CN117891028A - Ultra-compact broadband wavelength demultiplexer and design method thereof - Google Patents
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Abstract
The invention provides an ultra-compact broadband wavelength demultiplexer and a design method thereof, wherein the wavelength demultiplexer comprises a packaging layer, and an input waveguide and an output waveguide which are wrapped in the packaging layer; one end of the input waveguide is an input end, the other end of the input waveguide is an output end, a transition section is arranged between the input end and the output end of the input waveguide, a directional coupling region is formed between the transition section and the output waveguide, and rectangular gratings arranged in an array are arranged in the directional coupling region; the distance between the input end of the input waveguide and the output waveguide, the length of the directional coupling region, the length, the width, the pitch length and the pitch duty ratio of the rectangular grating are optimized by adopting a particle swarm optimization algorithm. The wavelength demultiplexer has the advantages of large bandwidth, compact structure, further improved integration level and better device performance.
Description
Technical Field
The invention belongs to the field of optical communication, and particularly relates to an ultra-compact broadband wavelength demultiplexer based on a particle swarm optimization reverse design method and a design method thereof.
Background
In order to meet the increasing demand of ultra-high link communication capacity, wavelength division multiplexing technology is widely applied in the field of optical communication. Wavelength division multiplexing uses each operating wavelength as an independent channel to transmit optical signal data. In recent years, on-chip wavelength demultiplexers built on silicon-on-insulator platforms have attracted considerable attention in the industry due to the potential of monolithic photonic/optoelectronic integrated circuits. In on-chip wavelength demultiplexers, duplex or triplexers are the core and fundamental components of multiplexing systems. In general, such devices have several major index requirements, namely low insertion loss, high extinction ratio, small size, and ease of fabrication. Wavelength demultiplexers designed based on different approaches have been reported to date with better performance, such as mach-zehnder interferometer multimode interference (MMI) couplers. However, they typically have relatively large device dimensions (e.g., greater than 50 μm). In order to improve the integration level, it is necessary to further reduce the device size, and therefore, it is necessary to design a wavelength demultiplexer having a more compact structure and more excellent operation performance.
However, the design concept and method of conventional on-chip wavelength demultiplexers is based on theoretical analysis of specific waveguide structures to obtain device optical transmission characteristics under specific waveguide structure conditions. By adjusting the relevant characteristic parameters, it is possible to adapt it to the characteristics of a particular application. The disadvantage of this design approach is that the designed device is based on a specific structure, lacks exploration of irregular structures, and does not ensure optimal device performance. Furthermore, in order to obtain optimal performance, it is often necessary to design multiple parameters, however, when the parameter space is greatly expanded, intuitive designs are hardly feasible.
Disclosure of Invention
The invention aims to overcome the defects and provide the ultra-compact broadband wavelength demultiplexer and the design method thereof, wherein the wavelength demultiplexer has large bandwidth, compact structure, further improved integration level and better device performance.
The invention is realized by the following technical scheme:
an ultra-compact broadband wavelength demultiplexer comprises an encapsulation layer, an input waveguide and an output waveguide which are wrapped in the encapsulation layer;
one end of the input waveguide is an input end, the other end of the input waveguide is an output end, a transition section is arranged between the input end and the output end of the input waveguide, a directional coupling region is formed between the transition section and the output waveguide, and rectangular gratings arranged in an array are arranged in the directional coupling region; the distance between the input end of the input waveguide and the output waveguide, the length of the directional coupling region, the length, the width, the pitch length and the pitch duty ratio of the rectangular grating are optimized by adopting a particle swarm optimization algorithm.
Preferably, the materials of the input waveguide, the output waveguide and the rectangular grating are all silicon, and the packaging layer is a silicon dioxide layer.
Preferably, the width of the directional coupling region gradually increases from both ends to the middle.
Further, the input waveguide and the output waveguide are bar-shaped waveguides, and the widths of the input waveguide and the output waveguide at the directional coupling region gradually decrease from two ends to the middle.
Preferably, the top surface of the input waveguide is parallel to the bottom surface, and the top surface of the output waveguide is parallel to the bottom surface.
