Multi-mode interference type on-chip waveguide crossing device and photonic integrated device

Abstract

The invention discloses a multi-mode interference type on-chip waveguide crossing device, which comprises a central multi-mode interference part in a prism shape, the central multi-mode interference part comprises N connecting side surfaces and N interval side surfaces, one interval side surface is arranged between every two connecting side surfaces, and the N connecting side surfaces directly face each other in pairs; n waveguide parts, wherein each waveguide part is fused on a corresponding connection side surface; wherein N is an even number greater than or equal to 6. According to the invention, by increasing the number of ports of the crossed waveguide, flexible routing and exchange of more optical signals can be realized, and the interconnection density and the data throughput capacity of the on-chip waveguide crossing device are remarkably improved. Meanwhile, the high-order cross structure of the on-chip waveguide cross device is beneficial to reducing the total number of cross units required on a chip, reducing the overall insertion loss and crosstalk accumulation, and optimizing the layout area and the power consumption efficiency.

Description

Technical Field

[0001] This invention belongs to the field of photonic integrated device technology, specifically, it relates to a multimode interference type on-chip waveguide crossover and photonic integrated device. Background Technology

[0002] With the development of information technology, the demand for low-cost, low-power, small-size, and large-scale devices is increasing in applications such as communication, sensing, and computing. Photonic integrated devices (or photonic chips) can integrate light sources, modulators, detectors, and amplifiers on a chip with a millimeter-sized footprint, which not only reduces power consumption but also enables large-scale integration.

[0003] Cross-waveguides are widely used in photonic chips, not only to improve the integration density of photonic chips but also to reduce the wiring complexity during chip design. However, existing cross-waveguides, due to their single cross structure, are no longer sufficient to meet the requirements of multi-channel parallel processing and complex optical path scheduling. Therefore, it is necessary to increase the number of ports in cross-waveguides. Summary of the Invention

[0004] To address the technical problems existing in the prior art, embodiments of the present invention provide a multimode interferometric on-chip waveguide crossover and a photonic integrated device.

[0005] According to one aspect of an embodiment of the present invention, a multimode interferometric on-chip waveguide crossover includes: a central multimode interferometer, which is prism-shaped, the central multimode interferometer including N connecting sides and N spaced sides, with a spaced side provided between every two connecting sides, the N connecting sides being opposite each other; and N waveguides, each waveguide being fused to a corresponding connecting side; wherein, N≥6 and N is an even number.

[0006] In one example of the multimode interferometric on-chip waveguide crossover provided above, the waveguide portion sequentially includes, along a direction away from its fused connection side: a first width-fixed portion fused to a corresponding connection side; a width-gradient portion fused to the first width-fixed portion; and a second width-fixed portion fused to the width-gradient portion; wherein the width of the width-gradient portion gradually decreases along the direction from the first width-fixed portion to the second width-fixed portion.

[0007] In one example of the multimode interferometric on-chip waveguide crossover provided above, the two waveguide sections corresponding to any pair of directly opposite connection sides among the N connection sides are set as horizontal waveguide sections, and the waveguide sections corresponding to the remaining connection sides among the N connection sides are set as tilted waveguide sections; wherein, the length of the first width fixed portion of the horizontal waveguide section is less than the length of the first width fixed portion of the tilted waveguide section, and the width of the first width fixed portion of the horizontal waveguide section is less than the width of the first width fixed portion of the tilted waveguide section.

[0008] In one example of the multimode interferometric on-chip waveguide crossover provided above, the length of the width gradient section of the horizontal waveguide is equal to the length of the width gradient section of the tilted waveguide.

[0009] In one example of the multimode interferometric on-chip waveguide crossover provided above, the second width fixing portion of the horizontal waveguide is the same as the second width fixing portion of the tilted waveguide.

[0010] In one example of the multimode interferometric on-chip waveguide crossover provided above, the waveguide portion is integrally formed, and the N waveguide portions are integrally formed with the central multimode interferometric portion.

[0011] In one example of the multimode interferometric on-chip waveguide crossover provided in the above aspect, both the waveguide portion and the central multimode interferometer portion are formed by the following structure: a substrate; a buried oxide layer formed on the substrate; a waveguide layer formed on the surface of the buried oxide layer facing away from the substrate; and an air cladding formed on the surface of the waveguide layer facing away from the buried oxide layer.

[0012] In one example of the multimode interferometric on-chip waveguide crossover provided above, the waveguide layer is a ridge waveguide layer.

[0013] In one example of the multimode interferometric on-chip waveguide crossover provided in the above aspect, the waveguide layer is made of lithium niobate.

