A wavelength-mode hybrid multiplexer based on cascaded multimode interferometer structure

Abstract

A wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure belongs to the field of silica integrated optics technology. From bottom to top, it consists of a silicon substrate, a silica lower cladding, a germanium-doped silica core layer, and a silica upper cladding. The germanium-doped silica core layer and the upper cladding are located together on the lower cladding, and the core layer is coated in the upper cladding. The germanium-doped silica core layer is composed of a 1×2 Y-branch waveguide, an optical phase modulator, a 2×2 multimode interferometer, a first 1×2 multimode interferometer, a second 1×2 multimode interferometer, a first 1×1 multimode interferometer, and a second 1×1 multimode interferometer. This wavelength-mode hybrid multiplexer adopts a passive structure. Through the optical phase modulator on the modulation arm waveguide and the self-imaging principle of the multimode interferometer structure, it can multiplex and demultiplex the four input signals: TE0 and TE1 at a wavelength of 1550nm and TE0 and TE1 at a wavelength of 1620nm.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon dioxide integrated optics, and in particular relates to a wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure. Background Art

[0002] Currently, due to the rapid development of information technology, demands for the communication capacity of optical communication systems are increasing. In optical communication networks, multiplexing and demultiplexing technologies can be used to increase communication system capacity. Generally speaking, multiplexing technologies include mode division multiplexing (MDM), wavelength division multiplexing (WDM), polarization multiplexing (PDM), and time division multiplexing (TDM). MDM is a technology that couples optical signals of different modes (fundamental mode, first-order mode, second-order mode, etc.) into the same waveguide for transmission at the input end through a MDM. WDM is a technology that couples optical signals of different wavelengths (which can carry different information) into the same waveguide for transmission at the input end through a WDM.

[0003] Research has shown that single-use technologies like mode division multiplexing (MDM), wavelength division multiplexing (WDM), and polarization multiplexing (PDM) are insufficient to meet the demand for ultra-high capacity in optical communication systems. Consequently, a new multiplexing technology, wavelength-mode hybrid multiplexing (WDM) has emerged. This hybrid multiplexing technology combines WDM and MDM. A WDM hybrid multiplexer can simultaneously multiplex and demultiplex multiple wavelength signals and multiple mode signals. This new combination can significantly increase communication system capacity and transmission efficiency.

[0004] The performance indicators of wavelength-mode hybrid multiplexers primarily include insertion loss, inter-mode crosstalk, and operating bandwidth. These performance indicators must be well-balanced and well-defined. Low inter-mode crosstalk must be maintained while ensuring low loss and wide bandwidth. This ensures optimal multiplexing and demultiplexing of mixed signals of different wavelengths and modes, improving the device's system capacity and transmission efficiency. Silica, with its mature manufacturing process, high process tolerances, and low loss, meets the design requirements of wavelength-mode hybrid multiplexers. Summary of the Invention

[0005] The present invention aims to provide a wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure for use in a wavelength division and mode division hybrid multiplexing system. This wavelength-mode hybrid multiplexer employs a passive structure. By utilizing optical phase modulators on modulator arm waveguides and the self-imaging principle of the multimode interferometer structure, it can multiplex and demultiplex four input signals: TE0 and TE1 at a wavelength of 1550 nm, and TE0 and TE1 at a wavelength of 1620 nm.

[0006] like Figure 1As shown, the wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure for a wavelength division and mode division hybrid multiplexing system described in the present invention is composed of, from bottom to top, a silicon substrate, a silica lower cladding, a germanium-doped silica core layer and a silica upper cladding, wherein the germanium-doped silica core layer and the upper cladding are located together on the lower cladding, and the core layer is coated in the upper cladding; the germanium-doped silica core layer is composed of a 1×2 Y-branch waveguide I, an optical phase modulator, a 2×2 multimode interferometer II, a first 1×2 multimode interferometer III, a second 1×2 multimode interferometer IV, a first 1×1 multimode interferometer V and a second 1×1 multimode interferometer VI.

