End face coupler

Abstract

The invention relates to the technical field of semiconductors, and discloses an end face coupler which comprises a substrate layer, a lower cladding, a waveguide core layer and an upper cladding which are sequentially stacked from bottom to top. Wherein the upper cladding layer is located on the upper surface of the lower cladding layer and wraps the upper surface and the side surface of the waveguide core layer; the two grooves are respectively positioned on two sides of the waveguide core layer and extend along a first direction; the groove penetrates through the upper cladding, the waveguide core layer, the lower cladding and the substrate layer; wherein the waveguide core layer comprises at least one conical waveguide; the tapered waveguide comprises a plurality of tapered waveguide sections which are connected end to end; the tapered waveguide extends in a first direction. The device size can be reduced, the device integration degree is improved, and meanwhile the alignment tolerance of the device is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to an end-face coupler. Background Technology

[0002] End-face couplers generally include types such as long adiabatic inverted conical end-face couplers, multilayer material-assisted end-face couplers, and metamaterial end-face couplers based on subwavelength structures. Although long adiabatic conical end-face couplers are simple to design, their device size is too large, severely sacrificing chip area and contradicting the concept of high integration. Fiber alignment during packaging has a significant impact on coupling efficiency. Multilayer material-assisted end-face couplers have significantly increased process complexity, requiring additional material deposition, photolithography, and etching steps, increasing manufacturing costs and uncontrollability. Although metamaterial end-face couplers based on subwavelength structures can reduce size, their performance (especially bandwidth and alignment tolerance) is extremely sensitive to the nanoscale size of the subwavelength structure, requiring extremely stringent processing precision and posing significant yield challenges.

[0003] Therefore, a solution is needed to improve device coupling efficiency, increase fiber alignment tolerance, reduce device size, and decrease structural complexity and fabrication difficulty. Summary of the Invention

[0004] This invention provides an end-face coupler to solve the problems of excessively large device size, low integration, complex fabrication process, and low alignment tolerance with optical fiber in existing end-face couplers.

[0005] In a first aspect, the present invention provides an end-face coupler, comprising: The substrate, lower cladding, waveguide core, and upper cladding are stacked sequentially from bottom to top; the upper cladding is located on the upper surface of the lower cladding and covers the upper surface and sides of the waveguide core. It also includes: two grooves, located on both sides of the waveguide core layer, and both extending along the first direction; the grooves penetrate the upper cladding layer and the lower cladding layer and extend into part of the substrate layer; The waveguide core layer includes at least one tapered waveguide; the tapered waveguide includes multiple tapered waveguide segments connected end to end; the tapered waveguide extends along a first direction; the width of the tapered waveguide gradually increases along the first direction in a nonlinear manner.

[0006] The end-face coupler provided by this invention, on the one hand, provides grooves on both sides of the waveguide core layer, which can shape the mode field of the integrated chip end face while allowing light to be coupled and confined in the upper cladding layer first, and then slowly coupled into the waveguide core layer, thereby improving the overall coupling efficiency and increasing the mode matching efficiency and mode conversion efficiency between the device end face and the optical fiber; on the other hand, by setting the width of the tapered waveguide to gradually increase along the first direction in a nonlinear manner, and dividing the tapered waveguide into multiple tapered waveguide segments connected end to end, the light collection speed of the tapered waveguide can be accelerated, the device length required for the optical power to be fully coupled into the end-face coupler can be shortened, the device size can be reduced, the device integration can be improved, and the alignment tolerance of the device can be improved.

[0007] In one alternative implementation, the tapered waveguide is a nonlinear tapered waveguide; the width of the tapered waveguide gradually increases from the starting end to the ending end. The tapered waveguide contains 3 to 7 tapered waveguide segments; each tapered waveguide segment includes a start end and an end end; the width of each tapered waveguide segment gradually increases from the start end to the end end in a nonlinear manner; The width of the tapered waveguide segment varies with its length as a function of:

[0008] Where wt is the starting width of the tapered waveguide segment, lt is the length of the tapered waveguide segment, m represents the nonlinearity, and w is the ending width of the tapered waveguide segment.

[0009] The end-face coupler provided by this invention has 3 to 7 tapered waveguide segments in the tapered waveguide. The width of each tapered waveguide segment gradually increases from the start end to the end in a non-linear manner. This effectively reduces the device size and increases the device integration density while ensuring optimal mode conversion efficiency, and also improves the device alignment tolerance. If the number of tapered waveguide segments in the tapered waveguide is less than 3, the device size is still relatively large; if the number of tapered waveguide segments in the tapered waveguide is greater than 7, the device size corresponding to the optimal mode conversion efficiency cannot be further reduced.

[0010] In one alternative implementation, the end-face coupler is a single-tip type end-face coupler; The waveguide core layer includes a tapered waveguide and a transmission waveguide; the tapered waveguide includes 7 tapered waveguide segments connected end to end.