[0014] According to another aspect of the embodiments of the present invention, a photonic integrated device includes the above-described multimode interference type on-chip waveguide crossover.

[0015] Beneficial effects: According to embodiments of the present invention, the multimode interferometric on-chip waveguide crossover can achieve more flexible routing and switching of optical signals by increasing the number of ports on the crossover waveguides, significantly improving the interconnection density and data throughput of the on-chip waveguide crossover. Simultaneously, the high-order crossover structure of the on-chip waveguide crossover helps reduce the total number of crossover units required on-chip, reducing overall insertion loss and crosstalk accumulation, and optimizing layout area and power efficiency. Attached Figure Description

[0016] The above and other aspects, features, and advantages of embodiments of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 This is a top plan view of a multimode interferometric on-chip waveguide crossover according to an embodiment of the present invention;

[0018] Figure 2 It is along Figure 1 Schematic diagram of the cross section of line AA;

[0019] Figure 3 This is a schematic diagram of the insertion loss of the three output ports when the three input ports of the waveguide crossover are simultaneously excited according to an embodiment of the present invention. Detailed Implementation

[0020] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention can be implemented in many different forms, and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the various embodiments of the invention and various modifications suitable for particular intended applications.

[0021] As used herein, the term "comprising" and its variations are open terms meaning "including but not limited to". The terms "based on", "according to", etc., mean "at least partially based on" or "at least partially according to". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other definitions, whether explicit or implicit, may be included below. Unless explicitly indicated by the context, the definition of a term remains consistent throughout the specification.

[0022] Figure 1 This is a top plan view of a multimode interferometric on-chip waveguide crossover according to an embodiment of the present invention.

[0023] Reference Figure 1 According to an embodiment of the present invention, a multimode interferometric on-chip waveguide crossover includes: a central multimode interferometer 10, and six waveguide sections 20 integrated with the central multimode interferometer 10. In this embodiment, the number of waveguide sections 20 is described as six, but it should be understood that the present invention is not limited thereto; the number of waveguide sections 20 can be eight, ten, or more. That is, the number of waveguide sections 20 is an even number greater than or equal to six.

[0024] Specifically, the central multimode interference section 10 is prism-shaped, therefore its cross-section (parallel to the XY plane) is polygonal. The central multimode interference section 10 includes six connecting sides 110 and six spaced sides 120; that is, the number of connecting sides 110 and spaced sides 120 is the same as the number of waveguide sections 20. Further, a spaced side 120 is provided between every two connecting sides 110, meaning the connecting sides 110 and spaced sides 120 are alternately connected. The six connecting sides 110 are paired and face each other, and the six spaced sides 120 are paired and face each other. In other words, after removing the six spaced sides 120, the six connecting sides 110 form a regular hexagon; similarly, after removing the six connecting sides 110, the six spaced sides 120 form a regular hexagon. In this embodiment, the width of the spaced sides 120 is much smaller than the width of the connecting sides 110.

[0025] Each waveguide portion 20 is fused to a corresponding connecting side 110. Specifically, the waveguide portion 20 sequentially includes, along the direction away from the fused connecting side 110: a first width-fixed portion 210 fused to the corresponding connecting side 110; a width-gradient portion 220 fused to the first width-fixed portion 210; and a second width-fixed portion 230 fused to the width-gradient portion 220; wherein the width of the width-gradient portion 220 gradually decreases along the direction from the first width-fixed portion 210 to the second width-fixed portion 230. That is, the width of the widest point of the width-gradient portion 220 is equal to the width of the first width-fixed portion 210, and the width of the narrowest point of the width-gradient portion 220 is equal to the width of the second width-fixed portion 230.

[0026] In this embodiment, two waveguide sections 20 arranged along the X-axis are designated as horizontal waveguide sections 20A, while the other four waveguide sections 20 are designated as tilted waveguide sections 20B. Of course, this is just an example, and the present invention is not limited thereto. Any two waveguide sections 20 corresponding to any pair of directly opposite connecting sides 110 among the six connecting sides 110 can be designated as horizontal waveguide sections.

[0027] In this embodiment, the four tilted waveguide sections 20B are identical, and the two horizontal waveguide sections 20A are identical.

