On-chip integrated wavelength division multiplexer and photonic integrated circuit chip

Abstract

Disclosed in the present application are an on-chip integrated wavelength division multiplexer and a photonic integrated circuit chip. The wavelength division multiplexer comprises a polarization-insensitive flat-top wavelength division multiplexing structure, wherein the flat-top wavelength division multiplexing structure has a first input waveguide group, a second input waveguide group and an output waveguide. In the flat-top wavelength division multiplexing structure, odd-even grouping is performed on central wavelengths configured for the first input waveguide group and the second input waveguide group, optical signals of different groups are respectively input into the wavelength division multiplexer in different polarization states, and on the basis of a single polarization-insensitive flat-top wavelength division multiplexing structure, two groups of multiple optical signals of different wavelengths and in different polarization states are multiplexed into one multi-wavelength and polarization multiplexed light, thereby reducing signal crosstalk between adjacent channels, simplifying the structural complexity of the wavelength division multiplexer, reducing the size of the wavelength division multiplexer, and thus facilitating an improvement in the integration level of the photonic integrated circuit chip.

Description

On-chip integrated wavelength division multiplexer and photonic integrated circuit chip

[0001] The application claims priority to the Chinese patent application filed with the China Patent Office on March 7, 2024, with application number 202420440975.5 and invention name “On-chip integrated wavelength division multiplexer and photonic integrated circuit chip”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of optical communication technology, and in particular to an on-chip integrated wavelength division multiplexer and a photonic integrated circuit chip. Background Art

[0003] Wavelength division multiplexing (WDM) carries multiple signals at different wavelengths, transmitting and exchanging them within a single optical fiber or waveguide. It is a key technology for achieving information capacity expansion in optical communications. The devices used to implement WDM and demultiplexing are called wavelength division multiplexing devices (MUX) and wavelength division demultiplexing devices (DEMUX), and are the core components of WDM systems. However, in the actual application scenarios of WDM devices, lasers are often affected by various unstable factors such as ambient temperature and manufacturing errors, which often cause the output wavelength to shift from the target wavelength, resulting in significant loss and crosstalk between channels. In this application scenario, wide-bandwidth, flat WDM devices are required to accommodate the wavelength deviation of the lasers and ensure the normal operation of the WDM system.

[0004] The on-chip integrated wavelength division multiplexer (WDM) structure shown in Figure 1, which includes a first-stage multiplexing module 100' and a second-stage multiplexing module 200', can significantly improve the channel bandwidth of the WDM device. It utilizes two flat-type WDM devices (flat-top WDM device 110') for first-stage multiplexing, and then uses a polarization multiplexing module 230' for second-stage multiplexing, thereby achieving flat output over a wider wavelength range. This structure, which only includes passive components and requires no external adjustments, is well-suited for practical applications. However, this WDM device structure, which uses at least two flat-type WDM devices to broaden the bandwidth, doubles the size of the entire WDM system, making it unsuitable for the implementation of high-density, high-speed photonic chips. Utility Model Content

[0005] The purpose of this application is to provide an on-chip integrated wavelength division multiplexer and a photonic integrated circuit chip to realize a flat wavelength division multiplexing function with a larger bandwidth while simplifying the complexity and size of the wavelength division multiplexing device structure.

[0006] According to one aspect of the present application, an on-chip integrated wavelength division multiplexer is provided. The wavelength division multiplexer is integrated on a photonic integrated circuit chip and includes a polarization-compatible flat-top wavelength division multiplexing structure. The flat-top wavelength division multiplexing structure has a first input waveguide group, a second input waveguide group, and an output waveguide. The first input waveguide group includes a plurality of first input waveguides, the second input waveguide group includes a plurality of second input waveguides, and the second input waveguide group is located on one side of the first input waveguide group.

[0007] The plurality of first input waveguides are configured to respectively receive a plurality of incident lights of a predetermined first wavelength group and a first polarization state, the plurality of second input waveguides are configured to respectively receive a plurality of incident lights of a predetermined second wavelength group and a second polarization state, the output waveguide is a polarization-compatible waveguide, and the output waveguide is configured to output multi-wavelength-polarization multiplexed light, wherein the first polarization state and the second polarization state are perpendicular to each other;

[0008] The first wavelength group is one of odd-numbered groups and even-numbered groups of wavelengths λ1, λ2, λ3 ... λn having a predetermined wavelength interval, and the second wavelength group is the other of the odd-numbered groups, where n ≥ 4, and n is a positive integer, and λ1, λ2, λ3 ... λn are arranged in ascending order or descending order according to the predetermined wavelength interval;

[0009] The flat-top wavelength division multiplexing structure is configured such that the effective refractive index of the transmission mode of the multiple incident lights with the first polarization state and the multiple incident lights with the second polarization state therein has a predetermined difference, so that the multiple incident lights with the first polarization state received by the multiple first input waveguides and the multiple incident lights with the second polarization state received by the multiple second input waveguides are combined into one multi-wavelength-polarization multiplexed light within the flat-top wavelength division multiplexing structure and output from the output waveguide.

[0010] According to some embodiments of the present application, the bandwidth of the channel corresponding to each first input waveguide or second input waveguide in the flat-top wavelength division multiplexing structure covers the frequency band range corresponding to the center wavelength of the incident light configured by the corresponding first input waveguide or second input waveguide plus a preset offset threshold.

[0011] According to some embodiments of the present application, the preset offset threshold is the offset specified by the ITU standard, the predetermined wavelength interval is the wavelength interval required by the communication system, the bandwidth is the 1dB bandwidth of the corresponding channel, and the 1dB bandwidth is greater than or equal to twice the offset threshold and less than twice the predetermined wavelength interval.

[0012] According to some embodiments of the present application, the further comprising a plurality of polarization rotators, wherein the number of the polarization rotators is consistent with the number of the first input waveguides or the number of the second input waveguides;

[0013] Each input waveguide of one of the first input waveguide group and the second input waveguide group is cascaded with a polarization rotator, which is used to change the polarization state of each wavelength signal input to the corresponding group so that the polarization state of the incident light incident to the first input waveguide group is perpendicular to the polarization state of the incident light incident to the second input waveguide group.

[0014] According to some embodiments of the present application, the flat-top wavelength division multiplexing structure includes multiple multimode interferometers, and any one of a polarization-compatible etched diffraction grating structure, an arrayed waveguide grating structure, and an angular multimode interferometer structure, and each of the first input waveguides and each of the second input waveguides are connected to the etched diffraction grating structure, the arrayed waveguide grating structure, or the angular multimode interferometer structure through one of the multimode interferometers.

[0015] According to some embodiments of the present application, the flat-top wavelength division multiplexing structure includes multiple multimode interferometers and a polarization-compatible etched diffraction grating structure, wherein the etched diffraction grating structure includes multiple first input channels, multiple second input channels, a free transmission area, etched diffraction grating tooth surfaces, and an output channel, wherein the multiple first input channels, the multiple second input channels, and the output channel are respectively located at different positions on the circumference of the Rowland circle of the free transmission area, each first input channel is connected to each first input waveguide via one of the multimode interferometers, and each second input channel is connected to each second input waveguide via one of the multimode interferometers;

[0016] The free transmission zone includes a slab waveguide, which is configured to make the effective refractive index of the transmission mode of the input multiple-path incident light with a first polarization state and the input multiple-path incident light with a second polarization state have the predetermined difference; the etched diffraction grating tooth surface is configured to diffract the multiple-path incident light with the first polarization state and the multiple-path incident light with the second polarization state passing through the free transmission zone respectively, so that the multiple-path incident light with the first polarization state and the multiple-path incident light with the second polarization state are both focused on the output channel and combined into a multi-wavelength-polarization multiplexed light to be output by the output waveguide.

