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

Abstract

The utility model discloses an on-chip integrated wavelength division multiplexer and a photon integrated circuit chip, the wavelength division multiplexer comprises a polarization compatible flat-topped wavelength division multiplexing structure, the flat-topped wavelength division multiplexing structure is provided with a first input waveguide group, a second input waveguide group and an output waveguide, the flat-topped wavelength division multiplexing structure performs odd-even grouping on the configured central wavelengths of the first input waveguide group and the second input waveguide group, and optical signals in different groups are respectively input into the wavelength division multiplexer in different polarization states; and on the basis of a single polarization compatible flat-topped wavelength division multiplexing structure, two groups of multi-path optical signals with different wavelengths in different polarization states are multiplexed into one path of multi-wavelength-polarization multiplexing light, so that signal crosstalk between adjacent channels is reduced, the structural complexity and size of the wavelength division multiplexer are simplified, and the integration level of a photon integrated circuit chip is improved.

Description

Technical Field

[0001] 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

[0002] Wavelength division multiplexing carries multiple signals through different wavelengths, transmits and exchanges them in a single optical fiber / waveguide, and is a key technology for optical communications to achieve information expansion. The devices used to achieve wavelength division multiplexing and demultiplexing are called wavelength division multiplexing devices (MUX) and wavelength division multiplexing devices (DEMUX), which are the core devices of wavelength division multiplexing systems. However, in the actual application scenarios of wavelength division multiplexing devices, since lasers are affected by various unstable factors such as ambient temperature and manufacturing errors, the output wavelength often deviates from the target wavelength, causing significant loss and crosstalk problems between channels. In this application scenario, a wide-bandwidth, flat wavelength division multiplexing device is required to accommodate the wavelength deviation of the laser and ensure the normal operation of the wavelength division multiplexing system.

[0003] like Figure 1 The structure of the on-chip integrated wavelength division multiplexer shown, which includes a first-stage multiplexing module 100' and a second-stage multiplexing module 200', can significantly improve the channel bandwidth of the wavelength division multiplexing device. It uses two flat wavelength division multiplexing devices (flat-top wavelength division multiplexing devices 110') for first-stage multiplexing, and then uses a polarization multiplexing module 230' for second-stage multiplexing, thereby achieving flat output within a larger wavelength range. In addition, the structure only includes passive devices and does not require external adjustment, which fits the actual application scenario. However, this wavelength division multiplexing device structure uses at least two flat wavelength division multiplexing devices to widen the bandwidth, which will double the size of the entire wavelength division multiplexing system, and is not conducive to the realization of high-density, high-speed photonic chips. Utility Model Content

[0004] The purpose of the present 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.

[0005] 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 at one side of the first input waveguide group;

[0006] The plurality of first input waveguides are configured to respectively receive a predetermined first wavelength group and a multi-path incident light with a first polarization state, the plurality of second input waveguides are configured to respectively receive a predetermined second wavelength group and a multi-path incident light with 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;

[0007] The first wavelength group is one of the odd-numbered groups and the even-numbered groups of wavelengths λ1, λ2, λ3, ... λn with a predetermined wavelength interval, and the second wavelength group is the other group thereof, wherein 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;

[0008] 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 in the flat-top wavelength division multiplexing structure and output from the output waveguide.

[0009] According to some embodiments of the present application, the bandwidth of the channel corresponding to each of the first input waveguide or the second input waveguide in the flat-top wavelength division multiplexing structure covers the frequency band range corresponding to the central wavelength of the incident light configured by the first input waveguide or the second input waveguide corresponding to it plus a preset offset threshold.

[0010] 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.

[0011] According to some embodiments of the present application, a plurality of polarization rotators are further included, and the number of the polarization rotators is consistent with the number of the first input waveguides or the number of the second input waveguides;

[0012] Each input waveguide of one of the first input waveguide group and the second input waveguide group is cascaded with a polarization rotator for changing 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.

[0013] According to some embodiments of the present application, the flat-top wavelength division multiplexing structure includes a plurality of 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 via one of the multimode interferometers.

[0014] According to some embodiments of the present application, the flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and a polarization-compatible etched diffraction grating structure, the etched diffraction grating structure includes a plurality of first input channels, a plurality of second input channels, a free transmission area, an etched diffraction grating tooth surface, 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 through one of the multimode interferometers, and each of the second input channels is connected to each of the second input waveguides through one of the multimode interferometers;

[0015] The free transmission zone includes a slab waveguide, which 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; the etched diffraction grating tooth surface is configured to diffract the multi-path incident light with a first polarization state and the multi-path incident light with a second polarization state passing through the free transmission zone respectively, so that the multi-path incident light with the first polarization state and the multi-path incident light with the second polarization state are both focused on the output channel and combined into a multi-wavelength-polarization multiplexed light output by the output waveguide.

