Optical filter, wavelength division multiplexer and system

Abstract

The embodiment of the invention discloses an optical filter, a wavelength division multiplexer and a system, the optical filter comprises a mode multiplexer, a substrate, a cladding, a first grating, a second grating and a waveguide, and the mode multiplexer is connected with the waveguide. The cladding is disposed on the substrate and covers the mode multiplexer, the first grating, the waveguide and the second grating. The mode multiplexer is used for receiving optical signals from the input end of the optical filter and transmitting the optical signals to the waveguide, the first grating and the second grating. The first grating, the waveguide and the second grating are arranged at intervals in the first direction, and the first direction is parallel to the surface of the substrate. The design of the optical filter can reduce the limitation of bandwidth on the size of the grating teeth and reduce the difficulty of the production process. The distance between the first grating and the waveguide and the distance between the second grating and the waveguide are both decreased and then increased in the light transmission direction, the light transmission direction is parallel to the surface of the substrate and is perpendicular to the first direction, and the side lobe suppression function is achieved.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of communications, and in particular to an optical filter, a wavelength division multiplexer and a system. Background Art

[0002] In the field of optical communications, optical filters can implement wavelength division multiplexing (WDM) to increase communication capacity, while chip-level wavelength division multiplexers can achieve high-density integration in a small size.

[0003] like Figure 3 As shown, the optical filter 1 includes: a mode multiplexer 10 and a multimode waveguide grating (MWG) filter 20, and the MWG filter 20 includes: a waveguide 21. The side walls of the waveguide 21 are etched to form a grating 22. The grating 22 includes: a plurality of grating teeth. The amplitudes of the grating teeth are the same, and a tapered waveguide is provided between the mode multiplexer 10 and the waveguide 21. The width variation trend of the waveguide 21 along the z direction is first reduced and then increased, which is an amplitude apodization technology, and can reduce the front end reflection.

[0004] However, currently chip-level wavelength division multiplexers usually adopt a 180nm process node, so the etching accuracy of the waveguide width and gap is 180nm. Figure 3 The etching depth of the grating teeth, that is, the size of the grating teeth, is related to the bandwidth of the optical filter. For example, in an optical filter with a bandwidth of 20nm, the etching depth of the grating teeth is δ = 185nm. However, in an optical filter with a bandwidth of 10nm, the etching depth of the grating teeth is δ = 160nm. Figure 3 Only the position of the grating teeth is shown in the figure, and the size is the size of the grating teeth under the same bandwidth, which is not used as a reference). In addition, amplitude toe cutting is required on the grating teeth to make the characteristic size of the grating smaller, which requires higher processing accuracy and is difficult to be compatible with the current process line. Summary of the invention

[0005] The embodiments of the present application provide an optical filter, a wavelength division multiplexer and a system, which solve the problem of excessively high precision requirements for the existing optical filter processing technology.

[0006] In order to achieve the above-mentioned purpose, the embodiment of the present application adopts the following technical solution.

[0007] In a first aspect of an embodiment of the present application, an optical filter is provided, comprising: a mode multiplexer, a substrate, a cladding, a first grating, a second grating and a waveguide, wherein the mode multiplexer is connected to the waveguide. The cladding is arranged on the substrate, and the cladding covers the mode multiplexer, the first grating, the waveguide and the second grating. The mode multiplexer is used to receive an optical signal from the input end of the optical filter and transmit the optical signal to the waveguide and the first grating and the second grating. The first grating, the waveguide and the second grating are arranged at intervals along a first direction, wherein the first direction is parallel to the surface of the substrate. The spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, are both first reduced and then increased along the light transmission direction, and the light transmission direction is parallel to the surface of the substrate and perpendicular to the first direction. Thus, in the present application, the first grating and the second grating are arranged in the cladding, so that the first grating, the second grating and the waveguide are arranged at intervals. Compared with the prior art arrangement of connecting the first grating, the second grating and the waveguide as a whole, the limitation of bandwidth on the size of the grating teeth can be reduced, so that the size of the grating teeth meets the requirements of the silicon photonics 180nm CMOS process line. In addition, the present application adjusts the spacing between the first grating, the second grating and the waveguide, so that the spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, first decrease and then increase along the light transmission direction, and the overall pattern is large-small-large, so as to achieve the function of sidelobe suppression.

[0008] In an optional implementation, the shape of the waveguide near the first grating and the second grating can be adjusted, and / or the shape of the first grating and the second grating can be adjusted so that the spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide are gradually changed. The spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, are both reduced first and then increased along the light transmission direction, so as to achieve the function of sidelobe suppression.

[0009] Optionally, the first grating and the second grating are both distributed in arc lines. Thus, the shapes of the first grating and the second grating can be adjusted so that the first grating and the second grating on both sides of the waveguide are arc-shaped and bend in the direction away from the waveguide respectively. The design of the grating makes the spacing between the first grating and the waveguide, as well as the spacing between the second grating and the waveguide, first decrease and then increase along the light transmission direction, thereby realizing the function of sidelobe suppression. Alternatively, the side of the waveguide close to the grating adopts an arc surface. Thus, the surface shape of the waveguide close to the grating side can be adjusted so that the two surfaces of the waveguide close to the first grating and the second grating are respectively arc-shaped surfaces, and are respectively bent in the direction close to the first grating and the second grating. The design of the waveguide makes the spacing between the first grating and the waveguide, as well as the spacing between the second grating and the waveguide, first decrease and then increase along the light transmission direction, thereby realizing the function of sidelobe suppression. Alternatively, the first grating and the second grating on both sides of the waveguide may be arc-shaped and bend in directions away from the waveguide, and the two surfaces of the waveguide close to the first grating and the second grating may be arc-shaped and bend in directions close to the first grating and the second grating. The design of the waveguide and the grating allows the spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide to decrease first and then increase along the light transmission direction, thereby achieving the function of sidelobe suppression.

[0010] In an optional implementation, the grating tooth periods of the first grating and the second grating first decrease and then increase along the light transmission direction, thereby further achieving the function of sidelobe suppression.

[0011] In an optional implementation, the period of the i-th grating tooth of the first grating and the second grating satisfies:

[0012]

[0013] Where i = 1, 2, ..., n, T0 is the initial period, β i is the propagation constant at the i-th grating location, κ i is the coupling coefficient at the i-th grating location, is the coupling coefficient of the n / 2th grating. Thus, the grating tooth periods of the first grating and the second grating can be reduced first and then increased along the light transmission direction.

[0014] In an optional implementation, the grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating are arranged in a staggered manner, and the displacement of the grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating is half of the grating tooth period. Thus, the first grating and the second grating are arranged asymmetrically with respect to the waveguide, and the staggered displacement is half of the grating tooth period, which effectively reduces the crosstalk between the band in which the filtered optical signal output by the optical filter is located and the adjacent band.

[0015] In an optional implementation, the first grating is distributed in an axisymmetric manner based on a first symmetry axis, and the second grating is distributed in an axisymmetric manner based on a second symmetry axis, and both the first symmetry axis and the second symmetry axis are parallel to the first direction. Thus, the first grating and the second grating are axisymmetric structures, and the spacing between the first grating and the waveguide changes gradually, and the spacing between the second grating and the waveguide changes symmetrically, and the side lobe suppression effect is also symmetrical, and the effect is better.

[0016] In an optional implementation, the waveguide, the first grating and the second grating are all connected to the surface of the substrate, thereby making the manufacturing process simpler.

[0017] In an optional implementation, the first grating and the second grating are spaced apart from the substrate in the second direction, and / or the waveguide is spaced apart from the substrate in the second direction, wherein the second direction is perpendicular to the surface of the substrate. Thus, the spacing between the grating and the waveguide and the substrate can be adjusted as needed, and the structure is more flexible.

[0018] In an optional implementation, the waveguide is a ridge waveguide or a strip waveguide, thereby making the structure of the waveguide more flexible.

[0019] In an optional implementation, the method further includes: a connecting waveguide, through which the mode multiplexer is connected to the waveguide, so that the optical signal mode transmitted by the connecting waveguide does not change inside the connecting waveguide, and the transmission stability is better.

[0020] The second aspect of the embodiment of the present application provides a wavelength division multiplexer, comprising a plurality of optical filters as described above, wherein the plurality of optical filters are cascaded, and the plurality of optical filters are connected by connecting waveguides. Thus, the wavelength division multiplexer adopts the above optical filters, which can reduce the limitation of bandwidth on the size of grating teeth, can adopt the requirements of 180nm CMOS process line, and is convenient for large-scale production. In addition, the function of sidelobe suppression can also be realized.

