Four-core beam-expanding oil-filled optical fiber connector and assembling method thereof

Abstract

The invention discloses a connector technology, and aims to provide a four-core beam-expanding oil-filled optical fiber connector and an assembling method thereof. According to the technical scheme, the oil-filled plug is characterized by comprising a threaded sleeve, a plug shell, a four-optical-fiber beam expanding insulator, a pressure compensator, an oil-filled plug tail clamp, a sealing assembly and a calibration gasket which is clamped between the butt joint end faces of the oil-filled plug tail clamp and the plug shell and used for adjusting the pre-compression stroke of the pressure compensator. The screw sleeve, the plug shell, the four-optical-fiber beam expanding insulator, the pressure compensator, the oil-filled plug tail clamp, the sealing assembly and the calibration gasket jointly define a completely-closed oil-filled cavity, fluorinated oil or synthetic hydrocarbon oil subjected to degassing treatment is injected into the oil-filled cavity through a valve, and the oil-filled cavity is matched with the pressure compensator to construct an active pressure compensation sealing system. The invention is suitable for the technical field of connectors.

Description

Technical Field

[0001] This invention relates to connector technology, and more specifically, to a four-core expander oil-filled fiber optic connector and its assembly method. Background Technology

[0002] Traditional expanded-beam four-fiber connector assemblies rely on a critical integration process for system-level watertightness: a permanent seal is achieved between the connector tail accessory and the fiber optic cable sheath using compression molding and vulcanization. This process aims to create a continuous, uninterrupted, elastic sealing barrier from the connector's metal housing to the cable's outer sheath. This approach places extremely stringent requirements on cable construction consistency, vulcanization material formulation and process stability, and interface pretreatment; any flaw in any step can lead to watertightness failure of the entire assembly. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a four-core expanded-beam oil-filled fiber optic connector and its assembly method.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a four-core expander type oil-filled fiber optic connector, comprising a screw sleeve, a plug housing, a four-fiber expander insulator, a pressure compensator, an oil-filled plug tail clip, a sealing assembly, and a calibration pad clamped between the mating end faces of the oil-filled plug tail clip and the plug housing for adjusting the pre-compression stroke of the pressure compensator. The plug housing has an insulator cavity for accommodating a four-fiber expander insulator and a compensation cavity for accommodating a pressure compensator. The screw sleeve is threaded onto the front end of the plug housing to coaxially fix the four fiber optic bundle expander insulator inside the plug housing and provide initial mechanical preload. The four-fiber beam expander insulator is installed inside the insulator cavity and integrates four independent optical beam expander channels for signal beam expander transmission of the four-core fiber unit. The outer wall of the four-fiber beam expander insulator is provided with an integrally formed anti-rotation key, which is adapted to the keyway on the inner wall of the plug housing. The pressure compensator is installed in the internal compensation cavity of the plug housing, and a uniform annular gap is formed between its outer wall and the inner wall of the compensation cavity. The outer surface of the pressure compensator is coated with a compatible silicone grease with a thickness of 0.02-0.05mm. The oil-filled plug tail clamp is connected to the rear end of the plug housing by a thread. Its front end is used to axially limit and initially pre-compress the pressure compensator. The side wall of the oil-filled plug tail clamp is provided with a valve for vacuum extraction, oil filling and final sealing functions. The sealing assembly includes a polyurethane buffer protection tube fitted onto the four-core fiber unit and inserted into the tail tube portion of the oil-filled plug tail clamp, and a stainless steel double-wire reinforced hose clamp for radially and uniformly pressing and fixing the overlapping area of ​​the polyurethane buffer protection tube and the tail tube portion to form a strain release and anti-kink barrier. The screw sleeve, plug housing, four-fiber expander insulator, pressure compensator, oil-filled plug tail clip, sealing assembly, and calibration gasket together form a completely sealed oil-filled cavity. This oil-filled cavity is injected with degassed fluorinated oil or synthetic hydrocarbon oil through a valve, which, together with the pressure compensator, constructs an active pressure compensation sealing system.

[0005] The present invention is further configured such that the ratio of the pre-compression stroke of the pressure compensator to the effective axial length of the compensation cavity inside the plug housing is 1:12-1:8, and within this ratio range, the initial micro-positive pressure of the oil-filled cavity under normal pressure can be stably maintained at 0.5-1 bar, which is used to form a self-sealing mechanism for active oil leakage.

[0006] The invention is further configured such that: the pressure compensator is a stainless steel bellows-type elastic structure, the ratio of its effective expansion and contraction to the free length of the bellows is 1:3-1:5, and the ratio of the elastic coefficient of the bellows to the volume of the oil-filled cavity is 0.02-0.05 MPa / mL, which is used to achieve a rapid dynamic response to changes in environmental pressure while avoiding sealing failure caused by excessive deformation.