[0016] 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 are 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, 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 have the predetermined difference, so that the multi-path incident light with the first polarization state and the multi-path incident light 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.

[0017] According to some embodiments of the present application, the flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and an angle-type multimode interferometer structure, the angle-type multimode interferometer structure includes a plurality of the first input waveguides, a plurality of the 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 through 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;

[0018] 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.

[0019] 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.

[0020] According to some embodiments of the present application, the wavelength division multiplexer also 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.

[0021] According to another aspect of the present application, a photonic integrated circuit chip is provided, wherein the photonic integrated circuit chip comprises any of the above-mentioned on-chip integrated wavelength division multiplexers.

[0022] 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. 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 makes optical signals of different groups input the wavelength division multiplexer in different polarization states, respectively, 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 multi-path incident light with different polarization states therein to have a predetermined difference, two groups of multi-path 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 improving the integration of the photonic integrated circuit chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0024] Figure 1 It is a schematic diagram of the structure of an on-chip integrated wavelength division multiplexer in the prior art;

[0025] Figure 2 A schematic diagram of the structure of an on-chip integrated wavelength division multiplexer provided in one embodiment of the present application;

[0026] Figure 3 A schematic structural diagram of an on-chip integrated wavelength division multiplexer provided in yet another embodiment of the present application;

[0027] Figure 4 A schematic diagram of the structure of an on-chip integrated wavelength division multiplexer provided in another embodiment of the present application;

[0028] Figure 5 for Figure 4 A schematic structural diagram of a polarization rotator (PR) in an on-chip integrated wavelength division multiplexer is shown;

[0029] Figure 6 This is a schematic diagram of using a polarization-compatible etched diffraction grating structure as a flat-top wavelength division multiplexing structure in an embodiment of the present application;

[0030] Figure 7 In one embodiment of the present application, Figure 6 Schematic diagram of the simulation of wavelength division multiplexing using the etched diffraction grating structure in FIG.

[0031] Figure 8 It is a schematic diagram of using a polarization-compatible arrayed waveguide grating structure as a flat-top wavelength division multiplexing structure in one embodiment of the present application;

[0032] Fig. 9 This is a schematic diagram of using a polarization-compatible angular multi-mode interferometer as a flat-top wavelength division multiplexing structure in an embodiment of the present application.

[0033] Main reference numerals:

[0034] 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;

[0035] 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;

[0036] 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;

[0037] 150. Arrayed waveguide grating structure; 151. Input slab waveguide; 152. Arrayed waveguide; 153. Output slab waveguide;

[0038] 160. Angular multimode interferometer; 161. First input waveguide; 162. Second input waveguide; 163. Multimode interference region; 164. Output waveguide. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0040] The terms "first" and "second" in this document are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0041] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0042] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed.

[0043] 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, wherein the flat-top wavelength division multiplexing structure has a first input waveguide group, a second input waveguide group and an output waveguide, wherein 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.

[0044] The plurality of first input waveguides are configured to respectively receive a predetermined first wavelength grouping and a multi-path incident light with 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 with 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.

[0045] Among them, the first wavelength grouping 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 grouping is the other group, 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.

[0046] 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 in the flat-top wavelength division multiplexing structure and output from the output waveguide.

[0047] 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 has a first input waveguide group, a second input waveguide group and an output waveguide, because the flat-top wavelength division multiplexing structure performs odd-even grouping on the central wavelengths configured for the first input waveguide group and the second input waveguide group, and makes optical signals of different groups input the wavelength division multiplexer in different polarization states respectively, 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, For example, multiple incident lights of 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 of multiple different wavelengths of different polarization states 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 of adjacent channels in the same group, thereby reducing signal crosstalk between adjacent channels. On the other hand, a single polarization-compatible flat-top wavelength division multiplexing structure is used to realize multi-wavelength-polarization multiplexing, thereby simplifying the structural complexity and size of the wavelength division multiplexer, and facilitating improving the integration of photonic integrated circuit chips.

[0048] Furthermore, the bandwidth of the channel corresponding to each of the first input waveguide or the second input waveguide in the flat-top wavelength division multiplexing structure covers the frequency band range corresponding to the central wavelength of the incident light configured by the first input waveguide or the second input waveguide corresponding to it plus the preset offset threshold. That is, each channel in the flat-top wavelength division multiplexing structure has a wider flat-top band bandwidth, allowing the actual working wavelength to shift within a larger range, which is conducive to reducing the sensitivity of the on-chip integrated wavelength division multiplexer to changes in waveguide width, waveguide height, waveguide inclination and ambient temperature. In addition, the flat-top wavelength division multiplexing structure does not require any feedback adjustment during operation, thereby improving work efficiency and reducing device energy consumption.

[0049] Figure 2 A schematic diagram of the structure of an on-chip integrated wavelength division multiplexer provided in one embodiment of the present application.

