CN115327703B - Nonvolatile multistage adjustable photonic synapse device based on phase change material - Google Patents
Nonvolatile multistage adjustable photonic synapse device based on phase change material Download PDFInfo
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/015—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction
- G02F1/025—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on semiconductor elements having potential barriers, e.g. having a PN or PIN junction in an optical waveguide structure
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12083—Constructional arrangements
- G02B2006/12097—Ridge, rib or the like
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Abstract
The invention discloses a nonvolatile multistage adjustable photonic nerve synapse device based on a phase change material, and belongs to the field of optical calculation. Comprises a substrate, a slab waveguide, a periodic land waveguide and a phase change film. The planar layer waveguide covers the whole substrate area, the periodic land waveguides are periodically distributed on the upper side of the planar layer waveguide, and the phase-change film covers the planar layer waveguide and the surfaces of the periodic land waveguides; the periodic land waveguide includes waveguide units periodically distributed along a propagation direction of the light beam, each of the waveguide units including two identical ridge waveguides and a slit structure therebetween. The geometry of the slab layer waveguide and the periodic land waveguide will affect the effective mode index of the transmission modes within the waveguide by optimizing the period and duty cycle of the periodic land waveguide to achieve different output intensity outputs. By changing the phase state (crystalline state, amorphous state) of the phase change film, the photonic nerve synapse is realized to have larger output intensity difference under the condition that the phase change film is in different phase states.
Description
Technical Field
The invention belongs to the field of optical computation, and in particular relates to a nonvolatile multistage adjustable photonic synapse device based on a phase change material.
Background
In recent 50 years, the semiconductor process is mature gradually, from the initial 180nm process to the current 5nm advanced process and the current 3nm process under development, so that the integrated circuit process is developed rapidly, the performance of an electrical computing system is improved rapidly, but the state is limited by strict requirements of processing precision, the state cannot be developed all the time, and the problems of power consumption, heat dissipation and the like of a chip are exposed gradually along with the gradual reduction of the size of a transistor, so that the traditional electrical computing system cannot continuously meet the requirements of high-speed, low-energy consumption and large-scale communication. To solve this problem, researchers have proposed high-performance optical signal processing systems such as optical processing chips based on neuromorphic computing network architectures. Typically, neuromorphic computational networks are approximately composed of 10 11 The artificial neurons are composed, and each artificial neuron is subjected to weight adjustment based on one adjustable light switch. Thus, the ability of a single optical switch will greatly impact the computational efficiency and power consumption of the optical neuromorphic network. Adjustment ofThe speed and the energy consumption are two key evaluation indexes of the optical switch, however, the current optical switch mainly depends on materials with weak and volatile thermo-optic or electro-optic modulation effect, so that the modulation speed is low, the energy consumption is high, and the occupied space is large, thereby limiting the development of an optical nerve morphology calculation network.
Chalcogenide phase change material Ge 2 Sb 2 Te 5 (GST) has excellent optical contrast between covalently bonded amorphous (a_GST) and resonance bonded crystalline (c_GST), and has been widely used in reconfigurable photonic devices such as optical switches, optical routers and supersurfaces. Optical switches based on phase change materials, which do not require a static power supply to maintain the switching state and have a modulation speed on the order of sub-nanoseconds, are considered to be ideal unit devices for designing optical neuromorphic networks. GST is more widely used to design reconfigurable optical switches due to its mature processing technology. However, when the GST film is sputtered directly on top of the silicon ridge waveguide, the light output intensity of the optical switch varies little when GST is in different phases due to the weak interaction between the waveguide mode and the phase change material. Thus, researchers have designed different waveguide structures, such as mach-zehnder (MZ) switches and ring coupler switches, whose optical output intensities are more sensitive to the phase state of the phase change material using interference effects and coupler effects, and thus can enhance the effect of the change in GST phase on the optical switch output intensity. Their device size is large and severely hampers large-scale integration of optical neuromorphic networks. To solve this problem, some reports propose to enhance the interaction effect between the waveguide and the phase change material by designing specific waveguide structures, such as a land waveguide and a surface plasmon waveguide. However, when GST is in a_gst state and a_gst state, the difference of the output intensities of the designed optical switches is about 40%, and the smaller output intensity modulation range is unfavorable for designing the multistage adjustable optical switch, so that the calculation precision of the photonic neuromorphic calculation network is limited.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a nonvolatile multistage adjustable photonic nerve synaptic device based on a phase change material, and aims to solve the problem that the range of normalized output intensity of photonic nerve synapses is too small.