[0021] In an optional implementation, the wavelength division multiplexer further comprises: a plurality of optical fibers, the plurality of optical fibers are respectively connected to the input ends of the plurality of optical filters and the output ends of the plurality of optical filters. Thus, the wavelength division multiplexer is connected to the optical fiber, and signals can be transmitted through the optical fiber.

[0022] The third aspect of the embodiment of the present application provides a passive optical network system, including: a plurality of optical line terminals; a wavelength division multiplexer, the wavelength division multiplexer is connected to the plurality of optical line terminals through optical fibers, the wavelength division multiplexer adopts the wavelength division multiplexer as described above; an optical distribution network, the optical distribution network is connected to the wavelength division multiplexer through optical fibers; a plurality of optical network terminals, the plurality of optical network terminals are connected to the optical distribution network through optical fibers. Thus, the passive optical network system adopts the wavelength division multiplexer as described above, which can improve the wavelength division multiplexing performance of the passive optical network system.

[0023] In an optional implementation, the optical modules of some of the optical line terminals are GPON optical modules, the optical modules of another part of the optical line terminals are 10GPON optical modules, and the optical modules of another part of the optical line terminals are 50G-PON optical modules. Thus, the wavelength division multiplexer can be used to realize the function of combining and / or dividing optical signals.

[0024] The fourth aspect of the embodiment of the present application provides a wavelength division multiplexing system, comprising: a first optical converter, the first optical converter is used to perform optical conversion on the received signal; a multiplexer, the multiplexer includes the optical filter as described above, the multiplexer is used to couple the optical signals of multiple wavelengths converted by the first optical converter to the optical fiber; a demultiplexer, the demultiplexer includes the optical filter as described above, the demultiplexer is connected to the multiplexer through the optical fiber, and the demultiplexer is used to separate the coupled optical signal; a second optical converter, the second optical converter is used to restore the optical signal transmitted by the demultiplexer. Therefore, the multiplexer and demultiplexer of the wavelength division multiplexing system adopt the above-mentioned optical filter, which can reduce the process accuracy requirements for the optical filter and reduce the difficulty of the production process. And realize the function of sidelobe suppression.

[0025] In an optional implementation, the wavelength division multiplexing system further includes: an optical amplifier, the optical amplifier is located between the multiplexer and the demultiplexer, the optical amplifier is used to amplify the power of the optical signal transmitted by the multiplexer, and send the optical signal after the optical power amplification to the demultiplexer. Thus, by setting the optical amplifier, the optical power amplification can be achieved.

[0026] The embodiment of the present application provides an optical filter, a wavelength division multiplexer and a system, wherein the optical filter includes: a mode multiplexer, a substrate, a cladding, a first grating, a second grating and a waveguide, the mode multiplexer and the waveguide are connected, wherein the cladding is arranged on the substrate, and the cladding covers the mode multiplexer, the first grating, the waveguide and the second grating; the mode multiplexer is used to receive an optical signal from the input end of the optical filter, and transmit the optical signal to the waveguide and the first grating and the second grating; wherein the first grating, the waveguide and the second grating are arranged at intervals along a first direction, and the first direction is parallel to the surface of the substrate; the bandwidth limitation on the grating tooth size can be reduced, and the difficulty of the production process can be reduced. The spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, are first reduced and then increased along the light transmission direction, and the light transmission direction is parallel to the surface of the substrate and perpendicular to the first direction, so as to realize the function of sidelobe suppression. Among them, the shape of the waveguide close to the first grating and the second grating side can be adjusted, and / or, the shape of the first grating and the second grating can be adjusted so that the spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide are gradually changed. The spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, are both reduced first and then increased along the light transmission direction, so as to achieve the function of sidelobe suppression. In some embodiments, the period of the grating teeth of the first grating and the second grating can also be adjusted so that the period of the grating teeth of the first grating and the second grating is reduced first and then increased along the light transmission direction. The function of sidelobe suppression can be further achieved. In addition, the grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating are arranged in a staggered position, and the displacement size of the position misalignment of the grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating is half of the grating tooth period. Thus, the first grating and the second grating are arranged asymmetrically about the waveguide, and the displacement is half of the grating tooth period, which effectively reduces the crosstalk between the band where the filtered light signal output by the optical filter is located and the adjacent band. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the upstream and downstream wavelengths of a passive optical network;

[0028] Figure 2 It is a structural schematic diagram of a passive optical network system;

[0029] Figure 3 is a structural schematic diagram of an optical filter;

[0030] Figure 4 for Figure 3 Simulation diagram of the transmission spectrum of the medium optical filter;

[0031] Figure 5 A schematic diagram of the structure of an optical filter provided in an embodiment of the present application;

[0032] Figure 6 A three-dimensional diagram of an optical filter provided in an embodiment of the present application;

[0033] Figure 7 For the first Figure 6 AA section view in;

[0034] Figure 8 For the second Figure 6 AA section view in;

[0035] Fig. 9 For the third Figure 6 AA section view in;

[0036] Fig.10 For the fourth Figure 6 AA section view in;

[0037] Fig.11 The fifth Figure 6 AA section view in;

[0038] Fig.12 A schematic diagram of the structure of a waveguide grating provided in an embodiment of the present application;

[0039] Fig.13 for Fig.12 A graph showing the variation of the spacing between the waveguide and the grating along the direction of light transmission;

[0040] Fig.14 A schematic diagram of a spectrum image of a grating when the spacing between the waveguide and the grating remains unchanged along the light transmission direction;

[0041] Fig.15 for Fig.12 Schematic diagram of the spectrum image of the waveguide grating shown;

[0042] Fig.16 A schematic diagram of the structure of another waveguide grating provided in an embodiment of the present application;

[0043] Fig.17 for Fig.16 A graph showing the variation of the waveguide width along the light transmission direction;

[0044] Fig.18 for Fig.16 Schematic diagram of the spectrum image of the waveguide grating shown;

[0045] Fig.19 A schematic diagram of the structure of another waveguide grating provided in an embodiment of the present application;

[0046] Fig. 20 for Fig.19 A graph showing the variation of the grating tooth period along the light transmission direction;

[0047] Fig.21 for Fig.19 Schematic diagram of the spectrum image of the waveguide grating shown;

[0048] Fig. 22 A schematic diagram of the structure of a wavelength division multiplexing system provided in an embodiment of the present application;

[0049] Fig.23 A schematic diagram of the structure of a wavelength division multiplexer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings.

[0051] In the following, the terms "first", "second", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0052] In addition, in the present application, directional terms such as "upper" and "lower" are defined relative to the orientation of the components in the drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, and they can change accordingly according to the changes in the orientation of the components in the drawings.

[0053] Passive Optical Network (PON): Passive optical network refers to the optical distribution network (ODN) between the optical line terminal (OLT) and the optical network terminal (ONT). OLT is used to provide the network side interface of the optical access network and is a device connected to one or more ODNs. ONT is directly located at the user end and is a device in the access network that provides the network for users. It can provide high-speed Internet access, IPTV, voice, Wi-Fi and other services. ODN is a fiber-to-the-home optical cable network based on PON equipment.

[0054] Wavelength Division Multiplexing (WDM): Wavelength division multiplexing is a technology that combines two or more optical carrier signals of different wavelengths (carrying various information) at the transmitting end through a multiplexer (also called a combiner) and couples them to the same optical fiber of the optical line for transmission; at the receiving end, the optical carriers of various wavelengths are separated by a demultiplexer (also called a splitter or demultiplexer), and then further processed by the optical receiver to restore the original signal. This technology of simultaneously transmitting two or more optical signals of different wavelengths in the same optical fiber is called wavelength division multiplexing.

[0055] Optical transmission module: referred to as optical module, including two parts: Bi-directional Optical sub-assembly (BOSA) and Electronic Subassembly (ESA). The pins of the optical transceiver assembly are electrically connected to the peripheral ESA, and then installed into the optical module housing to form an optical transmission module.

[0056] At present, with the increasing demand for communication capacity, access networks are gradually evolving from GPON and 10G PON to 50G PON. In order to ensure the compatibility and smooth evolution of multiple generations of PON, a low-cost coexistence solution of GPON, 10G PON and 50G PON is needed. The latest revised standard of 50G PON takes into account the need for coexistence of three generations and adds the 1284-1288nm band as a 50G uplink option. Figure 1 Figure 1 is a schematic diagram of the upstream and downstream wavelengths of a passive optical network. Figure 1 As shown, the upstream rates include: GPON upstream, 10G PON upstream and 50G PON upstream wavelength. The downstream rates include: GPON downstream, 10G PON downstream and 50GPON downstream wavelength.

