integrated device including the same, and manufacturing method thereof
JP2019004036A (en) Optical semiconductor element, optical subassembly, and optical module
WO2011021458A1 (en) Semiconductor laser, method for manufacturing same, optical module, and optical transmission system
JP2004266095A (en) Semiconductor optical amplifier
JPH06152059A (en) Semiconductor optical integrated element
US6363093B1 (en) Method and apparatus for a single-frequency laser
WO2012046639A1 (en) Semiconductor laser and optical module provided with same, optical communication device, and optical communication system
US20060222029A1 (en) Semiconductor laser and optical communication system using the same
CN113812049A (en) Distributed feedback laser device for photonic integrated circuit and improvement and manufacturing method thereof
JPH09298337A (en) Semiconductor distribution bragg reflecting mirror and surface light emitting type semiconductor laser
JP3700245B2 (en) Phase-shifted distributed feedback semiconductor laser
JP3311238B2 (en) Optical semiconductor device and method of manufacturing the same

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 10809803

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 10809803

Country of ref document: EP

Kind code of ref document: A1