Method and system for silver nanoparticles deposition on end face of large core optical fiber

Abstract

This invention relates to a method for depositing silver nanoparticles on the end face of a large-core multimode fiber, comprising: surface modification of the end face to be deposited in the large-core multimode fiber; dispersing pre-prepared silver nanoparticles in a solvent to form a silver nanoparticle suspension; fixing the end face to be deposited in the silver nanoparticle suspension; inputting deposition light from the end of the large-core multimode fiber away from the end face to be deposited; applying dynamic perturbation to the mode modulation section of the large-core multimode fiber away from the end face to be deposited, causing the phase relationship or coupling relationship between multiple transmission modes in the large-core multimode fiber to change over time; under the action of the output light field of the end face after dynamic perturbation, causing the silver nanoparticles to migrate to the region corresponding to the fiber core in the end face to be deposited and fix to the surface adsorption layer. The silver nanoparticle deposition method on the end face of a large-core multimode fiber provided by this invention can reduce the tendency of local aggregation at the fixed bright spot and make the distribution of silver nanoparticles in the region corresponding to the large-core fiber core more uniform.

Description

Technical Field

[0001] This invention relates to the field of optical fiber manufacturing technology, and in particular to a method and system for depositing silver nanoparticles on the end face of a large-core optical fiber. Background Technology

[0002] Constructing a layer of metal nanoparticles on the end face of an optical fiber can be used for surface-enhanced Raman scattering detection, fiber end face sensing, and the fabrication of micro / nano optical devices. The coverage location, particle distribution, and adhesion stability of the metal nanoparticle layer affect the detection sensitivity and repeatability of the fiber end face structure.

[0003] For small-core single-mode fibers, the end-face mode field area is small, and the spatial distribution of the output optical field is relatively simple. When using the fiber's own output optical field to induce the deposition of metal nanoparticles, the nanoparticles are easily confined to a small area corresponding to the fiber core. However, the situation is different for large-core multimode fibers, whose core diameter typically reaches the hundreds of micrometers, enabling them to support a wider range of transmission modes. When multiple modes are superimposed at the end face, the end-face output optical field tends to exhibit a speckle distribution. This speckle distribution includes localized bright and dark spots. When the fiber coupling, bending, and stress states remain essentially unchanged, the end-face speckle will maintain a relatively stable spatial distribution during the deposition time.

[0004] Under the aforementioned conditions, if conventional light-induced deposition is used directly, silver nanoparticles tend to preferentially migrate and adsorb near local bright spots, while the deposition amount in weak light regions is relatively insufficient. As the fiber core diameter increases and the end-face area expands, the optical power per unit area decreases, and the influence of fixed speckle on the deposition distribution becomes more pronounced. Therefore, the deposition of silver nanoparticles on the end face of large-core multimode fibers not only requires matching the deposition area with the fiber core area but also needs to suppress localized over-deposition caused by fixed speckle bright spots.

[0005] Vacuum coating, chemical in-situ reduction, and liquid surface self-assembly can all form metal nanostructures on the end face of optical fibers, but there are still problems such as high equipment requirements, insufficient regional selectivity, difficulty in controlling particle size, or insufficient matching between deposition position and fiber core light guiding area. Summary of the Invention

[0006] This invention addresses the technical problem of localized agglomeration and uneven coverage of silver nanoparticles on the end face of large-core multimode optical fibers due to fixed speckle distribution in existing technologies, and provides a method and system for depositing silver nanoparticles on the end face of large-core multimode optical fibers.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for depositing silver nanoparticles on the end face of a large-core optical fiber includes: The surface of the end face to be deposited in a large core diameter multimode optical fiber is modified to form a surface adsorption layer for fixing silver nanoparticles. Pre-fabricated silver nanoparticles are dispersed in a solvent to form a silver nanoparticle suspension; The end face to be deposited is fixed in a silver nanoparticle suspension; Deposition light is input from the end of a large-core multimode fiber furthest from the end face to be deposited; During the input deposition light process, dynamic perturbation is applied to the mode modulation section of the large core diameter multimode fiber that is far from the end face to be deposited, so that the phase relationship or coupling relationship between multiple transmission modes in the large core diameter multimode fiber changes with time, and the instantaneous speckle distribution of the end face to be deposited changes during the deposition process. Under the action of the output light field after dynamic disturbance, the silver nanoparticles migrate to the region corresponding to the fiber core in the end face to be deposited and are fixed on the surface adsorption layer to form a silver nanoparticle deposition layer.

[0008] Furthermore, an end fixing section is provided between the mode modulation section and the end face to be deposited; During the deposition process, the end fixing section is fixed to keep the end face to be deposited stable relative to the deposition container containing the silver nanoparticle suspension.

[0009] Furthermore, applying dynamic perturbations to the mode modulation section includes: Change the bending state and / or stress state of the mode modulation segment.

[0010] Furthermore, applying dynamic perturbations to the mode modulation section includes: The motion of the modulated segment is driven by a piezoelectric actuator, a vibration actuator, a rotary actuator, or an adjustable bending actuator. The dynamic disturbance has a disturbance frequency of 10Hz-2kHz and a disturbance amplitude of 1μm-100μm.

[0011] Furthermore, during the calibration stage before deposition, output light field images of the end face to be deposited are acquired in both undisturbed and dynamically disturbed states. The speckle contrast is calculated based on the output light field images, and the dynamic disturbance parameters are adjusted so that the speckle contrast in the dynamically disturbed state is lower than that in the undisturbed state.