[0007] like Figure 2As shown, along the transmission direction of light, the germanium-doped silica core layer consists of an input straight waveguide 1, a first curved waveguide 2 and a second curved waveguide 3 with the same structure and size, a first straight waveguide 4, a first tapered waveguide 5, a second tapered waveguide 6, a second straight waveguide 7, a third straight waveguide 8, a third tapered waveguide 9 and a fourth tapered waveguide 10 with the same structure and size, a 2×2 multimode interferometer II, a fifth tapered waveguide 11 and a sixth tapered waveguide 12 with the same structure and size, a first 1×2 multimode interferometer III and a second 1×2 multimode interferometer IV with the same structure and size, a seventh tapered waveguide 13 and a tenth tapered waveguide 16 with the same structure and size, an eighth tapered waveguide 14 and a ninth tapered waveguide 15 with the same structure and size, The invention comprises a first 1×1 multimode interferometer V and a second 1×1 multimode interferometer VI having the same structure and size, a fourth straight waveguide 17 and a fifth straight waveguide 18 having the same structure and size, an eleventh tapered waveguide 19 and a twelfth tapered waveguide 20 having the same structure and size, a third curved waveguide 21 and a fourth curved waveguide 22 having the same structure and size, a thirteenth tapered waveguide 23, a fourteenth tapered waveguide 24, a fifteenth tapered waveguide 25 and a sixteenth tapered waveguide 26 having the same structure and size, a first output straight waveguide 27, a second output straight waveguide 28, a third output straight waveguide 29 and a fourth output straight waveguide 30 having the same structure and size; wherein the input straight waveguide 1, the first curved waveguide 2 and the second curved waveguide 3 constitute The optical phase modulator is formed into a 1×2 Y-branch waveguide I, the first straight waveguide 4, the first tapered waveguide 5, the second tapered waveguide 6 and the second straight waveguide 7 are connected in sequence, the first curved waveguide 2 is connected to the optical phase modulator, the second curved waveguide 3, the third straight waveguide 8 and the fourth tapered waveguide 10 are connected in sequence; the third tapered waveguide 9 and the fourth tapered waveguide 10 are the two input ends of the 2×2 multimode interferometer II, the fifth tapered waveguide 11 and the sixth tapered waveguide 12 are the two output ends of the 2×2 multimode interferometer II, the fifth tapered waveguide 11 is also the input end of the first 1×2 multimode interferometer III, the seventh tapered waveguide 13 and the eighth tapered waveguide 14 are the two output ends of the first 1×2 multimode interferometer III, and the eighth tapered waveguide 15 is connected to the optical phase modulator. The first tapered waveguide 14, the fourth straight waveguide 17, the fourteenth tapered waveguide 24 and the second output straight waveguide 28 are connected in sequence; the sixth tapered waveguide 12 is also the input end of the second 1×2 multimode interferometer IV, the ninth tapered waveguide 15 and the tenth tapered waveguide 16 are the two output ends of the second 1×2 multimode interferometer IV, the ninth tapered waveguide 15, the fifth straight waveguide 18, the fifteenth tapered waveguide 25 and the third output straight waveguide 29 are connected in sequence; the seventh tapered waveguide 13 is the input end of the first 1×1 multimode interferometer V, the eleventh tapered waveguide 19 is the output end of the first 1×1 multimode interferometer V, the eleventh tapered waveguide 19, the third curved waveguide 21, the thirteenth tapered waveguide 23 and the first output straight waveguide 27 are connected in sequence;The tenth tapered waveguide 16 is the input end of the second 1×1 multimode interferometer VI, the twelfth tapered waveguide 20 is the output end of the second 1×1 multimode interferometer VI, and the twelfth tapered waveguide 20, the fourth curved waveguide 22, the sixteenth tapered waveguide 26 and the fourth output straight waveguide 30 are connected in sequence; the first curved waveguide 2 and the second curved waveguide 3, the third tapered waveguide 9 and the fourth tapered waveguide 10, the fifth tapered waveguide 11 and the sixth tapered waveguide 12, the first 1×2 multimode interferometer III and the second 1×2 multimode interferometer IV, the seventh tapered waveguide 13 and the tenth tapered waveguide 16, the eighth tapered waveguide 14 and the ninth tapered waveguide 15, the first 1×1 multimode interferometer V and the second 1×1 multimode interferometer VI, the fourth straight waveguide 17 and the fifth straight waveguide 18, the third curved waveguide 21 and the fourth curved waveguide 22, the thirteenth tapered waveguide 23 and the sixteenth tapered waveguide The 14th and 15th tapered waveguides 24 and 25, the first and fourth output straight waveguides 27 and 30, the second and third output straight waveguides 28 and 29 are symmetrical structures about the input straight waveguide 1 and its extension. One side edge of the 2×2 multimode interferometer II, the outer edge of the fifth tapered waveguide 11, the outer edge of the first 1×2 multimode interferometer III, the outer edge of the seventh tapered waveguide 13, and the outer edge of the first 1×1 multimode interferometer V are all aligned. The other side edge of the 2×2 multimode interferometer II, the outer edge of the sixth tapered waveguide 12, the outer edge of the second 1×2 multimode interferometer IV, the outer edge of the tenth tapered waveguide 16, and the outer edge of the second 1×1 multimode interferometer VI are all aligned. All straight waveguides or their extensions are parallel. Except for the waveguides with marked lengths, the remaining waveguides serve only as connectors and have no specific length requirements. The input straight waveguide 1 serves as the input end of the wavelength-mode hybrid multiplexer, and the first output straight waveguide 27, the second output straight waveguide 28, the third output straight waveguide 29, and the fourth output straight waveguide 30 serve as the output 1, output 2, output 3, and output 4 ends of the wavelength-mode hybrid multiplexer, respectively.

