TE10-TE00 / TE20-TE10 compact mode converter based on polymer optical waveguide

Abstract

The invention discloses a TE10-TE00 / TE20-TE10 compact mode converter based on a polymer optical waveguide, and belongs to the technical field of photon integration. The optical fiber is composed of a substrate, a lower cladding, a core layer waveguide and an upper cladding, wherein the core layer waveguide is wrapped by the upper cladding; the lower cladding and the upper cladding are EpoClads, and the core layer waveguide is EpoCore with the same height and is formed by sequentially connecting an input straight waveguide, a first middle asymmetric conical waveguide, a second middle asymmetric conical waveguide, a third middle asymmetric conical waveguide, a fourth middle asymmetric conical waveguide, a fifth middle asymmetric conical waveguide, an output symmetric conical waveguide and an output straight waveguide; when passing through the middle asymmetric tapered waveguide, different components of the mode are propagated in different effective lengths, so that different phase changes are caused, and finally a target mode is obtained; the method and the device can be applied to a mode addition / subdivision multiplexer (MADM) and a high-order mode filter, so that the channel transmission capacity is increased or the method and the device are applied.

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 new technologies such as 5G, cloud computing, big data, and artificial intelligence in recent years, communication capacity has increased exponentially year by year, and optical fiber transmission capacity has become a key issue restricting the further increase of data bandwidth. Affected by factors such as optical nonlinearity and fiber melting effect, the transmission capacity of single-mode optical fiber has approached the theoretical limit (100Tbit / s) and cannot meet future application needs, so it is urgent to expand the 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 are used as bus optical trunks to achieve parallel transmission of multiple orthogonal modes on a single physical channel, thus 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 the propagation of light. 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 mixed. 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 from the fundamental mode TE 00 To other modes (such as TE 10 or TE 20), there is less research on direct conversion between high-order modes, which can be applied to mode add / drop multiplexers (MADM) and high-order mode filters. In addition, existing work can only realize the conversion of one set of modes on the same device, and cannot realize the conversion of two sets of modes at the same time.

[0005] Mode converters are generally large in size, with limited working bandwidth and large insertion loss. The research direction has always been to improve integration, reduce loss, reduce process difficulty, and increase working bandwidth. In view of the current development of hybrid multiplexing technology, higher requirements are placed on the working bandwidth of mode converters. Therefore, it is still a major challenge to realize high-performance multi-order mode converters in a low-cost manner. There are many kinds of materials used to prepare planar optical waveguide mode converters, among which polymer materials have the advantages of low cost and simple process. Mode division multiplexing devices based on polymer waveguides have also achieved many 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 that 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 device applications. 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 2 is located on the substrate 1, 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 material of the lower cladding 2 and the upper cladding 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, and the refractive index is 3.455.

[0008] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0009] As shown in FIG. 2 (a), the input end (Input) 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] As shown in FIG2(b), a top view of the core waveguide 3 of the polymer mode converter of the present invention is shown, 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 transmission direction of light; the width W of the input straight waveguide 5 is 1 =21.5μm, length L 1 There is no specific requirement; the width of the first intermediate asymmetric tapered waveguide 6 is determined by W 1 Gradually widens to W 2 =40μm, length L 2 =480μm, the output end symmetry center is offset by 10μm relative to the input end symmetry center along the -x axis direction; the width of the second intermediate asymmetric tapered waveguide 7 is always W 2 , length L 3 =320μm, the output end symmetry center is offset by 7μm along the -x axis relative to the input end symmetry center; the width of the third intermediate asymmetric tapered waveguide 8 is W 2 Gradually narrows to W 3 =20μm, length is L 4 =400 μm, the output end symmetry center is offset by 18 μm along the -x axis relative to the input end symmetry center; the width of the fourth intermediate asymmetric tapered waveguide 9 is always W 3 , length L 5 =450μm, the symmetry center of the output end is offset by 10μm along the -x axis relative to the symmetry center of the input end; the width of the fifth intermediate asymmetric tapered waveguide 10 is always W 3 , length L 6 =440μm, the output end symmetry center is offset by 5μm along the -x axis relative to the input end symmetry center; the width of the output symmetrical tapered waveguide 11 is W 3 Gradually narrows to W 4 =13.2μm, length is L 7 =500μm; the width of the output straight waveguide 12 is W 4 , length L 8 There are no specific requirements.

