Integrated spin waveguide chip for terahertz wave synthesis

Abstract

The application discloses an integrated spin waveguide chip for terahertz wave synthesis, and belongs to the technical field of optical sensing, and solves the problems of electromagnetic wave compatibility and wave form synthesis of a spin optical waveguide chip in the prior art.The technical scheme of the application constructs a spin waveguide through a ferromagnetic hetero thin film, realizes the radiation of terahertz waves in the direction perpendicular to the plane of the waveguide through the preparation of a terahertz antenna knot structure or a dipole antenna structure and the like, and determines the customization and interference pattern of the far field of the terahertz emission through the layout of the waveguide and the relative position of the antenna.The parallel and serial antenna structures can customize the time and spectral characteristics of the terahertz radiation.The technical scheme of the application utilizes a spin waveguide structure to design an input-output coupling structure, realizes the excitation of a higher-power femtosecond laser, and controls the time, spectrum, phase, amplitude and far field characteristics of the generated wave form.

Description

Technical Field

[0001] This invention relates to an integrated spin waveguide chip for terahertz wave synthesis, and relates to the field of optical sensing technology. Background Technology

[0002] Terahertz (THz) radiation typically refers to electromagnetic waves with frequencies between 0.1 THz and 10 THz (wavelengths between 30 m and 3 mm), falling between microwaves and infrared light, belonging to the far-infrared band. It possesses rich physical and chemical information. Furthermore, the advantages of THz radiation make it a complementary technology to Fourier transform infrared spectroscopy and X-ray technology in many areas, enabling significant applications in basic research, industrial applications, and military applications. With the development of THz technology, its application areas are constantly expanding, showing great potential in biology, medicine, microelectronics, agriculture, and other fields. Currently, many research institutions worldwide have conducted in-depth research on THz technology and have achieved many important advancements.

[0003] A metasurface is a specific two-dimensional planar structure formed by arranging artificial atoms with unique electrical or magnetic properties using specific configurations. Metasurfaces can powerfully manipulate certain physical characteristics of light, such as polarization, amplitude, and phase, thus possessing highly efficient control over light fields. Therefore, metasurfaces have attracted widespread attention in recent years and have gradually become a popular research direction. In fact, a metasurface can be viewed as a two-dimensional version of a metamaterial. Compared to metamaterials, the most significant characteristic of a metasurface is that it can be considered a two-dimensional planar structure. This is also the main advantage of metasurfaces; their two-dimensional planar structure overcomes some of the problems encountered in the use of three-dimensional metamaterials, such as the difficulty of fabrication. Metasurfaces exhibit excellent performance, surpassing the best performance achievable by traditional ferromagnetic materials. The use of metasurfaces has greatly advanced the development of micro- and nano-devices. Using metasurfaces can facilitate the integration and miniaturization of nano-optical devices. The main working principle of a metasurface can be understood as follows: the unit size of the metasurface is smaller than the wavelength of its operating frequency band. Therefore, at the operating wavelength, the metasurface can be considered a material with uniform performance. The inherent properties of the metasurface material can be adjusted through artificial design, mainly including the dielectric constant and magnetic permeability. By adjusting these properties, characteristics distinct from or even superior to natural materials can be obtained. The excellent properties of metasurfaces make them widely applicable in many fields, such as holographic imaging, polarization conversion, beam deflection, and ultrathin lenses. Metasurfaces can be classified into acoustic metasurfaces, optical metasurfaces, and mechanical metasurfaces, etc., mainly determined by the type of wave being modulated. In applications of metasurfaces, the most widespread use is as an optical metasurface to modulate electromagnetic waves. Using metasurfaces, amplitude modulation can be achieved, enabling anti-reflection, increased transmission, magnetic mirroring, and EIT-like effects. By integrating metasurfaces onto patterned ferromagnetic heterostructures, active manipulation of terahertz waves can be achieved by changing the geometry of the metasurface.

