Silicon-based light modulator optical path monitoring structure and design method

Abstract

The application discloses a silicon-based light modulator light path monitoring structure and a design method. The silicon-based light modulator light path monitoring structure comprises a silicon-based substrate and a thin film lithium niobate optical waveguide layer, and the thin film lithium niobate optical waveguide layer is located on one side of the silicon-based substrate. The thin film lithium niobate optical waveguide layer comprises a directional coupler, a monitoring light path waveguide and a grating coupler, the monitoring light path waveguide is connected between the directional coupler and the grating coupler, and the grating coupler comprises a grating structure. The silicon-based light modulator light path monitoring structure realizes optical power monitoring at any position in an optical waveguide transmission route, reduces wavelength-dependent loss of the optical waveguide, and realizes stable monitoring of optical power under a large-bandwidth optical path structure.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to a design method for an optical path monitoring structure of a silicon-based optical modulator. Background Technology

[0002] With the increasing integration of lithium niobate integrated devices, it is difficult to decompose and troubleshoot the problem if an anomaly occurs at a certain node in the optical path transmission, relying solely on the monitoring of the terminal optical port.

[0003] Existing technologies are based on silicon materials. High-speed modulators can be integrated into silicon photonic chips, and optical path monitoring structures are often integrated with optical modulators. 2x2 MMI optical couplers or beam splitters are commonly used to achieve optical path monitoring. Optical path monitoring structures using lithium niobate modulators typically employ an external monitor photodiode (MPD) to monitor optical power.

[0004] Because silicon is temperature sensitive and silicon waveguides have high coupling loss, using only silicon for optical path monitoring has problems such as small bandwidth, high transmission loss and complex manufacturing process, making it unsuitable for optical power monitoring in high bandwidth and high speed devices. Summary of the Invention

[0005] This invention provides a silicon-based optical modulator optical path monitoring structure and design method, which enables optical power monitoring at any position in the optical waveguide transmission path, reduces wavelength correlation loss, and achieves stable optical power monitoring under large bandwidth.

[0006] In a first aspect, embodiments of the present invention provide a silicon-based optical modulator optical path monitoring structure, including a silicon-based substrate and a thin-film lithium niobate optical waveguide layer, wherein the thin-film lithium niobate optical waveguide layer is located on one side of the silicon-based substrate;

[0007] The thin-film lithium niobate optical waveguide layer includes a directional coupler, a monitoring optical path waveguide, and a grating coupler. The monitoring optical path waveguide connects the directional coupler and the grating coupler, and the grating coupler includes a grating structure.

[0008] Optionally, the directional coupler includes a main optical path waveguide and a coupling waveguide spaced apart by a first distance. The main optical path waveguide transmits optical signals in the main optical path, and the monitoring optical path waveguide connects the coupling waveguide and the grating coupler.

[0009] The first distance is greater than or equal to 0.5 μm and less than or equal to 1.5 μm.

[0010] Optionally, the duty cycle of the grating structure is 0.45-0.75.

[0011] Optionally, the period of the grating structure is 1.1μm-1.8μm, and the grating structure includes multiple spaced grating waveguides with a width of 0.5μm-1.3μm.

[0012] Optionally, the main optical path waveguide and the coupling waveguide have the same waveguide width.

[0013] Optionally, the main optical path waveguide and the coupling waveguide may have different waveguide widths.

[0014] Optionally, the width of the coupled waveguide is 1.1μm-1.5μm.

[0015] Secondly, embodiments of the present invention provide a design method for an optical path monitoring structure of a silicon-based optical modulator, comprising:

[0016] A thin-film lithium niobate optical waveguide layer is formed on one side of a silicon substrate. The thin-film lithium niobate optical waveguide layer is used to form a directional coupler, a monitoring optical path waveguide, and a grating coupler. The monitoring optical path waveguide connects the directional coupler and the grating coupler, and the grating coupler includes a grating structure.

[0017] Adjust the structure of the directional coupler and / or grating coupler to modulate the optical power variation curves of the directional coupler and grating coupler within a set wavelength range, thereby achieving complementarity between the optical power variation curves of the directional coupler and grating coupler.

[0018] Optionally, the directional coupler includes a main optical path waveguide and a coupling waveguide spaced apart by a first distance. The main optical path waveguide transmits optical signals in the main optical path, and the monitoring optical path waveguide connects the coupling waveguide and the grating coupler.

[0019] The first distance is greater than or equal to 0.5 μm and less than or equal to 1.5 μm;

[0020] The main optical path waveguide and the coupling waveguide have the same waveguide width;

[0021] Adjusting the structure of the directional coupler and / or grating coupler includes:

[0022] The structure of the fixed directional coupler is determined, and the duty cycle of the grating coupler is adjusted.

