CN115421231A - Sub-wavelength mixed Bloch surface excimer optical waveguide - Google Patents
Sub-wavelength mixed Bloch surface excimer optical waveguide Download PDFInfo
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Abstract
The invention discloses a mixed Bloch surface excimer optical waveguide with subwavelength optical field limiting capability and ultralow transmission loss. Based on the coupling of a Bloch surface excimer mode excited by the multilayer film structural element and a medium wave guide mode excited by the high-refractive-index medium nanowire, the optical field can be limited in the low-refractive-index medium gap layer, and meanwhile, the distribution range of the optical field can be further remarkably reduced in the high-refractive-index ridge medium region, so that the two-dimensional sub-wavelength constraint of the transmitted optical field is realized; meanwhile, the waveguide is of an all-dielectric structure, so that the transmission loss of a transmission optical field can be obviously reduced. The hybrid optical waveguide structure solves the problems of loss and interference in integrated optical waveguide devices.
Description
Technical Field
The invention relates to the technical field of optical waveguides, in particular to an ultralow-loss hybrid Bloch surface excimer optical waveguide constrained by a sub-wavelength optical field.
Background
Bloch surface plasmon is an electromagnetic wave mode that exists in the photonic band gap of periodic dielectric alternating layers. This mode exists near the interface of the medium and the medium, where the field strength is at a maximum and decays exponentially on both sides of the interface in a direction perpendicular to the interface. Excitation of bloch surface plasmon depends on the design of photonic crystal structure, with few wavelength and polarization limitations. In addition, because no metal exists in the structure, long-range optical transmission can be realized. Therefore, the design with more excellent performance is expected to be realized in the aspects of nano-photonic devices, sensing detection and the like.
The existing photon device structure for exciting the Bloch surface excimer is realized by plating a layer of dielectric material outside a truncated photonic crystal, and the excitation of the Bloch surface excimer is caused by coherent superposition effect of reflection and refraction of light beams in a photonic band gap structure, so that the field constraint capability is relatively poor, and the integration of the photon device is not facilitated. In order to overcome the defects of most existing bloch surface excimer optical waveguide structures in terms of transmission characteristics and more effectively achieve the balance between mode loss and optical field confinement capability, device structures and designs regarding bloch surface excimer have become the hot spot of recent research concerning bloch surface excimer correlation. The Konopsky research group of the Russian institute adopts a photonic crystal structure as a substrate, a layer of gold film is plated on the photonic crystal structure, a similar long-range surface plasmon mode is excited in a formed mixed structure, and the waveguide can realize stronger optical field constraint but has relatively shorter transmission distance. Descrovi et al, which has implemented effective guiding of bloch surface waves by loading two-dimensional dielectric strips on the surface of a photonic crystal structure, have implemented low transmission loss and large transmission distance, but at the cost that the mode field size is often relatively large, which is not favorable for integration of waveguides and devices. The subject group adopts the mode that the metal nano-wire is loaded on the surface of the photonic crystal structure, and the coupling of the surface plasmon mode and the Bloch surface plasmon mode can effectively enhance the optical field limiting capability, but the transmission distance is still in a micron order. And then, the surface of the photonic crystal structure is loaded with the medium nanowires, and based on the coupling of a medium mode and a Bloch surface excimer mode, the optical field can be constrained to a low-refractive-index medium slit between the medium nanowires and the photonic crystal interface for transmission, and meanwhile, lower transmission loss is kept.
The invention provides a sub-wavelength mixed Bloch surface excimer optical waveguide with stronger mode field limiting capability. On the basis of the mixed waveguide structure, the ridge medium with high refractive index is introduced into the low-refractive-index medium gap layer between the medium nanowire and the photonic crystal structure, so that the mode field limiting capability is further improved, and the transmission loss is low. The waveguide has very important significance for realizing various active and passive surface excimer optical devices and integrated photonic chips.
Disclosure of Invention
The invention aims to further improve the mode field limiting capability of the traditional mixed type Bloch surface excimer optical waveguide and provides a sub-wavelength and low-loss mixed type Bloch surface excimer optical waveguide structure.
