Preparation method of size-controllable ultrathin high-quality whispering gallery optical crystal microcavity and centering device

Abstract

The application provides a preparation method and a centering device of a size-controllable ultrathin high-quality echo wall optical crystal microcavity, and the method comprises the following steps: cutting a crystal material into a wafer and grinding and thinning the crystal thickness by using a polishing disc; placing an optical crystal microcavity blank on a microscope stage, adjusting two-dimensional adjustment knobs of the stage, and making the center of the optical crystal microcavity blank coincide with an origin of an objective micrometer scale; making a clamping rod with an adhesive adhered to a bottom end penetrate a top end through hole of a clamping rod fixing frame, and making the clamping rod align with the origin of the objective micrometer scale; adjusting the height of the clamping rod, making the optical crystal microcavity blank be pasted and fixed on the bottom end of the clamping rod by ultraviolet curing glue, and completing centering; taking the clamping rod off the clamping rod fixing frame, chamfering an outer circle of the optical crystal microcavity blank; grinding the outer circle surface of the optical crystal microcavity wafer by using sandpaper; polishing the optical crystal microcavity wafer, and obtaining the optical crystal microcavity based on the polished optical crystal microcavity wafer.

Description

Technical Field

[0001] This invention relates to the field of quantum optics technology for optical crystal microcavities, and particularly to a method for fabricating and centering an ultrathin, high-quality whispering-gallery optical crystal microcavity with controllable dimensions. Background Technology

[0002] High-quality factor whispering-gallery optical resonators (HMRs) possess extremely small mode volumes and extremely high energy densities, making them a crucial component for the integrated application of microwave photonic structures. Linear filtering using HMRs whispering-gallery microcavity chips can be combined with optoelectronic resonators to achieve integrated optoelectronic oscillators. The photonic filtering function of HMRs whispering-gallery microcavity chips is applied to single-frequency filtering, tunable filtering, reconfigurable filtering, and higher-order filtering applications. Whispering-gallery microcavity chips, made from various low-loss nonlinear optical materials, exhibit extremely high energy densities, resulting in a wide variety of nonlinear effects with extremely low thresholds, making them widely used in nonlinear effect research. Furthermore, whispering-gallery optical crystal microcavities have yielded novel and important research in cavity quantum optics, precision measurement, high-precision sensing, nonlinear dynamics, and cavity optomechanics, and hold great promise for developing more and higher-level integrated system engineering applications.

[0003] Although whispering-gallery optical microcavity chips (EMCs) have a simple structure, fabricating high-quality EMCs is challenging. For practical and integrated applications of EMCs, both the quality factor and structural stability of the fabricated chips are crucial. Since low loss within the dielectric of the EMC is key to improving energy storage, using low-loss materials is fundamental. Furthermore, the surface quality of the EMC profile affects the surface scattering loss of light waves within the cavity. Therefore, optimizing the surface roughness and improving the profile surface quality is one of the key challenges in achieving high-quality whispering-gallery EMC fabrication. Improving the quality factor of whispering-gallery EMCs requires effectively enhancing the surface smoothness of the chips. Extensive research has been conducted both domestically and internationally on improving the quality factor of whispering-gallery EMCs.

[0004] One existing method for fabricating optical microcavity chips is to use a carbon dioxide laser to melt and fabricate the optical microcavity chips, such as... Figure 1As shown, a pulsed carbon dioxide laser beam 3, generated by a carbon dioxide laser, is focused onto an optical fiber 1 through an optical lens 2. A displacement stage is used to control the position of the fiber relative to the beam waist, and a DC motor controls the speed of rotation around the fiber axis to achieve precise alignment. This allows for the fabrication of an optical microcavity chip through heating and melting. Polishing with a controlled electric arc improves the surface roughness of the chip's edge. This method of fabricating optical microcavity chips using a carbon dioxide laser can improve the quality factor of the chip to some extent. However, this method can only fabricate optical crystal microcavities using optical fiber materials, limiting the available materials. Furthermore, the size of the optical fiber also restricts the size of the fabricated optical crystal microcavity. These two factors significantly limit the application scenarios of this method, failing to meet the fabrication requirements of optical microcavity chips made of various materials and with different free spectral ranges. Moreover, during the heating and melting process, gravity can cause eccentricity of the optical crystal microcavity, making it difficult to control the final shape and leading to shape degradation. This affects the quality of the optical microcavity chip and limits the stability of its fabrication. Furthermore, the optical crystal microcavities prepared by this method are not easy to couple. Using a tapered coupling method to couple them results in poor anti-interference and anti-vibration performance, making it difficult to build a stable coupling module and unsuitable for engineering applications.

