Electro-optic modulator, method of making and modulation test system therefor

Abstract

The application discloses an electro-optical modulator, a preparation method thereof and a modulation test system, and relates to the technical field of optical communication. 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 arranged at two ends of the heterojunction respectively. 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 sequentially connected. The middle optical fiber has a fiber micro-ring with a ring structure, and the fiber micro-ring is arranged on the heterojunction. The electro-optical modulator is a full-fiber electro-optical modulator, and the coupling mode is simple. The electro-optical modulator replaces traditional section coupling or grating coupling with fiber-fiber light field coupling, thereby avoiding the problem of mode field matching. Evenly, the electro-optical modulator can realize plug-and-play, near-zero coupling loss optical interconnection and optical modulation. The electro-optical modulator has the advantages of fast modulation speed, low cost, high modulation bandwidth and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electro-optical modulation, and in particular to an electro-optical modulator, a preparation method thereof and a modulation test system. BACKGROUND

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

[0003] However, at present, when the electro-optical modulator is used in a system such as optical fiber communication, optical transmission coupling between the electro-optical modulator and the optical fiber is required. The coupling between the electro-optical modulator and the optical fiber is usually realized by end face coupling and grating coupling. These advanced coupling technologies can reduce the coupling loss, i.e. reduce the insertion loss, but these coupling methods require very precise alignment operation and packaging process, thereby increasing the cost. In addition, after precise coupling, the coupling loss is still high, which will inevitably lead to problems such as attenuation of optical signal transmission intensity, decrease of modulation efficiency and reduction of modulation bandwidth. Therefore, it is of great significance to develop an electro-optical modulator with simpler coupling method and lower coupling loss. SUMMARY

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

[0005] In a first aspect of the present application, an electro-optical modulator is provided, comprising:

[0006] 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, 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 connected in sequence, and the middle optical fiber has a fiber micro-ring with a ring structure, and the fiber micro-ring is arranged on the heterojunction.

[0008] According to the electro-optical modulator, the following advantages are achieved: the electro-optical modulator is a full-fiber-based electro-optical modulator, the coupling mode is simple, the traditional end-face coupling or grating coupling is replaced by fiber-fiber light field coupling, so that the mode field matching problem is avoided, and even plug-and-play, near-zero coupling loss optical interconnection and optical modulation can be realized, the modulation speed is fast, the cost is low, the modulation bandwidth is high, the electro-optical modulator can be applied to the demand of high integration field, and the complexity and cost of the modulation system can be reduced.

[0009] The modulation theory of the electro-optical modulator can be attributed to the plasmonic dispersion effect, that is, the effect of adjusting the real part and the imaginary part of the refractive index of the material by changing the electron and hole concentration, thereby causing the change of the properties of the transmitted light wave. Specifically, the following formula is used:

[0010] Δn = Δn e + Δn h

[0011] Δα = Δα e + Δα h

[0012] In the above formula, Δn and Δα are the changes of the real part and the imaginary part of the refractive index, respectively; Δn e and Δn h are the changes of the real part of the refractive index caused by the electrons and holes, respectively; Δα e and Δα h are the changes of the imaginary part of the refractive index caused by the electrons and holes, respectively. It can be seen that for the above electro-optical modulator, the carrier concentration of the heterojunction (generally a PN junction) can be adjusted by changing the voltage to realize refractive index modulation, and then the conversion from electrical signal to optical signal is completed.

[0013] Specifically, when the heterojunction works in the reverse bias mode, the depletion region in the heterojunction increases, the built-in electric field is enhanced, there is no free carrier 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 realize high modulation speed and meet the demand of high-speed optical modules.

[0014] In addition, the electro-optical modulator further comprises a micro-nano optical fiber comprising a fiber micro-ring, which functions as a micro-ring resonator. The resonance peak λ R of the micro-ring resonator can be expressed in the following formula:

[0015] mλ R = 2πRn

[0016] where m is the interference order, R is the radius of the fiber micro-ring, and n is the refractive index of the fiber. The above electric field will cause perturbation to the resonance wavelength by affecting n, resulting in a shift. The coupling of the fiber micro-ring has a higher coupling coefficient, lower coupling loss and lower cost compared with the waveguide.

