Optical multimode interference coupler

Abstract

The application provides an optical multimode interference coupler. The optical multimode interference coupler of the application directly connects a transmission waveguide with a slit structure and a bar-shaped multimode waveguide at an interface, and based on multimode excitation principle and self-imaging principle of the multimode interference coupler, the optical signal in the bar-shaped multimode waveguide is simultaneously split and the waveguide structure is converted at the interface in the slit single-mode waveguide, without using a traditional tapered bar-slit waveguide conversion structure, so that the length of the electronic component is effectively reduced and the integration of the component is improved. The application realizes that the input optical signal can be directly and evenly divided into two slit waveguides from the bar-shaped waveguide, without using a traditional combination structure of splitting light first and then converting. The device has the advantages of small size, low loss, high bandwidth and the like.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, and in particular relates to an optical multimode interference coupler. Background Technology

[0002] A multimode interference coupler (MMI coupler) is an optical device based on the self-imaging effect, utilizing mode interference in a multimode waveguide to achieve beam splitting, combining, or routing of optical power. Due to its advantages such as compact structure, wide bandwidth, and large manufacturing tolerance, MMI couplers are widely used in integrated photonics (such as silicon photonics, InP, PLC platforms) and fiber optic communication systems.

[0003] Existing optical switching modulation devices often require transition structures between strip waveguides and slit waveguides to connect strip beamsplitters, strip beam combiners, and slit modulation arm waveguides. Therefore, a large number of strip waveguide-slit waveguide transition structures are needed within the optical chip, reducing the integration density of the photonic chip. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an optical multimode interference coupler that solves the problem of low integration density of optical chips in existing technologies.

[0005] The present invention adopts the following technical solution:

[0006] This invention provides an optical multimode interference coupler, comprising:

[0007] Substrate;

[0008] An optical waveguide located on the surface of the substrate;

[0009] A cladding layer, which is located on the surface of the substrate and wraps around the optical waveguide;

[0010] The optical waveguide, from signal input to output direction, includes, in sequence: a single-mode input waveguide with a strip structure, a tapered input waveguide with a tapered shape, a multimode waveguide with a strip structure, a tapered output waveguide with a slit structure, and an output waveguide with a slit structure.

[0011] The tapered, tapered output waveguide of the slit structure includes a first low-refractive-index layer and a first high-refractive-index layer located on both sides of the first low-refractive-index layer.

[0012] The output waveguide of the slit structure includes a second low-refractive-index layer and a second high-refractive-index layer located on both sides of the second low-refractive-index layer;

[0013] The axis of the first low-refractive-index layer and the axis of the second low-refractive-index layer are on the same horizontal line;

[0014] The width of the single-mode input waveguide is equal to the minimum waveguide width of the tapered input waveguide;

[0015] The maximum waveguide width of the tapered input waveguide is equal to the maximum waveguide width of the tapered output waveguide of the slit structure.

[0016] The output waveguide width of the slit structure is equal to the minimum waveguide width of the gradient output waveguide of the slit structure.

[0017] Preferably, the materials of the strip-shaped single-mode input waveguide, the tapered input waveguide, and the strip-shaped multimode waveguide are all silicon.

[0018] Both the first high-refractive-index layer and the second high-refractive-index layer are made of silicon.

[0019] The materials of the first low-refractive-index layer and the second low-refractive-index layer are both silicon dioxide.

[0020] Preferably, the widths of the first low-refractive-index layer and the second low-refractive-index layer are the same;

[0021] The widths of the first low-refractive-index layer and the second low-refractive-index layer are 0.01–0.1 μm.

[0022] Preferably, the input waveguide width of the strip structure is 0.4–0.6 μm and the length is 4–10 μm.

[0023] Preferably, the tapered input waveguide has a maximum waveguide width of 0.8–1.2 μm and a length of 2–5 μm.

[0024] Preferably, the length of the strip-shaped multimode waveguide is 8–12 μm and the width is 2.8–3.5 μm.

[0025] Preferably, the length of the tapered, tapered output waveguide of the slit structure is 14–20 μm;

[0026] The output waveguide of the slit structure has a length of 4–10 μm and a width of 0.4–0.7 μm.

