Adjustable and controllable optical power beam splitter

Abstract

The utility model belongs to the technical field of optoelectronic integrated circuits, and particularly relates to an adjustable optical power beam splitter, which comprises an input waveguide, a multimode coupling area and an output waveguide which are sequentially connected, the multimode coupling area is made of phase change materials, and a notch is arranged on the multimode coupling area. And meanwhile, the loss is relatively low and the manufacturing tolerance is good.

Description

Technical Field

[0001] The utility model belongs to the technical field of optoelectronic integrated circuits, and in particular relates to an adjustable optical power beam splitter. Background Art

[0002] Photonic integrated circuits (PICs) are an emerging technology that integrates photonics and electronics on the same chip. Their high integration and small size make them ideal for processing large-capacity data transmission and have attracted much attention in recent years. In PICs, power beam splitters are one of the core basic components, and their main function is to effectively split the incident optical signal into two or more output channels to achieve accurate distribution of optical power. Power beam splitters play an important role in optical communications, optical network connections, and sensing applications. Currently, the types of power beam splitters widely used on-chip include Y branches, beam splitters based on directional coupling (DC), and beam splitters based on multimode interference (MMI) coupling. Among them, beam splitters based on multimode interference (MMI) are favored in optical communications and integrated optical systems due to their broadband performance, compact size, low loss, simple manufacturing, high reliability, and flexibility.

[0003] However, in many practical application scenarios, such as dynamic adjustment of optical signal power distribution in optical fiber communication, dynamic adjustment of laser beam in laser system, precise adjustment of beam intensity in optical measurement system, and optimization of sensor sensitivity and response speed in optical sensor, adjustable optical power beam splitter plays a vital role, thus triggering extensive research interest. At present, many methods have emerged for beam splitters based on MMI structure, which can realize precise control of arbitrary splitting ratio. Based on traditional forward design methods, for example, Qingzhong Deng et al. broke the symmetry of MMI multimode interference structure by changing the geometric structure of the device, and realized a 1×2 power beam splitter with adjustable power splitting ratio; Yanmei Lin et al. used asymmetric MMI structure and designed it on thin-film lithium niobate platform, and successfully realized arbitrary power distribution of 1×2 power beam splitter, and verified the consistency of simulation results with experimental results through experiments. In addition, based on the inverse design method, Huan Yuan et al. used the DBS algorithm to design a programmable ultra-compact arbitrary power divider based on the non-volatile optical phase change material GSST; Mohammad H. Tahersima et al. used a deep learning algorithm to reversely design an MMI power divider with different splitting ratios; Ke Xu et al. used a nonlinear fast search method to design an ultra-compact power beam splitter with a two-dimensional code-like nanostructure to achieve arbitrary power splitting ratio regulation. However, in the current research progress of beam splitters, traditional forward design methods have some limitations. These methods require manual adjustment of parameters, resulting in the beam splitting ratio being fixed once the device size is determined. In addition, the size of the forward-designed device is usually large, ranging from tens of microns to hundreds of microns. This limits the flexibility and applicability of these devices in micro-nanoscale applications. Current inverse design methods can usually achieve compact device structures when designing beam splitters. However, the structures obtained by inverse design often present complex geometries and microstructures, which may make experimental verification more difficult. The regulation of tiny structures may also face greater challenges, and the calculation and optimization processes will become more complicated, which will affect the feasibility and reliability in practical applications. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide an adjustable optical power beam splitter, which can be flexibly adjusted, has a small size, a large bandwidth, and at the same time has low loss and good manufacturing tolerance.

[0005] The utility model provides an adjustable optical power beam splitter, comprising an input waveguide, a multimode coupling region and an output waveguide connected in sequence, wherein the material of the multimode coupling region is a phase change material, and a notch is arranged on the multimode coupling region.

[0006] In one embodiment, the phase change material may be a chalcogenide phase change material, such as Ge 2 Sb 2 Te 5 and Sb 2 Se 3 , or other phase change materials, the utility model preferably uses indium selenide.

[0007] In one embodiment, the multimode coupling region is rectangular.

[0008] In one embodiment, when the input waveguide is located at the center of the multimode coupling region, the length of the rectangle meets the following requirements, that is, , L N is the length of the rectangle, N is the number of output waveguides, is the beat length of the lowest-order mode.

