Multifunctional silicon optical filter and design method thereof

Abstract

The invention relates to the field of optical elements, in particular to a multifunctional silicon optical filter and a design method thereof, an optical signal enters a vertical coupling grating and is output through the output end of the vertical coupling grating, and the output end of the vertical coupling grating is connected to the input end of a first multimode interference device; the two output ends of the first multi-mode interference device are connected to the two input ends of the second multi-mode interference device through the two waveguides respectively. Two output ends of the second multimode interference device are respectively connected with the input end of the dispersion-free box type response grating and the input end of the three-channel Hilbert transform type grating filter; a signal reflected by the dispersion-free box type response grating is output through the first output waveguide; and a signal reflected by the three-channel Hilbert transform type grating filter is output through the second output waveguide. The dispersion-free box type response grating enables the optical signal to have the characteristic of high side-mode rejection ratio, and can meet the requirements of a multifunctional silicon optical filter.

Description

Technical Field

[0001] The present invention belongs to the field of optical elements, and particularly relates to a multifunctional silicon optical filter and a design method thereof. Background Art

[0002] As a core component in all-optical communication network systems and optoelectronics fields, a silicon optical filter can be used for wavelength screening, separating optical signals of required wavelengths from mixed multi-wavelength optical signals, and filtering out optical signals of other wavelengths, thereby realizing the filtering function. It can be widely applied in directions such as wavelength selection, noise cancellation of optical amplifiers, gain equalization of optical signals, multiplexing / demultiplexing, frequency stabilization, channel selection of WDM (Wavelength Division Multiplexing), and add / drop channels.

[0003] However, the common vertical coupling grating of the existing silicon optical filter has a relatively low 3dB bandwidth, only about 30nm or so. When the input optical signal wavelength range is large, it is necessary to increase its bandwidth characteristics. It is difficult for a grating filter to achieve a box-shaped response with a high side mode suppression ratio. At the same time, it is also impossible to flexibly design the corresponding filter structure according to the required spectral lines. And grating devices such as grating filters are commonly used as band-stop filtering devices and cannot extract the required spectral signals. Summary of the Invention

[0004] In view of this, the present invention aims to provide a multifunctional silicon optical filter and a design method thereof. The dispersionless box-shaped response grating enables optical signals to have the characteristics of a high side mode suppression ratio and can meet the requirements of a multifunctional silicon optical filter.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows: A multifunctional silicon optical filter includes a vertical coupling grating, a first multimode interferometer, a second multimode interferometer, two grating structures, a first output waveguide, and a second output waveguide; the two grating structures include a dispersionless box-shaped response grating and a three-channel Hilbert transform type grating filter; An optical signal is incident on the vertical coupling grating and output through the output end of the vertical coupling grating. The output end of the vertical coupling grating is connected to the input end of the first multimode interferometer, and the two output ends of the first multimode interferometer are respectively connected to the two input ends of the second multimode interferometer through two waveguides; The two output ends of the second multimode interferometer are respectively connected to the input end of the dispersionless box-shaped response grating and the input end of the three-channel Hilbert transform type grating filter; the signal reflected by the dispersionless box-shaped response grating is output through the first output waveguide; the signal reflected by the three-channel Hilbert transform type grating filter is output through the second output waveguide.

[0006] Further, in the first direction, the size of the core layer of the vertical coupling grating is 10 μm to 30 μm; and / or In the second direction, the size of the core layer of the vertical coupling grating is 220 nm to 400 nm; and / or The core layer of the vertical coupling grating is provided with a plurality of engraved lines extending in the second direction and spaced apart in the first direction; wherein, the first direction is perpendicular to the second direction.

[0007] Further, it further includes a first thermal electrode and a second thermal electrode. The first thermal electrode is disposed at a position 2 μm to 5 μm above the core layer of one of the two waveguides, and the second thermal electrode is disposed at a position 2 μm to 5 μm above the core layer of the other of the two waveguides.

[0008] Further, the widths of the first thermal electrode and the second thermal electrode are 5 μm to 30 μm, and the lengths of the first thermal electrode and the second thermal electrode are 100 μm to 500 μm.

[0009] Further, the widths of the first multimode interferometer and the second multimode interferometer are 5 μm to 20 μm; the lengths of the first multimode interferometer and the second multimode interferometer are 50 μm to 1000 μm.

[0010] Further, the grating teeth of the grating structure are in a curve shape with periodic changes.

[0011] Further, the length of the grating structure is 500 μm to 2000 μm; and / or The width of the grating structure is 1 μm to 1.5 μm.

