A micro-ring core cavity with ultra-high quality factor and its preparation method and application

Abstract

The present invention provides a micro-ring core cavity with an ultra-high quality factor and a preparation method and application thereof. The micro-ring core cavity comprises a circular micro-disk, a solid circular ring arranged around the outer edge of the circular micro-disk, and a base supporting the circular micro-disk; the circular micro-disk and the solid circular ring are made of silicon oxide, and the base is made of silicon; the solid circular ring has an outer diameter of 3-6 mm; the quality factor of the micro-ring core cavity is ≥1×10 9 The present invention improves the traditional micro-ring core cavity preparation process and finally obtains a large-size micro-ring core cavity with ultra-high quality factor, which significantly improves the application value of the sample and is conducive to large-scale promotion and application.

Description

Technical Field

[0001] The invention belongs to the technical field of optical microcavities and relates to a micro-ring core cavity, in particular to a micro-ring core cavity with an ultra-high quality factor and a preparation method and application thereof. Background Art

[0002] Since the development of on-chip silicon oxide optical microcavities, people have tried to further improve their quality factor through continuous process optimization. The quality factor is a physical quantity used to characterize the optical loss inside the microcavity, and the occurrence of many optical phenomena in the microcavity is closely related to the quality factor. As we all know, the large-scale application of optical fiber since its inception is inseparable from the optimization of its preparation process and the reduction of optical loss, and the future development trend of on-chip silicon oxide microcavities is also the same.

[0003] According to the difference in shape and structure, on-chip silicon oxide optical microcavities can be divided into microsphere cavities, microring core cavities and microdisk cavities. In the previous process, the size of microsphere cavities and microring core cavities can only be achieved from tens of micrometers to two millimeters, and it is impossible to achieve a larger size; although microdisk cavities can be made of any size, they are limited by the process in terms of quality factor and it is difficult to make further breakthroughs.

[0004] As early as 1996, Gorodetsky et al. used a hydrogen microflame to heat silicon dioxide to melt it. The molten silicon dioxide shrank into small balls under the action of surface tension, thus obtaining an ultra-high quality factor whispering gallery microsphere cavity (see literature: ML Gorodetsky, AA Savchenkov, and VS Ilchenko, "Ultimate Q of optical microsphere resonators," Opt. Lett. 21, 453-455 (1996)).

[0005] In 2003, the Vahala research group first proposed the preparation process of on-chip micro-ring core cavity, which specifically includes the following steps: (1) prepare a silicon wafer with a 2μm thick silicon oxide layer on the silicon wafer; perform glue coating, photolithography, development and other steps on the silicon wafer to obtain a circular photoresist pattern with a diameter of 160μm; (2) bake the photoresist to make its edge smooth, and then immerse the silicon wafer in HF buffer solution for etching for a period of time; after the etching is completed, use acetone and other solutions to wash away the remaining photoresist to obtain a silicon oxide microdisk with the same diameter of 160μm; (3) place the sample in XeF2 gas for etching, and the etching pressure is 3Torr; XeF2 The gas has good selectivity when etching silicon and hardly reacts with silicon oxide. When etching is completed, the silicon below the edge of the silicon oxide disk is evenly etched, and finally a truncated cone-shaped silicon column supporting the silicon oxide microdisk is obtained. (4) The sample is irradiated with a carbon dioxide laser with a spot diameter of 200 μm. The wavelength of the carbon dioxide laser is 10.6 μm. Light in this band will be strongly absorbed by silicon oxide, while silicon absorbs very little light in this band. Therefore, the temperature of the silicon oxide microdisk sample will rise sharply after being irradiated with the carbon dioxide laser. In addition, the thermal conductivity of silicon is about 100 times higher than that of silicon oxide, which results in the silicon oxide temperature close to the silicon column being relatively low, and the silicon oxide temperature at the very edge of the microdisk being the highest. When the power of the irradiated carbon dioxide laser is high enough, the silicon oxide at the edge of the microdisk is heated to the melting point and melts, shrinking under the action of surface tension to eventually form a microring core cavity (see reference: Armani, DK, Kippenberg, TJ, Spillane, SM & Vahala, KJ Ultra-high-toroid microcavity on a chip. Nature 421, 925-928 (2003)).

