CN113295649B

CN113295649B - A photonic crystal for pathological section detection

Info

Publication number: CN113295649B
Application number: CN202110705260.9A
Authority: CN
Inventors: 李永逵
Original assignee: Hubei University of Science and Technology
Current assignee: Hubei University of Science and Technology
Priority date: 2021-06-24
Filing date: 2021-06-24
Publication date: 2024-11-19
Anticipated expiration: 2041-06-24
Also published as: CN113295649A

Abstract

The invention provides a photonic crystal for pathological section detection, and belongs to the technical field of optics. The device comprises a defect layer and two periodic crystals respectively positioned at two sides of the defect layer, wherein the periodic crystals comprise a plurality of dielectric layers I and a plurality of dielectric layers II which are in one-to-one correspondence with the dielectric layers I, the dielectric layers I and the dielectric layers II are alternately distributed, one side of the periodic crystals, which is far away from the defect layer, is provided with a prismatic coupling waveguide, and the cross section of the prismatic coupling waveguide is isosceles right triangle; the defect layer is a tissue section used for pathological detection. The invention has the advantages of improving the reflectivity of the defect layer to the tissue slice and the like.

Description

Photonic crystal for pathological section detection

Technical Field

The invention belongs to the technical field of optics, and relates to a photonic crystal for pathological section detection.

Background

The photonic crystal is formed by alternately arranging materials with different refractive indexes in space to form periodic distribution. In photonic crystals, there is a photonic band structure similar to the semiconductor electronic band. Light waves having wavelengths within the band gap cannot pass through the photonic crystal and are totally reflected back.

If a heterogeneous layer is embedded in the photonic crystal, a photonic crystal with defects is formed. In the bandgap of the defective photonic crystal, there is a defect mode. When the wavelength of the incident light is exactly equal to the defect mode, a resonant output is formed and the light waves pass through the photonic crystal without reflection.

Studies have shown that there is a large gust-hansen shift near the bandgap edge of the photonic crystal with weak loss and the defect mode of the defective photonic crystal. The Goos-Hansen displacement was originally measured in the laboratory by both Goos and Hansen and is therefore named. When light impinges on interfaces of different materials, there is a lateral displacement of the reflected light, the Goos-Hansen displacement, relative to the geometrically optically predicted path. When light waves with different wavelengths are reflected on the medium interface, the reflection coefficient phases of the light waves are different, and after the light waves of all the components are overlapped, the Goos-Hansen displacement of the reflected light beam is formed. The Goos-Hansen displacement may be positive or negative. Typically, the Goos-Hansen displacement is on the order of several to tens of wavelengths, and the beam has a line width, so it is difficult to detect such a lateral displacement of the reflected beam. In addition, in order to obtain larger Goos-Hansen displacement, the reflected light is generally weaker, so that the detection difficulty of the Goos-Hansen displacement is further increased experimentally. At present, the experimental study on the Goos-Hansen displacement is based on weak light observation.

It will be appreciated that when a light wave is incident on the interface of two media, some of the light penetrates the underlying media and then rapidly decays, which is an evanescent wave. Corresponding to the lower side of the interface, a virtual reflection surface is formed. The reflected light will be positively displaced laterally with respect to the predicted position of the geometrical ray. If the ghost surface is located on the upper side of the interface, the lateral displacement is negative.

The weaker the optical loss of the material, the greater the penetration depth of the light wave in the underlying dielectric of the interface, the greater the displacement that will be created upon reflection. In the defective photonic crystal, the reflectivity of the defective mode is minimum, and the phase of the reflection coefficient has uncertainty at the defective mode, that is, the phase has abrupt phenomenon. Therefore, embedding a lossy defect layer in the photonic crystal can increase the reflectance of the defect mode and cause the reflectance phase to change sharply in the vicinity of the defect mode. The Goos-Hansen shift is proportional to the rate of change of the phase of the reflection coefficient, so that a reflected beam with a large reflectivity and Goos-Hansen shift can be obtained near the defective mode.

When different tissues and organs of a human body are diseased, such as inflammation, canceration and the like, microscopic observation, assay, X-ray irradiation and the like are adopted in the traditional detection means for the diseased tissues and organs. The detection methods have the defects of long detection period, high misjudgment rate, high cost and the like.

