On-chip broadband robust mode multiplexing system based on abnormal adiabatic coupling process

Abstract

An on-chip broadband robust mode multiplexing system based on an abnormal adiabatic coupling process comprises a bus waveguide and three pairs of mode conversion units sequentially arranged on one side of the bus waveguide, and each mode conversion unit comprises an S-shaped bent waveguide and a narrow waveguide parallel to the bus waveguide and used for input or output. The three pairs of mode conversion units are respectively used for converting TM1-TM3 modes, and the widths of the bus waveguides are different when the bus waveguides correspond to different mode conversion units. According to the invention, an abnormal adiabatic coupling process is utilized, multiplexing and demultiplexing functions of four mode channels TM0-TM3 are supported, and a small-size broadband robust silicon-on-chip mode multiplexing system with the length of mode conversion units being smaller than 35 microns is realized.

Description

Technical Field

[0001] The present invention relates to a technology in the field of optical communications, in particular to an on-chip broadband robust mode multiplexing system based on an anomalous adiabatic coupling process. Background Art

[0002] The optical coupling performance in most existing designs is usually very sensitive to the waveguide structure and operating wavelength; the device size of most designs is relatively large or the structure is too complex, which is not conducive to large-scale manufacturing and integration; some designs have difficult to control inter-modal crosstalk, so the number of supported modes is small (only 2~3) and the operating bandwidth is limited to 40nm (1530nm~1570nm). Summary of the Invention

[0003] The present invention addresses the shortcomings of existing broadband robust silicon-based on-chip mode multiplexing systems, namely that the mode conversion units are large in size and generally longer than 100 μm. An on-chip broadband robust mode multiplexing system based on an anomalous adiabatic coupling process is proposed. By utilizing the anomalous adiabatic coupling process, i.e., the coupling order is anomalous and counterintuitive, when a narrow waveguide is input, coupling occurs first between the curved waveguide and the bus waveguide, and then between the curved waveguide and the narrow waveguide. This supports multiplexing and demultiplexing functions for the four mode channels TM0-TM3, and realizes a small-sized broadband robust silicon-based on-chip four-channel mode multiplexing system with a mode conversion unit length of less than 35 μm.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to an on-chip broadband robust mode multiplexing system based on an anomalous adiabatic coupling process, comprising: a bus waveguide and three pairs of mode conversion units sequentially arranged on one side thereof, each mode conversion unit comprising an S-shaped curved waveguide and a narrow waveguide parallel to the bus waveguide for input or output, the three pairs of mode conversion units being respectively used to convert TM1 to TM3 modes, and the width of the bus waveguide being different when corresponding to different mode conversion units.

[0006] When the narrow waveguide is used as the input waveguide and the TM0 mode is input, the curved waveguide in the middle first couples with the bus waveguide and then with the narrow waveguide, converting it into one of the TM1 to TM3 modes before entering the bus waveguide. The curved waveguide on the other side first couples with its corresponding narrow waveguide and then with the bus waveguide, converting one of the TM1 to TM3 modes from the bus waveguide into the TM0 mode and outputting it from the narrow waveguide.

[0007] The mode multiplexing system is obtained by etching a waveguide structure on a silicon dioxide buried oxide layer and depositing silicon dioxide as an upper cladding layer.

[0008] The bus waveguide includes: a wide waveguide located on one side of each mode conversion unit and an adiabatic trapezoidal waveguide connecting each wide waveguide, wherein: the width W3 of the wide waveguide varies according to different conversion modes.

[0009] The central angle of the curved waveguide , where: g is the minimum distance between the narrow waveguide, wide waveguide and the curved waveguide respectively, R is the curvature radius of the curved waveguide, and W2 is the width of the curved waveguide.

