High-Index-Clad Electro-Optic Waveguide for Low-Loss Modulation
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Solution Overview
Problem
Thin-film lithium niobate (TFLN) modulators face challenges in enhancing the efficiency of electrical-to-optical signal conversion due to the limitations of metal electrodes' light absorption and the weak refractive index of LN material, leading to increased optical loss and reduced modulation bandwidth.
Innovation Solution
The introduction of a cladding layer with a higher refractive index than the waveguide core, forming a hybrid waveguide structure that limits the optical field and reduces the spacing between electrodes, along with a ridge waveguide design to enhance modulation efficiency and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the distance between metal electrodes is shortened to generate higher electric field intensity, then the overlapping efficiency of electric field and optical field is improved, but the optical loss increases due to light absorption by metal electrodes
Solution Approach 1:
The patent introduces a cladding layer with higher refractive index than the waveguide core as an intermediary structure. This cladding layer confines the optical field more effectively within the waveguide core, allowing the optical field to extend closer to the metal electrodes without excessive loss. The cladding layer acts as a mediator that enables better electric-optical field overlap while maintaining acceptable optical transmission by reducing the optical field's exposure to lossy metal regions.
Solution Approach 2:
The patent changes the refractive index parameter by introducing a cladding layer with higher refractive index than the waveguide core. This parameter change fundamentally alters the optical field distribution and confinement characteristics, enabling the system to achieve both high electric field intensity (through reduced electrode spacing) and low optical loss simultaneously. The refractive index contrast creates stronger optical confinement that compensates for the increased metal interaction.
2Power
If the distance between metal electrodes is shortened, then the conversion efficiency from electrical signal to optical signal is improved, but the modulation area length increases which limits modulation bandwidth
Solution Approach 1:
The cladding layer serves as an intermediary that enables shorter electrode spacing by improving optical field confinement. This allows the system to achieve high conversion efficiency with reduced electrode distance while the enhanced optical confinement also reduces the required modulation area length, thereby increasing modulation bandwidth.
Solution Approach 2:
The patent creates a composite waveguide structure combining the waveguide core and cladding layer with different refractive indices. This composite structure provides superior optical field confinement compared to the core alone, enabling both high conversion efficiency (through closer electrodes) and high bandwidth (through reduced modulation length) to be achieved simultaneously.
3Loss of energy
If the metal electrodes are disposed at positions far away from the TFLN waveguide to avoid optical signal loss, then the optical loss is reduced, but the overlapping efficiency of electric field and optical field decreases
Solution Approach 1:
The cladding layer acts as an intermediary structure that enables the optical field to extend closer to the metal electrodes with reduced loss. By providing stronger optical confinement through its higher refractive index, the cladding layer allows the optical field to penetrate closer to the electrode regions without excessive attenuation, thereby improving overlapping efficiency while maintaining acceptable optical loss levels.
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 hybrid waveguide structure effectively reduces optical loss and increases modulation efficiency by improving the overlap of electric and optical fields, allowing for a shorter modulation area and higher bandwidth.
Implementation Method 1
Thanks to a refractive index difference between LN and silicon dioxide, an optical field can be propagated in the TFLN through total internal reflection
Implementation Method 2
a refractive index of the insulating substrate is less than a refractive index of the waveguide core, and a refractive index of the cladding layer is greater than the refractive index of the waveguide core
Implementation Method 3
According to linear electro-optic effect of the LN, when the electric field is applied, the applied electric field causes an obvious refractive index change of an LN material, significantly changes an effective refractive index of an optical mode, and further directly affects a phase of an optical signal in the waveguide
Data Source
AI summary
An optical waveguide component, a preparation method therefor, and an electro-optic modulator are disclosed. The optical waveguide component includes an insulating substrate, a waveguide core, at least two electrodes, and a cladding layer. The at least two electrodes and the waveguide core are all disposed on the insulating substrate, the at least two electrodes are distributed on two sides of the waveguide core, and the cladding layer covers at least a part of an outer wall of the waveguide core. The waveguide core includes an electro-optic material having an electro-optic effect. A refractive index of the insulating substrate is less than a refractive index of the waveguide core. A refractive index of the cladding layer is greater than the refractive index of the waveguide core.