[0011] The end-face coupler provided by this invention is a single-tip type end-face coupler. The tapered waveguide includes 7 tapered waveguide segments connected end to end, which can shorten the length of the tapered waveguide, reduce coupling loss, and thus achieve high coupling efficiency in a more compact manner. At the same time, the end-face coupler is not wavelength sensitive in the C+L band.

[0012] In one alternative implementation, the end-face coupler is a multi-tip type end-face coupler; The waveguide core layer includes a first tapered waveguide, a second tapered waveguide, and a third tapered waveguide that are spaced apart along a second direction and extend along a first direction; the third tapered waveguide is located between the first tapered waveguide and the second tapered waveguide. The first, second, and third tapered waveguides have the same length, and their widths gradually increase along the first direction; each of the first, second, and third tapered waveguides includes three tapered waveguide segments connected end to end. The projection of the first tapered waveguide onto the third tapered waveguide completely covers the third tapered waveguide; the projection of the second tapered waveguide onto the third tapered waveguide completely covers the third tapered waveguide.

[0013] In one alternative implementation, the edge of the first tapered waveguide away from the third tapered waveguide has a linear change with a fixed slope, while the edge closer to the third tapered waveguide has a nonlinear change. The edge of the second tapered waveguide away from the third tapered waveguide has a linear change with a fixed slope, while the edge closer to the third tapered waveguide has a nonlinear change. The fixed slope is defined as k = h / (lt1 + lt2 + lt3), where h is the total length of the three tapered waveguide segments along the second direction, and lt is the length of each tapered waveguide segment along the first direction.

[0014] In one alternative implementation, both sides of the third tapered waveguide exhibit nonlinear variations. The function relating the width of each tapered waveguide segment in the third tapered waveguide to its length is as follows:

[0015] Where wt is the width at the beginning of the tapered waveguide segment, lt is the length of the tapered waveguide segment, m represents the nonlinearity, and w is the width at the end of the tapered waveguide segment.

[0016] The end-face coupler provided by this invention is a multi-tip type end-face coupler, which can improve mode matching efficiency while completing optical power transmission using a three-pronged structure, further improving coupling efficiency and shortening device size; at the same time, the multi-tip type end-face coupler has greater design freedom and better performance.

[0017] In one alternative implementation, it further includes: a first straight waveguide connected to the end of the first tapered waveguide and extending along a first direction; The second straight waveguide is connected to the end of the second tapered waveguide and extends along the first direction; The third straight waveguide is connected to the end of the first tapered waveguide and extends along the first direction; The first, second, and third straight waveguides are of the same length; they are arranged along the second direction; the projection of the first straight waveguide onto the third straight waveguide completely covers the third straight waveguide; the projection of the second straight waveguide onto the third straight waveguide completely covers the third straight waveguide.

[0018] In one alternative implementation, it further includes: a first linear waveguide located between the first straight waveguide and the third straight waveguide, and extending along a first direction; The second linear waveguide is located between the second straight waveguide and the third straight waveguide, and extends along the second direction; The third linear waveguide is located on the side of the third straight waveguide away from the third tapered waveguide and extends along the first direction; The transmission waveguide is located on the side of the third linear waveguide that faces away from the third straight waveguide; One end of the third linear waveguide is connected to the third straight waveguide, and the other end is connected to the transmission waveguide.

[0019] In one alternative implementation, the first linear waveguide includes a first front waveguide and a first rear waveguide connected together; the width of the first front waveguide gradually increases along a first direction; the width of the first rear waveguide gradually decreases along the first direction. The second linear waveguide includes a second front waveguide and a second rear waveguide connected together; the width of the second front waveguide gradually increases along the first direction; the width of the second rear waveguide gradually decreases along the first direction. The positions of the first front waveguide, the second front waveguide, and the third straight waveguide correspond, and the lengths of the first front waveguide and the second front waveguide are the same as the length of the third straight waveguide; The positions of the first rear waveguide, the second rear waveguide, and the third linear waveguide correspond, and the lengths of the first rear waveguide, the second rear waveguide, and the third linear waveguide are the same.

