A silicon-based optical frequency comb generator with mach-zehnder interference self-coupled structure

Abstract

This invention proposes a silicon-based optical frequency comb generation device with a Mach-Zehnder interference self-coupled structure. The device includes a first MZI electro-optic modulator, a second MZI electro-optic modulator, and a third MZI electro-optic modulator arranged sequentially. The first and second MZI electro-optic modulators form a self-coupled structure, receiving a single-wavelength light source and modulating the optical signal. The third MZI electro-optic modulator receives the optical signal output from the self-coupled structure and modulates it, outputting an optical frequency comb signal. The first and second MZI electro-optic modulators together constitute a single-port push-pull drive configuration. All components of this invention are fabricated on a silicon-based SOI wafer, achieving silicon-based optoelectronic integration, effectively reducing the size and driving voltage of the optical frequency comb, and improving operational stability.

Description

Technical Field

[0001] This invention relates to an optical frequency comb generating device, belonging to the field of integrated device technology; and more particularly to a silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure. Background Technology

[0002] Optical frequency comb generators have important applications in fields such as optical communication, quantum key distribution, and microwave photonics.

[0003] Generally, the main methods for generating optical frequency combs include mode-locked laser generation, microcavity Kerr nonlinear generation, and optoelectronic modulator generation. While microcavity Kerr nonlinear generation can achieve a large number of frequency teeth, it requires precise temperature control to ensure the stability of the resonant wavelength. Mode-locked laser generation offers high stability, but its complex design makes miniaturization and integration difficult. Electro-optic modulator generation offers easily adjustable center frequencies and controllable repetition frequencies, but suffers from fewer teeth. While significantly increasing the driving voltage of the electro-optic modulator can increase the number of teeth, this also increases power consumption. In practical applications, small-sized, multi-tooth, and low-driving-voltage optical frequency combs are particularly important. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure to solve the problems of existing optical frequency combs that are difficult to balance in terms of structural simplicity, multiple tooth lines, and low driving power consumption.

[0005] To achieve the above objectives, the present invention includes:

[0006] The present invention discloses a silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure, comprising a self-coupling circuit. The self-coupling circuit includes a first MZI electro-optic modulator and a second MZI electro-optic modulator. One output port of the first MZI electro-optic modulator is connected to one input port of the second MZI electro-optic modulator, and then the output port of the second MZI electro-optic modulator is connected back to one input port of the first MZI electro-optic modulator. The other output port of the first MZI electro-optic modulator is connected to the input port of a lower-level photoelectric modulator. The output port of the lower-level photoelectric modulator serves as the output terminal of the optical frequency comb generating device, and the other input port of the first MZI electro-optic modulator serves as the input terminal of the optical frequency comb generating device.

[0007] In the optical frequency comb generating device of the present invention, one path of light output from the first MZI electro-optic modulator is coupled back to the input port of the first MZI electro-optic modulator through the second MZI electro-optic modulator to form a self-coupling loop. This path of light will interfere with the coherent non-resonant light input from another path when it is output. According to the Fano resonance principle, its output spectrum lines exhibit an asymmetrical shape, which can realize intensity modulation with low voltage drive. Compared with typical electro-optic modulator optical frequency comb generating devices, it can achieve more tooth line outputs under the same driving voltage.

[0008] Furthermore, the lower-level optoelectronic modulator includes a third MZI electro-optic modulator, the input port of which is the input port of the lower-level optoelectronic modulator, and the output port of which is the output port of the lower-level optoelectronic modulator.

[0009] Furthermore, the first MZI electro-optic modulator, the second MZI electro-optic modulator, and the third MZI electro-optic modulator are connected by a silicon waveguide.

[0010] This invention uses an MZI self-coupling structure to generate a resonance effect similar to that of a micro-ring resonator structure to achieve Fano resonance. Furthermore, the characteristics of Fano resonance can be controlled and the output spectrum can be adjusted by adjusting the operating point of the first MZI electro-optic modulator, thus exhibiting stability and ease of control.

