A multi-dimensional multiplexing modulation integrated photonics circuit based on thin film lithium niobate

Abstract

The application discloses a multi-dimensional multiplexing modulation integrated photonic circuit of thin film lithium niobate, which comprises eight MRR type modulators, eight wavelength multiplexers based on reflective Bragg gratings, two polarization rotation beam splitters, a tapered waveguide based on a subwavelength waveguide grating and a double-polarization first-order mode multiplexer / demultiplexer. The photonic integrated circuit modulates input wavelength signals of λ0 and λ1, then wavelength multiplexes the signals by using reflective Bragg gratings with different working wavelengths, and then performs mode-polarization multiplexing, so as to realize the functions of wavelength, mode and polarization mixed multiplexing and signal modulation. The multi-dimensional multiplexing modulation integrated photonic circuit has the expandable characteristics of channels, and is expected to be used in optical interconnection to realize super-large capacity data transmission in an optical network.

Description

Technical Field

[0001] This invention belongs to the field of integrated optical technology and relates to an on-chip photonic integrated circuit based on lithium niobate thin film waveguide for multidimensional multiplexing and modulation. Background Technology

[0002] In recent years, lithium niobate, with its excellent electro-optic, acousto-optic, and piezoelectric properties, has attracted widespread attention. However, due to limitations in waveguide fabrication methods, existing lithium niobate devices suffer from low refractive index differences and large device sizes, hindering high integration. With advancements in process technology, the lithium niobate-on-insulator (LNOI) platform has emerged. This platform's thin-film lithium niobate retains the characteristics of lithium niobate while also possessing the advantage of a high refractive index difference, making it easy for researchers to integrate multiple unit devices on the LNOI. Currently, many excellent electro-optic modulators based on the LNOI platform have been reported both domestically and internationally. For example, Marko Lončar's research group at Harvard University published a paper in Nature on a thin-film lithium niobate electro-optic modulator with CMOS-compatible driving voltages ("Integratedlithium niobate electro-optic modulators operating at CMOS-compatible voltages", Nature 562(7725), 101-104 (2018)). The research group of Cai Xinlun at Sun Yat-sen University published in Nature Photonics a high-performance hybrid silicon and lithium niobate Mach–Zehnder modulator for a modulation rate exceeding 100 Gbps. -1 and beyond” Nature Photonics, 13(5), 359-364(2019)).

[0003] However, with the ever-increasing demand for data capacity, the data modulation rate achieved by a single modulator is still insufficient to meet future needs. An ideal solution is to combine the modulator with advanced multiplexing technology to achieve an explosive increase in the data capacity transmitted in a single waveguide. Common optical multiplexing technologies include wavelength division multiplexing, mode multiplexing, and polarization multiplexing. Some LNOI-based multiplexing / demultiplexing devices and multiplexing-modulation integrated devices have been proposed. For example, the Cai Xinlun research group at Sun Yat-sen University published a dual-polarization thin-film lithium niobate in-phase quadrature modulators forterabit-per-second transmission in Optica (Optica, 9(1), 61-62 (2022)).

[0004] Most of the reported lithium niobate multiplexing technologies and multiplexing-modulation integrated devices are based on single-dimensional multiplexing, which has limited expansion of the number of channels and does not significantly improve the data transmission capacity in the waveguide. Moreover, lithium niobate material has complex mode characteristics, and mode hybridization occurs at a certain waveguide width (TM polarized light and TE polarized light can be converted into each other). For details, see the literature ("Mode and polarization-division multiplexing based on silicon nitrideloaded lithium niobate on insulator platform" Laser & Photonics Reviews, 16(1), 2100529 (2022)) and the literature ("High-Performance Mode-Multiplexing Device with Anisotropic Lithium-Niobate-on-Insulator Waveguides" Laser & Photonics Reviews, 2200774 (2023)). Summary of the Invention

[0005] The purpose of this invention is to provide a multidimensional multiplexing modulation integrated photonic circuit based on thin-film lithium niobate, which simultaneously multiplexes the three dimensions of modulation wavelength, mode, and polarization, enabling the simultaneous transmission of multiple channels in a single waveguide and improving data transmission capacity.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a multidimensional multiplexing and modulation integrated photonic circuit based on thin-film lithium niobate, characterized in that it includes eight MRR modulators, eight wavelength multiplexers, two polarization rotating beamsplitters, and one dual-polarization first-order mode multiplexer / demultiplexer; two wavelength multiplexers from the eight wavelength multiplexers and two MRR modulators from the eight MRR modulators form a combination, for a total of four combinations. Two combinations are respectively connected to one polarization rotating beamsplitter through waveguides. The polarization rotating beamsplitter is connected to the dual-polarization first-order mode multiplexer / demultiplexer through a subwavelength waveguide grating tapered waveguide. The other two combinations are respectively connected to another polarization rotating beamsplitter through another waveguide. The other polarization rotating beamsplitter is connected to the dual-polarization first-order mode multiplexer / demultiplexer.

