Back-integrated vertical coupler and photonic integrated chip
By employing a back-integrated vertical coupler in a photonic integrated chip and utilizing a ridge waveguide gradient structure to achieve stable transmission of optical signals, the problem of low interlayer coupling efficiency is solved and the interlayer coupling efficiency is improved.
Patent Information
- Application Number
- CN202423033884.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-09
- Publication Date
- 2025-11-18
- Estimated Expiration
- 2034-12-09
AI Technical Summary
In existing photonic integrated chips, the vertical coupling efficiency between layers is affected by factors such as interlayer distance, waveguide tip size, and alignment error, resulting in unstable optical signal transmission.
A back-integrated vertical coupler is used, and the optical signal is gradually coupled from the first coupling waveguide to the second coupling waveguide by using a ridge waveguide gradient structure in the first coupling waveguide, thereby reducing return loss and improving interlayer coupling efficiency.
Stable optical signal transmission between different layers was achieved, reducing the impact of interlayer distance and waveguide tip size on coupling efficiency and improving interlayer coupling efficiency.
Smart Images
Figure CN223565926U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of optical communication technology, specifically to a back-integrated vertical coupler and a photonic integrated chip. Background Technology
[0002] Photonic integrated chips use light waves (electromagnetic waves) as the carrier for information transmission or data processing. They generally rely on dielectric waveguides in integrated optics or silicon-based optoelectronics to transmit optical signals. Multiple waveguide devices, such as those for modulation, transmission, and demodulation of optical signals, can be integrated onto the same chip.
[0003] To further improve the performance of photonic integrated chips, the integration of waveguide devices made of various materials is an essential step for silicon photonic platforms. Waveguide devices made of different materials are located in different layers of the optical chip, and the transmission of optical signals between different layers needs to be accomplished through vertical couplers. However, many factors affect the vertical coupling efficiency, such as interlayer distance, waveguide tip size, alignment error, and effective refractive index. Interlayer interconnection of different materials requires a stable vertical coupler. Utility Model Content
[0004] The purpose of this application is to provide a back-integrated vertical coupler and photonic integrated chip that can achieve stable optical signal transmission between different layers and improve interlayer coupling efficiency.
[0005] In one aspect of this application, a back-integrated vertical coupler is provided, including a first coupling waveguide and a second coupling waveguide, wherein the first coupling waveguide and the second coupling waveguide extend in the same direction;
[0006] The first coupling waveguide includes a ridge waveguide, which includes a stacked planar portion and a ridge portion, and the second coupling waveguide is located on the side of the planar portion opposite to the ridge portion;
[0007] The first coupling waveguide has a first end and a second end opposite to each other along its extension direction. The planar portion includes a tapered planar portion, the waveguide width of which gradually decreases in the direction toward the second end to form a planar tip. The ridge portion includes a tapered ridge portion, the waveguide width of which gradually decreases in the direction toward the second end to form a ridge tip. The distance from the planar tip to the first end is greater than the distance from the ridge tip to the first end.
[0008] The projection of the second coupling waveguide onto the first coupling waveguide covers at least a portion of the second end of the first coupling waveguide to the gradient ridge, so as to couple the light transmitted in the first coupling waveguide into the second coupling waveguide.
[0009] Another aspect of the embodiments of the present application provides a photonic chip, the photonic integrated chip comprising a first waveguide located at a first waveguide layer and a second waveguide located at a second waveguide layer, the second waveguide layer being laminated to a back surface of the first waveguide layer;
[0010] The first waveguide and the second waveguide are optically coupled by the back-integrated vertical coupler described above, one end of the first waveguide and the second waveguide being provided with a first coupling waveguide of the vertical coupler, and one end of the second waveguide and the first waveguide being provided with a second coupling waveguide of the vertical coupler, so as to couple the light transmitted in the first waveguide to the second waveguide.
[0011] The back-integrated vertical coupler and the photonic integrated chip provided by the embodiments of the present application adopt a ridge waveguide gradual change structure to transmit the optical signal to the second coupling waveguide located at the back surface side of the flat plate part, so as to realize the optical coupling between the waveguides of different layers; the light is conducted through the gradual change ridge part of the first coupling waveguide to the gradual change flat plate part, and then coupled to the second coupling waveguide from the gradual change flat plate part, so as to reduce the echo loss in the coupling process; the thickness of the ridge part and the flat plate part of the ridge waveguide gradual change structure is relatively small, which is conducive to realizing a smaller size of the tip, and the tip of the gradual change structure also reduces the influence of the interlayer distance on the coupling efficiency; compared with the prior art, the back-integrated vertical coupler of the present application reduces the influence of the existing interlayer distance, waveguide tip size and other factors on the coupling efficiency, realizes stable optical signal transmission between different layers, and improves the interlayer coupling efficiency. BRIEF DESCRIPTION OF DRAWINGS
[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.
