Multifunctional silicon optical filter and its design method

Abstract

The present invention relates to the field of optical elements, and in particular to a multifunctional silicon optical filter and a design method thereof. An optical signal is incident on a 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 a first multimode interferometer. The two output ends of the first multimode interferometer are respectively connected to the two input ends of a second multimode interferometer through two waveguides. The two output ends of the second multimode interferometer are respectively connected to the input end of a dispersion-free box-type response grating and the input end of a three-channel Hilbert transform grating filter; the signal reflected by the dispersion-free box-type response grating is output through the first output waveguide; the signal reflected by the three-channel Hilbert transform grating filter is output through the second output waveguide. The dispersion-free box-type response grating enables the optical signal to have the characteristics of a high side mode suppression ratio, which can meet the needs of a multifunctional silicon optical filter.

Description

Technical Field

[0001] The present invention belongs to the field of optical elements, and in particular 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, silicon optical filters can be used for wavelength selection, separating the desired wavelength from a mixed multi-wavelength optical signal and filtering out other wavelengths, thereby achieving filtering. They are widely used in wavelength selection, noise cancellation for optical amplifiers, gain equalization of optical signals, multiplexing / demultiplexing, frequency stabilization, WDM (Wavelength Division Multiplexing) channel selection, and add / drop traffic.

[0003] However, the 3dB bandwidth of conventional vertically coupled gratings in existing silicon optical filters is relatively low, at only approximately 30nm. Therefore, wide-bandwidth input optical signals require increased bandwidth. Grating filters struggle to achieve a box-shaped response with a high side-mode suppression ratio, and the filter structure cannot be flexibly designed to meet the desired spectral requirements. Furthermore, grating devices such as grating filters are often used as band-stop filters, making it difficult to extract the desired 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 dispersion-free box-type response grating enables the optical signal to have the characteristics of high side mode suppression ratio, which can meet the needs of multifunctional silicon optical filters.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] A multifunctional silicon optical filter includes a vertically coupled 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-type response grating and a three-channel Hilbert transform grating filter;

[0007] The 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. 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.

[0008] The two output ends of the second multimode interferometer are respectively connected to the input end of the dispersion-free box-type response grating and the input end of the three-channel Hilbert transform grating filter; the signal obtained by reflection from the dispersion-free box-type response grating is output through the first output waveguide; the signal obtained by reflection from the three-channel Hilbert transform grating filter is output through the second output waveguide.

[0009] Furthermore, in the first direction, the size of the core layer of the vertical coupling grating is 10 μm to 30 μm; and / or

[0010] In the second direction, the core layer of the vertical coupling grating has a size of 220 nm to 400 nm; and / or

[0011] The core layer of the vertical coupling grating is provided with a plurality of scribed lines extending along the second direction and arranged at intervals in the first direction; wherein the first direction is perpendicular to the second direction.

[0012] Furthermore, it also includes a first thermode and a second thermode, the first thermode is arranged 2μm~5μm on the core layer of one of the two waveguides, and the second thermode is arranged 2μm~5μm on the core layer of the other of the two waveguides.

[0013] Furthermore, the width of the first thermode and the second thermode is 5 μm to 30 μm, and the length of the first thermode and the second thermode is 100 μm to 500 μm.

[0014] Furthermore, the width of the first multimode interferometer and the second multimode interferometer is 5 μm to 20 μm; the length of the first multimode interferometer and the second multimode interferometer is 50 μm to 1000 μm.

[0015] Furthermore, the grating teeth of the grating structure are in a periodically changing curved shape.

[0016] Furthermore, the length of the grating structure is 500 μm to 2000 μm; and / or

[0017] The width of the grating structure is 1μm~1.5μm.