Further, the heights of the input waveguide, the output waveguide and the rectangular grating are equal.
Preferably, the output end of the input waveguide or the output end of the output waveguide is a 90 ° curved waveguide with a radius R, and the distance between the output end of the input waveguide and the output end of the output waveguide gradually increases along the optical signal transmission direction.
The design method of the ultra-compact broadband wavelength demultiplexer comprises the following steps:
s1, at the transition section of the input waveguide and the output waveA directional coupling area is arranged between the conductors, and rectangular gratings arranged in an array are arranged in the directional coupling area; the rectangular gratings have the same pitch length lambda and pitch duty cycle w 3 Λ, length w 3 Width w 2 ；
S2, adopting a particle swarm optimization algorithm to obtain the distance g between the input end of the input waveguide and the output waveguide, the length Lc of the directional coupling region and the length w of the rectangular grating 3 Width w 2 A pitch length Λ and a pitch duty cycle w 3 Encoding/Λ; setting a search space and an objective function value for the obtained coding structure, searching an optimal structure of the wavelength demultiplexer with a minimum objective function value by using a particle swarm optimization algorithm, and searching to obtain an optimized interval g between an input end of an input waveguide and an output waveguide, a length Lc of a directional coupling region and a length w of a rectangular grating 3 Width w 2 A pitch length Λ and a pitch duty cycle w 3 And/Λ, thereby forming an ultra-compact broadband wavelength demultiplexer final structure.
Preferably, in S1, a transmission efficiency monitor is disposed at an output end of an input waveguide;
s2, monitoring the transmission efficiency T of the output end of the input waveguide by the transmission efficiency monitor in the process of searching the optimal structure of the wavelength demultiplexer with the minimum objective function value by using the particle swarm optimization algorithm forward And sets the objective function value as:
FOM＝(1-T forward ) 2
wherein T is forward Is the transmission efficiency of the output end of the input waveguide (2).
Preferably, in S2, the search space is: rectangular grating length w 3 And width w 2 The range of the directional coupling region length Lc is 0.4-0.7 μm, and the range of the pitch length Λ is 0.1-0.2 μm, and the range of the pitch length Λ is 0.05-0.2 μm.
Compared with the prior art, the invention has the following beneficial effects:
the invention utilizes Particle Swarm Optimization (PSO) reverse design method to perform wave alignmentThe parameters of each part of the long demultiplexer (including the spacing g between the input end of the input waveguide and the output waveguide, the length Lc of the directional coupling region, and the length w of the rectangular grating 3 Width w 2 A pitch length Λ and a pitch duty cycle w 3 Λ) to obtain an optimal value, the required structural size can be further reduced, the integration level and compactness of the wavelength demultiplexer can be improved, and the device performance of the wavelength demultiplexer can be improved. The wavelength demultiplexer reversely designed by the particle swarm optimization algorithm has the length of only 9.3 mu m, and compared with the prior similar wavelength demultiplexer, the wavelength demultiplexer has the size reduced by nearly 20 times. The wavelength demultiplexer provides a extinction ratio of 24.3dB and a low insertion loss of 0.17dB at a wavelength of 1.55 μm and a extinction ratio of 21.7dB and a low insertion loss of 0.9dB at a wavelength of 2.0 μm. Therefore, the invention adopts the optimized structure of searching the wavelength demultiplexer from the global by utilizing the particle swarm optimization algorithm, can overcome the problems caused by the design based on a specific structure, and has more obvious advantages when the parameter space is greatly expanded.
Furthermore, the wavelength demultiplexer of the invention adopts a silicon dioxide layer package so as to facilitate the integration of the wavelength demultiplexer with other devices.
Furthermore, the decoupling between the waveguides is realized by decoupling the output ends of the input waveguide and the output waveguide through C-bend.
The invention uses particle swarm optimization reverse design method to search different sizes of each part of the wavelength demultiplexer, initially sets the rectangular grating to have equal length and width, and conveniently uses PSO algorithm to optimize the rectangular grating to obtain an optimal value, thereby further reducing the required structural size, improving the integration level and compactness of the wavelength demultiplexer, improving the transmission efficiency of the wavelength demultiplexer, reducing the loss and improving the extinction ratio of the wavelength demultiplexer.