[0007] In the same combination: the output of one MRR modulator is connected to the input of one wavelength multiplexer, the output of another MRR modulator is connected to the input of another wavelength multiplexer, the multimode pass-through of one wavelength multiplexer is a free end, the output of one wavelength multiplexer is connected to the multimode pass-through of another wavelength multiplexer, and the output of the other wavelength multiplexer is connected to a polarization rotating beam splitter through a waveguide;

[0008] All wavelength multiplexers are based on reflective Bragg grating wavelength multiplexers.

[0009] The waveguide in the multidimensional multiplexing and modulation integrated photonic circuit of this invention is a thin-film lithium niobate waveguide loaded with silicon nitride. Because silicon nitride has a transparent window similar to lithium niobate and its refractive index is slightly lower, the mode field of the silicon nitride-lithium niobate composite waveguide is mostly located within the lithium niobate layer, and its operating bandwidth remains unaffected. Most importantly, silicon nitride has mature processing technology and, unlike traditional directly-etched lithium niobate waveguides, it does not have a waveguide tilt angle, making it easy to fabricate structures with ultra-small linewidths, such as subwavelength waveguide gratings, and facilitating large-scale device integration.

[0010] The integrated photonic circuit of this invention, which combines multidimensional multiplexing and modulation, comprises a polarization mode multiplexer / demultiplexer mainly consisting of two PSRs, a tapered waveguide based on a subwavelength waveguide grating, and a dual-polarization first-order mode multiplexer / demultiplexer. Due to the complex mode dispersion of lithium niobate material, a mode hybridization point exists at 2.1 micrometers. When the TM0 mode passes through this width, mode conversion occurs (TM0 mode will convert to TE1 mode), introducing crosstalk between channels. This invention uses a tapered waveguide based on a subwavelength waveguide grating structure for width transition, which can greatly reduce crosstalk caused by mode conversion, thus enabling the TM0 mode to pass through smoothly and ultimately achieving simultaneous multiplexing of multiple signals. The dual-polarization first-order mode multiplexer / demultiplexer in this invention uses a double-tapered structure for high-order mode coupling, which can simultaneously match the refractive indices of TM0 and TM1, and TE0 and TE1, thereby achieving efficient mode coupling. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the multidimensional multiplexing modulation integrated photonic circuit of the present invention.

[0012] Figure 2 This is a schematic diagram of the MRR type modulator in the multidimensional multiplexing modulation integrated photonic integrated circuit of the present invention.

[0013] Figure 3 This is a schematic diagram of the wavelength multiplexer in the multidimensional multiplexing modulation integrated photonic circuit of the present invention.

[0014] Figure 4 This is the transmission spectrum of the reflective Bragg grating with periods of 410nm and 415nm in the multidimensional multiplexing modulation integrated photonic circuit of this invention.

[0015] Figure 5 This is a schematic diagram of the first polarization rotation beam splitter in the multidimensional multiplexing modulation integrated photonic circuit of the present invention.

[0016] Figure 6 This is a schematic diagram of the grating tapered waveguide in the multidimensional multiplexing modulation integrated photonic circuit of this invention.

[0017] Figure 7 This is a schematic diagram of a common tapered waveguide in existing technology.

[0018] Figure 8 This is a simulation diagram of the transmission spectrum of the grating tapered waveguide transmitting TM0 mode in the multidimensional multiplexing modulation integrated photonic circuit of the present invention.

[0019] Figure 9 This is a simulation diagram of the transmission spectrum when a conventional tapered waveguide transmits in TM0 mode in the existing technology.

[0020] Figure 10This is a schematic diagram of the multiplexer / demultiplexer in the multidimensional multiplexing modulation integrated photonic circuit of the present invention.

[0021] Figure 11 yes Figure 10 The simulation transmission loss diagram of the multiplexer / demultiplexer is shown.

[0022] Figure 12 yes Figure 10 The simulation crosstalk diagram of the multiplexer / demultiplexer is shown.

[0023] Figure 13 This is a schematic diagram of the waveguide structure in the multidimensional multiplexing modulation integrated photonic circuit based on thin-film lithium niobate of the present invention.

[0024] In the figure: 1. First modulator, 2. Second modulator, 3. Third modulator, 4. Fourth modulator, 5. Fifth modulator, 6. Sixth modulator, 7. Seventh modulator, 8. Eighth modulator, 9. First wavelength multiplexer, 10. Second wavelength multiplexer, 11. Third wavelength multiplexer, 12. Fourth wavelength multiplexer, 13. Fifth wavelength multiplexing structure, 14. Sixth wavelength multiplexer, 15. Seventh wavelength multiplexer, 16. Eighth wavelength multiplexer, 17. First polarization rotating beamsplitter, 18. Second polarization rotating beamsplitter, 19. Grating tapered waveguide, 20. Multiplexer / demultiplexer, 21. Waveguide cladding, 22. Silicon nitride load layer, 23. Lithium niobate planar layer, 24. Silica buried layer, 25. Silicon substrate layer;

