A fiber optic collimator, a MEMS optical accelerometer, and their fabrication method

Abstract

This invention provides an optical fiber collimator, a MEMS optical accelerometer, and a fabrication method thereof. The optical fiber collimator includes a self-calibrating coupling unit, a self-focusing collimating unit, and a beam steering adjustment unit. The self-calibrating coupling unit has an axial inner hole, and both the self-focusing collimating unit and the beam steering adjustment unit are installed within this axial inner hole and arranged opposite to each other. The first end face of the beam steering adjustment unit facing the self-focusing collimating unit is arranged along an axis not perpendicular to the axial inner hole. Light incident through the self-focusing collimating unit is reflected by the first end face and redirected to exit the self-calibrating coupling unit. The optical fiber collimator integrates beam steering and angle adjustment functions. After system installation, the direction of the emitted beam can be optimized in real time by circumferentially adjusting the beam steering adjustment unit, greatly reducing installation difficulty.

Description

Technical Field

[0001] This invention relates to fiber optic collimators, MEMS optical accelerometers, and their fabrication methods, belonging to the field of optical sensor technology. Background Technology

[0002] Fiber optic collimators are core components of passive optical devices. Their core function is to convert divergent light transmitted in an optical fiber into collimated parallel light, or to efficiently couple parallel light in space into the optical fiber. They are key components in optical path coupling, optical interconnection, and fiber optic sensing systems. Traditional fiber optic collimators typically use ordinary single-mode fiber and C-lens, G-lens, or self-focusing lenses, precisely aligned and bonded together. The direction of their emitted beam is fixed and cannot be adjusted according to actual application requirements.

[0003] In practical applications such as free-space optical interconnects, optical switch arrays, and MEMS optical sensing, it is often necessary to change the propagation direction of the light beam, especially in space-constrained or vertically oriented board-level optical interconnect scenarios. Existing technologies typically use a combination of fixed-angle prisms / mirrors and fixed collimators to achieve optical path reversal. However, this combination method has significant drawbacks: during system integration and alignment, any tiny assembly error will cause optical axis misalignment, resulting in severe insertion loss. Furthermore, the error cannot be compensated or corrected after assembly, placing extremely high demands on machining precision and the operational experience of assembly personnel. Simultaneously, discrete prisms / mirrors and collimators occupy more optical path space, making it difficult to meet the application requirements of high-density integrated optical modules and miniaturized chip-level optical sensing units.

[0004] MEMS optical accelerometers are widely used in inertial navigation, earthquake monitoring, and other fields due to their advantages such as high sensitivity, resistance to electromagnetic interference, and suitability for harsh environments. The fiber optic collimator is the core component for achieving optical path coupling in MEMS optical accelerometers. Traditional optical accelerometers typically use discrete optical elements (lenses, mirrors, adjustment frames, etc.) for optical path construction and alignment, resulting in problems such as large size, complex assembly, poor stability, and high cost. In particular, the optical coupling process between the fiber and the MEMS optical chip requires manual or automatic alignment using a precise multi-dimensional adjustment frame, which is not only time-consuming and labor-intensive, but also prone to decreased coupling efficiency and reduced optical signal modulation accuracy due to material thermal expansion differences caused by vibration and environmental temperature changes during long-term use.

[0005] In related technologies, some solutions attempt to fix optical fibers and MEMS chips in a fixed package, but they still do not solve the core problems: First, the packaging process still requires precise adjustment and glue fixation, resulting in poor process consistency and difficulty in achieving batch automated assembly; second, there is a lack of mechanical limiting and self-aligning structures, and the coupling process relies on a high-precision six-dimensional adjustment device, which has a high operating threshold; third, the thermal matching of materials is not considered, and changes in ambient temperature can easily cause coupling shift, resulting in poor long-term stability of the sensor.

[0006] In summary, developing a fiber optic collimator with precisely adjustable output beam angle, capable of compensating for assembly errors, and with a compact structure, as well as an integrated MEMS optical accelerometer based on this collimator that achieves optical path self-coupling, simple assembly, and high stability, has become a pressing technical problem to be solved in this field. Summary of the Invention

[0007] In order to overcome at least one of the above-mentioned technical problems in the prior art, the present invention proposes an optical fiber collimator, a MEMS optical accelerometer, and a method for fabricating them.

[0008] The first aspect of this invention provides an optical fiber collimator.

[0009] It includes a self-calibrating coupling unit, a self-focusing collimating unit, and a beam steering adjustment unit;

[0010] The self-calibration coupling unit is provided with an axial inner hole, and the self-focusing collimation unit and the beam steering adjustment unit are both installed in the axial inner hole and are arranged opposite to each other;

[0011] The first end face of the beam steering adjustment unit facing the self-focusing collimation unit is arranged in an axis that is not perpendicular to the axial inner hole.

[0012] The light rays incident through the self-focusing collimating unit are reflected by the first end face and redirected to exit the self-calibration coupling unit.

[0013] In some optional embodiments, the self-focusing collimation unit includes a single-mode fiber and a graded-index fiber, with the graded-index fiber located between the single-mode fiber and the beam steering adjustment unit in the assembled state.

[0014] In some optional embodiments, the surface of the beam steering adjustment unit is coated with a high-reflectivity optical film, and / or the surface of the self-focusing collimation unit is coated with an anti-reflection film.

[0015] In some optional embodiments, a coreless fiber is connected between the single-mode fiber and the graded-index fiber; the single-mode fiber, the coreless fiber, and the graded-index fiber are sequentially fused together.

