A polarization beam splitter based on silica optical waveguide

Abstract

A polarization beamsplitter based on a silicon dioxide optical waveguide belongs to the field of photonic integration technology. It consists sequentially of a substrate, a lower cladding layer, a core waveguide, and an upper cladding layer, with the core waveguide covered by the upper cladding layer. Both the lower and upper cladding layers are made of silicon dioxide. The core waveguide has the same height and is made of germanium-doped silicon dioxide. It is composed of a first 1×1 MZI waveguide. 1 , middle straight waveguide Core 2 Second 1×1MZI waveguide Core 3 The structure is as follows: When the waveguide spacing in the middle region of the core waveguide is close enough, it can be regarded as a grating-like structure. This leads to a difference in the average effective refractive index of the TE mode and the TM mode in this region. At the same time, optical mode coupling and multimode interference occur. After a certain length, the TE mode and the TM mode generate a phase difference, and finally polarization separation is performed and output from two ports respectively. This is to realize the polarization multiplexing technology of low refractive index difference platform or to filter out unwanted polarization states in polarization-sensitive devices.

Description

A polarization beam splitter based on silicon dioxide optical waveguides Technical Field

[0001] This invention belongs to the field of photonic integration technology, specifically relating to a polarization beam splitter based on a silicon dioxide optical waveguide. Background Technology

[0002] With the development of artificial intelligence, big data, and optical communication systems, fiber optic transmission capacity has become a key issue restricting further increases in data bandwidth. Due to optical nonlinear effects, the transmission capacity of single-mode fiber is approaching its theoretical limit (100 Tbit / s), which cannot meet future application demands. Therefore, there is an urgent need to expand channel capacity. Multidimensional multiplexing technology is an effective means to further increase the transmission efficiency of single-mode fiber. Among optical multidimensional multiplexing technologies, polarization multiplexing is an important multiplexing technique used to increase the number of channels and polarization.

[0003] The polarization of light is one of the important physical parameters, which essentially affects the interaction between light and matter. Due to the two-dimensional light confinement effect of waveguides, the reflection and refraction of light at the boundary of the medium depend on the polarization of light, thus generating two different polarization modes: quasi-transverse electric mode (TE mode) and quasi-transverse magnetic mode (TM mode).

[0004] A polarization beam splitter (PBS) splits light in an optical fiber or waveguide into two orthogonal TE and TM modes, which can propagate in different directions to achieve polarization multiplexing or filter out unwanted polarization states in polarization-sensitive devices.

[0005] Current research on polarization beam splitters is conducted on platforms with high refractive index differences. For example, on the SOI platform, due to the high refractive index difference between the cladding and core of the silicon-on-insulator waveguide, it exhibits high polarization sensitivity. This not only effectively confines the optical field but also separates input light of different polarizations, thereby achieving polarization processing.

[0006] Integrated optical devices made of silica materials possess advantages such as low optical loss, large process tolerance, compatibility with CMOS processes, and good mode field matching with single-mode fibers, making them widely used in optical communication, optical interconnects, and integrated optics. However, the silica material platform is a low refractive index difference platform, with a low refractive index difference between the cladding and core layers, exhibiting polarization insensitivity. This makes it difficult to design and fabricate polarization beamsplitters on this platform, resulting in limited research on polarization beamsplitters on silica materials. To overcome these challenges, novel structures should be developed to overcome the polarization insensitivity of the low refractive index difference platform, improve polarization sensitivity to achieve polarization separation, and supplement research on polarization separation on the low refractive index difference platform. Summary of the Invention

[0007] The purpose of this invention is to provide a polarization beam splitter based on a silicon dioxide optical waveguide, which achieves polarization separation on a silicon dioxide platform, solving the technical problem that polarization separation is difficult on platforms with low refractive index differences.

[0008] This invention employs a traditional three-layer planar optical waveguide structure, which is widely used in optical communication and optical device applications. The polarization beamsplitter based on a silicon dioxide optical waveguide described in this invention comprises, from bottom to top, a substrate 21, a lower cladding layer 22, a core waveguide 23, and an upper cladding layer 24, as shown in Figure 1. The lower cladding layer is located on the substrate, and the core waveguide and upper cladding layer are both located on the lower cladding layer, with the core waveguide being covered by the upper cladding layer. The lower cladding layer 22 and upper cladding layer 24 of the silicon dioxide polarization beamsplitter are made of silicon dioxide, both with an effective refractive index of 1.4447. The core waveguide 23 is made of germanium-doped silicon dioxide, with an effective refractive index of 1.4741. The refractive index difference between the core layer and the cladding layer is 2%. The substrate 21 is a silicon wafer with a refractive index of 3.455. The core waveguide 23 is composed of a first 1×1 MZI waveguide Core1, an intermediate straight waveguide Core2, and a second 1×1 MZI waveguide Core3. Core1, Core2, and Core3 have the same height, and the bottom surfaces of Core1, Core2, and Core3 are located in the same plane and are all located on the upper surface of the lower cladding 22. From left to right along the direction of light transmission, the first 1×1 MZI waveguide Core1 and the second 1×1 MZI waveguide Core3 are symmetrical about the intermediate straight waveguide Core2.

