A TE based on polymer optical waveguide 10 -TE 00 / TE 20 -TE 10 Compact Mode Converter

Abstract

A TE based on polymer optical waveguide 10 ‑TE 00 / TE 20 ‑TE 10 This compact mode converter belongs to the field of photonic integration technology. It consists of a substrate, a lower cladding, a core waveguide, and an upper cladding. The core waveguide is covered by the upper cladding. The lower and upper claddings are EpoClad, and the core waveguide is EpoCore, with the same height. It is constructed by sequentially connecting an input straight waveguide, a first intermediate asymmetric tapered waveguide, a second intermediate asymmetric tapered waveguide, a third intermediate asymmetric tapered waveguide, a fourth intermediate asymmetric tapered waveguide, a fifth intermediate asymmetric tapered waveguide, an output symmetric tapered waveguide, and an output straight waveguide. When passing through the intermediate asymmetric tapered waveguide, different mode components propagate with different effective lengths, causing different phase changes, ultimately resulting in the target mode. This increases channel transmission capacity and can be used in mode add / drop multiplexers (MADMs) and high-order mode filters.

Description

Technical Field

[0001] The present invention belongs to the technical field of photonic integrated devices, and specifically relates to a TE based on polymer optical waveguide. 10 -TE 00 / TE 20 -TE 10 Compact mode converter. Background Art

[0002] With the rapid development of emerging technologies such as 5G, cloud computing, big data, and artificial intelligence in recent years, communication capacity has grown exponentially year by year. Optical fiber transmission capacity has become a key constraint on further increasing data bandwidth. Due to factors such as optical nonlinearity and fiber melting, the transmission capacity of single-mode optical fiber has reached its theoretical limit (100Tbit / s), which cannot meet future application needs. Therefore, it is urgent to expand channel capacity.

[0003] Mode Division Multiplexing (MDM) based on few-mode fiber uses different orthogonal optical modes in the optical fiber as independent transmission channels. Each channel carries a separate information flow. Multimode waveguides serve as bus optical trunks, enabling parallel transmission of multiple orthogonal modes on a single physical channel, thereby effectively improving the transmission capacity of the system. Optical modes are different field distributions formed by the spatial distribution of photons in a cavity or waveguide during light propagation. Common optical modes include TE 00 TE 10 TE 01 TE 20 TE 02 TE 11 wait.

[0004] Mode division multiplexing has a higher nonlinear tolerance and can realize more data multiplexing functions in a limited space, which not only improves the capacity of the optical transmission system, but also avoids the interference of nonlinear effects on the system. In addition, in terms of manufacturing, wiring and maintenance, it is more compatible with standard single-mode fiber (SMF) systems and can be used in combination. In terms of photonic integration, mode division multiplexing technology has two main advantages: one is to increase signal density, and the other is to improve efficiency. The key components in the mode division multiplexing system include mode multiplexers / demultiplexers, mode switches, mode converters, mode rotators, etc. A mode converter is a passive device that can convert a specific mode into another specific mode. Most of the existing work is based on the fundamental mode TE 00 To other modes (such as TE 10 or TE 20) conversion, while direct conversion between higher-order modes has been less studied. Direct conversion between higher-order modes can be applied to mode add / drop multiplexers (MADMs) and high-order mode filters. Furthermore, existing work can only achieve conversion of one set of modes on the same device, not two sets of modes simultaneously.

[0005] Mode converters are generally large in size and have problems such as limited operating bandwidth and large insertion loss. Research has been focused on improving integration, reducing losses, lowering process complexity, and increasing operating bandwidth. The current development of hybrid multiplexing technology places higher demands on the operating bandwidth of mode converters. Therefore, realizing high-performance multi-order mode converters in a low-cost manner remains a major challenge. There are many materials used to prepare planar optical waveguide mode converters, among which polymer materials have the advantages of low cost and simple processing. Mode division multiplexing devices based on polymer waveguides have also achieved considerable research results. Summary of the Invention

[0006] The present invention aims to provide a TE based on polymer optical waveguide 10 -TE 00 / TE 20 -TE 10 Compact mode converters, which are implemented on a polymer platform on the same device TE 10 -TE 00 and TE 20 -TE 10 Two sets of mode conversions solve technical problems such as large size and limited working bandwidth.

