Optical microcavity with on-chip support and packaging method thereof

Abstract

The invention relates to an optical microcavity with an on-chip support and a packaging method thereof.The optical microcavity with the on-chip support comprises a substrate, an optical microcavity body and an on-chip fork supporting structure, the forked end of the on-chip fork supporting structure comprises two prong structures, the tail ends of the prong structures face the optical microcavity body, and the prong structures are arranged on the substrate. And the roots of the fork tooth structures are combined into a single-beam structure which is fixedly supported on the substrate. On-chip supporting in the optical microcavity packaging process can be achieved, the coupling stability is obviously higher than that of an optical microcavity sample without on-chip supporting, and the influence of curing of ultraviolet curing glue on coupling loss is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and in particular to an optical microcavity with on-chip support and its packaging method. Background Technology

[0002] Optical microcavities, as excellent carriers for light-matter interactions, have important applications in many fields, such as Kerr frequency combs and Brillouin lasers. Among these, optical frequency combs are particularly valuable in precision optical measurement, optical communication, optical atomic clocks, and low-noise microwave sources. Traditional mode-locked lasers generate optical frequency combs with complex structures and large volumes, making integrated applications difficult. Optical microcavities, however, offer significant advantages and application potential in frequency comb fabrication. Coupled and packaged on-chip optical microcavities with tapered optical fibers, this is a crucial solution for promoting the practical application of microcavity optical frequency combs.

[0003] Optical frequency combs based on optical microcavities have attracted widespread attention in recent years due to their advantages of small size, low power consumption, and ease of integration. Their application value has been verified in many fields such as low-noise microwave sources, dual-comb ranging, and optical communication. As a core component, research on optical microcavities is still mostly limited to large and complex optical systems in laboratories. High-stability packaging of these microcavities is key to keeping pace with the trend of miniaturization and integration of photonic devices.

[0004] The core purpose of optical microcavity packaging is to isolate the microcavity's operating state from external environmental factors such as temperature, humidity, and mechanical vibration. High-quality packaging processes must ensure that the coupling state of the microcavity remains largely unchanged before and after packaging. Currently, the mainstream packaging coupling methods for optical microcavities include tapered fiber packaging, waveguide coupling packaging, prism coupling packaging, and embedded dual-core hollow fiber coupling packaging. Among these, tapered fiber coupling has been proven to be the most ideal coupling method for optical microcavities due to its excellent coupling efficiency (approaching 100% critical coupling efficiency).

[0005] Existing methods for coupling and encapsulating tapered optical fibers and microcavities mainly fall into three categories: first, full encapsulation by completely covering the tapered optical fiber and the optical microcavity with low-refractive-index adhesive; second, point encapsulation by applying UV-curable adhesive to the coupling gap after adjusting the coupling state; and third, side-support encapsulation.

[0006] When microcavities are directly encapsulated using support pillars, they are susceptible to changes in the volume of UV-cured adhesive, which can increase the coupling depth and consequently lead to increased coupling loss. While independent indirect support fork structures can mitigate the changes in coupling state caused by UV-cured adhesive to some extent, they suffer from large size and complex manufacturing processes, which are detrimental to the miniaturization and integration of photonic devices.

[0007] In summary, existing tapered fiber coupling packaging technologies for optical microcavities generally suffer from limitations in adaptability, poor coupling stability, and poor device integration. Therefore, how to achieve high coupling efficiency and high stability packaging for optical microcavities while also meeting the miniaturization and integration requirements of photonic devices has become an urgent technical problem to be solved. Summary of the Invention

[0008] To solve the above technical problems, this invention adds an on-chip fork support structure at the sample level and adjusts the overlay height to meet the tapered fiber coupling requirements of microcavities of various sizes. During the packaging process, the optical microcavities are coupled and packaged using the combined support of direct side support pillars and the on-chip fork support structure. The packaging scheme is simple, highly applicable, highly repeatable, stable, and highly reliable.

[0009] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides an optical microcavity with on-chip support, the optical microcavity with on-chip support comprising: a substrate, an optical microcavity body and an on-chip fork support structure, the forked end of the on-chip fork support structure comprising two fork tooth structures, the ends of the fork tooth structures facing the optical microcavity body, and the roots of the fork tooth structures merging into a single beam structure fixedly supported on the substrate.

