Terahertz signal modulation method based on oxygen vacancy engineering

Abstract

The invention relates to the technical field of terahertz technology and signal processing, in particular to a terahertz signal modulation method based on oxygen vacancy engineering. Oxygen vacancy regulation is introduced into the multi-layer dielectric structure, so that optical and magneto-optical response of the functional oxide layer is changed, and instantaneous current and terahertz radiation intensity under laser excitation are enhanced; the optical property of the medium is regulated and controlled by using an interface magnetic reconstruction effect induced by oxygen vacancies, so that stable, continuous and adjustable terahertz signal output is realized, and the limitation of traditional regulation depending on an external light path or a magnetic field is avoided; signals are enhanced and adjusted through regulation and control of intrinsic properties of materials, dependence on complex external light path reflection and synthesis is not needed, system complexity is reduced, and integration and stability of devices are improved; by optimizing the optical response of the dielectric layer, the interaction efficiency of light and a material is improved, so that the pumping laser energy can be more effectively converted into terahertz radiation, and the overall energy efficiency is improved.

Description

Technical Field

[0001] This invention relates to the fields of terahertz technology and signal processing technology, and in particular to a terahertz signal modulation method based on oxygen vacancy engineering. Background Technology

[0002] Terahertz (THz) waves, located between microwaves and infrared, possess characteristics such as high bandwidth, strong penetration, and no ionizing radiation, making them widely applicable in fields such as high-speed communication, radar detection, and security monitoring. Among these, terahertz communication, as an important candidate direction for the next generation of wireless communication, relies on the efficient modulation and flexible control of terahertz signals for its realization.

[0003] Currently, commonly used terahertz signal modulators mainly include modulators based on electronic devices, modulators based on nonlinear optical effects, and modulators based on two-dimensional materials. These approaches can achieve terahertz signal modulation to a certain extent, but still suffer from limitations in operating frequency, insufficient modulation efficiency, and low device stability. For example, electronic modulators based on field-effect transistors and superconducting devices have limited performance in the high-frequency range and are difficult to cover the broadband terahertz range; while two-dimensional material modulators based on graphene or transition metal sulfides exhibit certain optical-terahertz modulation capabilities, their fabrication processes are complex, and device consistency and long-term stability are insufficient.

[0004] Studies have shown that oxygen vacancies, as controllable point defects, can not only alter the refractive index and absorption characteristics of transition metal oxides but also induce interfacial magnetic reconstruction effects, thereby affecting the magneto-optical response of the material. Through this interfacial modulation, it is possible to effectively improve the charge and energy transfer processes under optical excitation, thereby enhancing terahertz emission performance.

[0005] Therefore, how to utilize the oxygen vacancy control mechanism in combination with the magnetic reconstruction effect to achieve controllable adjustment of the properties of the optical medium layer, thereby enhancing and flexibly adjusting the terahertz signal generated by optical excitation, has become a technical problem that urgently needs to be solved in this field.

[0006] Existing optically excited terahertz signal modulators mainly include nonlinear crystal optical rectifiers, photoconductive antennas, spin terahertz transmitters, and systems based on optical path enhancement. However, these technical solutions still have the following common drawbacks in practical applications:

[0007] ① Limited modulation depth: Nonlinear crystals (such as ZnTe and GaP) are limited by nonlinear coefficients and optical damage thresholds, resulting in a small modulation range; photoconductive antennas have limited output signal modulation capabilities due to carrier lifetime and mobility limitations; spin transmitters have wideband response, but the overall modulation amplitude is insufficient.

[0008] ② Limited control methods: Most existing solutions rely mainly on external conditions (laser power, external magnetic field direction, optical path structure) for adjustment, lacking effective control methods at the material or interface level, making it difficult to provide flexible and stable signal modulation.

[0009] ③ Limited modulation speed: The modulation process of electronic devices and some optical devices is limited by carrier migration or optical path adjustment, making it difficult to achieve a sub-picosecond fast response, which restricts their application potential in high-speed communication.

