Polarization beam splitter based on silicon dioxide optical waveguide

Abstract

The invention discloses a polarization beam splitter based on a silicon dioxide optical waveguide, and belongs to the technical field of photon integration. The optical fiber sequentially consists of a substrate, a lower cladding, a core layer waveguide and an upper cladding, wherein the core layer waveguide is coated by the upper cladding; the lower cladding layer and the upper cladding layer are made of silicon dioxide, the core layer waveguides have the same height, are made of germanium-doped silicon dioxide, and are composed of a first 1 * 1 MZI waveguide Core1, a middle straight waveguide Core2 and a second 1 * 1 MZI waveguide Core3; when the waveguide spacing in the middle area of the core layer waveguide is close enough, the core layer waveguide can be regarded as a grating-like structure, so that the average effective refractive indexes of a TE mode and a TM mode in the area are different, coupling and multi-mode interference of light modes are generated at the same time, and after a certain length, the TE mode and the TM mode generate a phase difference, so that the interference of the TE mode and the TM mode is reduced. And finally, carrying out polarization separation and respectively outputting from two ports. The polarization multiplexing technology of a low-refractive-index-difference platform is achieved, or unwanted polarization states are filtered out in a polarization-sensitive device.

Description

Technical Field

[0001] The invention belongs to the technical field of photon integration, and in particular relates to a polarization beam splitter based on silicon dioxide optical waveguide. Background Art

[0002] With the development of artificial intelligence, big data and optical communication systems, the transmission capacity of optical fiber has become a key issue that restricts the further increase of data bandwidth. Affected by optical nonlinear effects, the transmission capacity of single-mode optical fiber has approached the theoretical limit (100Tbit / s) and cannot meet the needs of future applications. Therefore, it is urgent to expand the channel capacity. Multidimensional multiplexing technology is an effective means to further increase the transmission efficiency of single-mode optical fiber. In the multidimensional multiplexing technology of light, polarization multiplexing is an important multiplexing technology 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 of the waveguide, the reflection and refraction of light at the medium boundary 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 modes and TM modes, and these two modes can propagate in different directions to achieve polarization multiplexing or filter out unwanted polarization states in polarization-sensitive devices.

[0005] At present, the research on polarization beam splitters is all realized on high refractive index difference platforms. 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 has high polarization sensitivity, which can not only well confine the light field, but also separate the input light of different polarizations, thereby realizing polarization processing.

[0006] Integrated optical devices made of silica materials have the advantages of low optical loss, large process tolerance, compatibility with CMOS processes, and good mode field matching with single-mode optical fibers. They are widely used in optical communications, optical interconnection, and integrated optics. The silica material platform belongs to a low refractive index difference platform. The refractive index difference between the cladding and the core layer is low, and it has polarization insensitivity. This makes it difficult to design and manufacture devices such as polarization beam splitters on the low refractive index difference platform. Therefore, there is little research on polarization beam splitters on the silica material platform. In order to overcome the above problems, new structures should be developed to break the polarization insensitivity of the low refractive index difference platform, improve polarization sensitivity to achieve polarization separation, and supplement the research on polarization separation of the low refractive index difference platform. Summary of the invention

[0007] The purpose of the present invention is to provide a polarization beam splitter based on a silica optical waveguide, which realizes polarization separation on a silica platform and solves the technical problem that polarization separation is difficult on a platform with a low refractive index difference.

[0008] The present invention adopts a traditional three-layer planar optical waveguide structure, which is widely used in the field of optical communication and optical device applications. The polarization beam splitter based on silicon dioxide optical waveguide described in the present invention is composed of a substrate 21, a lower cladding 22, a core waveguide 23 and an upper cladding 24 from bottom to top, as shown in the attached figure. Figure 1 As shown, the lower cladding is located on the substrate, the core waveguide and the upper cladding are located together on the lower cladding, and the core waveguide is covered by the upper cladding; the lower cladding 22 and the upper cladding 24 of the silica polarization beam splitter are made of silica, and the effective refractive index is 1.4447; the core waveguide 23 is made of germanium-doped silica, and the effective refractive index is 1.4741; the refractive index difference between the core layer and the cladding is 2%; the substrate 21 is a silicon wafer, and the refractive index is 3.455. The core waveguide 23 is composed of a first 1×1MZI waveguide Core1, an intermediate straight waveguide Core2 and a second 1×1MZI 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 located together on the upper surface of the lower cladding 22. From left to right along the transmission direction of light, the first 1×1MZI waveguide Core1 and the second 1×1MZI waveguide Core3 are symmetrical structures about the intermediate straight waveguide Core2.

