Silicon dioxide wavelength division multiplexer based on multi-mode interference device and asymmetric multi-mode interference device cascade structure

Abstract

The invention discloses a silicon dioxide wavelength division multiplexer based on a multi-mode interference device and an asymmetric multi-mode interference device cascade structure, and belongs to the technical field of silicon dioxide integrated optics. Silicon is used as a substrate, silicon dioxide is used as a lower cladding layer and an upper cladding layer, and a core layer is germanium-doped silicon dioxide; the core layer and the upper wrapping layer are both located on the lower wrapping layer, and the core layer is wrapped by the upper wrapping layer; wherein the core layer consists of a 1 * 2 multi-mode interference device (MMI), a first asymmetric multi-mode interference device (AMMI) for an O wave band and a second asymmetric multi-mode interference device (AMMI) for an S + C + L wave band; according to the core layer, separation of input optical signals of an O wave band and an S + C + L wave band is achieved through an MMI structure, and eight-channel multiplexing and demultiplexing are achieved through two follow-up cascaded AMMI structures. According to the device, a passive structure is adopted, and multiplexing and demultiplexing are carried out on optical signals of two different wavebands through the self-mapping principle of an MMI structure and an AMMI structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon dioxide integrated optics, and in particular relates to a silicon dioxide wavelength division multiplexer based on a cascade structure of a multimode interferometer (MMI) and an asymmetric multimode interferometer (AMMI). 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. Wavelength division multiplexing (WDM) leverages wavelength resources to achieve communication capacity expansion. WDM involves coupling optical signals of different wavelengths into the same waveguide for transmission at the input through a WDM. Demultiplexing devices are then used at the receiving end to separate the signals by wavelength. Because optical signals of different wavelengths can carry different information without interfering with each other, WDM can significantly increase the communication capacity of communication systems.

[0003] The performance indicators of a wavelength division multiplexer (WDM) primarily include insertion loss, crosstalk, and operating bandwidth. These performance indicators must be well-balanced and well-balanced to ensure low insertion loss, wide bandwidth, and low crosstalk at the operating wavelength. This ensures optimal multiplexing and demultiplexing of signals at different wavelengths, improving the device's system capacity and transmission efficiency. Silicon dioxide, with its mature manufacturing process, high process tolerances, and low loss, meets the design requirements of WDMs. Summary of the Invention

[0004] The purpose of the present invention is to provide a silica wavelength division multiplexer based on a cascade structure of a multimode interferometer (MMI) and an asymmetric multimode interferometer (AMMI).

[0005] The present invention describes a silica wavelength division multiplexer based on a cascaded structure of a multimode interferometer (MMI) and an asymmetric multimode interferometer (AMMI). The device uses silicon as a substrate, silica as the lower and upper cladding layers, and a germanium-doped silica core layer. Both the core and upper cladding layers are located above the lower cladding, with the core layer being covered by the upper cladding. The substrate has a thickness of 0.4 to 0.8 mm, the silica lower cladding has a thickness of 5 to 15 μm, the core has a thickness of 2 to 6 μm, and the silica upper cladding above the core has a thickness of 10 to 20 μm. The present invention first uses an MMI structure to separate input optical signals in two different wavelength bands: the O band (1260 to 1360 nm) and the S+C+L band (1500 to 1600 nm). Subsequently, two AMMI structures operating in different wavelength bands are cascaded to achieve eight-channel multiplexing and demultiplexing. The device of the present invention adopts a passive structure and multiplexes and demultiplexes optical signals of two different wavebands through the self-imaging principle of the MMI structure and the AMMI structure.

[0006] Specifically, the core layer is composed of a 1×2 multimode interferometer, a first asymmetric multimode interferometer for the O band, and a second asymmetric multimode interferometer for the S+C+L band; along the transmission direction of light, the core layer is composed of an input straight waveguide, a 1×2 multimode interferometer, a first tapered waveguide, a first curved waveguide, a second tapered waveguide, a first straight waveguide, a third tapered waveguide, a second curved waveguide, a fourth tapered waveguide, a second straight waveguide, a third curved waveguide, a fifth tapered waveguide, a first asymmetric multimode interferometer, a sixth tapered waveguide, a fourth curved waveguide, a first output straight waveguide , a seventh tapered waveguide, a fifth curved waveguide, a second output straight waveguide, an eighth tapered waveguide, a sixth curved waveguide, a third output straight waveguide, a ninth tapered waveguide, a seventh curved waveguide, a fourth output straight waveguide, an eighth curved waveguide, a tenth tapered waveguide, a second asymmetric multimode interferometer, an eleventh tapered waveguide, a ninth curved waveguide, an eighth output straight waveguide, a twelfth tapered waveguide, a tenth curved waveguide, a seventh output straight waveguide, a thirteenth tapered waveguide, an eleventh curved waveguide, a sixth output straight waveguide, a fourteenth tapered waveguide, a twelfth curved waveguide, and a fifth output straight waveguide;