[0005] Another method for fabricating optical microcavity chips is photolithography. This method first uses thermal oxidation to form a 1-2 micrometer-thick silicon oxide film on a silicon wafer. Then, photolithography is used to etch the microdisk shape of the optical microcavity chip. Next, hydrofluoric acid is used to etch the silicon oxide down to the silicon surface. After washing away the photoresist, XeF2 gas is used for selective etching to form the cylinders supporting the optical microcavity chip. Finally, a CO2 laser is used to melt the microdisk. Utilizing surface tension, a very smooth surface can be formed on the microdisk, improving the quality factor Q to achieve a quality factor as high as 10. 8 The fabrication of optical microcavity chips using photolithography allows for strict control over the chip structure. Subsequent surface melting enables a high quality factor and facilitates the design of different microcavity chip structures to meet specific application requirements. However, this method limits the materials used in fabricating the microcavity chips, and the chip size is typically on the micrometer scale, thus presenting significant limitations.

[0006] Another existing method for fabricating optical microcavity chips uses crystalline materials (such as lithium niobate, calcium fluoride, etc.) to prepare the crystalline optical microcavity by cutting the crystalline material. More specifically, the first method uses a single-point diamond turning tool to turn the outer diameter to the center point where the connecting rod and the crystal microcavity blank are bonded, forming an optical crystal microcavity blank. This method can achieve precise concentricity, but it cannot produce ultra-thin microcavities below 0.2 mm because it easily leads to the crystal blank cracking. In the process of developing this invention, the inventors discovered that if optical microcavities are prepared by cutting crystal blocks and then directly grinding and polishing the cut crystal blocks, although ultra-thin optical microcavities can be prepared, it is difficult to concentrically align the optical microcavity blank with the grinding control rod, thus making it difficult to accurately control the size of the ultra-thin optical microcavity chip.

[0007] With the continuous research on whispering-gallery optical crystal microcavities in numerous application fields, increasingly higher requirements are being placed on the fabrication of whispering-gallery optical crystal microcavities. How to fabricate optical crystal microcavities that have both high quality factors and stable structures, are easy to couple, and are suitable for engineering applications is an urgent problem to be solved. Summary of the Invention

[0008] In view of this, embodiments of the present invention provide a method for fabricating an ultrathin, high-quality whispering-gallery optical crystal microcavity with controllable dimensions and a centering device, in order to eliminate or improve one or more defects existing in the prior art.

[0009] One aspect of the present invention provides a method for fabricating a whispering-gallery optical crystal microcavity, the method comprising the following steps: cutting a crystal material into a circular wafer of a first thickness;

[0010] The two ends of the crystal wafer are ground with a polishing pad to reduce the thickness of the crystal wafer to the second thickness, thus obtaining an optical crystal microcavity blank.

[0011] The optical crystal microcavity blank is placed on the stage of the microscope in the centering device, and the two-dimensional adjustment knob of the stage is adjusted so that the center of the optical crystal microcavity blank coincides with the origin of the microscope objective micrometer.

[0012] The pre-adjusted clamping rod holder is placed in the pre-calibrated fixed position on the microscope stage. The top of the clamping rod holder has a vertical through hole, the clamping rod passes through the vertical through hole and is coated with ultraviolet curing adhesive at the bottom. The fixed position is such that the clamping rod is aligned with the origin of the microscope objective micrometer in the vertical direction.

[0013] Adjust the height of the clamping rod so that the ultraviolet curing adhesive contacts the optical crystal microcavity blank, thereby centering and fixing the optical crystal microcavity blank to the bottom end of the clamping rod;

[0014] The UV-curable adhesive is cured using ultraviolet light, and the clamping rod is removed from the clamping rod holder. The outer circle of the optical crystal microcavity blank at the bottom of the clamping rod is chamfered at a predetermined angle to obtain an optical crystal microcavity sheet.

[0015] The outer circular surface of the optical crystal microcavity sheet was polished using sandpaper;

[0016] The optical crystal microcavity sheet is polished using a combination of chemical polishing and mechanical polishing, and an optical crystal microcavity is obtained based on the polished optical crystal microcavity sheet.

[0017] In some embodiments of the present invention, the crystal material is lithium niobate or calcium fluoride; the method further includes: after chamfering the outer circle of the optical crystal microcavity blank at a predetermined angle or before grinding the outer circle surface of the optical crystal microcavity sheet with sandpaper, placing the clamping rod with the optical crystal microcavity sheet attached in a vacuum environment for annealing.

[0018] After polishing the optical crystal microcavity sheet, the clamping rod with the optical crystal microcavity sheet attached is placed in a vacuum environment for annealing.

[0019] In some embodiments of the present invention, the first thickness is 1 mm, the second thickness is 0.1-0.5 mm, and the chamfering treatment at the predetermined angle is a 30-degree chamfering treatment.

[0020] In some embodiments of the present invention, the clamping rod fixing frame includes: a square base frame; multiple support rods, one end of each support rod being fixed to a corner of the base frame, and the other end supporting the vertical through hole; the square base frame is tightly fitted or aligned with the base of the microscope.

[0021] In some embodiments of the present invention, the clamping rod holder is positioned by a limiting part or a marking point provided on the base of the microscope to be placed in a fixed position that is pre-calibrated with the stage, so that the clamping rod is aligned with the origin of the microscope objective micrometer in the vertical direction.