In order to achieve the above object, the present invention provides a nonvolatile multistage tunable photonic nerve synaptic device for phase change material, comprising a substrate, a slab waveguide, a periodic land waveguide, and a phase change film; the planar layer waveguide covers the whole substrate area, the periodic land waveguides are periodically distributed on the upper side of the planar layer waveguide, and the phase change film covers the surfaces of the planar layer waveguide and the periodic land waveguides; the periodic land waveguide comprises waveguide units which are periodically distributed along the propagation direction of the light beam, and each waveguide unit comprises two identical ridge waveguides and a slit structure between the two ridge waveguides; the section geometric parameters of the slab layer waveguide and the periodic land-type waveguide in the photonic nerve synaptic device are used for regulating and controlling the effective mode refractive index of the transmission mode of incident light; the period and the duty ratio of the periodic land-type waveguide are used for regulating and controlling the coupling efficiency between the transmission mode of the incident light and the periodic structure, and the period of the periodic land-type waveguide is also used for controlling the modulation length of the device; by optimizing the parameters, the regulation and control of the output intensity of the photonic nerve synapse is realized.
Light output by the laser enters the photonic nerve synapse device for transmission after passing through the coupling waveguide, and the section geometric parameters of different slab waveguides and periodic land-shaped waveguides influence the effective mode refractive index of a transmission mode in the photonic nerve synapse, wherein the imaginary part of the effective refractive index of the transmission mode influences the transmission loss of the mode in the photonic nerve synapse. By adjusting the phase state (crystalline state, amorphous state) of the phase-change film, the effective refractive index of the propagation mode in the photonic nerve synapse is changed, when the phase-change film is amorphous state, mode energy is mainly concentrated in the silicon waveguide area, and when the phase-change film is crystalline state, part of mode energy is coupled into the phase-change film, so that larger optical loss is caused, and the effect of regulating and controlling the output intensity of the photonic nerve synapse is achieved.
Further, when the phase change film is in different phases, the larger the effective refractive index imaginary part difference value of the intra-photonic nerve synapse mode is, the larger the regulating range of the phase change film on the output intensity of the photonic nerve synapse is, and meanwhile, the period and the duty ratio of the periodic land-shaped waveguide also influence the output intensity of the photonic nerve synapse. When the optical field is transmitted in the photonic synapse, the period and the duty ratio of the periodic land-shaped waveguide affect the coupling efficiency of different modes and the photonic synapse, and when the phase-change film is in an amorphous state, more optical field energy can be stably transmitted in the waveguide; when the phase-change film is in an amorphous state, most of light field energy needs to be lost in the transmission process, so that the aim of regulating and controlling the output intensity of the photonic nerve synapse is fulfilled.
Further, by optimizing the cross-sectional geometry parameters (height, width, period and duty cycle) of the slab layer waveguide and the periodic land waveguide, a nonvolatile multistage adjustable photonic synapse device based on phase change materials realizes the maximum optical output intensity regulation range when the phase change film is in different phases. Preferably, an initial cross-sectional geometry of a phase change material-based non-volatile multistage tunable photonic synapse device is: slab waveguide height (h slab ) The height of the periodic land-type waveguide was 240nm, and the silicon waveguide width (w si ) A groove width (w slot ) The period (period) of the periodic land-type waveguide was 100nm, and the duty cycle (h) was 50% at 200 nm.
Further, the material of the phase-change film (4) is a chalcogenide phase-change material Ge 2 Sb 2 Te 5 (GST)。
Further, the nonvolatile multistage tunable photonic synapse device based on phase change materials can be fabricated on silicon-on-insulator (SOI) platforms at 340nm height or other high semiconductor platforms.
