A waveguide grating filter, related apparatus and systems

Abstract

Embodiments of the present application disclose a waveguide grating filter, related equipment and system, which are used for improving the accuracy of filtering and reducing the loss of optical power of the straight-through output optical signal. The waveguide grating filter comprises a mode multiplexer, a connecting waveguide, a tapered grating and a straight-through waveguide connected in sequence. The tapered grating comprises a first grating region and a second grating region connected in sequence between the connecting waveguide and the straight-through waveguide. With the two sides of the connecting waveguide as a reference, the two sides of the first grating region are respectively concave to form a plurality of grating grooves. The lengths of the plurality of grating grooves increase in sequence along a first direction. The direction of the connecting waveguide pointing to the straight-through waveguide is the first direction. With the two sides of the straight-through waveguide as a reference, the two sides of the second grating region are respectively convex to form a plurality of external grating teeth. The lengths of the plurality of external grating teeth decrease in sequence along the first direction. The two sides of the tapered grating are both in an asymmetric structure.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, and in particular to a waveguide grating filter, related equipment and system. Background Technology

[0002] In the field of optical communication, waveguide grating filters can realize wavelength division multiplexing (WDM) to improve communication capacity.

[0003] Waveguide grating filters implement filtering based on axially apodized gratings. An axially apodized grating comprises a mode multiplexer and an axially apodized multimode waveguide grating (MWG). The mode multiplexer has an input waveguide and a downcarrier waveguide. The MWG has a through waveguide. This input waveguide receives a first optical signal. This first optical signal has a first wavelength and a fundamental mode. In the MWG, if the first optical signal satisfies the phase-matching condition, the axially apodized MWG transmits the first optical signal downcarrier to achieve filtering of the first optical signal.

[0004] However, in the MWG, the second optical signal also satisfies the phase-matching condition. This second optical signal has a second wavelength and an even-order mode. A portion of the optical power of this second optical signal is output via the input waveguide, resulting in a power loss in the second optical signal output from the through waveguide. Summary of the Invention

[0005] This application provides a waveguide grating filter, related devices, and a system for improving filtering accuracy and reducing the loss of optical power in the through-output optical signal.

[0006] A first aspect provides a waveguide grating filter. The waveguide grating filter includes a mode multiplexer, a connecting waveguide, an apodized grating, and a through waveguide connected in sequence. The mode multiplexer receives an optical signal from a first port of the mode multiplexer and transmits the optical signal via the connecting waveguide to the apodized grating. The apodized grating filters the optical signal to obtain a filtered optical signal. The apodized grating transmits the filtered optical signal to a second port of the mode multiplexer. The apodized grating includes a first grating region and a second grating region connected in sequence between the connecting waveguide and the through waveguide. Based on the two sides of the connecting waveguide, the two sides of the first grating region are respectively concave to form a plurality of grating grooves. The lengths of the plurality of grating grooves increase sequentially along a first direction. The direction from the connecting waveguide to the through waveguide is the first direction. Based on the two sides of the through waveguide, the two sides of the second grating region are respectively convex to form a plurality of first grating teeth. The lengths of the plurality of first grating teeth decrease sequentially along the first direction. The length of the connecting waveguide perpendicular to the first direction is greater than the length of the through waveguide perpendicular to the first direction. The lengths of the grating groove and the first grating tooth are both perpendicular to the first direction. Both sides of the apodized grating have an asymmetrical structure. The first grating tooth shown in this aspect can also be called an external grating tooth. This aspect improves the accuracy of optical signal filtering and achieves sidelobe suppression of the filtered optical signal. Furthermore, it reduces the optical power loss of the through output optical signal.

[0007] Based on the first aspect, in one optional implementation, the apodized grating has a first target grating tooth and a second target grating tooth. The first target grating tooth and the second target grating tooth are located on both sides of the apodized grating. The first target grating tooth and the second target grating tooth are adjacent in position. The first target grating tooth is either a second grating tooth or the first grating tooth. In the plurality of grating grooves, a second grating tooth is formed between any two adjacent grating grooves. After the first target grating tooth and the second target grating tooth are folded relative to each other along the axis of symmetry of the connecting waveguide in the first direction, there is a gap between the first target grating tooth and the second target grating tooth, or the first target grating tooth and the second target grating tooth partially overlap. The second grating tooth shown in this aspect can also be called an internal grating tooth. This implementation can improve the sidelobe suppression effect and effectively reduce crosstalk between the band of the filtered optical signal output by the waveguide grating filter and adjacent bands.

[0008] Based on the first aspect, in an optional implementation, the apodized grating further includes a third grating region. The third grating region connects the first grating region and the second grating region. Using the two sides of the through waveguide as a reference, the two sides of the third grating region bulge outwards to form multiple third grating teeth. The third grating teeth shown in this aspect can also be referred to as intermediate grating teeth. This implementation effectively reduces the optical power loss of the filtered optical signal.

[0009] Based on the first aspect, in one optional implementation, the side of the connecting waveguide located on the same side as the waveguide grating filter and the side of the third grating tooth are aligned. This implementation can effectively ensure the filtering accuracy of the waveguide grating filter.

[0010] Based on the first aspect, in one optional implementation, the proportion of the grating period in the third grating region is negatively correlated with the slope of the first curve. In the spectral image of the filtered optical signal, any optical power corresponding to the first curve is less than any optical power corresponding to a flat region of the spectral image. The proportion of the grating period in the third grating region is the percentage of the number of grating periods included in the third grating region to the total number of grating periods included in the apodized grating. This implementation, based on the correlation between the proportion of the grating period in the third grating region and the first curve, can reduce crosstalk between the waveguide grating filter output's filtered optical signal and adjacent wavebands.

[0011] Based on the first aspect, in one optional implementation, the flat region of the spectral image corresponds to the target band. The size of the target band's band range is negatively correlated with the proportion of the grating period in the third grating region. Based on the correlation between the target band's band range and the proportion of the grating period in the third grating region, the optical power of the filtered optical signal output by the waveguide grating filter can be adjusted.

[0012] Based on the first aspect, in one optional implementation, the first grating region has a first number of first grating periods. The second grating region has a second number of second grating periods. The ratio of the first number to the second number is negatively correlated with the slope of the second curve. In the spectral image of the filtered optical signal, any optical power corresponding to the second curve is less than any optical power corresponding to a flat region of the spectral image. This implementation, based on the correlation between the ratio of the first number and the second number and the slope of the second curve, can reduce crosstalk between the band of the filtered optical signal output by the waveguide grating filter and adjacent bands.