[0018] A design method for a multifunctional silicon optical filter is used to implement the design of the multifunctional silicon optical filter described above; the design method comprises:

[0019] Generating a basic structure of a vertically coupled grating, and iteratively optimizing the basic structure to determine an optimal optimization target value of an optimization objective function; and obtaining a target structure of the vertically coupled grating according to the optimal optimization target value;

[0020] The two grating structures are designed by layer decomposition method to obtain the target structures of the two grating structures;

[0021] Selecting a first multimode interferometer and a second multimode interferometer;

[0022] 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 are connected in sequence.

[0023] Furthermore, a basic structure of the vertically coupled grating is generated, and the basic structure is iteratively optimized to determine an optimal optimization target value of the vertically coupled grating, including:

[0024] generating a basic structure of a vertically coupled grating, dividing a design area of ​​the basic structure of the vertically coupled grating into equally spaced pixels, and representing a value of each pixel by a variable;

[0025] The basic structure of the divided vertical coupling grating is iteratively optimized until the change in the optimization target value of the optimization objective function is less than a threshold and the optimization target value is a maximum value. The optimization target value at this time is the optimal optimization target value.

[0026] Furthermore, the two grating structures are designed by layer decomposition method to obtain target structures of the two grating structures, including:

[0027] Design the ideal spectral line of the grating structure, and obtain the achievable target spectral line based on the ideal spectral line;

[0028] 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;

[0029] According to the coupling coefficient of each sub-grating, the phase corresponding to different positions of the grating structure is determined;

[0030] The target structure of the grating structure is determined according to the phases corresponding to different positions of the grating structure.

[0031] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0032] The multifunctional silicon optical filter of the present invention comprises a vertically coupled grating and two grating structures. The vertically coupled grating can reduce the frequency band requirements for the input optical signal, expanding the input wavelength range. The two grating structures include a dispersionless box-type response grating and a three-channel Hilbert transform grating filter. The dispersionless box-type response grating enables the optical signal to have a high side mode suppression ratio, while the three-channel Hilbert transform grating filter enables the optical signal to have three sharp notches, which can meet the requirements of a multifunctional silicon optical filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0034] Figure 1 This is a schematic structural diagram of the multifunctional silicon optical filter according to an embodiment of the present invention;

[0035] Figure 2 A flowchart of a method for designing a multifunctional silicon optical filter according to an embodiment of the present invention;

[0036] Figure 3 A correlation diagram of a vertically coupled grating of a multifunctional silicon optical filter according to an embodiment of the present invention;

[0037] Figure 4 This is a diagram illustrating the effect of the vertically coupled grating of the multifunctional silicon optical filter described in the embodiment of the present invention;

[0038] Figure 5 An ideal optical spectrum line diagram of the grating structure of the multifunctional silicon optical filter according to an embodiment of the present invention;

[0039] Figure 6 A graph showing the relationship between the relative intensity of the pulse response of the grating structure of the multifunctional silicon optical filter and the number of sampling cycles according to an embodiment of the present invention;

[0040] Figure 7 A target spectrum line diagram of the grating structure of the multifunctional silicon optical filter according to an embodiment of the present invention;

[0041] Figure 8 A diagram showing the corresponding relationship between the grating position and the coupling coefficient of the grating structure of the multifunctional silicon optical filter according to an embodiment of the present invention;

[0042] Figure 9 A diagram showing the corresponding relationship between the grating period and the phase of the grating structure of the multifunctional silicon optical filter according to an embodiment of the present invention;

[0043] Figure 10 This is a schematic diagram of the core layer of the grating structure of the multifunctional silicon optical filter described in an embodiment of the present invention, as well as a corresponding relationship diagram between the spacing between two adjacent protrusions and the period of the grating.

[0044] Description of reference numerals:

[0045] 10. Multifunctional silicon optical filter; 11. Vertically coupled 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 thermocouple; 21. Second thermocouple. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention. Similar elements in different embodiments use associated similar element numbers. In the following embodiments, many detailed descriptions are intended to enable the present invention to be 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, or methods. In some cases, some operations related to the present invention are not shown or described in the specification. This is 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. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0047] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other to form various implementation methods. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various orders in the description and the drawings are only for the purpose of clearly describing a certain embodiment and are not intended to be a required order, unless otherwise specified that a certain order must be followed.

