Electro-optical modulator, preparation method thereof and modulation test system

Abstract

The invention discloses an electro-optical modulator, a preparation method of the electro-optical modulator and a modulation test system. The electro-optical modulator comprises a field effect transistor and a micro-nano optical fiber. The field effect transistor comprises a silicon substrate, a dielectric layer, a heterojunction and an electrode layer which are sequentially stacked, the electrode layer comprises a source electrode and a drain electrode which are respectively arranged at two ends of the heterojunction; the micro-nano optical fiber comprises an input optical fiber, a first conical transition optical fiber, a middle optical fiber, a second conical transition optical fiber and an output optical fiber which are connected in sequence, the middle optical fiber is provided with an optical fiber micro-ring of an annular structure, and the optical fiber micro-ring is arranged on the heterojunction. The electro-optical modulator is based on all optical fibers, the coupling mode is simple, optical fiber-optical fiber light field coupling is used for replacing traditional section coupling or grating coupling, therefore, the problem of mode field matching is avoided, plug-and-play and near-zero coupling loss optical interconnection and optical modulation can even be achieved, the modulation speed is high, cost is low, and the electro-optical modulator is suitable for large-scale popularization and application. And the modulation bandwidth is high.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-optic modulation, and in particular to an electro-optic modulator, a preparation method thereof and a modulation test system. Background Art

[0002] Electro-optic modulators are mainly modulators made by using the electro-optic effect of certain electro-optic crystals, such as lithium niobate crystals (LiNbO3), gallium arsenide crystals (GaAs) and lithium tantalate crystals (LiTaO3), or the free carrier plasma dispersion effect of semiconductor waveguides. When voltage is applied to the electro-optic crystal or semiconductor waveguide, the complex refractive index of the electro-optic crystal or semiconductor waveguide changes due to the above effect, resulting in changes in the characteristics of the light wave passing through the crystal or semiconductor waveguide, thereby achieving modulation of the phase, amplitude, intensity and polarization state of the optical signal. Electro-optic modulators are widely used and are core devices in the fields of optical communication, optical interconnection, optical computing, optoelectronic test and measurement, microwave photonics, etc. The main performance indicators of electro-optic modulators include insertion loss, half-wave voltage, bandwidth and modulation depth. With the increasing demand for data centers and 5G / 6G communication networks, the performance requirements for modulators are also getting higher and higher, especially in terms of insertion loss, bandwidth, power consumption and integration.

[0003] However, currently, when electro-optic modulators are used in systems such as fiber-optic communications, optical transmission coupling between the electro-optic modulator and the optical fiber is required. The coupling of the electro-optic modulator and the optical fiber is usually achieved through end-face coupling and grating coupling. These advanced coupling technologies can reduce coupling loss, that is, reduce insertion loss, but these coupling methods require very precise alignment operations and packaging processes, which increases costs. In addition, the coupling loss is still high after precise coupling, which will inevitably lead to problems such as attenuation of optical signal transmission intensity, decreased modulation efficiency, and reduced modulation bandwidth. Therefore, it is of great significance to develop electro-optic modulators with simpler coupling methods and lower coupling losses. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides an electro-optic modulator and a preparation method thereof and a modulation test system.

[0005] A first aspect of the present invention provides an electro-optic modulator, comprising:

[0006] A field effect transistor comprises a silicon substrate, a dielectric layer, a heterojunction and an electrode layer which are stacked in sequence; the electrode layer comprises a source electrode and a drain electrode, and the source electrode and the drain electrode are respectively arranged at two ends of the heterojunction;

[0007] The micro-nano optical fiber comprises an input optical fiber, a first tapered transition optical fiber, a middle optical fiber, a second tapered transition optical fiber and an output optical fiber which are connected in sequence. The middle optical fiber has an optical fiber micro-ring with an annular structure, and the optical fiber micro-ring is arranged on the heterojunction.

[0008] The electro-optic modulator according to the embodiment of the present invention has at least the following beneficial effects: the electro-optic modulator is an all-optical fiber-based electro-optical modulator with a simple coupling method. It replaces the traditional end-face coupling or grating coupling with fiber-to-fiber optical field coupling, thereby avoiding the problem of mode field matching, and can even achieve plug-and-play, near-zero coupling loss optical interconnection and optical modulation. It has a fast modulation speed, low cost, and high modulation bandwidth, can be applied to the needs of high-integration fields, and can reduce the complexity and cost of the modulation system.