[0057] Figure 2 Figure 1 is a schematic diagram of the structure of a passive optical network system. Figure 2 As shown, in some embodiments, the PON network is composed of an OLT at the central office, an ONT at the user side, a wavelength division multiplexer and an ODN. Among them, the OLT is the convergence device of the PON system, providing an optical interface between the service network and the ODN. The ONT is located on the user side, providing an optical interface between the user and the ODN and an electrical interface on the user side. The ODN is responsible for the transmission, distribution and multiplexing of data information. The OLT end and the ONT end in the PON network adopt a point-to-multipoint topology.

[0058] In some embodiments, the OLT side includes OLTs with three rates: GPON, 10G PON, and 50G PON. Each rate corresponds to two wavelengths for upstream and downstream, for a total of 6 wavelengths. The ONT side includes ONTs with three rates: GPON, 10G PON, and 50G PON. Each rate corresponds to two wavelengths for upstream and downstream, for a total of 6 wavelengths.

[0059] For example, Figure 2 As shown, the passive optical network system includes: 3 OLTs: GPON OLT, 10G PON OLT, 50GPON OLT, each OLT is connected to the WDM through an optical fiber, the WDM is connected to the optical distribution network, and the optical distribution network is connected to the ONT.

[0060] The optical distribution network includes, for example, an optical splitter and an optical fiber connected to the optical splitter. The optical splitter is connected to a wavelength division multiplexer through an optical fiber, and the optical splitter is connected to an ONT through an optical fiber. Among them, there are three types of ONTs: GPON ONT, 10G PON ONT, and 50GPON ONT. Each ONT is connected to the optical splitter through an optical fiber. When working, the six wavelengths on the OLT side can be combined in the WDM, then enter the ODN for transmission, and then distributed to different ONTs through the optical splitter.

[0061] The optical communication system shown in the embodiment of the present application may also be an industrial optical network, a data center network, a wavelength division multiplexing network, or an optical transport network (OTN), etc., without specific limitation.

[0062] In some embodiments, the WDM can be used in a 50G PON passive optical network system.

[0063] In some embodiments, the optical modules of some of the optical line terminals are GPON optical modules, the optical modules of another part of the optical line terminals are 10GPON optical modules, and the optical modules of another part of the optical line terminals are 50G-PON optical modules. For example, the WDM can be integrated in a 50G PON optical module.

[0064] In some embodiments, the WDM is a packaged chip.

[0065] In some embodiments, the WDM further comprises: a plurality of optical fibers, and the plurality of optical fibers are respectively connected to the WDM. In the above embodiments, the wavelength division multiplexer can transmit the different wavelengths of the plurality of signals in a directional manner, and realize the simultaneous transmission of the plurality of signals through optical wave separation and optical wave synthesis. For example, the wavelength division multiplexer can transmit the plurality of optical signals in the same optical fiber, thereby improving the utilization rate of the optical fiber.

[0066] In some embodiments, WDM includes: a wavelength splitter, a wavelength combiner, and an optical filter. The wavelength splitter can separate multiple signals into signals of different wavelengths, and introduce each signal into a different channel to achieve wavelength multiplexing. The wavelength combiner can combine signals of different wavelengths from various channels into one signal and output it. The optical filter can filter out optical signals of non-target wavelengths and allow signals of target wavelengths to pass.

[0067] Figure 3 Figure 1 is a schematic diagram of the structure of an optical filter. Figure 3 As shown, Figure 3 As shown, the spacing between the grating teeth on both sides of the waveguide along the z direction is Δs, wherein Δs is gradually distributed along the light transmission direction (z direction), and the changing trend is first decreasing and then increasing. It is a phase apodization scheme that can achieve the function of suppressing side lobes.

[0068] The working process of the optical filter is as follows: the fundamental mode TE0 mode in the waveguide is input from the left side, and when the incident wavelength meets the corresponding phase matching condition, that is, (n0+nm)=λ / Λ, it will be reflected as the corresponding transverse electric (TE) m mode. Among them, n0 and nm are the effective refractive indexes of the TE0 mode and TEm mode, λ is the incident wavelength, and Λ is the grating period.

[0069] In some embodiments, Figure 3 As shown, when the TE0 mode is input into the waveguide and the incident wavelength does not meet the phase matching condition, it will be output from the right side of waveguide C in the TE0 mode. When the incident wavelength meets the corresponding phase matching condition, it will be reflected by the MWG filter 20. The mode multiplexer 10 can convert the TE1 mode in the A waveguide after reverse coupling (reflection) of the MWG filter 20 into the TE0 mode and output it from the B waveguide. Reverse coupling from the TE0 mode to the TE1 mode is achieved.

[0070] The device forms an input port at the left end of the A waveguide, a drop port at the left end of the B waveguide, and an output port at the right end of the C waveguide.

[0071] The mode multiplexer 10 can convert the TE1 mode in the A waveguide after reverse coupling by the MWG filter 20 into the TE0 mode, and output it from the B waveguide.

[0072] However, the etching depth of the grating teeth, that is, the size of the grating teeth, is related to the bandwidth of the optical filter. For example, in an optical filter with a bandwidth of 20nm, the etching depth of the grating teeth is δ = 185nm. However, in an optical filter with a bandwidth of 10nm, the etching depth of the grating teeth is δ = 160nm. Figure 3Only the position of the grating teeth is shown in the figure, and the size is the size of the grating teeth under the same bandwidth, which is not used as a reference). In addition, amplitude toe cutting is required on the grating teeth to make the characteristic size of the grating smaller, which requires higher processing accuracy. The existing silicon photonics 180nm complementary metal oxide semiconductor (CMOS) process line cannot meet the demand and is not suitable for large-scale mass production.

[0073] To this end, the embodiment of the present application provides an improved optical filter. The optical filter has low requirements on processing precision, and the existing silicon photonics 180nm CMOS process line can meet the production requirements, is suitable for large-scale mass production, and improves the transmission spectrum performance.

[0074] Figure 5 A schematic diagram of the structure of an optical filter provided in an embodiment of the present application. Figure 6 A three-dimensional diagram of an optical filter provided in an embodiment of the present application. Figure 5 , Figure 6 As shown, the optical filter comprises: a mode multiplexer 100, a connecting waveguide 300 and a waveguide grating 200, wherein the mode multiplexer 100 is connected to the waveguide grating 200 via the connecting waveguide 300. The mode multiplexer 100 is used to receive an optical signal from an input end 11 of the optical filter and transmit the optical signal to the waveguide grating 200.

[0075] In some embodiments, Figure 5 As shown, the mode multiplexer 100 includes: a single-mode waveguide 101 and a first gradient waveguide 102. One end of the single-mode waveguide 101 is connected to the input end 11, the other end of the single-mode waveguide 101 is connected to one end of the first gradient waveguide 102, the other end of the first gradient waveguide 102 is connected to one end of the connecting waveguide 300, the other end of the connecting waveguide 300 is connected to one end of the waveguide grating 200, and the other end of the waveguide grating 200 is connected to the output end 13.

[0076] The first gradient waveguide 102 gradually increases in size along the first direction (z direction) to become a multimode waveguide. For example, the single-mode waveguide 101 supports the transmission of the fundamental mode of the transverse electric mode (TE0). The first gradient waveguide 102 at least supports the transmission of TE0 and the first-order mode of the transverse electric mode (TE1).

[0077] The TE0 mode transmitted from left to right along the Z-axis may enter the waveguide grating 200 via the first graded waveguide 102 .

[0078] Next reference Figure 5, the mode multiplexer 100 also includes: a curved waveguide 103 and a second gradual change waveguide 104. One end of the curved waveguide 103 is connected to the download end 12. The spacing between the single-mode waveguide 101 and the curved waveguide 103 gradually decreases along the light transmission direction (z direction). The curved waveguide 103 is used to gradually change the single-mode waveguide 101 and the curved waveguide 103 from a weak coupling state at a longer distance to a strong coupling state at a closer distance along the z direction. The other end of the curved waveguide 103 is connected to one end of the second gradual change waveguide 104, and the other end of the second gradual change waveguide 104 does not support TE0 mode transmission and is suspended, and the second gradual change waveguide 104 is coupled to the first gradual change waveguide 102. The size of the second gradual change waveguide 104 along the z direction gradually decreases along the z direction. The second end of the second gradual change waveguide 104 is in a state of no guided mode. The connecting waveguide 300 is connected to the second end of the first gradual change waveguide 102. The connecting waveguide 300 extends along the z direction based on the size of the second end of the first gradient waveguide 102 along the x direction. In the case where the second end of the first gradient waveguide 102 is a multimode waveguide, the connecting waveguide 300 is also a multimode waveguide. For example, if the first gradient waveguide 102 supports the transmission of TE0 and TE1, then the connecting waveguide also supports the transmission of TE0 and TE1.

