Terahertz wave TE pass polarization filter

Abstract

The invention discloses a terahertz wave TE-pass polarization filter, and belongs to the technical field of terahertz communication and device integration. Comprising a substrate, a high-refractive-index waveguide region, a coating layer and a coating dielectric layer, the high-refractive-index waveguide area is arranged in the middle of the upper surface of the substrate, and the coating dielectric layer and the coating layer are arranged on the upper surface of the substrate and are sequentially arranged on the two sides of the middle of the high-refractive-index waveguide area; the high-refractive-index waveguide region comprises a rectangular input waveguide, a first wedge-shaped mode conversion waveguide, a rectangular hybrid plasmon waveguide, a second wedge-shaped mode conversion waveguide and a rectangular output waveguide which are connected in sequence and have the same height, and the rectangular input waveguide and the rectangular output waveguide are consistent in size; the size of the first wedge-type mode conversion waveguide is consistent with that of the second wedge-type mode conversion waveguide, and the width of the rectangular hybrid plasmon waveguide is smaller than that of the rectangular input waveguide and that of the rectangular output waveguide. The TM mode of terahertz waves is effectively filtered, the insertion loss is reduced, and the extinction ratio of the filter is improved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of terahertz communication and device integration, and particularly relates to a terahertz wave TE-pass polarization filter. Background Art

[0002] With the rapid development of terahertz optical communication featuring high penetrability, rich spectral information, strong anti-interference ability, and low atmospheric attenuation, the integration, miniaturization, and compactification of optical waveguide devices have become an important research direction in the optoelectronic field. Surface plasmon components provide new ideas for integrated photonic devices, and among them, metal-based surface plasmon components exhibit excellent performance in multiple frequency bands.

[0003] However, in the terahertz band, metals lose their negative dielectric constant characteristics, so they cannot support effective plasmon excitation. To address this limitation, new materials such as graphene can be introduced into surface plasmon components. Nevertheless, most of the existing terahertz polarization filters are TM-pass polarization filters, which have weak optical field confinement ability, high bending loss, limited penetration ability, and usually large sizes, making it difficult to meet the requirements of high integration. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a terahertz wave TE-pass polarization filter, which realizes high integration of the filter, effectively filters out the TM mode of terahertz waves, reduces insertion loss, and improves the extinction ratio of the filter.

[0005] The present invention provides the following technical solutions: Provide a terahertz wave TE-pass polarization filter, including a substrate, a high refractive index waveguide region, a coating layer, and a coating dielectric layer; the high refractive index waveguide region is arranged at the middle position of the upper surface of the substrate, and the coating dielectric layer and the coating layer are arranged on the upper surface of the substrate and are sequentially arranged on both sides of the middle of the high refractive index waveguide region; the high refractive index waveguide region includes a rectangular input waveguide, a first wedge-shaped mode conversion waveguide, a rectangular hybrid plasmon waveguide, a second wedge-shaped mode conversion waveguide, and a rectangular output waveguide that are sequentially connected and have the same height. The rectangular input waveguide and the rectangular output waveguide have the same size, the first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide have the same size, and the width of the rectangular hybrid plasmon waveguide is smaller than the widths of the rectangular input waveguide and the rectangular output waveguide.

[0006] As an optional technical solution of the present invention, the first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide are oppositely arranged at both ends of the rectangular hybrid plasmon waveguide.

[0007] As an alternative technical solution of the present invention, the coating dielectric layer and the coating layer are sequentially disposed on both sides of the first wedge-shaped mode conversion waveguide, the rectangular hybrid plasmonic waveguide, and the second wedge-shaped mode conversion waveguide from inside to outside.

[0008] As an alternative technical solution of the present invention, the material of the substrate is SiO2, the material of the high refractive index waveguide region is Si, the material of the coating layer is graphene, and the material of the coating dielectric layer is SiO2.

