Optical splitter with adjustable splitting ratio and non-volatile state

Abstract

This invention discloses an optical splitter with adjustable splitting ratio and non-volatile state. The optical splitter includes a first multimode interference coupler and a second multimode interference coupler. The two output ports of the first multimode interference coupler are connected to the two input ports of the second multimode interference coupler via a waveguide component. The waveguide component consists of two curved waveguides and a phase-change straight waveguide connected between the two curved waveguides. One waveguide component's phase-change straight waveguide is entirely covered with a layer of phase change material, while the other waveguide component's phase-change straight waveguide is covered with multiple segments of phase change material whose crystallization state can be independently adjusted. The splitting ratio of the optical splitter is achieved by adjusting the length of the crystallized phase change material on the other waveguide component, thereby changing the phase of the transmitted light. The optical splitter provided by this invention features adjustable splitting ratio, low loss, and non-volatility.

Description

Technical Field

[0001] This invention belongs to the field of silicon-based optoelectronics technology, and more specifically, relates to an optical splitter with adjustable splitting ratio and non-volatile state. Background Technology

[0002] With the development of modern technology, sending and receiving information has become more convenient and faster. With the advent of the 5G era, new terms such as artificial intelligence, big data, and cloud computing are constantly emerging, which places higher demands on data storage and processing. In the era of big data, more than 80% of the world's data has been generated in recent years. Following this trend, future data communication volumes will pose a huge challenge to modern information transmission systems. The emergence of optical communication technology provides a solution for high-speed, high-volume data transmission. Space division multiplexing (SDM), represented by mode division multiplexing, can significantly improve the capacity of communication systems and effectively enhance system performance. An optical splitter, also known as a passive device, is used to split and combine optical energy. In optical network topologies, optical splitters help users maximize network performance.

[0003] Optical splitters can be classified into two types based on their splitting principle: fused biconical taper (FBT) and planar waveguide (BBT) type. Planar waveguide optical splitters generally use photolithography to form optical waveguides on a dielectric or semiconductor substrate to achieve branching and distribution functions. Their loss is insensitive to the wavelength of light, allowing them to meet the transmission needs of different wavelengths. FBT optical splitters are formed by side-fusing two or more optical fibers, enabling arbitrary light distribution ratios. However, the splitting ratio of optical splitters manufactured using these methods is not adjustable; to change the splitting ratio, the optical splitter must be remade. Therefore, it is necessary to research an optical splitter with an adjustable splitting ratio. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an optical splitter with adjustable splitting ratio and non-volatile state, which can effectively solve the problems of difficult splitting ratio adjustment and high loss in traditional optical splitters.

[0005] To achieve the above objectives, in a first aspect, the present invention provides an optical splitter with adjustable splitting ratio and non-volatile state, comprising a first multimode interference coupler and a second multimode interference coupler, wherein the number of output ports of the first multimode interference coupler and the number of input ports of the second multimode interference coupler are both 2, and the two output ports of the first multimode interference coupler are respectively connected to the two input ports of the second multimode interference coupler through a waveguide component.

[0006] The first multimode interference coupler is used to uniformly split the input light into two beams for transmission. The waveguide component consists of two curved waveguides and a phase-modulated straight waveguide connected between the two curved waveguides. The phase-modulated straight waveguide in one waveguide component is entirely covered with a layer of phase change material, while the phase-modulated straight waveguide in the other waveguide component is covered with multiple segments of phase change material whose crystallization state can be independently adjusted. The splitting ratio of the optical splitter is achieved by adjusting the length of the crystallized phase change material on the phase-modulated straight waveguide in the other waveguide component, thereby changing the phase of the transmitted light. The second multimode interference coupler is used to couple the two phase-modulated transmitted beams into a single output beam.

[0007] In one embodiment, the phase change material is Sb2Se3 or Ge2Sb2Te5.

[0008] In one embodiment, the phase change material covering the two phase-tuned straight waveguides has a thickness of 5 nm to 30 nm.