Since different human tissue and organ slices correspond to different refractive indices, a large optical loss coefficient exists; in addition, when tissue and organ sections are diseased, the refractive index and loss factor will change. Therefore, it is considered that inserting human tissue and organ slices as defect layers into photonic crystals can not only improve the reflectivity of defect modes but also realize a large Goos-Hansen displacement. Importantly, these human tissue and organ slices are diseased, which can cause Goos-Hansen displacements of different magnitudes of the reflected light beams, thereby enabling pathological detection and analysis of the human tissue and organ slices.

Disclosure of Invention

The invention aims to solve the problems of the prior art and provide a photonic crystal for pathological section detection, and the technical problem to be solved by the invention is how to improve the reflectivity of a defect mode in the defect photonic crystal and increase the transverse displacement of a reflected light beam by using a tissue section so as to improve the pathological detection precision.

The aim of the invention can be achieved by the following technical scheme: the photonic crystal for pathological section detection is characterized by comprising a defect layer and two periodic crystals which are respectively positioned at two sides of the defect layer, wherein the periodic crystals comprise a plurality of dielectric layers I and a plurality of dielectric layers II which are in one-to-one correspondence with the dielectric layers I, the dielectric layers I and the dielectric layers II are alternately distributed, one side of the periodic crystals, which is far away from the defect layer, is provided with a prismatic coupling waveguide, and the cross section of the prismatic coupling waveguide is isosceles right triangle; the defect layer is a tissue slice for pathological detection; the photonic crystal may be represented As (AB) ^NC(BA)^N, N being the number of spatial periods of the photonic crystal.

Further, a second dielectric layer in the periodic crystal is close to the defect layer, and the second dielectric layer is zinc sulfide.

Further, the first dielectric layer is silicon dioxide.

Further, the thickness of the first dielectric layer and the second dielectric layer in the periodic crystal is 1/4 of the optical wavelength.

Further, the number of space periods n=1 in the periodic crystal.

Further, the periodic crystals enhance the reflectivity of the defect mode.

Further, the periodic crystal achieves a large Goos-Hansen shift of the reflected beam near the defect mode.

Further, the prismatic coupling waveguide is silicon.

Slicing human tissues or organs such as liver or colon, namely a defect layer, and embedding the slice into the photonic crystal to form the photonic crystal with defects. The photonic crystal is distributed in a central symmetry manner with respect to the defect layer. The larger optical loss in the defect layer can greatly improve the reflectivity of the defect mode; the reflectivity of the defect mode can be further improved by increasing the number of spatial periods of the photonic crystal. In particular, there is a large Goos-Hansen shift of the reflected beam near the bandgap edge and defect mode of the photonic crystal. The magnitude, polarity and peak position of the Goos-Hansen shift are extremely sensitive to the wavelength of the incident light. When a pathological section of liver or colon is placed in a photonic crystal, the refractive index changes and the resulting Goos-Hansen shift changes as compared to normal tissue sections. The refractive index of the pathological section can be accurately measured by scanning the incident wavelength to obtain the peak Goos-Hansen displacement of the corresponding reflected light beam, and further the quantitative analysis of the pathological section is realized.

Drawings

Fig. 1 is a schematic diagram of a photonic crystal structure for pathological section detection.

Fig. 2 (a) is a transmission spectrum of the photonic crystal when n=1; fig. 2 (b) is a reflection spectrum of the photonic crystal when n=1; fig. 2 (c) shows the variation of the reflection coefficient phase with the normalized frequency when n=1; fig. 2 (d) shows the change of the gust-hansen displacement with the normalized frequency when n=1.

Fig. 3 (a) is a transmission spectrum of the photonic crystal when n=5; fig. 3 (b) is a reflection spectrum of the photonic crystal when n=5; fig. 3 (c) shows the variation of the reflection coefficient phase with the normalized frequency when n=5; fig. 3 (d) shows the change of the gust-hansen displacement with the normalized frequency when n=5.

Fig. 4 (a) shows the transmittance corresponding to a pathological section of the liver; fig. 4 (b) shows the reflectivity corresponding to the pathological section of the liver; fig. 4 (c) shows the phase of the reflection coefficient corresponding to the pathological section of the liver; fig. 4 (d) shows the Goos-Hansen shift corresponding to the pathological section of the liver.

In the figure, A is a dielectric layer I; B. a second dielectric layer; C. a defect layer; D. prismatic coupling waveguides.

