Cross waveguide coupler insensitive to wavelength and polarization and preparation method thereof

Abstract

The invention relates to a crossed waveguide coupler insensitive to wavelength and polarization and a preparation method thereof. The crossed waveguide coupler comprises an input straight waveguide, a crossed waveguide, S-shaped bent waveguides and an output straight waveguide, and the crossed waveguide is formed by splicing and crossing a plurality of S-shaped bent waveguides; the curve profile of the S-shaped bent waveguide is formed by fitting through an optimization algorithm; by properly adjusting the direction and the position of the S-shaped bent waveguide in the crossed waveguide, light waves are input from any end of the input straight waveguide, and after the light waves are spread through the crossed waveguide, light power equalization is completed at the output straight waveguide. Compared with a traditional directional coupler, the crossed waveguide coupler provided by the invention is insensitive to wavelength and polarization, small in size, easy to process and low in insertion loss, and the preparation efficiency and the integration level of a photon chip are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated photonic chips, in particular to a wavelength and polarization insensitive cross waveguide coupler and a preparation method thereof. BACKGROUND

[0002] As one of the typical passive devices in integrated photonic chips, directional couplers are widely used in the field of integrated optoelectronics, such as electro-optic modulators, optical switches, quadrature detectors, beam splitters and other functional devices. However, the main problems faced by directional couplers include wavelength and polarization sensitivity, strict processing requirements for waveguide coupling pitch, large size and the like. Although researchers have continuously optimized the structure size of directional couplers, they cannot simultaneously solve the problems of wavelength and polarization sensitivity, difficulty in processing, large size and the like. Either polarization insensitive but large size, or polarization sensitive and strict processing conditions. Therefore, there is an urgent need for a solution that can simultaneously solve the problems of wavelength and polarization sensitivity, difficulty in processing, large size and the like. SUMMARY

[0003] In view of the deficiencies in the prior art, the purpose of the present application is to provide a wavelength and polarization insensitive cross waveguide coupler and a preparation method thereof.

[0004] In order to achieve the above-mentioned purpose, the technical scheme of the present application is a wavelength and polarization insensitive cross waveguide coupler and a preparation method thereof, specifically comprising:

[0005] The input straight waveguide, the cross waveguide, the S-shaped curved waveguide and the output straight waveguide are connected in series, and the cross waveguide is formed by splicing the S-shaped curved waveguides. The curve profile of the S-shaped curved waveguide is fitted by an optimization algorithm. By properly adjusting the direction and position of the S-shaped curved waveguide in the cross waveguide, the light wave is input from any one end of the input straight waveguide, propagates through the cross waveguide, and is evenly divided in the output straight waveguide.

[0006] Further, the plurality of S-shaped curved waveguides on any side of the cross waveguide are composed of, but not limited to, 2 S-shaped curved waveguides.

[0007] Further, the curve profile optimization algorithm of the S-shaped curved waveguide includes, but is not limited to, the adjoint method, particle swarm optimization, simulated annealing algorithm, genetic algorithm and deep learning neural network algorithm.

[0008] Further, the cross waveguide is insensitive to wavelength and polarization.

[0009] Further, the thin film material used in the cross waveguide coupler includes, but is not limited to, lithium niobate thin film material, silicon nitride thin film material and silicon thin film material.

[0010] A preparation method of a wavelength and polarization insensitive cross waveguide coupler, the specific steps of the method are:

[0011] Step one: implanting ion He + or Ar + into the thin film material with an energy of 30-90 keV, so that the Mohs hardness of the thin film material is reduced;

[0012] Step two: coating a layer of 300-600 nm thick mask material on the surface of the thin film to form a mask layer;

[0013] Step three: according to the cross waveguide coupler layout designed by simulation, a mask pattern of the cross waveguide coupler structure is prepared on the mask material by using a photolithography method;

[0014] Step four: a layer of foamed silica gel with a thickness of about 5-7 mm is laid under the polishing flannel, the exposed thin film material is first polished by using a coarse particle size silica abrasive polishing liquid for coarse chemical mechanical polishing (CMP), and then the exposed thin film material is polished by using a mixed particle size silica abrasive polishing liquid for fine chemical mechanical polishing (CMP), and finally the cross waveguide coupler structure with smooth surface and surface roughness of 0.1-0.2 nm is obtained.

