CN219642035U - Asymmetric MMI power distributor based on phase change material - Google Patents

Asymmetric MMI power distributor based on phase change material Download PDF

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CN219642035U
CN219642035U CN202320448550.4U CN202320448550U CN219642035U CN 219642035 U CN219642035 U CN 219642035U CN 202320448550 U CN202320448550 U CN 202320448550U CN 219642035 U CN219642035 U CN 219642035U
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phase change
silicon
change material
pixel point
waveguide layer
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刘鸿葆
赵瑛璇
朱子健
甘甫烷
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Shanghai Institute of Microsystem and Information Technology of CAS
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Shanghai Institute of Microsystem and Information Technology of CAS
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Abstract

The utility model relates to an asymmetric MMI power divider based on a phase change material, which comprises a silicon substrate, a silicon dioxide layer and a silicon waveguide layer which are arranged from bottom to top, wherein one side of the silicon waveguide layer is connected with a strip waveguide as input, and the other side of the silicon waveguide layer is connected with a plurality of strip waveguides as output; the silicon waveguide layer is divided into a plurality of nano pixel point type structures, filling areas are arranged in the nano pixel point type structures, and the material filled in each filling area is one of silicon, silicon dioxide and phase change materials. The utility model can realize on-chip adjustment of the splitting ratio without increasing the area of the device.