[0010] The fork-tooth structure of the on-chip fork support structure described in this invention is used to support the tapered optical fiber coupled to the optical microcavity during the packaging process. The single-beam structure is used to balance the support stress of the fork-tooth structure, improving support strength and stability. The on-chip fork support structure can provide stable support for the tapered optical fiber during subsequent packaging, improving packaging stability and reducing the impact of UV-curable adhesive curing shrinkage.

[0011] The optical microcavity with on-chip support described in this invention is suitable for samples with a body size of ≤6000μm, such as 660μm, 1000μm, 2000μm, 3000μm, 4000μm, 5000μm or 6000μm, etc.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] As a preferred technical solution of the present invention, the optical microcavity body and the on-chip fork support structure are both obtained by stepwise selective etching of the substrate and the functional layer on the substrate surface.

[0014] The substrate of the present invention includes a silicon substrate, and the surface functional layer includes a silicon dioxide layer.

[0015] As a preferred technical solution of the present invention, the stepwise selective etching includes simultaneous etching of the optical microcavity body and the on-chip fork support structure, and high-level etching of the on-chip fork support structure.

[0016] The synchronous etching process of the optical microcavity body and the on-chip fork support structure of this invention is as follows: a photoresist is uniformly coated on the surface of a silicon wafer with a silicon dioxide thin film layer. The photoresist in the corresponding areas of the optical microcavity body and the on-chip fork support structure is retained by photolithography. After wet etching, the photoresist is stripped off, and then the silicon substrate is dry etched with xenon difluoride gas to achieve selective etching of the silicon substrate, thereby obtaining a partially suspended optical microcavity body and on-chip fork support structure. The height etching of the on-chip fork support structure is as follows: the optical microcavity body is shielded by an overlay mask, and the exposed on-chip fork support structure is wet etched. By controlling the etching time, on-chip fork support structures of different heights can be prepared.

[0017] All etching steps described above in this invention can employ conventional etching agents and etching conditions in the art, as long as the optical microcavity structure described in this application can be obtained. This invention does not impose further limitations on these aspects.

[0018] As a preferred embodiment of the present invention, the height of the on-chip fork support structure is less than the height of the optical microcavity body.

[0019] The height of the on-chip fork support structure described in this invention is less than the height of the optical microcavity body. The specific height can be selected and optimized according to the packaging coupling effect, and is not further limited here. The optical microcavity with on-chip support provided by this invention is particularly suitable for large-diameter optical microcavity samples, and the height can be precisely adjusted. The mode field intensity distribution of large-diameter optical microcavity samples is concentrated inside the microcavity, requiring the height of the tapered optical fiber coupling to be lower than the height of the optical microcavity body, that is, coupled to the inclined surface of the microcavity.

[0020] As a preferred technical solution of the present invention, the single beam structure is a rectangle with an arc-shaped notch, the arc-shaped notch facing the optical microcavity body and matching the outer peripheral edge of the optical microcavity body.

[0021] The purpose of the arc-shaped notch on the side of the single beam structure near the optical microcavity in this invention is to increase the distance between the single beam structure and the optical microcavity body, thereby preventing the single beam structure from interfering with the resonant optical field of the optical microcavity body.

[0022] As a preferred technical solution of the present invention, the fork tooth structure is a rectangular fork tooth structure, and the aspect ratio of the rectangular fork tooth structure is 1.2 to 4.0, for example, it can be 1.2, 1.4, 1.6, 2.0, 2.5, 3.0, 3.5 or 4.0, etc.

[0023] The distance between the fork-tooth structure and the optical microcavity body described in this invention can be selected and optimized according to the encapsulation coupling effect, and is not further limited here.

[0024] In a second aspect, the present invention provides a packaging method for coupling an optical microcavity with on-chip support to a tapered optical fiber as described in the first aspect. The packaging method includes mounting the tapered optical fiber on the fork tooth structure of the on-chip fork support structure, adjusting it to a critical coupling position, and encapsulating it with UV-curable adhesive.

[0025] As a preferred technical solution of the present invention, the adjustment to the critical coupling position is performed using a high-precision displacement stage.

[0026] As a preferred technical solution of the present invention, the encapsulation is performed in an encapsulation box, which includes a housing, a substrate accommodating area, at least two support pillars and two fiber optic connectors, with the support pillars symmetrically arranged on both sides of the substrate accommodating area.

