Electro-refraction Modulator with Regrown P-N Junction
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Solution Overview
Problem
Existing silicon photonic modulators face limitations in energy efficiency, size, and bandwidth due to weak electro-optical effects in single-crystal silicon, requiring longer lengths and higher drive voltages, which are inadequate for high-speed applications.
Innovation Solution
An electro-refraction modulator with a single-crystal regrown p-n junction is implemented, featuring a stack of layers with varying doping levels, allowing for high-tuning efficiency without significant absorption loss, achieved through precise definition of p-n junctions using single-crystal regrowth techniques like MOCVD or MBE, rather than ion implantation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If reverse-biased p-n junctions are used for phase shifting, then bandwidth is improved (>50 GHz), but tuning efficiency decreases requiring millimeter-length modulators
Solution Approach 1:
The patent applies local quality by creating a highly localized high-doping region (1×10^19 to 1×10^20 atoms/cm³) confined to a thin layer (10-50 nm) at the p-n junction interface. This localized high-doping region provides strong electro-optical modulation exactly where the optical mode overlaps with the junction, maximizing tuning efficiency in a compact volume while maintaining the bandwidth benefits of reverse-biased operation.
Solution Approach 2:
The patent employs composite doping structures with multiple doping levels (outer regions at 1×10^17 to 1×10^18 atoms/cm³, intermediate regions at 1×10^18 to 1×10^19 atoms/cm³, and junction region at 1×10^19 to 1×10^20 atoms/cm³). This composite doping profile optimizes the balance between tuning efficiency (achieved through high junction doping) and absorption loss (mitigated by lower doping in outer regions), enabling compact modulator design with millimeter-scale length.
2Power
If higher doping levels are used to increase tuning efficiency, then phase change per unit length is improved, but absorption-induced propagation loss increases
Solution Approach 1:
The patent implements local quality by concentrating the highest doping level (1×10^19 to 1×10^20 atoms/cm³) in a thin layer (10-50 nm) precisely at the p-n junction interface where the optical mode has maximum overlap. This localized high-doping region provides strong electro-optical modulation without requiring the entire waveguide to be highly doped, thus achieving high tuning efficiency while minimizing overall absorption loss.
Solution Approach 2:
The patent applies parameter changes by varying the doping concentration across different spatial regions of the waveguide. The doping profile transitions from lower concentrations (1×10^17 to 1×10^18 atoms/cm³) in outer regions to intermediate concentrations (1×10^18 to 1×10^19 atoms/cm³) in transition regions, and finally to high concentrations (1×10^19 to 1×10^20 atoms/cm³) at the junction interface. This graded parameter change optimizes the balance between tuning efficiency and propagation loss.
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 modulator achieves high bandwidth, compact size, and reduced drive voltage, facilitating efficient silicon-photonic links for applications like wavelength-division multiplexing by decoupling high doping levels from absorption loss.
Implementation Method 1
These devices use the widening of the depletion zone of the p-n junction as a function of the applied reverse bias to modify the effective index of refraction of the optical waveguide in a modulator and, thus, to control the phase
Implementation Method 2
a first region of the semiconductor layer is to be regrown as a single crystal having a first doping type and a first doping concentration, and a second region of the semiconductor layer is to be regrown as a single crystal having a second doping type and a second doping concentration
Data Source
AI summary
An electro-refraction modulator includes a series of layers with different doping levels surrounding a single-crystal regrown p-n junction implemented in a silicon-on-insulator (SOI) technology. The regrown p-n junction is spatially abrupt and precisely defined, which significantly increases the tuning efficiency of the electro-refraction modulator while maintaining acceptable insertion loss. Consequently, the electro-refraction modulator (such as a resonator modulator or a Mach-Zehnder interferometer modulator) can have high bandwidth, compact size and reduced drive voltage. The improved performance of the electro-refraction modulator may facilitate silicon-photonic links for use in applications such as wavelength-division multiplexing.