Silicon Modulator ACLCPW Phase Shifter Bandwidth
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Solution Overview
Problem
Standard silicon electro-optic modulators face limitations due to microwave mode conversion and impedance mismatch, leading to reduced bandwidth and increased RF power consumption, particularly with asymmetric coplanar waveguide electrodes.
Innovation Solution
The implementation of an Alternative Capacitive Loading Coplanar Waveguide (ACLCPW) active phase shifter with balanced capacitive loading in both slots of the coplanar waveguide, allowing for symmetric operation and 50-ohm equivalent microwave impedance, which suppresses mode conversion and facilitates easier impedance matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an asymmetric CPW electrode scheme is used with capacitance loaded in one slot only, then the modulator can achieve high modulation bandwidth, but microwave mode conversion occurs causing impedance mismatch and reducing bandwidth
Solution Approach 1:
The patent applies asymmetry in reverse by using a symmetric CPW structure where capacitance is loaded in both slots equally. This symmetric design eliminates the mode conversion problem that occurs in asymmetric structures, while still achieving high bandwidth through proper impedance matching. The symmetric CPW provides stable microwave transmission without the harmful mode conversion effects.
Solution Approach 2:
The patent changes the capacitance loading configuration from asymmetric (one slot only) to symmetric (both slots equally). This parameter change transforms the CPW from asymmetric to symmetric, eliminating mode conversion and improving microwave stability. The capacitance values in both slots are designed to be equal, creating a balanced structure that maintains impedance consistency throughout the modulator.
2Power
If high capacitance per unit length is used to achieve high modulation efficiency, then modulation depth improves, but microwave impedance becomes low (20-30 ohm) making impedance matching difficult and increasing RF power consumption
Solution Approach 1:
The patent optimizes the capacitance per unit length parameter to achieve the desired modulation efficiency while maintaining microwave impedance at standard 50 ohm levels. By carefully designing the capacitance values in both slots and adjusting the geometric parameters of the CPW, the patent achieves high modulation depth without creating excessive impedance mismatch. This parameter optimization allows standard 50-ohm drivers to be used directly.
Solution Approach 2:
The symmetric CPW structure creates equipotential conditions in both slots, ensuring uniform capacitance distribution and consistent microwave impedance throughout the modulator. This equipotential design eliminates impedance variations that would otherwise occur in asymmetric structures, simplifying the impedance matching process and reducing RF power consumption.
3Power
If a longer modulator is used to increase modulation depth, then modulation efficiency improves, but the device length increases requiring more space and potentially affecting other design parameters
Solution Approach 1:
The patent changes the capacitance distribution parameter from concentrated (one slot) to distributed (both slots equally). This parameter change allows the modulator to achieve the required modulation depth with a shorter overall length, as the capacitance is more efficiently distributed throughout the device. The symmetric configuration provides better modulation efficiency per unit length, reducing the total device footprint.
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 enhances the 3 dB electro-optic bandwidth from 11 GHz to 20 GHz and enables 50-ohm impedance matching, reducing RF power consumption and improving compatibility with standard equipment.
Implementation Method 1
The active phase shifter, i.e., the PN junctions or MOS capacitors, is located in one slot of the CPW and connected to one of the two ground metals (G) and the signal metal (S) by properly impurity-doped regions. This common electrode scheme constructs an asymmetric CPW because only one slot is loaded with capacitance from the electrically-connected phase shifter.
Implementation Method 2
There are several electromagnetic field modes in an asymmetric CPW such as the CPW even mode, odd mode, and the surface wave-like mode, with different microwave impedance for each.
Implementation Method 3
Silicon electro-optic modulators play an increasing role in the field of optic communication owing to their process compatibility with CMOS technology.
Data Source
AI summary
Embodiments of the present disclosure provide a high-speed silicon modulator without the microwave mode conversion and provide 50-ohm impedance matching to drivers simultaneously. In one aspect, a device may include an input waveguide region, an optic splitter, two optic phase shifters, an optic splitter, and an output waveguide. The device may include two curved waveguides. Either or both of the curved waveguides may have specially doped regions including PN junctions or MOS capacitors. The PN junctions or MOS capacitors may be alternatively connected to both slots of a coplanar waveguide forming the electrodes.