[0020] In one alternative implementation, two grooves divide the end-face coupler into a functional region and edge regions on both sides; the waveguide core layer is located in the functional region; the grooves are adapted to be formed by a dry etching process; The groove extends into the substrate to a depth greater than 20 μm, and the width of the groove is 5 μm to 15 μm; the minimum distance between the groove and the edge of the waveguide core layer is 8 μm to 20 μm. The waveguide core layers are symmetrically distributed along the first direction; The waveguide core is a single-layer waveguide; the material of the waveguide core is silicon nitride. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of an end-face coupler according to an embodiment of the present invention; Figure 2 This is a top view schematic diagram of the waveguide core layer structure of an end-face coupler according to an embodiment of the present invention; Figure 3A This is an electric field transmission diagram in the xy plane of a three-section single-tip type end-face coupler according to an embodiment of the present invention; Figure 3B This refers to the wavelength-dependent coupling loss of a three-section structure single-tip type end-face coupler according to an embodiment of the present invention. Figure 4A This is an electric field transmission diagram in the xy plane of a seven-segment structure single-tip type end-face coupler according to an embodiment of the present invention. Figure 4B This refers to the wavelength-dependent coupling loss of a seven-segment structure single-tip type end-face coupler according to an embodiment of the present invention. Figure 5A This is the correlation between fiber vertical offset and coupling loss in a seven-segment single-tip end-face coupler according to an embodiment of the present invention. Figure 5B This is the correlation between fiber horizontal offset and coupling loss in a seven-segment single-tip end-face coupler according to an embodiment of the present invention. Figure 6 This is a schematic diagram of a multi-tip type end-face coupler according to an embodiment of the present invention; Figure 7 This is a mode field distribution diagram corresponding to each node end face of a multi-tip type end face coupler according to an embodiment of the present invention; Figure 8A This is an electric field transmission diagram in the xy plane of a multi-tip type end-face coupler according to an embodiment of the present invention; Figure 8B This refers to the wavelength-dependent coupling loss of the multi-tip type end-face coupler according to an embodiment of the present invention; Figure 9A The correlation between fiber vertical offset and coupling loss in a multi-tip end-face coupler according to an embodiment of the present invention; Figure 9B The correlation between fiber horizontal offset and coupling loss in a multi-tip type end-face coupler according to an embodiment of the present invention; Figure label: 10. Substrate layer; 20. Lower cladding layer; 30. Waveguide core layer; 40. Upper cladding layer; 50. Groove; 31. Tapered waveguide; 32. Transmission waveguide; 311. First tapered waveguide; 312. Second tapered waveguide; 313. Third tapered waveguide; 331. First straight waveguide; 332. Second straight waveguide; 333. Third straight waveguide; 341. First linear waveguide; 342. Second linear waveguide; 343. Third linear waveguide. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It is 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 invention and not all structures. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] In the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These drawings are not to scale, and some details are enlarged for clarity, and some details may be omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0025] With the rapid development of technologies such as data centers, high-performance computing, 5 / 6G communication, and optical sensing, higher demands are being placed on the transmission capacity, integration density, and cost-effectiveness of integrated optoelectronic chips. Silicon Photonics, as the core platform in this field, has become a hot topic in research and industrialization due to its advantages such as compatibility with CMOS processes, high integration density, and low cost.

[0026] However, a significant mode field mismatch exists between silicon photonic waveguides and standard single-mode fibers. The mode field diameter of standard single-mode fiber is approximately 9-10 µm, while the mode field size of waveguides is typically submicron. This huge size difference results in extremely low coupling efficiency when directly mated, severely limiting the performance and practicality of the chip. Therefore, a high-performance fiber-to-chip coupling interface has become one of the key technological bottlenecks for realizing the commercial application of silicon photonic technology.

[0027] End-face couplers and grating couplers are two mainstream solutions to the above problems. Compared with grating couplers, which have low integration and low coupling efficiency, end-face couplers have inherent advantages such as large operating bandwidth, easy packaging, and simple manufacturing process, and are especially suitable for applications that require broadband or wavelength division multiplexing (WDM) operation.

[0028] End face couplers generally include types such as long adiabatic inverted conical end face couplers, multilayer material-assisted end face couplers, and metamaterial end face couplers based on subwavelength structures.

[0029] Long, adiabatic, inverted conical end-face couplers, by designing linear or nonlinear conical waveguides of hundreds of micrometers, slowly expand the mode field of the waveguide, and are relatively simple to design; multilayer material-assisted end-face couplers broaden the mode field by covering the core waveguide with low refractive index material in the z-direction; metamaterial end-face couplers based on subwavelength structures, the high refractive index contrast of metamaterials allows for relatively high fabrication tolerances compared to traditional silicon waveguide devices, and the introduction of subwavelength structures effectively modulates the equivalent refractive index of the modes, thereby achieving mode field conversion over shorter distances.

[0030] While conventional long, adiabatic tapered end-face couplers are simple to design, their large device size significantly sacrifices chip area, contradicting the concept of high integration. Fiber alignment during packaging also has a significant impact on coupling efficiency. Multilayer material-assisted end-face couplers significantly increase process complexity, requiring additional material deposition, photolithography, and etching steps, increasing manufacturing costs and uncontrollability. Although metamaterial end-face couplers based on subwavelength structures can reduce size, their performance (especially bandwidth and alignment tolerance) is extremely sensitive to the nanoscale dimensions of the subwavelength structure, demanding extremely high processing precision and posing significant yield challenges.

[0031] Therefore, a solution is needed to improve device coupling efficiency, increase fiber alignment tolerance, reduce device size, and decrease structural complexity and fabrication difficulty.