The invention provides a low-loss hybrid Bloch surface excimer optical waveguide structure with subwavelength optical field limiting capability, wherein the cross section of the structure comprises a multilayer film structure element, a low-refractive-index dielectric gap layer positioned on the multilayer film structure element, a high-refractive-index ridge-type dielectric region embedded in the low-refractive-index dielectric gap layer, a high-refractive-index dielectric nanowire positioned on the high-refractive-index ridge-type dielectric region and a coating layer. The high-refractive-index medium nanowire is embedded in the cladding layer, and the low-refractive-index medium gap layer is located between the high-refractive-index medium nanowire and the multilayer film structure element. The width of the low-refractive-index medium slit layer is not less than 0.1 time of the wavelength of the transmitted optical signal, the height range is 0.01-0.05 time of the wavelength of the transmitted optical signal, the width of the high-refractive-index ridge medium region embedded in the low-refractive-index medium slit layer is not more than 0.03 time of the wavelength of the transmitted optical signal, the height range is 0.01-0.05 time of the wavelength of the transmitted optical signal and is equal to the height of the low-refractive-index medium slit layer, the width range of the high-refractive-index medium nanowire on the high-refractive-index ridge medium region is 0.01-0.4 time of the wavelength of the transmitted optical signal, and the height range is 0.01-0.4 time of the wavelength of the transmitted optical signal; the high-refractive-index medium nanowires embedded in the high-refractive-index ridge medium region and the high-refractive-index ridge medium region in the low-refractive-index medium gap layer can be made of the same or different materials, the refractive indexes of the high-refractive-index medium region and the high-refractive-index ridge medium region are higher than those of the low-refractive-index medium gap layer and the cladding layer, the materials of the low-refractive-index medium gap layer and the cladding layer can be made of the same or different materials, and the ratio of the maximum value of the refractive indexes of the materials of the low-refractive-index medium gap layer and the cladding layer to the minimum value of the refractive indexes of the high-refractive-index medium nanowires embedded in the high-refractive-index ridge medium region and the high-refractive-index ridge medium region of the low-refractive-index medium gap layer is smaller than 0.75.
The multilayer film structure element in the structure has the function of exciting Bloch surface excimer by adjusting the physical property of a certain layer structure.
In one example, the multilayer film structure element may be formed by alternately laminating two or more layers of all-dielectric material having different refractive indices; or may be comprised of one or more of transparent dielectrics, metals, absorptive materials, left handed artificial materials, and the like.
In a more preferred example, the multilayer film structured element includes, in order, a plurality of dielectric material layers, a high refractive index dielectric cut layer, wherein the plurality of dielectric material layers are formed by two or more dielectric material layers having different refractive indexes alternately.
In a more preferred example, the multilayer film structured element includes a transparent dielectric substrate, a plurality of dielectric material layers, and a high refractive index dielectric cut layer in this order, wherein the plurality of dielectric material layers are formed by two or more dielectric material layers having different refractive indexes alternately.
In an example, a ratio of a maximum value of material refractive indices of the low-refractive-index dielectric layer and the cladding layer to a material refractive index of the high-refractive-index dielectric cut layer is less than 0.75.
In one example, the high refractive index medium cut layer in the hybrid bloch surface optical waveguide structure may employ any one of silicon, titanium dioxide, silicon nitride, zinc sulfide, cerium oxide, zirconium oxide, gallium arsenide.
In one example, the low refractive index dielectric layer in the hybrid Bloch surface plasmon optical waveguide structure can employ any one of silicon dioxide, magnesium difluoride, cryolite.
Among the multiple dielectric material layers with different refractive indexes in the multilayer film structure element, preferably, the high refractive index dielectric material layer and the low refractive index dielectric material layer may be alternately stacked. Wherein the high refractive index and the low refractive index in the high refractive index medium material layer and the low refractive index medium material layer are relative to each other; i.e. the refractive index of the high refractive index dielectric material layer is higher than the refractive index of the low refractive index dielectric material layer.
Wherein, more preferably, the refractive indexes of the materials of the high refractive index medium material layer and the high refractive index medium interception layer may be the same or different, or more preferably, the materials of the high refractive index medium material layer and the high refractive index medium interception layer may be the same or different, and preferably, the materials of the high refractive index medium material layer and the high refractive index medium interception layer are selected from any one of silicon, titanium dioxide, silicon nitride, zinc sulfide, cerium oxide, zirconium oxide, and gallium arsenide.