[0009] In one embodiment, the notch is rectangular.

[0010] In one embodiment, the notch is located at a corner of the multimode coupling region close to the input waveguide.

[0011] In one embodiment, the length of the gap is 1 / 4-1 / 2 of the length of the multimode coupling region.

[0012] In one embodiment, the input waveguide and / or the output waveguide are both tapered, and the tapered shape is along the transmission direction of light, and has a non-uniform width.

[0013] In one embodiment, the width of the taper gradually decreases in a direction away from the multimode coupling region.

[0014] In one embodiment, the input waveguide is located at the center of the multimode coupling region.

[0015] In one embodiment, the present invention further comprises a silicon core layer and a silicon-on-insulator platform with a buried silicon dioxide layer. The input waveguide, the multimode coupling region and the output waveguide connected in sequence are located on the silicon-on-insulator platform with the buried silicon dioxide layer.

[0016] The beneficial effects of the utility model are: It is an emerging sulfur-based phase change material. Compared with traditional phase change materials, It is polymorphic and has multiple crystal phases, including five crystal states: α, β, γ, δ and κ. This utility model only uses the α and β states. The α and β states of the α-state are both crystalline, and the two states can be reversibly converted under thermal actuation. The α-state and β-state have similar topological structures, which also makes the energy required for the conversion of the two states smaller, which is similar to GST and Sb 2 Se 3 Compared with other chalcogenide materials, In addition to its crystal polymorphism and compatibility with various phase transition control methods, is back-end CMOS compatible, so for integrated photonic devices it can be used with Si and Integration avoids the technical challenges limited by changes in lattice constant and thermal expansion coefficient. In addition, in theory The material has no loss in the C band in these two states, and devices designed with it can reduce the loss caused by the material itself. Indium selenide also has the advantages of other sulfur materials such as high refractive index contrast, reversible phase change, and fast response.

[0017] The utility model proposes an ultra-compact low-loss 1×2 power beam splitter with adjustable arbitrary PSR based on indium selenide on a SOI platform, and the size of the device is only 4.27μm×2.4μm. The material used in the entire asymmetric multimode interference region of the proposed device is indium selenide, and the arbitrary splitting ratio can be continuously adjusted by adjusting the reversible phase transition of indium selenide from the α state to the β state. Theoretically, within the range of 1530nm-1560nm, the PSR range of the device can include 50:50 to 99:33. Through finite difference time domain (FDTD) simulation, the insertion loss (IL) of the device is less than 0.6dB at a wavelength of 1550nm. In addition, the power beam splitter has good manufacturing tolerance and is compatible with the COMS photonic device manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A symmetrical 1×2 MMI power splitter and normalized light field distribution diagram, where (a) is a symmetrical 1×2 MMI power splitter, and (d) is the normalized light field distribution diagram of (a) at 1550nm.

[0019] Figure 2 An asymmetric 1×2 MMI power splitter based on a rectangle and a normalized light field distribution diagram, where (b) is an asymmetric 1×2 MMI power splitter based on a rectangle, and (e) is the normalized light field distribution diagram of (b) at 1550nm.

[0020] Figure 3 The optimized asymmetric rectangular 1×2 MMI power splitter and the normalized light field distribution diagram, where (c) is the optimized asymmetric rectangular 1×2 MMI power splitter, and (f) is the normalized light field distribution diagram of (c) at 1550nm.

[0021] Figure 4 Based on A controllable asymmetric 1×2 MMI power splitter, wherein 1 is an input waveguide, 2 is an output waveguide I, 3 is an output waveguide II3, 4 is a multimode coupling region, and 5 is a gap.

[0022] Figure 5 When Lr = 1.83 μm, (a)-(c) are Light field distribution at 1550nm in the α state, intermediate state, and β state; (d)-(f) The transmission spectra of the upper and lower output channel ports of the corresponding structure in the three states; (g)-(i) The IL of the upper and lower output channel ports of the corresponding structure in the three states.

[0023] Figure 6 In the case of Lr=1.42μm, When controlled to the α state, (a) the light field distribution at 1550 nm; (b) the IL of the upper and lower output channel ports of the corresponding structure in the wavelength range of 1530-1560 nm; (c) the simulated power 1:1 splitting ratio of the upper and lower channels in the wavelength range of 1530-1560 nm.

