Nonlinear activator based on two-dimensional material and double-slit waveguide and application thereof

Abstract

The application discloses a kind of based on two-dimensional material and double slit waveguide nonlinear activator: the design of the nonlinear activator is based on SOI material platform, wherein the lowermost layer is silica substrate, on the basis of which silicon slit waveguide is made, and both sides are filled with silica;Then deposit aluminum oxide film on the silicon slit waveguide;Then layered two-dimensional material is transferred onto the film, and the material has saturation absorption effect on light, which is the source of nonlinearity;Then the upper layer is deposited with titanium as an adhesive layer to improve the contact stability of the metal slit waveguide and the two-dimensional material;Finally, a metal slit waveguide is made on the titanium layer to form a double slit waveguide structure, enhance the light field restriction, and improve the interaction between light and two-dimensional material. The application realizes a nonlinear activator with high response speed, large optical bandwidth, low power consumption and high integration. The application also discloses a method for manufacturing the nonlinear activator based on two-dimensional material and double slit waveguide and its application.

Description

Technical Field

[0001] This invention belongs to the field of optical computing technology, and more specifically, relates to a nonlinear activator based on two-dimensional materials and a double-slit waveguide and its application. Background Technology

[0002] Saturated absorption effect: The saturated absorption effect generally refers to the phenomenon where, when laser light enters a medium, the absorption coefficient of the medium decreases as the light intensity within the medium increases, resulting in an increase in transmittance with increasing light intensity, until a saturation value is reached. Under saturated absorption, the relationship between the absorption coefficient α(P) of the medium and the optical power P input into the medium can be expressed as: Where α s P represents the saturable absorption coefficient of the medium. sat Saturated optical power is the input optical power when the absorption coefficient of the medium decreases to a generalized value of its initial absorption coefficient.

[0003] SOI: Silicon-On-Insulator (SOI) is widely used in the chip manufacturing industry. This technology introduces a buried oxide layer between the top silicon layer and the back substrate. It utilizes the significant refractive index difference between Si and SiO2 to enhance the waveguide's ability to confine the light field, which is beneficial for reducing device size and increasing integration density. Furthermore, SOI perfectly inherits the process and cost advantages of Si / SiO2, making it the most reliable integration platform for photonic devices.

[0004] Limited by the von Neumann architecture and the slowdown of Moore's Law, traditional electronic chips are constrained in terms of speed and energy efficiency, failing to meet the ever-increasing computing demands. Therefore, photonic chips, which use higher-frequency light waves as information carriers, may become a future hot topic in the information technology industry. Compared to neural network technology based on electronic chips, implementing deep learning algorithms on photonic chips can leverage the high speed and high parallelism of light to accelerate algorithms. Combined with device optimization, this can lead to high-speed, low-power optical neural network computing chips.

[0005] Currently, optical neural networks on photonic chips are mainly implemented using methods such as Mach-Zehnder interferometer (MZI) arrays, microring resonator (MRR) arrays, and semiconductor optical amplifiers. However, optical neural networks with this structure can only perform linear matrix operations, which cannot meet complex computational needs and diverse application scenarios. Therefore, nonlinear activation functions are usually introduced into electrical neural networks to achieve nonlinear mapping from input data to output data, thereby accelerating the convergence speed of the network, improving recognition accuracy, and enriching application scenarios.

[0006] Nonlinear activators developed to date can be divided into two main categories based on their working mechanism: photoelectric conversion type and all-optical type. For photoelectric conversion type activators, the signal needs to be converted between various devices, and additional power is required to maintain its normal operation. Therefore, this method faces severe challenges in terms of integration, speed, and power consumption.

[0007] As an alternative to these methods, all-optical methods leverage the inherent advantages of optics and are crucial for the advancement of neural networks. However, the optical implementation of nonlinear activation functions is not yet mature enough to fully utilize the advantages of photonic chips.

[0008] Several methods for implementing all-optical nonlinear activation functions have been invented in the industry, including:

[0009] 1. Ordinary single-mode optical fiber is fused and tapered to obtain micro / nano-fibers. A tapered region is formed in the middle of the micro / nano-fiber, and then a two-dimensional material is deposited in this region. Because the diameter of the micro / nano-fiber is small, some light leaks out and is absorbed by the two-dimensional material. Two different nonlinear activation functions can be obtained by utilizing the saturation and anti-saturation absorption effects of the two-dimensional material. However, this scheme is based on a fiber-based nonlinear activator. Light needs to be coupled from the photonic chip into the fiber, complete the activation operation, and then coupled back into the photonic chip. This makes integration with the photonic chip difficult, significantly reducing the integration density of the photonic chip.