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

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

[0011] As shown in FIG2(b), which is a top view of the core waveguide of the silica polarization beam splitter of the present invention, the first 1×1 MZI waveguide Core1 is composed of, from left to right, a first input straight waveguide 1, a first input symmetric tapered waveguide 2, a first input asymmetric tapered waveguide 3, a second input asymmetric tapered waveguide 4, a first intermediate straight waveguide 5, a second intermediate straight waveguide 6, a first output asymmetric tapered waveguide 7, a second output asymmetric tapered waveguide 8, a first output symmetric tapered waveguide 9, and a first output straight waveguide 10; the first input symmetric tapered waveguide 2 has an input end and two output ends, the first output symmetric tapered waveguide 9 has two input ends and one output end, the input end of the first input symmetric tapered waveguide 2 is connected to the output end of the first input straight waveguide 1, and the output end of the first output symmetric tapered waveguide 9 is connected to the input end of the first output straight waveguide 10; the first input asymmetric tapered waveguide 2 has an input end and two output ends, the first output symmetric tapered waveguide 9 has two input ends and one output end, the input end of the first input symmetric tapered waveguide 2 is connected to the output end of the first input straight waveguide 1, and the output end of the first output symmetric tapered waveguide 9 is connected to the input end of the first output straight waveguide 10; the first input asymmetric tapered waveguide The waveguide 3, the first intermediate straight waveguide 5 and the first output asymmetric tapered waveguide 7 are sequentially connected between an output end of the first input symmetric tapered waveguide 2 and an input end of the first output symmetric tapered waveguide 9, and the second input asymmetric tapered waveguide 4, the second intermediate straight waveguide 6 and the 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; 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 edge of the first input asymmetric tapered waveguide 3, the upper edge of the first output asymmetric tapered waveguide 7 and the upper edge of the first intermediate straight waveguide 5 are collinearly arranged, and the lower edge of the second input asymmetric tapered waveguide 4, the lower edge of the second output asymmetric tapered waveguide 8 and the lower edge of the second intermediate straight waveguide 6 are collinearly arranged;

[0012] From left to right along the transmission direction of light, the width of the first input straight waveguide 1 and the first output straight waveguide 10 are the same, which is W1=4μm, and the length is the same, which is L1, and the length of L1 is arbitrary; the width of the first input symmetric tapered waveguide 2 gradually widens from W1 to W2=5.4μm, and the length is L2=300μm; the width of the first input asymmetric tapered waveguide 3 and the second input asymmetric tapered waveguide 4 gradually narrows from W2 / 2=2.7μm to W3=1.8μm, and the length is L3=116μm; the spacing 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 spacing 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 0. The distance between the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6 is W3; the width 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 widens from W3 to W2 / 2, and the length is L3=116μm; 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=300μm.

[0013] The second 1×1 MZI waveguide Core3 is composed from left to right of a second input straight waveguide 11, a second input symmetric tapered waveguide 12, a third input asymmetric tapered waveguide 13, a fourth input asymmetric tapered waveguide 14, a third intermediate straight waveguide 15, a fourth intermediate straight waveguide 16, a third output asymmetric tapered waveguide 17, a fourth output asymmetric tapered waveguide 18, a second output symmetric tapered waveguide 19, and a second output straight waveguide 20; the second input symmetric tapered waveguide 12 has an input end and two output ends, the second output symmetric tapered waveguide 19 has two input ends and one output end, the input end of the second input symmetric tapered waveguide 12 is connected to the output end of the second input straight waveguide 11, the output end of the second output symmetric tapered waveguide 19 is connected to the input end of the second output straight waveguide 20; the third input asymmetric tapered waveguide 13, the third intermediate straight waveguide 15, and the third output asymmetric tapered waveguide 17 are connected to the output end of the second output symmetric tapered waveguide 19. The output asymmetric tapered waveguide 17 is 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 edge of the third input asymmetric tapered waveguide 13, the upper edge of the third output asymmetric tapered waveguide 17 and the upper edge of the third intermediate straight waveguide 15 are arranged in a collinear manner, and the lower edge of the fourth input asymmetric tapered waveguide 14, the lower edge of the fourth output asymmetric tapered waveguide 18 and the lower edge of the fourth intermediate straight waveguide 16 are arranged in a collinear manner;