[0006] Although the above method has realized the preparation of on-chip ultra-high quality factor microcavity for the first time, its shortcomings are also obvious: the diameter of the sample prepared by this method is limited by the diameter of the carbon dioxide laser spot. For large-size samples with higher quality factors and wider applications, more optimized solutions are required, so there is still much room for improvement. Summary of the invention

[0007] The purpose of the present invention is to provide a micro-ring core cavity with an ultra-high quality factor and a preparation method and application thereof. By improving the traditional micro-ring core cavity preparation process, a large-sized micro-ring core cavity with an ultra-high quality factor is finally obtained, which significantly improves the application value of the sample and is conducive to large-scale promotion and application.

[0008] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a micro-ring core cavity with an ultra-high quality factor, wherein the micro-ring core cavity comprises a circular micro-disk, a solid circular ring arranged around the outer edge of the circular micro-disk, and a base supporting the circular micro-disk.

[0010] The circular micro-disk and the solid ring are made of silicon oxide, and the base is made of silicon.

[0011] The outer diameter of the solid circular ring is 3-6 mm, for example, it can be 3 mm, 3.2 mm, 3.4 mm, 3.6 mm, 3.8 mm, 4 mm, 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, 5 mm, 5.2 mm, 5.4 mm, 5.6 mm, 5.8 mm or 6 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0012] Compared with the traditional micro-ring core cavity whose size is limited to the range of tens of microns to two millimeters, the diameter of the micro-ring core cavity provided by the present invention is as high as 3-6 mm, which is a significant expansion in size and provides possibilities for a wider range of applications.

[0013] The quality factor of the micro-ring core cavity is ≥1×10 9 , for example, it can be 1×10 9 , 1.5×10 9 , 2×10 9 , 2.5×10 9 , 3×10 9 , 3.5×10 9 , 4×10 9 , 4.5×10 9 or 5×10 9 , but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] The quality factor of the micro-ring core cavity provided by the present invention reaches more than one billion, which is the on-chip optical microcavity with the highest quality factor known so far. The significant improvement in the quality factor means a significant reduction in the optical loss inside the microcavity, which helps to further improve the stability of the optical signal and enhance the observability of the optical phenomenon.

[0015] Preferably, the core cavity diameter of the solid circular ring is 50-60μm, for example, it can be 50μm, 51μm, 52μm, 53μm, 54μm, 55μm, 56μm, 57μm, 58μm, 59μm or 60μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] Preferably, the circular microdisk has a thickness of 10-14 μm, for example, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm or 14 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] In a second aspect, the present invention provides a method for preparing the micro-ring core cavity as described in the first aspect, the preparation method comprising the following steps:

[0018] (1) Selecting a silicon wafer provided with a silicon oxide layer;

[0019] (2) coating a photoresist layer on the surface of the silicon oxide layer and performing photolithography to obtain a circular photoresist pattern;

[0020] (3) wet-etching the silicon oxide layer using the circular photoresist pattern as a mask to obtain a circular microdisk;

[0021] (4) removing the photoresist on the surface of the circular microdisk and dry-etching the silicon wafer below the circular microdisk, that is, forming a silicon pillar between the circular microdisk and the silicon wafer;

[0022] (5) performing laser reflow on the circular microdisk, and controlling the light spot to rotate and move around the edge of the circular microdisk during the laser reflow process, that is, forming a solid ring around the outer edge of the circular microdisk;

[0023] (6) Annealing treatment is performed in an oxygen atmosphere to obtain a micro-ring core cavity with an ultra-high quality factor.

[0024] The preparation method provided by the present invention originally controls the light spot to rotate and move around the edge of the circular micro-disk during the laser reflow process, which significantly improves the heating uniformity of the large-sized micro-ring core cavity during the reflow process, and adds annealing treatment in an oxygen atmosphere after the preparation process, which helps to fully release the stress accumulated in the sample during the preparation process, thereby allowing the sample to maintain a high quality factor for a long time.

[0025] Preferably, the thickness of the silicon wafer in step (1) is 0.8-1.2 mm, for example, it can be 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1 mm, 1.05 mm, 1.1 mm, 1.15 mm or 1.2 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the thickness of the silicon oxide layer in step (1) is 10-14 μm, for example, it can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm or 14 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] The present invention selects a silicon oxide layer with a thickness of 10-14 μm, which is beneficial to reducing the influence of material stress during the silicon oxide growth process, expanding the size and controllable range of the micro-ring core cavity that can be prepared, and the thicker silicon oxide layer also makes it unnecessary to repeat the dry etching process, thereby simplifying the preparation process and improving production efficiency.

[0028] Preferably, in step (2), the silicon wafer is sequentially cleaned and subjected to surface adhesion enhancement treatment before coating the photoresist layer.