Further, the slab waveguide and the periodic land waveguide may be silicon waveguides or other low-loss waveguides.
Further, the phase change film should be selected to enhance the interaction between the optical field and the phase change film as much as possible.
Further, the phase change film is also distributed on the surface of the slab waveguide.
Further, the period of the periodic land-type waveguide can be fixed or multi-period mixed.
Further, the phase-change film is covered on the slab waveguide and the periodic land-shaped waveguide, wherein the thickness of the phase-change film 4 covered on the slab waveguide is more than or equal to 0.
Further, the cladding of the periodic land-type waveguide of the fixed-period or multi-period mixture may be air, or may be other materials, such as silica.
Further, an anti-oxidation layer, such as noble metal gold or ITO material, is coated on the phase change film to prevent oxidative denaturation of the phase change material.
Further, the cross-sectional geometry of the periodic land waveguide and the phase change film is constant or slowly varying in the propagation direction.
Compared with the prior art, the invention provides the nonvolatile multistage adjustable photonic synapse device based on the phase change material, and the nonvolatile multistage adjustable light switch based on the phase change material is realized by designing the periodic land waveguide on the silicon platform. The cross section of the waveguide designed by the invention is similar to a land waveguide, and can enhance the coupling effect between the optical field and the phase change material. Meanwhile, a periodic structure is designed in the transmission direction of the optical waveguide so as to increase the output intensity difference of the optical switch when the phase change film is in different phases. The invention provides a nonvolatile multistage adjustable photonic nerve synapse device which has very important significance and value in future optical neural network design, optical calculation and optical communication.
Drawings
FIG. 1 is a three-dimensional schematic and a two-dimensional schematic of a phase change material-based nonvolatile multistage tunable photonic synapse device.
Fig. 2 is a graph of simulation results of photonic neurite electric field distribution after optimization of cross-sectional geometry, and (a) and (b) represent electric field distribution in the case where the phase change film 4 is amorphous and crystalline, respectively.
Fig. 3 is a graph of simulation results of the distribution of the transmission electric field of the photonic nerve synapse after optimization of the cross-sectional geometry, where (a) and (b) represent the distribution of the transmission electric field of the phase change film 4 in an amorphous state and a crystalline state, respectively.
Fig. 4 is a graph of simulation results obtained by a nonvolatile multistage tunable photonic synapse device based on a phase change material, where (a) and (b) represent normalized electric field distributions of the phase change film 4 in amorphous and crystalline states, respectively.
Fig. 5 is a diagram of simulation results obtained by a nonvolatile multistage tunable photonic synapse device based on a phase change material, where (a) and (b) represent the distribution of the electric field transmitted by the amorphous and crystalline phase change films 4, respectively.
Fig. 6 is a graph of the relationship between the silicon waveguide width and the optical output intensity difference of the periodic land-type waveguide 3.
Fig. 7 is a graph showing the relationship between the height of the slab waveguide 2 and the optical output intensity difference.
Fig. 8 is a graph showing the relationship between the groove width and the optical output intensity difference of the periodic land-type waveguide 3.
Fig. 9 is a graph showing the relationship between the period of the periodic land-type waveguide 3 and the optical output intensity difference.
Fig. 10 is a graph showing the relationship between the duty ratio of the periodic land-type waveguide 3 and the optical output intensity difference.
Fig. 11 is a graph showing the relationship between the number of periods of the periodic land-type waveguide 3 and the difference in optical output intensity.
FIG. 12 is a bar graph of output intensity level modulation of a multi-level tunable photonic synapse device.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not interfere with each other.
The invention provides a nonvolatile multistage adjustable photonic synapse device for phase change materials, which comprises a substrate 1, a slab waveguide 2, a periodic land-shaped waveguide 3 and a phase change film 4, wherein the substrate is a transparent substrate; the planar layer waveguide 2 covers the whole area of the substrate 1, the periodic land-type waveguides 3 are periodically distributed on the upper side of the planar layer waveguide 2, and the phase-change film 4 covers the surfaces of the planar layer waveguide 2 and the periodic land-type waveguides 3; the periodic land-type waveguide 3 includes waveguide units periodically distributed in the direction of propagation of the light beam, each of the waveguide units including two identical ridge-type waveguides and a slit structure therebetween.