[0014] From left to right along the transmission direction of light, the second input straight waveguide 11 and the second output straight waveguide 20 have the same width of W1=4μm and the same length of L1, and the length of L1 is arbitrary; the width of the second input symmetric tapered waveguide 12 gradually widens from W1 to W2=5.4μm, and the length is L2=300μm; the width of the third input asymmetric tapered waveguide 13 and the fourth input asymmetric tapered waveguide 14 gradually narrows from W2 / 2=2.7μm to W3=1.8μm, and the length is L3=116μm; the spacing 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 spacing 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 third intermediate straight waveguide 16 is the same as W3, and the length is L4=25801μm; the spacing 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 widens from W3 to W2 / 2, and the length is L3=116μm; the spacing 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 spacing 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=300μm.

[0015] From left to right along the transmission direction of light, 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 in parallel; 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 width of the intermediate straight waveguide Core2 is W2=5.4μm, and the length is L4=25801μm; the spacing between the lower edge of the first 1×1MZI waveguide Core1 and the upper edge of the intermediate straight waveguide Core2, and the spacing between the lower edge of the intermediate straight waveguide Core2 and the upper edge of the second 1×1MZI waveguide Core3 are both W3=1.8μm.

[0016] From left to right along the transmission direction of light, the TE mode and the TM mode are input from the Input1 end of the first 1×1 MZI waveguide Core1 in turn, enter the first input straight waveguide 1 and the first input symmetric tapered waveguide 2, and then split into two beams by the first input asymmetric tapered waveguide 3 and the second input asymmetric tapered waveguide 4, respectively entering the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6, and then the two beams are coupled with the intermediate straight waveguide Core2 as a whole and enter the intermediate straight waveguide Core2, and then coupled with the second 1×1 MZI waveguide Core3. The third intermediate straight waveguide 15 and the fourth intermediate straight waveguide 16 are coupled and enter the third intermediate straight waveguide 15 and the fourth intermediate straight waveguide 16, and then reversely couple into the intermediate straight waveguide Core2, and then couple back into the first intermediate straight waveguide 5 and the second intermediate straight waveguide 6, and the coupling is repeated in this way. Finally, the TM mode light is combined by 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 is output from the Output1 end of the first 1×1 MZI waveguide Core1 (as shown in the attached figure). Figure 5 (a)), the TE mode light is combined by 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 is output from the Output2 end of the second 1×1 MZI waveguide Core3 (see Figure 2). Figure 5 (b)); or the TE mode and the TM mode are sequentially input from the Input2 end of the second 1×1 MZI waveguide Core3, and finally the TE mode is output from the Output1 end of the first 1×1 MZI waveguide Core1, and the TM mode is output from the Output2 end of the second 1×1 MZI waveguide Core3.

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

[0018] The function of the polarization beam splitter is to separate the TE mode and TM mode that enter the input waveguide at the same time and output them from different ports. The key to achieving this function is that the effective refractive index of the TE mode and TM mode must be different at the same wavelength and the same waveguide size, thereby generating a phase difference and finally outputting from different ports. The effective refractive index of the TE mode and TM mode of the low refractive index difference platform is very close. Take the silica material platform as an example, as shown in the attached figure. Figure 3 As shown in the figure, at a wavelength of 1550nm, when the core waveguide height H = 4μm, the effective refractive indexes of the TE mode and TM mode of the fundamental mode and the higher-order mode are very close; as shown in the attached figure Figure 4 (a) and Figure 4As shown in (b), the mode field and effective refractive index of the TE mode and TM mode of the square silica waveguide with a cross-sectional size of 4μm×4μm are the same; these all prove the polarization-insensitive characteristics of the low-refractive-index platform, which means that it is difficult to separate the TE mode and the TM mode in any traditional waveguide structure.