[0050] The following will be combined Figure 2 , the structure and working mechanism of the on-chip integrated wavelength division multiplexer 1000 are further described in detail.

[0051] See also Figure 2As shown, illustratively, in this embodiment, a four-wavelength on-chip integrated wavelength division multiplexer is taken as an example, which is used to multiplex four optical signals with predetermined wavelength intervals and wavelengths of λ1, λ2, λ3, and λ4 into one multi-wavelength-polarization multiplexed light, wherein λ1, λ2, λ3, and λ4 are arranged in order of wavelength size, for example, from small to large. The on-chip integrated wavelength division multiplexer 1000 includes a polarization-compatible flat-top wavelength division multiplexing structure 110, and the flat-top wavelength division multiplexing structure 110 has a first input waveguide group, a second input waveguide group, and an output waveguide 503, wherein the first input waveguide group includes two first input waveguides 501, and the second input waveguide group includes two second input waveguides 502, and the second input waveguide group is located on one side of the first input waveguide group, that is, all the second input waveguides are located outside the edgemost first input waveguide.

[0052] In this embodiment, the odd-numbered groups λ1 and λ3 of the four wavelengths λ1, λ2, λ3, and λ4 are set as the predetermined first wavelength groups, and the even-numbered groups λ2 and λ4 are set as the 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 the predetermined second wavelength groups λ2 and λ4, wherein the two incident lights of the first wavelength group have a first polarization state, such as a TE polarization mode, and the two incident lights 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 multi-wavelength-polarization multiplexed light of λ1, λ2, λ3, and λ4 combined into one path.

[0053] Specifically, two incident optical signals (λ1 and λ3) with a first polarization state (for example, 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 (for example, 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 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 two incident lights with the first polarization state received by the two first input waveguides 501 and the two incident lights 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, 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 of different wavelengths in different polarization states into one multi-wavelength-polarization multiplexed light, which simplifies the complexity and size of the wavelength division multiplexing structure and helps to improve the integration of photonic integrated circuit chips.

[0054] In addition, the 1dB flat-top band bandwidth of each channel in the flat-top wavelength division multiplexing structure 110 can cover the central wavelength of the incident light configured by the two first input waveguides 501 or the two second input waveguides 502 corresponding to it plus the frequency band range corresponding to the preset offset threshold. That is, the bandwidth of each channel of the flat-top wavelength division multiplexing structure 110 is greater than the frequency band bandwidth corresponding to the offset wavelength range on both sides of the central wavelength, that is, the frequency band range between (λn+Δλ) and (λn-Δλ), where n=1,2,3,4... (where Δλ is half of the passband width required by the system for the on-chip integrated wavelength division multiplexing device, that is, the above-mentioned preset offset threshold). The ITU standard stipulates that the working bandwidth of each channel in the flat-top wavelength division multiplexing structure 110 with a general wavelength interval of 20nm is the central wavelength ±6.5nm, that is, the offset threshold Δλ stipulated 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 central wavelength, that is, greater than 13nm, thereby ensuring that when the actual incident central 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 central wavelength.

[0055] 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 the bandwidth is less than 1dB compared with the loss of the central wavelength. The bandwidth referred to in the following embodiments also refers to the 1dB bandwidth.

[0056] 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 crosstalk between channels caused by the actual incident optical signal fluctuation deviating from the center wavelength.

[0057] Specifically, taking 4 (λ1, λ2, λ3, λ4) wavelength-divided optical signals as an example, the center wavelength interval between adjacent channels of λ1, λ2, λ3, and λ4, that is, the difference between two adjacent center wavelengths, is set to 20nm. Then, since each channel is grouped into odd and even numbers, the center wavelength interval between the corresponding channels of two adjacent first input waveguides 501 or two adjacent second input waveguides 502 in the same group is 40nm, which is twice that before grouping. The center wavelength interval between adjacent channels is increased, so that the bandwidth of each channel can be designed to be wider, and the crosstalk between channels will not increase. For example, the bandwidth of each channel can be greater than or equal to 2Δλ and less than 40nm, that is, the 1dB bandwidth of each channel is greater than or equal to twice the offset threshold and less than twice the predetermined wavelength interval. Exemplarily, the above Δλ is the center wavelength offset threshold required by the system. For example, the ITU standard stipulates that the offset threshold Δλ is 6.5nm, then the 1dB bandwidth of each channel of the wavelength division multiplexing structure filtering spectrum is in the range of 13nm to 40nm.

[0058] Since the flat-top wavelength division multiplexing structure 110 performs odd-even grouping on the central wavelengths configured for the first input waveguide group and the second input waveguide group, the central wavelength intervals of adjacent channels of the same polarization state in the flat-top wavelength division multiplexing structure are relatively large, thereby reducing crosstalk between channels; at the same time, the flat-top wavelength division multiplexing structure has a flat-top filtering spectrum, so that each channel has a wider bandwidth, so it can tolerate the crosstalk problem between adjacent channels caused by the central wavelength offset caused by the influence of waveguide width, waveguide inclination, waveguide height and temperature changes.