[0012] Furthermore, speckle contrast is the ratio of the standard deviation of light intensity to the average light intensity in the output light field image; When acquiring the output light field image under dynamic disturbance, the image exposure time shall not be less than ten disturbance cycles of the dynamic disturbance.

[0013] Furthermore, the process of inputting deposition light involves multiple deposition cycles; Each deposition cycle includes a photo-deposition phase and a pause in refueling phase; During the photo-deposition stage, deposition light is input and dynamic perturbation is applied. During the pause supply stage, the input of deposition light is stopped or the power of deposition light is reduced, so that the silver nanoparticle suspension near the end face to be deposited is replenished with particles.

[0014] Furthermore, fixing the end face to be deposited in the silver nanoparticle suspension includes: fixing the end face to be deposited in the confined deposition cavity, and allowing the silver nanoparticle suspension to flow through the area in front of the end face to be deposited.

[0015] The present invention also provides a large-core fiber end face silver nanoparticle deposition system for realizing the large-core fiber end face silver nanoparticle deposition method, comprising: a mounting base, a large-core multimode fiber, a laser, a fiber coupling module, a fiber fixing module, a deposition container, a dynamic disturbance module, and a control module; The large-core-diameter multimode fiber is provided with a deposition end face, an end fixing section, a mode modulation section and an incident end fixing section. The end fixing section is located between the deposition end face and the mode modulation section, and the mode modulation section is located between the end fixing section and the incident end fixing section. The deposition container is mounted on the mounting base and located on one side of the fiber optic fixing module. The deposition container is used to contain the silver nanoparticle suspension, and the end face to be deposited extends into the deposition container. The fiber coupling module is located on the side of the large-core multimode fiber away from the end face to be deposited. The laser and the fiber coupling module are positioned opposite each other. The fiber coupling module corresponds to the fixed section at the incident end so as to couple the deposition light output by the laser into the large-core multimode fiber. The fiber optic fixing module is mounted on the mounting base. The fiber optic fixing module includes a first fixing member and a second fixing member. The first fixing member clamps the end fixing section, and the second fixing member clamps the incident end fixing section, so as to keep the end face to be deposited stable relative to the deposition container. The dynamic disturbance module is disposed between the first fixing member and the second fixing member. The dynamic disturbance module includes a driving member and a clamping member connected to the output end of the driving member. The driving member is connected to the mounting base, and the clamping member clamps the mode modulation segment so that when the driving member moves, it causes the mode modulation segment to produce a bending state change or a force state change. The control module is electrically connected to both the laser and the drive unit.

[0016] Furthermore, it also includes a light field monitoring module, which comprises an imaging lens group, an image sensor, and a monitoring bracket; The monitoring bracket is mounted on the mounting base, and the imaging lens assembly and image sensor are mounted on the monitoring bracket. The deposition container is equipped with an observation window corresponding to the end face to be deposited. The optical axis of the imaging lens group is oriented towards the observation window or the end face to be deposited. The image sensor is located on the imaging side of the imaging lens group and is electrically connected to the control module.

[0017] The method and system for depositing silver nanoparticles on the end face of large-core optical fibers provided by this invention have at least the following beneficial effects: This invention provides a method for depositing silver nanoparticles on the end face of a large-core fiber. Deposition light is output through a large-core multimode fiber to guide silver nanoparticles towards the corresponding region of the fiber core. Dynamic perturbation is applied to the mode modulation section far from the end face to be deposited, altering the phase or coupling relationships between different transmission modes within the multimode fiber. Since the end face speckle pattern is formed by the superposition of multiple transmission modes, the instantaneous speckle distribution on the end face changes over time after the mode state changes. The migration, approach, and fixation of silver nanoparticles all exhibit time-cumulative characteristics; therefore, their deposition position is no longer primarily dominated by a single fixed speckle bright spot, but rather influenced by the average effect of the output light field over a period of time. This reduces the tendency for local aggregation at fixed bright spots, resulting in a more balanced distribution of silver nanoparticles within the corresponding region of the large-core fiber core.

[0018] The large-core fiber end-face silver nanoparticle deposition system provided by this invention comprises a first fixing member that secures the end-face near the deposition target, ensuring stability within the deposition container; and a second fixing member that secures the incident end-face near the incident end, stabilizing the fiber coupling. A dynamic disturbance module operates only on the mode modulation section between these two members, separating end-face stabilization and dynamic mode modulation in different fiber segments. This structural relationship enables the system to alter the internal transmission mode state of the large-core multimode fiber while reducing end-face liquid phase disturbance. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a large-core optical fiber end-face silver nanoparticle deposition system provided in an embodiment of the present invention. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the invention will be thorough and complete.

[0021] Example 1 This embodiment provides a method for depositing silver nanoparticles on the end face of a large-core multimode fiber. The method uses the end face 21 of a large-core multimode fiber 2 as the deposition target, allowing silver nanoparticles to form a silver nanoparticle deposition layer in the region corresponding to the fiber core within the end face 21. The core diameter of the large-core multimode fiber 2 is not less than 100 μm. Further, the core diameter of the large-core multimode fiber 2 is 200 μm-600 μm. The region corresponding to the fiber core refers to the area on the end face 21 occupied by the fiber core, which is also the region where the deposition light mainly acts on the silver nanoparticles after being output from the large-core multimode fiber 2.