[0012] A design method for a multifunctional silicon optical filter is used to implement the design of the multifunctional silicon optical filter as described above; the design method includes: Generating a basic structure of the vertical coupling grating, and performing iterative optimization on the basic structure to determine the optimal optimization target value of the optimization target function; according to the optimal optimization target value, obtaining the target structure of the vertical coupling grating; Designing two grating structures by the layer decomposition method to obtain the target structures of the two grating structures; Selecting the first multimode interferometer and the second multimode interferometer; Connecting the vertical coupling grating, the first multimode interferometer, the second multimode interferometer, the two grating structures, the first output waveguide, and the second output waveguide in sequence.

[0013] Further, generating a basic structure of the vertical coupling grating and performing iterative optimization on the basic structure to determine the optimal optimization target value of the vertical coupling grating, including: Generating a basic structure of the vertical coupling grating, dividing the design area of the basic structure of the vertical coupling grating into equally spaced pixels, and representing the value of each pixel with a variable; Iteratively optimize the basic structure of the divided vertical coupling grating until the change amount of the optimization target value of the optimization objective function is less than the threshold and the optimization target value is the maximum value. At this time, the optimization target value is the optimal optimization target value.

[0014] Furthermore, design the two grating structures by the layer decomposition method to obtain the target structures of the two grating structures, including: Design the ideal spectral line of the grating structure, and obtain the achievable target spectral line according to the ideal spectral line; Divide the grating structure into multiple sub-gratings evenly according to the number of sampling periods, and determine the coupling coefficient of each sub-grating according to the target spectral line of the grating structure; Determine the phase corresponding to different positions of the grating structure according to the coupling coefficient of each sub-grating; Determine the target structure of the grating structure according to the phase corresponding to different positions of the grating structure.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects: The multifunctional silicon optical filter of the embodiment of the present invention includes a vertical coupling grating and two grating structures. Using this vertical coupling grating can reduce the frequency band requirements for the input optical signal and expand the range of input wavelengths. The two grating structures include a dispersionless box-shaped response grating and a three-channel Hilbert transform type grating filter. The dispersionless box-shaped response grating enables the optical signal to have the characteristic of high side mode suppression ratio, and the three-channel Hilbert transform type grating filter enables the optical signal to have three sharp dips, which can meet the requirements of the multifunctional silicon optical filter. Description of the Drawings

[0016] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 It is a schematic structural diagram of the multifunctional silicon optical filter described in the embodiment of the present invention; Figure 2 It is a flowchart of the design method of the multifunctional silicon optical filter described in the embodiment of the present invention; Figure 3 It is a related diagram of the vertical coupling grating of the multifunctional silicon optical filter described in the embodiment of the present invention; Figure 4 It is an effect verification diagram of the vertical coupling grating of the multifunctional silicon optical filter described in the embodiment of the present invention; Figure 5The ideal spectral line diagram of the grating structure of the multifunctional silicon optical filter according to the embodiment of the present invention; Figure 6 The corresponding relationship diagram between the relative intensity of the pulse response and the number of sampling periods of the grating structure of the multifunctional silicon optical filter according to the embodiment of the present invention; Figure 7 The target spectral line diagram of the grating structure of the multifunctional silicon optical filter according to the embodiment of the present invention; Figure 8 The corresponding relationship diagram between the grating position and the coupling coefficient of the grating structure of the multifunctional silicon optical filter according to the embodiment of the present invention; Figure 9 The corresponding relationship diagram between the period where the grating is located and the phase of the grating structure of the multifunctional silicon optical filter according to the embodiment of the present invention; Figure 10 The schematic diagram of the core layer of the grating structure of the multifunctional silicon optical filter according to the embodiment of the present invention and the corresponding relationship diagram between the distance between two adjacent convex parts and the period where the grating is located.

[0017] Explanation of reference numerals: 10. Multifunctional silicon optical filter; 11. Vertical coupling grating; 12. First multimode interferometer; 13. Second multimode interferometer; 14, 15. Grating structure; 16. First output waveguide; 17. Second output waveguide; 18, 19. Waveguide; 20. First thermal electrode; 21. Second thermal electrode. Detailed implementation manners

[0018] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Similar elements in different embodiments are labeled with related similar element numbers. In the following embodiments, many details are described to make the present invention better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, and methods. In some cases, some operations related to the present invention are not shown or described in the specification, in order to avoid the core part of the present invention being overwhelmed by too much description. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0019] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other to form various implementation manners. At the same time, the steps or actions in the method description can also be reordered or adjusted in an obvious manner by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for clearly describing a certain embodiment, and do not mean that they are the necessary sequences, unless it is stated that a certain sequence must be followed.