[0004] A waveguide is a structure used to guide electromagnetic waves in a directional manner. Based on the type of wave guided, they can be divided into hollow metal waveguides and surface waveguides. Hollow metal waveguides completely enclose the electromagnetic wave to be transmitted within the waveguide structure, hence they are also called closed waveguides. Surface waveguides work by confining the guided electromagnetic wave around the waveguide structure, and are also called open waveguides. Waveguides play a crucial role in electromagnetic wave transmission, primarily connecting the transmitting and receiving ends of electromagnetic waves to antennas. Using waveguides for electromagnetic wave transmission has many advantages: low conductor and dielectric losses; high power capacity; no radiation loss; and most waveguide structures are simple in design, easy to manufacture, and their propagation can be solved using Maxwell's equations combined with boundary conditions. However, in the high-frequency band, the wavelength corresponding to the operating frequency of high-frequency devices is too small, and the size coherence effect further reduces the size of the devices, thus increasing the technological requirements for fabricating high-frequency devices. Fabricating nanolayered metal waveguides can meet the size requirements for transmitting terahertz electromagnetic waves. Furthermore, the transmission of electromagnetic waves using waveguides produces dispersion, which indicates a correlation between velocity and wave propagation. Common waveguide structures include rectangular waveguides, circular waveguides, microstrip lines, and parallel twin conductors. The waveguide described in this patent is similar to the principle of terahertz surface waveguides or optical waveguides.

[0005] Terahertz spin thin films are primarily generated by femtosecond lasers passing through ferromagnetic / non-ferromagnetic heterostructures, or through HM / FM / HM three-layer structures. The generation of terahertz radiation waves mainly consists of three stages: laser absorption, electron motion, and outward radiation of terahertz waves. The main generation principle is that when the femtosecond laser passes through a ferromagnetic structure, the energy of the photons is absorbed by the spin electrons in the ferromagnetic layer. At this point, the spin electrons are excited, reaching energy levels above the Fermi level. Due to the different spin directions, some of the selected electrons move upwards, and some move downwards. The physical parameters of the selected electrons moving upwards and downwards differ, such as density, velocity in the bandgap, lifetime, and mobility. Therefore, a longitudinal polarization current is generated along the propagation direction of the pump laser pulse. When the longitudinal polarization current enters the non-ferromagnetic layer, due to the spin Hall effect, the longitudinal polarization current changes into a transverse in-plane charge flow. Analyzing the obtained in-plane charge flow using Maxwell's equations reveals that the oscillation frequency of the charge flow pulse emitted by the femtosecond laser is in the terahertz band, thus yielding terahertz electromagnetic waves. Compared to other methods for obtaining terahertz electromagnetic waves, such as nonlinear frequency conversion, the spintronics-based method offers advantages such as high efficiency, ultra-wideband coverage, low cost, and ease of integration. The ease of integration, in particular, facilitates the manipulation of terahertz waves, demonstrating significant development potential and further promoting the advancement of terahertz science and applications.

[0006] Lithium niobate waveguides are a novel type of optical waveguide device. Lithium niobate, also known as "optical silicon," is one of the best materials for fabricating various high-performance electro-optic, nonlinear, and acousto-optic devices. In recent years, advancements in lithium niobate thin-film (LNOI) technology have truly propelled lithium niobate materials from "bulk" to "chip" applications. Following the thin-film fabrication of lithium niobate, the performance of lithium niobate devices has achieved a leap forward. For example, lithium niobate thin-film electro-optic modulators, nonlinear frequency converters, and surface acoustic wave filters have all broken through the performance limits of traditional devices. High-performance photonic devices based on second-order nonlinearity are of great significance in both classical and quantum optics. However, the key factors for the practical application of lithium niobate thin-film nonlinear waveguide devices lie in achieving efficient optical nonlinearity and solving problems related to large-scale fabrication processes and fiber optic compatibility in practical applications.

