Photoelectrically tunable dynamic switchable waveplate based on semiconductor metamaterials

Abstract

This invention discloses a photoelectrically tunable and dynamically switchable waveplate based on semiconductor metamaterials. Addressing the shortcomings of existing single-field modulation or simple superposition of multiple fields in doped semiconductors, such as high loss and poor coordination, this invention proposes a deep photoelectric-electrical synergistic modulation mechanism based on intrinsic semiconductors. The waveplate includes a substrate and a periodic array of intrinsic semiconductor cuboids formed thereon, with electrode structures at both ends. During modulation, a pump light is used as a pre-excitation condition to excite free carriers in the initially high-resistivity intrinsic semiconductor; simultaneously, a modulation voltage is applied to drive the nonlinear reconstruction of the spatial distribution and concentration of photogenerated carriers. Through the interlocking mechanism of the photoelectric dual fields, the effective dielectric constant and optical anisotropy of the cuboid units in the orthogonal directions are dynamically adjusted, thereby achieving efficient switching between multiple-dimensional polarization states, such as linear and circular polarization. This invention avoids the ohmic loss introduced by doping and has the advantages of compact structure, rich modulation dimensions, and high precision, making it suitable for fields such as optical communication and polarization imaging.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, specifically to a photoelectric tunable and dynamically switchable waveplate based on semiconductor metamaterials, applicable to multiple fields such as optical communication, polarization imaging, quantum information processing, spectral detection and sensing technology. Background Technology

[0002] With the rapid development of optical technology, dynamically tunable optical devices are becoming increasingly important in fields such as communication, imaging, and quantum information processing. Polarization control technology, as one of the core technologies in optics, is dedicated to precisely controlling the polarization state of light waves, encompassing key operations such as polarization state conversion. By rationally designing waveplate structures, the core characteristics of incident electromagnetic waves, such as polarization, amplitude, phase, and propagation mode, can be effectively controlled, playing an indispensable role in various optical applications.

[0003] Traditional optical waveplates primarily rely on naturally birefringent materials, utilizing the long-distance propagation of light waves within the material to accumulate the required phase delay, thereby achieving polarization state conversion. However, this method has significant limitations such as large size and limited functionality, making it difficult to meet the demands of modern optical systems for miniaturization, integration, and dynamic tunability.

[0004] Metamaterials, as an emerging nano-optical platform, provide new ideas for overcoming the limitations of traditional waveplates. Currently, the main ways to achieve dynamic control of optical properties of reconfigurable metamaterials rely on the following single external excitation mechanisms: (1) Purely electric control: usually using the carrier accumulation effect of transparent conductive oxides (such as ITO) or integrated diodes. Its advantage is that it is fast, but the control range is limited, and the introduced metal electrodes will bring insertion loss in the high-frequency range. (2) Purely optical control: using pump light to irradiate phase change materials or semiconductors to induce phase change or generate photogenerated carriers. Although this method can achieve non-contact control, the response is limited by the carrier recombination lifetime, and the spatial distribution is difficult to control precisely. (3) Thermal control: using the thermo-optic effect of liquid crystals or vanadium oxides, there are problems such as slow response, high power consumption, and difficulty in localizing the temperature field.

[0005] To overcome the bottleneck of a single physical field, the industry has attempted to introduce the combined effect of multiple physical fields. However, most existing "multi-field modulation" schemes are based on doped semiconductor materials (such as silicon-doped and indium gallium arsenide-doped materials). In doped semiconductors, there is already a certain concentration of intrinsic free carriers. Applying an external electric field or optical field merely changes the concentration or distribution of the existing carriers. This mechanism is essentially a simple linear superposition of the effects of multiple independent excitation fields, without creating deep coupling in the physical mechanism. Furthermore, the impurity ions introduced by doping significantly increase the carrier scattering probability, leading to high ohmic losses in the terahertz or infrared bands; and maintaining a high carrier concentration requires a continuous bias voltage, resulting in high static power consumption.