[0029] Preferably, the photoresist layer is pre-baked before the photolithography process in step (2).

[0030] Preferably, the photolithography process in step (2) includes exposure, development and hard baking performed in sequence.

[0031] In the present invention, the cleaning, surface viscosity enhancement treatment, pre-baking, exposure, development and hard baking are all routine operations of those skilled in the art, as long as they can achieve the corresponding effects, so the specific conditions of the above operations are not particularly limited here.

[0032] Preferably, the diameter of the circular photoresist pattern in step (2) is 3-6 mm, for example, it can be 3 mm, 3.2 mm, 3.4 mm, 3.6 mm, 3.8 mm, 4 mm, 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, 5 mm, 5.2 mm, 5.4 mm, 5.6 mm, 5.8 mm or 6 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] Preferably, the wet etching in step (3) is performed using a hydrofluoric acid solution.

[0034] Preferably, the removal of the photoresist in step (4) comprises: cleaning the silicon wafer with acetone, isopropanol and deionized water in sequence, and / or cleaning the silicon wafer with a mixed solution of concentrated sulfuric acid and hydrogen peroxide.

[0035] Preferably, the concentration of the concentrated sulfuric acid is ≥98wt%, for example, it can be 98wt%, 98.1wt%, 98.2wt%, 98.3wt%, 98.4wt% or 98.5wt%, and the concentration of hydrogen peroxide is ≥30wt%, for example, it can be 30wt%, 31wt%, 32wt%, 33wt%, 34wt% or 35wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0036] Preferably, the dry etching in step (4) is performed using xenon difluoride gas.

[0037] Preferably, the absolute gas pressure of the dry etching in step (4) is 2-4 Torr, for example, it can be 2 Torr, 2.2 Torr, 2.4 Torr, 2.6 Torr, 2.8 Torr, 3 Torr, 3.2 Torr, 3.4 Torr, 3.6 Torr, 3.8 Torr or 4 Torr, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, the distance between the silicon pillar and the edge of the circular microdisk in step (4) is 200-300 μm, for example, 200 μm, 210 μm, 220 μm, 230 μm, 240 μm, 250 μm, 260 μm, 270 μm, 280 μm, 290 μm or 300 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In the present invention, the distance between the silicon pillar and the edge of the circular microdisk is related to the thickness and diameter of the circular microdisk, and the thicker the thickness of the circular microdisk and the smaller the diameter, the greater the maximum value that the distance can reach. Taking a circular microdisk with a thickness of 12 μm and a diameter of 3 mm as an example, the maximum value of the distance between the silicon pillar and the edge of the circular microdisk is 220 μm.

[0040] Preferably, the laser reflow in step (5) is performed using a carbon dioxide laser, and the carbon dioxide laser is a Gaussian beam.

[0041] Preferably, the spot diameter of the carbon dioxide laser is 1-2 mm, for example, it can be 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm or 2 mm, and the laser power is 15-45 W, for example, it can be 15 W, 20 W, 25 W, 30 W, 35 W, 40 W or 45 W, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the laser reflow in step (5) comprises: firstly preheating the circular microdisk with a carbon dioxide laser of 10-15W laser power, then gradually increasing the laser power, and controlling the light spot to rotate and move around the edge of the circular microdisk for 2-3 circles each time the laser power is increased; when the laser power is increased to 20-30W, the silicon oxide at the edge of the circular microdisk begins to melt and shrink, and a solid circular ring is initially formed; as the laser power is gradually increased, the silicon oxide melts and shrinks and gradually approaches the silicon column, and the annular outer diameter of the solid circular ring gradually increases; when the laser power is increased to 40-50W, the annular outer diameter of the solid circular ring reaches 3-6mm, and the laser reflow is completed.

