On-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography

Abstract

The invention relates to the technical field of micro-nano optics, and particularly discloses an on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography, which comprises a metasurface, a waveguide and a substrate which are sequentially arranged from top to bottom, the complete unit of the super-structure surface comprises four nano columns, and the nano columns are arranged on the waveguide; the nanorod has an anisotropic structure and has a fixed relative position in a unit; the rotation angles of the nano columns are vertical to each other in the same row of one unit; the nanorods can extract light waves from the waveguide, and the light waves extracted by the four nanorods in the same unit can interfere with one another to form scattered light with specific amplitude, phase and polarization; the holographic image in any polarization state can be realized by changing the size and the rotation angle of the nano-columns and utilizing the abrupt change phase, the geometric phase and the circuitous phase with the fixed distance between the nano-columns.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano optics, and in particular to an on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography and a design method thereof. Background Art

[0002] Metasurfaces allow for complete control of electromagnetic field properties, including phase, amplitude, and polarization. Therefore, the current development of the combination of metasurfaces and waveguides has enhanced the ability of photonic integrated circuits to manipulate light, realizing functions such as aggregation, OAM, holograms, and grayscale display. Moreover, metasurfaces are extremely thin optical devices, which matches the compactness of photonic integrated circuits, allowing PICs to generate complex light fields. The schemes currently emerging for directly fabricating metasurface units on waveguides include schemes that utilize abrupt phase, geometric phase, detour phase, and a combination of several phases. Among them, geometric phase and detour phase can theoretically achieve continuous phase changes. If the waveguide mode is the TE fundamental mode, the output light of the metasurface using abrupt phase or detour phase is linearly polarized light with a polarization direction perpendicular to the propagation direction of the light wave in the waveguide. The output light of the metasurface using geometric phase is right-handed or left-handed circularly polarized light. Although the above schemes produce free-space light in a richer form than traditional grating couplers and end couplers, they lack further manipulation of polarization. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides an on-chip waveguide and metasurface integrated device and a design method thereof for realizing arbitrary polarization holography. By introducing an array of four nanopillars in a complete metasurface unit group on the waveguide, the interference between the scattered light extracted from the waveguide by the four nanopillars can be used to realize scattered light with a phase of 0-2π in any polarization state within a certain amplitude range, which utilizes the sudden phase, geometric phase and the circuitous phase at a fixed distance between units. Moreover, it is only necessary to establish a phase library of the metasurface unit of y-polarized light, and the Jones matrix can be used to derive the structural parameters required for the phase of other polarization states, which reduces the workload of simulation and provides a new method for manipulating the characteristics of free-space light for photonic integrated circuits.

[0004] To solve the above problems, the present invention adopts the following technical solutions:

[0005] An on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography, comprising a metasurface, a waveguide and a substrate arranged in sequence from top to bottom.

[0006] The complete unit of the metasurface includes four nanopillars arranged on a waveguide.

[0007] The nanorods have an anisotropic structure and have fixed relative positions in a unit cell;

[0008] The nanocolumns in the same row of a unit have mutually perpendicular rotation angles.

[0009] The nanocolumns can extract light waves from the waveguide. The light waves extracted by the four nanocolumns in the same unit will interfere to form scattered light with specific amplitude, phase, and polarization.

[0010] Furthermore, the distance between the nanocolumns in the same row in the x - direction is equal to half of the period of the complete unit in the x - direction, and the distance between the nanocolumns in different rows of the same unit in the y - direction is equal to half of the period of the complete unit in the y - direction.

[0011] The period of the complete unit of the metasurface in the x - direction is equal to the distance required for the light wave in the waveguide to generate a π - phase shift. The nanocolumns in different rows of the same unit are staggered by a quarter of the period in the x - direction.

[0012] The fixed distance between the nanocolumns generates a detour phase.