[0007] Optical waveguides are a mature concept with widespread applications. An optical waveguide is a dielectric device that guides the propagation of light waves; it is also called a dielectric waveguide. There are two main types of optical waveguides: integrated optical waveguides, including planar (thin-film) dielectric waveguides and strip dielectric waveguides, which are usually part of optoelectronic integrated devices (or systems), hence the name integrated optical waveguides; and cylindrical optical waveguides, commonly called optical fibers. Optical waveguides are guiding structures for transmitting optical frequency electromagnetic waves, constructed from optically transparent media (such as quartz glass). The transmission principle of optical waveguides differs from that of closed metal waveguides. At the interface between media with different refractive indices, the total internal reflection phenomenon confines the light wave to the waveguide and a limited area around it. Multimode and single-mode optical fibers have been successfully applied in communications. The transmission characteristics of optical fibers are sensitive to external factors such as temperature and pressure, thus they can be used to make fiber optic sensors for measuring physical quantities such as temperature, pressure, and sound fields. Summary of the Invention

[0008] This invention provides an integrated spin waveguide chip for terahertz wave synthesis, which uses an on-chip waveguide spin electron terahertz radiation source as the waveguide structure and combines it with a terahertz antenna structure to realize an integrated spin waveguide chip for terahertz wave synthesis.

[0009] The technical solution adopted in this invention is an integrated spin waveguide chip for terahertz wave synthesis, comprising a substrate dielectric substrate, a spin waveguide and a waveguide antenna, wherein the spin waveguide is constructed on the substrate dielectric substrate; The substrate dielectric substrate has a plurality of waveguide antennas, which are divided into a plurality of antenna groups, and each antenna group has at least one waveguide antenna. The waveguide antennas of the same antenna group are arranged symmetrically on both sides of the spin waveguide and located on the substrate dielectric substrate; or the waveguide antennas of the same antenna group are located on the substrate dielectric substrate and the middle part of the waveguide antenna crosses the spin waveguide.

[0010] The optimized integrated spin waveguide chip for terahertz wave synthesis described above has a ferromagnetic heterostructure as the spin waveguide. The spin waveguide is constructed from a ferromagnetic heterostructure thin film on a substrate dielectric substrate.

[0011] The optimized integrated spin waveguide chip for terahertz wave synthesis has the spin waveguide arranged in a channel-like pattern on the substrate dielectric substrate.

[0012] The optimized integrated spin waveguide chip for terahertz wave synthesis has a main channel and several branch channels formed by the confluence of the main channel after the branch channels split in the middle. The intervals between two adjacent branch channels are set.

[0013] In the optimized integrated spin waveguide chip for terahertz wave synthesis, the waveguide antennas of the same antenna group are arranged on both sides of the branch channel and located on the substrate dielectric substrate. Alternatively, waveguide antennas in the same antenna group may be located on a substrate dielectric substrate and the middle of the waveguide antenna may cross a branch channel.

[0014] In the optimized integrated spin waveguide chip for terahertz wave synthesis, all antenna groups are arranged in series along the length extension direction of the spin waveguide. Adjacent antenna groups are spaced apart.

[0015] In the optimized integrated spin waveguide chip for terahertz wave synthesis, all antenna groups are arranged in parallel on the branch channel; adjacent antenna groups are spaced apart.

[0016] The optimized integrated spin waveguide chip for terahertz wave synthesis has two adjacent antenna groups arranged in parallel and symmetrically on adjacent branch channels. Alternatively, two adjacent antenna groups can be arranged in parallel and staggered on adjacent branch channels.

[0017] The optimized integrated spin waveguide chip for terahertz wave synthesis described above has input coupling structures at both ends of the spin waveguide. The width of the input coupling structure gradually increases from the end closer to the spin waveguide to the end farther away from the spin waveguide.

[0018] The optimized integrated spin waveguide chip for terahertz wave synthesis has several strip-shaped isolation bands on its input coupling structure, with the length extension direction of the isolation bands perpendicular to the length extension direction of the spin waveguide.

[0019] The beneficial effects of this application are as follows: The technical solution of this application can realize far-field terahertz beam synthesis, and the solution of this application can be simply prepared and the preparation process is compatible.

[0020] In this application, the far-field synthesis and manipulation of terahertz emission are achieved through a spin waveguide using a special structural design, waveguide layout, and relative antenna position. The terahertz antenna structure is fabricated on a spin multilayer film structure on a silicon or glass substrate, followed by the formation of an on-chip waveguide structure.