[0048] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are 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 cannot be understood as a limitation on 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. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0049] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art can understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0050] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0051] See also Figure 1 As shown, an embodiment of the present invention provides a multifunctional silicon optical filter 10, which includes a vertically coupled grating 11, a first multimode interferometer 12, a second multimode interferometer 13, two grating structures 14 and 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.

[0052] The two grating structures 14 and 15 include a dispersionless box-type response grating and a three-channel Hilbert transform grating filter, wherein the grating structure 14 is a dispersionless box-type response grating and the grating structure 15 is a three-channel Hilbert transform grating filter.

[0053] The optical signal is incident on the vertical coupling grating 11 and output through the output of the vertical coupling grating 11. The output of the vertical coupling grating 11 is connected to the input of the first multimode interferometer 12. The two outputs of the first multimode interferometer 12 are connected to the two inputs of the second multimode interferometer 13 via two waveguides 18 and 19. The two outputs of the second multimode interferometer 13 are connected to the input of the dispersion-free box-type response grating and the input of the three-channel Hilbert transform grating filter, respectively. The signal reflected by the dispersion-free box-type response grating is output through the first output waveguide 16. The signal reflected by the three-channel Hilbert transform grating filter is output through the second output waveguide 17.

[0054] The multifunctional silicon optical filter 10 of the present invention comprises a vertically coupled grating 11 and two grating structures 14 and 15. The use of the vertically coupled grating 11 can reduce the frequency band requirements for the input optical signal, thereby expanding the input wavelength range. The two grating structures 14 and 15 comprise a dispersionless box-type response grating and a three-channel Hilbert transform grating filter. The dispersionless box-type response grating enables the optical signal to have a high side mode suppression ratio, while the three-channel Hilbert transform grating filter enables the optical signal to have three sharp notches, which can meet the requirements of the multifunctional silicon optical filter 10.

[0055] In one embodiment, the width of the first multimode interferometer 12 and the second multimode interferometer 13 is 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 length of the first multimode interferometer 12 and the second multimode interferometer 13 is 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 13 is 50 μm to 1000 μm. 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.

[0056] In one embodiment, the multifunctional silicon optical filter 10 further includes a first thermode 20 and a second thermode 21. The first thermode 20 is disposed 2 μm to 5 μm above the core layer of one of the two waveguides 18 and 19, and the second thermode 21 is disposed 2 μm to 5 μm above the core layer of the other of the two waveguides 18 and 19. The first thermode 20 and the second thermode 21 can be made of copper, aluminum, or the like. By varying the voltage applied to the first thermode 20 and the second thermode 21, the waveguides 18 and 19 can be heated to change their refractive indices, allowing optical signals to be selectively transmitted to either the input of the dispersionless box-type response grating or the input of the three-channel Hilbert transform grating filter, thereby achieving dynamic channel switching of the optical signal. Among them, the core layer material of the two waveguides 18 and 19 is silicon, and the outer cladding material is silicon dioxide, which makes the thermal conductivity larger and the channel switching speed of the optical signal fast. Experiments show that the channel switching time of the optical signal is within 20μs. The channel transmitting to the input end of the dispersionless box-type response grating and the channel transmitting to the input end of the three-channel Hilbert transform grating filter have a crosstalk between the two channels less than -20dB, which can achieve the effect of fast channel switching of the optical signal.

[0057] In one embodiment, the width of the first thermode 20 and the second thermode 21 is 5 μm to 30 μm, that is, the width of the first thermode 20 is 5 μm to 30 μm, and the width of the second thermode 21 is 5 μm to 30 μm. The length of the first thermode 20 and the second thermode 21 is 100 μm to 500 μm, that is, the length of the first thermode 20 is 100 μm to 500 μm, and the length of the second thermode 21 is 100 μm to 500 μm. In this way, the dimensions of the first thermode 20 and the second thermode 21 are appropriate, which is conducive to the rapid switching of the optical signal channel.