[0017] In some embodiments of the present application, the diameter of the fiber micro-ring is 0.2mm-2mm. Further, the diameter of the fiber micro-ring can be 0.5mm-1.5mm, 0.8mm-1.2mm, 1mm-2mm or 1mm-1.5mm.

[0018] In some embodiments of the present application, the middle fiber is a fiber micro-ring in a ring structure.

[0019] In some embodiments of the present application, the heterojunction comprises 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 working in the heterojunction reverse bias mode, the drain electrode (set to negative voltage) is generally arranged on the black phosphorus layer, and the source electrode (set to 0 voltage) is arranged on the molybdenum disulfide layer; while in the heterojunction positive bias mode, only the drain electrode voltage needs to be adjusted to positive voltage.

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

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

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

[0023] In some embodiments of the present application, 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 application, the thickness of the black phosphorus layer and / or the molybdenum disulfide layer is 5nm-30nm. Further, the thickness of the black phosphorus layer and / or the molybdenum disulfide layer can be 5nm-10nm, 8nm-12nm, 10nm-20nm, 15nm-25nm, 18nm-26nm, 22nm-28nm, etc.

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

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

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

[0028] In some embodiments of the present application, the material of the source electrode and / or the drain electrode is at least one of chromium, gold, titanium, silver, and tin. The source electrode and the drain electrode can be respectively arranged on or overlapped with the two ends of the heterojunction.

[0029] In some embodiments of the present application, the dielectric layer is a silicon dioxide dielectric layer. The thickness of the silicon dioxide dielectric layer can be controlled to be 50-300 nm, further, the thickness of the silicon dioxide dielectric layer can be 100-250 nm, 100-200 nm, 80-160 nm, 150-250 nm, 120-240 nm, etc. The thickness of the silicon dioxide dielectric layer will affect the size of the required gate voltage. For example, the gate voltage can be added to 60 V when the thickness of the SiO2 dielectric layer is 300 nm, and 10 V when the thickness of the dielectric layer is 50 nm, and so on in proportion.

[0030] In some embodiments of the present application, the electro-optical modulator further comprises a protective layer arranged on the dielectric layer and covering the heterojunction, the electrode layer, and the micro-nano optical fiber.

[0031] In a second aspect of the present application, a preparation method of any of the above-mentioned electro-optical modulators is provided, comprising the following steps:

[0032] The preparation of the field effect transistor comprises: providing a silicon substrate with a dielectric layer loaded on the surface; preparing a heterojunction on the dielectric layer; and preparing a source electrode and a drain electrode on the two ends of the heterojunction.

[0033] The optical fiber is subjected to a fusion tapering treatment to form a micro-nano optical fiber comprising 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; and a fiber micro-ring with a ring structure is formed by a splicing operation before or after the fusion tapering treatment.

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

[0035] The above-mentioned method for fabricating electro-optic modulators is simple, and the resulting 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, before setting a heterojunction on the dielectric layer loaded on the surface of the silicon substrate during the fabrication of the field-effect transistor, the silicon substrate with the dielectric layer loaded on the surface can be cleaned first. Specifically, it can be ultrasonically treated in acetone solution and isopropanol in sequence, then ultrasonically treated in deionized water, and then dried. The ultrasonic treatment time can be controlled within 3 min to 5 min. The drying method can be high-purity nitrogen gas blowing.

[0037] In some embodiments of the present invention, during the fabrication of a field-effect transistor, a heterojunction is fabricated on the dielectric layer, comprising: firstly, a black phosphorus layer is fabricated on the dielectric layer using black phosphorus nanosheets, and then a molybdenum disulfide layer is fabricated on the dielectric layer using molybdenum disulfide nanosheets, and one end of the molybdenum disulfide layer is brought into contact with one end of the black phosphorus layer to obtain a heterojunction.