[0027] Preferably, the optical multimode interference coupler is a 1×2 coupler;

[0028] The number of the single-mode input waveguide with strip structure, the tapered input waveguide, and the multimode waveguide with strip structure are all 1;

[0029] The number of tapered graded output waveguides in the slit structure and the number of output waveguides in the slit structure are both 2;

[0030] The two tapered output waveguides of the slit structure and the two output waveguides of the slit structure are symmetrically distributed vertically relative to the transverse central axis of the multimode waveguide of the strip structure;

[0031] The transverse central axis of the single-mode input waveguide and the tapered input waveguide of the strip structure is on the same horizontal line as the transverse central axis of the multimode waveguide of the strip structure.

[0032] The distances between the first high-refractive-index layer and the second high-refractive-index layer and the transverse central axis of the multimode waveguide of the strip structure are 0.8–0.9 μm;

[0033] The two first high refractive index layers are symmetrically distributed vertically relative to the transverse central axis of the first low refractive index layer, and the two second high refractive index layers are symmetrically distributed vertically relative to the transverse central axis of the second low refractive index layer.

[0034] Preferably, the thickness of the single-mode input waveguide with strip structure, the tapered input waveguide with tapered shape, the multimode waveguide with strip structure, the tapered output waveguide with slit structure, and the output waveguide with slit structure are all 0.2 to 0.3 μm.

[0035] Preferably, the substrate is an SOI substrate;

[0036] The cladding material is silicon dioxide.

[0037] The optical multimode interference coupler of the present invention has the following advantages compared with the prior art:

[0038] The optical multimode interference coupler of this invention directly connects the slit-structured transmission waveguide to the interface of the strip-shaped multimode waveguide. Based on the multimode excitation principle and self-image principle of the multimode interference coupler, the optical signal in the strip-shaped multimode waveguide simultaneously completes beam splitting and waveguide structure transformation at the interface of the slit-shaped single-mode waveguide. This eliminates the need for the traditional tapered strip slit waveguide conversion structure, effectively reducing the length of electronic components and improving device integration. This invention enables the input optical signal to be directly and evenly split from the strip waveguide into two slit waveguides, eliminating the need for the traditional combination structure of beam splitting followed by conversion. Furthermore, the device has advantages such as small size, low loss, and high bandwidth. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1This is a top view of the optical waveguide of the present invention;

[0041] Figure 2 This is a three-dimensional structural schematic diagram of the optical waveguide of the present invention;

[0042] Figure 3 This is a schematic diagram of the structure of the optical multimode interference coupler of the present invention, showing the direction of the input optical signal.

[0043] Figure 4 This is a schematic diagram of the structure of the optical multimode interference coupler of the present invention, showing the direction of the output optical signal.

[0044] Figure 5 This is a schematic diagram of the optical field propagation distribution of the optical multimode interference coupler in Embodiment 1 of the present invention;

[0045] Figure 6 This refers to the additional losses of the optical multimode interference coupler in Embodiment 1 of the present invention under different optical wavelength propagation conditions;

[0046] Figure 7 The optical power (P) at the output of the optical multimode interference coupler is calculated when the input light wavelength is 1.55 μm. OUT ) Length variation of tapered input waveguide;

[0047] Figure 8 The optical power (P) at the output of the optical multimode interference coupler is calculated when the input light wavelength is 1.55 μm. OUT ) Plot showing the variation of multimode waveguide length with strip structure;

[0048] Figure 9 The optical power (P) at the output of the optical multimode interference coupler is calculated when the input light wavelength is 1.55 μm. OUT The length of the tapered, gradually tapered output waveguide varies with the slit structure. Detailed Implementation

[0049] To facilitate understanding of the present invention, a more comprehensive description of the invention will be provided below in conjunction with specific embodiments. Preferred embodiments of the invention are given in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0050] The order in which the embodiments are described below is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0051] This invention provides an optical multimode interference coupler, such as... Figures 1-4 As shown, it includes:

[0052] Substrate 1;

[0053] An optical waveguide is located on the surface of a substrate;

[0054] Cladding 2, which is located on the substrate surface and wraps the optical waveguide;

[0055] Among them, the optical waveguides, from signal input to output direction, include: a strip-shaped single-mode input waveguide 3, a tapered graded input waveguide 4, a strip-shaped multimode waveguide 5, a slit-shaped tapered graded output waveguide 6, and a slit-shaped output waveguide 7.

[0056] The tapered graded output waveguide 6 with slit structure includes a first low refractive index layer 61 and a first high refractive index layer 62 located on both sides of the first low refractive index layer 61.

