CN111458792A - Bloch surface wave one-way coupling chip based on asymmetric double-slit structure - Google Patents
Bloch surface wave one-way coupling chip based on asymmetric double-slit structure Download PDFInfo
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- CN111458792A CN111458792A CN202010301643.5A CN202010301643A CN111458792A CN 111458792 A CN111458792 A CN 111458792A CN 202010301643 A CN202010301643 A CN 202010301643A CN 111458792 A CN111458792 A CN 111458792A
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- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
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Abstract
The invention relates to a bloch surface wave one-way coupling chip based on an asymmetric double-slit structure, which comprises a glass substrate and a Bragg reflection unit arranged on the glass substrate, wherein the Bragg reflection unit is internally provided with the asymmetric double-slit structure. The invention has simple structure, no strict requirement on the length of the slit, high fault tolerance rate of the width and the depth of the slit and low processing difficulty. Meanwhile, the invention has simple requirements on incident light, can realize the BSW unidirectional transmission function only by polarizing Gaussian light, and does not need a complex column vector light field.
Description
Technical Field
The invention relates to the field of micro-nano photonics, in particular to surface optics and unidirectional regulation and control of an optical field thereof, and specifically relates to a bloch surface wave unidirectional coupling chip based on an asymmetric double-slit structure.
Background
Surface plasmons (SPPs) are a local electromagnetic wave existing on the Surface of a structure, have a good constraint capability on an electromagnetic field, have the advantages of subwavelength propagation, local field enhancement, high sensitivity to the surrounding environment and the like, can break through the limit of the diffraction limit of a traditional photonic device, have a rich application prospect, and are widely applied to the aspects of micro-nano photonic integration, super-resolution imaging, high-sensitivity sensing and the like in recent years. However, since SPPs exist at the interface between metal and semi-infinite large medium, SPPs are relatively large in loss due to absorption loss and strong scattering loss of the metal material itself, and the preparation technology of the metal structure material is immature, so that the optical field regulation and control and application thereof are greatly limited, and researchers begin to search for a novel micro-nano structure of the whole medium to replace the metal micro-nano structure to better realize the regulation and control of the surface optical field.
The Bloch Surface Wave (BSW) can be regarded as a substitute of SPPs, exists in a multilayer dielectric film formed by periodic high-low refractive index dielectric materials alternately and an ambient air interface, and is a novel Surface Wave based on an all-dielectric micro-nano structure. Compared with surface plasmons, the surface plasmon polariton has the advantages of low transmission loss, high Q factor, multi-mode characteristics (both TE and TM modes, SPPs only have TM mode), CMOS compatibility and the like, so that the control and application based on BSW are increasingly becoming international leading edge research hotspots. A micro-nano structure is constructed on the surface of the multilayer dielectric film, BSW amplitude, phase and polarization can be regulated, photonic integration and control under the micro-nano scale are realized, and the method has a wide application prospect. The realization of high directivity of BSW is the basis for designing efficient sub-wavelength transmitters, receivers and sensors, and the research on the phenomenon of single directivity of BSW at home and abroad is very little at present. For example, the modulation of BSW unidirectionality by circular polarization with a fixed incident angle, the modulation by circular polarization and metaspace interface interaction, etc. have the main problems: (1) the surface micro-nano structure has low fault tolerance and needs precise equipment to prepare the surface micro-nano structure; (2) the regulation and control of an external space light field are needed to be realized; (3) it is difficult to achieve a BSW of high unidirectional transmission ratio.
Disclosure of Invention
In order to solve the problems, the invention provides a bloch surface wave unidirectional coupling chip based on an asymmetric double-slit structure, which has high fault tolerance rate on a surface micro-nano structure and can realize a bloch surface wave with a high unidirectional ratio without complex incident light.
The invention provides a bloch surface wave one-way coupling chip based on an asymmetric double-slit structure, which comprises a glass substrate and a Bragg reflection unit arranged on the glass substrate, wherein the Bragg reflection unit is internally provided with the asymmetric double-slit structure.
The Bragg reflection unit is composed of high-refractive-index medium layers and low-refractive-index medium layers in an alternating mode, and the top layer of the Bragg reflection unit is a low-refractive-index medium defect layer.
And an asymmetric double-slit structure is inscribed in the low-refractive-index medium defect layer.
The asymmetric double-slit structure comprises two single slits which are opposite in parallel.
The distance d between the two single slits satisfies kBSW× d is pi/2, wherein k isBSWRepresenting the bloch surface wave vector.
The width and depth of the two single slits are set to make the amplitude of the Bloch surface wave excited by the two single slits equal and the initial phase difference is pi/2.