[0079] This embodiment does not limit the length of the connecting waveguide 300 along the z direction. The description of the structure of the connecting waveguide 300 in this embodiment is an example and is not limited, as long as the connecting waveguide 300 at least supports the transmission of TE0 and TE1 and can ensure adiabatic coupling. Adiabatic coupling means that the optical signal mode transmitted by the connecting waveguide 300 does not change inside the connecting waveguide 300.

[0080] The second gradient waveguide 104 can couple the TE1 mode transmitted from right to left along the Z-axis into the TE0 mode.

[0081] The curved waveguide 103 can isolate the input end 11 and the download end 12 by a certain distance to avoid optical crosstalk.

[0082] During operation, the input end 11 receives the TE0 mode optical signal, which enters the connecting waveguide 300 after passing through the single-mode waveguide 101 and the first gradient waveguide 102, so that the TE0 mode transmitted from left to right along the Z axis can enter the waveguide grating 200 via the first gradient waveguide 102, complete filtering in the waveguide grating 200 and receive the reflected TE1 mode optical signal, and the TE1 mode signal passes through the second gradient waveguide 104, is coupled to the TE0 mode, and enters the download end 12 through the curved waveguide 103. In addition, the TE1 mode transmitted from right to left along the Z axis can be coupled to the curved waveguide 103 output.

[0083] When working, the mode multiplexer 100 receives multiple optical signals through the input end 11. The input end 11 may be a port of the input waveguide of the mode multiplexer 100 for receiving the multiple optical signals. Each optical signal in the multiple optical signals has TE0. The multiple optical signals are sequentially transmitted to the connecting waveguide 300 via the single-mode waveguide 101 and the first gradient waveguide 102. Since the size of the first gradient waveguide 102 in the x direction gradually increases along the z direction, the optical signal with the TE0 mode is directly transmitted to the connecting waveguide 300 via the first gradient waveguide 102. The connecting waveguide 300 transmits the first optical signal to the waveguide grating 200.

[0084] The multi-path optical signal includes a multi-path download optical signal whose wavelength is located in the first band. In the waveguide grating 200, the download optical signal located in the first band satisfies the phase matching condition. The download optical signal that satisfies the phase matching condition is reflected and transmitted to the connecting waveguide 300 as TE1. The connecting waveguide 300 receives the download optical signal from the waveguide grating 200, and the download optical signal received by the connecting waveguide 300 has TE1. The phase matching condition is (n0+n1)=λ / T, n0 is the effective refractive index of the TE0 mode, and n1 is the effective refractive index of the TE1 mode. λ is the wavelength of the download optical signal. T is the grating period of the waveguide grating 200. The grating period is the sum of the length of any grating tooth included in the waveguide grating 200 and the length of the grating groove adjacent to the grating tooth along the z direction.

[0085] The download optical signal with TE1 reflected to the connecting waveguide 300 is transmitted to the first gradient waveguide 102. TE1 in the first gradient waveguide 102 and TE0 in the second gradient waveguide 104 meet the phase matching condition, so that the download optical signal is coupled to the second gradient waveguide 104 with TE0. The download optical signal with TE0 is transmitted to the download end 12 via the second gradient waveguide 104 and the curved waveguide 103 in sequence.

[0086] The multi-path optical signals received by the input end 11 of the mode multiplexer 100 also include a multi-path direct optical signal whose wavelength is located in the second band. The first band is different from the second band. The direct optical signal located in the second band does not meet the phase matching condition. The direct optical signal that does not meet the phase matching condition is transmitted to the output end 13 along the waveguide grating 200. Moreover, the optical signal output via the waveguide grating 200 has TE0. The description of the mode of the optical signal input to the input end 11 and the mode of the optical signal reflected by the waveguide grating 200 to the connecting waveguide 300 in this embodiment is an example and is not limited.

[0087] In some embodiments, Figure 5 , Figure 6 As shown, the waveguide grating 200 includes: a first grating 2021 , a second grating 2022 and a waveguide 201 .

[0088] In some embodiments, Figure 6 , Figure 7 , Figure 8 , Fig. 9 , Fig.11 As shown, the optical filter 10 further includes: a substrate 203 (such as Figure 6 shown) and cladding ( Figure 6 The cladding is disposed on the substrate 203 , and the cladding covers the first grating 2021 , the waveguide 201 , the second grating 2022 and the mode multiplexer 100 .

[0089] For example, the cladding covers the first grating 2021, the waveguide 201, the second grating 2022 and the mode multiplexer 100, including: the first grating 2021, the waveguide 201, the second grating 2022 and the mode multiplexer 100 are all in contact with the surface of the substrate 203, at this time, the cladding covers the upper surface and side surfaces of the first grating 2021, the waveguide 201, the second grating 2022 and the mode multiplexer 100.

[0090] The mode multiplexer 100 is in contact with the surface of the substrate 203, and at least one of the first grating 2021, the waveguide 201, and the second grating 2022 is spaced apart from the surface of the substrate 203. At this time, for the structure in contact with the surface of the substrate 203, the cladding covers the upper surface and the side surface thereof, and for the structure spaced apart from the surface of the substrate 203, the cladding covers the upper surface and the side surface thereof and fills the gap between the structure and the surface of the substrate 203.

[0091] When preparing the waveguide grating 200, a mask plate may be set on the substrate, and the grating 202 and the waveguide 201 may be formed by etching, and then a cladding may be formed on the substrate so that the grating 202 and the waveguide 201 are wrapped by the cladding.

[0092] In some embodiments, Figure 5 , Figure 6 As shown, the first grating 2021, the waveguide 201 and the second grating 2022 are arranged along a first direction (ie Figure 6 The first direction is parallel to the surface of the substrate (the surface of the substrate is, for example, an xz plane).

[0093] Therefore, the grating is set in the cladding 2001, and the first grating 2021, the second grating 2022 and the waveguide 201 are arranged at intervals. Compared with the prior art in which the grating and the waveguide are arranged as one, the grating tooth size is more flexible, so that the minimum grating tooth size can meet the requirements of the existing silicon photonics 180nm CMOS process line and reduce the process accuracy requirements.

[0094] In some embodiments, Figure 5 , Figure 6As shown, the spacing between the first grating 2021 and the waveguide 201, and the spacing between the second grating 2022 and the waveguide 201, are all along the light transmission direction ( Figure 6 The z direction shown in FIG. 1 first decreases and then increases. The light transmission direction is parallel to the surface of the substrate and perpendicular to the first direction. For example, the spacing between the first grating 2021 and the waveguide 201, and the spacing between the second grating 2022 and the waveguide 201, are both along the light transmission direction ( Figure 6 The z direction shown in ) decreases first and then increases, which may include:

[0095] The shapes of the first grating 2021 and the second grating 2022 are adjusted so that the spacing between the grating and the waveguide 201 is gradually changed. Alternatively, the shape of the side of the waveguide 201 close to the grating is adjusted so that the spacing between the grating and the waveguide 201 is gradually changed. Alternatively, the shape of the side of the waveguide 201 close to the grating is adjusted, and the shapes of the first grating 2021 and the second grating 2022 are adjusted so that the spacing between the grating and the waveguide 201 is gradually changed.

[0096] like Figure 6 , Fig.12 As shown, the first grating 2021 and the second grating 2022 are both distributed in an arc shape, the top view of the waveguide 201 is a rectangle, the side of the waveguide 201 close to the grating is a plane, the bending direction of the arc line is a first direction, and the bending direction is away from the waveguide. The bending direction of the arc line refers to the opening direction of the arc line. For example, Figure 6 The opening directions of the arc lines of the first grating 2021 and the second grating 2022 are indicated by arrows. It can be seen that the opening direction of the arc line of the first grating 2021 is in the +x direction, and the opening direction of the arc line of the first grating 2021 is in the -x direction, which are perpendicular to the light transmission direction z direction, and are bent in the direction away from the waveguide 201 respectively.

[0097] In other embodiments, a curved surface is used on the side of the waveguide 201 close to the grating, the first grating 2021 and the second grating 2022 are both distributed in a straight line, the bending direction of the curved surface is a first direction, and the bending direction is away from the grating. The bending direction of the curved surface refers to the opening direction of the curved surface. For example, the opening direction of the curved surface of the waveguide 201 is as indicated by the arrow, and it can be seen that the opening direction of the curved surface of the waveguide 201 close to the first grating 2021 is the +x direction, and the opening direction of the curved surface of the waveguide 201 close to the second grating 2022 is the -x direction. The opening direction of the curved surface of the waveguide 201 is perpendicular to the light transmission direction z direction, and is bent in the direction close to the grating.