Wherein, more preferably, the material refractive indexes of the low refractive index medium material layer and the low refractive index medium gap layer can be the same or different, or more preferably, the materials of the low refractive index medium material layer and the low refractive index medium gap layer can be the same or different, and are preferably the same, and more preferably, the materials of the low refractive index medium material layer and the low refractive index medium gap layer are selected from any one of silicon dioxide, magnesium difluoride and cryolite.
In a more preferred example, the high refractive index dielectric material of the multilayer dielectric material layer in the multilayer film structured element employs silicon; the low-refractive-index dielectric material of the multilayer dielectric material layer in the multilayer film structure element adopts silicon dioxide; the high-refractive-index medium truncation layer in the multilayer film structural element adopts silicon; the low-refractive-index dielectric gap layer adopts silicon dioxide.
The thicknesses of all layers in the multilayer film structural element in the mixed Bloch surface excimer optical waveguide structure are selected to enable a photonic band gap to be generated in the multilayer film structural element under a certain working wavelength, and then Bloch surface excimer is excited.
The high-refractive-index dielectric cut-off layer in the multilayer film structure element in the mixed Bloch surface optical waveguide structure is connected with the multilayer dielectric material layer, and can be used for adjusting the excitation position of Bloch surface excimer in a photonic band gap.
In one example, the thickness d of the ith layer in a multilayer film structure i Is determined by the following formula:
where λ is the wavelength of the transmitted optical signal, n i 、θ i Respectively the refractive index of the medium of the ith layer and the incident angle of the light wave on the ith layer. Wherein i is a natural number between 1 and the maximum number of layers of the multilayer film structure.
In one example, the range of the thickness of the high refractive index dielectric cut-off layer in the multilayer film structure element in the structure is no more than 0.2 times the wavelength of the transmitted optical signal.
In one example, the hybrid Bloch surface plasmon optical waveguide structure low refractive index dielectric gap layer is contiguous with a high refractive index dielectric truncation layer in a multilayer film structure.
The material of the high-refractive-index ridge-type dielectric region embedded in the low-refractive-index dielectric gap layer in the hybrid Bloch surface optical waveguide structure is selected from any one of silicon, titanium dioxide, silicon nitride, zinc sulfide, cerium oxide, zirconium oxide and gallium arsenide.
The cross section of the high-refractive-index ridge-type dielectric region embedded in the low-refractive-index dielectric gap layer in the hybrid Bloch surface optical waveguide structure is in any one of a square shape, a rectangular shape, a circular shape, an elliptical shape, or a trapezoidal shape.
In one example, silicon is used as the material for the high index ridge dielectric regions embedded in the low index dielectric gap layer.
The material of the high refractive index medium nano wire in the mixed Bloch surface excimer optical waveguide structure is any one of silicon, titanium dioxide, silicon nitride, zinc sulfide, cerium oxide, zirconium oxide and gallium arsenide which can generate a medium wave guide mode.
The cross-sectional shape of the high refractive index dielectric nanowire in the hybrid Bloch surface excimer optical waveguide structure can be any one of square, rectangle, circle, ellipse or trapezoid.
In one example, silicon is used as the material for the high refractive index dielectric nanowires. The radius of the high refractive index dielectric nanowires is preferably 70 to 200nm, more preferably 90 to 180nm, more preferably 100 to 160nm, and more preferably 120 to 150nm.
The mixed Bloch surface excimer optical waveguide structure has the following advantages:
1. the hybrid Bloch surface excimer optical waveguide designed by the invention has strong mode field limiting capability, can realize sub-wavelength restriction of a mode field, and simultaneously keeps very low transmission loss. Therefore, the method can be used for constructing various integrated photonic devices and photonic chip structures.
2. The waveguide structure is matched with the processing technology of the existing planar waveguide, and is easy to be applied to an optical waveguide chip with high integration level.
Drawings
Fig. 1 is a schematic view of a sub-wavelength hybrid bloch surface plasmon waveguide structure.
Fig. 2 is a schematic view of the structure of the sub-wavelength hybrid bloch surface-active optical waveguide described in example 1.