[0009] The modulation theory of the electro-optic modulator can be attributed to the plasma dispersion effect, that is, the effect of adjusting the real and imaginary parts of the material's refractive index by changing the concentration of electrons and holes, thereby causing changes in the properties of the transmitted light waves. The specific formula is as follows:

[0010] Δn=Δn e +Δn h

[0011] Δα=Δα e +Δα h

[0012] In the above formula: Δn and Δα are the real and imaginary changes of the refractive index respectively; Δn e and Δn h are the changes in the real part of the refractive index caused by electrons and holes respectively; Δα e and Δα h They are the changes in the imaginary part of the refractive index caused by electrons and holes, respectively. It can be seen that for the above electro-optic modulator, the carrier concentration of the heterojunction (usually a PN junction) can be adjusted by changing the voltage to achieve refractive index modulation, thereby completing the conversion of electrical signals into optical signals.

[0013] Specifically, when the heterojunction works in reverse bias mode, the depletion region in the heterojunction increases, the built-in electric field is enhanced, there are no free carriers in the depletion region, the real part of the refractive index of the material increases, and the imaginary part decreases. This carrier depletion type structure can achieve high modulation speed and meet the needs of high-speed optical modules.

[0014] In addition, the electro-optic modulator also includes a micro-nano optical fiber containing an optical fiber micro-ring, which acts as a micro-ring resonator. R It can be expressed as the following formula:

[0015] mλ R =2πRn

[0016] Where m is the interference order, R is the radius of the fiber microring, and n is the fiber refractive index. The above electric field will cause a perturbation to the resonant wavelength by affecting n, causing it to shift. Compared with waveguides, the coupling of fiber microrings has a higher coupling coefficient, lower coupling loss and lower cost.

[0017] In some embodiments of the present invention, the diameter of the optical fiber microring is 0.2 mm to 2 mm. Further, the diameter of the optical fiber microring can be 0.5 mm to 1.5 mm, 0.8 mm to 1.2 mm, 1 mm to 2 mm, or 1 mm to 1.5 mm.

[0018] In some embodiments of the present invention, the middle optical fiber is an optical fiber micro-ring with a ring structure.

[0019] In some embodiments of the present invention, the heterojunction includes a black phosphorus layer and a molybdenum disulfide layer, one end of the black phosphorus layer is in contact with one end of the molybdenum disulfide layer; the source electrode and the drain electrode are respectively arranged at the other end of the black phosphorus layer and the other end of the molybdenum disulfide layer. Specifically, when the heterojunction is operated in a reverse bias mode, the drain electrode (set to a negative voltage) is generally arranged on the black phosphorus layer, and the source electrode (set to a voltage of 0) is arranged on the molybdenum disulfide layer; and when the heterojunction adopts a forward bias mode, it is only necessary to adjust the drain electrode voltage to a positive voltage.

[0020] In some embodiments of the present invention, the black phosphorus layer and the molybdenum disulfide layer are both single crystal layers.

[0021] The heterojunction is generally a PN junction, the black phosphorus layer may specifically be a P-type black phosphorus layer, and the molybdenum disulfide layer may be an N-type molybdenum disulfide layer.

[0022] The black phosphorus layer may specifically be a single crystal layer composed of black phosphorus nanosheets; and the molybdenum disulfide layer may be a single crystal layer composed of molybdenum disulfide nanosheets.

[0023] In some embodiments of the present invention, one end of the black phosphorus layer is overlapped with one end of the molybdenum disulfide layer.

[0024] In the heterojunction, the black phosphorus layer generally adopts a black phosphorus thin layer, and the molybdenum disulfide layer generally adopts a molybdenum disulfide thin layer. In some embodiments of the present invention, the thickness of the black phosphorus layer and / or the molybdenum disulfide layer is 5nm to 30nm. Furthermore, the thickness of the black phosphorus layer and / or the molybdenum disulfide layer may be 5nm to 10nm, 8nm to 12nm, 10nm to 20nm, 15nm to 25nm, 18nm to 26nm, 22nm to 28nm, etc.

[0025] In some embodiments of the present invention, the silicon substrate is selected from a P-type silicon substrate or an N-type silicon substrate.

[0026] In some embodiments of the present invention, the thickness of the silicon substrate is 300um-500um. Further, the thickness of the silicon substrate is 350um-450um, 320um-380um, 360um-420um, 400um-500um, 400um-450um, 420um-480um, 430um-470um, etc.

[0027] In some embodiments of the present invention, the resistivity of the silicon substrate is 1 Ω·cm to 10 Ω·cm.