[0027] The housing of the encapsulation box of the present invention is an aluminum cuboid structure, including a lower half housing and an upper half housing that interlock, and a rubber gasket is provided between the interlocking surfaces of the upper and lower half housings to improve the sealing performance of the encapsulation. Threaded holes are provided at the four corners for fixing by screws. Through holes matching the fiber optic connector are provided on the left and right walls of the housing for leading out the optical fiber to access the optical path. The UV curing adhesive encapsulation is performed by dripping UV curing adhesive onto the contact point between the optical fiber and the support column and then performing UV curing.

[0028] As a preferred embodiment of the present invention, the substrate receiving area of ​​the packaging box is further provided with a temperature control pad.

[0029] This invention enables the adjustment of the coupling depth of the resonant mode by integrating a temperature control pad inside the packaging box after packaging through temperature control.

[0030] Compared with the prior art, the present invention has at least the following beneficial effects: (1) This invention achieves integrated fabrication of the optical microcavity body and the on-chip fork support structure on a silicon substrate through stepwise selective etching. The height of the on-chip fork support structure can be precisely controlled by the overlay process and made lower than the height of the optical microcavity body, which can meet the coupling requirements of microcavities of different sizes and improve the coupling stability during the packaging process. Moreover, the support structure adopts a fork tooth and a single beam design with an arc notch, which not only improves the support strength and stability, but also avoids interference with the microcavity resonant light field. At the same time, the on-chip integrated design greatly reduces the structure volume, which is in line with the trend of miniaturization and integration of photonic devices, and is compatible with silicon-based micro-nano processing technology, which is conducive to mass production. (2) The present invention adopts a combination of on-chip fork support structure and package box support column to complete the coupling packaging. The UV curing adhesive is cured at the contact point between the optical fiber and the support column, which effectively prevents the increase of coupling loss. At the same time, the package box is a sealed aluminum structure and integrates a temperature control gasket, which not only isolates external environmental interference and improves the working stability of the device, but also can accurately adjust the coupling depth through temperature control to further optimize the coupling effect. The overall packaging scheme is simple and highly repeatable. Attached Figure Description

[0031] Figure 1 These are scanning electron microscope images of an optical microcavity with on-chip support provided in Embodiment 1 of the present invention; Figure 2 This is a scanning electron microscope image of the side height of an optical microcavity with on-chip support provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the structure of the tapered optical fiber coupled with the optical microcavity provided in Embodiment 1 of the present invention; Figure 4 This is the optical path diagram of the packaging test system used in the packaging method provided in Embodiment 1 of the present invention; Figure 5 Figure 1 is a structural diagram of the packaged sample box provided in Embodiment 1 of the present invention, wherein Figure a is a physical picture of the unfastened sample box, Figure b is a physical picture of the fastened sample box, and Figure c is a three-dimensional structural schematic diagram. Figure 6 This is the microcavity resonance transmission spectrum obtained by testing in Embodiment 1 of the present invention; In the figure: 1-Optical microcavity body, 2-On-chip fork support structure, 3-Tapered optical fiber, 4-Support column. Detailed Implementation

[0032] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0033] In the following embodiments, the tapered optical fibers used were all made by stripping the coating layer of 1550nm SMF-28E single-mode optical fibers with wire strippers to expose the fiber core layer, placing them at a hydrogen nozzle, and stretching them using an automatic displacement table while heating them.

[0034] Example 1 This embodiment provides an optical microcavity with on-chip support, such as... Figure 1As shown, the device includes: a substrate, an optical microcavity body 1, and an on-chip fork support structure 2. The forked end of the on-chip fork support structure includes two fork tooth structures, the ends of which face the optical microcavity body. The roots of the fork tooth structures merge into a single beam structure fixedly supported on the substrate. The single beam structure is a rectangle with an arc-shaped notch facing the optical microcavity body and matching the outer peripheral edge of the optical microcavity body. The diameter of the optical microcavity body 1 is 660 μm, the height of the fork support structure 2 is 2.2 μm, the fork tooth structure is a rectangular fork tooth structure with an aspect ratio of 2.5, and the distance between the on-chip fork support structure and the optical microcavity body is 80 μm.