[0013] Figure 1 is a schematic diagram of the back-integrated vertical coupler structure provided by an embodiment of the present application;
[0014] Figure 2a is a schematic diagram of the back-integrated vertical coupler structure provided by another embodiment of the present application;
[0015] Figure 2b is Figure 2a is an enlarged view of C in
[0016] Figure 3 is a schematic diagram of the photonic integrated chip comprising the back-integrated vertical coupler structure provided by an embodiment of the present application;
[0017] Figure 4is a schematic view of a photonic integrated chip including a back-integrated vertical coupler structure provided by another embodiment of the present application;
[0018] Figures 5 to 7 is a schematic view of a preparation process of a back-integrated vertical coupler structure provided by the embodiment.
[0019] Figure legend: 10-substrate; 11-buried oxygen layer; 12-substrate; 13-medium layer; 101A-first waveguide layer; 101-first coupling waveguide; 101a-flat plate part; 101b-ridge part; 102A-second waveguide layer; 102-second coupling waveguide; a1, a2-flat plate tip; b1, b2-ridge tip; Wa-stable flat plate part; Wb-stable ridge part; Ga, Ga2-tapered flat plate part; Gb, Gb2-tapered ridge part; Wa2-first tip stable section; Wb2-second tip stable section; 110-first waveguide; 120-second waveguide; 120a-flat plate part; 120b-ridge part; 103A-third waveguide layer; 130-third waveguide; 201-doped silicon layer; 202-light absorption layer; 203-modulation waveguide; 204-modulation electrode; A-first end; B-second end; F1-waveguide extension direction. DETAILED DESCRIPTION
[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.
[0021] In the description of the present application, it should be noted that the positions or location relationships indicated by the terms "inner", "outer" and the like are based on the positions or location relationships shown in the drawings, or the positions or location relationships in which the products of the present application are usually placed, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.
[0022] It should also be noted that, unless otherwise explicitly specified and limited, the terms "provided", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.
[0023] With the performance of photonic integrated chip continuously improving, different waveguide layers of different materials need to be stacked in the same chip to manufacture different waveguide devices, so as to improve the performance of each waveguide device. Different material waveguide devices are located in different waveguide layers, and vertical couplers are needed between different waveguide layers for optical coupling to realize the transmission of light between different waveguide layers. Therefore, the vertical coupler is one of the important waveguide devices in the photonic integrated chip.
[0024] The embodiment of the present application provides a back-integrated vertical coupler, please refer to Figure 1 The vertical coupler can be used to couple the light transmitted in the first coupling waveguide 101 into the second coupling waveguide 102, and the second coupling waveguide 102 is located at the back of the ridge waveguide of the first coupling waveguide 101.
[0025] The first coupling waveguide 101 has opposite first end A and second end B along the waveguide extension direction F1, the flat plate part 101a of the first coupling waveguide 101 includes a tapered flat plate part Ga, the waveguide width of the tapered flat plate part Ga gradually decreases to form a flat plate tip a1 along the direction towards the second end B; the ridge part 101b includes a tapered ridge part Gb, the waveguide width of the tapered ridge part Gb gradually decreases to form a ridge tip b1 along the direction towards the second end B. Wherein, the distance from the flat plate tip a1 to the first end A is greater than the distance from the ridge tip b1 to the first end A.
[0026] The projection of the second coupling waveguide 102 on the first coupling waveguide 101 covers at least the second end B of the first coupling waveguide 101 to the part of the tapered ridge part Gb, so as to couple the light transmitted in the first coupling waveguide 101 into the second coupling waveguide 102. That is, the projection of the second coupling waveguide 102 on the waveguide layer where the first coupling waveguide 101 is located overlaps with the second end B of the first coupling waveguide 101 and the part adjacent to the second end B, so as to realize the optical coupling from the first coupling waveguide 101 to the second coupling waveguide 102.
[0027] It should be noted that the waveguide width in the present application refers to the size of each waveguide in the direction D perpendicular to its extension direction on the plane where it is located.
[0028] In this embodiment, the first coupling waveguide 101 adopts a ridge waveguide gradual change structure, the gradual change flat portion Ga and the gradual change ridge portion Gb are respectively made in the flat portion 101a and the ridge portion 101b of the ridge waveguide, and in the extension direction thereof, the gradual change ridge portion Gb ends earlier than the gradual change flat portion Ga, so that the optical signal is "extruded" from the ridge portion 101b to the flat portion 101a of the first coupling waveguide 101, and then is adiabatic / capillary coupled from the flat portion 101a to the second coupling waveguide 102. Specifically, in the coupling process of the light transmitted from the first coupling waveguide 101 to the second coupling waveguide 102, the light field distribution is as follows: the light is laterally conducted from the first end A to the second end B of the first coupling waveguide 101, before the gradual change ridge portion Gb starts, most of the light field is bound in the ridge portion 101b, after entering the gradual change ridge portion Gb, the light field gradually diffuses to the flat portion 101a, and continues to conduct along the gradual change ridge portion Gb and the flat portion 101a to the second end B, after the light field enters the gradual change flat portion Ga, it is gradually diffused to the second coupling waveguide 102 by the gradual change flat portion Ga, and the optical coupling from the first coupling waveguide 101 to the second coupling waveguide 102 is completed.