[0007] An assembly method for a four-core expander type oil-filled fiber optic connector, characterized by comprising the following steps: S1. Align the anti-rotation key of the four-fiber expander insulator with the keyway on the inner wall of the plug housing precisely. Slowly push the four-fiber expander insulator into the insulator cavity of the plug housing along the axial direction to complete the initial coaxial assembly. Use a parallel light detector to check the parallelism between the optical end face and the reference surface at the front end of the housing to ensure that the parallelism deviation is ≤0.02°. S2. Place the threaded sleeve on the front end of the plug housing and tighten it with a torque wrench in a three-stage torque sequence: the first stage applies 30% of the target torque and lets it stand for 5 minutes to eliminate local stress; the second stage applies 60% of the target torque and lets it stand for 5 minutes again; the third stage applies 100% of the target torque to complete the final pre-tightening and achieve precise axial positioning of the optical end face. S3. Apply a layer of compatible silicone grease with a thickness of 0.02-0.05mm evenly to the outer wall of the pressure compensator. Slowly push the pressure compensator into the compensation cavity of the plug housing along the axial direction. Use a plug gauge to check the annular gap between the outer wall of the pressure compensator and the inner wall of the cavity to ensure that the gap uniformity deviation is ≤0.05mm. S4. Align the external thread of the oil-filled plug tail clamp with the internal thread at the rear end of the plug housing, select a calibration shim of preset thickness and place it on the connection end face, and pre-connect by manually screwing it in until the front end of the oil-filled plug tail clamp axially limits the pressure compensator to avoid deformation of the compensator caused by forced screwing in. S5. The screw-in depth of the oil filling plug tail clamp is monitored in real time by a high-precision displacement sensor. At the same time, the axial pre-pressure of the pressure compensator is detected by a micro pressure sensor. Combined with the adjustment of calibration shims of different thicknesses, the pressure compensator is compressed to the designed pre-pressure stroke, thereby establishing an initial micro-positive pressure of 0.5-1 bar for the oil filling chamber under normal pressure. S6. After cutting the polyurethane buffer protection tube to the preset length, fit it onto the outside of the four-core fiber optic unit to be connected. Insert the assembled fiber optic unit and the polyurethane buffer protection tube into the tail tube part of the oil-filled plug tail clip until the front end of the polyurethane buffer protection tube is completely attached to the inner stepped surface of the tail tube. S7. Place the stainless steel double wire reinforced hose clamp on the overlapping part of the polyurethane buffer protection tube and the oil-filled plug tail clamp tail tube, and tighten the hose clamp with a torque wrench to the specified torque so that the hose clamp forms a uniform radial clamping force on the polyurethane buffer protection tube, thus constructing a preliminary fiber strain release and anti-kink barrier. S8. Connect the valve on the tail clamp of the oil filling plug to the vacuum system and the oil storage and pressurization system respectively through the pressure-resistant pipeline. First, turn on the vacuum system and pump the oil filling chamber to a high vacuum of 1×10^-3Pa. Maintain this vacuum state for 30 minutes. Detect the residual gas components with a mass spectrometer to completely remove air, moisture and volatile impurities from inside the chamber. S9. While maintaining a high vacuum in the oil-filled chamber, shut down the vacuum system and switch to the oil storage and pressurization system. Slowly inject the low-viscosity, high-stability fluorinated oil or synthetic hydrocarbon oil that has undergone 72 hours of degassing treatment into the oil-filled chamber under a positive pressure of 0.2-0.3 MPa until the oil continuously overflows from the valve. S10. Close and seal the valve, place the assembled connector in a constant temperature and humidity environment of 25℃±1℃ and 50%±5% for 24 hours, detect the pressure change rate of the oil-filled cavity and the four-channel optical coupling loss, confirm that the pressure compensation system and optical transmission performance meet the design requirements, and complete the construction of the active pressure compensation sealing system.

[0008] The present invention is further configured such that: the control of the pre-pressure stroke of the pressure compensator in S5 includes: S51. First, the real-time screw-in depth L of the oil-filled plug tail clamp is collected by the displacement sensor. At the same time, the real-time axial pre-pressure F of the pressure compensator is collected by the miniature pressure sensor. In addition, the current ambient temperature T is collected by the temperature sensor. S52. Based on the preset elastic characteristic curve of the pressure compensator, establish the relationship between the preload stroke L0, the preload F0 and the temperature T: F0=k×[L0-α×(T-Tc)], where k is the elastic coefficient of the pressure compensator, α is the temperature-length conversion coefficient, and Tc is the preset standard reference temperature. S53. Substitute the real-time collected L, F, and T values ​​into the calculation to obtain the theoretical pre-compression pressure Fp = k × [L - α × (T - Tc)]. If the deviation between F and Fp, ΔF = |F - Fp|, is greater than the preset threshold ΔFmax, and ΔFmax = 0.02 × Fp, then the current pre-compression state is determined to be abnormal, and the following adjustment logic is executed: S54. If ΔF > ΔFmax and F < Fp, the pre-compression stroke is insufficient. In this case, increase the thickness of the calibration shim by 0.02mm each time, screw the oil filling plug tail clamp back in and monitor L and F until ΔF ≤ ΔFmax. S55. If ΔF > ΔFmax and F > Fp, the pre-compression stroke is too large. In this case, reduce the thickness of the calibration shim by 0.02mm each time, screw the oil filling plug tail clamp back in and monitor L and F until ΔF ≤ ΔFmax. S56. If ΔF≤ΔFmax, then calculate the initial micro-positive pressure P=F / S based on the effective force-bearing area S of the pressure compensator. If P is in the 0.5-1 bar range, then the pre-compression setting is complete. If P<0.5 bar, replace the calibration shim with a thickness reduced by 0.01 mm and screw it back in. If P>1 bar, replace the calibration shim with a thickness increased by 0.01 mm and screw it back in until P stabilizes in the 0.5-1 bar range.

[0009] The present invention is further configured such that the control method for the vacuum infusion process in S8 and S9 includes: During the vacuum extraction stage, the vacuum level Pr of the oil-filled cavity is monitored in real time by a vacuum gauge, and the residual gas components inside the cavity are detected by a mass spectrometer. If Pr drops to 1×10^-3 Pa and is maintained for ≥30 min, and the total content of moisture and volatile organic compounds in the residual gas is ≤0.1%, then the vacuum removal stage is considered complete. If Pr drops to 1×10^-3 Pa but to < 30 min, or the residual gas percentage > 0.1%, then extend the vacuum holding time and re-detect the gas composition and vacuum degree every 10 min until the conditions are met. During the oil filling stage, the oil injection flow rate Q is monitored by a flow sensor, the internal pressure Pb of the cavity is monitored by a pressure sensor, and the oil level H is monitored by a level sensor. Establish the injection rate: Qp = C × √(Pa - Pb), where C is the flow coefficient and Pa is the output pressure of the oil storage and pressurization system; If the deviation between the real-time flow rate Q and the calculated value Qp is ΔQ=|Q-Qp|>0.05×Qp, and Pa>0.35MPa, it is determined that the injection pipeline is blocked. Injection is suspended and inert gas is introduced to purge the pipeline for 30s before restarting injection. If ΔQ > 0.05 × Qp and Pa < 0.2 MPa, it is determined that the pressure of the oil storage and pressurization system is insufficient. Adjust the output pressure of the pressurization system to 0.25 MPa, and continue injection after the pressure stabilizes. When the liquid level H reaches the full liquid level threshold Hmax of the cavity, and the valve continues to overflow oil for ≥5s, the filling is considered complete and the valve is closed. If H reaches Hmax but no oil overflows from the valve, it is determined that the valve is blocked. In the reverse direction, 0.1MPa inert gas is introduced to purge the valve until the oil overflows steadily before the valve is sealed.