[0007] The present invention adopts a traditional three-layer planar optical waveguide structure, which is widely used in the field of optical communications and optical devices. 10 -TE 00 / TE 20 -TE 10 The compact mode converter is composed of a substrate 1, a lower cladding 2, a core waveguide 3 and an upper cladding 4 from bottom to top, as shown in the attached figure. Figure 1 As shown, the lower cladding layer 2 is located on the substrate 1, the core waveguide 3 and the upper cladding layer 4 are located together on the lower cladding layer 2, and the core waveguide 3 is covered by the upper cladding layer 4; the material of the lower cladding layer 2 and the upper cladding layer 4 of the polymer mode converter is EpoClad, and the effective refractive index is 1.559 (@1550nm); the material of the core waveguide 3 is EpoCore, and the effective refractive index is 1.569 (@1550nm); the substrate 1 is a silicon wafer with a refractive index of 3.455.

[0008] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0009] As shown in FIG2(a), the input end of the polymer mode converter is a rectangular structure in a cross section perpendicular to the input light, and the height of each part of the core waveguide is the same, which is H = 5 μm.

[0010] 2( b ) is a top view of the core waveguide 3 of the polymer mode converter according to the present invention, in which the surface of the lower cladding 2 is defined as the xy plane, the input light direction is the +y axis direction, and the right side of the input light direction is the +x axis direction; the core waveguide 3 of the polymer mode converter is composed of an input straight waveguide 5, a first intermediate asymmetric tapered waveguide 6, a second intermediate asymmetric tapered waveguide 7, a third intermediate asymmetric tapered waveguide 8, a fourth intermediate asymmetric tapered waveguide 9, a fifth intermediate asymmetric tapered waveguide 10, an output symmetric tapered waveguide 11, and an output straight waveguide 12 connected in sequence along the light transmission direction; the width of the input straight waveguide 5 is W1=21.5 μm, and the length L1 has no specific requirements; the width of the first intermediate asymmetric tapered waveguide 6 gradually widens from W1 to W2=40 μm, and the length L2=480 μm, and the symmetry center of the output end is offset by 10 μm relative to the symmetry center of the input end along the -x axis direction; the width of the second intermediate asymmetric tapered waveguide 7 starts at W1 and ends at W2=40 μm, and ends at L2=480 μm. The width of the third intermediate asymmetric tapered waveguide 8 gradually narrows from W2 to W3 = 20 μm, the length is L4 = 400 μm, and the symmetry center of the output end is offset by 18 μm relative to the symmetry center of the input end along the -x axis; the width of the fourth intermediate asymmetric tapered waveguide 9 is always W3, the length is L5 = 450 μm, and the symmetry center of the output end is offset by 10 μm relative to the symmetry center of the input end along the -x axis; the width of the fifth intermediate asymmetric tapered waveguide 10 is always W3, the length is L6 = 440 μm, and the symmetry center of the output end is offset by 5 μm relative to the symmetry center of the input end along the -x axis; the width of the output symmetric tapered waveguide 11 gradually narrows from W3 to W4 = 13.2 μm, and the length is L7 = 500 μm; the width of the output straight waveguide 12 is W4, and there is no specific requirement for the length L8.

[0011] Along the transmission direction of light, when TE 10 When the mode is input from the input end of the input straight waveguide 5, it passes through the first intermediate asymmetric tapered waveguide 6, the second intermediate asymmetric tapered waveguide 7 and the third intermediate asymmetric tapered waveguide 8 in sequence. 10 Mode gradually converted to TE 00 mode, then TE 00 The mode enters the fourth intermediate asymmetric tapered waveguide 9, the fifth intermediate asymmetric tapered waveguide 10 and the output symmetric tapered waveguide 11 in sequence and is finally output from the output end of the output straight waveguide 12 (see FIG. Figure 3 (a)); when TE 20When the mode is input from the input end of the input straight waveguide 5, it passes through the first intermediate asymmetric tapered waveguide 6, the second intermediate asymmetric tapered waveguide 7 and the third intermediate asymmetric tapered waveguide 8 in sequence. 20 Mode gradually converted to TE 10 mode, then TE 10 The mode enters the fourth intermediate asymmetric tapered waveguide 9, the fifth intermediate asymmetric tapered waveguide 10 and the output symmetric tapered waveguide 11 in sequence and is finally output from the output end of the output straight waveguide 12 (see FIG. Figure 3 (b)).

