Mode multiplexing demultiplexer based on sub-wavelength grating and preparation method thereof
By introducing subwavelength grating structures and chirped conical gratings into mode division multiplexing devices, the shortcomings of existing mode division multiplexing devices in terms of integration, loss, and bandwidth are solved, realizing wide bandwidth, low loss, and low crosstalk mode multiplexing and demultiplexing, which is suitable for compact photonic integrated circuits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-30
- Publication Date
- 2026-03-17
AI Technical Summary
Existing mode-division multiplexing devices cannot simultaneously meet the application requirements of optical communication in terms of integration, loss and bandwidth. In particular, the high insertion loss and crosstalk caused by structural mismatch and process error, as well as their large physical size, limit their application in compact photonic integrated circuits.
A mode multiplexer/demultiplexer based on a subwavelength grating is adopted, including a first-stage and a second-stage multimode interference coupler and a dual-arm phase shifter. The wavelength sensitivity of the device is reduced by the subwavelength grating structure, the phase matching bandwidth is extended, and the connection loss is reduced by the chirped conical grating structure, so as to achieve passive fixed phase difference control.
It achieves wide bandwidth, low loss and low crosstalk mode multiplexing and demultiplexing in an ultra-compact size, reduces the wavelength dependence of the device, avoids power consumption and signal distortion, and has good process compatibility and scalability.
Smart Images
Figure CN121679810A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the fields of optical communication and optical interconnection technology, and in particular to a mode multiplexer / demultiplexer based on a subwavelength grating and its fabrication method. Background Technology
[0002] With the rapid development of information technology, the demand for data transmission rates and capacity is increasing day by day. Compared with traditional copper wire electrical interconnects, on-chip optical interconnects based on silicon-on-insulator (SOI) technology have become a key technology for solving the bottleneck of internal chip interconnects due to their significant advantages such as low loss, high bandwidth and resistance to electromagnetic interference.
[0003] To enhance the data capacity of on-chip optical interconnect systems, researchers have proposed various multiplexing techniques, such as wavelength division multiplexing (WDM) and polarization division multiplexing (PDM). Furthermore, mode division multiplexing (MDM), as a complementary multiplexing method to WDM and PDM, opens up new dimensions for data transmission by exciting and manipulating different spatial modes in waveguides.
[0004] The implementation of MDM technology relies on mode multiplexers, which can effectively multiplex optical signals of different modes onto the same transmission channel and demultiplex them at the receiving end. Currently, various mode multiplexer designs have been proposed, including asymmetric directional couplers, thermal couplers, asymmetric Y-branch couplers, and multimode interference couplers, etc. These devices achieve mode multiplexing and demultiplexing through different physical mechanisms.
[0005] However, these existing mode-division multiplexing (MDM) devices generally suffer from some common problems. First, during mode switching and demultiplexing, structural mismatch or manufacturing errors can easily lead to high insertion loss and crosstalk. Second, the physical size of most devices is still in the millimeter range, limiting their application in compact photonic integrated circuits. Furthermore, their operating bandwidth is often narrow and typically optimized for only a single wavelength, making it difficult to cover the widely used communication bands in optical communication, thus limiting their application in flexible optical networks requiring flexible spectrum allocation. In short, existing technologies struggle to simultaneously meet the increasingly demanding application requirements in terms of integration density, loss, and bandwidth—the three key performance aspects. Summary of the Invention
[0006] In view of this, this application provides a mode multiplexer / demultiplexer based on a subwavelength grating and its fabrication method. The main purpose is to solve the technical problem that existing mode multiplexing devices are unable to simultaneously meet application requirements in terms of integration, loss and bandwidth.
