Semiconductor Optical Apparatus Mode Transformation via MQW Segmentation
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Solution Overview
Problem
Mach Zehnder modulators face challenges with optical loss and poor coupling efficiency due to tightly confined optical modes, requiring complex fabrication steps and additional growth processes for mode transformation, which increases costs and reduces device yield.
Innovation Solution
A semiconductor optical apparatus with a first waveguide region and a second active waveguide region, where the upper multiple quantum well layer is separated from the lower multiple quantum well layer by a spacer layer, and a mode transformation region is etched to reduce the optical mode size, allowing for simplified mode expansion and integration with active sections like SOAs or lasers without additional regrowth steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large number of quantum wells (20-30 or more) are used in the MZM core to minimize device length and maximize speed, then modulation speed is improved, but optical mode confinement becomes very tight resulting in large angular divergence and poor coupling efficiency
Solution Approach 1:
The patent divides the multiple quantum well layer into two separate multiple quantum well layers (first MQW layer and second MQW layer) separated by a spacer layer. This segmentation allows independent optimization of each layer's function while maintaining the total quantum well count needed for high-speed modulation.
Solution Approach 2:
The patent introduces a vertical dimension by stacking two MQW layers separated by a spacer layer, transforming the mode transformation function from a horizontal lateral expansion to a vertical layered structure. This enables mode size adjustment without increasing lateral device footprint.
2Reliability
If a waveguide mode transformer is incorporated to overcome tight mode confinement, then coupling efficiency is improved, but fabrication complexity increases due to additional selective area epitaxy growth steps
Solution Approach 1:
The patent merges the mode transformation function with the existing multiple quantum well structure by introducing a spacer layer between two MQW layers. This integration eliminates the need for separate mode transformer components and their associated selective area epitaxy growth steps.
Solution Approach 2:
The spacer layer between the two MQW layers automatically provides mode transformation functionality as an inherent part of the device structure, eliminating the need for external or additional mode transformer components.
3Reliability
If another mode transformer is added between SOA/laser active region and phase modulating region, then mode matching is improved, but device yield decreases due to additional regrowth steps
Solution Approach 1:
The first multiple quantum well layer serves dual functions: it provides the necessary optical confinement for high-speed modulation and simultaneously acts as a mode transformer to match modes between the SOA/laser active region and the phase modulating region. This multi-functionality eliminates the need for a separate mode transformer.
Solution Approach 2:
The patent combines the mode transformation function with the SOA/laser active region by using the first MQW layer as both the gain medium and the mode transformation element, eliminating the need for additional regrowth steps.
4Shape
If selective area epitaxy is used to create mode transformer, then mode size transformation is achieved, but manufacturing costs increase due to additional fabrication steps
Solution Approach 1:
The patent extracts the mode transformation function from a separate fabrication process (selective area epitaxy) and integrates it into the existing multiple quantum well structure through the spacer layer approach, eliminating additional manufacturing steps.
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 approach simplifies mode expansion and integration, reducing fabrication complexity and costs while maintaining high optical confinement factors, thereby improving coupling efficiency and device yield.
Implementation Method 1
The upper multiple quantum well layer comprises a mode transformation region configured to reduce the size of an optical mode from the first mode size to the second mode size
Implementation Method 2
The lower multiple quantum well layer is physically separated from the upper multiple quantum well layer by a spacer layer
Data Source
Figure 1a~1b
Figure 2a~2c
Figure 3
AI summary
The invention relates to a semiconductor optical apparatus (100), wherein the semiconductor optical apparatus (100) comprises a first waveguide region (101) defining a first mode size and a second active waveguide region defining a second mode size being smaller than the first mode size. The second active waveguide region is optically coupled to the first waveguide region (101) and the second active waveguide region comprises a lower multiple quantum well layer (103) and an upper multiple quantum well layer (105) located above the lower multiple quantum well layer (103). The lower multiple quantum well layer (103) is physically separated from the upper multiple quantum well layer (105) by a spacer layer (107). The upper multiple quantum well layer (105) comprises a mode transformation region (1 05a) configured to reduce the size of an optical mode from the first mode size to the second mode size. In an implementation form, the first waveguide region (101) is a first waveguide active region comprising a further multiple quantum well layer and the modal index defined by the further multiple quantum well layer is substantially equal to the modal index defined by the lower multiple quantum well layer (103).