[0006] More importantly, existing control theories have failed to establish an "interlocking and synergistic" mechanism among multiple physical fields. For intrinsic semiconductors with low loss potential, due to their extremely low initial free carrier concentration (exhibiting a high-resistivity state), a single external electric field cannot achieve effective dielectric constant modulation. While a single optical field excitation can break the intrinsic state and generate photogenerated carriers, the lack of external electric field constraint results in isotropic diffusion of carriers, which is difficult to meet the stringent requirements of complex polarization conversion for spatial anisotropic carrier distribution.

[0007] Therefore, exploring a novel multi-field cooperative architecture to achieve deep coupling of optical and electrical regulation in intrinsic semiconductors—that is, using photoexcitation as a "precondition" to generate carriers to break through the regulation threshold of intrinsic materials, and coordinating the electric field to perform "secondary nonlinear reconstruction" of the space and concentration of photogenerated carriers—is a technical challenge that urgently needs to be solved in this field.

[0008] To address this, this invention proposes a photoelectrically tunable, dynamically switchable waveplate based on semiconductor metamaterials, providing a novel solution. Its core advantage lies in breaking through the simple superposition logic of existing technologies, achieving switching of multiple polarization functions through a deep photoelectric-electric synergistic modulation mechanism under intrinsic semiconductors, demonstrating broad application potential in fields such as optical communication, imaging, and display. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a photoelectrically tunable, dynamically switchable waveplate based on semiconductor metamaterials. Unlike existing technologies that use doped semiconductors to control carrier concentration, this invention uses intrinsic semiconductor materials without artificial doping to construct metamaterial units. This waveplate achieves dual control over the concentration and distribution of free carriers through a synergistic mechanism of optical pumping and electrical modulation, thereby enabling dynamic and precise efficient switching between various electromagnetic wave polarization states.

[0010] This invention combines the electromagnetic resonance effect of subwavelength structural units, the polarization oscillation effect of free carriers, and the electromagnetic coupling mechanism to design an ultra-compact, multifunctional waveplate. Unlike existing technologies that use doped semiconductors to control carrier concentration, this invention uses intrinsic semiconductor materials without artificial doping to construct metamaterial units. By controlling the synergistic effect of pump light and control voltage, dual control over free carrier concentration and space is achieved, enabling dynamic and precise efficient conversion between various electromagnetic wave polarization states, covering dynamic switching between linear polarization, linear polarization and circular polarization, and circular polarization. The specific technical solution of this invention is as follows:

[0011] A photoelectric tunable and dynamically switchable waveplate based on semiconductor metamaterials, the waveplate being composed of subwavelength periodic units, each periodic unit comprising a substrate and intrinsic semiconductor metamaterial cuboid units formed on the substrate.

[0012] The height of the substrate is 0.23 to 0.4 times the wavelength of the working electromagnetic wave, and the height of the cuboid unit is 0.70 to 1.20 times the wavelength of the working electromagnetic wave. The long side of the cuboid unit is along the u-axis, and the short side is along the v-axis. The ratio of the length of the long side and the width of the short side of the resonant unit to the wavelength of the working electromagnetic wave ranges from 0.16 to 0.28 and from 0.09 to 0.16, respectively, and the length and width are not equal. The cuboid unit is made of intrinsic semiconductor.

[0013] Preferably, the intrinsic semiconductor may be silicon or gallium arsenide.

[0014] Furthermore, the intrinsic semiconductor metamaterial cuboid unit is irradiated with pulsed or continuous pump light with wavelengths near or within the intrinsic absorption edge of the intrinsic semiconductor. When the energy of the pump light photons exceeds the band gap energy of the intrinsic semiconductor, an intrinsic absorption effect is triggered. Specifically, valence band electrons are excited to transition to the conduction band, generating high-density electron-hole pairs. This interband transition creates a significant carrier concentration gradient in the irradiated region, altering the carrier distribution of the intrinsic semiconductor and consequently changing its dielectric constant. The specific formula is as follows: Where n represents the photogenerated carrier concentration, N photon V represents the number of photons per unit area, V represents the excitation volume per unit area, and E is the light intensity. photon The x-axis represents the photon energy, and R is the reflectivity of the intrinsic semiconductor. The x-axis is the polarization direction of the working electromagnetic wave, and its angle with the u-axis is α. The v-axis is perpendicular to the u-axis and forms an angle α with the x-axis.

