Mach-Zehnder Optical Circuit Mode Converter Integration
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Solution Overview
Problem
Optical circuits using Mach-Zehnder-type elements face challenges in achieving high integration and minimizing wavelength dependence due to strong coupling between higher-order modes and basic modes, which affects the on/off ratio and light blocking efficiency, especially when elements are closely spaced.
Innovation Solution
The optical circuit design includes a first and second Mach-Zehnder-type element with phase difference adjustment means, connected through branching/combining units with different configurations to reduce coupling between basic and higher-order modes, using 1×2-type and 2×2-type branching/combining units to minimize wavelength dependence and enhance light blocking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Mach-Zehnder-type elements are closely spaced to achieve high integration, then device density increases, but coupling between higher-order modes and basic modes increases causing wavelength dependence and reduced on/off ratio
Solution Approach 1:
A mode converter is introduced as an intermediary component between closely spaced Mach-Zehnder-type elements. This mode converter transforms higher-order modes into basic modes, preventing harmful coupling between higher-order modes of one element and basic modes of adjacent elements. The intermediary device enables high integration density while maintaining reliable on/off ratio performance.
Solution Approach 2:
The harmful higher-order modes are extracted and converted separately from the main signal path. By using a mode converter to isolate and transform higher-order modes into basic modes before they can couple with adjacent elements, the invention removes the source of wavelength dependence and on/off ratio degradation while maintaining compact spacing.
2Device complexity
If 2×2-type branching/combining units are used for compact configuration, then device complexity is reduced, but wavelength dependence increases due to stronger coupling between modes
Solution Approach 1:
A mode converter is inserted as an intermediary between the 2×2-type branching/combining unit and adjacent Mach-Zehnder elements. This converter transforms higher-order modes generated by the compact 2×2 configuration into basic modes, eliminating the wavelength dependence that would otherwise result from mode coupling, while preserving the simplicity of the 2×2 branching unit structure.
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 configuration achieves a high on/off ratio and reduced wavelength dependence, enabling high integration while maintaining effective light blocking, even when elements are closely spaced, thus addressing the limitations of existing optical switch designs.
Implementation Method 1
Signal light input from one of the 2×2-type directional couplers is directed to a bar path in accordance with the interference principle when a phase shifter is not operated. On the other hand, when a phase shift amount π corresponding to a half wavelength is generated in the phase shifter to eliminate the optical path length difference, the signal light is directed to a cross path.
Implementation Method 2
at least one of the coupling waveguides is provided with a phase shifter for changing a phase of guided light by changing a refractive index of the waveguide
Data Source
AI summary
In an optical circuit using a Mach-Zehnder-type element, it is difficult to obtain an optical circuit which has a less wavelength dependence and is suitable for achieving high integration. Accordingly, an optical circuit according to the present invention includes: a first Mach-Zehnder-type element including a first branch waveguide, a first branching/combining unit connected to one end of the first branch waveguide, and a second branching/combining unit connected to another end of the first branch waveguide and having a branch configuration different from that of the first branching/combining unit; and a second Mach-Zehnder-type element including a second branch waveguide, a third branching/combining unit connected to one end of the second branch waveguide, and a fourth branching/combining unit connected to another end of the second branch waveguide and having a branch configuration different from that of the third branching/combining unit. The first branch waveguide and the second branch waveguide each include a phase difference adjustment means. In the second branching/combining unit and the third branching/combining unit, light coupling between two basic modes with a phase inverted and a higher-order mode, is smaller than that in the first branching/combining unit and the fourth branching/combining unit. The first Mach-Zehnder-type element and the second Mach-Zehnder-type element are connected with each other through the second branching/combining unit and the third branching/combining unit.