WO2024100836A1 - Semiconductor laser, method of designing diffraction grating layer of semiconductor laser, and method of manufacturing semiconductor laser - Google Patents

Semiconductor laser, method of designing diffraction grating layer of semiconductor laser, and method of manufacturing semiconductor laser Download PDF

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WO2024100836A1
WO2024100836A1 PCT/JP2022/041901 JP2022041901W WO2024100836A1 WO 2024100836 A1 WO2024100836 A1 WO 2024100836A1 JP 2022041901 W JP2022041901 W JP 2022041901W WO 2024100836 A1 WO2024100836 A1 WO 2024100836A1
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semiconductor laser
diffraction grating
layer
phase shift
value
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French (fr)
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Nikolaos-Panteleimon DIAMANTOPOULOS
Takuma AIHARA
Shinji Matsuo
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Nippon Telegraph And Telephone Corporation
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    • 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
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0421—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers
    • H01S5/0422—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer
    • H01S5/0424—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer lateral current injection
    • 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
    • H01S5/124—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 incorporating phase shifts
    • H01S5/1246—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 incorporating phase shifts plurality of phase shifts
    • H—ELECTRICITY
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    • 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
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2004—Confining in the direction perpendicular to the layer structure
    • H01S5/2018—Optical confinement, e.g. absorbing-, reflecting- or waveguide-layers
    • H01S5/2031—Optical confinement, e.g. absorbing-, reflecting- or waveguide-layers characterized by special waveguide layers, e.g. asymmetric waveguide layers or defined bandgap discontinuities
    • H—ELECTRICITY
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    • 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
    • H01S2301/00—Functional characteristics
    • H01S2301/02—ASE (amplified spontaneous emission), noise; Reduction thereof
    • 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
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/0206—Substrates, e.g. growth, shape, material, removal or bonding
    • H01S5/021—Silicon based substrates
    • 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
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/042—Electrical excitation ; Circuits therefor
    • H01S5/0425—Electrodes, e.g. characterised by the structure
    • H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
    • H01S5/04257—Electrodes, e.g. characterised by the structure characterised by the configuration having positive and negative electrodes on the same side of the substrate
    • H—ELECTRICITY
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    • 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
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/227—Buried mesa structure ; Striped active layer
    • 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
    • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
    • H01S5/3211—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures characterised by special cladding layers, e.g. details on band-discontinuities
    • H01S5/3214—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures characterised by special cladding layers, e.g. details on band-discontinuities comprising materials from other groups of the Periodic Table than the materials of the active layer, e.g. ZnSe claddings and GaAs active layer
    • 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
    • H01S5/343—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 in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
    • H01S5/34306—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 in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength longer than 1000nm, e.g. InP based 1300 and 1500nm lasers

Definitions

  • the present invention relates to a semiconductor laser that operates in a single mode, a method of designing the diffraction grating layer of the semiconductor laser, and a method of manufacturing the semiconductor laser.
  • a photonic integrated circuit (PIC) used in a short-range link of 2 km or less in the networks and systems is desired to operate with low power consumption.
  • a semiconductor laser used in this circuit is necessary to consume low power, have an optical output enough to couple an optical fiber or an optical waveguide, and oscillate only in a single longitudinal mode.
  • DFB-LD distributed feedback laser diode
  • a general InP-base DFB-LD has a phase shift portion at the center of a uniform diffraction grating.
  • the shift amount at the phase shift portion is ⁇ /2, which is equivalent to ⁇ /4 in the length of the diffraction grating.
  • This DFB laser is therefore called a ⁇ /4-shifted DFB-LD.
  • the ⁇ /4-shifted DFB-LD has a spatial hole burning (SHB) problem.
  • SHB spatial hole burning
  • a carrier distribution arises from an optical intensity distribution within a laser resonator, and the carrier density at the center of an active layer decreases.
  • the refractive index at the center of the active layer becomes higher than those near two ends. That is, an effective Bragg wavelength becomes longer at the center of the active layer than those near the two ends.
  • the reflection wavelength becomes nonuniform, the reflectance decreases, and the oscillation mode of the laser becomes unstable.
  • non-patent literature 1 a membrane structure (non-patent literature 1) in which a thin film (350 nm or less) of a III-V semiconductor material is formed on an SiO 2 /Si substrate is applied to the ⁇ /4-shifted DFB-LD
  • the ⁇ /4-shifted DFB-LD obtains a very high optical confinement factor, but is greatly affected by the SHB effect and is hard to operate in the single mode.
  • a distributed feedback semiconductor laser in which a diffraction grating layer is arranged in a waveguide structure including an active layer, wherein the diffraction grating layer includes a uniform diffraction grating, and a plurality of phase shift portions that shift a phase of light traveling through the waveguide structure, the phase shift portion has a length of a value obtained by dividing the cycle by a predetermined integer of not less than 2, and the integer is set to maximize a difference between a threshold gain of a base mode and a threshold gain of a first mode out of oscillation modes of the distributed feedback semiconductor laser.
  • a method of designing a diffraction grating layer of a distributed feedback semiconductor laser in which a diffraction grating layer is arranged in a waveguide structure including an active layer, and the diffraction grating layer includes a uniform diffraction grating, and a plurality of phase shift portions that shift a phase of light traveling through the waveguide structure comprising steps of setting the cycle and a predetermined integer, calculating a length of the phase shift portion by dividing the cycle by the predetermined integer, calculating a difference between a maximum value and minimum value of an optical intensity distribution in a device length direction based on the cycle and the length of the phase shift portion, and determining the cycle and the length of the phase shift portion to set a value of the difference between the maximum value and the minimum value to be smaller than a value of a difference between the maximum value and minimum value of a distributed feedback semiconductor laser including one phase shift portion.
