TE1-TE0 mode conversion beam splitting method and device

Abstract

The invention belongs to the technical field of integrated photoelectronics, and particularly relates to a TE1-TE0 mode conversion beam splitting method and device. The method comprises the following steps: S1, injecting an optical signal in a TE1 mode from the input end of a central input waveguide; s2, the injected TE1 mode optical signal selectively excites a high-order eigenmode in a three-waveguide structure; and S3, performing adiabatic evolution on the high-order eigenmode in the adiabatic evolution region, outputting a first TE0 mode optical signal in the first side output waveguide at an output end, and outputting a second TE0 mode optical signal in the second side output waveguide at the same time. The invention aims to solve the technical blank that in the prior art, a compact integrated photonic device capable of demultiplexing a TE1 high-order mode into a two-path base-order TE0 mode signal efficiently in a broadband mode is lacked, and particularly, an effective technical scheme capable of simultaneously realizing mode order reduction and power beam splitting and controlling the phase relation of output signals is lacked.

Description

Technical Field

[0001] This invention belongs to the field of integrated optoelectronics technology, specifically relating to a TE1-TE0 mode conversion beam splitting method and device. Background Technology

[0002] In silicon-based photonic integration and mode multiplexing (MDM) systems, the flexible control of optical waveguide modes of different orders is crucial. Among these, converting higher-order modes (such as TE1 modes) back to the easily processed fundamental TE0 mode (i.e., mode cleanup or filtering) is a key step in achieving signal demultiplexing, mode crosstalk suppression, and interfacing with standard single-mode devices. In existing technologies, mode converters typically rely on asymmetric directional couplers, grating-assisted structures, etc., which generally suffer from narrow operating bandwidth and sensitivity to manufacturing processes.

[0003] It is worth noting that an adiabatic mode conversion beam splitter has been disclosed in the prior art (CN 117111214 B). This patent discloses a three-waveguide structure consisting of a central tapered waveguide and two symmetrical tapered waveguides on both sides, and elaborates in detail its function of evolving the input TE0 fundamental mode into two output TE1 higher-order modes along the fundamental eigenmode path of the system.

[0004] However, this prior art only discloses and teaches the function and working principle of the structure under the input of the TE0 fundamental mode. What physical effects the structure will produce, how the optical field will evolve, and whether it can achieve any valuable functions when the TE1 higher-order mode is used as input are completely unknown and unrevelation in this prior art. Therefore, how to achieve efficient TE1-TE0 mode conversion using a simple and robust device remains a pressing technical challenge in this field. Summary of the Invention

[0005] The present invention aims to address the technological gap in the existing technology of lacking a compact integrated photonic device that can efficiently and broadbandly demultiplex the TE1 high-order mode into two fundamental TE0 mode signals, and in particular, lacks an effective technical solution that can simultaneously achieve mode order reduction and power beam splitting, and control the phase relationship of the output signal.

[0006] To achieve the above-mentioned objective, the present invention adopts the following technical solution: a TE1-TE0 mode conversion beam splitting method, comprising the following steps: S1, injecting a TE1 mode optical signal into the input end of the central input waveguide; S2, selectively exciting a higher-order eigenmode in the three-waveguide structure using the injected TE1 mode optical signal; S3, the higher-order eigenmode undergoes adiabatic evolution in the adiabatic evolution region, and outputs a first TE0 mode optical signal in the first output waveguide at the output end, while simultaneously outputting a second TE0 mode optical signal in the second output waveguide.

[0007] Furthermore, as a preferred embodiment of the present invention, there is a phase difference of π between the first TEO mode optical signal and the second TEO mode optical signal.

[0008] Furthermore, as a preferred embodiment of the present invention, the optical power of the first TEO mode optical signal and the second TEO mode optical signal are equal.

[0009] Furthermore, as a preferred embodiment of the present invention, the effective refractive index evolution path of the higher-order intrinsic modes has an effective refractive index value greater than that of the fundamental intrinsic modes of the three-waveguide structure.

