Multifunctional high-efficiency beam splitter based on superlattice grating

Abstract

The application discloses a multifunctional and efficient beam splitter based on super-structured grating, which comprises a plurality of periodically distributed super-structured gratings, each of which comprises a plurality of spaced-apart dielectric layers, a plurality of air slits being formed between the dielectric layers, the thickness of the dielectric layers being equal to that of the air slits, the dielectric layers having different widths, the air slits having different widths, the phase delay of each super-structured grating spanning a phase range of 2pi, and the phase difference between adjacent air slits being equal. The beam splitter based on the diffraction mechanism of the super-structured grating can simultaneously realize efficient beam splitting in terms of energy and polarization, has a wideband response, and can be applied to the fields of imaging systems and optical communication.

Description

Technical Field

[0001] This invention belongs to the field of beam transmission technology, specifically relating to a multifunctional high-efficiency beam splitter based on metagratings. Background Technology

[0002] Light beam splitters (LBSs) can split an incident light beam into two parts. They are an indispensable optical component in modern advanced optical technology and play an important role in many applications and various optical devices, such as optical switches, optical polarimeters, quantum photonics integrated circuits, and communication devices. LBSs are usually gratings or semi-reflective mirrors, which are heavy and difficult to integrate into compact optical devices.

[0003] With the development of integrated photonics, there is an urgent need for compact and efficient light-based bionic switches (LBSs), prompting efforts to achieve this goal in various ways. Optical phase-gradient metasurfaces (PGMs) emerging in nanophotonics offer a new paradigm for designing compact, flat, and high-performance LBSs. PGMs are periodic arrangements of subwavelength atomic atoms. By appropriately designing the interactions between light and these atoms, the amplitude, phase, and polarization characteristics of electromagnetic waves (EM) can be effectively manipulated, thereby generating various functions such as ultrathin cloaking, superlenses, retroreflection, and asymmetric propagation.

[0004] However, most reported subsurface-based light source beam splitters (LBSs) can only achieve polarization splitting or energy separation for fixed-polarization light, and few studies report achieving both functions simultaneously in a single design. Photonic integrated systems require flexible and diverse optical flow control capabilities, thus necessitating multifunctional and high-efficiency LBSs.

[0005] Therefore, to address the aforementioned technical problems, it is necessary to provide a multifunctional and efficient beam splitter based on metagratings. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a multifunctional and efficient beam splitter based on metagratings.

[0007] To achieve the above objectives, an embodiment of the present invention provides the following technical solution:

[0008] A multifunctional high-efficiency beam splitter based on metagratings is disclosed. The beam splitter includes several periodically distributed metagratings, each metagrating including several spaced dielectric layers with multiple air slits formed between the dielectric layers. The dielectric layers and air slits have the same thickness, different widths, and different widths. The phase delay of each metagrating spans a phase range of 2π, and the phase difference ΔΦ between adjacent air slits is equal.

[0009] In one embodiment, the beam splitter is used to achieve polarization splitting of the incident beam, which includes transversely electrically polarized light and transversely magnetically polarized light. The beam splitter can achieve total internal reflection of transversely electrically polarized light and negative refraction with the lowest diffraction order of transversely magnetically polarized light.

[0010] In one embodiment, the metagrating includes m air slits, the period width of the metagrating is p, the thickness of the dielectric layer and the air slits is d, and the width of the air slits is w. i , i = 1 ~ m, the center distance between adjacent air slits is a = p / m, and the phase difference between adjacent air slits is ΔΦ = 2π / m.

[0011] In one embodiment, the transversely magnetically polarized light exists in only the fundamental mode within the air slit, and satisfies:

[0012]

[0013] Where, β i Let ε be the propagation constant, where its real part represents the propagating wave vector and its imaginary part represents the dissipation of surface plasmon polaritons in the air slit. k0 = 2π / λ is the wave vector in vacuum, λ is the wavelength of the incident beam, and ε is the propagation constant. m The dielectric constant of the dielectric layer;

[0014] Phase delay Φ of the i-th air slit i for:

[0015] Φ i =β i *d-δ;

[0016] Where δ is the additional phase generated by multiple reflections at the interface between the grating and the air.

[0017] In one embodiment, the dielectric layer is made of silver with a dielectric constant ε. m =-17.36+0.715i, the period width of the metagrating is p=λ, the thickness of the dielectric layer and the air slits is d=0.6λ~2.4λ, the metagrating includes 5 air slits with widths w1, w2, w3, w4 and w5 respectively, and the phase difference between adjacent air slits ΔΦ=2π / 5.