[0023] Optionally, the directional coupler includes a main optical path waveguide and a coupling waveguide spaced apart by a first distance. The main optical path waveguide transmits optical signals in the main optical path, and the monitoring optical path waveguide connects the coupling waveguide and the grating coupler.

[0024] The first distance is greater than or equal to 0.5 μm and less than or equal to 1.5 μm;

[0025] Adjusting the structure of the directional coupler and / or grating coupler includes:

[0026] The duty cycle of the fixed grating coupler is adjusted, and the width of the coupling waveguide is adjusted.

[0027] This invention provides a silicon-based optical modulator optical path monitoring structure and design method. It utilizes an integrated structure of a silicon substrate and a thin-film lithium niobate optical waveguide layer connected to an optical fiber. A directional coupler and a grating coupler are placed in the thin-film lithium niobate optical waveguide layer. By adjusting the parameters of the directional coupler and the grating coupler, their complementarity is achieved, enabling a monitorable wavelength range of 100nm. This achieves stable monitoring under a large bandwidth optical path, reduces wavelength-dependent loss, and solves the problems of small bandwidth and high coupling loss in traditional silicon-based optical modulator optical path monitoring structures. Attached Figure Description

[0028] Figure 1 This is a schematic cross-sectional view of an optical path monitoring structure for a silicon-based optical modulator provided in an embodiment of the present invention;

[0029] Figure 2 This is a schematic cross-sectional view of a directional coupler structure for a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the optical waveguide transmission of a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the grating structure of a grating coupler for an optical path monitoring structure of a silicon-based optical modulator provided in an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of a directional coupler design for a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of another directional coupler design for a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention;

[0034] Figure 7 This is a cross-sectional schematic diagram of another silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention;

[0035] Figure 8 This is a flowchart illustrating a design method for an optical path monitoring structure of a silicon-based optical modulator provided in an embodiment of the present invention.

[0036] Figure 9 This is a flowchart illustrating a design method for another silicon-based optical modulator optical path monitoring structure provided in this embodiment of the invention.

[0037] Figure 10 This is a schematic diagram of the transmission efficiency spectrum of the grating coupler as a function of wavelength in a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention;

[0038] Figure 11 This is a schematic diagram of the transmission efficiency spectrum of a directional coupler and a complementary directional coupler with a grating coupler in a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention, showing how these parameters change with wavelength.

[0039] In this embodiment of the invention, the reference numerals and corresponding feature names are as follows:

[0040] 1-Silicon substrate, 2-Planar region layer, 3-Grate coupler, 4-Silicon dioxide layer, 5-Silicon dioxide layer, 6-Air layer, 7-Fiber cladding, 8-Fiber core, 9-Directional coupler, 10-Main optical waveguide, 11-Coupled waveguide, 12-Monitoring optical waveguide, 13-First distance, 14-Grate structure, 15-Grate waveguide, 20-Thin film lithium niobate optical waveguide layer. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0042] The terminology used in the embodiments of this invention is for the purpose of describing specific embodiments only and is not intended to limit the invention. It should be noted that directional terms such as "upper," "lower," "left," and "right" described in the embodiments of this invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of this invention. Furthermore, in the context, it should be understood that when referring to an element being formed "upper" or "lower" of another element, it can be formed not only directly "upper" or "lower" of the other element, but also indirectly "upper" or "lower" of the other element through an intermediate element. Terms such as "first," "second," etc., are used for descriptive purposes only and do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] In the description of this application, unless otherwise expressly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0044] This invention provides a silicon-based optical modulator optical path monitoring structure, including a silicon substrate and a thin-film lithium niobate optical waveguide layer, the thin-film lithium niobate optical waveguide layer being located on one side of the silicon substrate; the thin-film lithium niobate optical waveguide layer includes a directional coupler, a monitoring optical path waveguide and a grating coupler, the monitoring optical path waveguide connecting the directional coupler and the grating coupler, the grating coupler including a grating structure.

[0045] The above technical solution utilizes an integrated structure of a silicon substrate and a thin-film lithium niobate optical waveguide layer connected to an optical fiber. A directional coupler and a grating coupler are placed within the thin-film lithium niobate optical waveguide layer. By adjusting the parameters of the directional coupler and the grating coupler, their complementarity is achieved, enabling a monitorable wavelength range of 100nm. This achieves stable monitoring under a large bandwidth optical path and reduces wavelength-dependent loss. This solves the problems of small bandwidth and high coupling loss in traditional silicon-based optical modulator optical path monitoring structures.