[0009] In one embodiment, the phase change material segments on the phase-tuned straight waveguide in the other waveguide component are of equal length or are arranged in a linearly increasing manner.

[0010] In one embodiment, the first multimode interference coupler is a 1×2 multimode interference coupler, and the second multimode interference coupler is a 2×2 multimode interference coupler.

[0011] Secondly, the present invention provides a method for fabricating an optical splitter with adjustable splitting ratio and non-volatile state as described above, comprising the following steps:

[0012] (1) A silicon dioxide lower cladding layer is deposited on the substrate, and a silicon nitride thin film is deposited on the upper surface of the silicon dioxide lower cladding layer; then photoresist is spin-coated on the silicon nitride thin film, and the device pattern is obtained by electron beam lithography (EBL) equipment. The exposed chip is then immersed in the corresponding developing solution to make the waveguide pattern visible; then the developed pattern is transferred to the wafer by dry etching to obtain a waveguide structure composed of two multimode interference couplers and two waveguide components.

[0013] (2) Photoresist is spin-coated on the waveguide structure, and then electron beam exposure is performed above the two phase-tuning straight waveguides of the optical splitter; then the device is placed in the developing solution for development, and then a phase change material film is coated on the surface of the device using a magnetron sputtering coating machine; finally, after the photoresist removal and peeling process, an optical splitter with phase change material covering the phase-tuning straight waveguide is obtained.

[0014] (3) Cover the structure obtained in step (2) with a silicon dioxide film, then spin-coat photoresist on the silicon dioxide film, and perform electron beam exposure on the corresponding position above the phase-tuning straight waveguide in another waveguide component; then place the device in the developing solution for development, and then use a magnetron sputtering coating machine to cover the surface of the device with heating electrode material; finally, after the photoresist removal and peeling process, the optical splitter with integrated electrode material is obtained.

[0015] (4) Cover the structure obtained in step (3) with a silicon dioxide cladding to obtain a complete optical splitter with adjustable splitting ratio and non-volatile state based on phase change material.

[0016] In one embodiment, the thickness of the lower and upper silicon dioxide cladding layers is 2 μm to 3 μm.

[0017] In one embodiment, the distance between the heating electrode on the other waveguide component and the upper surface of the phase-tuned straight waveguide below it is greater than 1 μm.

[0018] In one embodiment, the heating electrode material is platinum or tungsten.

[0019] In one embodiment, in step (3), the thickness of the covering heating electrode material is 200-300 nm.

[0020] The optical splitter with adjustable splitting ratio and non-volatile state provided by this invention covers the upper and lower waveguide components with phase change material and uses a segmented phase change method to change the phase of the transmitted light, which can effectively realize the adjustment of the splitter. In addition, the optical splitter achieves splitting ratio adjustment based on the phase change of the phase change material. Since the phase change material can switch rapidly and multiple times between crystalline and amorphous states, and the phase change is non-volatile, it will maintain the current state until the next stimulus arrives. It does not consume energy in steady state, so the optical splitter provided in this embodiment has the characteristics of non-volatility and low loss.

[0021] The method for fabricating an optical splitter with adjustable splitting ratio and non-volatile state provided by the present invention uses silicon dioxide as a substrate and upper cladding, fabricates a silicon nitride waveguide on the substrate, and covers part of the waveguide with a phase change material, which can change the effective refractive index of the waveguide to achieve the purpose of adjusting the splitting ratio. In addition, the fabrication process used in the present invention is simple, compatible with traditional CMOS processes, easy to integrate, and suitable for large-scale production, which is of great significance to the development of silicon photonic integrated circuits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of an optical splitter with adjustable splitting ratio and non-volatile state provided in an embodiment of the present invention;

[0023] Figure 2This is a schematic diagram of the structure of a multimode interference coupler A provided in a specific embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the structure of a multimode interference coupler B provided in a specific embodiment of the present invention;

[0025] Figure 4 This is a specific embodiment of the invention that shows the power of the two output ports T1 and T2 of the optical splitter as a function of the length of the lower arm crystalline phase change material covering the splitter.