[0016] A second aspect of the present invention provides a MEMS optical accelerometer, comprising any of the fiber optic collimators described in the first aspect.

[0017] The aforementioned MEMS optical accelerometer also includes an upper substrate, an inertial-sensitive elastic beam structure, a lower substrate, and a coupling base connected in sequence.

[0018] The coupling base includes a through-hole for mounting the fiber collimator, and in the assembled state, the fiber collimator is parallel to at least one of the upper substrate or the lower substrate.

[0019] In some optional embodiments, the coupling base and the lower substrate are provided with interconnected internal holes;

[0020] The light rays incident through the self-focusing collimating unit are reflected by the first end face and redirected to exit the self-calibrating coupling unit. They then pass through the connecting inner hole, the coupling base, and the lower substrate, and irradiate the inertial sensitive elastic beam structure.

[0021] A third aspect of the present invention provides a method for fabricating any of the fiber collimators described in the first aspect.

[0022] The self-focusing collimation unit and the beam steering adjustment unit are respectively inserted into the axial inner hole of the self-calibration coupling unit;

[0023] Adjust the beam steering adjustment unit circumferentially so that the light incident through the self-focusing collimating unit is reflected by the first end face and redirected to exit the self-calibration coupling unit.

[0024] The self-focusing collimation unit and the beam steering adjustment unit are respectively fixed in the self-calibration coupling unit.

[0025] In some optional embodiments, the self-focusing collimation unit is fabricated using the following method:

[0026] One end of the single-mode fiber is fused together with a graded-index fiber.

[0027] Cut the fused single-mode fiber and graded-index fiber separately to make their overall length reach the preset value range;

[0028] The cut single-mode fiber and graded refractive index fiber are polished.

[0029] AR coating treatment is applied to the polished optical fiber.

[0030] In some optional embodiments, the beam steering adjustment unit is manufactured using the following method:

[0031] One end of the single-mode fiber is polished to make its end face form a preset angle with the axis of the single-mode fiber.

[0032] After the polished single-mode optical fiber is acid-washed, it is coated with a high-reflectivity optical film.

[0033] In some optional embodiments, the self-calibration coupling unit is fabricated using the following method:

[0034] Fabricate a tubular structure and provide a radial through hole in the middle of the tubular structure;

[0035] The two ends of the tubular object are ground and polished.

[0036] A fourth aspect of the present invention provides a method for fabricating a MEMS optical accelerometer according to any of the second aspects:

[0037] The upper substrate, the inertial-sensitive elastic beam structure, the lower substrate, and the coupling base are bonded sequentially.

[0038] Insert the fiber collimator into the through hole of the coupling base.

[0039] The fiber collimator is rotated circumferentially so that the light emitted from the fiber collimator illuminates the inertial sensitive elastic beam structure, and the reflected light from the inertial sensitive elastic beam structure is received. When the optical signal coupling efficiency reaches the set value, the fiber collimator is fixed on the coupling base.

[0040] In some optional embodiments, the inertial-sensitive elastic beam structure is fabricated using the following method:

[0041] Define the sensor surface area on an SOI wafer or an ultra-flat double-polished single-crystal silicon wafer;

[0042] The SOI wafer or ultra-flat double-polished single-crystal silicon wafer is etched to form a movable inertial-sensitive elastic beam structure, which includes a mass block and a support beam.

[0043] The technical solution of the present invention has the following advantages or beneficial effects:

[0044] (1) The fiber collimator integrates beam steering and angle adjustment functions. After the system is installed, the direction of the emitted beam can be optimized in real time by adjusting the beam steering adjustment unit in the circumferential direction, which greatly reduces the installation difficulty.

[0045] (2) The fiber optic collimator integrates collimation and adjustable steering functions into a miniaturized tubular device, eliminating the need for separate prisms / mirrors and saving optical path space. It is particularly suitable for high-density integrated optical modules and miniaturized optical sensing units. The MEMS optical accelerometer integrates the fiber optic collimator with the MEMS optical chip. The fiber optic collimator and the chip are set parallel to each other, which can effectively protect the fiber from bending and breakage. Moreover, when multi-axis integrated, the multi-axis fibers can emerge in the same direction, further reducing the structural size and realizing the miniaturization of multi-axis sensing.

[0046] (3) The coupling substrate of the MEMS optical accelerometer is provided with a high-precision through hole, which forms a transition / micro-gap fit with the fiber collimator to realize automatic radial alignment of the optical path. Only circumferential rotation is needed to complete the angle alignment, eliminating the need for an external precision multi-dimensional adjustment frame, reducing the dependence on the operator's experience, and effectively improving assembly efficiency.

[0047] (4) The MEMS optical accelerometer adopts a thermal matching design with an upper substrate, a lower substrate, a coupling substrate and an inertial sensitive elastic beam structure made of silicon dioxide. This effectively reduces the difference in thermal expansion of materials caused by changes in ambient temperature, reduces coupling offset caused by temperature drift, and improves measurement accuracy and measurement stability.

