Optical Modulator Y-Multiplexer Mode Mismatch Suppression
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Solution Overview
Problem
Optical modulators with Mach-Zehnder type waveguides face issues with mode mismatching light generation and separation due to non-zero gaps between branching waveguides, leading to propagation loss and extinction ratio degradation, especially in thinned substrates where radiation-mode and signal light separation becomes difficult.
Innovation Solution
An optical modulator design featuring a multiple mode waveguide after multiplexing in the Y-multiplexer with a subsidiary high-order mode waveguide connected to the main output waveguide, where the multiple mode waveguide has a length of 150 μm or longer, and the waveguides are arranged axisymmetrically, with narrower branching waveguides and a thinner substrate to suppress mode mismatching light generation and recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the dielectric substrate is thinned to 20 μm or less to reduce drive voltage and match propagation velocities, then drive voltage is reduced and velocity matching is improved, but separation of radiation-mode light from mode mismatching light and signal light becomes difficult
Solution Approach 1:
The patent divides the waveguide structure into multiple functional sections: a first waveguide section for signal propagation, a Y-multiplexer for mode separation, and a second waveguide section for output. This segmentation allows radiation-mode light and signal light to be spatially separated at different locations, enabling effective separation even in thinned substrates where complete isolation is difficult.
Solution Approach 2:
The patent introduces a mode mismatching light suppression structure (such as a mode converter or intermediate waveguide section) between the Y-multiplexer and the output waveguide. This intermediary component converts mode mismatching light into a different mode or redirects it, preventing contamination of the signal light and enabling clearer separation of radiation-mode light.
2Difficulty of detecting and measuring
If the gap between branching waveguides in the Y-multiplexer is reduced to zero for ideal radiation-mode light radiation, then radiation-mode light separation is optimized, but manufacturing precision becomes difficult to achieve due to finite minimum line width
Solution Approach 1:
The patent applies different gap dimensions at different locations: a first gap dimension in the Y-multiplexer coupling portion optimized for mode separation, and a second gap dimension in the output waveguide section optimized for signal transmission. This local optimization allows the system to achieve both good radiation-mode light separation and manufacturability without requiring zero gap throughout the entire structure.
3Stability of the object's composition
If the optical waveguide line width is reduced to 2-4 μm in thinned substrates to maintain single-mode operation, then single-mode propagation is maintained, but the influence of gap in the Y-multiplexer increases and mode mismatching light generation becomes significant
Solution Approach 1:
The patent incorporates a mode converter or preliminary processing section before the Y-multiplexer that pre-conditioned the light mode. This preliminary action prepares the light field in advance to minimize mode mismatching when the light passes through the gap in the Y-multiplexer, thereby reducing harmful mode mismatching light generation while maintaining narrow waveguide dimensions.
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 design effectively suppresses mode mismatching light generation and recombination, allowing for stable extraction of radiation-mode and output light, reducing drive voltage and propagation loss while maintaining high extinction ratio characteristics.
Implementation Method 1
an optical modulator having a Mach-Zehnder type waveguide on a surface of an dielectric substrate
Implementation Method 2
radiation-mode light (high-order light) is radiated in a place where the shape is changed from the coupling portion 2 to the output waveguide 3
Implementation Method 3
an electric field is applied to at least an arm (branching waveguide) in the MZ-type waveguide to control phases of the light waves propagating through the corresponding arm
Data Source
AI summary
In order to provide an optical modulator capable of suppressing generation of mode mismatching light in the Y-multiplexer in the MZ-type waveguide or mixing of the mode mismatching light with the radiation-mode light or the output light, and separately extracting output light and radiation-mode light, there is provided an optical modulator having a Mach-Zehnder type waveguide on a surface of a dielectric substrate, wherein a waveguide after multiplexing in a Y-multiplexer in an output side of the Mach-Zehnder type waveguide is a multiple mode waveguide 2, a subsidiary output waveguide as a high-order mode waveguide 2 is connected to a portion where the multiple mode waveguide is changed to a main output waveguide 3 as a single mode waveguide, and the multiple mode waveguide 2 has a length equal to or longer than 150 μm.