Optical multimode interference coupler

Abstract

The invention provides an optical multimode interference coupler. According to the optical multi-mode interference coupler, the transmission waveguide of the slit structure is directly connected with the interface of the strip-shaped multi-mode waveguide, and based on the multi-mode excitation principle and the self-imaging principle of the multi-mode interference coupler, optical signals in the strip-shaped multi-mode waveguide are located at the interface in the slit single-mode waveguide; light splitting in the waveguide and transformation of a waveguide structure are completed at the same time, a traditional gradual deformation strip slit waveguide conversion structure does not need to be used, the length of an electronic component is effectively reduced, and the integration level of the device is improved. According to the invention, an input optical signal can be directly and equally divided into the two slit waveguides from the strip-shaped waveguide, and a traditional combined structure of first light splitting and then conversion is not needed. And the device has the advantages of small size, low loss, high bandwidth and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical communication, and particularly relates to an optical multimode interference coupler. BACKGROUND

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

[0003] In existing optical switch modulation devices, a transition structure of a strip waveguide and a slot waveguide is often used to connect a strip optical beam splitter, a strip optical beam combiner and a slot modulation arm waveguide. Therefore, a large number of transition structures of strip waveguides and slot waveguides are needed in the optical chip, which reduces the integration of the photonics chip. SUMMARY

[0004] In order to solve the defects in the prior art, the application provides an optical multimode interference coupler to solve the problem of low integration of the optical chip in the prior art.

[0005] The application adopts the following technical scheme:

[0006] The application provides an optical multimode interference coupler, which comprises:

[0007] a substrate;

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

[0009] a cladding layer located on the surface of the substrate and wrapping the optical waveguide;

[0010] The optical waveguide comprises, in sequence from the signal input to the output direction, a single-mode input waveguide with a strip structure, a tapered input waveguide, a multimode waveguide with a strip structure, a tapered output waveguide with a slot structure, and an output waveguide with a slot structure.

[0011] The tapered output waveguide with a slot structure comprises a first low refractive index layer and first high refractive index layers located on both sides of the first low refractive index layer.

[0012] The output waveguide with a slot structure comprises a second low refractive index layer and second high refractive index layers located on both sides of the second low refractive index layer.

[0013] The axis of the first low refractive index layer is on the same horizontal line as the axis of the second low refractive index layer.

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

[0015] the maximum waveguide width of the tapering input waveguide of the strip structure is equal to the maximum waveguide width of the tapering output waveguide of the strip structure;

[0016] the output waveguide width of the strip structure is equal to the minimum waveguide width of the tapering output waveguide of the strip structure.

[0017] Preferably, the materials of the single-mode input waveguide, the tapering input waveguide, and the multi-mode waveguide of the strip structure are all silicon;

[0018] the materials of the first high-refractive-index layer and the second high-refractive-index layer are both 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 width of the input waveguide of the strip structure is 0.4-0.6 μm, and the length is 4-10 μm.

[0023] Preferably, the maximum waveguide width of the tapering input waveguide is 0.8-1.2 μm, and the length is 2-5 μm.

[0024] Preferably, the length of the multi-mode waveguide of the strip structure is 8-12 μm, and the width is 2.8-3.5 μm.

[0025] Preferably, the length of the tapering output waveguide of the strip structure is 14-20 μm.

[0026] the length of the output waveguide of the strip structure is 4-10 μm, and the width is 0.4-0.7 μm.

[0027] Preferably, the optical multi-mode interference coupler is a 1x2 coupler.

