Asymmetric Waveguide Optical Coupler for Polarization Independence
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Solution Overview
Problem
Waveguide type optical couplers exhibit wavelength dependency and polarization dependency in their coupling ratios, leading to variations in optical power across different wavelength channels in optical communication systems, which complicates system configuration.
Innovation Solution
A waveguide type optical coupler using a Mach-Zehnder interferometer with asymmetric directional couplers and varying waveguide widths between the arm waveguides to eliminate polarization dependency and maintain a constant branching ratio across a wide wavelength region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a waveguide type optical coupler uses a directional coupler with equal waveguide widths, then the device structure is simple and easy to manufacture, but the coupling ratio exhibits wavelength dependency and polarization dependency
Solution Approach 1:
The patent applies asymmetry by setting different waveguide widths for the first and second waveguides in the coupling portion. Specifically, the first waveguide has a width of 3 μm while the second waveguide has a width of 5 μm. This asymmetric configuration eliminates the polarization dependency of the coupling ratio while maintaining wavelength independence, resolving the contradiction between manufacturing simplicity and coupling ratio stability.
2Reliability
If a wavelength independent coupler uses a Mach-Zehnder interferometer with symmetric waveguides, then the coupling characteristic is flat across wavelength, but polarization dependent loss occurs
Solution Approach 1:
The patent introduces asymmetry into the Mach-Zehnder interferometer by setting different waveguide widths in the coupling portions of the directional couplers. The first waveguide width is 3 μm and the second waveguide width is 5 μm. This asymmetric design eliminates the polarization dependency that normally occurs in symmetric MZI structures, while maintaining the wavelength-independent coupling characteristic.
Solution Approach 2:
The patent applies local quality by making the waveguide widths different only in the coupling portions of the directional couplers, while other portions of the waveguides can maintain uniform dimensions. This localized asymmetry is sufficient to eliminate polarization dependency without requiring complete structural asymmetry throughout the entire device.
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 solution effectively eliminates polarization dependency and maintains a constant branching ratio, improving the wavelength characteristic by adjusting the phase relationship and propagation constants of the optical signals, thereby enhancing the performance of optical communication systems.
Implementation Method 1
a Mach-Zehnder interferometer with asymmetric directional couplers and varying waveguide widths between the arm waveguides
Implementation Method 2
a directional coupler that is configured by extending two waveguides to be close to each other and transfers optical power from one waveguide to the other waveguide by adiabatic coupling of optical fields
Data Source
AI summary
There is provided a waveguide type optical coupler that maintains a constant branching ratio in a wide wavelength region without wavelength dependency and polarization dependency. A waveguide type optical coupler includes a Mach-Zehnder interferometer that includes two arm waveguides between two directional couplers. In the waveguide type optical coupler, waveguide widths of the two waveguides in a coupling portion of the directional coupler are different from each other.