[0026] Figure 5 The images show the spectroscopic characteristics (left) and loss (right) of the crystalline phase change material with a length of 5 μm provided by this invention.

[0027] Figure 6 The images show the spectral characteristics (left) and loss (right) of the crystalline phase change material with a length of 15 μm provided by this invention.

[0028] Figure 7 The images show the spectral characteristics (left) and loss (right) of the crystalline phase change material with a length of 25 μm provided by this invention.

[0029] Figure 8 The images show the spectral characteristics (left) and loss (right) of the crystalline phase change material with a length of 40 μm provided by this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the 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 merely illustrative and not intended to limit the invention.

[0031] To address the problems of difficult-to-adjust splitting ratio and high loss in traditional optical splitters, this invention provides an optical splitter with adjustable splitting ratio and non-volatile state, such as... Figure 1 As shown, the optical splitter includes two multimode interference couplers, namely multimode interference coupler A and multimode interference coupler B. The number of output ports of multimode interference coupler A and the number of input ports of multimode interference coupler B are both set to 2. The two output ports of multimode interference coupler A and the two input ports of multimode interference coupler B are connected through a waveguide structure.

[0032] Among them, the multimode interference coupler A is used to uniformly split the input light into two beams for transmission.

[0033] The waveguide structure consists of an upper waveguide component and a lower waveguide component. One output port of multimode interference coupler A is connected to one input port of multimode interference coupler B through the upper waveguide component, and the other output port of multimode interference coupler A is connected to the other input port of multimode interference coupler B through the lower waveguide component. Each waveguide component consists of two curved waveguides 12 and a phase-modulated straight waveguide 14 connected and disposed between the two curved waveguides 12. The phase-modulated straight waveguide in the upper waveguide component is entirely covered with a layer of phase change material, and the phase-modulated straight waveguide in the lower waveguide component is covered with multiple segments of phase change material whose crystallization state can be independently adjusted.

[0034] This embodiment combines phase change materials with optical waveguides, specifically by covering two waveguide components with phase change materials. When the phase change material covering the waveguide components changes state under control—that is, from crystalline to amorphous or from amorphous to crystalline—the effective refractive index of the optical waveguide combined with the phase change material changes due to the significant differences in its electrical and optical properties between the crystalline and amorphous states. This causes a change in the phase of the transmitted light. The relationship between this phase change and the change in effective refractive index is as follows:

[0035]

[0036] In the formula, Δn is the phase change; λ is the wavelength of light propagating in the optical waveguide; eff The change in effective refractive index is represented by L; L is the length of the crystallized phase change material in the lower arm waveguide component.

[0037] Phase change The relationship with the spectrophotometer ratio K is as follows:

[0038]

[0039] In the formula, T T1 The transmittance of port T1 of the optical splitter. T T2 The transmittance of port T2 of the optical splitter.

[0040] As shown in the above formula, when the phase change material in the upper waveguide component is amorphous and each segment of the phase change material in the lower waveguide component is crystalline, the phase difference between the two transmitted lights is π; when both the phase change materials in the upper and lower waveguide components are amorphous, the phase difference between the two transmitted lights is 0. Therefore, in this embodiment, the state of the phase change material in the upper waveguide component can be fixed as amorphous, and by adjusting the state of the phase change material in the lower waveguide component segment by segment, the effective refractive index can be changed, thereby allowing the phase difference of the light to vary between 0 and π, ultimately achieving the adjustment of the splitting ratio of the optical splitter.

[0041] Preferably, the lengths of each segment of phase change material in the lower arm waveguide component provided in this embodiment can be set to be equal or increase in a linear proportion. This facilitates the calculation of the required length of the crystallized phase change material in the lower arm waveguide component based on the length of each segment of phase change material according to the required splitting ratio. This allows for the determination of the segment number of the phase change material in the lower arm waveguide component that needs to be phase-change regulated, thereby enabling rapid and effective adjustment of the splitting ratio of the optical splitter.

