Optical Waveguide Cladding Structure for Refractive Index Stability
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Solution Overview
Problem
Existing silicon photonics optical devices with silicon oxide films as upper cladding layers face temporal changes in refractive index due to humidity absorption, affecting resonance wavelengths and device properties, which are not adequately suppressed by previous techniques using SiO2 and SiN films with low moisture content.
Innovation Solution
An optical waveguide structure with a core, a first silicon oxide cladding, a second silicon oxide cladding with higher fixed charge density, and a heater to control refractive indices through thermo-optical effects, where the first cladding has a lower fixed charge density than the second cladding, and a passivation film to reduce moisture absorption and oxygen vacancies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a TEOS film is used as the upper cladding layer to achieve fast film formation, then the manufacturing efficiency is improved, but the refractive index changes over time due to moisture absorption
Solution Approach 1:
The upper cladding layer is divided into multiple functional layers: a TEOS film for fast formation, an SiN film for moisture barrier protection, and an LPCVD film for additional stability. Each layer performs a specific function to collectively solve the contradiction between fast formation and long-term stability.
Solution Approach 2:
The patent uses a composite structure combining different materials (TEOS, SiN, LPCVD) in the upper cladding layer. The SiN film acts as a moisture barrier while the TEOS provides fast formation, and the LPCVD adds stability, creating a composite system that balances productivity and stability.
2Stability of the object's composition
If SiN films are added to suppress moisture absorption, then the refractive index stability is improved, but the device structure becomes more complex
Solution Approach 1:
The SiN film is strategically placed only in the upper cladding layer where moisture absorption occurs, rather than throughout the entire waveguide structure. This localized approach provides the necessary moisture protection while minimizing overall structural complexity.
3Reliability
If the refractive index of the upper cladding layer changes, then the resonance wavelength drifts, but this is a natural consequence of moisture absorption
Solution Approach 1:
The SiN film acts as an intermediary barrier between the external environment (humidity) and the TEOS/LPCVD films. It prevents moisture from reaching the silicon core and cladding layers, thereby eliminating the harmful effect of humidity absorption on resonance wavelength stability.
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 configuration effectively suppresses temporal changes in resonance wavelengths and device properties by controlling refractive indices and reducing moisture absorption, enhancing the reliability and stability of the optical waveguide over time.
Implementation Method 1
a heater disposed over the second cladding to heat the core
Implementation Method 2
heating the core by the heater, the oxygen vacancy density in the first cladding decreases, and consequently, a shift of a resonance wavelength of a ring resonator to a long wavelength side is suppressed
Data Source
AI summary
An optical waveguide includes a core, a first cladding, a second cladding, and a heater. The first cladding configured to cover the core. The second cladding disposed over the first cladding. The heater disposed over the second cladding to heat the core. The first cladding and the second cladding are silicon oxide films. A first fixed charge density of the first cladding is lower than a second fixed charge density of the second cladding.