[0013] Based on the first aspect, in one optional implementation, the duty cycle of the first grating teeth is negatively correlated with the slope of the third curve. In the spectral image of the filtered optical signal, the optical power corresponding to any one of the third curves is less than the optical power corresponding to any one of the flat regions of the spectral image. Furthermore, the wavelength corresponding to any one of the third curves is less than the wavelength corresponding to any one of the flat regions of the spectral image. In this implementation, based on the correlation between the duty cycle of the first grating teeth and the slope of the third curve, it is possible to reduce crosstalk between the waveband of the filtered optical signal output by the waveguide grating filter and adjacent wavebands.

[0014] Based on the first aspect, in one optional implementation, the duty cycle of the first grating teeth is positively correlated with the slope of the fourth curve. In the spectral image of the filtered optical signal, the optical power corresponding to any one of the fourth curves is less than the optical power corresponding to any one of the flat regions of the spectral image. Furthermore, the wavelength corresponding to any one of the fourth curves is greater than the wavelength corresponding to any one of the flat regions of the spectral image. This implementation, based on the correlation between the duty cycle of the first grating teeth and the slope of the fourth curve, can reduce crosstalk between the wavelength band of the filtered optical signal output by the waveguide grating filter and adjacent wavelength bands.

[0015] The second aspect provides a wavelength division multiplexer. The wavelength division multiplexer includes a plurality of waveguide grating filters connected in sequence, as shown in any of the first aspects above. The plurality of waveguide grating filters includes a first waveguide grating filter and a second waveguide grating filter connected in sequence. A through waveguide of the first waveguide grating filter is connected to a mode multiplexer of the second waveguide grating filter. For an explanation of the advantages of this aspect, please refer to the first aspect; specific details will not be repeated here.

[0016] Based on the second aspect, in one optional implementation, the mode multiplexer of the first waveguide grating filter has an input waveguide and a download waveguide. The mode multiplexer of the second waveguide grating filter also has an input waveguide and a download waveguide. The through waveguide of the first waveguide grating filter is connected to the input waveguide of the second waveguide grating filter. The first waveguide grating filter is used to demultiplex the optical signal from the input waveguide of the first waveguide grating filter. Alternatively, the first waveguide grating filter is used to combine the optical signal from the download waveguide of the second waveguide grating filter.

[0017] A third aspect provides an optical communication system. It includes an optical transmitting device, a receiving device, and a wavelength division multiplexer as described in any of the second aspects above. The transmitting device is connected to the receiving device via the wavelength division multiplexer.

[0018] A fourth aspect provides an optical communication system. It includes an optical amplifier and a waveguide grating filter, as described in any of the first aspects above, connected to the optical amplifier. The optical amplifier is used to send an amplified optical signal to the waveguide grating filter, and the waveguide grating filter is used to filter the amplified optical signal.

[0019] A fifth aspect provides an optical communication device. The optical communication device includes a wavelength division multiplexer (WDM), an optoelectronic processing module, and a processor, as shown in any of the second aspects above, connected in sequence. The WDM is used to send a first filtered optical signal to the optoelectronic processing module. The optoelectronic processing module is used to perform optoelectronic conversion on the first filtered optical signal to obtain a first electrical signal. The optoelectronic processing module is used to send the first electrical signal to the processor. Alternatively, the processor is used to send a second electrical signal to the optoelectronic processing module. The optoelectronic processing module is used to perform electro-optical conversion on the second electrical signal to obtain an optical signal to be filtered. The optoelectronic processing module is used to send the optical signal to be filtered to the WDM. The WDM is used to filter the optical signal to be filtered to output a second filtered optical signal. Attached Figure Description

[0020] Figure 1 This is an example diagram of the overall structure of the waveguide grating filter provided in the embodiments of this application;

[0021] Figure 2 for Figure 1 The diagram shows a top view of the waveguide layer included in the waveguide grating filter.

[0022] Figure 3 for Figure 1 The diagram shows an example of the first structure of the apodized grating included in the waveguide grating filter.

[0023] Figure 4 for Figure 3 An example image of the spectral image of the apodized grating is shown;

[0024] Figure 5a Example diagram of the orthographic projection structure of the first type of apodized grating provided in the embodiments of this application;

[0025] Figure 5b for Figure 3 An example diagram of the orthographic projection structure of the apodized grating is shown;

[0026] Figure 5c Example diagram of the orthographic projection structure of the second type of apodized grating provided in the embodiments of this application;

[0027] Figure 6 This is a structural example diagram of the second type of apodized grating provided in the embodiments of this application;

[0028] Figure 7 for Figure 6 An example image of the spectral image of the apodized grating is shown;

[0029] Figure 8 A structural example diagram of the first optical communication system provided in the embodiments of this application;

[0030] Figure 9 For application to Figure 8 A structural example diagram of a wavelength division multiplexer for an optical communication system;

[0031] Figure 10a for Figure 9 An example image of the first type of spectral image of the wavelength division multiplexer shown;

[0032] Figure 10b for Figure 9 Example image of the second spectral image of the wavelength division multiplexer shown;

[0033] Figure 11 A structural example diagram of the first type of optical communication device provided in the embodiments of this application;

[0034] Figure 12 This is a structural example diagram of a second optical communication system provided in an embodiment of this application. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] Figure 1 This is an example diagram of the overall structure of the waveguide grating filter provided in an embodiment of this application. Figure 1As shown, the waveguide grating filter includes a substrate 101 and a waveguide layer 102 disposed on the substrate 101. The waveguide layer 102 is used to filter the received optical signal. The waveguide layer 102 can be made of any of the following materials: silicon (Si), silicon nitride (SiN) waveguide, lithium niobate (LiNbO3), or silicon oxide (SiO2) waveguide, etc. The refractive index of the substrate 101 is less than the refractive index of the waveguide layer 102. The surface of the waveguide layer 102 is covered with a cladding layer (not shown in the figure). The refractive index of this cladding layer is less than the refractive index of the waveguide layer 102. The waveguide layer 102 located on the surface of the substrate 101 can be a strip waveguide structure or a ridge waveguide structure; the specific structure type is not limited in this embodiment.

[0037] Combination Figure 2 The structure of waveguide layer 102 is illustrated below. Figure 2 for Figure 1 The diagram shows a top view of the waveguide layer included in the waveguide grating filter. The waveguide layer 102 includes a mode multiplexer 201, a connecting waveguide 202, an apodized grating 203, and a through waveguide 204 connected in sequence.

