A device for manufacturing a double-clad optical fiber preform and a method for manufacturing the same

Abstract

The application discloses a preparation device of a double-clad optical fiber preform, which comprises a bottom die assembly and a cylindrical die vertically extending and having both ends open; an outer cladding glass sleeve matched with the internal structure of the cylindrical die is detachably installed in the cylindrical die, the outer cladding glass sleeve has both ends open, the inside of the outer cladding glass sleeve is used for extruding and filling inner cladding glass melt, and a top die is arranged in the cylindrical die and is butted at the top end of the outer cladding glass sleeve; a first feeding channel for allowing fiber core glass melt to flow and be absorbed into the inner cladding glass is formed in the top die, and the bottom end of the first feeding channel is provided with a discharge port coaxially communicated with the outer cladding glass sleeve; the bottom die assembly is used for plugging the bottom end of the outer cladding glass sleeve, and the bottom die assembly is provided with a cooling mechanism matched with the inner cladding glass cooling, so that the double-clad optical fiber preform with ideal interface, good fiber core diameter uniformity and wide adjustable range of fiber core / cladding ratio can be obtained.

Description

Technical Field

[0001] This invention relates to the field of optical fiber preform manufacturing technology, and in particular to a preparation apparatus and method for a double-clad optical fiber preform. Background Technology

[0002] Mid-infrared glass fibers have broad application prospects and research value in fields such as communication, medicine, military, and environmental monitoring, and have been extensively studied by many scholars in recent years. Currently, mid-infrared glass fibers mainly use multi-component glass as the matrix, including fluoride fibers, tellurate fibers, and sulfide fibers. Common multi-component glass fibers are generally single-clad structures, while double-clad fibers have some unique advantages due to their structural characteristics. For example, double-clad fibers have a very high surface area to volume ratio, good heat dissipation, and can operate at ambient temperatures ranging from -20°C to 70°C without requiring a large water-cooling system. Furthermore, double-clad fibers are essentially fiber optic devices, enabling high-efficiency coupling with fiber optic devices in current fiber optic communication systems. The core diameter of double-clad fibers can be made very small, restricting a very small number of laser modes within the core, making it easier to fabricate single-mode fibers, easily achieving high power density, and the inner cladding structure ensures high-power semiconductor pumping, thus improving pump efficiency and achieving high gain.

[0003] The fabrication technology of optical fiber preforms is the core of optical fiber manufacturing processes. Multi-component glass optical fiber preforms cannot be fabricated using chemical vapor deposition. Currently, common methods for fabricating single-clad optical fiber preforms include the tube-rod method (i.e., machining), the injection method, and the spin casting method. However, the fabrication technology for double-clad optical fiber preforms is based on the fabrication technology for single-clad optical fiber preforms. Typically, the hollow outer cladding glass tube is fabricated using machining or spin casting, while the core / inner cladding rod is fabricated using machining, injection, or spin casting methods. Then, based on the concept of the tube-rod method, the core / inner cladding rod is inserted into the outer cladding glass tube to obtain a double-clad multi-component glass optical fiber preform. For example, Chinese invention patent CN115395356A describes a method for preparing erbium-doped double-clad zirconium fluoride-based glass optical fiber preforms. This involves using a suction method to prepare the core / inner cladding rod, employing a rotation method to prepare a hollow outer cladding glass sleeve, and then inserting the core / inner cladding rod into the outer cladding glass sleeve to prepare the double-clad optical fiber preform. Chinese invention patent CN101923189B describes a method for preparing thulium tellurate glass double-clad optical fibers. The core and both the inner and outer cladding glass sleeves are prepared using mechanical processing methods. Subsequently, the core rod is inserted into the inner cladding sleeve and heated and drawn thinner, and then inserted into the outer cladding glass sleeve to obtain the double-clad optical fiber preform.

[0004] Most existing double-clad optical fiber preform fabrication technologies are based on the core-rod method, combined with other methods such as core injection and spin casting. Therefore, these methods inevitably retain some shortcomings during fabrication. For example, the core-rod method requires high optical quality of the bulk glass and precision of the machining equipment, and the unavoidable gap between the core rod and the cladding can easily introduce interface defects during fiber drawing. Core-rod fabricated fiber preforms have poor core diameter uniformity, resulting in a slender "V"-shaped structure in the cladding. To avoid blockage during core glass molten casting, the spin casting method requires a large cladding diameter, resulting in a limited adjustable range for the core / cladding ratio of the preform. Furthermore, air bubbles are easily introduced when pouring core glass molten into the cladding, increasing interface defects between the core and cladding. In addition, due to the size limitation of the inner diameter of the outer cladding glass tube, the core / inner cladding rod usually needs to undergo an additional heating and drawing process, which is very detrimental to suppressing the crystallization phenomenon of multi-component glass. Summary of the Invention

[0005] The purpose of this invention is to provide a preparation apparatus and method for double-clad optical fiber preforms to solve the problems existing in the prior art and to obtain double-clad optical fiber preforms with ideal interface, good core diameter uniformity, and a wide range of adjustable core / cladding ratio.