Drawings
FIG. 1 is a schematic 3D architecture of an ultra-compact broadband wavelength demultiplexer of the present invention;
FIG. 2 is a schematic diagram of the planar structure of a wavelength demultiplexer in an initial configuration according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a planar structure of a wavelength demultiplexer obtained after searching through a particle swarm optimization algorithm according to an embodiment of the present invention;
FIG. 4 is a graph showing an optimal effect field distribution diagram obtained by searching a particle swarm optimization algorithm according to an embodiment of the present invention.
In the figure: 1 is a packaging layer, 2 is an input waveguide, 3 is an output waveguide, 4 is a transition section, 5 is a directional coupling region, and 6 is a rectangular grating 6.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, the ultra-compact broadband wavelength demultiplexer based on the particle swarm optimization reverse design method of the invention comprises a packaging layer 1, and an input waveguide 2 and an output waveguide 3 which are wrapped in the packaging layer 1; the input waveguide 2 and the output waveguide 3 are bar-shaped waveguides and extend in a linear mode, the top surface of the input waveguide 2 is parallel to the bottom surface, and the top surface of the output waveguide 3 is parallel to the bottom surface.
One end of the input waveguide 2 is an input end, the other end of the input waveguide 2 is an output end, a transition section 4 is arranged between the input end and the output end of the input waveguide 2, a directional coupling region 5 is formed between the transition section 4 and the output waveguide 3, and the width of the directional coupling region 5 gradually increases from two ends to the middle. The directional coupling region 5 is provided with rectangular gratings 6 arranged in an array, and the interval g between the input end of the input waveguide 2 and the output waveguide 3, the length Lc of the directional coupling region 5 and the length w of the rectangular gratings 6 3 Width w 2 A pitch length Λ and a pitch duty cycle w 3 And (3) optimizing the lambda by adopting a PSO algorithm.
In the present invention, the widths of both ends of the input waveguide 2 and the output waveguide 3Are all w 1 The widths of the input waveguide 2 and the output waveguide 3 at the directional coupling region 5 are both w 1 Gradually change to w 4 The variation length is Lc.
In addition, in the present invention, the output end of the input waveguide 2 and the output end of the output waveguide 3 are separated by using a 90 ° curved waveguide having a radius R, and the distance between the output end of the input waveguide 2 and the output end of the output waveguide 3 is gradually increased along the optical signal transmission direction, thereby achieving decoupling between the waveguides. Specifically, the output end of the input waveguide 2 is set as a 90 ° curved waveguide, and the radius is R.
In a specific embodiment of the present invention, the ultra-compact broadband wavelength demultiplexer is manufactured in batches by using a standard SOI process platform, so that the heights of each part of the input waveguide 2 and the output waveguide 3 are equal, and the input waveguide 2, the output waveguide 3 and the rectangular grating 6 are preferably made of silicon dioxide as an upper substrate material and a lower substrate material, so as to facilitate the integration of the designed wavelength demultiplexer and other components.
In the specific embodiment of the invention, the directional coupling region 5 formed by the input waveguide 2, the output waveguide 3 and the rectangular grating 6 forms a silicon material platform with the height of 220nm, and the silicon material platform is wrapped by a silicon dioxide layer with the thickness of 2 mu m to form the final ultra-compact broadband wavelength demultiplexer.
The input waveguide 2 in the ultra-compact broadband wavelength demultiplexer is used for inputting and transmitting two optical signals with specific wavelengths, and the transmitted optical signals are separated into two optical signals with independent wavelengths through the directional coupling area 5 between the waveguides and are respectively output from the upper output port and the lower output port (namely the output end of the input waveguide 2 and the output end of the output waveguide 3).