[0022] In some embodiments of the present invention, the polishing agent used in the chemical polishing includes one or more of cerium oxide polishing liquid, aluminum oxide polishing liquid, polishing liquid, and polishing paste.

[0023] In another aspect, the present invention also provides a whispering-gallery optical crystal microcavity prepared using the above method.

[0024] In another aspect, the present invention also provides a centering device for fabricating whispering-gallery optical crystal microcavities, the centering device comprising:

[0025] Microscope and clamping rod holder;

[0026] The top of the clamping rod fixing bracket has a vertical through hole, the clamping rod passes through the vertical through hole and is used to adhere ultraviolet curing adhesive at the bottom end;

[0027] When the clamping rod holder is placed in the pre-calibrated fixed position of the microscope stage, the fixed position aligns the clamping rod with the origin of the microscope objective micrometer in the vertical direction.

[0028] The position of the clamping rod in the vertical through hole can be adjusted up and down. With a pre-positioned micrometer scale of the microscope objective placed at the lower part of the clamping rod fixing frame, the optical crystal microcavity blank is centered and fixed to the bottom of the clamping rod by contacting the ultraviolet curable adhesive at the bottom of the clamping rod with the optical crystal microcavity blank, so that the optical crystal microcavity blank can be chamfered, ground and polished to obtain the whispering-gallery optical crystal microcavity.

[0029] In some embodiments of the present invention, the clamping rod fixing frame includes: a square base frame; multiple support rods, one end of each support rod being fixed to a corner of the base frame, and the other end supporting the vertical through hole; the square base frame is tightly fitted or aligned with the base of the microscope.

[0030] In some embodiments of the present invention, the clamping rod holder is positioned by a limiting part or a marking point provided on the base of the microscope to be placed in a fixed position that is pre-calibrated with the stage, so that the clamping rod is aligned with the origin of the microscope objective micrometer in the vertical direction.

[0031] The method and centering device for fabricating whispering-gallery optical microcavities proposed in this invention can produce ultrathin, high-quality whispering-gallery optical microcavities that are easy to couple in various ways, easy to engineer and integrate, and have controllable dimensions. By combining chemical polishing and mechanical polishing, the surface roughing and fine processing of the optical crystal microcavities can be performed in stages, thereby achieving a quality factor of up to 10. 9 The above describes an optical crystal microcavity with a surface roughness on the nanometer scale. Furthermore, this invention features simple fabrication steps, mass production capability, and low cost.

[0032] Additional advantages, objects, and features of the invention will be set forth in part in the description which follows, and will also become apparent in part to those skilled in the art upon studying the description, or may be learned by practice of the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures specifically pointed out in the description and drawings.

[0033] Those skilled in the art will understand that the objectives and advantages achievable with the present invention are not limited to those specifically described above, and that the above and other objectives achievable with the present invention will become clearer from the following detailed description. Attached Figure Description

[0034] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, are not intended to limit the scope of the invention. The components in the drawings are not drawn to scale but are merely illustrative of the principles of the invention. For ease of illustration and description of certain parts of the invention, corresponding portions in the drawings may be enlarged, i.e., may appear larger relative to other components in an exemplary device actually manufactured according to the invention. In the drawings:

[0035] Figure 1 This is a schematic diagram of the existing technology for fabricating optical microcavity chips using carbon dioxide laser melting.

[0036] Figure 2 This is a schematic diagram of the fabrication process of a whispering-gallery optical crystal microcavity in one embodiment of the present invention.

[0037] Figure 3 This is a schematic diagram of the centering device in one embodiment of the present invention.

[0038] Figure 4 A schematic diagram of the centering device clamping rod fixing frame and microscope stage in one embodiment of the present invention.

[0039] Key reference numerals:

[0040] 101 Microscope eyepiece; 102 Microscope objective with micrometer; 103 Microscope base;

[0041] 104 Clamping rod holder; 105 Microscope stage with two-dimensional adjustment knob; 106 Clamping rod;

[0042] 107 Two-dimensional adjustment knob for microscope stage; 108 Square base frame for clamping rod holder;

[0043] 109 Clamping rod fixing bracket support rod; 110 Clamping rod fixing bracket vertical through hole. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and descriptions of this invention are used to explain the invention, but are not intended to limit the invention.

[0045] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0046] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0047] It should also be noted that, unless otherwise specified, the term "connection" in this article can refer not only to a direct connection, but also to an indirect connection involving an intermediary.

[0048] In practical applications, the thickness of high-quality whispering-gallery optical microcavity chips should be as thin as possible for easy packaging, and the structural dimensions of the microcavity chip also need to be precisely controlled. To overcome the problems of insufficient quality factor or unstable structure of optical microcavities caused by limitations in fabrication materials, microcavity eccentricity, and difficulty in controlling the shape and size of optical microcavities in existing fabrication methods, this invention proposes a fabrication scheme using crystalline materials (such as lithium niobate, calcium fluoride, etc.) and a turning and grinding process to produce ultra-thin, high-quality optical microcavity chips with controllable structural dimensions. The optical crystal microcavity is fabricated using crystalline materials with ultra-low loss. The original crystal material is cut and processed into a specific shape, and the size and structure of the optical crystal microcavity are precisely controlled through surface grinding. Polishing is then performed to improve the quality factor of the optical crystal microcavity, resulting in a size-controllable whispering-gallery optical crystal microcavity. Furthermore, to prevent the optical crystal microcavity from cracking, the optical microcavity or preform is annealed during the fabrication process to release internal stress and improve the performance of the optical microcavity.

