An integrated optical interlayer coupling structure with large overlay tolerance

Abstract

This invention relates to the field of optical couplers, specifically to an integrated optical interlayer coupling structure with large overlay tolerance, comprising an upper coupling waveguide and a lower coupling waveguide, which are separated by an isolation layer and overlap in opposite directions. The lower coupling waveguide includes an incident waveguide, a lower conversion waveguide, and a first waveguide, while the upper coupling waveguide includes a second waveguide, an upper conversion waveguide, and an exit waveguide. This application combines a subwavelength grating waveguide with an adiabatic coupler, utilizing the refractive index modulation effect of the subwavelength grating to significantly reduce the effective refractive index of the original ordinary waveguide and increase the mode size, thereby improving coupling efficiency and tolerance to overlay processes.

Description

Technical Field

[0001] This invention relates to the field of optical couplers, specifically to an integrated optical interlayer coupling structure with large overlay tolerance. Background Technology

[0002] With the ever-increasing information demands of people, silicon photonics, which is perfectly compatible with traditional microelectronic processes, has been vigorously developed in the field of optical communication. It has achieved low-cost, high-capacity, high-speed photonic integrated modules, which are widely used in data centers. To improve the integration level of integrated photonic systems, meet the demand for high throughput, and enhance the application potential of integrated photonic chips, heterogeneous integration is a commonly used technology. Achieving high-quality heterogeneous integrated optical chips requires interlayer couplers with high coupling efficiency and high fabrication tolerance to interconnect interlayer optical signals.

[0003] Existing silicon-based interlayer couplers all employ conventional single-mode tapered waveguides, which have small waveguide widths and limited local optical field coverage, resulting in small coupling regions. However, the field demands high overlay precision, requiring larger coupling regions to achieve efficient coupling. Current technologies increase the difficulty of practically fabricating low-loss interlayer couplers, hindering large-area applications. Therefore, interlayer couplers with large overlay tolerances urgently need development. Summary of the Invention

[0004] The purpose of this invention is to provide an integrated optical interlayer coupling structure with large overlay tolerance. This application improves the large overlay deviation while maintaining high interlayer coupling efficiency, so as to solve the existing technical defects and unmet technical requirements.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an integrated optical interlayer coupling structure with large tolerance, comprising an upper coupling waveguide and a lower coupling waveguide, wherein the upper coupling waveguide and the lower coupling waveguide are separated by an isolation layer and overlap in opposite directions, wherein: The lower coupling waveguide includes an incident waveguide, a lower conversion waveguide, and a first grating waveguide, and the incident waveguide, the lower conversion waveguide, and the first grating waveguide are connected in sequence. The upper coupling waveguide includes a second grating waveguide, an upper conversion waveguide, and an outgoing waveguide, and the second grating waveguide, the upper conversion waveguide, and the outgoing waveguide are connected in sequence. Both the first grating waveguide and the second grating waveguide are subwavelength grating waveguides.

[0006] This application increases the size of the evanescent optical field through the above-mentioned upper subwavelength grating waveguide design and lower subwavelength grating waveguide design, thereby achieving the purpose of increasing the coupling region. The above-mentioned reverse overlap means that the upper and lower coupled waveguides have the same structure but opposite directions. They overlap when viewed from above, but do not touch in space.

[0007] Preferably, the first grating waveguide is a lower-layer tapered subwavelength grating waveguide in the coupling region, and the second grating waveguide is an upper-layer tapered subwavelength grating waveguide in the coupling region.

[0008] Preferably, the lower conversion waveguide, the first grating waveguide, the second grating waveguide, and the upper conversion waveguide are subwavelength grating waveguides with equal periods.

[0009] The purpose of this application is to reduce the effective refractive index of the coupling region waveguide by using a subwavelength grating waveguide, thereby increasing the area of ​​optical field energy distribution in the coupling region cross section.

[0010] Preferably, the lower conversion waveguide, the first grating waveguide, the second grating waveguide, and the upper conversion waveguide form an interlayer coupling region and constitute a subwavelength grating interlayer coupling structure.