[0042] The multimode interference coupler B is used to couple two phase-modulated transmission beams into a single output beam.

[0043] The optical splitter with adjustable splitting ratio and non-volatile state provided in this embodiment covers the upper and lower waveguide components with phase change material and uses a segmented phase change method to change the phase of the transmitted light, which can effectively realize the adjustment of the splitter. In addition, the optical splitter achieves splitting ratio adjustment based on the phase change of the phase change material. Since the phase change material can switch rapidly and multiple times between crystalline and amorphous states, and the phase change is non-volatile, it will maintain the current state until the next stimulus arrives. It does not consume energy in steady state, which makes the optical splitter provided in this embodiment non-volatile and low loss.

[0044] The optical splitter provided by the present invention will be described in detail below with reference to specific embodiments:

[0045] like Figure 1 As shown, this invention provides a state-nonvolatile optical splitter with adjustable splitting ratio. Its basic structure consists of two multimode interference couplers, four curved waveguides, and two phase-tuned straight waveguides, both of which are covered with phase-change material. The entire device, from left to right, consists of: a 1×2 multimode interference coupler, two curved waveguides, two phase-tuned straight waveguides, two curved waveguides, and a 2×2 multimode interference coupler.

[0046] The structure of a 1×2 multimode interference coupler is as follows: Figure 2 As shown, from left to right, the components are the input straight waveguide, the input tapered waveguide, the multimode interference region, the two output tapered waveguides, and the two output straight waveguides. The input straight waveguide here is the input port of the optical splitter, and the 1×2 multimode interference coupler serves to uniformly split the input light into two beams.

[0047] The structure of a 2×2 multimode interference coupler is as follows: Figure 3 As shown, from left to right, there are two input straight waveguides, two input tapered waveguides, a multimode interference region, two output tapered waveguides, and two output straight waveguides. The two output straight waveguides serve as the two output ports T1 and T2 of the optical splitter.

[0048] The upper and lower modulation arms of the optical switch are covered with phase change materials Ge2Sb2Te5 or Sb2Se3, respectively. The phase change material in the upper arm is in an amorphous state, while the phase change material in the lower arm is set in multiple segments, each of which can be switched between crystalline and amorphous states independently.

[0049] When the phase change material being covered is Sb₂Se₃ and the thickness of the cover is 10 nm, by Figure 4 It can be seen that when the length of the lower arm crystallized phase change material is 0, light is emitted almost uniformly from the two output ports T1 and T2. When the length of the lower arm crystallized phase change material is approximately 26 μm, light is emitted almost entirely from output port T1, and the phase difference between the upper and lower arms is π / 2. When the length of the lower arm crystallized phase change material is approximately 56 μm, light is emitted almost entirely from output port T2, and the phase difference between the upper and lower arms is π. Therefore, by adjusting the state of the lower arm phase change material in segments, a 1×2 optical splitter with arbitrary splitting ratio can be realized.

[0050] In addition, the present invention also provides a method for fabricating the above-mentioned non-volatile waveguide-type optical splitter with adjustable splitting ratio, comprising the following steps:

[0051] (1) Fabrication of waveguide structure

[0052] A 2-3 μm thick silicon dioxide layer is deposited on a silicon substrate by PECVD. Then, an 800 nm thick silicon nitride film is deposited on the silicon dioxide as a lower cladding layer. Next, photoresist is spin-coated on the silicon nitride film, and the device pattern is obtained by exposure using electron beam lithography (EBL). The exposed chip is then immersed in the corresponding developer to reveal the waveguide pattern. After EBL and development, the developed pattern is transferred to a wafer by dry etching, thus obtaining an optical splitter waveguide structure consisting of two multimode interference couplers, a bent waveguide, and a phase-tuned straight waveguide.

