Optical Modulator Based on Spatial Distribution of Electron Concentration, Preparation Method Thereof and Application

Abstract

The present invention discloses an optical modulator based on the spatial distribution of electron concentration, its preparation method and application. The optical modulator is characterized by comprising a substrate, a first metal grating, a first insulating layer, a doped semiconductor layer, a second insulating layer and a second metal grating which are arranged in sequence from bottom to top. The doped semiconductor layer is composed of a semiconductor grating and a transmission layer which are arranged side by side. The first metal grating includes a plurality of first metal grating bars, and the second metal grating is provided with second metal grating bars having the same number as and corresponding to the first metal grating bars one by one. The advantage is that for different working wavelengths, by selecting a suitable electron concentration distribution period, modulation can be carried out, realizing broadband surface plasmon amplitude modulation, which is beneficial to further improving the modulation efficiency and depth and reducing the size of the device. This optical modulator has broad application prospects in the future high-density optical communication, optoelectronic integration and optical sensing fields.

Description

Technical Field

[0001] The present invention relates to the field of optical modulators, and in particular to an optical modulator based on the spatial distribution of electron concentration, a preparation method thereof, and an application thereof. Background Art

[0002] By applying an external electric field or optical field, an optical modulator can modulate the polarization, frequency, amplitude, phase and other characteristics of light, and plays a very important role in an integrated optical information processing system. Surface plasmon polaritons (SPPs) are optical wave modes that propagate along the metal surface formed by the interaction between optical waves and metal surface charges. Combining surface plasmon polaritons with traditional optical modulation effects can further enhance the interaction between light and dielectrics, thereby improving the modulation efficiency. Therefore, optical modulators based on surface plasmon polaritons have been favored by many researchers.

[0003] Based on the dependence of surface plasmon polaritons on electron concentration, it is a novel and meaningful research direction to use the electron concentration distribution to achieve optical modulation of light. Since it is difficult to adjust the electron concentration in metals, optical modulators based on the regulation of electron concentration distribution all study the regulation of electron concentration distribution in two-dimensional materials, doped semiconductor materials, transparent oxides and other materials. Doped semiconductor materials have great potential in the application of modern optoelectronic integration. Therefore, the study of the distribution of doped semiconductor electron concentration is of great significance.

[0004] The modulation effect based on the change of electron concentration not only comes from the change of the overall electron concentration, but also has a very significant impact on the change of the spatial electron concentration distribution with a wavelength-scale. Compared with the overall electron concentration regulation, the interaction between the spatial electron concentration distribution regulation and surface plasmon polaritons is stronger and the modulation efficiency is higher. However, the current regulation of electron concentration in doped semiconductor materials is based on the overall electron concentration regulation, resulting in larger device sizes and smaller modulation depths for devices made of doped semiconductor materials. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an optical modulator based on the regulation of the periodic distribution of electron concentration and a preparation method thereof, which can not only obtain a higher modulation depth and a smaller device size, but also can achieve a broadband modulation as long as a suitable spatial distribution period of electron concentration is selected for different working wavelengths.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows: An optical modulator based on the spatial distribution of electron concentration, which is composed of a substrate, a first metal grating, a first insulating layer, a doped semiconductor layer, a second insulating layer, and a second metal grating arranged in sequence from bottom to top. The doped semiconductor layer is composed of a semiconductor grating and a transmission layer arranged in parallel. The first metal grating includes a plurality of first metal grating bars, and the second metal grating is provided with second metal grating bars having the same number as and corresponding to the first metal grating bars one by one.

[0007] The material of the substrate is one of quartz, silicon, or glass. The thickness of the first metal grating is 100 - 250 nm, and the material of the first metal grating is one of gold, silver, or aluminum. The thickness of the first insulating layer is 200 - 500 nm, and the material of the first insulating layer is one of silicon dioxide, calcium fluoride, or magnesium fluoride. The thickness of the doped semiconductor layer is 50 - 100 nm, and the material of the doped semiconductor layer is one of indium tin oxide, gallium arsenide, or indium phosphide. The thickness of the second insulating layer is 200 - 500 nm, and the material of the second insulating layer is one of silicon dioxide, calcium fluoride, or magnesium fluoride. The thickness of the second metal grating is 100 - 250 nm, and the material of the second metal grating is one of gold, silver, or aluminum.

[0008] The first metal grating is located directly below the transmission layer, and the second metal grating is located directly above the transmission layer. The first metal grating includes at least two first metal grating bars, and the size and array arrangement of the first metal grating bars are the same as those of the second metal grating bars. When the size and array arrangement of the first metal grating bars and the second metal grating bars are the same, a larger periodic electric field can be generated, and the modulation effect on the electron concentration distribution is better.

[0009] The semiconductor grating is provided with grating bars having the same number and array arrangement as the first metal grating bars. The role of the semiconductor grating is to excite surface plasmons, achieve wavevector matching, and the excited surface plasmons propagate on the surface of the transmission layer. The period of the semiconductor grating determines the wavelength of the propagating surface plasmons, and the period of the first metal grating determines the period of the spatial electron concentration distribution. When the period of the spatial electron concentration distribution on the surface of the transmission layer is comparable to the wavelength size of the surface plasmons, the modulation effect is better. Therefore, it is more appropriate when the array arrangement of the first metal grating bars and the grating bars is the same.