[0059] It should be understood that Figure 3As shown, when the wavelength-divided optical signals λ1, λ2, λ3, λ4 ... λ7, λ8 with a predetermined wavelength interval and arranged in ascending order of wavelength are input into the plurality of input waveguides of the flat-top wavelength division multiplexing structure 110, similarly, a staggered grouping multiplexing method is adopted, and the incident optical signals of the odd group are input from the corresponding channel of each first input waveguide 501 of the flat-top wavelength division multiplexing structure 110, and the incident optical signals of the even group are input from the corresponding channel of each second input waveguide 502 of the flat-top wavelength division multiplexing structure 110. For example, the odd-grouped λ1, λ3, λ5, λ7 with the first polarization state are input into the corresponding channel of each first input waveguide 501 of the flat-top wavelength division multiplexing structure 110 for multiplexing, thereby obtaining the multiplexed wave of λ1 / λ3 / λ5 / λ7. The even-numbered grouped 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 the multiplexing 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 lights with different polarization states therein to have a predetermined difference, the multiple incident lights with the first polarization state and the multiple incident lights with the second polarization state are both focused to an output waveguide for output, thereby realizing 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 above can be adopted to achieve it, which will not be repeated here.

[0060] 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 a flat-top wavelength division multiplexing structure is arranged 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 arranging a flat-top wavelength division multiplexing structure on the silicon layer of a silicon-on-insulator structure, or arranging a flat-top wavelength division multiplexing structure on a lithium niobate layer (such as thin-film lithium niobate), and the utility model does not limit this.

[0061] The flat-top wavelength division multiplexing structure includes a plurality of 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 filtering spectrum, thereby increasing the 1dB bandwidth of each channel.

[0062] Figure 4 This is a schematic diagram of the structure of an on-chip integrated wavelength division multiplexer provided in another embodiment of the present application. Figure 5 for Figure 4 The schematic diagram of the structure of the polarization rotator (PR) in the on-chip integrated wavelength division multiplexer is shown.

[0063] Usually, in optical communication systems, multiple optical signals that need to be wavelength-division multiplexed generally have the same polarization state, such as Figure 4 and Figure 5 As shown, in this embodiment, the on-chip integrated wavelength division multiplexer 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 of λ1, λ2, λ3, λ4, ... λn with predetermined wavelength intervals and arranged in ascending order of wavelength are input into the plurality of first input waveguides 501 and the plurality of second input waveguides 502 of the flat-top wavelength division multiplexing structure, only one group of input waveguides is cascaded with each of the polarization rotators 220, respectively, to change the polarization state of the received light beam, 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. The polarization state of the incident light in the other group of input waveguides remains unchanged.

[0064] Optionally, the polarization rotator 220 may also 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 in the same photonic integrated circuit chip. In other embodiments, the polarization rotator (PR) may also be a discrete optical device, such as a half-wave plate or a Faraday rotator.

[0065] like Figure 5As shown, in this embodiment, the polarization rotator 220 is used to change the original polarization state of the received light beam into a polarization state perpendicular to the original polarization state. The polarization rotator 220 includes a ridge waveguide 221 and a partial 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 connected in sequence. The first wedge-shaped structure 221a serves as the input end of the polarization rotator 220, and its width gradually narrows along the optical path until it is flush with and connected to the linear structure 221b, and the width of the second wedge-shaped structure 221c gradually widens along the optical path until it is connected to the external optical waveguide. The height of the partial planar waveguide 222 is lower than that of 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 the side of the first wedge-shaped structure 221a, the fourth wedge-shaped structure 222b is adjacent to the side of the linear structure 221b, the tip of the third wedge-shaped structure 222a is adjacent to the side of the wider end of the first wedge-shaped structure 221a, and 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 from the wider end of the first wedge-shaped structure 221a of the ridge waveguide 221. In the first wedge-shaped structure 221a and the linear structure 221b, the light mode is distributed in the ridge waveguide 221 and the planar waveguide 222, so that the polarization state is rotated. When incident on the second wedge-shaped structure 221c, the polarization state has been rotated by 90 degrees, and then coupled to the external optical waveguide through the second wedge-shaped structure 221c.

[0066] Figure 6 It is a schematic diagram of using a polarization-compatible etched diffraction grating structure as a flat-top wavelength division multiplexing structure in an embodiment of the present application.