[0009] As an alternative technical solution of the present invention, the width of the rectangular hybrid plasmonic waveguide is set to 5 μm to 12 μm, the height is set to 20 μm to 30 μm, and the length is set to 60 μm to 80 μm.

[0010] As an alternative technical solution of the present invention, the widths of the rectangular input waveguide and the rectangular output waveguide are set to 25 μm to 35 μm, the height is set to 20 μm to 30 μm, and the length is set to 90 μm to 110 μm.

[0011] As an alternative technical solution of the present invention, the lengths of the first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide are set to 5 μm to 10 μm.

[0012] As an alternative technical solution of the present invention, the heights of the coating dielectric layer and the coating layer are the same as the height of the high refractive index waveguide region.

[0013] As an alternative technical solution of the present invention, the width of the coating layer is set to 0.5 nm to 2.5 nm.

[0014] As an alternative technical solution of the present invention, the width of the coating dielectric layer is set to 1 μm to 5 μm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: A terahertz wave TE-pass polarization filter provided by the present invention introduces a laterally distributed hybrid plasma in the high refractive index waveguide region, which can effectively confine the transmission of the TE mode in the waveguide, allowing it to pass through with negligible loss, while significantly suppressing the TM mode and causing it to leak into the substrate, achieving a high extinction ratio and low loss; the use of the first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide can significantly improve the mode conversion efficiency and reduce the transmission loss; by setting the coating dielectric layer and the coating layer, the mode confinement ability in the coating dielectric layer is effectively enhanced. When the terahertz wave is vertically incident, the TE mode is well confined in the low refractive index layer, thereby achieving a stronger mode confinement ability and a longer transmission distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of a terahertz wave TE-pass polarization filter in an embodiment of the present invention; Figure 2 It is a schematic cross-sectional diagram of a terahertz wave TE-pass polarization filter in an embodiment of the present invention; Figure 3 It is a top view of a terahertz wave TE-pass polarization filter in an embodiment of the present invention; Figure 4 It is a schematic diagram of the cross-sectional field distribution of a rectangular hybrid plasmonic waveguide at an incident wavelength λ = 100 μm in an embodiment of the present invention; Figure 5 It is a schematic diagram of the polarization extinction ratio and insertion loss in the wavelength band of incident wavelength λ = 90 μm to 105 μm in an embodiment of the present invention; Figure 6 It is a schematic diagram of the real part of the effective refractive index of the TM mode and TE mode when the width of the rectangular hybrid plasmonic waveguide in an embodiment of the present invention is in the range of 5 μm to 25 μm; Figure 7 It is a schematic diagram of the polarization extinction ratio and insertion loss when the length of the rectangular hybrid plasmonic waveguide in an embodiment of the present invention is in the range of 60 μm to 150 μm.

[0017] In the figure, the markings are: 1, substrate; 2, high refractive index waveguide region; 3, coating layer; 4, coated dielectric layer; 201, rectangular input waveguide; 202, first wedge-shaped mode conversion waveguide; 203, rectangular hybrid plasmonic waveguide; 204, second wedge-shaped mode conversion waveguide; 205, rectangular output waveguide. Specific embodiments

[0018] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0019] Embodiment 1 This embodiment provides a terahertz wave TE-pass polarization filter. As Figures 1 - 3 shown, it includes a substrate 1, a high refractive index waveguide region 2, a coating layer 3, and a coated dielectric layer 4.

[0020] The high refractive index waveguide region 2 is arranged at the middle position on the upper surface of the substrate 1, and the coated dielectric layer 4 and the coating layer 3 are arranged on the upper surface of the substrate 1 and are successively arranged on both sides of the middle of the high refractive index waveguide region 2.