[0048] (5) The adjustment mechanism of the fiber collimator is simple and reliable. The circumferential adjustment method is intuitive and easy to operate. After the adjustment is completed, the double fixing method of 3410uv glue + 353ND glue ensures the stability of angle and optical path performance during long-term use. The first end face of the beam turning adjustment unit is acid-washed to improve the roughness, which makes the adhesion of the high reflectivity optical film stronger and the film layer is not easy to fall off, further ensuring the transmission efficiency of the optical path. Attached Figure Description

[0049] Figure 1 This is a cross-sectional schematic diagram of an optical fiber collimator according to an embodiment of the present invention;

[0050] Figure 2 This is a side view schematic diagram of another fiber optic collimator according to an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram of a self-calibrating coupling unit according to an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of a self-focusing collimation unit according to an embodiment of the present invention;

[0053] Figure 5 This is a schematic diagram of a beam steering adjustment unit according to an embodiment of the present invention;

[0054] Figure 6This is a cross-sectional schematic diagram of a MEMS optical chip according to an embodiment of the present invention;

[0055] Figure 7 This is a cross-sectional schematic diagram of a MEMS optical accelerometer according to an embodiment of the present invention;

[0056] Figure 8 This is a schematic diagram of another self-focusing collimation unit according to an embodiment of the present invention. Detailed Implementation

[0057] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0058] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0059] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0060] To address at least one of the technical problems in the background art, the first aspect of the present invention provides an optical fiber collimator. The collimator includes a self-calibrating coupling unit, a self-focusing collimating unit, and a beam steering adjustment unit. The self-calibrating coupling unit has an axial inner hole, and both the self-focusing collimating unit and the beam steering adjustment unit are installed in the axial inner hole and arranged opposite to each other. The beam steering adjustment unit faces a first end face of the self-focusing collimating unit at an axis not perpendicular to the axial inner hole. Light rays incident through the self-focusing collimating unit are reflected by the first end face and redirected to exit the self-calibrating coupling unit.

[0061] See Figures 1 to 5The demonstrated fiber optic collimator 10 includes a self-calibrating coupling unit 101, a self-focusing collimating unit 103, and a beam steering adjustment unit 102. The self-calibrating coupling unit 101 has an axial inner hole, which is through-hole to facilitate the installation of corresponding devices from one end or both ends. Specifically, the self-focusing collimating unit 103 and the beam steering adjustment unit 102 are both installed in the axial inner hole and positioned using the inner wall of the hole. In practice, the self-focusing collimating unit 103 and the beam steering adjustment unit 102 are arranged opposite each other with a certain gap between them. That is, the light-emitting end face of the self-focusing collimating unit 103 is opposite to the first end face 1021 of the beam steering adjustment unit 102, ensuring that all parallel light emitted from the self-focusing collimating unit 103 can irradiate the first end face 1021 of the beam steering adjustment unit 102. The beam steering adjustment unit 102 faces the first end face of the self-focusing collimating unit 103 at an axis not perpendicular to the axial inner hole. This non-perpendicular arrangement causes the light rays incident through the self-focusing collimating unit to be reflected by the first end face and redirected to exit the self-calibration coupling unit 101.

[0062] In some embodiments, the self-calibrating coupling unit is a tubular object made of silicon dioxide, with an overall length of 10±0.1 mm and an outer diameter of 1±0.005 mm. An axial inner hole is formed along the axial direction, with an inner diameter of 127±0.5 μm. This high-precision dimension ensures accurate matching with the self-focusing collimating unit and the beam steering adjustment unit. A radial through-hole 301 is formed in the middle of the tubular object. This through-hole is preferably a circular hole with a diameter >9 μm, serving as a light emission channel to prevent light reflection loss within the self-calibrating coupling unit.

[0063] The first end face 1021 of the beam steering adjustment unit facing the self-focusing collimation unit is an inclined surface, not perpendicular to the axis of the axial inner hole. The included angle between the two can be set according to actual needs, such as 30°, 45°, 60°, etc. The specific value can be flexibly selected according to actual needs. The above angle is only an example and does not constitute a limitation on the scope of protection of this invention. Taking a 45° included angle as an example, it can achieve a 90° vertical steering of the beam, meeting the vertical steering requirement. When the laser 104 is used as the incident light, the parallel light emitted from the self-focusing collimation unit irradiates the first end face 1021 and undergoes a 90° reflection. The reflected beam is emitted from the self-calibration coupling unit along the radial through hole 301, completing the beam steering and emission.

[0064] In the above embodiments, a self-calibrating coupling unit is designed as the basic support structure of the fiber optic collimator. The axial inner hole enables precise positioning of the self-focusing collimating unit and the beam steering adjustment unit, solving the problems of low positioning accuracy and large assembly errors in traditional collimators. A radial through-hole is opened in the middle of the self-calibrating coupling unit as an exit channel for the reflected beam, ensuring smooth beam exit after steering. The diameter of the radial through-hole is sufficiently large to avoid beam obstruction and loss caused by an excessively small diameter. Furthermore, the first end face of the beam steering adjustment unit is designed as an inclined surface at a preset angle to the axis, replacing the traditional discrete prisms / reflectors, achieving integrated beam steering. The angle of the inclined surface can be flexibly selected according to requirements, solving the problem of a fixed beam direction in traditional collimators.

[0065] In some optional embodiments, the self-focusing collimation unit includes a single-mode fiber 1031 and a graded-index fiber 1032 (i.e., GRIN fiber). In the assembled state, the graded-index fiber is located between the single-mode fiber and the beam steering adjustment unit. In practice, one end of the single-mode fiber and the graded-index fiber are fused together with a fiber optic fusion splicer for high precision. During the splicing process, the optical axes of both fibers are kept coaxial to avoid beam divergence caused by splicing deviation. In the assembled state, the graded-index fiber is located between the single-mode fiber and the beam steering adjustment unit; that is, the spliced ​​end of the single-mode fiber is connected to the graded-index fiber, and the free end of the graded-index fiber faces the first end face of the beam steering adjustment unit. This ensures that the light transmitted from the single-mode fiber, after being collimated by the graded-index fiber, illuminates the first end face in the form of parallel light.