[0012] The mode converter works as follows:

[0013] The TE based on polymer optical waveguide of the present invention 10 -TE 00 / TE 20 -TE 10 The compact mode converter is connected by multiple asymmetric tapered waveguide structures. 10 When the mode is input into the device, TE 10 The two opposite components of the mode (with a phase difference of π) propagate with different effective lengths, causing different phase changes, which ultimately makes TE 10 The two components of the mode become in phase and convert to TE 00 Mode; when TE 20 When the mode is input into the device, TE 20 The three components of the mode (the phase difference between adjacent components is π, and the phase difference between non-adjacent components is 0) propagate with different effective lengths, causing different phase changes, and ultimately making TE 20 The three components of the mode become two opposite components, converting to TE 10 mode. This can increase channel transmission capacity or be applied in mode add / drop multiplexers (MADM) and high-order mode filters. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 : The TE based on polymer optical waveguide of the present invention 10 -TE 00 / TE 20 -TE 10 Schematic diagram of the compact mode converter;

[0015] Figure 2(a): TE based on polymer optical waveguide according to the present invention 10 -TE 00 / TE 20 -TE 10 A cross-sectional view of the compact mode converter at the input end;

[0016] Figure 2(b): TE based on polymer optical waveguide according to the present invention 10 -TE 00 / TE 20 -TE 10 Top view of the compact mode converter core waveguide;

[0017] Figure 3 (a): TE based on polymer optical waveguide according to the present invention 10 -TE 00 / TE 20 -TE 10 Compact mode converter, at 1550nm wavelength, TE 10 Mode is converted from Input to TE 00 Simulation diagram of light field transmission of the mode output from Output;

[0018] Figure 3 (b): TE based on polymer optical waveguide according to the present invention 10 -TE 00 / TE 20 -TE 10 Compact mode converter, at 1550nm wavelength, TE 20 Mode is converted from Input to TE 10 Simulation diagram of light field transmission of the mode output from Output;

[0019] Figure 4(a): TE based on polymer optical waveguide according to the present invention 10 -TE 00 / TE 20 -TE 10 Compact Mode Converter, TE 10 Mode is converted from Input to TE 00 The transmission curve of the mode output from the Output varies with the wavelength of light;

[0020] Figure 4(b): TE based on polymer optical waveguide according to the present invention 10 -TE 00 / TE 20 -TE 10 Compact Mode Converter, TE 20 Mode is converted from Input to TE 10 The transmission curve of the mode output from the Output varies with the wavelength of light;

[0021] Figure 5 : The TE based on polymer optical waveguide of the present invention 10 -TE 00 / TE 20 -TE10 Flowchart of the fabrication process for a compact mode converter. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below through specific implementations with reference to the accompanying drawings.

[0023] Example 1

[0024] 1. First, fix the height H of the polymer core waveguide 3 to 5 μm.

[0025] 2. Determine the input end width W1 of the input straight waveguide 5 and the first intermediate asymmetric tapered waveguide 6, the length L1 of the input straight waveguide 5, the output end width W4 of the output straight waveguide 12 and the output symmetric tapered waveguide 11, and the length L8 of the output straight waveguide 12. W1 is selected to be 21.5 μm to meet TE 10 and TE 20 Transmission conditions, the length of L1 is arbitrary, here we choose L1 = 300μm; W4 is selected as 13.2μm to meet TE 00 and TE 10 Transmission conditions, the length of L8 is arbitrary, here we choose L8 = 300μm.

