阅读说明：本技术 一种基于体布拉格光栅的高光谱成像系统 (Hyperspectral imaging system based on volume Bragg grating ) 是由 陈亮 张生秋 郭斐娜 徐瑞 张军杰 唐乔 黄帅 于 2019-09-24 设计创作，主要内容包括：本发明公开了一种基于体布拉格光栅的高光谱成像系统,包括载物台、卤钨灯、校准装置、第一驼峰体布拉格光栅、第二驼峰体布拉格光栅、成像透镜、电荷耦合器件、计算机；在载物台上安放待测物体,卤钨灯发出光线照射在待测物体上,光线漫反射后依次经过校准装置的校准、经过第一驼峰体布拉格光栅进行衍射、经过第二驼峰体布拉格光栅进行衍射与色散补偿、再经成像透镜达到电荷耦合器,最后经过电荷耦合器将待测物体的信息发送到计算机,经计算机处理得到待测物体的光谱信息和空间信息。本发明充分利用了厚驼峰体布拉格光栅的优越性能,不仅能够反映物体的成分和结构等内部品质,还能够清晰准确的反映物体的形状、颜色和表面缺陷等外部品质。(The invention discloses a hyperspectral imaging system based on volume Bragg gratings, which comprises an objective table, a halogen tungsten lamp, a calibration device, a first hump volume Bragg grating, a second hump volume Bragg grating, an imaging lens, a charge coupled device and a computer, wherein the objective table is provided with a plurality of optical fiber gratings; an object to be detected is placed on an objective table, a halogen tungsten lamp emits light to irradiate the object to be detected, the light is subjected to diffuse reflection, then is subjected to calibration by a calibration device, is subjected to diffraction by a first hump body Bragg grating, is subjected to diffraction and dispersion compensation by a second hump body Bragg grating, reaches a charge coupler through an imaging lens, and finally is sent to a computer through the charge coupler, and spectral information and spatial information of the object to be detected are obtained through computer processing. The invention fully utilizes the excellent performance of the thick hump body Bragg grating, not only can reflect the internal quality of components, structure and the like of an object, but also can clearly and accurately reflect the external quality of the shape, color, surface defect and the like of the object.)

1. A hyperspectral imaging system based on volume Bragg grating is characterized in that: the device comprises an object stage, a halogen tungsten lamp, a calibration device, a first hump body Bragg grating, a second hump body Bragg grating, an imaging lens, a charge coupling device and a computer;

an object to be detected is placed on an objective table, a halogen tungsten lamp emits light to irradiate the object to be detected, the light is subjected to diffuse reflection, then is subjected to calibration by a calibration device, is subjected to diffraction by a first hump body Bragg grating, is subjected to diffraction and dispersion compensation by a second hump body Bragg grating, reaches a charge coupler through an imaging lens, and finally is sent to a computer through the charge coupler, and spectral information and spatial information of the object to be detected are obtained through computer processing.

2. The volumetric bragg grating based hyperspectral imaging system of claim 1, wherein: the first hump body Bragg grating and the second hump body Bragg grating have the same structure.

3. The volumetric bragg grating based hyperspectral imaging system according to claim 1 or 2, wherein: the hump body Bragg grating is obtained in the following way:

firstly, obtaining volume Bragg diffraction efficiency; according to the coupled wave theory, the angular selectivity of a lossless transmission volume bragg grating can be described as:

wherein n is₁The refractive index modulation is adopted, d is the grating thickness, lambda and theta are respectively the wavelength and incident angle of incident beams in the grating, and delta theta is the angular deviation of the Bragg angle in the grating;

under the volume bragg condition, when Δ θ is 0, the diffraction efficiency can be simplified as:

wherein eta₀Is the central diffraction efficiency, θ, of the volume Bragg grating₀Arcsin (λ/2 Λ) is the bragg angle, Λ is the period of the volume bragg grating;

from equation (2), it can be concluded that by fine tuning n₁D, can obtain eta in the interval from 0 to 100 percent₀；

Obtaining a single-peak volume Bragg grating according to the Bragg angle of the volume Bragg diffraction efficiency and the period adjustment of the volume Bragg grating; i.e. when eta₀＝10When the concentration is 0%, the traditional single-peak volume Bragg grating can be obtained;

then obtaining the hump volume Bragg grating by adjusting the diffraction efficiency of the single-peak volume Bragg grating, namely the single-peak volume Bragg grating is in eta₀When 0, it becomes a hump volume bragg grating.