[0006] To achieve the above objectives, the present invention provides the following solution: The present invention provides a fabrication apparatus for a double-clad optical fiber preform, comprising a bottom mold assembly and a vertically extending cylindrical mold with openings at both ends;

[0007] The cylindrical mold is detachably installed with an outer cladding glass sleeve that matches its internal structure. The outer cladding glass sleeve is open at both ends, and the interior of the outer cladding glass sleeve is used to extrude and fill the inner cladding glass melt. The cylindrical mold is also provided with a top mold that is connected to the top of the outer cladding glass sleeve. The top mold has a first feeding channel for the fiber core glass melt to flow and be drawn into the inner cladding glass. The bottom end of the first feeding channel has a discharge port that is coaxially connected to the outer cladding glass sleeve.

[0008] The bottom mold assembly is used to seal the bottom end of the outer cladding glass sleeve, and the bottom mold assembly is equipped with a cooling mechanism for cooling the inner cladding glass.

[0009] Preferably, the first feeding channel extends vertically through the top mold, the radial cross-section of the first feeding channel gradually decreases from top to bottom, and the diameter of the discharge port matches the inner diameter of the outer cladding glass sleeve.

[0010] Preferably, the top mold is slidably installed inside the cylindrical mold, and a limiting component for abutting against the top surface of the top mold is detachably inserted into the outer peripheral wall of the cylindrical mold.

[0011] Preferably, the bottom mold assembly includes a bottom mold and a pressure head;

[0012] The top of the bottom mold is provided with a liquid storage tank for accommodating the inner cladding glass melt. The pressure head is slidably connected to the inside of the liquid storage tank in the vertical direction, and the outer peripheral wall of the pressure head and the inner peripheral wall of the liquid storage tank are slidably sealed together along their axial direction. The top of the pressure head is used to connect with the bottom end of the outer cladding glass sleeve, and the pressure head is provided with a second feeding channel in the vertical direction that is connected to the outer cladding glass sleeve.

[0013] Preferably, the second feed channel includes a straight section and a tapered section connected to the bottom of the straight section. The radial cross-section of the tapered section gradually expands from top to bottom, and the bottom of the tapered section is provided with an opening connected to the liquid storage tank. The top of the straight section is provided with an opening coaxially connected to and communicating with the outer glass sleeve, and the diameter of the straight section matches the inner diameter of the outer glass sleeve.

[0014] Preferably, the cylindrical mold is connected to a support platform that moves synchronously thereon, and a vertically extending limiting tube is connected below the support platform. The top end of the limiting tube is fixedly sleeved at the bottom position of the cylindrical mold, and the bottom end of the limiting tube is slidably sleeved at the top position of the pressure head along its axial direction.

[0015] Preferably, the portion of the limiting tube that mates with the pressure head has two strip-shaped through holes. The two strip-shaped through holes extend along the axial direction of the limiting tube and are symmetrically distributed along the diameter direction of the limiting tube. The limiting tube also has two notches, both of which are located between the two strip-shaped through holes and are symmetrically distributed along the diameter direction of the limiting tube. The notches extend along the axial direction of the limiting tube, with their top ends extending to the bottom of the support platform and their bottom ends penetrating the bottom edge of the limiting tube.

[0016] Two connecting holes are provided on the outer peripheral wall of the part of the pressure head that extends into the limiting tube. The two connecting holes are distributed in accordance with the two strip-shaped through holes along the circumference of the pressure head. A sliding rod that passes through the strip-shaped through hole is detachably inserted into the connecting hole. The sliding rod slides along the extension direction of the strip-shaped through hole.

[0017] Preferably, the support platform is connected to a connecting pipe coaxially connected to the top end of the limiting tube. The connecting pipe surrounds the outer periphery of the cylindrical mold and is connected to the outer wall of the cylindrical mold by a plurality of connecting members, each of the connecting members being equally spaced along the circumference of the connecting pipe.

[0018] Preferably, it further includes a preheating component, which is provided with a first heating mechanism for preheating the cylindrical mold and a second heating mechanism for preheating the heat storage tank and the pressure head.