[0046] The above is the core idea of ​​this application. The technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0047] Figure 1 This is a schematic cross-sectional view of an optical path monitoring structure for a silicon-based optical modulator provided in an embodiment of the present invention. Figure 2 This is a schematic cross-sectional view of a directional coupler structure for an optical path monitoring structure of a silicon-based optical modulator provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the optical waveguide transmission of a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention. The silicon-based optical modulator optical path monitoring structure is applicable to situations requiring optical power monitoring of large-bandwidth optical paths. For example... Figures 1-3As shown, the optical path monitoring structure of the silicon-based optical modulator includes a silicon substrate 1 and a thin-film lithium niobate optical waveguide layer 20, which is located on one side of the silicon substrate 1. The thin-film lithium niobate optical waveguide layer 20 includes a directional coupler 9, a monitoring optical path waveguide 12, and a grating coupler 3. The monitoring optical path waveguide 12 connects the directional coupler 9 and the grating coupler 3, and the grating coupler 3 includes a grating structure.

[0048] In this embodiment of the invention, the silicon substrate 1 is a basic substrate material with high-purity single-crystal silicon as its core, used to support and connect various functional devices, and possesses excellent physicochemical properties and compatibility; the thin-film lithium niobate optical waveguide layer 20 can be understood as a material based on lithium niobate (chemical formula: The ultra-thin functional layer of the material is used to constrain, transmit, and control optical signals in optoelectronic devices; the directional coupler (DC) is a core passive optical / electrical device in the fields of optoelectronics and microwave radio frequency, used to achieve directional and controllable power distribution or coupling of transmitted optical or electrical signals; the monitoring optical path waveguide can be understood as an optical waveguide structure in an integrated optical chip specifically used to extract and transmit weak optical signals for monitoring; the grating coupler (GC) is a core passive device in an integrated optical chip that realizes efficient optical signal conversion between external optical fiber and internal optical waveguide, and is a key device for connecting macroscopic optical fiber communication systems and microscopic integrated optical chips; the grating structure can be understood as being able to control the propagation direction, intensity, polarization, or wavelength of light using the diffraction or interference effect, and is a key basic structure in the field of optics for realizing optical coupling and beam splitting.

[0049] In this structure, a silicon substrate 1 is located at the bottom of the optical path monitoring structure of the silicon-based optical modulator, and a silicon dioxide layer 4 is attached thereon. A ridge-shaped thin-film lithium niobate optical waveguide layer 20 is fabricated on the silicon dioxide layer 4. The ridge-shaped thin-film lithium niobate optical waveguide layer 20 includes a planar region layer 2 and an etching layer located on the planar region layer 2. In one embodiment, for clarity, in Figure 1 The diagram illustrates two film layers. In reality, the planar region layer 2 and the etched layer on it can be the same film layer. A patterned etched layer on the planar region layer 2 forms the grating coupler 3. In the fabrication process, it can be assumed that the thin-film lithium niobate waveguide layer 20 is not etched through; only a portion of its thickness is etched. The unetched portion of the thin-film lithium niobate waveguide layer 20 constitutes the planar region layer 2. The grating coupler 3 and the planar region layer 2 are made of the same material. It should be noted that... Figure 1 The different filling patterns used for the grating coupler 3 and the flat plate region layer 2 are designed for easy observation and differentiation only, and are not actual structural differences. This embodiment of the invention does not limit this.

[0050] The thin-film lithium niobate optical waveguide layer 20 includes a directional coupler 9, which comprises two optical waveguides spaced a certain distance apart. The ridge height of the thin-film lithium niobate optical waveguide layer 20 can be understood as the overall thickness H of the planar region layer 2 and the grating coupler 3, where H can be one of 240nm-360nm, for example, 300nm. The thickness h of the planar region layer 2 can be a value less than 300nm, and the width of the thin-film lithium niobate optical waveguide layer 20 can be 1μm-2μm.

[0051] The silicon-based optical modulator optical path monitoring structure provided in this embodiment of the invention utilizes a silicon substrate 1 and a thin-film lithium niobate optical waveguide layer 20 to design the optical path monitoring structure. A directional coupler 9 and a grating coupler 3 are set on the thin-film lithium niobate optical waveguide layer 20, so that the two cooperate with each other during optical power monitoring and perform complementary functions to achieve stable monitoring under a large bandwidth optical path. Moreover, it does not require the introduction of additional related structures to reduce wavelength loss, and the fabrication process is simple, solving the problems of complex process and high coupling loss in traditional silicon-based optical modulator optical path monitoring structures.