The initial section geometrical parameters of a nonvolatile multistage adjustable photonic synapse device based on a phase change material are taken as the phase change film, wherein the initial section geometrical parameters are that the silicon waveguide width of the periodic land-type waveguide 3 is 140nm, the height of the flat plate waveguide 2 is 130nm, the groove width of the periodic land-type waveguide 3 is 100nm, the period of the periodic land-type waveguide 3 is 200nm, the duty ratio of the periodic land-type waveguide 3 is 50% and the period is 30 2 Sb 2 Te 5 (GST). At this time, when the phase change film 4 is in different phases (crystalline state, amorphous state), the difference in optical output intensity is 70.7%.
Examples
As shown in fig. 1, the multistage tunable photonic synapse of the present embodiment includes a substrate 1, a slab waveguide 2, a periodic land-type waveguide 3, and a phase change film 4; light output by the laser enters the photonic nerve synaptic device for transmission after passing through the coupling waveguide, the section geometric parameters of different slab waveguides 2 and periodic land-type waveguides 3 influence the effective mode refractive index of a transmission mode in the waveguide, the regulation and control of the output intensity of the waveguide are realized by changing specific parameters, and the period and the duty ratio of the periodic land-type waveguides 3 also influence the output intensity of the waveguide; when the light field is transmitted in the waveguide, part of energy is coupled into the phase-change film 4, and the output intensity of the waveguide is regulated and controlled by changing the phase state (crystalline state and amorphous state) of the phase-change film 4. In the case of the initial cross-sectional geometry, the normalized electric field distribution of the phase change film 4 in the amorphous state and the crystalline state is shown in fig. 2, and the transmitted electric field distribution is shown in fig. 3.
For the conventional ridge waveguide, the mode energy distribution change caused by the phase change of the phase change film is not obvious, and the nonvolatile multistage adjustable photonic nerve synaptic device based on the phase change material can realize obvious mode energy distribution change, as shown in fig. 4.
Compared with the traditional continuous waveguide structure, the non-volatile multistage adjustable photonic synapse device based on the phase change material has larger output intensity difference when the phase change material is in different phases, and the specific result is shown in fig. 5.
Specifically, the silicon waveguide width of the periodic land-type waveguide 3 is changed to observe the change in the optical output intensity difference when the phase-change film 4 is in different phases. The relationship between the silicon waveguide width and the optical output intensity difference of the periodic land-type waveguide 3 is shown in fig. 6. It can be found that the light output intensity of the periodic land waveguide slowly decreases as the silicon waveguide width of the periodic land waveguide 3 increases when the GST is in the amorphous and crystalline states. And the difference in optical output intensity at 140nm reached a maximum value of 67.6%. The reason why the difference in optical output intensity gradually decreases over the entire modulation range is that when the value of the silicon waveguide width of the periodic land-type waveguide 3 is small, the mode field cannot exist stably in the land area but exists in the slab layer waveguide 2, so that the interaction between the optical field and the phase-change film 4 is reduced, and thus the transmission loss caused by the GST material is reduced. It was also found that a local increase was accompanied by a gradual decrease in the difference in optical output intensity. This is because the real part of the effective refractive index of the transmission mode within the waveguide is also gradually changing, and the coupling efficiency between the electric field and the periodic land-type waveguide 3 also exhibits a periodic variation in the course of increasing the width of the silicon waveguide.