[0066] In actual production, the fused single-mode fiber and graded-index fiber are placed on a high-precision fiber cleaver and precisely cut with the aid of a microscope, so that the overall length of the two is controlled within a set length, such as a preset range of 830-880μm. This length range can ensure that the divergent light transmitted by the single-mode fiber is converted into highly parallel light after passing through the graded-index fiber.

[0067] As described above, the self-focusing collimation unit is designed as a fusion structure of single-mode fiber and graded-index fiber. Utilizing the self-focusing characteristics of the graded-index fiber, it achieves efficient conversion of divergent light to parallel light, replacing traditional G-lens / C-lens lenses, reducing the number of optical components, and further simplifying the structure. Furthermore, the fusion structure of single-mode fiber and graded-index fiber eliminates the adhesive gaps found in traditional lenses, avoiding light reflection and refraction losses caused by gaps, and further reducing insertion loss. The overall length of the fused fiber is 830-880 μm, a key process parameter for self-focusing collimation and the core of achieving efficient collimation, solving the problems of low collimation efficiency and poor beam parallelism in traditional collimators.

[0068] In other examples, a coreless fiber 1033 is connected between the single-mode fiber and the GRIN fiber, and the single-mode fiber, coreless fiber, and GRIN fiber are sequentially fused together. By incorporating the coreless fiber, the beam in the single-mode fiber is expanded, and the miniature GRIN collimating fiber with added coreless fiber can achieve a greater working distance. Specifically, by designing the coreless fiber to be 600μm long and the GRIN fiber to be 398μm long, a miniature collimating fiber can be obtained. The purpose of adding the coreless fiber here is to expand the beam in the single-mode fiber, making the beam diameter entering the GRIN fiber larger, thus enabling the miniature GRIN collimating fiber to achieve a greater working distance. Preferably, one end of the single-mode fiber is connected to a connector. The connector is an FC / APC or LC / APC connector.

[0069] In some optional embodiments, the surface of the beam steering adjustment unit is coated with a high-reflectivity optical film, and / or the surface of the self-focusing collimating unit is coated with an anti-reflection film. In practice, a high-reflectivity optical film is coated on the first end face 1021 of the beam steering adjustment unit. For example, the reflective film layer is prepared with silicon dioxide as a substrate, and the reflectivity of the film layer is ≥98%, thereby ensuring that the parallel light irradiated to the first end face is efficiently reflected and reducing reflection loss. Optionally, an AR film is coated on the end face of the graded refractive index fiber of the self-focusing collimating unit facing the beam steering adjustment unit. The anti-reflection band of the AR film matches the optical band transmitted by the optical fiber, ensuring that the parallel light emitted from the self-focusing collimating unit irradiates the first end face without loss. As can be seen from the above description, the present invention preferably adopts a film layer combination design of anti-reflection film + high-reflectivity film to achieve lossless transmission and efficient reflection of the beam, maximizing the transmission efficiency of the optical path. In some embodiments, the self-calibration coupling unit is made of silicon dioxide or zirconium oxide, both of which have the characteristics of high hardness, good wear resistance, and stable optical performance. The fiber optic collimator is less prone to scratches and deformation during assembly and use, thus extending its lifespan. Furthermore, both silica and zirconium oxide are optically inert materials, exhibiting no optical absorption or scattering, and therefore do not affect beam transmission, ensuring efficient optical path transmission. Preferably, the first end face of the beam steering adjustment unit is acid-etched with hydrofluoric acid after grinding. Acid etching of the fiber surface at the first end face increases surface roughness, after which a high-reflectivity optical film is deposited on the first end face to improve film adhesion and prevent peeling.

[0070] A second aspect of the present invention provides a MEMS optical accelerometer, comprising any of the fiber optic collimators described in the first aspect. The MEMS optical accelerometer further comprises an upper substrate, an inertial-sensitive elastic beam structure, a lower substrate, and a coupling base connected sequentially. The coupling base includes a through-hole for mounting the fiber optic collimator, and in the assembled state, the fiber optic collimator is parallel to at least one of the upper substrate or the lower substrate. Figure 6 As shown, the MEMS optical chip 60 comprises an upper substrate 605, an inertial-sensitive elastic beam structure, a lower substrate 602, and a coupling base 601, bonded together in sequence to form an integrated structure. The upper substrate, lower substrate, and coupling base are all made of silicon dioxide, while the inertial-sensitive elastic beam structure is made of SOI. The inertial-sensitive elastic beam structure consists of a mass block 604 and support beams 603. Multiple support beams are provided, with one end connected to the mass block, allowing the mass block to move when the MEMS optical accelerometer is subjected to acceleration, with the movement constrained by the support beams to approximately parallel motion. Preferably, the support beams are S-shaped. When subjected to acceleration, the S-shaped support beams undergo elastic deformation; after the acceleration disappears, the elastic restoring force of the S-shaped support beams resets the mass block. A through-hole with a diameter of 1 ± 0.005 mm is provided on the coupling base, precisely matching the outer diameter of the fiber optic collimator 10. The fiber optic collimator is inserted axially into the through-hole, with a transition fit or a micro-gap fit between the two to achieve automatic radial alignment of the optical path. For example... Figure 6 and 7 As shown, after the fiber collimator is inserted into the through hole, its entire structure is arranged parallel to the lower substrate 602 or the upper substrate 605. This arrangement can effectively protect the fiber optic cable leading out of the fiber collimator and prevent the fiber from breaking due to bending. At the same time, when multi-axis is integrated, the multi-axis fibers can emerge in the same direction, reducing the size of the device.