[0010] The preparation method of an optical modulator based on the spatial distribution of electron concentration includes the following steps:

[0011] Step 1): Select a substrate and clean it. Uniformly coat a layer of negative photoresist on the cleaned substrate. Place the first grating mask on the surface of the negative photoresist and perform the first exposure using ultraviolet lithography. Perform the first development process on the substrate after the first exposure to obtain the first grating photoresist template;

[0012] Step 2): Deposit a layer of metal material on the surface of the first grating photoresist template using thermal evaporation. Place the substrate coated with the metal material in an acetone solution and gently shake it to remove the negative photoresist, obtaining the first metal grating;

[0013] Step 3): Deposit a layer of the first insulating layer on the surface of the first metal grating using thermal evaporation;

[0014] Step 4): Uniformly coat a layer of negative photoresist on the surface of the first insulating layer. Place the second grating mask on the surface of the negative photoresist and perform the second exposure using ultraviolet lithography. Perform the second development process on the substrate after the second exposure to obtain the second grating photoresist template;

[0015] Step 5): Deposit a layer of doped semiconductor material on the surface of the second grating photoresist template using thermal evaporation and soak it in an acetone solution to remove the negative photoresist, obtaining a doped semiconductor material layer. The doped semiconductor layer is composed of semiconductor gratings and a transmission layer arranged side by side;

[0016] Step 6): Deposit a layer of the second insulating layer on the surface of the doped semiconductor layer using thermal evaporation;

[0017] Step 7): Uniformly coat a layer of negative photoresist on the surface of the second insulating layer. Place the third grating mask on the surface of the negative photoresist and perform the third exposure using ultraviolet lithography. Perform the third development process on the substrate after the third exposure to obtain the third grating photoresist template;

[0018] Step 8): Deposit a layer of metal material on the surface of the third grating photoresist template using thermal evaporation. Place the substrate coated with the metal material in an acetone solution and gently shake it to remove the negative photoresist, obtaining the second metal grating, and finally complete the preparation of the optical modulator.

[0019] The negative photoresist is SU-8 with a thickness of 100 - 200 nm.

[0020] The material of the substrate is one of quartz, silicon or glass. The thickness of the first metal grating is 100 - 250 nm, and the material of the first metal grating is one of gold, silver or aluminum. The thickness of the first insulating layer is 200 - 500 nm, and the material of the first insulating layer is one of silicon dioxide, calcium fluoride or magnesium fluoride. The thickness of the doped semiconductor layer is 50 - 100 nm, and the material of the doped semiconductor layer is one of indium tin oxide, gallium arsenide or indium phosphide. The thickness of the second insulating layer is 200 - 500 nm, and the material of the second insulating layer is one of silicon dioxide, calcium fluoride or magnesium fluoride. The thickness of the second metal grating is 100 - 250 nm, and the material of the second metal grating is one of gold, silver or aluminum.

[0021] The first metal grating is located directly below the transmission layer, and the second metal grating is located directly above the transmission layer. The first metal grating includes at least two first metal grating bars, and the size and array arrangement of the first metal grating bars are the same as those of the second metal grating bars.

[0022] The semiconductor grating is provided with grating bars that have the same number and array arrangement as those of the first metal grating bars.

[0023] The application of an optical modulator based on the spatial distribution of electron concentration in optical modulation, photoelectric detection and optical sensing is as follows: Vertically incident TM - polarized light on the semiconductor grating, and the excited surface plasmon polaritons are transmitted on the transmission layer. Connect the odd - numbered metal grating bars in the first metal grating and the even - numbered metal grating bars in the second metal grating to the positive electrode of an external power supply, and connect the even - numbered metal grating bars in the first metal grating and the odd - numbered metal grating bars in the second metal grating to the negative electrode of the external power supply. By adjusting the voltage of the external power supply, control the spatial distribution of the electron concentration on the doped semiconductor layer, thereby modulating the surface plasmon polaritons transmitted on the transmission layer.

[0024] Compared with the prior art, the advantages of the present invention are as follows: polarized light is incident perpendicularly on the grating to excite surface plasmons, which propagate on the surface of the transmission layer. The odd-numbered metal bars in the first metal grating and the even-numbered metal bars in the second metal grating are connected to the positive electrode of an external power supply, and the even-numbered metal bars in the first metal grating and the odd-numbered metal bars in the second metal grating are connected to the negative electrode of the external power supply to form an interleaved voltage, generating a spatially distributed periodic electric field. Through this electric field, the spatial concentration distribution of electrons on the surface of the transmission layer can be adjusted. The electron concentration on the surface of the transmission layer will exhibit an obvious periodic distribution under the action of the periodic electric field, so that the surface plasmons propagating on the transmission layer are modulated due to the scattering effect. Therefore, the spatial electron concentration distribution on the surface of the transmission layer is dynamically adjusted by the voltage of the external power supply, and the amplitude of the surface plasmons transmitted on the transmission layer is regulated by using the periodic electron concentration distribution. For different working wavelengths, by selecting a suitable period of the electron concentration distribution, modulation can be achieved, and broadband surface plasmon amplitude modulation can be realized, which is beneficial to further obtaining a higher modulation efficiency and modulation depth and a smaller device size. This optical modulator has broad application prospects in the fields of future high-density optical communication, optoelectronic integration, and optical sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a three-dimensional structural schematic diagram of the present invention;

[0026] Figure 2 is a schematic diagram of the working principle of the present invention;

[0027] Figure 3 is a two-dimensional electrostatic field simulation schematic diagram of Example 1;