[0067] like Figure 6As shown, in this embodiment, a polarization-compatible etched diffraction grating structure 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 an etched diffraction grating structure. The etched diffraction grating structure 140 includes a plurality of first input channels 141, a plurality of second input channels 142, a free transmission area 144, an etched diffraction grating tooth surface 145, and an output channel 143, wherein the plurality of first input channels 141, the plurality of 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 of the first input channels 141 is connected to each of the first input waveguides through a multimode interferometer, each of the second input channels 142 is connected to each of the second input waveguides through a multimode interferometer, the output channel is connected to the output waveguide, and the output waveguide is a polarization-compatible waveguide. Wherein, the free transmission zone 144 includes a slab waveguide, and the free transmission zone 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 have a predetermined difference in the etched diffraction grating structure based on the relationship between the effective refractive index of the fundamental mode in 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 a first polarization state and the multi-path incident light with a second polarization state passing through the free transmission zone according to the corresponding relationship between the wavelength, the effective refractive index of the fundamental mode 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 zone are combined into one multi-wavelength-polarization multiplexed light, and the output channel 143 is configured to output the multi-wavelength-polarization multiplexed light.

[0068] Exemplarily, in this embodiment, the etched diffraction grating structure includes 2 first input channels, 2 second input channels and 1 output channel. The incident light signals (λ1, λ3) of the odd groups and having the first polarization state (e.g., TE mode) received by the first input waveguide group are respectively input into the free transmission area from multiple first input channels (e.g., TE input channels) through multimode interferometers; the incident light signals (λ2, λ4) of the even groups and having the second polarization state (e.g., TM mode) received by the second input waveguide group are respectively input from multiple second input channels (e.g., TM input channels) through multimode interferometers. Wherein, when the initial polarization states of the multi-path incident light of the odd groups and the even groups are the same, for example, when they are all TE modes, a polarization rotation device can be cascaded in each of the second input waveguides to rotate the incident light signal originally having the first polarization state (e.g., TE mode) into the incident light signal having the second polarization state (e.g., TM mode), and then the incident light signal having the second polarization state is input into the etched diffraction grating structure through the second input waveguide. The etched diffraction grating structure realizes the focusing of light beams of different wavelengths on the Rowland circle by arranging the etched diffraction grating teeth that satisfy the optical path difference relationship. By inputting the multi-path incident light signals with the first polarization state and the multi-path incident light signals with the second polarization state at different input positions and different input angles, and calculating the position of the output channel on the corresponding Rowland circle, the multi-path incident light with the first polarization state of the odd-numbered group and the multi-path incident light with the second polarization state of the even-numbered group can be focused on the output channel located on the Rowland circle, and the multi-wavelength-polarization multiplexed light signal is output through the output waveguide. When working, the two-path incident light signals λ1 and λ3 of the odd-numbered group and with the first polarization state are input from the preset position and after passing through the interior of the Rowland circle, two input mode spots are generated, and then the two input mode spots enter the free transmission area 144 of the Rowland circle for propagation, and are incident on the corresponding reflection surface of the etched diffraction grating tooth surface 145, and are focused on the output channel located on the Rowland circle after being reflected by the etched diffraction grating tooth surface 145. Similarly, two even-grouped incident optical signals λ2 and λ4 having a second polarization state are input from a preset position and generate two input mode spots after passing through the inside of the Rowland circle. The two input mode spots then propagate into the free transmission area 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 on the output channel located on the Rowland circle, thereby outputting a multi-wavelength-polarization multiplexed optical signal (λ2 / λ4) from the output channel 143.

[0069] It should be understood that, since the incident light wavelengths configured in the first input waveguide group and the second input waveguide group of the polarization-compatible etched diffraction grating structure are grouped into odd and even groups, the center wavelength intervals of adjacent channels in the flat-top wavelength division multiplexing structure are relatively large, and the predetermined wavelength intervals of adjacent channels can be doubled. At the same time, the flat-top wavelength division multiplexing structure connects the MMI between the first input waveguide and the first input channel, and connects the MMI between the second input waveguide and the second input channel to achieve output spectrum flattening, so that each channel has a wider flat-top band bandwidth, so that when the actual incident center wavelength fluctuates, it can still pass through with low loss, avoiding the problem of excessive loss caused by the actual incident optical signal fluctuation deviating from the center wavelength.

[0070] In this embodiment, the Rowland circle radius expression formula is derived according to the grating equation of the etched diffraction grating EDG, wherein the Rowland circle radius expression formula is expressed by the following formula:

[0071]

[0072] Wherein, 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 zone 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.

[0073] In the slab waveguide, since it is a thin film slab structure, and the boundary conditions of the light in the TE polarization mode and the light in the TM polarization mode are different, there is a difference between the neff of the transmission mode of the light in the TE polarization mode and the neff of the transmission mode of the light in the TM polarization mode. Therefore, this difference can be used to design a predetermined difference between the two, so that the incident light of different polarization states input from different positions on the Rowland circle at different input angles are focused on the same output channel on the Rowland circle, and thus output from the same output waveguide. For example, the difference between the neff of the transmission mode of the light in the TE polarization mode and the neff of the transmission mode of the light in the TM polarization mode 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 value of the effective refractive index difference of different wavelengths in the same polarization mode, such as greater than the effective refractive index difference between the first wavelength and the last wavelength in 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 that, 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 product 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 wavelength between the first wavelength and the last wavelength in the same mode.