The design method of the ultra-compact broadband wavelength demultiplexer comprises the following steps:
s1, a directional coupling region 5 is arranged between a transition section 4 of an input waveguide 2 and an output waveguide 3, the width of the directional coupling region 5 gradually increases from two ends to the middle, a sub-wavelength grating (SWG) structure coupler is arranged in the directional coupling region 5, the sub-wavelength grating structure coupler comprises a plurality of grating strips which are perpendicular to the input waveguide 2, the grating strips have equal width and are vertically and laterally symmetrical, and the lengths of the grating strips gradually increase from two ends of the directional coupling region 5 to the middle; a transmission efficiency monitor is arranged at the output end of the input waveguide 2, and the output efficiency of the output end of the input waveguide 2 is monitored;
s2, dividing the grating strips into rectangular gratings 6 with the same size, wherein the rectangular gratings 6 have the same pitch length Λ and pitch duty ratio w 3 Λ, length w 3 Width w 2 ；
S3, adopting a PSO algorithm to control the length w of the rectangular grating 6 of the directional coupling region 5 3 Width w 2 Pitch length Λ, pitch duty cycle w 3 Λ, the length Lc of the directional coupling region 5, the spacing g between the input end of the input waveguide 2 and the output waveguide 3; setting reasonable search space and objective function value for the obtained coding structure, setting reasonable particle number, iteration number, cognitive factor, social factor and inertia weight, searching the optimal structure of the wavelength demultiplexer by using PSO algorithm and minimum objective function value (FOM value), and searching to obtain the optimized rectangular grating 6 length w 3 Width w 2 Pitch length Λ, pitch duty cycle w 3 And (3) the length Lc of the directional coupling region 5 and the interval g between the input end of the input waveguide 2 and the output waveguide 3 are respectively equal to/lambda, and the optimization targets are that the light with two different wavelengths is subjected to wavelength demultiplexing with low insertion loss and high extinction ratio through the directional coupling region 5, so that the final structure of the wavelength demultiplexer is formed.
Specifically, the search space is as follows: length w of rectangular grating 6 3 And width w 2 The range of (a) is 0.05-0.2 μm, the pitch length Λ is 0.2-0.5 μm, the length Lc of the directional coupling region 5 is 0.4-0.7 μm, and the spacing g between the input end of the input waveguide 2 and the output waveguide 3 is 0.1-0.2 μm.
Specifically, in searching for an optimal structure at a minimum objective function value (FOM value) using the PSO algorithm, the position and velocity of the particles are determined by:
v t ＝ωv t-1 +c 1 η 1 (p best,t-1 -x t-1 )+c 2 η 2 (g best,t-1 -x t-1 ) (1)
x t ＝x t-1 +v t (2)
wherein x is t And v t Respectively representing the position and the velocity of the t-th particle; in each iteration, p best,t-1 Represents the current best position of the t-1 st particle, g best,t-1 Indicating the t-1 th global optimum position of the particle; c 1 And c 2 Cognition and social factors, η, respectively 1 And eta 2 Is a random coefficient between 0 and 1, ω is an inertial weight.
Monitoring the transmission efficiency T of the output end of the input waveguide 2 by a transmission efficiency monitor during searching for an optimal structure with a minimum objective function value (FOM value) using the PSO algorithm forward And set the FOM value to:
FOM＝(1-T forward ) 2 (3)
wherein T is forward Which is the transmission efficiency of the output end of the input waveguide 2.
According to the design method of the ultra-compact broadband wavelength demultiplexer, the grating strips of the directional coupling region 5 are divided into rectangular gratings 6 with equal length and width, so that the rectangular gratings are conveniently optimized by using a PSO algorithm, the transmission efficiency is improved, the loss is reduced, and the extinction ratio of a device is improved.
Examples:
as shown in the perspective view of fig. 1 and the plan view of fig. 2, the ultra-compact broadband wavelength demultiplexer based on the particle swarm optimization reverse design method of the present embodiment includes a packaging layer 1, and an input waveguide 2 and an output waveguide 3 wrapped in the packaging layer 1; the input waveguide 2 and the output waveguide 3 are bar-shaped waveguides and extend in a linear mode, the top surface of the input waveguide 2 is parallel to the bottom surface, and the top surface of the output waveguide 3 is parallel to the bottom surface. One end of the input waveguide 2 is an input end, the other end of the input waveguide 2 is an output end, a transition section 4 is arranged between the input end and the output end of the input waveguide 2, a directional coupling region 5 is formed between the transition section 4 and the output waveguide 3, and the width of the directional coupling region 5 gradually increases from two ends to the middle. The directional coupling region 5 is provided with array arrangementA spacing g between the input end of the input waveguide 2 and the output waveguide 3, a length Lc of the directional coupling region 5, and a length w of the rectangular grating 6 3 Width w 2 A pitch length Λ and a pitch duty cycle w 3 And (3) optimizing the lambda by adopting a PSO algorithm.