[0021] In this application, femtosecond pulses can be directly input into the spin waveguide chip structure from the side. In addition, a spin-designed input-output structure is introduced, and femtosecond lasers can also achieve higher power incident by utilizing the input-output coupling structure. Attached Figure Description

[0022] Figure 1-1 This is a schematic diagram of the structure of Embodiment 1 of this application; Figure 1-2 This is a longitudinal cross-sectional view of an embodiment of this application; Figure 1-3 This is a schematic diagram of the process flow of an embodiment of this application; Figure 2 This is a schematic diagram of the structure of Embodiment 2 of this application; Figure 3 This is a schematic diagram of the structure of Embodiment 3 of this application; Figure 4 This is a schematic diagram of the structure of Embodiment 4 of this application; Figure 5-1 This is a schematic diagram of the structure of Embodiment 5 of this application; Figure 5-2 for Figure 5-1 Light incidence diagram under certain conditions. Detailed Implementation

[0023] The technical features of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] This application discloses an integrated spin waveguide chip for terahertz wave synthesis. It primarily utilizes a ferromagnetic heterostructure thin film to construct the spin waveguide, and then fabricates a terahertz antenna bowtie structure or dipole antenna structure to radiate terahertz waves perpendicular to the waveguide plane. Femtosecond pulses can be directly input to the spin waveguide chip structure from the side, or an input-output coupling structure can be designed using the spin waveguide structure to achieve higher-power femtosecond laser excitation. The waveguide layout and the relative positions of the antennas determine the customization of the far-field and interference pattern of the terahertz emission. Parallel and serial antenna blocks can customize the temporal and spectral characteristics of the terahertz radiation. The time, spectrum, phase, amplitude, and far-field characteristics of the generated waveform can be controlled.

[0025] The integrated spin waveguide chip for terahertz wave synthesis in this application can be used individually or in combination in a chip array. The terahertz antenna structure types in this application are widely applicable, and the antenna structure design is not unique. The terahertz antenna structure can adopt conventional photoconductive antenna structures such as tie-type, junction-type, and H-type. Furthermore, the terahertz antenna structure in this application can use metasurface antennas and artificial microstructure antennas, both of which can also generate terahertz waves.

[0026] In this application, the spin thin film or ferromagnetic heterojunction of the spin waveguide 2 is not unique. For example, two-layer NM / FM (non-magnetic / ferromagnetic), three-layer NM / FM / NM (non-magnetic / ferromagnetic / non-magnetic), or topological insulator structure or topological insulator heterojunction can all be used in this application.

[0027] The waveguide antenna 3 structure layer in this application is not unique. The following embodiments show a metal terahertz antenna fabricated separately. In fact, terahertz antennas can also be fabricated using spin thin films or ferromagnetic heterojunctions.

[0028] The terahertz excitation arrangement and position in this application are not limited to the structure of the following embodiments. In actual use, different terahertz far-field waveforms can be designed according to requirements to obtain the required spin waveguide chip design.

[0029] Example 1 This embodiment is an integrated spin waveguide chip for terahertz wave synthesis, comprising a substrate dielectric substrate 1, a spin waveguide 2, and a waveguide antenna 3. The spin waveguide 2 is fabricated on the substrate dielectric substrate 1. The spin waveguide 2 is a ferromagnetic heterostructure, constructed from a ferromagnetic heterofilm on the substrate dielectric substrate 1. The substrate dielectric substrate 1 has a plurality of waveguide antennas 3, which are divided into a plurality of antenna groups, each antenna group having at least one waveguide antenna 3. The waveguide antennas 3 of the same antenna group are arranged symmetrically on both sides of the spin waveguide 2 and are located on the substrate dielectric substrate 1.

[0030] In this application, apart from the terahertz antenna layer, the spin waveguide material system can adopt the following two types: Si / SiO2 / SiNx / Fe / Pt / SiNx arranged in sequence or SiO2 / SiNx / Fe / Pt / SiNx arranged in sequence on the substrate dielectric substrate 1.