[0074] This embodiment requires that all incident lights are focused to 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 and other parameters into the above-mentioned Rowland circle formula, the input angle θin that the incident light of each wavelength needs to satisfy 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 and other parameters into the above-mentioned Rowland circle formula, the input angle θin that the incident light of each wavelength needs to satisfy can be inferred. The equivalent refractive indexes of the two polarization modes need to satisfy that the input angles of the incident lights of each wavelength of the TE polarization mode and the input angles of the incident lights of each wavelength of the TM polarization mode do not overlap at all, 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 areas that are completely staggered from each other. By determining the positions of each first input channel and each second input channel on the Rowland circle through 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 one multi-wavelength-polarization multiplexed light, thereby realizing multi-wavelength-polarization multiplexing of a single wavelength division multiplexer.

[0075] Figure 7 In one embodiment of the present application, Figure 6 Schematic diagram of simulation of wavelength division multiplexing using an etched diffraction grating structure in FIG. The simulation is based on an etched diffraction grating structure on a silicon-based silicon nitride platform, including a substrate silicon, a buried oxide layer silicon dioxide and a silicon nitride layer, where the silicon nitride layer is the above-mentioned planar waveguide, that is, the aforementioned core layer material is silicon nitride. In this embodiment, the thickness of the silicon nitride layer is 350nm, the refractive index of silicon nitride is 2.15, and the equivalent refractive index difference between the transmission mode (fundamental mode) of the TE polarization mode and the TM polarization mode within it is about 0.115, or greater than 0.115, which can completely separate each first input channel from each second input channel.

[0076] The simulation results are as follows Figure 7As shown, λ1, λ2, λ3, and λ4 are 1271nm, 1291nm, 1311nm, and 1331nm respectively as specified in the ITU-TG.694.2 protocol, and the center wavelengths are spaced 20nm apart. In the left figure, the solid line is the filter spectrum of the odd-numbered wavelength channel (TE polarization signal input to EDG), and the bandwidth of the 1dB flat-top band of the two channels with center wavelengths of 1271nm and 1311nm is about 20nm, which is greater than 13nm, and can ensure that the center wavelengths of 1271nm±6.5nm and 1311nm±6.5nm required by the standard are both flat areas, and the optical loss is less than 1dB. In the right figure, the dotted line is the filter spectrum of the even-numbered wavelength channel (with TM polarization signal input to EDG), and the bandwidth of the 1dB flat-top band of the two channels with central wavelengths of 1291nm and 1331nm is also about 20nm, which is greater than 13nm, and can ensure that the central wavelengths of 1291nm±6.5nm and 1331nm±6.5nm are all flat areas, and the optical loss is less than 1dB. In the above two groups, the central wavelengths of adjacent channels are spaced 40nm apart, which is large enough to avoid signal crosstalk between channels. Therefore, even if the flat-top wavelength division multiplexing structure is affected by factors such as waveguide width, height, tilt angle and temperature changes, causing the central wavelength band to shift to the long wavelength band (red shift) or shift to the short wavelength band (blue shift), it can also ensure that it is a flat area within the offset range of the central wavelength ±6.5nm required by the standard. The 1dB bandwidth of the broadband wavelength division multiplexing device obtained by this design reaches 20nm, which is significantly larger 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.

[0077] Figure 8 It is a schematic diagram of using an arrayed waveguide grating structure as a polarization-compatible flat-top wavelength division multiplexing structure in one embodiment of the present application.

[0078] like Figure 8As shown, in this embodiment, a polarization-compatible arrayed waveguide grating structure (Array Waveguide Gratings, AWG) is used as a flat-top wavelength division multiplexing structure. Exemplarily, the flat-top wavelength division multiplexing structure includes multiple multimode interferometers and a polarization-compatible arrayed waveguide grating structure. The arrayed waveguide grating 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 slab waveguide and the output slab waveguide, and each of the first input waveguides and each of the second input waveguides are connected to the input slab waveguide 151 through a multimode interferometer. 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. Based on the difference in effective refractive index of the transmission mode of incident light with different polarizations in the input slab waveguide, the waveguide array and the output slab waveguide and the length difference of each arrayed waveguide, a polarization-wavelength related phase difference relationship is constructed, so that the multi-path incident light with the first polarization state and the multi-path incident light with the second polarization state are combined into a multi-wavelength-polarization multiplexed light after passing through the phase configuration of the input slab waveguide 151, the multiple arrayed waveguides 152 and the output slab waveguide 153, so as to realize multi-wavelength-polarization hybrid multiplexing through a single arrayed waveguide grating AWG. Specifically, in the 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 value of the effective refractive index difference of different wavelengths in the same polarization mode, such as greater than the effective refractive index difference between the first wavelength and the last wavelength in the same mode.