[0038] The mode multiplexer 201 includes an input waveguide 211, a first tapered waveguide 212, a download waveguide 213, and a second tapered waveguide 214. The first end of the first tapered waveguide 212 is connected to the input waveguide 211. The second end of the first tapered waveguide 212 is connected to a connecting waveguide 202. The length of the input waveguide 211 along the second direction Y remains constant. The length of the first tapered waveguide 212 along the second direction Y gradually increases along the first direction X, with the first end of the first tapered waveguide 212 as a reference. Here, the first direction X is the axial direction of the waveguide layer 102. For example, in this mode multiplexer 201, the direction from the input waveguide 211 to the second end of the first tapered waveguide 212 may be the first direction X. Similarly, the direction from the connecting waveguide 202 to the through waveguide 204 may also be the first direction X. The second direction Y is perpendicular to the first direction X. The input waveguide 211 is a single-mode waveguide. The first tapered waveguide 212 gradually increases in length along the second direction Y to become a multimode waveguide. For example, the input waveguide 211 supports the transmission of the transverse electric mode fundamental mode (TE0). The first tapered waveguide 212 supports at least the transmission of TE0 and the transverse electric mode first order mode (TE1).

[0039] The first end of the second tapered waveguide 214 is connected to the download waveguide 213. The download waveguide 213 has a curved structure. Along the second direction Y, the spacing between the input waveguide 211 and the download waveguide 213 gradually decreases along the first direction X. The download waveguide 213 is used to gradually change the weak coupling state of the input waveguide 211 and the download waveguide 213 from a relatively far distance to a relatively close strong coupling state along the first direction X. The length of the second tapered waveguide 214 along the second direction Y gradually decreases along the first direction X. The download waveguide 213 is a single-mode waveguide. The second end of the second tapered waveguide 214 is in a mode-free state.

[0040] The connecting waveguide 202 is connected to the second end of the first tapered waveguide 212. The connecting waveguide 202 extends along the first direction X, with the length of the second end of the first tapered waveguide 212 along the second direction Y as a reference. If the second end of the first tapered waveguide 212 is a multimode waveguide, then the connecting waveguide 202 is also a multimode waveguide. For example, if the first tapered waveguide 212 supports TE0 and TE1 transmission, then the connecting waveguide also supports TE0 and TE1 transmission. This embodiment does not limit the length of the connecting waveguide 202 along the first direction X. The description of the structure of the connecting waveguide 202 in this embodiment is illustrative and not limiting, as long as the connecting waveguide 202 at least supports TE0 and TE1 transmission and can guarantee thermal coupling. Thermal coupling means that the optical signal mode transmitted by the connecting waveguide 202 does not change inside the connecting waveguide 202. In this embodiment, the length of the connecting waveguide 202 along the second direction Y is greater than the length of the through waveguide 204 along the second direction Y. This embodiment uses a through waveguide 204 as a single-mode waveguide as an example. In this example, the number of modes supported by the connecting waveguide 202 is greater than the number of modes supported by the through waveguide 204. For example, the connecting waveguide 202 supports TE0 and TE1 transmission. The through waveguide 204 supports TE0 transmission.

[0041] Figure 3 for Figure 1The diagram illustrates a first structural example of an apodized grating included in a waveguide grating filter. The apodized grating 203 includes a first grating region 301 and a second grating region 302 sequentially connected between a connecting waveguide 202 and a through waveguide 204. Based on the two sides of the connecting waveguide 202, multiple grating grooves 311 are formed by recessing the two sides of the first grating region. Grating teeth are formed between any two adjacent grating grooves 311 in the first grating region 301. To distinguish between the grating teeth formed in the first grating region 301 and the grating teeth formed in the second grating region 302, the grating teeth formed in the first grating region 301 shown in this embodiment can be referred to as internal grating teeth 312 or second grating teeth 312. The grating teeth formed in the second grating region 302 can be referred to as external grating teeth 321 or first grating teeth 321. Multiple internal grating teeth 312 are arranged on both sides of the first grating region 301. Because the grating grooves 311 on both sides of the first grating region 301 are recessed with reference to the two sides of the connecting waveguide 202, the tips of the multiple internal grating teeth 312 located on the same side (e.g., the upper side) of the first grating region 301 are aligned and located on the same straight line 300. The upper side of the connecting waveguide 202 is also located on this straight line 300. The lengths of the multiple grating grooves 311 located on the same side of the first grating region 301 increase sequentially along the first direction X. The length of the grating groove 311 refers to the length of the grating groove 311 along the second direction Y. For example, the length of the grating groove closest to the second grating region 302 included in the first grating region 301 is... Figure 3 L1 is shown.

[0042] Based on the two sides of the through waveguide 204, multiple external grating teeth are formed by outward protrusion of the two sides of the second grating region 302. The lengths of the multiple external grating teeth 321 located on the same side of the second grating region 302 decrease sequentially along the first direction X. The length of the external grating tooth 321 refers to its length along the second direction Y. For example, the length of the external grating tooth 321 closest to the first grating region 301 in the second grating region 302 is... Figure 3 L2 is shown.

[0043] The first grating region 301 includes a first grating body 313 located in the middle. Multiple internal grating teeth 312 are formed on both sides of the first grating body 313. The length of the first grating body 313 along the second direction Y decreases sequentially along the first direction X. It can be understood that the length of the first grating body 313 near the connecting waveguide 202 is greater than the length of the first grating body 313 near the second grating region 302. The second grating region 302 includes a second grating body 322 located in the middle. Multiple external grating teeth 321 are formed on both sides of the second grating body 322. The length of the second grating body 322 along the second direction Y can remain constant. In this embodiment, the length of the second grating body 322 along the second direction Y is equal to the length of the through waveguide 204 as an example.

[0044] The second grating body 322 has an axis of symmetry 330. The length of the second grating body 322 along the second direction Y remains constant. The second grating body has an axisymmetric structure about the axis of symmetry 330. The apodized grating 203 has an asymmetric structure about the axis of symmetry 330. The filtering process of the waveguide layer 102 provided in this embodiment will be described below.

[0045] The first port of the mode multiplexer 201 receives multiple optical signals. This first port can be a port on the input waveguide of the mode multiplexer 201 used to receive the multiple optical signals. Each of the multiple optical signals has a TE0 mode. The multiple optical signals are transmitted sequentially through the input waveguide 211 and the first tapered waveguide 212 to the connecting waveguide 202. Because the length of the first tapered waveguide 212 gradually increases along the first direction X, the optical signal with the TE0 mode passes directly through the first tapered waveguide 212 to the connecting waveguide 202. The connecting waveguide 202 transmits the first optical signal to the apodized grating 203.