  • a semiconductor laser that can stably operate in a single mode with a simple structure, a method of designing the diffraction grating layer of the semiconductor laser, and a method of manufacturing the semiconductor laser can be provided.
  • Fig. 1A is a schematic view showing the top surface of a semiconductor laser according to the first embodiment of the present invention
  • Fig. 1B is a schematic view showing an IB-IB' section of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 1C is a schematic view showing an IC-IC' section of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 2 is schematic view showing the structure of the diffraction grating layer of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 3 is a graph for explaining the action of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 4 is a graph for explaining the action of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 1A is a schematic view showing the top surface of a semiconductor laser according to the first embodiment of the present invention
  • Fig. 1B is a schematic view showing an IB-IB' section of the semiconductor laser according to the first embodiment of the present invention
  • FIG. 5 is a graph for explaining the action of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 6A is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 6B is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 7A is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 7B is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention
  • Fig. 8 is a flowchart for explaining a method of designing the diffraction grating layer of the semiconductor laser according to the first embodiment of the present invention
  • FIG. 9A is a schematic view showing the top surface of a semiconductor laser according to the second embodiment of the present invention
  • Fig. 9B is a schematic view showing an IXB-IXB' section of the semiconductor laser according to the second embodiment of the present invention
  • Fig. 9C is a schematic view showing an IXC-IXC' section of the semiconductor laser according to the second embodiment of the present invention
  • Fig. 10A is a schematic view showing the top surface of an example of the semiconductor laser according to the second embodiment of the present invention
  • Fig. 10B is a schematic view showing an XB-XB' section of the example of the semiconductor laser according to the second embodiment of the present invention
  • Fig. 10C is a schematic view showing an XC-XC' section of the example of the semiconductor laser according to the second embodiment of the present invention.
  • a semiconductor laser (to be also referred to as a "DFB-LD" hereinafter) 10 according to the embodiment has a membrane structure in which an active layer 104 covered with InP is formed on a lower layer clad (SiO 2 ) 102 on an Si substrate 101, and a current is injected in the lateral direction (x direction in Figs. 1A to 1C) by a p-type InP layer 108 and an n-type InP layer 111 arranged to sandwich the active layer 104 in the horizontal direction (x direction in Figs. 1A to 1C).
  • a multi-quantum well MQW
  • MQW multi-quantum well
  • the semiconductor laser 10 includes in order the Si substrate 101, the lower layer clad 102, an InP lower layer 103, the MQW 104 serving as an active layer, an InP upper layer 105, a diffraction grating layer 106, and an upper layer clad 107.
  • the semiconductor laser 10 also includes the p-type InP layer 108 and the n-type InP layer 111 respectively on two sides of the MQW 104 in the horizontal direction.
  • the semiconductor laser 10 includes a p-type contact layer 109 and a p-type electrode 110 on the p-type InP layer 108, and an n-type contact layer 112 and an n-type electrode 113 on the n-type InP layer 111, respectively.
  • the InP lower layer 103, the active layer (MQW) 104, and the InP upper layer 105 constitute a waveguide structure, and the diffraction grating layer 106 is arranged (formed) on the waveguide structure.
  • the diffraction grating layer 106 may be arranged at least one of below and above the waveguide structure.
  • the MQW 104 is an InGaAlAs-base MQW of a 1.3- ⁇ m wavelength composition corresponding to the O-band, and the entire MQW 104 is 150 ⁇ m in layer thickness and 600 ⁇ m in width.
  • the InP lower layer 103 and the InP upper layer 105 each are 40 ⁇ m thick, and the p-type InP layer 108 and the n-type InP layer 111 each are 230 ⁇ m thick.
  • SiO 2 is used for the upper layer clad 107 and the lower layer clad 102.
  • a low-refractive-index material such as SiO x or BCB other than SiO 2 may be used.
  • a confinement factor ⁇ QW in the MQW 104 in this structure is about 23%.
  • the diffraction grating layer 106 is made of SiN and SiO 2 in a device length direction (z direction in Figs. 1A to 1C).
  • the diffraction grating layer 106 is constituted by dividing, into four regions by three phase shift portions 1062, a uniform diffraction grating, that is, a diffraction grating (to be referred to as a "uniform diffraction grating" hereinafter) 1061 constant in cycle and depth.
  • the phase shift portion 1062 shifts the phase of light traveling through the waveguide structure, and enables single-mode oscillation of the semiconductor laser 10.
  • the single-mode oscillation is an oscillation at a high side mode suppression ratio (SMSR) and is an oscillation at an SMSR of, for example, 20 dB or more.
  • SMSR high side mode suppression ratio
  • the diffraction grating layer 106 is formed by selectively etching SiN on the InP upper layer 105 and then depositing SiO 2 .
  • the phase shift portion 1062 may be formed from SiN or SiO 2 .
  • Fig. 2 schematically shows a detailed structure of the diffraction grating layer 106.
  • a pitch (cycle) ⁇ of the uniform diffraction grating 1061 is ⁇ B /2/n eff .
  • ⁇ B is the Bragg wavelength and is 1.26 to 1.360 ⁇ m equivalent to the O-waveband.
  • n eff is the average effective refractive index and is about 2.91 to 2.93 in the O-band in the structure of the DFB-LD 10.
  • the pitch is about 220 nm.
  • the total length L gr of the uniform diffraction grating 1061 is 500 ⁇ m.
  • the length L of the entire device is L gr + 3L ⁇ .
  • Fig. 3 shows the calculation results of the phase factor dependence of a threshold gain difference ( ⁇ g th ) when the ratio of L 1 and L 2 is changed.
  • a phase factor K is an integer.
  • the phase factor K at which the threshold gain difference becomes maximum that is, the optimal value of the phase factor K changes depending on the relationship between L 1 and L 2 , and the maximum value of the threshold gain difference also changes.
  • L 2 L 1 /3 to L 1 /4
  • L 2 L 1 /3 is set in the DFB-LD 10.