[0013] Furthermore, the waveguide is a multimode waveguide with sufficient area to carry the metasurface. The wave propagating in the waveguide is TE 0 wave, and the corresponding vector representation is E in = [0 1] T , where T represents the transpose of the vector.

[0014] When the size of the nanocolumn changes, the length offsets of the two orthogonal axes of the nanocolumn follow a fixed proportional relationship. The size change of the nanocolumn generates a discontinuous phase. Regarding the fixed proportional relationship: when the variable of the offset of one of the orthogonal axes is greater than 0, the offset of the other orthogonal axis is α times the offset of the orthogonal axis; when the variable of the offset of one of the orthogonal axes is less than 0, the offset of the other orthogonal axis is 1 / α times the offset of the orthogonal axis. Specifically, when the nanocolumn is composed of Si, the waveguide is composed of SiN x and the substrate part near the waveguide is composed of SiO 2 the fixed proportional relationship is specifically that when the variable of the offset of one of the orthogonal axes is greater than 0, the offset of the other orthogonal axis is 3 / 8 times the offset of the orthogonal axis; when the variable of the offset of one of the orthogonal axes is less than 0, the offset of the other orthogonal axis is 8 / 3 times the offset of the orthogonal axis.

[0015] When the rotation angle of the nanocolumn changes, the same nanocolumns within the same unit remain mutually perpendicular, and the change in the rotation angle of the nanocolumn generates a geometric phase.

[0016] Let the Jones matrix of a non - rotated nanocolumn be as follows, where ta and t b is a complex coefficient.

[0017]

[0018] Then the Jones matrix of another nanorod in the same row of a unit cell is

[0019]

[0020] e iπ It comes from the distance between the two nanopillars in the x direction, which is equal to the optical path difference of half a wavelength in the waveguide. The nanopillars in the same row of a unit rotate at perpendicular angles to each other, so the rotation angle of the other nanopillar is π / 2. R is the rotation matrix, R(θ) is the rotation matrix with an angle of θ, and R -1 (θ) is the inverse matrix of R(θ); i is the imaginary unit.

[0021] Assume t 1 =t a -t b , then the Jones matrix corresponding to the two nanocolumns in the upper row is:

[0022]

[0023] The downward nanocolumn is shifted by a quarter of a period in the direction of light propagation relative to the upward nanocolumn. Then the Jones matrix corresponding to the downward nanocolumn is

[0024]

[0025] Therefore, the total Jones matrix corresponding to the four nanopillars is

[0026]

[0027] The TE is used to set the propagation in the waveguide. 0 wave, the corresponding vector is represented by E in =[0 1] T , so the output light can be expressed as

[0028]

[0029] The output is y-polarized light.

[0030] Consider the rotation angle of the upward nanorod to be θ 1 , then the corresponding Jones matrix is

[0031]

[0032] Similarly, if the rotation angle of the descending nanorod is θ 2 ,but

[0033]

[0034] When θ 1 =θ 2 hour

[0035]

[0036] The output light is expressed as

[0037]

[0038] Therefore, the output light has a polarization direction with an angle of 2θ with the positive direction of the y-axis. 1 Linearly polarized light.

[0039] The following is the general case, θ 1 With θ 2 are not necessarily equal, the Jones matrix can be expressed as

[0040]

[0041] The output light is

[0042]

[0043] Equation (12) gives an expression for any polarized light, especially nonlinearly polarized light. A solution is given below. Assume that the electric field amplitude of the elliptically polarized light to be realized in the x direction is A 1 , the electric field amplitude in the y direction is A 2 , the electric field phase difference in the two directions is

[0044] (t 1 cos 2θ 1 ) 2 +(t 2 cos2θ 2 ) 2 =A 2 2 (13)

[0045] (t 1 sin 2θ 1 ) 2 +(t 2 sin 2θ 2 ) 2 =A 1 2 (14)

[0046]

[0047] Since the input light intensity is 1, the following restrictions apply.