[0071] The MEMS optical accelerometer of this invention adopts an integrated structure, which is simple to assemble. During manufacturing, the fiber optic collimator and the MEMS optical chip (i.e., Figure 6 The integrated structure (shown) eliminates the need for separate optical adjustment frames, resulting in a smaller overall device size. Assembly only requires inserting the fiber collimator into the through-hole, eliminating the need for complex alignment operations. Furthermore, the MEMS optical accelerometer of this invention employs self-radial alignment, achieving high coupling accuracy. Specifically, the transition fit between the through-hole and the fiber collimator enables automatic radial alignment of the optical path, significantly improving coupling accuracy. In addition, the device of this invention features excellent fiber protection and high integration. The parallel arrangement of the fiber collimator with the upper / lower substrates avoids fiber bending and prevents fiber breakage; in multi-axis integration, multi-axial fibers can emerge in the same direction, achieving miniaturization and integration of multi-axis sensing.

[0072] In some optional embodiments, the coupling base and the lower substrate are provided with interconnected internal holes; light rays incident through the self-focusing collimating unit are reflected by the first end face and redirected to exit the self-calibrating coupling unit, then pass through the interconnected internal holes, through the coupling base and the lower substrate, and irradiate the inertial sensitive elastic beam structure. Figure 6 and 7 As shown, interconnected internal holes are formed on the coupling substrate and the lower substrate, and the optical axis of the interconnected internal holes is aligned with the center position of the inertial sensitive elastic beam structure. Parallel light emitted from the self-focusing collimating unit of the fiber optic collimator is reflected by the first end face of the beam steering adjustment unit, exits through the radial through-hole, and then passes sequentially through the coupling substrate and the lower substrate, finally illuminating the center position of the inertial sensitive elastic beam structure. The inertial sensitive elastic beam structure is a movable structure. When the MEMS optical accelerometer is subjected to acceleration, the mass block 604 of the inertial sensitive elastic beam structure will displace along the acceleration direction, changing the optical gap between the inertial sensitive elastic beam structure and the upper / lower substrate, thereby interferomodulating the light signal illuminating it. The modulated light signal is reflected back to the fiber optic collimator through the original optical path, realizing acceleration detection.

[0073] The optical path transmission of the accelerometer of this invention is unobstructed, with low loss and high detection accuracy. Specifically, the modulation process of the optical signal is a purely optical process, free from electromagnetic interference. Furthermore, the displacement of the inertial-sensitive elastic beam structure is linearly related to the acceleration, and the change in the spatial cavity length of the optical interference cavity is proportional to the acceleration, ensuring the linearity and accuracy of the acceleration detection.

[0074] A third aspect of the present invention provides a method for fabricating any of the fiber collimators described in the first aspect. The method includes: inserting a self-focusing collimating unit and a beam steering adjustment unit into the axial inner hole of the self-calibrating coupling unit; adjusting the beam steering adjustment unit circumferentially so that light incident through the self-focusing collimating unit is reflected by the first end face and redirected to exit the self-calibrating coupling unit; and fixing the self-focusing collimating unit and the beam steering adjustment unit within the self-calibrating coupling unit.

[0075] In practice, the fabrication of the self-focusing collimation unit, beam steering adjustment unit, and self-calibration coupling unit can be carried out simultaneously to improve production efficiency. After completing the fabrication of each unit, the self-focusing collimation unit is inserted into the axial inner hole from one end of the self-calibration coupling unit, with the graded-index fiber facing the middle of the self-calibration coupling unit. The beam steering adjustment unit is then inserted into the axial inner hole from the other end of the self-calibration coupling unit, with its first end face facing the graded-index fiber of the self-focusing collimation unit; the two are positioned opposite each other. The self-calibration coupling unit is then fixed on the optical detection platform, and laser 104 is introduced into the single-mode fiber of the self-focusing collimation unit. After collimation, the laser irradiates the first end face of the beam steering adjustment unit and is reflected. Next, the circumferential beam steering adjustment unit is adjusted, and the exit position of the reflected beam is observed through the optical detection platform until the reflected beam completely exits from the radial through-hole, and the exit direction of the beam meets the preset requirements. Finally, apply 3410UV adhesive 201 to the connection points of the self-focusing collimation unit, beam steering adjustment unit, and self-calibration coupling unit, and irradiate with UV light for 10 seconds to cure the 3410UV adhesive, completing rapid fixation and preventing positional shifts after adjustment. After rapid fixation with the 3410UV adhesive, apply 353ND adhesive in a ring around the connection points of the self-focusing collimation unit, beam steering adjustment unit, and self-calibration coupling unit to reinforce fixation, forming a robust integrated structure between each unit and the self-calibration coupling unit.

[0076] Preferably, finished product testing can also be performed to confirm whether the equipment manufacturing is qualified. First, the prepared fiber collimator is connected to an optical testing device to test the performance indicators such as the parallelism, turning angle, and insertion loss of the emitted beam. If the indicators do not meet the preset requirements, the circumferential position of the beam turning adjustment unit can be readjusted by debonding; if the indicators meet the standards, it is a qualified finished fiber collimator.