  • L gr 500 ⁇ m
  • L 1 187.5 ⁇ m
  • L 2 62.5 ⁇ m.
  • Fig. 4 shows the calculation results of the dependence of the coupling coefficient ⁇ of the uniform diffraction grating 1061 with respect to the SiN layer thickness.
  • the coupling coefficient ⁇ was derived by calculating the difference in effective refractive index between SiN and SiO 2 in the diffraction grating using simulation software "FIMMWAVE" (Photon Design).
  • a SiN layer thickness satisfying ⁇ ⁇ 40 cm -1 is desirably about 12 nm or less.
  • the SiN layer thickness, that is, the depth of the diffraction grating layer 106 was set to be 10 nm in consideration of a high laser output.
  • phase factor K that defines the length L ⁇ of the three phase shift portions 1062 in the semiconductor laser 10 according to the embodiment will be described with reference to Fig. 5.
  • the threshold gain difference ( ⁇ g th ) between the dominant mode (longitudinal mode) and the first side mode (longitudinal mode) needs to be maximum.
  • Fig. 5 shows the calculation results of the phase factor dependence of the threshold gain in each of the dominant mode (solid line in Fig. 5) and the first side mode (broken line in Fig. 5).
  • the phase factor K is an integer.
  • the threshold gain in the dominant mode decreases and at the phase factor K of 4 or more, slightly increases.
  • the threshold gain in the first side mode increases and at the phase factor K of 6 or less, decreases.
  • the threshold gain difference ( ⁇ g th ) between the dominant mode and the first side mode becomes maximum at about 35/cm when the phase factor K is 6.
  • the DFB-LD 10 is therefore called a " ⁇ /12-shifted" DFB-LD.
  • ⁇ 220 nm
  • L ⁇ 37 nm.
  • Fig. 6A shows the simulation results of the spectrum of the ⁇ /12-shifted DFB-LD 10.
  • Fig. 6B shows the simulation results of the spectrum of a conventional semiconductor laser ( ⁇ /4-shifted DFB-LD).
  • the spectrum of the DFB-LD was calculated based on the transmittance of the DFB-LD based on the transfer matrix method.
  • ⁇ B 1.28 ⁇ m
  • n eff 2.93
  • ⁇ 38 cm -1
  • the structure of the diffraction grating of the DFB-LD is symmetrical in the device length direction (z direction in the drawings), so the same spectrum is output from two exit ends.
  • an oscillation spectrum in the single mode is obtained at an SMSR of 20 dB or more in the ⁇ /12-shifted DFB-LD 10. This is similar to the spectrum of the ⁇ /4-shifted DFB-LD shown in Fig. 6B.
  • Fig. 7A shows the calculation results of the optical intensity distribution of the ⁇ /12-shifted DFB-LD 10 in the device length direction (z direction in Fig. 7A).
  • Fig. 7B shows the calculation results of the optical intensity distribution of the conventional ⁇ /4-shifted DFB-LD in the device length direction (z direction in Fig. 7B).
  • the calculation was performed based on the transfer matrix method for the ⁇ /12-shifted DFB-LD 10 having a structure similar to the above-described one.
  • ⁇ I is about 0.62.
  • ⁇ I is about 0.5. This value is smaller by 21% than that in the ⁇ /4-shifted DFB-LD.
  • the optical intensity difference ( ⁇ I) in the resonator is smaller in the ⁇ /12-shifted DFB-LD 10 than in the ⁇ /4-shifted DFB-LD, the influence of the SHB can be reduced.
  • the ⁇ /12-shifted DFB-LD 10 is excellent in the stability of the single mode of the spectrum.
  • the optical intensity difference ( ⁇ I) is smaller, the influence of the SHB can be reduced.
  • Fig. 8 shows a flowchart for explaining an example of a method of designing the diffraction grating layer 106 of the semiconductor laser 10.
  • step S1 the cycle of the uniform diffraction grating of the semiconductor laser 10 and a predetermined integer of 2 or more as the phase factor K are set (step S1).
  • the length of the phase shift portion is calculated by dividing the cycle of the uniform diffraction grating by the factor K (step S2).
  • the difference ( ⁇ I) between the maximum and minimum values of the optical intensity distribution in the waveguide (device length) direction is calculated based on the cycle of the uniform diffraction grating and the length of the phase shift portion (step S3).
  • the ⁇ I value obtained by the calculation is compared with a predetermined value (step S4).
  • the cycle of the uniform diffraction grating and the length of the phase shift portion when the ⁇ I value obtained by the calculation becomes smaller than the predetermined value are determined as the cycle of the uniform diffraction grating 1061 and the length of the phase shift portion 1062 of the semiconductor laser 10 (step S5).
  • step S1 to S4 If the ⁇ I value obtained by the calculation is equal to or larger than the predetermined value or larger than it, the cycle of the uniform diffraction grating of the semiconductor laser 10 and the value of the factor K are changed to repeat the same steps (steps S1 to S4).
  • the designed diffraction grating layer 106 is formed and the semiconductor laser 10 is manufactured using a known distributed feedback semiconductor laser fabrication process.
  • a semiconductor laser 20 includes an Si waveguide 214 in a lower layer clad 202.
  • the remaining structure is the same as that in the first embodiment.
  • the Si waveguide 214 is arranged to couple a laser beam of the DFB-LD to another Si-base device (for example, an Si photonic device) in a PIC.
  • the Si waveguide 214 is arranged below a MQW 204, that is, below an InP lower layer 203.
  • the interval between the Si waveguide 214 and the InP lower layer 203 is 100 nm.
  • the width of the Si waveguide 214 is 800 nm or more, and its layer thickness is 150 to 220 nm.
  • the confinement factor ⁇ QW in the MQW 204 is about 19%. This value is almost as larger as the confinement factor ⁇ QW (about 23%) in the MQW in the structure (first embodiment) having no Si waveguide. Even in the structure having the Si waveguide, the DFB-LD can obtain a high output.
