A highly integrated filter and its manufacturing method

Abstract

This invention discloses a highly integrated mode filter and its fabrication method, comprising a silicon substrate, a lower cladding layer, and an upper cladding layer, with a core layer between the upper and lower cladding layers. The core layer includes an input waveguide, a first mode routing region for filtering out the fundamental mode and converting higher-order modes into the fundamental mode for output, a single-mode region for transmitting the single-mode waveguide in the first mode routing region, a second mode routing region for converting the fundamental mode transmitted in the single-mode region into higher-order modes, and an output waveguide. The waveguide inputs from the incident port and propagates through the left-side first mode routing region, where the fundamental mode TE0 is filtered out by the curved waveguide; the higher-order mode TE1 is converted into the fundamental mode TE0 through the left-side first mode routing region, propagates through the central straight waveguide to the right-side second mode routing region, is converted into the higher-order mode TE1, and then outputs from the output port via the output waveguide. This mode filter is simple to fabricate, small in size, has excellent performance, low processing cost, high mode conversion rate, and strong anti-crosstalk capability. It selectively filters out some modes of light, improving the quality and stability of optical communication.

Description

Technical Field

[0001] This invention relates to a modular multiplexing filter, and more particularly to a highly integrated filter and its manufacturing method. Background Technology

[0002] With the continuous advancement and development of communication technology, higher demands are being placed on data storage and transmission speeds. Mode division multiplexing (MDM) technology increases the number of optical modes transmitted within an optical fiber or waveguide, enabling the simultaneous transmission of multiple data streams in different optical modes on the same fiber, thereby improving transmission capacity. Mode filters in MDM systems are used to selectively filter or suppress certain modes of light, allowing only the desired modes to propagate, reducing crosstalk, and improving the transmission quality and reliability of optical signals. Currently, silicon-based mode filters are widely used, and the main technologies involved include Mach-Zehnder interferometers (MZI), asymmetric directional couplers (ADCs), multimode interference (MMI), one-dimensional photonic crystals, subwavelength gratings (SWGs), transparent conducting oxides (TCOs), and topology optimization.

[0003] In existing technologies, combining MZI and ADC converts unwanted low-order modes into high-order modes, which are then scattered through an adiabatic conical waveguide under cutoff conditions. This process suffers from significant phase difference effects, resulting in poor light transmission quality and stability. To eliminate the influence of relative phase difference, a Y-connection is used to implement MMI, decomposing the input TEO fundamental mode into two in-phase TEO fundamental modes, which are then filtered through single-mode waveguides on the two outer edges of the MMI. While the combination of MZI, ADC, and MMI can achieve bandwidth across the entire C-band, the mode filter is relatively large. To reduce the device size of the mode filter, a phase-matched one-dimensional photonic crystal and SWG reverse coupler have been proposed. However, their bandwidth is limited by phase matching and cannot achieve full C-band bandwidth. To improve bandwidth performance, plasma based on vanadium dioxide (VO2) and graphene and TCO have been proposed. S Multimode waveguides or bridge-type SWG mode absorption schemes are available, but the mode filters are also relatively large in size and require stringent manufacturing processes, limiting their applications. Topology optimization is widely used in the design of ultra-compact photonic devices, but its application in silicon-based mode filters is less reported. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to improve the quality and stability of optical communication by selectively filtering out certain modes of light and increasing the integration of devices, by providing a highly integrated filter and its fabrication method.

[0005] Technical solution: The highly integrated mode filter of the present invention includes a silicon substrate, a lower cladding layer and an upper cladding layer arranged sequentially, with a core layer disposed between the lower cladding layer and the upper cladding layer; the core layer includes an input waveguide, a first mode routing region for filtering out the fundamental mode in the input waveguide and converting the higher-order modes in the input waveguide into the fundamental mode output, a single-mode region for transmitting the single-mode waveguide in the first mode routing region, a second mode routing region for converting the fundamental mode transmitted in the single-mode region into the higher-order mode output, and an output waveguide for outputting the higher-order mode, the core layer being symmetrically distributed around the single-mode region.

