CN111856656A - Four-channel drop filter with photonic crystal structure - Google Patents
Four-channel drop filter with photonic crystal structure Download PDFInfo
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29331—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by evanescent wave coupling
- G02B6/29335—Evanescent coupling to a resonator cavity, i.e. between a waveguide mode and a resonant mode of the cavity
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- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
- G02B6/2938—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
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Abstract
The invention discloses a four-channel drop filter with a photonic crystal structure, which is a two-dimensional photonic crystal with a tetragonal lattice dielectric column structure and consists of an input waveguide, two through output waveguides and two resonant cavities with square double-ring structures. The dielectric column material of the whole structure is a phase change material, and the four-channel down-path filtering function meeting the requirements of a coarse wavelength division multiplexing optical communication system can be realized by inducing the inner ring dielectric columns of the two square double-ring structure resonant cavities and the upper and lower coupling dielectric columns to be in different phase change states through the outside. Compared with the four-channel drop filter with other photonic crystal structures, the filter has the advantages that the number of the resonant cavities is reduced by half, only two resonant cavities with square double-ring structures are needed except for input and output waveguides, the filter has the outstanding characteristics of simple structure, small size, easiness in realization and integration, high flexibility, drop output wavelength meeting the design requirement of the nominal wavelength of the optical communication system in actual application at present, and the filter has important application in future optical integrated systems.
Description
Technical Field
The invention relates to a four-channel drop filter with a photonic crystal structure, which is mainly applied to a wavelength division multiplexing communication system to realize selective drop of specific multiple wavelength signals.
Background
The emergence and development of Wavelength Division Multiplexing (WDM) technology have greatly improved the transmission capacity and transmission efficiency of optical communication networks, making people enter the era of high-capacity, low-loss, high-speed communications. The optical channel drop filter is an important component of a WDM system, can realize multiplexing and demultiplexing functions of optical signals, and has important application in the WDM system. With the further development of the WDM technology, the corresponding requirements on various optical devices are higher and higher, and designing and implementing a multichannel drop filter with a small size, a simple structure, and high drop efficiency and flexibility is of more and more important significance, and has significant effects on the aspects of improving the system integration level, improving the system resource utilization rate, reducing the device redundancy, and the like.
Prior art [1]Referring to Optik, Alipour-Banaiei H, MehdizadehF, SerajmohammadiS.2013,124: 5964-. The wavelengths of the down paths are 1563.5nm, 1566.2nm, 1569.7nm and 1572.6nm respectively, the average down path efficiency is 53 percent, and the overall structure size is about 800 mu m2. Therefore, the channel drop filter has low drop efficiency, the drop wavelength does not meet the design requirement of the nominal wavelength of the CWDM system or the DWDM system in practical application, and the channel drop filter is complex in structure and large in size because four resonant cavities with different parameters are needed in the structure.
Prior art [2]Referring to optical precision engineering, Shenhongjun, Liujie, Liting, Lixinlan 2015, 23:692-699, four hexagonal resonant cavities with six central medium columns inside are introduced into a two-dimensional photonic crystal of a triangular lattice, and the radius of the six central medium columns inside the four resonant cavities is adjusted, so that the channel drop output function of four different wavelengths is realized, the four resonant wavelengths are 1581.9nm, 1592.3nm, 1601.3nm and 1607.3nm respectively, the average drop efficiency is more than 90%, and the overall structure size is 655 μm2. Although the structure realizes the high-efficiency downlink output function, the four-channel downlink output still needs four resonant cavities with different parameters, and the structure is complex. In addition, the four downlink wavelengths do not meet the specific requirements of the currently and generally adopted WDM system, such as a Coarse Wavelength Division Multiplexing (CWDM) or Dense Wavelength Division Multiplexing (DWDM) system, on the wavelength of the transmission signal; the four resonators need to realize the four-channel down-path output based on the change of processing parameters, namely the radius of six central dielectric columns in the resonators, and therefore, the four resonators are not beneficial to actual preparation.
