CN117233888B - Grating filter and wavelength division multiplexing demultiplexer based on Bragg grating - Google Patents
Grating filter and wavelength division multiplexing demultiplexer based on Bragg grating Download PDFInfo
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Abstract
The invention relates to the field of photoelectrons, and discloses a grating filter and a wavelength division multiplexing demultiplexer based on Bragg gratings. The grating filter includes: the multimode Bragg grating comprises a multimode waveguide and grating teeth which are distributed in an antisymmetric way along the whole course of the multimode waveguide, wherein the grating teeth are periodically distributed at two sides of the multimode waveguide in a staggered way, the width of the multimode waveguide is kept unchanged, and meanwhile, the width of the grating teeth is gradually increased from two sides to the center, so that grating apodization is completed and the grating has positive dispersion characteristics; a mode multiplexing demultiplexer includes an upper coupling waveguide and a lower coupling waveguide. According to the invention, grating teeth which are distributed in the whole-course antisymmetric way along the multimode waveguide are used for exciting TE1/TE0 coupling peaks and simultaneously effectively inhibiting the occurrence of TE0/TE0 coupling peaks, so that multi-wavelength division multiplexing and demultiplexing based on the TE1/TE0 coupling peaks are realized; and the strong suppression effect of the side lobes in the long wave direction is realized by the apodization mode with gradually enlarged grating tooth width and the design of the grating positive dispersion, so that the crosstalk of the wave-division multiplexer is effectively reduced.
Description
Technical Field
The invention relates to the technical field of integrated photoelectrons, in particular to a grating filter and a wavelength division multiplexing demultiplexer based on Bragg gratings.
Background
With the development of technologies such as big data and cloud computing, communication data traffic has increased dramatically, and communication technologies are being upgraded to ultra wideband, wherein core devices include wideband optical modules. The bandwidth of the optical module can be effectively improved by adopting the wavelength division multiplexing technology, and the four-wave, six-wave and twelve-wave optical modules become the current main stream optical module gradually. Wavelength division multiplexer is a core device for realizing wavelength division multiplexing/demultiplexing, and as the volume of optical modules is continuously reduced, the demand of on-chip integrated wavelength division multiplexer is more and more urgent.
At present, the integrated wavelength division multiplexer is mainly divided into a waveguide array grating, an echelle grating, a cascade MZI, a cascade Bragg grating and the like, wherein the wavelength division multiplexer based on the Bragg grating has the advantages of low insertion loss, broadband, low crosstalk and the like, and is an ideal wavelength division multiplexer in an optical module. Four-channel wavelength division multiplexers based on silicon-based Bragg gratings have been reported [ IEEE Photonics Technology Letters, vol.32, no. 4, pp., 192-195]. As shown in FIG. 1a, the Bragg grating adopts a grating tooth symmetrical-antisymmetric distribution gradual mode to realize TE0/TE1 mode optical coupling and sidelobe suppression, and the coupling produces an optical transmission forbidden band in a spectrum (FIG. 1 a). After entering the grating from the port 1, the TE0 mode light in the forbidden band is reflected and converted into TE1 mode under the action of the anti-symmetric grating, and the reflected TE1 mode light is converted into TE0 light by the mode division multiplexer and is led out from the port 2. The Bragg gratings with different periods can reflect light with different wave bands, so that wavelength division multiplexing and demultiplexing can be realized.
However, such silicon-based symmetric-antisymmetric graded apodized multimode bragg gratings suffer from two problems. One aspect is the problem of operating wavelength drift with temperature. In practice, the wavelength division multiplexer is operated at a temperature in the range of-40 degrees to +80 degrees. Because the thermal-optical coefficient of the silicon material is higher, the working wavelength of the silicon-based Bragg grating can drift to 0.1nm/K along with the temperature, and the working bandwidth of the wavelength division multiplexer can deviate from a set wave band due to the temperature difference change of hundreds of degrees, so that the device is invalid.
On the other hand, the problem of collision between the TE0/TE1 coupling peak and the TE0/TE0 coupling peak is solved. The symmetrical-antisymmetric gradual apodization can effectively inhibit the intensity of side lobes at two sides of the TE0/TE1 coupling peak, but the existence of the symmetrical grating also excites the TE0/TE0 coupling peak. As shown in FIG. 1a, TE0/TE1 coupled light exits port 2 and TE0/TE0 coupled light returns from port 1 in the primary path, the two coupling creating two valleys in the transmission spectrum of port 3. In the wavelength division multiplexing/demultiplexing application scenario, the TE0/TE0 coupling peak may interfere with the TE0/TE1 coupling peaks of other wavelength filters. As shown in fig. 1b, the TE0/TE0 coupling peaks of the filters 1, 2, 3 correspond to the wavelengths λ1, λ2, λ3, respectively, while the TE0/TE0 coupling peak λ3 of the filter 1 coincides spectrally with the TE1/TE0 coupling peak λ3 of the filter 3. When three filters of different wavelengths are cascaded, the ports 2 of the original filters 1, 2, 3 should be separated by λ1, λ2 and λ3, respectively, but due to the presence of TE0/TE0 coupling peaks in the filter 1, a portion of λ3 light exits port 1 of the filter 1 and the remaining portion of λ3 light exits port 2 of the filter 3. The presence of the TE0/TE0 coupling peak is disadvantageous for wavelength division multiplexing and demultiplexing, as can be seen.
The foregoing is provided merely for the purpose of facilitating understanding of the technical solutions of the present invention and is not intended to represent an admission that the foregoing is prior art.