[0043] Preferably, the temperature of the annealing treatment in step (6) is 950-1050°C, for example, it can be 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C, 1040°C or 1050°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, the annealing time in step (6) is 30-40 h, for example, 30 h, 31 h, 32 h, 33 h, 34 h, 35 h, 36 h, 37 h, 38 h, 39 h or 40 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] As a preferred technical solution of the second aspect of the present invention, the preparation method comprises the following steps:

[0046] (1) Selecting a silicon wafer provided with a silicon oxide layer, wherein the thickness of the silicon wafer is 0.8-1.2 mm, and the thickness of the silicon oxide layer is 10-14 μm;

[0047] (2) cleaning and surface adhesion enhancement treatment are performed on the silicon wafer in sequence, and then a photoresist layer is coated on the surface of the silicon oxide layer and pre-baked, and then exposure, development and hard baking are performed in sequence to obtain a circular photoresist pattern with a diameter of 3-6 mm;

[0048] (3) immersing the silicon wafer in a hydrofluoric acid solution, and wet-etching the silicon oxide layer using the circular photoresist pattern as a mask to obtain a circular microdisk;

[0049] (4) washing the silicon wafer with acetone, isopropanol and deionized water in sequence, and / or washing the silicon wafer with a mixed solution of concentrated sulfuric acid with a concentration of ≥98wt% and hydrogen peroxide with a concentration of ≥30wt% to remove the photoresist on the surface of the circular microdisk; then dry-etching the silicon wafer under the circular microdisk with xenon difluoride gas, and controlling the absolute gas pressure of the dry etching to be 2-4Torr, that is, forming a silicon column between the circular microdisk and the silicon wafer, and the distance between the silicon column and the edge of the circular microdisk is 200-300μm;

[0050] (5) using a CO2 laser with a Gaussian beam and a spot diameter of 1-2 mm to perform laser reflow on the circular microdisk, specifically comprising: first preheating the circular microdisk with a CO2 laser with a laser power of 10-15 W, then gradually increasing the laser power, and controlling the spot to rotate and move around the edge of the circular microdisk for 2-3 circles each time the laser power is increased; when the laser power is increased to 20-30 W, the silicon oxide at the edge of the circular microdisk begins to melt and shrink, and a solid ring is initially formed; as the laser power is gradually increased, the silicon oxide melts and shrinks and gradually approaches the silicon column, and the annular outer diameter of the solid ring gradually increases; when the laser power is increased to 40-50 W, the annular outer diameter of the solid ring reaches 3-6 mm, and the laser reflow is completed, that is, a solid ring is formed around the outer edge of the circular microdisk;

[0051] (6) performing annealing in an oxygen atmosphere, and controlling the annealing temperature to 950-1050° C. and the annealing time to 30-40 h, thereby obtaining a micro-ring core cavity with an ultra-high quality factor.

[0052] In a third aspect, the present invention provides an application of the micro-ring core cavity as described in the first aspect, wherein the micro-ring core cavity is used to generate low-power consumption Kerr optical frequency combs and optical solitons.

[0053] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) Compared with the size of the traditional micro-ring core cavity which is limited to a range of tens of micrometers to two millimeters, the diameter of the micro-ring core cavity provided by the present invention is as high as 3-6 mm, which is a significant expansion in size and provides the possibility for a wider range of applications;

[0056] (2) The quality factor of the micro-ring core cavity provided by the present invention reaches more than one billion, which is the on-chip optical microcavity with the highest quality factor known so far. The significant improvement in the quality factor means a significant reduction in the optical loss inside the microcavity, which helps to further improve the stability of the optical signal and enhance the observability of the optical phenomenon.

[0057] (3) The preparation method provided by the present invention innovatively controls the light spot to rotate and move around the edge of the circular microdisk during the laser reflow process, significantly improving the heating uniformity of the large-sized microring core cavity during the reflow process. Annealing treatment in an oxygen atmosphere is added after the preparation process, which helps to fully release the stress accumulated in the sample during the preparation process, thereby enabling the sample to maintain a high quality factor for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 is a microscopic photograph of the ultra-high quality factor micro-ring core cavity provided in Example 1;

[0059] Figure 2 It is a schematic diagram of the process of preparing the micro-ring core cavity provided by the present invention;

[0060] Figure 3 is the Lorentz curve measured by the line width method of the micro-ring core cavity provided in Example 1;

[0061] Figure 4 It is the ringing curve measured by the micro-ring core cavity provided in Example 1 using the fast scanning method. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0063] Example 1

[0064] This embodiment provides a micro-ring core cavity with an ultra-high quality factor and a method for preparing the same. Figure 1 As shown, the micro-ring core cavity includes a circular micro-disk, a solid circular ring arranged around the outer edge of the circular micro-disk, and a base supporting the circular micro-disk. The circular micro-disk and the solid circular ring are made of silicon oxide, and the base is made of silicon. The annular outer diameter of the solid circular ring is 4.3 mm, and the core cavity diameter is 55 μm; the thickness of the circular micro-disk is 12 μm.