[0015] Further, the mask material includes but is not limited to metal Cr film, Au film, and silica film.

[0016] Further, the photolithography method includes but is not limited to femtosecond laser direct writing photolithography, projection photolithography, and step photolithography.

[0017] Further, the polishing flannel includes but is not limited to swan flannel and damping cloth; the coarse particle size silica abrasive polishing liquid has a particle size distribution of 80-150 nm; and the mixed particle size silica abrasive polishing liquid has mixed particle sizes of 120 nm and 20 nm, and a mixed mass ratio of 3:1.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] (1) The present application has simple structure, easy processing, small size, easy large-scale optoelectronic integration, and is applied to a microlens array.

[0020] (2) The present application adjusts the S-shaped curved waveguide direction and position in the cross waveguide to make the cross waveguide coupler insensitive to wavelength and polarization.

[0021] (3) The present application introduces an optimization algorithm to fit and smooth the curve profile of the S-shaped curved waveguide, which greatly reduces the insertion loss. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the cross-waveguide coupler structure of the present application;

[0023] Figure 2 is a light field transmission distribution diagram of the cross-waveguide coupler of the present application under different wavelengths, wherein (a) is wavelength 0.369 μm, (b) is wavelength 0.432 μm, (c) is wavelength 0.456 μm, (d) is wavelength 0.549 μm, (e) is wavelength 0.572 μm, (f) is wavelength 0.6328 μm, (g) is wavelength 0.665 μm, (h) is wavelength 0.758 μm;

[0024] Figure 3 is a light field transmission distribution diagram of the cross-waveguide coupler of the present application under different polarizations, wherein (a) is TE mode excitation, (b) is TM mode excitation;

[0025] Figure 4 is a light field transmission distribution diagram of the conventional directional coupler under different polarizations, wherein (a) is TE mode excitation, (b) is TM mode excitation;

[0026] Figure 5 is a light field transmission distribution diagram of the conventional gapless directional coupler under different polarizations, wherein (a) is TE mode excitation, (b) is TM mode excitation.

[0027] In the figure: 1 - input straight waveguide, 2 - cross-waveguide, 3 - S-shaped curved waveguide, 4 - output straight waveguide. DETAILED DESCRIPTION

[0028] The technical solutions of the present application are further described below in combination with the drawings and examples, but the protection scope of the present application should not be limited thereby.

[0029] Please refer to Figure 1 , Figure 1 is a schematic diagram of the cross-waveguide coupler structure of the present application, as shown in the figure, a cross-waveguide coupler insensitive to wavelength and polarization, comprising: an input straight waveguide 1, a cross-waveguide 2, an S-shaped curved waveguide 3, and an output straight waveguide 4.

[0030] The cross-waveguide 2 is formed by splicing the cross of a plurality of S-shaped curved waveguides 3; the curve profile of the S-shaped curved waveguide 3 is fitted by an optimization algorithm; by properly adjusting the direction and position of the S-shaped curved waveguides 3 in the cross-waveguide 2, the light wave is input from any one end of the input straight waveguide 1, propagates through the cross-waveguide 2, and completes the equal division of optical power in the output straight waveguide 4.

[0031] Specifically, the plurality of S-shaped curved waveguides 3 on any one side of the cross-waveguide 2 is composed of, but not limited to, 2 S-shaped curved waveguides 3.

[0032] Specifically, the curve profile optimization algorithm of the S-shaped curved waveguide 3 includes but is not limited to the adjoint method, particle swarm optimization, simulated annealing algorithm, genetic algorithm, deep learning neural network algorithm.

[0033] Specifically, the cross waveguide 2 is insensitive to both wavelength and polarization.