Disclosure of Invention
The invention mainly aims to provide a grating filter and a Bragg grating-based wavelength division multiplexing demultiplexer, and aims to solve the technical problem that the existing wavelength division multiplexer is difficult to meet high-performance requirements.
To achieve the above object, the present invention provides a grating filter comprising:
the multimode Bragg grating comprises a multimode waveguide, grating teeth which are distributed in an antisymmetric way along the multimode waveguide and a tapered waveguide with gradually changed width; the grating teeth are periodically distributed on two sides of the multimode waveguide in a staggered mode, the grating tooth widths of the grating teeth gradually increase towards the center direction along two ends of the multimode waveguide, and the multimode Bragg grating adopts a positive dispersion design;
the mode multiplexing demultiplexer comprises an upper coupling waveguide and a lower coupling waveguide, wherein the upper coupling waveguide is an optical path main waveguide, the lower coupling waveguide is an uplink downlink waveguide, and the upper coupling waveguide is connected with the multimode Bragg grating.
In some embodiments, the grating tooth width ranges from 150nm to 1mm.
In some embodiments, the positive dispersion design includes:
the grating tooth width of the grating tooth is gradually increased;
and/or the number of the groups of groups,
the width of the multimode waveguide is gradually increased;
and/or the number of the groups of groups,
the grating teeth have gradually increasing grating teeth.
In some embodiments, grating tooth widths of the grating teeth sequentially arranged along two ends of the multimode waveguide towards the center direction are gradually increased.
In some embodiments, the width of the multimode waveguide increases gradually toward the center along both ends of the multimode waveguide.
In some embodiments, the periodic intervals of the grating teeth sequentially arranged along the two ends of the multimode waveguide towards the center direction are gradually increased.
In some embodiments, the upper coupling waveguide of the mode multiplexing demultiplexer includes a first input waveguide, a first coupling waveguide, and a first output waveguide, and the lower coupling waveguide of the mode multiplexing demultiplexer includes a second input waveguide, a second coupling waveguide, and a second output waveguide; wherein the first output waveguide is connected with the multimode Bragg grating.
In some embodiments, the first input waveguide of the upper coupling waveguide is a euler curved waveguide with gradually changed width, and the first output waveguide is a straight waveguide; the second input waveguide of the lower coupling waveguide is a straight waveguide, and the second output waveguide is a circular curved waveguide.
In some embodiments, the waveguide material of the multimode bragg grating comprises silicon nitride.
In addition, in order to achieve the above object, the present invention also provides a wavelength division multiplexing demultiplexer based on bragg grating, including: the grating filters according to at least two embodiments, wherein each grating filter has a different operating wavelength, and the grating filters are cascaded in order of increasing operating wavelength.
The invention provides a grating filter, comprising: the multimode Bragg grating comprises a multimode waveguide, grating teeth which are distributed in an antisymmetric way along the multimode waveguide and a tapered waveguide with gradually changed width; the grating teeth are periodically distributed on two sides of the multimode waveguide in a staggered mode, the grating tooth widths of the grating teeth gradually increase towards the center direction along two ends of the multimode waveguide, and the multimode Bragg grating adopts a positive dispersion design; the mode multiplexing demultiplexer comprises an upper coupling waveguide and a lower coupling waveguide, wherein the upper coupling waveguide is an optical path main waveguide, the lower coupling waveguide is an uplink downlink waveguide, and the upper coupling waveguide is connected with the multimode Bragg grating. According to the invention, grating teeth which are distributed in the whole process along the multimode waveguide in an antisymmetric way are used for exciting TE1/TE0 coupling peaks and simultaneously effectively inhibiting the occurrence of TE0/TE0 coupling peaks, so that the effect of full transmission in the external long wave direction of the working wavelength is realized, the problem that the TE1/TE0 coupling peaks and the TE0/TE0 coupling peaks in the multimode Bragg grating spectrum are too close to each other to contain other wavelength TE1/TE0 coupling peaks is solved, and the multi-wavelength division multiplexing and demultiplexing based on the TE1/TE0 coupling peaks are realized. And secondly, by means of apodization mode with gradually increased grating tooth width and grating positive color design, the effect of strong suppression of side lobes in long wave direction is realized, the problem of strong side lobes caused by non-zero minimum grating tooth width is solved, the crosstalk of the wavelength division multiplexer is effectively reduced, and the technical problem that the existing wavelength division multiplexer is difficult to meet high performance requirements is solved.