[0010] 2. A 500nm wide and 100nm high silicon ridge waveguide is fabricated on SOI, and a germanium ridge waveguide of the same height is fabricated on the side, thus forming a germanium-silicon hybrid asymmetric coupler. Light is coupled sequentially from the silicon waveguide to the germanium waveguide and then back to the silicon waveguide. As the light propagates in the germanium waveguide, its refractive index changes, affecting the overall transmittance of the device and thus realizing a nonlinear activation function. However, the refractive index change utilized in this scheme is too slow, resulting in a slow response time for the nonlinear activator, which cannot meet the high-speed computing requirements of photonic chips.

[0011] 3. Two cascaded MZIs are fabricated on SOI. Then, two metal heaters are deposited on one arm of each MZI, and an MRR is fabricated on the side of the second MZI arm. The nonlinear activation function can be realized by utilizing the free carrier dispersion effect of silicon. However, this nonlinear activator has high power consumption, narrow optical bandwidth, and large device size due to the use of metal heaters and MRR, thus reducing the integration density of the photonic chip.

[0012] In general, some existing all-optical nonlinear activators require the use of devices such as MZI and MRR, resulting in smaller optical bandwidth and lower integration density. Others require the use of slower nonlinear effects in materials and additional energy to operate, leading to higher power consumption and slower response speed. Summary of the Invention

[0013] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a nonlinear activator based on two-dimensional materials and a double-slit waveguide. Utilizing the excellent saturation absorption effect of two-dimensional materials for light, and enhancing this absorption effect with a double-slit waveguide, a nonlinear activator with high response speed, large optical bandwidth, low power consumption, and high integration is achieved. This provides a high-performance all-optical nonlinear activator for optical neural networks in high-performance applications. The specific dimensions of each component need to be optimized based on the materials used and the actual situation.

[0014] To achieve the above objectives, according to one aspect of the present invention, a nonlinear activator based on a two-dimensional material and a double-slit waveguide is provided. The nonlinear activator is designed based on an SOI material platform, wherein the bottom layer is a silicon dioxide substrate, on which a silicon slit waveguide is fabricated, with both sides filled with silicon dioxide; then an aluminum oxide thin film is deposited on the silicon slit waveguide; next, a layered two-dimensional material is transferred onto the thin film, which exhibits a saturable absorption effect on light and is the source of nonlinearity; then, titanium is deposited on top as an adhesion layer to improve the contact stability between the metal slit waveguide and the two-dimensional material; finally, a metal slit waveguide is fabricated on the titanium layer to form a double-slit waveguide structure, which enhances optical field confinement and improves the interaction between light and the two-dimensional material.

[0015] In one embodiment of the present invention, the layered two-dimensional material is: graphene, black phosphorus, few-layer transition metal sulfides, or transition metal carbides.

[0016] In one embodiment of the present invention, the constituent metal of the metal slot waveguide includes gold or silver.

[0017] According to another aspect of the present invention, a method for fabricating a nonlinear activator based on two-dimensional materials and a double-slit waveguide is also provided, comprising: fabricating on a commercial SOI substrate; first fabricating a silicon slit waveguide, then depositing SiO2, and then planarizing the sample surface; then depositing an aluminum oxide thin film thereon; then transferring a single layer or few layers of two-dimensional material onto the thin film; and then fabricating a titanium isolation layer and a gold slit waveguide.

[0018] In one embodiment of the present invention, the top silicon layer of the SOI substrate has a thickness of 260 nm, and the underlying silicon dioxide layer has a thickness of 1 μm.

[0019] In one embodiment of the present invention, a silicon slit waveguide is fabricated using electron beam lithography and dry etching techniques, with a slit width of 90 nm.

[0020] In one embodiment of the present invention, SiO2 is deposited using surface plasmon-enhanced chemical vapor deposition (SPED) and the sample surface is planarized using chemical mechanical polishing (CMP).

[0021] In one embodiment of the present invention, an aluminum oxide thin film with a thickness of 7 nm is deposited on the deposited SiO2 using atomic layer deposition technology.

[0022] In one embodiment of the present invention, the patterning of the two-dimensional material is achieved using ultraviolet lithography and oxygen plasma etching techniques; a 3nm thick titanium isolation layer and a 25nm thick, 90nm wide gold slit waveguide are fabricated using electron beam lithography and deposition techniques; the nonlinear activator has a device length of 4.3μm and an overall device size of no more than 80μm. 2 .