[0065] like Figure 2 As shown, the preparation method provided in this embodiment comprises the following steps:

[0066] (1) Selecting a silicon wafer provided with a silicon oxide layer, wherein the thickness of the silicon wafer is 1 mm, and the thickness of the silicon oxide layer is 12 μm;

[0067] (2) cleaning and surface adhesion enhancement treatment of the silicon wafer in sequence, then coating a photoresist layer on the surface of the silicon oxide layer and pre-baking, and then sequentially exposing, developing and hard baking to obtain a circular photoresist pattern with a diameter of 4.5 mm;

[0068] (3) immersing the silicon wafer in a hydrofluoric acid solution, and wet-etching the silicon oxide layer using the circular photoresist pattern as a mask to obtain a circular microdisk;

[0069] (4) washing the silicon wafer with acetone, isopropanol and deionized water in sequence, and then washing the silicon wafer with a mixed solution of 98 wt % concentrated sulfuric acid and 30 wt % hydrogen peroxide to remove the photoresist on the surface of the circular microdisk; then dry etching the silicon wafer under the circular microdisk with xenon difluoride gas, and controlling the absolute gas pressure of the dry etching to 3 Torr, that is, forming a silicon column between the circular microdisk and the silicon wafer, and the distance between the silicon column and the edge of the circular microdisk is 230 μm;

[0070] (5) A CO2 laser with a Gaussian beam and a spot diameter of 1.5 mm was used to perform laser reflow on the circular microdisk, specifically comprising: firstly, the circular microdisk was preheated with a CO2 laser with a laser power of 10 W, and then the laser power was gradually increased, and each time the laser power was increased, the spot was controlled to rotate and move around the edge of the circular microdisk for 2 circles; when the laser power was increased to 25 W, the silicon oxide at the edge of the circular microdisk began to melt and shrink, and a solid circular ring was initially formed; as the laser power was gradually increased, the silicon oxide melted and shrunk gradually approached the silicon pillar, and the annular outer diameter of the solid circular ring gradually increased; when the laser power was increased to 45 W, the annular outer diameter of the solid circular ring reached 4.3 mm, and the laser reflow was completed, that is, a solid circular ring was formed around the outer edge of the circular microdisk;

[0071] (6) Annealing is performed in an oxygen atmosphere at a temperature of 1000° C. and a time of 35 h to obtain a micro-ring core cavity with an ultra-high quality factor.

[0072] Example 2

[0073] The present embodiment provides a micro-ring core cavity with an ultra-high quality factor and a preparation method thereof, wherein the micro-ring core cavity comprises a circular micro-disk, a solid circular ring arranged around the outer edge of the circular micro-disk, and a base supporting the circular micro-disk. The circular micro-disk and the solid circular ring are made of silicon oxide, and the base is made of silicon. The annular outer diameter of the solid circular ring is 3 mm, and the core cavity diameter is 50 μm; the thickness of the circular micro-disk is 10 μm.

[0074] like Figure 2 As shown, the preparation method provided in this embodiment comprises the following steps:

[0075] (1) Selecting a silicon wafer provided with a silicon oxide layer, wherein the thickness of the silicon wafer is 0.8 mm, and the thickness of the silicon oxide layer is 10 μm;

[0076] (2) cleaning and surface adhesion enhancement treatment of the silicon wafer in sequence, then coating a photoresist layer on the surface of the silicon oxide layer and pre-baking, and then sequentially exposing, developing and hard baking to obtain a circular photoresist pattern with a diameter of 3.2 mm;

[0077] (3) immersing the silicon wafer in a hydrofluoric acid solution, and wet-etching the silicon oxide layer using the circular photoresist pattern as a mask to obtain a circular microdisk;

[0078] (4) washing the silicon wafer with acetone, isopropanol and deionized water in turn to remove the photoresist on the surface of the circular microdisk; then dry etching the silicon wafer under the circular microdisk with xenon difluoride gas, and controlling the absolute gas pressure of the dry etching to be 2 Torr, that is, forming a silicon pillar between the circular microdisk and the silicon wafer, and the distance between the silicon pillar and the edge of the circular microdisk is 200 μm;