[0028] In some embodiments of the present invention, the source electrode and / or the drain electrode is made of at least one of chromium, gold, titanium, silver, and tin. The source electrode and the drain electrode may be disposed on both ends of the heterojunction, respectively, or overlapped with both ends of the heterojunction.

[0029] In some embodiments of the present invention, the dielectric layer is a silicon dioxide dielectric layer. The thickness of the silicon dioxide dielectric layer can be controlled at 50nm to 300nm. Further, the thickness of the silicon dioxide dielectric layer can be 100nm to 250nm, 100nm to 200nm, 80nm to 160nm, 150nm to 250nm, 120nm to 240nm, etc. The thickness of the silicon dioxide dielectric layer will affect the size of the required gate voltage. For example, for a SiO2 dielectric layer with a thickness of 300nm, the gate voltage can be added to 60V. When the dielectric layer thickness is 50nm, 10V is enough, and so on.

[0030] In some embodiments of the present invention, the electro-optic modulator further includes a protective layer, which is disposed on the dielectric layer and covers the heterojunction, the electrode layer and the micro-nano optical fiber arrangement.

[0031] A second aspect of the present invention provides a method for preparing any of the above-mentioned electro-optical modulators, comprising the following steps:

[0032] The method comprises: providing a silicon substrate having a dielectric layer on its surface; preparing a heterojunction on the dielectric layer; and preparing a source electrode and a drain electrode at both ends of the heterojunction.

[0033] The optical fiber is subjected to a melt-tapering process to form a micro-nano optical fiber including an input optical fiber, a first tapered transition optical fiber, a middle optical fiber, a second tapered transition optical fiber and an output optical fiber connected in sequence; a ring-wrapping knotting operation is performed before or after the melt-tapering process to make the middle optical fiber have an optical fiber micro-ring with a ring structure;

[0034] The micro-nano optical fiber is transferred and fixed on the heterojunction, and the optical fiber micro ring is arranged in contact with the heterojunction.

[0035] The preparation method of the above electro-optic modulator is simple in process, and the constructed all-fiber electro-optic modulator has ultra-low loss and can simultaneously achieve high-speed modulation, low cost and high integration.

[0036] In some embodiments of the present invention, during the preparation of a field effect transistor, before setting a heterojunction on a dielectric layer carried on the surface of a silicon substrate, the silicon substrate with a dielectric layer carried on the surface can be cleaned. Specifically, it can be placed in an acetone solution and isopropanol for ultrasonic treatment in sequence, and then placed in deionized water for ultrasonic treatment, and then dried; wherein the ultrasonic treatment time can be controlled within 3 minutes to 5 minutes; the drying method can be blown dry with high-purity nitrogen.

[0037] In some embodiments of the present invention, during the preparation of a field effect transistor, a heterojunction is prepared on the dielectric layer, including: first using black phosphorus nanosheets to prepare a black phosphorus layer on the dielectric layer, and then using molybdenum disulfide nanosheets to prepare a molybdenum disulfide layer on the dielectric layer, and making one end of the molybdenum disulfide layer contact with one end of the black phosphorus layer to obtain a heterojunction.

[0038] In some embodiments of the present invention, the preparation of black phosphorus nanosheets and molybdenum disulfide nanosheets may be performed by mechanical stripping. Furthermore, in the process of preparing a field effect transistor, a heterojunction is prepared on the dielectric layer, which may specifically include: obtaining black phosphorus nanosheets by mechanical stripping, and then transferring them to the dielectric layer to form a black phosphorus layer; obtaining molybdenum disulfide nanosheets by mechanical stripping, and then transferring them to the dielectric layer to form a molybdenum disulfide layer; and contacting one end of the molybdenum disulfide layer with one end of the black phosphorus layer to obtain a heterojunction.

[0039] The black phosphorus nanosheets are obtained by mechanical stripping, and then transferred to the dielectric layer to form a black phosphorus layer. Specifically, it may include: taking a small amount of black phosphorus single crystals and sticking them to a tape (such as Scotch tape), repeatedly tearing them 10 to 20 times to obtain black phosphorus nanosheets, and then transferring the torn black phosphorus nanosheets to a flexible polymer film, and then transferring the black phosphorus nanosheets on the flexible polymer film to the dielectric layer. Among them, the use of a flexible polymer film to assist in the transfer of black phosphorus nanosheets is convenient to operate and is not easy to leave residual glue. The flexible polymer film can be a polydimethylsiloxane (PDMS) film.