  • the DFB-LD stably operates in the single mode, similar to the first embodiment.
  • the DFB-LD and another Si-base device in the PIC can be preferably optically coupled and integrated.
  • Si waveguide 214 is arranged in the lower layer clad 202 in the semiconductor laser according to the embodiment, the present invention is not limited to this.
  • an Si waveguide 314 may be arranged in an upper layer clad 307.
  • Si waveguides may be arranged in both lower and upper layer clads.
  • the embodiment according to the present invention has exemplified a DFB-LD having the membrane structure in which a current is injected in the lateral direction (x direction), but the present invention may be applied to a DFB-LD in which a current is injected in the general longitudinal direction (y direction).
  • optical confinement is greater by the membrane structure than by the general structure, so the effects of the present invention are great.
  • the embodiment according to the present invention has described an example in which the DFB-LD includes three phase shift portions, but the present invention is not limited to this and the DFB-LD may include a plurality of phase shift portions.
  • the embodiment according to the present invention has described an example in which a plurality of phase shift portions have the same length, but the present invention is not limited to this and a plurality of phase shift portions may have different lengths.
  • simulation for the design of an optimal structure can be simplified.
  • the embodiment according to the present invention has described an example in which the structure of the diffraction grating of the DFB-LD is symmetrical in the device length direction.
  • the structure of the diffraction grating of the DFB-LD may be asymmetrical in the device length direction.
  • two outer regions have different lengths L 1
  • two inner regions have different lengths L 2 .
  • the embodiment according to the present invention has exemplified a DFB-LD corresponding to the O-waveband, but the waveband may be another one.
  • the embodiment according to the present invention has exemplified the use of an InGaAlAs-base MQW, but a MQW whose base is another material such as InGaAsP may be used.
  • the embodiment according to the present invention has exemplified the structure, dimensions, material, and the like of each constituent part in the structure, manufacturing method, and the like of a semiconductor laser, but the present invention is not limited to this as long as the function of a semiconductor laser is obtained and has effects.
  • the present invention is applicable to a communication network system and a computing system.
  • semiconductor laser 104 active layer (MQW) 106: diffraction grating layer 1061: uniform diffraction grating 1062: phase shift portion

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  • Condensed Matter Physics & Semiconductors (AREA)
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  • Semiconductor Lasers (AREA)

Abstract

A semiconductor laser (10) according to this invention is a distributed feedback semiconductor laser in which a diffraction grating layer (106) is arranged in a waveguide structure including an active layer (104). The diffraction grating layer includes a uniform diffraction grating (1061), and a plurality of phase shift portions (1062) that shift a phase of light traveling through the waveguide structure. The phase shift portion has a length of a value obtained by dividing the cycle by a predetermined integer of 2 or more. The integer is set to maximize a difference between a threshold gain of a base mode and a threshold gain of a first mode out of oscillation modes of the distributed feedback semiconductor laser. This invention can provide a semiconductor laser that can stably operate in a single mode with a simple structure.

Description

Semiconductor Laser, Method of Designing Diffraction Grating Layer of Semiconductor Laser, and Method of Manufacturing Semiconductor Laser
The present invention relates to a semiconductor laser that operates in a single mode, a method of designing the diffraction grating layer of the semiconductor laser, and a method of manufacturing the semiconductor laser.
Recently, the traffic surges in data center networks and high-performance computing systems. A photonic integrated circuit (PIC) used in a short-range link of 2 km or less in the networks and systems is desired to operate with low power consumption.
A semiconductor laser used in this circuit (PIC) is necessary to consume low power, have an optical output enough to couple an optical fiber or an optical waveguide, and oscillate only in a single longitudinal mode.
To satisfy these conditions, a distributed feedback laser diode (DFB-LD) is used. A general InP-base DFB-LD has a phase shift portion at the center of a uniform diffraction grating. The shift amount at the phase shift portion is π/2, which is equivalent to λ/4 in the length of the diffraction grating. This DFB laser is therefore called a λ/4-shifted DFB-LD.
Japanese Patent Laid-Open No. 2017-107958
T. Aihara, et al., "Membrane III-V/Si DFB Laser Using Uniform Grating and Width-Modulated Si Waveguide," J. Lightw. Technol., vol. 38, no. 11, pp. 2961-2967, June 2020.
However, the λ/4-shifted DFB-LD has a spatial hole burning (SHB) problem. In the SHB, a carrier distribution arises from an optical intensity distribution within a laser resonator, and the carrier density at the center of an active layer decreases. The refractive index at the center of the active layer becomes higher than those near two ends. That is, an effective Bragg wavelength becomes longer at the center of the active layer than those near the two ends. The reflection wavelength becomes nonuniform, the reflectance decreases, and the oscillation mode of the laser becomes unstable.
When the λ/4-shifted DFB-LD adopts a high optical confinement structure for low power consumption, the influence of the SHB becomes serious.
For example, when a membrane structure (non-patent literature 1) in which a thin film (350 nm or less) of a III-V semiconductor material is formed on an SiO2/Si substrate is applied to the λ/4-shifted DFB-LD, the λ/4-shifted DFB-LD obtains a very high optical confinement factor, but is greatly affected by the SHB effect and is hard to operate in the single mode.
To implement a stable operation of the λ/4-shifted DFB-LD in the single mode, a structure is disclosed in which the effective refractive index or the distribution of a diffraction grating is modulated (patent literature 1). However, implementation of this structure requires a complicated fabrication process and high cost.
