A terahertz wave tm polarization filter

Abstract

The application discloses a terahertz TM polarization filter, which comprises a substrate, a bracket layer, a high-refractive waveguide region, a coating layer and a coating medium layer. The high-refractive waveguide region is arranged at the middle position of the upper surface of the substrate, the bracket layer is arranged on the upper surface of the substrate and located at the two sides of the high-refractive waveguide region, the coating medium layer is supported above the high-refractive waveguide region by the bracket layer, and the coating layer is arranged between the lower surface of the coating medium layer and the bracket layer. The coating medium layer comprises a rectangular main body and a ridge waveguide arranged at the middle position of the rectangular main body. The two ends of the rectangular main body are in contact with the bracket layer. The cross section of the ridge waveguide is isosceles triangle, and the tip of the ridge waveguide faces the high-refractive waveguide region. The application can effectively filter out the TE mode near 3THz, has strong mode limiting capacity, high extinction ratio and low insertion loss.

Description

Technical Field

[0001] This invention relates to a terahertz wave™ pass-polarization filter, belonging to the fields of terahertz wave communication and device integration technology. Background Technology

[0002] With the rapid development of ultra-high bandwidth, high speed, wide bandwidth, and ultra-stable optical communication systems, the integration, miniaturization, and compactness of optical waveguide devices have become important trends in scientific and technological research and application. Surface plasmon resonance (SPR) devices offer new ideas for integrated photonic devices, and metallic SPR devices have shown good performance in multiple frequency bands. However, the application of metallic SPR devices in the terahertz band is limited because metals cannot achieve the negative dielectric properties required for the plasmon effect. Although introducing new materials into SPR devices can achieve local electric field enhancement and plasmon effects that overcome the optical diffraction limit at frequencies below the infrared band (terahertz and microwave bands), the generation of terahertz waves remains difficult. Furthermore, traditional polarization control devices are too large to integrate, further resulting in weak mode confinement capabilities of filters for terahertz waves. Therefore, compact terahertz polarization filters with high extinction ratios and strong mode confinement capabilities urgently need research and development. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention proposes a terahertz wave TM pass polarization filter. Through the combined design of filter structure, materials, and dimensions, it effectively filters out the TE mode of terahertz waves, reduces losses, and improves the filter extinction ratio.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical means:

[0005] This invention proposes a terahertz wave TM pass polarization filter, comprising a substrate, a frame layer, a high refractive index waveguide region, a coating layer, and a coating dielectric layer. The high refractive index waveguide region is disposed in the middle of the upper surface of the substrate. The frame layer is disposed on the upper surface of the substrate and located on both sides of the high refractive index waveguide region. The coating dielectric layer is supported by the frame layer above the high refractive index waveguide region. The coating layer is disposed between the lower surface of the coating dielectric layer and the frame layer.

[0006] The high refractive index waveguide region is arched; the coated dielectric layer includes a rectangular body and a ridge waveguide located in the middle of the rectangular body. The two ends of the rectangular body are in contact with the frame layer. The cross-section of the ridge waveguide is an isosceles triangle, and the tip of the ridge waveguide faces the high refractive index waveguide region.

[0007] Furthermore, the high-refractive-index waveguide region includes a cylindrical input waveguide, a first wedge-shaped mode conversion waveguide, a cylindrical hybrid plasmon waveguide, a second wedge-shaped mode conversion waveguide, and a cylindrical output waveguide connected in sequence; wherein, the cylindrical input waveguide and the cylindrical output waveguide have the same dimensions, the first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide have the same dimensions, and the width of the cylindrical hybrid plasmon waveguide is smaller than the width of the cylindrical input waveguide and the cylindrical output waveguide.

[0008] Furthermore, the coating layer and the coating dielectric layer are located directly above the first wedge-shaped mode conversion waveguide, the dome-shaped hybrid plasmon waveguide, and the second wedge-shaped mode conversion waveguide.

[0009] Furthermore, the air gap between the highest point of the high-refractive-index waveguide region and the lowest point of the coating layer constitutes a low-refractive-index layer, and the height of the low-refractive-index layer ranges from 0.5 μm to 1.5 μm.

[0010] Furthermore, the height of the ridge waveguide in the coated dielectric layer ranges from 10μm to 20μm, and the ridge angle at the tip of the ridge waveguide ranges from 30° to 90°.