[0017] According to some embodiments of the present application, the flat-top wavelength division multiplexing structure includes multiple multimode interferometers and an arrayed waveguide grating structure, the arrayed waveguide grating structure includes an input slab waveguide, an output slab waveguide, and multiple arrayed waveguides connected between the input slab waveguide and the output slab waveguide, each of the first input waveguide and each of the second input waveguide is connected to the input slab waveguide through a multimode interferometer, and the output waveguide is connected to the output slab waveguide; each of the arrayed waveguides includes a tapered waveguide, a straight waveguide and a curved waveguide, and there is a constant length difference between two adjacent arrayed waveguides. In the input slab waveguide and the output slab waveguide, the effective refractive index of the first polarization state and the second polarization state has the predetermined difference, so that the multiple incident lights with the first polarization state and the multiple incident lights with the second polarization state are combined into one multi-wavelength-polarization multiplexed light after passing through the phase configuration of the multiple arrayed waveguides in the arrayed waveguide grating structure and output by the output waveguide.

[0018] According to some embodiments of the present application, the flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and an angled multimode interferometer structure, wherein the angled multimode interferometer structure includes a plurality of first input waveguides, a plurality of second input waveguides, a multimode interference region, and an output waveguide, wherein each of the first input waveguides and each of the second input waveguides are connected to the same side of the multimode interference region via a multimode interferometer, and a horizontal axial distance between a connection point between each of the first input waveguides and the output waveguide and the multimode interference region and a horizontal axial distance between a connection point between each of the second input waveguides and the output waveguide and the multimode interference region are configured to have a preset difference;

[0019] The multimode interference zone is configured to make the effective refractive index of the transmission mode of the input multi-path incident light with a first polarization state and the input multi-path incident light with a second polarization state have the predetermined difference, so that the input multi-path incident light with the first polarization state and the input multi-path incident light with the second polarization state are focused to the output waveguide and synthesized into a multi-wavelength-polarization multiplexed light to be output by the output waveguide.

[0020] According to some embodiments of the present application, the on-chip integrated wavelength division multiplexer includes a substrate and a core layer located on the substrate, the flat-top wavelength division multiplexing structure is located in the core layer, and the core layer is any one of a silicon nitride layer, a silicon layer or a lithium niobate layer.

[0021] According to some embodiments of the present application, the wavelength division multiplexer further includes a coupling structure, which is connected to the output waveguide of the flat-top wavelength division multiplexing structure and is used to couple the multi-wavelength-polarization multiplexed optical signal output by the output waveguide of the flat-top wavelength division multiplexing structure to an external optical fiber.

[0022] According to another aspect of the present application, a photonic integrated circuit chip is provided, wherein the photonic integrated circuit chip includes any of the aforementioned on-chip integrated wavelength division multiplexers.

[0023] In the on-chip integrated wavelength division multiplexer and photonic integrated circuit chip provided in embodiments of the present application, the wavelength division multiplexer includes a polarization-compatible flat-top wavelength division multiplexing structure, which has a first input waveguide group, a second input waveguide group, and an output waveguide. Because the flat-top wavelength division multiplexing structure groups the central wavelengths configured for the first input waveguide group and the second input waveguide group into odd-even groups, and allows optical signals of different groups to be input into the wavelength division multiplexer in different polarization states, and based on a single polarization-compatible flat-top wavelength division multiplexing structure, by configuring corresponding parameters of the flat-top wavelength division multiplexing structure, such as configuring the effective refractive index of the transmission mode of the multiple incident light with different polarization states to have a predetermined difference, two groups of multiple optical signals of different wavelengths with different polarization states are multiplexed into one multi-wavelength-polarization multiplexed light, thereby reducing signal crosstalk between adjacent channels, simplifying the structural complexity and size of the wavelength division multiplexer, and facilitating improved integration of the photonic integrated circuit chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The following detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings will make the technical solutions and other beneficial effects of the present application apparent.

[0025] FIG1 is a schematic structural diagram of an on-chip integrated wavelength division multiplexer in the prior art;

[0026] FIG2 is a schematic structural diagram of an on-chip integrated wavelength division multiplexer provided in one embodiment of the present application;

[0027] FIG3 is a schematic structural diagram of an on-chip integrated wavelength division multiplexer provided in yet another embodiment of the present application;

[0028] FIG4 is a schematic structural diagram of an on-chip integrated wavelength division multiplexer provided in another embodiment of the present application;

[0029] Figure 5 is a schematic structural diagram of the polarization rotator (PR) in the on-chip integrated wavelength division multiplexer shown in Figure 4;

[0030] FIG6 is a schematic diagram of a polarization-compatible etched diffraction grating structure used as a flat-top wavelength division multiplexing structure in one embodiment of the present application;

[0031] FIG. 7 is a schematic diagram of a simulation of wavelength division multiplexing using the etched diffraction grating structure in FIG. 6 in one embodiment of the present application.

[0032] FIG8 is a schematic diagram of a polarization-compatible arrayed waveguide grating structure used as a flat-top wavelength division multiplexing structure in one embodiment of the present application;

[0033] FIG9 is a schematic diagram of a polarization-compatible angular multimode interferometer used as a flat-top wavelength division multiplexing structure in one embodiment of the present application.

[0034] Main reference numerals:

[0035] 1000, on-chip integrated wavelength division multiplexer; 110, flat-top wavelength division multiplexing structure; 501, first input waveguide; 502, second input waveguide; 503, output waveguide; 220, polarization rotator;

[0036] 221, ridge waveguide; 222, planar waveguide; 221a, first wedge-shaped structure; 221b, linear structure; 221c, second wedge-shaped structure; 222a, third wedge-shaped structure; 222b, fourth wedge-shaped structure;

[0037] 140. Etched diffraction grating structure; 141. First input channel; 142. Second input channel; 143. Output channel; 144. Free transmission area; 145. Etched diffraction grating tooth surface;

[0038] 150. Arrayed waveguide grating structure; 151. Input slab waveguide; 152. Arrayed waveguide; 153. Output slab waveguide;

[0039] 160. Angular multimode interferometer; 161. First input waveguide; 162. Second input waveguide; 163. Multimode interference region; 164. Output waveguide. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0041] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the specified features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0042] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections, electrical connections, or mutual communication; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal communication between two components or the interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0043] The disclosure below provides many different embodiments or examples for implementing different structures of the present application. In order to simplify the disclosure of the present application, the components and settings of specific examples are described below. Of course, these are merely examples and are not intended to limit the present application. In addition, the present application may repeat reference numbers and / or reference letters in different examples. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed.

[0044] An embodiment of the present application provides an on-chip integrated wavelength division multiplexer, which is integrated on a photonic integrated circuit chip and includes a polarization-compatible flat-top wavelength division multiplexing structure. The flat-top wavelength division multiplexing structure has a first input waveguide group, a second input waveguide group, and an output waveguide. The first input waveguide group includes multiple first input waveguides, the second input waveguide group includes multiple second input waveguides, and the second input waveguide group is located on one side of the first input waveguide group.

[0045] The plurality of first input waveguides are configured to respectively receive a predetermined first wavelength grouping and a multi-path incident light having a first polarization state. The plurality of second input waveguides are configured to respectively receive a predetermined second wavelength grouping and a multi-path incident light having a second polarization state. The output waveguide is a polarization-compatible waveguide configured to output multi-wavelength-polarization multiplexed light, wherein the first polarization state and the second polarization state are perpendicular to each other.