[0052] For example, a silicon-based silicon dioxide layer 4 is deposited on top of the silicon substrate 1. The silicon-based silicon dioxide layer 4 isolates the silicon substrate 1 from the thin-film lithium niobate optical waveguide layer 20, preventing the high refractive index of silicon from interfering with the optical field, and at the same time providing a flat adhesion surface for the subsequent thin-film lithium niobate optical waveguide layer 20. A silicon dioxide layer 5 with a thickness of 4μm-6μm is deposited on top of the thin-film lithium niobate optical waveguide layer 20 to protect it from external contamination, while also reducing optical field leakage, accurately acquiring optical signals, and achieving stable monitoring of optical power.

[0053] Optional, Figure 5 This is a schematic diagram of a directional coupler design for a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention. Figure 5 As shown, you can continue to refer to this. Figure 2 , Figure 3 and Figure 5 The directional coupler 9 includes a main optical path waveguide 10 and a coupling waveguide 11 spaced apart by a first distance 13. The main optical path waveguide 10 transmits optical signals in the main optical path, and a monitoring optical path waveguide 12 connects the coupling waveguide 11 and the grating coupler 3. One end of the monitoring optical path waveguide 12 is directly connected to the coupling waveguide 11, and the other end is directly connected to the grating coupler 3. Only a monitoring optical path waveguide 12 for light transmission is provided between the directional coupler 9 and the grating coupler 3; no functional elements with optical efficiency or processing functions are provided. Therefore, it does not affect the coordinated light regulation by the directional coupler 9 and the grating coupler 3. Specifically, the directional coupler 9 and the grating coupler 3 complement each other's functions to reduce wavelength loss. The first distance 13 is greater than or equal to 0.5 μm and less than or equal to 1.5 μm.

[0054] In this embodiment of the invention, the first distance 13 can be understood as the distance between the main optical path waveguide 10 and the coupling waveguide 11 in the directional coupler 9; the main optical path waveguide 10 can be understood as the optical waveguide structure in the integrated optical chip used to carry and transmit core service optical signals; the coupling waveguide 11 can be understood as the waveguide adjacent to the main optical path waveguide 10 in the directional coupler 9, used to receive part of the optical power coupled from the main optical path.

[0055] In this design, the directional coupler 9 couples the optical signal transmitted in the input optical waveguide to another adjacent waveguide in a specific ratio, forming a main optical path waveguide 10 and a coupling waveguide 11 separated by a first distance 13. The first distance 13 is greater than or equal to 0.5 μm and less than or equal to 1.5 μm. The output end of the coupling waveguide 11 is connected to the monitoring optical path waveguide 12. The optical waveguide passing through the directional coupler 9 can be split into two optical paths with a 95:5 optical power ratio. The main optical path waveguide 10 outputs 95% of the light, and the monitoring optical path waveguide 12 outputs 5% of the light. When the optical power of the monitoring optical path waveguide 12 is measured, the output light of the main optical path waveguide 10 can be calculated using the following formula, thereby indirectly reflecting the change in the optical power of the main optical path.

[0056]

[0057] Among them, Power Z This indicates the output light of the main optical path waveguide 10, Power. J This indicates the output light of the monitoring optical path waveguide 12. The monitoring optical path waveguide 12 is connected to the grating coupler 3. The optical signal of the monitoring optical path waveguide 12 enters the grating coupler 3, and is output after passing through the grating coupler 3 for feedback and monitoring.

[0058] This invention, through the inclusion of a directional coupler 9 in the optical path monitoring structure, utilizes the "coupling effect" between adjacent waveguides to distribute optical signals from the main optical path waveguide 10 to the coupling waveguide 11 within the directional coupler 9. A first distance 13 is set to be greater than or equal to 0.5 μm and less than or equal to 1.5 μm to precisely control the coupling effect. This avoids the two waveguides being too close, causing severe loss in the main optical path waveguide, while also preventing the distance from being too large, which would reduce coupling efficiency and prevent the monitoring optical path waveguide 12 from acquiring a sufficiently strong optical signal, thus reducing monitoring accuracy. The main optical path waveguide 10 transmits the optical signal in the main optical path, while the monitoring optical path waveguide 12 connects to a grating coupler 3, outputting the optical signal from the monitoring optical path waveguide 12 through the grating coupler 3. This achieves mutual cooperation between the directional coupler 9 and the grating coupler 3 in the optical path monitoring structure. Through their complementary functions, output loss is reduced, and the structure is compatible with i-line technology, reducing manufacturing difficulty and achieving integrated, highly stable, and low-cost optical path monitoring. The grating coupler adopts a large linewidth structure, is compatible with i-line technology, and does not require the introduction of additional related structures to reduce wavelength loss, thus achieving the effect of simple process.