[0009] The technical solution adopted by this invention to solve its technical problem is as follows:

[0010] As shown in Figure 2(a), the silicon dioxide polarization beam splitter has a rectangular structure in the middle position on the cross section perpendicular to the input light, and the height of each part is the same, H=4 μm;

[0011] Figure 2(b) is a top view of the silicon dioxide polarization beam splitter core waveguide of the present invention. The first 1×1 MZI waveguide Core1, from left to right, consists of a first input straight waveguide 1, a first input symmetrical tapered waveguide 2, a first input asymmetrical tapered waveguide 3, a second input asymmetrical tapered waveguide 4, a first intermediate straight waveguide 5, a second intermediate straight waveguide 6, a first output asymmetrical tapered waveguide 7, a second output asymmetrical tapered waveguide 8, a first output symmetrical tapered waveguide 9, and a first output straight waveguide 10. The first input symmetrical tapered waveguide 2 has one input end and two output ends, and the first output symmetrical tapered waveguide 9 has two input ends and one output end. The input end of the first input symmetrical tapered waveguide 2 is connected to the output end of the first input straight waveguide 1, and the output end of the first output symmetrical tapered waveguide 9 is connected to the input end of the first output straight waveguide 10. The first input asymmetrical tapered waveguide 1... Waveguide 3, first intermediate straight waveguide 5, and first output asymmetric tapered waveguide 7 are sequentially connected between one output end of the first input symmetric tapered waveguide 2 and one input end of the first output symmetric tapered waveguide 9. Second input asymmetric tapered waveguide 4, second intermediate straight waveguide 6, and second output asymmetric tapered waveguide 8 are sequentially connected between the other output end of the first input symmetric tapered waveguide 2 and the other input end of the first output symmetric tapered waveguide 9. First input straight waveguide 1, first intermediate straight waveguide 5, second intermediate straight waveguide 6, and first output straight waveguide 10 are arranged in parallel. The upper edges of the first input asymmetric tapered waveguide 3, the first output asymmetric tapered waveguide 7, and the first intermediate straight waveguide 5 are collinear. The lower edges of the second input asymmetric tapered waveguide 4, the second output asymmetric tapered waveguide 8, and the second intermediate straight waveguide 6 are collinear.

[0012] Along the light transmission direction from left to right, the first input straight waveguide 1 and the first output straight waveguide 10 have the same width, W1 = 4 μm, and the same length, L1, which is arbitrary. The width of the first input symmetrical tapered waveguide 2 gradually increases from W1 to W2 = 5.4 μm, and its length is L2 = 300 μm. The width of the first input asymmetrical tapered waveguide 3 and the second input asymmetrical tapered waveguide 4 gradually decreases from W2 / 2 = 2.7 μm to W3 = 1.8 μm, and its length is L3 = 116 μm. The distance between the lower edge of the input terminal of the first input asymmetrical tapered waveguide 3 and the upper edge of the input terminal of the second input asymmetrical tapered waveguide 4 is 0, and the distance between the lower edge of the output terminal of the first input asymmetrical tapered waveguide 3 and the upper edge of the output terminal of the second input asymmetrical tapered waveguide 4 is W3. The width of the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6 are the same, W3, and their length is L4 = 25801. μm; the distance between the lower edge of the first intermediate straight waveguide 5 and the upper edge of the second intermediate straight waveguide 6 is W3; the width of the first output asymmetric tapered waveguide 7 and the second output asymmetric tapered waveguide 8 gradually increases from W3 to W2 / 2, and the length is L3=116 μm; the distance between the lower edge of the input end of the first output asymmetric tapered waveguide 7 and the upper edge of the input end of the second output asymmetric tapered waveguide 8 is W3, and the distance between the lower edge of the output end of the first output asymmetric tapered waveguide 7 and the upper edge of the output end of the second output asymmetric tapered waveguide 8 is 0; the width of the first output symmetric tapered waveguide 9 gradually decreases from W2 to W1, and the length is L2=300 μm.

[0013] The second 1×1 MZI waveguide Core3, from left to right, consists of a second input straight waveguide 11, a second input symmetrical tapered waveguide 12, a third input asymmetrical tapered waveguide 13, a fourth input asymmetrical tapered waveguide 14, a third intermediate straight waveguide 15, a fourth intermediate straight waveguide 16, a third output asymmetrical tapered waveguide 17, a fourth output asymmetrical tapered waveguide 18, a second output symmetrical tapered waveguide 19, and a second output straight waveguide 20. The second input symmetrical tapered waveguide 12 has one input terminal and two output terminals, while the second output symmetrical tapered waveguide 19 has two input terminals and one output terminal. The input terminal of the second input symmetrical tapered waveguide 12 is connected to the output terminal of the second input straight waveguide 11, and the output terminal of the second output symmetrical tapered waveguide 19 is connected to the input terminal of the second output straight waveguide 20. The third input asymmetrical tapered waveguide 11... Waveguide 13, the third intermediate straight waveguide 15, and the third output asymmetric tapered waveguide 17 are sequentially connected between one output end of the second input symmetric tapered waveguide 12 and one input end of the second output symmetric tapered waveguide 19. The fourth input asymmetric tapered waveguide 14, the fourth intermediate straight waveguide 16, and the fourth output asymmetric tapered waveguide 18 are sequentially connected between the other output end of the second input symmetric tapered waveguide 12 and the other input end of the second output symmetric tapered waveguide 19. The second input straight waveguide 11, the third intermediate straight waveguide 15, the fourth intermediate straight waveguide 16, and the second output straight waveguide 20 are arranged in parallel. The upper edges of the third input asymmetric tapered waveguide 13, the third output asymmetric tapered waveguide 17, and the third intermediate straight waveguide 15 are collinear. The lower edges of the fourth input asymmetric tapered waveguide 14, the fourth output asymmetric tapered waveguide 18, and the fourth intermediate straight waveguide 16 are collinear.