[0010] The beneficial effects of this invention are: 1. Compared to existing technologies, the four-core expander oil-filled fiber optic connector of this invention achieves four-channel independent optical beam expansion transmission by integrating four fiber beam expanding insulators, significantly improving fiber optic transmission capacity. The beam expansion structure reduces the requirements for docking accuracy and is suitable for rapid docking under complex working conditions. The anti-rotation key and keyway cooperation prevent circumferential rotation of the insulator, ensuring the coaxiality of the optical channel. The calibration gasket can accurately adjust the pre-compression stroke of the pressure compensator. Combined with the closed oil-filled cavity and degassed fluorinated oil / synthetic hydrocarbon oil, it constructs an active pressure compensation sealing system, completely isolating external moisture and dust. The 0.02-0.05mm of compatible silicone grease on the outer wall of the pressure compensator improves lubrication and sealing performance, and the uniform annular gap ensures smooth expansion and contraction. The oil-filled plug tail clip integrates a multi-functional valve to realize integrated operation of vacuum extraction, oil filling, and final sealing. The sealing component adopts a polyurethane buffer tube and a stainless steel double wire hose clamp to form a strain release and anti-kink barrier. The overall structure takes into account optical transmission stability, mechanical reliability, and long-term sealing performance.

[0011] 2. The four-core expanded-beam oil-filled fiber optic connector of this invention precisely achieves a stable initial micro-positive pressure of 0.5-1 bar under normal pressure by limiting the ratio of the pre-compression stroke of the pressure compensator to the effective axial length of the compensation cavity to 1:12-1:8. This parameter design avoids the infiltration of external impurities due to negative pressure in the cavity and prevents overpressure from causing overload damage to the seals. The stable micro-positive pressure can form a self-sealing mechanism for active oil leakage, forming a dense oil film at the mating interface, further enhancing the sealing effect and achieving long-term protection without additional sealing consumables. This ratio range allows the elastic compensation capability of the pressure compensator to be perfectly matched with the cavity volume, which can quickly offset the changes in cavity volume caused by environmental pressure and temperature fluctuations, continuously maintaining stable internal pressure in the cavity, fundamentally avoiding oil leakage and water vapor intrusion problems, and significantly improving the sealing reliability and service life of the connector under high pressure and alternating pressure conditions.

[0012] 3. In this invention, a stainless steel bellows-type pressure compensator is used. Its effective expansion / contraction ratio to free length is 1:3-1:5, balancing elastic expansion range and structural strength, avoiding failures such as wrinkling and breakage during bellows expansion and contraction. The ratio of the elastic coefficient to the oil-filled cavity volume is 0.02-0.05 MPa / mL, enabling rapid dynamic response to changes in environmental pressure. It can compensate for volume differences in the cavity caused by temperature and external pressure changes in real time, preventing negative or overpressure in the cavity. The stainless steel material is oil-resistant and corrosion-resistant, suitable for media such as fluorinated oil and synthetic hydrocarbon oil. This ensures that the compensator quickly adjusts its deformation to follow pressure changes while limiting excessive deformation through a reasonable elastic coefficient, fundamentally preventing oil leakage caused by compensator failure, ensuring stable operation of the active pressure compensation system, and ensuring continuous and reliable optical transmission.

[0013] 4. The present invention has a simple and reasonable structure, is easy to manufacture and operate, avoids the defects of the prior art, and is suitable for promotion and application. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the four-core expander oil-filled fiber optic connector of the present invention.

[0015] Figure 2 This is a flowchart of the assembly method of the four-core expanded oil-filled fiber optic connector of the present invention.

[0016] Figure 1-2 Reference numerals in the attached drawings: 1. Screw sleeve; 2. Plug housing; 3. Four-fiber expander insulator; 4. Pressure compensator; 5. Oil-filled plug tail clip; 6. Insulator cavity; 7. Compensation cavity. Detailed Implementation

[0017] Reference Figure 1-2 The embodiments of the four-core expanded-beam oil-filled fiber optic connector and its assembly method of the present invention are further described.

[0018] For ease of explanation, spatial relative terms such as “up,” “down,” “left,” and “right” are used in the embodiments to describe the relationship of one element or feature shown in the figures relative to another element or feature. It should be understood that, in addition to the orientations shown in the figures, spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figures is inverted, an element described as being “down” of other elements or features would be positioned “up” of those other elements or features. Therefore, the exemplary term “down” can encompass both up and down orientations. The device may be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0019] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component from another that has the same name, without necessarily requiring or implying any such actual relationship or order between the components.