In this embodiment, the encapsulation layer 1 is a silicon dioxide layer, and the materials of the input waveguide 2, the output waveguide 3 and the rectangular grating 6 are all silicon.
In this embodiment, a 90 ° bend with radius R is used to separate the output end of the input waveguide 2 from the output waveguide 3; in this embodiment, the widths of the input waveguide 2 and the output waveguide 3 at the opposite positions are the same, the thicknesses of the input waveguide 2, the output waveguide 3 and the directional coupling region 5 are the same, and are 220nm, and are wrapped by a silicon dioxide layer with a thickness of 2 μm.
As shown in fig. 2, the directional coupling area 5 in the ultra-compact broadband wavelength demultiplexer is provided with a sub-wavelength grating (SWG) structural coupler, the sub-wavelength grating structural coupler comprises 20 grating strips perpendicular to the input waveguide 2, the grating strips have equal widths and are symmetrical up and down and left and right, and the lengths of the grating strips gradually increase from two ends of the directional coupling area 5 to the middle. Dividing the grating strips into rectangular gratings 6 of equal size, the rectangular gratings 6 having the same pitch length Λ, pitch duty cycle w 3 Λ, length w 3 Width w 2 The length w of the rectangular grating 6 of the directional coupling region 5 is calculated by adopting a PSO algorithm 3 Width w 2 A directional coupling region 5 domain length Lc, a pitch length Λ and a pitch duty cycle w 3 Λ, the spacing g between the input end of the input waveguide 2 and the output waveguide 3. A reasonable search space and an objective function value (FOM value) are set for the obtained code structure. 20 iterations were performed using 30 particles, when the FOM value no longer decreased, resulting in the final structure of the wavelength demultiplexer (fig. 3).
As shown in fig. 1, an input waveguide 2 in the ultra-compact broadband wavelength demultiplexer is used for inputting and transmitting a wavelength lambda 1 =1.55 μm and λ 2 Optical signal of =2.0 μm, the transmitted optical signal is split into two separate waves by a directional coupling region 5 between the input waveguide 2 and the output waveguide 3Long optical signal, wavelength lambda 1 Optical signal and λ=1.55 μm 2 An optical signal of =2.0 μm is output from the lower port (i.e., the output end of the input waveguide 2) and the upper port (i.e., the output end of the output waveguide 3) of the output end, respectively.
As shown in fig. 4, from the field evolution diagrams of the ultra-compact broadband wavelength demultiplexer at 1.55 μm and 2.0 μm, it can be seen that the incident light at 2.0 μm is strongly coupled in the transmission direction, output from the upper port, and output from the lower port at 1.55 μm, the loss is low, and little coupling occurs in the directional coupling region 5. Meanwhile, the PSO algorithm is adopted to search the optimal structure of the wavelength demultiplexer, so that the required structure size is further reduced, and the performance of the wavelength demultiplexer is improved. The length of the wavelength demultiplexer is therefore only 9.3 μm. Which is reduced by a factor of approximately 20 compared to the previous wavelength demultiplexers. And provides a extinction ratio of 24.3dB and a low insertion loss of 0.17dB at a wavelength of 1.55 μm and a extinction ratio of 21.7dB and a low insertion loss of 0.9dB at a wavelength of 2.0 μm. So far, the ultra-compact and broadband demultiplexing functions of the wavelength demultiplexer are effectively realized.