[0020] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0021] In the description of the present invention, it should be noted that, unless otherwise clearly defined and limited, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0022] The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0023] See Figure 1 As shown, an embodiment of the present invention provides a multifunctional silicon optical filter 10, and the multifunctional silicon optical filter 10 includes a vertical coupling grating 11, a first multimode interferometer 12, a second multimode interferometer 13, two grating structures 14, 15, a first output waveguide 16 and a second output waveguide 17. In this embodiment, the first multimode interferometer 12 is a 1×2 multimode interferometer, and the second multimode interferometer 13 is a 2×2 multimode interferometer.

[0024] The two grating structures 14 and 15 include a dispersionless box-type response grating and a three-channel Hilbert transform-type grating filter. Among them, the grating structure 14 is a dispersionless box-type response grating, and the grating structure 15 is a three-channel Hilbert transform-type grating filter.

[0025] The optical signal is incident on the vertical coupling grating 11 and is output through the output end of the vertical coupling grating 11. The output end of the vertical coupling grating 11 is connected to the input end of the first multimode interferometer 12. The two output ends of the first multimode interferometer 12 are respectively connected to the two input ends of the second multimode interferometer 13 through two waveguides 18 and 19. The two output ends of the second multimode interferometer 13 are respectively connected to the input end of the dispersionless box-type response grating and the input end of the three-channel Hilbert transform-type grating filter. The signal obtained by reflection from the dispersionless box-type response grating is output through the first output waveguide 16. The signal obtained by reflection from the three-channel Hilbert transform-type grating filter is output through the second output waveguide 17.

[0026] The multifunctional silicon optical filter 10 of the embodiment of the present invention includes a vertical coupling grating 11 and two grating structures 14 and 15. Using the vertical coupling grating 11 can reduce the frequency band requirements for the input optical signal and expand the range of input wavelengths. The two grating structures 14 and 15 include a dispersionless box-type response grating and a three-channel Hilbert transform-type grating filter. The dispersionless box-type response grating enables the optical signal to have the characteristic of high side mode suppression ratio, and the three-channel Hilbert transform-type grating filter enables the optical signal to have three sharp dips, which can meet the requirements of the multifunctional silicon optical filter 10.

[0027] In one embodiment, the widths of the first multimode interferometer 12 and the second multimode interferometer 13 are 5 μm to 20 μm, that is, the width of the first multimode interferometer 12 is 5 μm to 20 μm, and the width of the second multimode interferometer 13 is 5 μm to 20 μm. The lengths of the first multimode interferometer 12 and the second multimode interferometer 13 are 50 μm to 1000 μm, that is, the length of the first multimode interferometer 12 is 50 μm to 1000 μm, and the length of the second multimode interferometer 12 is 50 μm to 1000 μm. Among them, the length of the first multimode interferometer 12 is proportional to the square of the width, and the length of the second multimode interferometer 13 is proportional to the square of the width.

[0028] In one embodiment, the multifunctional silicon optical filter 10 further includes a first thermal electrode 20 and a second thermal electrode 21. The first thermal electrode 20 is disposed at a position 2 μm to 5 μm above the core layer of one of the two waveguides 18 and 19, and the second thermal electrode 21 is disposed at a position 2 μm to 5 μm above the core layer of the other of the two waveguides 18 and 19. The materials of the first thermal electrode 20 and the second thermal electrode 21 can be copper, aluminum, etc. By changing the voltages applied to the first thermal electrode 20 and the second thermal electrode 21, heating of the two waveguides 18 and 19 can be achieved to change the refractive indices of the two waveguides 18 and 19, so that the optical signal can be selectively transmitted to one of the input ends of the dispersionless box-shaped response grating and the input end of the three-channel Hilbert transform type grating filter, and dynamic channel switching of the optical signal can be realized. Among them, the material of the core layer of the two waveguides 18 and 19 is silicon, and the material of the outer cladding is silica, so that the thermal conductivity is relatively large and the channel switching speed of the optical signal is fast. Through experiments, it can be known that the channel switching time of the optical signal is within 20 μs, and the crosstalk between the channel for transmitting to the input end of the dispersionless box-shaped response grating and the channel for transmitting to the input end of the three-channel Hilbert transform type grating filter is less than -20 dB, and the effect of fast channel switching of the optical signal can be achieved.

[0029] In one embodiment, the widths of the first thermal electrode 20 and the second thermal electrode 21 are 5 μm to 30 μm, that is, the width of the first thermal electrode 20 is 5 μm to 30 μm, and the width of the second thermal electrode 21 is 5 μm to 30 μm. The lengths of the first thermal electrode 20 and the second thermal electrode 21 are 100 μm to 500 μm, that is, the length of the first thermal electrode 20 is 100 μm to 500 μm, and the length of the second thermal electrode 21 is 100 μm to 500 μm. In this way, the sizes of the first thermal electrode 20 and the second thermal electrode 21 are appropriate, which is beneficial to the fast channel switching of the optical signal.