Prior art [3]See applied optics, S.Yaw-DongWu, Tien-Tsing Shih, Jian-JangLee.2009, 48: F24-F30, four square ring resonators with nine dielectric columns in the center are introduced into a square two-dimensional photonic crystal, the radius of the dielectric columns in the four square resonators is selected appropriately, the down-path output of signals with four different wavelengths of 1510nm, 1530nm, 1550nm and 1570nm is realized, the average transmittance is more than 92%, and the overall structure size is about 384 mu m2. The structure also needs four resonant cavities for realizing the downlink output of four channels, and the downlink output for realizing the four channels needs to be based on processing parameters, namely the radius of nine medium columns in the center is changed, so that the structure is not beneficial to actual preparation.
Prior art [4]Referring to Photonic Network Communications, Hamed Alipay-Banaiei, Somaye Serajmohammadi and Farhad Mehdizadeh.2015,29: 146-2. Although the structure also realizes the high-efficiency downlink output function, four resonant cavities are needed for realizing the downlink output of four channels, and the whole size of the device is larger. In addition, the structure needs to change the processing parameter, namely the lattice constant of the dielectric column in the resonant cavity, so that the structure is not favorable for practical preparation. On the other hand, the four drop wavelengths do not meet the specific requirements of the WDM system commonly used at present, such as Coarse Wavelength Division Multiplexing (CWDM) or Dense Wavelength Division Multiplexing (DWDM), on the wavelength of the transmission signal.
Disclosure of Invention
In order to solve the problems in the prior art, the present invention aims to overcome the disadvantages in the prior art, and provide a four-channel drop filter with a photonic crystal structure, which has a simple structure, a small size, easy preparation, and excellent optical performance, and the wavelengths of multiple signals to be dropped meet the design requirements of the nominal wavelength of the CWDM system in practical application, and has stronger practicability.
In order to achieve the purpose of the invention, the invention adopts the following inventive concept:
the common characteristic that only one wavelength signal can be dropped by one resonant cavity of the existing multichannel drop filter is improved, a novel ring resonant cavity is designed, two wavelength signals can be dropped forwards and backwards at a drop waveguide at the same time, and other wavelengths are transmitted in high transmission mode continuously in an input waveguide. The novel ring resonator is the key to the design of the whole four-channel down-filter. After the two wavelengths are subjected to resonance and downlink by the first ring-shaped resonant cavity, the other two wavelengths which are transmitted in the input waveguide in a high transmission mode are subjected to resonance when passing through another ring-shaped resonant cavity with the same structure and the same processing parameters but different refractive indexes of the medium columns at certain positions, and finally, the two wavelengths are subjected to forward and backward downlink output simultaneously by another downlink waveguide, so that the downlink filtering function of the four-wavelength channel meeting the required wavelength is realized finally. The dielectric column material of the whole structure is selected as a phase change material, and the change of the refractive index of the dielectric column is flexibly realized by inducing the relevant dielectric columns in the two resonant cavities to different phase changes from the outside. The channel drop filter structurally only adopts two annular resonant cavities with the same physical structure, the refractive indexes of medium columns at certain positions are different, phase-change materials are preferentially selected as medium column materials, the medium column materials are induced to be in different phase states through the outside, the required refractive index is flexibly achieved, and drop output of four-wavelength signals can be achieved, so that the problems that the structure is complex, the size is large, and actual preparation is not facilitated due to the fact that four resonant cavities with different processing parameters are required for dropping four-wavelength signals commonly existing in the prior art are solved. By selecting proper lattice constants, refractive indexes, radiuses and the like of the background medium columns, the four wavelengths of the lower path meet the specific requirements of CWDM system application, and meanwhile, the lower path filter has excellent lower path filter characteristics.
According to the inventive concept, the invention adopts the following technical scheme:
a four-channel drop filter with a photonic crystal structure adopts a two-dimensional photonic crystal of a tetragonal lattice dielectric column type as a basic structure, and is composed of an input waveguide, two through output waveguides and two resonant cavities with square double-ring structures, wherein the two through output waveguides comprise an upper output waveguide and a lower output waveguide, the two resonant cavities with square double-ring structures comprise a first resonant cavity and a second resonant cavity, and the first resonant cavity and the second resonant cavity are arranged between the upper output waveguide and the lower output waveguide.
