Tapered Waveguide for Optical Receiver Bandwidth
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Solution Overview
Problem
In optical receivers with a MMI waveguide and photodiode, the high peak light intensity causes local variations in photo carrier density, leading to a narrow operating bandwidth due to increased photo carrier accumulation, especially when incident light intensity is high.
Innovation Solution
A tapered waveguide is introduced between the input waveguide and photodiode, with a half spread angle configured to excite higher-order modes, and the photodiode's width either remains constant or increases, matching or exceeding the tapered waveguide's half spread angle, to distribute light intensity more evenly and reduce peak intensities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a MMI waveguide is used to reduce peak light intensity, then light intensity distribution becomes more uniform, but light intensity variation in the width direction increases causing local photo carrier density increase
Solution Approach 1:
The photodiode width is varied in the width direction to create local quality differences. The width is smaller at regions corresponding to high light intensity peaks and larger at regions corresponding to low light intensity, thereby localizing photo carrier generation to maintain uniform overall density and prevent bandwidth narrowing.
Solution Approach 2:
The photodiode width parameter is changed in the width direction to match the light intensity distribution. By making the width variable rather than uniform, the photodiode adapts its geometric parameter to the spatial variation of light intensity, ensuring uniform photo carrier density distribution.
2Power
If incident light intensity is increased to improve signal strength, then detection sensitivity improves, but photo carrier accumulation increases causing operating bandwidth to narrow
Solution Approach 1:
The photodiode width is varied in the width direction to create local quality differences. The width is smaller at regions corresponding to high light intensity peaks and larger at regions corresponding to low light intensity, thereby localizing photo carrier generation to maintain uniform overall density and prevent bandwidth narrowing.
Solution Approach 2:
The photodiode width parameter is changed in the width direction to match the light intensity distribution. By making the width variable rather than uniform, the photodiode adapts its geometric parameter to the spatial variation of light intensity, ensuring uniform photo carrier density distribution.
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 configuration effectively levels the light intensity distribution, reducing peak intensities and preventing excessive photo carrier density increases, thereby broadening the operating bandwidth even under high incident light conditions.
Implementation Method 1
a half spread angle of the tapered waveguide is configured to cause higher-order mode excitation when receiving optical signal from the input waveguide
Implementation Method 2
a photodiode formed over the substrate... to allow the photodiode to receive an optical signal
Data Source
AI summary
A tapered waveguide is provided for connection between an input waveguide and a photodiode. The width of the tapered waveguide increases as it extends from the input end that is connected to the input waveguide towards the output end that is connected to the photodiode. The tapered waveguide has an optimum half spread angle to cause higher-order mode excitation when receiving optical signal from the input waveguide. The photodiode either has a constant width or increases in width as it extends away from the output end of the tapered waveguide, its half spread angle being equal to or less than the half spread angle of the tapered waveguide.