[0008] The width of the input straight waveguide 1 is W1=8 μm, which can accommodate the transmission of TE0 and TE1 modes. After passing through the 1×2 Y-branch waveguide I, the input straight waveguide 1 is divided into the first curved waveguide 2 and the second curved waveguide 3 with a width of W2=4 μm; the width of the first straight waveguide 4 and the second straight waveguide 7 is W2=4 μm, the width of the first tapered waveguide 5 linearly increases from W2=4 μm to W3=5 μm, and the width of the second tapered waveguide 6 linearly decreases from W3=5 μm to W2=4 μm. The lengths of the first tapered waveguide 5 and the second tapered waveguide 6 are both L1=200 μm. The width of the third straight waveguide 8 is W2=4 μm; the widths of the third tapered waveguide 9 and the fourth tapered waveguide 10 linearly increase from W2=4 μm to W4=6 μm. The distance between the symmetry center of the third tapered waveguide 9 and the fourth tapered waveguide 10 and the symmetry center of the 2×2 multimode interferometer II is X1=22 μm; the width of the 2×2 multimode interferometer II is W5=50 μm, and the length is L2=4945 μm; the fifth tapered waveguide 11 and the sixth tapered waveguide 12 are right-angled trapezoidal structures, and the widths of the fifth tapered waveguide 11 and the sixth tapered waveguide 12 decrease linearly from W6=23 μm to W7=20 μm, and the length is L3=500 μm; the width of the first 1×2 multimode interferometer III and the second 1×2 multimode interferometer IV is W7=20 μm, and the length is L4=1445 μm; the seventh tapered waveguide 13 and the tenth tapered waveguide 16 are right-angled trapezoidal structures, and the widths of the seventh tapered waveguide 13 and the tenth tapered waveguide 16 decrease linearly from W9=12 μm to W 10 =10 μm, and the length is L6=200 μm; the width of the eighth tapered waveguide 14 and the ninth tapered waveguide 15 decreases linearly from W8=6 μm to W 11 =2 μm, length L6=200 μm; width of the first 1×1 multimode interferometer V and the second 1×1 multimode interferometer VI is W 10 =10 μm, the length is L5=915 μm; the width of the fourth straight waveguide 17 and the fifth straight waveguide 18 is W 11 =2 μm; the width of the eleventh tapered waveguide 19 and the twelfth tapered waveguide 20 is W 12 =4 μm linearly reduced to W 13 =2 μm; the width W of the third curved waveguide 21 and the fourth curved waveguide 22 13 = 2 μm; the width of the thirteenth tapered waveguide 23, the fourteenth tapered waveguide 24, the fifteenth tapered waveguide 25 and the sixteenth tapered waveguide 26 is from W 13 =2 μm linearly increasing to W 14 =4 μm; the width of the first output straight waveguide 27, the second output straight waveguide 28, the third output straight waveguide 29 and the fourth output straight waveguide 30 is W 14 =4 μm;

[0009] The working principle of the wavelength-mode hybrid multiplexer is as follows:

[0010] The TE0 mode optical signal (including 1550 nm and 1620 nm) enters the input straight waveguide 1 and is evenly divided into two TE0 mode optical signals by the first curved waveguide 2 and the second curved waveguide 3. The optical signal of the first curved waveguide 2 reaches the third tapered waveguide 9 along the first straight waveguide 4, the first tapered waveguide 5, the second tapered waveguide 6, and the second straight waveguide 7, and the optical signal of the second curved waveguide 3 reaches the fourth tapered waveguide 10 along the third straight waveguide 8; the first straight waveguide 4, the first tapered waveguide 5, the second tapered waveguide 6, and the second straight waveguide 7 constitute an optical phase modulator. According to optical waveguide theory, changes in the width and length of the first tapered waveguide 5 and the second tapered waveguide 6 can affect the phase change of the optical signal in the waveguide. Therefore, when the optical signal passes through the optical phase modulator, a phase change will occur. The TE0 mode optical signal (including 1550 nm and 1620 nm) input by the input straight waveguide 1, the two TE0 mode optical signals generated by it have a 1 / 2 phase difference when they reach the third tapered waveguide 9 and the fourth tapered waveguide 10. The phase difference of π, such as Figure 4 As shown in (a), the two TE0 mode optical signals in the third tapered waveguide 9 and the fourth tapered waveguide 10 enter the 2×2 multimode interferometer II. According to the self-image principle, the optical signals are output from the sixth tapered waveguide 12. The optical signals continue to transmit and reach the second 1×2 multimode interferometer IV. Since the self-image period of the 1550 nm wavelength signal is longer, the 1550 nm wavelength optical signal is output from the ninth tapered waveguide 15 after passing through the second 1×2 multimode interferometer IV. It then continues along the fifth straight waveguide 18 and the fifteenth tapered waveguide 25 to reach the third output straight waveguide 29. Since the self-image period of the 1620 nm wavelength signal is shorter than that of the 1550 nm wavelength signal, the 1620 nm wavelength optical signal is output from the tenth tapered waveguide 16 after passing through the second 1×2 multimode interferometer IV. It then continues along the second 1×1 multimode interferometer VI, the twelfth tapered waveguide 20, the fourth curved waveguide 22, and the sixteenth tapered waveguide 26 to reach the fourth output straight waveguide 30.