[0038] In some embodiments of the present invention, black phosphorus nanosheets and molybdenum disulfide nanosheets can be prepared by mechanical exfoliation. Furthermore, in the process of fabricating a field-effect transistor, the fabrication of a heterojunction on the dielectric layer can specifically include: obtaining black phosphorus nanosheets by mechanical exfoliation and then transferring them to the dielectric layer to form a black phosphorus layer; obtaining molybdenum disulfide nanosheets by mechanical exfoliation 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] Black phosphorus nanosheets are obtained by mechanical exfoliation and then transferred to the dielectric layer to form a black phosphorus layer. Specifically, this process may include: taking a small amount of black phosphorus single crystals and adhering them to adhesive tape (such as Scotch tape), repeatedly tearing them 10-20 times to obtain black phosphorus nanosheets, then transferring the torn black phosphorus nanosheets to a flexible polymer film, and finally transferring the black phosphorus nanosheets from the flexible polymer film to the dielectric layer. Using a flexible polymer film to assist in the transfer of black phosphorus nanosheets is convenient and minimizes adhesive residue. The flexible polymer film can be a polydimethylsiloxane (PDMS) film.

[0040] The molybdenum disulfide layer can be prepared using molybdenum disulfide single crystals, following a similar procedure to that used for the black phosphorus layer. Specifically, a small amount of molybdenum disulfide single crystal can be adhered to adhesive tape, repeatedly torn 10-20 times to obtain molybdenum disulfide nanosheets. These nanosheets are then transferred to a flexible polymer film, and finally transferred from the flexible polymer film to a dielectric layer to form the molybdenum disulfide layer, with one end of the molybdenum disulfide layer in contact with 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 configured to overlap. Specifically, one end of the molybdenum disulfide layer may overlap one end of the black phosphorus layer.

[0042] In some embodiments of the present invention, the heterojunction can be prepared on the dielectric layer by first growing black phosphorus nanosheets on the surface of the dielectric layer by chemical vapor deposition to form a black phosphorus layer; then growing molybdenum disulfide nanosheets on the dielectric layer by chemical vapor deposition to form a molybdenum disulfide layer, and making one end of the molybdenum disulfide layer contact one end of the black phosphorus layer to form a heterojunction.

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

[0044] The photoresist layer can be applied by spin coating, with the spin coating speed controlled between 2000 rpm and 4000 rpm. After spin coating, the photoresist generally needs to be dried. The drying temperature can be controlled between 50℃ and 180℃, and the drying time can be controlled between 1 min and 5 min. Polymethyl methacrylate (PMMA) can be used as the photoresist.

[0045] To remove the photoresist and conductive layers from the un-photolithographic areas, the sample with the deposited conductive layer can be immersed in acetone and then heated to promote the reaction between the acetone and the photoresist, thus improving the removal efficiency. Afterward, it should be removed and dried. The heating temperature can be controlled between 30℃ and 50℃, and the time between 10 min and 30 min. Drying can be done using high-purity nitrogen gas.

[0046] In some embodiments of the present invention, the fabrication process of micro / nano optical fibers may employ single-mode optical fibers. Specifically, the fabrication of micro / nano optical fibers may include: removing the protective layer in the middle of the single-mode optical fiber to obtain a bare fiber segment, and then performing a fused tapering process on the bare fiber segment. The fused tapering process may specifically involve heating the bare fiber segment until it melts, while simultaneously and slowly pulling both ends of the bare fiber segment with a uniform, small force. The diameter of the molten bare fiber segment gradually decreases, forming a micro / nano optical fiber comprising an input fiber, a first tapered transition fiber, a middle fiber, a second tapered transition fiber, and an output fiber connected in sequence. The bare fiber segment may be heated uniformly using the outer flame of an alcohol lamp; the diameter of the middle fiber segment of the micro / nano optical fiber can be controlled to be 8 μm to 12 μm.

[0047] During the preparation of the micro-nano optical fiber, a loop knotting operation is performed before or after the melting and tapering process, so that the middle optical fiber has an optical fiber micro-ring with an annular structure. Since the optical fiber in the tapered area is thinner after the melting and tapering process, it is easy to break the optical fiber in the tapered area during the loop knotting after melting and tapering. Therefore, it is preferred to perform the loop knotting operation before the melting and tapering process.