[0049] Figure 2 This is a schematic diagram of the precision fabrication process of an ultrathin, high-quality whispering-gallery optical crystal microcavity with controllable dimensions, according to one embodiment of the present invention. Figure 2 As shown, the optical crystal microcavity fabrication process of the present invention is divided into two stages: roughing and surface polishing.

[0050] I. Rough Processing Stage: This stage mainly involves cutting, thinning, centering, chamfering, annealing, and grinding the original bulk crystal material to process the optical microcavity chip from the original bulk crystal material into an ultra-thin optical microcavity blank with a complete structure and precise dimensions.

[0051] II. Surface Polishing Stage: This stage mainly involves surface polishing of the optical microcavity blank with precise dimensions and structure obtained in the roughing stage. This further reduces the depth of the crack layer and surface unevenness, thereby improving the surface smoothness and ultimately producing a high-quality whispering-gallery optical resonator.

[0052] More specifically, the optical crystal microcavity fabrication method of this embodiment includes the following steps:

[0053] Step S1: Cut the crystal block material.

[0054] In this step, the crystal material is cut into a circular wafer of a first thickness, and then the two ends of the crystal wafer are ground with a polishing pad to reduce the thickness of the crystal wafer to a second thickness to obtain an optical crystal microcavity blank; the first thickness may be, for example, 1 mm or other values, and the second thickness may be, for example, 0.1 to 0.2 mm or other values ​​less than the first thickness.

[0055] Crystal materials such as lithium niobate and calcium fluoride, which exhibit ultra-low loss, can be selected. The original crystal material is typically a cylindrical block, requiring cutting and thinning to prepare circular wafers. A wire cutting method, which minimizes crystal breakage, can be used to first cut the crystal block into circular wafers approximately 1 mm thick. Then, a polishing pad is used to grind both ends of the crystal wafers, reducing the thickness of the crystal microcavity preform wafers to 0.1–0.2 mm. During the thinning process, careful control of the polishing pad's contact pressure is crucial to prevent crystal microcavity preform breakage.

[0056] In the embodiments of the present invention, other cutting methods that will not cause crystal breakage may also be used, such as using a crystal cutting machine. Depending on the different crystal materials to be prepared and the different sizes of the required optical crystal microcavities, the crystal block material may be cut into circular pieces of other sizes, such as 0.8, 1.5 mm or 2 mm. These thickness values ​​are only examples and the present invention is not limited thereto.

[0057] In this embodiment of the invention, the optical crystal microcavity can also be thinned to other required thickness values, such as 0.15, 0.25 or 0.3 mm, depending on the required optical crystal microcavity size. These thickness values ​​are only examples and the invention is not limited thereto.

[0058] Step S2: Centering of the crystal microcavity blank.

[0059] This step involves centering and fixing the crystal microcavity preform onto the clamping rod, enabling control over the preform in subsequent steps. First, to facilitate chamfering, grinding, and polishing processes in later fabrication steps, the optical microcavity preform sheet needs to be adhered and fixed to the cylindrical clamping rod, specifically to one end face. Second, if the optical microcavity preform and the clamping rod are too misaligned, the microcavity may detach or even crack during subsequent chamfering and grinding processes. Therefore, while fixing the optical microcavity preform, it is crucial to ensure it is as concentric as possible with the clamping rod.

[0060] This step achieves the centering and mounting of the crystal microcavity preform to the clamping rod as follows: First, place the optical crystal microcavity preform in the center of the microscope stage. Observe the relative position of the microcavity preform and the objective lens micrometer under the microscope. Adjust the position by electrically driving the x-axis and y-axis motors of the stage or manually adjusting the two-dimensional adjustment knob 107 of the stage (see...). Figure 4 This allows the origin of the microcavity preform and the objective lens micrometer to coincide, ensuring that the center of the optical crystal microcavity preform 111 is aligned with the center of the microscope objective lens. Then, using a pre-designed clamping rod fixing bracket, which is fixed to the microscope stage, the clamping rod is vertically aligned with the center of the microscope objective lens. The clamping rod is adjusted in height to fit against the microcavity, thus completing centering and bonding. The centering error accuracy achieved in this way can be controlled to below 0.1 mm. By fixing the clamping rod fixing bracket to a fixed position on the z-axis displacement stage of the microscope stage, the clamping rod is automatically aligned with the center of the microscope objective lens. At this point, the clamping rod is also vertically aligned with the center of the optical crystal microcavity preform. Under these conditions, the optical crystal microcavity preform is adhered to the clamping rod using adhesive, achieving precise centering and installation of the crystal microcavity preform.