[0020] Figures 1 to 2 The four-core expander type oil-filled fiber optic connector shown includes a screw sleeve 1, a plug housing 2, a four-fiber expander insulator 3, a pressure compensator 4, an oil-filled plug tail clip 5, a sealing assembly, and a calibration pad clamped between the mating end faces of the oil-filled plug tail clip 5 and the plug housing 2 for adjusting the pre-compression stroke of the pressure compensator 4. The plug housing 2 is provided with an insulator cavity 6 for accommodating the four-fiber expander insulator 3 and a compensation cavity 7 for accommodating the pressure compensator 4. The screw sleeve 1 is threadedly fitted onto the front end of the plug housing 2, and is used to coaxially fix the four fiber optic bundle expander insulator 3 inside the plug housing 2 and provide initial mechanical preload. The four-fiber beam expander insulator 3 is installed inside the insulator cavity 6. It integrates four independent optical beam expander channels for signal beam expander transmission of the four-core fiber unit. The outer wall of the four-fiber beam expander insulator 3 is provided with an integrally formed anti-rotation key, which is adapted to the keyway on the inner wall of the plug housing 2. The pressure compensator 4 is installed in the internal compensation cavity 7 of the plug housing 2, and a uniform annular gap is formed between its outer wall and the inner wall of the compensation cavity 7. The outer surface of the pressure compensator 4 is coated with a compatible silicone grease with a thickness of 0.02-0.05mm. The oil-filled plug tail clip 5 is connected to the rear end of the plug housing 2 by a thread. Its front end is used to axially limit and initially pre-compress the pressure compensator 4. The side wall of the oil-filled plug tail clip 5 is provided with a valve for vacuum extraction, oil filling and final sealing functions. The sealing assembly includes a polyurethane buffer protection tube fitted onto the four-core optical fiber unit and inserted into the tail tube portion of the oil-filled plug tail clip 5, and a stainless steel double wire reinforced hose clamp for radially and uniformly pressing and fixing the overlapping area of ​​the polyurethane buffer protection tube and the tail tube portion to form a strain release and anti-kink barrier. The screw sleeve 1, plug housing 2, four-fiber expander insulator 3, pressure compensator 4, oil-filled plug tail clip 5, sealing assembly and calibration gasket together form a completely closed oil-filled cavity. The oil-filled cavity is injected with degassed fluorinated oil or synthetic hydrocarbon oil through a valve, and together with the pressure compensator 4, an active pressure compensation sealing system is constructed. The four-fiber beam-expanding insulator 3 integrates four independent optical beam-expanding transmission channels, significantly increasing the fiber optic transmission capacity. The beam-expanding structure reduces the requirements for docking accuracy and is suitable for rapid docking under complex working conditions. The anti-rotation key and keyway cooperate to prevent the circumferential rotation of the insulator and ensure the coaxiality of the optical channels. The calibration shim can precisely adjust the pre-compression stroke of the pressure compensator 4. Together with the closed oil-filled cavity and degassed fluorinated oil / synthetic hydrocarbon oil, an active pressure compensation sealing system is constructed to completely isolate external moisture and dust. The 0.02-0.05mm of compatible silicone grease on the outer wall of the pressure compensator 4 improves lubrication and sealing performance, and the uniform annular gap ensures smooth expansion and contraction. The oil-filled plug and tail clamp 5 integrates a multi-functional valve to realize the integrated operation of vacuum extraction, oil filling and final sealing. The sealing component adopts polyurethane buffer tube and stainless steel double wire hose clamp to form a strain release and anti-kinking barrier. The overall structure takes into account optical transmission stability, mechanical reliability and long-term sealing performance. First, regarding the pressure resistance depth, traditional solutions are limited by the material mechanical properties of the elastomeric seal ring, especially its compression set, stress relaxation characteristics, and the risk of extrusion failure under high pressure. This application decouples the system's pressure resistance into two more controllable engineering parameters: the effective stroke design depth of the pressure compensator 4 and the structural strength and material yield strength of the main pressure-bearing plug housing 2. Based on this, the system's maximum working depth is no longer constrained by the nonlinear deformation behavior of organic materials, but is determined by the precisely calculable and testable mechanical properties of the metal / alloy. This allows for design based on full-depth hydrostatic loads, achieving linear scalability of pressure resistance. Second, regarding dynamic insertion / extraction durability, traditional seal rings must overcome hundreds of bar of high-pressure differential shear force at the insertion interface and are directly exposed to seawater, leading to accelerated abrasive wear, chemical aging, and fretting fatigue. This application significantly reduces the friction coefficient and contact stress by establishing a micro-positive pressure oil environment at the insertion interface. The ratio of the pre-compression stroke of the pressure compensator 4 to the effective axial length of the compensation chamber 7 inside the plug housing 2 is 1:12-1:8, and within this ratio range, the initial micro-positive pressure of the oil-filled chamber under normal pressure can be stably maintained at 0.5-1 bar, which is used to form a self-sealing mechanism for active oil leakage. By limiting the ratio of the pre-compression stroke of the pressure compensator 4 to the effective axial length of the compensation chamber 7 to 1:12-1:8, a stable initial micro-positive pressure of 0.5-1 bar under normal pressure is precisely achieved in the oil-filled chamber. This parameter design avoids the infiltration of external impurities due to negative pressure in the chamber, and also prevents overpressure from causing overload damage to the seals. The stable micro-positive pressure can form a self-sealing mechanism for active oil leakage, forming a dense oil film at the interface, further enhancing the sealing effect, and achieving long-term protection without additional sealing materials. This ratio range enables the pressure compensator 4 to have elastic compensation capacity. The force and cavity volume are perfectly matched, which can quickly offset changes in cavity volume caused by environmental pressure and temperature fluctuations, continuously maintaining stable internal pressure and fundamentally avoiding oil leakage and moisture intrusion. This significantly improves the sealing reliability and service life of the connector under high pressure and alternating pressure conditions. Furthermore, if this ratio is less than 1:12, meaning the pre-compression stroke of the pressure compensator 4 is too small, the initial pre-compression will be insufficient, failing to provide a stable initial pre-tightening force to the oil-filled cavity. Consequently, the oil-filled cavity will struggle to maintain a stable initial micro-positive pressure of 0.5 under normal pressure. Within the 1 bar range, the self-sealing mechanism for active oil leakage cannot be effectively established, and gaps easily appear at the sealing interface, allowing external moisture and impurities to easily penetrate into the cavity. Simultaneously, the pressure compensation adjustment margin is insufficient, failing to adapt to small pressure fluctuations. If the ratio is greater than 1:8, the pre-compression stroke accounts for an excessive proportion, excessively encroaching on the effective adjustment space of the compensation chamber 7. The initial stress of the pressure compensator 4 becomes too high, and the internal pressure of the oil-filled cavity easily exceeds the preset micro-positive pressure range. This not only exacerbates the load on the sealing components, leading to leakage, but also keeps the compensation element under high stress for extended periods, accelerating fatigue and aging. Furthermore, excessive pre-compression disrupts the balance of active oil leakage, resulting in a loss of self-sealing effect. Therefore, the ratio should be controlled between 1:12 and 1:8.