[0079] (5) A CO2 laser with a Gaussian beam and a spot diameter of 1 mm is used to perform laser reflow on the circular microdisk, specifically comprising: firstly, the circular microdisk is preheated with a CO2 laser with a laser power of 10 W, and then the laser power is gradually increased, and each time the laser power is increased, the spot is controlled to rotate and move around the edge of the circular microdisk for 3 circles; when the laser power is increased to 20 W, the silicon oxide at the edge of the circular microdisk begins to melt and shrink, and a solid ring is initially formed; as the laser power is gradually increased, the silicon oxide melts and shrinks gradually approaches the silicon pillar, and the annular outer diameter of the solid ring gradually increases; when the laser power is increased to 40 W, the annular outer diameter of the solid ring reaches 3 mm, and the laser reflow is completed, that is, a solid ring is formed around the outer edge of the circular microdisk;

[0080] (6) An annealing treatment is performed in an oxygen atmosphere, and the annealing temperature is controlled to be 950° C. and the time is controlled to be 40 h, thereby obtaining a micro-ring core cavity with an ultra-high quality factor.

[0081] Example 3

[0082] The present embodiment provides a micro-ring core cavity with an ultra-high quality factor and a preparation method thereof, wherein the micro-ring core cavity comprises a circular microdisk, a solid circular ring arranged around the outer edge of the circular microdisk, and a base supporting the circular microdisk. The circular microdisk and the solid circular ring are made of silicon oxide, and the base is made of silicon. The annular outer diameter of the solid circular ring is 6 mm, and the core cavity diameter is 57 μm; the thickness of the circular microdisk is 14 μm.

[0083] like Figure 2 As shown, the preparation method provided in this embodiment comprises the following steps:

[0084] (1) Selecting a silicon wafer provided with a silicon oxide layer, wherein the thickness of the silicon wafer is 1.2 mm, and the thickness of the silicon oxide layer is 14 μm;

[0085] (2) cleaning and surface adhesion enhancement treatment were performed on the silicon wafer in sequence, and then a photoresist layer was coated on the surface of the silicon oxide layer and pre-baked, and then exposure, development and hard baking were performed in sequence to obtain a circular photoresist pattern with a diameter of 6.3 mm;

[0086] (3) immersing the silicon wafer in a hydrofluoric acid solution, and wet-etching the silicon oxide layer using the circular photoresist pattern as a mask to obtain a circular microdisk;

[0087] (4) washing the silicon wafer with acetone, isopropanol and deionized water in turn to remove the photoresist on the surface of the circular microdisk; then dry etching the silicon wafer under the circular microdisk with xenon difluoride gas, and controlling the absolute gas pressure of the dry etching to 4 Torr, that is, forming a silicon pillar between the circular microdisk and the silicon wafer, and the distance between the silicon pillar and the edge of the circular microdisk is 270 μm;

[0088] (5) A CO2 laser with a Gaussian beam and a spot diameter of 2 mm is used to perform laser reflow on the circular microdisk, specifically comprising: firstly, the circular microdisk is preheated with a CO2 laser with a laser power of 10 W, and then the laser power is gradually increased, and each time the laser power is increased, the spot is controlled to rotate and move around the edge of the circular microdisk for 3 circles; when the laser power is increased to 30 W, the silicon oxide at the edge of the circular microdisk begins to melt and shrink, and a solid ring is initially formed; as the laser power is gradually increased, the silicon oxide melts and shrinks gradually approaches the silicon pillar, and the annular outer diameter of the solid ring gradually increases; when the laser power is increased to 50 W, the annular outer diameter of the solid ring reaches 6 mm, and the laser reflow is completed, that is, a solid ring is formed around the outer edge of the circular microdisk;

[0089] (6) Annealing is performed in an oxygen atmosphere, and the annealing temperature is controlled to be 1050° C. and the time is controlled to be 30 h, thereby obtaining a micro-ring core cavity with an ultra-high quality factor.

[0090] Example 4

[0091] This embodiment provides a micro-ring core cavity with an ultra-high quality factor and a method for preparing the same. Except that the thickness of the silicon oxide layer in step (1) is changed to 8 μm, the remaining steps and conditions are the same as those in Example 1 and are not described in detail here.

[0092] Example 5

[0093] This embodiment provides a micro-ring core cavity with an ultra-high quality factor and a preparation method thereof. Except that the spot diameter of the carbon dioxide laser in step (5) is changed to 0.8 mm, the remaining steps and conditions are the same as those in Example 1 and are not described in detail here.

[0094] Example 6

[0095] This embodiment provides a micro-ring core cavity with an ultra-high quality factor and a preparation method thereof. Except that the spot diameter of the carbon dioxide laser in step (5) is changed to 2.5 mm, the remaining steps and conditions are the same as those in Example 1 and are not described in detail here.