[0028] the number of the single-mode input waveguide, the tapering input waveguide, and the multi-mode waveguide of the strip structure is all 1;

[0029] the number of the tapering output waveguide of the strip structure and the output waveguide of the strip structure is both 2;

[0030] The two tapering output waveguides with the slit structure and the two output waveguides with the slit structure are symmetrically distributed above and below the transverse central axis of the multi-mode waveguide with the strip structure;

[0031] The transverse central axes of the single-mode input waveguide and the tapering input waveguide with the strip structure are on the same horizontal line with the transverse central axis of the multi-mode waveguide with 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 multi-mode waveguide with the strip structure are 0.8-0.9 μm;

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

[0034] Preferably, the thicknesses of the single-mode input waveguide and the tapering input waveguide with the strip structure, the multi-mode waveguide with the strip structure, the tapering output waveguide with the slit structure and the output waveguide with the slit structure are all 0.2-0.3 μm.

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

[0036] The cladding material is silicon dioxide.

[0037] Compared with the prior art, the optical multi-mode interference coupler has the following effects:

[0038] The optical multi-mode interference coupler directly connects the transmission waveguide with the slit structure and the multi-mode waveguide with the strip structure at the interface, based on the multi-mode excitation principle and the self-mirroring principle of the multi-mode interference coupler, so that the light signal in the multi-mode waveguide with the strip structure is simultaneously split in the waveguide and the waveguide structure is converted at the interface in the slit single-mode waveguide, without using the traditional tapering strip-slit waveguide conversion structure, effectively reducing the length of the electronic component and improving the integration of the component. The input light signal can be directly and evenly divided into two slit waveguides without the traditional combination structure of splitting light and then converting. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0040] Figure 1A top view of the optical waveguide of the present application;

[0041] Figure 2 A schematic diagram of the three-dimensional structure of the optical waveguide of the present application;

[0042] Figure 3 A schematic diagram of the structure of the input optical signal direction of the optical multimode interference coupler of the present application;

[0043] Figure 4 A schematic diagram of the structure of the output optical signal direction of the optical multimode interference coupler of the present application;

[0044] Figure 5 A schematic diagram of the optical field propagation distribution of the optical multimode interference coupler of the present application in Example 1;

[0045] Figure 6 The additional loss of the optical multimode interference coupler of the present application in Example 1 under different optical wavelength propagation;

[0046] Figure 7 A graph showing the change of the optical power (P OUT ) at the output end of the optical multimode interference coupler with the length of the tapered input waveguide when the input optical wavelength is 1.55 μm;

[0047] Figure 8 A graph showing the change of the optical power (P OUT ) at the output end of the optical multimode interference coupler with the length of the strip-shaped multimode waveguide when the input optical wavelength is 1.55 μm;

[0048] Figure 9 A graph showing the change of the optical power (P OUT ) at the output end of the optical multimode interference coupler with the length of the slit-shaped tapered output waveguide when the input optical wavelength is 1.55 μm. DETAILED DESCRIPTION

[0049] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the specific embodiments. The preferred embodiments of the present application are given in the specific embodiments. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0050] The order of description of the following embodiments is not intended to imply a preference. Also, in the description of the present application, the term "including" means "including but not limited to". Various embodiments of the present application can exist in a range of forms; it should be understood that the description in a range form is merely for convenience and brevity, and should not be construed as a hard limitation on the scope of the present application; therefore, it should be considered that all possible sub-ranges and single values within the range have been specifically disclosed. 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., as well as single values within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0051] The present application provides an optical multi-mode interference coupler, such as Figures 1-4 as shown, comprising:

[0052] a substrate 1;

[0053] an optical waveguide located on the surface of the substrate;

[0054] a cladding layer 2 located on the surface of the substrate and wrapping the optical waveguide;

[0055] wherein the optical waveguide comprises, in order from the signal input to the output direction, a single-mode input waveguide 3 of strip structure, a tapered input waveguide 4 of strip structure, a multi-mode waveguide 5 of strip structure, a tapered output waveguide 6 of slit structure, and an output waveguide 7 of slit structure;

[0056] the tapered output waveguide 6 of slit structure comprises 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 slit structure comprises 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 is on the same horizontal line as the axis of the second low refractive index layer 71;