[0014] Along the light transmission direction from left to right, the second input straight waveguide 11 and the second output straight waveguide 20 have the same width of W1 = 4 μm and the same length of L1, which is arbitrary; the width of the second input symmetrical tapered waveguide 12 gradually increases from W1 to W2 = 5.4 μm, and the length is L2 = 300 μm; the width of the third input asymmetrical tapered waveguide 13 and the fourth input asymmetrical tapered waveguide 14 gradually decreases from W2 / 2 = 2.7 μm to W3 = 1.8 μm, and the length is L3 = 116 μm; the distance between the lower edge of the input end of the third input asymmetrical tapered waveguide 13 and the upper edge of the input end of the fourth input asymmetrical tapered waveguide 14 is 0, and the distance between the lower edge of the output end of the third input asymmetrical tapered waveguide 13 and the upper edge of the output end of the fourth input asymmetrical tapered waveguide 14 is W3; the width of the third intermediate straight waveguide 15 and the fourth intermediate straight waveguide 16 is the same as W3, and the length is L4 = 25801. μm; the distance between the lower edge of the third intermediate straight waveguide 15 and the upper edge of the fourth intermediate straight waveguide 16 is W3; the width of the third output asymmetric tapered waveguide 17 and the fourth output asymmetric tapered waveguide 18 gradually increases from W3 to W2 / 2, and the length is L3=116 μm; the distance between the lower edge of the input end of the third output asymmetric tapered waveguide 17 and the upper edge of the input end of the fourth output asymmetric tapered waveguide 18 is W3, and the distance between the lower edge of the output end of the third output asymmetric tapered waveguide 17 and the upper edge of the output end of the fourth output asymmetric tapered waveguide 18 is 0; the width of the second output symmetric tapered waveguide 19 gradually decreases from W2 to W1, and the length is L2=300 μm.

[0015] Along the light transmission direction from left to right, the first intermediate straight waveguide 5, the second intermediate straight waveguide 6, the intermediate straight waveguide Core2, the third intermediate straight waveguide 15, and the fourth intermediate straight waveguide 16 are arranged parallel to each other. The input end of the intermediate straight waveguide Core2 is at the same position as the input ends of the first intermediate straight waveguide 5, the second intermediate straight waveguide 6, the third intermediate straight waveguide 15, and the fourth intermediate straight waveguide 16, and the output end of the intermediate straight waveguide Core2 is at the same position as the output ends of the first intermediate straight waveguide 5, the second intermediate straight waveguide 6, the third intermediate straight waveguide 15, and the fourth intermediate straight waveguide 16. The width of the intermediate straight waveguide Core2 is W2=5.4 μm, and the length is L4=25801 μm. The distance between the lower edge of the first 1×1 MZI waveguide Core1 and the upper edge of the intermediate straight waveguide Core2, and the distance between the lower edge of the intermediate straight waveguide Core2 and the upper edge of the second 1×1 MZI waveguide Core3, are both W3=1.8 μm.

[0016] From left to right along the light propagation direction, the TE mode and TM mode are sequentially input from the Intput1 terminal of the first 1×1 MZI waveguide Core1, entering the first input straight waveguide 1 and the first input symmetrical tapered waveguide 2. Then, they are split into two beams by the first input asymmetrical tapered waveguide 3 and the second input asymmetrical tapered waveguide 4, respectively entering the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6. These two beams are then coupled together as a whole with the intermediate straight waveguide Core2 and enter the intermediate straight waveguide Core2, before being coupled with the second 1×1 MZI waveguide Core6. The third intermediate straight waveguide 15 and the fourth intermediate straight waveguide 16 of the MZI waveguide Core3 are coupled and enter the third intermediate straight waveguide 15 and the fourth intermediate straight waveguide 16, and then coupled in the opposite direction into the intermediate straight waveguide Core2, and then coupled back into the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6. This coupling is repeated. Finally, the light of the TM mode is combined from the two beams of the first output asymmetric tapered waveguide 7 and the second output asymmetric tapered waveguide 8 into the first output symmetric tapered waveguide 9 and the first output straight waveguide 10, and output from the Output1 end of the first 1×1 MZI waveguide Core1 (as shown in Figure 5(a)). The light of the TE mode is combined from the two beams of the third output asymmetric tapered waveguide 17 and the fourth output asymmetric tapered waveguide 18 into the second output symmetric tapered waveguide 19 and the second output straight waveguide 20, and output from the Output2 end of the second 1×1 MZI waveguide Core3 (as shown in Figure 5(b)); or the TE mode and the TM mode are sequentially coupled from the second 1×1 The input is from the Intput2 terminal of the MZI waveguide Core3, and the TE mode is output from the Output1 terminal of the first 1×1 MZI waveguide Core1, while the TM mode is output from the Output2 terminal of the second 1×1 MZI waveguide Core3.

