Ultrahigh quality factor micro-ring resonator coupling structure

Abstract

The invention relates to an ultra-high quality factor micro-ring resonator coupling structure, and belongs to the technical field of optoelectronic integration. The micro-ring resonator coupling structure comprises a silicon substrate, a first silicon dioxide cladding, a micro-ring, a second silicon dioxide cladding, a straight waveguide and a third silicon dioxide cladding which are sequentially stacked from bottom to top. In the coupling structure, during light transmission, the upper surface of the micro-ring and the lower surface of the straight waveguide are coupled, the roughness of the surfaces is reduced to the greatest extent through growth and chemical mechanical polishing, and the defect that in a traditional same-plane coupling scheme, during light transmission, double-side-wall coupling is conducted on the micro-ring and the straight waveguide is overcome; and extra loss and reflection caused by relatively large roughness due to etching are reduced. According to the invention, the coupling spacing can be accurately controlled, the additional loss and reflection of the coupling structure are reduced, the quality factor of the micro-ring resonator is effectively improved, and a key solution is provided for a high-precision filtering and high-precision sensing photon integrated chip.

Description

Technical Field

[0001] The invention belongs to the technical field of optoelectronic integration and relates to an ultra-high quality factor micro-ring resonator coupling structure. Background Art

[0002] Microring resonators in photonic integrated chips have shown broad application prospects in optical communications, optical information processing, sensors and other fields due to their unique optical properties and advantages of small size, high integration, high quality factor and low loss. Microring resonators use the interference principle of light to achieve selective reflection or transmission of optical signals of specific wavelengths through the coupling of ring waveguides and straight waveguides. They can be used to construct wavelength selective devices such as filters, modulators, sensors, etc. However, the preparation of microring resonators faces multiple challenges, among which the control of the coupling spacing between the microring and the coupled straight waveguide is the key. Submicron-level feature sizes and high uniformity are required to reduce the loss at the coupling position and improve the quality factor. Traditional microring resonator structures prepare microrings and straight waveguides on the same plane, and the coupling spacing and coupling surface roughness between the two are determined by the photolithography etching process. When the spacing is less than 100 nanometers, the conventional process capabilities will not be able to meet the precision requirements. At the same time, the roughness of the waveguide sidewalls caused by etching will also cause additional losses and emissions, thereby reducing the quality factor of the microring resonator. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide an ultra-high quality factor micro-ring resonator coupling structure, by separating the micro-ring and the straight waveguide in the longitudinal direction, coupling them in the vertical direction, and utilizing the process of intermediate silicon dioxide layer growth and chemical mechanical polishing to simultaneously ensure high-precision control of the coupling spacing and a smooth waveguide surface, thereby solving the problems of difficult photolithography etching limit size and relatively high roughness of the waveguide side in traditional same-plane coupling schemes, and effectively improving the quality factor of the micro-ring resonator.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] An ultra-high quality factor micro-ring resonator coupling structure comprises a silicon substrate, a first silicon dioxide cladding, a micro-ring, a second silicon dioxide cladding, a straight waveguide and a third silicon dioxide cladding stacked in sequence from bottom to top. The micro-ring and the straight waveguide are vertically coupled between different layers through the second silicon dioxide cladding.

[0006] Furthermore, the thickness of the second silica cladding is the coupling thickness between the microring and the straight waveguide. The optical field coupling spacing can be precisely controlled by silica growth and chemical mechanical polishing, and the upper and lower surfaces of the coupling structure can achieve extremely small surface roughness, reducing coupling loss and emission, and improving the quality factor of the microring resonator.

[0007] Furthermore, the straight waveguide may be composed of a first straight waveguide and a second straight waveguide that are symmetrically distributed.

[0008] Furthermore, the microring may be a racetrack-type microring, and under the racetrack-type microring, the first straight waveguide and the second straight waveguide are correspondingly arranged above the straight waveguide of the racetrack-type microring.

[0009] The beneficial effects of the present invention are as follows: the present invention separates the micro-ring and the straight waveguide in the longitudinal direction, couples them in the vertical direction, and utilizes the process of intermediate silicon dioxide layer growth and chemical mechanical polishing to simultaneously ensure high-precision control of the coupling spacing and a smooth waveguide surface, thereby solving the problems of the difficulty of photolithography etching limit size and the relatively high roughness of the waveguide side in the traditional same-plane coupling scheme, and effectively improving the quality factor of the micro-ring resonator.

[0010] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0012] Figure 1 An ultra-high quality factor micro-ring resonator coupling structure provided by an embodiment of the present invention;

[0013] Figure 2 A schematic diagram of the waveguide coupling relationship in the microring resonator coupling structure of the present invention;

[0014] Figure 3 An add-drop type micro-ring coupler provided by one embodiment of the present invention;

[0015] Figure 4 A racetrack-type microring coupler is provided in one embodiment of the present invention.

[0016] Figure numerals: 1-101-silicon substrate, 102-silicon dioxide cladding I, 103-microring, 104-silicon dioxide cladding II, 105-straight waveguide, 106-silicon dioxide cladding III; 107-microring; 108-first straight waveguide; 109-second straight waveguide; 110-racetrack-type microring. DETAILED DESCRIPTION

[0017] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0018] Example 1

[0019] like Figure 1 As shown, the ultra-high quality factor microring resonator coupling structure provided in this embodiment includes a silicon substrate 101, a silicon dioxide cladding I 102, a microring 103, a silicon dioxide cladding II 104, a straight waveguide 105, and a silicon dioxide cladding III 106 stacked in sequence from bottom to top.