[0058] In one embodiment, the grating teeth of the grating structure are in the shape of a periodically changing curve. In other embodiments, the grating teeth of the grating structure can also be in the shape of a rectangle, a triangle, etc.

[0059] 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.

[0060] In one embodiment, the width A of the grating structure is 1 μm to 1.5 μm (e.g. Figure 10 As shown in FIG. 1 ). In this embodiment, the width A of the grating structure is 1.1 μm. This suitable width of the grating structure enables the grating structure to implement a multimode waveguide, and the grating structure can be transformed into a bandpass filter rather than a bandstop filter, making it easier to extract the response signal.

[0061] In one embodiment, the width A1 of the grating teeth of the grating structure is 50 nm to 200 nm (e.g. Figure 10 as shown), to form a grating structure to achieve spectral reflection.

[0062] In this embodiment, a wideband optical signal is incident on the vertical coupling grating 11, and 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 dispersion-free box-type response grating or the input end of the three-channel Hilbert transform grating filter. The signal reflected by the dispersion-free box-type response grating becomes the TE1 mode. Due to the gap between the grating structure 14 and the first output waveguide 16, the 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 grating filter becomes the TE1 mode. Due to the gap between the grating structure 15 and the second output waveguide 17, the TE1 mode is coupled into the TE0 mode and output through the second output waveguide 17.

[0063] The waveguides described above are all SOI (Silicon On Insulator) structures. This significantly reduces the size of the waveguides. In one embodiment, the core layer of the waveguides described above is made of silicon, and the cladding layer of the waveguides is made of silicon dioxide.

[0064] See also Figure 2 As shown, the present invention provides a design method for a multifunctional silicon optical filter, which is used to implement the design of a multifunctional silicon optical filter. The design method includes steps S1 to S4.

[0065] Step S1: Generate a basic structure of the vertical coupling grating 11, perform iterative optimization on the basic structure to determine the optimal optimization target value of the optimization objective function, and obtain the target structure of the vertical coupling grating 11 according to the optimal optimization target value.

[0066] In one embodiment, generating a basic structure of the vertical coupling grating 11 and iteratively optimizing the basic structure to determine an optimal optimization target value of the vertical coupling grating 11 includes:

[0067] Generate a basic structure of the vertical coupling grating 11, and divide the design area of ​​the basic structure of the vertical coupling grating 11 into equally spaced pixels, with the value of each pixel represented by a variable p. Here, p is 0 at the cladding layer of the vertical coupling grating 11, and p is 1 at the core layer of the vertical coupling grating 11.

[0068] The divided basic structure of the vertical coupling grating 11 is iteratively optimized until the change in the optimization target value of the optimization objective function is less than a threshold value and the optimization target value reaches a maximum value, at which point the optimization target value is the optimal optimization target value. An algorithm such as a 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 gradually stabilizes and reaches a maximum value, at which point the optimization target value is the optimal optimization target value.

[0069] Optimization objective function of vertically coupled grating 11 The expression is:

[0070]

[0071] in, is the wavelength number of the optical signal incident on the vertical coupling grating 11, is the coupled power at the corresponding wavelength, is the electric field corresponding to the mth wavelength.

[0072] In one embodiment, according to the optimal optimization target value of the vertical coupling grating 11, a target structure of the vertical coupling grating 11 is obtained, including:

[0073] Different vertical coupling grating 11 structures correspond to different optimization target values. The vertical coupling grating 11 structure corresponding to the optimal optimization target value is the target structure of the vertical coupling grating 11. The target structure of the vertical coupling grating 11 obtained in this way has the largest coupling bandwidth and good responsiveness to optical signals of different wavelengths. This reduces the frequency band requirements of the multifunctional silicon optical filter 10 for the input optical signal and expands the input wavelength range.