[0048] A 1 2 +A 2 2 =1(18)

[0049] By solving the equations (13) to (17), the required θ can be obtained 1 ,θ 2 ,t 1 and t 2 .

[0050] Let's first consider a type of polarization ellipse whose major axis is on the x-axis or y-axis. When , it means right-hand rotation, define the variable k 1 :

[0051]

[0052] Then θ 1 With k 1 The relationship is

[0053]

[0054] According to the above formula, θ can be obtained 1 , define the variable k 2 :

[0055]

[0056] In the same way, we can derive θ 2 .when When , it means left rotation, define the variable k 1 :

[0057]

[0058] Then θ 1 With k 1 The relationship is

[0059]

[0060] According to the above formula, θ can be obtained 1 , define the variable k 2 :

[0061]

[0062] In the same way, we can derive θ 2 .

[0063] We get θ 1 and θ 2Then, t is calculated by using equations (13) and (14): 1 2 and t 2 2 For right-handed light, t 1 >0,t 2 >0, for left-hand rotation, t 1 >0,t 2 <0. In order to unify t 1 and t 2 It is represented by a value greater than 0, for left-handed light θ 2 Add π / 2 to the original value. When the major axis of the polarization ellipse is not in the x-axis or y-axis direction, the θ calculated above is 1 and θ 2 Adding half the polarization angle gives the required rotation angle. This provides a method for producing non-linearly polarized light.

[0064] Furthermore, the phase required for the generated holographic image is obtained by a GS algorithm based on Fresnel diffraction and is assigned to the metasurface unit.

[0065] A phase library of the metasurface unit for y-polarized light is established. When constructing a hologram for y-polarized light, the structural parameters of the metasurface are selected from the phase library for y-polarized light. Metasurfaces for other polarized light can be derived by referring to the phase library for y-polarized light using the Jones matrix described above. Therefore, this design method can obtain holograms of arbitrary polarization.

[0066] There is a group of metasurface units for refractive index matching at both ends of the metasurface unit with phase, and the nanopillars of the units for refractive index matching do not have a size offset on the orthogonal axis. The radius of the nanopillars of the units for refractive index matching increases linearly as the distance from the metasurface unit with phase decreases.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] 1. Compared with free-space metasurfaces, the polarization state of input light of on-chip metasurfaces is often limited. The input light in the waveguide is TE or TM fundamental mode light, corresponding to the output y-polarized or x-polarized light. The present invention provides a polarization conversion method, so that the metasurface can generate scattered light of arbitrary polarization state, especially elliptical polarization state with polarization direction not on the x-axis or y-axis and arbitrary ellipticity.

[0069] 2. Usually, when using a metasurface with a sudden phase, only a limited number of units that generate phase can be selected from the phase library. If polarization conversion needs to be achieved, there will be fewer units that meet the function. The size of the nanocolumns of the metasurface unit of the present invention can be continuously changed, so a continuously changing phase can be generated. Through the interference between the scattered light of four units in a complete metasurface unit group on the waveguide, using the sudden phase, geometric phase and the circuitous phase at a fixed distance between units, the scattered light of any polarization state generated by the metasurface can carry a phase of 0-2π. Combined with the GS algorithm based on Fresnel diffraction, a hologram of any polarization can be achieved.

[0070] 3. The present invention only needs to establish a phase library of the metasurface unit of y-polarized light, and can use the Jones matrix to derive the metasurface unit structural parameters required for the phases of other polarization states, which reduces the workload of simulation.

[0071] 4. Because the phase of scattered light is mainly affected by the anisotropy of the same nanopillars and the interference of scattered light from the upper and lower nanopillars, the sudden phase of a single nanopillar does not play a decisive role, and there is no need to pursue a large aspect ratio. This means a larger process tolerance in the device manufacturing process.