[0007] Among them, the first tapered waveguide, the first curved waveguide, the second tapered waveguide, the first straight waveguide, the third curved waveguide and the fifth tapered waveguide are connected in sequence; the third tapered waveguide, the second curved waveguide, the fourth tapered waveguide, the second straight waveguide, the eighth curved waveguide and the tenth tapered waveguide are connected in sequence; the sixth tapered waveguide, the fourth curved waveguide and the first output straight waveguide are connected in sequence; the seventh tapered waveguide, the fifth curved waveguide and the second output straight waveguide are connected in sequence; the eighth tapered waveguide, the sixth curved waveguide and the third The output straight waveguide is connected in sequence, the ninth tapered waveguide, the seventh curved waveguide and the fourth output straight waveguide are connected in sequence, the eleventh tapered waveguide, the ninth curved waveguide and the eighth output straight waveguide are connected in sequence, the twelfth tapered waveguide, the tenth curved waveguide and the seventh output straight waveguide are connected in sequence, the thirteenth tapered waveguide, the eleventh curved waveguide and the sixth output straight waveguide are connected in sequence, the fourteenth tapered waveguide, the twelfth curved waveguide and the fifth output straight waveguide are connected in sequence; along the transmission direction of light in the input straight waveguide, the input The straight waveguide is arranged on the left side of the front end face of the multimode interferometer I as the input end of the 1×2 multimode interferometer. The first tapered waveguide and the third tapered waveguide are arranged on the left and right sides of the rear end face of the multimode interferometer as the two output ends of the 1×2 multimode interferometer. The input straight waveguide and the first tapered waveguide are located on the same side of the symmetry center of the 1×2 multimode interferometer. The fifth tapered waveguide is arranged on the right side of the front end face of the first asymmetric multimode interferometer as the input end of the first asymmetric multimode interferometer. The sixth tapered waveguide and the seventh tapered waveguide are arranged on the left and right sides of the rear end face of the multimode interferometer as the two output ends of the 1×2 multimode interferometer. The tapered waveguide, the eighth tapered waveguide, and the ninth tapered waveguide are arranged on the left side of the rear part of the first asymmetric multimode interferometer, which are the four output ends of the first asymmetric multimode interferometer; the tenth tapered waveguide is arranged on the left side of the front end of the second asymmetric multimode interferometer, which is the input end of the second asymmetric multimode interferometer; the eleventh tapered waveguide, the twelfth tapered waveguide, the thirteenth tapered waveguide, and the fourteenth tapered waveguide are arranged on the right side of the rear part of the second asymmetric multimode interferometer, which are the four output ends of the second asymmetric multimode interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic diagram of the cross-sectional structure of a wavelength division multiplexer;

[0009] Figure 2 1 is a schematic diagram of the top view structure of the core layer of the wavelength division multiplexer;

[0010] Figure 3 (a)-3(h) are the simulated light field diagrams of the device when eight different signal inputs are applied;

[0011] Figure 4 (a)-(b) are the simulated spectra of the device when inputting two different wavelength bands;

[0012] Figure 5 The process flow chart of the device preparation is shown in FIG. DETAILED DESCRIPTION

[0013] The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0014] Example 1

[0015] The present invention describes a silica wavelength division multiplexer based on a cascade structure of a multimode interferometer (MMI) and an asymmetric multimode interferometer (AMMI), with silicon as the substrate, silica (refractive index 1.4447) as the lower and upper cladding layers, and a core layer of germanium-doped silica (refractive index 1.4741). Figure 1 As shown, the core layer and the upper cladding layer are both located above the lower cladding layer, and the core layer is covered by the upper cladding layer.

[0016] The core layer consists of a 1×2 multimode interferometer I, a first asymmetric multimode interferometer II for the O band, and a second asymmetric multimode interferometer III for the S+C+L band, as shown in Figure 2 As shown, along the transmission direction of light, the core layer consists of an input straight waveguide 1, a 1×2 multimode interferometer I, a first tapered waveguide 2, a first curved waveguide 3, a second tapered waveguide 4, a first straight waveguide 5, a third tapered waveguide 6, a second curved waveguide 7, a fourth tapered waveguide 8, a second straight waveguide 9, a third curved waveguide 10, a fifth tapered waveguide 11, a first asymmetric multimode interferometer II, a sixth tapered waveguide 12, a fourth curved waveguide 13, a first output straight waveguide 14, a seventh tapered waveguide 15, a fifth curved waveguide 16, a second output straight waveguide 17, an eighth tapered waveguide 18, a sixth curved waveguide 19, a waveguide 19, a third output straight waveguide 20, a ninth tapered waveguide 21, a seventh curved waveguide 22, a fourth output straight waveguide 23, an eighth curved waveguide 24, a tenth tapered waveguide 25, a second asymmetric multimode interferometer III, an eleventh tapered waveguide 26, a ninth curved waveguide 27, an eighth output straight waveguide 28, a twelfth tapered waveguide 29, a tenth curved waveguide 30, a seventh output straight waveguide 31, a thirteenth tapered waveguide 32, an eleventh curved waveguide 33, a sixth output straight waveguide 34, a fourteenth tapered waveguide 35, a twelfth curved waveguide 36, and a fifth output straight waveguide 37;

[0017] Among them, the first tapered waveguide 2, the second tapered waveguide 4, the third tapered waveguide 6 and the fourth tapered waveguide 8 are isosceles trapezoidal structures; the fifth tapered waveguide 11 and the tenth tapered waveguide 25 are non-isosceles trapezoidal structures, and the signal light is input into the first asymmetric multimode interferometer II and the second asymmetric multimode interferometer III at a certain angle; the sixth tapered waveguide 12, the seventh tapered waveguide 15, the eighth tapered waveguide 18, the ninth tapered waveguide 21, the eleventh tapered waveguide 26, the twelfth tapered waveguide 29, the thirteenth tapered waveguide 32 and the fourteenth tapered waveguide 35 are all non-isosceles trapezoidal structures.