[0019] A method for preparing a double-clad optical fiber preform is also provided, comprising the following steps:

[0020] Preparation: Prepare a hollow outer glass sleeve of a preset size, fix the outer glass sleeve inside the cylindrical mold, install the top mold inside the cylindrical mold and align it with the top of the outer glass sleeve, install the cylindrical mold on the support platform, and slide the pressure head to the bottom position of the limiting tube through the slide rod, then connect the bottom mold below the pressure head, and set the second heating mechanism and cooling mechanism at the bottom mold;

[0021] Preheating: Move the support platform downwards and slide the pressure head into the liquid storage tank of the bottom mold. Then, set the first heating mechanism at the cylinder mold and turn on the first and second heating mechanisms according to the preset temperature for preheating.

[0022] Melting: Melting the inner cladding glass and the core glass;

[0023] Pouring the inner cladding glass melt: Turn off the first heating mechanism and the second heating mechanism, move the support platform upward to leave sufficient space between the pressure head and the bottom mold, take out the molten inner cladding glass melt and pour it into the liquid storage tank of the bottom mold;

[0024] Extrusion: Install the limiting component on the cylindrical mold, move the support platform downward and ensure that the pressure head is inserted into the liquid storage tank of the bottom mold, and then extrude the inner cladding glass melt into the outer cladding glass sleeve at a constant speed through the second feeding channel until the inner cladding glass melt reaches the bottom of the first feeding channel, at which point the support platform stops moving;

[0025] Casting the fiber core glass melt: After extrusion, allow it to cool for the required time, and then pour the fiber core glass melt into the first feed channel of the top mold;

[0026] Suction: Activate the cooling mechanism to accelerate the cooling and contraction of the inner cladding glass in the storage tank, and quickly suck the fiber core glass melt in the top mold into the inner cladding glass. When the liquid level in the first feeding channel drops to the designated position, close the cooling mechanism, then move the support platform upward and separate the pressure head from the bottom of the cylindrical mold, and use the sealing mechanism to seal the bottom of the inner cladding glass in the cylindrical mold for the required time.

[0027] Annealing: Remove the sealing mechanism, remove the cylindrical mold from the support platform, keep the cylindrical mold vertical and perform annealing treatment;

[0028] Remove the finished product: Disassemble the cylindrical mold and separate the top mold to obtain the double-clad optical fiber preform.

[0029] The present invention achieves the following technical effects compared to the prior art:

[0030] The cylindrical mold contains an outer cladding glass sleeve that matches its internal structure, and a top mold that is connected to the top of the outer cladding glass sleeve. The top mold has a first feed channel for the core glass melt to flow and be drawn into the inner cladding glass. The core glass melt is drawn into the inner cladding glass through the first feed channel. The bottom mold assembly is used to seal the bottom of the outer cladding glass sleeve, and the bottom mold assembly is equipped with a cooling mechanism for cooling the inner cladding glass. By setting the cooling mechanism, the cooling and contraction of the inner cladding glass is accelerated, thereby speeding up the process of the core glass melt being drawn into the outer solidified inner cladding glass, avoiding the V-shaped structure that is wider at the top and narrower at the bottom, and improving the uniformity of the core diameter. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0033] Figure 2 This is a diagram showing the preparation process steps of the present invention;

[0034] Among them, 1-upper heating sleeve, 2-limiting rod, 3-top mold, 4-outer cladding glass sleeve, 5-cylindrical mold, 6-support platform, 7-sliding rod, 8-pressure head, 9-bottom mold, 10-cooling plate, 11-heating plate, 12-inner cladding glass melt, 13-fiber core glass melt, 14-lower heating sleeve. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The purpose of this invention is to provide a preparation apparatus and method for double-clad optical fiber preforms to solve the problems existing in the prior art and to obtain double-clad optical fiber preforms with ideal interface, good core diameter uniformity, and a wide range of adjustable core / cladding ratio.