[0011] Furthermore, the width of the arched hybrid plasmon waveguide ranges from 8 μm to 12 μm, the height of the rectangular portion in the arched hybrid plasmon waveguide ranges from 24 μm to 26 μm, the radius of the arc portion in the arched hybrid plasmon waveguide is half the width of the arched hybrid plasmon waveguide, and the length of the arched hybrid plasmon waveguide ranges from 135 μm to 155 μm.

[0012] Furthermore, the width of the arch-shaped input waveguide ranges from 20μm to 24μm, the height of the rectangular portion of the arch-shaped input waveguide ranges from 18μm to 20μm, the radius of the arc portion of the arch-shaped input waveguide is half the width of the arch-shaped input waveguide, and the length of the arch-shaped input waveguide ranges from 80μm to 120μm.

[0013] Furthermore, in the high refractive index waveguide region, the arched input waveguide, the first wedge-shaped mode conversion waveguide, the arched hybrid plasmon waveguide, the second wedge-shaped mode conversion waveguide, and the arched output waveguide are all at the same height.

[0014] Furthermore, the length of the first wedge-shaped mode conversion waveguide is 10 μm.

[0015] Furthermore, the substrate is made of SiO2, the scaffold layer is made of PMMA, the high refractive index waveguide region is made of Si, the coating layer is made of graphene, and the coating dielectric layer is made of SiO2.

[0016] The following advantages can be obtained by adopting the above technical means:

[0017] This invention proposes a terahertz wave TM pass polarization filter. The high refractive index layer (i.e., the high refractive index waveguide region) is designed as an arch, and the coated dielectric layer is designed as a hollow ridge. A coating layer is placed at the bottom of the coated dielectric layer, thereby forming a low refractive index air gap between the high refractive index waveguide region and the coating layer. This effectively improves the mode confinement capability of the structure. When the terahertz wave is incident perpendicularly, the TM mode is well confined in the middle low refractive index air gap, thereby achieving stronger mode confinement capability and longer transmission distance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a terahertz wave TM pass polarization filter according to the present invention;

[0019] Figure 2 This is a schematic cross-sectional view of the TM pass-polarization filter of the present invention;

[0020] Figure 3 This is a top view of the TM pass-polarization filter of the present invention;

[0021] Figure 4 This is a schematic diagram of the cross-sectional field distribution of the arched hybrid plasmon waveguide at an incident wavelength of λ = 100 μm in Experiment 1 of this invention.

[0022] Figure 5 This is a schematic diagram showing the changes in mode area and transmission distance when the ridge angle of the ridge waveguide changes from 30° to 90° in Experiment 2 of this invention.

[0023] Figure 6 This is a schematic diagram of the transmittance of TM mode and TE mode when the length of the arched hybrid plasmonic waveguide is in the range of 100μm to 160μm in Experiment 3 of this invention.

[0024] Figure 7 This is a schematic diagram of the polarization extinction ratio and insertion loss when the length of the arched hybrid plasmon waveguide is in the range of 100μm to 160μm in Experiment 3 of the present invention.

[0025] In the figure, 1 is the substrate, 2 is the scaffold layer, 3 is the high refractive index waveguide region, 4 is the coating layer, and 5 is the coating dielectric layer. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings:

[0027] This invention proposes a terahertz wave TM pass polarization filter, such as... Figures 1-3As shown, the structure includes a substrate 1, a support layer 2, a high-refractive-index waveguide region 3, a coating layer 4, and a coating dielectric layer 5. The high-refractive-index waveguide region is located in the middle of the upper surface of the substrate and includes a cylindrical input waveguide, a first wedge-shaped mode conversion waveguide, a cylindrical hybrid plasmon waveguide, a second wedge-shaped mode conversion waveguide, and a cylindrical output waveguide connected in sequence. The support layer consists of two rectangular structures, located on the upper surface of the substrate and on both sides of the high-refractive-index waveguide region, providing support. The coating dielectric layer is an integrated structure consisting of a rectangular body and a ridge waveguide located in the middle of the rectangular body. The two ends of the rectangular body are in contact with the support layer, and the entire coating dielectric layer is supported by the support layer above the high-refractive-index waveguide region. The coating layer is located between the lower surface of the coating dielectric layer and the support layer. The air gap between the highest point of the high refractive index waveguide region (i.e., the apex of the arch) and the lowest point of the coating layer (i.e., the bottom of the ridge waveguide of the coating dielectric layer) constitutes a low refractive index layer. The high refractive index layer, the coating layer, and the coating dielectric layer together form the main filtering structure of the filter of this invention.

