Multimode optical switch based on reverse design

Abstract

The invention discloses a multimode optical switch based on reverse design, and belongs to the technical field of optical switching. Comprising a first straight waveguide, two cascaded multimode power dividers in mirror symmetry, a second straight waveguide and a phase shifter. The cascaded multi-mode power divider comprises N groups of cascaded multi-mode power dividers, each group of multi-mode power dividers comprises a reversely designed core multi-mode waveguide and two single-mode waveguides, the insertion loss and crosstalk are remarkably reduced by adopting a reverse design method, and in a specified wavelength range, the insertion loss of each mode signal is lower than 0.2 dB, and the crosstalk is lower than-20dB. The N groups of single-mode waveguides are respectively arranged in parallel on two sides of the core multi-mode waveguide, phase shifters are arranged in parallel areas, and temperature rise balance is realized by adjusting the size and spacing of parallel electrodes, so that pi phase shift is synchronously realized under the condition of low power consumption, and the extinction ratio is higher than 12dB. The multi-mode optical switch is compact in structure, can be expanded to a higher mode, and provides a high-performance solution for high-capacity optical switching and multi-mode signal processing.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical switching, and more specifically, relates to a multimode optical switch based on inverse design. Background Art

[0002] With the continuous development of optical communication and data exchange technologies, traditional electrical switching systems are facing bandwidth bottlenecks and high energy consumption problems. Optical switching has gradually become the mainstream due to its advantages of large bandwidth and low latency. In recent years, multimode multiplexing technology can transmit multiple mode signals on the same wavelength, providing the possibility to increase the transmission capacity. However, existing multimode optical switches still have deficiencies in aspects such as phase regulation, power consumption control, and manufacturing tolerance. Especially in multimode power splitters, it is often difficult to achieve both low insertion loss and large process tolerance in traditional designs; in the phase shifter part, uneven temperature control easily leads to poor synchronization of different modes, thus affecting the overall switch performance. Therefore, there is an urgent need for a multimode optical switch with a simple structure, flexible design, scalable number of modes, and wide adaptability. Summary of the Invention

[0003] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a multimode optical switch based on inverse design, aiming to solve the problems existing in the prior art multimode optical switches in aspects such as low insertion loss, temperature control balance, synchronous switching, and process tolerance.

[0004] To achieve the above purpose, the present invention provides a multimode optical switch based on inverse design, including:

[0005] A first straight waveguide, two mirror-symmetric cascaded multimode power splitters, a phase shifter, and a second straight waveguide. The cascaded multimode power splitter includes N groups of cascaded multimode power splitters. The multimode power splitter includes a core multimode waveguide based on inverse design and two single-mode waveguides. The core multimode waveguide includes a first wedge waveguide and a second wedge waveguide, where the waveguide width at the end of the first wedge waveguide is the same as the waveguide width at the beginning of the second wedge waveguide. The two single-mode waveguides are respectively located on both sides of the core multimode waveguide, are coupled to the first wedge waveguide at a fixed distance, and extend horizontally outside the second wedge waveguide. Multiple groups of single-mode waveguides are arranged in parallel on both sides at a fixed distance.

[0006] A multimode optical signal including N groups of modes is input into a first - stage cascaded multimode power splitter through a first straight waveguide and divided into upper and lower two - path signals. Single modes are sequentially coupled out from single - mode waveguides, then sequentially coupled to a core multimode waveguide through a mirror - symmetric second - stage cascaded multimode power splitter, and finally output through a second straight waveguide. A phase shifter is arranged in the parallel region of the single - mode waveguides on one side, which is used to regulate the phase difference between the upper and lower two - path signals. The phase shifter is provided with micro - electrodes arranged in parallel, and the size and spacing of the micro - electrodes are adjustable to achieve temperature - rise equilibrium of each waveguide, so as to achieve synchronous π - phase shift when a specific voltage is applied. If the phase difference is π, the energy output of the corresponding mode is 0.