[0032] like Figure 1 and Figure 2 As shown, this embodiment provides an end-face coupler, including: The substrate layer 10, the lower cladding layer 20, the waveguide core layer 30 and the upper cladding layer 40 are stacked sequentially from bottom to top; wherein, the upper cladding layer 40 is located on the upper surface of the lower cladding layer 20 and covers the upper surface and side surface of the waveguide core layer 30. It also includes: two grooves 50, located on both sides of the waveguide core layer 30, and both extending along the first direction; the grooves 50 penetrate the upper cladding layer 40, the waveguide core layer 30, the lower cladding layer 20 and the substrate layer 10; The waveguide core layer 30 includes at least one tapered waveguide 31; the tapered waveguide 31 includes multiple tapered waveguide segments connected end to end; the tapered waveguide 31 extends along a first direction; the width of the tapered waveguide 31 gradually increases along the first direction in a nonlinear manner.

[0033] In practical implementation, with the starting and ending ends of each tapered waveguide segment fixed, the mode size decreases as the tapered length increases. Therefore, when the width of the tapered waveguide segment increases to the target width, the mode is completely confined within the waveguide. Setting multiple non-linearly varying tapered waveguide segments before reaching the target width can increase the light collection speed, shorten the device length required for sufficient optical power coupling into the end-face coupler, and improve the device alignment tolerance.

[0034] The end-face coupler provided in this embodiment has two advantages. First, by setting grooves on both sides of the waveguide core layer, it can shape the mode field of the integrated chip end face while allowing light to be coupled and confined in the upper cladding layer first, and then slowly coupled into the waveguide core layer, thereby improving the overall coupling efficiency and increasing the mode matching efficiency and mode conversion efficiency between the device end face and the optical fiber. Second, by setting the width of the tapered waveguide to gradually increase along the first direction in a nonlinear manner, and dividing the tapered waveguide into multiple tapered waveguide segments connected end to end, it can accelerate the light collection speed of the tapered waveguide, shorten the device length required for the optical power to be fully coupled into the end-face coupler, and improve the alignment tolerance of the device.

[0035] Theoretically, neglecting alignment error loss, waveguide transmission loss, and Fresnel reflection, the coupling efficiency between the fiber and the integrated chip end-face coupler can be simplified to the product of two factors: the mode matching efficiency (η1) between the fiber mode and the integrated chip end-face mode, and the mode conversion efficiency (η2) of the end-face coupler. The mode matching efficiency (η1) is defined by the following formula:

[0036] Here, A represents the mode field distribution region, and E1 and E2 represent the electric fields in the fiber mode and the chip end-face mode, respectively. Therefore, the overall device performance can be improved by increasing η1 and η2.

[0037] Calculated using the above formula, the mode matching efficiency with grooves 50 on both sides of the waveguide core layer 30 is 89%. Under the same conditions, the mode matching efficiency without grooves 50 is 83%. Therefore, providing grooves 50 on both sides of the waveguide core layer 30 can effectively increase the mode matching efficiency between the device end face and the optical fiber, as well as the mode conversion efficiency.

[0038] In some alternative implementations, the end-face coupler is matched with a single-mode fiber SMF-28e, which has a mode field diameter of 10 μm (1550 nm).

[0039] In some alternative implementations, the end face width of the end face coupler is 0.1~0.25μm, for example 0.23μm.

[0040] In some alternative embodiments, the waveguide core layer 30 further includes a transmission waveguide connected to the end of the tapered waveguide 31; the width of the end of the tapered waveguide 31 is equal to the width of the transmission waveguide.

[0041] In some optional embodiments, the width of the starting end of the tapered waveguide 31 is the same as the end face width, and the width of the starting end of the tapered waveguide 31 is 0.1~0.25μm; the width of the ending end of the tapered waveguide 31 is 0.6~1μm.

[0042] In some optional implementations, the number of tapered waveguide segments in the tapered waveguide is 3 to 7. Along the first direction, the width of each tapered waveguide segment gradually increases from the start to the end, and the width of the entire tapered waveguide gradually increases. The width of the start end of the first tapered waveguide segment is the end face width, which depends on the fiber mode matching efficiency and is generally close to the feature size of the fabrication process. The width of the middle tapered waveguide segments is determined with reference to the overall performance variation of the device. The end width of the final tapered waveguide segment is consistent with the transmission waveguide width, satisfying the single-mode waveguide condition. In some examples, the start width of the first tapered waveguide segment is between 0.1 μm and 0.25 μm; the end width of the final tapered waveguide segment is between 0.6 μm and 1 μm; the start and end widths of the middle tapered waveguide segments are determined according to requirements, satisfying the rule that the width of each tapered waveguide segment gradually increases from the start to the end, and the width of the entire tapered waveguide gradually increases.

[0043] In some alternative embodiments, the tapered waveguide 31 is a nonlinear tapered waveguide; the width of the tapered waveguide 31 gradually increases from the starting end to the ending end; The tapered waveguide 31 has 3 to 7 tapered waveguide segments; each tapered waveguide segment includes a start end and an end end; the width of each tapered waveguide segment gradually increases from the start end to the end end in a nonlinear manner; The width of the tapered waveguide segment varies with its length as a function of:

[0044] Where wt is the starting width of the tapered waveguide segment, It is the length of the tapered waveguide segment, m represents the nonlinearity, and w is the ending width of the tapered waveguide segment.