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] like Figures 1 to 2 As shown, this embodiment provides a fabrication apparatus for a double-clad optical fiber preform, including a bottom mold assembly and a vertically extending cylindrical mold 5 with openings at both ends; preferably, the cylindrical mold 5 is a cylindrical structure; an outer cladding glass sleeve 4 that matches its internal structure is detachably installed inside the cylindrical mold 5, and the inner diameter of the cylindrical mold 5 matches the outer diameter of the outer cladding glass sleeve 4. Preferably, a fixing component for fixing the outer cladding glass sleeve 4 is detachably inserted into the outer peripheral wall of the cylindrical mold 5. The fixing component can be bolts, etc. A plurality of screw holes are opened in the middle of the cylindrical mold 5, and the screw holes are evenly distributed along the circumference of the cylindrical mold 5. During operation, the outer cladding glass sleeve 4 is fixed in the cylindrical mold 5 by the bolts abutting against the outer peripheral wall of the outer cladding glass sleeve 4, and the bottom ends of the outer cladding glass sleeve 4 and the cylindrical mold 5 are kept flush. The outer cladding glass sleeve 4 is open at both ends, and the interior of the outer cladding glass sleeve 4 is used to extrude and fill the inner cladding glass melt 12. The cylindrical mold 5 is also provided with a top mold 3 connected to the top end of the outer cladding glass sleeve 4. The top mold 3 has a first feeding channel for the fiber core glass melt 13 to flow through and be sucked into the inner cladding glass. The bottom end of the first feeding channel has a discharge port coaxially connected with the outer cladding glass sleeve 4. The fiber core glass melt 13 is sucked into the inner cladding glass through the first feeding channel. The bottom mold assembly is used to seal the bottom end of the outer cladding glass sleeve 4, and the bottom mold assembly is equipped with a cooling mechanism for cooling the inner cladding glass. Specifically, in the preparation process, the cylindrical mold 5 and the outer cladding glass sleeve 4 are preheated. Then, the inner cladding glass melt 12 is filled into the outer cladding glass sleeve 4. After standing and cooling for a period of time, the core glass melt 13 is poured into the first feed channel of the top mold 3, and the cooling mechanism is turned on to cool the inner cladding glass. This causes the inner cladding glass to cool and shrink rapidly, thereby accelerating the suction process of the core glass melt 13 being drawn into the solidified inner cladding glass on the periphery. This avoids the V-shaped structure that is wider at the top and narrower at the bottom that occurs in traditional suction methods, and improves the uniformity of the core diameter. In addition, by adjusting the inner diameter of the outer cladding glass sleeve 4 and the standing cooling time after extrusion, the freedom of setting the inner cladding and core diameters can be increased, thereby increasing the adjustable range of the core / cladding ratio.

[0039] In one specific embodiment, the first feeding channel extends vertically through the top mold 3. The radial cross-section of the first feeding channel gradually decreases from top to bottom. The diameter of the discharge port matches the inner diameter of the outer cladding glass sleeve 4, so that after the discharge port is coaxially connected with the top end of the outer cladding glass sleeve 4, the fiber core glass melt 13 can be smoothly drawn into the inner cladding glass. Specifically, the discharge port is tightly connected with the outer cladding glass sleeve 4 to avoid leakage.

[0040] In one specific embodiment, the top mold 3 is slidably installed inside the cylindrical mold 5. A limiting component for abutting against the top surface of the top mold 3 is detachably inserted into the outer peripheral wall of the cylindrical mold 5 to ensure that when the inner cladding glass melt 12 is squeezed into the outer cladding glass sleeve 4 and the fiber core glass melt 13 is poured into the first feed channel of the top mold 3, the top mold 3 can abut against the top of the outer cladding glass sleeve 4, and the top of the top mold 3 and the top of the outer cladding glass sleeve 4 are tightly fitted together to avoid separation of the top mold 3 and the outer cladding glass sleeve 4. Preferably, a limiting hole is opened on the outer peripheral wall of the top of the cylindrical mold 5, and a limiting rod 2 is slidably inserted into the limiting hole, abutting against the top surface of the top mold 3 through the limiting rod 2.

[0041] In one specific embodiment, the bottom mold assembly includes a bottom mold 9 and a pressure head 8. The top of the bottom mold 9 has a sump for accommodating the inner cladding glass melt 12. The pressure head 8 is slidably connected to the inside of the sump in a vertical direction, and the outer peripheral wall of the pressure head 8 and the inner peripheral wall of the sump slide in a sealing fit along their axial direction. Specifically, both the pressure head 8 and the sump are cylindrical, and the outer diameter of the pressure head 8 is the same as the inner diameter of the sump, so as to facilitate the sliding fit between the pressure head 8 and the sump, provided that their structures are matched. The top of the pressure head 8 is used for... The pressure head 8 is connected to the bottom end of the outer cladding glass sleeve 4 and has a second feeding channel that is vertically connected to the outer cladding glass sleeve 4. The pressure head 8 slides downward and squeezes the inner cladding glass melt 12 in the liquid storage tank, so that it is smoothly squeezed into the outer cladding glass sleeve 4 through the second feeding channel. The method of squeezing the inner cladding glass melt 12 into the outer cladding glass sleeve 4 in the reverse direction can replace the traditional tube and rod insertion method, which can increase the bonding strength between the inner and outer cladding glass, eliminate the adverse effects caused by the gap between the two, and thus reduce interface defects.