[0074] See also Figure 3 As shown, Figure 3 (a) is the number of iterations of the vertical coupling grating 11 and It can be seen that after about 50 iterations of optimization of the basic structure of the vertical coupling grating 11, The value gradually tends to be stable and reaches the maximum value, so 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 obtained as follows: Figure 3 As shown in (b), 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.

[0075] 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.

[0076] 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.

[0077] In one embodiment, the core layer of the vertical coupling grating 11 is provided with a plurality of scribed lines extending along the second direction and spaced apart in the first direction. The first direction is perpendicular to the second direction. In the second direction, the size Z2 of the scribed lines is 130nm~160nm. In this embodiment, the size Z2 of the scribed lines is 150nm. The sizes of the plurality of scribed lines provided on the vertical coupling grating 11 in the first direction may be the same or different. The distance between two adjacent scribed lines in the first direction may be the same or different. The sizes of the plurality of scribed lines provided on the waveguide of the vertical coupling grating 11 in the first direction and the distance between two adjacent scribed lines in the first direction are as follows: Figure 3 As shown in (c), it can be seen that the size of the scribed lines in the first direction is between 0.35 μm and 0.9 μm, and the distance between two adjacent scribed lines is between 0.1 μm and 0.3 μm.

[0078] See also Figure 4 As shown, Figure 4 (a) is a graph showing the relationship between the wavelength and normalized coupling power of the vertical coupling grating 11. It can be seen that when the vertical coupling grating 11 is the target structure, the maximum normalized coupling power is approximately 0.27, slightly greater than -6dB (i.e., the coupling power corresponding to a quarter of the input power, i.e., 0.25). Furthermore, within the wavelength range of 1500nm to 1570nm, the normalized coupling power is greater than 0.16. The 3dB bandwidth of the surface vertical coupling grating 11 is greater than 70nm (i.e., the difference between the two wavelengths corresponding to half the maximum coupling power). This effectively reduces the frequency band requirements for the input optical signal and expands the input wavelength range. Figure 4 (b) is a schematic diagram of the light field of the vertical coupling grating 11. It can be seen that the optical signal can be smoothly coupled on the vertical coupling grating 11 and can be stably transmitted.

[0079] Step S2: Design the two grating structures 14 and 15 by using a layer decomposition method to obtain target structures of the two grating structures 14 and 15.

[0080] The two grating structures 14 and 15 include a dispersion-free box-type response grating and a three-channel Hilbert transform grating filter. In addition to the dispersion-free box-type response grating and the three-channel Hilbert transform grating filter, the grating structure can also be a dispersion response compensation grating, a multi-channel dispersion-free box-type response grating, etc., or a grating with a customized spectral line. The two output ends of the second multimode interferometer 13 are respectively connected to the input end of the dispersion-free box-type response grating and the input end of the three-channel Hilbert transform grating filter. The dispersion-free box-type response grating enables the optical signal to have the characteristics of a high side mode suppression ratio, and the three-channel Hilbert transform grating filter enables the optical signal to have the characteristics of three sharp depressions, which has 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 size of each part of the grating structure can be dynamically adjusted according to the shape of the required spectral line.

[0081] In one embodiment, the two grating structures 14 and 15 are designed by a layer decomposition method to obtain target structures of the two grating structures 14 and 15, including step S21:

[0082] Step S21: Designing the ideal spectral lines of the grating structure, and obtaining the achievable target spectral lines based on the ideal spectral lines.

[0083] In this embodiment, the ideal spectrum line of the dispersion-free box-type response grating is expressed as for:

[0084]

[0085]

[0086] The expression of the ideal spectral line of the three-channel Hilbert transform grating filter for:

[0087]

[0088]

[0089] in, is the peak reflectivity of the dispersionless box-type response grating, is the detuning amount, is the wave value corresponding to the 3dB bandwidth of the ideal spectral line of the dispersion-free 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 reversely coupled into the TE1 mode by the grating structure, is the peak reflectivity of the three-channel Hilbert transform grating filter, is the bandwidth of the ideal spectral line of the three-channel Hilbert transform grating filter (in this embodiment, =8nm). The wavelength range of the grating structure is 1515nm~1585nm.