[0010] Technical Effects

[0011] Compared with the existing technology, the present invention realizes a mode conversion function with strong robustness against processing errors and working wavelength changes through an anomalous adiabatic coupling structure in a smaller size, that is, the coupling length is less than 35μm, and on this basis realizes a four-channel mode multiplexing system. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the structure of the present invention;

[0013] In the picture: Figure 1 (a) Schematic diagram of the on-chip broadband robust mode multiplexing system based on the anomalous adiabatic coupling process. Figure 1 (b) Schematic diagram of the mode conversion unit structure;

[0014] Figure 2 Schematic diagram of bus waveguide (single side);

[0015] Figure 3 (a) Simulated electric field distribution diagram of TM0-TM1 mode conversion unit, Figure 3 (b) Simulation diagram of TM0–TM1 mode conversion loss changing with waveguide width. Figure 3 (c) Simulation diagram of TM0–TM1 mode conversion loss changing with waveguide spacing;

[0016] Figure 4 (a) Simulated electric field distribution diagram of TM0-TM2 mode conversion unit, Figure 4 (b) Simulation diagram of TM0–TM2 mode conversion loss changing with waveguide width. Figure 4 (c) Simulation diagram of TM0–TM2 mode conversion loss changing with waveguide spacing;

[0017] Figure 5 (a) Simulated electric field distribution diagram of TM0-TM3 mode conversion unit, Figure 5 (b) Simulation diagram of TM0–TM3 mode conversion loss changing with waveguide width. Figure 5 (c) Simulation diagram of TM0–TM3 mode conversion loss changing with waveguide spacing;

[0018] Figure 6(a) Optical microscope image of a physical sample of the on-chip broadband robust mode multiplexing system based on the anomalous adiabatic coupling process. Figure 6 (b) SEM image of TM0-TM1 mode conversion unit. Figure 6 (c) SEM image of TM0–TM2 mode conversion unit. Figure 6 (d) SEM image of TM0–TM3 mode conversion unit;

[0019] Figure 7 Experimental transmission spectra of the on-chip broadband robust mode multiplexing system based on the anomalous adiabatic coupling process, i.e., the transmission spectra of the light input from (a) TM0, (b) TM1, (c) TM2, and (d) TM3 ports and the output from TM0, TM1, TM2, and TM3 ports. DETAILED DESCRIPTION

[0020] like Figure 1 As shown, this embodiment relates to an on-chip broadband robust mode multiplexing system based on an anomalous adiabatic coupling process, comprising: a bus waveguide 1 and three pairs of mode conversion units 2 sequentially arranged on one side thereof, each mode conversion unit 2 comprising an S-shaped curved waveguide 201 and a narrow waveguide 202 parallel to the bus waveguide for input or output, the three pairs of mode conversion units 2 being respectively used to convert TM1 to TM3 modes, and the width of the bus waveguide 1 corresponding to different mode conversion units being different.

[0021] When the narrow waveguide 202 is used as the input waveguide and the TM0 mode is input, the middle curved waveguide 201 first couples with the bus waveguide 1, then couples with the narrow waveguide 202, and is converted to one of the TM1 to TM3 modes before entering the bus waveguide 1. The curved waveguide 201 on the other side first couples with its corresponding narrow waveguide 202, then couples with the bus waveguide 1, and one of the TM1 to TM3 modes is converted from the bus waveguide to the TM0 mode and output from the narrow waveguide 202.

[0022] like Figure 2 As shown, the bus waveguide 1 includes: a wide waveguide 101 located on one side of each mode conversion unit and an adiabatic trapezoidal waveguide 102 connecting each wide waveguide 101, wherein: the width W3 of the wide waveguide varies according to different conversion modes, and the widths W3 of the wide waveguides TM1, TM2, and TM3 are 1.12 μm, 1.78 μm, and 2.48 μm, respectively.

[0023] The mode conversion unit length L is obtained through 3D finite-difference time-domain method simulation optimization. The mode conversion unit lengths L of TM1, TM2, and TM3 are 24.7 μm, 28.3 μm, and 32.0 μm, respectively.

