A wide spectrum and large field of view terahertz wave lens and its working method

Abstract

A wide-spectrum and wide-field-of-view terahertz wave lens comprises a first biconvex lens, an aperture, a second biconvex lens, a plano-convex lens, a biconcave lens and a detector protection sheet which are sequentially arranged along the optical axis from the object side to the image side, wherein the first biconvex lens, the second biconvex lens and the plano-convex lens are all of positive optical focal length, and the biconcave lens is of negative optical focal length. A working method of a wide-spectrum and wide-field-of-view terahertz wave lens is also disclosed. The lens has a simple structure, and all lenses are made of TPX material, which greatly reduces the cost and the weight of the system. It has the characteristics of large aperture, large field of view and high resolution, and can obtain excellent imaging quality in low light and in a wide band of 0.2 to 4 THz, making the targets that the objective lens can detect more diverse, greatly expanding the scope of application, and having great application prospects in the field of terahertz imaging optics.

Description

Technical Field

[0001] The invention relates to a terahertz wave lens with a wide spectrum and a large field of view. Background Art

[0002] Terahertz (THz) waves refer to electromagnetic radiation with a frequency range of 0.1 THz∼10 THz (3000 μm∼30 μm), and its wavelength is between millimeter waves and infrared. Since the spectral energy of terahertz waves is low, it will not ionize and damage biological tissues, and it has a strong penetrating ability for non-metallic materials such as clothing, making terahertz imaging technology widely used in the biomedical field and public safety detection. In the application of terahertz technology, imaging objective lenses are essential optical components in high-quality imaging systems. Among them, wide-band terahertz objective lenses can detect more diverse targets and have a wider range of applications. At the same time, terahertz objective lenses with large apertures and large fields of view can clearly image under low light conditions, and their shooting field of view is wider.

[0003] However, existing designs often cannot take into account the three aspects of wide spectrum, large aperture and large field of view at the same time. For example, the terahertz objective lens based on reflective elements has a wide spectral range, but its aperture and field of view are small; while the objective lens based on refractive elements is more likely to achieve large aperture and large field of view imaging only for a certain band of spectrum. In addition, terahertz objective lenses are currently often made of high-resistance silicon, which is expensive and heavy, and has a refractive index of up to 3.42, and has large reflection losses at the air-silicon interface. At the same time, most of these lenses use multiple aspherical surfaces, and their processing technology is more difficult than that of spherical surfaces, which greatly increases the cost. Therefore, it is of great practical application value to use new lightweight and cheap polymer materials, reduce the number of aspherical surfaces, and design a terahertz imaging objective lens with excellent performance such as low cost, wide spectrum, large aperture, large field of view, and high resolution. Summary of the invention

[0004] The purpose of the present invention is to provide a wide spectrum and large field of view terahertz wave lens, which can meet the requirements of wide band, large aperture and large field of view, and can also achieve the functions of high resolution and high imaging quality, while further reducing costs and achieving lightweight.

[0005] The technical solution of the present invention is: a wide-spectrum and large-field-of-view terahertz wave lens, comprising a first biconvex lens, an aperture, a second biconvex lens, a plano-convex lens, a biconcave lens and a detector protection sheet arranged in sequence from the object side to the image side along the optical axis, wherein the first biconvex lens, the second biconvex lens and the plano-convex lens all have positive focal power, and the biconcave lens has negative focal power.

[0006] Furthermore, the front surface of the first biconvex lens is an even-order aspheric surface, and the coefficients of the aspheric surface satisfy the equation: , the conic coefficient of the aspheric surface is -1.089, and the coefficients of the fourth, sixth and eighth terms are -2.122×10 -6 , 6.92×10 -10 , -5.604×10 -12 .

[0007] Furthermore, the front surface of the plano-convex lens is a convex surface, and the rear surface is a plane, and the front and rear surfaces of the detector protection sheet are both planes.

[0008] Furthermore, the front and rear surfaces of the second biconvex lens, the front and rear surfaces of the plano-convex lens, the front and rear surfaces of the biconcave lens, and the rear surface of the first biconvex lens are all standard spherical surfaces or standard plane surfaces.

[0009] Furthermore, the materials of the first biconvex lens, the second biconvex lens, the plano-convex lens, the biconcave lens and the detector protection sheet are all poly-4-methylpentene (TPX).

[0010] Furthermore, the center thicknesses of the first biconvex lens, the second biconvex lens, the plano-convex lens, the biconcave lens and the detector protection sheet are 9.5 mm, 8.1 mm, 6.4 mm, 2 mm and 1 mm respectively.

[0011] Furthermore, the total length L of the lens is 62.5 mm, the aperture is close to the first biconvex lens, and the air gap between the two is 2 mm, the air gap between the aperture and the second biconvex lens is 23.4 mm, the air gap between the second biconvex lens and the plano-convex lens is 0.12 mm, the air gap between the plano-convex lens and the biconcave lens is 6.3 mm, and the air gap from the biconcave lens to the detector protection sheet is 3.1 mm.

