Adiabatic Waveguide Coupler Back-Reflection Reduction
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Solution Overview
Problem
Current optical waveguide couplers in integrated photonics suffer from significant back-reflections, which limit their performance and are particularly problematic in resonator fiber optic gyroscopes (RFOGs) where low bias stability is critical.
Innovation Solution
The introduction of a second degree of freedom, namely physical separation between waveguides, allows for gradual alignment and de-alignment during the coupling process, reducing abrupt perturbations and thereby minimizing back-reflections through an adiabatic optical waveguide coupler design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional waveguide couplers are used to transition light between waveguides, then light coupling is achieved, but significant back-reflections are generated that limit performance
Solution Approach 1:
The waveguide geometry is made dynamic through gradual evolution of width and separation parameters along the propagation direction. The first waveguide width gradually decreases while the second waveguide width gradually increases, and the separation between waveguides gradually changes, creating a dynamic transition that minimizes back-reflections and improves bias stability in RFOG applications
Solution Approach 2:
The invention introduces the vertical separation dimension between waveguides as an additional degree of freedom for mode evolution. By controlling the separation distance between waveguides in addition to their widths, the system achieves more complete adiabatic transformation and reduces back-reflections by multiple orders of magnitude compared to conventional planar couplers
2Length of moving object
If abrupt waveguide introduction and termination are used, then device length is reduced, but substantial back-reflections are generated
Solution Approach 1:
Instead of abrupt geometric changes, the waveguide dimensions and separations are dynamically evolved along the propagation direction. The gradual narrowing of the first waveguide and widening of the second waveguide, combined with gradual separation changes, creates a smooth transition that minimizes back-reflections while maintaining a compact device footprint
Solution Approach 2:
Multiple geometric parameters (waveguide widths, separation distances, and their gradients) are simultaneously optimized and gradually changed along the propagation direction. This multi-parameter adiabatic evolution enables ultra-low back-reflection levels while keeping the coupler length practical for integrated photonics applications
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 results in ultra-low back-reflection levels, improving the efficiency of light transition between waveguides and enhancing the performance of RFOGs by reducing back-reflections by multiple orders of magnitude.
Implementation Method 1
Document 'Counterdiabatic mode-evolution based coupled-waveguide devices' by Tseng Shuo-yen et al discloses a universal formalism for the design of short and high-fidelity mode-evolution based coupled-waveguide devices
Implementation Method 2
In integrated photonics, there are many applications which require that light be transitioned between two waveguides
Data Source
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AI summary
An optical coupler comprises an adiabatic waveguide structure having a proximal end and a distal end, with the adiabatic waveguide structure comprising: a first waveguide comprising an input section at the proximal end; a first coupling section contiguous with the input section and extending toward the distal end; and a first laterally displaced section contiguous with the first coupling section. The first waveguide narrows along the first coupling section, from the input section to the first laterally displaced section. A second waveguide is separate from the first waveguide and comprises a second laterally displaced section adjacent to the proximal end; a second coupling section contiguous with the second laterally displaced section and extending toward the distal end; and an output section contiguous with the second coupling section. The second waveguide widens along the second coupling section, from the second laterally displaced section to the output section.