[0029] Figure 1 The end portion on the left side of the second coupling waveguide 102 is the joint of the first coupling waveguide 101 and the second coupling waveguide 102, at the waveguide joint, the effective refractive index of the waveguide will have a sudden change, and this refractive index sudden change will reflect the transmitted light field, causing the echo loss of the light. In this embodiment, the projection of the second coupling waveguide 102 at least covers a part of the second end B to the gradual change ridge portion Gb of the first coupling waveguide 101, and the second coupling waveguide 102 is located on the side of the flat portion 101a facing away from the ridge portion 101b, most of the light field of the gradual change ridge portion Gb is still bound in the ridge portion 101b, and the light field entering the flat portion 101a is very small, therefore, the influence of the refractive index sudden change at this joint on the light field is very small, and the reflection of the light at this joint is very small, thereby reducing the echo loss in the coupling process. It should be noted that the refractive index mentioned in this application refers to the effective refractive index of the waveguide.
[0030] If the second coupling waveguide 102 only covers the flat tip a1 of the flat portion 101a, because the light field starts to diffuse to the second coupling waveguide 102 from the flat tip a1 of the flat portion 101a, the refractive index sudden change at this time will cause a large echo loss.
[0031] The first coupling waveguide 101 adopts a ridge waveguide gradual change structure. The ridge 101b and the plate 101a of the ridge waveguide gradual change structure are relatively small in thickness, and it is easier to manufacture a small-size tip. The transmission of the optical field from the ridge 101b to the plate 101a gradually transitions through the gradual change ridge Gb. The size of the ridge tip b1 can be very small, avoiding the effective refractive index mutation between the ridge 101b and the plate 101a, and reducing the return loss at this point. Similarly, the transmission of the optical field from the gradual change plate Ga to the second coupling waveguide 102 gradually transitions through the gradual change plate Ga. The size of the plate tip a1 can also be very small, avoiding the refractive index mutation between the plate 101a and the second coupling waveguide 102, and reducing the return loss at this point. Thus, the overall return loss of the coupling process is effectively reduced, and the coupling efficiency is improved. On the other hand, the gradual change plate Ga has a small plate tip a1, so that the optical field in the gradual change plate Ga is more easily diffused into the second coupling waveguide 102, and the sensitivity to the distance between the upper and lower waveguides is low. Even if the distance between the upper and lower waveguides is as large as 300 nm, the interlayer optical transmission with ultra-low loss (<0.1) can be achieved, and the influence of the interlayer distance on the coupling efficiency is reduced. Compared with the prior art, the back-integrated vertical coupler of the present application reduces the influence of the existing interlayer distance, waveguide tip size and other factors on the coupling efficiency, realizes stable optical signal transmission between different layers, and improves the interlayer coupling efficiency.
[0032] In this embodiment, the refractive index of the first coupling waveguide 101 is greater than that of the second coupling waveguide 102, and the light is conducted from the first coupling waveguide 101 with a large refractive index to the second coupling waveguide 102 with a small refractive index.
[0033] Generally, it is easier to couple light from a material with a small refractive index to a material with a large refractive index, and vice versa. However, the back-integrated vertical coupler of the present application gradually pushes the optical field from the first coupling waveguide 101 with a large refractive index to the second coupling waveguide 102 with a small refractive index, thereby improving the coupling efficiency of the light from the first coupling waveguide 101 with a large refractive index to the second coupling waveguide 102 with a small refractive index, and solving the problem of the prior art.
[0034] For example, the first coupling waveguide 101 is any one of a silicon waveguide or a lithium niobate waveguide, or other waveguides with a high refractive index; the second coupling waveguide 102 is any one of a lithium niobate waveguide or a silicon nitride waveguide, or other waveguides with a low refractive index. The refractive indices of silicon, lithium niobate and silicon nitride are arranged from large to small.
[0035] In the present application, the material of the first coupling waveguide 101 is silicon, and the material of the second coupling waveguide 102 is lithium niobate, which is suitable for silicon-lithium niobate heterogeneous integrated chips.
[0036] Of course the first and second coupling waveguides 101, 102 can also be applicable to other material combinations, such as silicon-silicon nitride, lithium niobate-silicon nitride, etc.