[0018] Among them, the first tapered waveguide 2, the first curved waveguide 3, the second tapered waveguide 4, the first straight waveguide 5, the third curved waveguide 10 and the fifth tapered waveguide 11 are connected in sequence, the third tapered waveguide 6, the second curved waveguide 7, the fourth tapered waveguide 8, the second straight waveguide 9, the eighth curved waveguide 24 and the tenth tapered waveguide 25 are connected in sequence, the sixth tapered waveguide 12, the fourth curved waveguide 13 and the first output straight waveguide 14 are connected in sequence, the seventh tapered waveguide 15, the fifth curved waveguide 16 and the second output straight waveguide 17 are connected in sequence, the eighth tapered waveguide 18, the sixth curved waveguide 19 and the second output straight waveguide 20 are connected in sequence The first tapered waveguide 19 is connected to the third output straight waveguide 20 in sequence, the ninth tapered waveguide 21, the seventh curved waveguide 22 and the fourth output straight waveguide 23 are connected in sequence, the eleventh tapered waveguide 26, the ninth curved waveguide 27 and the eighth output straight waveguide 28 are connected in sequence, the twelfth tapered waveguide 29, the tenth curved waveguide 30 and the seventh output straight waveguide 31 are connected in sequence, the thirteenth tapered waveguide 32, the eleventh curved waveguide 33 and the sixth output straight waveguide 34 are connected in sequence, the fourteenth tapered waveguide 35, the twelfth curved waveguide 36 and the fifth output straight waveguide 37 are connected in sequence; along the input straight waveguide The transmission direction of the light in the guide (1) is as follows: the input straight waveguide 1 is arranged on the left side of the front end face of the multimode interferometer I, which is the input end of the 1×2 multimode interferometer I; the first tapered waveguide 2 and the third tapered waveguide 6 are arranged on the left and right sides of the rear end face of the multimode interferometer I, which are the two output ends of the 1×2 multimode interferometer I; the input straight waveguide 1 and the first tapered waveguide 2 are located on the same side of the symmetry center of the 1×2 multimode interferometer I; the fifth tapered waveguide 11 is arranged on the right side of the front end face of the first asymmetric multimode interferometer II, which is the input end of the first asymmetric multimode interferometer II; the sixth tapered waveguide 12, The seventh tapered waveguide 15, the eighth tapered waveguide 18, and the ninth tapered waveguide 21 are arranged on the left side of the rear portion of the first asymmetric multimode interferometer II, serving as the four output ends of the first asymmetric multimode interferometer II. The tenth tapered waveguide 25 is arranged on the left side of the front end of the second asymmetric multimode interferometer III, serving as the input end of the second asymmetric multimode interferometer III. The eleventh tapered waveguide 26, the twelfth tapered waveguide 29, the thirteenth tapered waveguide 32, and the fourteenth tapered waveguide 35 are arranged on the right side of the rear portion of the second asymmetric multimode interferometer III, serving as the four output ends of the second asymmetric multimode interferometer III.

[0019] The working principle of the wavelength division multiplexer is as follows:

[0020] The optical signal of TE0 mode (including O band (1260-1360nm) and S+C+L band (1500-1600nm)) enters the input straight waveguide 1 and transmits from the front face to the rear face. Then, it enters the 1×2 multimode interferometer I through the input straight waveguide 1. According to the self-imaging principle, since the self-imaging period of the O band wavelength signal is longer, the optical signal of O band is output in the first tapered waveguide 2, and then continues along the first curved waveguide 3, the second tapered waveguide 4, the first straight waveguide 5, and the second tapered waveguide 6. The optical signal in the S+C+L band passes through the 1×2 multimode interferometer I and is outputted from the third tapered waveguide 6. The optical signal then passes through the second curved waveguide 7, the fourth tapered waveguide 8, the second straight waveguide 9, the eighth curved waveguide 24, and the tenth tapered waveguide 25 to reach the second asymmetric multimode interferometer III. The O-band optical signal is input obliquely along the third curved waveguide 10 and the fifth tapered waveguide 11 into the first asymmetric multimode interferometer II. Based on the principle of self-imaging, the input signal is split into different wavelength channels due to the dispersion of the oblique input. These wavelength signals are imaged at different axial positions Y relative to the input waveguide. Therefore, the 1320 nm optical signal passes through the first asymmetric multimode interferometer II and is output from the sixth tapered waveguide 12. It then travels along the fourth curved waveguide 13 to the first output straight waveguide 14. The 1300 nm optical signal passes through the first asymmetric multimode interferometer II and is output from the seventh tapered waveguide 15. It then travels along the fifth curved waveguide 16 to the second output straight waveguide 17. The 1280 nm optical signal passes through the first asymmetric multimode interferometer II and is output from the eighth tapered waveguide 18. It then travels along the sixth curved waveguide 19 to the third output straight waveguide 20. The 1262 nm optical signal passes through the first asymmetric multimode interferometer II and is output from the ninth tapered waveguide 21. It then travels along the seventh curved waveguide 22 to the fourth output straight waveguide 23.Optical signals in the S+C+L band are input obliquely along the eighth curved waveguide 24 and the tenth tapered waveguide 25 into the second asymmetric multimode interferometer III. Based on the principle of self-imaging, the input signal is separated into different wavelength channels due to the dispersion of the oblique input. These wavelength signals are imaged at different axial positions Y relative to the input waveguide. Therefore, the 1576 nm optical signal passes through the second asymmetric multimode interferometer III and is output from the eleventh tapered waveguide 26. It then passes along the ninth curved waveguide 27 to the eighth output straight waveguide 28. The 1556 nm optical signal passes through the second asymmetric multimode interferometer III and is output from the twelfth tapered waveguide 29. It then passes along the tenth curved waveguide 30 to the seventh output straight waveguide 31. The 1536 nm optical signal passes through the second asymmetric multimode interferometer III and is output from the thirteenth tapered waveguide 32. It then passes along the eleventh curved waveguide 33 to the sixth output straight waveguide 34. The 1517 nm optical signal passes through the second asymmetric multimode interferometer III and is output from the fourteenth tapered waveguide 35. It then passes along the twelfth curved waveguide 36 to the fifth output straight waveguide 37.