[0030] In one embodiment, the grating teeth of the grating structure are in a curve shape with periodic changes. In some other embodiments, the shape of the grating teeth of the grating structure can also be rectangular, triangular, etc.

[0031] In one embodiment, the length of the grating structure is 500 μm to 2000 μm. In this embodiment, the length of the grating structure is 1200 μm.

[0032] In one embodiment, the width A of the grating structure is 1 μm to 1.5 μm (as Figure 10 shown). In this embodiment, the width A of the grating structure is 1.1 μm. In this way, the width of the grating structure is appropriate, so that the grating structure can realize a multimode waveguide, and the grating structure can become a band-pass filter instead of a band-stop filter, so that the response signal can be extracted more conveniently.

[0033] In one embodiment, the width A1 of the grating teeth of the grating structure is 50 nm to 200 nm (as Figure 10 shown) to form a grating structure for realizing spectral reflection.

[0034] In this embodiment, an optical signal in a wide wavelength band is incident on the vertical coupling grating 11. The power of the optical signal is evenly distributed through the first multimode interferometer 12. Then, by adjusting the voltages applied to the first heating electrode 20 and the second heating electrode 21, the optical signal passing through the second multimode interferometer 13 can enter the input end of the dispersionless box-shaped response grating or the input end of the three-channel Hilbert transform type grating filter. Among them, the signal reflected by the dispersionless box-shaped response grating becomes the TE1 mode. Due to the gap between the grating structure 14 and the first output waveguide 16, this TE1 mode is coupled into the TE0 mode and output through the first output waveguide 16. The signal reflected by the three-channel Hilbert transform type grating filter becomes the TE1 mode. Due to the gap between the grating structure 15 and the second output waveguide 17, this TE1 mode is coupled into the TE0 mode and output through the second output waveguide 17.

[0035] All the waveguides described above are of the SOI (Silicon On Insulator) structure. In this way, the size of the waveguide can be significantly reduced. In one embodiment, the material of the core layer of the waveguide described above is silicon, and the material of the cladding layer of the waveguide is silicon dioxide.

[0036] See Figure 2 shown. The present invention provides a design method for a multifunctional silicon optical filter for realizing the design of a multifunctional silicon optical filter. The design method includes steps S1 to S4.

[0037] Step S1: Generate the basic structure of the vertical coupling grating 11, and perform iterative optimization on the basic structure to determine the optimal optimization target value of the optimization target function. According to the optimal optimization target value, obtain the target structure of the vertical coupling grating 11.

[0038] In one embodiment, generating the basic structure of the vertical coupling grating 11 and performing iterative optimization on the basic structure to determine the optimal optimization target value of the vertical coupling grating 11 includes: Generate the basic structure of the vertical coupling grating 11, divide the design area of the basic structure of the vertical coupling grating 11 into equally spaced pixels, and represent the value of each pixel with the variable p. Among them, p at the cladding layer of the vertical coupling grating 11 is 0, and p at the core layer of the vertical coupling grating 11 is 1.

[0039] Iteratively optimize the basic structure of the divided vertical coupling grating 11 until the change amount of the optimization target value of the optimization objective function is less than the threshold and the optimization target value is the maximum value. At this time, the optimization target value is the optimal optimization target value. Algorithms such as the quasi-Newton method can be used to iteratively optimize the basic structure of the vertical coupling grating 11. As the number of iterative optimizations increases, the optimization target value can gradually tend to be stable and be the maximum value. At this time, the optimization target value is the optimal optimization target value.

[0040] The optimization objective function of the vertical coupling grating 11 The expression is:

[0041] Wherein, is the number of wavelengths of the optical signal incident on the vertical coupling grating 11, is the coupling power at the corresponding wavelength, is the electric field corresponding to the m-th wavelength.

[0042] In one embodiment, according to the optimal optimization target value of the vertical coupling grating 11, the target structure of the vertical coupling grating 11 is obtained, including: The structures of different vertical coupling gratings 11 correspond to different optimization target values. The structure of the vertical coupling grating 11 corresponding to the optimal optimization target value is the target structure of the vertical coupling grating 11. The coupling bandwidth of the target structure of the vertical coupling grating 11 obtained in this way is the largest, and it has a good response ability to optical signals of different wavelengths. Thus, the frequency band requirement of the input optical signal for the multifunctional silicon optical filter 10 can be reduced, and the range of input wavelengths is expanded.