[0011] The TE1 mode optical signal (including 1550 nm and 1620 nm) enters the input straight waveguide 1 and is evenly divided into two TE0 mode optical signals by the first curved waveguide 2 and the second curved waveguide 3. The optical signal of the first curved waveguide 2 reaches the third tapered waveguide 9 along the first straight waveguide 4, the first tapered waveguide 5, the second tapered waveguide 6, and the second straight waveguide 7. The optical signal of the second curved waveguide 3 reaches the fourth tapered waveguide 10 along the third straight waveguide 8. The first straight waveguide 4, the first tapered waveguide 5, the second tapered waveguide 6, and the second straight waveguide 7 constitute an optical phase modulator. According to optical waveguide theory, changes in the width and length of the first tapered waveguide 5 and the second tapered waveguide 6 can affect the phase change of the optical signal in the waveguide. Therefore, when the optical signal passes through, a phase change will occur. The TE1 mode optical signal (including 1550 nm and 1620 nm) input by the input straight waveguide 1 generates two TE0 mode optical signals with a phase difference of -1 / 2 π when they reach the third tapered waveguide 9 and the fourth tapered waveguide 10, as shown in FIG. Figure 4 As shown in (b), the two TE0 mode optical signals in the third tapered waveguide 9 and the fourth tapered waveguide 10 enter the 2×2 multimode interferometer II. According to the self-imaging principle, the optical signals are output from the fifth tapered waveguide 11. The optical signals continue to transmit and reach the first 1×2 multimode interferometer III. Since the self-imaging period of the 1550 nm wavelength signal is longer, the 1550 nm optical signal passes through the first 1×2 multimode interferometer III and is output from the eighth tapered waveguide 14. It then continues along the fourth straight waveguide 17 and the fourteenth tapered waveguide 24 to reach the second output straight waveguide 28. Since the self-imaging period of the 1620 nm wavelength signal is shorter than that of the 1550 nm wavelength signal, the 1620 nm optical signal passes through the first 1×2 multimode interferometer III and is output from the seventh tapered waveguide 13. It then passes along the first 1×1 multimode interferometer V, the eleventh tapered waveguide 19, the third curved waveguide 21, and the thirteenth tapered waveguide 23 to reach the first output straight waveguide 27.

[0012] That is, when a 1550 nm wavelength signal is input in TE0 mode, the optical signal is output at Output 3; when a 1620 nm wavelength signal is input in TE0 mode, the optical signal is output at Output 4; when a 1550 nm wavelength signal is input in TE1 mode, the optical signal is output at Output 2; and when a 1620 nm wavelength signal is input in TE1 mode, the optical signal is output at Output 1.

[0013] The simulation results of the device are as follows Figure 5 (a) ~ Figure 5 As shown in (d), insertion loss and crosstalk are two important indicators for measuring device performance. The calculation formula for insertion loss is: IL=-10×lg(P out / P in ), where Pin is the efficiency at the input of the device, P out is the efficiency of the device's target output port, IL is the device's insertion loss; the crosstalk calculation formula is: CT=10×lg(P other / P out ), where P out is the efficiency of the target output port of the device, P other is the efficiency of other output ports of the device, and CT is the crosstalk of the device.

[0014] When the device inputs TE0 mode and 1550nm wavelength signal, the simulation results are as follows: Figure 5 As shown in (a), the insertion loss of the wavelength-mode hybrid multiplexer is 0.45 dB, and the maximum crosstalk value of the remaining ports is -20.55 dB;

[0015] When the device inputs TE0 mode and 1620nm wavelength signal, the simulation results are as follows: Figure 5 As shown in (b), the insertion loss of the wavelength-mode hybrid multiplexer is 0.39 dB, and the maximum crosstalk value of the remaining ports is -22.18 dB;

[0016] When the device inputs TE1 mode and 1550nm wavelength signal, the simulation results are as follows: Figure 5 As shown in (c), the insertion loss of the wavelength-mode hybrid multiplexer is 0.46 dB, and the maximum crosstalk value of the remaining ports is -20.84 dB;

[0017] When the device inputs TE1 mode and 1620nm wavelength signal, the simulation results are as follows: Figure 5 As shown in (d), the insertion loss of the wavelength-mode hybrid multiplexer is 0.38 dB, and the maximum crosstalk value of the remaining ports is -22.02 dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of the cross-sectional structure of a wavelength-mode hybrid multiplexer;

[0019] Figure 2 1 is a schematic diagram of the top view structure of the core layer of the wavelength-mode hybrid multiplexer;

[0020] Figure 3 The graph shows the effective refractive index of different modes of the germanium-doped silica core waveguide changing with the waveguide width;

[0021] Figure 4 Phase diagrams of TE0 and TE1 mode optical signals at the end of 1×2 Y-branch waveguide I;

[0022] Figure 5Figures (a) to 5 (d) are the simulated light field diagrams of the device when four different signal inputs are applied;

[0023] Figure 6 The figure is a flow chart of the preparation process of the wavelength-mode hybrid multiplexer described in the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0025] Example 1

[0026] See attached Figure 1 The wavelength-mode hybrid multiplexer consists, from bottom to top, of a substrate, a lower cladding, a core layer, and an upper cladding. The upper cladding covers all but the lower surface of the core, with both the core and upper cladding located above the lower cladding. Both the lower and upper cladding layers are made of silica, with a refractive index of 1.4447. The core layer is made of germanium-doped silica, with a refractive index of 1.4741. The core layer thickness is 4μm.