[0019] The polarization beam splitter based on silica optical waveguide described in the present invention adopts a special structural design. When the spacing W3 of the five waveguides, namely 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 close enough, it can be regarded as a grating-like structure, which causes the average effective refractive index of the TE mode and the TM mode in this area to be different, and coupling and multi-mode interference of the optical modes occur at the same time. After a certain length, the TE mode and the TM mode produce a phase difference of π, and are finally separated and output from two ports respectively. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0021] FIG2( a ) is a cross-sectional view of a polarization beam splitter based on a silicon dioxide optical waveguide according to the present invention at a middle position;

[0022] FIG2( b ) is a top view of the core waveguide of the polarization beam splitter based on the silica optical waveguide according to the present invention;

[0023] Figure 3 : The relationship curve between the effective refractive index of each mode in the waveguide and the waveguide width when the silica core waveguide has a wavelength of 1550nm and a height of H = 4μm;

[0024] Figure 4 (a) TE mode pattern and effective refractive index in the first input direct wave 1 or the first output straight waveguide 10 (waveguide cross-sectional dimensions are 4 μm×4 μm) at a wavelength of 1550 nm;

[0025] Figure 4 (b) : The pattern pattern and effective refractive index of the TM mode in the first input direct wave 1 or the first output straight waveguide 10 (waveguide cross-sectional dimensions are 4 μm×4 μm) at a wavelength of 1550 nm;

[0026] Figure 5 (a) : A simulation diagram of the light field transmission of the polarization beam splitter based on silica optical waveguide of the present invention at a wavelength of 1550nm, with the TM mode input from Input1 and output from Output1;

[0027] Figure 5 (b) A simulation diagram of the light field transmission of the polarization beam splitter based on silica optical waveguide of the present invention at a wavelength of 1550nm, where the TE mode is input from Input1 and output from Output2;

[0028] FIG6(a) shows a polarization beam splitter based on a silicon dioxide optical waveguide according to the present invention, where the TE mode and the TM mode are input from Input1 respectively, and the transmission from the output port Output1 varies with the wavelength of light;

[0029] FIG6( b ) is a graph showing the variation of transmission from the output port Output2 with the wavelength of light when the TE mode and the TM mode are input from Input1 and Output2, respectively, of the polarization beam splitter based on the silica optical waveguide according to the present invention;

[0030] Figure 7 : Flow chart of the preparation process of the polarization beam splitter based on silica optical waveguide described in the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below through specific implementation modes in conjunction with the 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 of 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 L1=1000 μm is selected here;

[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 first intermediate straight waveguide 15 and the second intermediate straight waveguide 16 of the second 1×1 MZI waveguide Core3, the spacing W3 between the lower edge of the first intermediate straight waveguide 5 of the first 1×1 MZI waveguide Core1 and the upper edge of the second intermediate straight waveguide 6, the spacing W3 between the lower edge of the first intermediate straight waveguide 11 and the upper edge of the second intermediate straight waveguide 12 of the second 1×1 MZI waveguide Core3, the spacing 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 spacing 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 the TM mode, when the input is the TE mode, the signal light is output from the output port Output2, and the TE mode transmission is maximum and the inter-mode crosstalk (TM mode transmission-TE mode transmission) is minimum; when the input is the TM mode, the signal light is output from the output port Output1, and the TM mode transmission is maximum and the inter-mode crosstalk (TE mode transmission-TM mode transmission) is minimum. The final optimal value is W3=1.8μm, L4=25801μm.

[0036] 4. Based on W2=3W3, determine that the width of the input symmetric conical waveguide 2 of the first 1×1 MZI waveguide Core1 and the input symmetric conical waveguide 12 of the second 1×1 MZI waveguide Core3 gradually widens from W1=4μm to W2=5.4μm, and the width of the output symmetric conical waveguide 9 of the first 1×1 MZI waveguide Core1 and the output symmetric conical waveguide 19 of the second 1×1 MZI waveguide Core3 gradually narrows from W2=5.4μm to W1=4μm. At the same time, it is determined that the width of the first input asymmetric tapered waveguide 3 and the second input asymmetric tapered waveguide 4 of the first 1×1 MZI waveguide Core1, and the width of the first input asymmetric tapered waveguide 13 and the second input asymmetric tapered waveguide 14 of the second 1×1 MZI waveguide Core3 gradually narrows from W2 / 2=2.7μm to W3=1.8μm, and the width of the first output asymmetric tapered waveguide 7 and the second output asymmetric tapered waveguide 8 of the first 1×1 MZI waveguide Core1, and the width of the first output asymmetric tapered waveguide 17 and the second output asymmetric tapered waveguide 18 of the second 1×1 MZI waveguide Core3 gradually widens from W3=1.8μm to W2 / 2=2.7μm.