[0043] See Figure 3 as shown, Figure 3 (a) is the corresponding relationship diagram between the number of iterative optimizations of the vertical coupling grating 11 and the value. It can be known that after about 50 iterative optimizations of the basic structure of the vertical coupling grating 11, the value gradually tends to be stable and is the maximum value, and the optimal optimization target value is about 0.23. Figure 3 (b) is a schematic diagram of the target structure of the vertical coupling grating 11. According to the optimal optimization target value of the vertical coupling grating 11, the target structure of the vertical coupling grating 11 is as shown in Figure 3 (b). Among them, the material of the core layer (light-colored area) of the vertical coupling grating 11 is silicon, and the material of the cladding layer (dark-colored area) is silicon dioxide.

[0044] In one embodiment, in the first direction, the size X of the core layer of the vertical coupling grating is 10 μm to 30 μm. In this embodiment, the size X of the core layer of the vertical coupling grating is 17.3 μm.

[0045] In one embodiment, in the second direction, the size of the core layer Z1 of the vertical coupling grating 11 is 220 nm to 400 nm. In this embodiment, the size of the core layer Z1 of the vertical coupling grating 11 is 220 nm.

[0046] In one embodiment, the core layer of the vertical coupling grating 11 is provided with a plurality of engraved lines extending in the second direction and arranged at intervals in the first direction. Wherein, the first direction is perpendicular to the second direction. In the second direction, the size Z2 of the engraved lines is 130 nm to 160 nm. In this embodiment, the size Z2 of the engraved lines is 150 nm. The sizes of the plurality of engraved lines provided on the vertical coupling grating 11 in the first direction may be the same or different. The distances between two adjacent engraved lines in the first direction may be the same or different. The sizes of the plurality of engraved lines provided on the waveguide of the vertical coupling grating 11 in the first direction and the distances between two adjacent engraved lines in the first direction are as Figure 3 shown in (c). It can be known that the size of the engraved lines in the first direction is between 0.35 μm and 0.9 μm, and the distance between two adjacent engraved lines is between 0.1 μm and 0.3 μm.

[0047] See Figure 4 as shown Figure 4 Figure (a) is a corresponding relationship diagram between the wavelength and the normalized coupling power of the vertical coupling grating 11. It can be known that when the vertical coupling grating 11 is the target structure, the maximum value of the normalized coupling power is about 0.27, which is slightly greater than -6 dB (that is, the coupling power corresponding to when the output power is one-fourth of the input power, that is, 0.25). And in the wavelength range of 1500 nm to 1570 nm, the normalized coupling power is greater than 0.16. The 3 dB bandwidth of the surface vertical coupling grating 11 is greater than 70 nm (that is, the difference between the two wavelengths corresponding to reaching half of the maximum coupling power). In this way, the effect of effectively reducing the frequency band requirements for the input optical signal and expanding the range of the input wavelength can be achieved. Figure 4 Figure (b) is a schematic diagram of the optical field of the vertical coupling grating 11. It can be shown that the optical signal can be successfully coupled and stably transmitted on the vertical coupling grating 11.

[0048] Step S2: Design the two grating structures 14 and 15 by the layer decomposition method to obtain the target structures of the two grating structures 14 and 15.

[0049] The two grating structures 14 and 15 include a non-dispersive box-type response grating and a three-channel Hilbert transform type grating filter. In addition to the non-dispersive box-type response grating and the three-channel Hilbert transform type grating filter, the grating structure can also be a dispersion response compensation type grating, a multi-channel non-dispersive box-type response grating, etc., or a grating for customizing spectral lines. The two output ends of the second multimode interferometer 13 are respectively connected to the input end of the non-dispersive box-type response grating and the input end of the three-channel Hilbert transform type grating filter. The non-dispersive box-type response grating enables the optical signal to have the characteristic of high side mode suppression ratio, and the three-channel Hilbert transform type grating filter enables the optical signal to have the characteristic of three sharp dips, with obvious advantages. Among them, the two grating structures 14 and 15 are designed by the layer decomposition method. The grating structure designed by the layer decomposition method is more flexible, and the dimensions of each part of the grating structure can be dynamically adjusted according to the shape of the required spectral line.

[0050] In one embodiment, the two grating structures 14 and 15 are designed by the layer decomposition method to obtain the target structures of the two grating structures 14 and 15, including step S21: Step S21: Design the ideal spectral line of the grating structure, and obtain the achievable target spectral line according to the ideal spectral line.

[0051] In this embodiment, the expression of the ideal spectral line of the non-dispersive box-type response grating is:

[0052]

[0053] The expression of the ideal spectral line of the three-channel Hilbert transform type grating filter is:

[0054]

[0055] Among them, is the peak reflectivity of the non-dispersive box-type response grating, is the detuning amount, is the wave number corresponding to the 3dB bandwidth of the ideal spectral line of the non-dispersive box-type response grating (in this embodiment, = 24mm -1 ) is the wavelength used in the simulation process, is the designed resonant wavelength, is the group refractive index of the TE0 mode optical signal entering the input end of the grating structure, is the group refractive index of the optical signal that is reversely coupled into the TE1 mode by the grating structure, is the peak reflectivity of the three-channel Hilbert transform type grating filter, is the bandwidth of the ideal spectral line of the three-channel Hilbert transform type grating filter (in this embodiment, = 8 nm). The wavelength range of the grating structure is 1515 nm to 1585 nm.