[0059] Optional, Figure 4 This is a schematic diagram of the grating structure of a silicon-based optical modulator optical path monitoring structure grating coupler provided in an embodiment of the present invention, as shown below. Figure 4 As shown, the duty cycle of the grating structure is 0.45-0.75.

[0060] In this embodiment of the invention, the duty cycle of the grating structure can be understood as the ratio of the width of the "effective light-acting area" to the "entire grating period" within the periodic repeating unit of the grating.

[0061] Specifically, by changing the duty cycle of the grating structure according to the width setting of the coupling waveguide 11, complementary adjustment of the directional coupler 9 and the grating coupler 3 in the optical path monitoring structure can be achieved. That is, with the width of the coupling waveguide 11 set to a certain value, by adjusting the duty cycle of the grating structure in the grating coupler 3, the overall effect of reducing wavelength loss achieved synergistically by the directional coupler 9 and the grating coupler 3 can be changed. For example, when the width of the coupling waveguide 11 is 1 μm, the duty cycle of the grating structure is 0.45-0.75. The width of the coupling waveguide 11 can be the width of the coupling waveguide 11 along its extension direction perpendicular to its extension direction. The width of the main optical path waveguide 10 can be the width of the main optical path waveguide 10 along its extension direction perpendicular to its extension direction.

[0062] For example, during optical path transmission, the light beam can be split into the main optical path waveguide 10 and the coupling waveguide 11 after passing through the directional coupler 9. The output of the coupling waveguide 11 is connected to the monitoring optical path waveguide 12, and the optical signal generated by the monitoring optical path waveguide 12 is transmitted to the grating coupler 3. When the width of the coupling waveguide 11 is 1.1 μm, the duty cycle of the grating structure can be set to 0.45, so as to realize the complementarity of the directional coupler 9 and the grating coupler 3.

[0063] This invention, through a reasonable setting of the duty cycle of the grating structure in the grating coupler 3 according to the width of the coupling waveguide 11, allows the duty cycle of the grating structure to be appropriately adjusted according to the width of the coupling waveguide 11. This achieves complementarity between the directional coupler 9 and the grating coupler 3 in the optical path monitoring structure, improving the stability and compatibility of the monitoring structure and reducing related losses in optical power monitoring.

[0064] Optionally, refer to Figure 4 The grating structure 14 has a period of 1.1 μm-1.8 μm and includes multiple spaced grating waveguides 15 with a width of 0.5 μm-1.3 μm. The distance between adjacent grating waveguides 15 is the grating period of the grating structure, and the grating waveguide 15 is the "effective light-acting region" of the grating structure.

[0065] In this embodiment of the invention, the grating waveguide 15 can be understood as the basic unit constituting the grating structure 14 being a "waveguide morphology," and these units are arranged at periodic intervals to form an overall grating structure. The multiple spaced grating waveguides 15 are arranged at periodic intervals, and the width of the grating waveguide 15 is greater than 0.5 μm. For example, the period of the grating structure 14 can be 1.1 μm-1.8 μm, such as 1.18 μm, and the width of the grating waveguide 15 can be 0.5 μm-1.3 μm, such as 0.535 μm.

[0066] According to the period of the grating structure 14, this invention sets multiple grating waveguides 15 with widths greater than 0.5 μm in the grating structure 14. The bandwidth is broadened through a periodically varying design, adapting to multi-wavelength scenarios and enabling stable optical power monitoring over a larger bandwidth. It is compatible with i-line technology and meets the requirements of high efficiency, wide bandwidth, and high stability for high-speed optical monitoring. The width of the grating waveguide 15 is the width of the grating waveguide 15 along the extension direction of the grating structure 14. The key waveguide dimensions of the monitoring structure are all greater than 0.5 μm, eliminating the need for DUV fabrication; i-line technology can be used, significantly reducing fabrication difficulty. The key waveguides include the main optical path waveguide 10, the coupling waveguide 11, the grating coupler 3 (including the grating waveguide 15), and the monitoring optical path waveguide 12.

[0067] Optionally, refer to Figure 5The main optical path waveguide 10 and the coupling waveguide 11 have the same waveguide width.

[0068] The waveguide width can be understood as Figure 5 When the waveguide width H1 of the main optical path waveguide 10 and the waveguide width H2 of the coupling waveguide 11 are the same, that is, the directional coupler 9 adopts an equal-arm design, this setting solves the problems of accuracy, stability and compatibility in the optical path monitoring scenario through "optical characteristic symmetry", ensures the authenticity of the sampled signal in the optical path monitoring, and reduces the wavelength correlation loss in the optical path monitoring.