Preferably, the dielectric column material of the overall structure of the four-channel drop filter of the photonic crystal structure is a phase change material, the inner ring dielectric columns of the two square double-ring structure resonant cavities, the upper coupling dielectric columns and the lower coupling dielectric columns are induced to different phase changes by the outside, and the lattice constant, the refractive index and the radius of the background dielectric column, the radius of the dielectric column at other special positions and the like are simultaneously selected to form the four-channel drop filter structure of the Coarse Wavelength Division Multiplexing (CWDM) optical communication system.
Preferably, the input waveguide of the four-channel drop filter of the photonic crystal structure is formed by successively removing a plurality of dielectric pillars in the horizontal array direction at the input port, the ends of which do not form a via; the upper output waveguide and the lower output waveguide are respectively positioned at the upper side and the lower side of the input waveguide, and the dielectric columns of the whole array are continuously removed along the horizontal array direction, so that the straight-through output waveguide with the passage in both directions is formed.
Preferably, the first resonant cavity of the quad-ring structure of the four-channel drop filter of the photonic crystal structure is located between the input waveguide and the upper output waveguide; the second resonant cavity of the square double-ring structure is positioned between the input waveguide and the lower output waveguide; the first resonant cavity and the second resonant cavity of the square double-ring structure are different in position in the horizontal direction.
Preferably, the first resonant cavity and the second resonant cavity of the square double-ring structure of the four-channel drop filter of the photonic crystal structure are both composed of an inner dielectric column arrangement structure and an outer dielectric column arrangement structure which are arranged in a square shape; the medium column arrangement structure with the square outer shape is provided with an oval medium column as a scattering medium column at the inner positions of four corners; in the arrangement structure of the medium columns with square shapes, except the medium columns positioned at the four outermost corners, the medium columns in other horizontal directions are also oval and used as an upper coupling medium column and a lower coupling medium column; the inner and outer dielectric column arrangement structures which are arranged in a square shape are not adjacent to each other, and at least one row of dielectric columns are arranged at intervals to form an annular cavity which is used as the outer ring of the resonant cavity; the dielectric column arrangement structure with the square inner shape has no dielectric column inside, and forms another annular cavity as an inner ring of the resonant cavity, thereby forming the resonant cavity with a double-ring structure; the long axis and the short axis of the scattering medium column are not coincident with the horizontal direction and the vertical direction, and form a set included angle; the long and short axes of the upper and lower coupling medium columns are respectively coincided with the horizontal and vertical directions; the medium column interval of the medium column arrangement structure is not larger than that of the medium column arrangement structure with the square shape at the outer side.
Preferably, the refractive indexes of the inner ring dielectric columns and the outer ring dielectric columns of the first resonant cavity and the second resonant cavity of the four-channel drop filter of the photonic crystal structure are different; the refractive indexes of the upper coupling medium column and the lower coupling medium column in the second resonant cavity are different; the refractive index of the inner ring dielectric cylinder of the first resonant cavity is different from that of the inner ring dielectric cylinder of the second resonant cavity; the refractive indexes of the upper and lower coupling medium columns of the first resonant cavity are different from the refractive indexes of the upper and lower coupling medium columns of the second resonant cavity; during preparation, the dielectric column materials at all positions are selected as phase change materials, and based on the phase change characteristics of the dielectric column materials, the required refractive index of the dielectric column is realized by inducing the relevant dielectric columns of the two resonant cavities to different phase change states from the outside.
Preferably, by selecting a suitable lattice constant, a refractive index and a radius of the background dielectric column, a refractive index and a radius of the relevant dielectric column of the first resonant cavity and the second resonant cavity, a horizontal position of the first resonant cavity and the second resonant cavity, and the like, the downlink output of four wavelengths meeting the downlink wavelength size and wavelength interval requirements of the CWDM optical communication system is simultaneously realized, and simultaneously, the downlink efficiency is high.
Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. the four-channel drop filter of the filter is realized only based on two resonant cavities with square double-ring structures with the same processing parameters, so compared with the prior art that four resonant cavities are needed for realizing the drop output of four channels, the four-channel drop filter has the outstanding characteristics of simple structure, small size and easy realization; in addition, compared with the defect that the wavelength of the four downlink signals in the prior art cannot meet the application requirement of an actual system, the wavelength and the wavelength interval of the four downlink signals realized by the structure of the invention meet the design requirement of the CWDM system in the current actual application, and the invention has higher practicability; compared with the lower route taking efficiency in the prior art, the structure can realize higher route taking efficiency and has more excellent performance;
2. the resonant cavities of the two square double-ring structures of the filter have the same structural parameters required by the processing except for the refractive indexes of the medium columns at partial positions; during preparation, all dielectric column materials are selected as phase-change materials, and based on the phase-change characteristics of the dielectric column materials, the required refractive index of the dielectric column can be flexibly realized by simply inducing the dielectric columns at the relevant positions of the two resonant cavities to the phase-change state corresponding to the required refractive index from the outside, so that compared with the prior art that the structural parameters of each resonant cavity are different and a plurality of dielectric columns with different refractive indexes and radiuses need to be additionally prepared, the phase-change material is simple in structural preparation, easy to realize and has higher flexibility and practicability;
3. compared with the four-channel drop filter with other structures, the four-channel drop filter has the advantages that the number of the required resonant cavities is reduced by half, the structure is simple, the size is small, the implementation is easy, the drop output wavelength size and the gap meet the design requirements of the CWDM system in the current practical application, and the four-channel drop filter has important application in the future all-optical integrated optical communication network.
Drawings
Fig. 1 is a schematic diagram of a four-channel drop filter according to the present invention. Wherein 1 is an input waveguide, 2 and 3 are an upper output waveguide and a lower output waveguide respectively, and 4 and 5 are resonant cavities with square double-ring structures. A is the input port and B, C, D and E ports are the drop output ports.
Fig. 2 is a schematic structural diagram of the square dual-ring resonator shown in fig. 1. The medium columns which are positioned inside and arranged in a square shape are called inner ring medium columns; the medium columns are arranged in a square shape and positioned at the outer part, and the four medium columns are positioned at the four corners and have oval shapes, and are called outer ring medium columns.
FIG. 3 is a key dielectric column in the outer ring dielectric column of the quad-double ring resonator shown in FIG. 2. The medium columns shown by the upper and lower rounded rectangle frames are called upper and lower coupling medium columns; the dielectric cylinder with four corners shown as triangular boxes is called a scattering dielectric cylinder.
Table 1 shows the structural parameters of the key dielectric pillars of the first cavity 4 and the second cavity 5 according to the preferred embodiment of the present invention.
Fig. 4 is a transmission spectrum of four output ports of the preferred embodiment of the present invention.
FIG. 5 is a graph showing the distribution of the optical field at different drop wavelengths in a preferred embodiment of the present invention. Wherein the down-path wavelength (a) is 1550nm, (b) is 1570nm, (c) is 1590nm, and (d) is 1610 nm.