[0011] This application increases the effective coupling area through the above-mentioned subwavelength grating coupling region design, thereby achieving the purpose of large overlay tolerance.

[0012] Preferably, the larger of the bandgap bandwidths of the lower-layer conversion waveguide and the second grating waveguide is Δλ. sb The operating wavelength is λ0, and the two satisfy the following relationship: λ0>>Δλ sb .

[0013] The lower conversion waveguide, the first grating waveguide, the second grating waveguide, and the upper conversion waveguide all have a period of 250nm and a duty cycle of 0.5.

[0014] This application is configured in this way because, within the limits of micro-nano fabrication technology, using a grating with a period of 250nm and a duty cycle of 0.5 can meet the requirements of the working wavelength for the subwavelength grating waveguide, achieving better low-loss transmission than ordinary single-mode waveguides.

[0015] Preferably, both the incident waveguide and the outgoing waveguide are single-mode waveguides.

[0016] This application uses a single-mode waveguide to reduce crosstalk introduced by higher-order modes and improve the coupling efficiency of the interlayer coupler.

[0017] Preferably, the upper coupling waveguide and the lower coupling waveguide are parallel, both of which are axisymmetric structures, and their axes of symmetry are in the same plane.

[0018] The upper and lower subwavelength grating waveguides described in this application are symmetrically arranged based on the 180° rotation of the center point of the isolation layer.

[0019] To achieve phase matching in the overlapping portion of the first and second grating waveguides, the following conditions must be met: neff1 = neff2 Wherein, neff1 is the effective refractive index of the first grating waveguide at a point in the coupling region, and neff2 is the effective refractive index of the second grating waveguide at the phase-matching position of the first grating waveguide in the coupling region.

[0020] Preferably, for the incident waveguide to achieve phase mismatch, the following conditions must be met: neff1 > neff2.

[0021] Preferably, for the outgoing waveguide to achieve phase mismatch, the following conditions must be met: neff1 < neff2.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: all waveguide gratings in this application have equal periods and are much smaller than the bandgap of Bragg gratings. By combining subwavelength grating waveguides with thermal couplers and utilizing the refractive index modulation effect of subwavelength gratings, the effective refractive index of the original ordinary waveguides is greatly reduced, and the mode spot size is increased, thereby improving the coupling efficiency and tolerance to overlay processes. In other words, the subwavelength grating waveguides increase the mode field size when light propagates in the coupling region, which is beneficial for realizing a high-efficiency interlayer coupler. Attached Figure Description

[0023] Figure 1 This is a top view of the overall structure in Embodiment 1 of the present invention; Figure 2 This is a side view of the overall structure in Embodiment 1 of the present invention; Figure 3 This is a cross-sectional view of the overall structure in the coupling region in Embodiment 1 of the present invention; Figure 4 The transmittance of different modes of light received at the coupling output end of the overall structure in Embodiment 1 of the present invention; Figure 5 This is a diagram showing the electric field distribution of the overall structure at a symmetrical plane section in Embodiment 1 of the present invention. Figure 6 The coupling efficiency of the coupler in Embodiment 1 of the present invention under different overlay deviations in the direction perpendicular to the axis of symmetry is compared with that of a conventional thermally insulating coupler. Figure 7 The coupling efficiency of the coupler in Embodiment 1 of the present invention under different overlay deviations in the direction parallel to the axis of symmetry is compared with that of a conventional thermally insulating coupler. Figure 8 This is a top view of the low-fabrication integrated optical interlayer coupling structure of Embodiment 2; Figure 9This is a side view of the low-fabrication integrated optical interlayer coupling structure of Example 2 in the plane of symmetry; Figure 10 This is a top view of the segmented integrated optical interlayer coupling structure of Embodiment 3; Figure 11 Side view of the segmented integrated optical interlayer coupling structure in Example 3 under the plane of symmetry; In the figure: incident waveguide 101, lower conversion waveguide 102, first grating waveguide 103, second grating waveguide 104, upper conversion waveguide 105, and outgoing waveguide 106. Detailed Implementation