[0027] See attached Figure 2, the core layer of the wavelength-mode hybrid multiplexer is along the transmission direction of light, and the core layer of the wavelength-mode hybrid multiplexer is composed of an input straight waveguide 1, a first curved waveguide 2 and a second curved waveguide 3 with the same structure and size, a first straight waveguide 4, a first tapered waveguide 5, a second tapered waveguide 6, a second straight waveguide 7, a third straight waveguide 8, a third tapered waveguide 9 and a fourth tapered waveguide 10 with the same structure and size, a 2×2 multimode interferometer II, a fifth tapered waveguide 11 and a sixth tapered waveguide 12 with the same structure and size, a first 1×2 multimode interferometer III and a second 1×2 multimode interferometer IV with the same structure and size, a seventh tapered waveguide 13 and a tenth tapered waveguide 16 with the same structure and size, an eighth tapered waveguide with the same structure and size. The waveguide 14 and the ninth tapered waveguide 15, the first 1×1 multimode interferometer V and the second 1×1 multimode interferometer VI with the same structure and size, the fourth straight waveguide 17 and the fifth straight waveguide 18 with the same structure and size, the eleventh tapered waveguide 19 and the twelfth tapered waveguide 20 with the same structure and size, the third curved waveguide 21 and the fourth curved waveguide 22 with the same structure and size, the thirteenth tapered waveguide 23, the fourteenth tapered waveguide 24, the fifteenth tapered waveguide 25 and the sixteenth tapered waveguide 26 with the same structure and size, the first output straight waveguide 27, the second output straight waveguide 28, the third output straight waveguide 29 and the fourth output straight waveguide 30 with the same structure and size; wherein the input straight waveguide 1, the first curved waveguide 2 The first straight waveguide 4, the first tapered waveguide 5, the second tapered waveguide 6 and the second straight waveguide 7 form an optical phase modulator. The first curved waveguide 2 and the first straight waveguide 4 are connected in sequence. The second curved waveguide 3, the third straight waveguide 8 and the fourth tapered waveguide 10 are connected in sequence. The third tapered waveguide 9 and the fourth tapered waveguide 10 are the two input ends of the 2×2 multimode interferometer II. The fifth tapered waveguide 11 and the sixth tapered waveguide 12 are the two output ends of the 2×2 multimode interferometer II. The fifth tapered waveguide 11 is also the input end of the first 1×2 multimode interferometer III. The seventh tapered waveguide 13 and the eighth tapered waveguide 14 are the two output ends of the first 1×2 multimode interferometer III. The eighth tapered waveguide 14, the fourth straight waveguide 17, the fourteenth tapered waveguide 24, and the second output straight waveguide 28 are connected in sequence; the sixth tapered waveguide 12 is also the input end of the second 1×2 multimode interferometer IV, the ninth tapered waveguide 15 and the tenth tapered waveguide 16 are the two output ends of the second 1×2 multimode interferometer IV, the ninth tapered waveguide 15, the fifth straight waveguide 18, the fifteenth tapered waveguide 25, and the third output straight waveguide 29 are connected in sequence; the seventh tapered waveguide 13 is the input end of the first 1×1 multimode interferometer V, the eleventh tapered waveguide 19 is the output end of the first 1×1 multimode interferometer V, the eleventh tapered waveguide 19, the third curved waveguide 21, the thirteenth tapered waveguide 23, and the first output straight waveguide 27 are connected in sequence;The tenth tapered waveguide 16 is the input end of the second 1×1 multimode interferometer VI, the twelfth tapered waveguide 20 is the output end of the second 1×1 multimode interferometer VI, and the twelfth tapered waveguide 20, the fourth curved waveguide 22, the sixteenth tapered waveguide 26 and the fourth output straight waveguide 30 are connected in sequence; the first curved waveguide 2 and the second curved waveguide 3, the third tapered waveguide 9 and the fourth tapered waveguide 10, the fifth tapered waveguide 11 and the sixth tapered waveguide 12, the first 1×2 multimode interferometer III and the second 1×2 multimode interferometer IV, the seventh tapered waveguide 13 and the fourth output straight waveguide 30 are connected in sequence. The tenth tapered waveguide 16, the eighth tapered waveguide 14, the ninth tapered waveguide 15, the first 1×1 multimode interferometer V and the second 1×1 multimode interferometer VI, the fourth straight waveguide 17 and the fifth straight waveguide 18, the third curved waveguide 21 and the fourth curved waveguide 22, the thirteenth tapered waveguide 23 and the sixteenth tapered waveguide 26, the fourteenth tapered waveguide 24 and the fifteenth tapered waveguide 25, the first output straight waveguide 27 and the fourth output straight waveguide 30, and the second output straight waveguide 28 and the third output straight waveguide 29 are symmetrical structures about the extension line of the input straight waveguide 1.