[0017] The working principle of this polarization beam splitter is as follows:

[0018] The function of a polarization beamsplitter is to separate the TE and TM modes that simultaneously enter the input waveguide and output them from different ports. The core of this function lies in the fact that the effective refractive indices of the TE and TM modes must be different for the same wavelength and waveguide size, thus creating a phase difference and ultimately resulting in outputs from different ports. In low refractive index difference platforms, the effective refractive indices of the TE and TM modes are very close. Taking a silica platform as an example, as shown in Figure 3, at a wavelength of 1550 nm, when the core waveguide height H = 4 μm, the effective refractive indices of the fundamental and higher-order TE and TM modes are very close. As shown in Figures 4(a) and 4(b), the mode fields and effective refractive indices of the TE and TM modes in a square silica waveguide with a cross-sectional size of 4 μm × 4 μm are the same. These all demonstrate the polarization insensitivity of low refractive index platforms, indicating that it is difficult for any traditional waveguide structure to separate the TE and TM modes.

[0019] The polarization beam splitter based on silicon dioxide optical waveguides described in this invention employs a special structural design. When the spacing W3 of the five waveguides—the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6 of the first 1×1 MZI waveguide Core1, the intermediate straight waveguide Core2, and the third intermediate straight waveguide 15 and the fourth intermediate straight waveguide 16 of the second 1×1 MZI waveguide Core3—is sufficiently close, it can be regarded as a grating-like structure. This results in a difference in the average effective refractive index between the TE mode and the TM mode in this region, and simultaneous coupling and multimode interference of optical modes occur. After a certain length, the TE mode and the TM mode generate a phase difference of π, and finally separate and are output from two ports respectively. Attached Figure Description

[0020] Figure 1: Schematic diagram of the polarization beam splitter based on silicon dioxide optical waveguide according to the present invention;

[0021] Figure 2(a): Cross-sectional view of the polarization beam splitter based on silicon dioxide optical waveguide described in this invention at the middle position;

[0022] Figure 2(b): Top view of the core waveguide of the polarization beam splitter based on silicon dioxide optical waveguide according to the present invention;

[0023] Figure 3: Curves showing the relationship between the effective refractive index of each mode in the silicon dioxide core waveguide and the waveguide width at a wavelength of 1550 nm and a height of H = 4 μm.

[0024] Figure 4(a): Mode pattern and effective refractive index of TE mode in the first input direct wave 1 or the first output straight waveguide 10 (waveguide cross-section size is 4 μm × 4 μm) at a wavelength of 1550 nm.

[0025] Figure 4(b): Mode pattern and effective refractive index of TM mode in the first input direct wave 1 or the first output straight waveguide 10 (waveguide cross-section size is 4 μm × 4 μm) at a wavelength of 1550 nm.

[0026] Figure 5(a): Simulation diagram of the optical field transmission of the polarization beam splitter based on silicon dioxide optical waveguide described in this invention at a wavelength of 1550 nm, with TM mode input from Intput1 and output from Output1.

[0027] Figure 5(b): A simulation diagram of the optical field transmission of the polarization beam splitter based on silicon dioxide optical waveguide described in this invention at a wavelength of 1550 nm, with TE mode input from Intput1 and output from Output2.

[0028] Figure 6(a): The polarization beam splitter based on silicon dioxide optical waveguide described in this invention, with TE mode and TM mode input from Intput1 and transmission curves from output port Output1 as a function of light wavelength.

[0029] Figure 6(b): The polarization beam splitter based on silicon dioxide optical waveguide described in this invention, with TE mode and TM mode input from Intput1 and output from Output2 respectively, showing the transmission curves as a function of light wavelength.

[0030] Figure 7: Flowchart of the fabrication process of the polarization beam splitter based on silicon dioxide optical waveguide described in this invention. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0032] Example 1

[0033] 1. First, determine the height H of the core waveguide 23. Since the selected material platform is a silicon dioxide platform with a 2% refractive index difference, and the standard process core thickness for this refractive index difference is 4 μm, the height H of the core waveguide is determined to be 4 μm.

[0034] 2. Determine the width W1 and length L1 of the input straight waveguide 1 and output straight waveguide 10 of the first 1×1 MZI waveguide Core1, and the input straight waveguide 11 and output straight waveguide 20 of the second 1×1 MZI waveguide Core3. W1 is selected as 4 μm to meet the single-mode transmission condition. The length of L1 is arbitrary, and here L1 = 1000 μm is selected.