[0015] Furthermore, changing the length, width, and height of the cuboid element will affect the transmission coefficient modulus of the cuboid element in the x-axis and y-axis directions. and and its phase difference .

[0016] According to the ellipticity formula (The EP range is -1 to 1), the polarization state of the working electromagnetic wave can be determined. When EP = 0, it represents linearly polarized light. At this time, the amplitudes in two orthogonal directions are equal, but the phase difference is 0 or 180°; when EP = 1, it represents right-handed circularly polarized light. At this time, the amplitudes in two orthogonal directions are equal, and the phase difference is 90°; when EP = -1, it represents left-handed circularly polarized light. At this time, the amplitudes in two orthogonal directions are equal, and the phase difference is -90°; when -1 < EP < 0, it represents left-handed elliptically polarized light. At this time, the amplitudes in two orthogonal directions are not equal, and the phase difference is between -90° and 0°; when 0 < EP < 1, it represents right-handed elliptically polarized light. At this time, the amplitudes in two orthogonal directions are not equal, and the phase difference is between 0° and 90°.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) The optoelectronic tunable dynamic switchable wave plate based on semiconductor metamaterials provided by the present invention innovatively uses intrinsic semiconductors as metamaterial units, abandoning the traditional doping semiconductor regulation mode that relies on impurity carriers. Through the synergistic effect of light and electricity, different polarization function switching is realized. The regulation method is flexible and the regulation result is accurate, which makes the wave plate have broader application potential in various optical systems. (2) Through the synergistic effect of pump light excitation and voltage regulation, the inherent defects of single physical field regulation are overcome. Under the synergistic regulation, the ellipticity EP can be continuously and accurately adjusted within the full range (-1 to 1). (3) Based on the above synergistic regulation mechanism, a single device can realize multiple functions such as linear polarization mutual conversion and linear polarization - circular polarization conversion, with a high degree of functional integration. (4) The device is fabricated based on standard semiconductor processes, and the structural unit is of sub-wavelength scale, which is easy to integrate with existing silicon-based optoelectronic chips or terahertz systems, facilitating system miniaturization. Brief Description of the Drawings

[0019] In order to more clearly display the technical details of the embodiments of the invention, the drawings used in the embodiments are briefly introduced below. Obviously, the provided drawings only represent some embodiments of the present invention. For those skilled in the art, other possible forms of drawings can be deduced based on these drawings.

[0020] Figure 1 It is a schematic structural diagram of this wave plate.

[0021] Figure 2 It is a schematic diagram of the wave plate unit in the xoy plane.

[0022] Figure 3 It is the relationship between the carrier concentration and the height of the cuboid unit when the power of the pump light (wavelength is 800 nm) is 20 μW.

[0023] Figure 4The relationship between carrier concentration and height of the cuboid unit cell when the pump light (wavelength 800nm) power is 20μW and the bias voltage is 3V.

[0024] Figure 5 The transmission coefficient modulus when an X-ray polarized electromagnetic wave is incident on the local wave plate ( and ) spectrum, transmittance spectrum and ellipticity spectrum.

[0025] Figure 6 The trend of the ellipticity EP of the working electromagnetic wave as a function of the wavelength of the working electromagnetic wave and the power of the pump light (wavelength of 800nm) when the X-ray polarized working electromagnetic wave is incident on the local wave plate.

[0026] Figure 7 When the pump light (wavelength 800nm) has a power of 20μW, and the x-polarized working electromagnetic wave is incident on the local wave plate, the ellipticity EP of the working electromagnetic wave changes with the wavelength and voltage of the working electromagnetic wave.

[0027] Figure 8 The trend of the ellipticity EP of the working electromagnetic wave with the power and voltage of the pump light (wavelength 800nm) when the X-polarized working electromagnetic wave with a wavelength of 260μm is incident on the local wave plate.

[0028] In the diagram: 1 is a periodic unit, 2 is the substrate, 3 is the pump light, 4 is the operating electromagnetic wave, 5 is the control voltage, and α is the angle between the u-axis and the x-axis. It is the transmission coefficient modulus in the x-axis direction. EP is the transmission coefficient modulus in the y-axis direction, and EP is the ellipticity. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] The present invention aims to provide an optoelectronically tunable, dynamically switchable waveplate based on semiconductor metamaterials to achieve a better polarization control technology solution.