[0098] In some embodiments, Fig.16As shown, the side of the waveguide close to the grating adopts an arc surface, and the first grating and the second grating are both distributed in arc lines, the arc surface and the arc line have the same curvature direction, and the curvature of the arc line is greater than the curvature of the arc surface. The curvature refers to the degree of curvature, and the greater the curvature, the smaller the radius of the circle where the arc line is located.

[0099] like Fig.16 As shown, the opening direction of the curved surface of the waveguide 201 close to the first grating 2021 is in the +x direction, the opening direction of the curved surface of the waveguide 201 close to the second grating 2022 is in the -x direction, the opening direction of the curved line of the first grating 2021 is in the +x direction, the opening direction of the curved line of the first grating 2021 is in the -x direction, and the opening direction of the curved surface of the waveguide 201 and the opening direction of the curved line of the grating are perpendicular to the light transmission direction z direction.

[0100] The embodiment of the present application does not limit the degree of curvature and curvature direction of the grating and waveguide 201, and only needs to make the spacing between the grating and the waveguide first decrease and then increase along the light transmission direction. Those skilled in the art can adjust the shape of the grating and the waveguide as needed, and the present application does not limit this. Thus, by adjusting the spacing between the grating and the waveguide 201, a better sidelobe suppression effect is achieved on both sides of the flat region of the reflection spectrum.

[0101] In other embodiments, Fig.19 As shown, the grating tooth period of the first grating 2021 and the second grating 2022 first decreases and then increases along the light transmission direction. The grating tooth period is the distance between the centers of two adjacent grating teeth.

[0102] In some embodiments, the first grating 2021 and the second grating 2022 respectively include a plurality of grating teeth, and the duty cycle of each grating tooth is 50%. The duty cycle of the grating tooth is the ratio of the width of the grating tooth to the period, and the duty cycle of the grating tooth remains unchanged. When the period of the grating tooth changes along the light transmission direction, the width of the grating tooth changes accordingly. Therefore, by adjusting the period of the grating tooth, the sidelobe suppression effect of the transmission wave is better.

[0103] In some embodiments, Figure 5 As shown, the first grating 2021 is distributed in axisymmetric manner based on the first symmetry axis O, and the second grating 2022 is distributed in axisymmetric manner based on the second symmetry axis O', and the first symmetry axis O and the second symmetry axis O' are both parallel to the first direction. Thus, the first grating 2021 and the second grating 2022 are both axisymmetric structures, and the spacing between the first grating 2021 and the waveguide is gradually changed, and the spacing between the second grating 2022 and the waveguide is symmetrically gradually changed, and the side lobe suppression effect is also symmetrical, and the effect is better.

[0104] The embodiments of the present application do not limit the materials of the cladding 2001, the substrate 203, the waveguide 201 and the grating 202. In the present application, the same materials are represented by the same fill symbols, and different materials are represented by different fill symbols. Among them, the refractive index of the cladding is n1, the refractive index of the substrate 203 is n2, the refractive index of the waveguide 201 is n3, and the refractive index of the grating 202 is n4. n1, n2, n3, and n4 satisfy: the refractive index n3 of the waveguide 201 is greater than the refractive index n2 of the substrate 203, and the refractive index n3 of the waveguide 201 is greater than the refractive index n1 of the cladding 2001. The refractive index n4 of the grating 202 is greater than the refractive index n2 of the substrate 203, and the refractive index n4 of the grating 202 is greater than the refractive index n1 of the cladding 2001.

[0105] In some embodiments, the cladding 2001 and the substrate 203 are both made of silicon dioxide, and the waveguide 201 and the grating 202 are made of the same material. For example, the waveguide 201 and the grating 202 are both made of silicon, and have the same thickness. In other embodiments, the waveguide 201 and the grating 202 are made of different materials, for example, the waveguide 201 is made of silicon, and the grating 202 is made of silicon nitride.

[0106] The embodiment of the present application does not limit the height of the grating 202 and the waveguide 201 from the substrate 203 in the y direction. Figure 6 The cladding layer is on the substrate 203 shown, and covers the mode multiplexer 100 , the first grating 2021 , the waveguide 201 and the second grating 2022 .

[0107] In some embodiments, Figure 7 As shown, the first grating 2021, the second grating 2022 and the waveguide 201 are all disposed on the surface of the substrate 203. In other embodiments, as Fig. 9 As shown, the first grating 2021, the second grating 2022 and the waveguide 201 are all arranged in the cladding 2001 and are spaced apart from the substrate 203 along the y direction. Figure 8 As shown, the first grating 2021 and the second grating 2022 are arranged in the cladding 2001 and are spaced apart from the substrate 203 along the y direction, and the waveguide 201 is arranged on the surface of the substrate 203. In some other embodiments, such as Fig.10 As shown, the waveguide 201 is arranged in the cladding 2001 and is spaced apart from the substrate 203 along the y direction, and the first grating 2021 and the second grating 2022 are arranged on the surface of the substrate 203 .

[0108] In the above embodiment, the waveguide 201 is a strip waveguide. In other embodiments, Fig.11 As shown, the waveguide 101 is a ridge waveguide.

[0109] Combine the following Figure 7-Figure 11The structures and materials of the first grating 2021, the second grating 2022, and the waveguide 201 are described.

[0110] Figure 7 for Figure 6 An AA cross-sectional view in FIG. Figure 7 As shown, the waveguide 201 is a strip waveguide, the waveguide 201 and the first grating 2021 and the second grating 2022 are all arranged on the substrate 203, and the waveguide 201 and the grating 202 are spaced apart along the x direction, and the cladding 2001 covers the upper surface and side surfaces of the waveguide 201, the first grating 2021 and the second grating 2022.

[0111] In some embodiments, see Figure 7 The waveguide 201 and the first grating 2021 and the second grating 2022 have the same height.

[0112] In some embodiments, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of the same material. For example, they are all made of silicon, and the thickness of the waveguide 201 and the first grating 2021 and the second grating 2022 along the y direction may be different. In other embodiments, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of different materials, for example, the waveguide 201 is made of silicon material, and the first grating 2021 and the second grating 2022 are made of silicon nitride material. The thickness of the waveguide 201 and the first grating 2021 and the second grating 2022 along the y direction may be different.

[0113] Preparation Figure 7 When the waveguide grating 200 is shown, a mask plate can be set on the substrate, and the grating 202 and the waveguide 201 can be formed by etching, and then a cladding is formed on the substrate so that the grating 202 and the waveguide 201 are wrapped by the cladding.

[0114] Figure 8 for Figure 6 Another AA section view in Figure 8 As shown, the waveguide 201 is a strip waveguide, and the waveguide 201 is arranged on the first surface of the substrate 203. The first grating 2021, the second grating 2022 and the waveguide 201 are spaced apart in the x direction, and the gratings (the first grating 2021, the second grating 2022) and the substrate 203 are spaced apart in the z direction. The cladding 2001 covers the upper surface and side surfaces of the waveguide 201, the first grating 2021 and the second grating 2022, and fills the gap between the first grating 2021, the second grating 2022 and the substrate 203.

[0115] In some embodiments, Figure 8As shown, the height of the waveguide 201 in the z direction is lower than the height of the gratings (the first grating 2021 and the second grating 2022) in the z direction, that is, the distance between the surface of the waveguide 201 close to the substrate and the first surface of the substrate is smaller than the distance between the surface of the grating 202 close to the substrate and the first surface of the substrate. Figure 8 In the embodiment, the waveguide 201 is arranged on the first surface of the substrate 203, and the distance between the surface of the waveguide 201 close to the substrate and the first surface of the substrate is 0, while the gratings (the first grating 2021 and the second grating 2022) are spaced apart from the substrate 203 in the z direction, and the distance between the two is greater than 0, then the distance between the surface of the waveguide 201 close to the substrate and the first surface of the substrate is smaller than the distance between the surface of the gratings (the first grating 2021 and the second grating 2022) close to the substrate and the first surface of the substrate.

[0116] In some embodiments, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of the same material, for example, silicon, and have the same thickness. In other embodiments, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of different materials, for example, the waveguide 201 is made of silicon, and the first grating 2021 and the second grating 2022 are made of silicon nitride.

[0117] Preparation Figure 8 In the case of the waveguide grating 200 shown, a mask layer may be firstly provided on the substrate, and the waveguide 201 may be formed by etching. After the corresponding material is grown, a second mask layer may be formed, and the grating 202 may be formed by etching.

[0118] Fig. 9 for Figure 6 Another AA section view in Fig. 9 As shown, the first grating 2021, the second grating 2022 and the waveguide 201 are spaced apart in the x direction, the gratings (the first grating 2021, the second grating 2022) and the waveguide 201 have the same height in the z direction, and the waveguide 201 and the substrate are spaced apart in the z direction. The cladding 2001 covers the upper surface and side surfaces of the waveguide 201, the first grating 2021 and the second grating 2022, and fills the gaps between the waveguide 201, the first grating 2021 and the second grating 2022 and the substrate 203.