[0028] Figure 4 is a potential distribution diagram when the external voltage is 6V in Example 1;

[0029] Figure 5 is a charge density distribution diagram on the surface of the transmission layer under different external voltages in Example 1;

[0030] Fig. 6(a) shows the relationship between the real part of the refractive index of the transmission layer and the electron concentration in Example 1;

[0031] Fig. 6(b) shows the relationship between the imaginary part of the refractive index of the transmission layer and the electron concentration in Example 1;

[0032] Fig. 7(a) shows the distribution diagram of the y-component of the electric field in the "on" state in Example 1;

[0033] Fig. 7(b) shows the distribution diagram of the y-component of the electric field in the "off" state in Example 1;

[0034] Figure 8Electric field intensity distribution diagrams with and without modulation in Embodiment 1;

[0035] Figure 9 Schematic diagrams of transmittance under different electron concentration changes in Embodiment 1;

[0036] Figure 10(a) is the distribution diagram of the y-component of the electric field in Embodiment 1 at a working wavelength of 2.3 μm;

[0037] Figure 10(b) is the distribution diagram of the y-component of the electric field in Embodiment 1 at a working wavelength of 2.6 μm;

[0038] Figure 10(c) is the distribution diagram of the y-component of the electric field in Embodiment 1 at a working wavelength of 3 μm;

[0039] Figure 11 It is the graph of the variation of transmittance with wavelength in Embodiment 1. Specific implementation manners

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Embodiment 1: As Figure 1 shown, an optical modulator based on the spatial distribution of electron concentration is composed of a substrate 1, a first metal grating 2, a first insulating layer 3, a doped semiconductor layer 4, a second insulating layer 5, and a second metal grating 6 arranged in sequence from bottom to top. The doped semiconductor layer 4 is composed of a semiconductor grating 41 and a transmission layer 42 arranged in parallel. The first metal grating 2 includes a plurality of first metal grating bars, and the second metal grating 6 is provided with second metal grating bars having the same number as and corresponding one by one to the first metal grating bars;

[0042] In this embodiment, the material of the substrate 1 is quartz, the thickness of the first metal grating 2 is 250 nm, the material of the first metal grating 2 is gold, the thickness of the first insulating layer 3 is 500 nm, the material of the first insulating layer 3 is calcium fluoride, the thickness of the doped semiconductor layer 4 is 100 nm, the material of the doped semiconductor layer 4 is indium tin oxide, the thickness of the second insulating layer 5 is 500 nm, the material of the second insulating layer 5 is calcium fluoride, the thickness of the second metal grating 6 is 250 nm, and the material of the second metal grating 6 is gold;

[0043] In this embodiment, the first metal grating 2 is located directly below the transmission layer 42, the second metal grating 6 is located directly above the transmission layer 42. The first metal grating 2 includes eight first metal grating bars, the second metal grating 6 includes eight second metal grating bars. The size and array arrangement of the first metal grating bars are the same as those of the second metal grating bars, that is, the width of the first metal grating bars is the same as the width of the second metal grating bars, and the period of the first metal grating 2 is the same as the period of the second metal grating 6;

[0044] In this embodiment, the semiconductor grating 41 includes eight grating bars. The array arrangement of the grating bars is the same as that of the first metal grating bars, that is, the width of the grating bars is the same as the width of the first metal grating bars, and the period of the semiconductor grating 41 is the same as the period of the first metal grating 6;

[0045] In this embodiment, the manufacturing method of the optical modulator includes the following steps:

[0046] Step 1): Select a quartz substrate 1 and clean it. Uniformly apply a layer of negative photoresist with a thickness of 250 nm on the cleaned quartz substrate 1, then place it on a heating table and heat for 2 - 5 minutes, with the heating temperature being 150 - 200 degrees, dry the negative photoresist, place the first grating mask on the surface of the negative photoresist, and perform the first exposure using ultraviolet lithography. Perform the first development process on the quartz substrate 1 after the first exposure to obtain the first grating photoresist template;

[0047] Step 2): Deposit a layer of gold on the surface of the first grating photoresist template using thermal evaporation. Place the quartz substrate 1 coated with gold in an acetone solution and soak for 3 - 5 minutes, and gently shake to remove the negative photoresist to obtain the first metal grating 2;

[0048] Step 3): Deposit a layer of calcium fluoride with a thickness of 500 nm on the surface of the first metal grating 2 as the first insulating layer 3 using thermal evaporation;

[0049] Step 4): Uniformly apply a layer of negative photoresist with a thickness of 100 nm on the surface of the first insulating layer 3, then place it on a heating table and heat for 2 - 5 minutes, with the heating temperature being 150 - 200 degrees, dry the negative photoresist, place the second grating mask on the surface of the negative photoresist, and perform the second exposure using ultraviolet lithography. Perform the second development process on the quartz substrate 1 after the second exposure to obtain the second grating photoresist template; In this embodiment, the pattern of the second grating mask is the same as that of the first grating mask, and the second grating mask is placed on the left side of the surface of the negative photoresist;

[0050] Step 5): Deposit a layer of indium tin oxide on the surface of the second grating photoresist template using thermal evaporation, and place it in an acetone solution and soak for 3 - 5 minutes, and gently shake to remove the negative photoresist to obtain the doped semiconductor material layer. The doped semiconductor layer 4 is composed of a semiconductor grating 41 and a transmission layer 42 arranged in parallel; In this embodiment, the doped semiconductor layer 4 is the semiconductor grating 41 and the transmission layer 42 from left to right in sequence;