To solve the above-described problems, according to the present invention, there is provided a distributed feedback semiconductor laser in which a diffraction grating layer is arranged in a waveguide structure including an active layer, wherein the diffraction grating layer includes a uniform diffraction grating, and a plurality of phase shift portions that shift a phase of light traveling through the waveguide structure, the phase shift portion has a length of a value obtained by dividing the cycle by a predetermined integer of not less than 2, and the integer is set to maximize a difference between a threshold gain of a base mode and a threshold gain of a first mode out of oscillation modes of the distributed feedback semiconductor laser.
According to the present invention, there is provided a method of designing a diffraction grating layer of a distributed feedback semiconductor laser in which a diffraction grating layer is arranged in a waveguide structure including an active layer, and the diffraction grating layer includes a uniform diffraction grating, and a plurality of phase shift portions that shift a phase of light traveling through the waveguide structure, the method comprising steps of setting the cycle and a predetermined integer, calculating a length of the phase shift portion by dividing the cycle by the predetermined integer, calculating a difference between a maximum value and minimum value of an optical intensity distribution in a device length direction based on the cycle and the length of the phase shift portion, and determining the cycle and the length of the phase shift portion to set a value of the difference between the maximum value and the minimum value to be smaller than a value of a difference between the maximum value and minimum value of a distributed feedback semiconductor laser including one phase shift portion.
According to the present invention, a semiconductor laser that can stably operate in a single mode with a simple structure, a method of designing the diffraction grating layer of the semiconductor laser, and a method of manufacturing the semiconductor laser can be provided.
Fig. 1A is a schematic view showing the top surface of a semiconductor laser according to the first embodiment of the present invention; Fig. 1B is a schematic view showing an IB-IB' section of the semiconductor laser according to the first embodiment of the present invention; Fig. 1C is a schematic view showing an IC-IC' section of the semiconductor laser according to the first embodiment of the present invention; Fig. 2 is schematic view showing the structure of the diffraction grating layer of the semiconductor laser according to the first embodiment of the present invention; Fig. 3 is a graph for explaining the action of the semiconductor laser according to the first embodiment of the present invention; Fig. 4 is a graph for explaining the action of the semiconductor laser according to the first embodiment of the present invention; Fig. 5 is a graph for explaining the action of the semiconductor laser according to the first embodiment of the present invention; Fig. 6A is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention; Fig. 6B is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention; Fig. 7A is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention; Fig. 7B is a graph for explaining the effects of the semiconductor laser according to the first embodiment of the present invention; Fig. 8 is a flowchart for explaining a method of designing the diffraction grating layer of the semiconductor laser according to the first embodiment of the present invention; Fig. 9A is a schematic view showing the top surface of a semiconductor laser according to the second embodiment of the present invention; Fig. 9B is a schematic view showing an IXB-IXB' section of the semiconductor laser according to the second embodiment of the present invention; Fig. 9C is a schematic view showing an IXC-IXC' section of the semiconductor laser according to the second embodiment of the present invention; Fig. 10A is a schematic view showing the top surface of an example of the semiconductor laser according to the second embodiment of the present invention; Fig. 10B is a schematic view showing an XB-XB' section of the example of the semiconductor laser according to the second embodiment of the present invention; and Fig. 10C is a schematic view showing an XC-XC' section of the example of the semiconductor laser according to the second embodiment of the present invention.Best Mode for Carrying Out the Invention
<First Embodiment>
A semiconductor laser according to the first embodiment of the present invention will be described with reference to Figs. 1A to 8.
<Structure of Semiconductor Laser>
As shown in Figs. 1A to 1C, a semiconductor laser (to be also referred to as a "DFB-LD" hereinafter) 10 according to the embodiment has a membrane structure in which an active layer 104 covered with InP is formed on a lower layer clad (SiO2) 102 on an Si substrate 101, and a current is injected in the lateral direction (x direction in Figs. 1A to 1C) by a p-type InP layer 108 and an n-type InP layer 111 arranged to sandwich the active layer 104 in the horizontal direction (x direction in Figs. 1A to 1C). Here, a multi-quantum well (MQW) is used for the active layer 104.
More specifically, the semiconductor laser 10 includes in order the Si substrate 101, the lower layer clad 102, an InP lower layer 103, the MQW 104 serving as an active layer, an InP upper layer 105, a diffraction grating layer 106, and an upper layer clad 107. The semiconductor laser 10 also includes the p-type InP layer 108 and the n-type InP layer 111 respectively on two sides of the MQW 104 in the horizontal direction. Further, the semiconductor laser 10 includes a p-type contact layer 109 and a p-type electrode 110 on the p-type InP layer 108, and an n-type contact layer 112 and an n-type electrode 113 on the n-type InP layer 111, respectively.
The InP lower layer 103, the active layer (MQW) 104, and the InP upper layer 105 constitute a waveguide structure, and the diffraction grating layer 106 is arranged (formed) on the waveguide structure. The diffraction grating layer 106 may be arranged at least one of below and above the waveguide structure.
The MQW 104 is an InGaAlAs-base MQW of a 1.3-μm wavelength composition corresponding to the O-band, and the entire MQW 104 is 150 μm in layer thickness and 600 μm in width.
The InP lower layer 103 and the InP upper layer 105 each are 40 μm thick, and the p-type InP layer 108 and the n-type InP layer 111 each are 230 μm thick.
SiO2 is used for the upper layer clad 107 and the lower layer clad 102. A low-refractive-index material such as SiOx or BCB other than SiO2 may be used.
A confinement factor ΓQW in the MQW 104 in this structure is about 23%.
The diffraction grating layer 106 is made of SiN and SiO2 in a device length direction (z direction in Figs. 1A to 1C).
The diffraction grating layer 106 is constituted by dividing, into four regions by three phase shift portions 1062, a uniform diffraction grating, that is, a diffraction grating (to be referred to as a "uniform diffraction grating" hereinafter) 1061 constant in cycle and depth. The phase shift portion 1062 shifts the phase of light traveling through the waveguide structure, and enables single-mode oscillation of the semiconductor laser 10. The single-mode oscillation is an oscillation at a high side mode suppression ratio (SMSR) and is an oscillation at an SMSR of, for example, 20 dB or more.