[0028] In the high-refractive-index waveguide region, the dimensions of the domed input waveguide and the domed output waveguide are the same, as are the dimensions of the first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide. The width of the domed hybrid plasmon waveguide is smaller than the widths of the domed input and output waveguides. The heights of the domed input waveguide, the first wedge-shaped mode conversion waveguide, the domed hybrid plasmon waveguide, the second wedge-shaped mode conversion waveguide, and the domed output waveguide are the same. Therefore, the entire high-refractive-index waveguide region exhibits a structure that is wide at both ends and narrow in the middle. In the coated dielectric layer, the total length of the coated dielectric layer is equal to the sum of the lengths of the first wedge-shaped mode conversion waveguide, the domed hybrid plasmon waveguide, and the second wedge-shaped mode conversion waveguide. That is, the coated layer and the coated dielectric layer are actually located directly above the first wedge-shaped mode conversion waveguide, the domed hybrid plasmon waveguide, and the second wedge-shaped mode conversion waveguide. The ridge waveguide has an isosceles triangle cross-section, and its base is connected to the rectangular main body. The tip of the ridge waveguide faces the arched hybrid plasmon waveguide.

[0029] To achieve polarization control of terahertz waves, this invention features a targeted design for the filter's materials and dimensions. The substrate is made of SiO2, the scaffold layer is made of PMMA, the high-refractive-index waveguide region is made of Si, the coating layer is made of graphene, and the dielectric coating layer is made of SiO2. The use of graphene in the coating layer, due to its tunable optical properties, allows for more flexible device control.

[0030] The total height of the high-refractive-index waveguide region is h Si h Si It consists of the height of the rectangular section and the height of the circular arc section. The width of the arched input and output waveguides is W.Si The value ranges from 20μm to 24μm, with 20μm being preferred. The radius of the top arc portion of the arched input and output waveguides is W. Si / 2, the height of the rectangular portion in the arched input and output waveguides is h. Si -W Si / 2, with a value ranging from 18μm to 20μm, preferably 20μm; the length L of the arched input and output waveguides, ranging from 80μm to 120μm, preferably 100μm; and the width W of the arched hybrid plasmon waveguide. g The value ranges from 8μm to 12μm, with 10μm being preferred. The radius of the top arc portion of the arched hybrid plasmon waveguide is W. g / 2, the rectangular portion of the arched hybrid plasmon waveguide has a height of h. Si -W g / 2, with a value ranging from 24μm to 26μm, preferably 25μm, and the length of the arched hybrid plasmon waveguide is L. n The value ranges from 135μm to 155μm, with 150μm being preferred. The first and second wedge-shaped mode conversion waveguides serve as the narrowing regions connecting the preceding and following waveguides. Their cross-sections on both sides correspond to the arched input and output waveguides and the arched hybrid plasmon waveguide, respectively. The lengths of the first and second wedge-shaped mode conversion waveguides are L. c 10μm is preferred.

[0031] In the filter of this invention, the height of the frame layer is H, and the width between the two rectangular structures of the frame layer is W. m The thickness of the coating layer is f, and the length of the coating layer / coating medium layer is L. m =L n +2L c The height (or height of the isosceles triangle) of the ridge waveguide in the coated dielectric layer is H. w The value ranges from 10 μm to 20 μm, preferably 10 μm. The ridge angle at the tip of the ridge waveguide ranges from 30° to 90°, preferably 30°. The air gap height between the high-refractive-index waveguide region and the coating layer is h. air The value ranges from 0.5μm to 1.5μm.

[0032] In this embodiment of the invention, the materials of the high refractive index layer, low refractive index layer, and coating layer of the polarization filter are Si, air, and graphene, respectively, wherein the refractive index of Si is 3.478 and the refractive index of air is 1. Under terahertz frequency incident waves, the corresponding relative permittivity of graphene can be determined by… The calculation is performed using σ, where σ is the electrical conductivity of graphene, ε0 is the dielectric constant of vacuum, ω is the angular frequency, and d is the thickness of the graphene layer.