[0024] Figure 7 (a)-(b) are at a wavelength of 1550nm. The relationship between the splitting ratio of the upper and lower output ports and the removal rectangle length (Lr) under different states of phase change; (c) The relationship between the removal rectangle length (Lr) and the insertion loss (IL) at a wavelength of 1550nm.

[0025] Figure 8 The influence of different manufacturing errors on the power beam splitter. (a) In the α state, the thickness error is within the range of ±5nm and ±10nm; (b) In the intermediate state, the thickness error is within the balance error range of ±5nm and ±10nm; (c) In the β state, the thickness error is within the range of ±5nm and ±10nm; (d) IL whose thickness error is within the range of ±5nm and ±10nm in the α state; (e) IL with thickness error within the range of ±5nm and ±10nm in the intermediate state; (f) In the β state, the IL has a thickness error within the range of ±5nm and ±10nm. DETAILED DESCRIPTION

[0026] Example 1

[0027] Common symmetric 1×2 MMI power splitters such as Figure 1As shown in (a), polarized light passes through a single-mode input waveguide and is transmitted to the MMI multimode coupling region, which excites the high-order mode to produce a self-image effect. A single-mode output waveguide is placed at the double image point to obtain two equally divided beams of light.

[0028] On this basis, by cutting the lower left rectangular area, we can get an asymmetric 1×2 MMI power splitter as shown in Figure 2 (b), which breaks the symmetry of the MMI multimode region and leads to a drastic redistribution of the electric field as shown in Figure 2 As shown in (e), unequal power splitting ratios can be obtained.

[0029] Figure 3 (c) is the optimized asymmetric rectangular 1×2 MMI power splitter, which is Figure 2 The significant difference between (b) and (c) is the shape of the input and output waveguides. Figure 2 (e) and Figure 3 (f) are their electric field diagrams, respectively. It can be seen that compared with the traditional straight waveguide input, the connection between the tapered waveguide input port and the waveguide structure is smoother, so it can significantly reduce the waveguide connection loss, improve the energy transmission efficiency, and improve the waveguide docking performance, reduce the loss that may be caused by incomplete docking, and reduce the occurrence of uneven power distribution.

[0030] Example 2

[0031] Combination The schematic diagram of the designed adjustable power beam splitter is shown in Figure 4 As shown, the following devices only support mode. The device is on a silicon-on-insulator platform (SOI) with a 220 nm thick silicon core layer and a 3 µm thick buried silicon dioxide layer. The device consists of three parts: input single-mode waveguide (i.e. input waveguide 1), asymmetric multimode coupling region (i.e. multimode coupling region 4), and output single-mode waveguide (i.e. output waveguide I2, output waveguide II3). The multimode coupling region is a phase change material with a thickness of h1=220nm. , an asymmetric structure obtained by cutting the rectangular area in the lower left corner, the length and width of the cut rectangle are and , the size of the asymmetric multimode coupling region is L=4.27μm, W=2.4μm. The input and output single-mode waveguides are both tapered waveguides of the same size, and the width changes from 0.5µm to 0.8µm to support only single-mode transmission. Here, this application represents the optical power output by Output1 (output waveguide I2) and Output2 (output waveguide II3) as P1 and P2, respectively, and defines: PSR=P1:P2.

[0032] According to the self-image principle of MMI, the incident fundamental mode entering through the access waveguide will excite many higher-order modes in the MMI region to satisfy the continuity of the input field. Through the quadratic relation given by (1), the propagation constants of these excited state modes approximately follow:

[0033] (1)

[0034] in, is the propagation constant of the fundamental mode in the MMI waveguide, is the modulus, is the beat length of the two lowest-order modes. When the input waveguide is located at the center of the MMI, the length of the multimode interference region must meet the following conditions, and the input TE0 mode will have N-fold imaging:

[0035] (2)

[0036] This application is a 1×2 MMI beam splitter, so N is 2.

[0037] The traditional asymmetric 1×2 MMI beam splitter obtains different splitting ratios by optimizing the size, length and width of the cutting rectangle. However, when the length of the cutting rectangle is changed, according to the MMI self-image principle, the length of the multimode interference region of the device also needs to be changed accordingly. That is, the traditional asymmetric MMI beam splitter design needs to be optimized at the same time. , and L to obtain any desired OPS of PSR, which will increase the footprint of the device and fix the power splitting ratio, and it is impossible to obtain different power splitting ratios without changing the size of the device structure. The device designed in this application optimizes the length of Lr and then adjusts the multimode interference area The reversible phase transition between the α state and the β state can be continuously controlled to obtain different target splitting ratios.