Drawings
FIG. 1a is a diagram of a multimode Bragg grating filter with symmetric-antisymmetric graded apodization;
FIG. 1b is a schematic diagram of the optical path interference of a cascaded filter during the wavelength division multiplexing process;
FIG. 2a is a schematic diagram of a grating filter according to an embodiment of the present invention in a wavelength division multiplexing scenario;
FIG. 2b is a schematic diagram of an embodiment of the present invention involving a grating filter in a demultiplexing scenario;
FIG. 2c is a schematic diagram of a grating filter according to an embodiment of the present invention;
FIG. 2d is a schematic structural diagram and a schematic simulation diagram of a grating filter according to an embodiment of the present invention;
FIG. 3a is a schematic diagram of an anti-symmetric multimode Bragg grating according to an embodiment of the invention;
FIG. 3b is a graph showing the light transmission spectrum of a grating filter at port 3 of FIG. 3a according to an embodiment of the present invention;
FIG. 4a is a schematic diagram of a positive dispersion design of a grating filter according to an embodiment of the present invention;
FIG. 4b is a graph showing the light transmission spectrum of a grating filter at port 2 of FIG. 4a according to an embodiment of the present invention;
FIG. 4c is a graph showing the light transmission spectrum of a grating filter at port 3 of FIG. 4a according to an embodiment of the present invention;
FIG. 4d is a schematic diagram of a negative dispersion design of a grating filter;
FIG. 4e is a graph of light transmission through the port 2 shown in FIG. 4 d;
FIG. 4f is a graph of light transmission at port 3 of FIG. 4 d;
FIG. 4g is a schematic diagram of a zero dispersion design of a grating filter;
FIG. 4h is a graph of light transmission at port 2 shown in FIG. 4 g;
FIG. 4i is a graph of light transmission at port 3 shown in FIG. 4 g;
FIG. 5 is a graph showing the transmission spectrum of the port 2 of the grating filter when the grating width w1=w2=1.3 um of the multimode waveguide is increased by 150nm, 300nm, 450nm, 600 nm;
FIG. 6a is a schematic diagram of a different curved waveguide structure of a mode multiplexing demultiplexer according to an embodiment of the present invention;
FIG. 6b is a schematic diagram illustrating a simulation of the insertion loss of the mode multiplexing demultiplexer of FIG. 6a according to an embodiment of the present invention;
FIG. 6c is a schematic cross-talk simulation diagram of the mode multiplexing demultiplexer of FIG. 6a according to an embodiment of the present invention;
FIG. 7a is a schematic diagram of a first configuration of a six-wavelength division multiplexer comprising multimode Bragg gratings according to an embodiment of the present invention;
FIG. 7b is a first simulated spectrum diagram of the six-wavelength division multiplexer of FIG. 7a according to an embodiment of the present invention;
FIG. 7c is a second simulated spectrum of the six-wavelength division multiplexer of FIG. 7a according to an embodiment of the present invention;
FIG. 8a is a schematic diagram of a second configuration of a six-wavelength division multiplexer comprising multimode Bragg gratings according to an embodiment of the present invention;
FIG. 8b is a first simulated spectrum diagram of the six-wavelength division multiplexer of FIG. 8a according to an embodiment of the present invention;
FIG. 8c is a second simulated spectrum of the six-wavelength division multiplexer of FIG. 8a according to an embodiment of the present invention.
The achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the 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.
It should be noted that all directional indicators (such as up, down, left, right, front, and rear … …) in the embodiments of the present invention are merely used to explain the relative positional relationship, movement, etc. between the components in a particular posture (as shown in the drawings), and if the particular posture is changed, the directional indicator is changed accordingly.
Furthermore, the description of "first," "second," etc. in this disclosure is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to base that the technical solutions can be realized by those skilled in the art, and when the technical solutions are contradictory or cannot be realized, the combination of the technical solutions should be considered to be absent and not within the scope of protection claimed in the present invention. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Aiming at the problem of temperature drift failure of the existing wavelength division multiplexer based on the silicon-based grating filter, the invention adopts the silicon nitride material to process the grating filter to reduce the temperature sensitivity of the device. The thermo-optic coefficient of the silicon nitride material is nearly an order of magnitude lower than that of silicon, the working wavelength of the silicon nitride Bragg grating has a temperature drift of only about 0.01nm/K, and in practical application, the wavelength division multiplexer works in the temperature range of-40 degrees to +80 degrees, and the working wavelength drift of the wavelength division multiplexer of the silicon nitride Bragg grating is smaller (1 nm) in the working temperature range of-40 degrees to +80 degrees. The Bragg grating-based wavelength division multiplexer has a flat-top bandwidth of approximately 10nm, and wavelength errors caused by temperature drift are negligible relative to the working bandwidth of approximately 10nm, so that the Bragg grating-based wavelength division multiplexer made of the silicon nitride material has the advantages of temperature insensitivity, broadband, low insertion loss, low crosstalk, small size and the like.
However, the multimode Bragg grating of the structure shown in FIG. 1a based on silicon nitride material is more serious in that the TE0/TE1 coupling peaks collide with the TE0/TE0 coupling peaks. For the silicon-based multimode Bragg grating, because the refractive index difference between the waveguide core material silicon and the cladding material silicon oxide is larger, the effective refractive index difference between the TE0 and TE1 modes is larger, so that the TE0/TE1 coupling peak and the TE0/TE0 coupling peak are far apart on the spectrum, and a plurality of TE0/TE1 coupling peaks with other wavelengths can be inserted into the middle of the waveguide core material silicon and the cladding material silicon oxide, so that the wavelength division multiplexing and demultiplexing of a few wavelengths are realized. However, for the silicon nitride multimode base Bragg grating, as the refractive index difference between the silicon nitride of the waveguide core material and the silicon oxide of the cladding material is smaller, the effective refractive index difference between the TE0 and TE1 modes is smaller, and the TE0/TE1 coupling peak and the TE0/TE0 coupling peak are relatively close in spectrum, and the TE0/TE1 coupling peak with other wavelengths cannot be inserted, so that multiplexing and demultiplexing of multiple wavelengths are difficult to realize.
Aiming at the problem that the TE0/TE1 coupling peak and the TE0/TE0 coupling peak conflict in the existing wavelength division multiplexer based on the grating filter, the invention adopts the whole-course antisymmetric distribution of the grating to inhibit the TE0/TE0 coupling peak, and inhibits the side lobe of the TE0/TE0 coupling peak through the apodization mode of gradual change of grating tooth width and positive dispersion design.