[0046] The multiple optical signals include multiple download optical signals with wavelengths located in the first band. In the apodized grating 203, the download optical signals located in the first band satisfy the phase matching condition. The download optical signals satisfying the phase matching condition are reflected and transmitted to the connecting waveguide 202 via TE1. The connecting waveguide 202 receives the download optical signals from the apodized grating 203, and the download optical signals received by the connecting waveguide 202 have TE1. The phase matching condition is (n0+n1)=λ / Λ. n0 is the effective refractive index of TE0. n1 is the effective refractive index of TE1. λ is the wavelength of the download optical signal. Λ is the grating period of the apodized grating 203. The grating period is the sum of the length of any grating tooth included in the apodized grating 203 and the length of the grating groove adjacent to that grating tooth along the first direction X.

[0047] The download optical signal with TE1, reflected to the connecting waveguide 202, is transmitted to the first tapered waveguide 212. TE1 in the first tapered waveguide 212 and TE0 in the second tapered waveguide 214 satisfy a phase-matching condition, causing the download optical signal to couple to the second tapered waveguide 214 with TE0. The download optical signal with TE0 is then transmitted sequentially via the second tapered waveguide 214 and the download waveguide 213 to the second port. The second port shown in this example is the port on the download waveguide 213 used for outputting the download optical signal.

[0048] The multiplexed optical signals received at the first port of the mode multiplexer 201 also include multiple direct optical signals with wavelengths in the second band. The first band is different from the second band. The direct optical signals in the second band do not satisfy the phase matching condition. The direct optical signals that do not satisfy the phase matching condition are transmitted directly along the apodized grating 203 to the direct waveguide 204. Moreover, the direct optical signals output through the direct waveguide 204 have TE0. In this embodiment, the length of the direct waveguide 204 along the second direction Y is less than the length of the connecting waveguide 202 along the second direction Y. Therefore, the direct waveguide 204 can increase the loss of higher-order modes. This effectively ensures that the direct waveguide 204 only outputs direct optical signals with TE0. This ensures the purity of the mode of the direct optical signal output by the direct waveguide 204. The description of the mode of the optical signal input to the first port and the mode of the optical signal reflected by the apodized grating 203 to the connecting waveguide 202 in this embodiment is for illustrative purposes only and is not intended to limit the scope.

[0049] The apodized grating 203 shown in this embodiment can filter out multiple download optical signals with wavelengths located in the first band from multiple optical signals. These multiple download optical signals are the filtered optical signals output by the apodized grating 203 after filtering the multiple optical signals. Furthermore, based on the structure of the apodized grating 203, sidelobe suppression of the multiple download optical signals can be achieved.

[0050] The following explanation, using spectral images of the waveguide grating filter, illustrates the filtering and sidelobe suppression process achieved by the waveguide grating filter. Specifically, the waveguide layer 102 of the waveguide grating filter is made of SiN. The substrate and cladding of the waveguide grating filter are made of SiO2. The length of the connecting waveguide 202 along the second direction Y is 1.6 micrometers (µm). The length of the through waveguide 204 along the second direction Y is 0.8 µm. The first wavelength band is from 1280 nm to 1340 nm.

[0051] Figure 4 for Figure 3 An example image of the spectral image of the apodized grating is shown. Figure 4The spectral images shown are the optical signals output from the download waveguide and the through waveguide. The horizontal axis represents wavelength in nanometers (nm), and the vertical axis represents normalized optical power in decibels (dB). Specifically, the multiple download optical signals output by this download waveguide correspond to... Figure 4 The waveform 401 shown (i.e. Figure 4 (As shown by the solid line). The waveform 402 (i.e., the waveform corresponding to the multi-channel direct optical signal output from the direct waveguide) is shown. Figure 4 (As shown by the dashed line).

[0052] Waveform 401 has a flat region 403. This flat region 403 includes multiple peaks of waveform 401. The optical power corresponding to the waveforms located on both sides of the flat region 403 is lower than the optical power corresponding to the flat region 403. Waveform 401 corresponding to the download waveguide demonstrates the sidelobe suppression function of the apodized grating 203 for multiple download optical signals located in the first band. Specifically, the first grating region 301 is used to achieve sidelobe suppression on the left side of the flat region 403 in the spectral image. The second grating region 302 is used to achieve sidelobe suppression on the right side of the flat region 403 in the spectral image.

[0053] Because the multiple through-light optical signals located in the second band do not meet the phase matching condition in the apodized grating 203, multiple through-light optical signals can be output from the through-light waveguide without loss via the apodized grating. Lossless output means that the difference between the first optical power and the second optical power is less than or equal to a threshold. The first optical power is the optical power of the through-light signal input from the input waveguide. The second optical power is the optical power of the through-light signal output from the through-light waveguide. When the first optical power and the second optical power are equal, the curve in waveform 402 corresponding to the second band has a linear structure. Because the curve in waveform 402 corresponding to the second band has a linear structure, the waveguide grating filter can reduce the loss of optical power in the through-light signal output from the through-light waveguide. The above example uses the first port for receiving multiple optical signals as the port of the input waveguide, and the second port for outputting the filtered download optical signal as the port of the download waveguide. In other examples, the first port for receiving multiple optical signals can also be a port of the download waveguide. The apodized grating filters the multiple optical signals from the download waveguide, outputting the filtered download optical signal at a second port. This second port is a port of the output waveguide. For a description of the filtering process of the apodized grating shown in this example, please refer to the above description; further details will not be repeated here.

[0054] The two sides of an apodized grating may have various asymmetrical structures, which will be discussed below. Figures 5a to 5c Let me explain in detail.

[0055] The first and second target grating teeth shown in this embodiment are folded relative to each other along the axis of symmetry 500 of the connecting waveguide in the first direction X, and there is a gap between the first and second target grating teeth. See details below. Figure 5a As shown, where, Figure 5a This is an example diagram of the orthographic projection structure of a first apodized grating provided in this application embodiment. The orthographic projection of the apodized grating is the image of the apodized grating on a projection surface under illumination by multiple projection lines. The multiple projection lines are perpendicular to the projection surface. The orthographic projection of the apodized grating includes a first orthographic projection 501 and a second orthographic projection 502. The first orthographic projection is the orthographic projection of a first target grating tooth. The second orthographic projection 502 is the orthographic projection of a second target grating tooth. The first target grating tooth and the second target grating tooth are located on opposite sides of the apodized grating. The first target grating tooth and the second target grating tooth are adjacent in position along a first direction X. The first target grating tooth is any grating tooth included on the first side of the apodized grating. The second target grating tooth is the grating tooth closest to the first target grating tooth among the plurality of grating teeth included on the second side of the apodized grating. Figure 5a The example shown uses grating teeth where both the first and second target grating teeth are grating teeth included in the first grating region, but this is not a limitation. For example, both the first and second target grating teeth could be grating teeth included in the second grating region. Alternatively, one of the first and second target grating teeth could be a grating tooth included in the first grating region, while the other is a grating tooth included in the second grating region.

