Hybrid Si-LN Optical Modulator Velocity Matching
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Solution Overview
Problem
Existing SiPh optical modulators face challenges in achieving high bandwidth and fast baud rates due to high electrical resistance and frequency loss, which limits their ability to support baud rates equal to or greater than 96 G.
Innovation Solution
The optical modulator element incorporates a structure with two optical waveguide arms, each comprising a first and second optical waveguide made of different materials, along with a transition portion for optical transition between them. The substrate beneath the second optical waveguide is partially removed to create a hollow portion, which helps in matching the velocity of electrical signals with signal light, thereby enhancing bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a Si waveguide is used to strongly confine light, then the bend radius can be reduced to about 10 μm and element size is reduced, but the electrical resistance increases and high frequency loss increases, making it difficult to achieve bandwidth equal to or greater than 50 GHz
Solution Approach 1:
The patent uses a hybrid structure combining Si waveguide and LN waveguide. The Si waveguide provides strong light confinement with small bend radius, while the LN waveguide provides low electrical resistance and low high frequency loss. This composite material approach allows the system to achieve both compact size and high bandwidth performance (equal to or greater than 50 GHz) by leveraging the complementary strengths of the two materials.
2Speed
If electro-optical materials such as LiNbO3 are integrated on SiPh element to speed up baud rate, then baud rate equal to or greater than 96 G can be achieved, but the refractive index of electrical signal increases due to substrate electric permittivity, causing velocity mismatch and bandwidth limitation
Solution Approach 1:
The patent applies local quality by creating a hollow portion (air region) beneath the LN waveguide in the region where the electrical signal propagates. This local modification reduces the effective electric permittivity in that specific region, thereby reducing the refractive index of the electrical signal and increasing its propagation velocity to match the velocity of light in the LN waveguide. This enables velocity matching while maintaining the electro-optical effect needed for high baud rate operation.
3Loss of energy
If capacity-loaded electrodes are used to reduce high frequency loss, then available electrode size increases, but the refractive index of electrical signal increases due to capacity-loaded electrode influence, worsening velocity mismatch
Solution Approach 1:
The patent introduces a hollow portion (air region) as an intermediary structure between the capacity-loaded electrodes and the LN waveguide. This air region acts as a mediator that reduces the capacitive coupling and the influence of the capacity-loaded electrodes on the electrical signal propagation. By inserting this intermediary air layer, the patent reduces the refractive index increase caused by the capacity-loaded electrodes, thereby improving electrical signal velocity and reducing velocity mismatch while still maintaining the benefit of reduced high frequency loss from the larger electrode size.
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 enables wider bandwidth and faster baud rates, effectively addressing the limitations of existing SiPh modulators by ensuring velocity matching between electrical signals and signal light.
Implementation Method 1
The second optical waveguide includes a second material that has a higher electro-optical effect than the first material
Implementation Method 2
The substrate includes a hollow portion in which all or a part of the substrate located below the second optical waveguide in a plan view has been removed. This configuration enables wider bandwidth and faster baud rates, effectively addressing the limitations of existing SiPh modulators by ensuring velocity matching between electrical signals and signal light.
Data Source
AI summary
An optical modulator element includes, on a substrate, an optical branching portion and an optical multiplexing portion each of which includes a first material, two optical waveguide arms each of which connects the optical branching portion and the optical multiplexing portion, and electrodes that apply an electrical signal to the two optical waveguide arms waveguide. Each optical waveguides of the two optical waveguide arms includes a first optical waveguide that includes the first material, a second optical waveguide that includes a second material that has a higher electro-optical effect than the first material, and a transition portion that performs an optical transition between the first optical waveguide and the second optical waveguide. The substrate includes a hollow portion in which all or a part of the substrate located below the second optical waveguide in a plan view has been removed.