[0010] ④ High system complexity and difficult integration: Optical path enhancement schemes rely on multiple mirrors and precise optical path design, resulting in a large overall system that is not conducive to on-chip integration; while modulation devices based on nanostructures have extremely high requirements for process precision, which limits their reusability.

[0011] Existing terahertz modulation techniques generally suffer from insufficient modulation depth, limited control methods, finite modulation speed, and high system complexity. How to introduce a controllable modulation mechanism at the material level, and achieve efficient, rapid, and programmable modulation of terahertz signals by altering the optical and magneto-optical properties of the medium, has become a key technical problem urgently needing to be solved in this field.

[0012] In the existing technology, some scholars have proposed using semiconductor devices to modulate terahertz signals. For example, patent CN103034014A, "THz (Terahertz) wave modulator", discloses a terahertz wave modulator based on oxide semiconductor.

[0013] The scheme is constructed as follows:

[0014] ① Device structure: The modulation unit is constructed using oxide semiconductor material as the core and in the form of field-effect transistors (FETs);

[0015] ②Working principle: The carrier concentration in the semiconductor channel is adjusted under the action of an external electric field, thereby changing the transmittance of the material to terahertz waves and realizing the intensity modulation of the terahertz signal.

[0016] ③System Application: By adjusting the input voltage, the terahertz wave can be switched or its amplitude controlled within a certain range, thus enabling its use in basic communication or signal processing scenarios.

[0017] In this technical solution, the modulation of terahertz signals mainly relies on the manipulation of semiconductor charge carriers by an external electric field. While this approach is feasible to some extent, it still has the following shortcomings:

[0018] ① Limited modulation depth: The range of signal strength variation is limited by the adjustment range of the material's carrier concentration;

[0019] ② Limited response speed: The modulation process relies on carrier migration and accumulation, making it difficult to achieve an ultrafast response;

[0020] ③ High manufacturing cost: The device requires high-quality oxide semiconductor thin films and fine electrode technology, which makes the processing cost and large-scale preparation difficult.

[0021] Therefore, although this scheme can achieve electronically controlled modulation of terahertz signals, its modulation efficiency, response speed and economy are all insufficient, and new efficient and low-cost modulation methods based on material physics mechanisms still need to be explored. Summary of the Invention

[0022] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a terahertz signal modulation method based on oxygen vacancy engineering. By introducing oxygen vacancy modulation into a multilayer dielectric structure, the optical and magneto-optical responses of the functional oxide layer are changed, thereby enhancing the instantaneous current and terahertz radiation intensity under laser excitation. This solves the problem of limited emission power in the prior art. Oxygen vacancy modulation improves the interaction efficiency between the pump light and the multilayer dielectric structure, enabling the pump light energy to be converted into a terahertz signal more effectively. The overall energy utilization efficiency is improved by about 20-30%, which is significantly better than traditional nonlinear crystals and optical rectifiers.

[0023] This invention provides a terahertz signal modulation method based on oxygen vacancy engineering, comprising the following steps:

[0024] S1. Fabrication of multilayer dielectric structure: Functional thin film layers, including oxide dielectric layer, metal layer and high spin orbital coupling metal layer, are sequentially deposited on glass substrate. The functional thin film layers are prepared by magnetron sputtering. The oxide dielectric layer is deposited in Ar / O2 mixed atmosphere to obtain the sample. The deposition thickness and initial oxygen vacancy ratio are used to modulate THz signal. Then the metal layer and high spin orbital coupling metal layer are sequentially deposited.

[0025] S2, Optical Pumping: A femtosecond laser is used as the pump source. The femtosecond laser is incident perpendicularly from the substrate side onto the thin film sample, inducing the formation of oxygen vacancies in the oxide dielectric layer. The THz signal is modulated by adjusting the pump light power.

[0026] According to the terahertz signal modulation method based on oxygen vacancy engineering provided by the present invention, the oxide dielectric layer in S1 is nickel oxide, the metal layer is iron, and the high spin orbital coupling metal layer is platinum.

[0027] According to the terahertz signal modulation method based on oxygen vacancy engineering provided by the present invention, the thickness of the oxide dielectric layer in S1 is 2-11 nm, the thickness of the metal layer is 3 nm, and the thickness of the high spin orbital coupling metal layer is 3 nm.