[0079] Exemplarily, the number of channels of the plurality of arrayed waveguides 152 is 15, and of course it can be other numbers, which is not limited in this application. Specifically, the arrayed waveguide grating structure 150 is made on a silicon on insulator (SOI) material using an etching process, and the SOI material includes a top silicon, a buried oxide layer of silicon dioxide, and a substrate silicon. The thickness of the top silicon is 220nm, and the arrayed waveguide and other structures can be etched on the top silicon. The etching depth is, for example, 220nm, that is, the core layer is a silicon layer. When working, the two incident optical signals λ1 and λ3 are focused to the position of the output waveguide connected to the output waveguide 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, and a combined optical signal (λ1 / λ3) is synthesized and output by the output waveguide. Similarly, the two incident optical signals λ2 and λ4 are focused to the position of the output waveguide connected to the output waveguide after passing through the phase configuration of the input slab waveguide, multiple arrayed waveguides and output slab waveguide in the arrayed waveguide grating structure, and a combined optical signal (λ2 / λ4) is synthesized and output by the output waveguide, and finally a multi-wavelength-polarization multiplexed optical signal including λ1 / λ2 / λ3 / λ4 is output through the same output waveguide. The flat-top wavelength division multiplexing structure formed by the above-mentioned polarization-compatible arrayed waveguide grating structure can also make the flat-top band bandwidth of the flat-top wavelength division multiplexing structure wider. Based on the arrayed waveguide grating structure, two groups of multi-channel optical signals of different wavelengths in different polarization states are multiplexed into a multi-wavelength-polarization multiplexed light, thereby simplifying the structural complexity and size of the wavelength division multiplexer, which is conducive to improving the integration 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.

[0080] Fig. 9 This is a schematic diagram of using a polarization-compatible angular multi-mode interferometer as a flat-top wavelength division multiplexing structure in an embodiment of the present application.

[0081] like Fig. 9As shown, 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 the first input waveguides 161, a plurality of the second input waveguides 162, a multimode interference region 163 and an output waveguide 164, wherein each of the first input waveguides is connected to the multimode interference region via a multimode interferometer, 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 not equal to the horizontal axial distance between each of the second input waveguides and the output waveguide, and the connection position of each first input waveguide in the multimode interference region is completely separated from the connection position of each second input waveguide in the multimode interference region. Fig. 9 In the figure, 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.

[0082] 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 expression:

[0083]

[0084] 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 zone, Wmmi is the width of the multimode interference zone, 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 zone.

[0085] 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 multi-path incident light with a first polarization state and the multi-path incident light with a 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.

[0086] Exemplarily, 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 first input waveguides, the second input waveguides, and the output waveguide connected to the multimode interference region can all use tapered waveguides for mode field broadening.

[0087] The conventional angle-type multimode interferometer (MMI) realizes wavelength multiplexing and demultiplexing based on the different period lengths of different wavelengths in the multimode interference region 163. In the embodiment of the present application, the equivalent refractive index of different polarization modes transmitted in the multimode interference region is different, and the equivalent refractive index of the incident light signal with the first polarization state and the incident light signal with the second polarization state in the multimode interference region is designed to have a predetermined difference in the transmission fundamental mode, so that the multi-path incident light with the first polarization state and the multi-path incident light with the second polarization state are respectively incident to the multimode interference region from the first input waveguide and the second input waveguide located at different positions in the length direction of the multimode interference region. After being incident to the multimode interference region, they can all be focused to the same output waveguide and combined into a multi-wavelength-polarization multiplexed light output. Specifically, in the angle-type 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 value of the effective refractive index difference of different wavelengths in the same polarization mode, such as greater than the effective refractive index difference between the first wavelength and the last wavelength in the same mode.

[0088] Exemplarily, the input wavelength signals λ1, λ2, λ3, and λ4 are first divided into two polarization states according to odd and even staggering by a polarization rotation device, namely, λ1 (TE), λ2 (TM), λ3 (TE), and λ4 (TM), wherein λ1 (TE) and λ3 (TE) are respectively input by two first input waveguides, and λ2 (TM) and λ4 (TM) are respectively input by two second input waveguides. Subsequently, the four wavelength signals enter the multimode interference region 163 to form four input pattern spots. Due to the difference in effective refractive indexes of the four wavelength signal transmission modes, the fundamental mode transmission is used in this embodiment, and the effective refractive indexes of the TE and TM polarization state transmission modes have a predetermined difference, and the effect of the predetermined difference on the interference period is significantly greater than the effect of the difference in effective refractive indexes of different wavelengths on the interference period. For a fixed input position, the output positions of the TE and TM polarization state input pattern spots are different, and at the same time, the output positions of different wavelengths are also different. Conversely, incident light input into the TE polarization state and the TM polarization state from multiple different input positions can be output from the same output position. That is, the four input mode spots formed by the above four wavelength signals in the multimode interference region are focused to the same output position through the multimode interference region, and are combined into a multi-wavelength-polarization multiplexed light output from the same output waveguide, thereby achieving the following Fig. 9 The function shown in the figure is achieved by using odd-even grouping to double the interval between adjacent wavelengths in the same group, which is conducive to increasing the bandwidth and reducing the crosstalk between channels, thus meeting the requirements of the wavelength offset range in practical applications.