Fig. 3 is a partial enlarged view of the sub-wavelength hybrid bloch surface plasmon optical waveguide structure described in example 1.
Fig. 4 is a graph showing an electric field intensity distribution of a mixed-mode optical field of the sub-wavelength hybrid bloch surface plasmon waveguide described in example 1 when the wavelength of a transmission optical signal is 1.55 μm. Fig. 4 (a) is a distribution curve of the electric field intensity along the X-axis direction, and fig. 4 (b) is a distribution curve of the electric field intensity along the Y-axis direction.
FIG. 5 is a graph of the effective refractive index with height h of the mixed mode propagating in the sub-wavelength hybrid Bloch surface excimer optical waveguide described in example 1 at a wavelength of 1.55 μm for transmitting an optical signal r The change curve of (2).
FIG. 6 is a graph showing the propagation distance of a mixed mode propagating in the sub-wavelength hybrid Bloch surface excimer optical waveguide described in example 1 with a height h at a wavelength of 1.55 μm for propagating an optical signal r The variation curve of (c).
FIG. 7 is a normalized effective mode field area as a function of height h for a hybrid mode propagating in the sub-wavelength hybrid Bloch surface excimer optical waveguide described in example 1 at a wavelength of 1.55 μm for propagating optical signals r The change curve of (2).
Fig. 8 is a schematic view of the structure of the sub-wavelength hybrid bloch surface-active optical waveguide described in example 2.
Fig. 9 is a partial enlarged view of the sub-wavelength hybrid bloch surface plasmon optical waveguide structure of example 2.
FIG. 10 is a graph showing an electric field intensity distribution of a mixed mode optical field of the sub-wavelength hybrid Bloch surface plasmon waveguide described in example 2 when a wavelength of a transmission optical signal is 1.55 μm. Fig. 10 (a) is a distribution curve of the electric field intensity along the X-axis direction, and fig. 10 (b) is a distribution curve of the electric field intensity along the Y-axis direction.
FIG. 11 is a graph of the effective refractive index with height h of a mixed mode propagating in the sub-wavelength hybrid Bloch surface excimer optical waveguide described in example 2 at a wavelength of 1.55 μm for transmitting an optical signal r The change curve of (2).
FIG. 12 is a graph showing the propagation distance of a mixed mode propagating in the sub-wavelength hybrid Bloch surface excimer optical waveguide described in example 2 with height h at a wavelength of 1.55 μm for propagating an optical signal r The change curve of (2).
FIG. 13 is a normalized effective mode field area as a function of height h for a mixed mode propagating in the sub-wavelength hybrid Bloch surface excimer optical waveguide described in example 2 at a wavelength of 1.55 μm for propagating an optical signal r The variation curve of (c).
Detailed Description
Referring to fig. 1, the sub-wavelength hybrid bloch surface plasmon optical waveguide structure provided by the present invention includes a clad layer 1; a high refractive index dielectric nanowire 2; a high refractive index ridge dielectric region 3; a low refractive index dielectric gap layer 4; a multilayer film structured element 5. In fig. 1, the high refractive index dielectric nanowire 2 is embedded in the cladding layer 1, and the high refractive index ridge dielectric region 3, the low refractive index dielectric gap layer 4, and a portion of the top of the multilayer film structured element 5 are also embedded in the cladding layer 1, but this is not essential.
Mode characteristics of the hybrid bloch surface plasmon are important indexes for characterizing the hybrid bloch surface plasmon optical waveguide. Wherein the mode characteristic parameters mainly comprise an effective refractive index real part, a transmission distance and a normalized effective mode field area.
The transmission distance L is defined as the distance when the electric field strength on any interface is attenuated to an initial value of 1/e, and the expression is as follows:
L＝λ/[4π/Im(n eff )] (1)
wherein Im (n) eff ) λ is the wavelength of the transmitted optical signal, which is the imaginary part of the mode effective index.