[0046] Among them, the first wavelength group is one of the odd-numbered groups and the even-numbered groups in the wavelengths λ1, λ2, λ3...λn with a predetermined wavelength interval, and the second wavelength group is the other one of them, where n≥4, and n is a positive integer, and λ1, λ2, λ3...λn are arranged in order from small to large or from large to small according to the predetermined wavelength interval.

[0047] The flat-top wavelength division multiplexing structure is configured such that the effective refractive index of the transmission mode of the multiple incident lights with the first polarization state and the multiple incident lights with the second polarization state therein has a predetermined difference, so that the multiple incident lights with the first polarization state received by the multiple first input waveguides and the multiple incident lights with the second polarization state received by the multiple second input waveguides are combined into one multi-wavelength-polarization multiplexed light within the flat-top wavelength division multiplexing structure and output from the output waveguide.

[0048] In the on-chip integrated wavelength division multiplexer provided in the embodiment of the present application, the wavelength division multiplexer includes a polarization-compatible flat-top wavelength division multiplexing structure, the flat-top wavelength division multiplexing structure having a first input waveguide group, a second input waveguide group and an output waveguide. Since the flat-top wavelength division multiplexing structure groups the central wavelengths configured for the first input waveguide group and the second input waveguide group into odd and even groups, and enables optical signals of different groups to be input into the wavelength division multiplexer in different polarization states, and based on a single polarization-compatible flat-top wavelength division multiplexing structure, by configuring the corresponding parameters of the flat-top wavelength division multiplexing structure, compared with the flat-top wavelength division multiplexing structure, the flat-top wavelength division multiplexing structure can be used to realize the optical division multiplexing of the first input waveguide group and the second input waveguide group. For example, multiple incident lights with different polarization states are configured to have a predetermined difference in effective refractive index in the transmission mode therein, and two groups of optical signals with different polarization states and multiple different wavelengths are multiplexed into one multi-wavelength-polarization multiplexed light. On the one hand, the center wavelength odd-even grouping configuration doubles the center wavelength interval between adjacent channels in the same group, reducing signal crosstalk between adjacent channels. On the other hand, the use of a single polarization-compatible flat-top wavelength division multiplexing structure to achieve multi-wavelength-polarization multiplexing simplifies the structural complexity and size of the wavelength division multiplexer, which is conducive to improving the integration of photonic integrated circuit chips.

[0049] Furthermore, the bandwidth of the channel corresponding to each first input waveguide or second input waveguide in the flat-top WDM structure covers the frequency band corresponding to the center wavelength of the incident light configured by the corresponding first input waveguide or second input waveguide plus a preset offset threshold. In other words, each channel in this flat-top WDM structure has a wide flat-top bandwidth, allowing the actual operating wavelength to shift within a larger range. This helps reduce the sensitivity of the on-chip integrated WDM to changes in waveguide width, waveguide height, waveguide tilt, and ambient temperature. Furthermore, this flat-top WDM structure does not require any feedback adjustment during operation, thereby improving operating efficiency and reducing device energy consumption.

[0050] FIG2 is a schematic structural diagram of an on-chip integrated wavelength division multiplexer provided in an embodiment of the present application.

[0051] The structure and working mechanism of the on-chip integrated wavelength division multiplexer 1000 will be described in further detail below with reference to FIG. 2 .

[0052] 2 , in this embodiment, a four-wavelength on-chip integrated wavelength division multiplexer (WDM) is used to multiplex four optical signals with predetermined wavelength intervals and wavelengths λ1, λ2, λ3, and λ4, respectively, into a multi-wavelength-polarization multiplexed light source. The wavelengths λ1, λ2, λ3, and λ4 are arranged in order of wavelength, e.g., from smallest to largest. The on-chip integrated WDM 1000 includes a polarization-compatible flat-top WDM structure 110 having a first input waveguide group, a second input waveguide group, and an output waveguide 503. The first input waveguide group includes two first input waveguides 501, and the second input waveguide group includes two second input waveguides 502. The second input waveguide group is located to one side of the first input waveguide group, i.e., all second input waveguides are located outside the outermost first input waveguide.

[0053] In this embodiment, the odd-numbered groups λ1 and λ3 of the four wavelengths λ1, λ2, λ3, and λ4 are set as predetermined first wavelength groups, and the even-numbered groups λ2 and λ4 are set as predetermined second wavelength groups. The two first input waveguides 501 are respectively configured to receive the predetermined first wavelength groups λ1 and λ3, and the two second input waveguides 502 are respectively configured to receive predetermined second wavelength groups λ2 and λ4, wherein the two incident light paths of the first wavelength group have a first polarization state, such as a TE polarization mode, and the two incident light paths of the second wavelength group have a second polarization state, such as a TM polarization mode, and the first polarization state and the second polarization state are perpendicular to each other. The output waveguide 503 is configured to output a multi-wavelength-polarization multiplexed light of λ1, λ2, λ3, and λ4 combined into one path.

[0054] Specifically, two incident optical signals (λ1 and λ3) with a first polarization state (e.g., TE mode) are input by the two first input waveguides 501 of the flat-top wavelength division multiplexing structure 110, and two incident optical signals (λ2 and λ4) with a second polarization state (e.g., TM mode) are input by the two second input waveguides 502 of the flat-top wavelength division multiplexing structure 110. The flat-top wavelength division multiplexing structure 110 is configured so that the effective refractive index of the transmission mode of the multiple incident light with the first polarization state and the multiple incident light with the second polarization state therein has a predetermined difference, so that the two incident light with the first polarization state received by the two first input waveguides 501 and the two incident light with the second polarization state received by the two second input waveguides 502 are combined into a multi-wavelength-polarization multiplexed light of λ1, λ2, λ3, and λ4 and output from the output waveguide 503. This embodiment uses a single polarization-compatible flat-top wavelength division multiplexing structure to multiplex two groups of optical signals with different polarization states and different wavelengths into one multi-wavelength-polarization multiplexed light, which simplifies the complexity and size of the wavelength division multiplexing structure and helps improve the integration of photonic integrated circuit chips.

[0055] Furthermore, the 1dB flat-top bandwidth of each channel in the flat-top WDM structure 110 is capable of covering the frequency band corresponding to the center wavelength of the incident light configured by the corresponding two first input waveguides 501 or two second input waveguides 502 plus a preset offset threshold. In other words, the bandwidth of each channel in the flat-top WDM structure 110 is greater than the bandwidth corresponding to the offset wavelength range on either side of the center wavelength, i.e., the frequency band from (λn+Δλ) to (λn-Δλ), where n = 1, 2, 3, 4, etc. (where Δλ is half the passband required by the system for the on-chip integrated WDM device, i.e., the preset offset threshold). The ITU standard stipulates that the operating bandwidth of each channel in the flat-top WDM structure 110 with a typical 20nm wavelength spacing is ±6.5nm of the center wavelength, meaning the offset threshold Δλ specified by the standard is 6.5nm. This embodiment performs spectral flattening design on the flat-top wavelength division multiplexing structure, so that it has a flat-top filtering spectrum, so that the bandwidth of each channel is greater than the frequency band range corresponding to the 6.5nm offset of its corresponding center wavelength, that is, greater than 13nm. This ensures that when the actual incident center wavelength fluctuates within the offset threshold range, it can still pass with low loss, avoiding the problem of excessive loss caused by the actual incident optical signal fluctuation deviating from the center wavelength.

[0056] It should be noted that the above-mentioned channel bandwidth refers to the 1dB bandwidth of the filter spectrum of each channel, that is, the optical loss within this bandwidth is less than 1dB compared to the loss at the center wavelength. The bandwidth referred to in the following embodiments also refers to the 1dB bandwidth.