[0018] In one embodiment, the wavelength λ of the incident light beam is 590 nm to 668 nm, and the incident angle is θ. i ∈(-74°,-7°).

[0019] In one embodiment, when the wavelength of the incident beam is λ = 650 nm and d = 1.5λ, the widths of the air slits are w1 = 120 nm, w2 = 68 nm, w3 = 46 nm, w4 = 34 nm, and w5 = 27 nm, respectively.

[0020] In one embodiment, the incident angle and reflection angle of the transversely magnetically polarized light in the metagrating satisfy:

[0021] k0sinθ i =k0sinθ t +nG;

[0022] in, For the phase gradient, θ i and θ t Let θ be the angle of incidence and the angle of refraction, respectively. Let G = 2π / p be the reciprocal lattice vector, n be the diffraction order, and ζ = G.

[0023] In one embodiment, n = -1 is the lowest diffraction order of the transversely magnetically polarized light;

[0024] When the angle of incidence is less than the critical angle, the refracted light follows a diffraction order of n = -1;

[0025] When the incident angle is greater than the critical angle, the refracted light follows a diffraction order of n=1.

[0026] In one embodiment, the transversely electrically polarized light has a reflection extinction ratio (ERTE) greater than 10 dB, and the transversely magnetically polarized light has a transmission extinction ratio (ERTM) greater than 132 dB.

[0027] The present invention has the following beneficial effects:

[0028] The beam splitter of this invention is based on the diffraction mechanism of metagratings, which can simultaneously achieve high-efficiency beam splitting in terms of energy and polarization, and has a broadband response, making it suitable for imaging systems and optical communication fields. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the multifunctional high-efficiency beam splitter based on metagrating of the present invention;

[0031] Figure 2 In one embodiment of the present invention, the phase delay Φ i Width of air slit w i Correspondence curve;

[0032] Figure 3aThis is a graph showing the relationship between the incident angle of transversely magnetically polarized light (TM) and the diffraction efficiency of each diffraction order in one embodiment of the present invention.

[0033] Figure 3b This is a graph showing the relationship between the incident angle of transversely polarized light (TE) and the diffraction efficiency of each diffraction order in one embodiment of the present invention.

[0034] Figure 3c This is a magnetic field simulation diagram of transversely magnetically polarized light (TM) in one embodiment of the present invention;

[0035] Figure 3d This is a magnetic field simulation diagram of transversely polarized light (TE) in one embodiment of the present invention;

[0036] Figure 4a The reflection extinction ratio ER in one embodiment of the present invention TE A graph showing the relationship between the angle of incidence and the incident angle;

[0037] Figure 4b The transmission extinction ratio ER in one embodiment of the present invention TE A graph showing the relationship between the angle of incidence and the incident angle;

[0038] Figure 4c In one embodiment of the present invention, the incident angle θ i Frequency response curve of transversely polarized light (TE) at -30°;

[0039] Figure 4d In one embodiment of the present invention, the incident angle θ i Frequency response curve of transversely magnetically polarized light (TM) at -30°;

[0040] Figure 5a In one embodiment of the present invention, the incident angle and T are different thicknesses. -1 A graph of diffraction efficiency;

[0041] Figure 5b This is a graph showing the relationship between the incident angle and the R0 order diffraction efficiency at different thicknesses in one embodiment of the present invention.

[0042] Figure 5c This is a graph showing the relationship between absorption efficiency and thickness in one embodiment of the present invention;

[0043] Figure 5d In one embodiment of the present invention, the incident angle θ i Simulated magnetic field diagram at -30°. Detailed Implementation

[0044] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0045] Based on the concept of PGMs, this invention designs a multifunctional beam splitter (LBS) operating in the optical region by exploring and manipulating its diffraction properties. As is well known, PGMs are periodic gratings with supercells containing m cells with different optical responses, which discretely introduce abrupt phase shifts (APS) covering 2π. The introduced APS generates a phase gradient (i.e., an additional wave vector), which alters the fundamental laws of light reflection and refraction occurring at the interface. Diffraction effects are prevalent in PGMs, and higher-order diffraction is described by parity-dependent diffraction laws. Therefore, freely controlling the diffraction effects and their efficiency in PGMs is key to improving the performance of PGM-based devices, including beam splitters.