[0037] In this embodiment, the width of the slab tip a1 and the ridge tip b1 is less than or equal to one fifth of the width of the corresponding single-mode waveguide of the waveguide material, for example, when the first coupling waveguide 101 is a silicon waveguide, the width of the slab tip a1 and the ridge tip b1 is less than or equal to one fifth of the width of the single-mode silicon waveguide, so as to minimize the refractive index jump at the ridge tip b1 and the slab tip a1, thereby minimizing the back reflection loss. Due to the limitation of the etching process, the tip size of the strip waveguide is difficult to be small, and the application adopts the ridge waveguide gradual structure, the thickness of the ridge and the slab is thin respectively, and the tip structure is made respectively, the size of the tip can be made smaller, so as to realize smaller back reflection loss.
[0038] In the ridge waveguide, the width of the slab 101a is greater than the width of the ridge 101b, and the ridge 101b is located in the slab 101a. In the ridge waveguide gradual structure, the gradual ridge Gb is stacked on the gradual slab Ga, and at any position along the waveguide extension direction, the waveguide width of the gradual slab Ga is greater than the waveguide width of the gradual ridge Gb.
[0039] The slab 101a further comprises a stable slab Wa, the waveguide width of the stable slab Wa is constant, and one end of the stable slab Wa is connected to one side of the gradual slab Ga away from the slab tip a1; the ridge 101b further comprises a stable ridge Wb, the waveguide width of the stable ridge Wb is constant, and one end of the stable ridge Wb is connected to one side of the gradual ridge Gb away from the ridge tip b1. The stable ridge Wb and the stable slab Wa are stacked, and the end parts of the two away from the ridge tip b1 jointly form the first end A of the first coupling waveguide 101; the waveguide width of the stable slab Wa is greater than the waveguide width of the stable ridge Wb.
[0040] Figure 1 In the example, the lengths of the stable slab Wa and the stable ridge Wb in the waveguide extension direction F1 substantially coincide, and in other examples, the lengths of the stable slab Wa and the stable ridge Wb in the waveguide extension direction F1 can not coincide.
[0041] Figure 1 In the embodiment shown, along the waveguide extension direction F1, the length of the slab 101a is greater than the length of the ridge 101b, and the ridge tip b1 of the ridge 101b is located in the gradual slab Ga of the slab 101a. The slab tip a1 forms the second end B of the first coupling waveguide 101, and the projection of the ridge tip b1 in the plane of the first coupling waveguide 101 falls within the gradual slab Ga.
[0042] The tapered ridge of the ridge portion 101b ends first, and the tapered slab of the slab portion 101a ends later, so that the ridge tip b1 is located in the tapered slab Ga, and the ridge width at the ridge tip b1 is smaller than the width of the tapered slab Ga at this position. The light conducted by the tapered ridge Gb can be gradually spread to the tapered slab Ga, and then to the slab tip a1 of the tapered slab, and then gradually spread to the second coupling waveguide 102 by the tapered slab Ga.
[0043] In addition, Figure 1 In the illustrated embodiment, the tapered slab Ga and the tapered ridge Gb of the first coupling waveguide 101 are regular wedges, and the second coupling waveguide 102 is a strip waveguide. The waveguide width of the second coupling waveguide 102 is larger than the waveguide width of the first coupling waveguide 101, and the size of the tapered structure of the first coupling waveguide 101 is relatively small, so that the two can be easily aligned, reducing the influence of the ultraviolet exposure error in etching the waveguide on the performance of the device, and the tolerance of the etching precision of the waveguide is relatively large.
[0044] The second coupling waveguide 102 can be designed as a relatively thick multi-mode waveguide. The size of the multi-mode waveguide is larger, and the tolerance to processing errors is relatively large, which can reduce the influence of processing errors, such as the influence of ultraviolet exposure errors, etc. In this way, the influence of the alignment error between layers on the coupling efficiency can be ignored, which can reduce the influence of the existing alignment error between layers on the coupling efficiency, and realize stable optical signal interconnection between layers.
[0045] Of course, the tapered slab Ga and the tapered ridge Gb of the first coupling waveguide 101 can also be irregular wedges, such as asymmetric wedges. The second coupling waveguide 102 can also include a tapered waveguide, which can be a wedge or any of other function shapes (such as parabolic function, hyperbolic function, etc.). The waveguide width of the tapered waveguide gradually decreases along its extension direction, and the end with a larger width is connected to the strip waveguide, and the direction in which the width gradually decreases is opposite to the direction in which the tip of the tapered slab Ga of the first coupling waveguide 101 points. That is, the tapered waveguide and the tapered slab Ga and the tapered ridge Gb of the first coupling waveguide 101 form a wedge structure with opposite tip directions and overlap, which further reduces the refractive index discontinuity at the overlapping position of the second coupling waveguide 102 and the first coupling waveguide 101, and is beneficial to realizing adiabatic coupling of light from the first coupling waveguide 101 to the second coupling waveguide 102. For example Figure 1 In the illustrated embodiment, the section of the second coupling waveguide 102 corresponding to the tapered ridge Gb can form a tapered waveguide with a waveguide width gradually decreasing to the left side.