[0007] According to one aspect of this application, a mode multiplexing / demultiplexing device based on a subwavelength grating is provided, comprising: The first-stage multimode interference coupler is used to receive signals from multiple single-mode input waveguides and form a second-order image of the input waveguides; The second-stage multimode interference coupler, cascaded at the output of the first-stage multimode interference coupler, is used to achieve mode conversion and form a second-order image of the output waveguide; A dual-arm phase shifter, integrated between the first-stage multimode interference coupler and the second-stage multimode interference coupler, is used to introduce a fixed phase difference during optical transmission. The first-stage multimode interference coupler, the second-stage multimode interference coupler, and the dual-arm phase shifter all integrate subwavelength grating structures.
[0008] According to another aspect of this application, a method for fabricating a mode multiplexing / demultiplexing device based on a subwavelength grating is provided. This method is used to fabricate the aforementioned mode multiplexing / demultiplexing device based on a subwavelength grating, and the method includes: A silicon-based insulating substrate is provided, wherein the silicon-based insulating substrate is formed by sequentially stacking a silicon substrate, a silicon dioxide buried oxide layer, and a top silicon layer; Photoresist is spin-coated onto the top silicon layer, and an integrated pattern comprising an input waveguide, an output waveguide, a multimode interference region, and a subwavelength grating located in the multimode interference region is fabricated using a photolithography process. The integrated pattern is transferred to the top silicon layer using reactive ion etching to form a silicon waveguide structure, and the etching depth completely penetrates the top silicon layer and reaches the buried oxide layer of silicon dioxide. A silicon dioxide layer is deposited as an upper cladding layer on the etched structure surface using plasma-enhanced chemical vapor deposition. The structure after the deposition of the upper cladding layer is subjected to annealing treatment.
[0009] By employing the above technical solutions, this application provides a mode multiplexer / demultiplexer based on a subwavelength grating and its fabrication method. By introducing a subwavelength grating structure into a multimode interference coupler, the mode multiplexer / demultiplexer effectively reduces the device's wavelength sensitivity, improves mode conversion efficiency, and expands the phase-matching bandwidth, thereby achieving low insertion loss and low crosstalk mode multiplexing and demultiplexing over a wide spectral range. Furthermore, its passive dual-arm phase shifter can introduce a fixed phase difference during optical transmission and achieve stable equivalent refractive index control, avoiding power consumption and signal distortion issues without external driving. Based on this, the aforementioned mode multiplexer / demultiplexer can achieve excellent wide bandwidth, low loss, and low crosstalk performance in an ultra-compact size.
[0010] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description
[0011] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic diagram of a mode multiplexer / demultiplexer based on a subwavelength grating provided in an embodiment of this application is shown. Figure 2 This illustration shows a schematic diagram of the transmitted optical field in a fundamental mode according to an embodiment of this application; Figure 3 This illustration shows a schematic diagram of a transmitted optical field in a first-order mode according to an embodiment of this application; Figure 4 This illustration shows a schematic diagram of the transmission efficiency of a fundamental mode as a function of wavelength, according to an embodiment of this application. Figure 5 This illustration shows a schematic diagram of the transmission efficiency of a first-order mode as a function of wavelength, according to an embodiment of this application. Figure 6 This illustration shows a flowchart of a method for fabricating a mode multiplexer / demultiplexer based on a subwavelength grating according to an embodiment of this application. Figure 7 This illustration shows a schematic diagram of structural changes during the fabrication process of a mode multiplexer / demultiplexer based on a subwavelength grating provided in an embodiment of this application. Detailed Implementation
[0012] The present application will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present application can be combined with each other.
[0013] Current mode division multiplexing (MDM) devices, such as asymmetric directional couplers, thermally adiabatic couplers, asymmetric Y-branch couplers, cascaded asymmetric Y-branch couplers, and multimode interference couplers, cannot fully meet the performance requirements of ideal MDM devices. While asymmetric directional couplers offer large bandwidth, their manufacturing tolerance is small, requiring precise control of coupling length and waveguide width, and they are difficult to extend to more modes. Thermally adiabatic couplers, asymmetric Y-branch couplers, and cascaded asymmetric Y-branch couplers generally have large structures, hindering high-density integration. Although MDM devices based solely on multimode interference couplers have large bandwidth and small size, their manufacturing tolerance is significantly limited by cascaded phase shifters.