4. The volumetric bragg grating based hyperspectral imaging system according to claim 1 or 2, wherein: the first hump body Bragg grating is a thick hump body Bragg grating with thousand-fold thickness-to-period ratio, the thickness of the hump body Bragg grating is in mm magnitude, the period is in mum magnitude, the refractive index modulation degree is 10-4 magnitude, and the vector inclination angle is 90 degrees.

5. The volumetric bragg grating based hyperspectral imaging system according to claim 1 or 2, wherein: the first hump body Bragg grating is arranged in an inclined mode with the light propagation direction of 30 degrees, and the second hump body Bragg grating is arranged perpendicular to the light propagation direction.

Technical Field

The invention relates to an imaging system, in particular to a hyperspectral imaging system based on volume Bragg gratings.

Background

The hyperspectral imaging technology is an organic combination of the spectrum technology and the imaging technology, each pixel in the hyperspectral imaging system can acquire dozens to hundreds of continuous narrow-band information in the same spectrum interval, a smooth and complete spectrum curve is obtained, meanwhile, the whole spectrum imaging system can also acquire the spatial information of an object to be detected, the simultaneous detection of the internal components and the appearance characteristics of the object to be detected is realized, and a data cube containing target light intensity, spectrum and spatial information is formed.

At present, the spectral imaging technology based on the acousto-optic tunable filter and the liquid crystal tunable filter faces the problems of low spectral transmittance and the like due to the limitation of physical mechanisms.

Disclosure of Invention

The present invention is directed to a hyperspectral imaging system based on volume bragg gratings, which can solve one or more of the above technical problems.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

a hyperspectral imaging system based on volume Bragg gratings comprises an object stage, a halogen tungsten lamp, a calibration device, a first hump volume Bragg grating, a second hump volume Bragg grating, an imaging lens, a charge coupled device and a computer; an object to be detected is placed on an objective table, a halogen tungsten lamp emits light to irradiate the object to be detected, the light is subjected to diffuse reflection, then is subjected to calibration by a calibration device, is subjected to diffraction by a first hump body Bragg grating, is subjected to diffraction and dispersion compensation by a second hump body Bragg grating, reaches a charge coupler through an imaging lens, and finally is sent to a computer through the charge coupler, and spectral information and spatial information of the object to be detected are obtained through computer processing.

According to the invention, a first hump body Bragg grating and a second hump body Bragg grating form a hump body Bragg grating group, and the light field of the object to be measured irradiated by the illumination light source is subjected to narrow-band filtering by utilizing the wavelength selection characteristic of the hump body Bragg grating, so that the hyperspectral imaging is realized. Particularly, the two hump body Bragg gratings are creatively placed at a certain angle, the second hump body Bragg grating has a dispersion compensation effect on the first hump body Bragg grating, and the first hump body Bragg grating and the second hump body Bragg grating are mutually combined to achieve a good hyperspectral imaging effect.

The system discovers that different effects can be achieved when the thicknesses of the selected hump body Bragg gratings are different through numerical simulation on the premise of being based on a strict coupled wave theory. Therefore, various parameters of the hump body Bragg grating are not limited, and the hump body Bragg grating needs to be designed according to the actual use requirement.

The spectrum components in the diffraction light field are changed by changing the angle of the first hump body Bragg grating, so that the imaging results of the target light field at different incidence angles can be analyzed and compared to obtain more accurate spectrum information and space information of the object to be measured.

Preferably: the first hump body Bragg grating and the second hump body Bragg grating have the same structure. The Bragg gratings of the two hump bodies have the same structure, so that the installation and the adjustment are convenient.