[0034] Specifically, the thin film material used in the input straight waveguide 1, the cross waveguide 2, the S-shaped curved waveguide 3 and the output straight waveguide 4 in the cross waveguide coupler includes but is not limited to lithium niobate thin film material, silicon nitride thin film material, silicon thin film material.

[0035] A preparation method of a cross waveguide coupler insensitive to wavelength and polarization, the specific steps of the method are:

[0036] Step one: implanting ions He + or Ar + with energy of 30-90keV into the thin film material to reduce the Mohs hardness of the thin film material;

[0037] Step two: coating a layer of 300-600nm thick mask material on the surface of the thin film to form a mask layer;

[0038] Step three: according to the cross waveguide coupler layout designed by simulation, a mask pattern of the cross waveguide coupler structure is prepared on the mask material by using photolithography method;

[0039] Step four: a layer of foamed silica gel with a thickness of about 5-7mm is laid under the polishing flannel, the exposed thin film material is first coarsely chemical mechanical polished (CMP) by using coarse particle size silica abrasive polishing liquid, then finely chemical mechanical polished (CMP) by using mixed particle size silica abrasive polishing liquid, and finally the cross waveguide coupler structure with smooth surface and surface roughness of 0.1-0.2nm is obtained.

[0040] Specifically, the mask material includes but is not limited to metal Cr film, Au film, and silicon dioxide film.

[0041] Specifically, the photolithography method includes but is not limited to femtosecond laser direct writing photolithography, projection photolithography, and step photolithography.

[0042] Specifically, the polishing flannel includes but is not limited to swan flannel and damping cloth; the coarse particle size silica abrasive polishing liquid has a particle size distribution of 80-150nm; the mixed particle size silica abrasive polishing liquid has a mixed particle size of 120nm and 20nm, and a mixed mass ratio of 3:1.

[0043] During simulation, lithium niobate thin film material is used as a demonstration example.

[0044] Figure 2 The optical field transmission distribution diagram of the cross waveguide coupler of the present application under different wavelengths. The ridge waveguide width in the cross waveguide coupler is set to 2 μm, the S-shaped curved waveguide radius is 287 μm, and the optical wavelength is set to 0.3-0.8 μm, from which Figure 2 As can be seen from (a)-(h), when the optical wavelength gradually increases from 0.369 μm to 0.758 μm, the optical power at both ends of the output straight waveguide remains consistent, and the insertion loss is also low, which shows that the cross waveguide coupler is not sensitive to the wavelength.

[0045] Figure 3 The optical field transmission distribution diagram of the cross waveguide coupler of the present application under different polarization excitations. The ridge waveguide width in the cross waveguide coupler is set to 2 μm, the S-shaped curved waveguide radius is 287 μm, and the optical wavelength is set to 0.6328 μm, from which Figure 3 As can be seen from (a) and (b), whether it is TE mode or TM mode excitation, the optical power at both ends of the output straight waveguide remains consistent, and the insertion loss is also low, which shows that the cross waveguide coupler is not sensitive to the polarization.

[0046] Figure 4 The optical field transmission distribution diagram of the conventional directional coupler under different polarizations (waveguide coupling distance is 1 μm). From Figure 4 As can be seen from (a), under TE mode excitation, the optical power at both ends of the output straight waveguide is relatively consistent; from Figure 4 As can be seen from (b), under TM mode excitation, the optical power at both ends of the output straight waveguide is obviously inconsistent, and even the optical power at one end is almost 0. This reflects that the directional coupler is extremely sensitive to the polarization, and at the same time, the size of the directional coupler is larger than that of the cross waveguide coupler.

[0047] Figure 5 The optical field transmission distribution diagram of the conventional directional coupler without distance under different polarizations. From Figure 5 As can be seen from (a), under TE mode excitation, the optical power at both ends of the output straight waveguide is relatively consistent; from Figure 5 As can be seen from (b), under TM mode excitation, the optical power at both ends of the output straight waveguide is obviously inconsistent, and even the optical power at one end is almost 0. This reflects that although the size is comparable to that of the cross waveguide coupler, the directional coupler without distance is extremely sensitive to the polarization.