[0007] Through the above - mentioned technical solution conceived by the present invention, compared with the prior art, the following

[0008] Beneficial effects can be obtained:

[0009] 1. The multimode optical switch provided by the present invention includes a core multimode waveguide and single - mode waveguides designed in reverse. Compared with devices without reverse design, the insertion loss and crosstalk of multimode optical signals during distribution and coupling are significantly reduced, the signal transmission quality is improved, the overall power consumption of the system is reduced, and the insertion loss of each mode is lower than 0.2 dB and the crosstalk is lower than - 20 dB within a specified wavelength range.

[0010] 2. This optical switch is applicable to a multimode signal modulation and processing platform, and within a specified wavelength band, its extinction ratio is not lower than 12 dB.

[0011] 3. The electrode design can achieve synchronous phase shift of multiple modes, improving the stability and consistency of the optical switch.

[0012] 4. The device has a small size, a compact structure, flexible design, the number of modes can be expanded, is convenient for large - scale integration, and is suitable for multimode data transmission and processing applications.

[0013] 5. The manufacturing process tolerance and compatibility are enhanced, and it is applicable to multiple material platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of the multimode optical switch provided by the present invention.

[0015] Figure 2 It is a schematic structural diagram of the multimode power splitter.

[0016] Figure 3 It is the simulation results of the multimode power splitter for three different modes; (a) - (c) show the optical field distributions of the three - mode power splitter at a wavelength of 1.55 μm; (d) - (f) show the transmission spectra of the three modes in the range of 1.5 - 1.6 μm; (g) - (i) illustrate the influence of the waveguide width deviation of the device on the transmission spectrum at a wavelength of 1.55 μm.

[0017] Figure 4 Schematic diagram for the design of a phase shifter; (a) Cross-sectional view of the phase shifter, showing the waveguide and parallel electrodes of the phase shifter; (b) Effect of changing the distance G between waveguides on the temperature change at the center of the waveguide under the same power consumption. W

[0018] Figure 5 Experimental results of the multimode optical switch of the present invention; (a) Microscope image of the optical switch; (b) Curves of the transmission spectra of three modes at the output port varying with voltage at 1.55 μm; (c)-(e) Normalized transmission spectra in the "on" and "off" states. Detailed implementation manners

[0019] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] The present invention provides a multimode optical switch based on inverse design, including:

[0021] A first straight waveguide, two mirror-symmetric cascaded multimode power splitters, a phase shifter, and a second straight waveguide. The cascaded multimode power splitter includes N groups of cascaded multimode power splitters. The multimode power splitter includes a core multimode waveguide based on inverse design and two single-mode waveguides. The core multimode waveguide includes a first wedge waveguide and a second wedge waveguide, where the waveguide width at the tail end of the first wedge waveguide is the same as the waveguide width at the head end of the second wedge waveguide. The two single-mode waveguides are respectively located on both sides of the core multimode waveguide, are coupled with the first wedge waveguide at a fixed distance, and extend horizontally outside the second wedge waveguide. Multiple groups of single-mode waveguides are arranged in parallel on both sides at a fixed distance.

[0022] The multimode optical signal including N groups of modes is input through the first straight waveguide to the first cascaded multimode power splitter and is divided into two signals, one up and one down. Single modes are sequentially coupled out from the single-mode waveguides, and then are sequentially coupled to the core multimode waveguide through the mirror-symmetric second cascaded multimode power splitter, and finally are output through the second straight waveguide. A phase shifter is arranged in the parallel region of the single-mode waveguides on one side to adjust the phase difference between the two signals, one up and one down, to achieve synchronous π phase shift. If the phase difference is π, the energy output of the corresponding mode is 0.

[0023] Specifically, the shapes of the core multimode waveguide and the single-mode waveguide are optimized by an inverse design algorithm. Preferably, boundary optimization is obtained through a particle swarm optimization algorithm.