[0057] The output waveguide 7 of the slit structure includes a second low-refractive-index layer 71 and a second high-refractive-index layer 72 located on both sides of the second low-refractive-index layer 71.

[0058] The axis of the first low-refractive-index layer 61 and the axis of the second low-refractive-index layer 71 are on the same horizontal line.

[0059] The width of the single-mode input waveguide 3 is equal to the minimum waveguide width of the tapered input waveguide 4;

[0060] The maximum waveguide width of the tapered input waveguide 4 is equal to the maximum waveguide width of the tapered output waveguide 6 with the slit structure;

[0061] The width of the output waveguide 7 of the slit structure is equal to the minimum waveguide width of the gradient output waveguide 6 of the slit structure.

[0062] The optical multimode interference coupler of the present invention includes a substrate 1, an optical waveguide, and a cladding 2. The optical waveguide is located on the surface of the substrate 1, and the cladding 2 is also located on the surface of the substrate 1, completely covering the optical waveguide. The optical waveguide, from signal input to output direction, includes, in sequence: a strip-shaped single-mode input waveguide 3, a tapered input waveguide 4, a strip-shaped multimode waveguide 5, a slit-shaped tapered output waveguide 6, and a slit-shaped output waveguide 7. Specifically, the cross-section of the strip-shaped single-mode input waveguide 3 is rectangular (i.e., cuboid structure); the cross-section of the tapered input waveguide 4 is trapezoidal, with one end wider and the other end narrower, and the narrow end of the tapered input waveguide 4 intersecting the strip-shaped multimode waveguide 5. The single-mode input waveguide 3 of the structure is connected, and its wide end is connected to the multimode waveguide 5 of the strip structure. The narrow end of the tapered input waveguide 4 has the same width as the single-mode input waveguide 3 of the strip structure. The tapered output waveguide 6 of the slit structure has a trapezoidal cross-section, and is wide at one end and narrow at the other. The output waveguide 7 of the slit structure has a rectangular cross-section (i.e., a cuboid structure). The wide end of the tapered output waveguide 6 of the slit structure is connected to the multimode waveguide 5 of the strip structure, and the narrow end is connected to the output waveguide 7 of the slit structure. The narrow end of the tapered output waveguide 6 of the slit structure has the same width as the output waveguide 7 of the slit structure.

[0063] The tapered, tapered output waveguide 6 with a slit structure includes a first low-refractive-index layer 61 and first high-refractive-index layers 62 located on both sides of the first low-refractive-index layer 61; the slit is located between the two first high-refractive-index layers 62. The output waveguide 7 with a slit structure includes a second low-refractive-index layer 71 and second high-refractive-index layers 72 located on both sides of the second low-refractive-index layer 71; the slit is located between the two second high-refractive-index layers 72. The axis of the first low-refractive-index layer 61 and the axis of the second low-refractive-index layer 71 are on the same horizontal line, and the width of the axis of the first low-refractive-index layer 61 and the width of the second low-refractive-index layer 71 are the same (i.e., the two slits have the same width and are located on the same horizontal line).

[0064] The width of the single-mode input waveguide 3 is equal to the minimum waveguide width of the tapered input waveguide 4, that is, the width of the narrow end of the tapered input waveguide 4 is the same as the width of the strip-shaped single-mode input waveguide 3.

[0065] The maximum waveguide width of the tapered input waveguide 4 is equal to the maximum waveguide width of the tapered output waveguide 6 with the slit structure, that is, the width of the wide end of the tapered input waveguide 4 is the same as the width of the wide end of the tapered output waveguide 6.

[0066] The width of the output waveguide 7 of the slit structure is equal to the minimum waveguide width of the tapered output waveguide 6 of the slit structure, that is, the width of the narrow end of the tapered output waveguide 6 of the slit structure is the same as the width of the output waveguide 7 of the slit structure.

[0067] This invention directly connects the slit-structured transmission waveguide to the interface of the strip-shaped multimode waveguide. Based on the multimode excitation principle and self-image principle of the multimode interference coupler, the optical signal within the strip-structured multimode waveguide simultaneously completes beam splitting and waveguide structure transformation at the interface within the slit-structured single-mode waveguide. This eliminates the need for the traditional tapered strip slit waveguide conversion structure, effectively reducing the length of electronic components and improving device integration. This invention enables the input optical signal to be directly and evenly split from the strip waveguide into the two slit waveguides, eliminating the need for the traditional combination structure of beam splitting followed by conversion. Furthermore, the device boasts advantages such as small size, low loss, and high bandwidth.