[0035] 3. Determine the width W3 and length L4 of the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6 of the first 1×1 MZI waveguide Core1, the width W3 and length L4 of the third intermediate straight waveguide 15 and the fourth intermediate straight waveguide 16 of the second 1×1 MZI waveguide Core3, the distance W3 between the lower edge of the first intermediate straight waveguide 5 and the upper edge of the second intermediate straight waveguide 6 of the first 1×1 MZI waveguide Core1, the distance W3 between the lower edge of the third intermediate straight waveguide 15 and the upper edge of the fourth intermediate straight waveguide 16 of the second 1×1 MZI waveguide Core3, the distance W3 between the lower edge of the first 1×1 MZI waveguide Core1 and the upper edge of the intermediate straight waveguide Core2, and the distance W3 between the lower edge of the intermediate straight waveguide Core2 and the upper edge of the second 1×1 MZI waveguide Core3. According to the Beam Propagation Method (BPM), in order to separate the TE mode and TM mode, when the input is in TE mode, the signal light is output from the output port Output2, and the TE mode transmission is the maximum while the inter-mode crosstalk (TM mode transmission - TE mode transmission) is the minimum; when the input is in TM mode, the signal light is output from the output port Output1, and the TM mode transmission is the maximum while the inter-mode crosstalk (TE mode transmission - TM mode transmission) is the minimum. The optimal values ​​are W3 = 1.8 μm and L4 = 25801 μm.

[0036] 4. Based on W2=3W3, the width of the input symmetrical tapered waveguide 2 of the first 1×1 MZI waveguide Core1 and the input symmetrical tapered waveguide 12 of the second 1×1 MZI waveguide Core3 gradually increases from W1=4 μm to W2=5.4 μm, and the width of the output symmetrical tapered waveguide 9 of the first 1×1 MZI waveguide Core1 and the output symmetrical tapered waveguide 19 of the second 1×1 MZI waveguide Core3 gradually decreases from W2=5.4 μm to W1=4 μm. Simultaneously, it is determined that the widths of the first input asymmetric tapered waveguide 3 and the second input asymmetric tapered waveguide 4 of the first 1×1 MZI waveguide Core1, the third input asymmetric tapered waveguide 13 and the fourth input asymmetric tapered waveguide 14 of the second 1×1 MZI waveguide Core3 gradually narrow from W2 / 2=2.7 μm to W3=1.8 μm, and the widths of the first output asymmetric tapered waveguide 7 and the second output asymmetric tapered waveguide 8 of the first 1×1 MZI waveguide Core1, the third output asymmetric tapered waveguide 17 and the fourth output asymmetric tapered waveguide 18 of the second 1×1 MZI waveguide Core3 gradually widen from W3=1.8 μm to W2 / 2=2.7 μm.

[0037] 5. Finally, the lengths L2 of the input symmetrical tapered waveguide 2 and output symmetrical tapered waveguide 9 of the first 1×1 MZI waveguide Core 1, the input symmetrical tapered waveguide 12 and output symmetrical tapered waveguide 19 of the second 1×1 MZI waveguide Core 3, and the lengths L3 of the first input asymmetrical tapered waveguide 3, the second input asymmetrical tapered waveguide 4, the first output asymmetrical tapered waveguide 7, the second output asymmetrical tapered waveguide 8 of the first 1×1 MZI waveguide Core 1, the third input asymmetrical tapered waveguide 13, the fourth input asymmetrical tapered waveguide 14, the third output asymmetrical tapered waveguide 17, and the fourth output asymmetrical tapered waveguide 18 of the second 1×1 MZI waveguide Core 3 are determined. According to the Beam Propagation Method (BPM), to minimize the transmission loss of the device, preferably, L2 = 300 μm and L3 = 116 μm.

[0038] 6. Figure 5(a) shows a simulated optical field transmission diagram of TM mode input from Intput1 and output from Output1 at a wavelength of 1550 nm; Figure 5(b) shows a simulated optical field transmission diagram of TE mode input from Intput1 and output from Output2 at a wavelength of 1550 nm. It can be seen that the polarization beam splitter based on silicon dioxide optical waveguide described in this invention achieves polarization separation, that is, separating the TE mode and TM mode that simultaneously enter the input waveguide and outputting them from different ports.

[0039] 7. As shown in Figure 6(a), the transmission curves of the TE mode and TM mode inputs from Input1 and Output1 respectively are as a function of light wavelength. The results show that when the signal light wavelength is 1550 nm, Output1 mainly transmits the TM mode with a transmission of −0.18 dB and intermode crosstalk of −35.05 dB. In the wavelength range of 1500 nm to 1618 nm, the transmission is > −3 dB. In the wavelength range of 1500 nm to 1600 nm, the intermode crosstalk is < −10 dB.

[0040] 8. As shown in Figure 6(b), the transmission curves of TE mode and TM mode input from Input1 and Output2 are respectively as a function of light wavelength. The results show that when the signal light wavelength is 1550 nm, Output2 mainly transmits TE mode with a transmission of −0.22 dB and intermode crosstalk of −33.97 dB; in the wavelength range of 1500 nm-1620 nm, the transmission is >−3 dB; in the wavelength range of 1500 nm-1587 nm, the intermode crosstalk is <−10 dB.

[0041] 9. It can be seen that in the wavelength range of 1500 nm-1587 nm, the transmission of both TE mode and TM mode is >−3 dB, and the intermode crosstalk of the two output ports Output1 and Output2 is <−10 dB. Based on this, the bandwidth of the silicon dioxide polarization beam splitter is defined as 87 nm.