[0037] 5. Finally, determine the length L2 of the input symmetric tapered waveguide 2 and output symmetric tapered waveguide 9 of the first 1×1 MZI waveguide Core1, the input symmetric tapered waveguide 12 and output symmetric tapered waveguide 19 of the second 1×1 MZI waveguide Core3, and the length L3 of the first input asymmetric tapered waveguide 3, the second input asymmetric tapered waveguide 4, the first output asymmetric tapered waveguide 7, the second output asymmetric tapered waveguide 8 of the first 1×1 MZI waveguide Core1, and the first input asymmetric tapered waveguide 13, the second input asymmetric tapered waveguide 14, the first output asymmetric tapered waveguide 17, and the second output asymmetric tapered waveguide 18 of the second 1×1 MZI waveguide Core3. According to the Beam Propagation Method (BPM) calculation, in order to minimize the transmission loss of the device, preferably, L2 = 300 μm, L3 = 116 μm.

[0038] 6. As attached Figure 5 (a) shows the simulation diagram of the light field transmission of TM mode from Input1 to Output1 at a wavelength of 1550nm; Figure 5 (b) shows a simulated diagram of the light field transmission at 1550nm wavelength, where the TE mode is input from Input 1 and output from Output 2. It can be seen that the polarization beam splitter based on the silica optical waveguide of the present invention realizes polarization separation, that is, the TE mode and TM mode that enter the input waveguide at the same time are separated and output from different ports.

[0039] 7. As shown in Figure 6(a), the transmission curves of the output port Output1 vary with the wavelength of light when the TE mode and TM mode are input from Input1 respectively. The results show that when the wavelength of the signal light is 1550nm, the output port Output1 mainly transmits the TM mode, with a transmission of -0.18dB and an inter-mode crosstalk of -35.05dB; within the wavelength range of 1500nm-1618nm, the transmission is greater than -3dB; within the wavelength range of 1500nm-1600nm, the inter-mode crosstalk is less than -10dB.

[0040] 8. As shown in Figure 6(b), the transmission curves of the output port Output2 vary with the wavelength of light when the TE mode and TM mode are input from Input1 respectively. The results show that when the wavelength of the signal light is 1550nm, the output port Output2 mainly transmits the TE mode, with a transmission of -0.22dB and an inter-mode crosstalk of -33.97dB; in the wavelength range of 1500nm-1620nm, the transmission is greater than -3dB; in the wavelength range of 1500nm-1587nm, the inter-mode crosstalk is less than -10dB.

[0041] 9. It can be seen that within the wavelength range of 1500nm-1587nm, the transmission of the TE mode and the TM mode are both greater than -3dB, and the inter-mode crosstalk of the two output ports Output1 and Output2 are both less than -10dB, thereby defining the bandwidth of the silica polarization beam splitter to be 87nm.

[0042] Example 2

[0043] Combine the following Figure 7 The specific preparation method of the present invention is described in detail, and the specific steps are as follows:

[0044] 1. Cleaning the silicon substrate 21: Use a 1 mm thick single crystal silicon wafer as the substrate, use acetone and ethanol to ultrasonically clean it for 10 minutes in sequence, 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 22: At 1000°C, a layer of silicon dioxide film is grown on a clean silicon substrate by wet thermal oxidation method as the lower cladding. By controlling the water vapor flow, substrate temperature and reaction time, the thickness of the lower cladding 22 is maintained at 10 μm;

[0046] 3. Deposition of Ge-SiO2 (refractive index 1.4741) core layer: Use plasma enhanced chemical vapor deposition (PECVD) to deposit germanium (Ge)-doped high refractive index silicon dioxide, control the flow rates of reaction gases GeCl4, SiH4 and N2O to 32sccm, 20sccm and 40sccm respectively, the RF power to 50W, the substrate temperature to 200°C, and control the reaction time to form a Ge-SiO2 core layer with a thickness of H = 4μm on the lower cladding 22;