Description

Asymmetric MMI power distributor based on phase change material
Technical Field
The utility model relates to a power divider, in particular to an asymmetric MMI power divider based on a phase change material.
Background
With the information transmission and processing in the big data age, the requirements on hardware performance are continuously improved, and the traditional electric interconnection is challenged in various aspects such as bandwidth, time delay, power consumption and the like. Optical interconnection based on silicon photon technology is widely considered to replace electrical interconnection due to the advantages of high speed, low power consumption, compatibility of process and CMOS, and the like, and meets the requirements of mass data transmission on chip or between chips. One fundamental technology required to implement integrated optical internetworks is on-chip optical power distribution. A typical silicon-based passive device commonly used for optical power splitting in integrated optical circuits is a multimode interference coupler (Multimode Interference, MMI for short).
The MMI structure designed by the traditional method is generally based on a priori device model library, the adjustable structural parameters are few, the common size is tens of micrometers or hundreds of micrometers, the occupied area is large, and the requirement on the device integration level under the photoelectric integration background is difficult to meet. In recent years, reverse engineering has become the method of choice for designing compact passive devices. The designer firstly determines the core function of the device, defines a Figure of merit (FOM) to reflect the performance of the device, then divides the initial structure of the device into the combination of nano pixel points, continuously iterates simulation through an automatic control algorithm, and independently selects the material used by each pixel point, regulates the effective refractive index of the device, and gradually obtains the optimal FOM. The design method has the advantage that almost any initial structure can be optimized to have a well-behaved result, and can be used for designing an ultra-compact asymmetric multimode interference coupler structure.
With the deep development of the photoelectric integration technology, the defects of the traditional adjustable photon device are also increasingly prominent. Conventional on-chip tunable devices generally change the refractive index of silicon or polymer materials based on thermo-optic or electro-optic effects, but this approach is volatile and requires continuous energy to maintain a specific state, which is disadvantageous for large scale integration. The use of phase change materials mixed with silicon-based devices is an effective solution to achieve on-chip non-volatile tuning. The phase change material has two stable states of crystalline state and amorphous state, and can realize rapid, multiple and reversible conversion under the induction of electric or optical pulse. The two states of the phase change material have large refractive index differences and can be used for on-chip optical path or intensity adjustment, and meanwhile, as the two states are stable, no extra energy consumption is needed except for the phase change process.
The prior MMI power divider with reverse design comprises structural designs with special shapes such as asymmetry and the like, and has smaller occupied area, however, the design of combined phase change materials is less, the power distribution ratio of most structures is not adjustable, and the power distribution ratio is required to be optimized again in an iterating way to obtain a new pixel point arrangement structure so as to realize different light splitting ratios. If the beam splitting ratio is to be adjusted on the chip, other devices such as an optical switch and the like are required to be added at the output end of the device, so that the area of the device is indirectly increased.
Disclosure of Invention
The utility model aims to solve the technical problem of providing an asymmetric MMI power divider based on a phase change material, which can realize on-chip adjustment of a splitting ratio without increasing the area of a device.
The technical scheme adopted for solving the technical problems is as follows: the asymmetric MMI power distributor based on the phase change material comprises a silicon substrate, a silicon dioxide layer and a silicon waveguide layer which are arranged from bottom to top, wherein one side of the silicon waveguide layer is connected with a strip waveguide as input, and the other side of the silicon waveguide layer is connected with a plurality of strip waveguides as output; the silicon waveguide layer is divided into a plurality of nano pixel point type structures, filling areas are arranged in the nano pixel point type structures, and the material filled in each filling area is one of silicon, silicon dioxide and phase change materials.
The nano pixel point type structure is a square structure, and the filling area is positioned at the center of the square structure and is round.
The silicon waveguide is square, and the side length is 2.5 μm.
The strip waveguide as an input is provided at an edge position of one side of the silicon waveguide layer.
The phase change material is Ge 2 Sb 2 Se 4 Te 1 。
Advantageous effects
Due to the adoption of the technical scheme, compared with the prior art, the utility model has the following advantages and positive effects: the utility model combines the phase change material GSST with the 220nm SOI waveguide, provides a nonvolatile adjustable MMI power distributor, realizes on-chip switching of the splitting ratio through the refractive index difference of two states of the phase change material, and has practicability; the utility model realizes MMI power distributor with adjustable split ratio in compact design area of 2.5 μm and 2.5 μm, and has small occupation area, and meanwhile, the utility model adopts asymmetric structure, the input waveguide is arranged at the edge of the device, which is convenient for connection and expansion between devices and is beneficial for optical network integration.
Drawings
FIG. 1 is a schematic diagram of an asymmetric MMI power splitter in accordance with an embodiment of the utility model;
FIG. 2 is a flowchart of an optimization process for performing a first-round DBS algorithm in an embodiment of the utility model;
FIG. 3 is a block diagram of a device optimized by a first-round DBS algorithm in an embodiment of the utility model;
FIG. 4 is a 1550nm TE mode field diagram of the device after first round optimization in an embodiment of the utility model;
FIG. 5 is a flowchart of an optimization process of a secondary-round DBS algorithm of a device when a target crystalline state spectroscopic ratio is 1:1:2 in an embodiment of the utility model;
FIG. 6 is a block diagram of a device with GSST being amorphous after optimization by a secondary DBS algorithm in an embodiment of the utility model;
FIG. 7 is a graph of 1550nm TE mode field for a sub-round optimized GSST of the device in an amorphous state in an embodiment of the utility model;
FIG. 8 is a block diagram of a device with GSST being crystalline after optimization by a secondary DBS algorithm in an embodiment of the utility model;
FIG. 9 is a graph of 1550nm TE mode field for a sub-round optimized GSST of the device in crystalline state in an embodiment of the utility model;
FIG. 10 is a process diagram of optimization of the secondary DBS algorithm for a device with a target crystalline state split ratio of 1:2:1;
FIG. 11 is a graph of the optimization process of the secondary DBS algorithm for a device with a target crystalline state splitting ratio of 2:1:2.
Detailed Description
The utility model will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present utility model and are not intended to limit the scope of the present utility model. Furthermore, it should be understood that various changes and modifications can be made by one skilled in the art after reading the teachings of the present utility model, and such equivalents are intended to fall within the scope of the utility model as defined in the appended claims.
The embodiment of the utility model relates to an asymmetric MMI power divider based on a phase change material, which is shown in figure 1 and comprises a silicon substrate, a silicon dioxide layer and a silicon waveguide layer which are arranged from bottom to top, wherein one side of the silicon waveguide layer is connected with a strip waveguide as input, and the other side of the silicon waveguide layer is connected with a plurality of strip waveguides as output; the silicon waveguide layer is divided into a plurality of nano pixel point type structures, filling areas are arranged in the nano pixel point type structures, and the material filled in each filling area is one of silicon, silicon dioxide and phase change materials.