During specific design, a proper lattice constant, a background dielectric column refractive index and a radius are selected, so that the wavelengths of four signals which are to be dropped and meet the specific application of the CWDM are located in a photonic band gap of the photonic crystal. The four-wavelength signals to be dropped are input from the input port of the input waveguide 1, the refractive index and the radius of the inner ring dielectric column of the second resonant cavity 5, the refractive index of the upper coupling dielectric column and the refractive index of the lower coupling dielectric column as well as the length of the long half shaft and the length of the short half shaft, the length of the long half shaft and the short half shaft of the scattering dielectric column and the like are selected, two wavelength signals in the four-wavelength signals input through the input waveguide 1 can be coupled with the second resonant cavity 5, and are respectively dropped forwards and backwards after passing through the lower horizontal straight-through output waveguide 3 and output from the output ports D and E, and the rest two wavelengths are continuously transmitted in the input waveguide in a high transmission. And selecting the refractive index and the radius of the inner ring dielectric column of the first resonant cavity 4 to couple the other two wavelength signals with the first resonant cavity 4, and finally respectively outputting the other two wavelength signals from the output ports B and C after passing through the upper horizontal through output waveguide 2 in a forward and backward downward way, thereby finally realizing the downward filtering of the four wavelength signals. The phase-change material is selected as the dielectric column material, and the refractive index of the dielectric column at the relevant position can be flexibly changed based on the phase-change characteristics of the material, so that the practical application is facilitated.
Detailed Description
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:
the first embodiment is as follows:
in this embodiment, referring to fig. 1, a four-channel drop filter with a photonic crystal structure, whose basic structure adopts a two-dimensional photonic crystal of a tetragonal lattice dielectric column type, is composed of an input waveguide 1, two through output waveguides and two resonant cavities with a square double-ring structure, where the two through output waveguides include an upper output waveguide 2 and a lower output waveguide 3, the two resonant cavities with the square double-ring structure include a first resonant cavity 4 and a second resonant cavity 5, and the first resonant cavity 4 and the second resonant cavity 5 are disposed between the upper output waveguide 2 and the lower output waveguide 3.
Example two:
this embodiment is substantially the same as the first embodiment, and is characterized in that:
in this embodiment, referring to fig. 1 to 3, a four-channel drop filter of a photonic crystal structure is characterized in that: the dielectric column material of the whole structure is a phase change material, the inner ring dielectric columns of the two square double-ring structure resonant cavities, the upper coupling dielectric columns and the lower coupling dielectric columns are induced to different phase changes by the outside, and the lattice constant, the refractive index and the radius of the background dielectric column and the radius of the dielectric column at other special positions are selected at the same time to form a four-channel down-path filtering structure of a Coarse Wavelength Division Multiplexing (CWDM) optical communication system.
In the present embodiment, the input waveguide 1 is constituted by successively removing a plurality of dielectric pillars in the horizontal array direction at the input port, the ends of which do not constitute a passage; the upper output waveguide 2 and the lower output waveguide 3 are respectively positioned at the upper side and the lower side of the input waveguide 1, and a through output waveguide with a passage in both directions is formed by continuously removing the dielectric columns of the whole array along the horizontal array direction. The first resonant cavity 4 of the square double-ring structure is positioned between the input waveguide 1 and the upper output waveguide 2; the second resonant cavity 5 of the square double-ring structure is positioned between the input waveguide 1 and the lower output waveguide 3; the first resonant cavity 4 and the second resonant cavity 5 of the square double-ring structure are different in position in the horizontal direction.
Example three:
this embodiment is substantially the same as the previous embodiment, and is characterized in that:
in the present embodiment, referring to fig. 1 to 3, the first resonant cavity 4 and the second resonant cavity 5 of the square double-ring structure are both composed of an inner dielectric pillar arrangement structure and an outer dielectric pillar arrangement structure arranged in a square shape; the medium column arrangement structure with the square outer shape is provided with an oval medium column as a scattering medium column at the inner positions of four corners; in the arrangement structure of the medium columns with square shapes, except the medium columns positioned at the four outermost corners, the medium columns in other horizontal directions are also oval and used as an upper coupling medium column and a lower coupling medium column; the inner and outer dielectric column arrangement structures which are arranged in a square shape are not adjacent to each other, and at least one row of dielectric columns are arranged at intervals to form an annular cavity which is used as the outer ring of the resonant cavity; the dielectric column arrangement structure with the square inner shape has no dielectric column inside, and forms another annular cavity as an inner ring of the resonant cavity, thereby forming the resonant cavity with a double-ring structure; the long axis and the short axis of the scattering medium column are not coincident with the horizontal direction and the vertical direction, and form a set included angle; the long and short axes of the upper and lower coupling medium columns are respectively coincided with the horizontal and vertical directions; the medium column interval of the medium column arrangement structure is not larger than that of the medium column arrangement structure with the square shape at the outer side.