[0042] Example 2

[0043] The specific preparation method of the present invention will be described in detail below with reference to Figure 7. The specific steps are as follows:

[0044] 1. Cleaning the silicon substrate 21: Select a 1 mm thick single crystal silicon wafer as the substrate, and clean it with acetone and ethanol in sequence for 10 minutes, then rinse it with deionized water to remove impurities on the surface of the silicon substrate, and finally blow it dry with nitrogen.

[0045] 2. Thermal oxidation growth of SiO2 (refractive index 1.4447) lower cladding layer 22: At 1000 ℃, a silicon dioxide thin film is grown on a clean silicon substrate as a lower cladding layer using a wet thermal oxidation method. By controlling the water vapor flow rate, substrate temperature and reaction time, the thickness of the lower cladding layer 22 is maintained at 10 μm.

[0046] 3. Deposition of Ge-SiO2 (refractive index 1.4741) core layer: Plasma-enhanced chemical vapor deposition (PECVD) is used to deposit germanium-doped (Ge) high-refractive-index silicon dioxide. The flow rates of the reaction gases GeCl4, SiH4 and N2O are controlled to be 32 sccm, 20 sccm and 40 sccm, respectively. The radio frequency power is 50W, the substrate temperature is 200 ℃, and the reaction time is controlled to form a Ge-SiO2 core layer with H=4 μm on the lower cladding layer 22.

[0047] 4. Growth of polycrystalline silicon mask layer: Using SiH4 and H2 as reactant gases, hot wire chemical vapor deposition (HWCVD) was employed. Under the conditions of growth gas pressure of 1 Pa, substrate temperature of 200 ℃, and dilution ratio V(H2) / (V(SiH4)+V(H2))=98.4%, a 1μm thick polycrystalline silicon layer was grown on the surface of the Ge-SiO2 core layer as the etching mask layer for the core waveguide by controlling the reaction time.

[0048] 5. Etching the polysilicon mask layer to form the waveguide mask pattern: First, spin-coat photoresist (AZ1500) onto the surface of the polysilicon layer formed in step 4. The mask structure is the same as the Ge-SiO2 core waveguide structure to be prepared. After i-line (365 nm) ultraviolet lithography and development, the unexposed photoresist with the same waveguide pattern is left, and the exposed photoresist is removed. Then, using the reactive ion etching (RIE) method, under the condition of 100 W RF power, the flow rates of SF6, CHF3 and O2 are controlled at 25 sccm, 50 sccm and 35 sccm, respectively. Through the chemical etching and physical bombardment of fluoride ions, the polysilicon layer without photoresist protection is removed. After exposure and development to remove the photoresist on the polysilicon surface, a polysilicon mask layer with the same structure as the Ge-SiO2 core waveguide to be prepared is obtained.

[0049] 6. Etching to form the Ge-SiO2 core layer: The Ge-SiO2 core layer without polysilicon mask protection is removed by etching using inductively coupled plasma (ICP).

[0050] 7. Removal of polycrystalline silicon mask layer: The remaining polycrystalline silicon mask layer is removed using a 15% KOH aqueous solution to finally obtain the Ge-SiO2 core waveguide 23 to be prepared;

[0051] 8. Depositing SiO2 upper cladding 24: Using the PECVD method, SiO2 is deposited on the surface of the Ge-SiO2 core waveguide and the lower cladding obtained in step 7 as an upper cladding, so that the core waveguide and the upper cladding are both located on the lower cladding and the core waveguide is covered by the upper cladding. By adjusting the gas flow rate, reactant ratio, radio frequency power and time, the thickness of the silicon dioxide upper cladding film is controlled. Then, chemical mechanical polishing is used to make the thickness of the SiO2 upper cladding 20 μm, that is, the overall thickness of the silicon dioxide cladding is 10+20=30 μm, thereby preparing the polarization beam splitter based on silicon dioxide waveguide described in this invention.