[0077] In this invention, the rapid fixation with 3410UV adhesive prevents positional shifts after adjustment, while the reinforcing fixation with 353ND adhesive further enhances the connection strength of each unit. This ensures that the fiber optic collimator remains stable without unit loosening or positional shifts under harsh environments such as vibration and impact, resulting in excellent structural stability. The manufacturing method of this invention offers high assembly precision and good performance consistency.

[0078] In some optional embodiments, the self-focusing collimation unit is fabricated using the following method: one end of a single-mode fiber is fused to a graded-index fiber; the fused single-mode fiber and the graded-index fiber are cut separately to make their overall length reach a preset value range; the cut single-mode fiber and the graded-index fiber are polished; and the polished fiber is coated with AR coating.

[0079] The fabrication of the self-focusing collimating unit is a core pre-process in the fabrication of fiber optic collimators. The specific steps are as follows: First, single-mode fiber and graded-index (GRIN) fiber are selected and fused together with high precision using a fiber optic fusion splicer. During the splicing process, the coaxiality of the optical axes of both fibers is ensured to avoid beam divergence caused by splicing deviation. Next, the fused single-mode fiber and GRIN fiber are placed on a high-precision fiber cleaver. The fusion splice surface is observed under a microscope, and the fiber is precisely cleaved to ensure the overall length of the fused fiber is controlled between 830-880 μm. Then, the cleaved fiber is inserted into a fiber optic adapter for fixation. The adapter is placed on a dedicated fiber polishing machine to polish the fiber's output end face. The polishing loss is strictly controlled within 10 μm to ensure the flatness and smoothness of the end face. Finally, the polished fiber is removed from the adapter and fixed on a dedicated coating fixture for coating. For example, the fixture can be placed in a vacuum coating machine, and an AR film can be deposited on the fiber's output end face using electron beam evaporation. Optionally, the coated self-focusing collimating unit can be connected to an optical inspection device to test its performance indicators such as the roundness of the emitted light spot, the parallelism of the beam, and the working distance. If the indicators meet the standards, it is a qualified self-focusing collimating unit product for later use.

[0080] This invention controls the length of the self-focusing collimating unit to 830-880 μm, enabling graded-index optical fibers to completely convert divergent light from single-mode fibers into parallel light. A precise polishing loss of 10 μm ensures the fiber's output end face is free of scratches, burrs, and other defects, significantly improving the transmission efficiency of the optical path.

[0081] In some optional embodiments, the beam steering adjustment unit is manufactured by the following method: grinding one end of the single-mode fiber so that its end face is at a preset angle with the axis of the single-mode fiber; after acid washing, the ground single-mode fiber is coated with a high-reflectivity optical film.

[0082] In some embodiments, the beam steering adjustment unit is fabricated using the following method: First, a single-mode optical fiber is selected and coaxially fixed within an optical fiber adapter to ensure no movement of the fiber during polishing. Next, the adapter with the fixed fiber is placed on a dedicated optical fiber polishing machine, and the polishing angle is set according to the optical path steering requirements, such as 30°, 45°, 60°, etc. An angle polishing disc is used to polish the fiber end face to form the first end face. Then, the polished fiber is removed from the adapter, fixed on a dedicated fixture, and the first end face is immersed in a hydrofluoric acid solution for acid cleaning. After acid cleaning, it is rinsed clean with deionized water and dried. Acid cleaning improves the surface roughness of the first end face. Finally, the acid-cleaned fiber is fixed on a coating fixture and placed in a vacuum coating machine. A high-reflectivity optical film is deposited on the first end face using silica as a substrate. The reflectivity of the film layer is ≥98%, thus completing the beam steering adjustment unit.

[0083] Preferably, the coated beam steering adjustment unit is connected to an optical testing device to test the reflectivity, angular accuracy and other indicators of the first end face. If the indicators meet the standards, it is a qualified finished beam steering adjustment unit for later use.

[0084] The manufacturing method of this invention results in strong film adhesion and good long-term stability. Hydrofluoric acid pickling increases the roughness of the first end face, increasing the contact area between the film and the end face, thus enhancing film adhesion. Even under harsh environments such as vibration, the film does not peel off or crack, ensuring long-term stability. Crucially, the solution of this invention offers flexible turning angles and wide adaptability. Specifically, grinding angles such as 30°, 45°, and 60° can be selected according to actual optical path requirements to achieve beam deflection at different angles, meeting diverse optical path design needs.

[0085] In some optional embodiments, the self-calibrating coupling unit is fabricated using the following method: a tubular structure is fabricated, and a radial through-hole is provided in the middle of the tubular structure; the two ends of the tubular structure are ground and polished. The self-calibrating coupling unit is the basic support structure of the fiber optic collimator, and its fabrication process is as follows. First, silica or zirconium oxide material is selected as the substrate and processed into a tubular structure using precision micromachining equipment, strictly controlling the dimensional parameters of the tubular structure: length 10±0.1mm, outer diameter 1±0.005mm, and inner diameter of the axial inner hole 127±0.5μm. Next, a radial through-hole is formed in the central region of the tubular structure. The radial through-hole can be a circular hole, a U-shaped hole, or a conical hole, etc. A circular hole is preferred, and the hole diameter is strictly controlled to be >9μm, thereby ensuring that the reflected beam can pass through without obstruction. Then, the tubular object with radial through holes is placed on a special grinding and polishing machine, and the end faces at both ends are ground and polished to remove burrs, cracks and other defects, ensuring the flatness and smoothness of the end faces, while making the end faces perpendicular to the axis of the tubular object.