[0072] 5. The two ends of the metasurface unit with phase of the present invention each have a group of metasurface units for refractive index matching. The nanopillars of the units for refractive index matching do not have a size offset on the orthogonal axis, so that the scattered light of the units for refractive index matching can be reduced as much as possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 This is a three-dimensional schematic diagram of the on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to the present invention. The inset is a schematic diagram of a complete metasurface unit.

[0074] Figure 2 A top-down schematic diagram of a complete unit of a metasurface.

[0075] Figure 3 The simulation results of the metasurface structure parameter scanning. (a) The size change of the two nanopillars, and the (b) amplitude and (c) phase of the Ey of the escaped light as δ 1a and δ 1b D is the original diameter. (d) The size change of the complete metasurface unit group, and the (e) amplitude and (f) phase of the Ey of the escaped light as a function of δ 1 and δ 2 The relationship between the changes. (g)δ 1 =δ 2 =75nm, the rotation angle change of the complete metasurface unit group, and the (h)ψ and (i)χ of the escaped light with θ 1 and θ2 The relationship between the changes is as follows: ψ and χ represent the angle between the major axis of the polarization ellipse and the x-axis and the ellipticity, respectively.

[0076] Figure 4 The simulation results of holographic images. (a)-(c), (d)-(f), (g)-(i) and (j)-(l) are the total intensity, x-polarized light intensity and y-polarized light intensity of the y-polarized light holographic image letter "A", x-polarized light holographic image letter "B", right-handed circularly polarized light holographic image letter "C" and left-handed elliptically polarized light holographic image letter "D", respectively.

[0077] Figure 5 Metasurface unit for generating (a) x-polarized light, (b) right-handed circularly polarized light, and (c) left-handed elliptically polarized light with phases of 0, π / 2, π, and 3π / 2.

[0078] Figure 6 Device manufacturing process flow chart.

[0079] Figure 7 Actual images of the fabricated on-chip waveguide and metasurface integrated device that realizes arbitrary polarization holography. (a) Optical microscope image of the fabricated device. (b) Scanning electron microscope image of the fabricated device.

[0080] Figure 8 Schematic diagram of the measuring device.

[0081] Fig. 9 are the measurement results of holographic images. (a)-(c), (d)-(f), (g)-(k) and (m)-(q) are the measurement results of the holographic image letter "A" of y-polarized light, the holographic image letter "B" of x-polarized light, the holographic image letter "C" of right-handed circularly polarized light and the holographic image letter "D" of left-handed elliptically polarized light, respectively. Pol represents polarizer, QWP represents quarter-wave plate, and the angles are the angles between the transmission axis of the polarizer and the positive direction of the x-axis, and the x-axis direction coincides with the horizontal direction. (l) and (r) are the optical settings when the holographic image letter "C" and the holographic image letter "D" disappear.

[0082] Fig.10 This is the simulation result of the letter “B” in the x-polarized light holographic image under special circumstances.

[0083] (a)-(c), (d)-(f) and (g)-(i) are the total intensity, x-polarized light intensity and y-polarized light intensity of 200nm high silicon nanorods, 400nm high silicon nanorods and 300nm high silicon nanorods with 400nm thick HSQ layer, respectively.

[0084] The reference numerals are as follows:

[0085] 1. Metasurface; 2. Waveguide; 3. Substrate; 4. Nanopillar. DETAILED DESCRIPTION

[0086] The technical solutions in the embodiments will be described clearly and completely below in conjunction with the drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments, rather than all the embodiments.

[0087] Example

[0088] like Figure 1 and 2 As shown, an on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography, wherein a metasurface 1, a waveguide 2 and a substrate 3 are arranged in sequence from top to bottom.

[0089] The complete unit of the metasurface 1 includes four nanorods 4, which are arranged on the waveguide 2. It should be noted that Figure 1 In the embodiment shown, the nanorods 4 are composed of Si and the waveguide 2 is composed of SiN x The substrate 3 near the waveguide 2 is composed of SiO 2 Composition: the nanorods 4 are made of a single material.