[0020] Among them, the silicon substrate 101 has a thickness of about 700 microns. The refractive index of the silica cladding layer I 102 is about 1.44, and the thickness is about 2 microns. The cross-sectional size of the micro-ring 103 waveguide is about 500 nanometers × 220 nanometers, which meets the single-mode transmission conditions of the light field. The radius is determined by the required filtering curve and the quality factor, and is usually between a few microns and a few hundred microns. The refractive index of the silica cladding layer II 104 is about 1.44, and the thickness is the coupling thickness of the micro-ring and the straight waveguide, which is usually between tens of nanometers and one micron, which is determined by the required filtering curve and the quality factor design. The upper and lower surface roughness RQ is less than 1 nanometer, which is higher than the side wall roughness of about 5 nanometers after the waveguide is etched. The refractive index of the silica cladding layer III 106 is about 1.44, and the thickness is about 4 microns.

[0021] The microring 103 and the straight waveguide 105 are coupled between different layers. The optical field coupling spacing can be precisely controlled through silicon dioxide growth and chemical mechanical polishing. The upper and lower surfaces of the coupling structure can also achieve extremely small surface roughness, reducing coupling loss and emission, and improving the quality factor of the microring resonator.

[0022] In this embodiment, the specific process of preparing the three-layer key structure of micro-ring 103, silicon dioxide cladding II 104, and straight waveguide 105 is as follows:

[0023] The first step is photolithography-etching-annealing to prepare the desired micro-ring 103;

[0024] The second step is to deposit silicon dioxide - chemical mechanical polishing - ellipsometer to monitor the thickness of the silicon dioxide cladding - chemical mechanical polishing to prepare a silicon dioxide cladding II 104 that meets the coupling spacing requirements; the third step is to deposit a straight waveguide layer, which is usually consistent with the material of the microring 103 - photolithography - etching - annealing to prepare a straight waveguide 105 that has interlayer coupling with the microring 103.

[0025] The coupling between the microring and the straight waveguide can be found in Figure 2 ,like Figure 2 As shown, the microring and the straight waveguide are coupled at two different longitudinal heights.

[0026] In this embodiment, the micro-ring and the straight waveguide are separated in the longitudinal direction and coupled in the vertical direction, and the process of intermediate silicon dioxide layer growth and chemical mechanical polishing is used to simultaneously ensure high-precision control of the coupling spacing and a smooth waveguide surface, thereby reducing the reflection and additional loss of the micro-ring resonator coupling structure, improving the device quality factor, and providing a key solution for high-precision filtering and high-precision sensing photonic integrated chips.

[0027] In addition, the interlayer coupling concept can also be used for a racetrack-type microring and a microring coupled by two straight waveguides, which is described below through two embodiments.

[0028] Example 2

[0029] This embodiment demonstrates an add-drop type micro-ring coupler, such as Figure 3 As shown, two symmetrical first straight waveguides 108 and straight waveguides 109 are on the same layer, and are coupled with the micro-rings in the vertical direction. When the structure is symmetrical, the coupling coefficients of the two are the same. When different coupling coefficients are required, the width of the straight waveguides can be adjusted to control the power of the coupled light field between the waveguides, thereby achieving a difference in coupling coefficients and meeting the design requirements of the asymmetric coupled micro-rings.

[0030] Example 3

[0031] This embodiment demonstrates a racetrack-type microring coupler, such as Figure 4 As shown, similar to Example 2, the racetrack microring is deployed on the architecture proposed in the present invention. The double-sided coupled first straight waveguide 108 and the second straight waveguide 109 are respectively deployed above the straight waveguide of the racetrack microring 110. Similarly, the transfer function of the optical power is controlled by controlling the thickness of the silicon dioxide layer, thereby achieving precise control of the coupling coefficient.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An ultra-high quality factor micro-ring resonator coupling structure, characterized in that: The invention comprises a silicon substrate, a first silicon dioxide cladding, a micro-ring, a second silicon dioxide cladding, a straight waveguide and a third silicon dioxide cladding which are sequentially stacked from bottom to top; the micro-ring and the straight waveguide are vertically coupled between different layers through the second silicon dioxide cladding.

2. The ultra-high quality factor micro-ring resonator coupling structure according to claim 1, characterized in that: The thickness of the second silica cladding is the coupling thickness between the microring and the straight waveguide.

3. The ultra-high quality factor micro-ring resonator coupling structure according to claim 1, characterized in that: The straight waveguide includes a first straight waveguide and a second straight waveguide, and the first straight waveguide and the second straight waveguide are symmetrically distributed.

4. The ultra-high quality factor micro-ring resonator coupling structure according to claim 1, characterized in that: The microring is a racetrack-type microring.

5. The ultra-high quality factor micro-ring resonator coupling structure according to claim 3 or 4, characterized in that: The microring is a racetrack-type microring, and the first straight waveguide and the second straight waveguide are correspondingly arranged above the straight waveguide of the racetrack-type microring.

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