[0056] Figure 5a There is a gap between the first orthographic projection 501 and the first extension region 503 of the second orthographic projection 502. The first extension region 503 is formed by extending the second orthographic projection 502 toward the first orthographic projection 501 along the axial direction of the second orthographic projection 502.

[0057] In this embodiment, the first and second target grating teeth are partially overlapped after the connecting waveguide is folded relative to each other along the axis of symmetry 500 in the first direction X. See details for further explanation. Figure 5b As shown, where, Figure 5b for Figure 3 The diagram shows an example of the orthographic projection structure of an apodized grating. The orthographic projection of this apodized grating includes a third orthographic projection 511 and a fourth orthographic projection 512. The third orthographic projection 511 is the orthographic projection of the first target grating tooth. The fourth orthographic projection 512 is the orthographic projection of the second target grating tooth. Along the axial direction of the fourth orthographic projection 512, the fourth orthographic projection 512 extends towards the direction of the third orthographic projection 511 to form a second extension region 513. For a description of the first and second target grating teeth, please refer to [link to documentation]. Figure 5a As shown, the specifics will not be elaborated further.

[0058] Figure 5b The second extended region 513 of the third orthographic projection 511 and the fourth orthographic projection 512 shown partially overlap. This partial overlap means that the first sidewall of the third orthographic projection 511 coincides with the second sidewall of the second extended region 513. The first sidewall is the sidewall of the third orthographic projection 511 facing the second extended region 513. The second sidewall is the sidewall of the second extended region 513 facing the third orthographic projection 511. The first and second sidewalls face each other.

[0059] In this embodiment, the first target grating teeth and the second target grating teeth partially overlap. See details below. Figure 5c As shown, where, Figure 5c This is an example diagram of the orthographic projection structure of the second type of apodized grating provided in an embodiment of this application. In this example, the partial overlap of the third orthographic projection 511 and the second extended region 513 means that the coverage area of ​​the third orthographic projection 511 and the coverage area of ​​the second extended region 513 partially overlap.

[0060] The different structures of the apodized grating shown in this embodiment will change the spectral image of the filtered optical signal output by the waveguide grating filter.

[0061] Example 1, see Figure 6 As shown. Figure 6 This is a structural example diagram of a second apodized grating provided in an embodiment of this application. The apodized grating shown in this embodiment includes a first grating region 601 and a second grating region 602. For a detailed description of the first grating region 601 and the second grating region 602, please refer to... Figure 3 The corresponding implementation examples are not described in detail here.

[0062] The apodized grating shown in this embodiment may further include a third grating region 603. The third grating region 603 connects the first grating region 601 and the second grating region 602. The two sides of the third grating region 603 protrude outwards to form a plurality of intermediate grating teeth 604. The intermediate grating teeth 604 shown in this embodiment may also be referred to as third grating teeth. The plurality of intermediate grating teeth have the same length along the second direction Y. Specifically, based on the two sides of the through waveguide 204, the two sides of the third grating region 603 protrude outwards to form a plurality of intermediate grating teeth 604. The two sides of the third grating region 602 have an asymmetrical structure; for details, please refer to [link to relevant documentation]. Figures 5a to 5cThe asymmetrical structure of the first grating region shown in any embodiment is not detailed here. Specifically, the sides of the connecting waveguide 202 located on the same side (as above) as the waveguide grating filter, the sides of the internal grating teeth, and the sides of the intermediate grating teeth 604 are aligned and located on the same straight line 300. For a description of this straight line 300, please refer to... Figure 3 The corresponding embodiments are not described in detail here. The third grating region shown in this embodiment can reduce the loss of optical power in the filtered optical signal output from the lower port.

[0063] The percentage of grating periods in the third grating region 603 shown in this embodiment is the percentage of the number of grating periods included in the third grating region 603 of the apodized grating to the total number of grating periods included in the apodized grating. The total number of grating periods included in the apodized grating is the sum of the number of grating periods in the first grating region 601, the second grating region 602, and the third grating region 603 included in the apodized grating. For an explanation of grating periods, please refer to [link to documentation]. Figure 3 The corresponding embodiments are not detailed here. In this embodiment, the proportion of the grating period in the third grating region 603 is negatively correlated with the slope of the first curve. In this spectral image, any optical power corresponding to the first curve is less than any optical power corresponding to a flat region of the spectral image. Specifically, the first curve is located on one side of a flat region in the spectral image. For example, the first curve is located on the left side of a flat region in the spectral image. Or, for example, the first curve is located on the right side of a flat region in the spectral image. For a description of this spectral image, please refer to [link to relevant documentation]. Figure 4 The corresponding implementation examples are not described in detail here.

[0064] Figure 7 for Figure 6 An example image of the spectral image of the apodized grating is shown. Figure 7The diagram shows two distinct spectral images: spectral image 701 (solid line) and spectral image 702 (dashed line). Spectral image 701 corresponds to a first apodized grating. Spectral image 702 corresponds to a second apodized grating. The first apodized grating differs from the second apodized grating. Specifically, the total number of grating periods included in the first apodized grating is the same as the total number of grating periods included in the second apodized grating. However, the number of grating periods included in the third grating region of the first apodized grating differs from the number of grating periods included in the third grating region of the second apodized grating. The third grating region of the first apodized grating corresponds to a first percentage. The third grating region of the second apodized grating corresponds to a second percentage. The first percentage is the percentage of the number of grating periods included in the third grating region of the first apodized grating relative to the total number of grating periods included in the first apodized grating. The second percentage is the percentage of the number of grating periods included in the third grating region of the second apodized grating relative to the total number of grating periods included in the second apodized grating.

[0065] The proportion of the grating period in the third grating region is negatively correlated with the slope of the first curve. In this embodiment, the duty cycle of the first target is less than that of the second target. Regardless of whether the first curve is located to the left or right of the flat area in spectral images 701 and 702, the slope of the first curve in spectral image 701 is greater than the slope of the first curve in spectral image 702.

[0066] In this embodiment, the flat region of the spectral image corresponds to the target band. The size of the target band's range is negatively correlated with the proportion of the grating period in the third grating region. (Continue to see...) Figure 7 In the example shown, the target band corresponding to the flat region of the spectral image in spectral image 701 has a band range of 711. The target band corresponding to the flat region of the spectral image in spectral image 702 has a band range of 712. When the duty cycle of the first target is less than the duty cycle of the second target, the band range 711 is greater than the band range 712.