Claims

1. A polarization beamsplitter based on a silicon dioxide optical waveguide, characterized in that: From bottom to top, it consists of a substrate (21), a lower cladding layer (22), a core waveguide (23), and an upper cladding layer (24). The core waveguide (23) and the upper cladding layer (24) are both located above the lower cladding layer (22), and the core waveguide (23) is covered by the upper cladding layer (24). The core waveguide (23) is composed of a first 1×1 MZI waveguide, a middle straight waveguide Core2, and a second 1×1 MZI waveguide. From left to right along the direction of light transmission, the first 1×1 MZI waveguide and the second 1×1 MZI waveguide have a symmetrical structure about the middle straight waveguide Core2. The MZI waveguide, from left to right, consists of a first input straight waveguide (1), a first input symmetrical tapered waveguide (2), a first input asymmetrical tapered waveguide (3), a second input asymmetrical tapered waveguide (4), a first intermediate straight waveguide (5), a second intermediate straight waveguide (6), a first output asymmetrical tapered waveguide (7), a second output asymmetrical tapered waveguide (8), a first output symmetrical tapered waveguide (9), and a first output straight waveguide (10). The first input symmetrical tapered waveguide (2) has one input end and two output ends, and the first output symmetrical tapered waveguide (9) has two input ends and one output end. The input end of the first input symmetrical tapered waveguide (2) is connected to the output end of the first input straight waveguide (1), and the output end of the first output symmetrical tapered waveguide (9) is connected to the input end of the first output straight waveguide (10). The first input asymmetrical tapered waveguide (3), the first intermediate straight waveguide (5), and the first output asymmetrical tapered waveguide (10) are connected to each other. The first input symmetrical tapered waveguide (7) is connected sequentially between one output end of the first input symmetrical tapered waveguide (2) and one input end of the first output symmetrical tapered waveguide (9). The second input asymmetrical tapered waveguide (4), the second intermediate straight waveguide (6), and the second output asymmetrical tapered waveguide (8) are connected sequentially between the other output end of the first input symmetrical tapered waveguide (2) and the other input end of the first output symmetrical tapered waveguide (9). The first input straight waveguide (1), the first intermediate straight waveguide (5), the second intermediate straight waveguide (6), and the first output straight waveguide (10) are arranged in parallel. The upper edges of the first input asymmetrical tapered waveguide (3), the first output asymmetrical tapered waveguide (7), and the first intermediate straight waveguide (5) are arranged collinearly. The lower edges of the second input asymmetrical tapered waveguide (4), the second output asymmetrical tapered waveguide (8), and the second intermediate straight waveguide (6) are arranged collinearly. The MZI waveguide, from left to right, consists of a second input straight waveguide (11), a second input symmetrical tapered waveguide (12), a third input asymmetrical tapered waveguide (13), a fourth input asymmetrical tapered waveguide (14), a third intermediate straight waveguide (15), a fourth intermediate straight waveguide (16), a third output asymmetrical tapered waveguide (17), a fourth output asymmetrical tapered waveguide (18), a second output symmetrical tapered waveguide (19), and a second output straight waveguide (20).The second input symmetrical tapered waveguide (12) has one input terminal and two output terminals, and the second output symmetrical tapered waveguide (19) has two input terminals and one output terminal. The input terminal of the second input symmetrical tapered waveguide (12) is connected to the output terminal of the second input straight waveguide (11), and the output terminal of the second output symmetrical tapered waveguide (19) is connected to the input terminal of the second output straight waveguide (20). The third input asymmetrical tapered waveguide (13), the third intermediate straight waveguide (15), and the third output asymmetrical tapered waveguide (17) are sequentially connected between one output terminal of the second input symmetrical tapered waveguide (12) and one input terminal of the second output symmetrical tapered waveguide (19). The fourth input asymmetric tapered waveguide (14), the fourth intermediate straight waveguide (16), and the fourth output asymmetric tapered waveguide (18) are sequentially connected between the other output end of the second input symmetric tapered waveguide (12) and the other input end of the second output symmetric tapered waveguide (19); the second input straight waveguide (11), the third intermediate straight waveguide (15), the fourth intermediate straight waveguide (16), and the second output straight waveguide (20) are arranged in parallel; the upper edges of the third input asymmetric tapered waveguide (13), the third output asymmetric tapered waveguide (17), and the third intermediate straight waveguide (15) are arranged collinearly; the fourth input asymmetric tapered waveguide (14) The lower edge of the first 1×1 MZI waveguide (5), the lower edge of the fourth output asymmetric tapered waveguide (18), and the lower edge of the fourth intermediate straight waveguide (16) are collinearly arranged; from left to right along the light transmission direction, the first intermediate straight waveguide (5), the second intermediate straight waveguide (6), the intermediate straight waveguide Core2, the third intermediate straight waveguide (15), and the fourth intermediate straight waveguide (16) are arranged parallel to each other; the input end position of the intermediate straight waveguide Core2 is the same as the input end position of the first intermediate straight waveguide (5), the second intermediate straight waveguide (6), the third intermediate straight waveguide (15), and the fourth intermediate straight waveguide (16), and the output end position of the intermediate straight waveguide Core2 is the same as the output end position of the first intermediate straight waveguide (5), the second intermediate straight waveguide (6), the third intermediate straight waveguide (15), and the fourth intermediate straight waveguide (16); the first intermediate straight waveguide (5), the second intermediate straight waveguide (6), the intermediate straight waveguide Core2, and the second 1×1 MZI waveguide are collinearly arranged parallel to each other. The third and fourth intermediate straight waveguides (15) of the MZI waveguide form a grating structure. The average effective refractive indices of the TE and TM modes differ in this region, resulting in simultaneous optical mode coupling and multimode interference. This causes a π-phase difference between the TE and TM modes, ultimately leading to their separation and output from two separate ports.

2. A polarization beamsplitter based on a silicon dioxide optical waveguide as described in claim 1, characterized in that: The core waveguide (23) has the same height of H=4 μm.