In this embodiment, the refractive indexes of the inner ring dielectric cylinder and the outer ring dielectric cylinder of the first resonant cavity 4 and the second resonant cavity 5 are different; the refractive indexes of the upper coupling medium column and the lower coupling medium column in the second resonant cavity 5 are different; the refractive index of the inner ring dielectric cylinder of the first resonant cavity 4 is different from that of the inner ring dielectric cylinder of the second resonant cavity 5; the refractive indexes of the upper and lower coupling medium columns of the first resonant cavity 4 are different from the refractive indexes of the upper and lower coupling medium columns of the second resonant cavity 5; during preparation, the dielectric column materials at all positions are selected as phase change materials, and based on the phase change characteristics of the dielectric column materials, the required refractive index of the dielectric column is realized by inducing the relevant dielectric columns of the two resonant cavities to different phase change states from the outside.
In this embodiment, by selecting a suitable lattice constant, a refractive index and a radius of a background dielectric column, a refractive index and a radius of a dielectric column related to the first resonant cavity 4 and the second resonant cavity 5, and positions of the first resonant cavity 4 and the second resonant cavity 5 in the horizontal direction, etc., a drop output of four wavelengths meeting requirements of a drop wavelength size and a wavelength interval of the CWDM optical communication system is simultaneously realized, and a high drop efficiency is also achieved.
Example four:
this embodiment is substantially the same as the previous embodiment, and is characterized in that:
the implementation is applied to a CWDM optical communication system, and the lower wavelengths with the nominal wavelength interval of 20nm are respectively as follows: 1550nm, 1570nm, 1590nm and 1610 nm.
The whole optical system structure is shown in fig. 1. The photonic crystal is a two-dimensional photonic crystal with a square lattice dielectric column structure, the whole structure is a 27 multiplied by 31 dielectric column array, an A port is an input port, and B, C, D and E ports are downlink output ports. The background material is air, and the dielectric column material is phase-change material Ge2Sb2Se4Te1The refractive index n is 3.46, the dielectric cylinder radius R is 0.08 μm, and the lattice constant a is 0.58 μm. The input waveguide is formed by continuously removing 18 dielectric columns along the horizontal direction at the input end A, and the two output waveguides are formed by continuously removing a whole row of dielectric columns along the horizontal direction at the output end respectively. The first resonant cavity 4 and the second resonant cavity 5 are of a symmetrical structure, the middle axis position of the first resonant cavity 4 is separated from the first column of dielectric columns of the integral structure by 15 dielectric columns in the vertical direction, the middle axis position of the second resonant cavity 5 is separated from the first column of dielectric columns of the integral structure by 5 dielectric columns in the vertical direction, namely, the first resonant cavity 4 is compared with the second resonant cavity 5 and is shifted to the right by 10 dielectric columns along the horizontal direction. The first resonant cavity 4 and the second resonant cavity 5 have a half of lattice constant as the inner ring dielectric column spacing and a lattice constant equal to the outer ring dielectric column spacing. The structural parameters of the key dielectric columns of the first resonant cavity 4 and the second resonant cavity 5 are shown in Table 1, the other dielectric column parameters are the same as the background dielectric column parameters, and the size of the whole structure is 296 μm2。
TABLE 1 structural parameters of the key dielectric pillars of the first cavity 4 and the second cavity 5 of the fourth embodiment of the present invention
By inputting a gaussian pulse signal of TE polarization at the input port a and observing at the port B, the port C, the port D, and the port E, a transmission spectrum is obtained as shown in fig. 4. At the input waveguide port a, continuous wavelength signals with single wavelengths of 1550nm, 1570nm, 1590nm and 1610nm are input, respectively, and the obtained optical field distribution is shown in fig. 5. As can be seen from fig. 5, the filter simultaneously realizes the downstream output of the 1550nm wavelength, the 1570nm wavelength, the 1590nm wavelength and the 1610nm wavelength from the output ports C, B, E and D, respectively. It can be calculated from fig. 4 that the transmittance at ports C, B, E and D for the down wavelengths 1550nm, 1570nm, 1590nm and 1610nm is 90.81%, 80.31%, 84.72% and 96.84%, respectively.