[0057] This embodiment adopts the above-mentioned odd-even staggered channel grouping method, which can make the center wavelength interval of adjacent channels in the same group in the flat-top wavelength division multiplexing structure larger, for example, the center wavelength interval is doubled, thereby avoiding the problem of inter-channel crosstalk caused by the actual incident optical signal fluctuation deviating from the center wavelength.

[0058] Specifically, taking four wavelength-divided optical signals (λ1, λ2, λ3, and λ4) as an example, the center wavelength spacing between adjacent channels (λ1, λ2, λ3, and λ4), i.e., the difference between two adjacent center wavelengths, is set to 20 nm. Since the channels are grouped into odd-even groups, the center wavelength spacing between two adjacent first input waveguides 501 or two adjacent second input waveguides 502 in the same group is 40 nm, double the spacing before grouping. This increased center wavelength spacing between adjacent channels allows for a wider bandwidth design for each channel without increasing crosstalk between channels. For example, the bandwidth of each channel can be greater than or equal to 2Δλ and less than 40 nm. This means that the 1 dB bandwidth of each channel is greater than or equal to twice the offset threshold and less than twice the predetermined wavelength spacing. For example, Δλ represents the required center wavelength offset threshold for the system. For example, the ITU standard specifies a Δλ offset threshold of 6.5 nm. Therefore, the 1 dB bandwidth of each channel in the wavelength division multiplexing structure's filter spectrum is within the range of 13 nm to 40 nm.

[0059] Because the flat-top wavelength division multiplexing structure 110 groups the central wavelengths configured for the first input waveguide group and the second input waveguide group into odd and even groups, the central wavelengths of adjacent channels of the same polarization state in the flat-top wavelength division multiplexing structure are spaced relatively wide apart, thereby reducing crosstalk between channels. Furthermore, the flat-top wavelength division multiplexing structure has a flat-top filtering spectrum, which gives each channel a wide bandwidth. Therefore, the flat-top wavelength division multiplexing structure can tolerate crosstalk between adjacent channels caused by central wavelength shifts due to changes in waveguide width, waveguide inclination, waveguide height, and temperature.

[0060] It should be understood that, as shown in FIG3 , when wavelength-divided optical signals λ1, λ2, λ3, λ4, ..., λ7, and λ8, arranged at predetermined wavelength intervals and arranged in ascending order of wavelength, are input to the multiple input waveguides of the flat-top WDM structure 110, a staggered grouping approach is similarly employed, with odd-numbered grouped incident optical signals input from corresponding channels of each first input waveguide 501 of the flat-top WDM structure 110, and even-numbered grouped incident optical signals input from corresponding channels of each second input waveguide 502 of the flat-top WDM structure 110. For example, odd-numbered grouped optical signals λ1, λ3, λ5, and λ7 having a first polarization state are input to corresponding channels of each first input waveguide 501 of the flat-top WDM structure 110 for multiplexing, thereby generating a combined optical signal of λ1 / λ3 / λ5 / λ7. The even-numbered groups of λ2, λ4, λ6, and λ8 with the second polarization state are input into the corresponding channels of each second input waveguide 502 of the flat-top wavelength division multiplexing structure 110 for multiplexing, thereby obtaining a multiplex of λ2 / λ4 / λ6 / λ8. It can be understood that by configuring the corresponding parameters of the flat-top wavelength division multiplexing structure 110, such as configuring the effective refractive index of the transmission mode of the multiple incident light with different polarization states therein to have a predetermined difference, the multiple incident light with the first polarization state and the multiple incident light with the second polarization state are both focused into one output waveguide for output, thereby achieving multi-wavelength-polarization wavelength division multiplexing. In addition, when more wavelength-divided optical signals with predetermined wavelength intervals of λ1, λ2, λ3, λ4...λn are input into the multiple first input waveguides 501 and the multiple second input waveguides 502 of the flat-top wavelength division multiplexing structure 110, where n>8, the same method as described above can be used to achieve this, and no further details are given here.

[0061] The above-mentioned on-chip integrated wavelength division multiplexer includes a substrate and a core layer located on the substrate, wherein the flat-top wavelength division multiplexing structure is located in the core layer, and the core layer is any one of a silicon nitride layer, a silicon layer, or a lithium niobate layer. Specifically, the on-chip integrated wavelength division multiplexer in the above-mentioned embodiment is a silicon-based wavelength division multiplexer, and the core layer is a silicon nitride layer, which includes a silicon-based substrate, a buried oxide layer, and a silicon nitride layer, and the flat-top wavelength division multiplexing structure is provided on the silicon nitride layer. Of course, it can also be an on-chip integrated wavelength division multiplexer structure based on other semiconductor materials, for example, a wavelength division multiplexer based on silicon material or a wavelength division multiplexer based on lithium niobate material, such as providing a flat-top wavelength division multiplexing structure on the silicon layer of a silicon-on-insulator structure, or providing a flat-top wavelength division multiplexing structure on a lithium niobate layer (such as thin-film lithium niobate), and the present invention is not limited thereto.

[0062] The flat-top wavelength division multiplexing structure includes multiple multimode interferometers and any one of a polarization-compatible etched diffraction grating structure, an arrayed waveguide grating structure, and an angular multimode interferometer structure. Each of the first input waveguides and each of the second input waveguides is cascaded with one of the multimode interferometers to achieve flattening of the output filter spectrum, thereby increasing the 1dB bandwidth of each channel.

[0063] FIG4 is a schematic structural diagram of an on-chip integrated wavelength division multiplexer provided in another embodiment of the present application, and FIG5 is a schematic structural diagram of a polarization rotator (PR) in the on-chip integrated wavelength division multiplexer shown in FIG4 .

[0064] Typically, in optical communication systems, multiple optical signals requiring wavelength division multiplexing (WDM) typically have the same polarization state. As shown in Figures 4 and 5 , in this embodiment, the on-chip integrated WDM 1000 further includes a polarization rotator (PR) 220 for changing the polarization state of one group of incident light. For example, when wavelength-divided optical signals with predetermined wavelength intervals (λ1, λ2, λ3, λ4, ..., λn) arranged in ascending order of wavelength are input into the multiple first input waveguides 501 and the multiple second input waveguides 502 of the flat-top WDM structure, only one group of input waveguides is cascaded with each polarization rotator 220 to change the polarization state of the received light beams, such that the polarization state of the light incident on the first input waveguide group is perpendicular to the polarization state of the light incident on the second input waveguide group. The polarization state of the light incident on the other group of input waveguides remains unchanged.

[0065] Alternatively, the polarization rotator 220 may be a silicon-based polarization rotator (PR). In some embodiments, the silicon-based polarization rotator (PR) may be integrated with the flat-top wavelength division multiplexing structure within the same photonic integrated circuit chip. In other embodiments, the polarization rotator (PR) may be a discrete optical device, such as a half-wave plate or a Faraday rotator.