[0090] The nanopillars 4 have an anisotropic structure and have fixed relative positions in a unit cell;

[0091] The nanopillars 4 in the same row of a unit are rotated at perpendicular angles to each other;

[0092] The nanocolumns 4 can extract light waves from the waveguide 2, and the light waves extracted by four nanocolumns 4 in the same unit will interfere to form scattered light with specific amplitude, phase and polarization.

[0093] Specifically, the distance between nanopillars 4 in the same row in the x direction is equal to half of the period of the complete unit in the x direction, and the distance between nanopillars 4 in different rows of the same unit in the y direction is equal to half of the period of the complete unit in the y direction;

[0094] Specifically, the period of a complete unit of the metasurface in the x direction is equal to the distance required for the light wave transmission in the waveguide 2 to produce a π phase shift, and the nanopillars 4 in different rows of the same unit are staggered by a quarter of a period in the x direction.

[0095] The fixed distance between the nanopillars 4 creates a detour phase.

[0096] In this embodiment, the waveguide 2 is a multimode waveguide having a sufficient area to support the metasurface 1. The TE 0 wave, the corresponding vector is represented by E in =[0 1] T .

[0097] In this embodiment, when the size of the nanorod 4 changes, the length offsets of the two orthogonal axes of the nanorod 4 follow a fixed proportional relationship, and the size change of the nanorod 4 produces a sudden phase change.

[0098] When the rotation angle of the nanorod 4 changes, the same nanorod 4 in the same unit remains perpendicular to each other, and the change in the rotation angle of the nanorod 4 produces a geometric phase.

[0099] In this embodiment, when the nanorods 4 in the upper and lower rows in a unit rotate at the same angle, the scattered light of the unit can be described by the following Jones matrix:

[0100]

[0101] t 1 and t 2 Respectively reflects the size change of the nanorods 4 in the upper and lower rows of the unit, θ 1 and θ 2 Respectively reflect the rotation angle changes of the upper and lower rows of nanopillars in the unit. The scattered light of the metasurface unit is linearly polarized light. The polarization direction of the scattered light is determined by the rotation angle, and the phase of the scattered light is determined by the size change.

[0102] In this embodiment, when the nanorods 4 in the upper and lower rows in a unit rotate at different angles, the scattered light of the unit can be described by the following Jones matrix:

[0103]

[0104] The scattered light of the metasurface unit is non-linearly polarized light, and the scattered light and phase are determined by the rotation angle and size change.

[0105] In this embodiment, the nanorod 4 is a silicon nanorod, the waveguide 2 is a silicon nitride waveguide, and the substrate 3 is a silicon dioxide substrate.

[0106] In this embodiment, the height of the nanorods 4 is 300 nm, and the period of the nanorods is 950 nm in the x-direction and 700 nm in the y-direction.

[0107] In this embodiment, the thickness of the waveguide 2 is 300 nm.

[0108] In this embodiment, the operating wavelength of the device is 1570 nm.

[0109] The numerical simulation was carried out using the finite difference time domain (FDTD) method. A TE fundamental mode mode light source is set in the silicon nitride waveguide. Figure 3 The two elliptical cylinders on the waveguide shown in (a) have a rotation angle of 90°. Figure 3 (b) and Figure 3(c) reflects the amplitude and phase of the y-polarized scattered light. The elliptical cylinder starts from a cylinder with a radius of 110nm. By adding an offset on each of the orthogonal axes, the cylinder becomes an elliptical cylinder. The two offsets δ 1a and δ 1b The range of variation is from -150nm to 150nm. The simulation results are as follows. Figure 3 Most of the phase values ​​in (c) are around 0 and π, which only changes the positive and negative of the electric field. Figure 3 The amplitude of (b) changes and is verified by simulation when: δ 1a >0,δ 1b =3δ 1a / 8;δ 1a <0,δ 1b =8δ 1a / 3 hours (i.e. Figure 3 The dotted line in (b) allows the complete metasurface unit to produce a larger amplitude variation range.