[0046] In some embodiments, there is a dielectric layer between the first coupling waveguide 101 and the second coupling waveguide 102, and the distance between the first coupling waveguide 101 and the second coupling waveguide 102 is less than or equal to 300 nm, so as to facilitate the coupling of light between the first coupling waveguide 101 and the second coupling waveguide 102.
[0047] In another embodiment, referring to Figure 2a 、 Figure 2b Unlike the previous embodiments, in this embodiment, the flat portion 101a includes a first tip stabilization section Wa2 connected to the flat tip a1 of the tapered flat portion Ga, and the waveguide width of the first tip stabilization section Wa2 is constant and equal to the width of the flat tip a1 of the tapered flat portion Ga. The ridge portion 101b also includes a second tip stabilization section Wb2 connected to the ridge tip b1 of the tapered ridge portion Gb, and the waveguide width of the second tip stabilization section Wb2 is constant and equal to the width of the ridge tip b1 of the tapered ridge portion Gb. Moreover, the widths of the flat tip a1, the first tip stabilization section Wa2, the ridge tip b1, and the second tip stabilization section Wb2 are equal, and the second tip stabilization section Wb2 is partially laminated with the tapered flat portion Ga and partially laminated with the first tip stabilization section Wa2 to form a strip waveguide, and the second end B of the first coupling waveguide 101 is formed at the end of the strip waveguide away from the tapered flat portion Ga.
[0048] At this time, the tapered ridge portion Gb still ends first and the tapered flat portion Ga ends later, the ridge tip b1 is located within the tapered flat portion Ga, and the ridge portion 101b continues to extend towards the second end B from the waveguide width at the ridge tip b1 and maintains the waveguide width at the ridge tip b1 unchanged to form the second tip stabilization section Wb2 of the ridge portion 101b until it ends. That is, the ridge tip b1 of the ridge portion 101b is located within the tapered flat portion Ga of the flat portion 101a, the second tip stabilization section Wb2 of the ridge portion 101b is partially located on the tapered flat portion Ga and partially extends onto the first tip stabilization section Wa2 of the flat portion 101a, overlaps with the first tip stabilization section Wa2 to form a strip waveguide, and forms the second end B of the first coupling waveguide 101.
[0049] In this embodiment, both the ridge portion 101b and the flat portion 101a extend to the end B, so that there is no Figure 1 The step in the embodiment shown above has no refractive index mutation between the ridge portion 101b and the flat portion 101a, further reducing the echo loss caused by the effective refractive index mutation reflection, thereby having higher transmission efficiency, achieving lower insertion loss and echo loss.
[0050] In this embodiment, the width of the first tip stabilization section Wa2 (i.e. the width of the second tip stabilization section Wb2) is consistent with the size of the ridge tip b1 and the slab tip a1, and is less than or equal to 1 / 5 of the corresponding single-mode waveguide width of the material of the first coupling waveguide 101. That is, the size of the first tip stabilization section Wa2 and the second tip stabilization section Wb2 is as small as possible. The smaller the size of the tip stabilization section, the greater the outward diffusion of the light field, and thus the easier the transmission of light into the second coupling waveguide 102, which can improve the coupling efficiency or achieve a larger interlayer distance and reduce the impact of interlayer distance errors on the coupling efficiency.
[0051] On the basis of the above, another aspect of the embodiments of the present application also provides a photonic integrated chip, comprising a first waveguide 110 located in a first waveguide layer 101A and a second waveguide 120 located in a second waveguide layer 102A, wherein the second waveguide layer 102A is laminated to the back of the first waveguide layer 101A, and the two waveguide layers are back-integrated. The first waveguide 110 and the second waveguide 120 are optically coupled through the back-integrated vertical coupler of any of the above embodiments. The first waveguide 110 comprises the first coupling waveguide 101 of the vertical coupler, and is arranged at one end of the first waveguide 110 and the second waveguide 120. The second waveguide 120 comprises the second coupling waveguide 102 of the vertical coupler, and is arranged at one end of the second waveguide 120 and the first waveguide 110. The first waveguide 110 and the second waveguide 120 are optically coupled through the first coupling waveguide 101 and the second coupling waveguide 102 to couple the light transmitted in the first waveguide 110 to the second waveguide 120. That is, in the photonic integrated chip provided by the present application, the first waveguide 110 and the second waveguide 120 located in the back-integrated first waveguide layer 101A and the second waveguide layer 102A, respectively, are optically coupled through the back-integrated vertical coupler provided by any of the above embodiments, which can effectively improve the coupling efficiency between the first waveguide 110 and the second waveguide 120 and achieve stable light transmission.