The computational expression of the effective mode field area is as follows:
A eff ＝(∫∫W(r)dA) 2 /{max(W(r))} (2)
wherein A is eff W (r) is the energy density of the surface wave, defined as:
where Re represents a real part, E (r) is an electric field of a surface wave, H (r) is a magnetic field of a surface wave, ε (r) is electric conductivity, and μ 0 Is a vacuum magnetic permeability. The normalized effective mode field area is the ratio of the effective mode field area calculated by equation (3) to the mode field area at the free space diffraction limit. The mode field area of the free space diffraction limit is defined as follows:
A 0 ＝λ 2 /4 (4)
where λ is the wavelength of the transmitted optical signal. Thus, the normalized effective mode field area a is:
A＝A eff /A 0 (5)
the magnitude of the normalized effective mode field area characterizes the mode field confinement capability of the mode, and a value less than 1 corresponds to a size constraint of the subwavelength.
Example 1: optical waveguide with high-refractive-index ridge-type dielectric region with rectangular cross section
FIG. 2 is a structural view of a hybrid Bloch surface plasmon waveguide described in example 1. Fig. 3 is a partial enlarged view of the hybrid bloch surface plasmon optical waveguide of example 1. 201 is a cladding layer, n c Is its refractive index; 202 is a high refractive index dielectric nanowire, n w Is its refractive index, r w Is its radius; 203 is a high refractive index ridge dielectric region, n r Is its refractive index, h r To its height, w r Is its width; 204 is a low refractive index dielectric gap layer, n s Its height is the same as the high index ridge medium for its refractive index; 205 is a multilayer film structure element; 206 is a high refractive index medium cut-off layer of a multilayer film structure element, n d Is its refractive index, h d Is its height; 207. low refractive index dielectric layer of multi-layer dielectric material layer of multi-layer film structure element, n l Is its refractive index, h l Is its height; 208 is a high refractive index dielectric layer of the multi-layer dielectric material layer of the multi-layer film structure element, n h Is its refractive index, h h The height thereof (a plurality of low refractive index medium layers 207 and high refractive index medium layers 208 are stacked on each other to form a multilayer dielectric material layer of the multilayer film structure element).
In this example, the wavelength of the transmitted optical signal is selected to be 1.55 μm, the material of the cladding 201 is set to air, and the refractive index thereof is 1; the material of the high refractive index dielectric nanowires 202 is silicon, and the refractive index at a wavelength of 1.55 μm is 3.476; the material of the high-refractive-index ridge dielectric region 203 is silicon, and the refractive index at a wavelength of 1.55 μm is 3.476; the material of the low-refractive-index dielectric gap layer 204 is silicon dioxide, and the refractive index of the low-refractive-index dielectric gap layer is 1.444; the material of the high refractive index dielectric cut layer 206 in the multilayer film structured element 205 was silicon, and its refractive index was 3.476; the number of cycles of the multilayered dielectric material layer in the multilayered film structure element 205 is 7; the material of the low-refractive-index dielectric layer 207 of the multiple dielectric material layers is silicon dioxide, and the refractive index of the silicon dioxide is 1.444; the material of the high refractive index medium layer 208 of the multi-layer medium material layer is silicon, and the refractive index thereof is 3.476.
In this example, the radius r of the high index dielectric nanowires 202 w =120nm; height h of high refractive index ridge dielectric region 203 r Has a value range of 2-35 nm and a width w r =10nm; low refractive index mediumHeight and h of mass-gap layer 204 r The same; height h of high refractive index dielectric cutoff layer 206 d =100nm; height h of the low index of refraction dielectric layer 207 l =320nm; height h of high index dielectric layer 208 h ＝240nm。
The waveguide structure in this embodiment was simulated using a full-vector finite element method, and the mode field distribution and mode characteristics of the mixed bloch surface plasmon mode at a wavelength of 1.55 μm were calculated.
FIG. 4 is a graph showing an electric field intensity distribution curve of a hybrid Bloch surface plasmon mode optical field exemplifying the sub-wavelength hybrid Bloch surface plasmon optical waveguide in which the height h of the high refractive index ridge dielectric region 203 is set to 1.55 μm when the wavelength of a transmission optical signal is 1.55 μm r ＝5nm，w r =10nm. Fig. 4 (a) is a distribution curve of the electric field intensity along the X-axis direction, and fig. 4 (b) is a distribution curve of the electric field intensity along the Y-axis direction. As can be seen from FIG. 4, the electric field intensity of the optical field of the sub-wavelength hybrid Bloch surface excimer optical waveguide has a significant enhancement effect.
