VCSEL Top DBR Protrusion for Mode Dispersion Control
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Solution Overview
Problem
In short-distance optical fiber communication using VCSELs, mode dispersion limits transmission performance due to varying propagation velocities of laser light across different eigenmodes in multimode fibers, and existing solutions either fail to adequately limit lower mode oscillation or increase higher mode oscillation while also causing light diffusion and coupling losses.
Innovation Solution
A VCSEL design with a top distributed Bragg reflecting mirror featuring high and low refractive index layers alternately stacked, where the top high refractive index layer has a central region with a protrusion and a peripheral region, optimizing optical thickness to enhance reflectance ratio differences between modes and reduce light emission angles, thereby promoting higher mode oscillation and minimizing lower mode oscillation while reducing light diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protrusion (mirror extension) is provided in the center of the upper mirror stack layer to increase reflectance ratio, then low order modes oscillate more easily, but high order modes are suppressed and mode dispersion is not effectively reduced
Solution Approach 1:
The patent applies local quality by creating spatially varying reflectance ratios within the upper mirror stack layer. The central region has a different reflectance ratio than the peripheral region, achieved through selective removal of high refractive index layers in the center. This local differentiation enables preferential oscillation of specific eigenmodes (7th-10th orders) while suppressing others, thereby reducing mode dispersion without compromising overall laser performance
Solution Approach 2:
The patent changes the reflectance ratio parameter across different regions of the upper mirror stack layer. By removing high refractive index layers from the central region, the reflectance ratio is reduced in the center while maintaining higher reflectance at the periphery. This parameter variation creates the desired eigenmode distribution that minimizes propagation delay differences
2Reliability
If higher modes are promoted to reduce mode dispersion, then propagation delay difference is minimized, but light diffusion increases and coupling loss with optical fiber worsens
Solution Approach 1:
The patent uses local quality to create a reflectance ratio gradient within the upper mirror stack layer. The peripheral region maintains high reflectance to promote higher mode oscillation and reduce mode dispersion, while the central region has reduced reflectance to control beam divergence. This spatial differentiation allows simultaneous achievement of low mode dispersion and good fiber coupling efficiency
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
This design effectively reduces mode dispersion by favoring higher mode oscillation, improves transmission performance by minimizing propagation delay differences, and reduces coupling losses with optical fibers by controlling light emission angles and enhancing reflectance ratios.
Implementation Method 1
a top distributed Bragg reflecting mirror including high refractive index layers and low refractive index layers which are alternately stacked
Implementation Method 2
The optical thickness dp×n of the peripheral region of the top high refractive index layer corresponds to 1/4, 3/4, 5/4, etc. of the wavelength of laser light and increases the reflectance ratio
Implementation Method 3
The central region has a protrusion that projects relative to the peripheral region in a direction in which the laser light is emitted... the central region... generates the effect of collecting light toward the center and thereby limits the angle at which laser light is emitted
Data Source
AI summary
The top high refractive index layer of the top DBR mirror has a central region and a peripheral region. The central region has a protrusion that projects relative to the peripheral region in a direction in which the laser light is emitted. The VCSEL satisfies relationships below:dp×n=(1/4+N/2)×λ, anddc×n=dp×n+(1/4+M/2)×λwhereλ is a wavelength of the laser light in vacuum;dc is a film thickness of the top high refractive index layer in the central region;dp is a film thickness of the top high refractive index layer in the peripheral region;n is a refractive index of the top high refractive index layer; andN and M are zero or a natural number.