Evanescent-Wave Coupling for Terahertz Imaging Resolution
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Solution Overview
Problem
Terahertz imaging systems face challenges in achieving high resolution due to long wavelengths, which result in large diffraction spots and low resolution, and increasing the numerical aperture of optics is difficult due to manufacturing complexities and the risk of total internal reflections.
Innovation Solution
An imaging system utilizing evanescent-wave coupling between the exit surface of the sensor-adjacent optical element and the image sensor, with a gap width similar to or smaller than the penetration distance of evanescent-waves, to enhance optical power transfer and improve resolution without increasing the wavelength or optical element size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the numerical aperture of optics is increased to improve resolution, then the resolution improves, but manufacturing complexity increases and total internal reflections occur
Solution Approach 1:
The patent introduces an intermediary mechanism (evanescent wave coupling through a sub-wavelength gap) to transfer optical information from the optical element to the detector without requiring direct high-NA optical contact. This mediator approach allows high-resolution imaging while avoiding the manufacturing complexities and total internal reflection issues associated with traditional high-NA optics.
Solution Approach 2:
The patent changes the operating parameter regime by utilizing evanescent waves (which decay exponentially) rather than propagating waves. By operating in the evanescent wave regime with gap widths smaller than the wavelength, the system achieves enhanced resolution without requiring high numerical aperture optics, thereby avoiding the associated manufacturing complexities.
2Measurement precision
If the numerical aperture of optics is increased to improve resolution, then the resolution improves, but total internal reflections increase
Solution Approach 1:
The sub-wavelength gap acts as an intermediary that couples evanescent waves from the optical element to the detector surface. This coupling mechanism bypasses the need for high-angle ray propagation that causes total internal reflections, allowing efficient energy transfer while maintaining high resolution.
Solution Approach 2:
The patent replaces the traditional mechanical/optical high-NA lens system with an evanescent wave coupling mechanism. This substitution eliminates the need for high-angle ray tracking through optical interfaces, thereby preventing total internal reflections while achieving comparable or superior resolution.
3Ease of manufacture
If the gap between optical element and sensor is increased, then manufacturing ease improves, but optical power transfer efficiency decreases
Solution Approach 1:
The patent uses a gap width that is partially smaller than the wavelength (sub-wavelength but not necessarily extremely small), providing just enough evanescent wave coupling to maintain efficient power transfer while achieving sufficient manufacturing tolerance. This partial action approach balances the competing requirements without requiring extreme precision.
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 approach allows for improved image resolution by transferring optical power through evanescent-waves, minimizing total internal reflections, and maintaining the high numerical aperture, thereby achieving better image fidelity and reducing the distance between resolvable points in the scene.
Implementation Method 1
the exit surface of the sensor-adjacent optical element and the sensing surface of the image sensor are spaced apart by a gap having a gap width similar to or smaller than a penetration distance of evanescent-waves for light having wavelengths within the sensor spectral range, thus enabling a transfer of optical power from the exit surface to the sensing surface by evanescent-wave coupling
Implementation Method 2
Even for an imaging system free from any geometric aberrations (perfect optical system), the image of a point object is not a point, but a spot which generally consists of a bright core surrounded by rings or side lobes whose brightnesses decrease as we move away from the core. This is due to the phenomenon of diffraction.
Data Source
AI summary
An imaging system that includes an image sensor and imaging optics is provided. The image sensor has a sensing surface and it captures images of a scene. The imaging optics is optically coupled to the image sensor and is configured to form the images of the scene onto the sensing surface of the image sensor. The imaging optics includes a sensor-adjacent optical element having an exit surface located in close proximity to the sensing surface of the image sensor. The exit surface of the sensor-adjacent optical element and the sensing surface of the image sensor are spaced apart by a gap having a gap width enabling evanescent-wave coupling from the exit surface to the sensing surface for light having wavelengths within the sensor spectral range.