[0066] As shown in Figure 5, in this embodiment, the polarization rotator 220 is used to change the original polarization state of a received light beam into a polarization state perpendicular to the original polarization state. The polarization rotator 220 includes a ridge waveguide 221 and a partially planar waveguide 222 located on one side of the ridge waveguide 221. The ridge waveguide 221 includes a first wedge-shaped structure 221a, a linear structure 221b, and a second wedge-shaped structure 221c, which are connected in sequence. The first wedge-shaped structure 221a serves as the input end of the polarization rotator 220. Its width gradually narrows along the optical path until it is flush with and connected to the linear structure 221b. The width of the second wedge-shaped structure 221c gradually widens along the optical path until it connects to an external optical waveguide. The partially planar waveguide 222 is lower in height than the ridge waveguide 221 and includes a third wedge-shaped structure 222a and a fourth wedge-shaped structure 222b located on the same side of the ridge waveguide 221 and connected to each other. The third wedge-shaped structure 222a is adjacent to a side of the first wedge-shaped structure 221a, while the fourth wedge-shaped structure 222b is adjacent to a side of the linear structure 221b. The tip of the third wedge-shaped structure 222a is in close contact with the side of the wider end of the first wedge-shaped structure 221a, while the tip of the fourth wedge-shaped structure 222b is adjacent to the narrower end of the second wedge-shaped structure 221c. Linearly polarized light is incident on the wider end of the first wedge-shaped structure 221a of the ridge waveguide 221. Between the first wedge-shaped structure 221a and the linear structure 221b, the light mode is distributed within the ridge waveguide 221 and the planar waveguide 222, causing its polarization state to rotate. By the time it enters the second wedge-shaped structure 221c, the polarization state has already been rotated 90 degrees. It is then coupled into the external optical waveguide through the second wedge-shaped structure 221c.

[0067] FIG6 is a schematic diagram of an embodiment of the present application in which a polarization-compatible etched diffraction grating structure is used as a flat-top wavelength division multiplexing structure.

[0068] As shown in FIG6 , in this embodiment, a polarization-compatible etched diffraction grating structure is used as a flat-top wavelength division multiplexing structure. For example, the flat-top wavelength division multiplexing structure includes multiple multimode interferometers and an etched diffraction grating structure. The etched diffraction grating structure 140 includes multiple first input channels 141, multiple second input channels 142, a free transmission area 144, etched diffraction grating tooth surfaces 145, and an output channel 143. The multiple first input channels 141, the multiple second input channels 142, and the output channel 143 are respectively located at different positions on the circumference of the Rowland circle of the free transmission area 144. Each first input channel 141 is connected to each first input waveguide via a multimode interferometer, each second input channel 142 is connected to each second input waveguide via a multimode interferometer, and the output channel is connected to the output waveguide. The output waveguide is a polarization-compatible waveguide. In which, the free transmission area 144 includes a slab waveguide, and the free transmission area 144 is configured to make the effective refractive index of the transmission mode of the input multi-path incident light with a first polarization state and the multi-path incident light with a second polarization state in the etched diffraction grating structure have a predetermined difference based on the relationship between the fundamental mode effective refractive index of the slab waveguide under the core layer material and the thickness of the slab waveguide under the core layer material; the etched diffraction grating tooth surface 145 is configured to diffract the multi-path incident light with the first polarization state and the multi-path incident light with the second polarization state passing through the free transmission area according to the corresponding relationship between the wavelength, the fundamental mode effective refractive index of the slab waveguide under the core layer material and the diffraction angle, so that the multi-path incident light with the first polarization state and the multi-path incident light with the second polarization state passing through the free transmission area are combined into one multi-wavelength-polarization multiplexed light, and the output channel 143 is configured to output the multi-wavelength-polarization multiplexed light.

[0069] For example, in this embodiment, the etched diffraction grating structure includes two first input channels, two second input channels, and one output channel. Odd-numbered incident light signals (λ1, λ3) with a first polarization state (e.g., TE mode) received by the first input waveguide group are input into the free transmission region from multiple first input channels (e.g., TE input channels) via multimode interferometers. Even-numbered incident light signals (λ2, λ4) with a second polarization state (e.g., TM mode) received by the second input waveguide group are input into the free transmission region from multiple second input channels (e.g., TM input channels) via multimode interferometers. If the initial polarization states of the odd and even-numbered multiple incident light beams are the same, for example, both are TE mode, a polarization rotation device can be cascaded with each of the second input waveguides to rotate the incident light signals originally with a first polarization state (e.g., TE mode) into an incident light signal with a second polarization state (e.g., TM mode). The incident light signals with the second polarization state are then input into the etched diffraction grating structure via the second input waveguides. This etched diffraction grating structure achieves focusing of light beams of different wavelengths on the Rowland circle by arranging the etched diffraction grating teeth in a manner that satisfies the optical path difference. By inputting multiple incident light signals with a first polarization state and multiple incident light signals with a second polarization state at different input positions and angles, and calculating the positions of the corresponding output channels on the Rowland circle, the odd-numbered grouped multiple incident light signals with the first polarization state and the even-numbered grouped multiple incident light signals with the second polarization state are focused onto the output channels located on the Rowland circle, where they are then output via the output waveguide as multi-wavelength-polarization multiplexed optical signals. During operation, two odd-numbered grouped incident light signals λ1 and λ3 with the first polarization state are input from a preset position and, after passing through the interior of the Rowland circle, generate two input mode spots. These two input mode spots then propagate into the free propagation region 144 of the Rowland circle, impinging on the corresponding reflective surfaces of the etched diffraction grating tooth faces 145. After reflection from the etched diffraction grating tooth faces 145, they are focused onto the output channels located on the Rowland circle. Similarly, two even-numbered grouped incident optical signals λ2 and λ4 having a second polarization state are input from a preset position and, after passing through the interior of the Rowland circle, generate two input mode spots. The two input mode spots then propagate into the free transmission region 144 of the Rowland circle and are incident on the corresponding reflection surfaces of the etched diffraction grating tooth surfaces 145. After being reflected by the etched diffraction grating tooth surfaces 145, they are also focused onto the output channel located on the Rowland circle, thereby outputting a multi-wavelength-polarization multiplexed optical signal (λ2 / λ4) from the output channel 143.

[0070] It should be understood that because the first and second input waveguide groups of the polarization-compatible etched diffraction grating structure are configured with odd-even wavelengths for the incident light, the center wavelength spacing between adjacent channels in the flat-top wavelength division multiplexing structure is large, doubling the predetermined wavelength spacing between adjacent channels. Furthermore, by connecting an MMI between the first input waveguide and the first input channel, and between the second input waveguide and the second input channel, the flat-top wavelength division multiplexing structure achieves output spectrum flattening, resulting in a wide flat-top bandwidth for each channel. This allows low-loss transmission even when the actual incident center wavelength fluctuates, thus avoiding the problem of excessive loss caused by fluctuations in the actual incident optical signal that deviate from the center wavelength.

[0071] In this embodiment, the Rowland circle radius expression formula is derived based on the grating equation of the etched diffraction grating EDG, wherein the Rowland circle radius expression formula is expressed by the following formula:

[0072] ;

[0073] Where Lf is the Rowland circle diameter, D is the waveguide spacing, λ is the center wavelength, dλ is the wavelength spacing of the input channel, neff is the effective refractive index of the fundamental mode in the free propagation region of the slab waveguide, ng is the group refractive index, θin is the incident angle, and θout is the output angle in the first polarization state or the second polarization state mode.