[0053] (2) Coverage of phase change materials

[0054] Photoresist is spin-coated onto the waveguide structure obtained in step (1), and electron beam exposure is performed above the two phase-tuning straight waveguides of the optical splitter. Then, the device is placed in a developing solution for development. Next, a phase change material film of several nanometers to tens of nanometers (preferably 5nm to 30nm) thick is coated on the surface of the device using a magnetron sputtering coating machine. Finally, after the photoresist is removed and peeled off, an optical splitter with phase change material covering the phase-tuning straight waveguide is obtained.

[0055] (3) Integration of electrode materials

[0056] In the structure obtained in step (2), a 1 μm thick silicon dioxide film is coated using PECVD technology. Next, photoresist is spin-coated onto the silicon dioxide film, and electron beam exposure is performed at the corresponding position above the lower arm phase-tuning straight waveguide. The device is then developed in a developer solution. Following this, a 200–300 nm thick platinum or tungsten film is deposited on the device surface using a magnetron sputtering coating machine as the heating electrode material. Finally, after photoresist removal and stripping processes, an optical splitter with integrated electrode material is obtained. Preferably, the distance between the multiple independent heating electrodes disposed above the lower arm phase-tuning straight waveguide and the upper surface of the phase-tuning straight waveguide is greater than 1 μm.

[0057] (4) A 2-3 μm thick silicon dioxide film is coated on the structure obtained in step (3) using PECVD technology as the upper cladding layer to obtain a complete optical splitter with adjustable splitting ratio and non-volatile state based on phase change material.

[0058] In this embodiment, the waveguide height is 800 nm, the width is 800 nm, and the phase change material used is Sb₂Se₃. The phase change material covers the top and sidewalls of the upper and lower phase-tuned straight waveguides, with a film thickness of 10 nm on both the top and sidewalls. The coverage length of the phase change material on the phase-tuned straight waveguides is 55 μm. The multimode interference region lengths of the 1×2 multimode interference coupler and the 2×2 multimode interference coupler are 20 μm and 81 μm, respectively.

[0059] The upper arm phase-tuning straight waveguide is covered with an amorphous phase change material, while the lower arm phase-tuning straight waveguide is covered with multiple segments of individually adjustable phase change material. When the lengths of the crystalline phase change material on the lower arm phase-tuning straight waveguide are 5μm, 15μm, 25μm, and 40μm, the splitting performance and loss of the optical splitter are as follows: Figures 5 to 8 As shown. By adjusting the length of the crystalline phase change material on the lower arm phase-tuning straight waveguide, an optical splitter with an adjustable splitting ratio can be realized, and the loss in the wavelength range of 1520-1610nm is within 0.5dB.

[0060] The optical splitter fabrication method provided in this embodiment uses silicon dioxide as the substrate and upper cladding. A silicon nitride (Si3N4) waveguide with a height of 800nm ​​is fabricated on the substrate, and Sb2Se3 or Ge2Sb2Te5 phase change material is coated on part of the waveguide. This can change the effective refractive index of the waveguide to achieve the purpose of adjusting the splitting ratio. In addition, the fabrication process used in this embodiment is simple, compatible with traditional CMOS processes, easy to integrate, and suitable for large-scale production, which is of great significance to the development of silicon photonic integrated circuits.