[0010] As a further preferred embodiment of the present invention, in S3, the higher-order eigenmode evolves into a TE0 odd-mode supermode at the output end. This TE0 odd-mode supermode is characterized by two TE0 modes having a π phase difference in the first and second output waveguides.

[0011] A TE1-TE0 mode conversion beam splitter includes a central input waveguide; first and second side output waveguides symmetrically arranged on both sides of the central input waveguide; and an adiabatic evolution region connecting the central input waveguide and the side output waveguides. Within the adiabatic evolution region, the width of the central input waveguide decreases along the light propagation direction, while the widths of the first and second side output waveguides increase.

[0012] As a further preferred embodiment of the present invention, the structural parameters of the mode conversion beam splitter are configured such that when the TE1 mode is injected from the center input waveguide, the TE1 mode undergoes adiabatic evolution along a higher-order intrinsic mode path of the mode conversion beam splitter within the adiabatic evolution region, and outputs a first TE0 mode in the first side output waveguide at the output end, while simultaneously outputting a second TE0 mode in the second side output waveguide.

[0013] As a further preferred embodiment of the present invention, the structural parameters of the mode conversion beam splitter are configured such that the effective refractive index of the higher-order intrinsic mode path is greater than the effective refractive index of the basic-order intrinsic mode path of the mode conversion beam splitter throughout the entire adiabatic evolution region.

[0014] As a further preferred embodiment of the present invention, the mode conversion beam splitter is used to achieve a mode conversion beam splitting efficiency of TE1 to two TE0 modes greater than 90% at the center working wavelength of 1550nm, and a working bandwidth greater than 100nm.

[0015] The TE1-TE0 mode conversion beam splitting method and device described in this invention, compared with the prior art, have the following technical advantages:

[0016] (1) Novel Functionality: This invention realizes a novel device function—a TE1-to-2×TE0 mode conversion beam splitter. It solves the technical problem of demultiplexing higher-order mode signals and distributing them to multiple basic-order mode channels, filling a gap in existing technology.

[0017] (2) Functional Complementarity and Integration Advantages: The function of this invention (TE1 → two TE0s) and the function of the prior art (CN117111214B) (TE0 → two TE1s) constitute a perfect mode multiplexing and demultiplexing operation pair. This means that by using the exact same physical structure and only changing the input mode, two functions with opposite directions but equal importance can be realized, maximizing the value of "one device for two purposes", which is of great significance for improving the integration and functional diversity of photonic chips.

[0018] (3) Built-in phase control: The two TEO signals output by this method have a natural and stable π phase difference. This feature does not require any additional phase shifters, which is extremely attractive for advanced applications such as balanced detectors, push-pull optical modulators and optical phased arrays that require differential signal input.

[0019] (4) Excellent overall performance: This invention inherits the advantages of the adiabatic evolution principle and realizes high efficiency, ultra-wide bandwidth, simple structure and high process tolerance mode conversion beam splitting, with comprehensive performance. Attached Figure Description

[0020] Figure 1 This is a top view of the device structure used in the embodiments of the present invention;

[0021] Figure 2 This is a diagram showing the evolution of the effective refractive index of the mode in the embodiment of the present invention.

[0022] Figure 3 The following is a simulation diagram of the electric field distribution of the TE1-TE0 mode conversion beam splitting method in the embodiment of the present invention: (a) TE1 mode at the input end, (b) intermediate state of evolution, and (c) two TE0 modes that exist simultaneously in two waveguides and have opposite phases at the output end. Detailed Implementation

[0023] The present invention will be further explained in detail below with reference to the accompanying drawings, so that those skilled in the art can better understand and implement the present invention. However, the following examples are only used to explain the present invention and are not intended to limit the present invention.

[0024] This invention provides a novel mode conversion and beam splitting method and device. Utilizing a high-order intrinsic mode evolution channel in a symmetrical three-waveguide structure, this invention achieves a novel mode conversion and beam splitting function by actively injecting TE1 modes.