[0068] Specifically, the slit-structured transmission waveguide is directly connected to the strip-shaped multimode waveguide interface. Based on the multimode excitation principle of the multimode interference coupler, when the optical signal enters the multimode waveguide from the input waveguide, it excites multiple guided modes in the multimode waveguide. Each excited mode propagates forward with its own independent propagation constant. Due to the different propagation constants, a corresponding phase difference is generated during propagation. These modes with different phases propagate in the multimode waveguide and superimpose and interfere with each other. Due to the interference effect, the optical field periodically reproduces the spot of the input field at specific locations. For this invention, at a specific length (i.e., the degree of the strip-shaped multimode waveguide 5 of this invention), the optical signal will interfere to form two equally spaced and equally energetic optical signals, which is the self-image principle. Based on the multimode excitation principle and the self-image principle, the optical signal is evenly split into two centrally symmetrical optical signals at the interface connecting the strip-shaped multimode waveguide and the slit-shaped single-mode waveguide, and then transmitted to the two slit-shaped single-mode waveguides. This process simultaneously completes the beam splitting within the waveguide and the transformation of the waveguide structure.

[0069] In some embodiments, the materials of the strip-shaped single-mode input waveguide 3, the tapered taper input waveguide 4, and the strip-shaped multimode waveguide 5 are all silicon.

[0070] The first high refractive index layer 62 and the second high refractive index layer 72 are both made of silicon with a refractive index of 3.4.

[0071] The first low-refractive-index layer 61 and the second low-refractive-index layer 71 are both made of silicon dioxide with a refractive index of 1.44.

[0072] In some embodiments, the widths of the first low-refractive-index layer 61 and the second low-refractive-index layer 71 are the same.

[0073] The widths of the first low-refractive-index layer 61 and the second low-refractive-index layer 71 are 0.01 to 0.1 μm, which means that the width of the output waveguide 7 of the slit structure and the slit width of the gradient output waveguide 6 of the slit structure are 0.01 to 0.1 μm.

[0074] The axes of the single-mode input waveguide 3 (strip structure), the tapered input waveguide 4, and the multimode waveguide 5 (strip structure) are on the same horizontal line.

[0075] In some embodiments, the width of the strip-shaped input waveguide 3 is 0.4–0.6 μm and the length is 4–10 μm.

[0076] In some embodiments, the tapered input waveguide 4 has a maximum waveguide width of 0.8–1.2 μm and a length of 2–5 μm.

[0077] In some embodiments, the length of the strip-shaped multimode waveguide 5 is 8–12 μm and the width is 2.8–3.5 μm.

[0078] In some embodiments, the length of the tapered, tapered output waveguide 6 of the slit structure is 14–20 μm;

[0079] The output waveguide 7 of the slit structure has a length of 4–10 μm and a width of 0.4–0.7 μm.

[0080] In some embodiments, the optical multimode interference coupler is a 1×2 coupler; the number of the strip-structured single-mode input waveguide 3, the tapered input waveguide 4, and the strip-structured multimode waveguide 5 is all 1;

[0081] The number of both the tapered, tapered output waveguide 6 and the output waveguide 7 of the slit structure is 2; further as... Figure 1 As shown, the two tapered graded output waveguides 6 with slit structures and the two output waveguides 7 with slit structures are symmetrically distributed above and below the transverse central axis of the strip structure multimode waveguide 5.

[0082] The transverse central axis of the strip-structured single-mode input waveguide and the tapered taper input waveguide are on the same horizontal line as the transverse central axis of the strip-structured multimode waveguide;

[0083] The distances between the first and second high-refractive-index layers and the transverse central axis of the multimode waveguide of the strip structure are 0.8–0.9 μm.

[0084] In some embodiments, the two first high refractive index layers 62 are symmetrically distributed vertically relative to the transverse central axis of the first low refractive index layer 61, and the two second high refractive index layers 72 are symmetrically distributed vertically relative to the transverse central axis of the second low refractive index layer 71.

[0085] In some embodiments, the thicknesses of the strip-structured single-mode input waveguide 3, the tapered graded input waveguide 4, the strip-structured multimode waveguide 5, the slit-structured tapered graded output waveguide 6, and the slit-structured output waveguide 7 are all 0.2–0.3 μm.