[0011] Furthermore, the two adjacent MZI interferometer arms of the first and second MZI electro-optic modulators are of the same length and are arranged in parallel alignment; the waveguides of the two adjacent interferometer arms are both embedded in PN junction structures, and an N-type high-concentration doped region is set between the two PN junctions, and a P-type high-concentration doped region is set on the outer side of the two PN junctions respectively; the N-type particle doped region and the N-type high-concentration doped region of the two PN junctions are connected to form a back-to-back series enhancement PN junction structure.

[0012] Furthermore, a high-speed drive signal is applied between the two P-type high-concentration doped regions, and a DC bias signal is applied between one of the P-type high-concentration doped regions and the N-type high-concentration doped region, forming a single-port push-pull drive configuration.

[0013] The first MZI electro-optic modulator and the second MZI electro-optic modulator are placed in parallel alignment, such that two adjacent modulation arms of the two MZI electro-optic modulators form a single-port push-pull drive mode.

[0014] Furthermore, the lower-level optoelectronic modulator includes a third MZI electro-optic modulator and a fourth MZI electro-optic modulator. The third and fourth MZI electro-optic modulators form the same self-coupling loop as the first and second MZI electro-optic modulators. One output interface of the third MZI electro-optic modulator is connected to the input interface of the fourth MZI electro-optic modulator, and one output interface of the fourth MZI electro-optic modulator is connected to one input interface of the third MZI electro-optic modulator. The other output interface of the fourth MZI electro-optic modulator is connected to the other input interface of the second MZI electro-optic modulator. The other input port of the third MZI electro-optic modulator is the input port of the lower-level optoelectronic modulator, and the other output port of the third MZI electro-optic modulator is the output port of the lower-level optoelectronic modulator.

[0015] Furthermore, the first MZI electro-optic modulator, the second MZI electro-optic modulator, the third MZI electro-optic modulator, and the fourth MZI electro-optic modulator are connected by silicon waveguides.

[0016] Furthermore, the two adjacent MZI interferometer arms of the third and fourth MZI electro-optic modulators are of the same length and are arranged in parallel alignment; the waveguides of the two adjacent interferometer arms are both embedded with PN junction structures, and an N-type high-concentration doped region is set between the two PN junctions, and a P-type high-concentration doped region is set on the outer side of the two interferometer arms of the two PN junctions respectively; the N-type particle doped region and the N-type high-concentration doped region of the two PN junctions are connected to form a back-to-back series enhancement PN junction structure; a high-speed driving signal is loaded between the two P-type high-concentration doped regions, and a DC bias signal is loaded between one of the P-type high-concentration doped regions and the N-type high-concentration doped region, forming a single-port push-pull driving form.

[0017] Furthermore, the enhanced PN junction structure is fabricated through the following steps:

[0018] 1) Fabricate a photoresist protective layer for forming a first carrier region with high concentration of P-type doping, and implant P-type ions into the first carrier region to reach a preset concentration;

[0019] 2) Fabricate a photoresist protective layer for forming a second carrier region with high concentration of N-type doping, and implant N-type ions into the second carrier region to achieve a preset concentration;

[0020] 3) Fabricate a photoresist protective layer for the third carrier region of the PN junction P-type particle doping, and implant P-type ions into the third carrier region;

[0021] 4) A fourth carrier region is disposed above the third carrier region, and N-type ions are injected into the fourth carrier region;

[0022] 5) Fabricate a photoresist protective layer for the fifth carrier region of the PN junction N-type particle doping, inject N-type ions into the fifth carrier region, and connect the N-type ions in the fourth and fifth carrier regions.

[0023] Furthermore, each MZI electro-optic modulator is fabricated on a silicon-based SOI wafer using silicon photonics technology.

[0024] The present invention uses silicon-based chips for all the above-mentioned devices, which can improve the chip integration and reduce the device manufacturing cost.