[0025] The specific technical solution is as follows: A mode conversion beamsplitter with a three-waveguide structure is provided, and the mode evolution characteristics of this device are as follows: Figure 2 As shown in the figure, there are two independent eigenmode evolution paths (blue solid line and red dashed line); Figure 2 The red dashed line clearly illustrates the higher-order eigenmode evolution path utilized in this invention, which smoothly evolves from the TE1 mode at the input to the TE0 odd-mode supermode at the output. The blue solid line represents the basic-order eigenmode path utilized in the prior art.

[0026] Injecting a TE1 mode optical signal into the center input waveguide selectively excites the corresponding... Figure 2 The red dashed line represents the evolution path of higher-order eigenmodes.

[0027] The optical signal undergoes adiabatic evolution along this higher-order intrinsic mode path. During this process, the intrinsic mode smoothly and continuously evolves from the TE1 mode at the input end to the TE0 odd-mode / supermode at the output end. The continuity and independence of this evolution path ensure low loss and high fidelity in the conversion process.

[0028] At the device output, the TE0 odd-mode supermode at the evolution endpoint has the following physical form: a first TE0 fundamental mode is formed in the first output waveguide, and a second TE0 fundamental mode is formed in the second output waveguide.

[0029] Due to the antisymmetric field distribution characteristics of odd and supermodes, there is a natural phase difference of π between the first TE0 fundamental mode and the second TE0 fundamental mode, and their optical powers are basically equal.

[0030] Therefore, by activating a physical path that is ignored by the prior art, the present invention cleverly converts and splits a TE1 mode input signal into two TE0 fundamental mode output signals with opposite phases and equal power.

[0031] The present invention is applied to a three-waveguide structure including a central input waveguide and first and second side output waveguides symmetrically arranged on both sides thereof. The three-waveguide structure further includes an adiabatic evolution region in which the width of the central input waveguide decreases along the light propagation direction, while the width of the first and second side output waveguides increases.

[0032] This invention provides a TE1-TE0 mode converter implemented on an SOI (Silicon-on-Insulator) platform. The physical structure of this device can be referenced from the structure disclosed in Chinese Patent CN 117111214 B, as follows: Figure 1 As shown. It includes a central input waveguide A, and output waveguides B and C symmetrically distributed on both sides. In a preferred embodiment, the waveguide core is silicon (refractive index n). Si≈3.455), the cladding is silicon dioxide (refractive index ≈3.455), The waveguide width W is 1.2 μm and the thickness is 400 nm. The gap G between the output waveguides B and C is 400 nm. The length L of the adiabatic evolution region of the device is 250 μm.

[0033] Unlike existing technologies, the core working principle, operating method, and final technical effect of this invention are fundamentally different. The specific implementation steps of this invention are as follows:

[0034] Step 1: Pattern Injection.

[0035] A TE1 high-order mode optical signal with a center wavelength of 1550 nm is generated using a mode light source or an upstream mode converter. This signal is then precisely aligned and injected into the center input waveguide A of the device.

[0036] Step 2: Pattern Evolution.

[0037] The optical signal enters an adiabatic evolution region with a length of 250 μm. Within this region, the width of the input waveguide A decreases linearly from 1.2 μm to 0, while the widths of the output waveguides B and C increase linearly from 0 to 1.2 μm.

[0038] The key physical processes occur at this stage. (Refer to...) Figure 2 The injected TE1 mode selects the higher-order eigenmode evolution path of the system (red dashed line). As the optical signal propagates, its effective refractive index n eff The light field distribution follows this preset trajectory in a continuous and smooth adiabatic evolution. This evolution path always maintains a sufficient effective refractive index difference with the fundamental eigenmode path (blue solid line), avoiding crosstalk and energy leakage between modes and ensuring high fidelity of the conversion.

[0039] Step 3: Mode output.