[0040] The preparation of the molybdenum disulfide layer can be carried out by using a molybdenum disulfide single crystal and following a similar operation to the black phosphorus layer. Specifically, it may include taking a small amount of the molybdenum disulfide single crystal and sticking it to a tape, tearing it repeatedly 10 to 20 times to obtain a molybdenum disulfide nanosheet, then transferring the torn molybdenum disulfide nanosheet to a flexible polymer film, then transferring the molybdenum disulfide nanosheet on the flexible polymer film to a dielectric layer to form a molybdenum disulfide layer, and making one end of the molybdenum disulfide layer contact one end of the black phosphorus layer.

[0041] In some embodiments of the present invention, the molybdenum disulfide layer and the black phosphorus layer may be overlapped. Specifically, one end of the molybdenum disulfide layer may be overlapped on one end of the black phosphorus layer.

[0042] In some embodiments of the present invention, a heterojunction is prepared on a dielectric layer, and black phosphorus nanosheets may be first grown on the surface of the dielectric layer by chemical vapor deposition to form a black phosphorus layer; then molybdenum disulfide nanosheets are grown on the dielectric layer by chemical vapor deposition to form a molybdenum disulfide layer, and one end of the molybdenum disulfide layer is brought into contact with one end of the black phosphorus layer to form a heterojunction.

[0043] In some embodiments of the present invention, a source electrode and a drain electrode are prepared at both ends of a heterojunction, which may specifically include: firstly disposing a photoresist layer covering the heterojunction on the dielectric layer, and then forming a predetermined electrode pattern by photolithography through exposure and development; evaporating a conductive layer by thermal evaporation, and then removing the photoresist layer and the conductive layer in the un-photolithographic area to obtain an electrode layer including a source electrode and a drain electrode, wherein the structure of the electrode layer corresponds to the predetermined electrode pattern.

[0044] The photoresist layer can be provided by spin coating, and the spin coating speed can be controlled at 2000 rpm to 4000 rpm. After the photoresist is spin coated, it is generally necessary to perform a drying process, and the drying process temperature can be controlled at 50° C. to 180° C., and the drying process time can be controlled at 1 min to 5 min. The photoresist can be specifically polymethyl methacrylate (PMMA).

[0045] The photoresist layer and the conductive layer in the unlithographic area can be removed by soaking the sample with the evaporated conductive layer in acetone, and then heating it to promote the reaction and removal efficiency of acetone and photoresist, and then taking it out and drying it. The temperature of the heating treatment can be controlled at 30℃~50℃, and the time can be controlled at 10min~30min; the drying method can be blown with high-purity nitrogen.

[0046] In some embodiments of the present invention, in the process of preparing micro-nano optical fiber, the optical fiber can be a single-mode optical fiber. The preparation of micro-nano optical fiber can specifically include: removing the protective layer in the middle of the single-mode optical fiber to obtain a bare optical fiber segment, and then performing a melt-tapering process on the bare optical fiber segment. The melt-tapering process can specifically be performed by heating the bare optical fiber segment until it is melted, and at the same time, slowly pulling the two ends of the bare optical fiber segment with a uniform and small force, so that the diameter of the melted bare optical fiber segment gradually decreases, forming a micro-nano optical fiber including an input optical fiber, a first tapered transition optical fiber, a middle optical fiber, a second tapered transition optical fiber and an output optical fiber connected in sequence. Among them, the method of heating the bare optical fiber segment can be uniformly heated by the outer flame of an alcohol lamp; the diameter of the middle optical fiber segment of the micro-nano optical fiber can be controlled to be 8um to 12um.

[0047] In the process of preparing micro-nano optical fiber, a ring-wrapping knotting operation is performed before or after the melt-drawing taper treatment, so that the middle optical fiber has an optical fiber micro-ring with a ring structure. Since the optical fiber in the cone region is thinner after the melt-drawing taper treatment, the ring-wrapping knotting operation after the melt-drawing taper is easy to break the optical fiber in the cone region, so it is preferred to perform the ring-wrapping knotting operation before the melt-drawing taper treatment.

[0048] According to a third aspect of the present invention, a modulation test system is proposed, comprising a laser source, a polarizer, a polarization controller, an electro-optic modulator and a spectrum analyzer which are connected in sequence; the electro-optic modulator is any one of the aforementioned electro-optic modulators, and the input optical fiber and the output optical fiber in the electro-optic modulator are respectively connected to the polarization controller and the spectrum analyzer; the modulation test system is at least used to test the modulation efficiency of the electro-optic modulator.

