VCSEL Stepped Apertures for Single-Mode High-Speed Operation
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Solution Overview
Problem
Commercially available Vertical-cavity surface-emitting lasers (VCSELs) typically generate multi-mode light, which limits the distance and performance of optical communications due to modal dispersion and wavelength-dependent coupling, and previous methods to modify them for single-mode operation often result in increased laser threshold, lower bandwidth, and higher RIN noise, along with increased manufacturing costs and complexity.
Innovation Solution
A multiple-aperture VCSEL design with a two-element upper reflector, where a wider-diameter aperture is used for current injection and a narrower aperture for mode selection, allowing for improved mode selectivity without affecting electrical characteristics, achieved through lateral oxidation of layers with varying aluminum content in the upper reflector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single aperture is used in VCSEL for both current injection and mode selection, then the device structure is simple, but mode selectivity is poor and higher-order modes cannot be effectively suppressed
Solution Approach 1:
The single aperture is divided into two separate apertures: a current-injection aperture with larger diameter for efficient current delivery, and a mode-selection aperture with smaller diameter for filtering higher-order modes. This segmentation allows each aperture to perform its specific function optimally without compromising the other.
Solution Approach 2:
Different regions of the VCSEL structure are assigned different aperture diameters tailored to their specific functions. The current-injection region uses a larger aperture to minimize resistance, while the mode-selection region uses a smaller aperture to achieve single-mode operation. This local differentiation resolves the contradiction between current injection efficiency and mode selectivity.
2Manufacturing precision
If a smaller aperture is used for mode selection, then single-mode operation is achieved, but current injection efficiency decreases and input resistance increases
Solution Approach 1:
The current-injection aperture and mode-selection aperture are separated into different structural layers. The current-injection aperture (larger diameter) is positioned in the lower DBR layer to ensure efficient current delivery, while the mode-selection aperture (smaller diameter) is positioned in the upper DBR layer to filter modes. This vertical segmentation eliminates the trade-off between current injection and mode selection.
Solution Approach 2:
The solution moves from a single-plane aperture design to a multi-layer vertical structure. By stacking apertures at different heights with different diameters, the design exploits the vertical dimension to simultaneously achieve both large aperture for current injection and small aperture for mode selection, resolving the contradiction.
3Manufacturing precision
If previous modification methods are applied to achieve single-mode operation, then mode purity improves, but laser threshold increases and bandwidth decreases
Solution Approach 1:
The invention optimizes the diameters of the two apertures as key parameters: the current-injection aperture diameter is set to maximize current delivery efficiency, while the mode-selection aperture diameter is set to achieve single-mode operation. By carefully tuning these parameters, the design achieves mode purity without increasing threshold or reducing bandwidth.
Solution Approach 2:
Separating the current-injection function and mode-selection function into distinct apertures allows each to be optimized independently. The current-injection aperture can be large to minimize resistance and threshold, while the mode-selection aperture can be small to ensure single-mode operation. This independence prevents the degradation of data rate performance.
4Reliability
If a wider aperture is used for current injection, then current delivery improves, but higher-order modes are not suppressed and single-mode operation is not achieved
Solution Approach 1:
The current-injection aperture and mode-selection aperture are segmented into different vertical layers. The current-injection aperture (larger diameter) is in the lower DBR layer to maximize current delivery, while the mode-selection aperture (smaller diameter) is in the upper DBR layer to suppress higher-order modes. This vertical segmentation allows both functions to coexist without interference.
Solution Approach 2:
The design transitions from a single-plane aperture to a multi-layer vertical aperture structure. By utilizing the vertical dimension, the system accommodates both a large aperture for current injection and a small aperture for mode selection at different heights, resolving the contradiction between current delivery efficiency and mode selectivity.
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 enables stable single-mode operation with increased emitted beam power, reduced input resistance, and maintained power in the primary mode, achieving error-free data transmission up to 500 meters at 32 Gb/s and 1 km at 26 Gb/s at various temperatures without pre-emphasis or error-correction techniques.
Implementation Method 1
achieved through lateral oxidation of layers with varying aluminum content in the upper reflector
Data Source
AI summary
Vertical-cavity surface-emitting lasers (VCSELs) and methods for making such are provided. The VCSELs include stepped upper reflectors having respective differently-sized apertures. This allows the lower portion of the reflector to have formed therein a wider-diameter aperture to allow for increased current injection. The upper portion of the reflector has formed therein a narrower-diameter, mode-selecting aperture to allow higher-order modes to be reduced, leading to single-mode operation. The VCSELs are thus capable of higher-power emission in a single mode, allowing for longer-distance signaling over optical fiber, despite modal dispersion within the fiber and/or at the coupling between the VCSEL and the fiber. The two differently-sized apertures can be formed via respective lateral oxidation processes following etch-down to form the respective steps of the upper reflector. Differences in composition across the upper reflector results in temperature-dependence of the oxidation process, allowing the apertures to be formed with different sizes.