Large aperture terahertz-gigahertz lens system

Abstract

Lens systems used in a gigahertz / terahertz imaging system are proposed. Each proposed lens system may include two thin lens elements, spherical or aspherical, in which combined provides gigahertz-terahertz refractive power with a small f-number. The gigahertz-terahertz waves are diverted by the lens systems in such a way that it forms an image of an object, such as a human scale object, on a planar gigahertz-terahertz image sensor. The radius of curvatures, profile, sizes, spacing, and aspherical coefficients of the lens elements may be selected to achieve quality focusing performance. The spacing between the lens elements and the spacing between the lens elements and the image sensor may be adjusted to change both the focal length and the focusing distance to achieve optimum field of view and maximum imaging resolution. The size of the lens may be scaled with the size of the object or the lens aperture stop.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a terahertz-gigahertz lens system that may be used to focus terahertz-gigahertz waves reflected off or transmitted through an object to an image sensor. In particular, the present invention describes a terahertz-gigahertz lens system with large aperture (small f-number) and high resolution power (only limited by diffraction) simultaneously, while keeping the overall size and weight reasonably contained.BACKGROUND OF THE INVENTION[0002]Terahertz-gigahertz imaging and sensing rely upon the effectiveness to control and divert the flow of the terahertz-gigahertz waves in free space. Although terahertz-gigahertz waves have been used as a security screening tool because of its unique transmission properties that identifies concealed objects, such as a metal weapon hidden under the fiber clothing, a single large aperture lens systems (that mitigates the diffraction limitation) with reduced aberration to achieve high image resolut...

AI Technical Summary

Benefits of technology

The proposed lens systems can capture images of human-scale objects at a few meters away from the lens system with a large aperture size and high resolution. The lens elements can be separated or the image sensor can be adjusted to focus objects at different distances from the lens system.

Problems solved by technology

One of the serious problems with designing terahertz-gigahertz lenses is the material choice.

This means that making large or aspherical gigahertz-terahertz lens elements (to further reduce weight) out of these materials may be expensive, impractical, or readily unavailable.

In addition, polymers, albeit commonly used in making terahertz lenses, are in general less stable in harsh environmental conditions.

Moreover, the refractive indices of these polymers are usually small, which means less refractive power and higher degree of design limitations.

The lens design in terahertz-gigahertz system is critical because important features found in optical cameras are currently lacking in terahertz-gigahertz cameras.

For 1), the resolution in terahertz-gigahertz systems is intrinsically limited by the diffraction limitation of the lens.

For 2), at least two lens elements are required to adjust the focal length of an optical system, which increases the design complexity, especially when the material absorption is factored in, but at the same time allows further improvement of the image quality.

However, the downside of using a lens system is the increased weight, absorption, cost, housing design, and design complexity.

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