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

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

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

[0062] The optical multimode interference coupler of the present application comprises 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 and completely covers the optical waveguide; the optical waveguide comprises, in sequence from the signal input to the output direction, a single-mode input waveguide 3 of a strip structure, a tapered input waveguide 4, a multimode waveguide 5 of a strip structure, a tapered output waveguide 6 of a slit structure and an output waveguide 7 of a slit structure; specifically, the cross section of the single-mode input waveguide 3 of a strip structure is rectangular (i.e. cuboid structure); the cross section of the tapered input waveguide 4 is trapezoidal, the tapered input waveguide 4 is wide at one end and narrow at the other end, the narrow end of the tapered input waveguide 4 is connected with the single-mode input waveguide 3 of a strip structure, and the wide end is connected with the multimode waveguide 5 of a strip structure; the width of the narrow end of the tapered input waveguide 4 is the same as the width of the single-mode input waveguide 3 of a strip structure; the cross section of the tapered output waveguide 6 of a slit structure is trapezoidal, the tapered output waveguide 6 of a slit structure is wide at one end and narrow at the other end; the cross section of the output waveguide 7 of a slit structure is rectangular (i.e. cuboid structure); the wide end of the tapered output waveguide 6 of a slit structure is connected with the multimode waveguide 5 of a strip structure, and the narrow end is connected with the output waveguide 7 of a slit structure; the width of the narrow end of the tapered output waveguide 6 of a slit structure is the same as the width of the output waveguide 7 of a slit structure.

[0063] The tapered output waveguide 6 of a slit structure comprises 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; the two first high refractive index layers 62 are the slits; the output waveguide 7 of a slit structure comprises 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; the two second high refractive index layers 72 are the slits; the axis of the first low refractive index layer 61 is on the same horizontal line as the axis of the second low refractive index layer 71, and the width of the first low refractive index layer 61 is the same as the width of the second low refractive index layer 71 (i.e. the two slit widths are the same and are 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, i.e. the width of the narrow end of the tapered input waveguide 4 is the same as the width of the single-mode input waveguide 3 of a strip structure;

[0065] The maximum waveguide width of the tapered input waveguide 4 is equal to the maximum waveguide width of the tapered output waveguide 6 of a slit structure, i.e. 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 of a slit structure;

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

[0067] The present application directly connects the transmission waveguide with a slit structure to the bar-shaped multimode waveguide at the interface, based on the multimode excitation principle and self-imaging principle of the multimode interference coupler, so that 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 the traditional tapered slit waveguide conversion structure, effectively reducing the length of the electronic components and improving the integration of the device; the present application realizes that the input optical signal can be directly and evenly divided into two slit waveguides without the traditional combination structure of splitting and then converting.

[0068] Specifically, the transmission waveguide with a slit structure is directly connected to the bar-shaped multimode waveguide at the 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 will excite multiple guided modes in the multimode waveguide, each excited mode propagates forward with its own separate propagation constant, and due to the difference in the propagation constant, it will cause a corresponding phase difference in the propagation process. These different phase modes propagate and interfere with each other in the multimode waveguide. Due to the interference effect, the light field will periodically reproduce the input field spot at a specific location. For the present application, at a specific length (i.e. the length of the bar-shaped multimode waveguide 5 of the present application), the optical signal will interfere to form two equally spaced and equal energy optical signals, which is the self-imaging principle. Based on the multimode excitation principle and the self-imaging principle, the optical signal is evenly divided into two center-symmetric optical signals at the interface where the bar-shaped multimode waveguide and the slit single-mode waveguide are connected, and then transmitted into the two slit single-mode waveguides, which simultaneously completes the splitting of the waveguide and the conversion of the waveguide structure.