[0049] The modulation test system can be used in conjunction with a semiconductor feature analyzer and its supporting probe platform. In some embodiments, the modulation test system may also include a semiconductor feature analyzer and a probe platform supporting the semiconductor feature analyzer, the probe platform including a first probe, a second probe and a third probe; one end of the first probe and the second probe are respectively connected to the ground (GND) source port and the first output (SUM1) source port of the semiconductor feature analyzer through a three-coaxial cable, and the other end of the first probe and the second probe are respectively connected to the source electrode and the drain electrode on the electro-optic modulator; one end of the third probe is connected to the second output (SUM2) source port of the semiconductor feature analyzer through a three-coaxial cable, and the other end is connected to the silicon substrate on the electro-optic modulator, and the semiconductor feature analyzer is at least used to apply voltage to the electro-optic modulator, so as to control the amplitude (or intensity) and phase of the light wave by regulating the voltage, so as to realize the modulation efficiency test of the electro-optic modulator.

[0050] In a fourth aspect of the present invention, a modulation test system is proposed, comprising a laser, a polarizer, a polarization controller, an electro-optic modulator, a photodetector and an oscilloscope connected in sequence; the electro-optic modulator is any one of the aforementioned electro-optic modulators, and the input optical fiber and the output optical fiber in the electro-optic modulator are respectively connected to the polarization controller and the photodetector; and also includes a signal generator, which is connected to the electro-optic modulator and is used to apply a voltage to the electro-optic modulator; the modulation test system is used to test the modulation speed of the electro-optic modulator.

[0051] The signal generator is used as an output voltage, generally with one port output. If the signal generator is set to output a positive voltage, it is connected to the source electrode of the electro-optical modulator, and the drain electrode of the electro-optical modulator is grounded; if the signal generator is set to output a negative voltage, it is connected to the drain electrode of the electro-optical modulator, and the source electrode of the electro-optical modulator is grounded. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0053] Figure 1 is a flow chart of the method for preparing the electro-optic modulator in Example 1;

[0054] Figure 2 The preparation flow chart of the micro-nano optical fiber in Example 1;

[0055] Figure 3 A schematic diagram of the structure of the electro-optic modulator prepared in Example 1;

[0056] Figure 4 Schematic diagram of the structure of the modulation test system in Example 2;

[0057] Figure 5 This is a diagram showing the modulation efficiency test results of the electro-optic modulator by the modulation test system in Example 2;

[0058] Figure 6 This is a schematic diagram of the structure of the modulation test system of Example 3. DETAILED DESCRIPTION

[0059] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0060] Example 1

[0061] A method for preparing an electro-optic modulator, referring to Figure 1 , including the following steps:

[0062] S1, providing a silicon substrate 11 with a dielectric layer 12 on its surface. The process includes: using a silicon wafer cutter to cut a commercial standard 4-inch p-type doped single-throw silicon oxide wafer into 1×1 cm 2 The single-throw silicon oxide wafer comprises a silicon substrate 11 and a silicon dioxide (SiO2) dielectric layer supported on the surface of the silicon substrate, wherein the thickness of the silicon substrate 11 is 300-500um, the resistivity of the silicon substrate is 1-10Ω·cm, and the thickness of the SiO2 dielectric layer is 300nm. The cut silicon oxide wafer is then cleaned, specifically, it is sequentially ultrasonicated with acetone solution and isopropanol for 3-5 minutes, then ultrasonicated with deionized water for 5 minutes, and then quickly blown dry with high-purity nitrogen for standby use.

[0063] S2, prepare a two-dimensional material field effect transistor. It includes: taking a small amount of black phosphorus single crystal and sticking it to a tape (such as Scotch tape), repeatedly tearing it 10 to 20 times to obtain a black phosphorus nanosheet 131, then transferring the torn black phosphorus nanosheet 131 to a PDMS film 132, and then transferring the black phosphorus nanosheet 131 on the PDMS film 132 to the silicon dioxide dielectric layer loaded on the surface of the silicon substrate 11 obtained in step S1 to form a black phosphorus layer 133; repeating the above operation for a molybdenum disulfide single crystal, specifically, taking a small amount of disulfide The molybdenum disulfide single crystal is adhered to the Scotch tape and torn repeatedly for 10 to 20 times to obtain the molybdenum disulfide nanosheet 134, and then the torn molybdenum disulfide nanosheet 134 is transferred to the PDMS film 132, and then the molybdenum disulfide nanosheet 134 on the PDMS film 132 is transferred to the dielectric layer 12, and about 2 / 3 of the area of ​​the black phosphorus layer 133 is pressed to form a molybdenum disulfide layer 135, which forms a heterojunction 13 with the black phosphorus layer 133, that is, a black phosphorus / molybdenum disulfide heterojunction.