[0048] The above-described embodiments are the implementation manners of the present application, and it should be noted that for those skilled in the art, without departing from the concept of the present application, several improvements and refinements can be made, and these improvements and refinements all belong to the protection scope of the present application.

Claims

1. A cross-waveguide coupler insensitive to wavelength and polarization, characterized in that, include: An input straight waveguide (1) is used to receive the input optical signal; The cross waveguide (2) is formed by splicing together at least two S-shaped curved waveguides (3) in a centrally symmetrical manner; Output straight waveguide (4) is used to output the evenly split optical signal; The two ends of the input straight waveguide (1) are respectively connected to the two ends of the cross waveguide (2), and the two ends of the output straight waveguide (4) are respectively connected to the other two ends of the cross waveguide (2), forming a complete cross structure. By adjusting the direction and position of the S-shaped curved waveguide (3) in the cross waveguide (2), the light wave is input from either end of the input straight waveguide (1), and the light power is evenly distributed at the two output ports of the output straight waveguide (4), and it is not sensitive to the wavelength and polarization state of the incident light.

2. The cross-waveguide coupler insensitive to wavelength and polarization according to claim 1, characterized in that, The S-shaped curved waveguide (3) is a continuous and smooth transition curve, and its curve profile is fitted by an optimization algorithm.

3. The cross-waveguide coupler insensitive to wavelength and polarization according to claim 1, characterized in that, The optimization algorithm is the adjoint method, particle swarm optimization, simulated annealing algorithm, genetic algorithm, or deep learning neural network algorithm.

4. The cross-waveguide coupler insensitive to wavelength and polarization according to claim 1, characterized in that, The cross waveguide (2) is composed of four S-shaped curved waveguides (3) spliced ​​together at a 90° intersection angle. The input end of each S-shaped curved waveguide (3) is connected to the input straight waveguide (1), and the output end is connected to the output straight waveguide (4), forming a four-port symmetrical structure.

5. The cross-waveguide coupler according to claim 1, characterized in that, The cross waveguide coupler is made of lithium niobate thin film material, silicon nitride thin film material or silicon thin film material.

6. The cross-waveguide coupler according to claim 1, characterized in that, The connection between the input straight waveguide (1) and the output straight waveguide (4) and the cross waveguide (2) adopts a gradient width design to achieve impedance matching and reduce reflection loss.

7. A method for fabricating a cross-waveguide coupler according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Use He ions with energy of 30-90 keV + Or Ar + Injecting thin film material reduces the Mohs hardness of the film surface. Step 2: Deposit a 300-600nm thick mask material onto the thin film surface to form a mask layer; Step 3: Based on the simulated design of the cross-waveguide coupler layout, a mask pattern for the cross-waveguide coupler structure is fabricated on the mask layer using photolithography. Step 4: Lay a layer of foamed silicone with a thickness of about 5-7 mm under the polishing cloth. First, use coarse-particle-size silica abrasive polishing slurry to perform coarse chemical mechanical polishing (CMP) on the exposed thin film material. Then, use mixed-particle-size silica abrasive polishing slurry to perform fine chemical mechanical polishing (CMP) on the exposed thin film material. Finally, a smooth cross-waveguide coupler structure with a surface roughness of 0.1-0.2 nm is obtained.

8. The method for fabricating a cross-waveguide coupler according to claim 7, characterized in that, The mask material includes, but is not limited to, metallic Cr film, Au film, and silicon dioxide film.

9. The method for fabricating a cross-waveguide coupler according to claim 7, characterized in that, The lithography methods include, but are not limited to, femtosecond laser direct writing lithography, projection lithography, and step-by-step lithography.

10. The method for fabricating a cross-waveguide coupler according to claim 7, characterized in that, The polishing cloth includes, but is not limited to, velvet cloth and damping cloth; the coarse-grained silica abrasive polishing slurry has a particle size distribution between 80 and 150 nm; the mixed particle sizes of the mixed-grained silica abrasive polishing slurry are 120 nm and 20 nm, respectively, and the mixing mass ratio is 3:1.

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