[0006] Furthermore, the first mode routing area and the second mode routing area include a coupler composed of a tapered lower waveguide and a tapered upper waveguide similar to a direct trapezoid, and a functional area between the tapered lower waveguide and the tapered upper waveguide, with the narrow end of the tapered lower waveguide and the wide end of the tapered upper waveguide on one side.

[0007] Furthermore, the length and width of the upper and lower tapered waveguides, as well as the spacing between them, are adjustable. Adjusting the length and width of the upper and lower tapered waveguides and the spacing between them can adjust the coupling coefficient, conversion efficiency, polarization extinction ratio, and crosstalk immunity of the coupler.

[0008] Furthermore, the coupler composed of the tapered upper waveguide and the tapered lower waveguide is either an asymmetric directional coupler or an adiabatic coupler.

[0009] Furthermore, the right-angled surfaces of the tapered upper and lower waveguides of the asymmetric directional coupler are arranged opposite each other, and the inclined surfaces of the upper and lower tapered waveguides face the functional region. The spacing between the upper and lower tapered waveguides remains consistent and is 700-900nm. The functional region is composed of a mixture of silicon and air units based on the Direct Binary Search (DBS) algorithm. The functional region is divided into blocks according to the subwavelength units of the functional region. The calculation optimization is performed with silicon units as 1 and air units as 0. The size of the subwavelength units of the functional region is 50nm-150nm. The optimized functional region distribution structure can achieve the lowest optical loss.

[0010] Furthermore, the inclined surfaces of the tapered upper waveguide and tapered lower waveguide of the thermal coupler are arranged opposite each other, with the inclined surfaces of the upper and lower tapered waveguides facing away from the functional area. The spacing between the upper and lower tapered waveguides remains consistent and is 400-500nm. The functional area is composed of a mixture of silicon and air units based on the DBS algorithm. The functional area is divided into blocks according to the subwavelength units of the functional area. The calculation optimization is performed with silicon units as 1 and air units as 0. When the functional area coincides with the tapered lower waveguide and tapered upper waveguide, the waveguide area covers the functional area. The size of the subwavelength units of the functional area is 50nm-150nm. The optimized functional area distribution structure can achieve the lowest optical loss.

[0011] Furthermore, the single-mode region includes a central straight waveguide and a curved waveguide for transmitting single-mode waveguides. The central straight waveguide is connected in the middle of the two tapered upper waveguides, and the curved waveguides are respectively connected to the rear ends of the two tapered lower waveguides.

[0012] Furthermore, the center straight waveguide and the curved waveguide in the single-mode region have the same width.

[0013] Furthermore, a method for manufacturing a highly integrated filter includes the following steps:

[0014] (1) A 3 μm silicon dioxide undercladding layer was deposited on a silicon substrate by plasma-enhanced chemical vapor deposition to provide bottom optical insulation;

[0015] (2) A silicon layer with a thickness of 220 nm was deposited on the silicon dioxide cladding as a core layer using plasma-enhanced chemical vapor deposition.

[0016] (3) The layout of the core layer is visualized using electron beam lithography;

[0017] (4) Use inductively coupled plasma to etch according to the layout. The etching depth is consistent with the silicon layer thickness of 220nm to obtain the specific structure of the core layer.

[0018] (5) A silicon dioxide cladding layer with a thickness of 1 μm was deposited on the core layer using plasma-enhanced chemical vapor deposition.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The 3dB bandwidth of the two filter modes reaches 100-200nm, achieving high performance while maintaining high bandwidth; 2. The crosstalk of the two filter modes is less than -15dB at the center wavelength of 1550nm, demonstrating strong anti-interference capability; 3. In the reverse design of the functional area, not only is partial mode filtering achieved, improving mode coupling strength, but also the structure is simplified, the volume is reduced, and the manufacturing difficulty is lowered; 4. Compared with forward design, reverse design combined with the DBS algorithm can quickly reverse design the corresponding structure according to the required performance parameters, lowering the device design threshold. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the present invention;

[0021] Figure 2 This is a three-dimensional structural diagram of the present invention;

[0022] Figure 3 This is a schematic diagram of the planar structure of the present invention;

[0023] Figure 4 This diagram illustrates the propagation process of different modes of light within the structure of this invention.