The diffraction grating layer 106 is formed by selectively etching SiN on the InP upper layer 105 and then depositing SiO2. The phase shift portion 1062 may be formed from SiN or SiO2.
Fig. 2 schematically shows a detailed structure of the diffraction grating layer 106.
In the uniform diffraction grating 1061, two outer regions have the same length L1, and two inner regions have the same length L2. Hence, Lgr = 2(L1 + L2).
A pitch (cycle) Λ of the uniform diffraction grating 1061 is λB/2/neff. λB is the Bragg wavelength and is 1.26 to 1.360 μm equivalent to the O-waveband. neff is the average effective refractive index and is about 2.91 to 2.93 in the O-band in the structure of the DFB-LD 10. In the embodiment, the pitch is about 220 nm.
All the phase shift portions 1062 have the same length Lφ, and Lφ = Λ/K, where K is an integer constant of 2 or more (to be described later).
To obtain a sufficiently high output from the DFB-LD 10, the total length Lgr of the uniform diffraction grating 1061 is 500 μm. Thus, the length L of the entire device is Lgr + 3Lφ.
Fig. 3 shows the calculation results of the phase factor dependence of a threshold gain difference (Δgth) when the ratio of L1 and L2 is changed. Here, a phase factor K is an integer.
The calculation was performed based on the transfer matrix theory model at λB = 1.28 μm, neff = 2.93, κ = 38 cm-1, and Λ = 220 nm. L1 and L2 were changed at Lgr = 500 μm.
When L1 = L2, the threshold gain difference is maximum (about 20/cm) at K = about 2. When L2 = L1/2, the threshold gain difference is maximum (about 30/cm) at K = about 5. When L2 = L1/3 to L1/4, the threshold gain difference is maximum (about 35/cm) at K = about 6.
In this manner, the phase factor K at which the threshold gain difference becomes maximum, that is, the optimal value of the phase factor K changes depending on the relationship between L1 and L2, and the maximum value of the threshold gain difference also changes. For example, from the above-described results, when L2 = L1/3 to L1/4, the optimal value of the phase factor K is 6 and the threshold gain difference becomes maximum. It is therefore desirable that L2 = L1/3 or less.
For this reason, L2 = L1/3 is set in the DFB-LD 10. When Lgr = 500 μm, L1 = 187.5 μm and L2 = 62.5 μm.
Fig. 4 shows the calculation results of the dependence of the coupling coefficient κ of the uniform diffraction grating 1061 with respect to the SiN layer thickness.
In the calculation, the coupling coefficient κ was derived by calculating the difference in effective refractive index between SiN and SiO2 in the diffraction grating using simulation software "FIMMWAVE" (Photon Design).
For the single-mode operation, it is necessary in general to satisfy a condition of κL ＜ 2. Since L is about 500 μm in the embodiment, κ ＜ 40 cm-1. From Fig. 4, a SiN layer thickness satisfying κ ＜ 40 cm-1 is desirably about 12 nm or less. In the embodiment, the SiN layer thickness, that is, the depth of the diffraction grating layer 106 was set to be 10 nm in consideration of a high laser output.
The phase factor K that defines the length Lφ of the three phase shift portions 1062 in the semiconductor laser 10 according to the embodiment will be described with reference to Fig. 5.
To operate the DFB-LD 10 in the single mode at high SMSR, the threshold gain difference (Δgth) between the dominant mode (longitudinal mode) and the first side mode (longitudinal mode) needs to be maximum.
Fig. 5 shows the calculation results of the phase factor dependence of the threshold gain in each of the dominant mode (solid line in Fig. 5) and the first side mode (broken line in Fig. 5). Here, the phase factor K is an integer.
The calculation was performed based on the transfer matrix theory model at λB = 1.28 μm, neff = 2.93, κ = 38 cm-1, and Λ = 220 nm, similar to the above-described calculation (Fig. 3). L1 = 187.5 μm and L2 = 62.5 μm were set.
As the phase factor K increases from 2 to 4, the threshold gain in the dominant mode decreases and at the phase factor K of 4 or more, slightly increases. In contrast, as the phase factor K increases from 2 to 6, the threshold gain in the first side mode increases and at the phase factor K of 6 or less, decreases. The threshold gain difference (Δgth) between the dominant mode and the first side mode becomes maximum at about 35/cm when the phase factor K is 6.
From K = 6, the length of the three phase shift portions 1062 is Lφ = Λ/6 = λB/12/neff. In the embodiment, the DFB-LD 10 is therefore called a "λ/12-shifted" DFB-LD. When Λ = 220 nm, Lφ = 37 nm.
<Effects>
From the above-described results, the effects of the λ/12-shifted DFB-LD 10 at the phase factor K = 6 in the embodiment will be explained with reference to Figs. 6A to 7B.
Fig. 6A shows the simulation results of the spectrum of the λ/12-shifted DFB-LD 10. For comparison, Fig. 6B shows the simulation results of the spectrum of a conventional semiconductor laser (λ/4-shifted DFB-LD).
The spectrum of the DFB-LD was calculated based on the transmittance of the DFB-LD based on the transfer matrix method. Here, λB = 1.28 μm, neff = 2.93, κ = 38 cm-1, and Λ = 220 nm were set. In the λ/12-shifted DFB-LD 10, L1 = 187.5 μm and L2 = 62.5 μm were set.
In this calculation, the structure of the diffraction grating of the DFB-LD is symmetrical in the device length direction (z direction in the drawings), so the same spectrum is output from two exit ends.
As shown in Fig. 6A, an oscillation spectrum in the single mode is obtained at an SMSR of 20 dB or more in the λ/12-shifted DFB-LD 10. This is similar to the spectrum of the λ/4-shifted DFB-LD shown in Fig. 6B.