[0090] See also Figure 5 As shown, Figure 5 (a) is the ideal spectrum line diagram of the dispersion-free box-type response grating. Figure 5 (b) is the ideal spectrum line diagram of the three-channel Hilbert transform grating filter. Among them, the ideal bandwidth value of the dispersion-free box response grating is about 4.4nm, and the ideal peak reflectivity A m The ideal peak reflectivity B of the three-channel Hilbert transform grating filter is about 0.9. m It is about 0.8, and has three sharp reflection valleys near 1550nm, where the reflectivity can suddenly change from 0.8 to 0. Figure 5 The ideal spectral line shown is physically unrealizable. To obtain a achievable target spectral line, the ideal spectral line needs to be converted into an ideal optical spectrum and then subjected to an inverse Fourier transform to obtain its time-domain impulse response. The time-domain impulse response is truncated, so that the truncated time-domain impulse response has negative time (i.e., t < 0) and is symmetric about t = 0. The sampling period of the truncated time-domain impulse response must be greater than 50, less than the number of grating periods, and an integer. The larger the sampling period, the closer the target spectral line is to the ideal spectral line. However, a larger sampling period increases the simulation computational complexity and increases the processing requirements. In this embodiment, the sampling period of the truncated time-domain impulse response is 300, which is an appropriate number of sampling periods. The truncated time-domain impulse response is shifted toward the positive time domain until all negative time-domain impulse responses become positive. The shifted new time-domain impulse response can be Fourier transformed to obtain the target optical spectrum, thereby obtaining a achievable target spectral line.

[0091] See also Figure 6 As shown, Figure 6 (a) is a graph showing the relationship between the relative intensity of the impulse response of the dispersion-free box-type response grating and the number of sampling cycles. Figure 6 (b) is the corresponding relationship between the relative intensity of the impulse response of the three-channel Hilbert transform grating filter and the number of sampling cycles. Figure 6It can be seen that the number of sampling periods is 300, and the relative intensity of the impulse response is the largest at the position of half of the sampling period.

[0092] See also Figure 7 As shown, Figure 7 (a) is the target spectrum line diagram of the dispersion-free box-type response grating. Figure 7 (b) is the target spectrum line diagram of the three-channel Hilbert transform grating filter. Figure 7 In (a), the bandwidth of the dispersion-free box-type response grating is close to the ideal bandwidth, and the side mode suppression ratio of the dispersion-free box-type response grating is about 50 dB. Figure 7 In (b), the three-channel Hilbert transform grating filter exhibits three reflection dips near 1550nm, with a reflectivity of approximately -20dB in the dips and very low reflectivity outside the dips. This indicates that the target spectral lines of the dispersionless box-type response grating and the three-channel Hilbert transform grating filter meet the design requirements.

[0093] Step S22: The grating structure is evenly divided into multiple sub-gratings according to the number of sampling periods. The coupling coefficient of each sub-grating is determined based on the target spectral line of the grating structure. In this embodiment, the grating structure has a length of 1200 μm, the number of sampling periods is 300, and the length of each sub-grating is 4 μm.

[0094] In one embodiment, the coupling coefficient of the first sub-grating can be determined based on the target spectral line of the grating structure. A first iteration can be performed on the achievable target spectral line and the coupling coefficient of the first sub-grating can be determined. The expression is:

[0095]

[0096] in, is the length of each sub-grating, is the reflection coefficient of the first sub-grating, is the reflection coefficient of the first sub-grating The conjugate complex number of the first sub-grating The expression is:

[0097]

[0098] A wavelength of 1 nm may have a set number of sampling points, and the interval between two adjacent sampling points may be 0.001 nm. is the total number of sampling points, is the reflectivity of the mth sampling point in the target spectrum line that can be achieved in the first iteration. The target spectrum line that can be achieved for the grating structure mentioned above is r1(δ). When designing the grating structure, and It is impossible to simulate according to the continuous function. When M is large enough, Can be approximately replaced and .