[0025] 1-1. First grating coupler; 1-2. First fundamental mode straight waveguide; 1-3. First bent waveguide; 1-4. Second fundamental mode straight waveguide; 1-5. High-frequency electrode; 1-6. Second bent waveguide; 1-7. Third fundamental mode straight waveguide; 1-8. Hot electrode; 9-1. Third bent waveguide; 9-2. Fourth bent waveguide; 9-3. Fourth fundamental mode straight waveguide; 9-4. First Bragg grating; 9-5. First multimode waveguide; 17-1. Fifth fundamental mode straight waveguide; 17-2. Fifth bent waveguide; 17-3. Sixth bent waveguide; 17-4. Seventh fundamental mode straight waveguide 17-5. Eighth fundamental mode straight waveguide; 17-6. First tapered waveguide; 17-7. Second multimode waveguide; 17-8. Second tapered waveguide; 17-9. Third multimode waveguide; 17-10. Third tapered waveguide; 17-11. Ninth fundamental mode straight waveguide; 19-1. Tenth fundamental mode straight waveguide; 19-2. Tapered waveguide of subwavelength waveguide grating; 19-3. Fourth multimode waveguide; 20-1. Seventh curved waveguide; 20-2. First trapezoidal waveguide; 20-3. Fifth multimode waveguide; 20-4. Second trapezoidal waveguide; 20-5. Sixth multimode waveguide. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0027] like Figure 1 As shown, the integrated photonic circuit of the present invention includes a first modulator 1, a second modulator 2, a third modulator 3, a fourth modulator 4, a fifth modulator 5, a sixth modulator 6, a seventh modulator 7, and an eighth modulator 8.

[0028] The output of the first modulator 1 is connected to the input of the first wavelength multiplexer 9, the output of the second modulator 2 is connected to the input of the second wavelength multiplexer 10, and the output of the first wavelength multiplexer 9 is connected to the multimode pass-through of the second wavelength multiplexer 10.

[0029] The output of the third modulator 3 is connected to the input of the third wavelength multiplexer 11, the output of the fourth modulator 4 is connected to the input of the fourth wavelength multiplexer 12, and the output of the third wavelength multiplexer 11 is connected to the multimode pass-through of the fourth wavelength multiplexer 12.

[0030] The output terminals of the second wavelength multiplexer 10 and the fourth wavelength multiplexer 12 are both connected to the input terminal of the first polarization rotating beam splitter 17.

[0031] The output of the fifth modulator 5 is connected to the input of the fifth wavelength multiplexer 13, the output of the sixth modulator 6 is connected to the input of the sixth wavelength multiplexer 14, and the output of the fifth wavelength multiplexer 13 is connected to the multimode pass-through of the sixth wavelength multiplexer 14.

[0032] The output of the seventh modulator 7 is connected to the input of the seventh wavelength multiplexer 15, the output of the eighth modulator 8 is connected to the input of the eighth wavelength multiplexer 16, and the output of the seventh wavelength multiplexer 15 is connected to the multimode pass-through terminal of the eighth wavelength multiplexer 16.

[0033] The output terminals of the sixth wavelength multiplexer 14 and the eighth base wavelength multiplexer 16 are both connected to the input terminal of the second polarization rotating beam splitter 18.

[0034] The multimode pass-through terminals of the first wavelength multiplexer 9, the third wavelength multiplexer 11, the fifth wavelength multiplexer 13, and the seventh wavelength multiplexer 15 are all free terminals.

[0035] The output of the first polarization rotating beam splitter 17 is connected to the narrower end of the tapered waveguide 19, the wider end of the tapered waveguide 19 is connected to the multimode waveguide in the multiplexer / demultiplexer 20, and the output of the second polarization rotating beam splitter 18 is connected to the fundamental mode waveguide in the multiplexer / demultiplexer 20.

[0036] The first modulator 1, the second modulator 2, the third modulator 3, the fourth modulator 4, the fifth modulator 5, the sixth modulator 6, the seventh modulator 7, and the eighth modulator 8 are all MRR type modulators.

[0037] The first wavelength multiplexer 9, the second wavelength multiplexer 10, the third wavelength multiplexer 11, the fourth wavelength multiplexer 12, the fifth wavelength multiplexer 13, the sixth wavelength multiplexer 14, the seventh wavelength multiplexer 15, and the eighth wavelength multiplexer 16 are all wavelength multiplexers based on reflective Bragg gratings.

[0038] The tapered waveguide 19 employs a tapered waveguide based on a subwavelength waveguide grating.

[0039] The multiplexer / demultiplexer 20 adopts a dual-polarization first-order mode multiplexer / demultiplexer.

[0040] The eight modulators have identical structures, with Figure 2 The first modulator 1 shown is used as an example for explanation.

[0041] The first modulator 1 includes a first grating coupler 1-1, a first fundamental mode straight waveguide 1-2, and a racetrack-shaped micro-ring resonator. The micro-ring resonator is composed of a first curved waveguide 1-3, a second fundamental mode straight waveguide 1-4, a second curved waveguide 1-6, and a third fundamental mode straight waveguide 1-7 connected in sequence. The first fundamental mode straight waveguide 1-2 is coupled to the first curved waveguide 1-3. A rectangular high-frequency electrode 1-5 is mounted on the second fundamental mode straight waveguide 1-4. A hot electrode 1-8 is provided inside the micro-ring resonator, and the hot electrode 1-8 is arranged parallel to the third fundamental mode straight waveguide 1-7. The input end of the first fundamental mode straight waveguide 1-2 faces the first grating coupler 1-1, and the output end of the first fundamental mode straight waveguide 1-2 is connected to the input end of the first wavelength multiplexer 9.