The initial material structure of the device comprises a silicon substrate and SiO of 2 mu m from bottom to top 2 Layer, 220nm Si waveguide (design layer) and SiO on top 2 And (3) cladding. The area of the device design area is 2.5 μm by 2.5 μm, and the width of the input and output waveguides is 500nm. The design layer is divided into a plurality of nano pixel point matrixes, the size of each nano pixel point matrix is 100nm x 100nm, a cylindrical hole with the center diameter of 90nm and the height of 220nm of the nano pixel point matrix is used as a filling area, and three types of materials capable of being filled in the filling area are respectively: si, siO 2 Or a phase change material. Wherein the material filled in the filling area can be randomly arranged, the phase change material is combined with the 220nm SOI waveguide in the embodiment, and a nonvolatile adjustable MMI power divider is provided, which utilizes the phase change materialThe refractive index difference of the two states enables on-chip switching of the split ratio.
Taking the device of fig. 1 as an example, in order to make the spectral ratio of three waveguides at the output end adjustable from 1:1:1 to m:n:p, in determining the material filled in the filling area, the present embodiment may use two direct binary search methods, a first objective function and a second objective function to determine, and specifically design the following procedure:
step 1, determining the area of MMI design area and the position of input/output port. Considering that the optical network scene requires smaller area occupied by device expansion, an input waveguide is arranged at the edge of a multimode region, so that an asymmetric MMI structure is formed. The input light source is set as 1550nm TE mode light source, and the transmittance T of the upper, middle and lower three output ports is collected upper 、T mid 、T lower Determining a figure of merit FOM 1 The calculation mode of (namely, the first objective function) is as follows:
FOM 1 ＝α×(1-T upper -T mid -T lower )+β×(|T upper -T mid |+|T mid -T lower |+|T lower -T upper |)
the optimization objective is to obtain lower parasitic loss and ensure that the transmittance of each port is basically the same (1×3 optical power sharing is realized), and FOM in the process 1 The definition of (2) preferably ensures low loss, thus having the weight coefficient α=0.8, β=0.2;
and 2, equally dividing the multimode interference area (i.e. the design layer) of the device into a plurality of square pixel points (i.e. a nano pixel point matrix), wherein each pixel point only has a cylinder with a fixed center size as a design part, and independently selecting the used materials. First of all, siO is determined 2 Distribution of pixel points. Each pixel point has two states of 0 and 1, wherein 1 represents that the pixel point is not etched (the material is Si), and 0 represents that the pixel point is etched (the material is SiO of the cladding layer) 2 )；
Step 3, randomly extracting a pixel point to change the state (from 0 to 1 or from 1 to 0), performing FDTD simulation once, and calculating FOM 1 Junction of result and pixel before changing stateComparing the results, if FOM 1 If the pixel point is smaller, a new state of the pixel point is reserved, otherwise, the pixel point is restored to the original state;
step 4, covering the operation of step 3 to each pixel point and operating each pixel point only once, wherein the process is an iteration round, if FOM is obtained after the iteration round 1 FOM is considered to be hardly reduced or has reached a desired level 1 Converging, finishing the first round of optimization, entering a step 5, adding a phase change material to realize nonvolatile adjustable spectral ratio, and if FOM 1 If not, returning to the step 3 to continue iteration; in this embodiment, the phase change material is Ge 2 Sb 2 Se 4 Te 1 。
Step 5, verifying whether the optimal structure obtained in the steps 1-4 can reach higher transmissivity or not, and the light splitting ratio between the output ports is 1:1:1.
and 6, performing a second round of DBS algorithm optimization. In the optimization process, only the pixel point with Si material is changed, and SiO 2 The pixel points are fixed. The pixel point optimized in the round has two states of 0 and 1, wherein 1 represents that the pixel point material is silicon, and 0 represents that the pixel point material is changed into a phase change material GSST;
step 7, the phase change material GSST has two stable states of amorphous (amorphlus) and crystalline (crystalline), so that two FDTD electromagnetic simulations are needed in each quality factor calculation process, and the transmittance of upper, middle and lower ports of MMI devices is respectively collected when all the phase change material GSST in the devices are in amorphous (a state) and crystalline (c state), FOM 2 (i.e., the second objective function) is defined as:
FOM 2 ＝α×(1-T upper-a -T mid-a -T lower-a )+
β×(|n·T upper-c -m·T mid-c |+|p·T mid-c -n·T lower-c |+|m·T lower-c -p·T upper-c |)
wherein, the expected spectral ratio is m: n: p, FOM when the phase change material GSST of the device is crystalline 2 Consists of two parts of quality factors of amorphous state and crystalline state respectively, wherein the quality factor of the first part is the additional loss of the device in the amorphous state,the second part is the difference between the transmittance of each output port and the expected spectral ratio in the crystalline state. Since the optimization of steps 2-4 has reduced the loss of the whole device, and the refractive index of a-GSST is basically the same as that of silicon, the light absorption capacity at 1550nm wave band is very weak, so the weight coefficient alpha of the amorphous quality factor in the total FOM is set to be 0.2; the core of the optimization is that the effect of c-GSST on the light absorption output by different ports meets the expected light splitting ratio, so beta is set to be 0.8;
step 8, after randomly extracting pixel points with Si as filling material and changing the material, performing FDTD simulation twice, wherein the first simulation makes all the phase change materials GSST in the device amorphous, the second simulation makes all the phase change materials GSST in the device crystalline, and FOM in step 7 2 The calculation method is used for calculating, the calculation result is compared with the calculation result when the state is unchanged, if the calculation result is smaller, the state of the nano pixel point type structure is reserved, otherwise, the nano pixel point type structure is restored to the original state;
step 9, randomly executing the operation of step 8 to each non-SiO 2 Completes one round of iteration, if FOM 2 FOM is considered to be no longer reduced or has reached a desired level 2 Converging and finishing optimization; if FOM 2 If not, the operation of step 8 is continued.
Taking the target performance of crystalline state light splitting ratio 1:1:2 as an example, the target light splitting ratio of the first round design process of the embodiment is 1:1:1, and the results are as shown in fig. 2-4, and the normalized transmittance of the upper, middle and lower three output single-mode waveguides at 1550nm wavelength is respectively as follows: 0.3125, 0.3153, 0.3118, the device attach loss is about 0.27dB. Completing the first round of optimization and determining SiO 2 After pixel distribution, m: n: p=1:1:2 is substituted into the FOM 2 In the definition formula, the second round of DBS optimization is performed. The optimized quality factor is divided into an amorphous state and a crystalline state, and the spectral ratio under the crystalline state is greatly optimized while the amorphous loss of the device is not seriously influenced, and the optimization process is shown in figure 5. Final optimization results: when GSST is amorphous, the normalized transmittance of the upper, middle and lower ports is 0.3117, 0.3206 and 0.3025 respectively, the spectral ratio is slightly deviated, but the additional loss is still relatively highLow level (0.29 dB); the normalized transmittance of the upper, middle and lower ports in the crystalline state is 0.1815, 0.1820 and 0.3634, respectively, and the ratio is basically 1:1:2. The pixel structure and the mode field diagram of the device in the amorphous state and the crystalline state are shown in fig. 6-9. In addition, this embodiment also provides other examples, in which the amorphous state spectral ratio is set to be 1:1:1, and devices with crystalline state spectral ratios of 1:2:1 and 2:1:2 are designed, and it can be found that after a certain number of pixel points are selected by the sub-round optimized DBS algorithm, the quality factor of the device is improved to a great extent.
It is easy to find that the combination of the phase change material GSST and the 220nm SOI waveguide provides a nonvolatile adjustable MMI power divider, and the on-chip switching of the light splitting ratio is realized through the refractive index difference of the two states of the phase change material, so that the power divider has practicability; the utility model realizes MMI power distributor with adjustable split ratio in compact design area of 2.5 μm and 2.5 μm, and has small occupation area, and meanwhile, the utility model adopts asymmetric structure, the input waveguide is arranged at the edge of the device, which is convenient for connection and expansion between devices and is beneficial for optical network integration.