[0025] When the optical frequency comb generating device of the present invention is working, the continuous light output from the laser enters the first input port of the first MZI electro-optic modulator of the present invention through an optical fiber waveguide coupler. The thermo-optic phase shifter sets the operating point of the MZI. The first MZI electro-optic modulator outputs two optical signals, one of which is coupled to the second MZI electro-optic modulator. The first and second MZI electro-optic modulators form a single-port push-pull drive configuration, which can modulate the signal light. The modulated light is output back to the second input port of the first MZI electro-optic modulator, forming a coupling loop. This light is called the coupled light. The coupled light interferes with the input light at the first input port of the first MZI electro-optic modulator and is output at the second output port of the first MZI electro-optic modulator to the input port of the third MZI electro-optic modulator. The third MZI modulator modulates the output to generate an optical frequency comb. The structure of the optical frequency comb generating device of the present invention can achieve rapid amplitude changes under a small voltage drive, realizing low-voltage modulation. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the principle of Embodiment 1 of the silicon-based optical frequency comb generating device with Mach-Zehnder interference self-coupling structure of the present invention;

[0027] Figure 2 This is a schematic diagram of the structure of a silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure according to Embodiment 1 of the present invention;

[0028] Figure 3 for Figure 2 A cross-sectional schematic diagram of a single-port push-pull drive structure consisting of adjacent modulation arms of the first MZI electro-optic modulator and the second MZI electro-optic modulator (shown by the dashed line).

[0029] Figure 4(a) is a schematic diagram of the ion implantation process step S100 of the PN junction in an embodiment of the present invention;

[0030] Figure 4(b) is a schematic diagram of step S200 of the ion implantation process of the PN junction in an embodiment of the present invention;

[0031] Figure 4(c) Schematic diagram of ion implantation process step S300 of the PN junction in an embodiment of the present invention;

[0032] Figure 4(d) is a schematic diagram of step S400 of the ion implantation process of the PN junction in an embodiment of the present invention;

[0033] Figure 4(e) is a schematic diagram of step S500 of the ion implantation process of the PN junction in an embodiment of the present invention;

[0034] Figure 5 This is the output spectrum of the self-coupling structure in an embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram of the MZI normalized output spectrum of an embodiment of the present invention;

[0036] Figure 7 This is a simulation diagram of the output of the silicon-based optical frequency comb generator with the Mach-Zehnder interference self-coupling structure of the present invention.

[0037] Figure 8 This is a schematic diagram of the principle of Embodiment 2 of the silicon-based optical frequency comb generating device with Mach-Zehnder interference self-coupling structure of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0039] Example 1:

[0040] Please refer to Figure 1 and Figure 2 , Figure 1 The diagram shows the structure of a silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure according to Embodiment 1 of the present invention. Figure 2 The overall appearance of Embodiment 1 of the silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure according to the present invention is shown.

[0041] like Figure 1 As shown, a silicon-based optical frequency comb generating device with a Mach-Zehnder interferometer (MZI) self-coupled structure according to the present invention includes a first MZI electro-optic modulator, a second MZI electro-optic modulator, and a third MZI electro-optic modulator. One output port of the first MZI electro-optic modulator is shown. 14 With the input port of the second MZI electro-optic modulator 22 The output port of the second MZI electro-optic modulator is connected via a silicon waveguide. 21 With one input port of the first MZI electro-optic modulator 12The first MZI electro-optic modulator and the second MZI electro-optic modulator are connected in this way to form a self-coupled structure, and the second output port of the first MZI electro-optic modulator is connected. 13 With the input port of the third MZI electro-optic modulator 31 Connection; another input port of the first MZI electro-optic modulator 11 The input terminal of the silicon-based optical frequency comb generating device constituting the Mach-Zehnder interference self-coupling structure of the present invention, and the output port of the third MZI electro-optic modulator. 32 The output terminal of the silicon-based optical frequency comb generating device constituting the Mach-Zehnder interference self-coupling structure of the present invention.

[0042] In this embodiment, the MZI structure in the second and third MZI electro-optic modulators can be a 1×1 port MZI structure or a 2×2 port MZI structure, while the MZI structure in the first MZI electro-optic modulator adopts a 2×2 port MZI structure.