Detailed Description

The following are specific embodiments of the present invention and the technical solutions of the present invention will be further described with reference to the accompanying drawings, but the present invention is not limited to these embodiments.

The first dielectric layer A and the second dielectric layer B are alternately arranged to form the photonic crystal with the periodic structure. The tissue slice to be examined is placed in a central position to form a defect layer. The structure is centrally symmetric about the defect layer C and can be written As (AB) ^NC(BA)^N, where N is the number of spatial periods. The photonic crystal is truncated to form a finite length multilayer structure, as shown in fig. 1. Space cycle number n=1 in this structure; the two prismatic coupling waveguides D are respectively positioned at two ends of the dielectric multilayer structure, and the cross sections of the prismatic coupling waveguides are isosceles right triangles; Symbol I _i denotes an incident ray, I _t denotes a transmitted ray, I _r denotes a geometrically optically predicted reflected ray, I' _r denotes a reflected ray with a positive goosen-hansen shift, I' _r represents a reflected ray with a negative Goos-Hansen shift; the incident angle θ=45°. Dielectric one a is silicon dioxide with refractive index n _a =1.46 and thickness 1/4 optical wavelength, i.e. d _a＝λ₀/4n_a = 0.2654 μm (μm represents micrometers), where λ ₀ =1.55 μm is the center wavelength; The second dielectric layer B is zinc sulfide, the refractive index is n _b =2.35, and the thickness is d _b＝λ₀/4n_b = 0.1649 μm; the prismatic coupling waveguide D is silicon, and the refractive index is n _d =3.53; the defect layer C is a slice of human tissue or organ with a thickness d _c = 1 μm. Here we will take Liver (Liver) and Colon (Colon) as examples of test samples. The incident wavelength is near λ=1.55 μm, the refractive index of the liver is about n _c1 =1.3624+0.0026964 i, and the refractive index of the colon is about n _c2 =1.3257+0.0037148i, where i is an imaginary unit.

When the incident light is a Transverse Magnetic (TM) wave, the frequency of the input light is changed, and fig. 2 (a) shows the transmission spectrum of the light wave. The abscissa (ω - ω ₀)/ω_gap represents the normalized frequency, where ω=2ρc/λ, ω ₀＝2πc/λ₀, and ω _gap＝4ω₀arcsin│(n_a-n_b)/(n_a+n_b)|²/ρ represent the incident light frequency, the incident light center frequency, and the forbidden bandwidth, respectively, C is the speed of light in vacuum, arcsin is the arcsin function; the ordinate T indicates the transmittance, the solid line indicates the corresponding transmission spectrum when the defect layer C is a Liver (Liver) slice, the broken line indicates the corresponding transmission spectrum when the defect layer C is a Colon (Colon) slice, 3 transmission peaks exist on each transmission spectrum line in the interval of normalized frequencies of [ -1.5,2.5], when the defect layer is a Liver slice, the corresponding three transmission peak values are respectively about T= [0.9617,0.9262,0.9475], and the positions of the peak values are (omega-omega ₀)/ω_gap = [ -0.5781,0.7889,1.9847]; when the defect layer is a Colon slice, the corresponding three transmission peaks are each about t= [0.9437,0.8985,0.9305] and the peak positions are each (ω - ω ₀)/ω_gap = [ -0.5224,0.8883,2.0773]. It can be seen that the transmission spectrum corresponding to the Colon slice has a rightward shift in the whole with respect to the Liver.

When light waves are respectively incident on a multilayer structure including two kinds of slices, fig. 2 (b) shows the reflection spectrum of the light waves, and the ordinate letter R indicates the reflectivity. It can be seen that there are three valleys on each reflection spectrum line, and the positions of the valleys are respectively consistent with the positions of the transmission spectrum peaks. When the defect layer is a liver slice, the corresponding three reflection valleys are R= [0.0003,0.0012,0.0003] respectively; when the defect layer is a colon slice, the corresponding three reflection valleys are r= [0.0006,0.0022,0.0005], respectively. Likewise, there is a shift to the right of the trough of the reflectance spectrum comprising the multi-layer structure of the colon slice as a whole relative to the liver slice.