[0119] In some embodiments, Fig. 9 As shown, the waveguide 201 is a strip waveguide, the height of the waveguide 201 in the z direction is the same as the height of the grating (the first grating 2021 and the second grating 2022) in the z direction, and the distance between the surface of the waveguide 201 close to the substrate and the first surface of the substrate is equal to the distance between the surface of the grating 202 close to the substrate and the first surface of the substrate. For example, Fig. 9In the figure, the waveguide 201 and the grating (the first grating 2021 and the second grating 2022) are spaced apart from the substrate 203 in the z direction, the distance between the two is greater than 0, and the distance between the surface of the waveguide 201 close to the substrate and the first surface of the substrate is equal to the distance between the surface of the grating 202 close to the substrate and the first surface of the substrate.

[0120] In some embodiments, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of the same material, for example, silicon, and have the same thickness. In other embodiments, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of different materials, for example, the waveguide 201 is made of silicon, and the first grating 2021 and the second grating 2022 are made of silicon nitride.

[0121] Fig.10 for Figure 6 Another AA section view in Fig.10 As shown, the waveguide 201 is a strip waveguide, the first grating 2021 and the second grating 2022 are arranged on the first surface of the substrate 203, the first grating 2021, the second grating 2022 and the waveguide 201 are spaced apart in the x direction, and the waveguide 201 and the substrate 203 are spaced apart in the z direction. The cladding 2001 covers the upper surface and side surfaces of the waveguide 201, the first grating 2021 and the second grating 2022, and fills the gap between the waveguide 201 and the substrate 203.

[0122] In some embodiments, Fig.10 As shown, the height of the waveguide 201 in the z direction is higher than the height of the gratings (the first grating 2021 and the second grating 2022) in the z direction, that is, the distance between the surface of the waveguide 201 close to the substrate and the first surface of the substrate is greater than the distance between the surface of the grating 202 close to the substrate and the first surface of the substrate. Fig.10 In the embodiment, the gratings (the first grating 2021 and the second grating 2022) are arranged on the first surface of the substrate 203, and the distance between the surface of the gratings (the first grating 2021 and the second grating 2022) close to the substrate and the first surface of the substrate is 0, while the waveguide 201 is spaced apart from the substrate 203 in the z direction, and the distance between the two is greater than 0, then the distance between the surface of the waveguide 201 close to the substrate and the first surface of the substrate is greater than the distance between the surface of the gratings (the first grating 2021 and the second grating 2022) close to the substrate and the first surface of the substrate.

[0123] In some embodiments, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of the same material, for example, silicon, and have the same thickness. Fig.10As shown, the waveguide 201 and the first grating 2021 and the second grating 2022 are made of different materials. For example, the waveguide 201 is made of silicon material, and the first grating 2021 and the second grating 2022 are made of silicon nitride material.

[0124] Fig.11 for Figure 6 There is another AA section view in the figure. Fig.11 As shown, the waveguide 201 is a ridge waveguide, the waveguide 201 and the first grating 2021 and the second grating 2022 are all arranged on the first surface of the substrate 203, the waveguide 201 is connected to the substrate through the plate 204, the cladding 2001 covers the first grating 2021, the second grating 2022 and the surface and side of the waveguide, and covers the exposed part of the surface of the plate 204, the plate 204 is made of the same material as the waveguide 201, and the plate 204 and the waveguide 201 form a ridge waveguide.

[0125] In some embodiments, Fig.11 As shown, the waveguide 201 and the grating 202 have the same height, and the waveguide 201 and the grating 202 are made of the same material. For example, the waveguide 201 and the grating 202 are made of silicon, and have the same thickness. In other embodiments, the waveguide 201 is a ridge waveguide structure, the waveguide 201 and the grating 202 have different heights, and the grating 202 and the plate 204 are arranged at intervals.

[0126] Figure 3 The spacing Δs between the grating teeth on both sides of the waveguide along the z direction is gradually distributed along the light transmission direction, while the spacing between the grating teeth on both sides of the waveguide input and output ends is almost 0, close to a symmetrical distribution, which makes it easy for the TE0 mode and the even-order mode to be reversely coupled. For example, Figure 4 As shown, the target optical filter is located at 1270nm, but a concave peak appears at the 1380nm wavelength position, affecting the transmission spectrum performance of the through end.

[0127] To this end, the embodiments of the present application further improve the optical filter to achieve optimization of transmission spectrum performance.

[0128] In some embodiments, grating teeth of the first grating 2021 and grating teeth of the second grating 2022 corresponding to the grating teeth of the first grating 2021 are arranged in a staggered position, so that the grating teeth of the first grating 2021 and the second grating 2022 are asymmetrically distributed on both sides of the waveguide 201 .

[0129] In some embodiments, the displacement of the relative position misalignment between the grating teeth of the first grating 2021 and the grating teeth of the second grating 2022 corresponding to the grating teeth of the first grating 2021 remains unchanged along the propagation direction. The displacement of the relative position misalignment between the grating teeth of the first grating 2021 and the grating teeth of the second grating 2022 corresponding to the grating teeth of the first grating 2021 may be the spacing Δsi between the i-th grating tooth 2021i of the first grating 2021 and the i-th grating tooth 2022i of the second grating 2022 along the z direction. The displacement of the relative position misalignment between the grating teeth of the first grating 2021 and the grating teeth of the second grating 2022 corresponding to the grating teeth of the first grating 2021 remains unchanged along the propagation direction, which means that the spacing Δs1 between the first grating tooth of the first grating 2021 and the first grating tooth of the second grating 2022 along the z direction, the spacing Δs2 between the second grating tooth of the first grating 2021 and the second grating tooth of the second grating 2022 along the z direction…the spacing Δsi between the i grating teeth of the first grating 2021 and the i grating tooth of the second grating 2022 along the z direction…the spacing Δsn between the n grating tooth of the first grating 2021 and the n grating tooth of the second grating 2022 along the z direction are all equal.

[0130] For example, Figure 5 As shown, the first grating tooth of the first grating 2021 is 2021a, and the first grating tooth of the second grating 2022 is 2022a, wherein the spacing between 2021a and 2022a along the z direction is Δs1, the seventh grating tooth of the first grating 2021 is 2021g, and the seventh grating tooth of the second grating 2022 is 2022g, wherein the spacing between 2021g and 2022g along the z direction is Δs7, wherein Δs1 is equal to Δs7.

[0131] The present application does not limit the specific numerical value of the displacement of the grating teeth of the first grating 2021 and the grating teeth of the second grating 2022 corresponding to the grating teeth of the first grating 2021. It is only necessary to make the displacement of the grating teeth of the first grating 2021 and the second grating 2022 close to half of the grating teeth period. Those skilled in the art can adjust the displacement of the grating teeth of the first grating 2021 and the second grating 2022 as needed, which all belong to the protection scope of the present application. Among them, the displacement of the grating teeth position misalignment is close to half of the grating teeth period, and there may be errors. For example, the displacement of the grating teeth position misalignment can be 20%-80% of the grating teeth period.

[0132] For example, taking the two sides of the straight waveguide as the reference, the gratings on both sides are projected on the sides of the straight waveguide, and the displacement of adjacent grating teeth can be half of the grating period, that is, the displacement of the grating tooth positions of the first grating 2021 and the second grating 2022 can be half of the grating tooth period. The grating tooth period is the spacing between the centers of two adjacent grating teeth.

[0133] For example, the first grating 2021 and the second grating 2022 include a plurality of grating teeth respectively, the duty cycle of each grating tooth is 50%, and the displacement of the grating teeth of the first grating 2021 and the second grating 2022 can be half of the grating tooth period, that is, the width of one grating tooth.

[0134] For example, Figure 5 As shown, at the first position, the spacing Δs1 between the first grating tooth 2021a of the first grating 2021 and the first grating tooth 2022a of the second grating 2022 along the z direction is one grating tooth, that is, one half of the grating tooth period.

[0135] Next reference Figure 5 , at the second position, the spacing Δs7 between the 7th grating tooth 2021g of the first grating 2021 and the 7th grating tooth 2022g of the second grating 2022 along the z direction is one grating tooth, that is, half of the grating tooth period. In other words, the spacing between adjacent grating teeth of the first grating 2021 and the second grating 2022 remains unchanged, while the second grating 2022 moves half a period to the right relative to the first grating 2021 as a whole.