[0038] Example 3

[0039] Simulation and numerical analysis

[0040] Device control designed in this application In the process of phase change, there will be The intermediate state of the α state and the β state. This intermediate state with different proportions of the α state and the β state has different refractive indices. By externally regulating the mixing ratio of the intermediate states of the α state and the β state, continuous regulation can be achieved in the device to obtain different beam splitting ratios. The relationship between the intermediate state proportion of the α state and the β state and its dielectric constant is as follows:

[0041] (3)

[0042] in is the effective dielectric constant of the mixed state of the phase change material. and are the dielectric constants of the crystalline and amorphous states, respectively. The constant m represents the doping coefficient of the crystalline and amorphous states, which ranges from 0 to 1. This formula can be used to calculate The effective dielectric constant of the mixed state of α and β states.

[0043] In order to verify the feasibility of the method, this application first optimizes the length of Lr and takes Lr=1.83μm, demonstrating the reversible phase transition of the α state and β state of indium selenide to obtain different splitting ratios. Figure 5 The three splitting ratios (1.8:1, 1.5:1, 1.25:1) obtained for InSe in the α, intermediate and β states are shown. Figure 5 The simulation results show that the proposed controllable beam splitter has a good effect and can be changed by using electric pulses. The optical properties of the device will not be changed.

[0044] During the regulation process, the present application can obtain the device in Three different splitting ratios are obtained in the α state, intermediate state (50% α / β state), and β state respectively. Figure 5 (a)-(c) are the light field distribution at 1550nm, and the corresponding transmission spectra are shown in Figure 5 As shown in (d)-(f). Figure 5 (d) A splitting ratio of 1.8:1 was achieved in the α state. Figure 5 (e) A splitting ratio of 1.5:1 was achieved in the intermediate state (50% α / β state). Figure 5 (f) A splitting ratio of 1.25:1 was achieved in the α state. Figure 5 (g)-(i) is The IL corresponding to the three splitting ratios is realized in three states. It can be seen that when the splitting ratio is 1.8:1 at a wavelength of 1530nm-1560nm, the IL is less than 0.8dB, when the splitting ratio is adjusted to 1.5:1, the IL is less than 0.24dB, and when the splitting ratio is adjusted to 1.25:1, the IL is less than 0.4dB. It can be seen that the wavelength dependence of the insertion loss of the device is small.

[0045] In practical applications, power beam splitters are widely used to achieve 1:1 beam splitting. To achieve 1:1 beam splitting, this application can first optimize the value of Lr, taking Lr=1.42μm, The results obtained by adjusting to the α state are as follows Figure 6 shown. Figure 6 (a) When Lr=1.42μm, The normalized electric field distribution diagram of the structure at a wavelength of 1550nm when it is controlled to the α state. Figure 6 (b) is the IL of the upper and lower output ports in the wavelength range of 1530nm-1560nm. It can be seen that its insertion loss does not exceed 0.23dB, and the device performance is good. Figure 6 (c) shows the splitting ratio of the two output channels. It can be seen that the simulation results are consistent with the expected design and the device design effect is good.

[0046] By adjusting the value of Lr, combined with The power splitter PSR can be adjusted continuously. Under this condition, the performance of the power splitter. Figure 7 The simulation results show that with the increase of Lr value, PSR is also gradually increasing, and the device's beam splitting ratio control range is larger. Figure 7 (a) shows the In this state, the device PSR changes with the change of Lr. Figure 7 (b) shows different In this state, with the change of Lr, the change of device 1 / PSR, it can be seen that the device of the present application can also be adjusted to obtain various splitting ratios of Output2 / Output1. During this change process, the IL of the device still changes in a small value range, the minimum loss can reach 0.2dB, and the maximum insertion loss does not exceed 1.6dB, and the simulation effect is good.