[0042] The optical signal is input through the first grating coupler 1-1 and coupled to the first fundamental mode straight waveguide 1-2 for transmission. When the resonance condition is met, the optical signal in the first fundamental mode straight waveguide 1-2 is coupled to the first curved waveguide 1-3 and then transmitted in the micro-ring resonator. High-frequency electrical signals generated by external devices are applied to the high-frequency electrode 1-5. Due to the electro-optic properties of lithium niobate, the refractive index of the waveguide in the MRR can be adjusted by regulating the voltage, thereby regulating the resonant wavelength of the MRR and ultimately changing the optical signal. The hot electrode 1-8 is used to adjust the operating wavelength of different MRR modulators, thus controlling the operating wavelength of the MRR modulator. The operating wavelengths of the eight MRR modulators are divided into two groups: the operating wavelengths of the first modulator 1, third modulator 3, fifth modulator 5, and seventh modulator 7 are λ0. The operating wavelengths of the second modulator 2, fourth modulator 4, sixth modulator 6, and eighth modulator 8 are λ1. The modulated optical signal is output from the first fundamental mode straight waveguide 1-2 and enters the wavelength multiplexer.

[0043] The eight wavelength multiplexers have the same structure except for the grating period; Figure 3 The first wavelength multiplexer 9 shown is used as an example for explanation.

[0044] The first wavelength multiplexer 9 includes a first multimode waveguide 9-5 and a third curved waveguide 9-1, a fourth curved waveguide 9-2, and a fourth fundamental mode straight waveguide 9-3 connected in sequence. One end of the first multimode waveguide 9-5 is connected to one end of a first Bragg grating 9-4, and the fourth fundamental mode straight waveguide 9-3 is coupled to the first multimode waveguide 9-5. The third curved waveguide 9-1, the fourth curved waveguide 9-2, and the fourth fundamental mode straight waveguide 9-3 constitute the signal input terminal of the first wavelength multiplexer 9. The other end of the third curved waveguide 9-1 is connected to the output terminal of the first fundamental mode straight waveguide 9-2. The other end of the first Bragg grating 9-4 is connected to one end of the first multimode waveguide in the second wavelength multiplexer 10.

[0045] The other end of the second Bragg grating in the second wavelength multiplexer 10 and the other end of the fourth Bragg grating in the fourth wavelength multiplexer 12 are both connected to the input end of the first polarization rotating beam splitter 17; the other end of the sixth Bragg grating in the sixth wavelength multiplexer 14 and the other end of the eighth Bragg grating in the eighth wavelength multiplexer 16 are both connected to the input end of the second polarization rotating beam splitter 18.

[0046] Because the refractive index of the fundamental mode of the fourth fundamental mode straight waveguide 9-3 matches the refractive index of the first-order mode in the first multimode waveguide 9-5, when the modulated optical signal is input from the signal input terminal of the first wavelength multiplexer 9, it will couple into the first-order mode signal in the first multimode waveguide 9-5 and enter the first Bragg grating 9-4. According to the reflection condition of the Bragg grating: the refractive indices of the two Bloch modes in the Bragg grating ( n 1 and n 2) The sum is equal to the reflected wavelength (λ) divided by the grating period (Λ), that is... n 1+ n 2 = λ / Λ. By appropriately designing the input first-order mode optical signal so that the refractive index of the input signal and the reflected fundamental mode signal satisfy the reflection condition of the Bragg grating, the fundamental mode optical signal with a center wavelength of λ0 can be reflected and output from the multimode waveguide. Since the reflected fundamental mode optical signal with wavelength λ0 does not satisfy the operating wavelength of the second Bragg grating in the second wavelength multiplexer 10, it can directly pass through the second Bragg grating and enter the input port 2 of the first polarization rotating beam splitter 17. Figure 4The diagram shows the transmission spectrum of a reflective Bragg grating with different grating periods. Different reflection wavelengths can be achieved by designing the grating period, thus allowing optical signals modulated at operating wavelengths of λ0 and λ1 to enter the polarization rotating beam splitter. The operating wavelengths of the first wavelength multiplexer 9, the third wavelength multiplexer 11, the fifth wavelength multiplexer 13, and the seventh wavelength multiplexer 15 are λ0, while the operating wavelengths of the second wavelength multiplexer 10, the fourth wavelength multiplexer 12, the sixth wavelength multiplexer 14, and the eighth wavelength multiplexer 16 are λ1.

[0047] The two polarization rotating beam splitters have identical structural parameters, with Figure 5 The first polarization rotating beam splitter 17 shown is used as an example for illustration.

