Sub-wavelength Grating Terahertz Wave Extraction
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Solution Overview
Problem
Devices for generating terahertz waves face challenges in miniaturization and achieving high output power, particularly due to the high refractive index of crystals like lithium niobate, which leads to total internal reflection and significant optical loss, making it difficult to efficiently transmit terahertz waves from the crystal to air.
Innovation Solution
A sub-wavelength grating structure is formed on the surface of non-linear optical crystals using a peripheral cutting edge, comprising column-shaped bodies with a constant width and an arc-shaped base, allowing for efficient irradiation of terahertz waves by reducing reflection and enhancing transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high refractive index crystal like lithium niobate is used for generating terahertz waves, then the output power and generation efficiency are improved, but total internal reflection occurs at the crystal-air interface and optical loss increases, making it difficult to transmit terahertz waves efficiently to air
Solution Approach 1:
The invention transitions from a flat crystal surface to a three-dimensional microlens array structure. Each microlens element has a curved surface with specific radius of curvature, creating dimensional complexity that enables refraction and focusing of terahertz waves. This dimensional change allows the terahertz waves to be extracted from the high refractive index crystal into air by creating gradient refraction paths through the lens structures, thereby reducing total internal reflection and optical loss while maintaining high output power.
2Power
If a high refractive index crystal like lithium niobate is used for generating terahertz waves, then the output power and generation efficiency are improved, but total internal reflection occurs between the crystal and air, making it impossible to draw the terahertz wave into the air
Solution Approach 1:
The invention transitions from a flat crystal surface to a three-dimensional microlens array structure. Each microlens element has a curved surface with specific radius of curvature, creating dimensional complexity that enables refraction and focusing of terahertz waves. This dimensional change allows the terahertz waves to be extracted from the high refractive index crystal into air by creating gradient refraction paths through the lens structures, thereby reducing total internal reflection and optical loss while maintaining high output power.
Solution Approach 2:
The invention changes the geometric parameters of the crystal surface by forming microlens structures with specific radius of curvature (e.g., 0.5mm to 2mm) and pitch (e.g., 0.1mm to 1mm). These parameter changes create a gradient refraction interface that modifies the refraction angle and reduces total internal reflection, enabling efficient terahertz wave extraction into air while maintaining the high output power characteristics of the lithium niobate crystal.
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 sub-wavelength grating structure significantly increases the peak transmittance of terahertz waves, enabling efficient emission from high refractive index crystals like lithium niobate, achieving up to 99% transmittance at specific frequencies, while maintaining mechanical strength and ease of processing.
Implementation Method 1
the crystal has a refractive index as high as 5.2 with respect to sub-milli wave (terahertz wave) so that total internal reflection occurs between the crystal and air
Implementation Method 2
The sub wavelength grating structure includes column shaped bodies regularly arranged on a surface of the main body
Data Source
AI summary
A device for irradiating an electromagnetic wave irradiates an electromagnetic wave having a target frequency in a range of 0.1 THz to 30 THz to the outside of a non-linear optical crystal. The device includes a main body composed of a non-linear optical crystal and a sub wavelength grating structure formed on a surface of the main body. The sub wavelength grating structure includes column shaped bodies regularly arranged on a surface of the main body. Each of the column shaped bodies includes a constant width part having a constant width and a base part provided from the surface toward the constant width part. A surface of the base part has a shape of an arc having a center of curvature in the outside of the base part viewed in a cross section of the column shaped body cut along a direction in which the column shaped bodies are arranged.