[0021] The high refractive index waveguide region 2 includes a rectangular input waveguide 201, a first wedge-shaped mode conversion waveguide 202, a rectangular hybrid plasmonic waveguide 203, a second wedge-shaped mode conversion waveguide 204, and a rectangular output waveguide 205 that are connected in sequence and have the same height. The rectangular input waveguide 201 and the rectangular output waveguide 205 have the same dimensions. The first wedge-shaped mode conversion waveguide 202 and the second wedge-shaped mode conversion waveguide 204 have the same dimensions. The width of the rectangular hybrid plasmonic waveguide 203 is smaller than the widths of the rectangular input waveguide 201 and the rectangular output waveguide 205. Therefore, the high refractive index waveguide region 2 is symmetric about the center line of the rectangular hybrid plasmonic waveguide 203.

[0022] Further, the first wedge-shaped mode conversion waveguide 202 and the second wedge-shaped mode conversion waveguide 204 are relatively disposed at both ends of the rectangular hybrid plasmonic waveguide 203. One end of the rectangular hybrid plasmonic waveguide 203 is connected to the rectangular input waveguide 201 through the first wedge-shaped mode conversion waveguide 202, and the other end is connected to the rectangular output waveguide 205 through the second wedge-shaped mode conversion waveguide 204.

[0023] Further, the coating dielectric layer 4 and the coating layer 3 are sequentially disposed on both sides of the first wedge-shaped mode conversion waveguide 202, the rectangular hybrid plasmonic waveguide 203, and the second wedge-shaped mode conversion waveguide 204 from the inside out. The heights of the coating dielectric layer 4 and the coating layer 3 are the same as the height of the high refractive index waveguide region 2. The coating dielectric layer 4 between the high refractive index waveguide region 2 and the coating layer 3 forms a low refractive index layer.

[0024] Further, in order to achieve terahertz wave polarization control, in this embodiment, the material of the substrate 1 is SiO2, the material of the high refractive index waveguide region 2 is Si, the refractive index of Si is 3.478, the material of the coating layer 3 is graphene, and the material of the coating dielectric layer 4 is SiO2, and the refractive index of SiO2 is 1.445.

[0025] In this embodiment, the filter is mainly aimed at the terahertz optical communication requirements of a 100 μm wavelength. In order to improve the TE mode transmittance and transmission performance, the total height of the high refractive index waveguide region 2 h Si ranges from 20 μm to 30 μm, preferably 25 μm. The widths of the rectangular input waveguide 201 and the rectangular output waveguide 205 W Si range from 25 μm to 35 μm, preferably 30 μm. The lengths of the rectangular input waveguide 201 and the rectangular output waveguide 205 L range from 90 μm to 110 μm, preferably 100 μm. The width of the rectangular hybrid plasmonic waveguide 203 W gThe length of the rectangular hybrid plasmonic waveguide 203 has a value range of 5 μm to 12 μm, preferably 10 μm. L n The total height of the rectangular hybrid plasmonic waveguide 203 has a value range of 60 μm to 80 μm, preferably 70 μm. h Si The value range is 20 μm to 30 μm, preferably 25 μm.

[0026] Furthermore, the first wedge-shaped mode conversion waveguide 202 and the second wedge-shaped mode conversion waveguide 204 serve as a narrowing region connecting the rectangular input waveguide 201 and the rectangular output waveguide 205. The cross-sections on both sides are respectively consistent with the rectangular input waveguide 201, the rectangular output waveguide 205, and the rectangular hybrid plasmonic waveguide 203. The lengths of the first wedge-shaped mode conversion waveguide 202 and the second wedge-shaped mode conversion waveguide 204 L c have a value range of 5 μm to 10 μm, preferably 8 μm. As Figure 1 shown, the total length of the rectangular hybrid plasmonic waveguide 203, the first wedge-shaped mode conversion waveguide 202, and the second wedge-shaped mode conversion waveguide 204 is L m .

[0027] Furthermore, the coating layer 3 is made of graphene. The thickness of a single layer of graphene is 0.5 nm. The width of the coating layer 3 is set to be 0.5 nm to 2.5 nm, preferably 0.5 nm. The width of the coating dielectric layer W SiO2 has a value range of 1 μm to 5 μm, preferably 2 μm.