[0042] In one specific embodiment, the second feed channel includes a straight cylindrical section and a tapered section connected to the bottom of the straight cylindrical section. The radial cross-section of the tapered section gradually increases from top to bottom, and the bottom of the tapered section has an opening connected to the liquid storage tank. The top of the straight cylindrical section has an opening coaxially connected to and aligned with the outer cladding glass sleeve 4, and the diameter of the straight cylindrical section matches the inner diameter of the outer cladding glass sleeve 4. This ensures that when the inner cladding glass melt 12 is extruded, the outer cladding glass sleeve 4 is coaxially and sealed at the bottom at the top opening of the straight cylindrical section, allowing the inner cladding glass melt 12 to be quickly and smoothly extruded into the outer cladding glass sleeve 4.

[0043] In one specific embodiment, the cylindrical mold 5 is connected to a support platform 6 that moves synchronously with it. A vertically extending limiting tube is connected below the support platform 6. The top end of the limiting tube is fixedly sleeved at the bottom of the cylindrical mold 5, and the bottom end of the limiting tube slides along its axial direction at the top of the pressure head 8. The limiting tube connects the pressure head 8 and the cylindrical mold 5, ensuring that the pressure head 8 and the cylindrical mold 5 are coaxial during the extrusion and suction operations. Preferably, the support platform 6 is connected to a stepping system equipped with a motor. The motor drives the support platform 6 to move vertically up and down, thereby moving the cylindrical mold 5.

[0044] In one specific embodiment, the portion of the limiting tube that mates with the pressure head 8 has two strip-shaped through holes. The two strip-shaped through holes extend along the axis of the limiting tube and are symmetrically distributed along the diameter of the limiting tube. The limiting tube also has two notches, both located between the two strip-shaped through holes and symmetrically distributed along the diameter of the limiting tube. The notches extend along the axis of the limiting tube, with their tops extending to the bottom of the support platform 6 and their bottoms penetrating the bottom edge of the limiting tube. The outer peripheral wall of the portion of the pressure head 8 that extends into the limiting tube has two connecting holes, which are distributed along the circumference of the pressure head 8 and correspond to the two strip-shaped through holes. A sliding rod 7 that passes through the strip-shaped through hole is detachably inserted into the connecting hole, and the sliding rod 7 slides along the extension direction of the strip-shaped through hole. During the extrusion of the inner cladding glass melt 12, when the inner cladding glass melt 12 is extruded into the second feeding channel, the pressure head 8 abuts against the bottom of the cylindrical mold 5 through the limiting tube. Throughout the extrusion process, the top of the pressure head 8 and the bottom of the outer cladding glass sleeve 4 remain in close contact to prevent overflow and reduce the difficulty of separating the pressure head 8 and the cylindrical mold 5. Furthermore, by setting a notch, on the one hand, it can be used to observe the contact between the top of the pressure head 8 and the bottom of the outer cladding glass sleeve 4, and it can also facilitate the separation of the pressure head 8 and the cylinder mold 5 after the injection is completed: the top of the pressure head 8 and the bottom of the outer cladding glass sleeve 4 are sealed together without overflow. Then, after the injection is completed (or the cooling mechanism is turned off), only the outer solidified inner cladding glass sleeve is connected between the pressure head 8 and the outer cladding glass sleeve 4. Due to the setting of the notch, it is easy to generate bending deformation during the tapping and thus cut off the inner cladding glass, so that it can be separated. On the other hand, after separation, if the core is pre-sized, the unsolidified core glass melt 13 will spontaneously flow downward in the inner cladding glass sleeve that runs through both ends. At this time, the sealing mechanism (such as room temperature metal) can be passed through the notch to seal the bottom of the inner cladding glass sleeve, so that the core glass melt 13 solidifies quickly and achieves rapid sealing. Then it can be moved vertically to the annealing furnace for annealing. In actual operation, you can strike along the line connecting the two notches (perpendicular to the line connecting the slide bar 7) on the bottom mold 9 or the pressure head 8 to separate the pressure head 8 and the cylindrical mold 5.

[0045] Furthermore, the bottom of the cylindrical mold 5 is equipped with a sealing mechanism, preferably a metal knife, so that after the separation of the pressure head 8 and the cylindrical mold 5 is completed, the metal knife is sealed at the bottom of the cylindrical mold 5. It should be noted that when the preset diameter of the fiber core is large, after the separation of the pressure head 8 and the cylindrical mold 5, the unsolidified fiber core glass melt 13 at the axis may flow out from the bottom under the action of gravity. After the separation operation is completed, the bottom of the cylindrical mold 5 and the outer glass sleeve 4 is sealed by the metal knife, so that the fiber core glass melt 13 at the bottom can be quickly solidified to avoid leakage.