[0069] Optional, Figure 6 This is a schematic diagram of another directional coupler design for a silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention. Figure 6 As shown, the main optical path waveguide 10 and the coupling waveguide 11 have different waveguide widths. With the duty cycle of the grating structure in the grating coupler 3 set to a specific value, adjusting the width of the coupling waveguide 11 can alter the overall effect of reducing wavelength loss achieved collaboratively by the directional coupler 9 and the grating coupler 3. In other embodiments, both the duty cycle of the grating structure in the grating coupler 3 and the width of the coupling waveguide 11 can be adjusted simultaneously. It is understood that simultaneously adjusting both the duty cycle of the grating structure in the grating coupler 3 and the width of the coupling waveguide 11 increases the difficulty of adjustment.

[0070] Optionally, the width of the coupling waveguide 11 is 1.1μm-1.5μm.

[0071] Wherein, when the waveguide width H1 of the main optical path waveguide 10 and the waveguide width H2 of the coupling waveguide 11 are different, that is, when the directional coupler 9 adopts an unequal arm design, the waveguide width H1 of the main optical path waveguide 10 can be greater than the waveguide width H2 of the coupling waveguide 11 or less than the waveguide width H2 of the coupling waveguide 11. This embodiment of the invention does not impose any restrictions on this.

[0072] For example, when the waveguide widths of the main optical path waveguide 10 and the coupling waveguide 11 are different, the waveguide width H1 of the main optical path waveguide 10 can be 0.9 μm, and the waveguide width H2 of the coupling waveguide 11 can be 1.1 μm; the waveguide width H1 of the main optical path waveguide 10 can also be 1.4 μm, and the waveguide width H2 of the coupling waveguide 11 can also be 1.2 μm.

[0073] In this embodiment of the invention, by setting the main optical path waveguide 10 and the coupling waveguide 11 in the directional coupler 9 to have different waveguide widths, the stability of the coupling coefficient of the directional coupler 9 is improved through the differential width design, and the light intensity fluctuations in the optical signal transmission are smoothed. Moreover, the differential width design only requires adjustment of the waveguide size and does not require additional process steps, thus achieving the effect of simple process implementation.

[0074] The main optical path loss of the monitoring structure is 0.22dB, which has almost no impact on the overall performance of the integrated chip. The 5% signal optical loss at the monitoring end is about 13dB. This part of the signal optical is output from the integrated chip at an 8-degree angle through the grating coupler 3 and can be directly received by optical fiber or MPD.

[0075] Figure 7 This is a schematic cross-sectional view of another silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention; for example, refer to... Figures 1-7 When using optical fiber devices and silicon-based optical modulator optical path monitoring structure for optical power monitoring, directional coupler 9 splits the beam into 95%:5%, with 95% of the main beam entering the main optical path waveguide 10 and 5% entering the coupling waveguide 11. The coupling waveguide 11 transmits the probe light to the monitoring optical path waveguide 12, which outputs at an 8° angle through grating coupler 3 and is received by the optical fiber for feedback and monitoring.

[0076] For example, the optical fiber (including the fiber core 8 and the fiber cladding 7) is spatially connected to the 4μm-6μm thick silicon dioxide layer 5 above the thin-film lithium niobate optical waveguide layer 20 without direct contact, leaving a small gap (i.e., an air layer 6) between them.

[0077] Figure 8 This is a flowchart illustrating a design method for an optical path monitoring structure of a silicon-based optical modulator provided in an embodiment of the present invention. Figure 8 As shown, the design method of the optical path monitoring structure of the silicon-based optical modulator includes the following steps:

[0078] S601. A thin-film lithium niobate optical waveguide layer is formed on one side of a silicon substrate, and a directional coupler, a monitoring optical path waveguide, and a grating coupler are formed using the thin-film lithium niobate optical waveguide layer; wherein, the monitoring optical path waveguide connects the directional coupler and the grating coupler, and the grating coupler includes a grating structure.

[0079] S602. Adjust the structure of the directional coupler and / or the grating coupler, modulate the optical power variation curves of the directional coupler and the grating coupler within a set wavelength range, and realize that the optical power variation curves of the directional coupler and the grating coupler are complementary.

[0080] The design method in this embodiment of the invention is used to form the silicon-based optical modulator optical path monitoring structure described in the above embodiments. It has the same technical effects as the silicon-based optical modulator optical path monitoring structure described above, namely, it enables optical power monitoring at any position in the optical waveguide transmission path, reduces wavelength correlation loss, and achieves stable optical power monitoring over a large bandwidth.

