Silicon Modulator with Nonuniform Capacitance for Impedance Matching
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Solution Overview
Problem
Silicon electro-optic modulators face a trade-off between modulation efficiency and speed, with PN diode-based modulators requiring longer lengths for deeper modulation but resulting in higher capacitance per unit length, leading to increased microwave loss and power consumption, while MOS capacitor-based modulators have higher efficiency but lower impedance matching and longer lengths for high-speed modulation.
Innovation Solution
The design incorporates phase shifters with varying capacitance per unit length along the optical propagation direction, featuring sections with different PN junction widths to optimize modulation efficiency and impedance matching, allowing for shorter device lengths without sacrificing modulation depth, using a Mach-Zehnder Interferometer structure with specially doped regions and PN diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If PN diode-based modulators are used to achieve deeper modulation, then modulation depth is improved, but device length increases
Solution Approach 1:
The patent applies local quality by varying the capacitance per unit length at different sections of the modulator. The first section has lower capacitance for high-speed modulation, while the second section has higher capacitance for deeper modulation. This spatial variation in capacitance density allows each section to be optimized for its specific function, resolving the contradiction between modulation depth and device length.
2Manufacturing precision
If higher capacitance per unit length is used to improve modulation efficiency, then modulation efficiency is improved, but microwave loss increases
Solution Approach 1:
The modulator is segmented into multiple sections with different capacitance per unit length. The first section uses lower capacitance to minimize microwave loss and enable high-speed operation, while the second section uses higher capacitance to provide sufficient modulation efficiency. This segmentation allows the system to achieve both low loss and high efficiency without requiring uniform high capacitance throughout the entire device.
3Manufacturing precision
If higher capacitance per unit length is used to improve modulation efficiency, then modulation efficiency is improved, but modulation speed decreases
Solution Approach 1:
The modulator is divided into sections with different capacitance densities. The first section employs lower capacitance per unit length to maintain high modulation speed, while the second section uses higher capacitance per unit length to achieve sufficient modulation efficiency. This segmentation allows the device to simultaneously achieve both high speed and high efficiency, as each section is optimized for its specific operational requirement.
4Manufacturing precision
If higher capacitance per unit length is used, then modulation efficiency is improved, but impedance matching becomes difficult
Solution Approach 1:
The patent implements local quality by creating different capacitance densities in different sections, which correspond to different impedance levels. The first section with lower capacitance provides better impedance matching to standard 50-Ohm drivers, while the second section with higher capacitance provides the necessary modulation efficiency. This spatial differentiation of capacitance density allows both good impedance matching and high modulation efficiency to coexist.
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 enables high-speed silicon modulators with improved impedance matching to 50-Ohm drivers, reduced microwave loss, and maintained modulation depth, achieving bandwidths up to 20 GHz or greater while minimizing device length and power consumption.
Implementation Method 1
Silicon electro-optic modulators play an increasing role in the field of optic communication due to its process compatibility with CMOS technology
Implementation Method 2
at least one of the first and second phase shifters may have variant capacitance per unit length along a direction of optical propagation
Data Source
AI summary
A device, such as a silicon modulator, in accordance with the present disclosure employs PN diodes without sacrificing the modulation depth, while achieving lower loss and better impedance matching to 50-Ohm drivers. In one embodiment, the device includes an input waveguide, an input optical splitter coupled to the input waveguide, first and second optical phase shifters coupled to the input optical splitter, an output optical splitter coupled to the first and second phase shifters, and an output waveguide coupled to the output optical splitter. The phase shifters are designed with variant capacitance per unit length.