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

[0070] The materials of the first high-refractive-index layer 62 and the second high-refractive-index layer 72 are both silicon, and the refractive index is 3.4;

[0071] The materials of the first low-refractive-index layer 61 and the second low-refractive-index layer 71 are both silicon dioxide, and the refractive index is 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 0.01-0.1 μm, i.e. the width of the output waveguide 7 with a slit structure and the slit width of the tapered output waveguide 6 with a slit structure are 0.01-0.1 μm.

[0074] The single-mode input waveguide 3 of the strip structure, the tapered input waveguide 4, and the multi-mode waveguide 5 of the strip structure have their axes on the same horizontal line.

[0075] In some embodiments, the single-mode input waveguide 3 of the strip structure has a width of 0.4-0.6 μm and a length of 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 multi-mode waveguide 5 of the strip structure has a length of 8-12 μm and a width of 2.8-3.5 μm.

[0078] In some embodiments, the tapered output waveguide 6 of the slit structure has a length of 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 multi-mode interference coupler is a 1x2 coupler; the single-mode input waveguide 3 of the strip structure, the tapered input waveguide 4, and the multi-mode waveguide 5 of the strip structure each have a quantity of 1.

[0081] The tapered output waveguide 6 of the slit structure and the output waveguide 7 of the slit structure each have a quantity of 2; further as shown in Figure 1 the 2 tapered output waveguides 6 of the slit structure and the 2 output waveguides 7 of the slit structure are symmetrically distributed above and below the transverse central axis of the multi-mode waveguide 5 of the strip structure;

[0082] The transverse central axes of the single-mode input waveguide of the strip structure and the tapered input waveguide of the strip structure are on the same horizontal line as the transverse central axis of the multi-mode waveguide of the strip structure.

[0083] The first high-refractive-index layer and the second high-refractive-index layer are each 0.8-0.9 μm away from the transverse central axis of the multi-mode waveguide of the strip structure.

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

[0085] In some embodiments, the single-mode input waveguide 3 of the strip structure, the tapered input waveguide 4, the multi-mode waveguide 5 of the strip structure, the tapered output waveguide 6 of the slit structure, and the output waveguide 7 of the slit structure each have a thickness of 0.2-0.3 μm.

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

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

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

[0089] The following further describes the optical multimode interference coupler of the present application, and this part further describes the content of the present application in conjunction with specific embodiments, but should not be understood as a limitation of the present application. Unless otherwise specified, the technical means used in the embodiments are conventional means known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the art.

[0090] Embodiment 1

[0091] The present embodiment provides an optical multimode interference coupler, which is a 1x2 coupler, comprising:

[0092] A substrate; the substrate is an SOI substrate; a specific SOI substrate includes a Si substrate and a silicon dioxide layer on the Si substrate, the thickness of the Si substrate is 700 μm, and the thickness of the silicon dioxide layer is 2 μm;

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

[0094] A cladding layer on the surface of the substrate and wrapping the optical waveguide; the material of the cladding layer is silicon dioxide; the thickness of the cladding layer is 2 μm;

[0095] The optical waveguide includes, in order from the signal input to the output direction, a single-mode input waveguide of a strip structure, a tapered input waveguide, a multimode waveguide of a strip structure, a tapered output waveguide of a slit structure, and an output waveguide of a slit structure.

[0096] The tapered output waveguide of a slit structure includes a first low refractive index layer and first high refractive index layers on both sides of the first low refractive index layer;

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

[0098] The axis of the first low refractive index layer is on the same horizontal line as the axis of the second low refractive index layer;

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

[0100] The maximum waveguide width of the tapering input waveguide is equal to the maximum waveguide width of the tapering output waveguide of the slit structure;

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

[0102] The materials of the single-mode input waveguide of the bar structure, the tapering input waveguide, the multi-mode waveguide of the bar structure, the first high refractive index layer, and the second high refractive index layer are all silicon, and the refractive index is 3.4;

[0103] The materials of the first low refractive index layer and the second low refractive index layer are both silicon dioxide, and the refractive index is 1.44;

