Edge-Emitting Laser Vertical Angle Reduction via Passive Waveguide
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Solution Overview
Problem
Conventional edge-emitting laser diodes have a high vertical beam-spread angle, leading to inefficient optical-fiber coupling due to poor symmetric light-field patterns, which limits their application in optoelectronic systems.
Innovation Solution
Incorporating an AlInAs epitaxial layer with a passive waveguide structure, where the passive waveguide layer has a higher refractive index than the bottom cladding layer, to confine the light field and reduce the vertical emitting angle, achieving a more symmetrical and round far-field pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional edge-emitting laser diode structure is used, then the device achieves basic laser emission, but the vertical beam-spread angle becomes large (greater than 30 degrees), resulting in poor optical-fiber coupling efficiency
Solution Approach 1:
The bottom cladding layer is segmented into two distinct parts: a first bottom cladding layer and a second bottom cladding layer. This segmentation allows each layer to have different refractive indices, with the second layer having a higher refractive index to better confine the light field vertically and reduce the beam-spread angle, thereby improving optical-fiber coupling efficiency without compromising basic laser emission
Solution Approach 2:
The patent applies local quality by creating a spatial variation in refractive index within the bottom cladding region. The second bottom cladding layer is positioned specifically beneath the active region and has a higher refractive index than the first bottom cladding layer, providing localized light confinement exactly where needed to control the vertical emission pattern and reduce the beam-spread angle
2Power
If the light field is confined in the active region layer to achieve higher modal gain, then the threshold current decreases, but the vertical emitting angle increases due to the long narrow resonant cavity geometry
Solution Approach 1:
The patent addresses the dimensional constraint of the long narrow resonant cavity by introducing a vertical dimension solution through the two-layer bottom cladding structure. The higher refractive index of the second bottom cladding layer creates additional vertical light confinement, effectively counteracting the vertical divergence caused by the horizontal cavity geometry, thus maintaining low threshold current while reducing the vertical emitting angle
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces the vertical beam-spread angle to less than 30 degrees, improving optical-fiber coupling efficiency and achieving a more symmetrical light pattern, thereby enhancing the performance of edge-emitting laser diodes.
Implementation Method 1
Since a refractive index (an n value) of each of the top and bottom cladding layers 904, 902 is lower than that of any of the lower SCH layer 9031, the active region layer 903 and the upper SCH layer 9032, so the light field would be mature and then propagate in the material with a higher n value according to the total reflection theory
Implementation Method 2
a light refraction index of the passive waveguide layer is larger than that of the bottom cladding layer
Data Source
AI summary
An edge-emitting laser having a small vertical emitting angle includes an upper cladding layer, a lower cladding layer and an active region layer sandwiched between the upper and lower cladding layers. By embedding a passive waveguide layer within the lower cladding to layer, an extended lower cladding layer is formed between the passive waveguide layer and the active region layer. In addition, the refractive index (referred as n-value) of the passive waveguide layer is larger than the n-value of the extended lower cladding layer. The passive waveguide layer with a larger n-value would guide the light field to extend downward. The extended lower cladding layer can separate the passive waveguide layer and the active region layer and thus expand the near-field distribution of laser light field in the resonant cavity, so as to obtain a smaller vertical emitting angle in the far-field laser light field.