[0064] Then, a layer of photoresist PMMA (A4) covering the heterojunction 13 is spin-coated on the surface of the dielectric layer 12 carried on the surface of the silicon substrate 11, with a rotation speed of 3000 rpm, and baked on a heating plate for 5 minutes, and the drying temperature is 120°C to form a photoresist layer 141. Further, the sample coated with the photoresist layer 141 is subjected to electron beam exposure, and a specific electrode pattern is obtained through a development process. Then, a 5nm chromium layer 142 and a 40nm gold layer 143 are successively evaporated by a thermal evaporation method to form a chromium / gold composite conductive layer. Finally, the sample with the chromium / gold composite conductive layer evaporated is immersed in acetone, and placed on a heating plate for heating for 20 minutes, wherein the temperature of the heating plate is set to 50°C, and finally the sample is taken out and quickly blown dry with high-purity nitrogen, and a source electrode and a drain electrode are prepared at both ends of the black phosphorus / molybdenum disulfide heterojunction to form an electrode layer 14.

[0065] S3, preparing micro-nano optical fiber 15. Figure 2 As shown, it includes: cutting off a section of commercial SMF28e optical fiber (50-70cm), and stripping off a section of protective layer (3cm-5cm) in the middle of the optical fiber. Since it is easy to break the cone area after melting and tapering, the optical fiber is pre-knotted into a ring with a diameter of 5cm-10cm, so that the optical fiber stripped of the protective layer is in the ring. Furthermore, hold both ends of the optical fiber stripped of the protective layer with both hands, as shown in FIG. Figure 2 As shown in (a), use the outer flame of an alcohol lamp to uniformly heat the area where the protective layer is stripped to slowly melt the optical fiber. At the same time, pull it outwards with both hands evenly and with a small force until a tapered area of ​​optical fiber with a diameter of about 10μm and a length of 3cm to 6cm is pulled out. Figure 2 Finally, the fiber ring is shrunk toward the middle, and finally a fiber micro ring with a diameter of 1 mm to 2 mm in the fiber cone region is pulled out to obtain a micro-nano fiber 15, as shown in FIG. Figure 2As shown in (c), the micro-nano optical fiber 15 includes an input optical fiber 151, a first tapered transition optical fiber 152, a middle optical fiber 153, a second tapered transition optical fiber 154 and an output optical fiber 155 which are connected in sequence, wherein the middle optical fiber 153 has an optical fiber micro-ring with a ring structure.

[0066] S4, placing the micro-nano optical fiber 15 obtained in step S3 on the two-dimensional material field effect transistor obtained in step S2. Specifically, the input optical fiber 151 and the output optical fiber 155 at both ends of the micro-nano optical fiber 15 are first supported and fixed with a glass slide, and the optical fiber microring of the middle optical fiber 153 is hollowed out; the two-dimensional material field effect transistor is placed below the optical fiber microring, and the support sheet with the PDMS film layer 16 is suspended above the optical fiber microring. Then, the position of the PDMS film layer 16, the optical fiber microring and the two-dimensional material field effect transistor is observed and adjusted using a microscopic transfer platform, until the optical fiber microring of the micro-nano optical fiber 15 is finally transferred to the two-dimensional material field effect transistor for contact, and the PDMS film layer 16 plays a role in fixing and protecting, and an electro-optic modulator is obtained.

[0067] See also Figure 2 , Figure 3 , the electro-optic modulator includes a field effect transistor and a micro-nano optical fiber 15; wherein the field effect transistor includes a silicon substrate 11, a dielectric layer 12, a heterojunction 13 and an electrode layer 14; in this embodiment, the dielectric layer 12 is a silicon dioxide dielectric layer, the heterojunction 13 is composed of a black phosphorus layer 133 and a molybdenum disulfide layer 135, and one end of the black phosphorus layer 133 is overlapped with one end of the molybdenum disulfide layer 135; the electrode layer 14 includes a source electrode and a drain electrode arranged at both ends of the heterojunction 13, specifically, the source electrode and the drain electrode are arranged at the other end of the black phosphorus layer 133 and the other end of the molybdenum disulfide layer 135 respectively; the micro-nano optical fiber 15 includes an input optical fiber 151, a first tapered transition optical fiber 152, a middle optical fiber 153, a second tapered transition optical fiber 154 and an output optical fiber 155 connected in sequence; the middle optical fiber 153 is an optical fiber microring with an annular structure, which is fixed on the heterojunction 13. In addition, the electro-optic modulator also includes a protective layer ( Figure 3 The protective layer is disposed on the dielectric layer 12 and covers the heterojunction 13, the electrode layer 14 and the micro-nano optical fiber 15. In other embodiments, the protective layer may be omitted.