[0033] The electrical conductivity of graphene is σ = σ intra +σ inter , σ intra and σ inter These contributions originate from intraband and interband transitions of electrons in graphene, respectively. Under the random phase approximation condition, σ intra and σ inter It is given by the following formula:

[0034]

[0035] Where i is the imaginary unit, k b Here, T is the Boltzmann constant, and T is the temperature. Let μ be Planck's constant, τ be the electronic relaxation time of graphene, and μ be μ. c η represents the chemical potential of graphene.

[0036] Compared to near-infrared metallic TM pass-polarization filters, the filter of this invention uses graphene material and a specially designed filter size, which can greatly improve mode confinement capability. The mode area is 10 times that of metallic hybrid plasmonic waveguides. -2 The performance is even better, reaching 10. -3 Furthermore, the transmission distance can be doubled to 2700μm. In addition, this invention can achieve effective filtering of the TE mode near 3THz and high transmittance of the TM mode, resulting in a high extinction ratio of 30.23dB and a low insertion loss of 0.38dB.

[0037] To verify the effectiveness of the present invention, the following experiments are provided in the embodiments of the present invention:

[0038] Experiment 1:

[0039] Based on the polarization filter structure of this invention, the width W of the arched input waveguide... Si =20μm, rectangular portion h of the arched input waveguide Si -W Si / 2=20μm, the length of the arched input waveguide L=100μm, and the width of the arched hybrid plasmon waveguide W g =10μm, height h of the rectangular portion of the arched hybrid plasmon waveguide Si -W g / 2=25μm, the length L of the arched hybrid plasmon waveguide n =150μm, total height h of the first wedge mode conversion waveguide Si =30μm, length L c =10μm, length L of the coated dielectric layer m =170μm, the width of the coated dielectric layer is 300μm, and the height H of the ridge waveguide is... w=10μm, the ridge angle at the tip of the ridge waveguide is 30°, the coating thickness f = 2.5nm, which is the thickness of 5 stacked graphene layers (the thickness of a single graphene layer is 0.5nm), and the height h of the low refractive index layer between the high refractive index waveguide region and the coating layer. air The wavelength is 700 nm, the substrate width is 300 μm, the height is 50 μm, and the scaffold layer width is 40 μm.

[0040] An experiment was conducted using the aforementioned polarization filter at an incident wavelength of 100 μm for terahertz waves, yielding a schematic diagram of the cross-sectional field distribution of the arched hybrid plasmon waveguide, as shown below. Figure 4 As shown in the figure, the TM hybrid plasmon mode is well confined in the low refractive index region, and the energy distribution is uniform as can be seen from the contour lines in the figure.

[0041] Experiment 2:

[0042] While keeping other data from Experiment 1 unchanged, the ridge angle of the coated dielectric ridge waveguide was changed from 30° to 90°, and the terahertz wave was injected into the polarization filter again for the experiment. The changes in mode area and transmission distance are as follows: Figure 5 As shown in the figure, the TM hybrid plasmon mode can maintain 10 as the ridge angle changes. -3 The pattern area and achieve 10 3 Transmission distance at the μm level.

[0043] Experiment 3:

[0044] While keeping other data from Experiment 1 constant, the effects of different lengths of the arched hybrid plasmonic waveguide on the transmittance of TM and TE modes were investigated. Figure 6 , 7 As shown, when L n Within the range of 100μm to 160μm, the transmittance of the TM mode consistently remains above -2dB. n Within the range of 135μm to 155μm, the transmittance of the TE mode mostly remains below -20dB, and in the L... n The TE mode transmittance is lowest near 150 μm. This indicates that the filter can effectively filter out the TE mode in the TEM wave and achieve high-pass TM mode, and L n The extinction ratio is high at 150 μm.

[0045] This invention's polarization filter designs the high-refractive-index layer in an arched shape. Besides effectively filtering out TE modes, it also reduces losses caused by dielectric edge effects, effectively improving mode confinement capability. The low-refractive-index air gap between the high-refractive-index waveguide region and the coating layer effectively enhances the structure's mode confinement capability, and the multi-layer design of the graphene coating layer disperses losses. When terahertz waves enter the structure perpendicularly, TM modes are well confined within the low-refractive-index air gap, enabling the entire filter structure to effectively filter out TE modes near 3 THz. This not only achieves excellent mode confinement capability and long transmission characteristics but also features a high extinction ratio and low insertion loss.