[0031] like Figure 1-1As shown, in this embodiment, the spin waveguide 2 is arranged in a channel shape on the substrate dielectric substrate 1. All antenna groups are arranged in series along the length of the spin waveguide 2, with adjacent antenna groups spaced apart. Waveguide antennas 3 of the same antenna group are symmetrically arranged on both sides of the spin waveguide 2 and located on the substrate dielectric substrate 1. A single terahertz wave 4 is a terahertz wave excited by the waveguide antenna 3, which is finally synthesized into a terahertz wave 5 by far-field vector superposition, with its direction perpendicular to the substrate dielectric substrate 1. Figure 1-2 This embodiment shows a longitudinal cross-sectional view of the integrated spin waveguide chip for terahertz wave synthesis, in which SiO2 (101) and SiNx (102) are arranged sequentially.

[0032] Figure 1-3 A fabrication process for the aforementioned integrated spin waveguide chip is presented, mainly including: Step 1) depositing a layer of silicon dioxide on a silicon wafer; Step 2) growing silicon nitride; Step 3) growing a ferromagnetic heterostructure (NM / FM or NM / FM / NM); Step 4) etching the ferromagnetic heterojunction; Step 5) fabricating a terahertz antenna structure using a lift-off process; Step 6) growing silicon nitride again; and Step 7) dicing to form the spin waveguide chip. This scheme is a relatively mature solution in the prior art. Other process solutions applicable to this application also exist in the prior art, which will not be described in detail here.

[0033] In this embodiment, the integrated spin waveguide chip for terahertz wave synthesis arranged in series is also characterized by a femtosecond laser incident from the left side into the spin waveguide. As the femtosecond laser propagates along the spin waveguide, it sequentially excites three terahertz antenna structures. Therefore, the three excited sub-terahertz waves have a time delay, and their superposition in the far field results in different synthesized terahertz wave waveforms.

[0034] Example 2 The difference between this embodiment and Embodiment 1 is that in this embodiment, the channel formed by the spin waveguide 2 has a main channel 201 and several branch channels 202, which are formed by the confluence of the main channel 201 after branching in the middle section. Adjacent branch channels 202 are spaced apart.

[0035] The specific form of the spin waveguide 2 in this embodiment is as follows: Figure 2 As shown, all antenna groups are arranged in parallel on branch channel 202, and two adjacent antenna groups are arranged in parallel and symmetrically on adjacent branch channels 202, with a certain interval between the two adjacent antenna groups.

[0036] In this embodiment, the integrated spin waveguide chip for terahertz wave synthesis, arranged in parallel, generates terahertz waves that not only radiate outwards but also propagate along the spin waveguides after a femtosecond laser is incident from the left side. Because of the parallel structure, the waves arrive at both antenna structures at the same time, resulting in no time delay between the two excited terahertz waveforms. Essentially, the terahertz waves radiating into free space are a vector superposition of the terahertz waves excited by the spin thin film and the terahertz waves excited by the two terahertz antenna structures.

[0037] Example 3 The difference between this embodiment and embodiment 2 is that: Figure 3 As shown, two adjacent antenna groups are arranged in parallel and staggered on adjacent branch channels 202. In this embodiment, two key points, terahertz wave time delay and parallel excitation, are considered to form different terahertz wave composite waveforms. The femtosecond laser is also fed in from the side and emitted from a direction perpendicular to the chip normal.

[0038] Example 4 The difference between this embodiment and embodiment 2 is that the waveguide antenna 3 of the same antenna group is located on the substrate dielectric substrate 1, and the middle part of the waveguide antenna 3 crosses the spin waveguide 2. Figure 4 As shown, in this embodiment, the waveguide antenna 3 adopts the form of a metasurface antenna, with the middle of the waveguide antenna 3 spanning the spin waveguide 2. The terahertz wave waveform excited by each metasurface antenna is closely related to the metasurface structure design. By replacing the terahertz antenna structure with a metasurface antenna structure, far-field beamforming of terahertz waves can also be achieved.