[0061] Because the optical crystal microcavity preform and clamping rod are extremely small, on the order of millimeters, the traditional method of manually centering and fixing the microcavity preform with clamping rod using tweezers has a low success rate and suffers from problems such as poor concentricity and inability to achieve ultra-thin crystal microcavities.

[0062] This invention provides an auxiliary centering device to center a crystal microcavity blank, aligning the center of the end face of the crystal microcavity blank with the bottom center of the clamping rod, and fixing it to the clamping rod with an adhesive.

[0063] Figure 3 This is a schematic diagram of a centering device in one embodiment of the present invention. Figure 3As shown, the centering device includes: a microscope and a clamping rod holder 104, wherein the microscope includes an eyepiece 101, an objective lens 102 with a micrometer, a microscope stage 105 with a two-dimensional adjustment knob, and a microscope base 103, etc.; Figure 4 As shown, the clamping rod holder 104 may include: a frame-type square support base 108; multiple support rods, one end of each support rod being fixed to a corner of the square support base, and the other end supporting a clamping rod bearing portion, the clamping rod bearing portion having a vertical through hole in the middle for the clamping rod to pass through. In one embodiment of the invention, the frame of the square base is tightly fitted or aligned with the base of the microscope, and the two can be fixed by bolts, in which case there are screw holes at corresponding positions of the frame of the square base and the base of the microscope. In other embodiments of the invention, the frame of the square base and the base of the microscope can also be tightly fitted in other ways, such as providing recessed holes at the four corners of the microscope base and providing protrusions at corresponding positions of the frame of the square base. By placing the protrusions in the corresponding recessed holes, the clamping rod holder is fixedly installed on the microscope, and its position will not change. The above bolt installation method or the installation method of protrusion and recessed hole matching is only an example of the invention. As long as the clamping rod holder can be fixedly installed at a predetermined position on the microscope, other installation methods are also possible. For example, the microscope base 103 can also be fixedly engaged with the clamping rod holder by means of snap-fit, magnetic attraction based on marked points, etc. In other embodiments of the present invention, the shape of the base of the clamping rod holder can also be different based on the shape variation of the microscope base.

[0064] In this embodiment of the invention, the clamping rod holder 104 is configured such that, when the clamping rod holder 104 is fixedly mounted on the microscope base, the vertical through hole in the middle of the clamping rod bearing portion is aligned with the center of the microscope objective. Thus, when the clamping rod is installed in the vertical through hole, the clamping rod is aligned with the center of the microscope objective. Since the center of the optical crystal microcavity blank on the stage is aligned with the center of the microscope objective, the center of the optical crystal microcavity blank is also aligned with the clamping rod at this time.

[0065] In one embodiment of the invention, an adhesive is applied to the bottom end of the clamping rod before or after it is placed in the vertical through hole. The position of the clamping rod 106 within the vertical through hole 110 of the clamping rod holder is adjustable. When an optical crystal microcavity blank, pre-positioned to coincide with the origin of the microscope objective micrometer, is placed below the clamping rod holder, the bottom end of the clamping rod can be brought into contact with the optical crystal microcavity blank (or the adhesive can contact the optical crystal microcavity blank) by moving the clamping rod downwards. The adhesive can then be used to center and fix the optical crystal microcavity blank to the bottom end of the clamping rod. In one embodiment of the invention, the adhesive is a UV-curable adhesive, which cures rapidly upon UV irradiation. Considering the potential impact of subsequent annealing processes on the adhesive between the microcavity and the clamping rod, a high-temperature resistant optical adhesive is used in this invention.

[0066] The present invention moves the clamping rod 110, which is assembled into the vertical through hole 106 of the clamping rod fixing frame, up and down to a suitable position, so that the ultraviolet curing adhesive at the bottom of the clamping rod contacts the optical crystal microcavity blank, which is pre-placed to coincide with the origin of the micrometer on the microscope objective lens 102, thereby completing the centering of the optical crystal microcavity blank.

[0067] This centering method allows for precise control of the centering error to below 0.1mm, resulting in higher accuracy. Furthermore, it significantly improves the yield rate, reducing issues such as the optical crystal microcavity blank detaching from the clamping rod or even cracking due to eccentricity in subsequent processes. Moreover, this centering method enables more precise control over the overall microcavity diameter during subsequent processing, as the diameter of the microcavity chip is a crucial parameter in its use.

[0068] Step S3: Chamfering and shaping of the optical crystal microcavity blank.

[0069] After the optical microcavity blank is centered, the UV-curable adhesive is cured using ultraviolet light, and the clamping rod is removed from the clamping rod holder, the outer circle of the optical crystal microcavity blank is chamfered at a predetermined angle to prevent chipping of the outer circular surface during grinding and polishing, thereby obtaining the optical crystal microcavity sheet. In this invention, an external turning tool is used for chamfering, with a chamfer angle of 30°. Furthermore, the feed rate needs to be adjusted appropriately during the chamfering process to avoid microcavity chipping. Here, 30° is merely an example; the invention is not limited to this, and other values ​​can be reasonably set according to the crystal material to be prepared, the required optical crystal microcavity size, and the actual application scenario.