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] This invention relates to a photoelectrically tunable, dynamically switchable waveplate based on semiconductor metamaterials, comprising at least one substrate and an intrinsic semiconductor metamaterial cuboid unit formed on the substrate. An operating electromagnetic wave is incident on the intrinsic semiconductor metamaterial cuboid unit from top to bottom along its height direction (z-axis), i.e., perpendicularly incident on the waveplate. The height of the substrate is 0.23–0.4 times the wavelength of the operating electromagnetic wave, and the height of the cuboid unit is 0.70–1.20 times the wavelength of the operating electromagnetic wave. The long side of the cuboid unit is along the u-axis, and the short side is along the v-axis. The ratios of the length of the long side and the width of the short side of the cuboid unit to the wavelength of the operating electromagnetic wave are in the ranges of 0.16–0.28 and 0.09–0.16, respectively, and the length and width are not equal. The two sides of the substrate are the x-axis and y-axis directions, respectively. The angle α between the u-axis and the x-axis is 45°, and the y-axis is perpendicular to the x-axis and forms an angle of 45° with the u-axis. The substrate is preferably silicon dioxide. The intrinsic semiconductor is preferably silicon, gallium arsenide, or other semiconductors.

[0033] Furthermore, pump light (400nm–1550nm) irradiates the intrinsic semiconductor metamaterial cuboid unit. For example... Figure 3 As shown, taking a pump light (wavelength 800nm) power of 20μW as an example, since the photon energy of the pump light is absorbed by the intrinsic semiconductor, electrons in the valence band are excited to the conduction band, thereby generating electron-hole pairs. A further control voltage is applied to change the concentration distribution of the free carriers within the cuboid unit. Finally, the working electromagnetic wave is incident on the waveplate from top to bottom along the height direction (z-axis direction) of the cuboid unit. Figure 4 As shown, taking a pump light (wavelength 800nm) power of 20μW and a bias voltage of 3V as an example, the change in voltage causes the carrier concentration and distribution inside the resonant unit to change, which alters the electromagnetic resonance behavior of the free carriers inside the cuboid unit. This leads to a change in the effective relative permittivity of the cuboid unit in the x-axis and y-axis directions, which in turn brings about changes in the transmission coefficient modulus and the phase difference (i.e., ellipticity EP) of the working electromagnetic wave in the x-axis and y-axis directions, ultimately achieving the polarization conversion function.

[0034] This invention provides a method for fabricating the above-mentioned optoelectronically tunable and dynamically switchable waveplate based on semiconductor metamaterials, characterized by comprising the following steps:

[0035] Step 1: Use L-edit software to draw the mask file corresponding to the designed metamaterial structure, and use a high-precision laser printer to print a chromium mask with a diameter of 3-8 inches;

[0036] Step 2: A 50-200 nm thick layer of chromium metal is deposited on a high-resistivity silicon wafer using a metal vacuum sputtering machine, and a 2-6 μm thick layer of photoresist is spin-coated onto the surface of the deposited chromium metal.

[0037] Step 3: Using the fabricated chromium mask and photolithography machine, the photoresist layer is photolithographically etched to transfer the metamaterial structure onto the photoresist layer (exposing part of the chromium metal layer). Then, wet etching is performed using a chromium etchant to further transfer the metamaterial structure onto the chromium metal layer (exposing part of the high-resistivity silicon wafer).

[0038] Step 4: Deep reactive ion etching is performed on the exposed high-resistivity silicon wafer using an ion beam etching machine until the etching depth reaches 10-600 μm. During this process, etching gas SF6 and passivation gas C4F8 are used alternately.

[0039] Step 5: After etching is complete, use a chromium etchant to remove the chromium metal layer on the material surface, and then clean the entire material with piranha cleaning solution.