[0021] Example 2

[0022] In the core plane (such as Figure 2 The direction parallel to the transmission direction of light in the input straight waveguide 1 is defined as the length of the waveguide, the direction perpendicular to the transmission direction of light in the input straight waveguide 1 is defined as the width of the waveguide; the direction perpendicular to the core layer plane is defined as the thickness of the waveguide.

[0023] The dimensional parameters of each part of the core waveguide were determined by the beam propagation method: the thickness of the substrate was 0.6 mm, the thickness of the silica lower cladding was 10 μm, and the thickness of the silica upper cladding above the core layer was 15 μm. The thickness of the core layer is 4 μm; the width of the input straight waveguide 1 is W1 = 4 μm, which can accommodate TE0 mode transmission; the width of the 1×2 multimode interferometer I is W2 = 11.6 μm, and the length is L1 = 1563 μm; the distance between the symmetry center of the input straight waveguide 1 and the symmetry center of the 1×2 multimode interferometer I is X1 = 3.8 μm; the width of the first tapered waveguide 2 and the third tapered waveguide 6 both decrease linearly from W3 = 4 μm to W4 = 2 μm, and the length of the first tapered waveguide 2 and the third tapered waveguide 6 is L2 = 150 μm, and the distance between the symmetry center of the first tapered waveguide 2 and the third tapered waveguide 6 and the symmetry center of the 1×2 multimode interferometer I is X1 = 3.8 μm; the width of the second tapered waveguide 4 and the fourth tapered waveguide 8 both increase linearly from W4 = 2 μm to W5 = 4 μm, and the length of the second tapered waveguide 4 and the fourth tapered waveguide 8 is L3 = 200 μm;

[0024] The width of the fifth tapered waveguide 11 increases linearly from W6 = 4 μm to W7 = 40 μm, the length of the fifth tapered waveguide 11 is L4 = 700 μm, the distance between the symmetric center of the input end and the symmetric center of the output end of the fifth tapered waveguide 11 is X2 = 60 μm, and the distance between the symmetric center of the output end of the fifth tapered waveguide 11 and the symmetric center of the first asymmetric multimode interferometer II is X3 = 10 μm; the width of the first asymmetric multimode interferometer II is W8 = 60 μm, and the length is L5 = 19500 μm; the widths of the sixth tapered waveguide 12, the seventh tapered waveguide 15, the eighth tapered waveguide 18, and the ninth tapered waveguide 21 all decrease linearly from W9 = 248.9 μm to W 10 =6 μm, and the projected lengths along the first asymmetric multimode interferometer II are all equal to L6 = 501.1 μm; the projected widths of the sixth tapered waveguide 12, the seventh tapered waveguide 15, the eighth tapered waveguide 18, and the ninth tapered waveguide 21 along the first asymmetric multimode interferometer II are all equal to X4 = 38 μm, and the distances between the input ends of the sixth tapered waveguide 12, the seventh tapered waveguide 15, the eighth tapered waveguide 18, and the ninth tapered waveguide 21 and the input end of the first asymmetric multimode interferometer II are Y1 = 16418.6 μm, Y2 = 16668.6 μm, Y3 = 16923.6 μm, and Y4 = 17178.6 μm, respectively; the widths of the fourth curved waveguide 13, the fifth curved waveguide 16, the sixth curved waveguide 19, and the seventh curved waveguide 22 are all equal to W 10 =6μm reduced to W 11 = 4μm; the width of the first output straight waveguide 14, the second output straight waveguide 17, the third output straight waveguide 20 and the fourth output straight waveguide 23 is W 11 =4μm;

[0025] The width of the tenth tapered waveguide 25 increases linearly from W6 = 4 μm to W7 = 40 μm. The length of the tenth tapered waveguide 25 is L4 = 700 μm. The distance between the symmetric center of the input end and the symmetric center of the output end of the tenth tapered waveguide 25 is X5 = 60 μm. The distance between the symmetric center of the output end of the tenth tapered waveguide 25 and the symmetric center of the second asymmetric multimode interferometer III is X6 = 19 μm. The width of the second asymmetric multimode interferometer III is W 12 =78μm, the length is L7=30913μm; the widths of the eleventh tapered waveguide 26, the twelfth tapered waveguide 29, the thirteenth tapered waveguide 32 and the fourteenth tapered waveguide 35 are all from W 13 =270.3μm linearly reduced to W 14=6 μm, and the projected lengths along the second asymmetric multimode interferometer III are all equal to L8 = 479.7 μm; the projected widths of the eleventh tapered waveguide 26, the twelfth tapered waveguide 29, the thirteenth tapered waveguide 32, and the fourteenth tapered waveguide 35 along the second asymmetric multimode interferometer III are all equal to X7 = 39 μm; the distances between the input ends of the eleventh tapered waveguide 26, the twelfth tapered waveguide 29, the thirteenth tapered waveguide 32, and the fourteenth tapered waveguide 35 and the input end of the second asymmetric multimode interferometer III are Y5 = 23332.9 μm, Y6 = 23622.9 μm, Y7 = 23912.9 μm, and Y8 = 24207.9 μm, respectively; the widths of the ninth curved waveguide 27, the tenth curved waveguide 30, the eleventh curved waveguide 33, and the twelfth curved waveguide 36 are all equal to W 14 =6μm reduced to W 15 = 4μm; the width of the eighth output straight waveguide 28, the seventh output straight waveguide 31, the sixth output straight waveguide 34 and the fifth output straight waveguide 37 is W 15 =4μm.