[0024] The width W1 of the narrow waveguide 202 is 0.45 μm, and the width W2 of the curved waveguide 201 is 0.45 μm.

[0025] The central angle of the curved waveguide 201 , where: g is the minimum distance between the narrow waveguide 202, the wide waveguide 101 and the curved waveguide 201 respectively, R is the curvature radius of the curved waveguide 201, and W2 is the width of the curved waveguide 201.

[0026] In the mode conversion unit, the minimum distance g between the narrow waveguide 202 and the wide waveguide 101 and the curved waveguide 201 is 0.15 μm.

[0027] The curvature radius R of the curved waveguide 201 is 250 μm, 250 μm, and 500 μm for TM1, TM2, and TM3 modes, respectively.

[0028] The central angle of the curved waveguide 201 is 1.62, 1.62, and 1.15 for the TM1, TM2, and TM3 modes, respectively, and is expressed in angle values.

[0029] The height of all waveguide structures in the mode multiplexing system is 220 nm.

[0030] like Figure 1 As shown in (a), this embodiment relates to a method for preparing the above-mentioned on-chip broadband robust mode multiplexing system. After a 220nm waveguide structure is obtained on a 3μm thick silicon dioxide buried oxide layer by electron beam direct write exposure and inductively coupled plasma etching, a 1μm silicon dioxide upper cladding layer is further obtained on the waveguide structure by plasma enhanced chemical vapor deposition.

[0031] like Figure 7 As shown in (a), the experimental result of the loss of the TM0 mode channel in this embodiment is less than 2 dB in the wavelength range of 1480 nm to 1600 nm, and the experimental result of the inter-mode crosstalk at 1550 nm is -21 dB.

[0032] like Figure 7 As shown in (b), the experimental results of the TM1 mode channel loss in the wavelength range of 1480nm~1600nm in this embodiment are less than 2dB, that is, the single-side mode conversion loss is less than 1dB, and the experimental result of the inter-mode crosstalk at 1550nm is -23dB. Figure 3 As shown in (b) and (c), under the condition that the single-sided mode conversion loss is less than 3dB, the simulation results of the waveguide width tolerance are greater than the range of -60nm~+140nm, and the simulation results of the waveguide spacing tolerance are greater than the range of -70nm~+210nm.

[0033] like Figure 7As shown in (c), the experimental results of the TM2 mode channel loss in the wavelength range of 1480nm~1600nm in this embodiment are less than 2dB, that is, the single-side mode conversion loss is less than 1dB, and the experimental result of the inter-mode crosstalk at 1550nm is -21dB. Figure 4 As shown in (b) and (c), under the condition that the single-sided mode conversion loss is less than 3dB, the simulation results of the waveguide width tolerance are greater than the range of -50nm to +120nm, and the simulation results of the waveguide spacing tolerance are greater than the range of -60nm to +190nm.

[0034] like Figure 7 As shown in (d), the experimental results of the TM3 mode channel loss in the wavelength range of 1480nm~1600nm in this embodiment are less than 2dB, that is, the single-side mode conversion loss is less than 1dB, and the experimental result of the inter-mode crosstalk at 1550nm is -25dB. Figure 5 As shown in (b) and (c), under the condition that the single-sided mode conversion loss is less than 3dB, the simulation results of the waveguide width tolerance are greater than the range of -50nm~+110nm, and the simulation results of the waveguide spacing tolerance are greater than the range of -100nm~+210nm.

[0035] Compared with the prior art, the present invention utilizes an anomalous adiabatic coupling process to make the mode conversion process highly robust against processing errors and operating wavelength changes (most existing mode multiplexing systems do not have this), and the required coupling length is greatly reduced compared to the existing adiabatic coupling process, while supporting the multiplexing and demultiplexing functions of the four mode channels TM0-TM3. In this system, the length of a single mode conversion unit is less than 35μm. Simulations show that under the condition that the unilateral mode conversion loss of the system is less than 3dB, the waveguide width tolerance is greater than the range of -50nm~+110nm, and the waveguide spacing tolerance is greater than the range of -60nm~+190nm. Experimental measurements show that the 2dB bandwidth of each mode channel of the system is greater than 120nm (1480nm~1600nm), and the inter-mode crosstalk at 1550nm is less than -21dB.