3. A polarization beamsplitter based on a silicon dioxide optical waveguide as described in claim 1, characterized in that: Along the light transmission direction from left to right, the widths of the first input straight waveguide (1) and the first output straight waveguide (10) are the same, W1 = 4 μm, and their lengths are the same, L1; the width of the first input symmetrical tapered waveguide (2) gradually increases from W1 to W2 = 5.4 μm, and its length is L2 = 300 μm; the widths of the first input asymmetrical tapered waveguide (3) and the second input asymmetrical tapered waveguide (4) gradually decrease from W2 / 2 = 2.7 μm to W3 = 1.8 μm, and their lengths are L3 = 116 μm. μm; The distance between the lower edge of the input end of the first input asymmetric tapered waveguide (3) and the upper edge of the input end of the second input asymmetric tapered waveguide (4) is 0, and the distance between the lower edge of the output end of the first input asymmetric tapered waveguide (3) and the upper edge of the output end of the second input asymmetric tapered waveguide (4) is W3; The width of the first intermediate straight waveguide (5) and the second intermediate straight waveguide (6) is the same as W3, and the length is L4=25801 μm; The distance between the lower edge of the first intermediate straight waveguide (5) and the upper edge of the second intermediate straight waveguide (6) is W3; The width of the first output asymmetric tapered waveguide (7) and the second output asymmetric tapered waveguide (8) gradually increases from W3 to W2 / 2, and the length is L3=116 μm; the distance between the lower edge of the input end of the first output asymmetric tapered waveguide (7) and the upper edge of the input end of the second output asymmetric tapered waveguide (8) is W3, and the distance between the lower edge of the output end of the first output asymmetric tapered waveguide (7) and the upper edge of the output end of the second output asymmetric tapered waveguide (8) is 0; the width of the first output symmetric tapered waveguide (9) gradually narrows from W2 to W1, and the length is L2=300 μm.

4. A polarization beamsplitter based on a silicon dioxide optical waveguide as described in claim 1, characterized in that: Along the light transmission direction from left to right, the second input straight waveguide (11) and the second output straight waveguide (20) have the same width of W1 = 4 μm and the same length of L1; the width of the second input symmetrical tapered waveguide (12) gradually increases from W1 to W2 = 5.4 μm and the length is L2 = 300 μm; the width of the third input asymmetrical tapered waveguide (13) and the fourth input asymmetrical tapered waveguide (14) gradually decreases from W2 / 2 = 2.7 μm to W3 = 1.8 μm and the length is L3 = 116 μm. μm; the distance between the lower edge of the input end of the third input asymmetric tapered waveguide (13) and the upper edge of the input end of the fourth input asymmetric tapered waveguide (14) is 0, and the distance between the lower edge of the output end of the third input asymmetric tapered waveguide (13) and the upper edge of the output end of the fourth input asymmetric tapered waveguide (14) is W3; the width of the third intermediate straight waveguide (15) and the fourth intermediate straight waveguide (16) is the same as W3, and the length is L4=25801 μm; the distance between the lower edge of the third intermediate straight waveguide (15) and the upper edge of the fourth intermediate straight waveguide (16) is W3; the width of the third output asymmetric tapered waveguide (17) and the fourth output asymmetric tapered waveguide (18) gradually increases from W3 to W2 / 2, and the length is L3=116 μm; the distance between the lower edge of the input end of the third output asymmetric tapered waveguide (17) and the upper edge of the input end of the fourth output asymmetric tapered waveguide (18) is W3, and the distance between the lower edge of the output end of the third output asymmetric tapered waveguide (17) and the upper edge of the output end of the fourth output asymmetric tapered waveguide (18) is 0; the width of the second output symmetric tapered waveguide (19) gradually narrows from W2 to W1, and the length is L2=300 μm.

5. A polarization beamsplitter based on a silicon dioxide optical waveguide as described in claim 1, characterized in that: The width of the middle straight waveguide Core2 is W2=5.4 μm and the length is L4=25801 μm; the distance between the lower edge of the first 1×1 MZI waveguide and the upper edge of the middle straight waveguide Core2, and the distance between the lower edge of the middle straight waveguide Core2 and the upper edge of the second 1×1 MZI waveguide are both W3=1.8 μm.

6. A polarization beamsplitter based on a silicon dioxide optical waveguide as described in claim 1, characterized in that: The lower cladding (22) and upper cladding (24) are made of silicon dioxide with an effective refractive index of 1.4447; the core waveguide (23) is made of germanium-doped silicon dioxide with an effective refractive index of 1.4741; and the substrate (21) is a silicon wafer with a refractive index of 3.

455.

7. A polarization beamsplitter based on a silicon dioxide optical waveguide as described in claim 1, characterized in that: From left to right along the direction of light transmission, the TE mode and TM mode are input sequentially from the Intput1 terminal of the first 1×1 MZI waveguide, through the intermediate straight waveguide Core2 and the second 1×1 MZI waveguide, and finally the TM mode is output from the Output1 terminal of the first 1×1 MZI waveguide, while the TE mode is output from the Output2 terminal of the second 1×1 MZI waveguide; or the TE mode and TM mode are input sequentially from the Intput2 terminal of the second 1×1 MZI waveguide, through the intermediate straight waveguide Core2 and the first 1×1 MZI waveguide, and finally the TE mode is output from the Output1 terminal of the first 1×1 MZI waveguide, while the TM mode is output from the Output2 terminal of the second 1×1 MZI waveguide.

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