Tapered Waveguide Optical Attenuator for Stable Wavelength-Independent Signal
Solution Overview
Problem
Conventional optical attenuators in coherent optical communication systems exhibit significant wavelength dependence, leading to unstable optical attenuation, which is problematic for wavelength division multiplexing and high-speed communication due to the space-charge effect in photodetectors.
Innovation Solution
The optical device employs a tapered waveguide structure with varying core widths in the attenuating and removing units, increasing waveguide modes in one section and decreasing them in the other to achieve stable optical attenuation across a wide wavelength range, mitigating the space-charge effect and reducing unwanted mode interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional directional coupler is used as an optical attenuator, then the device can be compact and integrated in silicon photonics, but the optical attenuation becomes significantly wavelength-dependent and unstable
Solution Approach 1:
The patent changes the geometric parameters of the waveguide by introducing a tapered structure with varying core width along the light propagation direction. The core width transitions from a first width in the input section to a second width in the output section, which fundamentally alters the waveguide mode characteristics and enables wavelength-independent attenuation while maintaining compact integration in silicon photonics platforms
Solution Approach 2:
The optical attenuator is segmented into distinct functional sections: an input waveguide section, a tapered attenuating section with varying core width, and an output waveguide section. This segmentation allows each section to be optimized for its specific function, with the tapered section providing stable attenuation across wavelengths while the input/output sections ensure proper mode coupling
2Reliability
If the core width of the waveguide is increased to reduce wavelength dependence, then optical attenuation stability improves, but the device size increases
Solution Approach 1:
The patent employs a tapered waveguide structure where the core width continuously varies along the light propagation direction rather than remaining constant. This curved geometric transition creates a gradual mode evolution that stabilizes attenuation across wavelengths while minimizing the overall device footprint compared to abrupt width changes or extended straight waveguides
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 provides stable optical attenuation over a wide wavelength band, reducing the space-charge effect and enabling high-speed communication by efficiently transitioning optical power with low wavelength dependence and minimal reflection loss.
Implementation Method 1
light input into the first waveguide gradually transitions its optical power to the second waveguide adjacent along a traveling direction of light
Implementation Method 2
the mixed reception light is converted into photoelectric current by a photo detector (PD)
Implementation Method 3
when light input into the PD generates electron-hole pairs, the electric field generated by these carriers within the PD acts in a direction that cancels an applied bias to the PD
Data Source
AI summary
An optical device includes an optical waveguide that is constituted of a cladding and a core formed on a substrate. The optical waveguide includes an input waveguide, an attenuator section that is connected to the input waveguide, a removing section that is connected to the attenuator section, and an output waveguide that is connected to the removing section. The attenuator section is configured to have more waveguide modes that are guided on a cross section perpendicular to a traveling direction of light in a connecting portion connected to the removing section compared to a connecting portion connected to the input waveguide. The removing section is configured to have less waveguide modes that are guided on a cross section perpendicular to a traveling direction of light in a connecting portion connected to the output waveguide compared to a connecting portion connected to the attenuator section.