FIG. 5 is a graph illustrating the effective refractive index of a hybrid Bloch surface plasmon mode propagating in the sub-wavelength hybrid Bloch surface plasmon optical waveguide with height h at a wavelength of 1.55 μm for transmitting an optical signal r The change curve of (2). As can be seen from fig. 5, the effective refractive index of the mixed bloch surface plasmon mode of the sub-wavelength mixed bloch surface plasmon optical waveguide with the height h r The increase is less variable.
FIG. 6 is a graph illustrating the propagation distance of a hybrid Bloch surface plasmon mode propagating in the sub-wavelength hybrid Bloch surface plasmon optical waveguide with a height h when the wavelength of a propagating optical signal is 1.55 μm r The variation curve of (c). As can be seen from fig. 6, the transmission distance of the hybrid bloch surface plasmon mode of the sub-wavelength hybrid bloch surface plasmon optical waveguide with the height h r The increase of (a) is increased first and then decreased, and is between 6 and 10 millimeters. Under the same condition, the transmission distance of the conventional Bloch surface excimer optical waveguide mode is 0.6-1 mm. It is known that the hybrid bloch surface plasmon waveguide has lower transmission loss.
FIG. 7 is a drawing of a table topNormalized effective mode field area with height h of a mixed Bloch surface excimer mode propagating in the sub-wavelength mixed Bloch surface excimer optical waveguide when the wavelength of the optical transmission signal is 1.55 μm r The variation curve of (c). As can be seen from FIG. 7, the mode field area of the hybrid Bloch surface plasmon mode varies with height h r And increases, it is known that the increase in the transmission distance of the hybrid bloch surface plasmon mode comes at the expense of mode field confinement capability. Meanwhile, the normalized effective mode field area is still very small and is far less than 1. High index ridge dielectric regions embedded in low index dielectric gap layer (corresponding to h) are removed under the same conditions r =0, other parameters are held constant), the effective mode field area of the resulting bloch surface plasmon waveguide mode is about 2 times that of the hybrid bloch surface plasmon waveguide. It is known that the sub-wavelength hybrid bloch surface plasmon waveguide has a stronger mode field confinement capability.
Example 2: optical waveguide with high-refractive-index ridge-type dielectric region with square cross section
Fig. 8 is a structural diagram of the sub-wavelength hybrid bloch surface plasmon optical waveguide of example 2. Fig. 9 is a partial enlarged view of the hybrid bloch surface plasmon optical waveguide of example 2. 801 is a cladding layer, n c Is its refractive index; 802 is a high refractive index dielectric nanowire, n w Is its refractive index, r w Is its radius; 803 is a high refractive index ridge dielectric region, n r Is its refractive index, h r Its height and width; 804 is a low refractive index dielectric gap layer, n s The height of which is the same as the high refractive index ridge dielectric region for its refractive index; 805 is a multilayer film structure element; 806 is a high refractive index medium cut-off layer of the multilayer film structure element, n d Is its refractive index, h d Is its height; 807 is a low refractive index dielectric layer of a multilayer dielectric material layer of the multilayer film structure element l Is its refractive index, h l Is its height; 808 high refractive index medium layers of a multilayer medium material layer, n h Is its refractive index, h h For the height (multiple low refractive index medium layers 807 and high refractive index medium layers 808 are superposed to form multiple multilayer film structure elementsA layer of dielectric material).
In this example, the wavelength of the transmitted optical signal is selected to be 1.55 μm, the material of the cladding 801 is set to air, and the refractive index thereof is 1; the high index dielectric nanowire 802 is made of silicon and has a refractive index of 3.476 at a wavelength of 1.55 μm; the material of high-refractive-index ridge dielectric region 803 is silicon, and its refractive index is 3.476; the material of the low-refractive-index dielectric gap layer 804 is silicon dioxide, and the refractive index of the silicon dioxide is 1.444; the material of the high refractive index medium cut layer 806 of the multilayer film structure element 805 is silicon, and the refractive index thereof is 3.476; the number of cycles of the multilayered dielectric material layer of the multilayered film structure element 805 is 7; the material of the low-refractive-index dielectric layer 807 of the multiple dielectric material layers is silicon dioxide, and the refractive index of the silicon dioxide is 1.444; the material of the high refractive index dielectric layer 808 of the multi-layered dielectric material layer is silicon, and the refractive index thereof is 3.476.