In summary, the four-channel drop filter realizes the four-channel drop filtering function of 1550nm, 1570nm, 1590nm and 1610nm wavelengths meeting the standard wavelength interval of 20nm of a CWDM optical communication system only based on the two resonant cavities with the square double-ring structure, and has the advantages of simple structure, small size, easy integration and ideal drop filtering characteristics. In addition, the resonant cavities of the two square double-ring structures have the same structural parameters required by processing except that the refractive indexes of the medium columns at partial positions are different. During preparation, the required refractive index of the dielectric column can be realized by inducing the dielectric columns in the inner rings of the two resonant cavities and the upper and lower coupling dielectric columns to different phase changes from the outside under the condition that the materials of all the dielectric columns are the same. Therefore, compared with the prior art, the structure of the invention is easier to prepare and realize, and has higher flexibility and practicability.
In this embodiment, the four wavelengths of the drop filtering are 1550nm, 1570nm, 1590nm and 1610nm, and based on the design structure and design idea of the present invention, a four-channel drop filter in which the size and the interval of other drop output wavelengths meet the design requirements of the CWDM system in practical application at present can be realized. The wavelengths of the lower paths of the present embodiment are 1550nm, 1570nm, 1590nm and 1610nm, respectively, which are excellentThe lower filter characteristic and the integral structure size are 296 mu m2。
It can be known from the above embodiments that the four-channel drop filter of the photonic crystal structure of the present invention is a two-dimensional photonic crystal with a tetragonal lattice dielectric pillar structure, and is composed of an input waveguide, two through output waveguides, and two specially designed resonant cavities with a tetragonal double-ring structure. The dielectric column material of the whole structure is a phase change material, the inner ring dielectric columns of the two square double-ring structure resonant cavities, the upper coupling dielectric columns and the lower coupling dielectric columns are induced to different phase change states by the outside, and the proper lattice constant, the refractive index and the radius of the background dielectric column and the radius of the dielectric column at other special positions are selected at the same time, so that the four-channel down-path filtering function meeting the requirements of a Coarse Wavelength Division Multiplexing (CWDM) optical communication system can be realized. Compared with the four-channel drop filter with other photonic crystal structures, the four-channel drop filter has the advantages that the number of resonant cavities is reduced by half, only two resonant cavities with square double-ring structures are needed except for input and output waveguides, the four-channel drop filter has the outstanding characteristics of simple structure, small size and easiness in realization and integration, the flexibility is high, the drop output wavelength meets the design requirement of the nominal wavelength of the CWDM optical communication system in actual application at present, and the four-channel drop filter has important application in future optical integrated systems.
The embodiments of the present invention have been described with reference to the accompanying drawings, but the present invention is not limited to the embodiments, and various changes and modifications can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be equivalent substitutions, as long as the purpose of the present invention is met, and the present invention shall fall within the protection scope of the present invention without departing from the technical principle and inventive concept of the present invention.
Claims (7)
1. A four-channel drop filter of a photonic crystal structure is characterized in that: the two-dimensional photonic crystal adopts a square lattice dielectric column type, and is composed of an input waveguide (1), two through output waveguides and two resonant cavities with square double-ring structures, wherein the two through output waveguides comprise an upper output waveguide (2) and a lower output waveguide (3), the resonant cavities with the two square double-ring structures comprise a first resonant cavity (4) and a second resonant cavity (5), and the first resonant cavity (4) and the second resonant cavity (5) are arranged between the upper output waveguide (2) and the lower output waveguide (3).