[0045] In practical implementation, when designing the width of the tapered waveguide 31, the number of tapered waveguide segments and the starting and ending widths of each segment are first determined. Then, the width variation curve is obtained using a formula, and the nonlinearity is optimized to obtain the length lt of the tapered waveguide segment corresponding to the optimal mode conversion efficiency. The number of tapered waveguide segments in the tapered waveguide 31 can be 3, 4, 5, 6, or 7.

[0046] The end-face coupler provided in this embodiment has 3 to 7 tapered waveguide segments in the tapered waveguide. The width of each tapered waveguide segment gradually increases from the start end to the end in a non-linear manner. This can effectively reduce the device size and improve the device integration density while ensuring optimal mode conversion efficiency, and at the same time improve the device alignment tolerance. If the number of tapered waveguide segments in the tapered waveguide is less than 3, the device size is still relatively large; if the number of tapered waveguide segments in the tapered waveguide is greater than 7, the device size corresponding to the optimal mode conversion efficiency cannot be further reduced.

[0047] In some optional embodiments, as the width of the tapered waveguide 31 gradually increases from the starting end to the ending end, there exists a target width corresponding to the target position. When the width of the tapered waveguide 31 reaches the target width, the optical power is fully coupled into the end-face coupler. Therefore, by setting multiple non-linearly varying tapered waveguide segments before the width of the tapered waveguide 31 increases to the target width, the light collection speed can be increased, the device length required for the optical power to be fully coupled into the end-face coupler can be shortened, and the alignment tolerance of the device can be improved.

[0048] In some alternative implementations, the target width is 0.35 μm.

[0049] In some optional embodiments, the tapered waveguide 31 has n tapered waveguide segments. Along the first direction, the starting width of the first tapered waveguide is the end face width; the ending width of the (n-1)th tapered waveguide is the target width. The ending width of the nth tapered waveguide is the width of the output waveguide. By setting n-1 non-linearly varying tapered waveguide segments before the width of the tapered waveguide 31 increases to the target width, the light collection speed can be increased, the device length required for sufficient optical power coupling into the end face coupler can be shortened, and the alignment tolerance of the device can be improved.

[0050] In one example, the end face width is 0.23 μm; the transmission waveguide width is 0.6 μm; n is 7, and the number of tapered waveguide segments in tapered waveguide 31 is n. Along the first direction, the starting end width of the first tapered waveguide is 0.23 μm; the ending end width of the sixth tapered waveguide is 0.35 μm; and the ending end width of the seventh tapered waveguide is 0.6 μm.

[0051] In related technologies, using a single-segment tapered waveguide requires a device length greater than 2000μm to ensure an overall device coupling efficiency of over 90% (coupling loss of 0.46dB), resulting in low device integration.

[0052] In some alternative implementations, the end-face coupler is a single-tip type end-face coupler; The waveguide core layer 30 includes a tapered waveguide 31 and a transmission waveguide 32; the tapered waveguide 31 includes 7 tapered waveguide segments connected end to end.

[0053] In Example 1, the tapered waveguide 31 is a three-segment structure; the three-segment structure has the lowest coupling loss of 0.47dB and the degradation of 0.2dB in the C+L band, as measured by the finite-difference time-domain (FDTD) method, and the total length of the device is 520μm. Figure 3A The diagram shows the electric field transport of the three-segment structure in the xy plane. Figure 3B This represents the wavelength-dependent coupling loss of a three-segment structure.

[0054] In Example 2, the tapered waveguide 31 has a seven-segment structure; the seven-segment structure has the lowest coupling loss of 0.5dB and the degradation of 0.04dB in the C+L band, as measured by the finite-difference time-domain (FDTD) method, and the total length of the device is 340μm. Figure 4A The diagram shows the electric field transport of the seven-segment structure in the xy plane. Figure 4B The wavelength-dependent coupling loss is for a seven-segment structure.

[0055] Therefore, for a single-tip type end-face coupler, Example 2, compared to Example 1, increases the number of tapered waveguide segments. While maintaining high coupling efficiency, the length of the tapered waveguide 31 is also reduced, resulting in a smaller device size. Meanwhile, in comparison... Figure 3B and Figure 4B It can be seen that the seven-segment structure has lower coupling loss. Furthermore, experiments have verified that when the number of tapered waveguide segments exceeds seven, it is impossible to further reduce the device coupling loss and size.

[0056] To further verify the performance of the single-tip type end-face coupler in Example 2, an alignment tolerance analysis was performed on the seven-segment structure end-face coupler. The analysis mainly focused on the impact of fiber deviation in the y or z direction on the device performance. The coupling loss deviation refers to the difference between the coupling loss and the zero-offset coupling loss. Figure 5A and Figure 5BThe results show the alignment tolerance analysis of the seven-segment end-face coupler. It can be seen that a vertical offset of ±2μm results in a 1dB degradation of coupling loss, while for the same degree of degradation, the maximum horizontal offset is ±2.5μm. Therefore, the seven-segment end-face coupler exhibits good alignment tolerance performance.