[0028] According to the terahertz signal modulation method based on oxygen vacancy engineering provided by the present invention, the oxygen partial pressure ratio of the oxide medium layer in S11 during the deposition process under Ar / O2 mixed atmosphere is 5% to 25%, and the total pressure is 0.2 Pa.

[0029] According to the terahertz signal modulation method based on oxygen vacancy engineering provided by the present invention, the metal layer in S12 is deposited at room temperature in an Ar atmosphere at a rate of 2 nm / min.

[0030] According to the terahertz signal modulation method based on oxygen vacancy engineering provided by the present invention, the high spin-orbit coupled metal layer described in S13 is deposited at room temperature in an Ar atmosphere at a rate of 1.5 nm / min.

[0031] According to the terahertz signal modulation method based on oxygen vacancy engineering provided by the present invention, the wavelength of the femtosecond laser in S2 is 800 nm, the pulse width of the femtosecond laser is 50-120 fs, the repetition frequency of the femtosecond laser is 80 MHz, and the power of the pump light is 50-110 mW.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] This invention provides a terahertz signal modulation method based on oxygen vacancy engineering. By introducing oxygen vacancy modulation into a multilayer dielectric structure, the optical and magneto-optical responses of the functional oxide layer are altered, thereby enhancing the instantaneous current and terahertz radiation intensity under laser excitation and solving the problem of limited emission power in existing technologies. The interface magnetic reconstruction effect induced by oxygen vacancies allows for the modulation of the dielectric's optical properties (refractive index, absorption characteristics, magneto-optical response), achieving stable and continuously adjustable terahertz signal output, avoiding the limitations of traditional methods relying on external optical paths or magnetic fields. Signal enhancement and modulation are achieved through the modulation of the intrinsic properties of the material, eliminating the need for complex external optical path reflection and synthesis, reducing system complexity, and improving device integration and stability. Optimizing the optical response of the dielectric layer improves the interaction efficiency between light and materials, enabling pump laser energy to be more effectively converted into terahertz radiation, thus improving overall energy efficiency. Oxygen vacancy modulation enhances the interaction efficiency between the pump light and the multilayer dielectric structure, making the pump light energy more effectively converted into terahertz signals, resulting in an overall energy utilization efficiency improvement of approximately 20-30%, significantly superior to traditional nonlinear crystals and optical rectifier devices. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in this invention 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 A schematic diagram of a terahertz wave modulation principle based on oxygen vacancy control, fabricated using existing technology;

[0036] Figure 2 The range for adjusting different parameters;

[0037] Figure 3 The time curve of the THz signal induced by laser-induced oxygen vacancy modulation;

[0038] Figure 4 The THz time-domain spectral lines are after three representative adjustment times. Detailed Implementation

[0039] Example 1

[0040] This embodiment provides a terahertz signal modulation method based on oxygen vacancy engineering, including the following steps:

[0041] S1. Preparation of multilayer dielectric structures:

[0042] Functional thin film layers are sequentially deposited on a glass substrate. The functional thin film layers include an oxide dielectric layer (NiO, nickel oxide) with a thickness of 7 nm, which is used to provide tunable optical and magneto-optical responses and serve as modulation units.

[0043] The NiO layer thickness can be adjusted between 2 and 11 nm. The THz signal will have a maximum signal amplification range at 7 nm, which is the second opportunity to control the THz signal output.

[0044] A 3 nm thick metal layer (Fe) generates a transient charge flow under laser excitation; a 3 nm thick high-spin-orbit coupled metal layer (Pt) is used to achieve spin-charge conversion and radiate terahertz waves; the metal layer is deposited using magnetron sputtering, with an oxygen partial pressure ratio selectable from 5% to 25%. The sample exhibits maximum signal amplification at an oxygen partial pressure ratio of 12.5% ​​and maximum initial signal at 2%. By controlling the initial oxygen vacancy ratio of the sample, the THz signal output is adjusted, and the total pressure is fixed at 0.2 Pa.