[0061] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An optical splitter with adjustable splitting ratio and non-volatile state, characterized in that, It includes a first multimode interference coupler and a second multimode interference coupler. The number of output ports of the first multimode interference coupler and the number of input ports of the second multimode interference coupler are both 2. The two output ports of the first multimode interference coupler are connected to the two input ports of the second multimode interference coupler respectively through a waveguide component. The first multimode interference coupler is used to uniformly split the input light into two beams for transmission. The waveguide component consists of two curved waveguides and a phase-tuned straight waveguide connected between the two curved waveguides. The phase-tuned straight waveguide is made of silicon nitride. One waveguide component has a phase-change material in a fixed amorphous state covering the entire phase-tuned straight waveguide, while the other waveguide component has multiple segments of phase-change material with independently adjustable crystallization states covering the top and sidewalls of the phase-tuned straight waveguide. The thickness of the phase-change material covering the two phase-tuned straight waveguides is 5nm to 30nm. The splitting ratio of the optical splitter is achieved by independently adjusting the crystallization state of the multiple segments of phase-change material in the other waveguide component, thereby changing the effective refractive index of the phase-tuned straight waveguide in the other waveguide component and continuously changing the phase difference between the two transmitted beams. The second multimode interference coupler is used to couple the two phase-tuned transmitted beams into a single output beam.

2. The optical splitter with adjustable splitting ratio and non-volatile state according to claim 1, characterized in that, The phase change material is either Sb2Se3 or Ge2Sb2Te5.

3. The optical splitter with adjustable splitting ratio and non-volatile state according to claim 1, characterized in that, The phase change material segments on the phase-tuned straight waveguide in the other waveguide component are of equal length or increase in a linear proportion.

4. The optical splitter with adjustable splitting ratio and non-volatile state according to claim 1, characterized in that, The first multimode interference coupler is a 1×2 multimode interference coupler, and the second multimode interference coupler is a 2×2 multimode interference coupler.

5. A method for fabricating an optical splitter with adjustable splitting ratio and non-volatile state according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) A silicon dioxide lower cladding layer is deposited on the substrate, and a silicon nitride thin film is deposited on the upper surface of the silicon dioxide lower cladding layer; then photoresist is spin-coated on the silicon nitride thin film, and the device pattern is obtained by electron beam lithography (EBL) equipment. The exposed chip is then immersed in the corresponding developing solution to make the waveguide pattern visible; then the developed pattern is transferred to the wafer by dry etching to obtain a silicon nitride waveguide structure composed of two multimode interference couplers and two waveguide components. (2) Photoresist is spin-coated on the silicon nitride waveguide structure, and then electron beam exposure is performed on the two phase-tuning straight waveguides of the optical splitter; then the device is placed in the developing solution for development, and then a phase change material film is coated on the surface of the device using a magnetron sputtering coating machine, so that the phase change material covers the top and sidewalls of the phase-tuning straight waveguide; finally, after the photoresist removal and peeling process, an optical splitter with phase change material covering the phase-tuning straight waveguide is obtained. (3) Cover the structure obtained in step (2) with a silicon dioxide film, then spin-coat photoresist on the silicon dioxide film, and perform electron beam exposure at the corresponding position above the phase-tuning straight waveguide in another waveguide component; then place the device in the developing solution for development, and then use a magnetron sputtering coating machine to cover the surface of the device with heating electrode material, the heating electrode material being aligned with the phase change material through the corresponding development position on the silicon dioxide film; finally, after the photoresist removal and stripping process, an optical splitter with integrated electrode material is obtained; (4) Cover the structure obtained in step (3) with a silicon dioxide cladding to obtain a complete optical splitter with adjustable splitting ratio and non-volatile state based on phase change material.

6. The method for fabricating an optical splitter with adjustable splitting ratio and non-volatile state according to claim 5, characterized in that, The thickness of the lower and upper silica cladding layers is 2µm to 3µm.

7. The method for fabricating an optical splitter with adjustable splitting ratio and non-volatile state according to claim 5, characterized in that, The distance between the heating electrode on the other waveguide component and the upper surface of the phase-tuned straight waveguide below it is greater than 1µm.

8. The method for fabricating an optical splitter with adjustable splitting ratio and non-volatile state according to claim 5, characterized in that, The heating electrode material is platinum or tungsten.

9. The method for fabricating an optical splitter with adjustable splitting ratio and non-volatile state according to claim 5, characterized in that, In step (3), the thickness of the covering heating electrode material is 200-300 nm.

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