[0043] In this embodiment, the continuous light output from the laser passes through a fiber optic waveguide coupler and originates from the input port of the silicon-based optical frequency comb generator with the Mach-Zehnder interference self-coupling structure of this invention. 11 The light is input to the first MZI electro-optic modulator, where it is split into two paths. After electro-optic modulation, the light interferes with the 2×2 MMI (multimode interferometer) within the first MZI electro-optic modulator, resulting in interference from the two output ports of the first MZI electro-optic modulator. 13 and port 14 Port output, where port 14 The output light is input to the input port of the second MZI electro-optic modulator. 22 After being modulated by the second MZI electro-optic modulator, it exits from its output port. 21 The output is then coupled back to the input port of the first MZI electro-optic modulator. 12 This forms a self-coupling loop, and the light path is the coupled light.

[0044] The coupled light is connected to the input port of the optical frequency comb generating device of the present invention. 11 The uncoupled light input to the port interferes with the output of the first MZI electro-optic modulator. 13 Port output.

[0045] The operating point of the modulator can be controlled by adjusting the thermo-optical phase shifter of the first MZI electro-optic modulator, and the output port of the first MZI electro-optic modulator can be adjusted accordingly. 13 and port 14 Characteristics of the port output spectrum.

[0046] In the first MZI electro-optic modulator, the upper MZI interferometer arm and the lower MZI interferometer arm in the second MZI electro-optic modulator are of the same length and are placed parallel and aligned. The waveguide of the upper interferometer arm of the first MZI electro-optic modulator is embedded in a PN junction structure, and the waveguide of the lower interferometer arm of the second MZI electro-optic modulator is embedded in a PN junction structure. The inner side formed by these two arms is an N-type high-concentration doped region, and the outer side formed by these two arms is a P-type high-concentration doped region, forming a back-to-back series PN junction structure. Based on this back-to-back series PN junction structure, combined with CPS (coplanar stripline) traveling wave electrodes, a single-port push-pull driven electro-optic modulator structure is formed.

[0047] Figure 3 As shown Figure 2 The dashed line corresponds to the cross-sectional view of the single-port push-pull structure. PN junction structures are embedded in the upper interference arm of the MZI in the first MZI electro-optic modulator and the lower interference arm of the MZI in the second MZI electro-optic modulator, respectively. The outer sides of the two interference arms are doped with high-concentration P-type ions and low-concentration P-type ions, respectively, from the outside to the inside. The inner sides of the two interference arms are doped with high-concentration N-type ions and low-concentration N-type ions, respectively, from the inside to the outside. A high-speed driving signal is applied to the high-concentration P-type doped region through electrodes and vias, and a DC bias signal is applied to the high-concentration N-type doped region through electrodes and vias. Intensity modulation of the light wave can be achieved according to a preset modulation scheme.

[0048] like Figure 2 , Figure 3 As shown, the specific structure includes:

[0049] Silicon substrate 1.

[0050] The silicon dioxide lower cladding layer 2 is fabricated on the silicon substrate 1 and has a thickness of 2-3 μm.

[0051] Silicon waveguide layer 3, fabricated on the lower cladding layer 2, adopts a convex ridge waveguide structure with a height of 220 nm and a width of 450 nm to 600 nm. It only supports the transmission of the TEO mode. The ridge waveguide is low-concentration doped to form a depletion region enhancement-mode PN junction structure, including a low-concentration P-region 31 of P-type ions and a low-concentration N-region 32 of N-type ions, with a doping concentration of 10%. 17 cm -3 ~10 18 cm -3 Between the two planar layers on both sides of the waveguide, the height can be set to 60nm to 90nm, and high-concentration ion doping can be performed to form N-type ion-doped N. ++ Zone 33 and P-type ion high-concentration doped P ++ Zone 34, doping concentration greater than 10 20 cm -3 The edge of the high-concentration doped plate layer is 0.4µm to 1µm away from the side of the waveguide core region.

[0052] The upper cladding 4 is fabricated on the silicon waveguide layer 3. The material of the upper cladding is silicon dioxide, and the thickness is 0.5 to 2.0 μm. The upper cladding 4 contains a first through-hole conductor 7 and a second through-hole conductor 8, which are made of aluminum, copper, or gold.