[0067] Example 2: The first grating region included in the apodized grating has a first number of first grating periods. The second grating region included in the apodized grating has a second number of second grating periods. The ratio of the first number to the second number is negatively correlated with the slope of the second curve. Specifically, in this spectral image, any optical power corresponding to the second curve is less than any optical power corresponding to a flat region of the spectral image. Specifically, the second curve is located on one side of a flat region in the spectral image. For an explanation of this second curve, please refer to the explanation of the first curve shown in Example 1; further details will not be repeated here.

[0068] See also Figure 7 The example shown. In this example, Figure 7This includes spectral image 701 (shown by a solid line) and spectral image 702 (shown by a dashed line). Specifically, the first target ratio of the apodized grating corresponding to spectral image 701 is less than the second target ratio of the apodized grating corresponding to spectral image 702. The first target ratio is the number of first grating periods included in the first grating region and the number of second grating periods included in the second grating region in the apodized grating corresponding to spectral image 701. The second target ratio is the number of first grating periods included in the first grating region and the number of second grating periods included in the second grating region in the apodized grating corresponding to spectral image 702. In this example, the first target ratio is less than the second target ratio. Because the value of the target ratio is negatively correlated with the slope of the second curve, it can be understood that the slope of the second curve of spectral image 701 is greater than the slope of the second curve of spectral image 702.

[0069] The third target ratio of the apodized grating corresponding to spectral image 701 is less than the fourth target ratio of the apodized grating corresponding to spectral image 702. The third target ratio is the number of second grating periods included in the second grating region and the number of first grating periods included in the first grating region within the apodized grating corresponding to spectral image 701. The fourth target ratio is the number of second grating periods included in the second grating region and the number of first grating periods included in the first grating region within the apodized grating corresponding to spectral image 702. In this example, the third target ratio is less than the second target ratio. Since the target ratio is negatively correlated with the slope of the second curve, it can be understood that the slope of the second curve in spectral image 701 is greater than the slope of the second curve in spectral image 702.

[0070] Example 3: In this embodiment, the duty cycle of the target grating tooth is not limited. The duty cycle of the target grating tooth refers to the proportion of the length of the target grating tooth along the first direction X in one grating period within the apodized grating. The target grating tooth can be an internal grating tooth or an external grating tooth. For example... Figure 5b The duty cycle of each target grating tooth shown is 50%. For example, Figure 5a The duty cycle of each target grating tooth shown is 25%. For example, Figure 5c The duty cycle of each target grating tooth shown is 75%. In this example, the target band has the largest range in the spectral image of the filtered optical signal when the duty cycle of the target grating tooth is 50%. This target band corresponds to the band in the flat region of the spectral image. For a detailed explanation of the flat region of the spectral image, please refer to [link to relevant documentation]. Figure 6 The specific details of the corresponding embodiments are not elaborated here.

[0071] This example can also adjust the slope of the curves located on both sides of the flat region by adjusting the duty cycle of the target grating teeth. For example, the duty cycle of the target grating teeth is negatively correlated with the slope of the third curve. Alternatively, the duty cycle of the target grating teeth is positively correlated with the slope of the fourth curve. In the spectral image, any optical power corresponding to the third curve is less than any optical power corresponding to the flat region of the spectral image. Furthermore, any wavelength corresponding to the third curve is less than any wavelength corresponding to the flat region of the spectral image. It can be understood that the third curve is located to the left of the flat region of the spectral image. Similarly, in the spectral image, any optical power corresponding to the fourth curve is less than any optical power corresponding to the flat region of the spectral image. Furthermore, any wavelength corresponding to the fourth curve is greater than any wavelength corresponding to the flat region of the spectral image. It can be understood that the fourth curve is located to the right of the flat region of the spectral image.

[0072] The above example demonstrates how to adjust the slope of curves located on either side of flat regions in a spectral image. If a waveguide grating filter is used to combine or split multiple wavelengths, changing the slope of the curves on either side of flat regions in the spectral image can reduce crosstalk between different wavelengths. This effectively improves the sidelobe suppression performance of the waveguide grating filter.

[0073] This application also provides a wavelength division multiplexing (WDM) device. The WDM shown in this embodiment is applied to an optical communication network. This embodiment uses a passive optical network (PON) as an example. Figure 8 As shown, where, Figure 8 This is a structural example diagram of a first optical communication system provided in an embodiment of this application. The optical communication system includes an optical line terminal (OLT) 831 and an OLT 832. Both OLT 831 and OLT 832 are connected to a WDM 821, which in turn is connected to an optical distribution network (ODN) 811. The ODN 811 connects to multiple optical network units (ONUs). Figure 8 As shown, ODN811 is connected to four ODUs: ONU801-ONU804. It should be noted that, taking OLT831 as an example, the direction of optical signal transmission from OLT831 to ONU801 is called the downlink direction. The direction of optical signal transmission from ONU801 to OLT831 is called the uplink direction. The description of the number of OLTs and ONUs included in the optical communication system in this embodiment is optional and not limited.

[0074] The WDM implementation shown in this embodiment achieves optical signal multiplexing and / or demultiplexing. The following is combined with... Figure 9 The application shown is to Figure 8 The structure of the WDM optical communication system shown is explained. Figure 9 The applications provided in the embodiments of this application are to Figure 8 An example diagram of a WDM structure.

[0075] The WDM900 shown in this embodiment includes four waveguide grating filters. For a description of the structure of each waveguide grating filter, please refer to [link to documentation]. Figures 1 to 7 The embodiment shown is illustrated, and specific details will not be elaborated further. Specifically, the WDM900 includes waveguide grating filters 901, 902, 903, and 904 connected in sequence. The through waveguide of waveguide grating filter 901 is connected to the input waveguide of waveguide grating filter 902. The through waveguide of waveguide grating filter 902 is connected to the input waveguide of waveguide grating filter 903. The through waveguide of waveguide grating filter 903 is connected to the input waveguide of waveguide grating filter 904. Two adjacent waveguide grating filters shown in this embodiment can be connected via straight waveguides, wedge waveguides, or curved waveguides.