[0026] All straight waveguides or extensions of straight waveguides in the wavelength division multiplexer are parallel. Except for the lengths indicated above, the remaining waveguides only serve as connections and have no specific length requirements.

[0027] The simulation results of the device are as follows Figure 3 As shown in (a)-3(h), 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 P in 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 the other output ports of the device, and CT is the crosstalk of the device. The simulated spectrum of the device when two different bands are input is as follows: Figure 4 Output 1 to Output 8 correspond to the first output straight waveguide 14, the second output straight waveguide 17, the third output straight waveguide 20, the fourth output straight waveguide 23, the fifth output straight waveguide 37, the sixth output straight waveguide 34, the seventh output straight waveguide 31, and the eighth output straight waveguide 28, respectively.

[0028] The simulation spectrum scanning results of the device are as follows Figure 4 (a) and 4(b), Figure 4The CH1 to CH8 in the figure correspond to Output1 to Output8. This curve shows the relationship between the input wavelength of the entire device and the insertion loss at different ports. As shown in the spectrum scan, Figure 4 (a) is the output response of different ports when the input optical signal is O-band. Figure 4 (b) shows the output responses of different ports when the input optical signal is in the S+C+L band.

[0029] When the device inputs TE0 mode and 1262nm wavelength signal, the simulation results are as follows: Figure 3 As shown in (a), the insertion loss of the wavelength division multiplexer is 1.54dB, the 3dB bandwidth is 9nm, and the maximum crosstalk value of the remaining ports is -18.58dB;

[0030] When the device inputs TE0 mode and 1280nm wavelength signal, the simulation results are as follows: Figure 3 As shown in (b), the insertion loss of the wavelength division multiplexer is 0.91dB, the 3dB bandwidth is 11nm, and the maximum crosstalk value of the remaining ports is -19.06dB;

[0031] When the device inputs TE0 mode and 1300nm wavelength signal, the simulation results are as follows: Figure 3 As shown in (c), the insertion loss of the wavelength division multiplexer is 0.70dB, the 3dB bandwidth is 12nm, and the maximum crosstalk value of the remaining ports is -18.79dB;

[0032] When the device inputs TE0 mode and 1320nm wavelength signal, the simulation results are as follows: Figure 3 As shown in (d), the insertion loss of the wavelength division multiplexer is 0.89dB, the 3dB bandwidth is 12nm, and the maximum crosstalk value of the remaining ports is -18.35dB.

[0033] When the device inputs TE0 mode and 1517nm wavelength signal, the simulation results are as follows: Figure 3 As shown in (e), at this time, the insertion loss of the wavelength division multiplexer is 0.76dB, the 3dB bandwidth is 12nm, and the maximum crosstalk value of the remaining ports is -18.08dB.

[0034] When the device inputs TE0 mode and 1536nm wavelength signal, the simulation results are as follows: Figure 3 As shown in (f), at this time, the insertion loss of the wavelength division multiplexer is 0.62dB, the 3dB bandwidth is 12nm, and the maximum crosstalk value of the remaining ports is -18.17dB.

[0035] When the device inputs TE0 mode and 1556nm wavelength signal, the simulation results are as follows: Figure 3As shown in (g), the insertion loss of the wavelength division multiplexer is 0.76dB, the 3dB bandwidth is 11nm, and the maximum crosstalk value of the remaining ports is -17.62dB.

[0036] When the device inputs TE0 mode and 1576nm wavelength signal, the simulation results are as follows: Figure 3 As shown in (h), the insertion loss of the wavelength division multiplexer is 1.14dB, the 3dB bandwidth is 12nm, and the maximum crosstalk value of the remaining ports is -24.26dB.

[0037] Example 3

[0038] The following is combined with Figure 5 The specific preparation method of the present invention is shown and described, and the steps are as follows:

[0039] 1. Silicon substrate cleaning: Select 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. Then, rinse the wafer with deionized water to remove any ethanol residue from the surface. Finally, dry the wafer to remove any residual moisture on the surface.

[0040] 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. The substrate temperature, reaction ratio, and reaction time are controlled to grow a 10μm thick silica lower cladding layer on the cleaned silicon substrate in step 1.

[0041] 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 (PECVD) 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 rates of GeCl4, SiH4, and N2O are 32 sccm, 20 sccm, and 40 sccm, respectively. The substrate temperature is 200°C. By controlling the reaction time and chemical mechanical polishing (CMP), a 4 μm-thick germanium-doped silicon dioxide layer with 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.

[0042] 4. Growth of a polysilicon mask layer: Using hot-filament chemical vapor deposition (CVD), a 1μm-thick polysilicon mask layer was grown on the surface of the germanium-doped silicon dioxide layer with the chamber pressure controlled at 1Pa, the substrate temperature at 200°C, and the reaction ratio of SiH4 to H2 (V(H2) / (V(SiH4)+V(H2)) at 98.4%.

[0043] 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 core layer to be prepared.