The above is only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited by this, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. An ultra-compact broadband wavelength demultiplexer is characterized by comprising an encapsulation layer (1), and an input waveguide (2) and an output waveguide (3) which are wrapped in the encapsulation layer (1);
one end of the input waveguide (2) is an input end, the other end of the input waveguide is an output end, a transition section (4) is arranged between the input end and the output end of the input waveguide (2), a directional coupling region (5) is formed between the transition section (4) and the output waveguide (3), and the directional coupling region (5) is provided with rectangular gratings (6) which are arranged in an array; the distance between the input end of the input waveguide (2) and the output waveguide (3), the length of the directional coupling region (5), and the length, width, pitch length and pitch duty ratio of the rectangular grating (6) are optimized by adopting a particle swarm optimization algorithm.
2. The ultra-compact broadband wavelength demultiplexer according to claim 1, wherein the input waveguide (2), the output waveguide (3) and the rectangular grating (6) are all made of silicon, and the encapsulation layer (1) is a silicon dioxide layer.
3. Ultra-compact broadband wavelength demultiplexer according to claim 1, characterized in that the width of the directional coupling region (5) increases gradually from both ends towards the middle.
4. An ultra-compact broadband wavelength demultiplexer according to claim 3, characterized in that the input (2) and output (3) waveguides are each strip-shaped waveguides, the widths of the input (2) and output (3) waveguides at the directional coupling region (5) decreasing gradually from both ends to the middle.
5. The ultra-compact broadband wavelength demultiplexer according to claim 1, wherein the top surface of the input waveguide (2) is parallel to the bottom surface and the top surface of the output waveguide (3) is parallel to the bottom surface.
6. The ultra-compact broadband wavelength demultiplexer according to claim 5, wherein the heights of the input waveguide (2), the output waveguide (3) and the rectangular grating (6) are equal.
7. The ultra-compact broadband wavelength demultiplexer according to claim 1, wherein the output end of the input waveguide (2) or the output end of the output waveguide (3) is a 90 ° curved waveguide with a radius R, and the distance between the output end of the input waveguide (2) and the output end of the output waveguide (3) increases gradually along the optical signal transmission direction.
8. A method of designing an ultra-compact broadband wavelength demultiplexer as claimed in any one of claims 1 to 7 and comprising:
s1, at the transition section (4) of the input waveguide (2)) A directional coupling region (5) is arranged between the output waveguide (3), and rectangular gratings (6) which are arranged in an array are arranged in the directional coupling region (5); the rectangular gratings (6) have the same pitch length lambda, pitch duty cycle w 3 Λ, length w 3 Width w 2 ；
S2, adopting a particle swarm optimization algorithm to optimize the interval g between the input end of the input waveguide (2) and the output waveguide (3), the length Lc of the directional coupling region (5) and the length w of the rectangular grating (6) 3 Width w 2 A pitch length Λ and a pitch duty cycle w 3 Encoding/Λ; setting a search space and an objective function value for the obtained coding structure, searching an optimal structure of the wavelength demultiplexer with a minimum objective function value by using a particle swarm optimization algorithm, and searching to obtain a space g between an input end of the optimized input waveguide (2) and the output waveguide (3), a length Lc of the directional coupling region (5) and a length w of the rectangular grating (6) 3 Width w 2 A pitch length Λ and a pitch duty cycle w 3 And/Λ, thereby forming an ultra-compact broadband wavelength demultiplexer final structure.
9. The method for designing an ultra-compact broadband wavelength demultiplexer according to claim 8, wherein in S1, a transmission efficiency monitor is provided at an output end of the input waveguide (2);
s2, monitoring the transmission efficiency T of the output end of the input waveguide (2) by a transmission efficiency monitor in the process of searching the optimal structure of the wavelength demultiplexer with the minimum objective function value by using the particle swarm optimization algorithm forward And sets the objective function value as:
FOM＝(1-T forward ) 2
wherein T is forward Is the transmission efficiency of the output end of the input waveguide (2).
10. The method for designing an ultra-compact broadband wavelength demultiplexer according to claim 8, wherein in S2, the search space is: length w of rectangular grating (6) 3 And width w 2 In the range of 0.05-0.2 μm, and the pitch length Λ is in the range of 02-0.5 μm, the length Lc of the directional coupling region (5) being in the range 0.4-0.7 μm, the spacing g between the input end of the input waveguide (2) and the output waveguide (3) being in the range 0.1-0.2 μm.
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