[0045] S2, Optical Pump:

[0046] A femtosecond laser is used as the pump source, with a wavelength of 800 nm, a pulse width of 50–120 fs, and a repetition frequency of approximately 80 MHz. The femtosecond laser is incident perpendicularly onto the thin film sample from the substrate side. The pump power is set in the range of 50–110 mW to ensure that oxygen vacancies are induced in the NiO layer under threshold conditions and that there is sufficient modulation capability to change the output amplitude of the terahertz signal for the third time. This is also the most important method for modulating THz signals.

[0047] S3, Oxygen Vacancy Regulation Process:

[0048] Under continuous laser irradiation, oxygen vacancies are gradually formed and accumulated in the NiO layer, resulting in controllable changes in properties such as refractive index, absorption coefficient and magneto-optical response. This process is accompanied by interfacial magnetic reconstruction, which improves the charge / spin transfer efficiency, thereby changing the output amplitude of the terahertz signal. The concentration and distribution of oxygen vacancies can be adjusted by laser irradiation time and power, thereby realizing continuous programmable amplitude modulation of the terahertz signal.

[0049] S4. Generation and Modulation of Terahertz Signals:

[0050] Under laser pumping, the metal layer (Fe / Pt) generates an ultrafast transient current. Benefiting from the optical and magneto-optical responses of the medium after oxygen vacancy modulation, this transient current is dynamically adjusted, thereby achieving controllable modulation of the terahertz signal amplitude. The amplitude of the output terahertz signal can be flexibly controlled by adjusting the NiO thickness, oxygen partial pressure ratio, and pump light parameters, thereby achieving different modulation depths.

[0051] S5. Signal Detection and Verification:

[0052] Terahertz signals are detected by electro-optic sampling. The detector crystal can be ZnTe or GaP. Experimental results show that under the control of oxygen vacancy, the amplitude of the terahertz signal can be increased by up to 100% from the initial state, and can be continuously adjusted by the irradiation conditions, showing good programmability and stability.

[0053] By comprehensively adjusting three parameters—NiO layer thickness, oxygen partial pressure ratio, and pump light power—the amplitude of terahertz signals can be continuously controlled over a wide range, with a modulation depth exceeding 100%, demonstrating significant programmability and repeatability.

[0054] Different parameters have different adjustable ranges. During preparation, one or more parameters can be selected and adjusted according to the required range, allowing for unidirectional control to address different needs. The adjustment effect is as follows: Figure 2 As shown.

[0055] This invention effectively alters the optical and magneto-optical properties of an oxide dielectric layer by introducing oxygen vacancy modulation and combining it with the interfacial magnetic reconstruction effect, achieving the following technical advantages:

[0056] 1. Enhanced Terahertz Emission Intensity: By introducing oxygen vacancies to alter the optical and magneto-optical properties of the NiO layer, the instantaneous current under laser pumping is enhanced, resulting in a significant increase in the output terahertz wave amplitude. Experimental results show that, under typical conditions, the peak intensity of the terahertz signal can be increased by up to approximately two times, effectively solving the problem of insufficient emission intensity in existing optical devices.

[0057] 2. Achieving stable and tunable signal control: By adjusting the oxygen vacancy concentration, NiO film thickness, and laser power, the terahertz signal can be continuously adjusted within a certain range. This control method based on the intrinsic optical properties of the material is more stable and flexible than traditional methods that rely on external optical paths or external magnetic fields, and it also has the ability to maintain the effect over a long period of time.

[0058] 3. Simplified system structure and improved integration: This invention achieves signal enhancement through the engineered manipulation of the optical properties of materials, eliminating the need for complex mirror assemblies or external optical paths. This approach simplifies the experimental structure, improves the feasibility of device miniaturization and integration, and is more suitable for application in on-chip systems.

[0059] 4. Improved Energy Utilization Efficiency: Oxygen vacancy modulation enhances the interaction efficiency between the pump light and the multilayer dielectric structure, enabling the pump light energy to be converted into terahertz signals more effectively. Measurement results show that the overall energy utilization efficiency is improved by approximately 20-30%, significantly outperforming traditional nonlinear crystals and optical rectifiers.