[0026] 3. Determine the output end width of the first intermediate asymmetric tapered waveguide 6, the width of the second intermediate asymmetric tapered waveguide 7, and the input end width W2 of the third intermediate asymmetric tapered waveguide 8; the length L2 of the first intermediate asymmetric tapered waveguide 6 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction; the length L3 of the second intermediate asymmetric tapered waveguide 7 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction; the output end width of the third intermediate asymmetric tapered waveguide 8, the width of the fourth intermediate asymmetric tapered waveguide 9, the width of the fifth intermediate asymmetric tapered waveguide 10, and the output end width W3 of the output symmetric tapered waveguide 11; the length L4 of the third intermediate asymmetric tapered waveguide 8 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction; the length L5 of the fourth intermediate asymmetric tapered waveguide 9 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction; and the length L6 of the fifth intermediate asymmetric tapered waveguide 10 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction. According to the Beam Propagation Method (BPM) calculation, in order to make TE 10 Mode conversion to TE 00 Mode and TE 20 Convert to TE 10mode, and the final optimization is: W2=40μm, L2=480μm, the output end symmetry center of the first intermediate asymmetric tapered waveguide 6 is offset by 10μm relative to the input end symmetry center along the -x direction; L3=320μm, the output end symmetry center of the second intermediate asymmetric tapered waveguide 7 is offset by 7μm relative to the input end symmetry center along the -x direction; W3=20μm, L4=400μm, the output end symmetry center of the third intermediate asymmetric tapered waveguide 8 is offset by 18μm relative to the input end symmetry center along the -x direction; at the same time, in order to reduce transmission loss, L5=450μm, the output end symmetry center of the fourth intermediate asymmetric tapered waveguide 9 is offset by 10μm relative to the input end symmetry center along the -x direction; the length is L6=440μm, the output end symmetry center of the fifth intermediate asymmetric tapered waveguide 10 is offset by 5μm relative to the input end symmetry center along the -x direction; L7=500μm. The total length of the final device is approximately 3200 μm.

[0027] 4. As attached Figure 3 (a) shows the TE at a wavelength of 1550nm. 10 Mode is converted from Input to TE 00 The light field transmission simulation diagram of the mode output from Output is shown in the attached figure. Figure 3 (b) shows the TE at a wavelength of 1550nm. 20 Mode is converted from Input to TE 10 The light field transmission simulation diagram of the mode output from the output. It can be seen that the TE based on polymer optical waveguide described in the present invention 10 -TE 00 / TE 20 -TE 10 Compact mode converter enables TE 10 Mode to TE 00 Mode and TE 20 Mode to TE 10 Mode conversion, the input TE 10 Mode conversion to TE 00 Mode or enter the TE 20 Mode conversion to TE 10 model.

[0028] 5. As shown in Figure 4(a), TE 10 Mode is converted from Input to TE 00 The transmission curve of the mode output from the Output varies with the wavelength of light. The results show that when the signal light wavelength is 1550nm, the output port mainly transmits TE 00 mode, the transmission is -0.32dB (TE 10 -TE00 Mode conversion efficiency is 92.90%); in the wavelength range of 1500nm to 1620nm, the transmission is greater than -0.5dB (TE 10 -TE 00 Mode conversion efficiency>89.13%).

[0029] 6. As shown in Figure 4(b), TE 20 Mode is converted from Input to TE 10 The transmission curve of the mode output from the Output varies with the wavelength of light. The results show that when the signal light wavelength is 1550nm, the output port mainly transmits TE 10 mode, the transmission is -0.69dB (TE 20 -TE 10 Mode conversion efficiency is 85.31%); in the wavelength range of 1500nm to 1620nm, the transmission is greater than -0.9dB (TE 20 -TE 10 Mode conversion efficiency>81.28%).

[0030] 7. It can be seen that in the wavelength range of 1500nm to 1620nm, the output TE 00 Mode and TE 10 The transmission of the mode is >-0.9dB (TE 20 -TE 10 The mode conversion efficiency is greater than 81.28%), which is used to define the polymer TE 10 -TE 00 / TE 20 -TE 10 The bandwidth of the mode converter is at least 120 nm.