[0044] 6. Etching the silicon dioxide core layer: Using the reactive ion etching method in step 5, the exposed germanium-doped silicon dioxide layer is corroded and bombarded with fluorine ions under the same conditions to obtain a germanium-doped silicon dioxide core layer with the desired structure;

[0045] 7. Remove the polysilicon mask layer: Use a 15% KOH aqueous solution to remove the polysilicon mask layer remaining in step 6;

[0046] 8. Depositing a silica upper cladding layer: The steps are the same as those in step 3. A silica upper cladding layer is deposited on the surface of the germanium-doped silica core layer and the silica lower cladding layer. The thickness of the silica upper cladding layer above the core layer is controlled to 15 μm by chemical mechanical polishing, and the refractive index of the silica upper cladding layer is controlled to 1.4447; thereby obtaining the silica wavelength division multiplexer based on the cascade structure of multimode interferometer (MMI) and asymmetric multimode interferometer (AMMI).

Claims

1. A silica wavelength division multiplexer based on a cascade structure of a multimode interferometer and an asymmetric multimode interferometer, characterized by: The invention adopts silicon as substrate, silicon dioxide as lower cladding and upper cladding, and the core layer is germanium-doped silicon dioxide. The core layer and the upper cladding are both located on the lower cladding. Along the transmission direction of light, the core layer is composed of an input straight waveguide (1), a 1×2 multimode interferometer (Ⅰ), a first tapered waveguide (2), a first curved waveguide (3), a second tapered waveguide (4), a first straight waveguide (5), a third tapered waveguide (6), a second curved waveguide (7), a fourth tapered waveguide (8), a second straight waveguide (9), a third curved waveguide (10), a fifth tapered waveguide (11), a first straight waveguide for O band, and a second tapered waveguide (12). an asymmetric multimode interferometer (II), a sixth tapered waveguide (12), a fourth curved waveguide (13), a first output straight waveguide (14), a seventh tapered waveguide (15), a fifth curved waveguide (16), a second output straight waveguide (17), an eighth tapered waveguide (18), a sixth curved waveguide (19), a third output straight waveguide (20), a ninth tapered waveguide (21), a seventh curved waveguide (22), a fourth output straight waveguide (23), an eighth curved waveguide (24), a tenth tapered waveguide (25), a second asymmetric multimode interferometer for the S+C+L band, interferometer (III), an eleventh tapered waveguide (26), a ninth curved waveguide (27), an eighth output straight waveguide (28), a twelfth tapered waveguide (29), a tenth curved waveguide (30), a seventh output straight waveguide (31), a thirteenth tapered waveguide (32), an eleventh curved waveguide (33), a sixth output straight waveguide (34), a fourteenth tapered waveguide (35), a twelfth curved waveguide (36), and a fifth output straight waveguide (37); wherein the first tapered waveguide (2), the second tapered waveguide (4), the third tapered waveguide (6), and the fourth tapered waveguide (7) are connected to each other. The waveguide (8) is an isosceles trapezoidal structure; the fifth tapered waveguide (11) and the tenth tapered waveguide (25) are non-isosceles trapezoidal structures, and the signal light is tilted at a certain angle and input into the first asymmetric multimode interferometer (II) and the second asymmetric multimode interferometer (III); the sixth tapered waveguide (12), the seventh tapered waveguide (15), the eighth tapered waveguide (18), the ninth tapered waveguide (21), the eleventh tapered waveguide (26), the twelfth tapered waveguide (29), the thirteenth tapered waveguide (32) and the fourteenth tapered waveguide (35) are all non-isosceles trapezoidal structures;The first tapered waveguide (2), the first curved waveguide (3), the second tapered waveguide (4), the first straight waveguide (5), the third curved waveguide (10) and the fifth tapered waveguide (11) are connected in sequence; the third tapered waveguide (6), the second curved waveguide (7), the fourth tapered waveguide (8), the second straight waveguide (9), the eighth curved waveguide (24) and the tenth tapered waveguide (25) are connected in sequence; the sixth tapered waveguide (12), the fourth curved waveguide (13) and the first output straight waveguide (14) are connected in sequence; the seventh tapered waveguide (15), the fifth curved waveguide (16) and the second output straight waveguide (17) are connected in sequence; the eighth tapered waveguide (18), the sixth curved waveguide (19) and the tenth tapered waveguide (25) are connected in sequence; The curved waveguide (19) and the third output straight waveguide (20) are connected in sequence, the ninth tapered waveguide (21), the seventh curved waveguide (22) and the fourth output straight waveguide (23) are connected in sequence, the eleventh tapered waveguide (26), the ninth curved waveguide (27) and the eighth output straight waveguide (28) are connected in sequence, the twelfth tapered waveguide (29), the tenth curved waveguide (30) and the seventh output straight waveguide (31) are connected in sequence, the thirteenth tapered waveguide (32), the eleventh curved waveguide (33) and the sixth output straight waveguide (34) are connected in sequence, the fourteenth tapered waveguide (35), the twelfth curved waveguide (36) and the fifth output straight waveguide (37) are connected in sequence, Along the transmission direction of light in the input straight waveguide (1), the input straight waveguide (1) is arranged on the left side of the front end face of the multimode interferometer (Ⅰ) as the input end of the 1×2 multimode interferometer (Ⅰ), the first tapered waveguide (2) and the third tapered waveguide (6) are arranged on the left and right sides of the rear end face of the multimode interferometer (Ⅰ) as the two output ends of the 1×2 multimode interferometer (Ⅰ), and the input straight waveguide (1) and the first tapered waveguide (2) are located on the same side of the symmetry center of the 1×2 multimode interferometer (Ⅰ); the fifth tapered waveguide (11) is arranged on the right side of the front end face of the first asymmetric multimode interferometer (Ⅱ) as the input end of the first asymmetric multimode interferometer (Ⅱ), and the sixth tapered waveguide ( 12), the seventh tapered waveguide (15), the eighth tapered waveguide (18), and the ninth tapered waveguide (21) are arranged on the left side of the rear part of the first asymmetric multimode interferometer (II) and are the four output ends of the first asymmetric multimode interferometer (II); the tenth tapered waveguide (25) is arranged on the left side of the front end of the second asymmetric multimode interferometer (III) and is the input end of the second asymmetric multimode interferometer (III); the eleventh tapered waveguide (26), the twelfth tapered waveguide (29), the thirteenth tapered waveguide (32), and the fourteenth tapered waveguide (35) are arranged on the right side of the rear part of the second asymmetric multimode interferometer (III) and are the four output ends of the second asymmetric multimode interferometer (III).