[0074] Because a slab waveguide is a thin-film slab, the neff of the transmission mode for TE polarization mode light and the neff of the transmission mode for TM polarization mode light differ due to different boundary conditions. This difference can be exploited to design a predetermined difference between the two, so that incident light of different polarization states, input at different positions on the Rowland circle and at different input angles, is focused onto the same output channel on the Rowland circle and output from the same output waveguide. For example, the difference between the neff of the transmission mode for TE polarization mode light and the neff of the transmission mode for TM polarization mode light can be configured by changing the material type or thickness of the slab waveguide. The difference between the effective refractive index of the TE polarization mode and the effective refractive index of the TM polarization mode is greater than the maximum effective refractive index difference between different wavelengths within the same polarization mode, such as the effective refractive index difference between the first and last wavelengths within the same mode. In this embodiment, according to the above formula, the difference in effective refractive index between the TM polarization mode and the TE polarization mode needs to satisfy the following requirement: at the center wavelength, the difference between the ratio of the effective refractive index to the group refractive index of the TE polarization mode and the ratio of the effective refractive index to the group refractive index of the TM polarization mode, respectively multiplied by the wavelength, is greater than the maximum value of the difference between the ratio of the effective refractive index to the group refractive index and the wavelength between different wavelengths in the same polarization mode, for example, greater than the difference between the ratio of the effective refractive index to the group refractive index and the product of the corresponding wavelengths between the first wavelength and the last wavelength in the same mode.

[0075] This embodiment requires that all incident light beams be focused onto the same output channel, so that all wavelengths on the above-mentioned Rowland circle have the same output angle θout. Substituting the equivalent refractive index neff-TE of the TE polarization mode and the corresponding grouped wavelengths, group refractive index, and output angle parameters into the above-mentioned Rowland circle formula, the input angle θin required for incident light beams of each wavelength can be inferred. Similarly, substituting the equivalent refractive index neff-TM of the TM polarization mode and the corresponding grouped wavelengths, group refractive index, and output angle parameters into the above-mentioned Rowland circle formula, the input angle θin required for incident light beams of each wavelength can be inferred. The equivalent refractive indices of the two polarization modes must satisfy that the input angles of incident light beams of each wavelength in the TE polarization mode do not overlap at all with the input angles of incident light beams of each wavelength in the TM polarization mode, that is, the positions of the input channels of the wavelength channels corresponding to the TE polarization mode on the Rowland circle are completely separated from the positions of the input channels of the wavelength channels corresponding to the TM polarization mode on the Rowland circle, and are distributed in two completely offset regions. By determining the positions of each first input channel and each second input channel on the Rowland circle using the above method, each incident light of the first polarization state input from each first input channel and each incident light of the second polarization state input from each second input channel can be focused onto the same output channel to output a multi-wavelength-polarization multiplexed light, thereby realizing multi-wavelength-polarization multiplexing of a single wavelength division multiplexer.

[0076] Figure 7 is a schematic diagram of a simulation of wavelength division multiplexing using the etched diffraction grating structure shown in Figure 6 in one embodiment of the present application. This simulation is based on an etched diffraction grating structure on a silicon-on-silicon nitride platform, comprising a silicon substrate, a buried oxide layer of silicon dioxide, and a silicon nitride layer. The silicon nitride layer serves as the aforementioned planar waveguide, i.e., the core layer is made of silicon nitride. In this embodiment, the silicon nitride layer has a thickness of 350 nm and a refractive index of 2.15. The effective refractive index difference between the transmission modes (fundamental modes) of the TE polarization mode and the TM polarization mode within the 350 nm layer is approximately 0.115, or greater than 0.115, which allows for complete separation of the first input channels from the second input channels.

[0077] The simulation results are shown in Figure 7. λ1, λ2, λ3, and λ4 are 1271 nm, 1291 nm, 1311 nm, and 1331 nm, respectively, as specified in the ITU-TG.694.2 protocol, with center wavelengths spaced 20 nm apart. In the left figure, the solid line represents the filter spectrum for odd-numbered wavelength channels (with TE polarization signals input to the EDG). The 1 dB flat-top bandwidth for the two channels with center wavelengths of 1271 nm and 1311 nm both reaches approximately 20 nm, exceeding 13 nm. This ensures a flat region within the standard's central wavelength ranges of 1271 nm ± 6.5 nm and 1311 nm ± 6.5 nm, with optical loss below 1 dB. In the figure on the right, the dotted line represents the filter spectrum for even-numbered wavelength channels (with TM polarization signals input to the EDG). The 1dB flat-top bandwidth for the two channels with center wavelengths of 1291nm and 1331nm both reaches approximately 20nm, greater than 13nm. This ensures a flat region within the center wavelength ranges of 1291nm ±6.5nm and 1331nm ±6.5nm, with optical loss below 1dB. Furthermore, in these two groups, the center wavelengths of adjacent channels are separated by 40nm, a sufficient spacing to prevent crosstalk between channels. Therefore, even if the center wavelength shifts toward the longer wavelength band (red shift) or the shorter wavelength band (blue shift) due to factors such as waveguide width, height, tilt, and temperature, this flat-top WDM structure maintains a flat region within the standard-required range of ±6.5nm. The 1dB bandwidth of the broadband wavelength division multiplexing device obtained through this design reaches 20nm, which is significantly higher than the bandwidth of the wavelength division multiplexing device that does not adopt this design structure. The polarization-compatible broadband output response of the wavelength division multiplexing device is successfully achieved, verifying the feasibility of this scheme.

[0078] FIG8 is a schematic diagram of an arrayed waveguide grating structure used as a polarization-compatible flat-top wavelength division multiplexing structure in one embodiment of the present application.

[0079] As shown in Figure 8, in this embodiment, a polarization-compatible arrayed waveguide grating (AWG) structure is used as a flat-top wavelength division multiplexing (WDM) structure. Exemplarily, the flat-top WDM structure includes multiple multimode interferometers and a polarization-compatible arrayed waveguide grating (AWG) structure. The AWG structure 150 includes an input slab waveguide 151, an output slab waveguide 153, and multiple arrayed waveguides 152 (also referred to as waveguide channels) connected between the input and output slab waveguides. Each of the first input waveguides and each of the second input waveguides is connected to the input slab waveguide 151 via a multimode interferometer. Each arrayed waveguide includes a tapered waveguide, a straight waveguide, and a curved waveguide, with a constant length difference between adjacent arrayed waveguides. Based on the differences in effective refractive index of the transmission modes of incident light with different polarizations in the input slab waveguide, the waveguide array, and the output slab waveguide, as well as the length differences of the arrayed waveguides, a polarization-wavelength-dependent phase difference relationship is constructed, so that multiple incident lights with a first polarization state and multiple incident lights with a second polarization state are combined into a multi-wavelength-polarization multiplexed light after phase configuration of the input slab waveguide 151, the multiple arrayed waveguides 152, and the output slab waveguide 153, thereby achieving multi-wavelength-polarization hybrid multiplexing through a single arrayed waveguide grating (AWG). Specifically, in this polarization-compatible arrayed waveguide grating structure, the predetermined difference between the effective refractive index of the TE polarization mode and the effective refractive index of the TM polarization mode is greater than the maximum effective refractive index difference between different wavelengths in the same polarization mode, such as greater than the effective refractive index difference between the first and last wavelengths in the same mode.