[0024] The following will refer to the appendices in the embodiments of the present invention. Figure 1-11 The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0025] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] Please see Figure 1-11 Embodiments of the present invention Example 1: Figure 1 Figure 2 shows a top view of the upper and lower layer structures of the coupler in Embodiment 1. The dashed lines in the figure represent the planes of symmetry of each structure. In the actual coupler, the symmetry of the two layers is formed by rotating the center point of the isolation layer by 180 degrees. Figure 3 A cross-section showing a gradually changing coupling region width for the coupler in Embodiment 1 is provided. Figure 4 The transmission spectra of different modes of light received at the output end of the coupler in Example 1 are given. As can be seen from the figure, in the wavelength range of 1550nm, a coupling efficiency of more than 95% can be achieved while maintaining low crosstalk between different modes. Figure 5 The electric field distribution of the entire structure at the cross section of the plane of symmetry is shown when the operating wavelength is 1550 nm. Figure 6 It was demonstrated that when the deviation of the symmetry axis of the upper and lower coupled waveguides in the direction perpendicular to the symmetry axis is 0.8 micrometers, the coupling efficiency of the coupler still remains at about 95%, which is higher than that of ordinary thermal couplers and meets the needs of interlayer couplers with large tolerance. Figure 7 The results show that when the working wavelength is 1550nm, the coupling efficiency of the coupler remains above 96% when the deviation of the symmetry axis of the upper and lower coupled waveguides in the direction parallel to the symmetry axis is within 5 micrometers. This is higher than that of ordinary thermal couplers and meets the requirements of interlayer couplers with large tolerance.

[0027] like Figure 1-3 As shown: An integrated optical interlayer coupling structure with large tolerance includes an upper coupling waveguide and a lower coupling waveguide, which are separated by an isolation layer and overlap in opposite directions, wherein: The lower coupling waveguide includes an incident waveguide 101, a first grating waveguide 102 and a first grating waveguide 103, and the incident waveguide 101, the lower conversion waveguide 102 and the first grating waveguide 103 are connected in sequence. The upper coupling waveguide includes a second grating waveguide 104, an upper conversion waveguide 105, and an outgoing waveguide 106. The second grating waveguide 104, the upper conversion waveguide 105, and the outgoing waveguide 106 are sequentially connected to the first grating waveguide 103 and the second grating waveguide 104, both of which are subwavelength grating waveguides.

[0028] This application increases the size of the evanescent optical field through the above-mentioned upper subwavelength grating waveguide design and lower subwavelength grating waveguide design, thereby achieving the purpose of increasing the coupling region. The reverse overlap mentioned above means that the upper and lower coupling waveguides have the same structure but opposite directions. They overlap when viewed from above, but do not touch in space. Specifically, the lower coupling waveguides, with the incident waveguide direction as the reference, are, in sequence, the incident waveguide 101, the first grating waveguide 102, and the first grating waveguide 103. The upper coupling waveguides, with the exit waveguide direction as the reference, are, in sequence, the exit waveguide 106, the upper conversion waveguide 105, and the second grating waveguide 104. The directions of the incident waveguide and the exit waveguide are opposite. Specifically, the upper coupling waveguide is made of chalcogenide glass, and the lower coupling waveguide is made of silicon.

[0029] Silicon, with its high refractive index, large transparency, and mature processing technology, is currently the most commonly used material for fabricating optical components. Silicon nitride, in particular, meets the requirement of low loss due to its low two-photon absorption. Lithium niobate, with its high nonlinear coefficient, provides modulators with higher modulation efficiency.

[0030] To achieve low crosstalk silicon-chalcogenide heterogeneous integration, an interlayer coupler composed of three layers of materials—silicon-isolation layer-chalcogenide glass—can realize low crosstalk and low loss optical field conversion between different optical materials.