[0048] The first polarization rotating beam splitter 17 includes a fifth fundamental mode straight waveguide 17-1, a fifth curved waveguide 17-2, a sixth curved waveguide 17-3, and a seventh fundamental mode straight waveguide 17-4 connected in sequence; the fifth fundamental mode straight waveguide 17-1, the fifth curved waveguide 17-2, the sixth curved waveguide 17-3, and the seventh fundamental mode straight waveguide 17-4 constitute the input port 1 of the polarization rotating beam splitter;

[0049] The first polarization rotating beam splitter 17 also includes an eighth fundamental mode straight waveguide 17-5, a first tapered waveguide 17-6, a second multimode waveguide 17-7, a second tapered waveguide 17-8, a third multimode waveguide 17-9, a third tapered waveguide 17-10, and a ninth fundamental mode straight waveguide 17-11 connected in sequence; the eighth fundamental mode straight waveguide 17-5 is the input port 2 of the first polarization rotating beam splitter 17.

[0050] The seventh fundamental mode straight waveguide 17-4 is coupled to the second multimode waveguide 17-7. The other end of the fifth fundamental mode straight waveguide 17-1 is connected to the other end of the fourth Bragg grating in the fourth wavelength multiplexer 12, and the other end of the eighth fundamental mode straight waveguide 17-5 is connected to the other end of the second Bragg grating in the second wavelength multiplexer 10.

[0051] The other end of the fifth fundamental mode straight waveguide in the second polarization rotating beam splitter 18 is connected to the other end of the fourth Bragg grating in the eighth wavelength multiplexer 16, and the other end of the eighth fundamental mode straight waveguide in the second polarization rotating beam splitter 18 is connected to the other end of the second Bragg grating in the sixth wavelength multiplexer 14.

[0052] When a TE0 mode optical signal is input from input port 1, it will be coupled into the TE1 mode in the second multimode waveguide 17-7 due to the refractive index matching condition. It then enters the third multimode waveguide 17-9 through the second tapered waveguide 17-8 for mode hybridization, i.e., the TE1 mode evolves into the TM0 mode. Finally, the TM0 mode enters the ninth fundamental mode straight waveguide 17-11 through the third tapered waveguide 17-10 for output. When a TE0 mode optical signal is input from input port 2, it is directly output from the ninth fundamental mode straight waveguide 17-11 in the form of TE0 mode because the refractive index matching condition is not met. The specific working principle of the polarization rotating beam splitter can be found in the literature (“Mode and Polarization-Division Multiplexing Based on Silicon NitrideLoaded LithiumNiobate on Insulator Platform” Laser Photonics Rev.16(1),2100529 (2022)).

[0053] like Figure 6 As shown, the grating tapered waveguide 19 in the multidimensional multiplexing and modulation integrated photonic circuit of the present invention includes a tenth fundamental mode straight waveguide 19-1, a subwavelength waveguide grating tapered waveguide 19-2, and a fourth multimode waveguide 19-3 connected in sequence. The tenth fundamental mode straight waveguide 19-1 is connected to the ninth fundamental mode straight waveguide 17-11, and the fourth multimode waveguide 19-3 is connected to the multiplexer / demultiplexer 20.

[0054] The grating tapered waveguide 19 is mainly used to suppress mode hybridization at 2.1 μm, preventing the input TM0 signal from becoming a TE1 signal and avoiding crosstalk. The grating tapered waveguide 19 and... Figure 7 The transmission performance of the tapered waveguide in the prior art shown is simulated in TM0 mode. Figure 8 This is a simulation diagram of the TM0 mode signal transmission performance of the grating tapered waveguide 19 in this invention. Figure 9 The figure shows a simulation of the TM0 mode signal transmission performance of a tapered waveguide in the prior art. It can be seen that using a subwavelength waveguide grating tapered waveguide for waveguide width transition can effectively reduce mode crosstalk in the device (the mode crosstalk of the tapered waveguide in the prior art is -11.3 dB, while the mode crosstalk of the grating tapered waveguide 19 used in this invention is -18.5 dB), thereby improving the overall performance of the device.

[0055] like Figure 10This invention relates to a multiplexer / demultiplexer 20 in a multidimensional multiplexing and modulation integrated photonic circuit. The multiplexer / demultiplexer 20 is a multiplexed and modulated dual-polarization first-order mode multiplexer / demultiplexer. It includes a seventh curved waveguide 20-1 and a first trapezoidal waveguide 20-2 connected in sequence. The width of the seventh curved waveguide 20-1 is the same as the width of the wider base of the first trapezoidal waveguide 20-2. The seventh curved waveguide 20-1 is connected to the wider base of the first trapezoidal waveguide 20-2. The cross-sectional shape of the first trapezoidal waveguide 20-2 is a right trapezoid.

[0056] The seventh curved waveguide 20-1 is connected to the seventh fundamental mode straight waveguide in the second polarization rotating beam splitter 18. The seventh curved waveguide 20-1 and the first trapezoidal waveguide 20-2 form the output port of the first-order mode multiplexing / demultiplexing.