[0057] The end-face coupler provided in this embodiment is a single-tip type end-face coupler. The tapered waveguide includes 7 tapered waveguide segments connected end to end, which can shorten the length of the tapered waveguide, reduce coupling loss, and thus achieve high coupling efficiency in a more compact manner. At the same time, the end-face coupler is not wavelength sensitive in the C+L band.

[0058] In some alternative implementations, the end-face coupler is a multi-tip type end-face coupler; The waveguide core layer 30 includes a first tapered waveguide 311, a second tapered waveguide 312, and a third tapered waveguide 313, which are spaced apart along a second direction and extend along a first direction; the third tapered waveguide 313 is located between the first tapered waveguide 311 and the second tapered waveguide 312. The first tapered waveguide 311, the second tapered waveguide 312, and the third tapered waveguide 313 have the same length, and their widths gradually increase along the first direction; each of the first tapered waveguide 311, the second tapered waveguide 312, and the third tapered waveguide 313 includes three tapered waveguide segments connected end to end; The projection of the first tapered waveguide 311 onto the third tapered waveguide 313 completely covers the third tapered waveguide 313; the projection of the second tapered waveguide 312 onto the third tapered waveguide 313 completely covers the third tapered waveguide 313.

[0059] In specific implementation, the tapered waveguide 31 includes a first tapered waveguide 311, a second tapered waveguide 312, and a third tapered waveguide 313; that is, the waveguide core layer 30 includes three tapered waveguides arranged in parallel.

[0060] In some alternative implementations, the edge of the first tapered waveguide 311 away from the third tapered waveguide 313 has a linear change with a fixed slope, while the edge closer to the third tapered waveguide 313 has a nonlinear change. The edge of the second tapered waveguide 312 away from the third tapered waveguide 313 has a linear change with a fixed slope, while the edge closer to the third tapered waveguide 313 has a nonlinear change. The fixed slope is defined as k = h / (lt1 + lt2 + lt3), where h is the total length of the three tapered waveguide segments along the second direction, and lt is the length of each tapered waveguide segment along the first direction.

[0061] In some alternative implementations, both sides of the third tapered waveguide 313 exhibit nonlinear variations. The function relating the width of each tapered waveguide segment in the third tapered waveguide 313 to its length is as follows:

[0062] Where wt is the width at the beginning of the tapered waveguide segment, lt is the length of the tapered waveguide segment, m represents the nonlinearity, and w is the width at the end of the tapered waveguide segment.

[0063] The end-face coupler provided in this embodiment is a multi-tip type end-face coupler, which can improve mode matching efficiency while using a three-pronged structure to complete optical power transmission, further improving coupling efficiency and shortening device size; at the same time, the multi-tip type end-face coupler has greater design freedom and better performance.

[0064] In some alternative implementations, it further includes: a first straight waveguide 331, connected to the end of the first tapered waveguide 311, and extending along a first direction; The second straight waveguide 332 is connected to the end of the second tapered waveguide 312 and extends along the first direction; The third straight waveguide 333 is connected to the end of the first tapered waveguide 311 and extends along the first direction; The first straight waveguide 331, the second straight waveguide 332, and the third straight waveguide 333 have the same length; they are arranged along the second direction; the projection of the first straight waveguide 331 onto the third straight waveguide 333 completely covers the third straight waveguide 333; the projection of the second straight waveguide 332 onto the third straight waveguide 333 completely covers the third straight waveguide 333.

[0065] In some alternative implementations, such as Figure 6 As shown, it also includes: a first linear waveguide 341, located between the first straight waveguide 331 and the third straight waveguide 333, and extending along the first direction; The second linear waveguide 342 is located between the second straight waveguide 332 and the third straight waveguide 333, and extends along the second direction; The third linear waveguide 343 is located on the side of the third straight waveguide 333 opposite to the third tapered waveguide 313 and extends along the first direction; Transmission waveguide 32 is located on the side of the third linear waveguide 343 that is opposite to the third straight waveguide 333; One end of the third linear waveguide 343 is connected to the third straight waveguide 333, and the other end is connected to the transmission waveguide 32.

[0066] In some alternative implementations, the first linear waveguide 341 includes a first front waveguide and a first rear waveguide connected together; the width of the first front waveguide gradually increases along a first direction; and the width of the first rear waveguide gradually decreases along the first direction. The second linear waveguide 342 includes a second front waveguide and a second rear waveguide connected together; the width of the second front waveguide gradually increases along the first direction; the width of the second rear waveguide gradually decreases along the first direction. The positions of the first front waveguide, the second front waveguide, and the third straight waveguide 333 correspond, and the lengths of the first front waveguide and the second front waveguide are the same as the length of the third straight waveguide 333. The positions of the first rear waveguide, the second rear waveguide, and the third linear waveguide 343 correspond, and the lengths of the first rear waveguide and the second rear waveguide are the same as the length of the third linear waveguide 343.