[0052] In this embodiment, as shown in Figure 3 The photonic integrated chip has a substrate 12 and a dielectric layer 13, the first waveguide layer 101A and the second waveguide layer 102A are located in the dielectric layer 13, and the substrate 12 is arranged at the bottom as the substrate of the photonic integrated chip, and the front of the first waveguide layer faces the substrate 12 located at the bottom.
[0053] In some embodiments, the photonic integrated chip can also include a photodetector, which includes a doped silicon layer 201 and a light absorption layer 202. The doped silicon layer 201 is located in the first waveguide layer 101A, and the light absorption layer 202 is laminated to one side of the doped silicon layer 201 facing the second waveguide layer 102A. That is, the first waveguide layer 101A is a silicon waveguide layer, and the photodetector is made based on the silicon waveguide layer, and one side of the photodetector provided with the light absorption layer 202 faces the substrate 12 at the bottom.
[0054] In some embodiments, the photonic integrated chip can further comprise an optical modulator, the optical modulator comprising a modulation waveguide 203 located at the second waveguide layer 102A and a modulation electrode 204 located at a side of the modulation waveguide 203 opposite to the first waveguide layer 101A and connected to the modulation waveguide 203. That is, the modulator waveguide is fabricated based on the back-integrated second waveguide layer 102A, and the modulator electrode is fabricated based on the back process, and the modulator waveguide is opposite to the bottom substrate 12.
[0055] Please refer to Figure 4 different from the above embodiments, the photonic integrated chip further comprises a third waveguide 130 located at a third waveguide layer 103A laminated to the back of the second waveguide layer 102A, the first waveguide 110 and the second waveguide 120 are optically coupled through a back-integrated vertical coupler of any of the above embodiments, and the end of the second waveguide 120 away from the first waveguide 110 and the third waveguide 130 are also optically coupled through a back-integrated vertical coupler to couple the light transmitted in the first waveguide 110 to the second waveguide 120 and then to the third waveguide 130. That is, when it is needed to couple the light from the first waveguide 110 to the third waveguide 130 which is far away from the first waveguide 110, a second waveguide 120 can be added as a transition between the first waveguide 110 and the third waveguide 130, and two back-integrated vertical couplers are used between the first waveguide 110, the second waveguide 120 and the third waveguide 130 to finally couple the light transmitted in the first waveguide 110 to the third waveguide 130 through the second waveguide 120, so as to realize the transmission of optical signals between waveguides of multi-layer waveguide layers and improve the coupling efficiency.
[0056] In other words, the back-integrated vertical coupler between the first waveguide 110 and the second waveguide 120 is taken as a first vertical coupler, and the back-integrated vertical coupler between the second waveguide 120 and the third waveguide 130 is taken as a second vertical coupler.
[0057] Specifically, in this embodiment, the first waveguide 110 includes the first coupling waveguide 101 of the back-integrated vertical coupler (i.e., the first vertical coupler) described above, which is arranged at the end of the first waveguide 110 coupled with the second waveguide 120. The end of the second waveguide 120 coupled with the first waveguide 110 is provided with the second coupling waveguide 102 of the first vertical coupler described above, and the end of the second waveguide 120 coupled with the third waveguide 130 is provided with the first coupling waveguide 101 of the second vertical coupler described above. The end of the third waveguide 130 coupled with the second waveguide 120 is provided with the second coupling waveguide 102 of the second vertical coupler described above. In other words, the second waveguide 120 includes the second coupling waveguide 102 (a strip waveguide in this embodiment) of the first vertical coupler and the first coupling waveguide 101 (a ridge waveguide in this embodiment) of the second vertical coupler connected in series.
[0058] In this embodiment, the ridge waveguide of the second vertical coupler has the same size as the strip waveguide of the first vertical coupler at the end away from the tip, and the waveguide width of the strip waveguide of the second vertical coupler is greater than the waveguide widths of the second waveguide 120 and the first waveguide 110, i.e., the waveguide width of the third waveguide 130 is greater than the waveguide width of the second waveguide 120. That is, the first coupling waveguide 101 of the first vertical coupler and the first coupling waveguide 101 of the second vertical coupler can both adopt the structure of the first coupling waveguide 101 of the back-integrated vertical coupler described in any of the above embodiments, and the waveguide sizes thereof are matched with the sizes of the first waveguide 110 and the second waveguide 120 respectively. Similarly, the second coupling waveguide 102 of the first vertical coupler and the second coupling waveguide 102 of the second vertical coupler can both adopt the structure of the second coupling waveguide 102 of the back-integrated vertical coupler described in any of the above embodiments, and the waveguide sizes thereof are matched with the sizes of the second waveguide 120 and the third waveguide 130 respectively. Therefore, the structure of the second vertical coupler between the second waveguide 120 and the third waveguide 130 will not be described here again.
