Optical Modulator Rib Waveguide Low Drive Voltage
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Solution Overview
Problem
Conventional Mach-Zehnder type optical modulators face challenges in achieving high modulation speed, low optical loss, and low drive voltage due to tradeoffs between electrode length and phase inversion voltage, leading to increased optical loss and resistance values that affect modulation efficiency.
Innovation Solution
The optical modulator design incorporates a rib waveguide structure with specific slab portion thicknesses and doping concentrations to minimize optical loss and electrical resistance, allowing for high-speed operation with reduced phase inversion voltage and drive voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the electrode length is increased to reduce phase inversion voltage, then the drive voltage is reduced, but the optical loss increases
Solution Approach 1:
The patent applies different doping concentrations to different regions of the semiconductor layer: high doping concentration in contact regions for low electrical resistance, and low doping concentration in the optical waveguide core region for low optical loss. This local differentiation allows the electrode to have low drive voltage while the waveguide maintains low optical loss, resolving the contradiction between these two parameters.
Solution Approach 2:
The semiconductor layer is segmented into functionally distinct regions: contact regions with high doping for electrical conduction, intermediate regions with moderate doping, and core waveguide regions with low doping for optical transmission. This segmentation allows each region to be optimized for its specific function without compromising the other, enabling long electrode length for low drive voltage while maintaining low optical loss.
2Use of energy by stationary object
If the doping concentration is increased to reduce electrical resistance, then the drive voltage is reduced, but the optical loss increases
Solution Approach 1:
The patent implements spatially varying doping concentrations within the semiconductor layer, with high doping levels localized to contact regions to minimize electrical resistance and drive voltage, while low doping levels are maintained in the optical waveguide core to minimize optical loss from free-carrier absorption. This local quality differentiation directly resolves the contradiction between electrical and optical performance.
Solution Approach 2:
The semiconductor structure is divided into multiple doped regions with distinct concentration profiles: heavily doped contact regions, moderately doped intermediate regions, and lightly doped core waveguide regions. This segmentation strategy allows independent optimization of electrical conduction paths and optical transmission paths, achieving low drive voltage without sacrificing optical efficiency.
3Loss of energy
If the slab portion thickness is reduced to minimize optical loss, then the optical confinement is improved, but the electrical resistance increases
Solution Approach 1:
The patent creates a vertical doping gradient through the slab portion thickness, with higher doping concentrations near the contact interfaces to reduce electrical resistance, and lower doping concentrations toward the optical mode confinement region to minimize optical loss. This local quality variation in the vertical dimension resolves the contradiction between electrical and optical performance requirements.
Solution Approach 2:
The patent resolves the two-dimensional trade-off between optical confinement and electrical conduction by introducing a vertical dimension for doping concentration variation. The doping profile changes through the thickness of the slab portion, with different concentrations at different vertical positions, allowing simultaneous optimization of both optical and electrical properties in the same 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 design enables efficient optical modulation with reduced optical loss and low drive voltage, supporting high-frequency operation while maintaining low optical loss and small electrical resistance values.
Implementation Method 1
When a voltage is applied to the optical waveguide by traveling wave electrodes arranged in the vicinity of the optical waveguide, the phase of the light is changed. In regard to a principle of changing the phase of the light, primarily a Pockels effect is used in LiNbO3
Implementation Method 2
a Pockels effect and a quantum confined stark effect (QCSE) are used in InP and GaAs
Implementation Method 3
a carrier plasma effect is used in Si
Data Source
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AI summary
The present invention provides an optical modulator including a substrate and a phase modulation portion on the substrate. The phase modulation portion includes an optical waveguide comprised of a first clad layer, a semiconductor layer that is laminated on the first clad layer and has a refraction index higher than the first clad layer and a second clad layer that is laminated on the semiconductor layer and has a refraction index lower than the semiconductor layer, a first traveling wave electrode, and a second traveling wave electrode. The semiconductor layer includes a rib that is formed in the optical waveguide in an optical axis direction and is a core of the optical waveguide, a first slab that is formed in the optical axis direction in one side of the rib, a second slab that is formed in the optical axis direction in the other side of the rib, a third slab that is formed in the first slab in the optical axis direction at the opposite side to the rib, and a fourth slab that is formed in the second slab in the optical axis direction at the opposite side to the rib. The first slab is formed to be thinner than the rib and the third slab, and the second slab is formed to be thinner than the rib and the fourth slab.