[0021] The pressure compensator 4 is a stainless steel bellows-type elastic structure. The ratio of its effective expansion and contraction to the free length of the bellows is 1:3-1:5, and the ratio of the elastic coefficient of the bellows to the volume of the oil-filled cavity is 0.02-0.05MPa / mL. This is used to achieve a rapid dynamic response to changes in environmental pressure while avoiding sealing failure caused by excessive deformation. The stainless steel bellows-type pressure compensator 4 employs an effective expansion / contraction ratio of 1:3 to 1:5 to its free length, balancing elastic expansion range with structural strength to prevent failures such as wrinkling and breakage during bellows expansion and contraction. The ratio of the elastic coefficient to the oil-filled chamber volume (0.02-0.05 MPa / mL) enables rapid dynamic response to changes in environmental pressure, providing real-time compensation for volume differences in the chamber caused by temperature and external pressure variations, preventing negative or overpressure. The stainless steel material is oil- and corrosion-resistant, suitable for media such as fluorinated oil and synthetic hydrocarbon oil. This ensures the compensator quickly adjusts its deformation to follow pressure changes while limiting excessive deformation through a reasonable elastic coefficient, fundamentally preventing oil leakage caused by compensator failure. This guarantees stable operation of the active pressure compensation system and ensures continuous and reliable optical transmission. If the ratio of the effective expansion / contraction to the free length of the bellows is less than 1:3, its effective expansion / contraction stroke is too low, resulting in insufficient adjustment range to cope with changes in environmental pressure. It cannot quickly match the volume changes of the oil-filled cavity, leading to a lag in dynamic pressure response and a tendency for internal pressure imbalance. At the same time, too small an expansion / contraction amount will cause stress concentration, which can easily lead to plastic deformation of the bellows. If the ratio is greater than 1:5, the expansion / contraction amount is too large, the rigidity of the bellows structure is greatly reduced, and the axial resistance to deformation is worse. Under the action of internal and external pressure differences, it is prone to excessive bending, twisting, and other inelastic deformations. Once the elastic recovery limit is exceeded, the compensation function is directly lost.

[0022] An assembly method for a four-core expander type oil-filled fiber optic connector, characterized by comprising the following steps: S1. Align the anti-rotation key of the four-fiber expansion insulator 3 precisely with the keyway on the inner wall of the plug housing 2, and slowly push the four-fiber expansion insulator 3 into the insulator cavity 6 of the plug housing 2 along the axial direction to complete the initial coaxial assembly. Use a parallel light detector to check the parallelism between the optical end face and the reference surface at the front end of the housing to ensure that the parallelism deviation is ≤0.02°. S2. Place the threaded sleeve 1 on the front end of the plug housing 2 and tighten it with a torque wrench in a three-stage torque sequence: in the first stage, apply 30% of the target torque and let it stand for 5 minutes to eliminate local stress; in the second stage, apply 60% of the target torque and let it stand for 5 minutes again; in the third stage, apply 100% of the target torque to complete the final pre-tightening and achieve precise axial positioning of the optical end face. S3. Apply a layer of compatible silicone grease with a thickness of 0.02-0.05mm evenly to the outer wall of the pressure compensator 4 to reduce friction and prevent fretting wear. Slowly push the pressure compensator 4 into the compensation cavity 7 of the plug housing 2 along the axial direction. Use a plug gauge to check the annular gap between the outer wall of the pressure compensator 4 and the inner wall of the cavity to ensure that the gap uniformity deviation is ≤0.05mm, thereby ensuring that its radial freedom is not constrained. S4. Align the external thread of the oil-filled plug tail clip 5 with the internal thread at the rear end of the plug housing 2, select a calibration shim of preset thickness and place it on the connection end face, and pre-connect by manually screwing it in until the front end of the oil-filled plug tail clip 5 axially limits the pressure compensator 4 to avoid deformation of the compensator caused by forced screwing in. S5. The screw-in depth of the oil filling plug tail clip 5 is monitored in real time by a high-precision displacement sensor. At the same time, the axial pre-pressure of the pressure compensator 4 is detected by a micro pressure sensor. Combined with the adjustment of calibration shims of different thicknesses, the pressure compensator 4 is compressed to the designed pre-pressure stroke, thereby establishing an initial micro-positive pressure of 0.5-1 bar for the oil filling chamber under normal pressure. S6. After cutting the polyurethane buffer protection tube to the preset length, fit it onto the outside of the four-core fiber optic unit to be connected. Insert the assembled fiber optic unit and the polyurethane buffer protection tube together into the tail tube part of the oil-filled plug tail clip 5 until the front end of the polyurethane buffer protection tube is completely attached to the inner stepped surface of the tail tube. S7. Place the stainless steel double wire reinforced hose clamp on the overlapping part of the polyurethane buffer protection tube and the oil-filled plug tail clamp 5 tail tube, and tighten the hose clamp with a torque wrench to the specified torque so that the hose clamp forms a uniform radial clamping force on the polyurethane buffer protection tube, thus constructing a preliminary fiber strain release and anti-kink barrier. S8. Connect the valve on the oil-filling plug tail clamp 5 to the vacuum system and the oil storage pressurization system respectively through the pressure-resistant pipeline. First, turn on the vacuum system and pump the oil-filling chamber to a high vacuum of 1×10^-3Pa. Maintain this vacuum state for 30 minutes. Detect the residual gas components with a mass spectrometer to completely remove air, moisture and volatile impurities from inside the chamber. S9. While maintaining a high vacuum in the oil-filled chamber, shut down the vacuum system and switch to the oil storage and pressurization system. Slowly inject the low-viscosity, high-stability fluorinated oil or synthetic hydrocarbon oil that has undergone 72 hours of degassing treatment into the oil-filled chamber under a positive pressure of 0.2-0.3 MPa until the oil continuously overflows from the valve. S10. Close and seal the valve, place the assembled connector in a constant temperature and humidity environment of 25℃±1℃ and 50%±5% for 24 hours, detect the pressure change rate of the oil-filled cavity and the four-channel optical coupling loss, confirm that the pressure compensation system and optical transmission performance meet the design requirements, and complete the construction of the active pressure compensation sealing system. Through precise control throughout the entire process, the standardization and high precision of connector structure assembly and sealing performance are achieved: Four-fiber expander insulators 3 anti-rotation alignment + parallelism detection ensure optical transmission accuracy; Sleeve 1 undergoes three-stage sequential torque tightening to eliminate assembly stress and ensure accurate optical end-face positioning; Pressure compensator 4 is coated with silicone grease of specified thickness + annular gap detection to ensure smooth expansion and contraction and sealing effect; Calibration gaskets, combined with multi-sensor adjustment of pre-pressure stroke, accurately establish initial micro-positive pressure; Layered assembly and uniform compression of sealing components form a reliable strain release structure; High-vacuum extraction, long-term degassing, and positive pressure oil injection processes thoroughly eliminate cavity impurities and moisture, preventing oil deterioration; Finally, constant temperature and humidity static testing provides dual verification of pressure compensation and optical performance. This method offers strong assembly controllability and high precision, effectively avoiding sealing failures and excessive optical losses caused by assembly defects.