Further, detailed effects of the semiconductor laser 10 according to the embodiment will be explained with reference to Figs. 7A and 7B.
Fig. 7A shows the calculation results of the optical intensity distribution of the λ/12-shifted DFB-LD 10 in the device length direction (z direction in Fig. 7A). For comparison, Fig. 7B shows the calculation results of the optical intensity distribution of the conventional λ/4-shifted DFB-LD in the device length direction (z direction in Fig. 7B).
The calculation was performed based on the transfer matrix method for the λ/12-shifted DFB-LD 10 having a structure similar to the above-described one.
The SHB effect that affects the mode singularity of the DFB-LD heavily depends on the optical intensity distribution. That is, when the optical intensity distribution is constant, the SHB effect is reduced. As a change of the optical intensity distribution increases, the SHB effect increases.
To quantify the uniformity of the optical intensity distribution, a difference (ΔI) between the maximum and minimum values of a normalized optical intensity distribution is used.
In the λ/4-shifted DFB-LD, as shown in Fig. 7B, the optical intensity is about 0.4 at two ends (z = 0, 500 μm), increases up to the center (z = 250 μm) where the phase shift portion is arranged, and exhibits a maximum value (1.0) at the center. At this time, ΔI is about 0.62.
In the λ/12-shifted DFB-LD 10, as shown in Fig. 7A, the optical intensity is about 0.55 at two ends (z = 0, 500 μm), increases up to the center (z = 250 μm) where the phase shift portion 1062 is arranged, and exhibits a maximum value (1.0). A change of the optical intensity exhibits a cusp at a portion (z = 187.5 μm, 312.5 μm) where the phase shift portion 1062 is arranged. At this time, ΔI is about 0.5. This value is smaller by 21% than that in the λ/4-shifted DFB-LD.
Since the optical intensity difference (ΔI) in the resonator is smaller in the λ/12-shifted DFB-LD 10 than in the λ/4-shifted DFB-LD, the influence of the SHB can be reduced. Hence, the λ/12-shifted DFB-LD 10 is excellent in the stability of the single mode of the spectrum. As the optical intensity difference (ΔI) is smaller, the influence of the SHB can be reduced.
<Method of Designing Diffraction Grating of Semiconductor Laser>
An example of a method of designing the diffraction grating layer 106 of the semiconductor laser 10 according to the embodiment will be described with reference to Fig. 8. Fig. 8 shows a flowchart for explaining an example of a method of designing the diffraction grating layer 106 of the semiconductor laser 10.
First, the cycle of the uniform diffraction grating of the semiconductor laser 10 and a predetermined integer of 2 or more as the phase factor K are set (step S1).
Then, the length of the phase shift portion is calculated by dividing the cycle of the uniform diffraction grating by the factor K (step S2).
Similar to the above description (Figs. 7A and 7B), the difference (ΔI) between the maximum and minimum values of the optical intensity distribution in the waveguide (device length) direction is calculated based on the cycle of the uniform diffraction grating and the length of the phase shift portion (step S3).
Then, the ΔI value obtained by the calculation is compared with a predetermined value (step S4). As the predetermined value, the ΔI value of a distributed feedback semiconductor laser having one phase shift portion is used (for example, ΔI = 0.62 in Fig. 7B).
Finally, the cycle of the uniform diffraction grating and the length of the phase shift portion when the ΔI value obtained by the calculation becomes smaller than the predetermined value are determined as the cycle of the uniform diffraction grating 1061 and the length of the phase shift portion 1062 of the semiconductor laser 10 (step S5).
If the ΔI value obtained by the calculation is equal to or larger than the predetermined value or larger than it, the cycle of the uniform diffraction grating of the semiconductor laser 10 and the value of the factor K are changed to repeat the same steps (steps S1 to S4).
As the predetermined value, a value having an effect of reducing the SHB may be used (for example, ΔI = 0.5 in Fig. 7A). Then, the cycle of the uniform diffraction grating and the length of the phase shift portion when the ΔI value obtained by the calculation becomes equal to or smaller than the predetermined value may be determined as the cycle of the uniform diffraction grating 1061 and the length of the phase shift portion 1062 of the semiconductor laser 10. The cycle of the uniform diffraction grating and the length of the phase shift portion may be so determined as to minimize the ΔI value.
<Method of Manufacturing Semiconductor Laser>
After designing the diffraction grating in the above-described way, the designed diffraction grating layer 106 is formed and the semiconductor laser 10 is manufactured using a known distributed feedback semiconductor laser fabrication process.
<Second Embodiment>
Next, a semiconductor laser according to the second embodiment of the present invention will be described with reference to Figs. 9A to 10C.
<Structure of Semiconductor Laser>
As shown in Figs. 9A to 9C, a semiconductor laser 20 according to the embodiment includes an Si waveguide 214 in a lower layer clad 202. The remaining structure is the same as that in the first embodiment.
The Si waveguide 214 is arranged to couple a laser beam of the DFB-LD to another Si-base device (for example, an Si photonic device) in a PIC. The Si waveguide 214 is arranged below a MQW 204, that is, below an InP lower layer 203. The interval between the Si waveguide 214 and the InP lower layer 203 is 100 nm.
The width of the Si waveguide 214 is 800 nm or more, and its layer thickness is 150 to 220 nm. For example, when the width of the Si waveguide 214 is 3 μm or more and its layer thickness is 150 nm, the confinement factor ΓQW in the MQW 204 is about 19%. This value is almost as larger as the confinement factor ΓQW (about 23%) in the MQW in the structure (first embodiment) having no Si waveguide. Even in the structure having the Si waveguide, the DFB-LD can obtain a high output.
In the semiconductor laser according to the embodiment, the DFB-LD stably operates in the single mode, similar to the first embodiment.
According to the embodiment, the DFB-LD and another Si-base device in the PIC can be preferably optically coupled and integrated.