[0039] Example 5 The difference between this embodiment and embodiment 2 is that: Figure 5-1 As shown, the two ends of the spin waveguide 2 have an input coupling structure 203 and an output coupling structure 205, respectively. The input coupling structure 203 and the output coupling structure 205 are horn-shaped, and their widths gradually increase from the end closer to the spin waveguide 2 to the end farther away from the spin waveguide 2.

[0040] The input coupling structure 203 and the output coupling structure 205 have several strip-shaped isolation strips 204, and the length extension direction of the isolation strips 204 is set perpendicular to the length extension direction of the spin waveguide 2.

[0041] When a femtosecond laser is incident from the side (spot diameter μm-cm), and the spin waveguide thin film size is small (μm), a significant portion of the femtosecond laser energy is wasted. To address this issue, this embodiment directly introduces an output-output coupling structure into the spin waveguide, i.e., by fabricating it within the thin film layer (silicon nitride, ferromagnetic heterojunction, antenna structure, silicon nitride). Figure 5-1The input coupling structure 203 shown, or an approximate structure, is used to allow the femtosecond laser radiated from the optical fiber to enter the spin waveguide through the coupling structure, which can greatly improve the incident power of the terahertz wave.

[0042] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. An integrated spin waveguide chip for terahertz wave synthesis, comprising a substrate dielectric substrate (1), a spin waveguide (2), and a waveguide antenna (3), wherein the spin waveguide (2) is constructed on the substrate dielectric substrate (1); characterized in that: The substrate dielectric substrate (1) has a plurality of waveguide antennas (3), the waveguide antennas (3) are divided into a plurality of antenna groups, and each antenna group has at least one waveguide antenna (3). The waveguide antennas (3) of the same antenna group are arranged symmetrically on both sides of the spin waveguide (2) and located on the substrate dielectric substrate (1); or the waveguide antennas (3) of the same antenna group are located on the substrate dielectric substrate (1) and the middle part of the waveguide antennas (3) crosses the spin waveguide (2). The spin waveguide (2) has an input coupling structure (203) and an output coupling structure (205) at its two ends, respectively. The input coupling structure (203) and the output coupling structure (205) are horn-shaped, and the width of the input coupling structure (203) and the output coupling structure (205) gradually increases from the end closer to the spin waveguide (2) to the end farther away from the spin waveguide (2); The input coupling structure (203) and the output coupling structure (205) have several strip-shaped partitions (204), and the length extension direction of the partitions (204) is perpendicular to the length extension direction of the spin waveguide (2). The spin waveguide (2) is constructed from a ferromagnetic heterostructure thin film on a substrate dielectric substrate (1); The spin waveguide (2) is arranged in a channel shape on the substrate dielectric substrate (1); The channel formed by the spin waveguide (2) has a main channel (201) and several branch channels (202). The branch channels (202) are formed by the confluence of the bifurcation in the middle section of the main channel (201). The adjacent branch channels (202) are spaced apart; Waveguide antennas (3) of the same antenna group are arranged on both sides of the branch channel (202) and located on the substrate dielectric substrate (1); Alternatively, the waveguide antenna (3) of the same antenna group is located on the substrate dielectric substrate (1) and the middle part of the waveguide antenna (3) crosses the branch channel (202). All antenna groups are arranged in parallel on the branch channel (202); adjacent antenna groups are spaced apart. Two adjacent antenna groups are arranged in parallel and symmetrically on adjacent branch channels (202); Alternatively, two adjacent antenna groups can be arranged in parallel and interleaved on adjacent branch channels (202); One method for fabricating an integrated spin waveguide chip includes: Step 1) Deposit a layer of silicon dioxide on the silicon wafer; Step 2) Grow silicon nitride; Step 3) Grow ferromagnetic heterostructures NM / FM or NM / FM / NM; Step 4) Etch the ferromagnetic heterostructure; Step 5) Fabricate the terahertz antenna structure using a lift-off process; Step 6) Regrow silicon nitride; Step 7) Cutting to form the spin waveguide chip.

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