[0051] Step 6): Deposit a layer of calcium fluoride with a thickness of 500 nm on the surface of the doped semiconductor layer 4 as the second insulating layer 5 using thermal evaporation;

[0052] Step 7): Uniformly apply a layer of negative photoresist with a thickness of 250 nm on the surface of the second insulating layer 5, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 °C to dry the negative photoresist. Place the third grating mask on the surface of the negative photoresist, and perform the third exposure using ultraviolet lithography. Perform the third development process on the quartz substrate 1 after the third exposure to obtain the third grating photoresist template; in this embodiment, the pattern of the third grating mask is the same as that of the first grating mask, and the third grating mask is placed directly above the transmission layer 42;

[0053] Step 8): Deposit a layer of gold on the surface of the third grating photoresist template using thermal evaporation. Place the quartz substrate 1 coated with gold in acetone solution for 3 - 5 minutes and gently shake to remove the negative photoresist, obtaining the second metal grating 6, and finally complete the preparation of the optical modulator;

[0054] The negative photoresist in this embodiment is SU - 8;

[0055] In this embodiment, the applications of the optical modulator in optical modulation, photoelectric detection, and optical sensing are as follows: Vertically incident TM - polarized light on the semiconductor grating 41 to excite surface plasmon polaritons. The excited surface plasmon polaritons propagate on the transmission layer 42. Connect the odd - numbered metal bars in the first metal grating 2 and the even - numbered metal bars in the second metal grating 6 to the positive pole of an external power supply, and connect the even - numbered metal bars in the first metal grating 2 and the odd - numbered metal bars in the second metal grating 6 to the negative pole of the external power supply. By adjusting the voltage of the external power supply, control the spatial distribution of the electron concentration on the transmission layer 42, thereby modulating the surface plasmon polaritons propagating on the surface of the transmission layer 42;

[0056] The role of the semiconductor grating 41 is to excite surface plasmon polaritons to achieve wave - vector matching. The excited surface plasmon polaritons propagate on the surface of the transmission layer 42, and the period of the semiconductor grating 41 determines the wavelength of the propagating surface plasmon polaritons. Connect the odd - numbered metal bars in the first metal grating 2 and the even - numbered metal bars in the second metal grating 6 to the positive pole of an external power supply, and connect the even - numbered metal bars in the first metal grating 2 and the odd - numbered metal bars in the second metal grating 6 to the negative pole of the external power supply to form an interleaved voltage, constructing a periodically distributed electric field on the transmission layer 42, making the electron concentration on the transmission layer 42 show a periodic spatial distribution, so that the surface plasmon polaritons propagating on the transmission layer 42 are modulated due to the scattering effect. When the period of the spatial electron concentration on the surface of the transmission layer 42 is comparable to the wavelength size of the surface plasmon polaritons, the modulation effect is better;

[0057] Such as Figure 2As shown in the figure, the working principle in this embodiment is as follows: The TM polarized light is vertically incident on the semiconductor grating 41 to excite surface plasmons. The excited surface plasmons propagate from left to right on the surface of the transmission layer 42. The odd-numbered metal grating bars in the first metal grating 2 and the even-numbered metal grating bars in the second metal grating 6 are connected to the positive pole of an external power supply, and the even-numbered metal grating bars in the first metal grating 2 and the odd-numbered metal grating bars in the second metal grating 6 are connected to the negative pole of the external power supply. That is, different polar voltages are externally connected to every two adjacent metal grating bars in the first metal grating 2, and different polar voltages are externally connected to the corresponding metal grating bars of the first metal grating 2 and the second metal grating 6, generating a spatially distributed electric field, thereby forming a potential difference. Therefore, the electron concentration on the surface of the transmission layer 42 shows an obvious periodic distribution. The spatial electron concentration distribution on the surface of the transmission layer 42 can be adjusted through the potential difference. Therefore, by adjusting the voltage of the external power supply, the spatial distribution of the electron concentration in the transmission layer 42 can be controlled, thereby dynamically regulating the amplitude of the surface plasmons transmitted on the surface of the transmission layer 42;

[0058] In this embodiment, the length of the optical modulator is 14 μm, the width is 5 μm, and the height is 8 μm. The first metal grating 2 has 8 first metal grating bars, the second metal grating 6 has 8 second metal grating bars, each first metal grating bar is aligned with each second metal grating bar one by one, and the semiconductor grating 41 has 8 grating bars. The widths and periods of the grating bars, the first metal grating bars, and the second metal grating bars are the same;

[0059] In order to analyze the electron concentration distribution in the transmission layer 42 under different voltages, this embodiment uses the finite element method (FEM, Finite Element Method) to simulate the optical modulator. Its simulation model is as Figure 3 shown. Considering the symmetry of the structure, a two-dimensional model is used in this embodiment for simulation, which can effectively reduce the amount of calculation. To simplify the model, this embodiment only analyzes the electron concentration distribution in the case of two pairs of metal grating bars. The size of the metal grating bars is 0.5×0.25 μm, the period is 2 μm, and the thickness of the middle transmission layer 42 is 0.1 μm;

[0060] Analyze the potential distribution and space charge density distribution of the model in the case of an electrostatic field: When opposite voltages are applied to the electrodes, the potential distribution when the voltage is 6V is as Figure 4 shown. It can be seen that its potential obviously shows a periodic spatial distribution. Therefore, by using an external electric field, the spatial distribution of the electron concentration in the transmission layer 42 can be controlled;

[0061] As Figure 5As shown, the greater the voltage, the greater the fluctuation in the distribution of electron concentration and the more obvious the difference in optical properties. When surface plasmons propagate on the surface of the transmission layer 42, the scattering effect is more obvious. Therefore, it is very effective to use an alternating voltage to regulate the spatial distribution of electron concentration, thereby achieving the regulation of the amplitude of surface plasmons.