2. The photonic crystal structured four-channel drop filter of claim 1, wherein: the dielectric column material of the whole structure is a phase change material, the inner ring dielectric columns of the two square double-ring structure resonant cavities, the upper coupling dielectric column and the lower coupling dielectric column are induced to different phase changes by the outside, and the lattice constant, the refractive index and the radius of the background dielectric column and the radius of the dielectric column at other special positions are selected at the same time, so that the four-channel down-path filtering structure of the Coarse Wavelength Division Multiplexing (CWDM) optical communication system is formed.
3. The photonic crystal structured four-channel drop filter of claim 1, wherein: the input waveguide (1) is formed by continuously removing a plurality of dielectric pillars in a horizontal array direction at an input port, and the end thereof does not form a passage; the upper output waveguide (2) and the lower output waveguide (3) are respectively positioned at the upper side and the lower side of the input waveguide (1), and the dielectric columns of the whole array are continuously removed along the horizontal array direction, so that a through output waveguide with the passage in both directions is formed.
4. The photonic crystal structured four-channel drop filter of claim 1, wherein: the first resonant cavity (4) of the square double-ring structure is positioned between the input waveguide (1) and the upper output waveguide (2); the second resonant cavity (5) of the square double-ring structure is positioned between the input waveguide (1) and the lower output waveguide (3); the positions of the first resonant cavity (4) and the second resonant cavity (5) of the square double-ring structure in the horizontal direction are different.
5. The photonic crystal structured four-channel drop filter of claim 1, wherein: the first resonant cavity (4) and the second resonant cavity (5) of the square double-ring structure are both composed of an inner dielectric column arrangement structure and an outer dielectric column arrangement structure which are arranged in a square shape;
the medium column arrangement structure with the square outer shape is provided with an oval medium column as a scattering medium column at the inner positions of four corners;
in the arrangement structure of the medium columns with square shapes, except the medium columns positioned at the four outermost corners, the medium columns in other horizontal directions are also oval and used as an upper coupling medium column and a lower coupling medium column;
the inner and outer dielectric column arrangement structures which are arranged in a square shape are not adjacent to each other, and at least one row of dielectric columns are arranged at intervals to form an annular cavity which is used as the outer ring of the resonant cavity;
the dielectric column arrangement structure with the square inner shape has no dielectric column inside, and forms another annular cavity as an inner ring of the resonant cavity, thereby forming the resonant cavity with a double-ring structure;
the long axis and the short axis of the scattering medium column are not coincident with the horizontal direction and the vertical direction, and form a set included angle; the long and short axes of the upper and lower coupling medium columns are respectively coincided with the horizontal and vertical directions; the medium column interval of the medium column arrangement structure is not larger than that of the medium column arrangement structure with the square shape at the outer side.
6. The photonic crystal structured four-channel drop filter of claim 1, wherein: the refractive indexes of the inner ring dielectric columns and the outer ring dielectric columns of the first resonant cavity (4) and the second resonant cavity (5) are different; the refractive indexes of the upper coupling medium column and the lower coupling medium column in the second resonant cavity (5) are different; the refractive index of the inner ring dielectric column of the first resonant cavity (4) is different from that of the inner ring dielectric column of the second resonant cavity (5); the refractive indexes of the upper and lower coupling medium columns of the first resonant cavity (4) are different from the refractive indexes of the upper and lower coupling medium columns of the second resonant cavity (5); during preparation, the dielectric column materials at all positions are selected as phase change materials, and based on the phase change characteristics of the dielectric column materials, the required refractive index of the dielectric column is realized by inducing the relevant dielectric columns of the two resonant cavities to different phase change states from the outside.
7. The photonic crystal structured four-channel drop filter of any one of claims 1 to 6, wherein: by selecting proper lattice constant, background medium column refractive index and radius, relevant medium column refractive index and radius of the first resonant cavity (4) and the second resonant cavity (5), horizontal direction positions of the first resonant cavity (4) and the second resonant cavity (5) and the like, the four-wavelength downlink output meeting the downlink wavelength size and wavelength interval requirements of the CWDM optical communication system is realized simultaneously, and high downlink efficiency is achieved simultaneously.
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