[0024] Figure 5 This is a structural design diagram of the functional area of ​​the present invention;

[0025] Figure 6 This is a transmittance spectrum result diagram of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0027] Example 1

[0028] like Figure 3 The left side shows a highly integrated mode filter based on an adiabatic coupler, including a silicon substrate 113, a lower cladding layer 112, and an upper cladding layer 111. A core layer 114 is disposed between the upper cladding layer 111 and the lower cladding layer 112. The core layer 114 includes an input waveguide 1, a first mode routing region 2 for filtering out the fundamental mode in the input waveguide 1 and converting the higher-order modes in the input waveguide 1 into the fundamental mode output, a single-mode region for transmitting the single-mode waveguide in the first mode routing region 2, a second mode routing region 5 for converting the fundamental mode transmitted in the single-mode region into the higher-order mode output, and an output waveguide 6 for outputting the higher-order mode. The core layer 114 is symmetrically distributed around the single-mode region. The mode routing region of the core layer 114 includes an adiabatic coupler composed of a tapered lower waveguide 7 and a tapered upper waveguide 9, which are similar to a right-angled trapezoid, and a functional region 8 between the tapered lower waveguide 7 and the tapered upper waveguide 9. The functional region is as follows: Figure 5 As shown on the left. The tapered lower waveguide 7 and the tapered upper waveguide 9 are arranged with their inclined surfaces facing each other, with the inclined surfaces facing the functional region 8. The functional region 8 is composed of a mixture of silicon and air units based on the DBS algorithm. The functional region is divided into blocks according to the subwavelength units of 100nm. Calculation optimization is performed with silicon units as 1 and air units as 0. Multiple groups of silicon and air units used to change the mode form a structure similar to a QR code. The optimized functional region distribution structure can achieve the lowest optical loss. The specific structure of the functional region is as follows:

[0029]

[0030] The single-mode region includes a central straight waveguide 4 and a curved waveguide 3 for transmitting single-mode waveguides. The central straight waveguide 4 is connected in the middle of the two tapered upper waveguides 9, and the curved waveguide 3 is connected at the rear end of the two tapered lower waveguides 7.

[0031] The fabrication of a highly integrated filter based on an adiabatic coupler includes the following steps:

[0032] (1) Deposit a 220nm silicon substrate 113 on a silicon wafer;

[0033] (2) A 3μm oxide layer is deposited on the silicon substrate as the lower cladding layer 112;

[0034] (3) The layout of the core layer 114 is imaged using electron beam lithography, and the widths W of the input waveguide 1 and the output waveguide 6 are shown. a1 =1μm, the width W of the curved waveguide 3 and the center straight waveguide 4 a2 =W a3 =400nm, the lengths of the tapered lower waveguide 7 and the tapered upper waveguide 9 are L. a =4μm, the distance between the tapered lower waveguide 7 and the tapered upper waveguide 9 is set as g. a =450nm, the side length W of the small square in the functional region a4 =100nm;

[0035] (4) It was etched using inductively coupled plasma to a depth of 220 nm;

[0036] (5) Deposit a silicon dioxide overcoating layer 111 with a thickness of 1 μm.

[0037] like Figure 4 As shown in (a) and (c) on the left, light enters from port I through input waveguide 1 and propagates through the first mode routing area 2 on the left. The TE0 fundamental mode propagates through the tapered lower waveguide and is filtered out by the curved waveguide 3. The TE1 higher-order mode is converted into TE0 through the first mode routing area 2 on the left and propagates to the tapered upper waveguide 9. It then propagates through the central straight waveguide 4 to the second mode routing area 5 on the right. The TE0 fundamental mode is converted into the TE1 higher-order mode and propagates to the tapered lower waveguide 7. It then exits from port O through the output waveguide 6.

[0038] like Figure 6 As shown, the mode crosstalk of the highly integrated filter based on the thermal coupler has an incident loss of less than 2.43dB in the wavelength range of 1500nm to 1630nm, while the mode crosstalk of the highly integrated filter based on the asymmetric directional coupler exceeds 3dB in the 125nm range. Therefore, the highly integrated filter based on the thermal coupler has a large bandwidth.