[0060] Example 2

[0061] Figure 1 A schematic diagram of the terahertz wave modulation principle based on oxygen vacancy control, prepared using existing technology.

[0062] Initial state: When the sample is not laser excited, the NiO layer maintains a stable antiferromagnetic spin arrangement, and there is no obvious spin flow injection at the interface, only a limited charge transfer process. At this time, the emitted terahertz signal is the weakest.

[0063] After laser stimulation, oxygen-rich regions (Ni-rich) are formed locally within the NiO layer, leading to a local magnetic reconstruction effect. The THz signal gradually begins to increase, but due to the limited number of oxygen vacancies, the THz signal remains relatively weak at this stage.

[0064] After repeated laser excitation, oxygen vacancies in the NiO layer gradually accumulate and tend to stabilize, the interfacial magnetic coupling is enhanced, and the spin injection efficiency is further improved. At this time, the terahertz signal radiated by the Pt layer is significantly enhanced, exhibiting an amplitude modulation effect.

[0065] See Figure 1 The heterojunction structure is suitable for heterostructure systems containing transition metal oxides (such as NiO) and strongly spin-orbit coupled metals (such as Pt). By adjusting the laser power and irradiation time, the oxygen vacancy concentration of the NiO layer and the degree of interfacial magnetic reconstruction are changed, which ultimately affects the instantaneous current amplitude under laser pumping, thus achieving effective modulation of terahertz signals.

[0066] In Example 1, thin films were sequentially deposited on a transparent glass substrate using a magnetron sputtering process to form the following structure:

[0067] NiO (7 nm): As a dielectric modulation layer, it is responsible for the introduction and regulation of oxygen vacancies;

[0068] Fe (3 nm): as a ferromagnetic layer, providing the instantaneous charge / spin response under laser excitation;

[0069] Pt (3 nm): as a heavy metal layer, it enhances spin-charge conversion and radiates terahertz waves.

[0070] The deposition conditions were as follows: the NiO layer was grown in an Ar / O2 mixed atmosphere with an oxygen partial pressure ratio controlled at 12% and a total pressure of 0.2 Pa; the Fe and Pt layers were deposited at room temperature in an Ar atmosphere with deposition rates of 2 nm / min and 1.5 nm / min, respectively. All target materials used had a purity of 99.99%.

[0071] 2. Oxygen vacancy regulation mechanism and interfacial interaction

[0072] Under femtosecond laser irradiation, oxygen vacancies are locally formed in the NiO layer, leading to Ni 2+ / Ni 3+ The equilibrium is disrupted, inducing an interfacial magnetic reconstruction effect. This process manifests as follows:

[0073] (1) The optical refractive index and absorption coefficient of NiO can be controlled to change;

[0074] (2) Enhanced interface exchange coupling improves charge / spin transfer efficiency;

[0075] (3) Changes in optical and magneto-optical properties lead to the controllability of instantaneous current amplitude, which in turn affects the intensity of terahertz signals.

[0076] (4) The oxygen vacancy concentration can be adjusted by the pump light power and irradiation time to form a continuous and irreversible signal modulation mechanism.

[0077] In terms of static relationship, NiO, as the modulation unit, determines the steady-state optical properties of the interface by its oxygen vacancy distribution state; in terms of dynamic relationship, the instantaneous current amplitude triggered by laser pumping is regulated by this property, thereby realizing real-time modulation of terahertz waves.

[0078] 3. Performance Testing and Experimental Results

[0079] After the sample was prepared, it was pumped and excited by a femtosecond laser pulse, and the emitted terahertz waveform was measured by electro-optic sampling.

[0080] Laser source: center wavelength 800 nm, pulse width approximately 100 fs, repetition frequency 80 MHz;

[0081] Detection method: Electro-optic sampling of ZnTe crystal (1 mm thickness);

[0082] External magnetic field: 1000 Oe in the plane;

[0083] Incident mode: Pump light is incident perpendicularly from the substrate side, with a real-time power of 68mW.