[0028] In this embodiment, under the incidence of terahertz waves, the relative permittivity of the corresponding graphene is expressed as: ; where represents the conductivity of graphene, represents the permittivity of vacuum, represents the angular frequency, d represents the thickness of the graphene layer.

[0029] The conductivity of graphene is determined by the Kubo equation and is expressed as: ; ; where represents the relaxation time of graphene, T represents the temperature, represents the chemical potential of graphene, represents the electron energy of graphene, represents the reduced Planck constant,j represents the imaginary unit, and represents the Boltzmann constant.

[0030] Example 2 The polarization filter provided in Example 1 can effectively filter out the TM mode near 3 THz and achieve low-loss transmission of the TE mode, realizing a high extinction ratio of 40.33 dB and a low insertion loss of 0.17 dB. The effective length of the device is only 86 μm, which is beneficial to integrated photonic circuits. To verify the effect of the polarization filter, the following experiment is given in this example.

[0031] The parameters of the TE-pass polarization filter are as follows: the width of the rectangular input waveguide W Si = 30 μm, the length L of the rectangular input waveguide is 100 μm, the width of the rectangular hybrid plasmonic waveguide W g = 10 μm, the length of the rectangular hybrid plasmonic waveguide L n = 70 μm, the height of the first wedge-shaped mode conversion waveguide h Si = 25 μm, the length L c = 8 μm, the width of the coated dielectric layer W SiO2 = 2 μm, the width of the coating layer d = 0.5 nm, the width of the substrate is 150 μm, and the height is 50 μm.

[0032] An experiment was carried out using the above polarization filter at the terahertz wave incident wavelength λ = 100 μm, and the cross-sectional field distribution of the rectangular hybrid plasmonic waveguide was obtained. As Figure 4 shown, the TE hybrid plasmonic mode is well confined in the low refractive index region, which is beneficial to the low-loss transmission of the TE mode.

[0033] Let the incident wavelength be in the band of λ = 90 μm to 105 μm, and an experiment was carried out using the above polarization filter to obtain the polarization extinction ratio and insertion loss. As Figure 5 shown, in the band of 90 μm to 105 μm, the insertion loss always remains at a low level, but the polarization extinction ratio fluctuates significantly. It can only reach the polarization extinction ratio > 25 dB in the bands of [95.5, 96.5] μm and [97.5, 100] μm. However, when the wavelength is 100 μm, the polarization extinction ratio reaches a maximum value of 40.33 dB, indicating that this filter can effectively filter out the TM mode in the TEM wave at a specific wavelength and achieve the high-pass of the TE mode.

[0034] Example 3 In this embodiment, based on the second embodiment, the width of the rectangular hybrid plasmon waveguide is set to W g By changing the range of 5 μm to 25 μm, while keeping other parameters in Example 2 unchanged, the real part of the effective refractive index of the TM mode and the TE mode is obtained. Figure 6 As shown, the TM mode is sensitive to width changes and is cut off at a width of about 12.5 μm, while the TE mode always maintains a relatively high real part of the effective refractive index, which is beneficial for suppressing the TM mode as much as possible while allowing the TE mode to transmit with low loss.

[0035] Example 4 In this embodiment, based on the second embodiment, the length of the rectangular hybrid plasmon waveguide is L n The polarization extinction ratio and insertion loss are obtained by changing the wavelength within the range of 60 μm to 150 μm while keeping other parameters in Example 2 unchanged. Figure 7 As shown in Figure 2, the insertion loss is stable in the range of [0,0.5] dB, always maintained at an acceptable low level. L n There are multiple local extreme values ​​under the value of L n When the wavelength is 70 μm, the polarization extinction ratio reaches a maximum value of 40.33 dB, at which time the polarizer has the strongest suppression on the TM mode.