Specifically, the silicon waveguide width of the periodic land-type waveguide 3 was set to 140nm, and the height of the slab waveguide 2 was changed to observe the change in the optical output intensity difference when the phase-change film 4 was in different phases. Note that the sum of the heights of the slab waveguide 2 and the periodic land-type waveguide 3 is always 340nm. The relationship between the height of the slab waveguide 2 and the optical output intensity difference is shown in fig. 7. When the height of the slab waveguide 2 is less than 60nm, the light output intensity of the periodic land waveguide is very low regardless of whether GST is in the agtst state or the cgt state. This is because the waveguide having the height of the slab waveguide 2 of less than 60nm cannot confine the electric field on the premise that the silicon waveguide width of the periodic land waveguide 3 is 140nm, resulting in a corresponding waveguide mode having a large mode loss. When the height of the slab waveguide 2 is increased so that the waveguide can confine the electric field, the light output intensity of the periodic land waveguide will gradually increase when GST is in the a GST state or c GST state. The increase in the height of slab waveguide 2 allows more optical field to be distributed in the slab, reducing the interaction of the optical field with the GST, and thus reducing the transmission loss caused by GST material loss. Finally, when the silicon waveguide width of the periodic land-type waveguide 3 is 140nm and the height of the slab waveguide 2 is 130nm, the optical output intensity difference reaches the maximum value, which is 70.7%.
Specifically, when GST is in different phases, the optical output intensity of the periodic land waveguide gradually decreases as the groove width of the periodic land waveguide 3 increases. When the silicon waveguide width of the periodic land-type waveguide 3 was 140nm, the height of the slab waveguide 2 was 130nm, and the groove width of the periodic land-type waveguide 3 was 100nm, the optical output intensity difference reached a maximum value of 70.7%. As shown in fig. 8.
In particular, since the output intensity of the periodic land waveguide is related to the period of the sub-wavelength grating, adjusting the period of the periodic land waveguide 3 can also significantly affect the difference in optical output intensity when GST is in different phases, as shown in FIG. 9. The optical output intensity difference of the periodic land waveguide decreases and then increases as the period increases when GST is in the a GST state. This is because the effective refractive index of the propagation mode in the waveguide is determined after determining the values of the silicon waveguide width of the periodic land-type waveguide 3, the height of the slab waveguide 2, and the groove width of the periodic land-type waveguide 3. When the relation between the real part of the effective refractive index of the propagation mode in the waveguide and the grating period satisfies the Bragg reflection condition, the light energy that can pass through the periodic land waveguide is very small. This may also be supported by another detail in fig. 9. When the phase of the phase change film 4 is amorphous, the optical output intensity of the periodic land waveguide should be greater than that of the waveguide when the phase of the phase change film 4 is crystalline, because the optical loss of cgt is much greater than that of agt. However, the difference in optical output intensity of the periodic land waveguide when GST is in different phases is negative at a period of 310 nm. This is because when the phase change material is a GST, the real part of the effective refractive index of the propagation mode in the waveguide satisfies the bragg reflection condition with respect to the grating period, resulting in a significant decrease in the optical output intensity. Finally, the optical output intensity difference reached a maximum value of 70.7% when the silicon waveguide width of the periodic land-type waveguide 3 was 140nm, the height of the slab waveguide 2 was 130nm, the groove width of the periodic land-type waveguide 3 was 100nm, and the period of the periodic land-type waveguide 3 was 200 nm.
Specifically, changing the duty cycle of the periodic land-type waveguide 3 affects the average refractive index of the grating, which in turn affects the coupling efficiency between the propagating modes within the waveguide and the periodic land-type waveguide 3. Thus, it can be seen in FIG. 10 that the difference in light output intensity of the periodic land waveguide has a peak when GST is in a different phase. When the silicon waveguide width of the periodic land-type waveguide 3 is 140nm, the height of the slab waveguide 2 is 130nm, the groove width of the periodic land-type waveguide 3 is 100nm, and the period of the periodic land-type waveguide 3 is 200nm, the output intensity difference reaches the maximum value, i.e., 70.7%, when the duty ratio of the periodic land-type waveguide 3 is 50%.