The hump volume bragg grating is obtained as follows:

firstly, obtaining volume Bragg diffraction efficiency; according to the coupled wave theory, the angular selectivity of a lossless transmission volume bragg grating can be described as:

wherein n is₁The refractive index modulation is adopted, d is the grating thickness, lambda and theta are respectively the wavelength and incident angle of incident beams in the grating, and delta theta is the angular deviation of the Bragg angle in the grating;

under the volume bragg condition, when Δ θ is 0, the diffraction efficiency can be simplified as:

wherein eta₀Is the central diffraction efficiency, θ, of the volume Bragg grating₀Arcsin (λ/2 Λ) is the bragg angle, Λ is the period of the volume bragg grating;

from equation (2), it can be concluded that by fine tuning n₁D, can obtain eta in the interval from 0 to 100 percent₀；

Obtaining a single-peak volume Bragg grating according to the Bragg angle of the volume Bragg diffraction efficiency and the period adjustment of the volume Bragg grating; i.e. when eta₀When the percentage is 100 percent, the traditional single-peak volume Bragg grating can be obtained;

then obtaining the hump volume Bragg grating by adjusting the diffraction efficiency of the single-peak volume Bragg grating, namely the single-peak volume Bragg grating is in eta₀When 0, it becomes a hump volume bragg grating.

Preferably: the first hump body Bragg grating is a thick hump body Bragg grating with thousand-fold thickness-to-period ratio, the thickness of the hump body Bragg grating is in mm magnitude, the period is in mum magnitude, and the refractive index modulation degree is 10^-4And magnitude, the vector tilt angle is 90 °.

Preferably: the first hump body Bragg grating is arranged in an inclined mode with the light propagation direction of 30 degrees, and the second hump body Bragg grating is arranged perpendicular to the light propagation direction.

The invention has the technical effects that:

based on the characteristics of the volume Bragg grating, the invention adopts the thick hump volume Bragg grating with special performance to carry out hyperspectral imaging, fully utilizes the superior performance of the thick hump volume Bragg grating, not only can reflect the internal quality of the components, the structure and the like of an object, but also can clearly and accurately reflect the external quality of the shape, the color, the surface defect and the like of the object.

The imaging technology adopting the thick hump body Bragg grating has the advantages of high spectral transmittance, wide spectral adjustment range, high spectral resolution, no need of complex temperature control and electric control systems and the like, and has unique advantages in the field of spectral imaging with extremely narrow filtering bandwidth.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a schematic diagram of a hyperspectral imaging system based on volume Bragg gratings;

FIG. 2 is a schematic view of the installation of a first hump volume Bragg grating and a second hump volume Bragg grating;

in fig. 1 and 2, the reference numerals are: the device comprises an object stage 1, a halogen tungsten lamp 2, a calibration device 3, a first hump body Bragg grating 4, a second hump body Bragg grating 5, an imaging lens 6, a charge coupling device 7 and a computer 8; an object to be measured 9 and a light 10.

FIG. 3 is a graph showing the angular selectivity contrast between a hump volume Bragg grating and a conventional volume Bragg grating;

FIG. 4 is an angular selectivity plot of a selected hump volume Bragg grating;

FIG. 5 is a graph of wavelength selectivity for different thickness-to-period ratios for a hump Bragg grating;

FIG. 6 is a graph showing the relative intensity of diffracted light of each order at different positions along the thickness direction of the grating.

Detailed Description

The present invention will now be described in detail with reference to the drawings and specific embodiments, wherein the exemplary embodiments and descriptions are provided only for the purpose of illustrating the present invention and are not to be construed as unduly limiting the invention.