[0039] Example 2

[0040] like Figure 3The right side shows a highly integrated mode filter based on an asymmetric directional coupler, comprising a silicon substrate 113, a lower cladding layer 112, and an upper cladding layer 111. A core layer 114 is disposed between the upper cladding layer 111 and the lower cladding layer 112. The core layer 114 includes an input waveguide 1, a first mode routing region 2 for filtering out the fundamental mode in the input waveguide 1 and converting the higher-order modes in the input waveguide 1 into the fundamental mode output, a single-mode region for transmitting the single-mode waveguide in the first mode routing region 2, a second mode routing region 5 for converting the fundamental mode transmitted in the single-mode region into the higher-order mode output, and an output waveguide 6 for outputting the higher-order mode. The core layer 114 is symmetrically distributed around the single-mode region. The mode routing region of the core layer 114 includes an asymmetric directional coupler composed of a tapered lower waveguide 7 and a tapered upper waveguide 9, and a functional region 8 between the tapered lower waveguide 7 and the tapered upper waveguide 9. The functional region is as follows: Figure 5 As shown on the right. The right-angled surfaces of the tapered lower waveguide 7 and the tapered upper waveguide 9 are arranged opposite each other, with their inclined surfaces facing away from functional area 8. Functional area 8 is composed of a mixture of silicon and air units based on the DBS algorithm. The functional area is divided into blocks according to the subwavelength units of 100nm. Calculation optimization is performed with silicon units as 1 and air units as 0. Multiple groups of silicon and air units used to change the mode form a structure similar to a QR code. The optimized functional area distribution structure can achieve the lowest optical loss. The specific structure is as follows:

[0041]

[0042] The single-mode region includes a central straight waveguide 4 and a curved waveguide 3 for transmitting single-mode waveguides. The central straight waveguide 4 is connected in the middle of the two tapered upper waveguides 9, and the curved waveguide 3 is connected at the rear end of the two tapered lower waveguides 7.

[0043] The fabrication of a highly integrated filter based on an asymmetric directional coupler includes the following steps:

[0044] (1) Deposit a 220nm silicon substrate 113 on a silicon wafer;

[0045] (2) A 3μm oxide layer is deposited on the silicon substrate as the lower cladding layer 112;

[0046] (3) The layout of the core layer 114 is imaged using electron beam lithography, and the widths W of the input waveguide 1 and the output waveguide 6 are shown. b1 =1μm, the width W of the curved waveguide 3 and the center straight waveguide 4 b2 =W b3 =400nm, the lengths of the tapered lower waveguide 7 and the tapered upper waveguide 9 are L. b =4μm, the distance between the tapered lower waveguide 7 and the tapered upper waveguide 9 is set as g. b =800nm, the side length W of the small square in the functional region b4 =100nm;

[0047] (4) It was etched using inductively coupled plasma to a depth of 220 nm.

[0048] (5) Deposit a silicon dioxide overcoating layer 111 with a thickness of 1 μm.

[0049] like Figure 4 As shown in (b) and (d) on the right, light enters from port I through input waveguide 1 and propagates through the first mode routing area 2 on the left. The TE0 fundamental mode propagates through the tapered lower waveguide and is filtered out by the curved waveguide 3. The TE1 higher-order mode is converted into TE0 through the first mode routing area 2 on the left and propagates to the tapered upper waveguide 9. It then propagates through the central straight waveguide 4 to the second mode routing area 5 on the right. The TE0 fundamental mode is converted into the TE1 higher-order mode and propagates to the tapered lower waveguide 7. It is then output from port O through the output waveguide 6.

[0050] like Figure 6 As shown, the mode crosstalk of the highly integrated filter based on the asymmetric directional coupler is relatively narrow in the wavelength range of 1523.7nm to 1630nm, and the mode crosstalk is less than -15dB in this wavelength range, indicating low mode crosstalk.