[0036] In summary, the terahertz wave TE pass polarization filter of the present application utilizes the lateral structure to excite the hybrid plasmon, which can not only effectively filter out the TM mode in the 90μm~105μm band, but also effectively improve the mode confinement capability of the TE mode. The first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide significantly improve the mode conversion efficiency and reduce the transmission loss. When the terahertz wave enters the structure vertically, the TE mode is effectively confined in the low refractive index covering medium layer, so that the entire filter structure can efficiently suppress the TM mode near the 3THz frequency band, which can not only achieve excellent mode confinement capability and long-distance transmission characteristics, but also has the significant advantages of high extinction ratio and low insertion loss.

[0037] This application stimulates the TE-type hybrid plasmon mode on the basis of exciting the traditional mode waveguide, and realizes the filtering of the TM mode, realizing the polarization filtering function, and breaking through the performance bottleneck of the traditional structure. The structural dimensions of the terahertz polarization filter are all in the μm order, and its manufacturing difficulty is greatly reduced compared to optical waveguide devices. In addition, the graphene coating technology is mature, the material preparation is simple and low-cost, and provides strong support for the large-scale production of devices.

[0038] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0039] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", "coupled" shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0040] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A terahertz wave TE pass polarization filter, characterized in that: It comprises a substrate (1), a high refractive index waveguide region (2), a coating layer (3) and a coating medium layer (4); The high refractive index waveguide region (2) is arranged in the middle of the upper surface of the substrate (1), and the coating medium layer (4) and the coating layer (3) are arranged on the upper surface of the substrate (1) and are arranged in sequence on both sides of the middle of the high refractive index waveguide region (2); The high refractive index waveguide region (2) comprises a rectangular input waveguide (201), a first wedge-shaped mode conversion waveguide (202), a rectangular hybrid plasmon waveguide (203), a second wedge-shaped mode conversion waveguide (204) and a rectangular output waveguide (205) which are connected in sequence and have the same height; the rectangular input waveguide (201) and the rectangular output waveguide (205) have the same size; the first wedge-shaped mode conversion waveguide (202) and the second wedge-shaped mode conversion waveguide (204) have the same size; and the width of the rectangular hybrid plasmon waveguide (203) is smaller than the widths of the rectangular input waveguide (201) and the rectangular output waveguide (205).

2. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The first wedge-shaped mode conversion waveguide (202) and the second wedge-shaped mode conversion waveguide (204) are arranged at two ends of the rectangular hybrid plasmon waveguide (203) in a relative manner.

3. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The coating medium layer (4) and the coating layer (3) are sequentially arranged from the inside to the outside on both sides of the first wedge-shaped mode conversion waveguide (202), the rectangular hybrid plasmon waveguide (203) and the second wedge-shaped mode conversion waveguide (204).

4. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The material of the substrate (1) is SiO2, the material of the high refractive index waveguide region (2) is Si, the material of the coating layer (3) is graphene, and the material of the coating medium layer (4) is SiO2.

5. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The width of the rectangular hybrid plasmon waveguide (203) is set to 5 μm-12 μm, the height is set to 20 μm-30 μm, and the length is set to 60 μm-80 μm.

6. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The width of the rectangular input waveguide (201) and the rectangular output waveguide (205) is set to 25 μm to 35 μm, the height is set to 20 μm to 30 μm, and the length is set to 90 μm to 110 μm.

7. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The lengths of the first wedge-shaped mode conversion waveguide (202) and the second wedge-shaped mode conversion waveguide (204) are set to be 5 μm to 10 μm.

8. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The heights of the coating medium layer (4) and the coating layer (3) are consistent with the height of the high refractive index waveguide region (2).

9. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The width of the coating layer (3) is set to 0.5 nm to 2.5 nm.

10. The terahertz wave TE pass polarization filter according to claim 1, characterized in that: The width of the coating medium layer (4) is set to 1 μm to 5 μm.

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