Claims (5)

1. An asymmetric MMI power divider based on phase change materials comprises a silicon substrate, a silicon dioxide layer and a silicon waveguide layer which are arranged from bottom to top, and is characterized in that one side of the silicon waveguide layer is connected with one strip waveguide as input, and the other side of the silicon waveguide layer is connected with a plurality of strip waveguides as output; the silicon waveguide layer is divided into a plurality of nano pixel point type structures, filling areas are arranged in the nano pixel point type structures, and the material filled in each filling area is one of silicon, silicon dioxide and phase change materials.
2. The asymmetric MMI power divider based on phase change material of claim 1, wherein the nano-pixel dot structure is a square structure, and the filling region is located at the center of the square structure and is circular.
3. The asymmetric MMI power divider based on phase change material according to claim 1, wherein the silicon waveguide is square with a side length of 2.5 μm.
4. The asymmetric MMI power splitter based on phase change material according to claim 1, characterized in that a strip waveguide as input is arranged at an edge position on one side of the silicon waveguide layer.
5. The asymmetric MMI power divider based on phase change material of claim 1, wherein the phase change material is Ge 2 Sb 2 Se 4 Te 1 。
CN202320448550.4U 2023-03-10 2023-03-10 Asymmetric MMI power distributor based on phase change material Active CN219642035U (en)

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