[0040] The specific parameters for the embodiment are as follows:

[0041] Example 1 (Pure Light Control)

[0042] (1) Experimental methods

[0043] like Figure 1 As shown, the substrate material is silicon dioxide. The cuboid unit has a height of 300 μm, a length of 70 μm, and a width of 40 μm. The resonant unit is an intrinsic silicon semiconductor, and the angle α between the u-axis and the x-axis is 45°. Figure 2 As shown, the period of the cuboid unit is 100 μm.

[0044] When the working electromagnetic wave is incident on the local wave plate, the modulus of the transmission coefficient of the working electromagnetic wave is... and The trend of ellipticity EP changing with different wavelengths, such as Figure 5 As shown. Further, the intrinsic semiconductor metamaterial cuboid unit is irradiated with a pulsed pump light or a continuous pump light (wavelength 800nm), and the pump light power is adjusted to obtain the ellipticity spectrum.

[0045] (2) Experimental results

[0046] like Figure 5 As shown, at a working wavelength of 300 μm, i.e., x-polarized incident light, transmission only occurs along the y-axis, and the ellipticity EP is 0, meaning that all x-polarized incident light is converted into y-polarized outgoing light; at a working wavelength of 260 μm, the transmission coefficient moduli are equal in both the x-axis and y-axis directions. = Furthermore, the ellipticity EP is -1, meaning that the x-linearly polarized incident light is converted into left-handed circularly polarized outgoing light; at a working wavelength of 360 μm, the transmission coefficient moduli are equal in the x-axis and y-axis directions. = Furthermore, the ellipticity is 1, meaning that the x-linearly polarized incident light is converted into right-hand circularly polarized outgoing light.

[0047] like Figure 6 As shown, the ellipticity EP exhibits a corresponding trend as the wavelength of the working electromagnetic wave and the pump light power change.

[0048] Specifically, as the pump light power changes (i.e., when the pump light power is 0), the ellipticity EP at the operating wavelengths of 250μm, 275μm, and 310μm is -1, 0, and 1, respectively. Polarization conversion can be achieved by adjusting the pump light intensity, which can cause a corresponding change in EP. However, the operating state exhibits significant instability, indicating that single optical excitation cannot achieve precise and stable polarization control.

[0049] Example 2 (Pure Electric Control)

[0050] (1) Experimental methods

[0051] like Figure 1 As shown, the substrate material is silicon dioxide. The cuboid unit has a height of 300 μm, a length of 70 μm, and a width of 40 μm. The resonant unit is an intrinsic silicon semiconductor, and the angle α between the u-axis and the x-axis is 45°. Figure 2 As shown, the period of the cuboid unit is 100 μm.

[0052] When the working electromagnetic wave is incident on the local wave plate, the modulus of the transmission coefficient of the working electromagnetic wave is... and The trend of ellipticity EP changing with different wavelengths, such as Figure 5 As shown. Furthermore, by applying a regulating voltage between the far-substrate end and the near-substrate end of the intrinsic semiconductor metamaterial cuboid unit and adjusting the voltage magnitude, an ellipticity spectrum is obtained.

[0053] (2) Experimental results

[0054] like Figure 5 As shown, at a working wavelength of 300 μm, i.e., x-polarized incident light, transmission only occurs along the y-axis, and the ellipticity EP is 0, meaning that all x-polarized incident light is converted into y-polarized outgoing light; at a working wavelength of 260 μm, the transmission coefficient moduli are equal in both the x-axis and y-axis directions. = Furthermore, the ellipticity EP is -1, meaning that the x-linearly polarized incident light is converted into left-handed circularly polarized outgoing light; at a working wavelength of 360 μm, the transmission coefficient moduli are equal in the x-axis and y-axis directions. = Furthermore, the ellipticity is 1, meaning that the x-linearly polarized incident light is converted into right-hand circularly polarized outgoing light.

[0055] With changes in the wavelength of the operating electromagnetic wave and the magnitude of the control voltage, the ellipticity EP shows a very small trend. As the control voltage increases from 0V to 4V, at a working wavelength of 300μm, the ellipticity EP is 0, meaning that the x-polarized incident light is completely converted to y-polarized outgoing light without any change; at a working wavelength of 260μm, the transmission coefficient moduli are equal in both the x-axis and y-axis directions. = Furthermore, the ellipticity EP is -1, meaning that the x-linearly polarized incident light remains unchanged when converted to left-hand circularly polarized outgoing light; at a working wavelength of 360 μm, the transmission coefficient moduli are equal in the x-axis and y-axis directions. = Furthermore, the ellipticity is 1, meaning that the x-linearly polarized incident light does not change when converted to right-hand circularly polarized outgoing light.