[0011] Along the transmission direction of light, when TE 10When 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 mode gradually changes 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 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 The mode gradually changes 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 entered 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 make TE 10 The two components of the mode become in phase and convert to TE 00 Mode; when TE 20 When the mode is entered into the device, TE 20 The three components of the mode (the phase difference of adjacent components is π, and the phase difference of non-adjacent components is 0) propagate with different effective lengths, thus causing different phase changes, and finally making TE 20 The three components of the mode become two opposite components and are converted to TE 10 Mode. To achieve the increase of channel transmission capacity or applied in mode add / drop multiplexer (MADM) and high-order mode filter. 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 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 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 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 / TE20 -TE 10 Compact Mode Converter, TE 20 Mode is converted from Input to TE 10 The transmission curve of the mode output from 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 -TE 10 Flow chart of the fabrication process of a compact mode converter. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below through specific implementation modes in conjunction with 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 W of the input straight waveguide 5 and the first intermediate asymmetric tapered waveguide 6 1 、Input straight waveguide 5 length L 1 , the output straight waveguide 12 and the output symmetrical tapered waveguide 11 have an output end width W 4 , output straight waveguide 12 length L 8 .W 1 21.5 μm is selected to meet TE 10 and TE 20 Transmission conditions, L 1 The length of is arbitrary, here we choose L 1 =300μm; W 4 13.2μm is selected to meet TE 00 and TE 10 Transmission conditions, L 8 The length of is arbitrary, here we choose L 8 =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 W of the third intermediate asymmetric tapered waveguide 8. 2 , the length L of the first intermediate asymmetric tapered waveguide 6 2 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction, the length L of the second intermediate asymmetric tapered waveguide 7 3and 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 W of the output symmetric tapered waveguide 11 3 , the length L of the third intermediate asymmetric tapered waveguide 8 4 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction, the length L of the fourth intermediate asymmetric tapered waveguide 9 5 and the offset of the output end symmetry center relative to the input end symmetry center along the -x direction, the length L of the fifth intermediate asymmetric tapered waveguide 10 6 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), in order to make TE 10 Mode conversion to TE 00 Mode and TE 20 Convert to TE 10 Mode, final selection: W 2 =40μm, L 2 =480 μm, the output end symmetry center of the first intermediate asymmetric tapered waveguide 6 is offset by 10 μm relative to the input end symmetry center along the -x direction; L 3 =320 μm, the output end symmetry center of the second intermediate asymmetric tapered waveguide 7 is offset by 7 μm relative to the input end symmetry center along the -x direction; W 3 =20μm, L 4 =400 μm, the output end symmetry center of the third intermediate asymmetric tapered waveguide 8 is offset by 18 μm relative to the input end symmetry center along the -x direction; at the same time, in order to reduce the transmission loss, L 5 =450 μm, the output end symmetry center of the fourth intermediate asymmetric tapered waveguide 9 is offset by 10 μm relative to the input end symmetry center along the -x direction; the length is L 6 =440 μm, the output end symmetry center of the fifth intermediate asymmetric tapered waveguide 10 is offset by 5 μm relative to the input end symmetry center along the -x direction; L 7 =500μm. The total length of the final device is about 3200μm.

[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 TE10 The simulation diagram of the light field transmission of the mode output from the Output. It can be seen that the TE based on the polymer optical waveguide described in the present invention 10 -TE 00 / TE 20 -TE 10 Compact mode converter realizes 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 curve of the transmission of the mode from the Output as a function of the wavelength of light shows that when the signal light wavelength is 1550nm, the output port Output mainly transmits TE 00 mode, transmission is -0.32dB(TE 10 -TE 00 Mode conversion efficiency is 92.90%); within the wavelength range of 1500nm to 1620nm, the transmission is > -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 curve of the transmission of the mode from the Output as a function of the wavelength of light shows that when the signal light wavelength is 1550nm, the output port Output mainly transmits TE 10 mode, 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 >-0.9dB (TE 20 -TE 10 Mode conversion efficiency>81.28%).