[0031] The first grating waveguide 103 is a lower-layer tapered subwavelength grating waveguide in the coupling region, and the second grating waveguide 104 is an upper-layer tapered subwavelength grating waveguide in the coupling region.

[0032] like Figure 1-3 As shown: the lower conversion waveguide 102, the first grating waveguide 103, the second grating waveguide 104, and the upper conversion waveguide 105 are subwavelength grating waveguides with equal periods.

[0033] This application increases the effective coupling area through the above-mentioned subwavelength grating coupling region design, thereby achieving the purpose of large overlay tolerance.

[0034] like Figure 1-3 As shown: the lower conversion waveguide 102, the first grating waveguide 103, the second grating waveguide 104, and the upper conversion waveguide 105 form an interlayer coupling region and constitute a subwavelength grating interlayer coupling structure.

[0035] like Figure 4-7 As shown: the larger value of the bandgap bandwidth between the lower conversion waveguide 102 and the second grating waveguide 103 is Δλ. sb With an operating wavelength of λ0, and satisfying the following relationship, interlayer coupling based on a low-loss subwavelength grating waveguide is achieved: λ0>>Δλ sb .

[0036] like Figure 1-3 and Figure 8-11 As shown: Both the incident waveguide 101 and the outgoing waveguide 106 are single-mode waveguides.

[0037] like Figure 1-3 and Figure 8-11 As shown: the symmetry axes of the upper and lower subwavelength grating waveguides of this coupler structure are located in the same plane.

[0038] like Figure 1-2 and Figure 8-11 As shown: To achieve phase matching in the overlapping portion of the lower conversion waveguide 102 and the second grating waveguide 103, the following conditions must be met: neff1 = neff2 Wherein, neff1 is the effective refractive index of the lower conversion waveguide 102 at a point in the coupling region, and neff2 is the effective refractive index of the second grating waveguide 103 and the lower conversion waveguide 102 at the phase-matching position in the coupling region.

[0039] like Figure 1-2 and Figure 8-11 As shown: For the incident waveguide 101 to achieve phase mismatch, the following conditions must be met: neff1 > neff2.

[0040] like Figure 1-2 and Figure 8-11 As shown: For the outgoing waveguide 106 to achieve phase mismatch, the following conditions must be met: neff1 < neff2.

[0041] The incident waveguide 101 is a single-mode waveguide with a width of 500 nm. The lower conversion waveguide 102 is composed of a subwavelength grating waveguide with a width of 500 nm that gradually decreases to 800 nm and a tapered waveguide with a width of 500 nm that gradually decreases to 200 nm, which are symmetrically overlapped at the center. The first grating waveguide 103 is a subwavelength grating waveguide with a width of 800 nm that gradually decreases to 200 nm. The second grating waveguide 104 is a subwavelength grating waveguide with a width of 200 nm that gradually decreases to 2000 nm. The upper conversion waveguide 105 is composed of a subwavelength grating waveguide with a width of 200 nm that gradually decreases to 1200 nm and a tapered waveguide with a width of 200 nm that gradually decreases to 1200 nm, which are symmetrically overlapped at the center. The waveguide is rectangular, with an etching depth (waveguide height) of 220 nm, a middle isolation layer thickness of 300 nm, and all grating periods of 250 nm.

[0042] Working principle: In this embodiment, when the interlayer coupler is in use, a swept-frequency continuous laser is injected into the incident waveguide 101 of the coupler. The laser is coupled into the coupling region through the side-coupled waveguide structure. The laser near the resonant wavelength satisfies the phase matching condition at a certain point in the coupling region where the width gradually changes, and is coupled from the first grating waveguide 103 to the second grating waveguide 104, and finally coupled into the output waveguide 106, thereby realizing the mutual coupling of optical fields between optical waveguides formed by different optical materials.