[0070] Step S4, first annealing process.

[0071] After the cutting, thinning, and chamfering processes in the pre-processing stage, the residual internal stress accumulated inside the optical crystal microcavity needs to be released in time. Otherwise, the subsequent grinding and polishing process may cause local cracking near the surface of the optical crystal microcavity, which will affect the quality of the optical crystal microcavity.

[0072] Therefore, preferably, the present invention employs an annealing process for optical crystal microcavities: the optical crystal microcavities are placed in a vacuum quartz tube in a vacuum annealing furnace, the annealing temperature is set to about 800-900°C, the constant temperature heating time is set to about 24 hours, and finally the temperature is naturally cooled down to room temperature.

[0073] After high-temperature annealing, the residual stress inside the optical crystal microcavity is effectively released.

[0074] In this embodiment of the invention, depending on the different crystal materials to be prepared and the different sizes of the required optical crystal microcavities, the annealing temperature and annealing time can be other values. For example, the annealing temperature can be 600℃-1000℃ and the annealing time can be 12-24 hours.

[0075] In another embodiment of the present invention, step S4 may also be omitted.

[0076] Step S5: Grind and shape the outer circular surface of the optical crystal microcavity sheet.

[0077] After the previous centering and chamfering processes, an optical crystal microcavity sheet with a preliminary shape has been produced. Based on this, its diameter can be precisely controlled by grinding.

[0078] More specifically, low-grit abrasive paper, such as 800 grit, 1500 grit, and 2500 grit, is used to sequentially grind the outer circular surface of the optical crystal microcavity. The diameter is then further checked using a microscope and a micrometer with an objective lens to ensure it meets requirements (step S6). If the size is still too large and does not meet requirements, grinding continues; if it meets requirements, the surface polishing stage begins. By changing the abrasive paper grit, grinding time, and grinding intensity, the amount of material removed from the optical crystal microcavity surface can be controlled. Through repeated grinding, precise dimensional control can be achieved. Through this roughing process, an ultrathin optical microcavity chip with precise dimensions and a complete structure can be fabricated.

[0079] The surface polishing stage includes steps S7-S11.

[0080] While the roughing stage achieves the fabrication of the optical microcavity chip structure, surface / subsurface layer damage during turning and grinding processes results in poor surface roughness of the obtained optical microcavity chip. Considering the characteristics of optical crystal materials, such as low hardness, anisotropy, and high coefficient of thermal expansion, this invention employs a combination of chemical and mechanical polishing in the surface polishing stage to polish the optical whispering-gallery microcavity. The mechanical action of the polishing paper and the chemical action of the polishing slurry work together to polish, avoiding the mechanical damage caused by pure mechanical polishing and solving the problem of low surface flatness caused by pure chemical polishing. During the polishing process, the optical crystal microcavity will adsorb impurities from the polishing slurry and crystal material falling from the polishing pad. To improve polishing precision and efficiency, the microcavity is cleaned with an organic solvent after each polishing cycle to remove contaminants remaining on the microcavity surface. Furthermore, the polishing process is divided into rough polishing and fine polishing according to the diameter of the polishing particles. This enables the fabrication of ultrathin, high-quality whispering-gallery optical crystal microcavities with controllable dimensions.

[0081] Step S7: The optical crystal microcavity is rough polished using a combination of chemical polishing and mechanical polishing.

[0082] To address the characteristics of optical crystal materials, such as low hardness, anisotropy, and high coefficient of thermal expansion, this invention employs a combination of chemical and mechanical polishing methods for coarse polishing of whispering-gallery optical crystal microcavities. The choice of polishing agent particle size significantly impacts the final polishing result, and the particle size parameter can be determined based on different crystal materials. This invention allows the addition of chemical abrasives to the polishing agent during the coarse polishing process to improve polishing efficiency. As an example, in the coarse polishing step, the polishing agent particle size can be selected from the following values: 6 micrometers, 3 micrometers, 1 micrometer, 0.5 micrometers, and 0.25 micrometers.

[0083] As an example, mechanical polishing can use one or more of sandpaper, sanding belt, polishing powder, abrasive, etc., while chemical polishing can use one or more of cerium oxide polishing slurry, aluminum oxide polishing slurry, polishing liquid, or polishing paste, etc. The choice of polishing agent should be based on the crystal type and the highest precision required for polishing.

[0084] Step S8: After coarse polishing, determine whether the surface meets the requirements for coarse polishing results. In this embodiment of the invention, this requirement may be, for example, observed under a microscope, to determine whether the microcavity polished surface is sufficiently smooth and flat, and whether there are obvious scratches and defects.

[0085] Step S9: If the surface of the optical crystal microcavity meets the requirements of the coarse polishing result, then further fine polishing is performed.

[0086] In this embodiment of the invention, the difference between fine polishing and coarse polishing lies in the different particle sizes of the polishing agent. In the fine polishing step, a finer-particle polishing agent and abrasive are required. As an example, in the fine polishing step, the particle size of the polishing agent can be selected from the following particle size values: 0.2 micrometers, 0.15 micrometers, 0.1 micrometers, and 0.05 micrometers, but the invention is not limited to these.