[0067] In Example 3, such as Figure 6 As shown, a multi-tip type end-face coupler is provided. Figure 7 In the diagram, CS1, CS2, CS3, and CS4 represent the mode field distribution corresponding to each node end face of the device. It can be seen that the mode field shows a gradual convergence trend and is confined within the waveguide.

[0068] On the one hand, the multi-tip type end face coupler of Example 3 was optimized and tested through FDTD calculation. Figure 8A For electric field transport in the xy plane of the device, the total length of the device is only 259μm; Figure 8B The wavelength-dependent coupling loss is shown. It can be seen that the device exhibits the lowest coupling loss of 0.35 dB in the 1.3 μm to 1.8 μm wavelength band, with a 1 dB bandwidth greater than 450 nm. Specifically, the wavelength-dependent loss in the C+L band is only 0.08 dB. It can be seen that, compared to a single-tip end-face coupler, the multi-tip end-face coupler provided in Example 3 achieves both reduced size and low loss, as well as wavelength insensitivity.

[0069] On the other hand, performance analysis was conducted on the horizontal and vertical positions of the optical fiber, and the results are as follows: Figure 9A and Figure 9B The fiber vertical deviation is ±2μm, resulting in a 1dB performance degradation. For the same degree of degradation, the maximum horizontal offset is ±2.8μm. It can be seen that compared to the single-tip end-face couplers of Examples 1 and 2, the multi-tip end-face coupler provided in Example 3 can further improve fiber alignment tolerance performance.

[0070] The end-face coupler provided in this embodiment is a multi-tip type. While maintaining the same performance, the device size is reduced from 2000μm for conventional adiabatic tapered waveguides to 259μm, improving integration density. Simultaneously, it offers a 1dB bandwidth greater than 450nm, with less performance degradation. Specifically, the wavelength-dependent loss in the C+L band is only 0.08dB, and the coupling loss is as low as 0.35dB. It is also more tolerant of fiber location degradation, with a degradation within 1dB, a vertical offset of ±2μm, and a horizontal offset of ±2.8μm.

[0071] In some alternative implementations, two grooves 50 divide the end-face coupler into a functional region and edge regions on both sides; the waveguide core layer 30 is located in the functional region; the grooves 50 are adapted to be formed by a dry etching process; The groove 50 extends into the substrate layer 10 to a depth greater than 20 μm, and the width of the groove 50 is 5 μm to 15 μm; the minimum distance between the groove 50 and the edge of the waveguide core layer 30 is 8 μm to 20 μm.

[0072] In some examples, the depth of groove 50 is greater than 20 μm and less than or equal to 120 μm.

[0073] In some examples, the width of the groove 50 is 10 μm; the minimum distance between the edge of the groove 50 and the edge of the waveguide core layer 30 is 15 μm.

[0074] In some alternative implementations, the waveguide core layer 30 is symmetrically distributed along a first direction; The waveguide core layer 30 is a single-layer waveguide; the material of the waveguide core layer 30 is silicon nitride.

[0075] The end-face coupler provided in this embodiment has a single-layer waveguide core structure, which has low fabrication complexity. The waveguide core is made of silicon nitride, which can be fabricated using a mature silicon nitride wafer fabrication platform. Furthermore, the minimum feature size of the waveguide core is greater than 200nm, which can reduce the complexity of the fabrication process and improve the reliability of the device.

[0076] In the description of this specification, the references to terms such as "this embodiment," "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0077] The above description does not provide detailed explanations of the technical aspects of each layer's patterning, etching, etc. However, those skilled in the art should understand that various technical means can be used to form layers and regions of the desired shape. Furthermore, to form the same structure, those skilled in the art can also design methods that are not entirely identical to those described above. Additionally, although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination.

[0078] 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 above, 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 protection of the present invention is determined by the scope of the appended claims.

Claims

1. An end-face coupler, characterized in that, include: The waveguide core layer, the lower cladding layer, and the upper cladding layer are stacked sequentially from bottom to top; wherein the upper cladding layer is located on the upper surface of the lower cladding layer and covers the upper surface and side surface of the waveguide core layer. It also includes: two grooves, located on both sides of the waveguide core layer, and both extending along a first direction; the grooves penetrate the upper cladding layer, the lower cladding layer, and extend into a portion of the substrate layer; The waveguide core layer includes at least one tapered waveguide; the tapered waveguide includes multiple tapered waveguide segments connected end to end; the tapered waveguide extends along a first direction; the width of the tapered waveguide gradually increases along the first direction in a nonlinear manner.