[0023] According to another aspect of the present invention, an application of a nonlinear activator based on two-dimensional materials and double-slit waveguides is also provided, wherein the nonlinear activator based on two-dimensional materials and double-slit waveguides is used in an optical neural network on a photonic chip.

[0024] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0025] (1) This invention utilizes the ultrafast relaxation time of photogenerated carriers and the flat absorption over a wide wavelength range of two-dimensional materials to realize a nonlinear activator with fast response speed and large working optical bandwidth, which helps to develop new high-speed computing application scenarios for photonic computing chips and improve the flexibility of photonic computing chips.

[0026] (2) This invention utilizes the special design of the double-slit waveguide, which can not only strengthen the optical field confinement and improve the absorption effect of two-dimensional materials, but also introduce excessive losses and reduce the device size, realizing a low-power, highly integrated nonlinear activator, which helps to reduce the overall power consumption of photonic computing chips.

[0027] (3) The present invention is designed based on the SOI material platform. The designed nonlinear activator is compatible with silicon-based photonic chip technology and can be directly integrated with photonic chips. It is a general-purpose all-optical nonlinear activator, which helps to reduce the complexity of photonic computing systems and improve the overall integration density. Attached Figure Description

[0028] Figure 1 This is a three-dimensional structural diagram of the nonlinear activator based on two-dimensional materials and double-slit waveguides described in this invention;

[0029] Figure 2 This is a cross-sectional view of the nonlinear activator based on two-dimensional material and double-slit waveguide described in this invention;

[0030] Figure 3 This is a graph showing the saturable absorption characteristics of the nonlinear activator obtained in the embodiments of the present invention in the wavelength range of 1547nm-1565nm.

[0031] Figure 4 It is the nonlinear activation function of the nonlinear activator at 1550nm obtained by testing in the embodiments of the present invention;

[0032] Figure 5 This is a pulse curve showing the change in the transmittance of the nonlinear activator probe light as a function of the delay difference between the probe light and the pump light, obtained in an embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram of the structure of the nonlinear activator based on two-dimensional materials and double-slit waveguides used in optical neural networks according to the present invention.

[0034] Figure 7 This is used in the embodiments of the present invention. Figure 4 The curve showing the change in accuracy with training rounds during the training process when the activation function is shown.

[0035] Figure 8 This is used in the embodiments of the present invention. Figure 4 The diagram shows the confusion matrix calculated on the test dataset when the activation function is shown. Detailed Implementation

[0036] 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. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Figure 1 A three-dimensional structure of a nonlinear activator based on two-dimensional materials and a double-slit waveguide is shown. Figure 2The cross-sectional view of the activator details the structure of the entire device. The device design is based on an SOI material platform, with a silicon dioxide substrate at the bottom. A silicon slit waveguide is then fabricated on this substrate, with both sides filled with silicon dioxide. An aluminum oxide thin film is then deposited on the silicon slit waveguide. Next, a layered two-dimensional material is transferred onto the thin film; this material exhibits saturable absorption of light and is a source of nonlinearity. Titanium is then deposited on top as an adhesion layer to improve contact stability with the two-dimensional material. Finally, a metal slit waveguide is fabricated on the titanium layer, forming a double-slit waveguide structure to enhance optical field confinement and improve the interaction between light and the two-dimensional material.

[0038] Generally, the two-dimensional material can be graphene, black phosphorus, few-layer transition metal sulfides, or transition metal carbides; the metal used in the metal slit waveguide can be gold or silver.

[0039] The first key point of this invention is the use of two-dimensional materials as the source of nonlinearity, based on the principle of the saturation absorption effect of two-dimensional materials.

[0040] The saturation absorption effect typically refers to the phenomenon where, when laser light enters a medium, the absorption coefficient of the medium decreases as the light intensity increases, leading to an increase in transmittance with increasing light intensity until a saturation value is reached. Thanks to the short photogenerated carrier relaxation time and narrow band gap of two-dimensional materials, the saturation absorption effect of two-dimensional materials usually exhibits fast response speed and flat absorption over a wide wavelength range. Therefore, nonlinear activators designed based on two-dimensional materials have the advantages of high response speed and large optical bandwidth.