In this example, the radius r of the high index dielectric nanowire 802 w =120nm; height h of high refractive index ridge dielectric region 803 r The value range of (A) is 2-35 nm; height sum h of low index dielectric gap layer 804 r The same; height h of high refractive index dielectric cutoff layer 806 d =100nm; height h of low index dielectric layer 807 l =320nm; height h of high index dielectric layer 808 h ＝240nm。
The waveguide structure in this embodiment was simulated using a full-vector finite element method, and the mode field distribution and mode characteristics of the mixed bloch surface plasmon mode at a wavelength of 1.55 μm were calculated.
FIG. 10 is a graph showing an electric field intensity distribution curve of a hybrid Bloch surface plasmon mode optical field exemplifying the sub-wavelength hybrid Bloch surface plasmon waveguide when the wavelength of a transmission optical signal is 1.55 μm, in which the height h of the high-refractive-index ridge dielectric region 803 is r =4nm. Fig. 10 (a) is a distribution curve of the electric field intensity along the X-axis direction, and fig. 10 (b) is a distribution curve of the electric field intensity along the Y-axis direction. As can be seen from FIG. 10, the electric field intensity of the optical field of the hybrid Bloch surface excimer optical waveguide has a significant enhancement effect.
FIG. 11 illustrates an example of the sub-wavelength when the wavelength of the transmitted optical signal is 1.55 μmEffective refractive index of hybrid Bloch surface excimer mode propagating in hybrid Bloch surface excimer optical waveguide with height h r The change curve of (2). As can be seen from fig. 11, the effective refractive index of the mixed bloch surface plasmon mode of the sub-wavelength mixed bloch surface plasmon optical waveguide with the height h r The increase change is smaller.
FIG. 12 is a graph illustrating the propagation distance of a hybrid Bloch surface plasmon mode propagating in the sub-wavelength hybrid Bloch surface plasmon optical waveguide with a height h when the wavelength of a propagating optical signal is 1.55 μm r The change curve of (2). As can be seen from fig. 12, the transmission distance of the mixed bloch surface plasmon mode of the sub-wavelength mixed bloch surface plasmon optical waveguide according to the height h r The increase of (a) increases first and then decreases and is between 7.5 and 10.5 mm. Under the same condition, the transmission distance of the conventional Bloch surface excimer optical waveguide mode is 0.6-1 mm. It is known that the hybrid bloch surface plasmon waveguide has lower transmission loss.
FIG. 13 is a normalized effective mode field area with height h illustrating a hybrid Bloch surface plasmon mode propagating in the sub-wavelength hybrid Bloch surface plasmon optical waveguide for a 1.55 μm wavelength of the propagating optical signal r The variation curve of (c). As can be seen from FIG. 13, the mode field area of the hybrid Bloch surface plasmon mode varies with height h r The propagation distance of the hybrid bloch surface plasmon mode is increased at the expense of mode field confinement capability. Meanwhile, the normalized effective mode field area is still very small and is far smaller than 1. Removing the high refractive index ridge dielectric region embedded in the low refractive index dielectric gap layer under the same conditions (corresponding to h) r =0, other parameters are held constant), the effective mode field area of the resulting bloch surface plasmon waveguide mode is about 2 times that of the hybrid bloch surface plasmon waveguide. It is known that the sub-wavelength hybrid bloch surface plasmon optical waveguide has a stronger mode field confinement capability.
The simulation results of example 1 and example 2 show that the cross-sectional shape of the high refractive index ridge dielectric region embedded in the low refractive index dielectric gap layer in the waveguide structure according to the present invention can be realized by adopting a rectangle, a square and the similar shapes thereof.