Referring to fig. 2a to 2d, an embodiment of the present invention relates to a structure of a grating filter as shown in fig. 2a, the grating filter including:
the multimode Bragg grating 100 comprises a multimode waveguide 101, grating teeth 102 distributed in an antisymmetric way along the whole course of the multimode waveguide 101 and a tapered waveguide 103 with gradually changed width; the grating teeth 102 are periodically distributed at two sides of the multimode waveguide 101 in a staggered manner, the grating tooth widths of the grating teeth 102 gradually increase along two ends of the multimode waveguide 101 towards the center, the multimode bragg grating 100 adopts a positive dispersion design, and the grating teeth 102 adopt an apodization mode with gradually changed widths, namely the grating tooth widths gradually increase from two ends to the center according to a gaussian function;
the mode multiplexing demultiplexer 200 includes an upper coupling waveguide and a lower coupling waveguide, where the upper coupling waveguide is an optical path main waveguide, the lower coupling waveguide is an uplink downlink waveguide, and the upper coupling waveguide is connected with the multimode bragg grating 100. The upper coupling waveguide comprises a first input waveguide 201, a first coupling waveguide 202, a first output waveguide 203, the lower coupling waveguide comprises a second input waveguide 204, a second coupling waveguide 205, a second output waveguide 206, the output end of the first output waveguide 203 of the upper coupling waveguide being connected to the input end of the multimode waveguide 101.
Specifically, as shown in FIG. 2a, a multimode waveguide 101 having a typical width, including but not limited to 1 to 1.7mm, may support transmission of TE1 modes. Grating teeth 102 are periodically distributed on the upper and lower sides of multimode waveguide 101 in a staggered manner, and the width of grating teeth 102 gradually increases from wg1 to wg2 from both ends to the center, and in consideration of the process line width requirement, the width wg1 of the grating teeth is 150nm at minimum, and the width of the grating teeth can gradually increase from 150nm to 1mm according to a gaussian function. The grating teeth p include, but are not limited to, 350nm to 450nm, and by properly setting the period interval p, the TE0 mode and TE1 mode of light of a particular wavelength can be back-coupled within the multimode bragg grating 100. The tapered waveguide 103 is width-shifted to facilitate matching with the width of the input waveguide of the next stage grating filter.
It should be noted that the mode multiplexing/demultiplexing device 200 may convert the TE0 mode light in the lower coupling waveguides (204-206) into the TE1 mode and couple the TE1 mode light in the multimode waveguide 101 into the multimode waveguide 101, and may also convert the TE1 mode light in the multimode waveguide 101 into the TE0 mode and couple the TE0 mode light into the lower coupling waveguides (204-206). The Bragg grating 100 is a dielectric grating with a periodically varying refractive index that reflects light of a particular wavelength and undergoes a TE0/TE1 mode transition. The mode multiplexing demultiplexer 200 and the bragg grating 100 cooperate to separate light with different wavelengths and form different spectrum channels, so as to realize multiplexing and demultiplexing of signals with different wavelengths.
The working principle of the grating filter in the wavelength division multiplexing and demultiplexing scene refers to fig. 2a and 2b, and fig. 2a is a schematic diagram of the grating filter in the wavelength division multiplexing scene according to the embodiment of the invention; fig. 2b is a schematic diagram of an embodiment of the present invention related to a grating filter in a demultiplexing scenario.
In an exemplary wavelength division multiplexing application scenario, as shown in fig. 2a, TE0 light with a specific wavelength enters from a port 2 of a second input waveguide 204 of the lower coupling waveguide, is uploaded into the multimode waveguide 101 through the mode multiplexing demultiplexer 200 and is converted into TE1 mode light, the TE1 mode light is reversely coupled with the TE0 mode light in the multimode bragg grating 100, and the reflected TE0 mode light is transmitted in the multimode waveguide 101 toward the port 1, so as to realize coupling of light with the specific wavelength from the lower coupling waveguide to the optical path main waveguide. In practical application, a plurality of grating filters are cascaded, so that light with different wavelengths can be coupled into the main waveguide, and wavelength division multiplexing is realized.
In an exemplary wavelength division multiplexing application scenario, as shown in fig. 2b, the multi-wavelength TE0 mode light enters the main waveguide from the port 1, where a certain wavelength TE0 mode light is reversely coupled with the TE1 mode light in the multimode bragg grating 100, the reflected TE1 mode light is coupled into the lower coupling waveguide (204-206) through the mode multiplexing demultiplexer 200 and converted into the TE0 mode light, and finally the light is output from the port 2, so as to separate the light with a certain wavelength from the main waveguide. In practical application, a plurality of grating filters are cascaded, so that multi-wavelength division multiplexing can be realized.
It should be noted that, as shown in fig. 3a, the multimode bragg grating 100 in this embodiment adopts a full-scale antisymmetric arrangement, and grating teeth 102 are periodically distributed on both sides of the multimode waveguide 101 in a staggered manner. In contrast, in the conventional scheme, the symmetrical-antisymmetric graded grating is shown in fig. 3b, the grating teeth at both ends are completely symmetrical along both sides of the main waveguide, and the grating teeth at the center are distributed in a staggered manner along both sides of the main waveguide, i.e., completely antisymmetric. In both fig. 3a and fig. 3b, the grating teeth adopt apodization with gradually increasing grating tooth width, and the width of the multimode waveguide 101 gradually narrows slightly while the grating teeth widen, so as to ensure that the refractive index during the period of the grating is unchanged, i.e. ensure zero dispersion of the grating.