[0022] See Figure 1 The method for depositing silver nanoparticles on the end face of a large-core optical fiber provided in this embodiment of the invention includes the following steps.

[0023] Step S1. Surface modification is performed on the end face 21 of the large core diameter multimode fiber 2 to form a surface adsorption layer for fixing silver nanoparticles on the end face 21.

[0024] Before surface modification, the large-core-diameter multimode fiber 2 is cut to obtain a flat end face 21 to be deposited. The large-core-diameter multimode fiber 2 can be a step-index multimode silica fiber. In one specific embodiment, the large-core-diameter multimode fiber 2 is a step-index multimode silica fiber with a core diameter of 400 μm, a cladding diameter of 440 μm, and a numerical aperture of 0.22.

[0025] Surface modification may include cleaning, hydroxylation, and amination. During cleaning, the end face 21 to be deposited is ultrasonically treated in ethanol to remove surface organic and particulate contaminants; after ultrasonic treatment, the end face 21 is removed and dried. During hydroxylation, an oxidizing cleaning solution is used to treat the end face 21 to be deposited, forming hydroxyl sites on the quartz surface. The oxidizing cleaning solution can be a mixture of sulfuric acid and hydrogen peroxide, or other oxidizing cleaning systems capable of hydroxylating quartz end faces. After hydroxylation, the end face 21 is rinsed with deionized water and dried.

[0026] During the amination treatment, the end face 21 to be deposited is placed in a modified solution containing an aminosilane coupling agent, causing an amino-containing surface adsorption layer to form on the end face 21. The modified solution containing the aminosilane coupling agent can be an APTES solution. The concentration of the APTES solution can be 1%-5%, preferably 3%. The treatment time of the end face 21 in the APTES solution can be 20 min-90 min, preferably 45 min. After the amination treatment, the end face 21 to be deposited is rinsed with ethanol, and the large-core multimode optical fiber 2 is placed in an oven to dry. The drying temperature can be 70℃-100℃, and the drying time can be 30 min-120 min. Through the above treatment, a surface adsorption layer capable of adsorbing and fixing silver nanoparticles is formed on the end face 21 to be deposited.

[0027] The surface adsorption layer, in conjunction with the subsequent optical field-induced migration process, ensures that the silver nanoparticles reaching the deposition end face 21 are retained on the end face. For large-core multimode fiber 2, the end face area is large. If the particles only randomly contact the end face, the fixed position of the particles on the end face is difficult to correspond to the fiber core light guiding area. In this embodiment, the surface adsorption layer is formed first, and then the optical field output from the end face is used to induce the silver nanoparticles to migrate to the corresponding area of ​​the fiber core, which is beneficial to matching the deposition area with the fiber core light guiding area.

[0028] Step S2. Disperse the pre-made silver nanoparticles in a solvent to form a silver nanoparticle suspension.

[0029] The silver nanoparticles used are pre-fabricated, rather than generated through in-situ reduction of silver ions near the deposition facet 21. Using pre-fabricated silver nanoparticles allows for better control of particle size distribution before deposition and reduces the impact of in-situ reduction byproducts on the deposition layer. The pre-fabricated silver nanoparticles can be prepared using the sodium citrate reduction method. After the reaction, the silver nanoparticles are centrifuged for purification and dispersed in ethanol to form a silver nanoparticle suspension. The particle size of the silver nanoparticles can be 20 nm–100 nm. The concentration of silver nanoparticles in the suspension can be 0.01 mg / mL–0.25 mg / mL. If the concentration is too low, the particle supply near the deposition facet 21 is insufficient, resulting in low deposition efficiency; if the concentration is too high, the probability of particle aggregation in the suspension increases, and scattering near the facet is enhanced, which is detrimental to stable deposition.

[0030] Step S3. Fix the end face 21 to be deposited in the silver nanoparticle suspension.

[0031] Specifically, a large-core multimode fiber 2 is installed onto the fiber fixing module 7, fixing the end fixing section 22 near the deposition face 21, and immersing the deposition face 21 in the silver nanoparticle suspension within the deposition container 5. The end fixing section 22 is used to stabilize the deposition face 21 relative to the deposition container 5 during deposition, reducing mechanical movement of the deposition face 21 in the silver nanoparticle suspension. Through this fixing method, subsequent dynamic disturbances are directed at the fiber segment away from the deposition face 21, rather than directly agitating the suspension near the deposition face 21. This alters the mode transmission state within the large-core multimode fiber 2 while maintaining a relatively stable particle adsorption environment near the deposition face 21.

[0032] Step S4. Input deposition light from the end of the large-core multimode fiber 2 that is away from the end face 21 to be deposited.

[0033] After being transmitted through a large-core multimode fiber 2, the deposition light is output from the deposition facet 21 and acts on the silver nanoparticles near the deposition facet 21. The deposition light can be a 532nm continuous laser. The deposition light power can be 30mW-100mW, and the deposition time can be 5min-300min. The output light field from the facet guides the silver nanoparticles to migrate towards the region in the deposition facet 21 corresponding to the fiber core. After the silver nanoparticles approach the deposition facet 21, they are fixed by the surface adsorption layer, gradually forming a silver nanoparticle deposition layer.