[0110] The amplitude and phase simulation results of the y-polarized scattered light of a complete metasurface unit composed of four elliptical cylinders are as follows Figure 3 In (e) and (f), the size of the elliptical cylinder changes as Figure 3 As shown in (d). 1a >0, δ 1 =δ 1a , when δ 1a <0, δ 1 =δ 1b . Figure 3 The results of (e) and (f) in 3 are basically consistent with formula (6), δ 1 and δ 2 Respectively with t 1 and t 2 Proportional to. Figure 3 As shown in (g), the size offset of the upper and lower rows of elliptical cylinders is fixed so that δ 1 =δ 2 =75nm, and they rotate separately, so that the polarization of the scattered light changes. The changes of the major axis angle ψ and the ellipticity χ of the polarization ellipse are shown as follows: Figure 3 Therefore, by the previous Jones matrix derivation and Figure 3 From the parameter scanning results, we can control the polarization of the scattered light, and all types of polarized light have the same phase control range of π at the same amplitude.

[0111] In order to verify the effect, in this embodiment, holographic images with different polarizations generated by the metasurface on four different waveguides are simulated and measured experimentally.

[0112] In this embodiment, the holographic phase image is obtained by the GS (Gerchberg-Saxton) algorithm based on Fresnel diffraction, and the holographic image is designed to be 100 μm above the metasurface 1.

[0113] In this embodiment, there are 40×30 metasurface unit groups forming a holographic phase, the radius of the cylinder is 110 nm, and sqrt(δ 1 2 +δ 2 2 )=150nm to keep the amplitude unchanged.

[0114] In this embodiment, by adding several complete metasurface units with increasing radius, the effective refractive index is gradually increased, and δ 1 =δ 2 =0nm, which minimizes the amplitude of scattered light. The radius of the cylinder increases linearly from 100nm to 110nm.

[0115] In this embodiment, four periods are used at each end to match the effective refractive index, so there are a total of 48×30 complete metasurface units.

[0116] Specifically, the metasurface parameters are set in FDTD according to the phase diagram, and the far-field results are obtained in FDTD. Figure 3 The amplitude and phase relationship between (e) and (f) can be used to design a metasurface structure that uses y-polarized light to produce reconstructed images. Figure 4 (a)-(c) are the simulation results of the letter "A" in the y-polarized light holographic image, and there is almost no x-polarized component. According to formula (10), combined with Figure 3 The simulation results can be used to obtain the structural parameters required for linear polarized light holograms. The nanorods need to be rotated 45° to produce x-polarized light. Figure 4 (e)-(g) are the simulation results of the x-polarized light holographic image letter "B". There is almost no y-polarized component, indicating that polarization conversion has occurred. More generally, the holographic image letter "C" of right-handed circularly polarized light and the holographic image letter "D" of left-handed elliptically polarized light are designed. 1 :A 2 =1:2, the polarization angle is 60°. Figure 4 (g)-(i) and Figure 4 (j)-(l) show the simulation results of right-handed circularly polarized light and left-handed elliptically polarized light, respectively, both of which have both x-polarization and y-polarization components.

[0117] Figure 5Metasurface units that provide 0, π / 2, π, and 3π / 2 phase shifts for x-polarized light, right-handed circularly polarized light, and left-handed elliptically polarized light are given. The general rule is that the nanopillars that produce linearly polarized light have the same rotation direction and only produce phase shifts by changing their size; the nanopillars that produce circularly polarized light have exactly the same size and produce phase shifts by rotating the four nanopillars in a metasurface unit by the same angle; producing elliptically polarized light with phase shift requires the nanopillars to change both size and rotation angle at the same time.