Compared with the symmetrical-antisymmetric graded grating shown in fig. 3b, the multimode bragg grating (shown in fig. 3 a) which is arranged in a whole-process antisymmetric way can effectively inhibit the occurrence of TE0/TE0 coupling peaks (compare fig. 3a and 3 b) because of the absence of the symmetrical grating, so that only the TE0/TE1 coupling peaks exist in the whole spectrum (fig. 3 a), the effect of full transmission in the wavelength direction outside the working wavelength is realized, and the problem of conflict between the TE0/TE1 coupling peaks and the TE0/TE0 coupling peaks of the multimode bragg grating based on the silicon nitride material (the structure shown in fig. 1 a) is solved.
The present embodiment provides a grating filter including: the multimode Bragg grating 100 comprises a multimode waveguide 101, grating teeth 102 which are distributed in an antisymmetric way along the multimode waveguide 101, and a tapered waveguide 103; the grating teeth 102 are periodically distributed on two opposite sides of the multimode waveguide 101 in a staggered manner, and the grating teeth 102 adopt an apodization mode with gradually changed width, namely the width of the grating teeth gradually increases from two ends to the center according to a Gaussian function; the mode multiplexing demultiplexer 200 comprises a first input waveguide 201 of an upper coupling waveguide, a first coupling waveguide 202, a first output waveguide 203, and a second input waveguide 204, a second coupling waveguide 205, a second output waveguide 206 of a lower coupling waveguide, the output end of the first output waveguide 203 of the upper coupling waveguide being connected to the input end of the multimode waveguide 101. In this embodiment, grating teeth distributed in the whole process along the multimode waveguide are antisymmetric, so that the occurrence of a TE0/TE0 coupling peak can be effectively inhibited while a TE1/TE0 coupling peak is excited, the effect of total transmission in the external long wavelength direction of the working wavelength is realized, the problem that the TE1/TE0 coupling peak and the TE0/TE0 coupling peak cannot accommodate other wavelength TE1/TE0 coupling peaks due to too close distance in the multimode Bragg grating spectrum is solved, the multi-wavelength division multiplexing and demultiplexing based on the TE1/TE0 coupling peak are realized, and the working wavelength range can be expanded from the O band to the C band or even longer.
In some embodiments, the multimode bragg grating 100 employs a positive dispersion design that includes:
the grating tooth width of the grating tooth 102 is gradually increased;
and/or the number of the groups of groups,
the width of the multimode waveguide 101 gradually increases;
and/or the number of the groups of groups,
the grating teeth 102 have gradually increasing grating teeth spacing.
It can be appreciated that, compared to the symmetric-antisymmetric graded grating shown in fig. 3b, in this embodiment, the multimode bragg grating 100 adopts a full-scale antisymmetric arrangement (as shown in fig. 3 a), and the multimode bragg grating 100 has no symmetric grating, so that the occurrence of the TE0/TE0 coupling peak can be effectively suppressed, so that only the TE0/TE1 coupling peak exists in the whole spectrum (fig. 3 a). However, the multimode bragg grating 100 arranged in the whole-course antisymmetric manner does not have the apodization effect caused by the symmetrical-antisymmetric gradient, and can generate side lobes. Although the apodization method with gradually increasing grating tooth width can also suppress side lobes, the minimum grating tooth width cannot start from zero due to the limitation of the process line width, and the typical minimum grating width is 150nm, and the effect of the apodization of the grating on side lobe suppression is reduced by the non-zero minimum grating tooth width. As can be seen from the transmission spectrum of port 2 in fig. 3a, there are still strong side lobes on both sides of the operating wavelength.
In order to further suppress side lobes, in the embodiment, the side lobes in the long wave direction are strongly suppressed through the positive dispersion design, so that the effect of strong suppression of side lobes in the outer long wave direction and weak suppression of side lobes in the short wave direction of the working wavelength is achieved, and the problem that the side lobes of the coupling peak are stronger due to the non-zero minimum grating tooth width is solved. Specifically, the method for realizing positive dispersion includes, but is not limited to, the grating tooth width of the grating tooth 102, the width of the main waveguide, i.e., the multimode waveguide 101, gradually becoming wider, the grating tooth spacing gradually increasing, and the like.
In some embodiments, referring to fig. 2a, grating tooth widths of the grating teeth 102 sequentially arranged along two ends of the multimode waveguide 101 toward a center direction gradually increase.
Illustratively, the multimode waveguide 101 is a straight waveguide with a constant width, and the grating tooth widths wg1 and wg2 of the grating teeth 102 gradually increase along the two ends of the multimode waveguide 101 toward the center.
In some embodiments, referring to fig. 2a, the width of the multimode waveguide 101 increases gradually toward the center along both ends of the multimode waveguide 101.
As shown in fig. 2a, the width of the multimode waveguide 101 at both ends is w1, the width of the center of the multimode waveguide 101 is w2, and the widths gradually increase toward the center direction w1 to w2 along both ends of the multimode waveguide 101.
In some embodiments, referring to fig. 2a, the periodic intervals of the grating teeth 102 sequentially arranged in the center direction along both ends of the multimode waveguide 101 are gradually increased.
As shown in fig. 2a, the periodic interval of the grating teeth 102 is p, and the periodic interval p gradually increases toward the center along the two ends of the multimode waveguide 101.
It can be understood that, as shown in fig. 4a, a positive dispersion mode is adopted to shift the side lobe to the short wave direction outside the working wavelength, so as to realize the effect of strong suppression of the side lobe in the long wave direction and weak suppression of the side lobe in the short wave direction. The position of the side lobes depends on the dispersion of the bragg grating. As shown in fig. 4a to 4c, when the width of the multimode waveguide 101 is unchanged and the grating tooth width (e.g., wg1 to wg 2) is widened from narrow to narrow from the entrance to the central region, the multimode bragg grating 100 is positively dispersed, the light in the short wavelength direction of the working wavelength edge is reflected at the entrance of the multimode bragg grating 100, the light in the long wavelength direction is reflected at the center of the multimode bragg grating 100, and strong side lobes occur in the short wavelength direction of the working wavelength edge and weak side lobes in the long wavelength direction due to imperfect apodization of the grating at the entrance.