[0084] See details Figure 3 and 4 Modulation curve, Figure 3 The THz signal modulation curve shows that the THz amplitude is different at each moment. Figure 4 The THz time-domain spectra at three key moments are shown, and some experimental results are as follows:

[0085] When the duration is 0 s, the signal strength is normalized to 1.0;

[0086] When the duration is 1500 s, the signal increases by approximately 1.5 times;

[0087] When the duration is 3000 s, the signal increases by approximately 1.8 times;

[0088] When the duration is 6000 s, the signal tends to saturate, and the intensity reaches about 2.0 times.

[0089] Therefore, when it is necessary to switch between THz signals of different intensities, it is only necessary to provide stimulation for different durations at high power to obtain a THz signal of fixed intensity, and this signal has the characteristic of remaining stable under low power stimulation.

[0090] 4. Summary of Effects and Benefits

[0091] This embodiment verifies the feasibility and effectiveness of the technical solution of the present invention, and has the following advantages:

[0092] a) Achieve continuously adjustable terahertz modulation: By adjusting the laser power and time, the signal amplitude can be stably changed within a range of about 1 to 2 times, providing a flexible amplitude modulation method.

[0093] b) Adaptable to multiple application scenarios: Low-damage modulation can be achieved at low power (suitable for biological detection and sensing); large modulation depth can be obtained at medium power (suitable for spectral analysis); and it can be extended to nonlinear terahertz applications at high power.

[0094] c) Simplified system structure: No need for complex external optical path design, the modulation function is directly implemented by the device, which is more conducive to miniaturization and on-chip integration.

[0095] d) Strong process compatibility: It can be prepared using conventional magnetron sputtering process, which is conducive to large-scale production and promotion.

[0096] e) Providing a novel modulation approach: Programmable adjustment of the optical and magneto-optical properties of the dielectric layer is achieved through oxygen vacancy control, breaking through the limitations of traditional modulators that rely on external fields or optical paths, and providing possibilities for the design of novel terahertz modulation devices.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for modulating terahertz signal based on oxygen vacancy engineering, characterized in that, The method comprises the following steps: S1, preparation of a multilayer medium structure: sequentially depositing functional thin film layers on a glass substrate, the functional thin film layers comprising an oxide medium layer, a metal layer and a high spin-orbit coupling metal layer, the layers being prepared by a magnetron sputtering method, the oxide medium layer being deposited under an Ar / O2 mixed atmosphere to obtain a sample, the thickness and initial oxygen vacancy ratio of the oxide medium layer being used to modulate a THz signal, and then sequentially depositing the metal layer and the high spin-orbit coupling metal layer; S2, optical pumping: using a femtosecond laser as a pumping source, the femtosecond laser being vertically incident to the thin film sample from the substrate side to induce the formation of oxygen vacancies in the oxide medium layer, and a THz signal being modulated by adjusting the pumping light power. 2.The method of claim 1, wherein the method is characterized by, The oxide medium layer in S1 is nickel oxide, the metal layer is iron, and the high spin-orbit coupling metal layer is platinum. 3.The method of claim 2, wherein the method is characterized by, The thickness of the oxide medium layer in S1 is 2-11 nm, the thickness of the metal layer is 3 nm, and the thickness of the high spin-orbit coupling metal layer is 3 nm.

4. The method of claim 1, wherein the method is based on oxygen vacancy engineering. The oxygen partial pressure ratio during deposition of the oxide medium layer in S1 under an Ar / O2 mixed atmosphere is 5%-25%, and the total pressure is 0.2 Pa.

5. The method of claim 1, wherein the method is based on oxygen vacancy engineering. The deposition rate of the metal layer in S1 under an Ar atmosphere at room temperature is 2 nm / min.

6. The method of claim 1, wherein the method is based on oxygen vacancy engineering. The deposition rate of the high spin-orbit coupling metal layer in S1 under an Ar atmosphere at room temperature is 1.5 nm / min.

7. The method of claim 1, wherein the method is based on oxygen vacancy engineering. The wavelength of the femtosecond laser in S2 is 800 nm, the pulse width of the femtosecond laser is 50-120 fs, the repetition frequency of the femtosecond laser is 80 MHz, and the power of the pumping light is 50-110 mW.

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