[0014] To address the aforementioned technical problems, in one embodiment, a mode multiplexing / demultiplexing device based on a subwavelength grating is provided. (Refer to...) Figure 1 The aforementioned mode multiplexing / demultiplexing unit includes: a first-stage multimode interference coupler for receiving signals from multiple single-mode input waveguides and forming a second-order image of the input waveguides; a second-stage multimode interference coupler cascaded at the output of the first-stage multimode interference coupler for achieving mode conversion and forming a second-order image of the output waveguide; and a dual-arm phase shifter integrated between the first-stage and second-stage multimode interference couplers for introducing a fixed phase difference during optical transmission. Subwavelength grating structures are integrated in the first-stage, second-stage, and dual-arm phase shifters.
[0015] Among them, the multi-mode interference (MMI) coupler is an optical power distribution and synthesis device based on the multi-mode interference effect. The second-order image refers to the stable optical field distribution formed after the optical field undergoes two self-imaging processes in the multi-mode interference region. In this embodiment, the dual-arm phase shifter is a passive structure that introduces a specific phase difference at the output end by controlling the phase of light propagating in two parallel arms. The subwavelength grating structure refers to a periodic structure with a grating period smaller than the operating wavelength, which can adjust the equivalent refractive index of the waveguide by changing its duty cycle, thereby achieving flexible control over the phase and propagation characteristics of the optical field.
[0016] In this embodiment, the fabrication of the aforementioned mode multiplexing / demultiplexing device can begin with a standard SOI (Silicon-on-Insulator) wafer, which sequentially comprises a silicon substrate, a silicon dioxide buried oxide layer, and a top silicon layer. Photoresist is then spin-coated onto the top silicon layer, and a pattern including an input waveguide, an output waveguide, two-stage multimode interference couplers, and an integrated subwavelength grating is defined using photolithography. Subsequently, reactive ion etching (RIE) is used to precisely transfer this pattern into the top silicon layer, ensuring the etching depth completely penetrates the top silicon layer to reach the underlying silicon dioxide buried oxide layer, forming the final silicon waveguide structure. After etching and photoresist removal, a layer of silicon dioxide is completely deposited on the etched waveguide structure using plasma-enhanced chemical vapor deposition (PECVD) as the device's top cladding. Throughout the device fabrication process, key structural parameters of the subwavelength grating, such as the duty cycle, are controlled between 0.4 and 0.6, and the grating period manufacturing tolerance is maintained within ±10 nanometers, thus balancing device performance and process feasibility.
[0017] The mode multiplexer / demultiplexer based on a subwavelength grating provided in this embodiment effectively reduces the device's wavelength sensitivity, improves mode conversion efficiency, and expands the phase-matching bandwidth by introducing a subwavelength grating structure into the multimode interference coupler. This allows for low insertion loss and low crosstalk mode multiplexing and demultiplexing across a wide spectral range. Furthermore, its passive dual-arm phase shifter introduces a fixed phase difference during optical transmission and achieves stable equivalent refractive index control, avoiding power consumption and signal distortion issues without external driving. In addition, the entire device structure can be fabricated using standard SOI lithography and etching processes, exhibiting good process compatibility and scalability, and possessing the potential to expand to more modes and splitting ratios. Therefore, the aforementioned mode multiplexer / demultiplexer achieves excellent wide bandwidth, low loss, and low crosstalk performance in an ultra-compact size, with good process compatibility and easy scalability.
[0018] In one embodiment, both arms of the dual-arm phase shifter integrate subwavelength gratings, and the subwavelength gratings of the two arms have different duty cycles. The dual-arm phase shifter is used to apply a fixed phase delay to the second-order image of the input waveguide output from the first-stage multimode interference coupler, and then combines the two beams with different phase delays into a composite optical field before inputting it into the second-stage multimode interference coupler.