[0068] Example 2

[0069] A modulation test system, such as Figure 4 As shown, it includes a laser source, a polarizer, a polarization controller, an electro-optic modulator and a spectrum analyzer which are connected in sequence. In this embodiment, the electro-optic modulator specifically adopts the electro-optic modulator prepared in Example 1, and the input optical fiber and the output optical fiber in the electro-optic modulator are respectively connected to the polarization controller and the spectrum analyzer; the modulation test system is used to test the modulation efficiency of the electro-optic modulator.

[0070] When in use, the modulation test system can be used in conjunction with a semiconductor characteristic analyzer and its matching probe platform. Specific test methods include:

[0071] (1) Turn on the laser source and set the parameters of the spectrum analyzer (such as central wavelength, scanning range, test accuracy, etc.) until an interference spectrum pattern appears, and then adjust the polarization controller to maximize the extinction ratio of the interference spectrum pattern;

[0072] (2) Place the electro-optic modulator on the probe platform of the semiconductor characteristic analyzer, and find the exact position of the electro-optic modulator on the silicon wafer through the matching CCD imaging system;

[0073] (3) Select two probes from the probe station to connect the source electrode and drain electrode of the electro-optic modulator respectively, and select another probe to connect the silicon substrate to serve as the back gate electrode of the electro-optic modulator;

[0074] (4) Open the semiconductor characteristic analyzer test software, connect the probe of the drain electrode, select the voltage bias mode, the range is -2V to 2V, the step size is 0.5V, set the source voltage to 0V, and the gate voltage to 0V;

[0075] (5) Run the test software and observe the spectrum analyzer to obtain the optical test graphs of the electro-optic modulator under the bias voltages of -2V, -1.5V, -1V, -0.5V, and 0V, and obtain the intensity modulation test results of the electro-optic modulator. Figure 5 As shown in (a).

[0076] (6) Select the voltage bias mode for the probe connected to the drain electrode, set it to -0.5V, set the source voltage to 0V, and the gate voltage to -60V~60V with a step size of 20V.

[0077] (7) Run the test software and observe the spectrum analyzer to obtain the optical test graphs of the electro-optic modulator under the conditions of gate voltages of 0 V, 20 V, 40 V, and 60 V. Specifically, the phase modulation test results of the electro-optic modulator are as follows: Figure 5 As shown in (b).

[0078] Depend on Figure 5It can be seen that the electro-optic modulator shows regular intensity and phase shift under different DC bias and gate voltage, achieving the modulation effect, that is, the above electro-optic modulator can adjust the intensity and phase of the light wave by voltage regulation. The working principle of the modulation test system is: due to the resonance of the optical fiber microring in the electro-optic modulator, the interference spectrum is observed on the spectrum analyzer. After the optical fiber is stripped and tapered, the light wave transmitted in it will have some evanescent field leakage, which is conducive to the interaction with the field effect transistor. Based on this, when a voltage is applied to the field effect transistor, it will cause a change in the carrier concentration and the change in the width of the depletion region, resulting in a change in the refractive index (plasma scattering effect). Therefore, the light transmitted in the optical fiber will be regulated by the external voltage, and finally manifested as the movement of the interference spectrum in the spectrum.

[0079] Example 3

[0080] A modulation test system, such as Figure 6 As shown, the modulation test system includes a laser source, a polarizer, a polarization controller, an electro-optic modulator, a photodetector and an oscilloscope which are connected in sequence. In this embodiment, the electro-optic modulator specifically adopts the electro-optic modulator prepared in Example 1, and the input optical fiber and the output optical fiber in the electro-optic modulator are respectively connected to the polarization controller and the photodetector; the modulation test system also includes a signal generator, which is connected to the electro-optic modulator and is used to apply a voltage to the electro-optic modulator, and obtain the response speed of the electro-optic modulator by adjusting the frequency of the signal generator.

[0081] As described above, the electro-optic modulator of the present invention is an all-optical electro-optic modulator based on an all-optical fiber, and has a simple coupling method. It replaces the traditional cross-section coupling or grating coupling by optical fiber-to-optic fiber optical field coupling, thereby avoiding the problem of mode field matching, and even realizing plug-and-play, optical interconnection and optical modulation with near-zero coupling loss. It has a fast modulation speed, low cost, and high modulation bandwidth, and can be applied to the needs of high-integration fields, and can reduce the complexity and cost of the modulation system.