[0056] See Figure 5 as shown Figure 5 (a) is the ideal spectral line diagram of the dispersionless box-type response grating. Figure 5 (b) is the ideal spectral line diagram of the three-channel Hilbert transform type grating filter. Among them, the ideal bandwidth value of the dispersionless box-type response grating is about 4.4 nm, and the ideal peak reflectivity A m is about 0.9. The ideal peak reflectivity B m of the three-channel Hilbert transform type grating filter is about 0.8, and there are three sharp reflection valleys near 1550 nm, where the reflectivity can suddenly change from 0.8 to 0. However, Figure 5 the ideal spectral line shown is physically unrealizable. In order to obtain a realizable target spectral line, the ideal spectral line needs to be converted into an ideal optical frequency spectrum, and the inverse Fourier transform is performed on the ideal optical frequency spectrum to obtain its time-domain pulse response. The time-domain pulse response is truncated, and the truncated time-domain pulse response has negative time (i.e., t < 0) and is symmetric about the moment of t = 0. Among them, the number of sampling periods of the truncated time-domain pulse response needs to be greater than 50, less than the grating period number, and an integer. The larger the number of sampling periods, the closer the target spectral line is to the ideal spectral line. However, the larger the number of sampling periods, the greater the simulation calculation amount and the higher the processing requirement. In this embodiment, the number of sampling periods of the truncated time-domain pulse response is 300, and such a selected number of sampling periods is appropriate. The truncated time-domain pulse response is shifted to the positive time domain until all the pulse responses in the negative time domain become positive time domain. The Fourier transform can be performed on the new shifted time-domain pulse response to obtain the target optical frequency spectrum, and thus a realizable target spectral line can be obtained.

[0057] See Figure 6 as shown Figure 6 (a) is the corresponding relationship diagram between the pulse response relative intensity of the dispersionless box-type response grating and the number of sampling periods. Figure 6 (b) is the corresponding relationship diagram between the pulse response relative intensity of the three-channel Hilbert transform type grating filter and the number of sampling periods. It can be seen from Figure 6 that the number of sampling periods is 300, and at the position of half of the sampling period, the pulse response relative intensity is the largest.

[0058] SeeFigure 7 As shown Figure 7 Figure (a) is the target spectral line diagram of the dispersionless box-type response grating. Figure 7 Figure (b) is the target spectral line diagram of the three-channel Hilbert transform-type grating filter. In Figure 7 Figure (a), the bandwidth of the dispersionless box-type response grating is close to the ideal bandwidth, and the side mode suppression ratio of the dispersionless box-type response grating is about 50 dB. In Figure 7 Figure (b), the three-channel Hilbert transform-type grating filter has three reflection valleys near 1550 nm, the reflectivity at the reflection valleys is about -20 dB, and the reflectivity at the reflection valleys is very low. It can be known that the target spectral lines of the dispersionless box-type response grating and the three-channel Hilbert transform-type grating filter can meet the design requirements.

[0059] Step S22: The grating structure is evenly divided into multiple sub-gratings according to the number of sampling periods, and the coupling coefficient of each sub-grating is determined according to the target spectral line of the grating structure. In this embodiment, the length of the grating structure is 1200 μm, the number of sampling periods is 300, and the length of each sub-grating is 4 μm.

[0060] In one embodiment, the coupling coefficient of the first sub-grating can be determined according to the target spectral line of the grating structure. The first iteration can be performed on the achievable target spectral line, and the coupling coefficient of the first sub-grating can be determined. The coupling coefficient of the first sub-grating is expressed as:

[0061] where is the length of each sub-grating, is the reflection coefficient of the first sub-grating, is the conjugate complex number of the reflection coefficient of the first sub-grating. The reflection coefficient of the first sub-grating is expressed as:

[0062] where, a wavelength of 1 nm can have a set number of sampling points, and the adjacent two sampling points can be spaced 0.001 nm apart. is the total number of sampling points, is the reflectivity of the m-th sampling point in the achievable target spectral line during the first iteration. The achievable target spectral line of the grating structure described above is r1(δ). When designing the grating structure, and cannot be simulated according to a continuous function. When M is large enough, can approximately replace and 。

[0063] The spectral lines obtained after the (j - 1)-th iteration can be subjected to the j-th iteration, and the coupling coefficient of the j-th sub-grating can be determined. The coupling coefficient of the j-th sub-grating has the following expression:

