A high-sensitivity optical wavelength sensor based on Goos-Hansen shift

Abstract

The present invention provides a high-sensitivity optical wavelength sensor based on Goos-Hansen shift, which belongs to the field of optical technology. The photonic crystal of the high-sensitivity optical wavelength sensor includes a graphene monolayer, a first periodic crystal is arranged on the incident side of the graphene monolayer, a second periodic crystal is arranged on the exit side of the graphene monolayer, and a defect layer is embedded between the graphene monolayer and the first periodic crystal and between the graphene monolayer and the second periodic crystal respectively; the first periodic crystal includes a plurality of first dielectric layers and a plurality of second dielectric layers that are alternately distributed, and the second periodic crystal includes a plurality of third dielectric layers and a plurality of fourth dielectric layers that are alternately distributed. The present invention can detect the wavelength of incident light and simultaneously realize a large reflectivity and a Goos-Hansen shift near a topological boundary state.

Description

Technical Field

[0001] The invention belongs to the technical field of optics and relates to a high-sensitivity optical wavelength sensor based on Goos-Hansen shift. Background Art

[0002] When light is irradiated by two refractive indices n 1 and n 2 When a light beam is reflected on a dielectric medium, if total reflection occurs at the interface of the dielectric, part of the light field will penetrate into the lower medium. This is equivalent to placing a virtual reflection interface behind the actual interface. Then, relative to the position predicted by the original geometric optics, the reflected light will have a lateral shift. This displacement is called the Goos-Hansen shift. This phenomenon is called the Goos-Hansen phenomenon and was first proposed by Goos and Hansen. It has been observed experimentally. The schematic diagram of the formation of the Guth-Hansen shift is shown in Figure 1 As shown, the symbol Δ represents the lateral displacement of the reflected light beam, and the arrow line represents the central axis of the light beam.

[0003] Goos-Hansen shift can be widely used in high-sensitivity sensors and optical switches. In particular, Goos-Hansen shift is particularly sensitive to the incident light wavelength, incident angle, etc., so it can be used in high-brightness wavelength and angle sensors. However, under normal circumstances, the Goos-Hansen shift is relatively weak, usually only a few wavelengths or a dozen wavelengths, so this causes great difficulties in the detection and application of the Goos-Hansen shift in experiments. Therefore, in order to obtain a high-sensitivity wavelength and angle sensor based on the Goos-Hansen shift, the magnitude of the Goos-Hansen shift must first be increased.

[0004] People have taken various approaches to enhance the Goos-Hansen shift, such as using the bandgap edge states of photonic crystals and the weak loss of materials to obtain larger Goos-Hansen shifts. In particular, near the exceptional points (EPs) and coherent-perfect-absorption-laser point (CPA-LP) in non-Hermitian photonic systems (containing optical gain and optical loss, or one of them), the Goos-Hansen extremum appears, which theoretically reaches infinity. However, the reflectivity at EPs is zero, and near it, the reflectivity is also very low. In addition, CPA-LP is not a stable photon state. Therefore, this inspires us to explore stable photonic devices with large reflectivity and can achieve large Goos-Hansen shifts.

[0005] The Goos-Hansen shift is proportional to the phase of the reflection coefficient. Near the band gap edge and defect mode of the photonic crystal, the phase of the reflection coefficient changes dramatically, which inevitably leads to a larger Goos-Hansen shift. In order to further increase the rate of change of the reflection coefficient phase, two different photonic crystals can be compounded to obtain a topological boundary state. Near the topological edge state, the phase change of the reflection coefficient is more dramatic. In addition, graphene is an emerging two-dimensional material with adjustable conductivity, and its surface conductivity is a function of its chemical potential. Single-layer graphene is transparent, but there is a weak optical loss coefficient in graphene. Therefore, graphene can be compounded with photonic crystals to enhance the Goos-Hansen shift, thereby realizing a high-sensitivity wavelength or angle sensor. Summary of the invention

[0006] The purpose of the present invention is to provide a high-sensitivity optical wavelength sensor based on Goos-Hansen shift in view of the above-mentioned problems existing in the prior art. The technical problem to be solved by the present invention is to obtain a high-sensitivity optical wavelength sensor capable of detecting the wavelength of incident light.