[0043] Example 2: The only difference between Example 2 and Example 1 is that the second grating waveguide 104 and the upper conversion waveguide 105 in Example 1 are replaced with ordinary multimode waveguides. The increased processing difficulty introduced by the multi-layer fabrication required for the interlayer coupler makes the second-layer structure less complex. Figure 8 As shown, the simple upper-layer multimode tapered waveguide 104 can greatly reduce the processing difficulty.

[0044] Example 3: The only difference between Embodiment 3 and Embodiment 1 is that the second grating waveguide 104 in Embodiment 1 is changed from a linearly tapered width scheme to a piecewise tapered width scheme. For example... Figure 10 As shown, the segmented tapered subwavelength grating waveguide 104 is segmented according to the number of segments, with each segment using a subwavelength grating waveguide of different widths, and the width gradually changes between each segment. The width of each segment is determined by the optimal solution obtained through iterative particle swarm optimization algorithm.

[0045] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An integrated optical interlayer coupling structure with large overlay tolerance, characterized in that, Including upper coupled waveguide and lower layer Coupled waveguides, wherein the upper coupled waveguide and the lower coupled waveguide are separated by an isolation layer and overlap in opposite directions, wherein: The lower coupling waveguide includes an incident waveguide (101), a lower conversion waveguide (102), and a first grating waveguide (103), and The incident waveguide (101), the lower conversion waveguide (102), and the first grating waveguide (103) are connected in sequence; The upper coupling waveguide includes a second grating waveguide (104), an upper conversion waveguide (105), and an outgoing waveguide (106), and The second grating waveguide (104), the upper conversion waveguide (105), and the outgoing waveguide (106) are connected in sequence; Both the first grating waveguide (103) and the second grating waveguide (104) are subwavelength grating waveguides; The first grating waveguide (103) is a lower-layer tapered subwavelength grating waveguide in the coupling region, and the second grating waveguide (104) is an upper-layer tapered subwavelength grating waveguide in the coupling region; The lower conversion waveguide (102), the first grating waveguide (103), the second grating waveguide (104) and the upper conversion waveguide (105) are subwavelength grating waveguides with equal periods; The larger of the bandgap bandwidths of the lower conversion waveguide (102), the first grating waveguide (103), the second grating waveguide (104), and the upper conversion waveguide (105) is Δλ. sb The operating wavelength is λ0, and the two satisfy the following relationship: λ0>>Dλ sb ; The upper and lower coupled waveguides are parallel, both of which are axisymmetric structures, and their axes of symmetry lie in the same plane.

2. The integrated optical interlayer coupling structure with large overlay tolerance according to claim 1, characterized in that, The lower conversion waveguide (102), the first grating waveguide (103), the second grating waveguide (104) and the upper conversion waveguide (105) form an interlayer coupling region and constitute a subwavelength grating interlayer coupling structure.

3. The integrated optical interlayer coupling structure with large overlay tolerance according to claim 1, characterized in that, To achieve phase matching in the overlapping portion of the first grating waveguide (103) and the second grating waveguide (104), the following conditions must be met: neff1 = neff2 Wherein, neff1 is the effective refractive index of the first grating waveguide (103) at a point in the coupling region, and neff2 is the effective refractive index of the second grating waveguide (104) and the first grating waveguide (103) at the phase-matching position in the coupling region.

4. The integrated optical interlayer coupling structure with large overlay tolerance according to claim 3, characterized in that, For the incident waveguide (101) to achieve phase mismatch, the following conditions must be met: neff1 > neff2.

5. The integrated optical interlayer coupling structure with large overlay tolerance according to claim 4, characterized in that, For the outgoing waveguide (106) to achieve phase mismatch, the following conditions must be met: neff1 < neff2.

6. An integrated optical interlayer coupling structure with large overlay tolerance according to claim 1, 3, 4 or 5, characterized in that, Both the incident waveguide (101) and the outgoing waveguide (106) are single-mode waveguides; The lower conversion waveguide (102), the first grating waveguide (103), the second grating waveguide (104), and the upper conversion waveguide (105) all have a period of 250 nm and a duty cycle of 0.5.

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