[0087] Polishing utilizes both the mechanical and chemical actions of polishing sandpaper, avoiding the mechanical damage caused by purely mechanical polishing while addressing the issue of low surface smoothness caused by purely chemical polishing. During the polishing process, the optical crystal microcavity absorbs impurities from the polishing slurry and crystal material that falls from the polishing pad. To improve polishing precision and efficiency, the optical crystal microcavity is cleaned with an organic solvent after each polishing cycle to remove contaminants remaining on its surface. Furthermore, the polishing process is divided into coarse polishing and fine polishing based on the diameter of the polishing particles. This enables the fabrication of ultrathin, high-quality whispering-gallery optical crystal microcavities with controllable dimensions.

[0088] Step S10: After fine polishing, determine whether the surface meets the requirements for fine polishing results. In this embodiment of the invention, this requirement may be, for example, by observing under a microscope whether the microcavity polished surface is sufficiently smooth and flat.

[0089] Step S11, second annealing process.

[0090] After grinding and polishing, residual stress accumulated during the grinding and polishing process exists within the optical crystal microcavity. Annealing this stress using the annealing process described in step S4 can further improve the quality factor of the optical crystal microcavity. The annealing process parameters can be the same as those for the first annealing process. Alternatively, the annealing process parameters in this step can differ from those in step S4.

[0091] After the above steps, an optical microcavity with controllable size and high quality factor is obtained.

[0092] The method for fabricating whispering-gallery optical microcavities proposed in this invention can produce ultrathin, high-quality whispering-gallery optical microcavities that are easy to couple in various ways, easy to engineer and package, and have controllable dimensions. By combining chemical polishing and mechanical polishing in stages to process the surface of the optical crystal microcavities, a quality factor of 10 can be achieved. 9 The above describes an optical crystal microcavity with a surface roughness on the nanometer scale. Furthermore, this invention features simple fabrication steps, mass production capability, and low cost.

[0093] The centering scheme provided by this invention can efficiently and accurately complete the centering process of the microcavity and clamping rod, providing a supporting foundation for subsequent processes. Because the method of this invention can precisely control the size of the ultra-thin optical microcavity chip, it can meet different application requirements in practical applications.

[0094] This invention addresses the annealing process for optical microcavities, eliminating residual stress within the microcavities through a two-stage annealing process, thereby further improving the quality of the microcavities.

[0095] Example 1

[0096] This example uses high-purity lithium niobate crystals with ultra-low light absorption loss to fabricate a whispering-gallery optical microcavity chip.

[0097] Phase 1: Fabrication and processing of optical crystal microcavities.

[0098] High-purity lithium niobate crystals were pre-processed into cylinders with a radius of 2.3 mm and cut into 1 mm thick circular sheets. These sheets were then thinned to 0.5 mm, and the optical crystal microcavity blanks were centered using an optical adhesive bonded to a clamping rod. Next, the clamping rod and the optical crystal microcavity blanks were clamped in a chuck, and an external turning tool was used to chamfer them, controlling the angle to 30°. The first annealing was then performed at 900°C for 24 hours, followed by natural cooling to room temperature. A grinding and shaping process was then carried out using 600-grit sandpaper. The diameter was checked under a microscope using a micrometer to ensure it met the expected standard of 2 mm. After two grinding processes, the diameter of the optical crystal microcavity was precisely controlled to 2 mm. At this point, the fabrication of the optical crystal microcavity sheet was complete.

[0099] Phase 2: Surface polishing of optical crystal microcavities.

[0100] After the fabrication and processing of the optical crystal microcavity, its structure is determined. To improve its surface smoothness, the polishing process begins. A combined mechanical and chemical polishing method is used. The choice of polishing agent particle size has a significant impact on the final polishing result. During the rough polishing process, chemical abrasives can be added to the polishing agent to improve polishing efficiency. Polishing agents can include cerium oxide polishing slurry, alumina polishing slurry, polishing liquid, or polishing paste, etc. Furthermore, the choice of polishing agent should be based on the crystal type and the highest precision required for polishing.

[0101] After initial polishing, the surface gloss of the optical crystal microcavity is significantly improved, allowing it to reflect more light and exhibiting better surface smoothness. The surface roughness of the microcavity can be observed using a roughness profilometer; after processing, the surface roughness reaches the 10nm level, which is sufficient to demonstrate the microcavity's performance. After processing, the polished surface of the optical crystal microcavity is inspected using microscopes of different magnifications. For example, an optical microscope with a maximum objective magnification of 100x is used as the inspection device. During testing, it was found that as the polishing equipment continuously optimizes the polishing of the optical crystal microcavity, the surface roughness gradually decreases. Fine surface profiling analysis of the optical crystal microcavity surface shows that its roughness can be reduced to the tens of nanometers level, meeting the preset standards.

