Semiconductor Optical Grating Structure for Stable Reflectance
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Solution Overview
Problem
Semiconductor optical devices with diffraction gratings formed on silicon-on-insulator substrates face challenges in maintaining stable characteristics and mechanical strength due to variations in refractive index and etching depth, leading to potential distortion during the joining process.
Innovation Solution
A semiconductor optical device with a waveguide featuring bent and straight portions, where a diffraction grating is formed using a first and second semiconductor layer with different refractive indices, embedded in the first layer, positioned above the straight portions, and including tapered portions for improved coupling efficiency and reduced light loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the length of the diffraction grating is increased to increase the reflectance, then the reflectance is improved, but the mechanical strength deteriorates and the device is easily distorted
Solution Approach 1:
The patent transforms the diffraction grating structure from a single-layer planar configuration to a multi-layer three-dimensional structure. The first semiconductor layer contains the diffraction grating pattern, while the second semiconductor layer with different refractive index is embedded within it, creating a layered configuration that enhances optical performance without requiring increased lateral dimensions, thereby maintaining mechanical strength.
Solution Approach 2:
The patent employs composite material structure by combining two semiconductor layers with different refractive indices. The first semiconductor layer (e.g., AlGaInP) and the second semiconductor layer (e.g., GaP) are stacked to form a composite diffraction grating structure that achieves high reflectance through refractive index contrast rather than relying on increased grating length, thus preserving mechanical integrity.
2Measurement precision
If a diffraction grating is formed on a silicon layer with greatly differing refractive index from air, then the wavelength control is achieved, but the characteristics greatly vary due to variations of the depth of the projecting-and-recessed pattern
Solution Approach 1:
The patent changes the refractive index parameter by selecting semiconductor materials with refractive indices closer to each other compared to silicon and air. This reduces the sensitivity of diffraction grating characteristics to depth variations, making the device less susceptible to manufacturing tolerances while maintaining wavelength control capability.
Solution Approach 2:
The patent applies local quality by embedding the second semiconductor layer with different refractive index specifically within regions of the first semiconductor layer to create the diffraction grating structure. This localized modification optimizes the optical characteristics at the grating location while maintaining overall structural stability and reducing sensitivity to depth variations.
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 enhances mechanical strength, stabilizes diffraction grating characteristics, and reduces light loss by allowing for efficient heat conduction and wavelength control, while maintaining high reflectance and optical performance.
Implementation Method 1
A wavelength of light can be controlled by using a diffraction grating. For example, a projecting-and-recessed pattern that functions as a diffraction grating is formed on a silicon (Si) layer of an SOI substrate.
Implementation Method 2
Since Si has a refractive index that greatly differs from that of air, the characteristics of the diffraction grating greatly vary due to variations of the depth of the projecting-and-recessed pattern.
Implementation Method 3
The waveguide includes a bent portion and a plurality of straight portions that are connected to each other by the bent portion and that extend straight.
Data Source
AI summary
A semiconductor optical device includes a substrate including a waveguide made of silicon and a semiconductor layer joined to the substrate so as to overlap the waveguide and including a diffraction grating formed of a first semiconductor layer and a second semiconductor layer having different refractive indices. The waveguide includes a bent portion and a plurality of straight portions that are connected to each other by the bent portion and that extend straight. The first semiconductor layer and the second semiconductor layer are each made of a compound semiconductor. The second semiconductor layer is embedded in the first semiconductor layer and includes a plurality of portions arranged in a direction in which the plurality of straight portions extend. The diffraction grating is positioned above the plurality of straight portions.