[0053] The first electrode 5 is fabricated in the cladding 4 and is made of aluminum, copper, and gold.

[0054] The second electrode 6 is fabricated on the cladding 4 and is made of aluminum, copper, and gold.

[0055] The first layer via conductor 7 is used to connect the first layer electrode 5 and the silicon waveguide, and the second layer via conductor 8 is used to connect the second layer electrode 6 and the first layer electrode 5.

[0056] High-frequency electrical signal V s Loaded onto the two high-speed electrodes of the first layer and highly doped with P-type ions in the silicon waveguide ++ Area connection, reverse bias voltage V b One end is loaded onto the second layer electrode 6, and the other end is loaded onto the first layer DC electrode and connected to the silicon waveguide with a high concentration of N-type ion doped N. ++ The districts are connected.

[0057] The third MZI electro-optic modulator has N-type doping between its two arms and P-type doping on the outer sides of its two arms, forming a back-to-back PN junction. Combined with the CPS traveling wave electrode, it forms a single-port push-pull driven electro-optic modulator structure.

[0058] The first, second, and third MZI electro-optic modulators are fabricated using silicon photonics technology. From bottom to top, they consist of a silicon substrate, a silicon dioxide lower cladding, a silicon waveguide layer, a silicon dioxide upper cladding, a first electrode layer, and a second electrode layer.

[0059] The silicon dioxide cladding contains through-hole conductors made of aluminum or copper. The first electrode layer and the second electrode layer are connected through the through-hole conductors, and the first electrode layer and the waveguide layer are connected through the through-hole conductors.

[0060] The silicon waveguide layer is composed of a convex ridge waveguide in the middle and planar waveguides on both sides. The convex waveguide can be doped with low concentration ions to form a low-doped region, and the planar waveguides can be doped with high concentration ions to form a high-doped region.

[0061] The doping process for forming the enhanced PN junction structure of the silicon waveguide layer is as follows: Figures 4(a) to 4(e) As shown, it includes the following steps:

[0062] S100, used to form P ++ The photoresist protective layer of the first carrier region is used to implant P-type ions into the first carrier region to reach a preset concentration, as shown in Figure 4(a);

[0063] S200, used to form N ++ The photoresist protective layer of the second carrier region is used to implant N-type ions into the second carrier region to reach a preset concentration, as shown in Figure 4(b);

[0064] S300, fabricate a photoresist protective layer for the third carrier region with low concentration of P-type doping, and implant P-type ions into the third carrier region, as shown in Figure 4(c);

[0065] S400, a fourth carrier region is set above the third carrier region, and N-type ions are injected into the fourth carrier region, as shown in Figure 4(d);

[0066] S500, a photoresist protective layer is fabricated for the fifth carrier region with low concentration of N-type doping. N-type ions are injected into the fifth carrier region, and the N-type ions in the fourth and fifth carrier regions are connected, as shown in Figure 4(e).

[0067] The entire self-coupling loop, i.e., Port 12 and Port 14 By connecting a second MZI electro-optic modulator, a Fano resonant structure is constructed, and the output spectrum is as follows: Figure 5 As shown.

[0068] Compared to a conventional single MZI modulator, this invention, under the same half-wave voltage, produces a normalized output spectrum with a wavelength of 1560.546 nm, as shown below. Figure 6 As shown, the silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure of the present invention can achieve rapid amplitude changes under a small voltage drive, realizing low-voltage modulation.

[0069] The output light modulated by the first MZI electro-optic modulator, compared with a typical MZI structure electro-optic modulator, can generate more high-order harmonics at the same driving voltage than a traditional single MZI structure electro-optic modulator. This is evident from the output port of the first MZI electro-optic modulator. 13 Output to the input port of the third MZI electro-optic modulator 31 After being modulated by the third MZI electro-optic modulator, the output port of the third MZI electro-optic modulator, which is also the output port of the silicon-based optical frequency comb generator with the Mach-Zehnder interference self-coupling structure of this invention, is used. 32 Output, forming an optical frequency comb with more teeth. Figure 7 This is a simulation diagram of the optical frequency comb output according to the present invention.