Specifically, FIG. 11 shows the effect of the number of periods (period numbers) on the intensity of the periodic land waveguide light output. Since the optical switch has a certain transmission loss, the optical transmittance of the periodic land waveguide gradually decreases as the transmission distance increases when the GST is in an amorphous state and a crystalline state. However, when GST is in amorphous and crystalline states, the modes propagating in the periodic land waveguide have different transmission losses, and thus the rate at which the light output intensity of the SWGST waveguide drops is also different when GST is in a different phase state. As can be seen from fig. 11, when the silicon waveguide width of the periodic land-type waveguide 3 is 140nm, the height of the slab waveguide 2 is 130nm, the groove width of the periodic land-type waveguide 3 is 100nm, and the period of the periodic land-type waveguide 3 is 200nm, the duty ratio of the periodic land-type waveguide 3 is 50%, and the period number is 30, the output intensity difference reaches the maximum value, 70.7%, which is almost twice that of the existing structure, and the design is suitable for the design of the multistage adjustable nonvolatile optical switch in practical application.
In the multi-stage tunable optical switch, the optical refractive index of the phase-change thin film 4 can be changed by changing the degree of crystallization of the phase-change thin film 4, wherein the relationship between the degree of crystallization and the optical refractive index satisfies:
wherein p represents the degree of crystallization, e a And e c The phase change material used in the present invention is preferably GST, and the refractive index of the crystalline state and the amorphous state thereof are 4.6+0.18i and 7.2+1.9i, respectively. Simulation results indicate that a multi-stage dimmable switch can control the light output intensity at 65 different levels, approximately corresponding to a 6-bit programming resolution, as shown in fig. 12. The nonvolatile multistage adjustable photonic synapse device based on the phase change material has a larger optical output intensity regulation range, and can realize 64-stage (6-bit) coding on the basis that the output intensity difference of adjacent regulation levels is ensured to be 1%, which is twice that of other output intensity regulation type nonvolatile optical switches.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (8)
1. The nonvolatile multistage adjustable photonic synapse device based on phase change materials is characterized by comprising a substrate (1), a slab waveguide (2), a periodic land waveguide (3) and a phase change film (4), wherein the slab waveguide (2) covers the whole area of the substrate (1), the periodic land waveguide (3) is distributed on the upper side of the slab waveguide (2), and the phase change film (4) covers the surface of the periodic land waveguide (3); the periodic land waveguide (3) comprises waveguide units which are periodically distributed along the propagation direction of the light beam, and each waveguide unit comprises two identical ridge waveguides and a slit structure between the two identical ridge waveguides;
the period, duty cycle and cycle number of the periodic land waveguide (3) are selected so that the coupling efficiency difference between the transmission mode in the waveguide and the periodic structure is the largest when the phase change material is in different phases;
the section geometric parameters of the slab waveguide (2) and the periodic land waveguide (3) are selected so that when the phase change material is in different phases, the mode loss difference of a transmission mode in the waveguide is the largest;
when the phase change film (4) is amorphous, mode energy is mainly concentrated in the silicon waveguide region, and when the phase change film (4) is crystalline, part of the mode energy is coupled into the phase change film (4).
2. The non-volatile multistage tunable photonic synapse device according to claim 1, characterized in that the cross-sectional geometry of the periodic land waveguide (3) and the phase-change film (4) is constant in propagation direction.
3. The non-volatile multistage tunable photonic synapse device according to claim 1, characterized in that the period of the periodic land waveguide (3) is a fixed period or a multi-period mixture.
4. The non-volatile multistage tunable photonic synapse device of claim 1, wherein the phase change film (4) is further distributed on the surface of the slab waveguide (2).
5. The non-volatile multilevel tunable photonic synapse device of claim 1, wherein the material of the phase change film (4) is a chalcogenide phase change material Ge 2 Sb 2 Te 5 。
6. The non-volatile multistage tunable photonic synapse device of claim 1, wherein the slab waveguide (2) and the periodic land waveguide (3) are silicon waveguides or silicon nitride waveguides.
7. The non-volatile multistage tunable photonic synapse device according to claim 1 or 6, characterized in that the cladding of the periodic land waveguide (3) is air or silica.
8. The non-volatile multistage tunable photonic synapse device according to claim 1, characterized in that the phase-change film (4) is further covered with an anti-oxidation layer, the material being gold or ITO material.
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