[0059] In some embodiments, the number of the second waveguides 120 arranged in the middle as a transition can be set according to the spacing between the first waveguide 110 and the third waveguide 130, for example, two layers of second waveguides 120 can be arranged to realize gradual transition, and the two adjacent waveguides are coupled through the back-integrated vertical coupler described in any of the above embodiments, which will not be described here again.
[0060] The structure of this embodiment can be used when the refractive index of the first waveguide 110 is greater than the refractive index of the second waveguide 120, and the refractive index of the second waveguide 120 is greater than the refractive index of the third waveguide 130, to improve the coupling efficiency of light from the waveguide with a large refractive index to the waveguide with a small refractive index.
[0061] In addition, coupling from a waveguide with a small refractive index to a waveguide with a large refractive index also belongs to the scope of the vertical coupler of the back-integrated application.
[0062] The vertical coupler of the back-integrated application can be prepared by a semiconductor back-integrated process. Specifically, in the preparation, a standard process (such as a semiconductor etching process) is used to complete the processing of the first coupling waveguide 101. As shown in Figure 5 The first coupling waveguide 101 is a waveguide made based on a SOI (Silicon On Insulator) structure, which includes a substrate 10, a buried oxide layer 11 (BOX), and a top silicon layer stacked in sequence. Various waveguide devices and optical waveguides required are made on the top silicon layer, including the first coupling waveguide 101, to form a first waveguide layer 101A in which the first coupling waveguide is located. Then, the wafer is flipped, and the substrate 10 and the buried oxide layer 11 are removed, leaving a thin insulating buried oxide film and the first coupling waveguide 101, as shown in Figure 6 The buried oxide film is omitted in the figure.
[0063] As can be seen, the back surface of the first coupling waveguide 101 is the surface from which the substrate 10 and the buried oxide layer 11 are removed. The buried oxide layer is not completely ground off, but a thin buried oxide film is retained. Generally, a buried oxide film with a thickness of about 200 nm is retained to protect the silicon waveguide layer and other front devices from being damaged, thereby ensuring the integrity of the silicon waveguide layer and other front devices.
[0064] Referring to Figure 7 A second waveguide layer 102A is further made on the buried oxide film. The second waveguide layer 102A can be a layer of semiconductor material, such as a lithium niobate layer or a silicon nitride layer, on another substrate, which is bonded to the back surface of the first coupling waveguide 101, i.e., the buried oxide film. Then, after the substrate and the buried oxide layer are removed, the standard process described above is used to make the required waveguide devices and optical waveguides on the layer of semiconductor material, including the second coupling waveguide 102, to form the second waveguide layer 102A. Thus, the preparation of the vertical coupler of the back-integrated application is completed. Finally, a dielectric layer 13 is further covered on the second waveguide layer 102A to play a protective role.
[0065] The second coupling waveguide 102 can be prepared as a multi-mode strip waveguide to better receive light from the flat plate part 101a of the first coupling waveguide 101, thereby improving the coupling efficiency and reducing the influence of ultraviolet exposure errors on the performance of the device.
[0066] The above merely provides an example of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims
1. A back-integrated vertical coupler, characterized by, The application relates to a coupling waveguide, comprising: a first coupling waveguide and a second coupling waveguide, the first coupling waveguide and the second coupling waveguide extending in the same direction; the first coupling waveguide comprises a ridge waveguide, the ridge waveguide comprises a laminated flat plate part and a ridge part, and the second coupling waveguide is located on the side of the flat plate part away from the ridge part; the first coupling waveguide has opposite first and second ends along the extending direction thereof, the flat plate part comprises a tapered flat plate part, the waveguide width of the tapered flat plate part gradually decreases in the direction towards the second end to form a flat plate tip, the ridge part comprises a tapered ridge part, the waveguide width of the tapered ridge part gradually decreases in the direction towards the second end to form a ridge tip, and the distance from the flat plate tip to the first end is greater than the distance from the ridge tip to the first end; the projection of the second coupling waveguide on the first coupling waveguide covers at least the second end of the first coupling waveguide to a part of the tapered ridge part, so as to couple the light transmitted in the first coupling waveguide to the second coupling waveguide.
2. The back-integrated vertical coupler of claim 1, wherein, The refractive index of the first coupling waveguide is greater than the refractive index of the second coupling waveguide.
3. The back-integrated vertical coupler of claim 2, wherein, The first coupling waveguide is any one of a silicon waveguide or a lithium niobate waveguide; The second coupling waveguide is any one of a lithium niobate waveguide or a silicon nitride waveguide.