[0012] Furthermore, the focal length of the lens is f, and the focal length of the first biconvex lens is f E1 , f E1 The ratio to f satisfies the relationship: 1.4 < f E1 / f < 2.1; the focal length of the second biconvex lens is f E2 , f E2 The ratio to f satisfies the relationship: 1.5< f E2 / f < 2.2; the focal length of the plano-convex lens E3 is f E3 , f E3 The ratio to f satisfies the relationship: 1.3 < f E3 / f <2; the focal length of the biconcave lens is f E4 , f E4 The ratio to f satisfies the relationship: -1.3 < f E4 / f < -0.8.

[0013] Compared with the prior art, the present invention has the following advantages: the lens structure is simple, all lenses are made of TPX material, which greatly reduces the cost and lightens the weight of the system. It has the characteristics of large aperture, large field of view, and high resolution, and can obtain excellent imaging quality in low light and 0.2 ~ 4THz wide band, making the targets that the objective lens can detect more diverse, greatly expanding the scope of application, and has great application prospects in the field of terahertz imaging optics. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the optical structure of the present invention;

[0015] Figure 2 This is the MTF curve of the present invention at 0.2 ~ 0.214 THz;

[0016] Figure 3 This is the MTF curve of the present invention at 1.5 ~ 2 THz;

[0017] Figure 4 This is the MTF curve of the present invention at 2.4 ~ 4 THz;

[0018] Figure 5 This is the distortion diagram of the present invention at 0.2 ~ 0.214 THz;

[0019] Figure 6 This is the distortion diagram of the present invention at 1.5 ~ 2 THz;

[0020] Figure 7 This is the distortion diagram of the present invention at 2.4 ~ 4 THz;

[0021] In the figure: 1-first biconvex lens, 2-second biconvex lens, 3-plano-convex lens, 4-biconcave lens, 5-detector protection plate, 6-aperture, 7-object image. DETAILED DESCRIPTION

[0022] In order to make the above features and advantages of the present invention more easily understood, embodiments are given below with reference to the accompanying drawings for detailed description, but the present invention is not limited thereto.

[0023] refer to Figure 1-Figure 7 .

[0024] A wide-spectrum and large-field-of-view terahertz wave lens comprises a first biconvex lens, an aperture, a second biconvex lens, a plano-convex lens, a biconcave lens and a detector protection sheet which are arranged in sequence from the object side to the image side along the optical axis direction, wherein the first biconvex lens, the second biconvex lens and the plano-convex lens all have positive focal power, and the biconcave lens has negative focal power.

[0025] In this embodiment, the front surface of the first biconvex lens is an even-order aspheric surface to correct the aberration on the axis and reduce the thickness of the lens. The coefficient of the aspheric surface satisfies the equation: , where z is the aspheric surface sag, c is the curvature of the aspheric surface at a fixed point, r is the semi-aperture of the light on the aspheric surface, k is the cone coefficient, and a 4 、a 6 、a 8 is the aspheric coefficient.

[0026] In this embodiment, the conic coefficient k of the aspheric surface is -1.089, and the fourth-order coefficient a 4 , sixth-order coefficient a 6 and the eighth-order coefficient a 8 They are: -2.122×10 -6 , 6.92×10 -10 , -5.604×10 -12 .

[0027] In this embodiment, the front surface of the plano-convex lens is a convex surface, and the rear surface is a plane. The front and rear surfaces of the detector protection sheet are both planes.

[0028] In this embodiment, the front and rear surfaces of the second biconvex lens, the front and rear surfaces of the plano-convex lens, the front and rear surfaces of the biconcave lens, and the rear surface of the first biconvex lens are all standard spherical surfaces or standard planes to facilitate processing and testing and reduce costs.

[0029] In this embodiment, the materials of the first biconvex lens, the second biconvex lens, the plano-convex lens, the biconcave lens and the detector protection sheet are all poly-4-methylpentene (TPX), which has a simpler manufacturing process and can be obtained by injection molding, greatly reducing costs and achieving lightweight.

[0030] In this embodiment, the center thicknesses of the first biconvex lens, the second biconvex lens, the plano-convex lens, the biconcave lens and the detector protection sheet are 9.5 mm, 8.1 mm, 6.4 mm, 2 mm and 1 mm respectively.

[0031] In this embodiment, the total length L of the lens is 62.5 mm. The aperture is close to the first biconvex lens, which can reduce the aperture of the lens. The air gap between the two is 2 mm. The air gap between the aperture and the second biconvex lens is 23.4 mm. The air gap between the second biconvex lens and the plano-convex lens is 0.12 mm. The air gap between the plano-convex lens and the biconcave lens is 6.3 mm. The air gap from the biconcave lens to the detector protection sheet is 3.1 mm.