[0081] Figure 9 This is a flowchart illustrating a design method for another silicon-based optical modulator optical path monitoring structure provided in an embodiment of the present invention. Figure 9 As shown, the design method of the optical path monitoring structure of the silicon-based optical modulator includes the following steps:

[0082] S701. A thin-film lithium niobate optical waveguide layer is formed on one side of a silicon substrate. A directional coupler, a monitoring optical path waveguide, and a grating coupler are formed using the thin-film lithium niobate optical waveguide layer. The monitoring optical path waveguide connects the directional coupler and the grating coupler, and the grating coupler includes a grating structure.

[0083] S702. Adjust the structure of the directional coupler and / or grating coupler.

[0084] S703, the curve of optical power variation between the modulation directional coupler and the grating coupler within a set wavelength range.

[0085] S704, achieves complementary optical power variation curves between the directional coupler and the grating coupler.

[0086] Figure 10 This is a schematic diagram of the transmission efficiency spectrum of the grating coupler as a function of wavelength in a silicon-based optical modulator optical path monitoring structure provided by an embodiment of the present invention, as shown below. Figure 10 As shown, the grating coupler can achieve coupling in the 1525-1625nm band, and can reach a monitoring wavelength range of 100nm. Figure 11 This is a schematic diagram showing the transmission efficiency spectrum of a directional coupler and a complementary directional coupler with a grating coupler in a silicon-based optical modulator optical path monitoring structure provided by an embodiment of the present invention, varying with wavelength. Figure 11 As shown, the transmission efficiency of the monitoring port of the directional coupler changes monotonically within the wavelength range of 1525-1625nm, which can be referenced. Figure 11 The DC curve in the image shows how, by changing the duty cycle of the grating coupler, the optical power variation of the grating coupler within the wavelength range of 1525-1625nm is adjusted to be opposite to the optical power variation at the monitoring port, thus achieving complementarity between the optical power variations of the directional coupler and the grating coupler. Figure 11 The DC+GC curve in the figure represents the transmission efficiency curve of the grating coupler at the monitoring port as a function of wavelength after the directional coupler and the grating coupler are complementary. At this time, the wavelength-dependent loss is only 1.5dB.

[0087] It should be noted that the duty cycle of the grating coupler is greater than or equal to 0.5.

[0088] This invention, through adjusting the structure of the directional coupler and / or grating coupler, modulates the optical power variation curves of the directional coupler and grating coupler within a set wavelength range, achieving complementarity between the optical power variation curves of the directional coupler and grating coupler. The process is simple, requiring no additional structures to reduce wavelength correlation loss, and achieves a wavelength correlation loss of only 1.5dB within the monitored wavelength range of 100nm. This solves the problems of traditional optical power monitoring structures, such as small monitoring wavelength range, complex implementation process, and large wavelength correlation loss.

[0089] Optional, you can continue to refer to Figure 2 and Figure 3 The directional coupler 9 includes a main optical path waveguide 10 and a coupling waveguide 11 spaced apart by a first distance 13. The main optical path waveguide 10 transmits optical signals in the main optical path, and the monitoring optical path waveguide 12 connects the coupling waveguide 11 and the grating coupler 3. The first distance 13 is greater than or equal to 0.5 μm and less than or equal to 1.5 μm. The main optical path waveguide 10 and the coupling waveguide 11 have the same waveguide width. Adjusting the structure of the directional coupler 9 and / or the grating coupler 3 includes fixing the structure of the directional coupler 9 and adjusting the duty cycle of the grating coupler 3.

[0090] Specifically, the duty cycle of the grating coupler 3 is changed according to the waveguide spacing and / or waveguide width in the directional coupler 9 to achieve complementarity between the directional coupler 9 and the grating coupler 3 in the optical path monitoring structure. For example, when the width of the coupling waveguide 11 in the directional coupler 9 is set to 1.1 μm, the duty cycle of the grating coupler 3 can be 0.45.

[0091] According to the waveguide spacing and / or waveguide width in the directional coupler 9, the duty cycle of the grating structure in the grating coupler 3 is reasonably set so that the duty cycle of the grating structure can be appropriately adjusted according to the fixed structure in the directional coupler 9. In the optical path monitoring structure, the directional coupler 9 and the grating coupler 3 complement each other, realize the stable monitoring of optical power in the optical path structure with a large bandwidth, and reduce the correlation loss of optical path wavelength.

[0092] Optional, you can continue to refer to Figure 2 and Figure 3 The directional coupler 9 includes a main optical path waveguide 10 and a coupling waveguide 11 spaced apart by a first distance 13. The main optical path waveguide 10 transmits optical signals in the main optical path, and the monitoring optical path waveguide 12 connects the coupling waveguide 11 to the grating coupler 3. The first distance 13 is greater than or equal to 0.5 μm and less than or equal to 1.5 μm. Adjusting the structure of the directional coupler 9 and / or the grating coupler 3 includes fixing the duty cycle of the grating coupler 3 and adjusting the width of the coupling waveguide 11.

