Adiabatic TE0 Add/Drop Filter for Low-Crosstalk Multimode Waveguides
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Solution Overview
Problem
Existing photonic devices face challenges in achieving low cross-talk and minimal footprint while maintaining high performance, particularly in mode multiplexers (modemux) used in integrated wavelength division multiplexing (WDM) filters, where back-reflection for spectral reject bands leads to suboptimal return loss and increased insertion loss.
Innovation Solution
A multimode waveguide with an adiabatic TE0 add/drop filter design, utilizing a bus waveguide with lower and upper waveguides that maintain pseudo-symmetry to prevent TE1-TM0 mode hybridization, allowing TE1 and TE0 modes to be multiplexed without conversion, resulting in a compact footprint and low cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If back-reflection is used to form a spectral reject band in integrated Bragg WDM filter, then filtering performance is improved, but return loss deteriorates
Solution Approach 1:
The patent converts the harmful back-reflection effect into a beneficial forward transmission filter. Instead of using back-reflection to form spectral reject bands (which causes poor return loss), the invention uses forward transmission through a multimode interference filter to achieve the same filtering function with excellent return loss performance
Solution Approach 2:
The patent inverts the conventional filtering approach by using forward transmission instead of back-reflection. The multimode interference filter transmits light forward through controlled mode coupling between waveguides, achieving spectral filtering without the harmful back-reflection effects
2Adaptability or versatility
If TE1 to TE0 mode conversion is performed in conventional modemux, then mode multiplexing is achieved, but cross-talk increases
Solution Approach 1:
The patent extracts the harmful TE1 to TE0 mode conversion from the system by using a different approach. Instead of converting modes, the invention uses direct TE0 mode coupling between waveguides through adiabatic transition, eliminating the source of cross-talk while maintaining mode multiplexing capability
Solution Approach 2:
The patent introduces an adiabatic transition region as an intermediary between waveguides with different mode profiles. This gradual transition region enables efficient TE0 mode coupling without the need for abrupt mode conversion, thereby reducing cross-talk between modes
3Measurement precision
If adiabatic components are added to support integrated Bragg gratings, then filtering performance is improved, but device footprint increases
Solution Approach 1:
The patent merges the filtering function and mode multiplexing function into a single integrated multimode interference filter structure. This eliminates the need for separate adiabatic components and Bragg gratings, achieving compact footprint while maintaining filtering performance
Solution Approach 2:
The multimode interference filter performs multiple functions simultaneously: spectral filtering, mode multiplexing, and polarization maintenance. This multi-functionality eliminates the need for additional specialized components, reducing overall device footprint
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 design achieves low TE0-TE1 cross-talk and insertion loss, enabling efficient mode multiplexing with a significantly reduced device length, suitable for WDM filters and polarization rotating applications.
Implementation Method 1
A first adiabatic section transfers the TE0 mode optical signal from the first waveguide to the bus waveguide. A second adiabatic section mode multiplexes the TE1 mode optical signal and the TE0 mode optical signal
Implementation Method 2
the upper waveguide substantially matches a path of the lower waveguide... maintain pseudo-symmetry to prevent TE1-TM0 mode hybridization
Data Source
AI summary
A device and method are provided. The device includes a bus waveguide having a longitudinal axis, a lower waveguide disposed on a first side of the bus waveguide, and an upper waveguide disposed on a second side of the bus waveguide opposite to the first side of the bus waveguide, wherein the upper waveguide substantially matches a path of the lower waveguide. The method includes receiving a TE1 mode optical signal on a bus waveguide, receiving a TE0 mode optical signal on a lower waveguide disposed below the bus waveguide, mode multiplexing the TE1 mode optical signal and the TE0 mode optical signal without converting the TE0 mode optical signal or the TE1 mode optical signal to another mode, and outputting the TE0 mode optical signal and the TE1 mode optical signal on the bus waveguide.