[0047] The device designed in this application occupies a very small space (4.27μm×2.4μm). Compared with the conventional forward-designed MMI power splitter, the device of this application is smaller in size. In addition, most conventional forward-designed devices are not non-volatile, and the designed device has a fixed power splitting ratio, which cannot dynamically adjust the target power splitting ratio. However, the device of this application can be used The state of the material can be reversibly converted to achieve continuous regulation of the splitting ratio, and it is non-volatile. Compared with the reverse-designed device, the size is not much different, and The imaginary part of this material in the C band is almost zero, and compared with other power splitters designed with GST and GSST materials, it has lower loss (less than 0.6dB).

[0048] Example 4

[0049] Manufacturing Tolerance Analysis

[0050] In the device manufacturing process, manufacturing defects are inevitable, and the manufacturing of devices requires good manufacturing tolerances, so the manufacturing tolerance of OPS will also be analyzed. Here, this application changes the etching depth (H) of PCM to perform a numerical analysis of the device manufacturing tolerance. The device of this application has an etching depth of 220nm. In order to study the manufacturing tolerance of the power splitter, this application takes the device structure when Lr=1.83μm as an example to simulate the impact of different PCM etching depths on device performance. Here, in order to describe the power splitting ratio of the upper and lower output ports of the device, this application sets a port balance error, which is defined as:

[0051] (4)

[0052] Where a is the target splitting ratio, and the a used below is the PSR when H=0nm. It can be used to approximate the deviation between the simulated value and the target value obtained by the device. The smaller the balance error Error, the smaller the deviation, and the designed device is more in line with the target expectation. Figure 8 (a)-(c) respectively describe Balance error analysis of etching depth in the range of ±5nm and ±10nm in the α state, intermediate state and β state. It can be seen that in the wavelength range of 1530nm-1560nm, In the process of phase change regulation of different splitting ratios, The etching depth varies within the range of -10nm to +10nm, and the balance error is within 0.1. The balance error is very small, indicating that the device has good robustness. Figure 8 (d)-(f) respectively describe Insertion loss analysis of the etching depth in the range of ±5nm and ±10nm in the α state, intermediate state and β state. It can be seen that in the wavelength range of 1530nm-1560nm, The etching depth varies from -10nm to +10nm, and the insertion loss is less than 1dB, indicating Thickness disturbance has little effect on device transmission loss and has good processing tolerance.

[0053] This application proposes a The asymmetric rectangular 1×2MMI ultra-compact power splitter is designed and numerically analyzed. The reversible phase transition between the α and β states can theoretically realize a power splitter with any desired PSR that can be continuously adjusted within the bandwidth range of 1530nm-1560nm, with a simple and compact structure. Simulation results show that the power splitter has low insertion loss, with an IL below 0.6dB at a wavelength of 1550nm, weak sensitivity to wavelength and manufacturing defects, and good manufacturing tolerance. This work provides a method for designing adjustable multifunctional photonic components that can achieve target functions with simple and compact structures.

[0054] A person skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the concept of the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0055] One or more embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the present application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of the present application should be included in the protection scope of the present application.

Claims

1. An adjustable optical power beam splitter, characterized in that: The invention comprises an input waveguide, a multimode coupling region and an output waveguide which are connected in sequence. The material of the multimode coupling region is a phase change material and a notch is arranged on the multimode coupling region.

2. The adjustable optical power beam splitter according to claim 1, characterized in that: The phase change material is indium selenide.

3. The adjustable optical power beam splitter according to claim 1 or 2, characterized in that: The multimode coupling region is rectangular.

4. The adjustable optical power beam splitter according to claim 3, characterized in that: When the input waveguide is located at the center of the multimode coupling region, the length of the rectangle meets the following requirements, namely , L N is the length of the rectangle, N is the number of output waveguides, is the beat length of the lowest-order mode.

5. The adjustable optical power beam splitter according to claim 3, characterized in that: The notch is rectangular.

6. The adjustable optical power beam splitter according to claim 5, characterized in that: The notch is located at a corner of the multimode coupling region close to the input waveguide.

7. The adjustable optical power beam splitter according to claim 5 or 6, characterized in that: The length of the gap is 1 / 4-1 / 2 of the length of the multimode coupling region.

8. The adjustable optical power beam splitter according to claim 1 or 2, characterized in that: The input waveguide and / or the output waveguide are both tapered.

9. The adjustable optical power beam splitter according to claim 8, characterized in that: The width of the taper gradually decreases in a direction away from the multi-mode coupling region.

10. The adjustable optical power beam splitter according to claim 1, characterized in that: The input waveguide is located at the center of the multimode coupling region.

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