[0007] The objective of the present invention can be achieved through the following technical solutions: a high-sensitivity optical wavelength sensor based on Goos-Hansen shift, characterized in that the photonic crystal of the high-sensitivity optical wavelength sensor includes a graphene monolayer, a first periodic crystal is arranged on the incident side of the graphene monolayer, a second periodic crystal is arranged on the exit side of the graphene monolayer, a defect layer is embedded between the graphene monolayer and the first periodic crystal and between the graphene monolayer and the second periodic crystal respectively; the first periodic crystal includes a plurality of first dielectric layers and a plurality of second dielectric layers that are alternately distributed, and the second periodic crystal includes a plurality of third dielectric layers and a plurality of fourth dielectric layers that are alternately distributed.

[0008] Furthermore, the first dielectric layer is magnesium fluoride.

[0009] Furthermore, the defective layer is magnesium fluoride.

[0010] Furthermore, the second dielectric layer is zinc sulfide.

[0011] Furthermore, the third dielectric layer is silicon.

[0012] Furthermore, the second dielectric layer is silicon dioxide.

[0013] There is a band gap in the energy band of the photonic crystal. When light is irradiated onto the photonic crystal, if the frequency of the light is within the band gap, no light will pass through the photonic crystal and the light beam will be totally reflected. However, if a defect layer is added to the photonic crystal, there will be a defect mode in the band gap of the energy band. When the frequency of the incident light is equal to the frequency of the defect mode, the light beam will pass through the photonic crystal without reflection. The reflectivity at this time is zero, so the defect mode is also called the transmission mode. The energy of the defect mode is mainly distributed in the defect layer, and the energy distribution at the center of the defect layer is the strongest. Extending from the center of the defect layer to both sides of the photonic crystal, the energy distribution of the defect mode decays exponentially.

[0014] The Goos-Hansen position of the reflected beam is proportional to the derivative of the phase of the reflection coefficient with respect to the wave vector. Since the reflectivity of the defect mode is zero, there is uncertainty in the phase of the reflection coefficient of the defect mode. Therefore, the reflected beam of the defect mode may have a large Goos-Hansen shift. However, for a photonic crystal with no gain and loss, the reflectivity of the defect mode is zero. Even if there is a large Goos-Hansen shift at this time, it is actually meaningless.

[0015] By combining two different photonic crystals with a defect layer, we can obtain a topological boundary state (also a defect mode). Then, graphene is embedded into the defect layer of the photonic crystal, and the weak loss of graphene is used to weaken the transmittance of the photonic crystal to the boundary state, thereby increasing the reflectivity of light. At the same time, the weak loss of graphene will also cause a sharp change in the phase of the reflection coefficient. Since the Goos-Hansen shift of the reflected light beam is proportional to the rate of change of the phase of the reflection coefficient, a larger Goos-Hansen shift of the reflected light beam is obtained. The Goos-Hansen shift is a function of the incident angle, wavelength, and refractive index. Therefore, when this dependence is close, this effect can be applied to high-sensitivity sensors. At the same time, a large reflectivity of the boundary state and a large Goos-Hansen shift can also be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the Guth-Hansen displacement.

[0017] Figure 2 Schematic diagram of the structure of a photonic crystal used as a highly sensitive light wavelength sensor.

[0018] Figure 3 (a) is the reflectivity near the edge state in a defective photonic crystal without graphene; Figure 3 (b) is the reflection coefficient phase of the edge state in a defect photonic crystal without graphene embedded.

[0019] Figure 4 (a) is the reflectivity of the photonic crystal in the defective photonic crystal embedded with graphene; Figure 4 (b) is the reflection coefficient phase of the photonic crystal in the defective photonic crystal embedded with graphene.

[0020] Figure 5 It is the Goos-Hansen shift of a reflected light beam in a photonic crystal used as a highly sensitive light wavelength sensor.

[0021] Figure 6 is the sensitivity coefficient of an optical wavelength sensor based on the Goos-Hansen shift.