[0019] In the above embodiments, the subwavelength gratings integrated in the two arms of the dual-arm phase shifter have different duty cycles. For example, the dual-arm phase shifter can introduce and maintain a fixed phase difference of approximately π / 2 over a wide wavelength range by designing the subwavelength gratings of its upper and lower arms to have different duty cycles. By precisely designing the duty cycle difference between the two arms' subwavelength gratings, a stable phase delay with a fixed phase difference can be achieved without external driving. This phase difference can compensate for phase mismatch in the multimode interference region, ensuring the accuracy of mode switching, thereby achieving passive, broadband, stable phase shifting and avoiding signal distortion problems.
[0020] In one embodiment, the duty cycle difference of the subwavelength gratings of the two arms of the dual-arm phase shifter is adjustable, and / or, the length of different regions of the duty cycle of the subwavelength gratings of the two arms of the dual-arm phase shifter is adjustable.
[0021] Among them, adjustable duty cycle difference refers to adjusting the equivalent refractive index difference by changing the ratio of grating line width to period; adjustable duty cycle length in different regions refers to achieving segmented phase control by using gratings with different duty cycles in different sections of the phase shifter.
[0022] In the above embodiments, during the device design phase, the duty cycle of the subwavelength gratings in both arms of the dual-arm phase shifter can be simulated and optimized, and the range of duty cycle difference and the length allocation of different duty cycle regions can be determined. Then, during the photolithography mask stage, these parameters can be designed and controllably adjusted, enabling the device to flexibly adapt to different phase compensation requirements. The above embodiments, through the adjustable duty cycle parameters of the dual-arm phase shifter, can enhance the flexibility of device design and improve adaptability to different process deviations.
[0023] In one embodiment, both the first-stage multimode interference coupler and the second-stage multimode interference coupler integrate a periodic subwavelength grating, wherein the period and duty cycle of the periodic subwavelength grating are adjustable and used to change the effective refractive index for light propagation.
[0024] In the above embodiments, by optimizing the design of the subwavelength grating's period (e.g., controlling it below the operating wavelength) and duty cycle (e.g., adjusting it within the range of 0.4 to 0.6), the equivalent refractive index distribution of light in the multimode interference region can be precisely controlled, thereby reducing the device's performance sensitivity to the operating wavelength. This embodiment, through the flexible control of the equivalent refractive index using a subwavelength grating, can significantly extend the device's operating bandwidth, thereby achieving a wavelength-insensitive self-imaging effect.
[0025] In one embodiment, the first-stage multimode interference coupler is a 3×3 single-mode input paired interference type multimode interference coupler, and the second-stage multimode interference coupler is a 1×3 multimode input flat plate interference type multimode interference coupler.
[0026] Among them, the 3×3 single-mode input paired interferometric multimode interferometer refers to a multimode interferometric structure with three single-mode input ports and three output ports; the 1×3 multimode input flat plate interferometric multimode interferometer refers to a multimode interferometric structure with one multimode input port and three single-mode output ports.
[0027] In the above embodiment, the first-stage multimode interference coupler can be used to route the signals from the three input waveguides and form a second-order image of the input waveguides. The second-stage multimode interference coupler can be used to perform mode conversion on the optical field after phase shifter processing and form a second-order image of the output waveguide. This embodiment achieves efficient mode conversion and routing functions by designing a cascaded structure of two specifically configured multimode interference couplers.
[0028] In one embodiment, the operating mode of the first-stage multimode interference coupler is as follows: the optical signal received at the input port of the middle path is routed to the output port of the middle path; the optical signals received at the input ports of the two side paths interfere within the region of the first-stage multimode interference coupler and are coupled to the output ports of the two side paths in the same phase.
[0029] In the above embodiment, when light enters the first-stage multimode interference coupler from the three input ports, the light input in the middle can be directly transmitted to the middle output, while the light input on both sides is evenly distributed to the output ports on both sides after multimode interference, thereby forming a specific light field distribution. This specific light field distribution provides the necessary input conditions for subsequent mode conversion.