[0064] where, is the reflection coefficient of the j-th sub-grating, is the reflection coefficient of the j-th sub-grating and its conjugate complex number. The reflection coefficient of the j-th sub-grating has the following expression:

[0065]

[0066] where, , is the number of sampling periods, is the total number of sampling points, is the imaginary unit, is the reflectivity of the m-th sampling point in the spectral lines during the j-th iteration, is the spectral lines of the grating structure during the j-th iteration, is the backward transmission field before the (j - 1)-th sub-grating, is the forward transmission field before the (j - 1)-th sub-grating, is the spectral lines of the grating structure during the (j - 1)-th iteration, is the reflection coefficient of the (j - 1)-th sub-grating. In this way, the coupling coefficient of each sub-grating can be determined by the above method.

[0067] See Figure 8 as shown. Figure 8 Figure (a) is a diagram showing the correspondence between the grating position and the coupling coefficient of a dispersionless box-type response grating. Figure 8 Figure (b) is a diagram showing the correspondence between the grating position and the coupling coefficient of a three-channel Hilbert transform type grating filter. As can be seen from Figure 8 Figure (a), the coupling coefficient at the middle position of the dispersionless box-type response grating is relatively large, exceeding 15 mm -1 , and the coupling coefficients at both ends are relatively small, so that a box-type response with a high side mode suppression ratio can be achieved.

[0068] Step S23: Determine the phases corresponding to different positions of the grating structure according to the coupling coefficient corresponding to each sub-grating.

[0069] According to the coupling coefficient corresponding to each sub-grating, the phases corresponding to both ends of each sub-grating can be determined. The phase The expression is as follows:

[0070]

[0071] Wherein, is the normalized value of the coupling coefficient corresponding to each sub-grating, is the length of each sub-grating, is the corresponding grating position (in this embodiment, when n = 0, the grating position is 0; when n = 1, the grating position is 4 μm; when n = 2, the grating position is 8 μm...), is the argument of the coupling coefficient corresponding to each sub-grating.

[0072] According to the phases corresponding to both ends of each sub-grating, the phases corresponding to different positions of each sub-grating can be determined through an interpolation algorithm, so as to determine the phases corresponding to different positions of the grating structure. In this embodiment, the grating structure can be divided according to the number of grating periods. The number of grating periods is 4000, and the grating period is about 300 nm, that is, the phase values corresponding to the positions every 300 nm on the grating structure can be determined.

[0073] See Figure 9 as shown in Figure 9 Figure (a) is a diagram showing the correspondence between the grating period and the phase of a dispersion-free box-shaped response grating. Figure 9 Figure (b) is a diagram showing the correspondence between the grating period and the phase of a three-channel Hilbert transform type grating filter. It can be known the specific phase values corresponding to different positions of the grating structure.

[0074] Step S24: Determine the target structure of the grating structure according to the phases corresponding to different positions of the grating structure.

[0075] See Figure 10 as shown in Figure 10 Figure (a) is a schematic diagram of the core layer of the grating structure. Among them, the width of the core layer of the grating structure is 1 μm to 1.5 μm. In this embodiment, the width of the core layer of the grating structure is 1.1 μm. The length of the convex part of the core layer of the grating structure is , Λ g is the grating period, and d(j) is the distance between two adjacent convex parts.

[0076] The expression for the distance d(j) between two adjacent convex parts is:

[0077] Wherein, is the number of grating periods, is the grating period, is the phase corresponding to the period where the grating is located.

[0078] Figure 10 (b) is a diagram showing the correspondence between the distance between two adjacent protrusions of the dispersion-free box-shaped response grating and the period where the grating is located. Figure 10 (c) is a diagram showing the correspondence between the distance between two adjacent protrusions of the three-channel Hilbert transform type grating filter and the period where the grating is located. It can be seen from this that the distance between two adjacent protrusions oscillates with the change of the grating position. In this way, the target structure of the grating structure can be determined, and the target structure of the grating structure can achieve the transmission effect of the required spectrum. Among them, the reflected signal obtained through the grating structure is the TE1 mode.

[0079] Step S3: Select the first multimode interferometer 12 and the second multimode interferometer 13. In this embodiment, the first multimode interferometer 12 is a 1×2 multimode interferometer, and the second multimode interferometer 13 is a 2×2 multimode interferometer.

[0080] Step S4: Connect the vertical coupling grating 11, the first multimode interferometer 12, the second multimode interferometer 13, two grating structures 14, 15, the first output waveguide 16 and the second output waveguide 17 in sequence. Specifically, the first output waveguide 16 can be connected to the grating structure 14, and the second output waveguide 17 can be connected to the grating structure 15. In this way, there is a gap between the grating structure 14 and the first output waveguide 16, and the TE1 mode is coupled into the TE0 mode and output through the first output waveguide 16. Similarly, the TE1 mode passing through the grating structure 15 can be output in the TE0 mode through the second output waveguide 17.

