Thin Waveguide Optical Modulator for Low-Voltage CMOS Integration
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Solution Overview
Problem
Current optical modulators face challenges in achieving low modulation voltage, high modulation bandwidth, low optical loss, and compact size simultaneously, with existing devices having high power consumption and limited compatibility with CMOS circuits due to high modulation voltage and significant optical loss.
Innovation Solution
The development of optical modulators with a refractive index change mechanism based on carrier band-filling effects, utilizing higher carrier doping densities and thin waveguide structures to enhance refractive index change and reduce modulation voltage, while maintaining high modulation frequency and low optical loss, and employing low-refractive-index Ohmic transparent conducting materials for efficient electrical conduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional optical modulators are used, then modulation function is achieved, but power consumption is very high (0.5 Watt) and optical loss is significant (6 dB insertion loss)
Solution Approach 1:
The patent changes the fundamental operating parameters of the modulator by using carrier band-filling effects in heavily doped semiconductor layers instead of conventional electro-optic effects. This enables operation at much lower voltages (below 1 Volt) and reduces optical loss by eliminating the need for long device lengths, achieving both low power consumption and low optical loss simultaneously
Solution Approach 2:
The patent replaces the conventional electro-optic modulation mechanism with a carrier band-filling mechanism in semiconductors. This substitution allows the modulator to operate with significantly lower voltage and power consumption while maintaining high modulation efficiency and low optical loss
2Adaptability or versatility
If modulation voltage is reduced to be compatible with CMOS circuits, then compatibility is improved, but device length must be increased which leads to high optical loss (>75% loss)
Solution Approach 1:
The patent changes the modulation mechanism to use carrier band-filling effects in heavily doped semiconductor layers, which provides strong modulation efficiency at low voltages. This enables CMOS-compatible operation below 1 Volt without requiring increased device length, thereby avoiding the optical loss problem that plagues conventional low-voltage modulators
3Productivity
If higher carrier doping densities are used to enhance refractive index change, then modulation efficiency is improved, but optical loss may increase
Solution Approach 1:
The patent applies local quality by using heavily doped semiconductor layers only in the active modulation region where carrier band-filling effects are needed, while keeping other waveguide regions lightly doped or undoped. This localized doping strategy enhances modulation efficiency where required while minimizing optical loss in the overall device
Solution Approach 2:
The patent optimizes the doping density parameter to achieve the right balance between modulation efficiency and optical loss. By using heavy doping specifically in the active region where the optical mode overlaps with the semiconductor layer, the patent maximizes the refractive index change while minimizing free-carrier absorption losses
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 resulting modulators achieve significantly higher relative figure of merit, enabling ultra-low-voltage, high-speed, and low-loss operation with compact size, surpassing the performance of prior art by 10 to 1,000 times in terms of figure of merit, making them suitable for integration in electronic-photonic integrated circuits and photonic integrated circuits.
Implementation Method 1
a refractive index change mechanism based on carrier band-filling effects, utilizing higher carrier doping densities and thin waveguide structures to enhance refractive index change
Implementation Method 2
employing low-refractive-index Ohmic transparent conducting materials for efficient electrical conduction
Data Source
AI summary
Integrated optical intensity or phase modulators capable of very low modulation voltage, broad modulation bandwidth, low optical power loss for device insertion, and very small device size are of interest. Such modulators can be of electro-optic or electro-absorption type made of an appropriate electro-optic or electro-absorption material in particular or referred to as an active material in general. An efficient optical waveguide structure for achieving high overlapping between the optical beam mode and the active electro-active region leads to reduced modulation voltage. In an embodiment, ultra-low modulation voltage, high-frequency response, and very compact device size are enabled by a semiconductor modulator device structure, together with an active semiconductor material that is an electro-optic or electro-absorption material, that are appropriately doped with carriers to substantially lower the modulator voltage and still maintain the high frequency response. In another embodiment, an efficient optical coupling structure further enables low optical loss. Various embodiments combined enable the modulator to reach lower voltage, higher frequency, low optical loss, and more compact size than previously possible in the prior arts.