[0062] In the actual simulation process, the dielectric constants of materials are used. Therefore, in the model of this embodiment, the dielectric constants corresponding to different electron concentrations , and its calculation formula can be obtained from the Drude model: , where represents the high-frequency dielectric constant, ω represents the angular frequency, ω p represents the plasma frequency, Γ represents the relaxation frequency, represents a complex number;

[0063] The relationship between the plasma frequency ω p and the free carrier concentration is: , where N represents the free carrier concentration, e represents the charge of an electron, ɛ0 = 8.85×10 -12 Fm -1 represents the permittivity of free space, m* = 0.35m0 represents the effective mass of an electron, m0 = 9.1×10 -31 kg represents the mass of an electron; According to the above formula, the relationship between the dielectric constant and the electron concentration is obtained. Further, the real part n and the imaginary part k of the effective refractive index at different electron concentrations can be calculated. Therefore, during the simulation, a one-to-one correspondence between the electron concentration and the real part n and the imaginary part k of the effective refractive index can be achieved; At a wavelength of 1550 nm, the variation relationships of the real part n and the imaginary part k of the refractive index in the transmission layer with the electron concentration are shown in FIGS. 6(a) and 6(b).

[0064] In order to analyze the effectiveness of the spatial electron concentration distribution in regulating the amplitude of surface plasmons, in this embodiment, the FEM simulation method is used to analyze the electric field distribution during the propagation of surface plasmons on the surface of the transmission layer 42 (only the transmission layer 42 is simulated). When no external voltage is applied, all the transmission layers 42 are set to the same electron concentration. The surface plasmons are excited on the surface of the transmission layer 42 using the port mode. At this time, the propagating surface plasmons are just a normal attenuation, and the distribution of the y-component of the electric field is shown in FIG. 7(a) (the working wavelength is fixed at 1.55 μm, the thickness of the transmission layer 42 is 0.1 μm, and the electron concentration is 9.5×10 20 cm -3 ). When the plasmon signal can be detected at the right end, this state is defined as the "on" state; When an external voltage is applied, there is a periodic electron concentration distribution on the surface of the transmission layer 42. Assume that the electron concentrations are 9.5×1020 cm -3 and 5×10 20 cm -3 , the distribution of the y-component of the electric field is shown in Fig. 7(b). It can be seen that the spatially distributed electron concentration has a good modulation effect on the amplitude of the surface plasmon propagating in the transmission layer 42. Basically, no plasmon signal can be detected at the right end. This state is defined as the "off" state;

[0065] To further analyze the change in the electric field distribution during the transmission of surface plasmons, a cut line is set at a position 50 nm above the upper surface of the transmission layer 42 to analyze the change in the electric field intensity distribution on the cut line. As shown in Fig. 7, in the "on" state, that is, without modulation, the surface plasmon in the transmission layer 42 is just a normal attenuation; in the "off" state, that is, with modulation, when there is a periodic spatial electron concentration distribution, it can be seen that the change in the electric field intensity is very obvious, indicating that the spatial electron concentration distribution has an obvious modulation effect on the amplitude of the surface plasmon;

[0066] To further analyze the influence of different electron concentrations on the optical modulator, this embodiment also analyzes the transmittance of the ports under different voltages, that is, different electron concentration differences, as Figure 9 shown. As the applied voltage increases, the difference in electron concentration gradually increases, and the scattering effect becomes more and more obvious, resulting in a lower transmittance of the right port. The lower the transmittance, the smaller the amplitude. Therefore, the amplitude of the surface plasmon can be dynamically regulated by the applied voltage;

[0067] For different working wavelengths, the response of the spatial distribution change of the electron concentration to the working wavelength is also different. In this embodiment, the periodic distribution of the electron concentration is fixed at 9.5×10 20 cm -3 and 5×10 20 cm -3 . When the working wavelengths are 2.3 μm, 2.6 μm, and 3.0 μm respectively, the distributions of the y-component of the electric field are shown in Fig. 10(a), Fig. 10(b), and Fig. 10(c) respectively. When the electron concentration period is fixed, the longer the working wavelength, the worse the scattering effect and the lower the modulation efficiency;

[0068] To further analyze the modulation characteristics of the periodic electron concentration distribution, this embodiment analyzes the transmittance at different wavelengths. Figure 11The relationship between the transmittance and wavelength under the conditions of uniform electron concentration distribution and periodic electron concentration distribution. It can be clearly seen that in the wavelength range of 2.0 - 6.0 μm, the transmittance of the periodic electron concentration distribution is below that of the uniform electron concentration distribution, indicating that the spatial electron concentration distribution has a good modulation effect in this range. At a wavelength of 3.66 μm, the transmittance drops from -4.0 dB to -41.7 dB, and the modulation depth reaches 37.7 dB, achieving a large on-off ratio. And this modulation of the surface plasmon amplitude is due to the scattering effect and does not depend on the wavelength. Therefore, as long as the appropriate period of the electron concentration distribution is selected, broadband modulation of the surface plasmon amplitude can be achieved, that is, adjustment can be performed for a very wide frequency band (wavelength band).