[0028] However, the dimensions of the tilted waveguide portion 20B and the horizontal waveguide portion 20A are not exactly the same. Specifically, the second width fixing portion 230 of the tilted waveguide portion 20B and the second width fixing portion 230 of the horizontal waveguide portion 20A are exactly the same. However, the length of the first width fixing portion 210 of the horizontal waveguide portion 20A is less than the length of the first width fixing portion 210 of the tilted waveguide portion 20B, and the width of the first width fixing portion 210 of the horizontal waveguide portion 20A is less than the width of the first width fixing portion 210 of the tilted waveguide portion 20B. Furthermore, the length of the width transition portion 220 of the horizontal waveguide portion 20A is equal to the length of the width transition portion 220 of the tilted waveguide portion 20B.

[0029] Therefore, according to the embodiments of the present invention, by independently optimizing the length and width of the first width fixing portion of the horizontal waveguide portion 20A and the tilted waveguide portion 20B, the effective refractive index and mode size of each propagation direction (the propagation direction along the Y-axis and the propagation direction along the Z-axis perpendicular to the XY plane) are uniformly matched at the central multimode interference portion 10, thereby ensuring that each input port (In1, In2, In3) forms the expected self-imaging point position within the central multimode interference portion 10, and ensuring that the six-port star waveguide crossover still has low loss and low crosstalk output performance under multi-port conditions.

[0030] Furthermore, the length of the width-gradient section 220 of the horizontal waveguide section 20A is 14 μm, the length of the first width-fixed section 210 of the horizontal waveguide section 20A is 9.94 μm, the length of the first width-fixed section 210 of the tilted waveguide section 20B is 10 μm, the width of the first width-fixed section 210 of the horizontal waveguide section 20A is 3.62 μm, and the width of the first width-fixed section 210 of the tilted waveguide section 20B is 3.873 μm. Therefore, the overall size of the waveguide crossover is 44.9 μm × 39.3 μm.

[0031] Furthermore, in this embodiment, the waveguide portion 20 is integrally formed, and each waveguide portion 20 is integrally formed with the central multimode interference portion 10. The structure of the waveguide portion 20 and the central multimode interference portion 10 will be described in detail below. Figure 2 It is along Figure 1 A cross-sectional view of line AA in the middle.

[0032] Reference Figure 2 The waveguide portion 20 includes: a substrate 100, which is a silicon substrate; a buried oxide layer 200 formed on the substrate 100; a waveguide layer 300 formed on the surface of the buried oxide layer 200 facing away from the substrate 100; and an air cladding 400 formed on the surface of the waveguide layer 300 facing away from the buried oxide layer 200. In one example, the waveguide layer 300 is a ridge waveguide layer, and the sidewalls of the ridge waveguide layer make an angle of 62° with the horizontal direction. In one example, the waveguide layer 300 is made of lithium niobate.

[0033] Furthermore, it should be noted that since each waveguide section 20 is integrally formed with the central multimode interference section 10, the layer structure of the central multimode interference section 10 is the same as that of the waveguide section 20. Figure 2 The waveguide section 20 shown has the same layer structure.

[0034] Figure 3 This is a schematic diagram of the insertion loss of the three output ports when the three input ports of the waveguide crossover are simultaneously excited according to an embodiment of the present invention.

[0035] Reference Figure 3 According to an embodiment of the present invention, the waveguide crossover operates in the wavelength range of 1525-1625nm, and the TE polarization modes of the input ports In1, In2 and In3 are simultaneously excited. From the perspective of the insertion loss of the output ports Out1, Out2 and Out3, the light input into the three input ports In1, In2 and In3 simultaneously does not interfere with each other.

[0036] Therefore, compared with the prior art, the central multimode interferometer 10 of the waveguide crossover according to the present invention is based on the self-imaging effect: the input field is expanded into several transverse modes in the central multimode interferometer 10, and these modes accumulate different phases along the propagation direction, reconstructing the input field or its equally distributed image according to the phase rule at a specific propagation distance. Under the planar waveguide approximation, the inter-mode reference phase length L can be defined. π =π / (β0-β1), which can be written as L under appropriate approximation. π ≈4n eff W e 2 / λ. Where W e For the equivalent width, n eff Where λ is the effective refractive index and λ is the operating wavelength. By designing the equivalent width and length of the central multimode interferometer 10 and rationally arranging the input / output port positions, multiple non-overlapping self-imaging points can be formed in the central multimode interferometer 10. This allows beams from different input ports to be reconstructed and output within the central multimode interferometer 10 according to a defined path, thereby effectively suppressing optical crosstalk between different ports.

[0037] Furthermore, the angles between the ports are significantly reduced, the equivalent propagation length of the central multimode interferometer 10 increases, and the lateral spread of the beam within the central multimode interferometer 10 is greatly enhanced. Therefore, the six-port waveguide crossover is designed with a crossover region based on a multimode interferometric self-imaging mechanism to ensure that the beams from different ports are distributed in independent imaging channels within the central multimode interferometer 10, thereby achieving low crosstalk transmission under multi-port conditions.