[0080] Exemplarily, the number of channels in the plurality of arrayed waveguides 152 is 15, but other numbers are possible, and this application does not impose any limitation thereto. Specifically, the arrayed waveguide grating structure 150 is fabricated on a silicon-on-insulator (SOI) material using an etching process. The SOI material includes a top silicon layer, a buried oxide layer of silicon dioxide, and a substrate silicon layer. The top silicon layer has a thickness of 220 nm, and structures such as arrayed waveguides can be etched on the top silicon layer. The etching depth is, for example, 220 nm, meaning that the core layer is a silicon layer. During operation, two incident optical signals λ1 and λ3, after passing through the phase configuration of the input slab waveguide, the plurality of arrayed waveguides, and the output slab waveguide in the arrayed waveguide grating structure, are focused to the position of the output waveguide connected to the output slab waveguide, and are synthesized into a combined optical signal (λ1 / λ3) that is output by the output waveguide. Similarly, after passing through the phase configuration of the input slab waveguide, multiple arrayed waveguides, and output slab waveguide in the arrayed waveguide grating structure, the two incident optical signals λ2 and λ4 are focused onto the output waveguide connected to the output slab waveguide. A combined optical signal (λ2 / λ4) is then output from the output waveguide, ultimately outputting a multi-wavelength-polarization multiplexed optical signal containing λ1 / λ2 / λ3 / λ4 through the same output waveguide. Using this polarization-compatible arrayed waveguide grating structure to form a flat-top wavelength division multiplexing structure also broadens the flat-top bandwidth of the flat-top wavelength division multiplexing structure. This arrayed waveguide grating structure multiplexes two sets of multiple optical signals of different wavelengths with different polarization states into a single multi-wavelength-polarization multiplexed light signal, thereby simplifying the structural complexity and size of the wavelength division multiplexer and improving the integration density of photonic integrated circuit chips. Compared with the flat-top wavelength division multiplexing structure composed of multiple cascaded Mach-Zehnder interferometer structures, the above-mentioned array grating structure has the advantages of compact structure, small size, low insertion loss, narrow wavelength division multiplexing interval and low process difficulty.

[0081] FIG9 is a schematic diagram of a polarization-compatible angular multimode interferometer used as a flat-top wavelength division multiplexing structure in one embodiment of the present application.

[0082] As shown in FIG9 , in this embodiment, a polarization-compatible angular multimode interferometer is used as a flat-top wavelength division multiplexing structure. Exemplarily, the flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and a polarization-compatible angular multimode interferometer. The angular multimode interferometer (MMI) 160 includes a plurality of first input waveguides 161, a plurality of second input waveguides 162, a multimode interference region 163, and an output waveguide 164. Each of the first input waveguides is connected to the multimode interference region via a multimode interferometer, and each of the second input waveguides is connected to the multimode interference region via a multimode interferometer. The horizontal axial distance between each of the first input waveguides and the output waveguide is unequal to the horizontal axial distance between each of the second input waveguides and the output waveguide. Furthermore, the connection position of each of the first input waveguides in the multimode interference region is completely separated from the connection position of each of the second input waveguides in the multimode interference region. In FIG9 , L1 represents the horizontal axial distance between the first first input waveguide (λ1) and the output waveguide, L3 represents the horizontal axial distance between the second first input waveguide (λ3) and the output waveguide, L2 represents the horizontal axial distance between the first second input waveguide (λ2) and the output waveguide, and L4 represents the horizontal axial distance between the second second input waveguide (λ4) and the output waveguide.

[0083] In this embodiment, the horizontal axial distance between the input waveguide and the output waveguide in the multimode interference region can be expressed by the following formula:

[0084] ;

[0085] Wherein, m is the imaging order, in this embodiment, m=1, neff is the effective refractive index of the fundamental mode in the multimode interference region, Wmmi is the width of the multimode interference region, λn is the fundamental mode wavelength corresponding to the nth channel, and L represents the distance between the center of each input waveguide and the center of the output waveguide along the length direction of the multimode interference region.

[0086] The multimode interference zone 163 is configured based on the relationship between the horizontal axial distance between the incident light of different polarization states and different wavelengths from input to output and the effective refractive index of the fundamental mode transmitted in the multimode interference zone with different polarization states, so that the input multiple incident lights with the first polarization state and the multiple incident lights with the second polarization state are focused onto the output waveguide and combined into one multi-wavelength-polarization multiplexed light to be output by the output waveguide.

[0087] For example, taking four-channel wavelength division multiplexing as an example, the angle-type multimode interferometer 160 includes two first input waveguides, two second input waveguides, and one output waveguide, wherein the ends of the above-mentioned first input waveguides, second input waveguides and output waveguides connected to the multimode interference region can all use tapered waveguides for mode field broadening.

[0088] Conventional angular multimode interferometers (MMIs) achieve wavelength multiplexing and demultiplexing based on the different period lengths of different wavelengths within the multimode interference region 163. In this embodiment of the present application, the different effective refractive indices of different polarization modes transmitted within the multimode interference region are designed to have a predetermined difference in the equivalent refractive index of the fundamental mode of an incident light signal with a first polarization state and an incident light signal with a second polarization state within the multimode interference region. This allows multiple incident light beams with the first polarization state and multiple incident light beams with the second polarization state, after entering the multimode interference region from first and second input waveguides located at different positions along the length of the multimode interference region, to be focused into the same output waveguide and combined into a single multi-wavelength-polarization multiplexed light output. Specifically, in this angular multimode interferometer, the predetermined difference between the effective refractive index of the TE polarization mode and the effective refractive index of the TM polarization mode is greater than the maximum effective refractive index difference between different wavelengths within the same polarization mode, such as the effective refractive index difference between the first and last wavelengths within the same mode.

[0089] For example, input wavelength signals λ1, λ2, λ3, and λ4 are first separated into two polarization states, namely, λ1 (TE), λ2 (TM), λ3 (TE), and λ4 (TM), by an odd-even staggered polarization rotation device. λ1 (TE) and λ3 (TE) are input via two first input waveguides, respectively, while λ2 (TM) and λ4 (TM) are input via two second input waveguides, respectively. Subsequently, the four wavelength signals enter the multimode interference region 163, forming four input pattern spots. Due to the different effective refractive indices of the four wavelength signal transmission modes—in this embodiment, fundamental mode transmission—and the predetermined difference in effective refractive indices between the TE and TM polarization states, the effect of this predetermined difference on the interference period is significantly greater than the effect of the difference in effective refractive indices of different wavelengths. For a fixed input position, the output positions of the TE and TM polarization input pattern spots are different. Similarly, the output positions of different wavelengths are also different. Conversely, incident light with TE and TM polarization states input from multiple different input positions can be output from the same output position. That is, the four input mode spots formed by the four wavelength signals in the multimode interference region are focused to the same output position by the multimode interference region and combined into a multi-wavelength-polarization multiplexed light beam, which is output from the same output waveguide, thus achieving the function shown in Figure 9. Furthermore, using odd-even grouping, the interval between adjacent wavelengths in the same group is doubled, which facilitates bandwidth expansion while reducing crosstalk between channels and meeting the wavelength offset range requirements in practical applications.

[0090] Furthermore, as shown in FIG2 , the on-chip integrated wavelength division multiplexer 1000 further includes a coupling structure 310. The coupling structure 310 is connected to the output waveguide of the flat-top wavelength division multiplexing structure 110 and is configured to couple the combined optical signal outputted by the output waveguide of the flat-top wavelength division multiplexing structure 110 to an external optical fiber to output the combined optical signal. The coupling structure 310 has high coupling efficiency and can reduce coupling optical path loss. Specifically, the coupling structure 310 can be a low polarization-dependent loss (PDL) edge coupler.

[0091] The present application also proposes a photonic integrated circuit chip, which includes the on-chip integrated wavelength division multiplexer described in any of the aforementioned embodiments.

[0092] In the on-chip integrated wavelength division multiplexer and photonic integrated circuit chip provided in the embodiments of the present application, the wavelength division multiplexer includes a polarization-compatible flat-top wavelength division multiplexing structure, which has a first input waveguide group, a second input waveguide group, and an output waveguide. Because the flat-top wavelength division multiplexing structure groups the central wavelengths configured for the first input waveguide group and the second input waveguide group into odd-even groups, and allows optical signals of different groups to be input into the wavelength division multiplexer in different polarization states, and based on a single polarization-compatible flat-top wavelength division multiplexing structure, by configuring corresponding parameters of the flat-top wavelength division multiplexing structure, such as configuring the effective refractive index of the transmission mode of multiple incident light with different polarization states to have a predetermined difference within the flat-top wavelength division multiplexing structure, two groups of multiple optical signals of different wavelengths with different polarization states are multiplexed into one multi-wavelength-polarization multiplexed light, thereby simplifying the structural complexity and size of the wavelength division multiplexer, and facilitating improved integration of the photonic integrated circuit chip.

