Optical Modulator Waveguide Asymmetry for Extinction Ratio
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Solution Overview
Problem
Mach-Zehnder optical modulators face deterioration in extinction ratio due to asymmetry between optical waveguides caused by differences in effective refractive indices, leading to increased background light in the OFF state.
Innovation Solution
The optical modulator design involves making the lengths of sections with larger and smaller line widths in the first and second waveguides equal to each other, with a folded structure and alternating straight and curved parts, to equalize effective refractive indices and improve symmetry, thereby preventing extinction ratio deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the line widths of the first and second waveguides are made equal throughout, then manufacturing is simplified, but asymmetry in effective refractive indices causes wavelength dependence and deteriorates the extinction ratio
Solution Approach 1:
The patent applies asymmetry principle by intentionally creating asymmetric line width sections in the waveguides. Specifically, the first waveguide has a first asymmetric section where its line width differs from the second waveguide, and the second waveguide has a second asymmetric section with corresponding asymmetry. These asymmetric sections are designed to compensate for manufacturing variations and equalize the effective refractive indices of the two waveguides, thereby improving the extinction ratio without requiring perfect line width uniformity throughout.
Solution Approach 2:
The patent implements local quality by introducing localized asymmetric sections at specific positions along the waveguides rather than maintaining uniform characteristics throughout. The first asymmetric section and second asymmetric section are positioned strategically to compensate for cumulative manufacturing errors. This localized adjustment allows the majority of the waveguide to maintain simple symmetric geometry while providing precise control over effective refractive index matching in the critical regions.
2Reliability
If the length of the Mach-Zehnder optical waveguide is increased to improve modulation performance, then the extinction ratio improves, but the device size increases to about 10 cm
Solution Approach 1:
The patent applies parameter changes by modifying the line width parameters of the waveguides in specific sections. By adjusting the line widths in the first and second asymmetric sections, the effective refractive indices are equalized, which improves the extinction ratio. This parameter optimization allows achieving high extinction ratio performance without requiring excessive waveguide length, thus reducing the overall device size from the conventional 10 cm scale.
3Reliability
If asymmetric sections are introduced to equalize effective refractive indices, then the extinction ratio improves, but the waveguide structure becomes more complex
Solution Approach 1:
The patent implements segmentation by dividing the waveguide structure into distinct sections: a first asymmetric section, a second asymmetric section, and connecting straight sections. This segmentation allows each section to have optimized characteristics - the asymmetric sections provide refractive index compensation while the straight sections maintain simple geometry for easy fabrication. The segmented approach makes the complex structure more manageable and manufacturable compared to a completely uniform or continuously varying design.
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 design effectively prevents extinction ratio deterioration by ensuring equal effective refractive indices in the waveguides, enhancing symmetry and reducing optical loss, while also reducing the size of the modulator and lowering operating voltage.
Implementation Method 1
a signal electrode controlling the phase of light propagating in the Mach-Zehnder optical waveguide
Implementation Method 2
an optical waveguide (Mach-Zehnder optical waveguide) having a Mach-Zehnder interferometer structure that separates light emitted from one light source into two beams, makes the two beams pass through different paths, and then recombines the two beams to cause interference
Data Source
AI summary
To prevent deterioration in an extinction ratio due to asymmetry between a pair of optical waveguides.An optical modulator has a Mach-Zehnder optical waveguide including mutually parallel first and second waveguides and a signal electrode for controlling the phase of light propagating in the Mach-Zehnder optical waveguide. The first and second waveguides have a first section in which the second waveguide has a line width smaller than that of the first waveguide and a second section in which the first waveguide has a line width smaller than that of the second waveguide. The first section and the second section are replaced with each other in curved parts.