[0034] Step S5. During the input deposition light process, a dynamic perturbation is applied to the mode modulation section 23 of the large-core multimode fiber 2, which is far from the end face 21 to be deposited. Under the action of the output light field of the end face after dynamic perturbation, the silver nanoparticles migrate to the region corresponding to the fiber core in the end face to be deposited and are fixed on the surface adsorption layer to form a silver nanoparticle deposition layer. The mode modulation section 23 is located between the end fixing section 22 and the incident end fixing section 24. The dynamic perturbation can be achieved by changing the bending state and / or the force state of the mode modulation section 23. Further, the clamping member can be driven by the driving member to cause the clamping member to drive the mode modulation section 23 to produce a small displacement, periodic bending or periodic force change. The driving member can be a piezoelectric driving member, a vibration driving member, a rotation driving member or an adjustable bending member. The perturbation frequency of the dynamic perturbation can be 10Hz-2kHz, and the perturbation amplitude can be 1μm-100μm. During implementation, the bending radius of the mode modulation section 23 should not be less than the allowable bending radius of the large core diameter multimode fiber 2, in order to avoid fiber damage or abnormal increase in transmission loss.

[0035] Large-core multimode fiber 2 can support multiple transmission modes. When the deposited light propagates within the large-core multimode fiber 2, different modes have their own spatial field distribution and propagation phase. Multiple modes are superimposed at the deposition end face 21 to form the end face output light field. If the coupling state, bending state, and stress state of the fiber remain unchanged, the phase relationship between different modes is relatively stable, and a relatively fixed speckle pattern is easily formed at the deposition end face 21. The local bright spots in the fixed speckle pattern have high light intensity, which makes it easy for silver nanoparticles to migrate and be adsorbed preferentially at these locations; the deposition amount in dark spots or weak light regions is relatively small.

[0036] This embodiment applies dynamic perturbation to the mode modulation section 23, causing its bending or stress state to change over time, thereby altering the phase or coupling relationship between multiple transmission modes within the large-core multimode fiber 2. Since the end-face speckle distribution is related to the superposition state of the transmission modes, the instantaneous speckle distribution at the end-face 21 to be deposited changes accordingly after the transmission mode state changes.

[0037] It should be noted that the dynamic disturbance module 8 does not need to transmit mechanical disturbances to the deposition face 21. After the first fixing member fixes the end fixing section 22, the mechanical displacement of the mode modulation section 23 is mainly limited between the first and second fixing members. When the deposition light propagates along the large-core multimode fiber 2, it will pass through the mode modulation section 23. Changes in the bending or stress state of the mode modulation section 23 will change the optical field mode state passing through this section. The changed multimode optical field continues to propagate through the end fixing section 22 to the deposition face 21. Therefore, the mechanical position of the deposition face 21 remains stable, and the instantaneous speckle distribution of the output optical field of the face will still change with the dynamic disturbance of the mode modulation section 23.

[0038] Silver nanoparticles require a certain amount of time to migrate from the suspension to the deposition surface 21 and stabilize. During this time, if the instantaneous speckle distribution on the surface continues to change, the optical field effect on the silver nanoparticles can be approximated as an average effect over a period of time. Let r represent the surface position and t represent time. I The instantaneous light intensity at the end face is represented by equation (1), and the average light intensity at the end face during the deposition time T can be expressed as follows: (1); in, This represents the time-averaged light intensity at position r on the end face. This embodiment does not require the deposition end face 21 to form a uniform light field at any given moment. Instead, it dynamically changes the multimode transmission state to reduce the continuous dominance of the fixed speckle bright spots throughout the deposition process, thereby improving the deposition distribution of silver nanoparticles in the corresponding region of the fiber core. The aforementioned dynamic disturbance, combined with the stable fixation of the end-fixed section 22, distinguishes the action path of this embodiment from simply mechanically stirring the suspension or directly shaking the fiber end face.

[0039] In some feasible implementations, end-face speckle calibration is performed before formal deposition. The end face 21 to be deposited is placed in air or a transparent liquid, and deposition light with the same or lower power as the deposition process is input. An image of the output light field of the end face in an undisturbed state is acquired, and the speckle contrast in the undisturbed state is calculated. Then, dynamic perturbation is initiated, and an image of the output light field of the end face in a dynamically perturbed state is acquired. When acquiring the image in a dynamically perturbed state, the image exposure time is set to more than ten times the dynamic perturbation period. The speckle contrast C can be calculated according to formula (2): (2); in, This represents the light intensity of a pixel in the output light field image. Indicates the standard deviation of light intensity. This represents the average light intensity. The perturbation frequency, amplitude, or waveform of the dynamic perturbation are adjusted according to the speckle contrast to ensure that the speckle contrast under dynamic perturbation is lower than that under undisturbed conditions. After calibration, the end face 21 to be deposited is placed in a silver nanoparticle suspension, and deposition is performed using the calibrated perturbation parameters. This method allows the dynamic perturbation parameters to be matched with the specific optical fiber and coupling state, avoiding large fluctuations in deposition results caused by differences in end face speckle under different optical fibers or coupling states.