[0046] In one specific embodiment, the support platform 6 is connected to a connecting pipe coaxially connected to the top end of the limiting tube. The connecting pipe and the limiting tube are located at the top and bottom ends of the support platform 6, respectively. The connecting pipe surrounds the outer periphery of the cylindrical mold 5 and is connected to the outer wall of the cylindrical mold 5 by multiple connectors. The connectors are evenly spaced along the circumference of the connecting pipe. Preferably, the connectors are bolts. Multiple threaded holes are opened through the connecting pipe, and the threaded holes are evenly spaced along the circumference of the connecting pipe. The bolts are detachably inserted into the threaded holes and abut against the outer periphery of the cylindrical mold 5 to complete the connection between the connecting pipe and the cylindrical mold 5.

[0047] In one specific embodiment, a preheating assembly is also included. The preheating assembly is provided with a first heating mechanism for preheating the cylindrical mold 5 and a second heating mechanism for preheating the heat storage tank and the pressure head 8. Preferably, the first heating mechanism includes an upper heating sleeve 1, the inner diameter of which is larger than the outer diameter of the cylindrical mold 5, and surrounds the outer periphery of the cylindrical mold 5. When preheating the mold, the preheating temperature of the upper heating sleeve 1 is set to be near the glass transition temperature of the inner cladding glass. During the preparation process, the cylindrical mold 5 and the outer cladding glass sleeve 4 are preheated by the upper heating sleeve 1. The inner cladding glass melt 12 is filled into the outer cladding glass sleeve 4. Then, the upper heating sleeve 1 is closed and removed. After standing and cooling for a period of time, the fiber core glass melt 13 is poured into the first feed channel of the top mold 3. The second heating mechanism includes a lower heating sleeve 14 and a heating plate 11. The inner diameter of the lower heating sleeve 14 is larger than the outer diameter of the bottom mold 9, and it surrounds the outer periphery of the bottom mold 9. When preheating the mold, the preheating temperature of the lower heating sleeve 14 is set near the softening temperature of the inner cladding glass. A preferred cooling mechanism includes a cooling plate 10 attached to the bottom surface of the bottom mold 9, with the heating plate 11 installed at the bottom end of the cooling plate 10. The preheating temperature of the heating plate 11 is set near the glass transition temperature of the inner cladding glass. Furthermore, since the cooling plate 10 is located above the heating plate 11, and the bottom mold 9 is located above the cooling plate 10, and the size of the cooling plate 10 is larger than that of the bottom mold 9, the bottom end of the bottom mold 9 and the cooling plate 10 always maintain a tight fit. After the cooling plate 10 is turned on, the heat exchange process is accelerated, and the cooling and shrinkage of the inner cladding glass in the bottom mold 9 is accelerated, allowing the core glass melt 13 to be quickly drawn into the inner cladding glass, thereby improving the uniformity of the core diameter.

[0048] A method for preparing a double-clad optical fiber preform is also provided, comprising the following steps:

[0049] Preparation: Prepare a hollow outer glass sleeve 4 of a predetermined size. Fix the outer glass sleeve 4 inside the cylindrical mold 5, making the bottom end of the outer glass sleeve 4 flush with the bottom end of the cylindrical mold 5. Install the top mold 3 inside the cylindrical mold 5 and align it with the top end of the outer glass sleeve 4. Install the cylindrical mold 5 on the support platform 6, specifically inside the connecting pipe connected to the support platform 6. The cylindrical mold 5 extends into the limiting pipe connected to the support platform 6, and the pressure head 8 is slidably connected to the limiting pipe via the sliding rod 7. The bottom of the tube is located below the cylindrical mold 5, and the bottom mold 9 is connected below the pressure head 8. The second heating mechanism and the cooling mechanism are set at the bottom mold 9. The preferred second heating mechanism includes a lower heating sleeve 14 and a heating plate 11, and the cooling mechanism includes a cooling plate 10. The cooling plate 10 is attached to the bottom end surface of the bottom mold 9, and the heating plate 11 is attached to the side of the cooling plate 10 away from the bottom mold 9. Before preheating, the support platform 6 is moved upward and the lower heating sleeve 14 is set on the outer periphery of the bottom mold 9.