[0035] The optical microcavity with on-chip support is fabricated using the following method: A photoresist is uniformly coated onto the surface of a silicon wafer with a grown silicon dioxide thin film (silicon wafer thickness 525 μm, silicon dioxide layer thickness 4 μm). The photoresist is retained in the corresponding areas of the optical microcavity body and the on-chip fork support structure via photolithography. After wet etching using a mixture of hydrofluoric acid and ammonium fluoride etchant, the photoresist is stripped off. Then, the silicon substrate is dry-etched using xenon difluoride gas to achieve selective etching of the silicon substrate, resulting in a partially suspended optical microcavity body and on-chip fork support structure. An overlay mask is used to shield the optical microcavity body, and the exposed on-chip fork support structure is wet-etched to reduce its height. Figure 2 As shown; The tapered fiber is fabricated using an optical microcavity with on-chip support coupled and packaged with the aforementioned tapered fiber. The pre-travel distance of the tapered fiber is 15 μm, and the stretch distance is 22.5 μm. The coupling state between the tapered fiber 3 and the optical microcavity is as follows: Figure 3 As shown, and through as Figure 5 The package box shown is connected as follows Figure 4 In the test optical path shown, the light emitted from the 1550nm tunable laser passes sequentially through an amplifier attenuation controller and a polarization controller before entering the encapsulation box and coupling with the optical microcavity body. The exit beam is split at a 1:9 ratio and connected to a spectrometer and an oscilloscope, respectively. A power meter is used to observe and calculate the actual incoming power. The encapsulation box is made of aluminum and measures 40×25×6.5mm. A rubber gasket is added between the shell and the cover to improve sealing performance. The metal shell provides multiple support pillars for UV-cured adhesive fixation, and fiber optic connectors are provided at both ends for direct connection to the optical path.

[0036] During encapsulation, a pre-fabricated tapered optical fiber is used to couple the microcavity with on-chip support. The tapered fiber is mounted on a rectangular fork structure, and their relative positions are adjusted using a high-precision displacement stage. The tapered fiber is positioned in the middle of the microcavity's inclined surface during coupling, ensuring that the microcavity resonant mode is close to critical coupling as observed on the oscilloscope. This indicates that the tapered fiber thickness at the coupling point is appropriate, and the relative distance and position meet the low coupling loss requirements. To ensure low coupling loss, adhesive is applied to the support pillars on the encapsulation box, allowing sufficient space for UV curing adhesive shrinkage. UV lamps are used to cure the adhesive at the application point, fixing the relative position of the tapered fiber and the microcavity body. The resonant mode coupling loss remains almost unchanged before and after UV curing. The coupling depth of the resonant mode can be adjusted using temperature-controlled pads. The microcavity resonant transmission spectrum obtained after curing is shown below. Figure 6 As shown, the quality factor Q is 2.23 × 10⁻⁶. 7 Furthermore, there is almost no change before and after UV curing.

[0037] Example 2 This embodiment provides an optical microcavity with on-chip support. Except for the aspect ratio of the rectangular fork structure being 5.0, the rest is the same as in embodiment 1. In this embodiment, the rectangular fork structure breaks and falls off due to stress during the process of supporting the tapered optical fiber.

[0038] Example 3 This embodiment provides an optical microcavity with on-chip support. Except for not performing overlay on-chip fork support structure to reduce the height of the on-chip fork support structure, and directly using an on-chip fork support structure with the same height as the optical microcavity body for packaging, the rest is the same as in embodiment 1. In this embodiment, the microcavity body and the tapered optical fiber cannot be coupled in microcavity mode.

[0039] Comparative Example 1 This comparative example provides an optical microcavity. The optical microcavity is identical to that of Example 1, except that it lacks an on-chip fork support structure and is supported only by the support pillars of the encapsulation box during packaging. In this comparative example, the coupling loss increases significantly during UV curing, and the quality factor Q obtained after curing is 7.1 × 10⁻⁶. 6 .

[0040] The test results show that: (1) As can be seen from Example 1, by setting an on-chip fork support structure and combining the arc-shaped notch with the outer peripheral edge of the optical microcavity body, the present invention can achieve stable cooperation between the optical microcavity body and the support structure, while ensuring the high quality factor of the microcavity. Moreover, within a reasonable fork tooth aspect ratio range, the influence of the support structure on the optical performance of the microcavity can be effectively reduced, while ensuring stable support and ensuring that the microcavity has a good coupling effect.