[0024] ​Specifically, the width of the core multimode waveguide is widened to be greater than 1 μm to reduce the phase error, and the waveguide spacing is greater than 0.5 μm to prevent unnecessary inter-waveguide coupling. At the same time, microelectrodes arranged in parallel are integrated on the core waveguide. By adjusting the size and spacing of the electrodes (such as width greater than 1 μm, length greater than 50 μm, and the spacing can be optimized to achieve synchronous phase shift under a specified voltage), precise synchronous regulation of multiple modes is achieved.

[0025] Specifically, the microelectrode material of the phase shifter is selected from at least one of Ti, TiN, Pt, and NiCr.

[0026] Specifically, the core layer material of all waveguides is at least one of Si, Si3N4, GaAs, LiNbO3, and InP, and the cladding layer material is at least one of SiO2 and polymer.

[0027] As Figure 1 shown, the multimode optical switch of this embodiment adopts a centrosymmetric structure with dimensions of 325×80 μm 2 , and is composed of two cascaded multimode power splitters and phase shifters. The input port receives an optical signal containing three modes of TE0, TE1, and TE2. The signal first enters the core multimode waveguide for transmission through the first straight waveguide; then, the optical signal is divided into upper and lower paths by the cascaded multimode power splitter, and then enters the phase shift region through single-mode waveguides corresponding to the number of modes. Finally, it is coupled back to the second straight waveguide by the second cascaded multimode power splitter and output from the right end. Multiple wavelengths can be loaded simultaneously for each mode.

[0028] Figure 2 Shown is the design schematic diagram of the multimode power splitter. Taking the TE2 mode conversion as an example: TE0 to TE2 three modes are input from the left. Among them, the TE2 mode is converted into the fundamental mode and evenly divided into upper and lower ports after 3dB splitting, and the remaining modes continue to be transmitted. The upper side of the core multimode waveguide is arranged in parallel with the upper single-mode waveguide with a gap of 180 nm; the lower single-mode waveguide is symmetric with the upper side. The input width of the core multimode waveguide is W A1 , and the output width is W A2 , and the length L A2 of the tapered waveguide connected to the next-stage power splitter is 5 μm. The widths of the single-mode waveguides are successively W A3 to W AN , where W AN is 500 nm and is connected to a curved waveguide with a radius of 5 μm. The parameters L A1 and W A1 to W AN–1 are all obtained through inverse design optimization.

[0029] Figure 3(a)-(c) in it show the optical field distributions of the TE2, TE1, and TE0 mode power splitters at a wavelength of 1.55 μm. Taking the TE2 mode power splitter as an example, the simulation results need to consider the insertion loss from TE2 to TE0 modes and the crosstalk caused by the TE1 and TE0 mode conversions. (d)-(f) show that in the range of 1.5 - 1.6 μm, the maximum insertion losses of the TE2, TE1, and TE0 modes are 0.12, 0.18, and 0.06 dB respectively, and all crosstalk is below -20 dB. (g)-(i) illustrate the influence of the waveguide width deviation of the device at a wavelength of 1.55 μm on the insertion loss and crosstalk, where ΔW varies from -20 nm to 20 nm in 5 nm steps. In the range of ±15 nm, the insertion losses of the three modes are all less than 0.3 dB, and the crosstalk is all below -20 dB, indicating that the designed device has a large manufacturing tolerance.

[0030] Figure 4 (a) in it shows the cross-sectional view of the phase shifter, which consists of three Si waveguides (W G1 -W G3 ) with a spacing of 0.5 μm. To reduce the random phase error, the width of each waveguide is 2 μm, and it is covered with a 1 μm thick SiO2 layer. The key design lies in keeping the temperature rise uniform between W G1 -W G3 so that a single electrode can control all modes simultaneously. Directly widening the traditional metal electrode will cause the temperature of W G2 to be higher than that of W G1 and W G3 , so two parallel TiN thin films (2 μm wide, 140 μm long, 0.1 μm thick) are used as micro heaters. (b) shows the influence of changing the waveguide spacing G W on the temperature change of W G1 -W G3 at the same power consumption. After scanning, the spacing G W is set to 1.92 μm, so that uniform temperature rise can be achieved at a constant power to ensure the synchronous switching of the three modes.