2. The end-face coupler according to claim 1, characterized in that, The tapered waveguide is a nonlinear tapered waveguide; the width of the tapered waveguide gradually increases from the starting end to the ending end. The tapered waveguide has 3 to 7 tapered waveguide segments; each tapered waveguide segment includes a start end and an end end; the width of each tapered waveguide segment gradually increases from the start end to the end end in a non-linear manner; The width of the tapered waveguide segment varies with its length as follows: Where wt is the starting width of the tapered waveguide segment, lt is the length of the tapered waveguide segment, m represents the nonlinearity, and w is the ending width of the tapered waveguide segment.

3. The end-face coupler according to claim 2, characterized in that, The end-face coupler is a single-tip type end-face coupler; The waveguide core layer includes a tapered waveguide and a transmission waveguide; the tapered waveguide includes 7 tapered waveguide segments connected end to end.

4. The end-face coupler according to claim 1, characterized in that, The end-face coupler is a multi-tip type end-face coupler; The waveguide core layer includes a first tapered waveguide, a second tapered waveguide, and a third tapered waveguide, which are spaced apart along a second direction and extend along a first direction; the third tapered waveguide is located between the first tapered waveguide and the second tapered waveguide. The first tapered waveguide, the second tapered waveguide, and the third tapered waveguide have the same length, and their widths gradually increase along the first direction; each of the first tapered waveguide, the second tapered waveguide, and the third tapered waveguide includes three tapered waveguide segments connected end to end; The projection of the first tapered waveguide onto the third tapered waveguide completely covers the third tapered waveguide; the projection of the second tapered waveguide onto the third tapered waveguide completely covers the third tapered waveguide.

5. The end-face coupler according to claim 4, characterized in that, The edge of the first tapered waveguide away from the third tapered waveguide has a linear change with a fixed slope, while the edge closer to the third tapered waveguide has a nonlinear change. The edge of the second tapered waveguide away from the third tapered waveguide has a linear change with a fixed slope, while the edge closer to the third tapered waveguide has a nonlinear change. The fixed slope is defined as k = h / (lt1 + lt2 + lt3), where h is the total length of the three tapered waveguide segments along the second direction, and lt is the length of each tapered waveguide segment along the first direction.

6. The end-face coupler according to claim 4, characterized in that, Both sides of the third tapered waveguide exhibit nonlinear changes. The width of each tapered waveguide segment in the third tapered waveguide varies with its length as follows: Where wt is the width at the beginning of the tapered waveguide segment, lt is the length of the tapered waveguide segment, m represents the nonlinearity, and w is the width at the end of the tapered waveguide segment.

7. The end-face coupler according to claim 4, characterized in that, It also includes: a first straight waveguide, connected to the end of the first tapered waveguide and extending along a first direction; The second straight waveguide is connected to the end of the second tapered waveguide and extends along the first direction; The third straight waveguide is connected to the end of the first tapered waveguide and extends along the first direction; The first straight waveguide, the second straight waveguide, and the third straight waveguide have the same length; they are arranged along a second direction; the projection of the first straight waveguide onto the third straight waveguide completely covers the third straight waveguide; the projection of the second straight waveguide onto the third straight waveguide completely covers the third straight waveguide.

8. The end-face coupler according to claim 7, characterized in that, It also includes: a first linear waveguide, located between the first straight waveguide and the third straight waveguide, and extending along a first direction; The second linear waveguide is located between the second straight waveguide and the third straight waveguide, and extends along the second direction; The third linear waveguide is located on the side of the third straight waveguide opposite to the third tapered waveguide and extends along the first direction; A transmission waveguide is located on the side of the third linear waveguide that faces away from the third straight waveguide; One end of the third linear waveguide is connected to the third straight waveguide, and the other end is connected to the transmission waveguide.

9. The end-face coupler according to claim 8, characterized in that, The first linear waveguide includes a first front waveguide and a first rear waveguide connected to each other; the width of the first front waveguide gradually increases along a first direction; the width of the first rear waveguide gradually decreases along the first direction. The second linear waveguide includes a second front waveguide and a second rear waveguide connected together; the width of the second front waveguide gradually increases along the first direction; the width of the second rear waveguide gradually decreases along the first direction. The positions of the first front waveguide, the second front waveguide, and the third straight waveguide correspond, and the lengths of the first front waveguide and the second front waveguide are the same as the length of the third straight waveguide; The first rear waveguide, the second rear waveguide, and the third linear waveguide are positioned correspondingly, and the lengths of the first rear waveguide and the second rear waveguide are the same as the length of the third linear waveguide.

10. The end-face coupler according to claim 1, characterized in that, The two grooves divide the end-face coupler into a functional region and its two edge regions; the waveguide core layer is located in the functional region; the grooves are suitable for formation by a dry etching process. The groove extends into the substrate layer to a depth greater than 20 μm, and the width of the groove is 5 μm to 15 μm; the minimum distance between the groove and the edge of the waveguide core layer is 8 μm to 20 μm. The waveguide core layer is symmetrically distributed along the first direction; The waveguide core layer is a single-layer waveguide; the material of the waveguide core layer is silicon nitride.

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