[0041] (2) As can be seen from Examples 1, 2 and 3, the present invention can achieve better microcavity support stability and lower coupling loss by further optimizing the aspect ratio of the fork structure and precisely controlling the height of the on-chip fork support structure, thereby obtaining superior optical resonance performance. In Example 2, the aspect ratio of the fork was increased to 5.0, which caused the fork structure to break and fall off due to stress during the packaging process, making it impossible to achieve stable support; in Example 3, the height of the fork support structure was not adjusted, and the height of the support structure was not suitable, resulting in the inability to couple.

[0042] (3) As can be seen from Example 1 and Comparative Example 1, the present invention, by setting an on-chip fork support structure, can achieve a stable microcavity support effect, lower coupling loss, and better optical resonance performance. However, when the on-chip fork support structure is not used and only the package box support pillar is used for support, it is impossible to achieve stable positioning and support of the microcavity. In Comparative Example 1, the on-chip fork support structure is missing. During the UV curing process, the relative position of the microcavity and the tapered optical fiber shifts, resulting in a significant increase in coupling loss and a significant decrease in the Q value of the microcavity, which is much lower than that of Example 1. This fully demonstrates that the on-chip fork support structure can effectively fix the position of the microcavity, reduce the displacement of the microcavity during packaging and curing, reduce coupling loss, and ensure the stability of the optical performance of the microcavity.

[0043] In summary, this invention achieves stable support for the microcavity, reduces coupling loss, and ensures excellent optical resonance performance of the microcavity by setting an on-chip fork support structure with a specific structure, optimizing the aspect ratio of the fork teeth, and precisely controlling the height of the support structure. It solves the technical problems of unstable support, high coupling loss, and easy impact on optical performance of existing optical microcavities, and has significant technical advantages.

[0044] The applicant declares that the above description is only a specific embodiment 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 conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An optical microcavity with on-chip support, characterized in that, The optical microcavity with on-chip support includes: a substrate, an optical microcavity body, and an on-chip fork support structure. The forked end of the on-chip fork support structure includes two fork tooth structures. The ends of the fork tooth structures face the optical microcavity body, and the roots of the fork tooth structures merge into a single beam structure and are fixedly supported on the substrate.

2. The optical microcavity with on-chip support according to claim 1, wherein, Both the optical microcavity body and the on-chip fork support structure are fabricated by stepwise selective etching of the substrate and the functional layer on the substrate surface.

3. The optical microcavity with on-chip support according to claim 2, characterized in that, The stepwise selective etching includes simultaneous etching of the optical microcavity body and the on-chip fork support structure, and high-level etching of the on-chip fork support structure.

4. The optical microcavity with on-chip support according to claim 1, characterized in that, The height of the on-chip fork support structure is less than the height of the optical microcavity body.

5. The optical microcavity with on-chip support according to claim 1, characterized in that, The single beam structure is a rectangle with an arc-shaped notch, which faces the optical microcavity body and is adapted to the outer peripheral edge of the optical microcavity body.

6. The optical microcavity with on-chip support according to claim 1, characterized in that, The fork tooth structure is a rectangular fork tooth structure, and the aspect ratio of the rectangular fork tooth structure is 1.2 to 4.

0.

7. A packaging method for coupling an optical microcavity with on-chip support to a tapered optical fiber as described in any one of claims 1 to 6, characterized in that, The encapsulation method includes mounting a tapered optical fiber on the fork tooth structure of the on-chip fork support structure, adjusting it to the critical coupling position, and encapsulating it with UV-curable adhesive.

8. The packaging method according to claim 7, characterized in that, The adjustment to the critical coupling position is performed using a high-precision displacement stage.

9. The packaging method according to claim 7 or 8, characterized in that, The encapsulation is performed within an encapsulation box, which includes a housing, a substrate receiving area, at least two support pillars, and two fiber optic connectors. The support pillars are symmetrically arranged on both sides of the substrate receiving area.

10. The packaging method according to any one of claims 7 to 9, characterized in that, The substrate receiving area of ​​the packaging box is also provided with a temperature control pad.

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