[0089] Furthermore, if Figure 2As shown, the on-chip integrated wavelength division multiplexer 1000 also includes a coupling structure 310, which is connected to the output waveguide of the flat-top wavelength division multiplexing structure 110, and is used to couple the combined optical signal output by the output waveguide of the flat-top wavelength division multiplexing structure 110 to an external optical fiber to output the combined optical signal, which has a high coupling efficiency and can reduce the loss of the coupling optical path. Specifically, the coupling structure 310 can be a low polarization dependent loss edge coupler (low PDL edge coupler).

[0090] 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.

[0091] 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, and the flat-top wavelength division multiplexing structure has 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 makes optical signals of different groups input the wavelength division multiplexer in different polarization states, respectively, 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 multi-path incident light with different polarization states therein to have a predetermined difference, the two groups of multi-path 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 improving the integration of the photonic integrated circuit chip.

[0092] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0093] The on-chip integrated wavelength division multiplexer and photonic integrated circuit chip provided by the present application are introduced in detail 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 solution and its core idea 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 make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present application.

Claims

1. An on-chip integrated wavelength division multiplexer, It is 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, wherein the flat-top wavelength division multiplexing structure has a first input waveguide group, a second input waveguide group and an output waveguide, wherein 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 at one side of the first input waveguide group; The plurality of first input waveguides are configured to respectively receive a predetermined first wavelength group and a multi-path incident light with a first polarization state, the plurality of second input waveguides are configured to respectively receive a predetermined second wavelength group and a multi-path incident light with 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 the odd-numbered groups and the even-numbered groups of wavelengths λ1, λ2, λ3, ... λn with a predetermined wavelength interval, and the second wavelength group is the other group thereof, wherein 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 in 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, It is characterized in that The bandwidth of the channel corresponding to each of the first input waveguide or the second input waveguide in the flat-top wavelength division multiplexing structure covers the frequency band range corresponding to the central wavelength of the incident light configured by the corresponding first input waveguide or the second input waveguide plus a preset offset threshold.

3. The on-chip integrated wavelength division multiplexer according to claim 2, It is characterized in that 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, It is characterized in that Also comprising a plurality of polarization rotators, the number of the polarization rotators being consistent with 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 for changing 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, It is characterized in that The flat-top wavelength division multiplexing structure includes a plurality of 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 are connected to the etched diffraction grating structure, the arrayed waveguide grating structure, or the angular multimode interferometer structure via one of the multimode interferometers.

6. The on-chip integrated wavelength division multiplexer according to claim 1, It is characterized in that 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, an etched diffraction grating tooth surface, 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 one of the multimode interferometers, and each of the second input channels is connected to each of the second input waveguides via one of the multimode interferometers; The free transmission zone includes a slab waveguide, which 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; the etched diffraction grating tooth surface is configured to diffract the multi-path incident light with a first polarization state and the multi-path incident light with a second polarization state passing through the free transmission zone respectively, so that the multi-path incident light with the first polarization state and the multi-path incident light with the second polarization state are both focused on the output channel and combined into a multi-wavelength-polarization multiplexed light output by the output waveguide.

7. The on-chip integrated wavelength division multiplexer according to claim 1, It is characterized in that The flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and an arrayed waveguide grating structure, wherein the arrayed waveguide grating structure includes an input slab waveguide, an output slab waveguide, and a plurality of 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 are 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, 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 effective refractive index of the second polarization state have the predetermined difference, so that the multi-path incident light with the first polarization state and the multi-path incident light with the second polarization state are combined into a multi-wavelength-polarization multiplexed light after passing through the phase configuration of the plurality of 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, It is characterized in that The flat-top wavelength division multiplexing structure includes a plurality of multimode interferometers and an angle-type multimode interferometer structure, wherein the angle-type multimode interferometer structure includes a plurality of the first input waveguides, a plurality of the 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 through 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, It is characterized in that The on-chip integrated wavelength division multiplexer comprises 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, It is characterized in that The wavelength division multiplexer further comprises a coupling structure connected to the output waveguide of the flat-top wavelength division multiplexing structure and used for coupling the multi-wavelength-polarization multiplexed optical signal outputted by the output waveguide of the flat-top wavelength division multiplexing structure to an external optical fiber.

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

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