[0102] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0103] In this invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications and variations of the embodiments of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a whispering gallery optical crystal microcavity, characterized in that, The method is realized based on a centering device, and the centering device comprises a microscope and a clamping rod fixing frame. The crystal material is cut into a crystal wafer with a first thickness, and both end surfaces of the crystal wafer are ground by using a polishing disc, so that the thickness of the crystal wafer is thinned to a second thickness, and an optical crystal microcavity blank is obtained. The optical crystal microcavity blank is placed on a stage of the microscope in the centering device, and two-dimensional adjusting knobs of the stage are adjusted, so that the center of the optical crystal microcavity blank and an origin of a micrometer scale of an objective lens of the microscope are coincided. The clamping rod fixing frame which is adjusted in advance is placed at a fixed position which is marked in advance on the stage of the microscope, and a top end position of the clamping rod fixing frame which is fixed and supported has a vertical through hole, and a clamping rod penetrates through the vertical through hole and has ultraviolet curing glue adhered to a bottom end of the clamping rod, and the fixed position is such that the clamping rod is aligned with the origin of the micrometer scale of the objective lens of the microscope in a vertical direction. The height of the clamping rod is adjusted, so that the ultraviolet curing glue contacts the optical crystal microcavity blank, and the optical crystal microcavity blank is fixed and adhered to the bottom end of the clamping rod. The ultraviolet curing glue is cured by using ultraviolet rays, and the clamping rod is taken off from the clamping rod fixing frame, and an outer circle of the optical crystal microcavity blank at the bottom of the clamping rod is chamfered at a predetermined angle, and an optical crystal microcavity piece is obtained. The outer circle surface of the optical crystal microcavity piece is ground by using sandpaper. The optical crystal microcavity piece is polished by using a combination of chemical polishing and mechanical polishing, and an optical crystal microcavity is obtained based on the optical crystal microcavity piece after polishing.

2. The method of claim 1, wherein, The crystal material is lithium niobate or calcium fluoride. The method further comprises: After the outer circle of the optical crystal microcavity blank is chamfered at the predetermined angle or before the outer circle surface of the optical crystal microcavity piece is ground by using sandpaper, the clamping rod with the optical crystal microcavity piece adhered thereto is placed in a vacuum environment, and annealing treatment is performed. After the optical crystal microcavity piece is polished, the clamping rod with the optical crystal microcavity piece adhered thereto is placed in a vacuum environment, and annealing treatment is performed.

3. The method according to claim 1, wherein The first thickness is 1 mm, and the second thickness is 0.1-0.5 mm. The chamfering at the predetermined angle is chamfering at 30 degrees.

4. The method of claim 1, wherein, The clamping rod fixing frame comprises a square base frame, a plurality of support rods, one end of each support rod is fixed to each corner of the square base frame, and the other end supports the vertical through hole, and the square base frame is tightly matched with or aligned with a base of the microscope.

5. The method of claim 4, wherein, The clamping rod fixing frame is positioned at the fixed position which is marked in advance on the stage of the microscope by using a limiting part or a mark point arranged on the base of the microscope, so that the clamping rod is aligned with the origin of the micrometer scale of the objective lens of the microscope in the vertical direction.

6. The method of claim 1, wherein, The polishing agent used in the chemical polishing comprises one or more of a polishing liquid and a polishing paste.

7. An optical crystal microcavity of echo wall prepared by using the method according to any one of claims 1-6.

8. A centering device for the preparation of an acoustic whispering gallery optical crystal microcavity, characterized in that, The centering device comprises a microscope and a clamping rod fixing frame. The top end of the fixed support of the clamping rod fixing frame has a vertical through hole, the clamping rod penetrates through the vertical through hole and is used for adhering ultraviolet curing glue at the bottom end; In the case that the clamping rod fixing frame is placed in the pre-marked fixed position of the microscope stage, the fixed position is such that the clamping rod is aligned with the origin of the microscope objective micrometer in the vertical direction; The position of the clamping rod in the vertical through hole can be adjusted up and down, and in the case that a pre-positioned origin of the microscope objective micrometer is placed at the lower part of the clamping rod fixing frame, the optical crystal microcavity blank is centered and fixed by the ultraviolet curing glue at the bottom end of the clamping rod to contact the optical crystal microcavity blank, so as to perform chamfering, grinding and polishing processing on the optical crystal microcavity blank to obtain a whispering gallery optical crystal microcavity.

9. The centering device of claim 8, wherein, The clamping rod fixing frame comprises a square base frame, a plurality of support rods, one end of each support rod is fixed to each corner of the square base frame, and the other end supports the vertical through hole; the square base frame is tightly matched or aligned with the base of the microscope.

10. The centering device of claim 8, wherein, The clamping rod fixing frame is positioned by being placed in the pre-marked fixed position of the stage through the limiting part or the mark point arranged on the base of the microscope, so that the clamping rod is aligned with the origin of the microscope objective micrometer in the vertical direction. The clamping rod fixing frame is positioned by being placed in the pre-marked fixed position of the stage through the limiting part or the mark point arranged on the base of the microscope, so that the clamping rod is aligned with the origin of the microscope objective micrometer in the vertical direction.

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