In conclusion, the invention improves the multilayer dielectric layer Bloch surface excimer optical waveguide structure, integrates the high refractive index dielectric nanowire on the basis of the structure, and introduces the low refractive index dielectric gap layer and the high refractive index ridge-type dielectric region between the high refractive index dielectric cut-off layer and the dielectric nanowire to form a composite structure, so that the novel mixed Bloch surface excimer optical waveguide can effectively reduce the mode field size and the transmission loss. In addition, because the high and low refractive index medium layers, the high refractive index ridge-type medium region and the high refractive index medium nanowire of the waveguide can be made of semiconductor materials, the two-dimensional structure can be matched with a semiconductor planar chip processing technology, is easy to apply to an optical waveguide chip with high integration level, and has very important significance for realizing a large-scale integrated optical circuit.
Finally, it should be noted that the examples in the above figures are only intended to illustrate the sub-wavelength hybrid bloch surface plasmon waveguide structure of the present invention, but not to limit it. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or substituted with equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications should be included in the scope of the claims of the present invention.
Claims (5)
1. A low-loss hybrid Bloch surface optical waveguide structure with subwavelength optical field limiting capability comprises a multilayer film structure element, a low-refractive-index dielectric gap layer, a high-refractive-index ridge dielectric region, a high-refractive-index dielectric nanowire and a coating layer, wherein the low-refractive-index dielectric gap layer is arranged on the multilayer film structure element, the high-refractive-index ridge dielectric region is embedded in the low-refractive-index dielectric gap layer, and the high-refractive-index dielectric nanowire and the coating layer are arranged on the high-refractive-index ridge dielectric region. The high-refractive-index medium nanowire is embedded in the coating layer, and the low-refractive-index medium gap layer is positioned between the high-refractive-index medium nanowire and the multilayer film structural element. The width of the low-refractive-index dielectric slit layer is not less than 0.1 time of the wavelength of the transmitted optical signal, the height range is 0.01-0.05 time of the wavelength of the transmitted optical signal, the width of the high-refractive-index ridge type dielectric region embedded in the low-refractive-index dielectric slit layer is not more than 0.03 time of the wavelength of the transmitted optical signal, the height range is 0.01-0.05 time of the wavelength of the transmitted optical signal and is equal to the height of the low-refractive-index dielectric slit layer, the width range of the high-refractive-index dielectric nanowire on the high-refractive-index ridge type dielectric region is 0.01-0.4 time of the wavelength of the transmitted optical signal, and the height range is 0.01-0.4 time of the wavelength of the transmitted optical signal; the high-refractive-index medium nanowires embedded in the high-refractive-index ridge medium region and the high-refractive-index ridge medium region in the low-refractive-index medium gap layer can be made of the same or different materials, the refractive indexes of the high-refractive-index medium region and the high-refractive-index ridge medium region are higher than those of the low-refractive-index medium gap layer and the cladding layer, the materials of the low-refractive-index medium gap layer and the cladding layer can be made of the same or different materials, and the ratio of the maximum value of the refractive indexes of the materials of the low-refractive-index medium gap layer and the cladding layer to the minimum value of the refractive indexes of the high-refractive-index medium nanowires embedded in the high-refractive-index ridge medium region and the high-refractive-index ridge medium region of the low-refractive-index medium gap layer is smaller than 0.75.
2. The optical waveguide structure of claim 1 wherein the high index ridge dielectric regions embedded in the low index dielectric gap layer are made of a material selected from the group consisting of silicon, titanium dioxide, silicon nitride, zinc sulfide, cerium oxide, zirconium oxide, gallium arsenide.
3. The optical waveguide structure of claim 1, wherein the cross-section of the high index dielectric regions embedded in the low index dielectric gap layer in the structure has a shape of any one of a square, rectangle, circle, ellipse, or trapezoid.
4. The optical waveguide structure of claim 1, wherein the high refractive index medium nanowires on the high refractive index ridge medium region in the structure are made of any one of silicon, titanium dioxide, silicon nitride, zinc sulfide, cerium oxide, zirconium oxide, and gallium arsenide capable of generating a medium guided wave mode; the low-refractive-index dielectric gap layer is made of any one of silicon dioxide, magnesium difluoride and cryolite.
5. The optical waveguide structure of claim 1, wherein the cross-sectional shape of the high refractive index medium nanowires on the high refractive index ridge medium region in the structure can be any one of square, rectangular, circular, elliptical or trapezoidal.
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