[0086] Preferably, the polished tubular object is connected to a dimensional inspection device to check its length, outer diameter, inner diameter, radial through hole diameter, and other dimensional parameters. If all parameters are within the error range, it is a qualified self-calibrating coupling unit product for later use.

[0087] In this invention, all dimensional parameters of the tubular structure are controlled at the micrometer level. The fit gap between the axial inner hole and the self-focusing collimation unit and beam steering adjustment unit is <0.005mm, achieving a precise fit and avoiding unit wobbling caused by the fit gap, thus ensuring the structural stability of the fiber optic collimator. Furthermore, the silica / zirconia material has a high Mohs hardness and good wear resistance, preventing scratches and deformation during assembly and use. Both materials are optically inert, exhibiting no optical absorption or scattering, and will not affect beam transmission. Additionally, the ends of the tubular structure are polished to remove burrs and cracks, effectively preventing scratches on the optical fiber and extending the service life of the fiber optic collimator. The radial through-hole diameter is >0.5mm and is located in the central region of the tubular structure, precisely corresponding to the exit position after beam steering. The reflected beam can pass through unobstructed, without beam cutting or scattering, further reducing optical path loss.

[0088] A fourth aspect of this invention provides a fabrication method for preparing any of the MEMS optical accelerometers described in the second aspect, or a MEMS optical pressure sensor or a MEMS optical acoustic pressure sensor having a similar chip structure. The steps include: sequentially bonding an upper substrate, an inertial-sensitive elastic beam structure, a lower substrate, and a coupling base; inserting an optical fiber collimator into a through-hole in the coupling base; rotating the optical fiber collimator circumferentially so that the light emitted from the optical fiber collimator illuminates the inertial-sensitive elastic beam structure, and receiving the reflected light from the inertial-sensitive elastic beam structure; and fixing the optical fiber collimator to the coupling base when the optical signal coupling efficiency reaches a set value. The fabrication method of the MEMS optical accelerometer mainly includes two core steps: fabrication... Figure 6The steps for fabricating a MEMS optical chip and its assembly are shown below. For example, the MEMS optical accelerometer is fabricated using the following steps: First, a silicon dioxide upper substrate, a lower substrate, a coupling substrate, and a single-crystal silicon inertial-sensitive elastic beam structure are selected. The lower substrate, the inertial-sensitive elastic beam structure, the upper substrate, and the coupling substrate are sequentially bonded using a bonding process to form an integrated MEMS optical chip. Next, an optical fiber collimator is inserted axially into the through-hole of the coupling substrate of the MEMS optical chip. The outer diameter of the optical fiber collimator and the through-hole are in a transition fit to achieve automatic radial alignment of the optical path. Then, the MEMS optical chip with the optical fiber collimator inserted is placed on an optical detection platform. A laser signal is introduced into the optical fiber collimator. After being redirected and emitted, the laser light passes through the connecting hole between the coupling substrate and the lower substrate and irradiates the inertial-sensitive elastic beam structure. The optical fiber collimator is slowly rotated circumferentially. The coupling efficiency of the reflected light signal is demodulated using an optical detection device. When the coupling efficiency reaches a set value, the rotation is stopped, and the position of the optical fiber collimator is maintained. Finally, once the optical signal coupling efficiency meets the standard, the connection between the fiber collimator and the coupling substrate is fixed using UV-curable adhesive, low-temperature solder, or glass solder 701. Preferably, a dual fixing method using UV-curable adhesive and glass solder is employed. That is, UV-curable adhesive is used for rapid positioning first, followed by encapsulation using glass solder to enhance mechanical strength and sealing.

[0089] Preferably, the prepared MEMS optical accelerometer is connected to a sensing performance testing device to test its acceleration detection sensitivity, linearity, temperature drift, vibration resistance and other performance indicators. If all indicators meet the preset requirements, it is a qualified MEMS optical accelerometer finished product.

[0090] In some optional embodiments, the inertial-sensitive elastic beam structure is fabricated using the following method: a sensor surface region is defined on an SOI wafer or an ultra-flat double-polished single-crystal silicon wafer; the SOI wafer or ultra-flat double-polished single-crystal silicon wafer is etched to form a movable inertial-sensitive elastic beam structure, which includes a mass block and a support beam. An exemplary fabrication method is as follows: First, a high-purity SOI wafer or ultra-flat double-polished single-crystal silicon wafer is selected, and the wafer is cleaned and dried to remove surface oil, dust, and other impurities, ensuring the cleanliness of the wafer surface. Then, the sensor surface region is defined on the device layer surface of the SOI wafer or ultra-flat double-polished single-crystal silicon wafer using thermal oxidation and photolithography. Then, reactive ion etching (RIE) or deep reactive ion etching (DRIE) processes are used to etch the photolithographically etched SOI wafer or ultra-flat double-polished single-crystal silicon wafer, etching away excess silicon material according to the contour pattern of the inertial-sensitive elastic beam structure to form an S-shaped support beam structure and release the cavity in the mass block-support beam region. Next, the SOI wafer or ultra-flat double-polished single-crystal silicon wafer is flipped over, and deep reactive ion etching (DRIE) is used to etch from the back of the wafer to release the mass block and S-shaped support beam, making the inertial sensitive elastic beam structure a movable structure, thus completing the fabrication of the inertial sensitive elastic beam structure.