[0081] It should be understood that various forms of the flow shown above can be used, re-ordered, steps added or deleted. For example, the steps recorded in the disclosure of the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution disclosed in the present invention can be achieved. No limitation is made herein.

[0082] The above specific embodiments do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multifunctional silicon optical filter, characterized in that, It includes a vertical coupling grating, a first multimode interferometer, a second multimode interferometer, two grating structures, a first output waveguide and a second output waveguide; the two grating structures include a dispersionless box-shaped response grating and a three-channel Hilbert transform type grating filter; An optical signal is incident on the vertical coupling grating and output through the output end of the vertical coupling grating. The output end of the vertical coupling grating is connected to the input end of the first multimode interferometer, and the two output ends of the first multimode interferometer are respectively connected to the two input ends of the second multimode interferometer through two waveguides; The two output ends of the second multimode interferometer are respectively connected to the input end of the dispersionless box-shaped response grating and the input end of the three-channel Hilbert transform type grating filter; the signal obtained by reflection through the dispersionless box-shaped response grating is output through the first output waveguide; the signal obtained by reflection through the three-channel Hilbert transform type grating filter is output through the second output waveguide.

2. The multifunctional silicon optical filter according to claim 1, wherein In the first direction, the size of the core layer of the vertical coupling grating is 10μm - 30μm; and / or In the second direction, the size of the core layer of the vertical coupling grating is 220nm - 400nm; and / or The core layer of the vertical coupling grating is provided with a plurality of engraved lines extending in the second direction and arranged at intervals in the first direction; wherein, the first direction is perpendicular to the second direction.

3. The multifunctional silicon optical filter according to claim 1, wherein It further includes a first thermal electrode and a second thermal electrode. The first thermal electrode is disposed at a position 2μm - 5μm above the core layer of one of the two waveguides, and the second thermal electrode is disposed at a position 2μm - 5μm above the core layer of the other of the two waveguides.

4. The multifunctional silicon optical filter according to claim 3, wherein The widths of the first thermal electrode and the second thermal electrode are 5μm - 30μm, and the lengths of the first thermal electrode and the second thermal electrode are 100μm - 500μm.

5. The multifunctional silicon optical filter according to claim 1, characterized in that The widths of the first multimode interferometer and the second multimode interferometer are 5μm - 20μm; the lengths of the first multimode interferometer and the second multimode interferometer are 50μm - 1000μm.

6. The multifunctional silicon optical filter according to claim 1, wherein The grating teeth of the grating structure are in a curve shape with periodic changes.

7. The multifunctional silicon optical filter according to claim 6, wherein The length of the grating structure is 500μm - 2000μm; and / or The width of the grating structure is 1μm - 1.5μm.

8. A design method for a multifunctional silicon optical filter, characterized in that, For realizing the design of the multifunctional silicon optical filter as described in any one of claims 1 - 7; the design method includes: Generating the basic structure of the vertical coupling grating, performing iterative optimization on the basic structure to determine the optimal optimization target value of the optimization target function; obtaining the target structure of the vertical coupling grating according to the optimal optimization target value; Designing the two grating structures by the layer decomposition method to obtain the target structures of the two grating structures; Selecting the first multimode interferometer and the second multimode interferometer; Connecting the vertical coupling grating, the first multimode interferometer, the second multimode interferometer, the two grating structures, the first output waveguide and the second output waveguide in sequence.

9. The design method of the multifunctional silicon optical filter according to claim 8, characterized in that The basic structure for generating the vertical coupling grating is iteratively optimized to determine the optimal optimization target value of the vertical coupling grating, including: Generate the basic structure of the vertical coupling grating, divide the design area of the basic structure of the vertical coupling grating into equally spaced pixels, and represent the value of each pixel with a variable; Iteratively optimize the divided basic structure of the vertical coupling grating until the change amount of the optimization target value of the optimization target function is less than the threshold and the optimization target value is the maximum value. At this time, the optimization target value is the optimal optimization target value.

10. The design method of the multifunctional silicon optical filter according to claim 8, characterized in that, The design of the two grating structures by the layer decomposition method to obtain the target structures of the two grating structures includes: Design the ideal spectral line of the grating structure, and obtain the achievable target spectral line according to the ideal spectral line; Divide the grating structure into multiple sub-gratings evenly according to the number of sampling periods, and determine the coupling coefficient of each sub-grating according to the target spectral line of the grating structure; Determine the phases corresponding to different positions of the grating structure according to the coupling coefficient of each sub-grating; Determine the target structure of the grating structure according to the phases corresponding to different positions of the grating structure.

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