[0050] Preheating: Move the support platform 6 downward and slide the pressure head 8 into the liquid storage tank of the bottom mold 9. Then, set the first heating mechanism at the cylindrical mold 5 and turn on the first heating mechanism and the second heating mechanism according to the preset temperature for preheating. Preferably, the first heating mechanism is the upper heating sleeve 1. After moving the support platform 6 downward so that the pressure head 8 enters the liquid storage tank, the upper heating sleeve 1 is set on the outer periphery of the cylindrical mold 5. The preheating temperature of the upper heating sleeve 1 and the heating plate 11 is set near the glass transition temperature of the inner cladding glass, and the preheating temperature of the lower heating sleeve 14 is set near the softening temperature of the inner cladding glass. After turning on the heating system, preheat for 30-120 minutes.

[0051] Melting: Melting the inner cladding glass and the core glass; preferably, an electric furnace is used to melt the inner cladding glass and the core glass;

[0052] Pouring the inner cladding glass melt 12: Turn off the first heating mechanism and the second heating mechanism to stop heating, move the support platform 6 upward to leave sufficient space between the pressure head 8 and the bottom mold 9, take out the molten inner cladding glass 12 and pour it into the liquid storage tank of the bottom mold 9; preferably, both the first heating mechanism and the second heating mechanism are equipped with a heating system to control their opening and closing. When it is necessary to stop preheating, turn off the heating system. Specifically, in operation, move the upper heating sleeve 1, then move the support platform 6 upward to leave sufficient space between the pressure head 8 and the bottom mold 9, and remove the lower heating sleeve 14. Then take out the molten inner cladding glass 12 and pour it into the liquid storage tank of the bottom mold 9.

[0053] Extrusion: Install the limiting component on the cylindrical mold 5, so that the bottom end of the top mold 3 is in close contact with the top end of the outer cladding glass sleeve 4. Move the support platform 6 downward and ensure that the pressure head 8 is inserted into the liquid storage tank of the bottom mold 9. After the top end of the pressure head 8 is in close contact with the bottom end of the outer cladding glass sleeve 4, the inner cladding glass melt 12 is then uniformly extruded into the outer cladding glass sleeve 4 through the second feeding channel until the inner cladding glass melt 12 reaches the bottom of the first feeding channel, at which point the support platform 6 stops moving. The method of extruding the inner cladding glass melt 12 into the outer cladding glass sleeve 4 in the reverse direction instead of the traditional tube and rod insertion method can increase the bonding strength between the inner and outer cladding glass, eliminate the adverse effects caused by the gap between the two, and thus reduce interface defects.

[0054] Casting the core glass melt 13: After extrusion, allow it to cool for the required time, preferably 60-600s. Then, pour the core glass melt 13 into the first feed channel of the top mold 3. At the moment after the core glass melt 13 is cast, the inner cladding glass in the cavity formed by the outer cladding glass sleeve 4, the pressure head 8 and the bottom mold 9 is in a state of solidified outer periphery but flowable interior. The diameter of the core depends on the cooling time.

[0055] Suction: The cooling mechanism is turned on to accelerate the cooling and contraction of the inner cladding glass in the liquid storage tank, and the core glass melt 13 in the top mold 3 is quickly sucked into the inner cladding glass, thereby accelerating the suction process of the core glass melt 13 being sucked into the outer solidified inner cladding glass. This avoids the V-shaped structure that is wider at the top and narrower at the bottom that occurs in the traditional suction method and improves the uniformity of the core diameter. When the liquid level in the first feed channel drops to the designated position, the cooling mechanism is turned off. Then the support platform 6 is moved upward and the pressure head 8 is separated from the bottom of the cylindrical mold 5. That is, the outer solidified inner cladding glass is cut off at the connection between the pressure head 8 and the outer cladding glass sleeve 4. The bottom of the inner cladding glass in the cylindrical mold 5 is sealed with a sealing mechanism for the required time. Preferably, the sealing mechanism is a metal knife. The metal knife is pressed against the bottom of the outer cladding glass sleeve 4 and waits for 10-60 seconds to allow the core glass melt 13 at the bottom to solidify quickly.

[0056] Annealing: Remove the sealing mechanism, remove the cylindrical mold 5 from the support platform 6, keep the cylindrical mold 5 in a vertical position and perform annealing treatment, preferably in an electric furnace;

[0057] Remove the finished product: Disassemble the cylindrical mold 5 and separate the top mold 3 to obtain the double-clad optical fiber preform.

[0058] It should be noted that the existing fabrication process for double-clad optical fiber preforms typically includes three steps: fabrication of the outer cladding glass tube 4, fabrication of the core / inner cladding rod, and heating and thinning. The reverse extrusion and injection method proposed in this invention greatly simplifies the fabrication process of double-clad optical fiber preforms, avoiding the additional heating and thinning step required due to the inner diameter limitation of the outer cladding glass tube 4, thus effectively suppressing glass crystallization. Furthermore, by adjusting the inner diameter of the outer cladding glass tube 4 and the static cooling time after extrusion, the freedom in setting the inner cladding and core diameters can be increased, thereby expanding the adjustable range of the core / cladding ratio. Moreover, this invention has good applicability to non-chalcogenide mid-infrared glasses, such as fluoride glasses, tellurate glasses, and fluorotellurate glasses.