[0031] Example 2

[0032] The following combination Figure 5 The specific preparation method of the present invention is described in detail, and the specific steps are as follows:

[0033] 1. Cleaning silicon substrate 1: Select a 1mm thick single crystal silicon wafer as the substrate, cut it into appropriate sizes, and ultrasonically clean it with acetone and ethanol 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.

[0034] 2. Spin coating EpoClad lower cladding layer 2: Using the spin coating process, the organic polymer EpoClad material is spin-coated on the cleaned silicon wafer substrate 1. By adjusting the spin coating speed, the thickness of the film can be controlled. The sample is then cured in high temperature and i-line ultraviolet light to enhance the cross-linking of the material. The spin coating speed is 1800 rpm, and then baked at 120℃ for 5 minutes, cooled to room temperature, and the whole is exposed for 20 seconds (exposure wavelength is 365nm, exposure intensity is 40mW / cm 2 ), then baked at 120° C. for 3 minutes, cooled to room temperature, and finally obtained a polymer lower cladding layer 2 with a thickness of 7 μm;

[0035] 3. Spin coating the EpoCore core layer: Spin coating the organic polymer EpoCore material on the prepared lower cladding layer 2 using a spin coating process at a spin coating speed of 3000 rpm, bake at 90°C for 5 minutes, and then cool to room temperature to form a polymer core layer with a thickness of H = 5 μm;

[0036] 4. Photolithography: The prepared polymer core film is subjected to alignment photolithography. The wavelength of i-line ultraviolet light is 365nm. The structure of the optical waveguide mask is complementary to the structure of the core waveguide of the polymer mode converter to be prepared. When the mask and the polymer core film are in close contact, exposure is performed for 20 seconds to expose the core film of the device to ultraviolet light. The device is heated at 85°C for 5 minutes and then naturally cooled to room temperature.

[0037] 5. Development: The photolithographic polymer core layer film is wet-etched. First, wet-etch in the developer corresponding to EpoCore for 60 seconds to remove the unexposed core layer material. Then, wet-etch in isopropyl alcohol solution for 20 seconds to wash away the developer and the remaining unexposed core layer material. The film is then rinsed with deionized water and dried with nitrogen. The film is hardened and heated at 130°C for 30 minutes to obtain the polymer core waveguide 3 to be prepared.

[0038] 6. Spin coating EpoClad upper cladding 4: The polymer material EpoClad is spin coated on the optical waveguide core layer and the lower cladding layer using a spin coating process at a spin coating speed of 1100 rpm, heated at 120°C for 5 minutes, and after the entire exposure for 34 seconds, heated at 120°C for 3 minutes. The thickness of the upper cladding layer obtained is 15 μm (the thickness of the upper cladding layer above the lower cladding layer), that is, the overall thickness of the silica cladding layer (above the silicon substrate) is 7+15=22 μm, thereby preparing the TE based on polymer optical waveguide of the present invention. 10 -TE 00 / TE 20 -TE 10 Compact mode converter.