[0086] In some embodiments, substrate 1 is an SOI substrate; specifically, the SOI substrate includes a Si substrate 11 and a silicon dioxide layer 12 located on the Si substrate 11.

[0087] The material of cladding layer 2 is silicon dioxide.

[0088] In some embodiments, the Si substrate 11 has a thickness of 700–775 μm, the silicon dioxide layer 12 has a thickness of 2–3 μm, and the cladding layer 2 has a thickness of 1.5–2.5 μm.

[0089] The following further describes the optical multimode interference coupler of the present invention. This section, in conjunction with specific embodiments, further illustrates the content of the present invention, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0090] Example 1

[0091] This embodiment provides an optical multimode interference coupler, which is a 1×2 coupler, including:

[0092] Substrate; The substrate is an SOI substrate; Specifically, the SOI substrate includes a Si substrate and a silicon dioxide layer on the Si substrate. The Si substrate has a thickness of 700 μm, and the silicon dioxide layer has a thickness of 2 μm.

[0093] An optical waveguide is located on the surface of a substrate;

[0094] The cladding layer is located on the substrate surface and wraps around the optical waveguide; the cladding layer is made of silicon dioxide; the thickness of the cladding layer is 2 μm.

[0095] The optical waveguides, from signal input to output, sequentially include: a single-mode input waveguide with a strip structure, a tapered input waveguide with a tapered shape, a multimode waveguide with a strip structure, a tapered output waveguide with a slit structure, and an output waveguide with a slit structure.

[0096] The tapered graded output waveguide with a slit structure includes a first low-refractive-index layer and a first high-refractive-index layer located on both sides of the first low-refractive-index layer.

[0097] The output waveguide of the slit structure includes a second low-refractive-index layer and a second high-refractive-index layer located on both sides of the second low-refractive-index layer;

[0098] The axis of the first low-refractive-index layer and the axis of the second low-refractive-index layer are on the same horizontal line;

[0099] The width of the strip-shaped single-mode input waveguide is equal to the minimum waveguide width of the tapered input waveguide;

[0100] The maximum waveguide width of the tapered input waveguide is equal to the maximum waveguide width of the tapered output waveguide with the slit structure.

[0101] The output waveguide width of the slit structure is equal to the minimum waveguide width of the tapered output waveguide of the slit structure;

[0102] The materials of the strip-structured single-mode input waveguide, the tapered graded input waveguide, the strip-structured multimode waveguide, the first high-refractive-index layer, and the second high-refractive-index layer are all silicon, with a refractive index of 3.4.

[0103] The first and second low-refractive-index layers are both made of silicon dioxide with a refractive index of 1.44.

[0104] The widths of the first low-refractive-index layer and the second low-refractive-index layer are the same; the widths of the first low-refractive-index layer and the second low-refractive-index layer are both 0.05 μm, which means that the width of the output waveguide of the slit structure is the same as the slit width of the graded output waveguide of the slit structure.

[0105] The input waveguide of the strip structure has a width of 0.5 μm, a length of 5 μm, and a height (i.e., thickness) of 0.22 μm;

[0106] The tapered input waveguide has a maximum waveguide width of 1.2 μm, a length of 3.4 μm, and a height (i.e., thickness) of 0.22 μm.

[0107] The length of the strip-shaped multimode waveguide is preset to be 9.375 μm, the width to be 3.2 μm, and the height (i.e., the thickness) to be 0.22 μm;

[0108] The tapered output waveguide with slit structure has a preset length of 17μm, a height (i.e., thickness) of 0.22μm, and a minimum width of 0.55μm.

[0109] The output waveguide of the slit structure has a length of 7 μm, a height (i.e., thickness) of 0.22 μm, and a width of 0.55 μm;

[0110] The number of single-mode input waveguides with strip structure, tapered input waveguides, and multimode waveguides with strip structure is all 1;

[0111] The number of tapered output waveguides in the slit structure and the number of output waveguides in the slit structure are both 2; further as... Figure 1 As shown, the two tapered output waveguides with slit structures and the two output waveguides with slit structures are symmetrically distributed vertically relative to the transverse central axis of the strip structure multimode waveguide.

[0112] The transverse central axis of the strip-structured single-mode input waveguide and the tapered taper input waveguide are on the same horizontal line as the transverse central axis of the strip-structured multimode waveguide;

[0113] The distance between the first and second high-refractive-index layers and the transverse central axis of the multimode waveguide of the strip structure is 0.8 μm.