[0040] In some feasible implementations, the process of inputting deposition light includes multiple deposition cycles. Each deposition cycle includes a photo-deposition phase and a pause-replenishment phase. The photo-deposition phase lasts 5-120 seconds, during which deposition light is input and dynamic perturbation is applied, causing silver nanoparticles to migrate towards and be fixed at the deposition end face 21. The pause-replenishment phase lasts 1-60 seconds, during which the input of deposition light is stopped, or the deposition light power is reduced to 5%-30% of the power of the photo-deposition phase, so that the local low-concentration area near the deposition end face 21 formed by deposition consumption is replenished with particles. Multiple deposition cycles are repeated until the preset deposition time is reached. This periodic deposition method can reduce the impact of local particle depletion near the end face on the deposition distribution and is suitable for deposition processes with larger core areas. Since the photo-deposition phase still maintains dynamic perturbation, the periodic replenishment does not change the basic mechanism of reducing the effect of fixed speckle with dynamic mode modulation in this embodiment.

[0041] In some feasible implementations, the end face 21 to be deposited is fixed within a confined deposition cavity, and a silver nanoparticle suspension flows through the area in front of the end face 21. The flow rate of the silver nanoparticle suspension can be 0.1 μL / min to 50 μL / min. This flow rate range can replenish the silver nanoparticles near the end face 21 while avoiding excessive fluid shearing that could cause adsorbed particles to detach. By combining the confined deposition cavity with dynamic perturbation, both the particle supply conditions and the optical field conditions near the end face 21 can be improved. The confined deposition cavity is mainly used to stabilize the local particle supply, while the dynamic perturbation is mainly used to change the temporal distribution of the optical field on the end face; the two respectively act on the particle supply and optical field distribution aspects.

[0042] In a specific process example, the large-core multimode fiber 2 is a step-index multimode silica fiber with a core diameter of 400 μm, a cladding diameter of 440 μm, and a numerical aperture of 0.22. The deposition end face 21 is ultrasonically treated with ethanol for 15 min, then dried, followed by treatment with an oxidizing cleaning solution for 20 min, and then rinsed with deionized water and dried. Afterward, the deposition end face 21 is placed in a 3% APTES solution for 45 min, rinsed with ethanol, and dried at 85°C for 90 min. Silver nanoparticles are pre-fabricated using a sodium citrate reduction method, with a particle size controlled between 20 nm and 100 nm, and dispersed in anhydrous ethanol at a concentration of 0.05 mg / mL to 0.15 mg / mL. The deposition light is a 532 nm continuous laser with a power of 60 mW. Dynamic perturbation is applied to the mode modulation segment 23, which has a length of 50mm-100mm, with a perturbation frequency of 100Hz-500Hz and a perturbation amplitude of 5μm-50μm. The deposition time is 30min-120min. After deposition, the deposition end face 21 is gently rinsed with ethanol to remove any loosely attached silver nanoparticles, and then dried with clean gas.

[0043] Through the above process, the formation of the silver nanoparticle deposition layer mainly depends on the following relationships: the surface adsorption layer provides the conditions for particle fixation, the end-face output light field provides the localized migration conditions corresponding to the fiber core region, the dynamic perturbation of the far-end mode modulation section 23 reduces the continuous effect of the fixed speckle bright spots, and the end-fixing section 22 keeps the position of the end face 21 to be deposited stable in the suspension. The combined effect of these components enables this embodiment to address the localized aggregation problem caused by the fixed speckle on the end face of large-core multimode optical fibers.

[0044] Example 2 like Figure 1 This invention provides a large-core fiber end-face silver nanoparticle deposition system for implementing the large-core fiber end-face silver nanoparticle deposition method described in Embodiment 1. The system includes a mounting base 1, a large-core multimode fiber 2, a laser 3, a fiber coupling module 4, a fiber fixing module 7, a deposition container 5, a dynamic disturbance module 8, and a control module.

[0045] Mounting base 1 is used to support fiber fixing module 7, deposition container 5, dynamic perturbation module 8, and other components. Large-core multimode fiber 2 is arranged along the length of mounting base 1. Large-core multimode fiber 2 is provided with a deposition end face 21, an end fixing section 22, a mode modulation section 23, and an incident end fixing section 24. End fixing section 22 is located between the deposition end face 21 and the mode modulation section 23, and mode modulation section 23 is located between the end fixing section 22 and the incident end fixing section 24. By dividing the large-core multimode fiber 2 into the above sections, end face stability can be achieved near the deposition end face 21, and mode perturbation can be achieved away from the deposition end face 21.

[0046] The deposition container 5 is mounted on the mounting base 1 and located on one side of the fiber fixing module 7. When the large-core multimode fiber 2 passes through the deposition container 5, its connection point needs to be sealed. The deposition container 5 is used to contain the silver nanoparticle suspension. The end face 21 to be deposited extends into the deposition container 5 and is immersed in the silver nanoparticle suspension. The deposition container 5 remains fixed relative to the mounting base 1, and the end face 21 to be deposited is kept relatively stable by the fiber fixing module 7. During the deposition process, the end face 21 to be deposited will not experience significant shaking in the silver nanoparticle suspension due to the movement of the dynamic disturbance module 8.

[0047] Laser 3 is used to output deposition light. The deposition light can be a continuous laser. In one specific embodiment, the deposition light is a 532nm continuous laser. Fiber coupling module 4 is disposed on the side of large-core multimode fiber 2 away from the deposition face 21. Laser 3 and fiber coupling module 4 are disposed opposite each other, and fiber coupling module 4 corresponds to the incident end fixed section 24. The output end of fiber coupling module 4 is aligned with the incident end of large-core multimode fiber 2 to couple the deposition light output from laser 3 into large-core multimode fiber 2. The deposition light is transmitted through large-core multimode fiber 2 to the deposition face 21 and output from the deposition face 21.