Although the Si waveguide 214 is arranged in the lower layer clad 202 in the semiconductor laser according to the embodiment, the present invention is not limited to this. As shown in Figs. 10A to 10C, an Si waveguide 314 may be arranged in an upper layer clad 307. Alternatively, Si waveguides may be arranged in both lower and upper layer clads.
The embodiment according to the present invention has exemplified a DFB-LD having the membrane structure in which a current is injected in the lateral direction (x direction), but the present invention may be applied to a DFB-LD in which a current is injected in the general longitudinal direction (y direction). However, optical confinement is greater by the membrane structure than by the general structure, so the effects of the present invention are great.
The embodiment according to the present invention has described an example in which the DFB-LD includes three phase shift portions, but the present invention is not limited to this and the DFB-LD may include a plurality of phase shift portions.
The embodiment according to the present invention has described an example in which a plurality of phase shift portions have the same length, but the present invention is not limited to this and a plurality of phase shift portions may have different lengths. When a plurality of phase shift portions have the same length, simulation for the design of an optimal structure can be simplified.
The embodiment according to the present invention has described an example in which the structure of the diffraction grating of the DFB-LD is symmetrical in the device length direction. For example, in the diffraction grating, two outer regions have the same length L1, and two inner regions have the same length L2. The present invention is not limited to this, and the structure of the diffraction grating of the DFB-LD may be asymmetrical in the device length direction. For example, in the diffraction grating, two outer regions have different lengths L1, and two inner regions have different lengths L2. When the structure of the diffraction grating is symmetrical in the device length direction, simulation for the design of an optimal structure can be simplified.
The embodiment according to the present invention has exemplified a DFB-LD corresponding to the O-waveband, but the waveband may be another one. The embodiment according to the present invention has exemplified the use of an InGaAlAs-base MQW, but a MQW whose base is another material such as InGaAsP may be used.
The embodiment according to the present invention has exemplified the structure, dimensions, material, and the like of each constituent part in the structure, manufacturing method, and the like of a semiconductor laser, but the present invention is not limited to this as long as the function of a semiconductor laser is obtained and has effects.
The present invention is applicable to a communication network system and a computing system.
10: semiconductor laser
104: active layer (MQW)
106: diffraction grating layer
1061: uniform diffraction grating
1062: phase shift portion

Claims (8)

  1. 　　　　　　　A distributed feedback semiconductor laser in which a diffraction grating layer is arranged in a waveguide structure including an active layer,
    　　　　　　　wherein the diffraction grating layer includes a uniform diffraction grating, and a plurality of phase shift portions that shift a phase of light traveling through the waveguide structure,
    　　　　　　　the phase shift portion has a length of a value obtained by dividing the cycle by a predetermined integer of not less than 2, and
    　　　　　　　the integer is set to maximize a difference between a threshold gain of a base mode and a threshold gain of a first mode out of oscillation modes of the distributed feedback semiconductor laser.
  2. 　　　　　　　The semiconductor laser according to claim 1, wherein a value of a difference between a maximum value and minimum value of an optical intensity distribution in a device length direction is smaller than a value of a difference between the maximum value and minimum value of a distributed feedback semiconductor laser including one phase shift portion.
  3. 　　　　　　　The semiconductor laser according to claim 1 or 2, wherein the predetermined integer is 6.
  4. 　　　　　　　The semiconductor laser according to claim 1 or 2, wherein the uniform diffraction grating is divided into four regions by three phase shift portions, and
    　　　　　　　a length of each of two inner regions in a device length direction out of the four regions of the uniform diffraction grating is not larger than 1/3 of a length of each of two outer regions in the device length direction out of the four regions.
  5. 　　　　　　　The semiconductor laser according to claim 1 or 2, wherein an optical waveguide is arranged at least one of below and above the active layer.
  6. 　　　　　　　The semiconductor laser according to claim 1 or 2, further comprising:
    　　　　　　　the waveguide structure including in order a first semiconductor layer, the active layer, and a second semiconductor layer;
    　　　　　　　a p-type semiconductor layer arranged in contact with one side surface of the active layer; and
    　　　　　　　an n-type semiconductor layer arranged in contact with the other side surface of the active layer,
    　　　　　　　wherein the diffraction grating layer is arranged at least one of below and above the waveguide structure.
  7. 　　　　　　　A method of designing a diffraction grating layer of a distributed feedback semiconductor laser in which a diffraction grating layer is arranged in a waveguide structure including an active layer, and the diffraction grating layer includes a uniform diffraction grating, and a plurality of phase shift portions that shift a phase of light traveling through the waveguide structure, the method comprising steps of:
    　　　　　　　setting the cycle and a predetermined integer;
    　　　　　　　calculating a length of the phase shift portion by dividing the cycle by the predetermined integer;
    　　　　　　　calculating a difference between a maximum value and minimum value of an optical intensity distribution in a device length direction based on the cycle and the length of the phase shift portion; and
    　　　　　　　determining the cycle and the length of the phase shift portion to set a value of the difference between the maximum value and the minimum value to be smaller than a value of a difference between the maximum value and minimum value of a distributed feedback semiconductor laser including one phase shift portion.
  8. 　　　　　　　A method of manufacturing a semiconductor laser, comprising a step of forming a diffraction grating layer designed by the method of designing a diffraction grating layer of a semiconductor laser defined in claim 7.
PCT/JP2022/041901 2022-11-10 2022-11-10 Semiconductor laser, method of designing diffraction grating layer of semiconductor laser, and method of manufacturing semiconductor laser WO2024100836A1 (en)

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JPS63299390A (en) * 1987-05-29 1988-12-06 Nec Corp Semiconductor laser device
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JP2008103466A (en) * 2006-10-18 2008-05-01 Nippon Telegr & Teleph Corp <Ntt> Semiconductor laser
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