[0076] For example, the WDM821 is used to implement wavelength division multiplexing (WDM) functionality. Specifically, the ODN receives multiple first uplink optical signals from the ONU801 and multiple second uplink optical signals from the ONU802. The first uplink optical signals are optical signals with wavelengths within a first band (e.g., 1290nm to 1330nm). The second uplink optical signals are optical signals with wavelengths within a second band (e.g., 1260nm to 1280nm). The ODN811 combines the multiple first and second uplink optical signals into a single third uplink optical signal. The WDM821 is used to demultiplex the received third uplink optical signal to extract multiple first uplink optical signals and send them to the OLT831. The WDM821 is also used to demultiplex the third uplink optical signal to extract multiple second uplink optical signals and send them to the OLT832. Specifically, the waveguide grating filter 901 receives this third uplink optical signal. The apodized grating of the waveguide grating filter 901 reflects multiple first uplink optical signals to the download waveguide 911 of the waveguide grating filter 901. The download waveguide 911 is connected to the OLT831. Therefore, the download waveguide 911 can send multiple first uplink optical signals to the OLT831. The spectral image of these multiple first uplink optical signals is shown below. Figure 10a As shown. Figure 10a for Figure 9 An example image of the first type of spectral image of the wavelength division multiplexer is shown. Figure 10aAs shown, the waveguide grating filter 901 can filter out multiple first uplink optical signals located in the first band from the third uplink optical signal, and achieve sidelobe suppression of the multiple first uplink optical signals. Furthermore, the curves corresponding to the second band correspond to the same or similar optical power in the spectral image 1001. Multiple second uplink optical signals located in the second band can be directly transmitted to the waveguide grating filter 902 with almost no optical power loss via the waveguide grating filter 901. After receiving the multiple direct-through optical signals from the waveguide grating filter 901, the input waveguide of the waveguide grating filter 902 can filter out multiple direct-through optical signals. The download waveguide of the waveguide grating filter 902 is connected to the OLT832. The download waveguide of the waveguide grating filter 902 sends multiple second uplink optical signals to the OLT832. For a description of the filtering process of the waveguide grating filter 902, please refer to the description of the waveguide grating filter 901; details will not be elaborated here.

[0077] For example, the WDM821 can also perform wavelength division multiplexing (WDM). Specifically, the WDM821 receives multiple first downlink optical signals from the OLT831 and multiple second downlink optical signals from the OLT832. The multiple first downlink optical signals are optical signals with wavelengths within a third wavelength band, specifically 1480nm to 1450nm. The multiple second downlink optical signals are optical signals with wavelengths within a fourth wavelength band, specifically 1574.5nm to 1579.5nm.

[0078] In this example, the download waveguide 912 of the waveguide grating filter 903 is connected to the OLT831. The download waveguide 912 receives multiple first downlink optical signals from the OLT831. The apodized grating of the waveguide grating filter 903 reflects the filtered multiple first downlink optical signals to the input waveguide 914. The optical power of the multiple first downlink optical signals output from the input waveguide 914 is almost lossless, passing through the waveguide grating filters 902 and 901 directly to the input waveguide 915 of the waveguide grating filter 901. Similarly, the download waveguide 913 of the waveguide grating filter 904 is connected to the OLT832. The download waveguide 913 receives multiple second downlink optical signals from the OLT832. The apodized grating of the waveguide grating filter 904 reflects the filtered multiple second downlink optical signals to the input waveguide 916. The optical power of the multiple second downlink optical signals output from the input waveguide 916 is almost lossless and passes through the waveguide grating filter 903 and the waveguide grating filter 902 directly to the input waveguide 915 of the waveguide grating filter 901.

[0079] The downlink optical signal output from input waveguide 915 combines the filtered first downlink optical signals and the filtered second downlink optical signals. Specifically, see the spectral image of this input waveguide. Figure 10b As shown. Among them, Figure 10b for Figure 9 An example image of the second type of spectral image of the wavelength division multiplexer shown. Figure 10b As shown in the spectral image 1002, the input waveguide 915 of the waveguide grating filter 901 can combine multiple first downlink optical signals and multiple filtered second downlink optical signals. Furthermore, both the multiple first downlink optical signals and the multiple second downlink optical signals output from the input waveguide 915 can achieve sidelobe suppression. This input waveguide 915 is connected to ODN 811. ODN 811 is used to transmit the multiple first downlink optical signals to ONU 803. ODN 811 is also used to transmit the multiple second downlink optical signals to ONU 804.

[0080] The optical communication system shown in this embodiment can also be an industrial optical network, a data center network, a wavelength division multiplexing network, or an optical transport network (OTN), etc., and there is no specific limitation.

[0081] Figure 11 This is a structural example diagram of a first type of optical communication device provided in an embodiment of this application. The optical communication device 1100 includes a processor 1101, an optoelectronic processing module 1102, and a wavelength division multiplexer 1103 connected in sequence.

[0082] The functionality of processor 1101 can be partially or entirely implemented in hardware. Processor 1101 can be one or more chips, or one or more integrated circuits. For example, processor 1101 can be one or more field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), system-on-chips (SoCs), central processing units (CPUs), network processors (NPs), digital signal processors (DSPs), microcontroller units (MCUs), programmable logic devices (PLDs), or other integrated chips, or any combination of the above chips or processors.

[0083] When optical communication device 1100 receives a first optical signal from another optical communication device, the wavelength division multiplexer 1103 included in optical communication device 1100 is used to filter the first optical signal to obtain a first filtered optical signal. The wavelength division multiplexer 1103 sends the first filtered optical signal to the optoelectronic processing module 1102. The optoelectronic processing module 1102 is used to perform optoelectronic conversion on the first filtered optical signal to obtain a first electrical signal. The optoelectronic processing module 1102 shown in this example can be a photodetector. This example does not limit the device type of the optoelectronic processing module 1102, as long as the optoelectronic processing module 1102 can perform optoelectronic conversion. The optoelectronic processing module 1102 is used to send the first electrical signal to the processor.

[0084] When optical communication device 1100 needs to send an optical signal to another optical communication device, the processor 1101 included in optical communication device 1100 sends a second electrical signal to the optoelectronic processing module 1102. The optoelectronic processing module 1102 performs electro-optical conversion on the second electrical signal to obtain an optical signal to be filtered. The optoelectronic processing module 1102 shown in this example can be a modulator. This example does not limit the device type of the optoelectronic processing module 1102, as long as the optoelectronic processing module 1102 can perform electro-optical conversion. The optoelectronic processing module 1102 sends the optical signal to be filtered to wavelength division multiplexer 1103. The wavelength division multiplexer 1103 filters the optical signal to be filtered to output a second filtered optical signal.

[0085] Figure 12 This is a structural example diagram of a second optical communication system provided in this application embodiment. The optical communication device 1200 includes an optical amplifier 1201 and a waveguide grating filter 1202. The structure of the grating filter 1202 is as shown in the above embodiment, and will not be described in detail here. The optical amplifier 1201 is used to amplify the optical power of the received optical signal. The optical amplifier 1201 sends the amplified optical signal to the waveguide grating filter 1202. The waveguide grating filter 1202 is used to filter the amplified optical signal. The waveguide grating filter 1202 shown in this embodiment filters the amplified optical signal, which can suppress noise and thus improve the signal-to-noise ratio of the optical signal.