As shown in fig. 4d to 4f, when the width of the multimode waveguide 101 is narrowed from the entrance to the central region, the multimode bragg grating 100 is negatively dispersed, light in the long wavelength direction of the operating wavelength edge is reflected at the entrance of the multimode bragg grating 100, and light in the short wavelength direction is reflected at the center of the multimode bragg grating 100, and then stronger side lobes fall in the long wavelength direction of the operating wavelength edge.
In the case of zero dispersion, as shown in fig. 4g to 4i, the width of the multimode waveguide 101 is slightly reduced while the grating tooth width is increased, and when the effects of the increase and decrease of the grating tooth width on the refractive index of the waveguide mode cancel each other, the multimode bragg grating 100 is zero dispersion, and light within the operating wavelength range is reflected in a similar place in the multimode bragg grating 100, and the imperfect apodization at the entrance has an effect on the light on both sides of the edge of the operating wavelength, so that stronger side lobes can appear on both sides of the operating wavelength.
It should be noted that, in this embodiment, the multimode bragg grating 100 adopting the positive dispersion design realizes strong suppression of the side lobe in the long wave direction of the working wavelength edge, and the spectrum of the strong suppression of the side lobe in the long wave direction is favorable for realizing wavelength division multiplexing/demultiplexing.
Illustratively, the positive dispersion is achieved by, but not limited to, the grating tooth width of the grating tooth 102, the width of the main waveguide, i.e., the multimode waveguide 101, being gradually widened, and the grating tooth spacing being gradually increased. The positive dispersion mode can also be used for increasing the bandwidth of the working wavelength so as to adapt to different application scenes. As shown in fig. 5, when the grating tooth widths are sequentially increased by 150nm, 300nm, 450nm, and 600nm (as wg2 to wg1 in fig. 2 a), the corresponding operating wavelength bandwidths are 14nm, 18nm, 22nm, and 25nm, respectively. Therefore, by gradually widening the grating tooth width of the grating tooth 102, the width of the main waveguide, i.e., the multimode waveguide 101, and gradually increasing the grating tooth spacing, and the like, an increase in the operating wavelength bandwidth can also be achieved.
In some embodiments, referring to fig. 6a, the mode multiplexing demultiplexer 200 includes upper and lower coupling waveguides, the upper coupling waveguide including a first input waveguide 201, a first coupling waveguide 202, and a first output waveguide 203, and the lower coupling waveguide including a second input waveguide 204, a second coupling waveguide 205, and a second output waveguide 206.
The core functional areas of the mode multiplexing/demultiplexing device 200 are the first coupling waveguide 202 and the second coupling waveguide 205. However, since the waveguide spacing between the first coupling waveguide 202 and the second coupling waveguide 205 is only 100-300nm, and the width of both ends of the two waveguides is generally too wide or too narrow, the first input waveguide 201, the first output waveguide 203, the second input waveguide 204, and the second output waveguide 206 function to pull the spacing between the upper and lower waveguides by bending on the one hand, and waveguide width transition on the other hand. The bending position is selected from among the first input waveguide 201, the first output waveguide 203, the second input waveguide 204, and the second output waveguide 206, and the shape of the bending waveguide has a great influence on the loss crosstalk of the module multiplexer.
In this embodiment, as in structure 1 of fig. 6a, the first input waveguide 201 and the second output waveguide 206 are selected for bending because: the first input waveguide 201 and the second input waveguide 204 are measured in the input waveguide, compared with the second input waveguide 204, the width of the second input waveguide 204 is narrower, the bending of the second input waveguide 204 can cause larger loss and crosstalk, and the width of the first input waveguide 201 is wider, and the bending of the first input waveguide 201 can not cause excessive loss and crosstalk; on the output waveguide side, there are a first output waveguide 203 and a second output waveguide 206, in which, in comparison with the first output waveguide 203 being the main optical path channel and being required to carry TE1 mode, bending of the first output waveguide 203 causes greater loss and crosstalk, and the second output waveguide 206 is a non-output waveguide, and the light absorbing device is generally connected to dissipate the residual light therein, so that bending of the second output waveguide 206 does not increase loss and crosstalk.
In this embodiment, referring to structure 1 in fig. 6a, the first input waveguide 201 is an euler-curved waveguide with gradually changed width.
Specifically, the first input waveguide 201 of the mode multiplexing demultiplexer 200 is an euler curved waveguide with a gradual width. The loss caused by mode mismatch between the bent-straight waveguide is further reduced through the Euler bending design, meanwhile, the waveguide width is gradually widened in the Euler bending process, and finally the standard width (1 mm) of the silicon nitride waveguide is achieved. In addition, compared with the generally adopted waveguide arrangement mode of bending before widening, in this embodiment, the first input waveguide 201 is an euler bending waveguide with gradually changed width, and the mode of synchronously performing bending and widening can effectively reduce the area of the device, so that the method has better device design advantages when aiming at the silicon nitride waveguide device with larger bending radius.