[0082] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. An electro-optic modulator, characterized in that: include: A field effect transistor comprises a silicon substrate, a dielectric layer, a heterojunction and an electrode layer which are stacked in sequence; the electrode layer comprises a source electrode and a drain electrode, and the source electrode and the drain electrode are respectively arranged at two ends of the heterojunction; The micro-nano optical fiber comprises an input optical fiber, a first tapered transition optical fiber, a middle optical fiber, a second tapered transition optical fiber and an output optical fiber which are connected in sequence. The middle optical fiber has an optical fiber micro-ring with an annular structure, and the optical fiber micro-ring is arranged on the heterojunction.

2. The electro-optic modulator according to claim 1, characterized in that The heterojunction includes a black phosphorus layer and a molybdenum disulfide layer, one end of the black phosphorus layer is in contact with one end of the molybdenum disulfide layer; the source electrode and the drain electrode are respectively arranged at the other end of the black phosphorus layer and the other end of the molybdenum disulfide layer.

3. The electro-optic modulator according to claim 2, characterized in that The thickness of the black phosphorus layer and / or the molybdenum disulfide layer is 5nm to 30nm; And / or, the black phosphorus layer and the molybdenum disulfide layer are single crystal layers.

4. The electro-optic modulator according to claim 1, characterized in that The silicon substrate satisfies at least one of the following conditions: The silicon substrate is selected from a P-type silicon substrate or an N-type silicon substrate; The thickness of the silicon substrate is 300um to 500um; The resistivity of the silicon substrate is 1 Ω·cm to 10 Ω·cm.

5. The electro-optic modulator according to any one of claims 1 to 4, characterized in that: The material of the source electrode and / or the drain electrode is at least one of chromium, gold, titanium, silver, and tin; And / or, the dielectric layer is a silicon dioxide dielectric layer.

6. The electro-optic modulator according to any one of claims 1 to 4, characterized in that: It also includes a protective layer, which is arranged on the dielectric layer and covers the heterojunction, the electrode layer and the micro-nano optical fiber arrangement.

7. The method for preparing the electro-optic modulator according to any one of claims 1 to 6, comprising the following steps: The method comprises: providing a silicon substrate having a dielectric layer on its surface; preparing a heterojunction on the dielectric layer; and preparing a source electrode and a drain electrode at both ends of the heterojunction. The optical fiber is subjected to a melt-tapering process to form a micro-nano optical fiber including an input optical fiber, a first tapered transition optical fiber, a middle optical fiber, a second tapered transition optical fiber and an output optical fiber connected in sequence; a ring-wrapping knotting operation is performed before or after the melt-tapering process to make the middle optical fiber have an optical fiber micro-ring with a ring structure; The micro-nano optical fiber is transferred and fixed on the heterojunction, and the optical fiber micro ring is arranged in contact with the heterojunction.

8. The method for preparing an electro-optic modulator according to claim 7, characterized in that: In the process of preparing a field effect transistor, a heterojunction is prepared on the dielectric layer, including: first using black phosphorus nanosheets to prepare a black phosphorus layer on the dielectric layer; using molybdenum disulfide nanosheets to prepare a molybdenum disulfide layer on the dielectric layer, and making one end of the molybdenum disulfide layer contact with one end of the black phosphorus layer to obtain a heterojunction.

9. A modulation test system, characterized in that: It comprises a laser light source, a polarizer, a polarization controller, an electro-optic modulator and a spectrum analyzer which are connected in sequence; the electro-optic modulator is the electro-optic modulator according to any one of claims 1 to 6, the input optical fiber and the output optical fiber in the electro-optic modulator are respectively connected to the polarization controller and the spectrum analyzer; the modulation test system is at least used to test the modulation efficiency of the electro-optic modulator.

10. A modulation test system, characterized in that: The invention comprises a laser, a polarizer, a polarization controller, an electro-optic modulator, a photodetector and an oscilloscope which are connected in sequence; the electro-optic modulator is the electro-optic modulator according to any one of claims 1 to 6, the input optical fiber and the output optical fiber in the electro-optic modulator are respectively connected to the polarization controller and the photodetector; the invention also comprises a signal generator which is connected to the electro-optic modulator and is used to apply a voltage to the electro-optic modulator; the modulation test system is used to test the modulation speed of the electro-optic modulator.

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