[0028] Example 2

[0029] Determine the size parameters of each part of the core waveguide. The core waveguide height is fixed at 4μm. The input straight waveguide 1 can support TE0 and TE1 modes. Figure 3 The effective refractive index of different modes in the silica waveguide changes with the waveguide width. The width of the input straight waveguide 1 is set to W1 = 8 μm. The optical signal exists in the TE0 mode in the first straight waveguide 4, the second straight waveguide 7, the third straight waveguide 8, the first output straight waveguide 27, the second output straight waveguide 28, the third output straight waveguide 29, and the fourth output straight waveguide 30. The widths of the first straight waveguide 4, the second straight waveguide 7, the third straight waveguide 8, the first output straight waveguide 27, the second output straight waveguide 28, the third output straight waveguide 29, and the fourth output straight waveguide 30 are equal, W2 = 4 μm. The optical signal exists in the TE0 mode in the fourth straight waveguide 17 and the fifth straight waveguide 18. The widths of the fourth straight waveguide 17 and the fifth straight waveguide 18 are equal, W 11 =2 μm. The optical signal exists in the TE0 mode in both the first curved waveguide 2 and the second curved waveguide 3. The widths of the first curved waveguide 2 and the second curved waveguide 3 are equal, W2 = 4 μm. The optical signal exists in the TE0 mode in both the third curved waveguide 21 and the fourth curved waveguide 22. The widths of the third curved waveguide 21 and the fourth curved waveguide 22 are equal, W 13=2 μm. The width of the first tapered waveguide 5 increases linearly from W2=4 μm to W3=5 μm, while the width of the second tapered waveguide 6 decreases linearly from W3=5 μm to W2=4 μm. Their lengths are both L1=200 μm. The widths of the third and fourth tapered waveguides 9 and 10 increase linearly from W2=4 μm to W4=6 μm. The distance between their centers of symmetry and that of the 2×2 multimode interferometer II is X1=22 μm. The widths of the fifth and sixth tapered waveguides 11 and 12 decrease from W6=23 μm to W7=20 μm. Their lengths are both L3=500 μm. The outer sides of the fifth and sixth tapered waveguides 11 and 12 are rectangular structures, and their outer sides are aligned with the upper and lower sides of the 2×2 multimode interferometer II. The width of the seventh tapered waveguide 13 and the tenth tapered waveguide 16 is reduced from W9=12 μm to W 10 =10 μm, and the length is L6=200 μm. The outer sides of the seventh tapered waveguide 13 and the tenth tapered waveguide 16 are right-angle structures, and are respectively on the same straight line with the upper side of the first 1×2 multimode interferometer III and the lower side of the second 1×2 multimode interferometer IV. The width of the eighth tapered waveguide 14 and the ninth tapered waveguide 15 decreases linearly from W8=6 μm to W 11 =2 μm. The width of the eleventh tapered waveguide 19 and the twelfth tapered waveguide 20 is W 12 =4 μm linearly reduced to W 13 =2 μm. The widths of the thirteenth tapered waveguide 23, the fourteenth tapered waveguide 24, the fifteenth tapered waveguide 25, and the sixteenth tapered waveguide 26 are W 13 =2 μm linearly increasing to W 14 =4 μm.

[0030] The width of the 2×2 multimode interferometer II is determined to be W5=50 μm and the length is L2=4945 μm by the beam propagation method. The width of the first 1×2 multimode interferometer III and the second 1×2 multimode interferometer IV is W7=20 μm and the length is L4=1445 μm. The width of the first 1×1 multimode interferometer V and the second 1×1 multimode interferometer VI is W 10 =10 μm, length is L5=915 μm.

[0031] Example 3

[0032] The following is combined with Figure 6 The specific preparation method of the device of the present invention is demonstrated, and the steps are as follows:

[0033] 1. Silicon substrate cleaning: Use a 0.6mm thick silicon wafer as the substrate. First, clean the wafer with acetone to remove organic impurities on the surface of the wafer. Then, clean the wafer with ethanol to remove any acetone residue from the previous step. Finally, clean the wafer with deionized water to remove any ethanol residue from the surface. Then, dry the wafer to remove any residual moisture on the surface.

[0034] 2. Deposition of a silica lower cladding layer: The silica lower cladding layer has a refractive index of 1.4447 and is deposited using a wet thermal oxidation method. The temperature during deposition is maintained at 1000 degrees Celsius. By controlling the water vapor flow rate, substrate temperature, and reaction time, a 10μm thick silica lower cladding layer is grown on the cleaned silicon substrate in step 1.

[0035] 3. Deposition of a germanium-doped silicon dioxide layer: The germanium-doped silicon dioxide layer has a refractive index of 1.4741. Plasma-enhanced chemical vapor deposition is used to deposit the germanium-doped silicon dioxide layer on the surface of the silicon dioxide lower cladding. During the deposition process, the reaction gas flow rate of GeCl4 is 32 sccm, the reaction gas flow rate of SiH4 is 20 sccm, and the reaction gas flow rate of N2O is 40 sccm. The substrate temperature is 200°C. By controlling the reaction time and chemical mechanical polishing, a germanium-doped silicon dioxide layer with a thickness of 4 μm and a refractive index of 1.4741 is deposited on the surface of the silicon dioxide lower cladding with a refractive index of 1.4447 in the second step.

[0036] 4. Growth of polysilicon mask layer: Using hot-filament chemical vapor deposition, the chamber pressure is controlled at 1 Pa, the substrate temperature is 200°C, and the reaction ratio of SiH4 and H2, V(H2) / (V(SiH4)+V(H2)), is 98.4%. A 1μm thick polysilicon mask layer is grown on the surface of the germanium-doped silicon dioxide layer.

[0037] 5. Etching polysilicon: Spin-coat a UV-curable photoresist on the surface of the polysilicon mask layer grown in step 4, and remove the exposed photoresist using UV photolithography and wet development. Control the gas flow rates of SF6, CHF3, and O2 to 25 sccm, 50 sccm, and 35 sccm, respectively, and use reactive ion etching to remove the polysilicon mask layer without photoresist protection. Then, remove the photoresist on the surface of the polysilicon mask layer to obtain a polysilicon mask layer with the same structure as the germanium-doped silicon dioxide core layer to be prepared.