[0030] In one embodiment, the operating mode of the second-stage multimode interference coupler is as follows: the fundamental mode light in the middle path is routed to the output port to form the fundamental mode of the output waveguide; the two fundamental mode lights with a fixed phase difference on both sides interfere with each other in the region of the second-stage multimode interference coupler and are coupled to the output port to form the first-order mode of the output waveguide.
[0031] In the above embodiment, the fundamental mode light from the middle arm of the phase shifter can be directly output and maintained in the second-stage multimode interference coupler, while the two beams with a fixed phase difference from the two side arms are combined into a first-order mode after interference, thereby realizing the multiplexing output of the fundamental mode and the first-order mode. This embodiment can achieve efficient multiplexing of the fundamental mode and the first-order mode by interferometric synthesis of light fields with different phases through the second-stage multimode interference coupler.
[0032] In one embodiment, refer to Figure 1 The mode multiplexer / demultiplexer based on subwavelength gratings also includes: an input layer, comprising multiple single-mode input waveguides, which can be used to receive signals from multiple single-mode input waveguides; and an output layer, comprising a bus output waveguide supporting two-order modes, which can be used to output multiplexed or demultiplexed optical signals. The two-order modes include the fundamental mode (TE0) and the first-order mode (TE1).
[0033] The input layer couples external optical signals into the device, while the output layer outputs the processed optical signals to the bus waveguide. In the above embodiment, the input layer may include three single-mode input waveguides, each connected to one of the three input ports of the first-stage multimode interference coupler; the output layer is a multimode bus waveguide supporting TE0 and TE1 mode transmission, connected to the output port of the second-stage multimode interference coupler. This embodiment achieves efficient coupling between the device and the on-chip optical system by optimizing the input / output interfaces.
[0034] In one embodiment, chirped conical gratings are provided at the connection points between the multiple single-mode input waveguides of the input layer and the first-stage multimode interference coupler, and at the connection points between the second-stage multimode interference coupler and the bus output waveguide of the output layer. The chirped conical gratings can be used to realize the conversion between ordinary waveguide modes and Bloch modes.
[0035] Here, a chirped conical grating refers to a subwavelength grating structure whose grating width linearly varies along the propagation direction. In the above embodiment, the width of the chirped conical grating can gradually change from a conventional waveguide size (e.g., 0.5 μm) to a deep subwavelength size (e.g., 0.03 μm). This gradual change in structure allows for a smooth transition in the mode field distribution, effectively reducing mode conversion losses. This embodiment, by using a chirped conical grating structure, enables efficient conversion between ordinary waveguide modes and Bloch waveguide modes, thereby significantly reducing insertion loss at the connection points.
[0036] In one specific embodiment, a mode multiplexing / demultiplexing device based on a subwavelength grating is provided, such as... Figure 1 As shown, the aforementioned mode multiplexing / demultiplexing unit includes a 3×3 multimode hybrid interferometer, a two-arm phase shifter with a subwavelength grating, and a 1×3 multimode hybrid interferometer, with the following specific structure: Input layer: Consists of 3 single-mode input waveguides, which can be used to receive signals from the 3 single-mode input waveguides.
[0037] First-stage processing: One 3×3 single-mode input paired interferometric multimode interferometer, which can be used to form a second-order image of the input waveguide.
[0038] Second-stage processing: a two-arm phase shifter of a subwavelength grating is used to apply a fixed phase difference (e.g., π / 2) delay to the second-order image of the input waveguide and synthesize it.
[0039] Third-level processing: One 1×3 multimode input planar interferometer is used to form the second-order image of the output waveguide.
[0040] Output layer: One bus output waveguide supporting two-order modes, including the fundamental mode and the first-order mode.