2. The silica wavelength division multiplexer based on a cascade structure of a multimode interferometer and an asymmetric multimode interferometer according to claim 1, characterized in that: The thickness of the substrate is 0.4-0.8 mm, the thickness of the silicon dioxide lower cladding is 5-15 μm, the thickness of the core layer is 2-6 μm, and the thickness of the silicon dioxide upper cladding above the core layer is 10-20 μm; the refractive index of silicon dioxide is 1.4447, and the refractive index of germanium-doped silicon dioxide is 1.4741.

3. The silica wavelength division multiplexer based on a cascade structure of a multimode interferometer and an asymmetric multimode interferometer according to claim 1, characterized in that: In the core layer plane, the direction parallel to the transmission direction of light in the input straight waveguide (1) is defined as the length of the waveguide, and the direction perpendicular to the transmission direction of light in the input straight waveguide (1) is defined as the width of the waveguide; The direction perpendicular to the core plane is defined as the thickness of the waveguide; the thickness of the core layer is 4 μm; the width of the input straight waveguide (1) is W1 = 4 μm, which can accommodate TE0 mode transmission; the width of the 1×2 multimode interferometer (I) is W2 = 11.6 μm, and the length is L1 = 1563 μm; the distance between the symmetry center of the input straight waveguide (1) and the symmetry center of the 1×2 multimode interferometer (I) is X1 = 3.8 μm; the width of the first tapered waveguide (2) and the third tapered waveguide (6) both decrease linearly from W3 = 4 μm to W4 = 2 μm, the length of the first tapered waveguide (2) and the third tapered waveguide (6) are both L2 = 150 μm, and the distance between the symmetry center of the first tapered waveguide (2) and the third tapered waveguide (6) and the symmetry center of the 1×2 multimode interferometer (I) is X1 = 3.8 μm; the width of the second tapered waveguide (4) and the fourth tapered waveguide (8) both decrease linearly from W3 = 4 μm to W4 = 2 μm, the length of the first tapered waveguide (2) and the third tapered waveguide (6) are both L2 = 150 μm, and the distance between the symmetry center of the first tapered waveguide (2) and the third tapered waveguide (6) and the symmetry center of the 1×2 multimode interferometer (I) is X1 = 3.8 μm; the width of the second tapered waveguide (4) and the fourth tapered waveguide (8) both decrease linearly from W4=2μm increases linearly to W5=4μm, and the lengths of the second tapered waveguide (4) and the fourth tapered waveguide (8) are both L3=200μm; the width of the fifth tapered waveguide (11) increases linearly from W6=4μm to W7=40μm, and the length of the fifth tapered waveguide (11) is L4=700μm; the distance between the symmetry center of the input end and the symmetry center of the output end of the fifth tapered waveguide (11) is X2=60μm, and the distance between the symmetry center of the output end of the fifth tapered waveguide (11) and the symmetry center of the first asymmetric multimode interferometer (II) is X3=10μm; the width of the first asymmetric multimode interferometer (II) is W8=60μm, and the length is L5=19500μm; the widths of the sixth tapered waveguide (12), the seventh tapered waveguide (15), the eighth tapered waveguide (18), and the ninth tapered waveguide (21) all decrease linearly from W9=248.9μm to W 10 =6 μm, and the projection lengths along the first asymmetric multimode interferometer (II) are equal to L6 = 501.1 μm; the projection widths of the sixth tapered waveguide (12), the seventh tapered waveguide (15), the eighth tapered waveguide (18) and the ninth tapered waveguide (21) along the first asymmetric multimode interferometer (II) are equal to X4 = 38 μm, and the distances between the input ends of the sixth tapered waveguide (12), the seventh tapered waveguide (15), the eighth tapered waveguide (18) and the ninth tapered waveguide (21) and the input end of the first asymmetric multimode interferometer (II) are Y1 = 16418.6 μm, Y2 = 16668.6 μm, Y3 = 16923.6 μm and Y4 = 17178.6 μm respectively; the widths of the fourth curved waveguide (13), the fifth curved waveguide (16), the sixth curved waveguide (19) and the seventh curved waveguide (22) are all from W 10 =6μm reduced to W 11 =4μm; the width of the first output straight waveguide (14), the second output straight waveguide (17), the third output straight waveguide (20) and the fourth output straight waveguide (23) is W 11 =4μm; the width of the tenth tapered waveguide (25) increases linearly from W6=4μm to W7=40μm, the length of the tenth tapered waveguide (25) is L4=700μm, the distance between the symmetric center of the input end and the symmetric center of the output end of the tenth tapered waveguide (25) is X5=60μm, the distance between the symmetric center of the output end of the tenth tapered waveguide (25) and the symmetric center of the second asymmetric multimode interferometer (III) is X6=19μm; the width of the second asymmetric multimode interferometer (III) is W 12 =78 μm, the length is L7=30913 μm; the widths of the eleventh tapered waveguide (26), the twelfth tapered waveguide (29), the thirteenth tapered waveguide (32) and the fourteenth tapered waveguide (35) are all from W 13 =270.3μm linearly reduced to W 14 =6 μm, and the projection lengths along the second asymmetric multimode interferometer (III) are equal to L8 = 479.7 μm; the projection widths of the eleventh tapered waveguide (26), the twelfth tapered waveguide (29), the thirteenth tapered waveguide (32) and the fourteenth tapered waveguide (35) along the second asymmetric multimode interferometer (III) are equal to X7 = 39 μm, and the projection widths of the eleventh tapered waveguide (26), the twelfth tapered waveguide (29), the thirteenth tapered waveguide (32) and the fourteenth tapered waveguide (35) along the second asymmetric multimode interferometer (III) are equal to X7 = 39 μm. The distances between the input ends of the waveguide (32) and the fourteenth tapered waveguide (35) and the input end of the second asymmetric multimode interferometer (III) are Y5=23332.9 μm, Y6=23622.9 μm, Y7=23912.9 μm and Y8=24207.9 μm respectively. The widths of the ninth curved waveguide (27), the tenth curved waveguide (30), the eleventh curved waveguide (33) and the twelfth curved waveguide (36) are all from W 14 =6μm reduced to W 15 =4μm; the width of the eighth output straight waveguide (28), the seventh output straight waveguide (31), the sixth output straight waveguide (34) and the fifth output straight waveguide (37) is W 15 =4μm.