[0046] The LBS of this invention is a pure plasmon polariton (PGM) that introduces the desired active power (APS) along the transmission interface by adjusting the width of the air slit, which determines the propagation wave vector of the surface plasmons passing through it. It has been demonstrated that the designed LBS can simultaneously achieve efficient beam splitting in terms of both energy and polarization, and possesses a broadband and wide-angle response. For example, when transversely electrically polarized light (TE) and transversely magnetically polarized light (TM) are at θ... i When incident at an angle of -30°, LBS can completely reflect transversely polarized light (TE) at a reflection angle of θ. r = -30°, i.e., perfect specular reflection occurs; while for transversely magnetically polarized light (TM), due to the diffraction effect in PGM, the lowest diffraction order efficient negative refraction can be seen in LBS, and the refraction angle is θ. t =30°. Polarization splitting can be achieved in this way. Furthermore, the ohmic loss of the metal plays a crucial role in determining the diffraction efficiency of each diffraction order on both the reflection and transmission sides of TM polarization. Based on these physical principles, LBS can also uniformly transfer the incident energy of TM polarization to both the reflection and refraction sides. This invention is fundamental to the research of PGM-based LBS, and the proposed design shows great application potential in fields such as integrated optical communication or optical measurement.

[0047] In one specific embodiment of the present invention, a multifunctional high-efficiency beam splitter (LBS) based on metagratings is presented. The beam splitter includes several periodically distributed metagratings, and the structural parameters of a single periodic metagrating are... Figure 1As shown, the metagrating includes several spaced dielectric layers 10, with multiple air slits 20 formed between the dielectric layers 10. The dielectric layers and air slits have the same thickness, different widths, and different widths. The phase delay of each metagrating spans a phase range of 2π, and the phase difference ΔΦ between adjacent air slits is equal.

[0048] A beam splitter is used to split the polarization of an incident beam, which includes transversely electrically polarized (TE) light and transversely magnetically polarized (TM) light. The beam splitter can achieve total internal reflection of transversely electrically polarized light and negative refraction of transversely magnetically polarized light with the lowest diffraction order.

[0049] The metagrating comprises m air slits, with a period width of p, a dielectric layer and air slit thickness of d, and an air slit width of w. i i = 1 to m, the center distance between adjacent air slits is a = p / m, the phase difference between adjacent air slits is ΔΦ = 2π / m, and w i It has subwavelength dimensions and satisfies w i <<λ.

[0050] Specifically, in this embodiment, the meta-grating includes five air slits with widths of w1, w2, w3, w4, and w5, and the dielectric layer is made of metallic silver.

[0051] Transversely magnetically polarized light exists in only the fundamental modes within an air slit, and satisfies:

[0052]

[0053] Where, β i Let ε be the propagation constant, where its real part represents the propagating wave vector and its imaginary part represents the dissipation of surface plasmon polaritons in the air slit. k0 = 2π / λ is the wave vector in vacuum, λ is the wavelength of the incident beam, and ε is the propagation constant. m The dielectric constant of the dielectric layer;

[0054] When the incident beam passes through the i-th air slit and reaches the transmission interface, the total phase delay Φ i for:

[0055] Φ i =β i *d-δ;

[0056] Here, δ is the additional phase generated by multiple reflections at the interface between the grating and the air, and the value of δ is the same for all air slits.

[0057] According to the concept of PGM, the phase delay of each metagrating spans a phase range of 2π, and the phase difference ΔΦ between adjacent air slits is equal. Therefore, by adjusting the width w of each air slit...i The required phase shift can be achieved discretely.

[0058] In this embodiment, the wavelength of the incident light beam is set to λ = 650 nm, and the dielectric constant of the dielectric layer is ε. m = -17.36 + 0.715i, the metagrating includes 5 air slits (i.e., m = 5), the period width of the metagrating is p = λ, the thickness of the dielectric layer and the air slits is d = 1.5λ, and the phase delay Φ i Width of air slit w i The correspondence is as follows Figure 2 As shown, in order to ensure that the phase difference ΔΦ between adjacent air slits is equal, the widths of the air slits in this embodiment are w1 = 120nm, w2 = 68nm, w3 = 46nm, w4 = 34nm, and w5 = 27nm, respectively.

[0059] When transversely magnetically polarized light is incident, a phase gradient is introduced on the transmission side. It controls the direction of the emitted light. The angle of incidence and the angle of reflection satisfy:

[0060] k0sinθ i =k0sinθ t +nG;

[0061] in, For the phase gradient, θ i and θ t Let G = 2π / p be the incident angle and the refraction angle, respectively. Let G = 2π / p be the reciprocal lattice vector, and n be the diffraction order, n = v⁻¹, and ζ = G.

[0062] v = 0 (i.e., n = -1) is the lowest diffraction order of transversely magnetically polarized light, which predicts the critical angle θ for the appearance of higher-order diffraction. i =0°. When the angle of incidence is less than the critical angle (θ) i <0°), the refracted light follows a diffraction order of n=-1; when the incident angle is greater than the critical angle (θ) i (>0°), the refracted light follows a diffraction order of n=1.

