Rib-type waveguide silicon modulators for high extinction ratio
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Solution Overview
Problem
Silicon modulators in CMOS processes face high propagation loss due to absorption and scattering at grain boundaries, limiting their extinction ratio performance, especially in 100 G long-haul coherent transmission systems, where extending modulator length is necessary but high driving voltage poses risks of oxide breakdown.
Innovation Solution
A silicon-based rib-waveguide modulator with a silicon-on-insulator substrate and a ring resonator structure, featuring multiple top silicon layers and a thin dielectric gate layer, allows for low driving voltage operation by accumulating, depleting, or inverting free carriers to modulate the refractive index, thereby enhancing extinction ratio without increasing voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the modulator length is extended to achieve high extinction ratio, then the extinction ratio performance is improved, but the propagation loss increases due to absorption and scattering at grain boundaries
Solution Approach 1:
The patent changes the physical state and properties of the silicon material by transitioning from polycrystalline silicon to single-crystal silicon. This parameter change eliminates grain boundaries, thereby reducing absorption and scattering losses while allowing the modulator length to be extended for high extinction ratio performance.
Solution Approach 2:
The patent employs a composite structure combining single-crystal silicon layers with specific dielectric materials (such as silicon dioxide and silicon nitride) to create a waveguide structure that minimizes propagation loss while enabling extended length operation for high extinction ratio modulation.
2Measurement precision
If the driving voltage is increased to improve extinction ratio, then the extinction ratio performance is improved, but the risk of oxide breakdown increases
Solution Approach 1:
The patent changes the material parameter from polycrystalline to single-crystal silicon, which fundamentally alters the propagation characteristics. This enables achieving high extinction ratio through increased modulator length rather than increased voltage, thereby maintaining reliability and avoiding oxide breakdown.
3Ease of manufacture
If polycrystalline silicon is used in CMOS process, then the manufacturing compatibility is improved, but the propagation loss increases due to grain boundary absorption and scattering
Solution Approach 1:
The patent transitions the silicon material parameter from polycrystalline to single-crystal form. Single-crystal silicon can be integrated into CMOS processes through established techniques such as silicon-on-insulator (SOI) technology, maintaining manufacturing compatibility while eliminating grain boundary losses.
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
The solution reduces optic loss and increases modulation efficiency, enabling longer modulator lengths with very low driving voltage, thus addressing the limitations of existing silicon modulators in achieving high extinction ratios.
Implementation Method 1
When one or more electric signals are applied on the first and second electric contacts, free carriers may accumulate, deplete or invert within the first and second top silicon layers on the first and second sides of the thin dielectric gate layer beneath the ring-shape rib-type waveguide, simultaneously, and a refractive index of the ring-shape rib-type waveguide confining optical fields may be modulated
Data Source
AI summary
A ring optical modulator includes a SOI substrate, including at least first and second top silicon layers, and a silicon-based ring resonator formed on the SOI substrate. The silicon-based ring resonator includes first and second top silicon layers, a thin dielectric gate layer disposed between the top silicon layers, first and second electric contacts, and first rib-type waveguide and ring-shape rib-type waveguide formed on the second top silicon layer. The thin dielectric layer includes a first side in contact with the first top silicon layer and a second side in contact with the second top silicon layer. With electric signals applied on the electric contacts, free carriers accumulate, deplete or invert within the top silicon layers on the first and second sides of the thin dielectric gate layer beneath the ring-shape rib-type waveguide, simultaneously, and a refractive index of the ring-shape rib-type waveguide confining optical fields is modulated.