[0114] The two first high refractive index layers are symmetrically distributed vertically relative to the transverse central axis of the first low refractive index layer, and the two second high refractive index layers are symmetrically distributed vertically relative to the transverse central axis of the second low refractive index layer.

[0115] The multimode interference coupler in Example 1 was simulated using the Eigenmode expansion method (EME) in the commercial numerical calculation software Lumerical Mode. When light (wavelength 1.55 μm) is input in the fundamental mode from the single-mode input waveguide of the strip structure, the optical field transmission diagram can be obtained after calculation by the EME solver, as shown below. Figure 5 As shown. Figure 5 The units of the horizontal and vertical coordinates are both in meters (m). The origin of the vertical coordinate (y) is the intersection of the horizontal central axis of the single-mode input waveguide and its edge in the strip structure, and the origin of the horizontal coordinate (x) is the center of the multimode waveguide in the strip structure.

[0116] Depend on Figure 5 As can be seen, light enters from the single-mode input waveguide of the strip structure, passes through the tapered waveguide, and is excited into multiple modes at the multimode waveguide of the strip structure. These modes interfere and superimpose with each other, splitting into two beams of equal energy that enter the tapered output waveguide and the output waveguide of the slit structure, respectively. In this process, this embodiment successfully splits the input light from the single-mode input waveguide of the strip structure into two beams of equal energy that exit from the output waveguide of the slit structure with minimal energy leakage.

[0117] Figure 6 To simulate the multimode interference coupler in Example 1 using the eigenmode expansion method (EME) in the commercial numerical calculation software Lumerical Mode, the additional loss was calculated under different input light wavelengths (1.40–1.65 μm). The results are as follows: Figure 6 As shown. The additional loss is calculated as follows: EL(dB)=-10lg(∑P OUT / P IN ), where EL(dB) is the additional loss, ∑P OUT P is the sum of the optical power at all output ports of the coupler (in Example 1, the coupler has two output ports). IN This represents the optical power at the input of the coupler.

[0118] Depend on Figure 6It can be seen that, with an input light wavelength of 1.55 μm, the coupler in Example 1 has the lowest additional loss of 0.265 dB, and the additional loss is less than 0.5 dB within a bandwidth of 0.2 μm (1.43 to 1.63 μm).

[0119] Based on Example 1, only the length of the tapered input waveguide (1-5 μm) is changed; all other parameters of the coupler remain the same as in Example 1. With an input light wavelength of 1.55 μm, the output optical power (P) is... OUT The length of the tapered input waveguide varies as follows: Figure 7 As shown; Figure 7 Optical power (P) at the output of the middle vertical axis OUT ) represents the optical power at a single output terminal of the coupler, and the total input power of the coupler is denoted as 1.

[0120] Based on Example 1, only the length of the strip-structured multimode waveguide (1–30 μm) is changed; all other parameters of the coupler remain the same as in Example 1. With an input light wavelength of 1.55 μm, the output optical power (P) is... OUT The length of the multimode waveguide varies with the strip structure, as shown below. Figure 8 As shown; Figure 8 Optical power (P) at the output of the middle vertical axis OUT ) represents the optical power at a single output terminal of the coupler, and the total input power of the coupler is denoted as 1.

[0121] Based on Example 1, only the length of the tapered output waveguide of the slit structure is changed (1-30 μm), while all other parameters of the coupler remain the same as in Example 1. With an input light wavelength of 1.55 μm, the output optical power (P) is... OUT The length of the tapered, gradually tapered output waveguide of the slit structure varies as follows: Figure 9 As shown; Figure 9 Optical power (P) at the output of the middle vertical axis OUT ) represents the optical power at a single output terminal of the coupler, and the total input power of the coupler is denoted as 1.

[0122] from Figure 7 As can be seen, the optical power at the output of the coupler is the maximum when the length of the tapered input waveguide is 2.1 μm.

[0123] from Figure 8 As can be seen, the optical power at the output of the coupler is the largest when the length of the multimode waveguide with the strip structure is 9.4 μm.

[0124] from Figure 9 As can be seen, the optical power at the output of the coupler is the maximum when the length of the tapered output waveguide of the slit structure is 17.5 μm.

[0125] In summary, this invention not only enables the input optical signal to be directly and evenly distributed from the strip waveguide to the two slit waveguides, but also has the advantages of low loss and high bandwidth.