[0048] The fiber optic fixing module 7 is mounted on the mounting base 1. The fiber optic fixing module 7 includes a first fixing member and a second fixing member. The first fixing member clamps the end fixing section 22, and the second fixing member clamps the incident end fixing section 24. The first fixing member is positioned near the deposition container 5, and the second fixing member is positioned near the fiber coupling module 4. By fixing the end fixing section 22 with the first fixing member, the position of the end face 21 to be deposited 21 within the deposition container 5 can be kept stable; by fixing the incident end fixing section 24 with the second fixing member, the coupling state between the large-core multimode fiber 2 and the fiber coupling module 4 can be kept relatively stable.

[0049] The first and second fixing components can be fiber clamps, fiber clamping seats, or other clamping structures capable of locally fixing the large-core multimode fiber 2. The clamping force of the first fixing component should be able to limit the displacement of the end fixing section 22, so that the end face 21 to be deposited remains stable within the deposition container 5; the clamping force of the second fixing component should be able to limit the displacement of the incident end fixing section 24, so that the coupling state of the deposited light is not easily significantly shifted due to the dynamic disturbance of the mode modulation section 23. The first and second fixing components are spaced apart along the extension direction of the large-core multimode fiber 2, and the mode modulation section 23 is located between the first and second fixing components.

[0050] The dynamic disturbance module 8 is positioned between the first and second fixing members. The dynamic disturbance module 8 includes a driving member and a clamping member. The driving member is connected to the mounting base 1, and the clamping member is connected to the output end of the driving member. The clamping member clamps the mode modulation segment 23. When the driving member operates, the clamping member causes the mode modulation segment 23 to produce minute displacements, periodic bending, or periodic force changes. The driving member can be a piezoelectric driving member, a vibration driving member, a rotary driving member, or an adjustable bending member.

[0051] In the embodiment employing a piezoelectric actuator, the fixed end of the piezoelectric actuator is connected to the mounting base 1, and the output end of the piezoelectric actuator is connected to the clamping member. After the control module outputs a drive signal to the piezoelectric actuator, the piezoelectric actuator drives the clamping member to reciprocate along a direction perpendicular to the extension direction of the large-core multimode fiber 2, causing the mode modulation section 23 to generate periodic micro-bending. This micro-bending changes the phase relationship or coupling relationship between multiple transmission modes within the large-core multimode fiber 2, thereby causing the instantaneous speckle distribution at the deposition end face 21 to change over time.

[0052] It should be noted that after the first fixing member fixes the end fixing segment 22, the mechanical disturbance applied by the dynamic disturbance module 8 to the mode modulation segment 23 is not intended to displace the end face 21 to be deposited. Instead, the first fixing member is used to isolate the mechanical disturbance of the mode modulation segment 23, preventing the end face 21 to be deposited from swaying in the silver nanoparticle suspension. The effect of the dynamic disturbance module 8 on the deposition end is mainly manifested in optical effects: after the deposition light passes through the disturbed mode modulation segment 23, its multimode transmission state changes, and the changed light field continues to propagate to the end face 21 to be deposited, causing the instantaneous speckle distribution of the end face 21 to change over time. The system can mechanically fix the end face 21 to be deposited, while simultaneously optically modulating the output light field of the end face.

[0053] The clamping member may include two opposing clamping arms, forming a clamping space between the two clamping arms for accommodating the mode modulation section 23. A flexible pad may be provided within the clamping space to reduce indentation of the large-core multimode fiber 2 by the clamping member. The clamping force of the clamping member on the mode modulation section 23 should be sufficient to transmit the motion of the drive member to the mode modulation section 23, while not causing breakage or irreversible damage to the large-core multimode fiber 2.

[0054] The control module is electrically connected to both the laser 3 and the driver. The control module controls the output state of the laser 3 and the perturbation parameters of the driver. The control module can control the power, input duration, and input period of the deposition light, as well as the perturbation frequency, perturbation amplitude, and perturbation waveform of the driver. In an embodiment employing multiple deposition cycles, the control module controls the laser 3 to output deposition light during the photodeposition stage and controls the driver to generate dynamic perturbations in the mode modulation section 23 during the photodeposition stage. During the pause-feed stage, the control module controls the laser 3 to stop outputting deposition light or reduce the deposition light power to replenish the silver nanoparticle suspension near the deposition end face 21.

[0055] In some feasible implementations, the large-core fiber end-face silver nanoparticle deposition system also includes an optical field monitoring module 6. The optical field monitoring module 6 includes an imaging lens assembly, an image sensor, and a monitoring bracket. The monitoring bracket is mounted on the mounting base 1, and the imaging lens assembly and image sensor are mounted on the monitoring bracket. The deposition container 5 has an observation window corresponding to the end face 21 to be deposited. The optical axis of the imaging lens assembly faces the observation window or the end face 21 to be deposited, and the image sensor is located on the imaging side of the imaging lens assembly. The image sensor is electrically connected to the control module.

[0056] The observation window can be formed of transparent glass, transparent quartz sheet, or transparent polymer sheet. The observation window is positioned opposite the deposition surface 21, allowing the light field monitoring module 6 to acquire output light field images or scattered light images of the deposition surface 21 through the observation window. During the pre-deposition calibration stage, the deposition surface 21 can be placed in air, a transparent liquid, or a low-concentration silver nanoparticle suspension, and the light field monitoring module 6 can acquire output light field images of the surface under undisturbed and dynamically disturbed states. The control module calculates the speckle contrast based on the output light field images of the surface and adjusts the disturbance parameters of the driving component.