[0041] Reference Figure 1 The implementation principle of the above mode multiplexing and demultiplexing interferometer is as follows: Due to the self-imaging principle of the multimode hybrid interferometer, the length of the multimode interference region will affect the self-imaging position. According to the beat length formula (Formula 1), the length of the 3×3 multimode hybrid interferometer is set to 3L. π The length of the / 2, 1×3 multimode hybrid interferometer is 3L. π / 4, where, in a 3×3 multimode hybrid interferometer, the fundamental mode light from port 1 is output at port 4, while the light from port 2, after being split, can be output in phase at ports 3 and 5. In a two-arm phase shifter of a subwavelength grating, the light from ports 3 and 4, after phase shifting, can generate a phase difference of π / 2. In a 1×3 multimode hybrid interferometer, the fundamental mode light from port 4 is output at port 6, and the fundamental mode light from ports 3 and 5, with a phase difference of π / 2, forms a first-order mode at port 6. The transmitted optical fields of the two different modes, the fundamental mode and the first-order mode, are respectively as follows: Figure 2 and Figure 3 As shown.
[0042] (Formula 1) Furthermore, the aforementioned pattern multiplexer / demultiplexer also possesses the following core innovations: 1. Introduce a periodic subwavelength grating in the region of the multimode interference coupler. By changing the duty cycle to adjust the effective refractive index, the wavelength dependence of the device can be significantly reduced, thereby achieving a wavelength-insensitive self-imaging effect.
[0043] 2. Use a chirped conical grating structure to reduce connection loss. For example, using a chirped conical grating structure with a linearly tapered width from 0.5 micrometers to 0.03 micrometers can achieve efficient conversion from ordinary waveguide modes to Bloch modes, thereby reducing connection loss.
[0044] 3. A dual-arm phase shifter using subwavelength gratings. By adjusting the duty cycle of the upper and lower subwavelength gratings and introducing a fixed phase difference such as π / 2 into the dual-arm phase shifter, phase mismatch in the multimode region can be compensated.
[0045] 4. Improve device performance by optimizing duty cycle and grating period. For example, the duty cycle can be optimized to the range of 0.4 to 0.6, and the grating period can be controlled within a tolerance of ±10 nanometers, thereby achieving a balance between performance and fabrication feasibility and improving the device's resistance to process errors.
[0046] Reference Figure 4 , Figure 4 The graph shows the transmission efficiency of the fundamental mode (TE0) as a function of wavelength, where the black line represents IL (Insertion Loss) and the red line represents CT (Crosstalk). Figure 4As shown, the curve remains flat and high over a wide wavelength range of 1.45 μm to 1.65 μm, approaching 0 dB, and achieves excellent performance with an average insertion loss of -0.2 dB, a 1 dB bandwidth of 200 nm, and crosstalk of -30 dB. The extremely low insertion loss and extremely wide bandwidth are attributed to the introduction of a subwavelength grating in the multimode interference coupler region, which achieves a wavelength-insensitive self-imaging effect, thus significantly reducing the device's wavelength dependence. Furthermore, by controlling the effective refractive index through the subwavelength grating, a stable operating bandwidth of up to 200 nm can be achieved. In addition, the chirped conical grating structure ensures efficient conversion from ordinary waveguide modes to Bloch modes, thereby achieving ultra-low insertion loss.
[0047] Reference Figure 5 , Figure 5 The graph shows the transmission efficiency of the first-order mode (TE1) as a function of wavelength, where the black line represents IL (Insertion Loss) and the red line represents CT (Crosstalk). Figure 5 As shown, the transmission efficiency remains at an extremely low level throughout the entire band. This low crosstalk is attributed to the precise introduction of a fixed π / 2 phase difference by the dual-arm phase shifter of the subwavelength grating, which effectively compensates for phase mismatch in the multimode interference region, thus strongly suppressing intermode coupling and crosstalk. The subwavelength grating phase shifter based on duty cycle control is key to achieving low crosstalk; it precisely controls the phase passively, avoiding signal distortion and suppressing crosstalk to below -20dB.
