Oblique Fiber Cut Optical Coupling Circuit Reduces Polarization Dependency
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Solution Overview
Problem
Existing optical coupling configurations face challenges such as high polarization dependency, inability to couple with multi-core fibers, and significant wavelength dependency due to the use of directional coupling and diffraction gratings.
Innovation Solution
An optical coupling circuit device is designed with an optical circuit board and an optical fiber, where the optical fiber has a cut surface obliquely cut at an angle between 3° and 30°, and is coupled to the optical circuit board. The optical coupling waveguide on the board is configured to optically couple the optical fiber and the optical circuit, with the leading end of the optical fiber's core offset in the x and z directions from the coupling end of the optical coupling waveguide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If directional coupling is used to couple optical fiber and silicon wire waveguide, then coupling efficiency can be improved, but polarization dependency increases to about 0.7 dB
Solution Approach 1:
The patent applies asymmetry by obliquely cutting the optical fiber end surface at a specific angle (3°-30°) relative to the optical axis, creating an asymmetric geometry that breaks the polarization dependency. This asymmetric cut angle is specifically designed to equalize the coupling efficiency for different polarization modes, thereby reducing polarization dependency while maintaining high coupling efficiency through directional coupling mechanisms.
2Object-affected harmful factors
If the gap between cut surface and silicon wire core is controlled to reduce polarization dependency, then polarization dependency decreases, but coupling efficiency decreases by about 1 dB
Solution Approach 1:
The patent applies parameter changes by optimizing the cut angle parameter to a specific range (3°-30°) and controlling the gap distance parameter to achieve both reduced polarization dependency and maintained coupling efficiency. This parameter optimization balances the competing requirements by finding the optimal operating point where the asymmetric geometry reduces polarization dependency without creating excessive gap-induced losses.
3Device complexity
If grating coupler is used for optical coupling, then coupling configuration is simplified, but wavelength dependency becomes high and diffraction to other orders occurs
Solution Approach 1:
The patent extracts the grating coupling mechanism from the optical coupling system and replaces it with direct directional coupling through oblique fiber cutting. This extraction eliminates the grating structure that causes wavelength dependency and multi-order diffraction, while maintaining a relatively simple coupling configuration through the asymmetric geometric arrangement of the cut fiber end and waveguide.
4Loss of energy
If silicon wire sub-waveguide is used to increase coupling efficiency, then coupling efficiency improves, but the configuration cannot be used for coupling to multi-core fiber
Solution Approach 1:
The patent applies universality by designing a coupling configuration that can accommodate both single-mode and multi-core fibers through the same oblique cutting approach. The asymmetric cut geometry and directional coupling mechanism are universally applicable to different fiber types, allowing the same coupling structure to efficiently couple to single-mode fibers while also being adaptable to multi-core fiber configurations, thereby enhancing versatility.
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 proposed solution achieves a reduced polarization dependency of coupling efficiency and enables coupling with multi-core fibers, while minimizing wavelength dependency and light loss.
Implementation Method 1
an optical coupling waveguide that is formed in the optical circuit board and configured to optically couple the optical fiber and the optical circuit
Implementation Method 2
the end surface of the optical fiber is cut obliquely with respect to the optical axis, the cut face is caused to face a tapered silicon wire waveguide
Data Source
AI summary
An optical coupling circuit device includes an optical circuit board including an optical circuit; an optical fiber coupled to the board; and an optical coupling waveguide formed in the board and configured to optically couple the fiber and the optical circuit. The fiber includes a cut surface obliquely cut at 3° to 30° to an optical axis of the fiber, and is coupled to the board at the cut surface. With a direction normal to the board being z-direction, a plane orthogonal to z-direction being xy-plane, a direction in which an optical axis of the optical coupling waveguide extends toward the fiber in xy-plane being x-direction, and a direction orthogonal to x-direction and z-direction being y-direction, second position of a leading end of a core end surface exposed at the cut surface is offset from first position of a coupling end of the optical coupling waveguide in x-direction and z-direction.