[0069] Example 2: The rest is the same as in Example 1, except that the material of the substrate 1 is silicon, the thickness of the first metal grating 2 is 225 nm, the material of the first metal grating 2 is silver, the thickness of the first insulating layer 3 is 350 nm, the material of the first insulating layer 3 is silicon dioxide, the thickness of the doped semiconductor layer 4 is 75 nm, the material of the doped semiconductor layer 4 is gallium arsenide, the thickness of the second insulating layer 5 is 350 nm, the material of the second insulating layer 5 is silicon dioxide, the thickness of the second metal grating 6 is 225 nm, and the material of the second metal grating 6 is silver;

[0070] In this embodiment, the preparation method of the optical modulator includes the following steps:

[0071] Step 1): Select a silicon substrate 1 and clean it. Uniformly apply a layer of 225-nm-thick negative photoresist on the cleaned silicon substrate 1, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the first grating mask plate on the surface of the negative photoresist, and perform the first exposure using ultraviolet lithography. Perform the first development treatment on the silicon substrate 1 after the first exposure to obtain the first grating photoresist template;

[0072] Step 2): Deposit a layer of silver on the surface of the first grating photoresist template using thermal evaporation. Immerse the silver-deposited silicon substrate 1 in an acetone solution for 3 - 5 minutes and gently shake it to remove the negative photoresist, obtaining the first metal grating 2;

[0073] Step 3): Deposit a layer of 350-nm-thick silicon dioxide as the first insulating layer 3 on the surface of the first metal grating 2 using thermal evaporation;

[0074] Step 4): Uniformly apply a layer of negative photoresist with a thickness of 75 nm on the surface of the first insulating layer 3, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the second grating mask on the surface of the negative photoresist, and perform a second exposure using ultraviolet lithography. Perform a second development process on the silicon substrate 1 after the second exposure to obtain a second grating photoresist template; in this embodiment, the pattern of the second grating mask is the same as that of the first grating mask, and the second grating mask is placed on the left side of the surface of the negative photoresist.

[0075] Step 5): Use thermal evaporation to deposit a layer of gallium arsenide on the surface of the second grating photoresist template, soak it in acetone solution for 3 - 5 minutes, and gently shake to remove the negative photoresist, obtaining a doped semiconductor material layer. The doped semiconductor layer 4 is composed of semiconductor gratings 41 and a transmission layer 42 arranged in parallel; in this embodiment, the doped semiconductor layer 4 is the semiconductor grating 41 and the transmission layer 42 from left to right in sequence.

[0076] Step 6): Use thermal evaporation to deposit a layer of 350 nm thick silicon dioxide on the surface of the doped semiconductor layer 4 as the second insulating layer 5.

[0077] Step 7): Uniformly apply a layer of negative photoresist with a thickness of 225 nm on the surface of the second insulating layer 5, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the third grating mask on the surface of the negative photoresist, and perform a third exposure using ultraviolet lithography. Perform a third development process on the silicon substrate 1 after the third exposure to obtain a third grating photoresist template; in this embodiment, the pattern of the third grating mask is the same as that of the first grating mask, and the third grating mask is placed directly above the transmission layer 42.

[0078] Step 8): Use thermal evaporation to deposit a layer of silver on the surface of the third grating photoresist template. Place the silicon substrate 1 coated with silver in acetone solution for 3 - 5 minutes, and gently shake to remove the negative photoresist, obtaining the second metal grating 6, and finally completing the preparation of the optical modulator.

[0079] Example 3: The rest is the same as Example 1, except that the material of the substrate 1 is glass, the thickness of the first metal grating 2 is 100 nm, the material of the first metal grating 2 is aluminum, the thickness of the first insulating layer 3 is 200 nm, the material of the first insulating layer 3 is magnesium fluoride, the thickness of the doped semiconductor layer 4 is 50 nm, the material of the doped semiconductor layer 4 is indium phosphide, the thickness of the second insulating layer 5 is 200 nm, the material of the second insulating layer 5 is magnesium fluoride, the thickness of the second metal grating 6 is 100 nm, and the material of the second metal grating 6 is aluminum.

[0080] In this embodiment, the preparation method of the optical modulator includes the following steps:

[0081] Step 1): Select a glass substrate 1 and wash it. Apply a 100-nm-thick negative photoresist evenly on the washed glass substrate 1, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the first grating mask on the surface of the negative photoresist, and perform the first exposure using ultraviolet lithography. Perform the first development treatment on the glass substrate 1 after the first exposure to obtain the first grating photoresist template.

[0082] Step 2): Deposit a layer of aluminum on the surface of the first grating photoresist template using thermal evaporation. Immerse the glass substrate 1 coated with aluminum in an acetone solution for 3 - 5 minutes and gently shake to remove the negative photoresist, obtaining the first metal grating 2.

[0083] Step 3): Deposit a 200-nm-thick magnesium fluoride layer on the surface of the first metal grating 2 as the first insulating layer 3 using thermal evaporation.

[0084] Step 4): Apply a 50-nm-thick negative photoresist evenly on the surface of the first insulating layer 3, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the second grating mask on the surface of the negative photoresist, and perform the second exposure using ultraviolet lithography. Perform the second development treatment on the glass substrate 1 after the second exposure to obtain the second grating photoresist template. In this embodiment, the pattern of the second grating mask is the same as that of the first grating mask, and the second grating mask is placed on the left side of the surface of the negative photoresist.