[0038] 6. Etching the germanium-doped silicon dioxide core layer: Using the reactive ion etching method in step 5, fluorine ions are used to etch and bombard the exposed germanium-doped silicon dioxide layer under the same conditions to obtain a germanium-doped silicon dioxide core layer of the desired structure;

[0039] 7. Remove the polysilicon mask layer: Use a 15% KOH aqueous solution to remove the polysilicon mask layer remaining in step 6;

[0040] 8. Depositing a silica upper cladding layer: Using the same process as step 2, a silica upper cladding layer was deposited on the surface of the germanium-doped silica core layer and the silica lower cladding layer. Chemical mechanical polishing was used to control the thickness of the silica upper cladding layer to 15 μm and the refractive index of the silica upper cladding to 1.4447; thereby, the wavelength-mode hybrid multiplexer of the present invention was prepared.

Claims

1. A wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure, characterized in that: From bottom to top, it is composed of a silicon substrate, a silica lower cladding, a germanium-doped silica core layer and a silica upper cladding, the germanium-doped silica core layer and the upper cladding are located together on the lower cladding, and the germanium-doped silica core layer is coated in the upper cladding; along the transmission direction of light, the germanium-doped silica core layer is composed of an input straight waveguide (1), a first curved waveguide (2) and a second curved waveguide (3) with the same structure and size, a first straight waveguide (4), a first tapered waveguide (5), a second tapered waveguide (6), a second straight waveguide (7), a third straight waveguide (8), a third tapered waveguide (9) and a fourth tapered waveguide (10) with the same structure and size, a 2×2 multimode interferometer (Ⅱ), a first curved waveguide (2) and a second curved waveguide (3) with the same structure and size, The fifth tapered waveguide (11) and the sixth tapered waveguide (12), the first 1×2 multimode interferometer (III) and the second 1×2 multimode interferometer (IV) having the same structure and size, the seventh tapered waveguide (13) and the tenth tapered waveguide (16) having the same structure and size, the eighth tapered waveguide (14) and the ninth tapered waveguide (15) having the same structure and size, the first 1×1 multimode interferometer (V) and the second 1×1 multimode interferometer (VI) having the same structure and size, the fourth straight waveguide (17) and the fifth straight waveguide (18) having the same structure and size, the eleventh tapered waveguide (19) and the twelfth tapered waveguide (20) having the same structure and size, the third curved waveguide (21) and the fourth curved waveguide (22) having the same structure and size. The invention relates to a waveguide (22), a thirteenth tapered waveguide (23), a fourteenth tapered waveguide (24), a fifteenth tapered waveguide (25) and a sixteenth tapered waveguide (26) having the same structure and size, a first output straight waveguide (27), a second output straight waveguide (28), a third output straight waveguide (29) and a fourth output straight waveguide (30) having the same structure and size; wherein the input straight waveguide (1), the first curved waveguide (2) and the second curved waveguide (3) constitute a 1×2 Y-branch waveguide (I), the first straight waveguide (4), the first tapered waveguide (5), the second tapered waveguide (6) and the second straight waveguide (7) are sequentially connected to form an optical phase modulator, and the first curved waveguide (2) and the optical phase modulator are connected , the second curved waveguide (3), the third straight waveguide (8) and the fourth tapered waveguide (10) are connected in sequence; the third tapered waveguide (9) and the fourth tapered waveguide (10) are the two input ends of the 2×2 multimode interferometer (Ⅱ), the fifth tapered waveguide (11) and the sixth tapered waveguide (12) are the two output ends of the 2×2 multimode interferometer (Ⅱ), the fifth tapered waveguide (11) is also the input end of the first 1×2 multimode interferometer (Ⅲ), the seventh tapered waveguide (13) and the eighth tapered waveguide (14) are the two output ends of the first 1×2 multimode interferometer (Ⅲ), the eighth tapered waveguide (14), the fourth straight waveguide (17), the fourteenth tapered waveguide (24) and the second output straight waveguide (28) are connected in sequence;The sixth tapered waveguide (12) is also the input end of the second 1×2 multimode interferometer (IV), the ninth tapered waveguide (15) and the tenth tapered waveguide (16) are the two output ends of the second 1×2 multimode interferometer (IV), the ninth tapered waveguide (15), the fifth straight waveguide (18), the fifteenth tapered waveguide (25) and the third output straight waveguide (29) are connected in sequence; the seventh tapered waveguide (13) is the input end of the first 1×1 multimode interferometer (V), the eleventh tapered waveguide (19) is the input end of the first 1×1 multimode interferometer (V), and the tenth tapered waveguide (16) is the output end of the second 1×2 multimode interferometer (IV). The output end of the interferometer (V), the eleventh tapered waveguide (19), the third curved waveguide (21), the thirteenth tapered waveguide (23) and the first output straight waveguide (27) are connected in sequence; the tenth tapered waveguide (16) is the input end of the second 1×1 multimode interferometer (VI), the twelfth tapered waveguide (20) is the output end of the second 1×1 multimode interferometer (VI), and the twelfth tapered waveguide (20), the fourth curved waveguide (22), the sixteenth tapered waveguide (26) and the fourth output straight waveguide (30) are connected in sequence.