[0023] The control of the pre-pressure stroke of the pressure compensator 4 in S5 includes: S51. First, the real-time screw-in depth L of the oil filling plug tail clip 5 is collected by the displacement sensor, and the real-time axial pre-pressure F of the pressure compensator 4 is collected by the micro pressure sensor. In addition, the current ambient temperature T is collected by the temperature sensor. S52. Based on the preset elastic characteristic curve of the pressure compensator 4, establish the relationship between the preload stroke L0, the preload F0 and the temperature T: F0=k×[L0-α×(T-Tc)], where k is the elastic coefficient of the pressure compensator 4, α is the temperature-length conversion coefficient, and Tc is the preset standard reference temperature. S53. Substitute the real-time collected L, F, and T values ​​into the calculation to obtain the theoretical pre-compression pressure Fp = k × [L - α × (T - Tc)]. If the deviation between F and Fp, ΔF = |F - Fp|, is greater than the preset threshold ΔFmax, and ΔFmax = 0.02 × Fp, then the current pre-compression state is determined to be abnormal, and the following adjustment logic is executed: S54. If ΔF > ΔFmax and F < Fp, the pre-compression stroke is insufficient. At this time, increase the thickness of the calibration shim by 0.02mm each time, screw the oil filling plug tail clip 5 back in and monitor L and F until ΔF ≤ ΔFmax. S55. If ΔF > ΔFmax and F > Fp, the pre-compression stroke is too large. At this time, reduce the thickness of the calibration shim by 0.02mm each time, screw the oil filling plug tail clip 5 back in and monitor L and F until ΔF ≤ ΔFmax. S56. If ΔF≤ΔFmax, then based on the effective force-bearing area S of the pressure compensator 4, calculate the initial micro-positive pressure P=F / S. If P is in the 0.5-1 bar range, then the pre-compression setting is complete. If P<0.5 bar, replace the calibration shim with a thickness reduced by 0.01 mm and screw it back in. If P>1 bar, replace the calibration shim with a thickness increased by 0.01 mm and screw it back in until P stabilizes in the 0.5-1 bar range. By collecting data in real time from multiple sensors (displacement, pressure, and temperature) and combining this data with elastic characteristic curves to establish a model, the interference of ambient temperature on pre-compression settings is eliminated, enabling quantitative determination of the pre-compression state. A deviation threshold of 0.02×Fp and the logic of 0.02mm and 0.01mm graded fine-tuning calibration shims can accurately correct for insufficient or excessive pre-compression stroke, avoiding errors and randomness inherent in manual assembly. Initial micro-positive pressure is calculated using the effective force-bearing area, strictly controlling the 0.5-1 bar pressure range to ensure the initial state of the pressure compensator 4 fully meets design requirements. This closed-loop control method significantly improves the accuracy and stability of pre-compression settings, eliminating sealing failures and pressure compensation lag caused by improper pre-compression from the assembly source, ensuring the performance of the active pressure compensation system meets standards, and improving the overall performance consistency of the connector.