[0099] The spectral line obtained after the j-1th iteration can be iterated for the jth time, and the coupling coefficient of the jth sub-grating can be determined. The expression is:

[0100]

[0101] in, is the reflection coefficient of the j-th sub-grating, is the reflection coefficient of the j-th sub-grating The conjugate complex number of the j-th sub-grating. The expression is:

[0102]

[0103]

[0104] in, , is the number of sampling cycles, is the total number of sampling points, is an imaginary unit, is the reflectance of the mth sampling point in the spectrum line at the jth iteration, is the spectral line of the grating structure at the jth iteration, is the backward transmission field before the j-1th sub-grating, is the forward transmission field before the j-1th sub-grating, is the spectral line of the grating structure at the j-1th iteration, is the reflection coefficient of the j-1th sub-grating. In this way, the coupling coefficient of each sub-grating can be determined by the above method.

[0105] See also Figure 8 As shown, Figure 8 (a) is the corresponding relationship between the grating position and the coupling coefficient of the dispersion-free box-type response grating. Figure 8 (b) is the corresponding relationship between the grating position and the coupling coefficient of the three-channel Hilbert transform grating filter. Figure 8(a) It can be seen that the coupling coefficient in the middle of the dispersion-free box-type response grating is large, exceeding 15mm -1 , the coupling coefficient at both ends is small, so a box-type response with high side mode suppression ratio can be achieved.

[0106] Step S23: determining the phases corresponding to different positions of the grating structure according to the coupling coefficient corresponding to each sub-grating.

[0107] The phases at both ends of each sub-grating can be determined based on the coupling coefficients of each sub-grating. The expression is as follows:

[0108]

[0109]

[0110] in, 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 4μm; when n=2, the grating position is 8μm...), is the argument of the coupling coefficient corresponding to each sub-grating.

[0111] Based on the phases at both ends of each sub-grating, an interpolation algorithm can be used to determine the phases corresponding to different positions of each sub-grating, thereby determining 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. If the number of grating periods is 4000, the grating period is approximately 300 nm, meaning that the phase values ​​corresponding to positions every 300 nm on the grating structure can be determined.

[0112] See also Figure 9 As shown, Figure 9 (a) is the corresponding relationship between the grating period and phase of the dispersion-free box-type response grating. Figure 9 (b) shows the relationship between the period and phase of the grating in a three-channel Hilbert transform grating filter. It can be seen that different positions of the grating structure correspond to specific phase values.

[0113] Step S24: determining the target structure of the grating structure according to the phases corresponding to different positions of the grating structure.

[0114] See also Figure 10 As shown, Figure 10(a) is a schematic diagram of the core layer of the grating structure. 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 raised 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 protrusions.

[0115] The expression of the distance d(j) between two adjacent protrusions is:

[0116]

[0117] in, is the grating period number, is the grating period, is the phase corresponding to the period of the grating.

[0118] Figure 10 (b) is a graph showing the relationship between the spacing between two adjacent raised parts of the dispersion-free box-type response grating and the period of the grating. Figure 10 (c) shows the relationship between the spacing between two adjacent raised portions of a three-channel Hilbert transform grating filter and the grating period. As can be seen, the spacing between two adjacent raised portions fluctuates with the grating position, thus determining the target structure of the grating structure, which can achieve the desired spectral transmission effect. The reflected signal obtained after the grating structure is the TE1 mode.

[0119] Step S3: Selecting a first multimode interferometer 12 and a 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.

[0120] Step S4: The vertically coupled grating 11, the first multimode interferometer 12, the second multimode interferometer 13, the two grating structures 14 and 15, the first output waveguide 16, and the second output waveguide 17 are sequentially connected. 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 to the TE0 mode and output through the first output waveguide 16. Similarly, the TE1 mode passing through the grating structure 15 can be output as the TE0 mode through the second output waveguide 17.