4. The silica wavelength division multiplexer based on a cascade structure of a multimode interferometer and an asymmetric multimode interferometer according to claim 1, characterized in that: An optical signal of TE0 mode including O band and S+C+L band enters the input straight waveguide 1 and is transmitted from the front face to the back face, and enters the 1×2 multimode interferometer (Ⅰ) through the input straight waveguide (1). According to the self-imaging principle, since the self-imaging period of the O band wavelength signal is longer, the optical signal of the O band is output from the first tapered waveguide (2), and then continues along the first curved waveguide (3), the second tapered waveguide (4), the first straight waveguide (5), the third curved waveguide (10), and the fifth tapered waveguide (11) to reach the first asymmetric multimode interferometer (Ⅱ); since the self-imaging period of the S+C+L band wavelength signal is shorter than the self-imaging period of the O band wavelength signal, the optical signal of the S+C+L band passes through the 1×2 multimode interferometer. The optical signal of the O band is tilted along the third curved waveguide (10) and the fifth tapered waveguide (11) to be inputted into the first asymmetric multimode interferometer (II). According to the self-imaging principle, the input signal is divided into different wavelength channels due to the dispersion of the tilted input. These wavelength signals are imaged at different axial positions Y relative to the input waveguide. Therefore, the optical signal of 1320 nm passes through the first asymmetric multimode interferometer (II) and is outputted at the sixth tapered waveguide (12). The optical signal of 1300nm passes through the first asymmetric multimode interferometer (II) and is outputted at the seventh tapered waveguide (15), and then passes along the fifth curved waveguide (16) to reach the second output straight waveguide (17); the optical signal of 1280nm passes through the first asymmetric multimode interferometer (II) and is outputted at the eighth tapered waveguide (18), and then passes along the sixth curved waveguide (19) to reach the third output straight waveguide (20); the optical signal of 1262nm passes through the first asymmetric multimode interferometer (II) and is outputted at the ninth tapered waveguide (21), and then passes along the seventh curved waveguide (22) to reach the fourth output straight waveguide (23); the optical signal of S+C+L band is outputted at the ninth tapered waveguide (21), and then passes along the seventh curved waveguide (22) to reach the fourth output straight waveguide (23); the optical signal of S+C+L band is outputted at the eighth tapered waveguide (18), and then passes along the sixth curved waveguide (19) to reach the third output straight waveguide (20). The optical signal is tilted along the eighth curved waveguide (24) and the tenth tapered waveguide (25) and is inputted into the second asymmetric multimode interferometer (III). According to the self-imaging principle, the input signal is divided into different wavelength channels due to the dispersion of the tilted input. These wavelength signals are imaged at different axial positions Y relative to the input waveguide. Therefore, the optical signal of 1576 nm passes through the second asymmetric multimode interferometer (III) and is outputted at the eleventh tapered waveguide (26), and then arrives at the eighth output straight waveguide (28) along the ninth curved waveguide (27); the optical signal of 1556 nm passes through the second asymmetric multimode interferometer (III) and is outputted at the twelfth tapered waveguide (29), and then arrives at the seventh output straight waveguide (31) along the tenth curved waveguide (30).The 1536nm optical signal passes through the second asymmetric multimode interferometer (III) and is output from the thirteenth tapered waveguide (32), and then arrives at the sixth output straight waveguide (34) along the eleventh curved waveguide (33); the 1517nm optical signal passes through the second asymmetric multimode interferometer (III) and is output from the fourteenth tapered waveguide (35), and then arrives at the fifth output straight waveguide (37) along the twelfth curved waveguide (36).

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