[0057] The speckle contrast C can be calculated using formula (2) in Example 1. When acquiring the output light field image under dynamic disturbance, the image exposure time can be set to be no less than ten disturbance cycles of the dynamic disturbance, so that the image reflects the average light intensity distribution over a period of time. The control module adjusts the disturbance frequency, disturbance amplitude, or disturbance waveform of the driving component so that the speckle contrast under dynamic disturbance is lower than that under undisturbed conditions. The system can set the disturbance parameters according to the actual end-face light field state before or during deposition, rather than relying solely on fixed empirical parameters.

[0058] In some feasible embodiments, the deposition container 5 includes a confined deposition chamber. The confined deposition chamber has an end face receiving cavity 51, a liquid inlet 52, and a liquid outlet 53. The end face 21 to be deposited extends into the end face receiving cavity 51. The liquid inlet 52 and the liquid outlet 53 are respectively connected to the end face receiving cavity 51. The liquid inlet 52 and the liquid outlet 53 may be distributed on opposite sides of the end face 21 to be deposited, or they may be spaced apart along the liquid flow direction in front of the end face 21 to be deposited, so that the silver nanoparticle suspension flows through the area in front of the end face 21 to be deposited.

[0059] The infusion module is connected to the inlet 52 and is used to deliver a silver nanoparticle suspension to the end face receiving cavity 51. The silver nanoparticle suspension enters the end face receiving cavity 51 through the inlet 52, flows through the area in front of the end face 21 to be deposited, and is discharged through the outlet 53. The infusion module can be a syringe pump or a peristaltic pump. The flow rate of the silver nanoparticle suspension can be 0.1 μL / min-50 μL / min. This flow rate range can replenish the silver nanoparticles near the end face 21 to be deposited, while avoiding excessive fluid shearing that could cause adsorbed particles to detach. The confined deposition cavity can be made of a transparent material, or an observation window can be set at the position corresponding to the end face 21 to be deposited in the confined deposition cavity, so that the light field monitoring module 6 can observe the scattering changes of the end face 21 to be deposited or during the deposition process.

[0060] In this embodiment, a clear structural fit is formed between the first fixing member, the second fixing member, and the dynamic disturbance module 8. The first fixing member fixes the end fixing section 22 near the deposition surface 21, keeping the deposition surface 21 stable within the deposition container 5 or confined deposition cavity. The second fixing member fixes the incident end fixing section 24 near the fiber coupling module 4, keeping the laser coupling state relatively stable. The dynamic disturbance module 8 acts on the mode modulation section 23 between the first and second fixing members, transmitting the motion of the driving member to the mode modulation section 23 through the clamping member. The system structurally separates the stable fixation of the deposition surface 21 and the dynamic disturbance of the mode modulation section 23.

[0061] The aforementioned structure ensures that the dynamic disturbance primarily manifests as altering the transmission mode state within the large-core multimode fiber 2, rather than causing the end face 21 to be deposited to reciprocate within the silver nanoparticle suspension. While reducing flow field disturbances and the risk of particle desorption, the instantaneous speckle distribution on the end face can change over time, thereby improving the deposition distribution of silver nanoparticles within the corresponding region of the large-core fiber core, in conjunction with the method of Example 1.

[0062] The method and system for depositing silver nanoparticles on the end face of large-core optical fibers provided in this invention have at least the following beneficial effects: The silver nanoparticle deposition method for large-core fiber endfaces provided in this invention uses deposition light output through a large-core multimode fiber to guide silver nanoparticles to enrich the corresponding region of the fiber core. Dynamic perturbation is applied to the mode modulation section far from the endface to be deposited, thereby changing the phase relationship or coupling relationship between different transmission modes within the multimode fiber. Since the endface speckle pattern is formed by the superposition of multiple transmission modes, the instantaneous speckle distribution on the endface to be deposited changes over time after the mode state changes. The migration, approach to the endface, and fixation of silver nanoparticles all have time-cumulative characteristics, so their deposition position is no longer mainly dominated by a single fixed speckle bright spot, but is affected by the average effect of the output light field of the endface over a period of time. This reduces the tendency for local aggregation at fixed bright spots, making the distribution of silver nanoparticles more uniform in the corresponding region of the large-core fiber core.

[0063] The large-core fiber end-face silver nanoparticle deposition system provided in this invention comprises a first fixing member that secures the end-face near the deposition target, ensuring stability within the deposition container; and a second fixing member that secures the incident end-face near the incident end, stabilizing the fiber coupling. A dynamic disturbance module operates only on the mode modulation section between these two members, separating end-face stabilization and dynamic mode modulation in different fiber segments. This structural relationship enables the system to alter the internal transmission mode state of the large-core multimode fiber while reducing end-face liquid phase disturbance.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 depositing silver nanoparticles on the end face of a large-core optical fiber, characterized in that, include: The surface of the end face to be deposited in a large core diameter multimode optical fiber is modified to form a surface adsorption layer for fixing silver nanoparticles. Pre-fabricated silver nanoparticles are dispersed in a solvent to form a silver nanoparticle suspension; The end face to be deposited is fixed in a silver nanoparticle suspension; Deposition light is input from the end of a large-core multimode fiber furthest from the end face to be deposited; During the input deposition light process, dynamic perturbation is applied to the mode modulation section of the large core diameter multimode fiber that is far from the end face to be deposited, so that the phase relationship or coupling relationship between multiple transmission modes in the large core diameter multimode fiber changes with time, and the instantaneous speckle distribution of the end face to be deposited changes during the deposition process. Under the action of the output light field after dynamic disturbance, the silver nanoparticles migrate to the region corresponding to the fiber core in the end face to be deposited and are fixed on the surface adsorption layer to form a silver nanoparticle deposition layer.