The reflection coefficient is written in the form of a modulo plus angle: Wherein the method comprises the steps of The amplitude angle of the reflection coefficient is the phase of the reflection coefficient. Fig. 2 (c) shows the variation of the reflection coefficient phase with the normalized frequency. The reflection coefficient phase changes sharply near the band gap edge and defect modes by changing the frequency of the incident light. The lateral displacement of the reflected beam is proportional to the rate of change of the amplitude angle of the reflection coefficient: Where k=λ/2pi, a huge Goos-Hansen shift of the reflected beam can be obtained around the three reflective valleys. The change of the Goos-Hansen displacement with the normalized frequency is shown in FIG. 2 (d). Three displacement peaks appear in each curve, the positions of which are located near the three reflectivity valleys. For liver sections, the corresponding three peak guls-hansen shifts are Δ= 108.541 λ,88.7478 λ and 120.2891 λ in order from left to right; for colon slices, the corresponding three peak guls-hansen shifts are Δ= 73.2632 λ,61.2488 λ and 90.3812 λ in order from left to right. Different human tissue sections cause different Goos-Hansen displacements, and the positions of the peak Goos-Hansen displacements are also different; for the same tissue slice, the Goos-Hansen shift of the reflected beam is extremely sensitive to the wavelength of the incident light near the reflective valley. Thus, changing the wavelength of incident light, the human tissue type, and lesions of various tissue sections, are determined by the measured Goos-Hansen displacement.

Although larger Goos-Hansen displacements can be obtained near the bandgap edge and defect modes, the reflected beam intensities are weaker, which increases the difficulty of experimental detection. To increase the reflectivity near the bandgap edge and the defect mode, this can be achieved by increasing the number of spatial periods N of the photonic crystal. Fig. 3 (a) shows the transmittance corresponding to n=5, and it can be seen that there are many transmission peaks in the transmission spectrum, where the middle transmission peak has a peak size corresponding to the defect mode, and is marked with a pentagram. The transmittance of the intermediate defect mode is reduced more significantly than n=1. The defect modes for liver slices were (ω - ω ₀)/ω_gap = 0.6364, transmittance was t= 0.4782; the defect modes for colon slices were (ω - ω ₀)/ω_gap = 0.6945, transmittance was t= 0.4563. For both slices, the reflectance of the middle defect mode was greatly improved over n=1, as shown in fig. 3 (b),. The reflectance of the defect mode for liver slices was r=0.095, the reflectance of the defect mode for colon slices was r= 0.1051. The reflectance of the bandgap edge was still close to 0, in which case even if there was a large guls-function shift near the bandgap edge, it was difficult to observe experimentally due to the weak light intensity, therefore we focused on the guls-hansen shift near the middle defect mode.

Fig. 3 (c) shows the reflectance phase near the defective mode, the rate of change of the reflectance phase is maximum at the valley of the transmittance, and the slope of the curve may be positive or negative. Thus, varying the wavelength of the incident light, a larger positive and negative Goos-Hansen shift can be achieved, as shown in FIG. 3 (d). It can be seen that on each Goos-Hansen displacement curve there is one peak and two valleys. The peak Goos-Hansen shift is positive and the valley Goos-Hansen shift is negative. For liver sections, the maximum positive Goos-Hansen displacement was obtained as Δ=100.3λ, and the two maximum negative Goos-Hansen displacements were respectively Δ= -0.7217λ and-11.571 λ. For colon slices, a maximum positive Goos-Hansen displacement of Δ=74.2λ can be achieved, with two maximum negative Goos-Hansen displacements of Δ= -9.4455 λ and-7.7931 λ, respectively.

Keeping n=5 unchanged, and embedding healthy and diseased liver pathological sections into the photonic crystal respectively to obtain the transmittance of the light wave as shown in fig. 4 (a). The solid line represents the transmission spectrum corresponding to a slice of healthy liver (HEALTHY LIVER) and the dashed line represents the transmission spectrum corresponding to a slice of diseased liver (DISEASED LIVER). When the liver is cancerous, i.e. hardened, the refractive index of the pathological section of the liver increases relative to normal. Here, the refractive index of the diseased liver is set to n _c1 =1.5+0.0026964i. It can be seen that the defective mode in which lesions occur moves in the low frequency direction. The refractive index of the diseased liver is greater than that of the normal liver, which increases the wavelength of the resonant mode in the defective photonic crystal.