[0085] Step 5): Deposit a layer of indium phosphide on the surface of the second grating photoresist template using thermal evaporation, and immerse it in an acetone solution for 3 - 5 minutes and gently shake to remove the negative photoresist, obtaining a doped semiconductor material layer. The doped semiconductor layer 4 is composed of a semiconductor grating 41 and a transmission layer 42 arranged in parallel. In this embodiment, the doped semiconductor layer 4 is the semiconductor grating 41 and the transmission layer 42 from left to right in sequence.

[0086] Step 6): Deposit a 200-nm-thick magnesium fluoride layer on the surface of the doped semiconductor layer 4 as the second insulating layer 5 using thermal evaporation.

[0087] Step 7): Uniformly apply a layer of negative photoresist with a thickness of 100 nm on the surface of the second insulating layer 5, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the third grating mask plate on the surface of the negative photoresist, and perform the third exposure using ultraviolet lithography. Perform the third development process on the glass substrate 1 after the third exposure to obtain the third grating photoresist template; in this embodiment, the pattern of the third grating mask plate is the same as that of the first grating mask plate, and the third grating mask plate is placed directly above the transmission layer 42;

[0088] Step 8): Deposit a layer of aluminum on the surface of the third grating photoresist template using thermal evaporation. Place the glass substrate 1 coated with aluminum in an acetone solution for 3 - 5 minutes and gently shake to remove the negative photoresist, obtaining the second metal grating 6, and finally complete the preparation of the optical modulator.

[0089] Example 4: The rest is the same as Example 1, except that the material of the substrate 1 is silicon, the thickness of the first metal grating 2 is 250 nm, the material of the first metal grating 2 is silver, the thickness of the first insulating layer 3 is 400 nm, the material of the first insulating layer 3 is silicon dioxide, the thickness of the doped semiconductor layer 4 is 75 nm, the material of the doped semiconductor layer 4 is gallium arsenide, the thickness of the second insulating layer 5 is 500 nm, the material of the second insulating layer 5 is magnesium fluoride, the thickness of the second metal grating 6 is 250 nm, and the material of the second metal grating 6 is silver;

[0090] In this embodiment, the preparation method of the optical modulator includes the following steps:

[0091] Step 1): Select a silicon substrate 1 and wash it. Uniformly apply a layer of negative photoresist with a thickness of 250 nm on the washed silicon substrate 1, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the first grating mask plate on the surface of the negative photoresist, and perform the first exposure using ultraviolet lithography. Perform the first development process on the silicon substrate 1 after the first exposure to obtain the first grating photoresist template;

[0092] Step 2): Deposit a layer of silver on the surface of the first grating photoresist template using thermal evaporation. Place the silicon substrate 1 coated with silver in an acetone solution and soak for 3 - 5 minutes, and gently shake to remove the negative photoresist, obtaining the first metal grating 2;

[0093] Step 3): Deposit a layer of 400 nm thick silicon dioxide as the first insulating layer 3 on the surface of the first metal grating 2 using thermal evaporation;

[0094] Step 4): Uniformly apply a layer of 75 nm thick negative photoresist on the surface of the first insulating layer 3, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the second grating mask on the surface of the negative photoresist, and perform a second exposure using ultraviolet lithography. Perform a second development process on the silicon substrate 1 after the second exposure to obtain a second grating photoresist template; in this embodiment, the pattern of the second grating mask is the same as that of the first grating mask, and the second grating mask is placed on the left side of the surface of the negative photoresist.

[0095] Step 5): Use thermal evaporation to deposit a layer of gallium arsenide on the surface of the second grating photoresist template, then immerse it in acetone solution for 3 - 5 minutes and gently shake to remove the negative photoresist, obtaining a doped semiconductor material layer. The doped semiconductor layer 4 is composed of semiconductor gratings 41 and a transmission layer 42 arranged in parallel; in this embodiment, the doped semiconductor layer 4 is, from left to right, the semiconductor grating 41 and the transmission layer 42.

[0096] Step 6): Use thermal evaporation to deposit a layer of 500 nm thick magnesium fluoride on the surface of the doped semiconductor layer 4 as the second insulating layer 5.

[0097] Step 7): Uniformly apply a layer of 250 nm thick negative photoresist on the surface of the second insulating layer 5, then place it on a heating table and heat for 2 - 5 minutes at a heating temperature of 150 - 200 degrees to dry the negative photoresist. Place the third grating mask on the surface of the negative photoresist, and perform a third exposure using ultraviolet lithography. Perform a third development process on the silicon substrate 1 after the third exposure to obtain a third grating photoresist template; in this embodiment, the pattern of the third grating mask is the same as that of the first grating mask, and the third grating mask is placed directly above the transmission layer 42.

[0098] Step 8): Use thermal evaporation to deposit a layer of silver on the surface of the third grating photoresist template. Place the silicon substrate 1 coated with silver in acetone solution for 3 - 5 minutes and gently shake to remove the negative photoresist, obtaining the second metal grating 6, and finally completing the preparation of the optical modulator.

