In recent years, vertical-cavity surface-emitting lasers (VCSELs) have received extensive attention from researchers due to their low threshold current and light emission properties perpendicular to the substrate surface.
Vertical-cavity surface-emitting lasers (VCSELs) have outstanding advantages in terms of threshold current, lifetime, and large-array integration.
Among them, long-wavelength surface vertical emitting lasers have unique application advantages in optical communication, atomic clocks, medical detection and gas detection, so the research on long-wavelength vertical cavity surface emitting lasers is of great significance.
Structure and Principle of Vertical Cavity Surface Emitting Laser
From top to bottom, the structures are P-type electrode, P-type Bragg reflector (P-DBR), active gain region, N-type Bragg reflector (N-DBR), N-type electrode, and substrate.
Compared with edge-emitting semiconductor lasers, the light-emitting direction of VCSELs is perpendicular to the substrate surface, and the Fabry-Perot resonator is shorter. In order to achieve light-emitting conditions, the DBR mirrors in VCSELs require higher reflection efficiency (>99%) .
The performance of the DBR mirror directly affects the threshold current, output power and other main parameters of the VCSEL device. At this stage, it is mainly made of AlGaAs/GaAs materials grown layer by layer, and the optical thickness of each layer is 1/4 of the center wavelength. Oxidation confinement holes are sandwiched between the DBR mirror and the active region for electric and optical field confinement.
The AlGaAs material with high Al composition is used above and below the active region of the VCSEL device, and placed in a high temperature and humid environment, a uniform and dense oxide layer can be formed by a wet oxidation process.
The active region is sandwiched between P-DBR and N-DBR. When the VCSEL device is working, a standing wave will be formed in the active region, so that the photon energy is amplified and finally lasing is formed. In order to form standing waves, the optical thickness of the active region should be an integral multiple of half wavelength.
The material of the quantum well in the active region is generally selected from the InGaAs/GaAsP material system, because InGaAs is generally in a state of compressive strain, and GaAsP can provide strain compensation, which solves the phenomenon that the strain of traditional materials increases with the increase of the lasing wavelength, and can also provide higher gain.
Compared with traditional edge-emitting semiconductor lasers, VCSELs have many unique advantages due to the characteristic of emitting light perpendicular to the surface of the substrate.
Generally, the DBR mirror reflection efficiency in edge-emitting semiconductor lasers only needs to reach 60% to form lasing, while the DBR mirror reflection efficiency in VCSEL devices needs to reach more than 99%.
Although it increases the difficulty of the manufacturing process, due to the higher reflectivity, the threshold current of the VCSEL is lower, which greatly reduces the power and intra-cavity damage of the device, and improves the service life of the device; and due to the light output direction of the VCSEL, It is more suitable for two-dimensional array integration; combined with the MEMS process, the wavelength modulation function can be realized, so that a single device can be used more; Unique advantages such as circuit coupling.
In recent years, vertical-cavity surface-emitting lasers (VCSELs) have received extensive attention from researchers due to their low threshold current and light emission properties perpendicular to the substrate surface.
Vertical-cavity surface-emitting lasers (VCSELs) have outstanding advantages in terms of threshold current, lifetime, and large-array integration.
Among them, long-wavelength surface vertical emitting lasers have unique application advantages in optical communication, atomic clocks, medical detection and gas detection, so the research on long-wavelength vertical cavity surface emitting lasers is of great significance.
Structure and Principle of Vertical Cavity Surface Emitting Laser
From top to bottom, the structures are P-type electrode, P-type Bragg reflector (P-DBR), active gain region, N-type Bragg reflector (N-DBR), N-type electrode, and substrate.
Compared with edge-emitting semiconductor lasers, the light-emitting direction of VCSELs is perpendicular to the substrate surface, and the Fabry-Perot resonator is shorter. In order to achieve light-emitting conditions, the DBR mirrors in VCSELs require higher reflection efficiency (>99%) .
The performance of the DBR mirror directly affects the threshold current, output power and other main parameters of the VCSEL device. At this stage, it is mainly made of AlGaAs/GaAs materials grown layer by layer, and the optical thickness of each layer is 1/4 of the center wavelength. Oxidation confinement holes are sandwiched between the DBR mirror and the active region for electric and optical field confinement.
The AlGaAs material with high Al composition is used above and below the active region of the VCSEL device, and placed in a high temperature and humid environment, a uniform and dense oxide layer can be formed by a wet oxidation process.
The active region is sandwiched between P-DBR and N-DBR. When the VCSEL device is working, a standing wave will be formed in the active region, so that the photon energy is amplified and finally lasing is formed. In order to form standing waves, the optical thickness of the active region should be an integral multiple of half wavelength.
The material of the quantum well in the active region is generally selected from the InGaAs/GaAsP material system, because InGaAs is generally in a state of compressive strain, and GaAsP can provide strain compensation, which solves the phenomenon that the strain of traditional materials increases with the increase of the lasing wavelength, and can also provide higher gain.
Compared with traditional edge-emitting semiconductor lasers, VCSELs have many unique advantages due to the characteristic of emitting light perpendicular to the surface of the substrate.
Generally, the DBR mirror reflection efficiency in edge-emitting semiconductor lasers only needs to reach 60% to form lasing, while the DBR mirror reflection efficiency in VCSEL devices needs to reach more than 99%.
Although it increases the difficulty of the manufacturing process, due to the higher reflectivity, the threshold current of the VCSEL is lower, which greatly reduces the power and intra-cavity damage of the device, and improves the service life of the device; and due to the light output direction of the VCSEL, It is more suitable for two-dimensional array integration; combined with the MEMS process, the wavelength modulation function can be realized, so that a single device can be used more; Unique advantages such as circuit coupling.
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