Fig. 4 (b) shows the reflectivity corresponding to a pathological section of the liver. The reflectivity of the intermediate defect modes corresponding to normal and diseased liver slices was r=0.095 and r= 0.1233, respectively. Thus, after a lesion has occurred, the reflectivity increases, which also facilitates the observation of the lateral displacement of the reflected beam. Fig. 4 (c) shows the variation of the reflection coefficient phase with respect to the normalized frequency. Likewise, near the defect mode, the reflectance phase change is also very severe, and the slope of the curve may be positive or negative, which necessarily results in a large or negative or positive Goos-Hansen shift. The position of the resonant mode wavelength corresponding to the diseased liver slice changes relative to the healthy liver slice, and therefore the position of the sharp change in the reflection coefficient phase also changes. Fig. 4 (c) shows the change of the gust-hansen displacement with the normalized frequency. The wavelength of the incident light was varied and healthy and diseased liver sections corresponded to different Goos-Hansen displacement curves, respectively. For healthy liver slices, the normalized frequency corresponding to the peak Goos-Hansen shift is (ω - ω ₀)/ω_gap = 0.6362, i.e. the incident wavelength is λ= 1.3014 μm, while for diseased liver slices, for example, when n _c1 =1.5+0.0026964i, the incident wavelength corresponding to the peak Goos-Hansen shift is λ= 1.3216 μm. By scanning the incident wavelength, the transverse shift of the reflected beam, particularly the relationship between the incident wavelength corresponding to the peak Goos-Hansen shift and the refractive index, can be obtained, and further the pathological characteristics of the liver can be diagnosed.

In summary, in symmetric photonic crystals containing pathological sections of the liver and colon, there is a bandgap structure and a central defect mode of greater reflectivity. The reflectivity of the center defect mode can be further improved by increasing the number of space periods of the photonic crystal. Near the band gap edge and the defect mode, the reflection coefficient phase changes sharply with the change of wavelength, thereby realizing the extremely large Goos-Hansen displacement of the reflected light beam. The magnitude, polarity and peak position of the Goos-Hansen shift corresponding to different pathological slices are extremely sensitive to the incident wavelength. Thus, the device can accurately measure refractive indexes of the liver and the colon through Goos-Hansen displacement of the reflected light beam, and further quantitatively analyze and diagnose pathology of the liver and the colon.

The specific embodiments described herein are offered by way of example only to illustrate the spirit of the invention. Those skilled in the art may make various modifications or additions to the described embodiments or substitutions thereof without departing from the spirit of the invention or exceeding the scope of the invention as defined in the accompanying claims.

Claims

1. A photonic crystal for pathological section detection, characterized in that it comprises a defect layer (C) and two periodic crystals respectively located on both sides of the defect layer (C), wherein the periodic crystal comprises a plurality of dielectric layers one (A) and a plurality of dielectric layers two (B) corresponding one to one with the dielectric layers one (A), wherein the dielectric layers one (A) and the dielectric layers two (B) are alternately distributed, and a prism-shaped coupling waveguide (D) is arranged on one side of the periodic crystal away from the defect layer, wherein the cross section of the prism-shaped coupling waveguide (D) is an isosceles right triangle; the defect layer (C) is a tissue section for pathological detection, and the photonic crystal can be expressed as (AB) ^N C(BA) ^N , where N is the number of spatial periods of the photonic crystal;

The second dielectric layer (B) in the periodic crystal is close to the defect layer (C), and the second dielectric layer (B) is zinc sulfide;

The dielectric layer 1 (A) is silicon dioxide;

The thickness of dielectric layer 1 (A) and dielectric layer 2 (B) is 1/4 optical wavelength;

The spatial period number N of the photonic crystal is 1;

The photonic crystal enhances the reflectivity of the defect mode;

The photonic crystal realizes a huge Goos-Hansen shift of the reflected light beam near the defect mode;

When the pathological section is diseased, the reflectivity of the photonic crystal will increase; when the pathological section is a healthy liver section, the incident wavelength corresponding to the peak Goos-Hansen shift is 1.3014 μm; when the pathological section is a healthy liver section and has a disease, the incident wavelength corresponding to the peak Goos-Hansen shift is 1.3216 μm.

2. A photonic crystal for pathological section detection according to claim 1, characterized in that the prismatic coupling waveguide (D) is made of silicon.