The two single slits are the same length.
The length of the two single slits is greater than 4 μm.
The high-refractive-index dielectric layer is made of Si3N4The low-refractive-index dielectric layer is made of SiO2。
The Bragg reflection unit is provided with 18 layers.
The invention has simple structure, only needs to arrange an asymmetric double-slit structure on the top layer of the Bragg reflection unit, and realizes the unidirectional transmission of the Bloch surface wave by the combined action of the two. The invention has no strict requirement on the slit length, has high slit width and depth fault tolerance rate and reduces the processing difficulty. Meanwhile, the invention has simple requirements on incident light, can realize the BSW unidirectional transmission function only by polarizing Gaussian light, and does not need a complex column vector light field.
Drawings
FIG. 1 is a schematic diagram of a Bloch surface wave unidirectional coupled chip structure based on an asymmetric double slit structure according to the present invention;
FIG. 2 is a cross-sectional view of FIG. 1;
FIG. 3(a) is a graph showing the variation of amplitude of a Bloch surface wave with respect to the slit width and depth at a wavelength of 600nm, and FIG. 3(b) is a graph showing the variation of phase of a Bloch surface wave with respect to the slit width and depth at a wavelength of 600 nm;
FIG. 4 is a schematic representation of the unidirectional transmission ratio of a Bloch surface wave as a function of wavelength;
fig. 5(a) is an xz interface field distribution diagram of the uni-directional coupled chip of the present invention simulated by FDTD, fig. 5(b) is a schematic diagram of fourier transform results of FDTD calculation on a surface optical field, and fig. 5(c) is a schematic diagram of experimental results corresponding to fig. 5 (b).
Detailed Description
The following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will serve to better explain the functions and features of the invention.
The bloch surface wave unidirectional coupling chip based on the asymmetric double slit structure of the present invention, as shown in fig. 1 and fig. 2, includes a glass substrate 1, a bragg reflection unit 2, and an asymmetric double slit structure 6. The Bragg reflection unit 2 is arranged on the glass substrate 1, the asymmetric double-slit structure 6 is etched and written on the top layer 5 of the Bragg reflection unit 2 through methods such as a focused ion beam etching method, electron beam exposure or Reactive Ion Etching (RIE), and the like, and the Bragg reflection unit 2 and the asymmetric double-slit structure 6 jointly act to realize unidirectional transmission of the Bloch surface wave.
The Bragg reflection unit 2 is composed of high-refractive-index medium layers 3 and low-refractive-index medium layers 4 alternately, and the top layer 5 is a low-refractive-index medium defect layer. Wherein the high refractive index medium layer is made of Si3N4The low refractive index medium layer is made of SiO2. Although the number of periodic pairs of the high-index dielectric layer and the low-index dielectric layer does not affect the mode refractive index of the bloch surface wave, it affects its local performance, with more periodic pairs giving better local performance and vice versa. Therefore, in order to balance the local area and leakage of the bloch surface wave, so that the local area performance can be kept excellent, and the phenomenon can be conveniently observed by leaking to a far field, the Bragg reflection unit 2 of the invention is provided with 18 layers.
Wherein the top defect layer 5 directly affects the effective refractive index of the bloch surface wave, and the thicker the thickness is, the higher the effective refractive index of the bloch surface wave is, the shorter the wavelength is. Adjustment of the wavelength range of the bloch surface wave can be achieved by adjusting the thickness of the top defect layer 5. The thickness of the high refractive index medium layer and the low refractive index medium layer are approximate to the thickness of a Bloch meterOne quarter of the wavelength of the surface wave can be adjusted according to the effective refractive index of the bloch surface wave in the actual structure design. In this embodiment, the top defect layer 5 has a thickness of 390nm and is made of high refractive index medium Si3N4Layer 3 is 80nm thick, low refractive index medium SiO2The thickness of layer 4 is 100 nm.
The asymmetric double slit structure 6 is composed of two parallel single slits which are opposite, the lengths of the two single slits are the same, and the widths and the depths of the two single slits are different. The incident light used by the invention is polarized Gaussian light, and the beam waist radius of the incident light field is about 2 μm, so the length of the two slits needs to be more than 4 μm.