In comparison to structure 1 of fig. 6a, structures 2 (207-212) and 3 (213-218) of fig. 6a have a conventional circular bend at the input waveguide 210 and the input waveguide 216, so that both the loss and crosstalk of structures 2 and 3 are relatively high. As shown in fig. 6b and 6c, the insertion loss and crosstalk of the structure 1 are respectively 0.04dB and-22 dB, the insertion loss and crosstalk of the structure 2 are respectively 0.4dB and-15 dB, and the insertion loss and crosstalk of the structure 3 are respectively 0.08dB and-20 dB, so that the loss and crosstalk of the structure 1 are better than those of the structures 2 and 3.
In this embodiment, the mode multiplexing and de-multiplexer 200 is selected to bend the first input waveguide 201 and the second output waveguide 206, and the first input waveguide 201 adopts euler bending with gradually changed width, so that the insertion loss and crosstalk of the mode multiplexing and de-multiplexer 200 are effectively reduced, and the size of the mode multiplexing and de-multiplexer 200 is reduced.
In some embodiments, the waveguide material of the multimode bragg grating 100 comprises silicon nitride.
It is understood that the waveguide material of the multimode bragg grating 100 includes, but is not limited to, silicon nitride material, silicon base, silicon oxide, etc., which is not limited in this embodiment.
In addition, the invention also provides a wavelength division multiplexing demultiplexer based on the Bragg grating, which comprises the following components: the grating filters according to at least two embodiments, wherein each grating filter has a different operating wavelength, and the grating filters are cascaded in order of increasing operating wavelength.
In this embodiment, the wavelength division multiplexer/demultiplexer based on the silicon nitride material has advantages of temperature insensitivity, broadband, low insertion loss, low crosstalk, small size, and the like, and has practical application value in the field of optical communication. The wavelength division multiplexer/demultiplexer is formed by cascading a plurality of wavelength grating filters, each comprising a multimode bragg grating 100 and a mode multiplexing demultiplexer 200. The wavelength division multiplexing demultiplexer based on the Bragg grating can realize the simultaneous processing and transmission of a plurality of wavelength signals, and improves the efficiency of optical communication and signal processing; high-density wavelength division multiplexing can be realized, and the bandwidth and capacity of optical communication are improved; the interval and the number of the spectrum channels can be flexibly adjusted by changing the parameters of the multimode Bragg grating 100; multimode bragg gratings 100 may be fabricated on different materials and wavelength bands to meet different application requirements. The multiplexing demultiplexer based on multimode Bragg grating has wide application prospect in the fields of optical communication, spectrum analysis, signal processing and the like, and can be used for wavelength division multiplexing transmission, optical signal processing, spectrum measurement, optical sensing and the like in an optical fiber communication system.
It should be noted that, aiming at the strong suppression characteristic of the single side lobe in the long wave direction of the multimode bragg grating in the filter, the embodiment provides a grating filter in which a plurality of wavelengths are connected in series according to the order in which the wavelengths are sequentially increased, and the cascade order in which the wavelengths are sequentially increased can effectively suppress the problem of high crosstalk caused by the single side strong side lobe in the short wave direction in the multimode bragg grating, thereby realizing the wavelength division multiplexing with low crosstalk.
Specifically, in terms of the architecture design of a wavelength division multiplexing demultiplexer, for a multimode bragg grating with strong suppression of single side lobes in a long-wave direction, a multimode bragg grating filter is proposed in which a plurality of wavelengths are connected in series in order of increasing wavelengths sequentially. Fig. 7a is a schematic diagram of a wavelength division multiplexer of six wavelengths 1271nm, 1291nm, 1311nm, 1331nm, 1351nm and 1371nm, where port 3 of the 1271nm bragg grating filter is connected to port 1 of the 1291nm bragg grating filter and port 3 of the 1291nm bragg grating filter is connected to port 1 of the 1311nm bragg grating filter, and in this way the 1331nm, 1351nm and 1371nm bragg grating filters are connected in this order, resulting in a wavelength division multiplexer/demultiplexer.
In practical applications, for example, in a wavelength division multiplexing application scenario, as shown in fig. 7a, light with different wavelengths enters from the ports 2 of the respective multimode bragg grating filters, and then is reflected by the multimode bragg grating 100 and is converged into the multimode waveguide 101. After light of 1371nm is converged into the multimode waveguide 101, the light needs to sequentially pass through multimode bragg grating filters of 1351nm, 1331nm, 1311nm, 1291nm and 1271nm, and the multimode bragg grating filters are nondestructive to light in the wavelength direction outside the working wavelength (as shown in fig. 3 a), so that the light of 1371nm can almost reach a port 1 of the multimode bragg grating filter of 1271nm in a nondestructive manner, and is converged with light of other wavelengths, and finally wavelength division multiplexing is completed.
FIGS. 7b and 7c are graphs of the transmission of light at port 1 of a 1271nm Bragg grating filter, which yields six wavelengths that are well-tuned, each waveguide having a long band top that is nearly flat with a flat top bandwidth of 15nm or more. As can be seen from fig. 7c, the insertion loss of 1271nm light is about 0.2dB, and the insertion loss of 1371nm light is about 0.7dB, because the long wavelength light travels longer and needs to pass through the multi-mode multiplexer-demultiplexer 200, the insertion loss is larger.