[0048] Based on this Figure 4 and Figure 5 Experimental data demonstrates that the mode multiplexer / demultiplexer provided in this embodiment can achieve wide bandwidth, low loss, and low crosstalk performance in an ultra-compact size.
[0049] The technical effects of the above embodiments are as follows: 1. Ultra-compact size and wide bandwidth performance: The aforementioned mode multiplexer / demultiplexer can achieve mode multiplexing and demultiplexing of the fundamental mode and first-order mode within a device size of only 100 micrometers by 6 micrometers by employing a cascaded structure of two-stage subwavelength grating multimode interference couplers. Specifically, the fundamental mode can achieve a 1dB bandwidth of 200nm in the wavelength range of 1450nm to 1650nm, with an average insertion loss of only 0.2dB and crosstalk not exceeding -25dB; the first-order mode can achieve a 1dB bandwidth of 150nm in the wavelength range of 1500nm to 1650nm, with an average insertion loss of 0.8dB and crosstalk not exceeding -20dB.
[0050] 2. Core contribution of subwavelength grating anisotropy: By utilizing subwavelength gratings to modulate the equivalent refractive index of the waveguide, phase errors in the multimode interference region can be effectively reduced, and mode conversion efficiency can be improved. Simultaneously, the phase matching bandwidth can be extended, directly supporting broadband stable beam splitting exceeding 150nm, and high-order mode crosstalk can be effectively suppressed, achieving an average crosstalk level of no more than -20dB.
[0051] 3. Wideband Stable Phase Shifter Design: By using a subwavelength grating phase shifter with adjustable duty cycle, the equivalent refractive index difference can be controlled by adjusting the duty cycle of the cascaded two-arm gratings. This allows for a phase shift deviation of no more than ±0.02 radians within a bandwidth of 1210nm to 1650nm, without the need for external drive, thus effectively avoiding the problems of increased power consumption and signal distortion.
[0052] 4. In terms of process implementation, it exhibits excellent process compatibility and scalability: the overall structure is based on standard SOI lithography and etching processes, eliminating the need for complex epitaxial growth or doping steps. Furthermore, this design method offers excellent scalability, flexibly adapting to the needs of other mode types and spectral ratios.
[0053] Furthermore, in one embodiment, such as Figure 6 and Figure 7 As shown, a method for fabricating a mode multiplexer / demultiplexer based on a subwavelength grating is provided. This method can be used to fabricate the mode multiplexer / demultiplexer based on a subwavelength grating described in any of the above embodiments. The method includes the following steps: Step 101: Provide a silicon-based insulating substrate, wherein the silicon-based insulating substrate is formed by sequentially stacking a silicon substrate, a silicon dioxide buried oxide layer and a top silicon layer.
[0054] In this step, a standard SOI wafer can be used as the starting material. The thickness of the top silicon layer is usually 220 nanometers, the thickness of the buried oxide layer of silicon dioxide is about 2 to 3 micrometers, and the thickness of the silicon substrate is usually several hundred micrometers. This structure can provide an ideal material basis for the fabrication of optical waveguides.
[0055] Step 102: Spin-coat photoresist onto the top silicon layer and use photolithography to fabricate an integrated pattern including an input waveguide, an output waveguide, a multimode interference region, and a subwavelength grating located in the multimode interference region.
[0056] In this step, a uniform photoresist layer can be formed on the top silicon surface using a spin coating process, and then the pre-designed waveguide and grating composite pattern can be exposed and developed using photolithography techniques such as electron beam lithography or deep ultraviolet lithography. During this process, it is necessary to precisely control the period and duty cycle of the subwavelength grating (e.g., between 0.4 and 0.6) to ensure the function of adjusting the equivalent refractive index.
[0057] Step 103: The integrated pattern is transferred to the top silicon layer using reactive ion etching process to form a silicon waveguide structure, and the etching depth completely penetrates the top silicon layer and reaches the buried oxide layer of silicon dioxide.