[0093] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0094] The above is a detailed introduction to the on-chip integrated wavelength division multiplexer and photonic integrated circuit chip provided by the present application in combination with the embodiments. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core ideas of the present application. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An on-chip integrated wavelength division multiplexer, characterized in that: The wavelength division multiplexer is integrated on a photonic integrated circuit chip and includes a polarization-compatible flat-top wavelength division multiplexing structure. The flat-top wavelength division multiplexing structure has a first input waveguide group, a second input waveguide group, and an output waveguide. The first input waveguide group includes a plurality of first input waveguides, the second input waveguide group includes a plurality of second input waveguides, and the second input waveguide group is located on one side of the first input waveguide group. The plurality of first input waveguides are configured to respectively receive a plurality of incident lights of a predetermined first wavelength group and a first polarization state, the plurality of second input waveguides are configured to respectively receive a plurality of incident lights of a predetermined second wavelength group and a second polarization state, the output waveguide is a polarization-compatible waveguide, and the output waveguide is configured to output multi-wavelength-polarization multiplexed light, wherein the first polarization state and the second polarization state are perpendicular to each other; The first wavelength group is one of odd-numbered groups and even-numbered groups of wavelengths λ1, λ2, λ3 ... λn having a predetermined wavelength interval, and the second wavelength group is the other of the odd-numbered groups, where n ≥ 4, and n is a positive integer, and λ1, λ2, λ3 ... λn are arranged in ascending order or descending order according to the predetermined wavelength interval; The flat-top wavelength division multiplexing structure is configured such that the effective refractive index of the transmission mode of the multiple incident lights with the first polarization state and the multiple incident lights with the second polarization state therein has a predetermined difference, so that the multiple incident lights with the first polarization state received by the multiple first input waveguides and the multiple incident lights with the second polarization state received by the multiple second input waveguides are combined into one multi-wavelength-polarization multiplexed light within the flat-top wavelength division multiplexing structure and output from the output waveguide.

2. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: The bandwidth of the channel corresponding to each first input waveguide or second input waveguide in the flat-top wavelength division multiplexing structure covers a frequency band range corresponding to the center wavelength of the incident light configured by the corresponding first input waveguide or second input waveguide plus a preset offset threshold.

3. The on-chip integrated wavelength division multiplexer according to claim 2, wherein: The preset offset threshold is the offset specified by the ITU standard, the predetermined wavelength interval is the wavelength interval required by the communication system, the bandwidth is the 1dB bandwidth of the corresponding channel, and the 1dB bandwidth is greater than or equal to twice the offset threshold and less than twice the predetermined wavelength interval.

4. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: Also comprising a plurality of polarization rotators, wherein the number of the polarization rotators is the same as the number of the first input waveguides or the number of the second input waveguides; Each input waveguide of one of the first input waveguide group and the second input waveguide group is cascaded with a polarization rotator, which is used to change the polarization state of each wavelength signal input to the corresponding group so that the polarization state of the incident light incident to the first input waveguide group is perpendicular to the polarization state of the incident light incident to the second input waveguide group.

5. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: The flat-top wavelength division multiplexing structure includes multiple multimode interferometers and any one of a polarization-compatible etched diffraction grating structure, an arrayed waveguide grating structure, and an angular multimode interferometer structure. Each of the first input waveguides and each of the second input waveguides is connected to the etched diffraction grating structure, the arrayed waveguide grating structure, or the angular multimode interferometer structure through one of the multimode interferometers.

6. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: The flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and a polarization-compatible etched diffraction grating structure, wherein the etched diffraction grating structure includes a plurality of first input channels, a plurality of second input channels, a free transmission area, etched diffraction grating tooth surfaces, and an output channel, wherein the plurality of first input channels, the plurality of second input channels, and the output channel are respectively located at different positions on the circumference of the Rowland circle of the free transmission area, each of the first input channels is connected to each of the first input waveguides via a multimode interferometer, and each of the second input channels is connected to each of the second input waveguides via a multimode interferometer; The free transmission zone includes a slab waveguide, which is configured to make the effective refractive index of the transmission mode of the input multiple-path incident light with a first polarization state and the input multiple-path incident light with a second polarization state have the predetermined difference; the etched diffraction grating tooth surface is configured to diffract the multiple-path incident light with the first polarization state and the multiple-path incident light with the second polarization state passing through the free transmission zone respectively, so that the multiple-path incident light with the first polarization state and the multiple-path incident light with the second polarization state are both focused on the output channel and combined into a multi-wavelength-polarization multiplexed light to be output by the output waveguide.

7. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: The flat-top wavelength division multiplexing structure includes multiple multimode interferometers and an arrayed waveguide grating structure. The arrayed waveguide grating structure includes an input slab waveguide, an output slab waveguide, and multiple arrayed waveguides connected between the input slab waveguide and the output slab waveguide. Each of the first input waveguides and each of the second input waveguides is connected to the input slab waveguide via a multimode interferometer, and the output waveguide is connected to the output slab waveguide. Each of the arrayed waveguides includes a tapered waveguide, a straight waveguide, and a curved waveguide. There is a constant length difference between two adjacent arrayed waveguides. In the input slab waveguide and the output slab waveguide, the effective refractive index of the first polarization state and the effective refractive index of the second polarization state have a predetermined difference, so that multiple incident lights with the first polarization state and multiple incident lights with the second polarization state are combined into one multi-wavelength-polarization multiplexed light after passing through the phase configuration of the multiple arrayed waveguides in the arrayed waveguide grating structure and output by the output waveguide.

8. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: The flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and an angled multimode interferometer structure, wherein the angled multimode interferometer structure includes a plurality of first input waveguides, a plurality of second input waveguides, a multimode interference region, and an output waveguide, wherein each of the first input waveguides and each of the second input waveguides are connected to the same side of the multimode interference region via a multimode interferometer, and a horizontal axial distance between a connection point between each of the first input waveguides and the output waveguide and the multimode interference region and a horizontal axial distance between a connection point between each of the second input waveguides and the output waveguide and the multimode interference region are configured to have a preset difference; The multimode interference zone is configured to make the effective refractive index of the transmission mode of the input multi-path incident light with a first polarization state and the input multi-path incident light with a second polarization state have the predetermined difference, so that the input multi-path incident light with the first polarization state and the input multi-path incident light with the second polarization state are focused to the output waveguide and synthesized into a multi-wavelength-polarization multiplexed light to be output by the output waveguide.

9. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: The on-chip integrated wavelength division multiplexer includes a substrate and a core layer located on the substrate. The flat-top wavelength division multiplexing structure is located on the core layer, and the core layer is any one of a silicon nitride layer, a silicon layer or a lithium niobate layer.

10. The on-chip integrated wavelength division multiplexer according to claim 1, wherein: The wavelength division multiplexer further comprises a coupling structure connected to the output waveguide of the flat-top wavelength division multiplexing structure, for coupling the multi-wavelength-polarization multiplexed optical signal output by the output waveguide of the flat-top wavelength division multiplexing structure to an external optical fiber.

11. A photonic integrated circuit chip, characterized in that: The invention comprises an on-chip integrated wavelength division multiplexer as claimed in any one of claims 1 to 10.