The two asymmetric single slits can respectively excite the Bloch surface wave to realize the unidirectional coupling of the Bloch surface wave, and the Bloch surface waves excited by the two slits satisfy the following conditions: the amplitudes are approximately equal, the initial phase difference is pi/2, and the central distance d between the two slits satisfies kBSW× d is pi/2, wherein k isBSWThe wave vector of the Bloch surface wave is expressed, so that the BSW unidirectional transmission condition is met, the phases of all points of the Gaussian optical field are the same under the condition that the beam waist radius of the Gaussian optical field is larger, and no additional phase factor is introduced, so that the BSW unidirectional transmission can be realized. As shown in fig. 3(a) and 3(b), the amplitude and phase of the bloch surface wave excited by the slit are different depending on the width and depth of the slit, and therefore the width and depth of the two slits need to be adjusted to satisfy the condition of unidirectional coupling of the bloch surface wave. That is, the BSW excited by the two slits respectively satisfies a certain amplitude-phase relationship, so that unidirectional coupling of the bloch surface wave can be realized.
In addition, as shown in fig. 4, the unidirectional ratio of the bloch surface wave is different under different wavelength conditions, and therefore the unidirectional ratio of the bloch surface wave and the wavelength range in which unidirectional transmission exists can be adjusted in the same chip by adjusting the width, depth, and center-to-center distance of the two single slits in the asymmetric double-slit structure 6.
In the present embodiment, the two slits have a length of 20 μm, a width of 530nm and 400nm, a depth of 230nm and 90nm, and a center-to-center distance d of 755 nm. The Bloch surface waves excited by the two slits are subjected to destructive interference on the side with wider slit width and deeper slit depth, and are subjected to constructive interference on the side with narrower slit width and shallower slit depth, so that unidirectional transmission of the Bloch surface waves is realized. And at an incident wavelength of 600nm, the maximum theoretical transmission ratio of the Bloch surface wave is 860, and the experiment is 92. Fig. 5(a) shows the xz interface field distribution of the unidirectional coupling chip of the present invention simulated by FDTD, fig. 5(b) shows the result of fourier transform on the surface optical field calculated by FDTD, and fig. 5(c) shows the corresponding experimental result of fig. 5(b), which is obtained by testing with a far-field measuring device. As can be seen from fig. 5(a), a bloch surface wave is observed near the interface between the chip and the air with z ═ 0, and the bloch surface wave is observed to be transmitted along the x axis in the positive direction, and the optical field transmission in the negative direction is almost zero, which indicates that the bloch surface wave is transmitted in the one direction, and the incident gaussian optical field is in the middle of the stronger field. As can be seen from fig. 5(b), the abscissa and the ordinate are wave vector space ranges, which represent the range of the optical field that can be collected, and a small bright arc, that is, a bloch surface wave, can be observed on the right side of the graph, while nothing is observed on the left side, which indicates that the bloch surface wave is only transmitted along the x-axis in the forward direction.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.
Claims (10)
1. The Bloch surface wave one-way coupling chip based on the asymmetric double-slit structure comprises a glass substrate and a Bragg reflection unit arranged on the glass substrate, and is characterized in that the Bragg reflection unit is internally provided with the asymmetric double-slit structure.
2. The bloch surface wave unidirectional coupling chip based on the asymmetric double slit structure as claimed in claim 1, wherein the bragg reflection unit is composed of high refractive index medium layers and low refractive index medium layers alternately, and the top layer thereof is a low refractive index medium defect layer.
3. The bloch surface wave uni-directional coupled chip based on asymmetric double slit structure as claimed in claim 2, wherein the low refractive index dielectric defect layer is written with an asymmetric double slit structure.
4. The bloch surface wave unidirectional coupling chip based on asymmetric double slit structure as claimed in claim 1, wherein the asymmetric double slit structure comprises two parallel and opposite single slits.
5. The bloch surface wave unidirectional coupling chip based on asymmetric double-slit structure as claimed in claim 4, wherein the distance d between the two single slits satisfies kBSW× d is pi/2, wherein k isBSWRepresenting the bloch surface wave vector.
6. The unidirectional coupled chip of bloch surface wave based on asymmetric double-slit structure as claimed in claim 4, wherein the width and depth of the two single slits are set to make the bloch surface wave excited by the two single slits equal in amplitude and pi/2 in initial phase difference.
7. The bloch surface wave unidirectional coupling chip based on asymmetric double-slit structure as claimed in claim 4, wherein the length of the two single slits is the same.
8. The bloch surface wave unidirectional coupling chip based on asymmetric double-slit structure as claimed in claim 7, wherein the length of the two single slits is greater than 4 μm.
9. The unidirectional coupled chip of bloch surface wave based on asymmetric double slit structure as claimed in claim 2, wherein the chip is characterized byThe high refractive index medium layer is made of Si3N4The low-refractive-index dielectric layer is made of SiO2。
10. The bloch surface wave unidirectional coupling chip based on the asymmetric double slit structure as claimed in claim 2, wherein the bragg reflection unit is provided with 18 layers in total.
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