[0048] In the third aspect of the present invention, a modulation test system is proposed, which includes a laser source, a polarizer, a polarization controller, an electro-optic modulator, and a spectrum analyzer connected in sequence; the electro-optic modulator is any one of the foregoing 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] This modulation test system can be used in cooperation with a semiconductor characteristic analyzer and its supporting probe platform. In some embodiments, the modulation test system may also include a semiconductor characteristic analyzer and a probe platform supporting the semiconductor characteristic analyzer. The probe platform includes a first probe, a second probe, and a third probe; one ends 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 characteristic analyzer through a triaxial coaxial cable, and the other ends 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 characteristic analyzer through a triaxial coaxial cable, and the other end is connected to the silicon substrate on the electro-optic modulator. The semiconductor characteristic analyzer is at least used to apply a voltage to the electro-optic modulator 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 the fourth aspect of the present invention, a modulation test system is proposed, which includes 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 foregoing 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; a signal generator is further included, and the signal generator is connected to the electro-optic modulator and 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 to output a voltage. Generally, it outputs through one port. If the signal generator is set to output a positive voltage, it is connected to the source electrode of the electro-optic modulator, and the drain electrode of the electro-optic modulator is grounded; if the signal generator is set to output a negative voltage, it is connected to the drain electrode of the electro-optic modulator, and the source electrode of the electro-optic modulator is grounded. 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 This is a flowchart of the fabrication method of the electro-optic modulator in Example 1;

[0054] Figure 2 This is a flowchart illustrating the fabrication process of the micro / nano optical fiber in Example 1;

[0055] Figure 3 This is a schematic diagram of the electro-optic modulator fabricated in Example 1;

[0056] Figure 4 This is a schematic diagram of the modulation test system in Example 2;

[0057] Figure 5 The graph shows 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 modulation test system in Example 3. Detailed Implementation

[0059] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0060] Example 1

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

[0062] S1. A silicon substrate 11 with a dielectric layer 12 loaded on its surface is provided. This includes cutting a commercially available standard 4-inch p-type doped single-sided polished silicon oxide wafer into 1×1cm pieces using a wafer cutter. 2 The single-layer polished silicon oxide wafer comprises a silicon substrate 11 and a silicon dioxide (SiO2) dielectric layer loaded on the surface of the silicon substrate. The thickness of the silicon substrate 11 is 300–500 μm, the resistivity of the silicon substrate is 1–10 Ω·cm, and the thickness of the SiO2 dielectric layer is 300 nm. The cut silicon oxide wafer is then cleaned by sequentially passing it through an acetone solution and isopropanol, followed by ultrasonication for 3–5 minutes each, then ultrasonication with deionized water for 5 minutes, and finally rapid drying with high-purity nitrogen gas before use.

[0063] S2. Fabrication of a two-dimensional material field-effect transistor. This includes: taking a small amount of black phosphorus single crystal and attaching it to adhesive tape (such as Scotch tape), repeatedly tearing it 10-20 times to obtain black phosphorus nanosheets 131, then transferring the torn black phosphorus nanosheets 131 onto a PDMS film 132, and then transferring the black phosphorus nanosheets 131 on the PDMS film 132 onto 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 on molybdenum disulfide single crystal, specifically, taking a small amount of molybdenum disulfide... Molybdenum disulfide single crystals are adhered to Scotch tape and repeatedly torn 10-20 times to obtain molybdenum disulfide nanosheets 134. The torn molybdenum disulfide nanosheets 134 are then transferred to PDMS film 132, and then the molybdenum disulfide nanosheets 134 on PDMS film 132 are transferred to dielectric layer 12, pressing about 2 / 3 of the area of ​​black phosphorus layer 133 to form molybdenum disulfide layer 135. It and black phosphorus layer 133 form a heterojunction 13, namely black phosphorus / molybdenum disulfide heterojunction.

[0064] Then, a layer of photoresist PMMA (A4) covering the heterojunction 13 is spin-coated onto the dielectric layer 12 loaded on the silicon substrate 11 at a spin speed of 3000 rpm and baked on a hot plate for 5 minutes at a drying temperature of 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 5 nm chromium layer 142 and a 40 nm gold layer 143 are successively deposited by thermal evaporation to form a chromium / gold composite conductive layer. Finally, the sample with the deposited chromium / gold composite conductive layer is immersed in acetone and heated on a hot plate for 20 minutes at a temperature of 50°C. The sample is then removed and rapidly dried with high-purity nitrogen gas, forming source and drain electrodes at both ends of the black phosphorus / molybdenum disulfide heterojunction, constituting electrode layer 14.