In practical applications, the wavelength division multiplexer has the same structure as that of the wavelength division multiplexer, and as shown in fig. 8a, when light with multiple wavelengths enters from the port 1 of the 1271nm bragg grating filter, the light sequentially passes through the 1271nm, 1291nm, 1311nm, 1331nm, 1351nm and 1371nm bragg grating filters, and the light with 1271nm, 1291nm, 1311nm, 1331nm, 1351nm and 1371nm is sequentially separated. Fig. 8b and 8c show the transmission spectra of the ports 2 of the bragg grating filters of each stage, so that the flat top bandwidth of the bragg grating filters of each stage is larger than or equal to 15nm. In terms of crosstalk performance, the wavelength interval of the six-wave multiplexer is 20nm, and light outside the 20nm bandwidth is regarded as crosstalk by taking the central wavelength of each channel as the center. Taking 1291nm channel as an example, the crosstalk in the short wave region (< 1281 nm) is less than-30 db, and the crosstalk in the long wave region (> 1301 nm) is less than-20 db. As shown in fig. 4b, the side lobe of the short wave direction outside the operating wavelength is larger, but in fig. 8b, the side lobe of the short wave direction is greatly suppressed, because the front stage 1271nm filter has already separated the light in the 1261 to 1281nm interval, and thus the crosstalk generated by the light in this interval to the next stage grating filter is very small. Although the 1271nm channel still maintains a large crosstalk in the short wavelength region, the wavelengths of light are set in consideration of practical communication applications, i.e., 1271nm, 1291nm, 1311nm, 1331nm, 1351nm and 1371nm, and only the problem of wavelength drift with temperature needs to be solved, so that no crosstalk occurs in the short wavelength region due to the fact that there is no wavelength shorter than 1271 nm.
The embodiment provides the grating filters with a plurality of wavelengths connected in series according to the sequence of the sequentially increased wavelengths, and the cascade sequence of the sequentially increased wavelengths can effectively inhibit the problem of high crosstalk caused by single-side strong side lobes in the short wave direction in the multimode Bragg grating, thereby realizing the wavelength division multiplexing with low crosstalk.
In addition, technical details not described in the embodiment of the bragg grating-based wavelength division multiplexing demultiplexer are applicable to the grating filter according to any embodiment of the present invention, and are not described herein.
It should be understood that the foregoing is illustrative only and is not limiting, and that in specific applications, those skilled in the art may set the invention as desired, and the invention is not limited thereto.
It should be noted that the above-described working procedure is merely illustrative, and does not limit the scope of the present invention, and in practical application, a person skilled in the art may select part or all of them according to actual needs to achieve the purpose of the embodiment, which is not limited herein.
Furthermore, it should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or system. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or system that comprises the element.
The foregoing embodiment numbers of the present invention are merely for the purpose of description, and do not represent the advantages or disadvantages of the embodiments.
From the above description of the embodiments, it will be clear to those skilled in the art that the above-described embodiment method may be implemented by means of software plus a necessary general hardware platform, but of course may also be implemented by means of hardware, but in many cases the former is a preferred embodiment. Based on such understanding, the technical solution of the present invention may be embodied essentially or in a part contributing to the prior art in the form of a software product stored in a storage medium (e.g. Read Only Memory)/RAM, magnetic disk, optical disk) and including several instructions for causing a terminal device (which may be a mobile phone, a computer, a server, or a network device, etc.) to perform the method according to the embodiments of the present invention.
The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the scope of the invention, but rather is intended to cover any equivalents of the structures or equivalent processes disclosed herein or in the alternative, which may be employed directly or indirectly in other related arts.
Claims (7)
1. A grating filter, the grating filter comprising:
the multimode Bragg grating comprises a multimode waveguide, grating teeth which are distributed in an antisymmetric way along the multimode waveguide and a tapered waveguide with gradually changed width; the grating teeth are periodically distributed on two sides of the multimode waveguide in a staggered mode, the grating tooth widths of the grating teeth gradually increase towards the center direction along two ends of the multimode waveguide, the multimode Bragg grating adopts a positive dispersion design, and the positive dispersion design comprises: the grating tooth width of the grating tooth is gradually increased; and/or the width of the multimode waveguide is gradually increased; and/or the grating teeth are gradually increased in grating teeth interval;
the mode multiplexing demultiplexer comprises an upper coupling waveguide and a lower coupling waveguide, wherein the upper coupling waveguide is an optical path main waveguide, the lower coupling waveguide is an uplink downlink waveguide, and the upper coupling waveguide is connected with the multimode Bragg grating; wherein,
the upper coupling waveguide of the mode multiplexing demultiplexer comprises a first input waveguide, a first coupling waveguide and a first output waveguide, and the lower coupling waveguide of the mode multiplexing demultiplexer comprises a second input waveguide, a second coupling waveguide and a second output waveguide; wherein the first output waveguide is connected with the multimode Bragg grating; the first input waveguide of the upper coupling waveguide is an Euler bending waveguide with gradually changed width, and the first output waveguide is a straight waveguide; the second input waveguide of the lower coupling waveguide is a straight waveguide, and the second output waveguide is a circular curved waveguide.
2. The grating filter of claim 1 wherein the grating tooth width ranges from 150nm to 1mm.
3. The grating filter of claim 1, wherein grating teeth of the grating teeth sequentially arranged in a central direction along both ends of the multimode waveguide have gradually increasing grating tooth widths.
4. The grating filter of claim 1, wherein the width of the multimode waveguide increases gradually toward the center along both ends of the multimode waveguide.
5. The grating filter of claim 1, wherein the periodic intervals of the grating teeth sequentially arranged in a central direction along both ends of the multimode waveguide are gradually increased.
6. The grating filter of any one of claims 1-5 wherein the waveguide material of the multimode bragg grating comprises silicon nitride.
7. A bragg grating-based wavelength division multiplexing demultiplexer, comprising: at least two grating filters according to any one of claims 1 to 6, each of which has a different operating wavelength, the grating filters being cascaded in order of increasing operating wavelength.
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