[0022] In the figure, A, the first dielectric layer; B, the second dielectric layer; C, the third dielectric layer; D, the fourth dielectric layer; E, the defect layer; G, the graphene monolayer. DETAILED DESCRIPTION

[0023] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0024] like Figure 2 As shown, the photonic crystal for the optical wavelength sensor is composed of a graphene monolayer G, two defect layers E, a first periodic crystal and a second periodic crystal. The first periodic crystal and the second periodic crystal are symmetrically distributed on both sides of the graphene monolayer G, one defect layer E is embedded between the first periodic crystal and the graphene monolayer G, and the other defect layer E is embedded between the second periodic crystal and the graphene monolayer G. The first periodic crystal is located on the incident side, and the second periodic crystal is located on the exit side. The first periodic crystal includes a plurality of first dielectric layers A and a plurality of second dielectric layers B that are alternately distributed, and the second periodic crystal includes a plurality of third dielectric layers C and a plurality of fourth dielectric layers D that are alternately distributed.

[0025] The graphene monolayer G is embedded in the center of two defective layers E, such as Figure 2 As shown. The refractive indices of the first dielectric layer A, the second dielectric layer B, the third dielectric layer C, the fourth dielectric layer D and the defect layer E are n respectively. a =1.38, n b =2.35,n c =3.53, n d =1.46 and n e =2.35. The first dielectric layer A and the defect layer E are both magnesium fluoride, the second dielectric layer B is zinc sulfide, the third dielectric layer C is silicon, the fourth dielectric layer D is silicon dioxide, and the thickness of the first dielectric layer A is d a =0.281, the thickness of the second dielectric layer B is d b =0.165, the thickness of the third dielectric layer C is d c =0.11, the thickness of the fourth dielectric layer D is d d = 0.258, the thickness of the defect layer E is d e= 0.165 μm. The incident ray is marked as 1, the reflected ray is marked as 2, and the transmitted ray is marked as 3.

[0026] Graphene is embedded in the middle of two defective layers, which is the zero point of the z-axis. Graphene is a two-dimensional material with no thickness, and its surface conductivity can be described by the Kubo formula.

[0027]

[0028] Among them, f d =1 / (1+exp[(ε-μ c ) / (k B T)]) is the Fermi-Dirac statistics, ε is the particle energy, μ c is the graphene chemical potential (also called the Fermi level E F ), T is the ambient temperature, e is the electron charge, τ is the momentum relaxation time, k B is the Boltzmann constant.

[0029] Graphene can be regarded as an equivalent dielectric with a certain thickness. When its equivalent thickness is less than 1nm, the influence of this equivalent method on the calculation of reflectivity and transmittance can be ignored. At this time, we take the thickness of graphene as 0.34nm, which is equivalent to the thickness of a single layer of atoms. The equivalent dielectric constant of graphene is ε g =1+iσ g η 0 / (kd g ), where k is the incident wave vector, η 0 is the vacuum impedance. The ambient temperature is T = 27 °C, the momentum relaxation time τ = 0.5 ps, μ c =0.15eV.

[0030] The entire structure can be recorded as (AB) N EGE(CD) N , where the Bragg period number N = 5.

[0031] The incident light is a transverse magnetic (TM) wave, propagating along the z-axis. The electromagnetic fields at both ends of each dielectric layer can be linked by the transmission matrix. For example, the electromagnetic fields at both ends of the lth dielectric layer can be linked by the following relationship:

[0032]

[0033] Among them, M l is called the transmission matrix of the lth layer, where η l =ε l (ε 0 / μ 0 ) 1 / 2 / (ε l-sin 2 θ) 1 / 2 , θ is the incident angle of light, which is set here as θ = 20°. The transmission matrix of the entire system is

[0034]

[0035] Where n is the total number of layers in the structure. The reflection coefficient is

[0036]

[0037] where η 1 =η N+1 =(ε 0 / μ 0 ) 1 / 2 (1-sin 2 θ) 1 / 2 , are the impedances of the incident and output ends respectively, and the reflectivity is R = rr*. The band gap of the photonic crystal is ω gap =4ω 0 arcsin|(n b -n a ) / (n b +n a )| 2 / π, where ω 0 =2πc / λ 0 ,λ 0 =1.55μm.