[0057] The multiplexer / demultiplexer 20 also includes a fifth multimode waveguide 20-3, a second trapezoidal waveguide 20-4, and a sixth multimode waveguide 20-5 connected in sequence; the fifth multimode waveguide 20-3 is connected to the fourth multimode waveguide 19-3. The cross-sectional shape of the second trapezoidal waveguide 20-4 is a right trapezoid. The narrower base of the second trapezoidal waveguide 20-4 is connected to the fifth multimode waveguide 20-3, and the width of the narrower base of the second trapezoidal waveguide 20-4 is the same as the width of the fifth multimode waveguide 20-3; the wider base of the second trapezoidal waveguide 20-4 is connected to the sixth multimode waveguide 20-5, and the width of the wider base of the second trapezoidal waveguide 20-4 is the same as the width of the sixth multimode waveguide 20-5.

[0058] The first trapezoidal waveguide 20-2 is coupled to the second trapezoidal waveguide 20-4, and the right-angled waist of the first trapezoidal waveguide 20-2 is adjacent to the right-angled waist of the second trapezoidal waveguide 20-4.

[0059] When TE0 and TM0 mode optical signals are input from the seventh curved waveguide 20-1, due to the satisfying of the mode refractive index matching condition, they will be coupled into TE1 and TM1 modes in the multimode waveguide and transmitted in the sixth multimode waveguide 20-5. The transmission loss and crosstalk diagrams from the simulation of the dual-polarization first-order mode multiplexer / demultiplexer are shown below. Figure 11 and Figure 12 As shown. Figure 11 The transmission loss diagrams of different modes detected at the end of the sixth multimode waveguide 20-5 when the TE0 mode is input to the port of the seventh curved waveguide 20-1 show that the TE0 mode is basically coupled into the TE1 mode after passing through the mode multiplexer / demultiplexer 20. Its intermode crosstalk is less than -19.1 dB and its loss is less than 0.4 dB. Figure 12The transmission loss diagrams of different modes detected at the end of the sixth multimode waveguide 20-5 when the TM0 mode is input to the port of the seventh bent waveguide 20-1 show that the TM0 mode is basically coupled into the TM1 mode after passing through the mode multiplexer / demultiplexer 20, with intermode crosstalk below -17.0 dB and loss below 0.5 dB. This demonstrates that the multidimensional multiplexing-modulation integrated photonic circuit of this invention exhibits excellent first-order mode multiplexing performance.

[0060] like Figure 13 As shown, the waveguide in the multidimensional multiplexing and modulation integrated photonic circuit of this invention includes, from top to bottom, a waveguide cladding 21, a lithium niobate planar layer 23, a silicon dioxide buried layer 24, and a silicon substrate layer 25. A silicon nitride loading layer 22 is disposed on the lithium niobate planar layer 23, and the silicon nitride loading layer 22 is located within the waveguide cladding 21. This waveguide structure uses a silicon nitride-loaded thin-film lithium niobate waveguide. During etching, only the silicon nitride layer needs to be etched, and the lithium niobate layer is not etched. The etched silicon nitride layer and the lithium niobate layer together constitute a composite waveguide.

[0061] Because lithium niobate and silicon nitride have higher refractive indices than silicon dioxide and air, light can be well confined in silicon nitride-lithium niobate waveguides. The fabrication method of this waveguide is detailed in the literature (“Lowloss CMOS-compatible silicon nitride photonics utilizing reactive sputtered thin films,” Opt. Express 27(26), 37795-37805 (2019)).

[0062] This invention relates to a multidimensional multiplexing and modulation integrated photonic circuit comprising eight microring resonator (MRR) modulators, eight wavelength multiplexers, and a wavelength-mode-polarization hybrid multiplexer / demultiplexer. Each MRR modulator is positioned at one of the eight input waveguides of the multiplexer / demultiplexer to modulate the input optical signal. The eight input waveguides are connected to coarse wavelength division multiplexers (CWDMs) based on reflective Bragg waveguide gratings for wavelength multiplexing. The eight CWDMs are divided into two groups: one group with a reflection center wavelength of λ1 and the other with a reflection center wavelength of λ2. The eight signals passing through the CWDMs are then passed through a polarization rotating beam splitter (PSR), where four signals are converted to transverse magnetic mode (TM0) and the other four remain in transverse electric mode (TE0). The four signals passing through the PSR0 then enter the corresponding channels in the multimode waveguide after passing through a tapered waveguide composed of a subwavelength waveguide grating. The four signals from PSR1 are coupled into a first-order mode by a first-order multiplexer / demultiplexer. The TE0 mode is coupled into the TE1 mode, and the TM0 mode is coupled into the TM1 mode. Then, they enter the corresponding channels in the multimode waveguide, thus realizing the multiplexing and demultiplexing of eight channels with dual wavelengths, dual modes, and dual polarizations in a single multimode waveguide.

[0063] Eight MRR modulators control the operating wavelength by heating the hot electrode.