[0096] Comparative Example 1

[0097] This comparative example provides a micro-ring core cavity and a preparation method thereof, except that the spot diameter of the carbon dioxide laser in step (5) is changed to 5.5 mm so that the spot completely covers the circular micro-disk and the spot is kept stationary during the laser reflow process, the remaining steps and conditions are the same as those in Example 1 and are not described in detail here.

[0098] Comparative Example 2

[0099] This comparative example provides a micro-ring core cavity and a preparation method thereof. Except for deleting step (6), that is, no annealing treatment is performed, the remaining steps and conditions are the same as those in Example 1, and thus are not described in detail here.

[0100] Performance Testing

[0101] A fiber-cone coupling system is used to characterize the quality factor of the micro-ring core cavity obtained in Examples 1-6 and Comparative Examples 1-2. An ordinary commercial optical fiber is heated with a hydrogen flame and drawn into a cone. A laser is introduced into the fiber cone. The sample is moved using a translation stage so that its edge approaches the fiber cone. At this time, the laser energy in the fiber cone is coupled into the microcavity through the evanescent field. The coupling state of the fiber cone and the microcavity can be observed by a photodetector and an oscilloscope, and the corresponding transmission spectrum curve can be obtained. The quality factor can be obtained by fitting the transmission spectrum curve.

[0102] In order to obtain more accurate test results, the present invention uses two characterization methods: line width method and fast scanning method, as follows:

[0103] (A) Linewidth method: A low-frequency triangular wave scanning signal (10 Hz) is added to the piezoelectric ceramic of the laser, and the laser will output a laser with a frequency that varies within a certain range. The laser is coupled through the fiber cone, and the light with a frequency that meets the resonance condition will enter the microcavity, showing a Lorentz curve in the transmission spectrum.

[0104] (B) Fast scanning method: Based on the line width method, the frequency of the triangle wave is increased (100 Hz to 1 kHz). At this time, the laser scanning frequency is very fast. The time it takes for the laser frequency to scan the cavity mode is equal to or even less than the photon lifetime of the cavity mode. The light in the microcavity interferes with the light in the fiber cone, and a ringing curve is displayed on the oscilloscope.

[0105] Taking the micro-ring core cavity obtained in Example 1 as an example, the Lorentz curve measured by the line width method is shown in Figure 3The transmission spectrum of the Mach–Zehnder interferometer used to calibrate the laser scanning frequency is shown in the lower part of the figure. It is a sin function shape. The quality factor obtained by fitting the Lorentz curve is 1.44×10 9 ; The ringing curve measured by the fast scanning method is shown in Figure 4 The quality factor obtained by fitting is 1.40×10 9 .

[0106] After summarizing, the quality factors of the micro-ring core cavities obtained in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1 below.

[0107] Table 1

[0108]

[0109]

[0110] Among them, in comparative example 1, a large-diameter light spot is used in step (5) to completely cover the circular microdisk, and the light spot is kept stationary during the laser reflow process. Although a microring core cavity can also be produced, the required laser power is as high as 80W, the preparation process is relatively energy-consuming, and the safety is low. At the same time, high power can easily cause the silicon column to overheat or even produce black spots, causing defects in the sample; comparative example 2 is not annealed. Although it has a high quality factor when it is just prepared, the quality factor will gradually decrease with the increase of the placement time. This is mainly because the large-sized microring core cavity will accumulate stress during the laser reflow process. The gradual release of stress will cause slight deformation of the microcavity, which will eventually lead to a decrease in the quality factor.

[0111] It can be seen that compared with the traditional micro-ring core cavity whose size is limited to the range of tens of microns to two millimeters, the diameter of the micro-ring core cavity provided by the present invention is as high as 3-6 mm, which is a significant expansion in size and provides possibility for a wider range of applications.

[0112] In addition, the quality factor of the micro-ring core cavity provided by the present invention reaches more than one billion, which is the highest known on-chip optical microcavity. The significant improvement in the quality factor means a significant reduction in the optical loss inside the microcavity, which helps to further improve the stability of optical signals and enhance the observability of optical phenomena.

[0113] Furthermore, the preparation method provided by the present invention originality controls the light spot to rotate and move around the edge of the circular micro-disk during the laser reflow process, which significantly improves the heating uniformity of the large-sized micro-ring core cavity during the reflow process, and adds annealing treatment in an oxygen atmosphere after the preparation process, which helps to fully release the stress accumulated in the sample during the preparation process, thereby enabling the sample to maintain a high quality factor for a long time.