[0041] The second key aspect of this invention is the use of a double-slit waveguide to enhance the light-matter interaction between light and two-dimensional materials. Researchers typically use metallic slit waveguides to strongly confine light, significantly increasing the interaction between two-dimensional materials and light. However, metals also suffer from significant light absorption losses, resulting in low absorption rates in the two-dimensional material and consequently, greatly increasing device power consumption. Silicon slit waveguides, on the other hand, exhibit relatively low light absorption, and consequently, their light confinement is relatively weak. Therefore, this invention innovatively combines metallic and silicon slit waveguides, ensuring strong light field confinement while reducing light absorption by the metallic slit waveguide, thereby reducing power consumption and minimizing device size. Furthermore, because this invention proposes a nonlinear activator fabricated on an SOI material platform, it can be easily integrated directly with photonic chips, achieving high integration density.

[0042] Device Fabrication: This embodiment is fabricated on a commercial SOI substrate with a top silicon layer thickness of 260 nm and a bottom silicon dioxide layer thickness of 1 μm. First, a silicon slit waveguide with a slit width of 90 nm is fabricated using electron beam lithography and dry etching. Then, SiO2 is deposited using surface plasmon-enhanced chemical vapor deposition (SPV), followed by chemical mechanical polishing (CMP) to planarize the sample surface. Next, a 7 nm thick alumina film is deposited on top using atomic layer deposition (ALD). Then, a single-layer two-dimensional material (which could be graphene, black phosphorus, few-layer transition metal sulfides, or transition metal carbides) is transferred onto the film. The graphene patterning is achieved using ultraviolet lithography and oxygen plasma etching. Finally, a 3 nm thick titanium isolation layer and a 25 nm thick, 90 nm wide gold slit waveguide are fabricated using electron beam lithography and deposition techniques. In this embodiment, the device length is 4.3 μm, and the overall device size is no greater than 80 μm. 2 Its small size is beneficial for improving the integration of photonic computing chips.

[0043] Performance Testing: To measure the saturable absorption characteristics of the nonlinear activator, a tunable narrow-linewidth laser was used as the laser source, with wavelengths of 1547nm, 1550nm, 1555nm, 1560nm, and 1565nm selected as input light. The output optical power of the laser first passes through an adjustable attenuator for rapid power adjustment, and then through an optical beam splitter to divide the optical power into two parts. 95% of the optical power passes through the nonlinear activator proposed in this invention and then enters the optical power meter, while the remaining 5% of the optical power directly enters the optical power meter as a reference power. Therefore, the relationship between the relative transmittance ΔT and the input optical power P can be obtained: Where α s The saturation absorption coefficient is P. sat This represents the saturated optical power. Figure 3 The relative transmittance curve of the nonlinear activator proposed in this invention is shown. It can be seen that the transmittance of the activator increases with the increase of light intensity and remains basically consistent in the range of 1547-1565nm, which proves that the activator achieves a large optical bandwidth of at least 18nm, and the saturation power of the activator is only 5.41mw. Figure 4 The nonlinear activation function of the activator is shown based on the relative transmittance curve when the incident light wavelength is 1550 nm.

[0044] To verify the response speed of the nonlinear activator, this embodiment uses a pump-probe method to test the device's response time. This method uses two picosecond pulses with a time delay difference. The higher-energy pulse is used as the pump light to excite the nonlinear effect of the activator, while the lower-energy pulse is used as the probe light to detect the activator's transmittance. During the test, by adjusting the time delay difference between the two pulses reaching the activator, the activator's transmittance at different times can be obtained. Scanning this time delay difference yields a curve showing the activator's transmittance changing with the time delay difference, as shown below. Figure 5 As shown, the activator's transmittance decreases with increasing delay difference, reaching its highest level when the delay difference is zero, thus forming a pulse-shaped transmittance variation curve. The full width at half maximum (FWHM) of this pulse is approximately 96.3 ps, indicating that the activator's response time is approximately 96.3 ps, corresponding to a response bandwidth greater than 10 GHz. Combined with the aforementioned saturation power, it can be demonstrated that the activator consumes approximately 0.51 pJ per nonlinear operation, showcasing its ultra-low power consumption characteristics.