[0121] It should be understood that the various forms of the processes shown above can be used to reorder, add, or delete steps. For example, the steps described in the present disclosure can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solutions disclosed in the present disclosure can be achieved. This is not limited herein.

[0122] The above specific embodiments do not limit the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may be made based on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A multifunctional silicon optical filter, characterized in that: The invention comprises a vertically coupled 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 are a dispersionless box-type response grating and a three-channel Hilbert transform grating filter respectively; 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 dispersion-free box-type response grating and the input end of the three-channel Hilbert transform grating filter; the signal obtained by reflection from the dispersion-free box-type response grating is output through the first output waveguide; the signal obtained by reflection from the three-channel Hilbert transform grating filter is output through the second output waveguide.

2. The multifunctional silicon optical filter according to claim 1, characterized in that: In the first direction, the core layer of the vertical coupling grating has a size of 10 μm to 30 μm; and / or In the second direction, the core layer of the vertical coupling grating has a size of 220 nm to 400 nm; and / or The core layer of the vertical coupling grating is provided with a plurality of scribed lines extending along 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, characterized in that: It also includes a first thermode and a second thermode, wherein the first thermode is arranged 2 μm to 5 μm above the core layer of one of the two waveguides, and the second thermode is arranged 2 μm to 5 μm above the core layer of the other of the two waveguides.

4. The multifunctional silicon optical filter according to claim 3, characterized in that: The widths of the first thermode and the second thermode are respectively 5 μm to 30 μm, and the lengths of the first thermode and the second thermode are respectively 100 μm to 500 μm.

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 5 μm to 20 μm respectively; the lengths of the first multimode interferometer and the second multimode interferometer are 50 μm to 1000 μm respectively.

6. The multifunctional silicon optical filter according to claim 1, characterized in that: The grating teeth of the grating structure are in a periodically changing curve shape.

7. The multifunctional silicon optical filter according to claim 6, characterized in that: 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.

8. A design method for a multifunctional silicon optical filter, characterized in that: Used to implement the design of a multifunctional silicon optical filter according to any one of claims 1 to 7; the design method comprises: Generating a basic structure of the vertically coupled grating, and iteratively optimizing the basic structure to determine an optimal optimization target value of an optimization objective function; and obtaining a target structure of the vertically coupled grating according to the optimal optimization target value; Designing the two grating structures by a layer decomposition method to obtain target structures of the two grating structures; Selecting the first multimode interferometer and the second multimode interferometer; 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 are connected in sequence.

9. The method for designing a multifunctional silicon optical filter according to claim 8, wherein: Generating a basic structure of the vertical coupling grating and iteratively optimizing the basic structure to determine an optimal optimization target value of the vertical coupling grating includes: generating a basic structure of the vertically coupled grating, dividing a design area of ​​the basic structure of the vertically coupled grating into equally spaced pixels, wherein the value of each pixel is represented by a variable; The divided basic structure of the vertical coupling grating is iteratively optimized until the change in the optimization target value of the optimization objective function is less than a threshold value and the optimization target value is a maximum value, and the optimization target value at this time is the optimal optimization target value.

10. The design method of a multifunctional silicon optical filter according to claim 8, characterized in that: The step of designing the two grating structures by a layer decomposition method to obtain target structures of the two grating structures includes: Designing an ideal spectral line of the grating structure, and obtaining an achievable target spectral line based on the ideal spectral line; Evenly dividing the grating structure into multiple sub-gratings according to the number of sampling periods, and determining the coupling coefficient of each sub-grating according to the target spectral line of the grating structure; Determining the phases corresponding to different positions of the grating structure according to the coupling coefficient of each sub-grating; The target structure of the grating structure is determined according to the phases corresponding to different positions of the grating structure.

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