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

[0105] The input waveguide of the bar 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 maximum waveguide width of the tapering input waveguide is 1.2 μm, the length is 3.4 μm, and the height (i.e., thickness) is 0.22 μm;

[0107] The multi-mode waveguide of the bar structure has a length of 9.375 μm, a width of 3.2 μm, and a height (i.e., thickness) of 0.22 μm;

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

[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 the single-mode input waveguide of the bar structure, the tapering input waveguide, and the multi-mode waveguide of the bar structure is all 1;

[0111] The number of the tapering output waveguide of the slit structure and the output waveguide of the slit structure is both 2; further as shown in the figure, the two tapering output waveguides of the slit structure and the two output waveguides of the slit structure are symmetrically distributed above and below the transverse central axis of the multi-mode waveguide of the bar structure; Figure 1

[0112] The transverse central axes of the single-mode input waveguide of the bar structure and the tapering input waveguide are on the same horizontal line as the transverse central axis of the multi-mode waveguide of the bar structure; ​

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

[0114] Both of the first high refractive index layers are symmetrically distributed above and below the transverse central axis of the first low refractive index layer, and both of the second high refractive index layers are symmetrically distributed above and below the transverse central axis of the second low refractive index layer.

[0115] The multi-mode interference coupler in Example 1 is simulated and calculated by using Eigenmode expansion method (EME) in commercial numerical calculation software lumerical mode, and the light field transmission diagram can be obtained by EME solver calculation when the light (the wavelength of the light is 1.55 μm) is input from the single-mode input waveguide of the strip structure in the fundamental mode, as shown in Figure 5 . Figure 5 The units of the transverse and longitudinal coordinates are both m, wherein the origin of the longitudinal coordinate (y) is the intersection of the transverse central axis of the single-mode input waveguide of the strip structure and its edge, and the origin of the transverse coordinate (x) is the central position of the multi-mode waveguide of the strip structure.

[0116] As can be seen from Figure 5 , the light is input from the single-mode input waveguide of the strip structure, passes through the tapered waveguide, is excited into multiple modes at the multi-mode waveguide of the strip structure, and is divided into two beams of the same energy after mutual interference and superposition, and then is output into the tapered output waveguide of the slit structure and the output waveguide of the slit structure. In this process, the input light is successfully divided into two beams of the same energy in this embodiment, and the light energy leakage is less.

[0117] Figure 6 In order to simulate and calculate the multi-mode interference coupler in Example 1 by using Eigenmode expansion method (EME) in commercial numerical calculation software lumerical mode, the additional loss under different input light wavelengths (1.40-1.65 μm) is scanned and calculated, and the obtained results are shown in Figure 6 . The calculation method of the additional loss is: EL (dB) = -10lg(∑P OUT / P IN ), wherein EL (dB) is the additional loss, ∑P OUT is the sum of the light powers of all output ports of the coupler (the coupler in Example 1 has two output ports), and P IN is the input light power of the coupler.

[0118] As can be seen from 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, 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 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 multimode waveguide with the strip 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 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, the application can not only realize the direct equal division of input optical signals from a strip waveguide into two slot waveguides, but also has the advantages of low loss and high bandwidth.

[0126] It can be understood that the technical features of the above-described embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, it should be considered that they are within the scope of the present disclosure.

[0127] The above is only a preferred embodiment of the present application, and only the technical principles of the present application are specifically described. These descriptions are only for the purpose of explaining the principles of the present application and cannot be interpreted in any way as a limitation on the scope of protection of the present application. Based on the explanations here, any modifications, equivalent replacements and improvements made within the spirit and principles of the present application, and other specific embodiments of the present application that can be easily conceived by those skilled in the art without creative labor, should be included within the scope of protection of the present 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, 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. 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 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.

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 0.01–0.1 μm.

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

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

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

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

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 0.8–0.9 μm; 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 0.2–0.3 μm.

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.

Images