[0047] 4. Growth of polysilicon mask layer: SiH4 and H2 are used as reaction gases, and hot wire chemical vapor deposition (HWCVD) is used. Under the conditions of growth pressure of 1Pa, substrate temperature of 200°C, and dilution ratio V(H2) / (V(SiH4)+V(H2))=98.4%, a 1 μm thick polysilicon layer is grown on the surface of the Ge-SiO2 core layer as the etching mask layer of the core waveguide by controlling the reaction time;

[0048] 5. Etching the polysilicon mask layer to form a waveguide mask pattern: first spin-coat a photoresist (AZ1500) on the surface of the polysilicon layer formed in step 4, the mask structure being the same as the Ge-SiO2 core waveguide structure to be prepared, subjecting the photoresist to i-line (365nm) ultraviolet lithography and development, leaving the unexposed photoresist that is the same as the waveguide pattern, and removing the exposed photoresist; then, using a reactive ion etching (RIE) method, under a radio frequency power of 100W, controlling the SF6, CHF3 and O2 gas flow rates to 25sccm, 50sccm and 35sccm, the polysilicon layer without photoresist protection is removed through chemical corrosion and physical bombardment of fluorine ions, and after exposure and development to remove the photoresist on the polysilicon surface, a polysilicon mask layer that is the same as the Ge-SiO2 core waveguide structure to be prepared is obtained;

[0049] 6. Etching to form a Ge-SiO2 core layer: using inductively coupled plasma (ICP) etching to remove the Ge-SiO2 core layer without polysilicon mask protection;

[0050] 7. Removing the polysilicon mask layer: using a 15% by mass KOH aqueous solution to remove the remaining polysilicon mask layer, and finally obtaining the Ge-SiO2 core waveguide 23 to be prepared;

[0051] 8. Deposit SiO2 upper cladding layer 24: Deposit SiO2 as upper cladding layer on the surface of Ge-SiO2 core waveguide and lower cladding layer obtained in step 7 by PECVD method, so that the core waveguide and upper cladding layer are located on the lower cladding layer and the core waveguide is covered by the upper cladding layer. The thickness of the silica upper cladding film is controlled by adjusting the gas flow rate, reactant ratio, RF power and time. Then, chemical mechanical polishing is used to make the thickness of the SiO2 upper cladding layer 20 μm, that is, the thickness of the entire silica cladding layer is 10+20=30 μm, thereby preparing the polarization beam splitter based on silica waveguide described in the present invention.

Claims

1. A polarization beam splitter based on a silicon dioxide optical waveguide, characterized in that: The optical waveguide (23) is composed of a substrate (21), a lower cladding (22), a core waveguide (23) and an upper cladding (24) from bottom to top. The core waveguide (23) and the upper cladding (24) are located on the lower cladding (22) and the core waveguide (23) is covered by the upper cladding (24). 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). From left to right along the transmission direction of light, the first 1×1 MZI waveguide (Core1) and the second 1×1 MZI waveguide (Core3) are symmetrical structures with respect to the intermediate straight waveguide (Core2). The first 1×1 MZI waveguide (Core1) is composed from left to right 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 an input end and two output ends, 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 The output asymmetric tapered waveguide (7) is sequentially connected between an output end of the first input symmetric tapered waveguide (2) and an input end of the first output symmetric tapered waveguide (9); the second input asymmetric tapered waveguide (4), the second intermediate straight waveguide (6) and the 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); 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 edge of the first input asymmetric tapered waveguide (3), the upper edge of the first output asymmetric tapered waveguide (7) and the upper edge of the first intermediate straight waveguide (5) are arranged in a collinear manner; the lower edge of the second input asymmetric tapered waveguide (4), the lower edge of the second output asymmetric tapered waveguide (8) and the lower edge of the second intermediate straight waveguide (6) are arranged in a collinear manner; The second 1×1 MZI waveguide (Core3) is composed from left to right 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 an input end and two output ends, the second output symmetrical tapered waveguide (19) has two input ends and one output end, the input end of the second input symmetrical tapered waveguide (12) is connected to the output end of the second input straight waveguide (11), the output end of the second output symmetrical tapered waveguide (19) is connected to the input end 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 (18) are connected to the input end of the second output straight waveguide (20); The output asymmetric tapered waveguide (17) is sequentially connected between an output end of the second input symmetric tapered waveguide (12) and an 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 edge of the third input asymmetric tapered waveguide (13), the upper edge of the third output asymmetric tapered waveguide (17), and the upper edge of the third intermediate straight waveguide (15) are arranged in a collinear manner, and the lower edge of the fourth input asymmetric tapered waveguide (14), the lower edge of the fourth output asymmetric tapered waveguide (18), and the lower edge of the fourth intermediate straight waveguide (16) are arranged in a collinear manner; From left to right along the transmission direction of light, 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 in parallel; 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); 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).