[0056] Specifically: As the control voltage changes, for intrinsic semiconductor metamaterials, due to the extremely low initial free carrier concentration (high resistance state), the dielectric constant and optical anisotropy cannot be effectively controlled by simply relying on an external electric field, and the ellipticity EP changes very little. This indicates that a large-scale dynamic polarization control cannot be achieved by a single electric excitation.

[0057] Example 3 (Photoelectric Synergistic Regulation)

[0058] (1) Experimental methods

[0059] like Figure 1 As shown, the substrate material is silicon dioxide. The cuboid unit has a height of 300 μm, a length of 70 μm, and a width of 40 μm. The resonant unit is an intrinsic silicon semiconductor, and the angle α between the u-axis and the x-axis is 45°. Figure 2 As shown, the period of the cuboid unit is 100 μm.

[0060] When the working electromagnetic wave is incident on the local wave plate, the modulus of the transmission coefficient of the working electromagnetic wave is... and The trend of ellipticity EP changing with different wavelengths, such as Figure 5 As shown. Further, the intrinsic semiconductor metamaterial cuboid unit is irradiated with a pulsed or continuous pump light (wavelength 800nm), and the pump light power and the magnitude of the control voltage are adjusted to obtain the ellipticity spectrum.

[0061] (2) Experimental results

[0062] like Figure 5 As shown, at a working wavelength of 300 μm, i.e., x-polarized incident light, transmission only occurs along the y-axis, and the ellipticity EP is 0, meaning that all x-polarized incident light is converted into y-polarized outgoing light; at a working wavelength of 260 μm, the transmission coefficient moduli are equal in both the x-axis and y-axis directions. = Furthermore, the ellipticity EP is -1, meaning that the x-linearly polarized incident light is converted into left-handed circularly polarized outgoing light; at a working wavelength of 360 μm, the transmission coefficient moduli are equal in the x-axis and y-axis directions. = Furthermore, the ellipticity is 1, meaning that the x-linearly polarized incident light is converted into right-hand circularly polarized outgoing light.

[0063] like Figure 7 As shown, when the pump light power is 20μW, the ellipticity EP exhibits a corresponding trend as the wavelength of the working electromagnetic wave and the control voltage change.

[0064] Specifically: when the pump light power is 20μW and no control voltage is applied (i.e., the control voltage is 0), the ellipticity EP at the working wavelengths of 260μm, 300μm, and 360μm are -1, 0, and 1, respectively. Polarization conversion is achieved by adjusting the control voltage, which causes the ellipticity EP to change accordingly.

[0065] like Figure 8 As shown, at a working wavelength of 260 μm, the ellipticity EP exhibits a certain trend with changes in pump light and control voltage.

[0066] Specifically: at a working wavelength of 260μm, the ellipticity EP changes from -1 to 1 as the pump power and control voltage change, that is, the x-polarized incident light is converted into left-handed circularly polarized light, right-handed circularly polarized light, and y-polarized outgoing light; by adjusting the pump power, a wide range of changes in ellipticity EP can be achieved, and by further adjusting the voltage, a small range of precise control of ellipticity EP can be achieved.

[0067] In summary, at a working wavelength of 300 μm, this invention can convert right-handed circularly polarized incident light into left-handed circularly polarized outgoing light. At working wavelengths of 260 μm and 360 μm, this invention achieves the function of converting circularly polarized state to linearly polarized state. While the polarization modulator can achieve polarization state switching over a wide range of pump light power, as the pump light intensity increases, the ellipticity becomes extremely sensitive to fluctuations in pump light power. Even small perturbations in pump light power can cause significant jumps in ellipticity, making it difficult to maintain a specific target polarization state. Therefore, a control voltage is introduced for adjustment. By controlling the magnitude of the control voltage, the ellipticity EP can be precisely controlled, further dynamically adjusting the polarization function of the polarization modulator.