[0136] Therefore, the grating teeth of the first grating 2021 and the second grating 2022 are misaligned, and the displacement Δs of the misaligned grating teeth of the first grating 2021 and the second grating 2022 remains unchanged, which can avoid reverse coupling of TE0 and TE2 modes and optimize transmission spectrum performance.

[0137] The present application does not impose any specific restrictions on the specific shape of the grating in the top view, for example, it can be rectangular, circular, hexagonal, etc.

[0138] Combine the following Figure 12-Figure 21 The scheme of the present application is described.

[0139] The cross section of the waveguide grating in the embodiment shown below is, for example, Figure 7 In the structure shown, the waveguide 201 and the grating 202 are both made of silicon nitride material with a thickness of 250 nm, and the cladding 2001 and the substrate 203 are both made of silicon dioxide material. The projection shape of the waveguide grating 200 is, for example, a rectangle.

[0140] The spacing between the waveguide 201 and the grating 202 can be adjusted, and the distribution of the coupling coefficient can be adjusted to match the target apodization function to achieve a sidelobe suppression effect.

[0141] Fig.12 A schematic diagram of the structure of a waveguide grating provided in an embodiment of the present application. In some embodiments of the present application, such as Fig.12 As shown, the waveguide 201 is a rectangular waveguide with a width of W. The grating structure is a rectangle with a period of T, a width of D, a duty cycle of 50%, and the number of periods is N. The minimum spacing between the waveguide 201 and the grating 202 is d1, and the maximum spacing is d2. The minimum size of the grating 202 meets the 180nm process line requirements.

[0142] In some embodiments, the waveguide 201 includes two operating modes: TE0 mode and TE1 mode. In some embodiments, the waveguide 201 does not support other higher-order modes.

[0143] The period of the grating 202 is T. In some embodiments, T satisfies the following formula:

[0144] (n0+n1)=λ / T Formula (1)

[0145] Where n0 is the effective refractive index of the TE0 mode, n1 is the effective refractive index of the TE1 mode, and λ is the target filtering wavelength.

[0146] In some embodiments, W, d1, d2, D, T, and N may satisfy: W=1.1um, d1=0.2um, d2=0.5um, D=0.4um, T=0.41um, and N=400.

[0147] The light transmission direction is the z direction, and the spacing between the waveguide 201 and the grating 202 (the spacing between the waveguide 201 and the first grating 2021, or the spacing between the waveguide 201 and the second grating 2022) is denoted as d(z), and d(z) presents a large-small-large distribution in the transmission direction. In some embodiments, d(z) satisfies the following formula:

[0148] d(z)=d1+c(z-Lg / 2) 2 Formula (2)

[0149] c in formula (2) satisfies:

[0150] c=4(d2-d1) / Lg 2 Formula (3)

[0151] Lg in formula (2) and formula (3) satisfies:

[0152] Lg=N*T Formula (4)

[0153] Wherein, d1 is the minimum distance between the waveguide 201 and the grating 202 , and d2 is the maximum distance between the waveguide 201 and the grating 202 .

[0154] Fig.13 FIG1 is a graph showing the variation of the spacing between the waveguide and the grating in the light transmission direction. Fig.13 As shown, the spacing d between the waveguide 201 and the grating 202 presents a large-small-large distribution along the z direction. Fig.14 Schematic diagram of the spectrum image of the grating when the spacing between the waveguide and the grating remains unchanged along the light transmission direction, that is, the transmission spectrum under the structure of d2 = d1 = 200nm, as shown in Fig.14 As shown, the side lobes on both sides of the flat region of the reflection spectrum are strong, and the side lobe suppression ratio (SLSR) of the first side lobe is less than 5dB. Fig.15 for Fig.12 Schematic diagram of the spectrum image of the waveguide grating shown in Fig.15 As shown, the SLSR on the right side of the flat region of the reflection spectrum is greater than 20 dB, and the SLSR on the left side maintains the original level. Therefore, by setting the waveguide 201 and the grating 202 with a gradually varying spacing, a better suppression effect of the right side lobe can be achieved.

[0155] In the above embodiment, the side lobe suppression can be achieved by adjusting the distance between the waveguide 201 and the grating 202. In other embodiments of the present application, the shape of the waveguide 201 can be adjusted to further achieve the side lobe suppression.

[0156] Fig.16 A schematic diagram of the structure of another waveguide grating provided in an embodiment of the present application. Fig.16 and Fig. 9 The difference is that the side of the waveguide 201 close to the grating 202 adopts a curved side wall. The waveguide 201 adopts a curved surface structure with a width of W. The grating structure adopts a rectangular structure with a period of T, a width of D, a duty cycle of 50%, and the number of periods is recorded as N. Among them, the light transmission direction is the z direction, the spacing between the waveguide 201 and the grating 202 is recorded as d, and d presents a large-small-large distribution in the transmission direction. The minimum spacing between the waveguide 201 and the grating 202 is d1, and the maximum spacing is d2. The minimum size of the grating 202 meets the requirements of the 180nm process line.

[0157] The light transmission direction is the z direction. In some embodiments, the change W(z) of the width W of the waveguide 201 along the light transmission direction z satisfies the following formula:

[0158] W(z)=1100+p*(500 q -d(z) q ) / m Formula (5)

[0159] Among them, p = 1.607, q = -0.004298, m = 7.088*10-5 .

[0160] Fig.17 FIG. 2 is a schematic diagram showing the variation of the width W of the waveguide 201 along the z direction. Fig.17 As shown, the width W(z) of the waveguide 201 presents a large-small-large distribution along the z direction. Fig.18 for Fig.16 Schematic diagram of the spectrum image of the waveguide grating shown in Fig.18 As shown in FIG. 1 , the SLSR of the first side lobe on the left is greater than 25 dB, and the SLSR of the first side lobe on the right is greater than 10 dB. Fig.12 Compared with the waveguide grating, Fig.16 The side lobes on both sides of the transmission wave of the waveguide grating shown have a better suppression effect. Therefore, by setting the waveguide 201 and the grating 202 with a gradually changing spacing, the side lobes on both sides of the passband can be effectively suppressed.

[0161] Fig.19 A schematic diagram of the structure of another waveguide grating 200 provided in an embodiment of the present application is shown in FIG. Fig.19 As shown, the waveguide grating 200 and Fig.12 The waveguide gratings shown differ in that: Fig.19 The period T of the grating 202 of the waveguide grating 200 is no longer a constant, but is distributed in a large-small-large pattern along the transmission direction z.

[0162] In some embodiments, the grating period satisfies the following formula:

[0163]

[0164] Among them, T i is the period of the i-th grating tooth, T0 is the initial period set, β i is the propagation constant at the i-th grating location, κ i is the coupling coefficient at the i-th grating location, is the coupling coefficient of the n / 2th grating.

[0165] In some embodiments, T0=400 nm, and the variation pattern of T with z can be obtained according to the structural parameters determined by the above formula.

[0166] like Fig. 20 As shown, at both ends of the transmission direction, the grating period is about 402.5nm, and at the center, the grating period is 400nm. It can be seen that the grating period is symmetrically distributed about the grating center.

[0167] Fig.21 for Fig.19 Schematic diagram of the spectrum image of the waveguide grating shown in Fig.21As shown in the figure, the side lobes on both sides of the passband are effectively suppressed. The SLSR of the first side lobe on the left is greater than 25dB, and the SLSR of the first side lobe on the right is greater than 10dB. Fig.12 Compared with the waveguide grating, Fig.19 The waveguide grating shown has a better suppression effect on the side lobes on both sides of the transmission wave. Fig. 22 A schematic diagram of the structure of a wavelength division multiplexing system provided in an embodiment of the present application. Fig. 22 As shown, the wavelength division multiplexing system includes: a first optical transponder unit (Optical Transponder Unit, OTU) 1, a multiplexer (Multiplexer, MUX), a demultiplexer (Demultiplexer, DMUX) and a second optical transponder unit OTU2.

[0168] The first optical converter unit OTU1 is used to perform optical conversion on the received signal and transmit the converted optical signal to the multiplexer. The multiplexer MUX includes the above optical filter, and the multiplexer MUX is used to couple the optical signals of multiple wavelengths converted by the first optical converter OTU1 to the optical fiber. The demultiplexer DMUX includes the above optical filter, and the demultiplexer DMUX is connected to the multiplexer MUX through the optical fiber, and the demultiplexer DMUX is used to separate the coupled optical signal.

[0169] In some embodiments, reference is then made to Fig. 22 The wavelength division multiplexing system also includes: an optical amplifier (Optical Amplifier, OA), the optical amplifier OA is located between the multiplexer MUX and the demultiplexer DMUX, the optical amplifier is used to amplify the optical signal transmitted by the multiplexer and send the optical signal with amplified optical power to the demultiplexer.

