Graphene Electro-Absorption Modulator for High-Speed Optical Signal Control
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Solution Overview
Problem
Conventional optical modulators have limited bandwidth, are difficult to manufacture at high speeds due to RC delay, and require larger sizes due to small modulation depth per unit length, limiting their performance.
Innovation Solution
The use of graphene with a bent structure covering the upper and side surfaces of a semiconductor ridge portion, along with insulating layers, to enhance modulation depth and reduce size while maintaining high operating speed, forming an optical waveguide with graphene layers on the center portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional optical modulators use semiconductor waveguides with electro-absorption, then they can modulate light intensity, but the operation bandwidth is narrow (about 20 nm or less) and the modulation depth per unit length is relatively small
Solution Approach 1:
The patent changes the material parameter from conventional semiconductor to graphene, which has unique optical properties with constant absorption coefficient across a broad spectral range. This material parameter change enables both deep modulation depth and wide operational bandwidth simultaneously, resolving the contradiction between these two parameters.
Solution Approach 2:
The patent creates a composite structure combining graphene layers with semiconductor waveguide (silicon or germanium). This composite material approach leverages the high carrier mobility and broadband optical absorption of graphene while maintaining the waveguide functionality of semiconductor, achieving both deep modulation and wide bandwidth.
2Speed
If conventional optical modulators use semiconductor materials, then they can be manufactured, but high speed operation is difficult due to resistance-capacitance (RC) delay
Solution Approach 1:
The patent changes the electrical parameter by replacing semiconductor material with graphene, which has carrier mobility about 100 times higher than silicon. This drastic improvement in electrical conductivity reduces RC delay and enables high-speed operation above 100 GHz, resolving the speed limitation of conventional semiconductor-based modulators.
3Illumination intensity
If the modulation depth per unit length is relatively small in conventional modulators, then the device can be compact, but a larger size is required to modulate light sufficiently
Solution Approach 1:
The patent changes the optical absorption parameter by using graphene instead of semiconductor material. Graphene's unique optical properties provide strong light-matter interaction with constant absorption coefficient, achieving deep modulation depth in a compact device structure. This allows sufficient light modulation with shorter waveguide lengths, reducing overall device size while maintaining high modulation depth.
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 deeper modulation depth, smaller size, and higher operating speed for optical modulators, addressing the limitations of conventional devices by optimizing light absorption and transmission.
Implementation Method 1
An electro-absorption optical modulator operates based on a change of a light-absorption rate caused by a change in a bandgap size due to the Franz Keldysh effect after applying a bias voltage to an optical waveguide
Data Source
AI summary
An optical electro-absorption modulator (100) includes a first graphene layer (141), a second graphene layer (142), a ridge optical waveguide (124, 150) formed on the upper surface of a semiconductor layer 120, a first electrode (161) on the first graphene layer (141) and a second electrode (162) on the second graphene layer (142). The first graphene layer (141) and the second graphene layer (142) are formed on the upper surface and the side surfaces of the ridge optical waveguide (124, 150) and are mutually separated.