[0046] This invention enables the excitation of hybrid plasmon modes in TM (Transient Electron) waves while exciting traditional waveguides, thereby filtering out TE (Transient Electron) modes and achieving polarization filtering. It also overcomes the limitations of existing structures. The polarization filter operates in the terahertz band, with structural dimensions in the μm range. Therefore, its manufacturing difficulty is significantly reduced compared to optical waveguides. Furthermore, graphene coating technology is currently quite mature, the material is readily available, manufacturing is simple, and the cost is low.

[0047] Compared with some existing filters, the filter of this invention has a compact structure, is easy to integrate, can be applied to ultra-high density integrated optical paths, and is easy to apply to highly integrated waveguide chips. It is of great significance for realizing photonic devices with higher integration.

[0048] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A terahertz wave TM pass polarization filter, characterized in that, The device includes a substrate, a support layer, a high-refractive-index waveguide region, a coating layer, and a coating dielectric layer. The high-refractive-index waveguide region is located in the middle of the upper surface of the substrate. The support layer is located on the upper surface of the substrate and on both sides of the high-refractive-index waveguide region. The coating dielectric layer is supported by the support layer above the high-refractive-index waveguide region. The coating layer is located between the lower surface of the coating dielectric layer and the support layer. The high refractive index waveguide region is arched; the coated dielectric layer includes a rectangular body and a ridge waveguide located in the middle of the rectangular body. The two ends of the rectangular body are in contact with the frame layer. The cross-section of the ridge waveguide is an isosceles triangle, and the tip of the ridge waveguide faces the high refractive index waveguide region. The high-refractive-index waveguide region includes, in sequence, an arched input waveguide, a first wedge-shaped mode conversion waveguide, an arched hybrid plasmon waveguide, a second wedge-shaped mode conversion waveguide, and an arched output waveguide; wherein, the arched input waveguide and the arched output waveguide have the same dimensions, the first wedge-shaped mode conversion waveguide and the second wedge-shaped mode conversion waveguide have the same dimensions, and the width of the arched hybrid plasmon waveguide is smaller than the width of the arched input waveguide and the arched output waveguide; The coating material is graphene; The air gap between the highest point of the high refractive index waveguide region and the lowest point of the coating layer constitutes a low refractive index layer. The coating layer and the coating medium layer are located directly above the first wedge-shaped mode conversion waveguide, the domed hybrid plasmon waveguide, and the second wedge-shaped mode conversion waveguide.

2. The TM pass polarization filter according to claim 1, characterized in that, The height of the low refractive index layer ranges from 0.5 μm to 1.5 μm.

3. The TM pass polarization filter according to claim 1, characterized in that, The height of the ridge waveguide in the coated dielectric layer ranges from 10μm to 20μm, and the ridge angle at the tip of the ridge waveguide ranges from 30° to 90°.

4. The TM pass polarization filter according to claim 1, characterized in that, The width of the arch-shaped hybrid plasmon waveguide ranges from 8 μm to 12 μm, the height of the rectangular portion of the arch-shaped hybrid plasmon waveguide ranges from 24 μm to 26 μm, the radius of the arc portion of the arch-shaped hybrid plasmon waveguide is half the width of the arch-shaped hybrid plasmon waveguide, and the length of the arch-shaped hybrid plasmon waveguide ranges from 135 μm to 155 μm.

5. The TM pass polarization filter according to claim 1, characterized in that, The width of the arch-shaped input waveguide ranges from 20μm to 24μm, the height of the rectangular portion of the arch-shaped input waveguide ranges from 18μm to 20μm, the radius of the arc portion of the arch-shaped input waveguide is half the width of the arch-shaped input waveguide, and the length of the arch-shaped input waveguide ranges from 80μm to 120μm.

6. The TM pass polarization filter according to claim 1, characterized in that, In the high refractive index waveguide region, the arched input waveguide, the first wedge-shaped mode conversion waveguide, the arched hybrid plasmon waveguide, the second wedge-shaped mode conversion waveguide, and the arched output waveguide are all at the same height.

7. The TM pass polarization filter according to claim 1, characterized in that, The length of the first wedge-shaped mode conversion waveguide is 10 μm.

8. The TM pass polarization filter according to claim 1, characterized in that, The substrate is made of SiO2, the scaffold layer is made of PMMA, the high refractive index waveguide region is made of Si, and the coating dielectric layer is made of SiO2.

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