[0068] This document illustrates the principles and implementation methods of the present invention through specific embodiments, aiming to help those skilled in the art understand the invention, rather than limiting it. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A photoelectrically tunable, dynamically switchable waveplate based on semiconductor metamaterials, characterized in that, The waveplate includes: a substrate; an intrinsic semiconductor metamaterial layer formed on the substrate and composed of cuboid units arranged in a subwavelength periodic pattern; the long side of each cuboid unit is the u-axis, and the short side is the v-axis, the plane containing the u-axis and v-axis is parallel to the substrate surface, and the dimensions of the long side and the short side are not equal; electrode structures are respectively disposed at the far-substrate end and the near-substrate end of each cuboid unit for applying a control voltage; the waveplate is configured for dynamic control based on a photoelectric synergistic mechanism, the control mechanism being: using pump light with photon energy not less than the bandgap width of the intrinsic semiconductor as a pre-excitation bar. The device excites free carriers in the cuboid unit in its initial high-resistivity state; using the control voltage applied through the electrode structure as a spatial reconstruction condition, it drives the free carriers excited by the pump light to change their spatial distribution within the cuboid unit; when the working electromagnetic wave is incident on the waveplate in a direction perpendicular to the substrate surface, by synergistically changing the irradiation state of the pump light and the magnitude of the control voltage, it dynamically adjusts the effective dielectric constant and optical anisotropy of the cuboid unit in the mutually orthogonal x-axis and y-axis directions, thereby realizing the dynamic switching of the waveplate between different polarization states.

2. The waveplate according to claim 1, characterized in that, The height of the substrate is 0.23 to 0.4 times the wavelength of the working electromagnetic wave, and the height of the cuboid unit is 0.70 to 1.20 times the wavelength of the working electromagnetic wave. The ratios of the length of the long side and the width of the short side of the cuboid unit to the wavelength of the working electromagnetic wave are 0.16 to 0.28 and 0.09 to 0.16, respectively. The side lengths of the substrate are parallel to the x-axis and y-axis, respectively. The angle α between the u-axis and the x-axis is 45°, and the y-axis is perpendicular to the x-axis and forms a 45° angle with the u-axis. The cuboid unit is composed of intrinsic semiconductor.

3. The waveplate according to claim 2, characterized in that, The substrate is preferably silicon dioxide; the intrinsic semiconductor is preferably silicon or gallium arsenide.

4. The waveplate according to claim 1, characterized in that, The photon energy of the pump light is less than or equal to the intrinsic semiconductor indirect bandgap width. The pump light wavelength range is 400nm to 1550nm, preferably 400nm or 800nm.

5. The waveplate according to claim 4, characterized in that, The pump light is an ultrafast pulse pump light with a power between 0.1 μW and 70 μW.

6. The waveplate according to claim 1, characterized in that, The voltage range of the regulated power supply is 0V to 4V.

7. A method for fabricating a photoelectric tunable dynamic switchable waveplate based on semiconductor metamaterials, characterized in that, Includes the following steps: Step 1: Use L-edit software to draw the mask file corresponding to the designed metamaterial structure, and use a high-precision laser printer to print a chromium mask with a diameter of 3-8 inches; Step 2: A 50-200 nm thick layer of chromium metal is deposited on a high-resistivity silicon wafer using a metal vacuum sputtering machine, and a 2-6 μm thick layer of photoresist is spin-coated onto the surface of the deposited chromium metal. Step 3: Using the fabricated chromium mask and photolithography machine, the photoresist layer is photolithographically etched to transfer the metamaterial structure onto the photoresist layer (exposing part of the chromium metal layer). Then, wet etching is performed using a chromium etchant to further transfer the metamaterial structure onto the chromium metal layer (exposing part of the high-resistivity silicon wafer). Step 4: Deep reactive ion etching is performed on the exposed high-resistivity silicon wafer using an ion beam etching machine until the etching depth reaches 10-600 μm. During this process, etching gas SF6 and passivation gas C4F8 are used alternately. Step 5: After etching is complete, use a chromium etchant to remove the chromium metal layer on the material surface, and then clean the entire material with piranha cleaning solution.

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