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

3. A polarization beam splitter based on a silicon dioxide optical waveguide as claimed in claim 1, characterized in that: From left to right along the transmission direction of light, the first input straight waveguide (1) and the first output straight waveguide (10) have the same width of W1=4μm and the same length of L1; the width of the first input symmetrical tapered waveguide (2) gradually widens from W1 to W2=5.4μm, and the length is L2=300μm; the width of the first input asymmetrical tapered waveguide (3) and the second input asymmetrical tapered waveguide (4) gradually narrows from W2 / 2=2.7μm to W3=1.8μm, and the length is L3=116μm; the spacing between the lower edge of the input end of the first input asymmetrical tapered waveguide (3) and the upper edge of the input end of the second input asymmetrical tapered waveguide (4) is 0, and the spacing between the lower edge of the output end of the first input asymmetrical tapered waveguide (3) and the upper edge of the output end of the second input asymmetrical tapered waveguide (4) is W3; The width of the intermediate straight waveguide (5) and the second intermediate straight waveguide (6) is the same, which is W3, and the length is L4=25801μm; 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 widens from W3 to W2 / 2, and the length is L3=116μm; 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=300μm.

4. A polarization beam splitter based on a silicon dioxide optical waveguide as claimed in claim 1, characterized in that: From left to right along the transmission direction of light, the second input straight waveguide (11) and the second output straight waveguide (20) have the same width of W1=4μm and the same length of L1; the width of the second input symmetrical tapered waveguide (12) gradually widens from W1 to W2=5.4μm and the length is L2=300μm; the width of the third input asymmetrical tapered waveguide (13) and the fourth input asymmetrical tapered waveguide (14) gradually narrows from W2 / 2=2.7μm to W3=1.8μm and the length is L3=116μm; the spacing 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 spacing 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 waveguide (13) and the fourth intermediate ... The straight waveguide (15) and the third intermediate straight waveguide (16) have the same width of W3 and a length of 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 widens 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 beam splitter based on a silicon dioxide optical waveguide as claimed in claim 1, characterized in that: The width of the middle straight waveguide (Core2) is W2=5.4μm, and the length is L4=25801μm; the distance between the lower edge of the first 1×1MZI waveguide (Core1) 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 1×1MZI waveguide (Core3) are both W3=1.8μm.

6. A polarization beam splitter based on a silicon dioxide optical waveguide as claimed in claim 1, characterized in that: The materials of the lower cladding (22) and the upper cladding (24) are silicon dioxide, both of which have an effective refractive index of 1.4447; the material of the core waveguide (23) is 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 beam splitter based on a silicon dioxide optical waveguide as claimed in claim 1, characterized in that: From left to right along the transmission direction of light, the TE mode and the TM mode are sequentially input from the Input1 end of the first 1×1 MZI waveguide (Core1), pass through the intermediate straight waveguide (Core2) and the second 1×1 MZI waveguide (Core3), and finally the TM mode is output from the Output1 end of the first 1×1 MZI waveguide (Core1), and the TE mode is output from the Output2 end of the second 1×1 MZI waveguide (Core3); or the TE mode and the TM mode are sequentially input from the Input2 end of the second 1×1 MZI waveguide (Core3), pass through the intermediate straight waveguide (Core2) and the first 1×1 MZI waveguide (Core1), and finally the TE mode is output from the Output1 end of the first 1×1 MZI waveguide (Core1), and the TM mode is output from the Output2 end of the second 1×1 MZI waveguide (Core3).

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