[0091] Preferably, the completed inertial sensitive elastic beam structure is placed under a metallographic microscope to observe its structural integrity, and the dimensional accuracy and mobility of the mass block and S-shaped support beam are tested. If the structure is undamaged, the dimensional accuracy is within the error range, and the mobility is good, it is a qualified finished inertial sensitive elastic beam structure for later use.

[0092] This invention is made using SOI wafers or ultra-flat double-polished single-crystal silicon wafers, which have the characteristics of high elastic modulus and low internal stress. The S-shaped support beam has good linearity of elastic deformation, and the mass block can produce significant displacement when subjected to small acceleration. This improves the sensing sensitivity of the inertial sensitive elastic beam structure and meets the requirements of high-precision acceleration detection.

[0093] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art, after considering the specification and practicing the technical solutions disclosed in this application, will readily conceive of other embodiments of this application. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary technical means in the art not disclosed in this application. The specification and embodiments are considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0094] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. An optical fiber collimator, characterized in that: It includes a self-calibrating coupling unit, a self-focusing collimating unit, and a beam steering adjustment unit; The self-calibration coupling unit is provided with an axial inner hole, and the self-focusing collimation unit and the beam steering adjustment unit are both installed in the axial inner hole and are arranged opposite to each other, with a certain gap between them; The inner diameter of the axial inner hole of the self-calibrating coupling unit is 127±0.5μm; The first end face of the beam steering adjustment unit facing the self-focusing collimation unit is arranged in an axis that is not perpendicular to the axial inner hole. The light rays incident through the self-focusing collimating unit are reflected by the first end face and redirected to exit the self-calibration coupling unit.

2. The fiber optic collimator according to claim 1, characterized in that, The self-focusing collimation unit includes a single-mode fiber and a graded-index fiber. In the assembled state, the graded-index fiber is located between the single-mode fiber and the beam steering adjustment unit.

3. The fiber optic collimator according to claim 1, characterized in that, The surface of the beam steering adjustment unit is coated with a high-reflectivity optical film, and / or the surface of the self-focusing collimation unit is coated with an anti-reflection film.

4. The fiber optic collimator according to claim 2, characterized in that, A coreless fiber is connected between the single-mode fiber and the graded-index fiber; the single-mode fiber, the coreless fiber, and the graded-index fiber are fused together in sequence.

5. A MEMS optical accelerometer, comprising the fiber collimator as described in any one of claims 1 to 4, characterized in that: The aforementioned MEMS optical accelerometer also includes an upper substrate, an inertial-sensitive elastic beam structure, a lower substrate, and a coupling base connected in sequence. The coupling base includes a through-hole for mounting the fiber collimator, and in the assembled state, the fiber collimator is parallel to at least one of the upper substrate or the lower substrate.

6. The MEMS optical accelerometer according to claim 5, characterized in that, The coupling base and the lower substrate are provided with interconnected internal holes; The light rays incident through the self-focusing collimating unit are reflected by the first end face and redirected to exit the self-calibrating coupling unit. They then pass through the connecting inner hole, the coupling base, and the lower substrate, and irradiate the inertial sensitive elastic beam structure.

7. A method for fabricating an optical fiber collimator as described in any one of claims 1 to 4, characterized in that: The self-focusing collimation unit and the beam steering adjustment unit are respectively inserted into the axial inner hole of the self-calibration coupling unit; Adjust the beam steering adjustment unit circumferentially so that the light incident through the self-focusing collimating unit is reflected by the first end face and redirected to exit the self-calibration coupling unit. The self-focusing collimation unit and the beam steering adjustment unit are respectively fixed in the self-calibration coupling unit.

8. The preparation method according to claim 7, characterized in that, The self-focusing collimation unit is fabricated using the following method: One end of the single-mode fiber is fused together with a graded-index fiber. Cut the fused single-mode fiber and graded-index fiber separately to make their overall length reach the preset value range; The cut single-mode fiber and graded refractive index fiber are polished. AR coating treatment is applied to the polished optical fiber.

9. The preparation method according to claim 7, characterized in that, The beam steering adjustment unit is manufactured using the following method: One end of the single-mode fiber is polished to make its end face form a preset angle with the axis of the single-mode fiber. After the polished single-mode optical fiber is acid-washed, it is coated with a high-reflectivity optical film.

10. The preparation method according to claim 7, characterized in that, The self-calibration coupling unit is fabricated using the following method: Fabricate a tubular structure and provide a radial through hole in the middle of the tubular structure; The two ends of the tubular object are ground and polished.

11. A method for fabricating a MEMS optical accelerometer as described in any one of claims 5 or 6, characterized in that: The upper substrate, the inertial-sensitive elastic beam structure, the lower substrate, and the coupling base are bonded sequentially. Insert the fiber collimator into the through hole of the coupling base. The fiber collimator is rotated circumferentially so that the light emitted from the fiber collimator illuminates the inertial sensitive elastic beam structure, and the reflected light from the inertial sensitive elastic beam structure is received. When the optical signal coupling efficiency reaches the set value, the fiber collimator is fixed on the coupling base.

12. The preparation method according to claim 11, characterized in that, The inertial-sensitive elastic beam structure is fabricated using the following method: Define the sensor surface area on an SOI wafer or an ultra-flat double-polished single-crystal silicon wafer; The SOI wafer or ultra-flat double-polished single-crystal silicon wafer is etched to form a movable inertial-sensitive elastic beam structure, which includes a mass block and a support beam.

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