[0126] It is understood that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0127] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. An optical multimode interference coupler, characterized in that, include: Substrate; An optical waveguide located on the surface of the substrate; A cladding layer, which is located on the surface of the substrate and wraps around the optical waveguide; The optical waveguide, from signal input to output direction, includes, in sequence: a single-mode input waveguide with a strip structure, a tapered input waveguide with a tapered shape, a multimode waveguide with a strip structure, a tapered output waveguide with a slit structure, and an output waveguide with a slit structure. The tapered gradient output waveguide of the slit structure includes a first low refractive index layer and a first high refractive index layer located on both sides of the first low refractive index layer. The two first high refractive index layers are distributed vertically relative to the transverse central axis of the first low refractive index layer. The output waveguide of the slit structure includes a second low-refractive-index layer and a second high-refractive-index layer located on both sides of the second low-refractive-index layer. The two second high-refractive-index layers are distributed vertically relative to the transverse central axis of the second low-refractive-index layer. The axis of the first low-refractive-index layer and the axis of the second low-refractive-index layer are on the same horizontal line; The width of the single-mode input waveguide is equal to the minimum waveguide width of the tapered input waveguide; The maximum waveguide width of the tapered input waveguide is equal to the maximum waveguide width of the tapered output waveguide of the slit structure. The output waveguide width of the slit structure is equal to the minimum waveguide width of the gradient output waveguide of the slit structure. The tapered input waveguide and the tapered output waveguide of the slit structure are located on the left and right sides of the multimode waveguide of the strip structure, respectively, and are directly connected to the multimode waveguide of the strip structure.

2. The optical multimode interference coupler as described in claim 1, characterized in that, The materials for the strip-structured single-mode input waveguide, the tapered input waveguide, and the strip-structured multimode waveguide are all silicon. Both the first high-refractive-index layer and the second high-refractive-index layer are made of silicon. The materials of the first low-refractive-index layer and the second low-refractive-index layer are both silicon dioxide.

3. The optical multimode interference coupler as described in claim 1, characterized in that, The first low-refractive-index layer and the second low-refractive-index layer have the same width; The widths of the first low-refractive-index layer and the second low-refractive-index layer are 0.01~0.1μm.

4. The optical multimode interference coupler as described in claim 1, characterized in that, The input waveguide width of the strip structure is 0.4~0.6μm and the length is 4~10μm.

5. The optical multimode interference coupler as described in claim 1, characterized in that, The tapered input waveguide has a maximum waveguide width of 0.8~1.2μm and a length of 2~5μm.

6. The optical multimode interference coupler as described in claim 1, characterized in that, The length of the strip-shaped multimode waveguide is 8~12μm and the width is 2.8~3.5μm.

7. The optical multimode interference coupler as described in claim 1, characterized in that, The tapered, tapered output waveguide of the slit structure has a length of 14~20μm; The output waveguide of the slit structure has a length of 4~10μm and a width of 0.4~0.7μm.

8. The optical multimode interference coupler as described in claim 1, characterized in that, The optical multimode interference coupler is a 1×2 coupler; The number of the single-mode input waveguide with strip structure, the tapered input waveguide, and the multimode waveguide with strip structure are all 1; The number of tapered graded output waveguides in the slit structure and the number of output waveguides in the slit structure are both 2; The two tapered output waveguides of the slit structure and the two output waveguides of the slit structure are symmetrically distributed vertically relative to the transverse central axis of the multimode waveguide of the strip structure; The transverse central axis of the single-mode input waveguide and the tapered input waveguide of the strip structure is on the same horizontal line as the transverse central axis of the multimode waveguide of the strip structure. The distances between the first high-refractive-index layer and the second high-refractive-index layer and the transverse central axis of the multimode waveguide of the strip structure are 0.8~0.9μm; The two first high refractive index layers are symmetrically distributed vertically relative to the transverse central axis of the first low refractive index layer, and the two second high refractive index layers are symmetrically distributed vertically relative to the transverse central axis of the second low refractive index layer.

9. The optical multimode interference coupler as described in claim 1, characterized in that, The thicknesses of the single-mode input waveguide with strip structure, the tapered input waveguide with tapered shape, the multimode waveguide with strip structure, the tapered output waveguide with slit structure, and the output waveguide with slit structure are all 0.2~0.3μm.

10. The optical multimode interference coupler as described in claim 1, characterized in that, The substrate is an SOI substrate; The cladding material is silicon dioxide.

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