[0024] The control methods for the vacuum infusion process in S8 and S9 include: During the vacuum extraction stage, the vacuum level Pr of the oil-filled cavity is monitored in real time by a vacuum gauge, and the residual gas components inside the cavity are detected by a mass spectrometer. If Pr drops to 1×10^-3 Pa and is maintained for ≥30 min, and the total content of moisture and volatile organic compounds in the residual gas is ≤0.1%, then the vacuum removal stage is considered complete. If Pr drops to 1×10^-3 Pa but to < 30 min, or the residual gas percentage > 0.1%, then extend the vacuum holding time and re-detect the gas composition and vacuum degree every 10 min until the conditions are met. During the oil filling stage, the oil injection flow rate Q is monitored by a flow sensor, the internal pressure Pb of the cavity is monitored by a pressure sensor, and the oil level H is monitored by a level sensor. Establish the injection rate: Qp = C × √(Pa - Pb), where C is the flow coefficient and Pa is the output pressure of the oil storage and pressurization system; If the deviation between the real-time flow rate Q and the calculated value Qp is ΔQ=|Q-Qp|>0.05×Qp, and Pa>0.35MPa, it is determined that the injection pipeline is blocked. Injection is suspended and inert gas is introduced to purge the pipeline for 30s before restarting injection. If ΔQ > 0.05 × Qp and Pa < 0.2 MPa, it is determined that the pressure of the oil storage and pressurization system is insufficient. Adjust the output pressure of the pressurization system to 0.25 MPa, and continue injection after the pressure stabilizes. When the liquid level H reaches the full liquid level threshold Hmax of the cavity, and the valve continues to overflow oil for ≥5s, the filling is considered complete and the valve is closed. If H reaches Hmax but no oil overflows from the valve, it is determined that the valve is blocked. In the reverse direction, 0.1MPa inert gas is introduced to purge the valve until the oil overflows steadily before the valve is sealed. By controlling vacuum level, pressure holding time, and residual gas composition, air, moisture, and volatile impurities inside the oil-filled cavity are thoroughly eliminated, preventing oil oxidation, emulsification, and deterioration. Based on pressure difference, the injection rate ensures a uniform and slow injection of oil, preventing sudden pressure changes or seal displacement caused by impact. Real-time monitoring by multiple sensors for flow rate, pressure, and level allows for rapid identification of faults such as pipeline blockage, insufficient system pressure, and valve blockage, and includes emergency handling logic such as inert gas purging and pressure regulation to ensure a smooth injection process. A 5-second continuous oil overflow criterion ensures the cavity is completely filled without air bubbles and the oil is densely packed. This method significantly improves the sealing integrity of the oil-filled cavity and the quality of the oil, ensuring the long-term operation of the active pressure compensation system and reducing optical transmission loss and the risk of seal failure. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Ordinary variations and substitutions made by those skilled in the art within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A four-core expander type oil-filled fiber optic connector, characterized in that: Includes a screw sleeve (1), a plug housing (2), a four-fiber expander insulator (3), a pressure compensator (4), an oil-filled plug tail clip (5), a sealing assembly, and a calibration shim that is held between the mating end faces of the oil-filled plug tail clip (5) and the plug housing (2) and is used to adjust the pre-compression stroke of the pressure compensator (4). The plug housing (2) is provided with an insulator cavity (6) for accommodating a four-fiber expander insulator (3) and a compensation cavity (7) for accommodating a pressure compensator (4); The screw sleeve (1) is fitted onto the front end of the plug housing (2) via a threaded connection, and is used to coaxially fix the four-fiber bundle expander insulator (3) inside the plug housing (2) and provide initial mechanical preload. The four-fiber beam expander insulator (3) is installed in the insulator cavity (6) and has four independent optical beam expander channels for signal beam expander transmission of the four-core fiber unit. The outer wall of the four-fiber beam expander insulator (3) is provided with an integrally formed anti-rotation key, which is adapted to the keyway on the inner wall of the plug housing (2). The pressure compensator (4) is installed in the internal compensation cavity (7) of the plug housing (2), and a uniform annular gap is formed between its outer wall and the inner wall of the compensation cavity (7). The outer surface of the pressure compensator (4) is coated with a compatible silicone grease with a thickness of 0.02-0.05mm. The oil-filled plug tail clip (5) is connected to the rear end of the plug housing (2) by a thread. Its front end is used to axially limit and initially pre-compress the pressure compensator (4). The side wall of the oil-filled plug tail clip (5) is provided with a valve for vacuum extraction, oil filling and final sealing functions. The sealing assembly includes a polyurethane buffer protection tube fitted onto the four-core fiber unit and fitted into the oil-filled plug tail clip (5), and a stainless steel double wire reinforced hose clamp for radially and uniformly pressing and fixing the overlapping area of ​​the polyurethane buffer protection tube and the tail tube to form a strain release and anti-twist barrier. The screw sleeve (1), plug housing (2), four-fiber expander insulator (3), pressure compensator (4), oil-filled plug tail clip (5), sealing assembly and calibration gasket together form a completely closed oil-filled cavity. The oil-filled cavity is injected with degassed fluorinated oil or synthetic hydrocarbon oil through a valve, and together with the pressure compensator (4), an active pressure compensation sealing system is constructed.

2. A four-core expanded-beam oil-filled fiber optic connector according to claim 1, characterized in that, The ratio of the pre-compression stroke of the pressure compensator (4) to the effective axial length of the compensation cavity (7) inside the plug housing (2) is 1:12-1:8, and the initial micro-positive pressure of the oil-filled cavity under normal pressure can be stably maintained at 0.5-1 bar within this ratio range, which is used to form a self-sealing mechanism for active oil leakage.

3. A four-core expanded-beam oil-filled fiber optic connector according to claim 1, characterized in that, The pressure compensator (4) is a stainless steel bellows type elastic structure. Its effective expansion and contraction amount is in the ratio of the free length of the bellows to 1:3-1:5, and the ratio of the elastic coefficient of the bellows to the volume of the oil-filled cavity is 0.02-0.05MPa / mL. It is used to achieve a rapid dynamic response to changes in environmental pressure while avoiding sealing failure caused by excessive deformation.

4. An assembly method for a four-core expanded-beam oil-filled fiber optic connector as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Align the anti-rotation key of the four-fiber expansion insulator (3) with the keyway on the inner wall of the plug housing (2) precisely, and slowly push the four-fiber expansion insulator (3) into the insulator cavity (6) of the plug housing (2) along the axial direction to complete the initial coaxial assembly. Use a parallel light detector to check the parallelism between the optical end face and the front reference surface of the housing to ensure that the parallelism deviation is ≤0.02°. S2. Place the threaded sleeve (1) on the front end of the plug housing (2) and tighten it with a torque wrench in a three-stage torque sequence: in the first stage, apply 30% of the target torque and let it stand for 5 minutes to eliminate local stress; in the second stage, apply 60% of the target torque and let it stand for 5 minutes again; in the third stage, apply 100% of the target torque to complete the final pre-tightening and achieve precise axial positioning of the optical end face. S3. Apply a layer of compatible silicone grease with a thickness of 0.02-0.05mm evenly to the outer wall of the pressure compensator (4), and slowly push the pressure compensator (4) into the compensation cavity (7) of the plug housing (2) along the axial direction. Use a plug gauge to check the annular gap between the outer wall of the pressure compensator (4) and the inner wall of the cavity to ensure that the gap uniformity deviation is ≤0.05mm. S4. Align the external thread of the oil-filled plug tail clip (5) with the internal thread at the rear end of the plug housing (2), select a calibration shim of preset thickness and place it on the connection end face, and use manual screwing to pre-connect until the front end of the oil-filled plug tail clip (5) axially limits the pressure compensator (4) to avoid deformation of the compensator caused by forced screwing. S5. The screw-in depth of the oil filling plug tail clip (5) is monitored in real time by a high-precision displacement sensor. At the same time, the axial pre-pressure of the pressure compensator (4) is detected by a micro pressure sensor. Combined with the adjustment of calibration shims of different thicknesses, the pressure compensator (4) is compressed to the designed pre-pressure stroke, so that an initial micro-positive pressure of 0.5-1 bar is established for the oil filling chamber under normal pressure. S6. After cutting the polyurethane buffer protection tube to the preset length, fit it on the outside of the four-core fiber unit to be connected. Insert the completed fiber unit and the polyurethane buffer protection tube into the tail tube part of the oil-filled plug tail clip (5) until the front end of the polyurethane buffer protection tube is completely attached to the inner step surface of the tail tube. S7. Place the stainless steel double wire reinforced hose clamp on the overlapping part of the polyurethane buffer protection tube and the oil-filled plug tail clamp (5) tail tube, and tighten the hose clamp with a torque wrench according to the specified torque so that the hose clamp forms a uniform radial clamping force on the polyurethane buffer protection tube, and construct a preliminary fiber strain release and anti-kink barrier. S8. Connect the valve on the oil-filling plug tail clip (5) to the vacuum system and the oil storage pressurization system through the pressure-resistant pipeline. First, turn on the vacuum system and pump the oil-filling chamber to a high vacuum of 1×10^-3Pa. Maintain this vacuum state for 30 minutes. Detect the residual gas components using a mass spectrometer to completely remove air, moisture and volatile impurities from inside the chamber. S9. While maintaining a high vacuum in the oil-filled chamber, shut down the vacuum system and switch to the oil storage and pressurization system. Slowly inject the low-viscosity, high-stability fluorinated oil or synthetic hydrocarbon oil that has undergone 72 hours of degassing treatment into the oil-filled chamber under a positive pressure of 0.2-0.3 MPa until the oil continuously overflows from the valve. S10. Close and seal the valve, place the assembled connector in a constant temperature and humidity environment of 25℃±1℃ and 50%±5% for 24 hours, detect the pressure change rate of the oil-filled cavity and the four-channel optical coupling loss, confirm that the pressure compensation system and optical transmission performance meet the design requirements, and complete the construction of the active pressure compensation sealing system.