[0036] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. An on-chip broadband robust mode multiplexing system based on an anomalous adiabatic coupling process, characterized in that: include: A bus waveguide and three pairs of mode conversion units sequentially arranged on one side thereof. Each mode conversion unit includes an S-shaped curved waveguide and a narrow waveguide parallel to the bus waveguide for input or output. The three pairs of mode conversion units are respectively used to convert TM1 to TM3 modes. The width of the bus waveguide varies depending on the mode conversion unit. When the narrow waveguide is used as the input waveguide and the TM0 mode is input, the curved waveguide in the middle first couples with the bus waveguide and then with the narrow waveguide, converting it into one of the TM1 to TM3 modes before entering the bus waveguide. The curved waveguide on the other side first couples with its corresponding narrow waveguide and then with the bus waveguide, converting one of the TM1 to TM3 modes from the bus waveguide into the TM0 mode and outputting it from the narrow waveguide.

2. The on-chip broadband robust mode multiplexing system based on anomalous adiabatic coupling process according to claim 1, characterized in that: The bus waveguide includes: a wide waveguide located on one side of each mode conversion unit and an adiabatic trapezoidal waveguide connecting each wide waveguide, wherein: the width W3 of the wide waveguide varies according to different conversion modes.

3. The on-chip broadband robust mode multiplexing system based on anomalous adiabatic coupling process according to claim 1, characterized in that: The central angle of the curved waveguide , where: g is the minimum distance between the narrow waveguide, wide waveguide and the curved waveguide respectively, R is the curvature radius of the curved waveguide, and W2 is the width of the curved waveguide.

4. The on-chip broadband robust mode multiplexing system based on anomalous adiabatic coupling process according to claim 1 or 2, characterized in that: In the bus waveguide, the wide waveguide widths W3 corresponding to TM1, TM2, and TM3 are 1.12 μm, 1.78 μm, and 2.48 μm, respectively.

5. The on-chip broadband robust mode multiplexing system based on anomalous adiabatic coupling process according to claim 1 or 2, characterized in that: The length L of the mode conversion unit is obtained through 3D finite-difference time-domain method simulation optimization. The lengths L of the mode conversion units of TM1, TM2, and TM3 are 24.7 μm, 28.3 μm, and 32.0 μm, respectively.

6. The on-chip broadband robust mode multiplexing system based on anomalous adiabatic coupling process according to claim 1 or 2, characterized in that: The width W1 of the narrow waveguide is 0.45 μm, and the width W2 of the curved waveguide is 0.45 μm.

7. The on-chip broadband robust mode multiplexing system based on anomalous adiabatic coupling process according to claim 1 or 3, characterized in that: In the mode conversion unit, the minimum distance g between the narrow waveguide, the wide waveguide and the curved waveguide is 0.15 μm.

8. The on-chip broadband robust mode multiplexing system based on anomalous adiabatic coupling process according to claim 7, characterized in that: The curvature radius of the curved waveguide is 250 μm, 250 μm, and 500 μm for TM1, TM2, and TM3 modes, respectively; The central angle of the curved waveguide is 1.62, 1.62, and 1.15 for the TM1, TM2, and TM3 modes, respectively, and is expressed in angle values.

9. A method for preparing an on-chip broadband robust mode multiplexing system based on an anomalous adiabatic coupling process as claimed in any one of claims 1 to 8, characterized in that: On a 3μm-thick silicon dioxide buried oxide layer, a 220nm waveguide structure was obtained by electron beam direct write exposure and inductively coupled plasma etching, and then a 1μm silicon dioxide upper cladding layer was further obtained on the waveguide structure by plasma enhanced chemical vapor deposition.

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