[0063] On the other hand, for transversely polarized light, due to the presence of subwavelength air slits, it will be completely reflected by the meta-grating.

[0064] Next, we will analyze how the incident beam achieves polarization splitting in the metagrating.

[0065] Figure 3a This represents the relationship between the incident angle of transversely magnetically polarized light (TM) and the diffraction efficiency of each diffraction order. When θ i At <0°, the transmission of the lowest diffraction order dominates (i.e., n = -1), and the incident angle θ iAt θ = 30°, the transmission efficiency is approximately 70%. i At angles >0°, diffraction is primarily controlled by higher-order n=1 reflections, due to the parity check of m (where m=5). The incident light will be effectively coupled to the n=1 order reflected light, meaning that back reflection will occur under these conditions, especially at the incident angle θ. i When θ = 30°, r = -30°, R -1 ≈40%. In higher-order diffraction, more dissipation or lower diffraction efficiency is caused by multiple reflections within the grating.

[0066] Figure 3b This represents the relationship between the incident angle of transversely polarized light (TE) and the diffraction efficiency of each diffraction order. Only the n=0 order reflection is left-handed and dominant, due to the subwavelength air slit being much lower than the cutoff frequency through which TE passes. Specular reflection occurs for TE incident beams, θ i =θ r When the incident angle θ i At an angle of 30°, the reflection efficiency is R0 = 96%.

[0067] Figure 3c and Figure 3d The magnetic field simulation diagrams for transversely magnetically polarized light (TM) and transversely electrically polarized light (TE) are shown respectively. It can be seen that TM undergoes efficient negative refraction, while TE exhibits perfect reflection. Therefore, the meta-grating of the present invention can achieve efficient polarization beam splitting.

[0068] Extinction ratio is often an important parameter for evaluating the performance of polarization beam splitters. Extinction ratio is also known as reflection extinction ratio (ER). TE and transmission extinction ratio ER TM ,Right now:

[0069]

[0070] Reflection extinction ratio ER TE Transmission extinction ratio (ER) refers to the ratio of the reflection efficiency of transversely electrically polarized light (TE) to that of transversely magnetically polarized light (TM). TM It refers to the ratio of the transmission efficiency of transversely magnetically polarized light (TM) to that of transversely electrically polarized light (TE).

[0071] Figure 4a In this embodiment, the reflection extinction ratio ER TE The relationship between the incident angle and the incident angle θ i When ∈(-74°, -7°), the reflection extinction ratio ER TE All are above 10dB, while when θ i At -62°, the reflection extinction ratio ER TE The highest level reached 18dB. Figure 4bFor the transmission extinction ratio ER in this embodiment TE and the relationship with the incident angle, within the entire angular range, the transmission extinction ratio ER TM is relatively high (ER TE > 130 dB). Generally, when the incident angle θ i ∈ (-74°, -7°), both the reflection extinction ratio ER TE and the transmission extinction ratio ER TM are greater than 10 dB, and the device is considered to have a good polarization splitting effect. Therefore, the metasurface grating in the present invention has a wide-angle response characteristic.

[0072] In addition, Figure 4c and Figure 4d are respectively the frequency response curves of the incident angle θ i = -30° in this embodiment. Although the wavelength λ in the above embodiment is illustrated by taking 650 nm as an example, due to the tolerance in the PGM design, it still has a broadband response of polarization splitting. When ER TE > 10 dB, the bandwidth is about 78 nm, and the wavelength λ is 590 nm to 668 nm, where ER TM is greater than 132 dB.

[0073] Furthermore, the metasurface grating in this embodiment can also achieve the energy splitting of only transverse magnetic polarized light (TM). Refer to Figure 3a or Figure 3c shown, the incident energy is divided into three parts, corresponding to the R0, T0, and T -1 order diffractions respectively. Due to the losses of the two metal structures themselves and the interaction between the surface plasmons passing through the air slit, the energy splitting can be controlled by controlling the thickness of the grating, thereby determining the diffraction efficiency of each diffraction order. Figure 5a and Figure 5b are respectively the graphs of the incident angle and the diffraction efficiencies of the T -1 and R0 orders at different thicknesses. The thicknesses are d = 0.6λ, d = λ, d = 1.5λ, d = 2.4λ. In the above cases, the phase gradient remains unchanged. As the thickness changes, the propagation constant β i (w) changes accordingly to obtain a constant APS (i.e., φ i = β i (w)d - δ), which can be satisfied by selecting an appropriate air slit width. As shown in Figure 5a , 5b shown, as d increases from 0.6λ to 2.4λ, the diffraction efficiency of the T -1 order first increases and then decreases, and the diffraction efficiency of the R0 order gradually decreases.