[0170] The present application also provides a wavelength division multiplexer. In some embodiments, the wavelength division multiplexer includes a plurality of Figure 5 The optical filter shown in FIG. A wavelength division multiplexer formed by cascading multiple optical filters can realize the functions of combining and demultiplexing multiple wavelengths.

[0171] For example, Fig.23 As shown, the wavelength division multiplexer includes: a first optical filter 10a, a second optical filter 10b and a third optical filter 10c.

[0172] like Fig.23 As shown, taking three grating optical filters cascaded as an example, the wavelength division multiplexer is composed of a first optical filter 10a, a first connecting waveguide 300a, a second optical filter 10b, a second connecting waveguide 300b, a third optical filter 10c ... and the Nth connecting waveguide 300n connected end to end in sequence.

[0173] The N optical filters, such as the first optical filter 10a, the second optical filter 10b and the third optical filter 10c, can be designed for different wavelengths and bandwidths respectively and have different structural parameters.

[0174] The embodiment of the present application does not limit the structure of the connecting waveguide. The connecting waveguide can be designed in various forms, such as a straight waveguide, a curved waveguide or a wedge-shaped waveguide.

[0175] The wavelength division multiplexer can support wavelength download and upload functions. Fig.23 Take the structure of the wavelength division multiplexer shown in as an example, wherein the first wavelength is input through the first input terminal 11a, and is downloaded from the first output terminal 12a through the first optical filter 10a. The second wavelength can be input from the first input terminal 11a, and sequentially pass through the first optical filter 10a, the first connecting waveguide 300a, and the second optical filter 10b, and is downloaded from the second output terminal 12b. The third wavelength is input from the second input terminal 11b, and is reflected by the third optical filter 10c and enters the second connecting waveguide 300b, and then sequentially passes through the second optical filter 10b and the first connecting waveguide 300a to enter the first optical filter 10a, and is output from the first output terminal 12a.

[0176] The wavelength division multiplexer adopts the above optical filter, which can reduce the bandwidth limitation on the grating tooth size, can adopt the 180nm CMOS process line requirements, and is convenient for large-scale production. In addition, the sidelobe suppression function can also be realized.

[0177] The embodiment of the present application provides an optical filter, a wavelength division multiplexer and a system. The optical filter in the present application includes: a mode multiplexer, a substrate, a cladding, a first grating, a second grating and a waveguide, wherein the mode multiplexer is connected to the waveguide, wherein the cladding is arranged on the substrate, and the cladding covers the mode multiplexer, the first grating, the waveguide and the second grating; the mode multiplexer is used to receive an optical signal from the input end of the optical filter, and transmit the optical signal to the waveguide and the first grating and the second grating; wherein the first grating, the waveguide and the second grating are arranged at intervals along a first direction, and the first direction is parallel to the surface of the substrate; the bandwidth limitation on the grating tooth size can be reduced, and the difficulty of the production process can be reduced. The spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, are both first reduced and then increased along the light transmission direction, and the light transmission direction is parallel to the surface of the substrate and perpendicular to the first direction, so as to realize the function of sidelobe suppression. Among them, the shape of the waveguide close to the first grating and the second grating side can be adjusted, and / or, the shape of the first grating and the second grating can be adjusted so that the spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide are gradually changed. The spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, are both reduced first and then increased along the light transmission direction, so as to achieve the function of sidelobe suppression. In some embodiments, the period of the grating teeth of the first grating and the second grating can also be adjusted so that the period of the grating teeth of the first grating and the second grating is reduced first and then increased along the light transmission direction. The function of sidelobe suppression can be further achieved. In addition, the grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating are arranged in a staggered position, and the displacement size of the position misalignment of the grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating is half of the grating tooth period. Thus, the first grating and the second grating are arranged asymmetrically about the waveguide, and the displacement is half of the grating tooth period, which effectively reduces the crosstalk between the band where the filtered light signal output by the optical filter is located and the adjacent band.

[0178] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An optical filter, characterized in that: include: A mode multiplexer, a substrate, a cladding, a first grating, a second grating, and a waveguide, wherein: The mode multiplexer is connected to the waveguide, wherein the cladding is disposed on the substrate, and the cladding covers the mode multiplexer, the first grating, the waveguide and the second grating; The mode multiplexer is used to receive an optical signal from an input end of the optical filter and transmit the optical signal to the waveguide and the first grating and the second grating; The first grating, the waveguide and the second grating are spaced apart along a first direction, wherein the first direction is parallel to the surface of the substrate; the spacing between the first grating and the waveguide, and the spacing between the second grating and the waveguide, both first decrease and then increase along a light transmission direction, and the light transmission direction is parallel to the surface of the substrate and perpendicular to the first direction.

2. The optical filter according to claim 1, characterized in that The first grating and the second grating are both distributed in arc lines.

3. The optical filter according to claim 1 or 2, characterized in that The side of the waveguide close to the grating adopts an arc-shaped surface.

4. The optical filter according to any one of claims 1 to 3, characterized in that: The grating tooth periods of the first grating and the second grating first decrease and then increase along the light transmission direction.

5. The optical filter according to claim 4, characterized in that The period of the i-th grating tooth of the first grating and the second grating satisfies: Where i = 1, 2, ..., n, T0 is the initial period, β i is the propagation constant at the i-th grating location, κ i is the coupling coefficient at the i-th grating location, is the coupling coefficient of the n / 2th grating.

6. The optical filter according to any one of claims 1 to 5, characterized in that: The grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating are arranged in a staggered position, and the grating teeth of the first grating and the grating teeth of the second grating corresponding to the grating teeth of the first grating have a positional staggered displacement of half a grating tooth period.

7. The optical filter according to any one of claims 1 to 6, characterized in that: The first gratings are distributed in an axisymmetric manner based on a first symmetry axis, and the second gratings are distributed in an axisymmetric manner based on a second symmetry axis. Both the first symmetry axis and the second symmetry axis are parallel to the first direction.

8. The optical filter according to any one of claims 1 to 7, characterized in that: The waveguide, the first grating and the second grating are all connected to the surface of the substrate.

9. The optical filter according to any one of claims 1 to 7, characterized in that: The first grating and the second grating are spaced apart from the substrate in a second direction, and / or the waveguide is spaced apart from the substrate in a second direction, wherein the second direction is perpendicular to a surface of the substrate.

10. The optical filter according to any one of claims 1 to 9, characterized in that: The waveguide is a ridge waveguide or a strip waveguide.

11. The optical filter according to any one of claims 1 to 10, characterized in that: Also includes: A connecting waveguide, wherein the mode multiplexer is connected to the waveguide via the connecting waveguide.

12. A wavelength division multiplexer, characterized in that: The optical filter comprises a plurality of optical filters as claimed in any one of claims 1 to 11, wherein the plurality of optical filters are cascaded and connected via connecting waveguides.

13. The wavelength division multiplexer according to claim 12, characterized in that: The wavelength division multiplexer further comprises: a plurality of optical fibers, wherein the plurality of optical fibers are respectively connected to the input ends of the plurality of optical filters and the output ends of the plurality of optical filters.

14. A passive optical network system, characterized in that: include: multiple optical line terminals; A wavelength division multiplexer, the wavelength division multiplexer is connected to the plurality of optical line terminals via optical fibers, the wavelength division multiplexer adopts the wavelength division multiplexer according to claim 12 or 13; an optical distribution network connected to a wavelength division multiplexer via an optical fiber; A plurality of optical network terminals are connected to the optical distribution network via optical fibers.

15. The passive optical network system according to claim 14, characterized in that: The optical modules of some of the multiple optical line terminals are GPON optical modules, the optical modules of another part of the optical line terminals are 10GPON optical modules, and the optical modules of another part of the optical line terminals are 50G-PON optical modules.

16. A wavelength division multiplexing system, characterized in that: include: a first optical converter, the first optical converter being used to optically convert a received signal; A multiplexer, the multiplexer comprising the optical filter according to any one of claims 1 to 11, the multiplexer being used to couple the optical signals of multiple wavelengths converted by the first optical converter to an optical fiber; A demultiplexer, the demultiplexer comprising the optical filter according to any one of claims 1 to 11, the demultiplexer being connected to the multiplexer via the optical fiber, and the demultiplexer being used to separate the coupled optical signal; A second optical converter, wherein the second optical converter is used to restore the optical signal transmitted by the demultiplexer.

17. The wavelength division multiplexing system according to claim 16, characterized in that: Also includes: An optical amplifier is located between the multiplexer and the demultiplexer, and is used to amplify the power of the optical signal transmitted by the multiplexer and send the optical signal with amplified optical power to the demultiplexer.

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