[0070] According to embodiments of the present invention, the relevant devices are all fabricated on silicon (SOI) wafers on an insulator substrate, and the waveguide structure is designed to only support TE mode transmission. It should be noted that using silicon-based chips for all the above devices can improve chip integration and reduce device fabrication costs.

[0071] Example 2:

[0072] like Figure 8 As shown, this is a silicon-based optical frequency comb generating device with a Mach-Zehnder interference self-coupling structure according to another embodiment of the present invention. Unlike embodiment 1, this embodiment includes a first MZI electro-optic modulator, a second MZI electro-optic modulator, a third MZI electro-optic modulator, and a fourth MZI electro-optic modulator.

[0073] Light from the port of the first MZI electro-optic modulator 11 Input from the port of the third MZI electro-optic modulator 33 Output, port of the first MZI electro-optic modulator 14 port with the second MZI electro-optic modulator 23 Port connection, port of the second MZI electro-optic modulator 21 port of the first MZI electro-optic modulator 12 Port connection, port of the third MZI electro-optic modulator 34 port with the fourth MZI electro-optic modulator 43 Port connection, port of the fourth MZI electro-optic modulator 41 port with the third MZI electro-optic modulator 32 Port connection, port of the second MZI electro-optic modulator 24 port with the fourth MZI electro-optic modulator 42 Port connection. The structure of the MZI electro-optic modulator in this embodiment is the same as that of the MZI electro-optic modulator in Embodiment 1.

[0074] In this embodiment, the MZI structures in the first, second, third, and fourth MZI electro-optic modulators all adopt a 2×2 port MZI structure.

[0075] The device in this embodiment can establish multi-level self-coupling loops, including a self-coupling loop from the first MZI electro-optic modulator to the second MZI electro-optic modulator and back to the first MZI electro-optic modulator; a self-coupling loop from the third MZI electro-optic modulator to the fourth MZI electro-optic modulator and back to the third MZI electro-optic modulator; and a self-coupling circuit from the first MZI electro-optic modulator to the second MZI electro-optic modulator, the third MZI electro-optic modulator to the fourth MZI electro-optic modulator, and back to the third MZI electro-optic modulator.

[0076] In this invention, one path of light output from the first MZI electro-optic modulator is coupled back to the input port of the first MZI electro-optic modulator through the second MZI electro-optic modulator to form a self-coupling loop. This path of light will interfere with the other path of coherent non-resonant light input at the output. According to the Fano resonance principle, its output spectrum lines exhibit an asymmetrical shape, which can realize intensity modulation driven by low voltage. Compared with typical electro-optic modulator optical frequency comb generating devices, more tooth lines are output under the same driving voltage.

[0077] This invention uses an MZI self-coupling structure to generate a resonance effect similar to that of a micro-ring resonator structure to achieve Fano resonance. Furthermore, the characteristics of Fano resonance can be controlled and the output spectrum can be adjusted by adjusting the operating point of the first MZI electro-optic modulator, thus exhibiting stability and ease of control.

Claims

1. A silicon-based optical frequency comb generator of Mach-Zehnder interferometric self-coupled structure, characterized in that, It includes a self-coupling circuit, which includes a first MZI electro-optic modulator and a second MZI electro-optic modulator. An output port of the first MZI electro-optic modulator is connected to an input port of the second MZI electro-optic modulator, and then the output port of the second MZI electro-optic modulator is connected back to an input port of the first MZI electro-optic modulator. The other output port of the first MZI electro-optic modulator is connected to the input port of the next-stage opto-modulator; The output port of the lower-level optoelectronic modulator serves as the output of the optical frequency comb generating device, and the other input port of the first MZI electro-optic modulator serves as the input of the optical frequency comb generating device. The two adjacent MZI interference arms of the first and second MZI electro-optic modulators are of the same length and are arranged in parallel alignment. The waveguides of the two adjacent interference arms are embedded in PN junction structures. The inner side of the two arms is an N-type high-concentration doped region, and the outer side of the two arms is a P-type high-concentration doped region, forming a back-to-back series PN junction structure. Based on this back-to-back series PN junction structure, a single-port push-pull driven electro-optic modulator structure is formed by combining coplanar stripline traveling wave electrodes.

2. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device according to claim 1, characterized in that, The lower-level optoelectronic modulator includes a third MZI electro-optic modulator, the input port of which is the input port of the lower-level optoelectronic modulator, and the output port of which is the output port of the lower-level optoelectronic modulator.

3. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device according to claim 2, characterized in that, The first MZI electro-optic modulator, the second MZI electro-optic modulator, and the third MZI electro-optic modulator are connected by a silicon waveguide.

4. The silicon-based optical frequency comb generator based on Mach-Zehnder interferometric self-coupled structure according to claim 1, wherein, The outer sides of the two interference arms are doped with high concentrations of P-type ions and low concentrations of P-type ions from the outside to the inside, respectively, while the inner sides of the two interference arms are doped with high concentrations of N-type ions and low concentrations of N-type ions from the inside to the outside.

5. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device according to claim 4, wherein, A high-speed drive signal is applied between the two P-type high-concentration doped regions, and a DC bias signal is applied between one of the P-type high-concentration doped regions and the N-type high-concentration doped region, forming a single-port push-pull drive configuration.

6. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device of claim 1, wherein, The lower-level optoelectronic modulator includes a third MZI electro-optic modulator and a fourth MZI electro-optic modulator. The third and fourth MZI electro-optic modulators form the same self-coupling loop as the first and second MZI electro-optic modulators. One output interface of the third MZI electro-optic modulator is connected to the input interface of the fourth MZI electro-optic modulator, and one output interface of the fourth MZI electro-optic modulator is connected to one input interface of the third MZI electro-optic modulator. The other output interface of the fourth MZI electro-optic modulator is connected to the other input interface of the second MZI electro-optic modulator. The other input port of the third MZI electro-optic modulator is the input port of the lower-level optoelectronic modulator, and the other output port of the third MZI electro-optic modulator is the output port of the lower-level optoelectronic modulator.

7. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device according to claim 6, characterized in that, The first, second, third, and fourth MZI electro-optic modulators are connected via silicon waveguides.

8. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device according to claim 6, wherein, The third and fourth MZI electro-optic modulators have two adjacent MZI interferometer arms of the same length and are arranged in parallel alignment. The waveguides of the two adjacent interferometer arms are embedded in PN junction structures. An N-type high-concentration doped region is set between the two PN junctions, and a P-type high-concentration doped region is set on the outer side of the two interferometer arms of the two PN junctions. The N-type particle doped region and the N-type high-concentration doped region of the two PN junctions are connected to form a back-to-back series enhancement PN junction structure. A high-speed driving signal is loaded between the two P-type high-concentration doped regions, and a DC bias signal is loaded between one of the P-type high-concentration doped regions and the N-type high-concentration doped region, forming a single-port push-pull driving form.

9. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device according to claim 8, characterized in that, The enhanced PN junction structure is fabricated using the following steps: A photoresist protective layer is fabricated to form a first carrier region with high concentration of P-type doping, and P-type ions are implanted into the first carrier region to reach a preset concentration; A photoresist protective layer is fabricated to form a second carrier region with a high concentration of N-type doping, and N-type ions are implanted into the second carrier region to reach a preset concentration; A photoresist protective layer is fabricated for the third carrier region of the PN junction with P-type particle doping, and P-type ions are injected into the third carrier region. A fourth carrier region is disposed above the third carrier region, and N-type ions are injected into the fourth carrier region; A photoresist protective layer is fabricated for the fifth carrier region of the PN junction to be doped with N-type particles. N-type ions are injected into the fifth carrier region, and the N-type ions in the fourth and fifth carrier regions are connected.

10. The Mach-Zehnder interferometric self-coupled silicon-based optical frequency comb generator device according to any one of claims 1 to 8, characterized in that, It is obtained by fabricating each MZI electro-optic modulator on a silicon-based SOI wafer using silicon photonics technology.

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