[0074] Refer to Figure 5cAs shown, the absorption efficiency of the entire structure gradually increases with increasing thickness. This is because decreasing the thickness reduces the width of the air slit, and the duty cycle of the metal in the grating increases accordingly, leading to decreased transmission and increased reflection. However, on the other hand, the thickness cannot be too large. This is because when the incident beam propagates in the air slit, increasing the thickness will lead to more losses, thus increasing the absorption efficiency and decreasing the transmission efficiency. Therefore, there is a critical thickness for transmission due to losses. When d = 0.6λ and θ i At -30°, the transmission efficiency of the n=1st order is almost equal to the reflection efficiency of the n=0th order, which are 43% and 39%, respectively. Figure 5d The corresponding magnetic field simulation diagram clearly shows that the incident light is split into two beams (reflected light and transmitted light), and the two beams are in a straight line. Therefore, the designed grating can achieve multiple beam splitting functions.

[0075] As can be seen from the above technical solutions, the present invention has the following advantages:

[0076] The beam splitter of this invention is based on the diffraction mechanism of metagratings, which can simultaneously achieve high-efficiency beam splitting in terms of energy and polarization, and has a broadband response, making it suitable for imaging systems and optical communication fields.

[0077] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A multifunctional high-efficiency beam splitter based on metagratings, characterized in that, The beam splitter comprises a plurality of periodically distributed metagratings, each metagrating comprising a plurality of spaced dielectric layers with multiple air slits formed between the dielectric layers. The dielectric layers and air slits have equal thicknesses but different widths, and the air slits have different widths. The phase delay of each metagrating spans 2π. π The phase range, the phase difference between adjacent air slits ΔΦ equal; When the wavelength of the incident beam λ for 590nm~668nm Angle of incidence is At that time, the reflection extinction ratio ERTE of transversely electrically polarized light is greater than 10dB, and the transmission extinction ratio ERTM of transversely magnetically polarized light is greater than 132dB. The dielectric layer is made of silver, and its dielectric constant is... The period width of the metagrating is p=λ= 650nm The thickness of the dielectric layer and the air slit is d=1.5λ Metagratings include 5 There are several air slits, with widths of... w 1 = 120nm , w 2 =68nm , w 3 =46nm , w 4 =34nm , w 5 =27nm Phase difference between adjacent air slits ΔΦ=2π / 5 .

2. The multifunctional high-efficiency beam splitter based on metagrating according to claim 1, characterized in that, The beam splitter is used to split the polarization of the incident beam, which includes transversely electrically polarized light and transversely magnetically polarized light. The beam splitter can achieve total internal reflection of transversely electrically polarized light and negative refraction with the lowest diffraction order of transversely magnetically polarized light.

3. The multifunctional high-efficiency beam splitter based on metagrating according to claim 1, characterized in that, The meta-grating includes m There are several air slits, and the period width of the meta-grating is... p The thickness of the dielectric layer and the air slit is d The width of the air slit is w i , i=1~m The center distance between adjacent air slits is a=p / m Phase difference between adjacent air slits ΔΦ =2π / m .

4. The multifunctional high-efficiency beam splitter based on metagrating according to claim 3, characterized in that, Transversely magnetically polarized light exists in only the fundamental mode within the air slit, and satisfies: ； in, β i Let be the propagation constant, where its real part represents the propagating wave vector and its imaginary part represents the dissipation of surface plasmon polarons in the air slit. k 0 =2π / λ The wave vector in vacuum. λ Let be the wavelength of the incident light beam. ε m The dielectric constant of the dielectric layer; No. i Phase delay of an air slit Φ i for: Φ i =β i *d-δ ； in, δ The additional phase generated by multiple reflections at the interface between the grating and the air.

5. The multifunctional high-efficiency beam splitter based on metagrating according to claim 1, characterized in that, The incident angle and reflection angle of transversely magnetically polarized light in the metagrating satisfy: ； in, For phase gradient, θ i and θ t These are the angle of incidence and the angle of refraction, respectively. Let n be the reciprocal lattice vector, and n be the diffraction order. .

6. The multifunctional high-efficiency beam splitter based on metagrating according to claim 5, characterized in that, n=-1 is the lowest diffraction order of transversely magnetically polarized light; When the angle of incidence is less than the critical angle, the refracted light follows a diffraction order of n=-1; When the incident angle is greater than the critical angle, the refracted light follows a diffraction order of n=1.

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