4. The back-integrated vertical coupler of claim 1, wherein, The widths of the flat plate tip and the ridge tip are both less than or equal to one fifth of the width of the corresponding single-mode waveguide of the waveguide material.
5. The back-integrated vertical coupler of claim 1, wherein, The flat plate tip forms the second end of the first coupling waveguide, and the projection of the ridge tip on the plane where the first coupling waveguide is located falls within the tapered flat plate part.
6. The back-integrated vertical coupler of claim 1, wherein, The flat plate part further comprises a first tip stabilizing section, the first tip stabilizing section is connected with the flat plate tip of the tapered flat plate part, the waveguide width of the first tip stabilizing section is equal to the width of the flat plate tip of the tapered flat plate part, and the width is constant; The ridge part further comprises a second tip stabilizing section, the second tip stabilizing section is connected with the ridge tip of the tapered ridge part, the waveguide width of the second tip stabilizing section is equal to the width of the ridge tip of the tapered ridge part, and the width is constant; The widths of the flat plate tip, the first tip stabilizing section, the ridge tip and the second tip stabilizing section are equal, a part of the second tip stabilizing section is laminated with the tapered flat plate part, another part is laminated with the first tip stabilizing section to form a strip waveguide, and one end of the strip waveguide away from the tapered flat plate part forms the second end of the first coupling waveguide.
7. Back-integrated vertical coupler according to claim 5 or 6, characterized in that The flat plate part further comprises a stabilizing flat plate part, the waveguide width of the stabilizing flat plate part is constant, and one end of the stabilizing flat plate part is connected with the side of the tapered flat plate part away from the flat plate tip; The ridge part further comprises a stabilizing ridge part, the waveguide width of the stabilizing ridge part is constant, and one end of the stabilizing ridge part is connected with the side of the tapered ridge part away from the ridge tip; The stabilizing ridge part and the stabilizing flat plate part are laminated, and the end parts away from the ridge tip of the two parts jointly form the first end of the first coupling waveguide.
8. The back-integrated vertical coupler of claim 1, wherein, The second coupling waveguide comprises a strip waveguide, and the waveguide width of the strip waveguide of the second coupling waveguide is greater than the waveguide width of any part of the first coupling waveguide.
9. The back-integrated vertical coupler of claim 8, wherein, The second coupling waveguide further comprises a tapered waveguide, a waveguide width of the tapered waveguide gradually decreases along its extending direction, and a larger width end of the tapered waveguide is connected to the strip waveguide, and a gradually decreasing direction of the width is opposite to a direction in which the tip of the tapered slab of the first coupling waveguide points.
10. The back-integrated vertical coupler of claim 1, wherein, The first coupling waveguide and the second coupling waveguide have a dielectric layer therebetween, and a spacing between the first coupling waveguide and the second coupling waveguide is less than or equal to 300 nm.
11. A photonic integrated chip, characterized by The photonic integrated chip comprises a first waveguide located in a first waveguide layer and a second waveguide located in a second waveguide layer, and the second waveguide layer is laminated to a back surface of the first waveguide layer. The first waveguide and the second waveguide are optically coupled by the back-integrated vertical coupler according to any one of claims 1 to 10, and a first coupling waveguide of the vertical coupler is arranged at an end of the first waveguide and the second waveguide, and a second coupling waveguide of the vertical coupler is arranged at an end of the second waveguide and the first waveguide, so as to couple light transmitted in the first waveguide to the second waveguide.
12. The photonic integrated chip according to claim 11, wherein, A third waveguide located in a third waveguide layer is further included, and the third waveguide layer is laminated to a back surface of the second waveguide layer. An end of the second waveguide away from the first waveguide and the third waveguide are optically coupled by the back-integrated vertical coupler, a first coupling waveguide of the vertical coupler is arranged at an end of the second waveguide and the third waveguide, and a second coupling waveguide of the vertical coupler is arranged at an end of the third waveguide and the second waveguide, so as to couple light transmitted in the second waveguide to the third waveguide.
13. The photonic integrated chip according to claim 12, wherein, The refractive index of the first waveguide is greater than the refractive index of the second waveguide, and the refractive index of the second waveguide is greater than the refractive index of the third waveguide.
14. The photonic integrated chip of claim 11, wherein, The photonic integrated chip further comprises a photodetector, the photodetector comprises a doped silicon layer and a light absorption layer, the doped silicon layer is located in the first waveguide layer, and the light absorption layer is laminated to a side of the doped silicon layer away from the second waveguide layer. And / or, the photonic integrated chip further comprises an optical modulator, the optical modulator comprises a modulation waveguide and a modulation electrode, the modulation waveguide is located in the second waveguide layer, the modulation electrode is located on a side of the modulation waveguide away from the first waveguide layer, and the modulation electrode is connected to the modulation waveguide.