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As shown in fig. 1, a hyperspectral imaging system based on volume bragg gratings comprises an object stage 1, a tungsten halogen lamp 2, a calibration device 3, a first hump volume bragg grating 4, a second hump volume bragg grating 5, an imaging lens 6, a charge-coupled device 7 and a computer 8; an object to be measured 9 is placed on an objective table 1, a halogen tungsten lamp 2 emits light to irradiate on the object to be measured 9, the light 10 is subjected to diffuse reflection, then is subjected to calibration by a calibration device 3, is subjected to diffraction by a first hump body Bragg grating 4, is subjected to diffraction and dispersion compensation by a second hump body Bragg grating 5, reaches a charge coupler 7 through an imaging lens 6, and finally is sent to a computer 8 through the charge coupler 7, and spectral information and spatial information of the object to be measured 9 are obtained through processing of the computer 8.

As shown in fig. 2, the first hump body bragg grating is disposed at an angle of 30 ° to the light propagation direction, and the second hump body bragg grating is disposed perpendicular to the light propagation direction.

The hump volume bragg grating is obtained as follows:

firstly, obtaining volume Bragg diffraction efficiency; according to the coupled wave theory, the angular selectivity of a lossless transmission volume bragg grating can be described as:

wherein n is₁For adjusting refractive indexD is the thickness of the grating, lambda and theta are respectively the wavelength and incident angle of an incident beam in the grating, and delta theta is the angular deviation of a Bragg angle in the grating;

under the volume bragg condition, when Δ θ is 0, the diffraction efficiency can be simplified as:

wherein eta₀Is the central diffraction efficiency, θ, of the volume Bragg grating₀Arcsin (λ/2 Λ) is the bragg angle, Λ is the period of the volume bragg grating;

from equation (2), it can be concluded that by fine tuning n₁D, can obtain eta in the interval from 0 to 100 percent₀；

Obtaining a single-peak volume Bragg grating according to the Bragg angle of the volume Bragg diffraction efficiency and the period adjustment of the volume Bragg grating; i.e. when eta₀When the percentage is 100 percent, the traditional single-peak volume Bragg grating can be obtained;

then obtaining the hump volume Bragg grating by adjusting the diffraction efficiency of the single-peak volume Bragg grating, namely the single-peak volume Bragg grating is in eta₀When 0, it becomes a hump volume bragg grating.

As shown in fig. 3, compared with the conventional unimodal volume bragg grating, the kyphosis volume bragg grating has zero diffraction efficiency under the bragg condition, and the maximum diffraction is symmetrically located at two sides of the bragg condition, so that it has a special angular selectivity.

As shown in fig. 4, the angular selectivity of the hump volume bragg grating used in the present system is-1.388 mrad in terms of off-bragg angle, and the diffraction efficiency is 82.758%, and the hump volume bragg grating has good characteristics at this time.

As shown in fig. 5, under the condition of plane wave incidence, when the hump volume bragg grating has a thickness-to-period ratio of thousand-fold magnitude, the wavelength selection width is several nm magnitude, and the hyperspectral imaging can be well realized, that is, the filter spectrum width is about one percent of the wavelength. At this time, the diffracted light includes only a narrow band of spectral components, and the remaining spectral components are transmitted in the original direction.

The hump body Bragg grating used in the system is a thick hump body Bragg grating with thousand-fold thickness-period ratio, the thickness of the hump body Bragg grating is 2.5mm, the period is 2.2 mu m, the refractive index modulation degree is 0.00015, and the vector inclination angle is 90 degrees.

As shown in FIG. 6, for a specific wavelength, the relative diffraction efficiency η of the diffracted beam of +1 order at the exit surface can be found by the parameters of the preferred grating_rCan approach 100% while other diffraction orders are severely suppressed. Therefore, the +1 order diffracted beam is used in the system to achieve high transmittance spatial two-dimensional quasi-monochromatic imaging.

The invention provides a hyperspectral imaging system based on volume Bragg gratings, which fully utilizes the special angular selectivity and wavelength selection characteristics of a hump volume Bragg grating, particularly a thick hump volume Bragg grating to realize hyperspectral imaging, and diffracts and performs dispersion compensation on a target light field of an object to be detected through the thick hump volume Bragg grating group to obtain more accurate spectral information and spatial information of the object to be detected.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.