Optical Modulator Narrow Waveguide Mode Filtering
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Solution Overview
Problem
Mach-Zehnder optical modulators face challenges in achieving high optical quenching ratios due to the presence of noise light from higher-order modes, which deteriorates communication quality, especially when multimode waveguides are used and higher-order modes are not effectively removed before combining with primary modes.
Innovation Solution
Incorporating narrow portions in the optical waveguide arms that are narrower than the rest of the waveguide, positioned to avoid overlap with electrodes, to filter out higher-order modes and ensure only primary mode light is propagated, thereby enhancing the optical quenching ratio without increasing drive voltage or modulator size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multimode waveguides are used in the optical modulator, then the waveguide can support multiple light modes, but higher-order modes generate noise light that deteriorates the optical quenching ratio and communication quality
Solution Approach 1:
The optical waveguide is segmented into different width portions along its length. The waveguide includes a first portion with a first width and a second portion with a second width that is different from the first width. This segmentation allows the waveguide to selectively guide primary mode light while filtering out higher-order modes, thereby improving the optical quenching ratio without requiring complete mode rejection structures.
Solution Approach 2:
Different portions of the optical waveguide are given different local properties through varying width. The first portion has a first width optimized for primary mode propagation, while the second portion has a different width that creates conditions unfavorable for higher-order mode propagation. This local quality variation enables selective mode guidance and improves communication quality.
2Reliability
If narrow portions are added to the optical waveguide to filter higher-order modes, then the optical quenching ratio improves, but the modulator size increases
Solution Approach 1:
The optical waveguide is segmented into different width portions along its length. The waveguide includes a first portion with a first width and a second portion with a second width that is different from the first width. This segmentation allows the waveguide to selectively guide primary mode light while filtering out higher-order modes, thereby improving the optical quenching ratio without requiring complete mode rejection structures.
Solution Approach 2:
The waveguide width parameter is changed at specific locations to create the first portion and second portion with different widths. By carefully selecting the width values and their positions, the waveguide achieves effective higher-order mode filtering while minimizing the overall increase in modulator size. The parameter change is localized rather than uniform, optimizing the balance between performance and size.
3Reliability
If voltage is increased to improve modulation depth, then the optical quenching ratio improves, but power consumption increases
Solution Approach 1:
The optical waveguide is pre-designed with specific width variations (first portion and second portion) that preliminarily filter out higher-order modes before they can cause degradation. This preliminary structural action reduces the need for high drive voltages to achieve good optical quenching ratios, thereby lowering power consumption while maintaining communication quality.
Solution Approach 2:
The waveguide width parameter is changed at specific locations to create the first portion and second portion with different widths. By carefully selecting the width values and their positions, the waveguide achieves effective higher-order mode filtering while minimizing the overall increase in modulator size. The parameter change is localized rather than uniform, optimizing the balance between performance and size.
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 effectively removes noise light from higher-order modes, improving the optical quenching ratio from -24.6 dB to -35.2 dB, enhancing communication quality without increasing power consumption or modulator size.
Implementation Method 1
an optical waveguide that includes a split section that splits light into two light waves
Implementation Method 2
The optical waveguide is formed by, for example, forming a metal film such as titanium on part of a surface of the substrate and thermally diffusing the same into the substrate
Implementation Method 3
The MZ optical modulator performs modulation by generating an electric field by applying a voltage to an electrode provided above the waveguide and controlling the refractive index of light in the waveguide by utilizing the Pockels effect
Implementation Method 4
the optical waveguide having a narrow portion that is narrower than another portion of the optical waveguide and is arranged so that the electrode does not overlap with the narrow portion
Implementation Method 5
a combining section that combines the light waves from the pair of arms with each other
Data Source
AI summary
An optical modulator includes: a substrate that having an optical waveguide that includes a split section that splits light into two light waves, a pair of arms through which the light waves propagate, and a combining section that combines the light waves from the pair of arms with each other; and an electrode that overlaps part of the optical waveguide and generates an electric field by a voltage applied to the electrode. The optical waveguide has a narrow portion that is narrower than another portion of the optical waveguide and is arranged so that the electrode does not overlap with the narrow portion.