[0038] Figure 3 (a) is the reflectivity of the defect mode in a defect photonic crystal without graphene. It can be seen that the reflectivity is a function of the frequency of the incident light. There is a band gap in the middle of the reflection spectrum, and the light in this band gap will be completely reflected. However, the reflectivity of the topological boundary state (also a defect mode) at the * position is zero, and the light in the topological boundary state will be completely transmitted, so it is also called a transmission mode. Write the reflection coefficient in the form of an exponential in is the phase of the reflection coefficient. Figure 3 (b) is the reflection coefficient phase of the edge state in the defective photonic crystal without graphene embedded. It can be seen that there is a phase jump of π at the edge state position. Because the reflectivity of the edge state is zero, there is uncertainty in the phase of the reflection coefficient. At the same time, near the edge state, the reflection coefficient phase changes more dramatically. According to the relationship between the Goos-Hansen shift of the reflected beam and the reflection coefficient phase

[0039]

[0040] It can be seen that the Goos-Hansen shift of the reflected light beam near the boundary state is large. However, the reflectivity is small at this time, so we embed graphene into the defect layer to obtain a larger reflectivity.

[0041] Figure 4 (a) is the reflectivity of the photonic crystal in the defective photonic crystal embedded with graphene. It can be seen that the reflectivity of the edge state at the * position is not zero, R = 0.212. Figure 4 (b) is the reflection coefficient phase of the photonic crystal in the defective photonic crystal embedded with graphene. It can be seen that the phase at the edge state position does not jump, but the change is quite drastic, so a reflected beam with relatively large reflectivity and Goos-Hansen shift can be obtained.

[0042] Figure 5 is the Goos-Hansen shift of the reflected light beam in the graphene-embedded photonic crystal. It can be seen that the Goos-Hansen shift is a function of the wavelength of the incident light; when the wavelength of the incident light is at the boundary state, the Goos-Hansen shift of the reflected light beam is the largest, and its maximum value is Δ=124λ.

[0043] This device is used as a sensor to detect the wavelength of incident light using the Goos-Hansen shift of the reflected light beam. A section of the graph with better linearity can be selected as the working area. The sensitivity coefficient of the sensor can be obtained by the formula

[0044]

[0045] It is found that for this optical wavelength sensor based on the Goos-Hansen shift of the reflected light beam, Figure 6 The sensitivity coefficient varies with the wavelength of the incident light. At the center of the working area, the maximum sensitivity coefficient is S = 4.75 × 10 4 .

[0046] The advantages of the present invention are as follows: defects are introduced into the two photonic crystals, and graphene is embedded in the defect layer, so that a large reflectivity and Goos-Hansen shift can be obtained at the same time, with a maximum reflectivity R = 0.212 and a maximum Goos-Hansen shift Δ = 124λ; the Goos-Hansen shift in the device is applied to the detection of the wavelength of the incident light, and its sensitivity coefficient is as high as S = 4.75×10 4 .

[0047] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A high-sensitivity optical wavelength sensor based on Goos-Hansen shift, characterized in that: The photonic crystal of the high-sensitivity optical wavelength sensor includes a graphene monolayer (G), a first periodic crystal is arranged on the incident side of the graphene monolayer (G), a second periodic crystal is arranged on the exit side of the graphene monolayer (G), a defect layer (E) is embedded between the graphene monolayer (G) and the first periodic crystal, and between the graphene monolayer (G) and the second periodic crystal; the first periodic crystal includes a plurality of first dielectric layers (A) and a plurality of second dielectric layers (B) that are alternately distributed, and the second periodic crystal includes a plurality of third dielectric layers (C) and a plurality of fourth dielectric layers (D) that are alternately distributed; the entire structure is (AB) N EGE(CD) N , N is the Bragg period number.

2. The high-sensitivity optical wavelength sensor based on Goos-Hansen shift according to claim 1, characterized in that: The first dielectric layer (A) is magnesium fluoride.

3. The high-sensitivity optical wavelength sensor based on Goos-Hansen shift according to claim 2, characterized in that: The defective layer (E) is magnesium fluoride.

4. The high-sensitivity optical wavelength sensor based on Goos-Hansen shift according to claim 2, characterized in that: The second dielectric layer (B) is zinc sulfide.

5. The high-sensitivity optical wavelength sensor based on Goos-Hansen shift according to claim 2, characterized in that: The third dielectric layer (C) is silicon.

Images