[0038] In a six-port waveguide crossover design, multimode interference is used as the core of the central multimode interferometer 10, which can be considered as simultaneously forming multiple self-imaging points, corresponding to multiple input / output ports. Since the width of the single-mode input waveguide is relatively narrow, while the width of the multimode region of the central multimode interferometer 10 is significantly increased, directly connecting the two would cause abrupt changes in the optical field, leading to reflection, scattering, and excitation of unwanted higher-order modes, severely affecting the self-imaging quality. To solve this problem, a linearly tapered trapezoidal structure (i.e., a width-gradient section) is set at the input end, allowing the waveguide width to gradually transition from the single-mode region to the multimode region. Through multiple linear or curved width gradients, approximately adiabatic mode unfolding can be achieved, ensuring good mode-field matching when the input field enters the multimode region, effectively reducing insertion loss and ensuring the stability of self-imaging reconstruction. This structure enables beams from different ports to form clear, non-overlapping self-imaging points in the central multimode interferometer, achieving low crosstalk output from multiple ports.

[0039] Furthermore, according to another embodiment of the present invention, a photonic integrated device (or photonic chip) having the above-described on-chip waveguide crossover is also provided.

[0040] In summary, the multimode interferometric on-chip waveguide crossover according to embodiments of the present invention, by increasing the number of ports on the crossover waveguides, enables more flexible routing and switching of optical signals, significantly improving the interconnection density and data throughput of the on-chip waveguide crossover. Simultaneously, the high-order crossover structure of the on-chip waveguide crossover helps reduce the total number of crossover units required on-chip, lowering overall insertion loss and crosstalk accumulation, and optimizing layout area and power efficiency.

[0041] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

Claims

1. A multimode interferometric on-chip waveguide crossover, characterized in that, The multimode interferometric on-chip waveguide crossover includes: The central multimode interference section is prism-shaped and includes N connecting sides and N spaced sides. A spaced side is provided between every two connecting sides, and the N connecting sides face each other in pairs. N waveguide sections, each waveguide section is fused to a corresponding connecting side; Where N≥6 and N is an even number.

2. The multimode interferometric on-chip waveguide crossover according to claim 1, characterized in that, The waveguide portion includes, sequentially along the direction away from its fused connection side, the following: The first width fixing part is integrated into the corresponding connecting side; A width gradient portion is integrated into the first width fixed portion; The second width-fixed portion is integrated into the width-gradient portion; The width of the width-gradient portion gradually decreases along the direction from the first width-fixed portion to the second width-fixed portion.

3. The multimode interferometric on-chip waveguide crossover according to claim 1 or 2, characterized in that, The two waveguide sections corresponding to any pair of directly opposite connecting sides among the N connecting sides are set as horizontal waveguide sections, and the waveguide sections corresponding to the remaining connecting sides among the N connecting sides are set as tilted waveguide sections. Wherein, the length of the first width fixed portion of the horizontal waveguide is less than the length of the first width fixed portion of the tilted waveguide, and the width of the first width fixed portion of the horizontal waveguide is less than the width of the first width fixed portion of the tilted waveguide.

4. The multimode interferometric on-chip waveguide crossover according to claim 3, characterized in that, The length of the width gradient section of the horizontal waveguide is equal to the length of the width gradient section of the tilted waveguide.

5. The multimode interferometric on-chip waveguide crossover according to claim 3, characterized in that, The second width fixing part of the horizontal waveguide is the same as the second width fixing part of the tilted waveguide.

6. The multimode interferometric on-chip waveguide crossover according to claim 1 or 2, characterized in that, The waveguide section is integrally formed, and the N waveguide sections are integrally formed with the central multimode interference section.

7. The multimode interferometric on-chip waveguide crossover according to claim 6, characterized in that, Both the waveguide section and the central multimode interferometer section are formed by the following structure: Substrate; A buried oxide layer is formed on the substrate; A waveguide layer is formed on the surface of the buried oxide layer facing away from the substrate; An air cladding is formed on the surface of the waveguide layer facing away from the buried oxide layer.

8. The multimode interferometric on-chip waveguide crossover according to claim 7, characterized in that, The waveguide layer is a ridge waveguide layer.

9. The multimode interferometric on-chip waveguide crossover according to claim 7, characterized in that, The waveguide layer is made of lithium niobate.

10. A photonic integrated device, characterized in that, Including the multimode interferometric on-chip waveguide crossover as described in any one of claims 1 to 9.

Images