2. The method for depositing silver nanoparticles on the end face of a large-core optical fiber according to claim 1, characterized in that, An end-fixing section is provided between the mode modulation section and the end face to be deposited; During the deposition process, the end fixing section is fixed to keep the end face to be deposited stable relative to the deposition container containing the silver nanoparticle suspension.

3. The method for depositing silver nanoparticles on the end face of a large-core optical fiber according to claim 1, characterized in that, Applying dynamic perturbations to the mode modulation section includes: Change the bending state and / or stress state of the mode modulation segment.

4. The method for depositing silver nanoparticles on the end face of a large-core optical fiber according to claim 1, characterized in that, Applying dynamic perturbations to the mode modulation section includes: The motion of the modulated segment is driven by a piezoelectric actuator, a vibration actuator, a rotary actuator, or an adjustable bending actuator. The dynamic disturbance has a disturbance frequency of 10Hz-2kHz and a disturbance amplitude of 1μm-100μm.

5. The method for depositing silver nanoparticles on the end face of a large-core optical fiber according to claim 1, characterized in that, During the calibration stage before deposition, output light field images of the end face to be deposited are acquired in both undisturbed and dynamically disturbed states. The speckle contrast is calculated based on the output light field images, and the dynamic disturbance parameters are adjusted so that the speckle contrast in the dynamically disturbed state is lower than that in the undisturbed state.

6. The method for depositing silver nanoparticles on the end face of a large-core optical fiber according to claim 5, characterized in that, Speckle contrast is the ratio of the standard deviation of light intensity to the average light intensity in the output light field image; When acquiring the output light field image under dynamic disturbance, the image exposure time shall not be less than ten disturbance cycles of the dynamic disturbance.

7. The method for depositing silver nanoparticles on the end face of a large-core optical fiber according to claim 1, characterized in that, The process of inputting deposition light involves multiple deposition cycles; Each deposition cycle includes a photo-deposition phase and a pause in refueling phase; During the photo-deposition stage, deposition light is input and dynamic perturbation is applied. During the pause supply stage, the input of deposition light is stopped or the power of deposition light is reduced, so that the silver nanoparticle suspension near the end face to be deposited is replenished with particles.

8. The method for depositing silver nanoparticles on the end face of a large-core optical fiber according to claim 1, characterized in that, Fixing the end face to be deposited in the silver nanoparticle suspension includes: fixing the end face to be deposited in the confined deposition cavity and allowing the silver nanoparticle suspension to flow through the area in front of the end face to be deposited.

9. A silver nanoparticle deposition system for the end face of a large-core optical fiber, used to implement the silver nanoparticle deposition method for the end face of a large-core optical fiber as described in any one of claims 1-8, characterized in that, include: Mounting base, large-core multimode fiber, laser, fiber coupling module, fiber fixing module, deposition container, dynamic disturbance module and control module; The large-core-diameter multimode fiber is provided with a deposition end face, an end fixing section, a mode modulation section and an incident end fixing section. The end fixing section is located between the deposition end face and the mode modulation section, and the mode modulation section is located between the end fixing section and the incident end fixing section. The deposition container is mounted on the mounting base and located on one side of the fiber optic fixing module. The deposition container is used to contain the silver nanoparticle suspension, and the end face to be deposited extends into the deposition container. The fiber coupling module is located on the side of the large-core multimode fiber away from the end face to be deposited. The laser and the fiber coupling module are positioned opposite each other. The fiber coupling module corresponds to the fixed section at the incident end so as to couple the deposition light output by the laser into the large-core multimode fiber. The fiber optic fixing module is mounted on the mounting base. The fiber optic fixing module includes a first fixing member and a second fixing member. The first fixing member clamps the end fixing section, and the second fixing member clamps the incident end fixing section, so as to keep the end face to be deposited stable relative to the deposition container. The dynamic disturbance module is disposed between the first fixing member and the second fixing member. The dynamic disturbance module includes a driving member and a clamping member connected to the output end of the driving member. The driving member is connected to the mounting base, and the clamping member clamps the mode modulation segment so that when the driving member moves, it causes the mode modulation segment to produce a bending state change or a force state change. The control module is electrically connected to both the laser and the drive unit.

10. The large-core-diameter optical fiber end-face silver nanoparticle deposition system according to claim 9, characterized in that, It also includes a light field monitoring module, which comprises an imaging lens group, an image sensor, and a monitoring bracket; The monitoring bracket is mounted on the mounting base, and the imaging lens assembly and image sensor are mounted on the monitoring bracket. The deposition container is equipped with an observation window corresponding to the end face to be deposited. The optical axis of the imaging lens group is oriented towards the observation window or the end face to be deposited. The image sensor is located on the imaging side of the imaging lens group and is electrically connected to the control module.

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