[0030] 7. It can be seen that within the wavelength range of 1500nm to 1620nm, the output TE 00 Mode and TE 10 The transmission of each mode is >-0.9dB (TE 20 -TE 10The mode conversion efficiency is >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 120nm.

[0031] Example 2

[0032] Combine the following 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, 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 2: Spin coating the organic polymer EpoClad material on the cleaned silicon wafer substrate 1. The thickness of the film can be controlled by adjusting the spin coating speed. Then the sample is cured in high temperature and i-line ultraviolet light in turn to enhance the cross-linking of the material. The spin coating speed is 1800 rpm, then baked at 120℃ for 5 minutes, cooled to room temperature, and exposed for 20 seconds (exposure wavelength is 365nm, exposure intensity is 40mW / cm 2 ), and then baked at 120° C. for 3 minutes, and cooled to room temperature, to finally obtain a polymer lower cladding layer 2 with a thickness of 7 μm;

[0035] 3. Spin coating EpoCore core layer: Spin coating the organic polymer EpoCore material on the prepared lower cladding layer 2 with 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 photolithography. The wavelength of the 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, so that the core film of the device is exposed to ultraviolet light, heated at 85°C for 5 minutes, and then naturally cooled to room temperature.

[0037] 5. Development: wet-etch the polymer core layer film after photolithography, first wet-etch in the developer corresponding to EpoCore for 60 seconds to remove the unexposed core layer material, then wet-etch in isopropanol solution for 20 seconds, wash away the developer and the remaining unexposed core layer material, then rinse with deionized water and blow dry with nitrogen, harden the film, heat at 130°C for 30 minutes, and obtain the polymer core layer waveguide 3 to be prepared;

[0038] 6. Spin coating EpoClad upper cladding 4: Spin coating the polymer material EpoClad on the optical waveguide core layer and the lower cladding layer, the spin coating speed is 1100 rpm, and the temperature is heated at 120°C for 5 minutes. After the entire layer is exposed for 34 seconds, the temperature is heated at 120°C for 3 minutes. The thickness of the upper cladding layer is 15 μm (the thickness of the upper cladding layer above the lower cladding layer), that is, the overall thickness of the silicon dioxide cladding layer (above the silicon substrate) is 7+15=22 μm, thereby preparing the TE based on the 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 A compact mode converter, characterized in that: The optical waveguide (1) is composed of a substrate (1), a lower cladding (2), a core waveguide (3) and an upper cladding (4) in order from bottom to top. The core waveguide (3) and the upper cladding (4) are located 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) and the output end of the input straight waveguide (5) are connected to each other. The output end of the output symmetric tapered waveguide (11) is connected to the output end of the fifth intermediate asymmetric tapered waveguide (10), 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).

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

3. A polymer optical waveguide TE as claimed in claim 1 10 -TE 00 / TE 20 -TE 10 A compact mode converter, characterized in that: 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 the 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 direction; 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 direction; the width of the third intermediate asymmetric tapered waveguide (8) gradually narrows from W2 to W3 =20μm, the length is L4=400μm, and the center of the output end is offset by 18μm relative to the center of the input end along the -x axis direction; the width of the fourth intermediate asymmetric tapered waveguide (9) is always W3, the length is L5=450μm, and the center of the output end is offset by 10μm relative to the center of the input end along the -x axis direction; the width of the fifth intermediate asymmetric tapered waveguide (10) is always W3, the length is L6=440μm, and the center of the output end is offset by 5μm relative to the center of the input end along the -x axis direction; the width of the output symmetric tapered waveguide (11) gradually narrows from W3 to W4=13.2μm, and the length is L7=500μm; the width of the output straight waveguide (12) is W4, and the length is L8.

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

455.

5. A polymer optical waveguide TE as claimed in claim 1 10 -TE 00 / TE 20 -TE 10 A compact mode converter, characterized in that: 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 mode gradually changes to TE 00 mode, then TE 00 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); 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 The mode gradually changes 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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