Optical Modulator Trench Depth Optimization for Impedance Matching
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Solution Overview
Problem
Conventional Mach-Zehnder interferometer type optical modulators fail to simultaneously achieve reduced driving voltage and improved microwave characteristics due to inadequate consideration of ridge shape, electrode shape, and location, leading to impedance mismatch and degradation of optical modulation signals, especially in high-frequency applications like DQPSK and QAM modulators.
Innovation Solution
The optical modulator features an electro-optic substrate with trench portions of different digging depths to form ridge-shaped optical waveguides, allowing for optimized digging depths that reduce driving voltage and enhance microwave characteristics, while minimizing stress and impedance mismatch by adjusting the digging depths of first and second trench portions based on their widths and ridge shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the ridge shape and electrode configuration are optimized to reduce driving voltage, then the effective overlap integral of electric field and light wave is improved, but the impedance of the electrode deviates from the standard 50Ω RF signal connector impedance
Solution Approach 1:
The patent applies different ridge widths and digging depths to different portions of the optical waveguide. Specifically, the ridge width is set to 3-5 μm in the modulation section to reduce driving voltage, while the electrode portion is designed with specific dimensions (signal electrode 5-15 μm width, ground electrode 10-20 μm width) to achieve 50Ω impedance matching. This local differentiation allows each section to be optimized for its specific function.
Solution Approach 2:
The optical waveguide is divided into distinct sections with different ridge shapes: a modulation section with narrower ridge (3-5 μm) for voltage reduction, and electrode portions with specific dimensions for impedance matching. The trench portions are also segmented with different digging depths (first trench 2-5 μm, second trench 3-6 μm) to independently control optical and electrical characteristics.
2Speed
If the active electrode is lengthened and the groove is deepened to match refractive indices and reduce driving voltage, then velocity matching between electrical signal and light wave is improved, but the return loss increases due to impedance mismatch
Solution Approach 1:
The patent optimizes multiple geometric parameters simultaneously: ridge width (3-5 μm in modulation section), trench digging depth (first trench 2-5 μm, second trench 3-6 μm), and electrode dimensions (signal electrode 5-15 μm, ground electrode 10-20 μm). These parameter changes collectively achieve both velocity matching (effective refractive index of 2.0-2.5) and impedance matching (50Ω) while maintaining acceptable return loss.
3Use of energy by moving object
If the ridge shape is optimized with base angle of 70° or more to reduce driving voltage, then the effective overlap integral is improved, but the microwave characteristics and impedance matching are degraded
Solution Approach 1:
The patent specifies a ridge base angle of 70° or more (preferably 75°-85°) in the modulation section to reduce driving voltage, while the electrode portion is designed with different dimensions to ensure proper microwave characteristics and 50Ω impedance matching. This local differentiation allows the modulation section to optimize for optical field overlap while the electrode section optimizes for electrical signal transmission.
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 approach effectively reduces driving voltage and improves microwave characteristics, achieving impedance matching and enhancing transmission quality in multi-level modulation and analog modulation signals, particularly in high-frequency applications.
Implementation Method 1
an optical modulator having an optical waveguide structure in which an optical waveguide is formed on an electro-optic substrate
Data Source
AI summary
An aspect of the present invention is an optical modulator including an electro-optic substrate, an optical waveguide, and a signal electrode for applying an electric field corresponding to a modulation signal to the optical waveguide. The electro-optic substrate includes a trench portion, which is formed by digging a surface of the electro-optic substrate, and a ridge portion, which is formed in a ridge shape by the trench portion so that an optical waveguide is provided. The trench portion includes a first trench portion, which is a trench portion between a pair of branched optical waveguides, and a second trench portion, which is a trench portion other than the first trench portion. Digging depths of the first and second trench portions are different.