[0065] S3, Fabrication of micro / nano optical fibers 15. For example... Figure 2 As shown, the process includes: cutting a section of commercial SMF28e optical fiber (50-70cm), and stripping a section of the protective layer (3-5cm) from the middle of the fiber. Since fusion tapering followed by knotting can easily break the taper area, the fiber is pre-knotted into a 5-10cm diameter loop, with the stripped fiber inside the loop. Further, the ends of the stripped fiber are held with both hands, as shown... Figure 2 As shown in (a), the area where the protective layer has been stripped is uniformly heated using the outer flame of an alcohol lamp to slowly melt the optical fiber. Simultaneously, the fiber is pulled outwards with gentle, even force by both hands until a tapered section of optical fiber with a diameter of approximately 10 μm and a length of 3 cm to 6 cm is drawn out. Figure 2 As shown in (b). Finally, the fiber loop is contracted towards the center, ultimately pulling out a fiber micro-loop with a diameter of 1mm to 2mm in the fiber taper region, resulting in micro / nano fiber 15, as shown. 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 connected in sequence, wherein the middle optical fiber 153 has an optical fiber micro-ring with a ring structure.

[0066] S4. Place the micro / nano fiber 15 obtained in step S3 onto the two-dimensional material field-effect transistor (FET) obtained in step S2. Specifically, first, support and fix the input fiber 151 and output fiber 155 at both ends of the micro / nano fiber 15 with glass slides, and hollow out the fiber micro-ring of the middle fiber 153; place the FET below the fiber micro-ring, and suspend the support sheet with the PDMS film layer 16 above the fiber micro-ring. Then, observe and adjust the positions of the PDMS film layer 16, the fiber micro-ring, and the FET using a micro-transfer platform until the fiber micro-ring of the micro / nano fiber 15 is transferred to contact with the FET. The PDMS film layer 16 plays a fixing and protective role, resulting in an electro-optic modulator.

[0067] See Figure 2 , Figure 3 The electro-optic modulator includes a field-effect transistor and a micro / nano fiber 15. 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, and the heterojunction 13 is composed of a black phosphorus layer 133 and a molybdenum disulfide layer 135, with one end of the black phosphorus layer 133 overlapping with one end of the molybdenum disulfide layer 135. The electrode layer 14 includes a source electrode and a drain electrode at both ends of the heterojunction 13, specifically, the source electrode and drain electrode are respectively located at the other end of the black phosphorus layer 133 and the other end of the molybdenum disulfide layer 135. The micro / nano fiber 15 includes an input fiber 151, a first tapered transition fiber 152, a middle fiber 153, a second tapered transition fiber 154, and an output fiber 155 connected in sequence. The middle fiber 153 is a ring-shaped fiber microring fixed to the heterojunction 13. Furthermore, the electro-optic modulator also includes a protective layer (…). Figure 3 (Not shown in the diagram), 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, the system includes a laser source, a polarizer, a polarization controller, an electro-optic modulator, and a spectrometer connected in sequence. In this embodiment, the electro-optic modulator is specifically the one fabricated in Example 1. The input and output optical fibers of this electro-optic modulator are connected to the polarization controller and the spectrometer, respectively. The modulation test system is used to test the modulation efficiency of the electro-optic modulator.

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

[0071] (1) Turn on the laser source and set the parameters of the spectrometer (such as center wavelength, scanning range, test accuracy, etc.) until the interference spectrum pattern appears. 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 feature analyzer and use the matching CCD imaging system to find the exact location of the electro-optic modulator on the silicon wafer.

[0073] (3) Select two probes from the probe station and connect them to the source electrode and drain electrode of the electro-optic modulator respectively. Select another probe to connect to the silicon substrate and make it the back gate electrode of the electro-optic modulator.

[0074] (4) Open the semiconductor feature analyzer test software, select the voltage bias mode for the probe connected to the drain electrode, with a range of -2V to 2V and a step size of 0.5V, and 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 patterns of the electro-optic modulator under bias voltages of -2V, -1.5V, -1V, -0.5V, and 0V, respectively, 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, the gate voltage to -60V to 60V, and the step size to 20V.