[0040] After passing through the adiabatic evolution region, the optical signal reaches the output of the device. At this point, the higher-order intrinsic modes have completely evolved into the TE0 odd-mode supermode. Figure 3 The simulation diagram shows the electric field distribution of the TE1-TE0 mode conversion beam splitting method of this invention, clearly illustrating (a) the input TE1 mode, (b) the intermediate evolution state, and (c) the output two TE0 modes that coexist in two waveguides and have opposite phases. (Refer to...) Figure 3 The simulation results show that the supermode is physically clearly represented as follows: in the upper output waveguide B, a single-lobe TE0 fundamental mode field with positive phase and clear outline is formed; at the same time, in the lower output waveguide C, another single-lobe TE0 fundamental mode field with negative phase and clear outline is formed.

[0041] The results show that an input TE1 mode signal was successfully converted and uniformly split into two output ports at the same time, and the signals at both output ports are TE0 fundamental modes that are easy to process later, and there is an inherent π phase difference between them.

[0042] Simulation results for this embodiment show that, with a compact device length of 250 μm, the total conversion beam splitting efficiency from the input TE1 mode to the two output TE0 modes can reach up to 91%. Within the wavelength range of 1500 nm to 1600 nm, the overall device efficiency remains above 88%, demonstrating a wide operating bandwidth exceeding 100 nm.

[0043] The specific implementation schemes described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific implementation schemes of the present invention and are not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A TE1-TE0 mode conversion beam splitting method, characterized in that, Includes the following steps: S1. Inject TE1 mode optical signal from the input end of the center input waveguide; S2, The injected TE1 mode optical signal selectively excites a higher-order eigenmode in the three-waveguide structure; S3. The higher-order intrinsic modes undergo adiabatic evolution within the adiabatic evolution region and output the first TEO mode optical signal in the first output waveguide at the output end, while simultaneously outputting the second TEO mode optical signal in the second output waveguide.

2. The TE1-TE0 mode conversion beam splitting method according to claim 1, characterized in that, There is a phase difference of π between the first TEO mode optical signal and the second TEO mode optical signal.

3. The TE1-TE0 mode conversion beam splitting method according to claim 2, characterized in that, The optical power of the first TEO mode optical signal is equal to that of the second TEO mode optical signal.

4. The TE1-TE0 mode conversion beam splitting method according to claim 3, characterized in that, The effective refractive index evolution path of the higher-order eigenmodes shows that the effective refractive index value is greater than that of the basic eigenmodes of the three-waveguide structure.

5. The TE1-TE0 mode conversion beam splitting method according to claim 4, characterized in that, In S3, the higher-order eigenmode evolves into a TE0 odd-mode supermode at the output end. This TE0 odd-mode supermode is manifested as two TE0 modes with a π phase difference in the first and second output waveguides.

6. A mode conversion beam splitter based on the TE1-TE0 mode conversion beam splitting method according to any one of claims 1-5, characterized in that, It includes a central input waveguide; first and second side output waveguides symmetrically arranged on both sides of the central input waveguide; and an adiabatic evolution region connecting the central input waveguide and the side output waveguides, wherein the width of the central input waveguide decreases along the light propagation direction, while the width of the first and second side output waveguides increases.

7. The mode conversion beam splitter according to claim 6, characterized in that, The structural parameters of the mode conversion beam splitter are configured such that when the TE1 mode is injected by the center input waveguide, the TE1 mode undergoes adiabatic evolution along a higher-order eigenmode path of the mode conversion beam splitter within the adiabatic evolution region, and at the output end, a first TE0 mode is output in the first side output waveguide, and a second TE0 mode is output in the second side output waveguide.

8. The mode conversion beam splitter according to claim 7, characterized in that, The structural parameters of the mode conversion beam splitter are configured such that the effective refractive index of the higher-order intrinsic mode path is greater than the effective refractive index of the basic-order intrinsic mode path of the mode conversion beam splitter throughout the entire adiabatic evolution region.

9. The mode conversion beam splitter according to claim 8, characterized in that, The mode conversion beam splitter is used to achieve mode conversion beam splitting from TE1 to two TE0 modes with an efficiency greater than 90% at the center operating wavelength of 1550nm and an operating bandwidth greater than 100nm.

Images