[0045] Furthermore, the nonlinear activator based on two-dimensional materials and double-slit waveguides provided by this invention can be used in optical neural networks on photonic chips. To verify the feasibility of using the nonlinear activator based on two-dimensional materials and double-slit waveguides in optical neural networks, we used the nonlinear activation function obtained above in a fully connected neural network to realize MNIST handwritten digit recognition. This is because handwritten digit recognition is one of the typical tasks for evaluating neural network performance. We constructed a three-layer fully connected neural network, containing 782, 100, and 10 neurons respectively, where the nonlinear activation function used was the nonlinear activation function measured above. Figure 6 This diagram illustrates the application of the nonlinear activator based on two-dimensional materials and a double-slit waveguide described in this invention in an optical neural network. In this network, the optical linear operation part uses a commonly used MZI array, while the optical nonlinear operation part consists of the nonlinear activator prepared in this embodiment, realizing nonlinear computation. During the training phase, we used 60,000 digital images, and during the testing phase, we used 10,000 digital images. Figure 7 The results show that the accuracy of the network increases rapidly and converges with each training round, and the final recognition accuracy of the training set reaches 97.18%. Figure 8 The confusion matrix obtained from the training set is shown. It can be seen that the average recognition accuracy for all ten digits from 0 to 9 reached 96.01%, and the recognition accuracy for each individual digit reached 94%, which verifies the feasibility of the nonlinear activator proposed in this invention.

[0046] 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. A nonlinear activator based on two-dimensional materials and a double-slit waveguide, characterized in that, The nonlinear activator is designed based on an SOI material platform, with a silicon dioxide substrate as the bottom layer. A silicon slit waveguide is then fabricated on this substrate, with silicon dioxide filling both sides. An aluminum oxide thin film is then deposited on the silicon slit waveguide. Next, a layered two-dimensional material is transferred onto the thin film. This material exhibits a saturated absorption effect on light, which is the source of nonlinearity. Titanium is then deposited on top as an adhesion layer to improve the contact stability between the metal slit waveguide and the two-dimensional material. Finally, a metal slit waveguide is fabricated on the titanium layer to form a double-slit waveguide structure, which enhances the light field confinement and improves the interaction between light and the two-dimensional material.

2. The nonlinear activator based on two-dimensional materials and a double-slit waveguide as described in claim 1, characterized in that, The layered two-dimensional material is: graphene, black phosphorus, few-layer transition metal sulfides, or transition metal carbides.

3. The nonlinear activator based on two-dimensional materials and a double-slit waveguide as described in claim 1, characterized in that, The metal slit waveguide is composed of gold or silver.

4. The method for fabricating a nonlinear activator based on two-dimensional materials and a double-slit waveguide as described in any one of claims 1 to 3, characterized in that, include: Fabrication is performed on a commercial SOI substrate; first, a silicon slit waveguide is fabricated, then SiO2 is deposited, and then the sample surface is planarized. Then, an aluminum oxide thin film is deposited on it; then, a single layer or few layers of two-dimensional material are transferred onto the thin film; and then a titanium isolation layer and a gold slit waveguide are fabricated.

5. The fabrication method of the nonlinear activator based on two-dimensional materials and double-slit waveguides as described in claim 4, characterized in that, The top silicon layer of the SOI substrate is 260 nm thick, and the silicon dioxide layer below it is 1 μm thick.

6. The fabrication method of the nonlinear activator based on two-dimensional materials and double-slit waveguides as described in claim 4, characterized in that, Silicon slit waveguides were fabricated using electron beam lithography and dry etching techniques, with a slit width of 90 nm.

7. The fabrication method of the nonlinear activator based on two-dimensional materials and double-slit waveguides as described in claim 4, characterized in that, SiO2 was deposited using surface plasmon-enhanced chemical vapor deposition (SPED), and the sample surface was planarized using chemical mechanical polishing (CMP).

8. The fabrication method of the nonlinear activator based on two-dimensional materials and double-slit waveguides as described in claim 4, characterized in that, Alumina films with a thickness of 7 nm were deposited on deposited SiO2 using atomic layer deposition technology.

9. The fabrication method of the nonlinear activator based on two-dimensional materials and double-slit waveguides as described in claim 4, characterized in that, The patterning of two-dimensional materials was achieved using ultraviolet lithography and oxygen plasma etching techniques; a 3nm thick titanium isolation layer and a 25nm thick, 90nm wide gold slit waveguide were fabricated using electron beam lithography and deposition techniques; the nonlinear activator has a device length of 4.3μm and an overall device size of no more than 80μm. 2 .

10. An application of a nonlinear activator based on two-dimensional materials and a double-slit waveguide, characterized in that, The nonlinear activator based on two-dimensional materials and double-slit waveguides as described in any one of claims 1 to 3 is used in an optical neural network on a photonic chip.

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