Claims

1. An optical modulator based on the spatial distribution of electron concentration, characterized in that It is composed of a substrate, a first metal grating, a first insulating layer, a doped semiconductor layer, a second insulating layer, and a second metal grating arranged successively from bottom to top. The doped semiconductor layer is composed of a semiconductor grating and a transmission layer arranged in parallel. The first metal grating is located directly below the transmission layer, and the second metal grating is located directly above the transmission layer. The first metal grating includes at least two first metal grating bars. The second metal grating is provided with second metal grating bars having the same number as and corresponding one by one to the first metal grating bars. The size and array arrangement of the first metal grating bars are the same as those of the second metal grating bars. The semiconductor grating is provided with grating bars having the same number and array arrangement as the first metal grating bars.

2. The optical modulator based on the spatial distribution of electron concentration according to claim 1, wherein The material of the substrate is glass. The thickness of the first metal grating is 100 - 250 nm, and the material of the first metal grating is one of gold, silver, or aluminum. The thickness of the first insulating layer is 200 - 500 nm, and the material of the first insulating layer is one of silicon dioxide, calcium fluoride, or magnesium fluoride. The thickness of the doped semiconductor layer is 50 - 100 nm, and the material of the doped semiconductor layer is one of indium tin oxide, gallium arsenide, or indium phosphide. The thickness of the second insulating layer is 200 - 500 nm, and the material of the second insulating layer is one of silicon dioxide, calcium fluoride, or magnesium fluoride. The thickness of the second metal grating is 100 - 250 nm, and the material of the second metal grating is one of gold, silver, or aluminum.

3. The preparation method of an optical modulator based on the spatial distribution of electron concentration according to claim 1, characterized in that It includes the following steps: Step 1): Select a substrate and wash it. Uniformly apply a layer of negative photoresist on the washed substrate. Place the first grating mask on the surface of the negative photoresist, and perform the first exposure using ultraviolet lithography. Perform the first development treatment on the substrate after the first exposure to obtain the first grating photoresist template. Step 2): Deposit a layer of metal material on the surface of the first grating photoresist template using thermal evaporation. Place the substrate coated with the metal material in acetone solution to remove the negative photoresist, and obtain the first metal grating. Step 3): Deposit a layer of the first insulating layer on the surface of the first metal grating using thermal evaporation. Step 4): Uniformly apply a layer of negative photoresist on the surface of the first insulating layer. Place the second grating mask on the surface of the negative photoresist, and perform the second exposure using ultraviolet lithography. Perform the second development treatment on the substrate after the second exposure to obtain the second grating photoresist template. Step 5): Deposit a layer of doped semiconductor material on the surface of the second grating photoresist template using thermal evaporation, and soak it in acetone solution to remove the negative photoresist, obtaining the doped semiconductor material layer. The doped semiconductor layer is composed of a semiconductor grating and a transmission layer arranged in parallel. Step 6): Deposit a layer of the second insulating layer on the surface of the doped semiconductor layer using thermal evaporation. Step 7): Uniformly apply a layer of negative photoresist on the surface of the second insulating layer, place the third grating mask on the surface of the negative photoresist, and perform the third exposure using ultraviolet lithography. Then, perform the third development process on the substrate after the third exposure to obtain a third grating photoresist template; Step 8): Deposit a layer of metal material on the surface of the third grating photoresist template using thermal evaporation. Place the substrate coated with the metal material in an acetone solution to remove the negative photoresist, obtaining a second metal grating, and finally complete the preparation of the optical modulator.

4. The preparation method of an optical modulator based on the spatial distribution of electron concentration according to claim 3, characterized in that The negative photoresist is SU-8 with a thickness of 100-250 nm.

5. The preparation method of an optical modulator based on the spatial distribution of electron concentration according to claim 3, wherein The material of the substrate is glass. The thickness of the first metal grating is 100-250 nm, and the material of the first metal grating is one of gold, silver, or aluminum. The thickness of the first insulating layer is 200-500 nm, and the material of the first insulating layer is one of silicon dioxide, calcium fluoride, or magnesium fluoride. The thickness of the doped semiconductor layer is 50-100 nm, and the material of the doped semiconductor layer is one of indium tin oxide, gallium arsenide, or indium phosphide. The thickness of the second insulating layer is 200-500 nm, and the material of the second insulating layer is one of silicon dioxide, calcium fluoride, or magnesium fluoride. The thickness of the second metal grating is 100-250 nm, and the material of the second metal grating is one of gold, silver, or aluminum.

6. The preparation method of an optical modulator based on the spatial distribution of electron concentration according to claim 3, characterized in that The first metal grating is located directly below the transmission layer, and the second metal grating is located directly above the transmission layer. The first metal grating includes at least two first metal grating bars, and the size and array arrangement of the first metal grating bars are the same as those of the second metal grating bars.

7. The preparation method of an optical modulator based on the spatial distribution of electron concentration according to claim 6, characterized in that The semiconductor grating is provided with grating bars that have the same number and array arrangement as the first metal grating bars.

8. Application of the optical modulator based on the spatial distribution of electron concentration in optical modulation, photoelectric detection or optical sensing, characterized in that The specific method is as follows: Vertically incident TM-polarized light on the semiconductor grating. The excited surface plasmon polaritons are transmitted on the transmission layer. Connect the odd-numbered metal grating bars in the first metal grating and the even-numbered metal grating bars in the second metal grating to the positive pole of an external power supply, and connect the even-numbered metal grating bars in the first metal grating and the odd-numbered metal grating bars in the second metal grating to the negative pole of the external power supply. By adjusting the voltage of the external power supply, control the spatial distribution of the electron concentration on the doped semiconductor layer, thereby modulating the surface plasmon polaritons transmitted on the transmission layer.

Images