[0064] The multidimensional multiplexing modulation integrated photonic circuit of the present invention utilizes a first polarization rotating beamsplitter 17 to input the modulated signal after passing through the wavelength multiplexer into the λ0-TE0, λ1-TE0, λ0-TM0, and λ1-TM0 channels in the multimode waveguide. It utilizes a second polarization rotating beamsplitter 18 and a connected dual polarization first-order mode multiplexer / demultiplexer 20 to input the modulated signal after passing through the wavelength multiplexer into the λ0-TE1, λ1-TE1, λ0-TM1, and λ1-TM1 channels in the multimode waveguide, thereby realizing the simultaneous multiplexing of eight signals.

[0065] This invention provides a multidimensional multiplexing and modulation integrated photonic circuit that enables simultaneous multiplexing of modulated optical signals of multiple wavelengths, modes, and polarizations, thereby significantly increasing the number of channels and data capacity in multimode waveguides. Furthermore, this photonic integrated circuit has a certain degree of scalability, allowing for the implementation of even more channels and thus greater data communication capacity.

Claims

1. A multidimensional multiplexing modulation integrated photonic circuit based on thin-film lithium niobate, characterized in that, It includes eight MRR modulators, eight wavelength multiplexers, two polarization rotating beamsplitters, and one dual-polarization first-order mode multiplexer / demultiplexer. Two wavelength multiplexers from the eight wavelength multiplexers and two MRR modulators from the eight MRR modulators form a combination, for a total of four combinations. Two combinations are connected to a polarization rotating beamsplitter via waveguides. The polarization rotating beamsplitter is connected to the dual-polarization first-order mode multiplexer / demultiplexer via a grating tapered waveguide of a subwavelength waveguide. The other two combinations are connected to another polarization rotating beamsplitter via another waveguide. The other polarization rotating beamsplitter is connected to the dual-polarization first-order mode multiplexer / demultiplexer. In the same combination: the output of one MRR modulator is connected to the input of one wavelength multiplexer, the output of another MRR modulator is connected to the input of another wavelength multiplexer, the multimode pass-through of one wavelength multiplexer is a free end, the output of one wavelength multiplexer is connected to the multimode pass-through of another wavelength multiplexer, and the output of the other wavelength multiplexer is connected to a polarization rotating beam splitter through a waveguide; All wavelength multiplexers are based on reflective Bragg grating wavelength multiplexers.

2. The multidimensional multiplexing and modulation integrated photonic circuit based on thin-film lithium niobate as described in claim 1, characterized in that, All MRR modulators whose output terminals are connected to the input terminals of wavelength multiplexers with the multimode pass-through terminals being free terminals have the same operating wavelength. All other MRR modulators have the same operating wavelength, but these two operating wavelengths are different.

3. The multidimensional multiplexing and modulation integrated photonic circuit based on thin-film lithium niobate as described in claim 1, characterized in that, All MRR modulators have the same structure, and all wavelength multiplexers have the same structure except for the grating period; the connection between the MRR modulator and the wavelength multiplexer in each combination is also exactly the same. Of the four combinations: The first combination includes a first modulator (1), a second modulator (2), a first wavelength multiplexer (9), and a second wavelength multiplexer (10). The output of the first modulator (1) is connected to the input of the first wavelength multiplexer (9), the output of the second modulator (2) is connected to the input of the second wavelength multiplexer (10), and the output of the first wavelength multiplexer (9) is connected to the multimode pass-through of the second wavelength multiplexer (10). The second combination includes a third modulator (3), a fourth modulator (4), a third wavelength multiplexer (11), and a fourth wavelength multiplexer (12). The output of the third modulator (3) is connected to the input of the third wavelength multiplexer (11), the output of the fourth modulator (4) is connected to the input of the fourth wavelength multiplexer (12), and the output of the third wavelength multiplexer (11) is connected to the multimode pass-through of the fourth wavelength multiplexer (12). The output terminals of the second wavelength multiplexer (10) and the fourth wavelength multiplexer (12) are both connected to the input terminal of the first polarization rotating beam splitter (17); The third combination includes a fifth modulator (5), a sixth modulator (6), a fifth wavelength multiplexer (13), and a sixth wavelength multiplexer (14). The output of the fifth modulator (5) is connected to the input of the fifth wavelength multiplexer (13), the output of the sixth modulator (6) is connected to the input of the sixth wavelength multiplexer (14), and the output of the fifth wavelength multiplexer (13) is connected to the multimode pass-through of the sixth wavelength multiplexer (14). The fourth combination includes a seventh modulator (7), an eighth modulator (8), a seventh wavelength multiplexer (15), and an eighth wavelength multiplexer (16). The output of the seventh modulator (7) is connected to the input of the seventh wavelength multiplexer (15), the output of the eighth modulator (8) is connected to the input of the eighth wavelength multiplexer (16), and the output of the seventh wavelength multiplexer (15) is connected to the multimode pass-through of the eighth wavelength multiplexer (16). The output of the sixth wavelength multiplexer (14) and the output of the eighth wavelength multiplexer (16) are both connected to the input of the second polarization rotating beam splitter (18).