[0032] In this embodiment, the focal length of the lens is f, and the focal length of the first biconvex lens is fE1 , f E1 The ratio to f satisfies the relationship: 1.4 < f E1 / f < 2.1; the focal length of the second biconvex lens is f E2 , f E2 The ratio to f satisfies the relationship: 1.5 < f E2 / f < 2.2; the focal length of the plano-convex lens E3 is f E3 , f E3 The ratio to f satisfies the relationship: 1.3 <f E3 / f < 2; the focal length of the biconcave lens is f E4 , f E4 The ratio to f satisfies the relationship: -1.3 < f E4 / f < -0.8.

[0033] A working method of a wide-spectrum and large-field terahertz wave lens: light is imaged after passing through a first biconvex lens, an aperture, a second biconvex lens, a plano-convex lens, a biconcave lens and a detector protection sheet in sequence from left to right.

[0034] In this embodiment, the specific performance parameters of this optical structure are: (1) spectral range of 0.2 ~ 4 THz; (2) focal length of 39.5 mm; (3) relative aperture of 1:0.9; (4) full field of view of 24°; (5) matched with a terahertz detector with a pixel size of 384*288 and a pixel size of 35μm.

[0035] Table 1. Specific lens parameters

[0036]

[0037] Depend on Figure 2~Figure 4 It can be seen that the MTF value of the lens in this embodiment in the 0.2 ~ 4THz band is close to the diffraction limit, indicating that the lens has a high resolution and good imaging quality.

[0038] like Figure 5~Figure 7 As shown, the distortion in this embodiment is all within 1%, meeting the imaging quality requirements of the optical system.

[0039] The above description is only a preferred embodiment of the present invention. For ordinary technicians in this field, according to the teachings of the present invention, it does not require creative labor to design different forms of wide-spectrum and large-field-of-view terahertz wave lenses. Without departing from the principles and spirit of the present invention, all equal changes, modifications, substitutions and variations made within the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A terahertz wave lens with a wide spectrum and a large field of view, characterized in that: It comprises a first biconvex lens, an aperture, a second biconvex lens, a plano-convex lens, a biconcave lens and a detector protection sheet which are arranged in sequence from the object side to the image side along the optical axis, wherein the first biconvex lens, the second biconvex lens and the plano-convex lens all have positive focal powers, and the biconcave lens has negative focal powers; The front surface of the first biconvex lens is an even-order aspheric surface, and the coefficients of the aspheric surface satisfy the equation: , the conic coefficient of the aspheric surface is -1.089, and the coefficients of the fourth, sixth and eighth terms are -2.122×10 -6 , 6.92×10 -10 , -5.604×10 -12 ; The total length L of the lens is 62.5 mm, the aperture is close to the first biconvex lens, the air gap between the two is 2 mm, the air gap between the aperture and the second biconvex lens is 23.4 mm, the air gap between the second biconvex lens and the plano-convex lens is 0.12 mm, the air gap between the plano-convex lens and the biconcave lens is 6.3 mm, and the air gap between the biconcave lens and the detector protection sheet is 3.1 mm; The focal length of the lens is f, and the focal length of the first biconvex lens is f E1 , f E1 The ratio to f satisfies the relationship: 1.4 <f E1 / f < 2.1; the focal length of the second biconvex lens is f E2 , f E2 The ratio to f satisfies the relationship: 1.5 < f E2 / f <2.2; the focal length of the plano-convex lens E3 is f E3 , f E3 The ratio to f satisfies the relationship: 1.3 < f E3 / f < 2; the focal length of the biconcave lens is f E4 , f E4 The ratio to f satisfies the relationship: -1.3 < f E4 / f < -0.

8.

2. The wide spectrum and large field of view terahertz wave lens according to claim 1, characterized in that: The front surface of the plano-convex lens is a convex surface, and the rear surface is a plane. The front and rear surfaces of the detector protection sheet are both planes.

3. The wide spectrum and large field of view terahertz wave lens according to claim 2, characterized in that: The front and rear surfaces of the second biconvex lens, the front and rear surfaces of the plano-convex lens, the front and rear surfaces of the biconcave lens, and the rear surface of the first biconvex lens are all standard spherical surfaces or standard plane surfaces.

4. The wide spectrum and large field of view terahertz wave lens according to claim 1, characterized in that: The first biconvex lens, the second biconvex lens, the plano-convex lens, the biconcave lens and the detector protection sheet are all made of poly-4-methylpentene (TPX).

5. The wide spectrum and large field of view terahertz wave lens according to claim 1, characterized in that: The center thicknesses of the first biconvex lens, the second biconvex lens, the plano-convex lens, the biconcave lens and the detector protection sheet are 9.5 mm, 8.1 mm, 6.4 mm, 2 mm and 1 mm respectively.

6. A method for operating a wide-spectrum and wide-field-of-view terahertz wave lens, using the wide-spectrum and wide-field-of-view terahertz wave lens as claimed in any one of claims 1 to 5, characterized in that: The light passes through the first biconvex lens, the aperture, the second biconvex lens, the plano-convex lens, the biconcave lens and the detector protection sheet from left to right to form an image.

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