[0093] Specifically, the width of the coupling waveguide 11 is adjusted according to the duty cycle of the grating coupler 3 to achieve complementarity between the directional coupler 9 and the grating coupler 3 in the optical path monitoring structure. For example, when the duty cycle of the grating coupler 3 is 0.45, the width of the coupling waveguide 11 can be 1.1 μm.

[0094] This invention, through dynamically adjusting the width of the coupling waveguide 11 based on the duty cycle of the grating coupler 3, achieves a matching adjustment of their parameters, thereby realizing functional complementarity between the directional coupler 9 and the grating coupler 3 in the optical path monitoring structure. This design can effectively stabilize optical power monitoring and reduce wavelength-dependent losses in high-bandwidth optical path monitoring scenarios.

[0095] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A silicon-based optical modulator optical path monitoring structure, characterized in that, It includes a silicon-based substrate and a thin-film lithium niobate optical waveguide layer, wherein the thin-film lithium niobate optical waveguide layer is located on one side of the silicon-based substrate; The thin-film lithium niobate optical waveguide layer includes a directional coupler, a monitoring optical path waveguide, and a grating coupler. The monitoring optical path waveguide connects the directional coupler and the grating coupler. The grating coupler includes a grating structure. The optical power variation curves of the directional coupler and the grating coupler within a set wavelength range are modulated to make the optical power variation curves of the directional coupler and the grating coupler complementary, so that the directional coupler and the grating coupler have complementary cooperative functions.

2. The optical path monitoring structure according to claim 1, characterized in that, The directional coupler includes a main optical path waveguide and a coupling waveguide spaced apart by a first distance. The main optical path waveguide transmits optical signals in the main optical path, and the monitoring optical path waveguide connects the coupling waveguide to the grating coupler. The first distance is greater than or equal to 0.5 μm and less than or equal to 1.5 μm.

3. The optical path monitoring structure according to claim 2, characterized in that, The duty cycle of the grating structure is 0.45-0.

75.

4. The optical path monitoring structure according to claim 3, characterized in that, The period of the grating structure is 1.1μm-1.8μm, and the grating structure includes multiple spaced grating waveguides with a width of 0.5μm-1.3μm.

5. The optical path monitoring structure according to claim 3, characterized in that, The main optical path waveguide and the coupling waveguide have the same waveguide width.

6. The optical path monitoring structure according to claim 2, characterized in that, The main optical path waveguide and the coupling waveguide have different waveguide widths.

7. The optical path monitoring structure according to claim 6, characterized in that, The width of the coupled waveguide is 1.1μm-1.5μm.

8. A design method for an optical path monitoring structure of a silicon-based optical modulator, characterized in that, include: A thin-film lithium niobate optical waveguide layer is formed on one side of a silicon substrate. A directional coupler, a monitoring optical path waveguide, and a grating coupler are formed using the thin-film lithium niobate optical waveguide layer. The monitoring optical path waveguide connects the directional coupler and the grating coupler, and the grating coupler includes a grating structure. Adjust the structure of the directional coupler and / or the grating coupler to modulate the optical power variation curves of the directional coupler and the grating coupler within a set wavelength range, thereby achieving complementarity between the optical power variation curves of the directional coupler and the grating coupler.

9. The design method according to claim 8, characterized in that, The directional coupler includes a main optical path waveguide and a coupling waveguide spaced apart by a first distance. The main optical path waveguide transmits optical signals in the main optical path, and the monitoring optical path waveguide connects the coupling waveguide to the grating coupler. The first distance is greater than or equal to 0.5 μm and less than or equal to 1.5 μm; The main optical path waveguide and the coupling waveguide have the same waveguide width; Adjusting the structure of the directional coupler and / or the grating coupler includes: The structure of the directional coupler is fixed, and the duty cycle of the grating coupler is adjusted.

10. The design method according to claim 8, characterized in that, The directional coupler includes a main optical path waveguide and a coupling waveguide spaced apart by a first distance. The main optical path waveguide transmits optical signals in the main optical path, and the monitoring optical path waveguide connects the coupling waveguide to the grating coupler. The first distance is greater than or equal to 0.5 μm and less than or equal to 1.5 μm; Adjusting the structure of the directional coupler and / or the grating coupler includes: The duty cycle of the grating coupler is fixed, and the width of the coupling waveguide is adjusted.

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