4. The multidimensional multiplexing and modulation integrated photonic circuit based on thin-film lithium niobate as described in claim 3, characterized in that, The first wavelength multiplexer (9) includes a first multimode waveguide (9-5) and a third curved waveguide (9-1), a fourth curved waveguide (9-2), and a fourth fundamental mode straight waveguide (9-3) connected in sequence. One end of the first multimode waveguide (9-5) is connected to one end of the first Bragg grating (9-4), and the fourth fundamental mode straight waveguide (9-3) is coupled to the first multimode waveguide (9-5). The other end of the third curved waveguide (9-1) is connected to the output end of the first fundamental mode straight waveguide (9-2). The other end of the first Bragg grating (9-4) is connected to one end of the first multimode waveguide in the second wavelength multiplexer (10). The other end of the second Bragg grating in the second wavelength multiplexer (10) and the other end of the fourth Bragg grating in the fourth wavelength multiplexer (12) are both connected to the input end of the first polarization rotating beam splitter (17); the other end of the sixth Bragg grating in the sixth wavelength multiplexer (14) and the other end of the eighth Bragg grating in the eighth wavelength multiplexer (16) are both connected to the input end of the second polarization rotating beam splitter (18).

5. The multidimensional multiplexing and modulation integrated photonic circuit based on thin-film lithium niobate as described in claim 4, characterized in that, The structural parameters of the first polarization rotating beam splitter (17) and the second polarization rotating beam splitter (18) are exactly the same. The first polarization rotating beam splitter (17) includes a fifth fundamental mode straight waveguide (17-1), a fifth curved waveguide (17-2), a sixth curved waveguide (17-3), and a seventh fundamental mode straight waveguide (17-4) connected in sequence. The first polarization rotating beam splitter (17) also includes an eighth fundamental mode straight waveguide (17-5), a first tapered waveguide (17-6), a second multimode waveguide (17-7), a second tapered waveguide (17-8), a third multimode waveguide (17-9), a third tapered waveguide (17-10), and a ninth fundamental mode straight waveguide (17-11) connected in sequence; the seventh fundamental mode straight waveguide (17-4) is coupled to the second multimode waveguide (17-7); the ninth fundamental mode straight waveguide (17-11) is connected to the grating tapered waveguide (19); The other end of the fifth fundamental mode straight waveguide (17-1) in the first polarization rotating beam splitter (17) is connected to the other end of the fourth Bragg grating in the fourth wavelength multiplexer (12), and the other end of the eighth fundamental mode straight waveguide (17-5) in the first polarization rotating beam splitter (17) is connected to the other end of the second Bragg grating in the second wavelength multiplexer (10). The other end of the fifth fundamental mode straight waveguide in the second polarization rotating beam splitter (18) is connected to the other end of the fourth Bragg grating in the eighth wavelength multiplexer (16), and the other end of the eighth fundamental mode straight waveguide in the second polarization rotating beam splitter (18) is connected to the other end of the second Bragg grating in the sixth wavelength multiplexer (14).

6. The multidimensional multiplexing and modulation integrated photonic circuit based on thin-film lithium niobate as described in claim 5, characterized in that, The grating tapered waveguide (19) includes a tenth fundamental mode straight waveguide (19-1), a subwavelength waveguide grating tapered waveguide (19-2), and a fourth multimode waveguide (19-3) connected in sequence; the tenth fundamental mode straight waveguide (19-1) is connected to the ninth fundamental mode straight waveguide (17-11), and the fourth multimode waveguide (19-3) is connected to the multiplexer / demultiplexer (20).

7. The multidimensional multiplexing and modulation integrated photonic circuit based on thin-film lithium niobate as described in claim 6, characterized in that, The multiplexer / demultiplexer (20) includes a seventh curved waveguide (20-1) and a first trapezoidal waveguide (20-2) connected in sequence. The width of the seventh curved waveguide (20-1) is the same as the width of the wider bottom of the first trapezoidal waveguide (20-2). The seventh curved waveguide (20-1) is connected to the wider bottom of the first trapezoidal waveguide (20-2). The cross-sectional shape of the first trapezoidal waveguide (20-2) is a right trapezoid. The seventh curved waveguide (20-1) is connected to the seventh fundamental mode straight waveguide in the second polarization rotating beam splitter (18); The multiplexer / demultiplexer (20) also includes a fifth multimode waveguide (20-3), a second trapezoidal waveguide (20-4), and a sixth multimode waveguide (20-5) connected in sequence; the fifth multimode waveguide (20-3) is connected to the fourth multimode waveguide (19-3); The cross-sectional shape of the second trapezoidal waveguide (20-4) is a right trapezoid. The narrower bottom of the second trapezoidal waveguide (20-4) is connected to the fifth multimode waveguide (20-3). The width of the narrower bottom of the second trapezoidal waveguide (20-4) is the same as the width of the fifth multimode waveguide (20-3). The wider bottom of the second trapezoidal waveguide (20-4) is connected to the sixth multimode waveguide (20-5). The width of the wider bottom of the second trapezoidal waveguide (20-4) is the same as the width of the sixth multimode waveguide (20-5). The first trapezoidal waveguide (20-2) is coupled to the second trapezoidal waveguide (20-4). The right-angled waist of the first trapezoidal waveguide (20-2) is adjacent to the right-angled waist of the second trapezoidal waveguide (20-4).

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