2. The wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure according to claim 1, characterized in that: The width of the input straight waveguide (1) is W1=8 μm, which can accommodate the transmission of TE0 and TE1 modes. After passing through the 1×2 Y-branch waveguide (Ⅰ), the input straight waveguide (1) is divided into the first curved waveguide (2) and the second curved waveguide (3) with a width of W2=4 μm; the width of the first straight waveguide (4) and the second straight waveguide (7) is W2=4 μm, the width of the first tapered waveguide (5) increases linearly from W2=4 μm to W3=5 μm, and the width of the second tapered waveguide (6) decreases linearly from W3=5 μm to W2=4 μm. The lengths of the first tapered waveguide (5) and the second tapered waveguide (6) are both L1=200 μm. The width of the third straight waveguide (8) is W2=4 μm; the widths of the third tapered waveguide (9) and the fourth tapered waveguide (10) increase linearly from W2=4 μm to W4=6 μm, the distance between the symmetry center of the third tapered waveguide (9) and the fourth tapered waveguide (10) and the symmetry center of the 2×2 multimode interferometer (Ⅱ) is X1=22 μm; the width of the 2×2 multimode interferometer (Ⅱ) is W5=50 μm, and the length is L2=4945 μm; the fifth tapered waveguide (11) and the sixth tapered waveguide (12) are right-angled trapezoidal structures, and the width of the fifth tapered waveguide (11) and the sixth tapered waveguide (12) decreases linearly from W6=23 μm to W7=20 μm, and the length is L3=500 μm; the width of the first 1×2 multimode interferometer (Ⅲ) and the second 1×2 multimode interferometer (Ⅳ) is W7=20 μm, and the length is L4=1445 μm; the seventh tapered waveguide (13) and the tenth tapered waveguide (16) are right-angled trapezoidal structures, and the widths of the seventh tapered waveguide (13) and the tenth tapered waveguide (16) decrease linearly from W9=12 μm to W 10 =10 μm, length L6=200 μm; The width of the eighth tapered waveguide (14) and the ninth tapered waveguide (15) decreases linearly from W8=6 μm to W 11 =2 μm, length L6=200 μm; width of the first 1×1 multimode interferometer (V) and the second 1×1 multimode interferometer (VI) is W 10 =10 μm, the length is L5=915 μm; the width of the fourth straight waveguide (17) and the fifth straight waveguide (18) is W 11 =2 μm; the width of the eleventh tapered waveguide (19) and the twelfth tapered waveguide (20) is W 12 =4 μm linearly reduced to W 13 =2 μm; the width W of the third curved waveguide (21) and the fourth curved waveguide (22) 13 =2 μm; the widths of the thirteenth tapered waveguide (23), the fourteenth tapered waveguide (24), the fifteenth tapered waveguide (25) and the sixteenth tapered waveguide (26) are from W 13 =2 μm linearly increasing to W 14 =4 μm; the width of the first output straight waveguide (27), the second output straight waveguide (28), the third output straight waveguide (29) and the fourth output straight waveguide (30) is W 14 =4 μm.

3. The wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure according to claim 1, characterized in that: The first curved waveguide (2) and the second curved waveguide (3), the third tapered waveguide (9) and the fourth tapered waveguide (10), the fifth tapered waveguide (11) and the sixth tapered waveguide (12), the first 1×2 multimode interferometer (III) and the second 1×2 multimode interferometer (IV), the seventh tapered waveguide (13) and the tenth tapered waveguide (16), the eighth tapered waveguide (14) and the ninth tapered waveguide (15), the first 1×1 multimode interferometer (V) and the second 1×1 multimode interferometer (VI) ), the fourth straight waveguide (17) and the fifth straight waveguide (18), the third curved waveguide (21) and the fourth curved waveguide (22), the thirteenth tapered waveguide (23) and the sixteenth tapered waveguide (26), the fourteenth tapered waveguide (24) and the fifteenth tapered waveguide (25), the first output straight waveguide (27) and the fourth output straight waveguide (30), the second output straight waveguide (28) and the third output straight waveguide (29) are symmetrical structures about the input straight waveguide (1) and its extension line.

4. The wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure according to claim 1, characterized in that: One side edge of the 2×2 multimode interferometer (II), the outer edge of the fifth tapered waveguide (11), the outer edge of the first 1×2 multimode interferometer (III), the outer edge of the seventh tapered waveguide (13), and the outer edge of the first 1×1 multimode interferometer (V) are on the same straight line; the other side edge of the 2×2 multimode interferometer (II), the outer edge of the sixth tapered waveguide (12), the outer edge of the second 1×2 multimode interferometer (IV), the outer edge of the tenth tapered waveguide (16), and the outer edge of the second 1×1 multimode interferometer (VI) are on the same straight line.

5. The wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure according to claim 1, characterized in that: All straight waveguides or extensions of straight waveguides in the wavelength-mode hybrid multiplexer are arranged in a parallel relationship.

6. The wavelength-mode hybrid multiplexer based on a cascaded multimode interferometer structure according to claim 1, Its characteristics are: The input straight waveguide (1) serves as the input end of the wavelength-mode hybrid multiplexer, and the first output straight waveguide (27), the second output straight waveguide (28), the third output straight waveguide (29) and the fourth output straight waveguide (30) serve as the Output 1, Output 2, Output 3 and Output 4 ends of the wavelength-mode hybrid multiplexer respectively; when a 1550 nm wavelength signal is input in TE0 mode, the optical signal is output at the Output 3 port; when a 1620 nm wavelength signal is input in TE0 mode, the optical signal is output at the Output 4 port; when a 1550 nm wavelength signal is input in TE1 mode, the optical signal is output at the Output 2 port; when a 1620 nm wavelength signal is input in TE1 mode, the optical signal is output at the Output 1 port.

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