[0114] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a micro-ring core cavity with an ultra-high quality factor, characterized in that: The preparation method comprises the following steps: (1) Selecting a silicon wafer having a silicon oxide layer; (2) coating a photoresist layer on the surface of the silicon oxide layer and performing photolithography to obtain a circular photoresist pattern; (3) wet-etching the silicon oxide layer using the circular photoresist pattern as a mask to obtain a circular microdisk; (4) removing the photoresist on the surface of the circular microdisk and dry-etching the silicon wafer under the circular microdisk to form a silicon pillar between the circular microdisk and the silicon wafer; (5) performing laser reflow on the circular microdisk, and controlling the light spot to rotate and move around the edge of the circular microdisk during the laser reflow process, that is, forming a solid ring around the outer edge of the circular microdisk; (6) Annealing treatment is performed in an oxygen atmosphere to obtain a micro-ring core cavity with an ultra-high quality factor; Wherein, the micro-ring core cavity comprises a circular micro-disk, a solid circular ring arranged around the outer edge of the circular micro-disk, and a base supporting the circular micro-disk; The circular micro-disk and the solid ring are made of silicon oxide, and the base is made of silicon; The solid annular ring has an outer diameter of 3-6 mm and a core cavity diameter of 50-60 μm; the thickness of the circular microdisk is 10-14 μm; the quality factor of the microring core cavity is ≥1×10 9 .

2. The preparation method according to claim 1, characterized in that: The thickness of the silicon wafer in step (1) is 0.8-1.2 mm.

3. The preparation method according to claim 1, characterized in that: The thickness of the silicon oxide layer in step (1) is 10-14 μm.

4. The preparation method according to claim 1, characterized in that: Step (2) is to sequentially clean and perform surface adhesion enhancement treatment on the silicon wafer before coating the photoresist layer.

5. The preparation method according to claim 1, characterized in that: Step (2) The photoresist layer is pre-baked before the photolithography process.

6. The preparation method according to claim 1, characterized in that: The photolithography process in step (2) includes exposure, development and hard baking performed in sequence.

7. The preparation method according to claim 1, characterized in that: The diameter of the circular photoresist pattern in step (2) is 3-6 mm.

8. The preparation method according to claim 1, characterized in that: The wet etching in step (3) is performed using a hydrofluoric acid solution.

9. The preparation method according to claim 1, characterized in that: The removal of the photoresist in step (4) comprises: cleaning the silicon wafer with acetone, isopropyl alcohol and deionized water in sequence, and / or cleaning the silicon wafer with a mixed solution of concentrated sulfuric acid and hydrogen peroxide.

10. The preparation method according to claim 9, characterized in that: The concentration of the concentrated sulfuric acid is ≥98wt%, and the concentration of the hydrogen peroxide is ≥30wt%.

11. The preparation method according to claim 1, characterized in that: The dry etching in step (4) is performed using xenon difluoride gas.

12. The preparation method according to claim 1, characterized in that: The absolute gas pressure of the dry etching in step (4) is 2-4 Torr.

13. The preparation method according to claim 1, characterized in that: In step (4), the distance between the silicon pillar and the edge of the circular microdisk is 200-300 μm.

14. The preparation method according to claim 1, characterized in that: The laser reflow in step (5) is performed using a carbon dioxide laser, and the carbon dioxide laser is a Gaussian beam.

15. The preparation method according to claim 14, characterized in that: The spot diameter of the carbon dioxide laser is 1-2 mm, and the laser power is 10-45 W.

16. The preparation method according to claim 1, characterized in that: The laser reflow in step (5) comprises: firstly preheating the circular microdisk with a carbon dioxide laser of 10-15W laser power, then gradually increasing the laser power, and controlling the light spot to rotate and move around the edge of the circular microdisk for 2-3 circles each time the laser power is increased; when the laser power is increased to 20-30W, the silicon oxide at the edge of the circular microdisk begins to melt and shrink, and a solid circular ring is initially formed; as the laser power is gradually increased, the silicon oxide melts and shrinks and gradually approaches the silicon column, and the annular outer diameter of the solid circular ring gradually increases; when the laser power is increased to 40-50W, the annular outer diameter of the solid circular ring reaches 3-6mm, and the laser reflow is completed.

17. The preparation method according to claim 1, characterized in that: The temperature of the annealing treatment in step (6) is 950-1050°C.

18. The preparation method according to claim 1, characterized in that: The annealing time in step (6) is 30-40 hours.

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