Claims

1. A TE based on polymer optical waveguide 10 -TE 00 / TE 20 -TE 10 Compact mode converter, characterized by: From bottom to top, it is composed of a substrate (1), a lower cladding (2), a core waveguide (3) and an upper cladding (4); the core waveguide (3) and the upper cladding (4) are located together on the lower cladding (2) and the core waveguide (3) is covered by the upper cladding (4); the core waveguide (3) is composed of an input straight waveguide (5), a first intermediate asymmetric tapered waveguide (6), a second intermediate asymmetric tapered waveguide (7), a third intermediate asymmetric tapered waveguide (8), a fourth intermediate asymmetric tapered waveguide (9), a fifth intermediate asymmetric tapered waveguide (10), an output symmetric tapered waveguide (11) and an output straight waveguide (12); along the transmission direction of light, the input end of the first intermediate asymmetric tapered waveguide (6) is connected to the output end of the input straight waveguide (5), the input end of the second intermediate asymmetric tapered waveguide (7) is connected to the input end of the first intermediate asymmetric tapered waveguide (6 ), the input end of the third intermediate asymmetric tapered waveguide (8) is connected to the output end of the second intermediate asymmetric tapered waveguide (7), the input end of the fourth intermediate asymmetric tapered waveguide (9) is connected to the output end of the third intermediate asymmetric tapered waveguide (8), the input end of the fifth intermediate asymmetric tapered waveguide (10) is connected to the output end of the fourth intermediate asymmetric tapered waveguide (9), the input end of the output symmetric tapered waveguide (11) is connected to the output end of the fifth intermediate asymmetric tapered waveguide (10), and the input end of the output straight waveguide (12) is connected to the output end of the output symmetric tapered waveguide (11); wherein, the surface of the lower cladding (2) is defined as the xy plane, the input light direction is the +y axis direction, and the right side of the input light direction is the +x axis direction; along the transmission direction of light, the width of the input straight waveguide (5) is W1=21.5 μm; the width of the first intermediate asymmetric tapered waveguide (6) gradually widens from W1 to W2 = 40 μm, the length is L2 = 480 μm, and the center of the output end is offset by 10 μm relative to the center of the input end along the −x axis; the width of the second intermediate asymmetric tapered waveguide (7) is always W2, the length is L3 = 320 μm, and the center of the output end is offset by 7 μm relative to the center of the input end along the −x axis; the width of the third intermediate asymmetric tapered waveguide (8) gradually narrows from W2 to W3 = 20 μm, the length is L4 = 400 μm, and the center of the output end is offset by 18 μm relative to the center of the input end along the −x axis; the width of the fourth intermediate asymmetric tapered waveguide (9) is always W3, the length is L5 = 450 μm, and the center of the output end is offset by 10 μm relative to the center of the input end along the −x axis; the width of the fifth intermediate asymmetric tapered waveguide (10) is always W3, the length is L6 = 440 μm, and the center of the output end is offset by 5 μm relative to the center of the input end along the −x axis; the width of the output symmetrical tapered waveguide (11) gradually narrows from W3 to W4 = 13.2 μm, and the length is L7 = 500 μm; the width of the output straight waveguide (12) is W4, and the length is L8.

2. A polymer optical waveguide TE as claimed in claim 1 10 -TE 00 / TE 20 -TE 10 Compact mode converter, characterized by: The height of each part of the core waveguide (3) is the same as H = 5 μm.

3. A polymer optical waveguide TE as claimed in claim 1 10 -TE 00 / TE 20 -TE 10 Compact mode converter, characterized by: The lower cladding (2) and upper cladding (4) are made of EpoClad, both with an effective refractive index of 1.559 (@1550 nm); the core waveguide (3) is made of EpoCore, with an effective refractive index of 1.569 (@1550 nm); and the substrate (1) is a silicon wafer with a refractive index of 3.

455.

4. A polymer optical waveguide TE as claimed in claim 1 10 -TE 00 / TE 20 -TE 10 Compact mode converter, characterized by: The transmission direction of light, when TE 10 When the mode is input from the input end of the input straight waveguide (5), it passes through the first intermediate asymmetric tapered waveguide (6), the second intermediate asymmetric tapered waveguide (7) and the third intermediate asymmetric tapered waveguide (8) in sequence. 10 The model gradually shifts to TE 00 mode, then TE 00 The mode enters the fourth intermediate asymmetric tapered waveguide (9), the fifth intermediate asymmetric tapered waveguide (10) and the output symmetric tapered waveguide (11) in sequence and is finally output from the output end of the output straight waveguide (12); when TE 20 When the mode is input from the input end of the input straight waveguide (5), it passes through the first intermediate asymmetric tapered waveguide (6), the second intermediate asymmetric tapered waveguide (7) and the third intermediate asymmetric tapered waveguide (8) in sequence. 20 Mode gradually converted to TE 10 mode, then TE 10 The mode sequentially enters the fourth intermediate asymmetric tapered waveguide (9), the fifth intermediate asymmetric tapered waveguide (10) and the output symmetric tapered waveguide (11), and is finally output from the output end of the output straight waveguide (12).

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