[0031] Figure 5 (a) in it is the microscope image of the device, with a heat insulation groove set in the center to prevent unnecessary thermal crosstalk; (b) is the curve of the transmission spectra of the three modes at the output port varying with voltage at 1.55 μm. The results show that at 3.6 V, all modes switch simultaneously, and the power consumption for π phase shift is 23.6 mW. (c)-(e) are the normalized transmission spectra in the "on" and "off" states respectively. The dotted lines represent the insertion loss, and the solid lines represent the crosstalk between modes (values below -30 dB are omitted). In the C band, the insertion losses of the TE2, TE1, and TE0 modes are 2.1, 1.3, and 1.5 dB respectively, and the maximum crosstalks are -13.2, -14.3, and -17.1 dB respectively, and the extinction ratios all exceed 12 dB.

[0032] The present invention provides a multi-mode optical switch with a simple structure, large process tolerance, and low power consumption, and a design method thereof. By reverse designing and optimizing the key parameters of the multi-mode power splitter and performing a special design on the phase shifter, synchronous switching of multi-mode signals with low insertion loss is achieved. In addition, the present invention can support a larger number of modes by connecting power splitters of higher-order modes, and has an extinction ratio higher than 12 dB in the C band, with broad application prospects.

[0033] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multimode optical switch based on reverse design, characterized in that, Comprising: A first straight waveguide, two mirror-symmetric cascaded multimode power splitters, a second straight waveguide, and a phase shifter. The two cascaded multimode power splitters are respectively a first cascaded multimode power splitter and a second cascaded multimode power splitter. Each of the cascaded multimode power splitters includes N groups of cascaded multimode power splitters. The multimode power splitter includes a core multimode waveguide based on inverse design and two single-mode waveguides. The core multimode waveguide includes a first wedge waveguide and a second wedge waveguide. The waveguide width at the end of the first wedge waveguide is the same as the waveguide width at the beginning of the second wedge waveguide. The two single-mode waveguides are respectively located on both sides of the core multimode waveguide, are coupled with the first wedge waveguide at a fixed spacing, and extend horizontally outside the second wedge waveguide. Multiple groups of single-mode waveguides are arranged in parallel on both sides at a fixed spacing; When the first straight waveguide receives a multimode optical signal including N groups of modes, the multimode optical signal is input into the first cascaded multimode power splitter through the first straight waveguide and is divided into upper and lower two-way signals. Single modes are sequentially coupled out from the single-mode waveguides, and then are sequentially coupled to the core multimode waveguide through the mirror-symmetric second cascaded multimode power splitter, and finally are output through the second straight waveguide; A phase shifter is arranged in the parallel region of the single-mode waveguides on one side, and is used to adjust the phase difference between the upper and lower two-way signals to achieve a synchronous π phase shift; If the phase difference is π, the energy output of the corresponding mode is 0.

2. The multimode optical switch according to claim 1, wherein The shapes of the core multimode waveguide and the single-mode waveguide are optimized by a particle swarm optimization algorithm.

3. The multimode optical switch according to claim 2, characterized in that, The width of the core multimode waveguide is greater than 1 μm.

4. The multi-mode optical switch according to claim 2, characterized in that, The spacing between the single-mode waveguide and the first wedge waveguide is greater than 0.5 μm.

5. The multimode optical switch according to claim 1, characterized in that, The phase shifter includes parallel microelectrodes.

6. The multimode optical switch according to claim 5, characterized in that, The width of the microelectrode is greater than 1 μm and the length is greater than 50 μm.

7. The multimode optical switch according to claim 5, characterized in that, The microelectrode material of the phase shifter is selected from at least one of Ti, TiN, Pt, and NiCr.

8. The multimode optical switch according to claim 1, wherein, The core layer material of all waveguides is at least one of Si, Si3N4, GaAs, LiNbO3, and InP, and the cladding layer material is at least one of SiO2 and polymer.

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