[0058] In this step, etching methods based on fluorine-based or chlorine-based gases can be used. By controlling parameters such as radio frequency power, gas flow rate and chamber pressure, anisotropic etching can be achieved to ensure that the waveguide sidewalls are steep and the surface is smooth. The etching must also be strictly terminated at the buried oxide layer interface to form a high-quality silicon waveguide structure.
[0059] Step 104: A silicon dioxide layer is deposited as an upper cladding layer on the etched structure surface using plasma-enhanced chemical vapor deposition.
[0060] In this step, the sample can be placed in the reaction chamber of a PECVD (Plasma Enhanced Chemical Vapor Deposition) device, and a silicon dioxide thin film can be deposited at a relatively low temperature (e.g., about 300-350°C) using silane and nitrous oxide as reaction gas sources. This film completely covers the waveguide structure, thereby serving to confine the optical field and protect the device.
[0061] Step 105: Anneal the structure after the cladding is deposited.
[0062] In this step, the device can be rapidly thermally annealed at high temperature in a nitrogen or oxygen atmosphere. This process can effectively repair silicon lattice damage introduced during etching and deposition, reduce waveguide sidewall scattering loss, and optimize the density of the silicon dioxide cladding, thereby improving the overall optical performance of the device.
[0063] The fabrication method provided in this embodiment, based on standard SOI lithography and etching processes, can realize the fabrication of mode multiplexers and demultiplexers based on subwavelength gratings without the need for complex epitaxial growth or doping steps, and has good process compatibility and reproducibility. Furthermore, the above-described fabrication method has good scalability and can be flexibly adapted to the needs of other mode types and dispersive ratios.
[0064] It should be noted that the labels corresponding to each step in the above embodiments are only for identification purposes and are not intended to limit the execution order of the steps. The execution order of the steps in each embodiment can be set according to the actual situation.
[0065] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0066] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.
Claims
1. A mode multiplexing / demultiplexing device based on subwavelength gratings, characterized by, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating.
2. The subwavelength grating based mode multiplexing / demultiplexing device of claim 1, wherein, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating.
4. The subwavelength grating based mode multiplexing / demultiplexing device of claim 1, wherein, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating.
5. The subwavelength grating based mode multiplexing / demultiplexing device of claim 1, wherein, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating.
6. The sub-wavelength grating based mode multiplexer-demultiplexer according to any of claims 1 to 5, characterized in that, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating.
7. The sub-wavelength grating based mode multiplexer-demultiplexer according to any of claims 1 to 5, characterized in that, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating.
8. The sub-wavelength grating based mode multiplexer-demultiplexer of claim 1, wherein, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating.
9. The sub-wavelength grating based mode multiplexer-demultiplexer according to claim 8, characterized in that, The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplexing / demultiplexing device based on a subwavelength grating. The application relates to a mode multiplex 10. A method of fabricating a mode multiplexing / demultiplexing device based on subwavelength gratings, characterized in that, The method is used for preparing the sub-wavelength grating-based mode multiplexer / demultiplexer as claimed in any one of claims 1 to 9, and the method comprises the following steps: providing a silicon-based insulator substrate, wherein the silicon-based insulator substrate is stacked by a silicon substrate, a buried oxygen layer of silicon dioxide and a top layer of silicon in sequence; spinning photoresist on the top layer of silicon, and preparing an integrated pattern comprising an input waveguide, an output waveguide, a multimode interference region and a sub-wavelength grating located at the multimode interference region by using a photoetching process; transferring the integrated pattern to the top layer of silicon by using a reactive ion etching process to form a silicon waveguide structure, and the etching depth completely penetrates the top layer of silicon and reaches the buried oxygen layer of silicon dioxide; depositing a silicon dioxide layer as an upper cladding layer on the surface of the etched structure by using a plasma-enhanced chemical vapor deposition process; performing annealing treatment on the structure after the upper cladding layer is deposited.