[0118] Devices were prepared to verify the above simulation results, such as Figure 6 As shown. First, 300nm thick silicon nitride is deposited on the thermal oxide silicon wafer by inductively coupled plasma chemical vapor deposition (ICP-CVD) at a low temperature of 300℃. Alignment marks are defined by electron beam lithography (EBL) followed by evaporation of a 5nm titanium adhesion layer and 100nm gold and then lift-off. The silicon nitride waveguide is positioned on the thermal oxide silicon wafer by electron beam lithography and reactive ion etching (RIE). 300nm thick amorphous silicon is deposited and the metasurface is positioned on the waveguide by electron beam lithography and inductively coupled plasma (ICP) etching. Figure 7 (a) and Figure 7 (b) shows the optical microscope image and scanning electron microscope (SEM) image of the fabricated device.

[0119] Sample passed Figure 8 The optical path shown in the figure is used for testing. The laser light leaves the tapered fiber and is coupled into the waveguide through the end coupler. The light is scattered from the metasurface and collected by an x-objective lens and finally captured by an infrared camera. Polarizers and quarter-wave plates are used in the optical path as required for testing. Polarizers and quarter-wave plates are used in the optical path as required for testing.

[0120] Fig. 9 The test results of the holographic image are shown. When the polarizer is at 0°, x-polarized light can pass through, and when the polarizer is at 90°, y-polarized light can pass through. Therefore, the y-polarized letter "A" cannot be displayed when the polarizer is at 0°, and the situation of the x-polarized letter "B" is just the opposite. Figure 4 The simulation results are consistent with . Fig. 9 The light intensity ratio of (f) Fig. 9 The large value in (b) is due to the y-polarized background light that has not undergone polarization conversion. Regardless of the angle between the optical axis of the quarter-wave plate and the x-axis, right-handed circularly polarized light can be converted to linearly polarized light. When the quarter-wave plate is set to 135°, right-handed circularly polarized light will be converted to x-polarized light, as shown in Fig. 9As shown in (j) and (k), the letter "C" can be seen when the polarizer is at 0°, but not when the polarizer is at 90°. For left-handed elliptically polarized light, the optical axis of the quarter-wave plate needs to coincide with the major axis or minor axis of the polarization ellipse in order to convert it into linearly polarized light. When the quarter-wave plate is set to 60°, the angle between the linear polarized light converted from left-handed elliptically polarized light and the x-axis is

[0121] arctan(2 / 1)-60°≈-3.43°. Fig. 9 As shown in (p) and (q), the letter "D" does not appear when the polarizer is at 86°, but the letter "D" appears when the polarizer is at -4°.

[0122] like Fig.10 As shown in the figure, in the special case where the metasurface is composed of 200nm high silicon nanopillars, 400nm high silicon nanopillars, and 300nm high silicon nanopillars with a 400nm thick HSQ (Hydrogen Silsesquioxane Polymers) layer, the scattered light can still form a holographic image letter B. This is because the phase of the scattered light is mainly affected by the anisotropy of the nanopillars in the same row and the interference of the scattered light of the nanopillars in the upper and lower rows. The sudden phase of a single nanopillar does not play a decisive role. When manufacturing metasurface nanopillars, there will be large process tolerances, especially when growing and etching silicon.

[0123] Although the embodiments of the present application have been shown and described above, the scope of protection of the present invention is not limited thereto, and any changes or substitutions that are not conceivable through creative work should be included in the scope of protection of the present invention; unless explicitly stated, any elements, actions or instructions used in this document should not be interpreted as critical or necessary.

Claims

1. An on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography, characterized in that: include: A metasurface (1), a waveguide (2), and a substrate (3) are arranged in sequence from top to bottom; A complete unit of the metasurface (1) comprises four nanopillars (4), wherein the nanopillars (4) are arranged on a waveguide (2); The nanorods (4) have an anisotropic structure and have fixed relative positions in a unit; The nanorods (4) are rotated at perpendicular angles to each other in the same row of a unit; The nanocolumns (4) extract light waves from the waveguide (2), and the light waves extracted by four nanocolumns (4) in the same unit interfere with each other to form scattered light with specific amplitude, phase and polarization.

2. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 1, characterized in that: The distance between the nanorods (4) in the same row in the x direction is equal to half of the period of the complete unit in the x direction, and the distance between the nanorods (4) in different rows in the same unit in the y direction is equal to half of the period of the complete unit in the y direction; The period of the complete unit of the metasurface in the x direction is equal to the distance required for the light wave transmission in the waveguide (2) to produce a π phase shift, and the nanopillars (4) in different rows of the same unit are staggered by a quarter of a period in the x direction; The fixed distance between the nanopillars (4) produces a detour phase.

3. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 1, characterized in that: The waveguide (2) is a multimode waveguide having a sufficient area to support the metasurface. The wave propagating in the waveguide (2) is a TE0 wave, and the corresponding vector is represented by E in =[0 1] T , where T represents the transpose of the vector.

4. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 2, characterized in that: When the nanocolumn (4) changes in size, the length offsets of the two orthogonal axes of the nanocolumn (4) follow a fixed proportional relationship, and the size change of the nanocolumn (4) produces a sudden phase change; When the rotation angle of the nanocolumn (4) changes, the same nanocolumns (4) in the same unit remain perpendicular to each other, and the change in the rotation angle of the nanocolumn (4) produces a geometric phase.

5. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 4, characterized in that: The fixed proportional relationship is specifically that when the variable of the offset of one of the orthogonal axes is greater than 0, the offset of the other orthogonal axis is α of the offset of the orthogonal axis; when the variable of the offset of one of the orthogonal axes is less than 0, the offset of the other orthogonal axis is 1 / α of the offset of the orthogonal axis.

6. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 5, characterized in that: When the nanopillars are made of Si, the waveguide is made of SiN x When the substrate portion close to the waveguide is composed of SiO2, the fixed proportional relationship is specifically that when the variable of the offset of one of the orthogonal axes is greater than 0, the offset of the other orthogonal axis is 3 / 8 of the offset of the orthogonal axis; when the variable of the offset of one of the orthogonal axes is less than 0, the offset of the other orthogonal axis is 8 / 3 of the offset of the orthogonal axis.

7. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 4, characterized in that: When the upper and lower rows of nanorods in a unit rotate at the same angle, the scattered light of the unit is described by the following Jones matrix: t1 and t2 respectively reflect the size changes of the nanopillars in the upper and lower rows of the unit, and θ1 and θ2 respectively reflect the rotation angle changes of the nanopillars in the upper and lower rows of the unit; the scattered light of the unit is linearly polarized light, the polarization direction of the scattered light is determined by the rotation angle, and the phase of the scattered light is determined by the size change; where i is the imaginary unit.

8. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 4, characterized in that: When the upper and lower rows of nanorods in a unit rotate at different angles, the scattered light of the unit can be described by the following Jones matrix: t1 and t2 respectively reflect the size changes of the nanopillars in the upper and lower rows of the unit, and θ1 and θ2 respectively reflect the rotation angle changes of the nanopillars in the upper and lower rows of the unit; The scattered light of the unit is non-linearly polarized light, and the scattered light and phase are determined by the rotation angle and the size change.

9. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 1, characterized in that: The phase required to generate the holographic image is obtained by the GS algorithm based on Fresnel diffraction and is assigned to the metasurface unit.

10. The on-chip waveguide and metasurface integrated device for realizing arbitrary polarization holography according to claim 1, characterized in that: A group of metasurface units for refractive index matching is respectively disposed at two ends of the metasurface unit with phase, and the nanopillars of the metasurface units for refractive index matching do not have a size offset on an orthogonal axis; The radius of the nano-pillar of the metasurface unit for refractive index matching increases linearly as the distance from the metasurface unit with phase decreases.

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