Claims

1. A highly integrated filter module, comprising a silicon substrate (113), a lower cladding layer (112), and an upper cladding layer (111) arranged sequentially, wherein a core layer (114) is provided between the lower cladding layer (112) and the upper cladding layer (111), characterized in that, The core layer (114) includes an input waveguide (1), a first mode routing region (2) for filtering out the fundamental mode in the input waveguide (1) and converting the higher-order modes in the input waveguide (1) into the fundamental mode output, a single-mode region for transmitting the single-mode waveguide in the first mode routing region (2), a second mode routing region (5) for converting the fundamental mode transmitted in the single-mode region into the higher-order mode output, and an output waveguide (6) for outputting the higher-order mode. The core layer (114) is symmetrically distributed around the single-mode region. The first mode routing region (2) and the second mode routing region (5) include a coupler composed of a tapered lower waveguide (7) and a tapered upper waveguide (9) and a functional region (8) between the tapered lower waveguide (7) and the tapered upper waveguide (9). The narrow end of the tapered lower waveguide (7) and the tapered upper waveguide (9) are connected. The wide end of the guide (9) is on one side; the single-mode region includes a central straight waveguide (4) and a curved waveguide (3) for transmitting single-mode waveguides. The central straight waveguide (4) is connected in the middle of the two tapered upper waveguides (9), and the curved waveguide (3) is connected to the rear end of the two tapered lower waveguides (7) respectively. The light enters through the input waveguide (1) and propagates through the first mode routing region (2) on the left. The TE0 fundamental mode propagates through the tapered lower waveguide (7) and is filtered out by the curved waveguide (3). The higher-order mode is converted into the TE0 fundamental mode through the first mode routing region (2) on the left and propagates to the tapered upper waveguide (9). It then propagates through the central straight waveguide (4) to the second mode routing region (5) on the right. The TE0 fundamental mode is converted into a higher-order mode and propagates to the tapered lower waveguide (7). It is then output through the output waveguide (6).

2. The highly integrated filter module according to claim 1, characterized in that, The tapered lower waveguide (7) is a right-angled trapezoidal structure.

3. The highly integrated filter module according to claim 2, characterized in that, The length, width, and spacing between the lower and upper tapered waveguides (7) and the upper tapered waveguide (9) are adjustable.

4. The highly integrated filter module according to claim 2, characterized in that, The coupler is either an asymmetric directional coupler or an adiabatic coupler.

5. The highly integrated filter module according to claim 4, characterized in that, The right-angled surfaces of the asymmetric directional coupler tapered lower waveguide (7) and tapered upper waveguide (9) are arranged opposite each other, and the spacing between them is 700nm-900nm; the functional region (8) is composed of a mixture of silicon units and air units based on the direct binary algorithm, with silicon units as 1 and air units as 0 to form a complex structure, and the size of the subwavelength unit of the functional region is 50nm-150nm.

6. The highly integrated filter module according to claim 4, characterized in that, The inclined surfaces of the thermal coupler tapered lower waveguide (7) and tapered upper waveguide (9) are arranged opposite each other, and the spacing between them is 400nm-500nm; the functional area (8) is composed of silicon units and air units based on direct binary algorithm, with silicon units as 1 and air units as 0 to form a complex structure. The size of the subwavelength unit of the functional area is 50nm-150nm. When the functional area coincides with the tapered lower waveguide (7) and tapered upper waveguide (9), the waveguide area covers the functional area (8).

7. The highly integrated filter module according to claim 1, characterized in that, The central straight waveguide (4) and the curved waveguide (3) have the same width.

8. A method for manufacturing a highly integrated filter module as described in claim 1, characterized in that, Includes the following steps: (1) A 3 µm silicon dioxide undercoat (112) was deposited on a silicon substrate (113) by plasma-enhanced chemical vapor deposition. (2) A 220 nm silicon layer was deposited on the silicon dioxide undercoat as a core layer by plasma-enhanced chemical vapor deposition (114). (3) The layout of the core layer is visualized using electron beam lithography; (4) Use inductively coupled plasma to etch according to its layout, with an etching depth of 220 nm, to prepare the specific structure of the core layer; (5) A silicon dioxide cladding layer with a thickness of 1 μm was deposited on the core layer using plasma-enhanced chemical vapor deposition (111).

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