Monolithic E-O Modulator Comb-Shaped Transmission Line
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Monolithic electro-optical modulators face a significant velocity mismatch between optical and electrical paths, which compromises their bandwidth and operating speed due to the mismatch in propagation velocities, especially when fabricated on silicon or silicon-on-insulator substrates.
Innovation Solution
The implementation of a slow-wave transmission line with recesses or slots in the electrical conductors slows down the propagation velocity of the electrical modulation signal to match it with the optical signal's velocity, reducing the velocity mismatch and enhancing the modulator's bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional transmission line is used in parallel with the optical waveguide, then the electrical modulation signal can be applied to the modulator, but the propagation velocity of the electrical signal does not match the propagation velocity of the optical signal, resulting in velocity mismatch that compromises bandwidth and operating speed
Solution Approach 1:
The patent modifies the electrical transmission line parameters by introducing periodic slots or recesses in the ground conductor, which changes the effective inductance and capacitance per unit length. This parameter modification slows down the electrical signal propagation velocity to match the optical signal velocity in the waveguide, resolving the velocity mismatch problem and improving both operating speed and bandwidth
Solution Approach 2:
The ground conductor of the transmission line is segmented by introducing periodic slots or recesses along its length. This segmentation creates a slow-wave structure that reduces the phase velocity of the electrical signal without affecting the optical signal path, thereby achieving velocity matching between electrical and optical domains
2Reliability
If the propagation velocity of the electrical modulation signal is increased to match the optical signal velocity, then bandwidth can be improved, but this would require changing the transmission line structure in ways that may increase complexity or loss
Solution Approach 1:
Rather than fundamentally redesigning the transmission line topology, the patent achieves velocity matching by modifying existing parameters of the microstrip or coplanar waveguide structure through the addition of periodic slots or recesses in the ground conductor. This approach improves bandwidth while maintaining relative structural simplicity and using standard fabrication processes
Data Source
AI summary
Various embodiments of a monolithic electro-optical (E-O) modulator are described, which may be fabricated on a silicon-on-insulator substrate. The monolithic E-O modulator includes an optical waveguide that allows an optical signal to propagate therein. The monolithic E-O modulator also includes a comb-shaped transmission line for conducting an electrical modulation signal that modulates the optical signal. The comb-shaped transmission line includes electrical conductors running in parallel with the optical waveguide. At least one of the conductors includes recesses or thin slots that form the conductor into a shape having a plurality of teeth, like a comb. The comb-shaped transmission line can be engineered to realize a close matching between a propagation velocity of the optical signal along the optical waveguide and a group velocity of the electrical modulation signal along the comb-shaped transmission line, which helps to achieve a high operating speed of the monolithic E-O modulator.