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

[0078] Depend on Figure 5It is known that the electro-optic modulator exhibits regular intensity and phase shifts under different DC bias and gate voltages, achieving a modulation effect. This means that the electro-optic modulator can control the intensity and phase of the light wave through voltage regulation. The working principle of this modulation test system is as follows: Due to the resonance effect of the fiber micro-ring in the electro-optic modulator, interference spectra are observed on the spectrometer. After the fiber is stripped and tapered, some evanescent field leakage occurs in the transmitted light wave, which facilitates interaction with the field-effect transistor. Based on this, when a voltage is applied to the field-effect transistor, it causes a change in the carrier concentration and the width of the depletion region, leading to a change in the refractive index (plasma scattering effect). Therefore, the light transmitted in the fiber is modulated by the external voltage, ultimately manifesting as a shift in the interference 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 connected in sequence. In this embodiment, the electro-optic modulator is specifically the one fabricated in Example 1. The input and output optical fibers of this electro-optic modulator are connected to the polarization controller and the photodetector, respectively. The modulation test system also includes a signal generator connected to the electro-optic modulator, used to apply a voltage to the electro-optic modulator, and to 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 this invention is an all-fiber electro-optic modulator with a simple coupling method. It replaces the traditional cross-sectional coupling or grating coupling with fiber-to-fiber optical field coupling, thereby avoiding the mode field matching problem. It can even realize plug-and-play, near-zero coupling loss optical interconnection and optical modulation. It has a fast modulation speed, low cost, and high modulation bandwidth, which can be applied to the needs of high integration fields and reduce the complexity and cost of modulation systems.

[0082] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. An electro-optic modulator, characterized in that, include: A field-effect transistor includes a silicon substrate, a dielectric layer, a heterojunction, and an electrode layer stacked sequentially; the electrode layer includes a source electrode and a drain electrode, which are respectively disposed at both ends of the heterojunction. The micro / nano fiber includes an input fiber, a first tapered transition fiber, a middle fiber, a second tapered transition fiber, and an output fiber connected in sequence. The middle fiber has a fiber microring with a ring structure, and the fiber microring is disposed 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, with one end of the black phosphorus layer in contact with one end of the molybdenum disulfide layer; the source electrode and the drain electrode are respectively located 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 5 nm to 30 nm. And / or, the black phosphorus layer and the molybdenum disulfide layer are monocrystalline 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 source electrode and / or the drain electrode are made of 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 disposed on the dielectric layer and covering the heterojunction, the electrode layer and the micro / nano optical fiber.

7. A method for fabricating the electro-optic modulator according to any one of claims 1 to 6, comprising the following steps: Fabricating a field-effect transistor includes: providing a silicon substrate with a dielectric layer loaded on its surface; fabricating a heterojunction on the dielectric layer; and fabricating a source electrode and a drain electrode at both ends of the heterojunction. The optical fiber is subjected to fused tapering to form a micro / nano fiber comprising an input fiber, a first tapered transition fiber, a middle fiber, a second tapered transition fiber, and an output fiber connected in sequence; a loop-forming operation is performed before or after the fused tapering process to give the middle fiber a fiber micro-ring with a ring structure. The micro-nano optical fiber is transferred and fixed onto the heterojunction, and the optical fiber microring is positioned in contact with the heterojunction.

8. The method for fabricating the electro-optic modulator according to claim 7, characterized in that, In the process of fabricating a field-effect transistor, a heterojunction is fabricated on the dielectric layer, including: firstly, a black phosphorus layer is fabricated on the dielectric layer using black phosphorus nanosheets; secondly, a molybdenum disulfide layer is fabricated on the dielectric layer using molybdenum disulfide nanosheets, and one end of the molybdenum disulfide layer is brought into contact with one end of the black phosphorus layer to obtain a heterojunction.

9. A modulation testing system, characterized in that, The system includes a laser source, a polarizer, a polarization controller, an electro-optic modulator, and a spectrometer connected in sequence; the electro-optic modulator is the electro-optic modulator according to any one of claims 1 to 6, and the input fiber and the output fiber of the electro-optic modulator are respectively connected to the polarization controller and the spectrometer; the modulation test system is used to test the modulation efficiency of the electro-optic modulator at least.

10. A modulation testing system, characterized in that, The system includes 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, and the input optical fiber and the output optical fiber of the electro-optic modulator are respectively connected to the polarization controller and the photodetector. The system also includes a signal generator connected to the electro-optic modulator for applying 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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