5. The assembly method of the four-core expanded-beam oil-filled fiber optic connector according to claim 4, characterized in that, The control of the pre-pressure stroke of the pressure compensator (4) in S5 includes: S51. First, the real-time screw-in depth L of the oil filling plug tail clip (5) is collected by the displacement sensor, and the real-time axial pre-pressure F of the pressure compensator (4) is collected by the micro pressure sensor. In addition, the current ambient temperature T is collected by the temperature sensor. S52. Based on the preset elastic characteristic curve of the pressure compensator (4), establish the relationship between the pre-pressure stroke L0, the pre-pressure F0 and the temperature T: F0=k×[L0-α×(T-Tc)], where k is the elastic coefficient of the pressure compensator (4), α is the temperature-length conversion coefficient, and Tc is the preset standard reference temperature. S53. Substitute the real-time collected L, F, and T values ​​into the calculation to obtain the theoretical pre-compression pressure Fp = k × [L - α × (T - Tc)]. If the deviation between F and Fp, ΔF = |F - Fp|, is greater than the preset threshold ΔFmax, and ΔFmax = 0.02 × Fp, then the current pre-compression state is determined to be abnormal, and the following adjustment logic is executed: S54. If ΔF > ΔFmax and F < Fp, the pre-compression stroke is insufficient. At this time, increase the thickness of the calibration shim by 0.02mm each time, screw the oil-filling plug tail clip (5) back in and monitor L and F until ΔF ≤ ΔFmax. S55. If ΔF > ΔFmax and F > Fp, the pre-compression stroke is too large. At this time, reduce the thickness of the calibration shim by 0.02mm each time, screw in the oil filling plug tail clip (5) again and monitor L and F until ΔF ≤ ΔFmax. S56. If ΔF≤ΔFmax, then calculate the initial micro-positive pressure P=F / S based on the effective force-bearing area S of the pressure compensator (4). If P is in the range of 0.5-1 bar, then the pre-compression setting is completed. If P<0.5 bar, then replace the calibration shim with a thickness reduced by 0.01 mm and screw it back in. If P>1 bar, then replace the calibration shim with a thickness increased by 0.01 mm and screw it back in until P is stable in the range of 0.5-1 bar.

6. The assembly method of the four-core expanded-beam oil-filled fiber optic connector according to claim 4, characterized in that, The control methods for the vacuum infusion process in S8 and S9 include: During the vacuum extraction stage, the vacuum level Pr of the oil-filled cavity is monitored in real time by a vacuum gauge, and the residual gas components inside the cavity are detected by a mass spectrometer. If Pr drops to 1×10^-3 Pa and is maintained for ≥30 min, and the total content of moisture and volatile organic compounds in the residual gas is ≤0.1%, then the vacuum removal stage is considered complete. If Pr drops to 1×10^-3 Pa but to < 30 min, or the residual gas percentage > 0.1%, then extend the vacuum holding time and re-detect the gas composition and vacuum degree every 10 min until the conditions are met. During the oil filling stage, the oil injection flow rate Q is monitored by a flow sensor, the internal pressure Pb of the cavity is monitored by a pressure sensor, and the oil level H is monitored by a level sensor. Establish the injection rate: Qp = C × √(Pa - Pb), where C is the flow coefficient and Pa is the output pressure of the oil storage and pressurization system; If the deviation between the real-time flow rate Q and the calculated value Qp is ΔQ=|Q-Qp|>0.05×Qp, and Pa>0.35MPa, it is determined that the injection pipeline is blocked. Injection is suspended and inert gas is introduced to purge the pipeline for 30s before restarting injection. If ΔQ > 0.05 × Qp and Pa < 0.2 MPa, it is determined that the pressure of the oil storage and pressurization system is insufficient. Adjust the output pressure of the pressurization system to 0.25 MPa, and continue injection after the pressure stabilizes. When the liquid level H reaches the full liquid level threshold Hmax of the cavity, and the valve continues to overflow oil for ≥5s, the filling is considered complete and the valve is closed. If H reaches Hmax but no oil overflows from the valve, it is determined that the valve is blocked. In the reverse direction, 0.1MPa inert gas is introduced to purge the valve until the oil overflows steadily before the valve is sealed.

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