High-order mode filter using alternating waveguide widths
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Solution Overview
Problem
Existing high-order mode filters face challenges in effectively removing higher modes in optical waveguides due to limitations in manufacturing precision, increased element length, and issues with reflected and stray light, which affect the performance of optical communication technologies.
Innovation Solution
A high-order mode filter design featuring a planar slab region with a band-shaped projection and alternately arranged first and second optical waveguides, where the first waveguide includes a disturbance element with a lower refractive index and the second waveguide does not, allowing for precise control of refractive indices and lengths to maximize high-order mode loss through interference, while minimizing manufacturing complexity and stray light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light-wave reducing loss element is disposed at a predetermined position in an optical waveguide to remove higher modes, then higher mode removal efficiency is improved, but the element length must be increased to sufficiently attenuate higher modes
Solution Approach 1:
The optical waveguide is segmented into multiple sections with alternating waveguide widths. The first waveguide has a first width and the second waveguide has a second width different from the first width. This segmentation creates multiple interfaces that collectively remove higher modes through mode mismatch, achieving effective higher mode attenuation without requiring a single long element.
Solution Approach 2:
Different sections of the waveguide are given different local properties - specifically, alternating sections have different waveguide widths. The first waveguide section has a first width optimized for certain mode propagation, while the second waveguide section has a second width that creates mode mismatch for higher modes. This local variation in geometry enables selective higher mode removal while maintaining compact overall length.
2Reliability
If alternating waveguides with different widths are used to remove higher modes, then higher mode loss is improved, but manufacturing precision requirements increase
Solution Approach 1:
The invention changes the geometric parameter (waveguide width) alternately between different sections. The first waveguide has width W1 and the second waveguide has width W2, where W1 ≠ W2. This parameter variation creates the necessary mode mismatch for higher mode removal. The specific width values can be optimized to achieve desired performance while relaxing manufacturing tolerances compared to other approaches.
3Reliability
If very thin single-mode waveguides are used to remove higher modes in taper-structured waveguides, then higher mode removal is improved, but basic-mode loss increases due to processing roughness
Solution Approach 1:
Instead of using a single taper-structured waveguide with very thin dimensions, the invention segments the structure into alternating waveguide sections. Each section maintains sufficient thickness to minimize sensitivity to processing roughness, while the alternating width pattern provides the necessary mode mismatch for higher mode removal. This segmentation allows achieving higher mode attenuation without the severe basic-mode loss associated with extremely thin waveguides.
Solution Approach 2:
The waveguide structure can be viewed as a composite of alternating sections with different geometric properties. By combining sections of different widths in an alternating pattern, the structure achieves both higher mode removal (through mode mismatch at interfaces) and reduced basic-mode loss (by avoiding extremely thin single-mode waveguides). This composite approach balances the competing requirements.
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 filter achieves efficient removal of high-order modes with reduced reflected and stray light, enabling high-performance optical elements and miniaturization, suitable for various optical applications.
Implementation Method 1
The lengths L1 and L2 of a first optical waveguide and a second optical waveguide in an optical waveguide direction are determined to fix the phase relationship between a removable high-order mode and an intentional high-order mode at a connecting face between the first optical waveguide and the second optical waveguide, thus causing a large high-order mode loss due to interference between the removable high-order mode and the intentional high-order mode
Data Source
AI summary
A high-order mode filter includes a slab region, a band-shaped projection elongated in an optical waveguide direction, a first optical waveguide including a disturbance element and a second optical waveguide. The disturbance element is formed by doping impurities into the slab region, thus indicating a lower refractive index than the slab region. Both the first optical waveguide and the second optical waveguide are alternately arranged. The first optical waveguide may include a disturbance element positioned close to the projection, while the second optical waveguide may include a disturbance element distanced from the projection in the slab region. The high-order mode filter causes a large high-order mode loss due to interference between a removable high-order mode and an intentional high-order mode at the connecting face between the first optical waveguide and the second optical waveguide, thus reducing reflected light and stray light.