[0086] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A waveguide grating filter, characterized in that, It includes a mode multiplexer, a connecting waveguide, an apodized grating, and a through waveguide connected in sequence, wherein: The mode multiplexer is used to receive an optical signal from a first port of the mode multiplexer and to transmit the optical signal via the connected waveguide to the apodized grating; The apodized grating is used to filter the optical signal to obtain a filtered optical signal, and the apodized grating is used to transmit the filtered optical signal to the second port of the mode multiplexer; The apodized grating includes a first grating region and a second grating region sequentially connected between the connecting waveguide and the through waveguide; with the two sides of the connecting waveguide as a reference, the two sides of the first grating region are respectively recessed to form a plurality of grating grooves, the length of the plurality of grating grooves increases sequentially along a first direction, and the direction of the connecting waveguide pointing to the through waveguide is the first direction; Based on the two sides of the through waveguide, the two sides of the second grating region respectively bulge outward to form a plurality of first grating teeth, the length of the plurality of first grating teeth decreasing sequentially along the first direction; wherein, the length of the connecting waveguide along the perpendicular direction is greater than the length of the through waveguide along the perpendicular direction, and the length of the grating trench and the length of the first grating teeth are both perpendicular to the first direction. Both sides of the apodized grating have an asymmetrical structure.

2. The waveguide grating filter according to claim 1, characterized in that, The apodized grating has a first target grating tooth and a second target grating tooth. The first target grating tooth and the second target grating tooth are located on both sides of the apodized grating and are adjacent to each other. The first target grating tooth is either the second grating tooth or the first grating tooth. In the plurality of grating grooves, the second grating tooth is formed between any two adjacent grating grooves. The first target grating tooth and the second target grating tooth are folded relative to each other along the axis of symmetry of the connecting waveguide in the first direction, and there is a gap between the first target grating tooth and the second target grating tooth, or the first target grating tooth and the second target grating tooth partially overlap.

3. The waveguide grating filter according to claim 1 or 2, characterized in that, The apodized grating further includes a third grating region, which is used to connect the first grating region and the second grating region. With the two sides of the through waveguide as a reference, the two sides of the third grating region bulge outward to form a plurality of third grating teeth.

4. The waveguide grating filter according to claim 3, characterized in that, The side of the connecting waveguide located on the same side as the waveguide grating filter and the side of the third grating tooth are aligned.

5. The waveguide grating filter according to claim 3 or 4, characterized in that, The proportion of the grating period in the third grating region is negatively correlated with the slope of the first curve. In the spectral image of the filtered optical signal, any optical power corresponding to the first curve is less than any optical power corresponding to the flat area of ​​the spectral image. The proportion of the grating period in the third grating region is the percentage of the number of grating periods included in the third grating region to the total number of grating periods included in the apodized grating.

6. The waveguide grating filter according to claim 5, characterized in that, The flat region of the spectral image corresponds to the target band, and the size of the target band's range is negatively correlated with the proportion of the grating period in the third grating region.

7. The waveguide grating filter according to any one of claims 1 to 6, characterized in that, The first grating region has a first number of first grating periods, and the second grating region has a second number of second grating periods. The ratio of the first number to the second number is negatively correlated with the slope of the second curve. In the spectral image of the filtered optical signal, any optical power corresponding to the second curve is less than any optical power corresponding to the flat area of ​​the spectral image.

8. The waveguide grating filter according to any one of claims 1 to 7, characterized in that, The duty cycle of the first grating tooth is negatively correlated with the slope of the third curve. In the spectral image of the filtered optical signal, any optical power corresponding to the third curve is less than any optical power corresponding to the flat region of the spectral image, and any wavelength corresponding to the third curve is less than any wavelength corresponding to the flat region of the spectral image.

9. The waveguide grating filter according to any one of claims 1 to 8, characterized in that, The duty cycle of the first grating tooth is positively correlated with the slope of the fourth curve. In the spectral image of the filtered optical signal, any optical power corresponding to the fourth curve is less than any optical power corresponding to the flat region of the spectral image, and any wavelength corresponding to the fourth curve is greater than any wavelength corresponding to the flat region of the spectral image.

10. A wavelength division multiplexer, characterized in that, The wavelength division multiplexer includes a plurality of waveguide grating filters as described in any one of claims 1 to 9 connected in sequence; The plurality of waveguide grating filters include a first waveguide grating filter and a second waveguide grating filter connected in sequence, wherein the through waveguide of the first waveguide grating filter is connected to the mode multiplexer of the second waveguide grating filter.

11. The wavelength division multiplexer according to claim 10, characterized in that, The mode multiplexer of the first waveguide grating filter has an input waveguide and a download waveguide, and the mode multiplexer of the second waveguide grating filter has an input waveguide and a download waveguide. The through waveguide of the first waveguide grating filter is connected to the input waveguide of the second waveguide grating filter. The first waveguide grating filter is used to perform wave division on the optical signal from the input waveguide of the second waveguide grating filter, or the first waveguide grating filter is used to perform wave combination on the optical signal from the download waveguide of the second waveguide grating filter.

12. An optical communication system, characterized in that, It includes an optical transmitting device, a receiving device, and a wavelength division multiplexer as described in claim 10 or 11, wherein the transmitting device is connected to the receiving device via the wavelength division multiplexer.

13. An optical communication system, characterized in that, The device includes an optical amplifier and a waveguide grating filter as described in any one of claims 1 to 9 connected to the optical amplifier. The optical amplifier is used to send an optically amplified optical signal to the waveguide grating filter, and the waveguide grating filter is used to filter the optically amplified optical signal.

14. An optical communication device, characterized in that, The optical communication device includes a wavelength division multiplexer, an optoelectronic processing module, and a processor as described in claim 10 or 11, connected in sequence, wherein: The wavelength division multiplexer is used to send a first filtered optical signal to the optoelectronic processing module, the optoelectronic processing module is used to perform optoelectronic conversion on the first filtered optical signal to obtain a first electrical signal, and the optoelectronic processing module is used to send the first electrical signal to the processor. Alternatively, the processor is configured to send a second electrical signal to the optoelectronic processing module, the optoelectronic processing module is configured to perform electro-optical conversion on the second electrical signal to obtain an optical signal to be filtered, the optoelectronic processing module is configured to send the optical signal to be filtered to the wavelength division multiplexer, and the wavelength division multiplexer is configured to filter the optical signal to be filtered to output a second filtered optical signal.

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