[0059] In summary, existing double-clad optical fiber preform manufacturing processes include at least three independent steps: preparation of the outer cladding glass tube 4, preparation of the core / inner cladding rod, and insertion of the core / inner cladding rod into the outer cladding glass tube 4 (which often requires additional heating and thinning due to size limitations). The entire process is quite cumbersome, and interface defects between the inner and outer cladding layers, as well as the heating and thinning process, can adversely affect the double-clad optical fiber preform. This invention provides a double-clad optical fiber preform manufacturing apparatus, comprising a bottom mold assembly and a vertically extending cylindrical mold 5 with openings at both ends. The cylindrical mold 5 has a detachably installed outer cladding glass tube 4 that matches its internal structure. The outer cladding glass tube 4 is open at both ends, and its interior can be used to extrude the inner cladding glass melt 12. The cylindrical mold 5 also has a top mold 3 docked at the top of the outer cladding glass tube 4. The top mold 3 has a first feed channel for the core glass melt 13 to flow through and be drawn into the inner cladding glass. The bottom mold assembly is used to seal the outer cladding glass tube 4. The bottom end of the cladding glass sleeve 4; This invention prepares double-clad optical fiber preforms by simultaneously setting a top mold 3 and a bottom mold assembly at both ends of the outer cladding glass sleeve 4, and by using a combination of reverse extrusion and injection. On the one hand, this not only greatly simplifies the preparation process of double-clad optical fiber preforms, but also avoids the additional heating and thinning process required due to the inner diameter limitation of the outer cladding glass sleeve 4, effectively suppressing the crystallization phenomenon of the glass. On the other hand, by using the method of reverse extrusion of the inner cladding glass melt 12 into the outer cladding glass sleeve 4 instead of the traditional tube-rod method of insertion, the bonding strength between the inner and outer cladding glasses can be increased, eliminating the adverse effects of the traditional insertion method and reducing interface defects. At the same time, the bottom mold assembly is equipped with a cooling mechanism for cooling the inner cladding glass, which can accelerate the cooling and shrinkage of the inner cladding glass, thereby accelerating the injection process of the core glass melt 13 into the outer solidified inner cladding glass, avoiding the V-shaped structure that is wider at the top and narrower at the bottom, and improving the uniformity of the core diameter.

[0060] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0061] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0062] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. An apparatus for producing a double-clad optical fiber preform, characterized by comprising: The bottom die assembly and the vertically extending and open-ended barrel die; The outer cladding glass sleeve is detachably installed in the barrel die and matches the internal structure of the barrel die, the outer cladding glass sleeve is open-ended, the inside of the outer cladding glass sleeve is used for extruding and filling the inner cladding glass melt, the barrel die is further provided with a top die which is butted at the top end of the outer cladding glass sleeve, the top die is provided with a first feeding channel for the flow of the fiber core glass melt and the injection into the inner cladding glass, and the bottom end of the first feeding channel has a discharge port which is coaxially communicated with the outer cladding glass sleeve; The bottom die assembly is used for blocking the bottom end of the outer cladding glass sleeve, and the bottom die assembly is matched with a cooling mechanism for cooling the inner cladding glass; The bottom die assembly includes a bottom die and a pressure head, the top end of the bottom die is provided with a liquid storage groove for accommodating the inner cladding glass melt, the pressure head is slidingly connected inside the liquid storage groove in the vertical direction, the outer peripheral wall of the pressure head is slidingly and sealingly matched with the inner peripheral wall of the liquid storage groove along the axial direction, the top end of the pressure head is used for butting at the bottom end of the outer cladding glass sleeve, and the pressure head is vertically and penetratingly provided with a second feeding channel which is communicated with the outer cladding glass sleeve.

2. The apparatus for producing a double-clad optical fiber preform according to claim 1, wherein The first feeding channel penetrates the top die in the vertical direction, the radial cross section of the first feeding channel gradually decreases from top to bottom, and the diameter of the discharge port matches the inner diameter of the outer cladding glass sleeve.

3. The apparatus for producing a double-clad optical fiber preform according to claim 2, wherein The top die is slidingly installed in the barrel die, and a limiting assembly for abutting against the top end face of the top die is detachably inserted on the outer peripheral wall of the barrel die.

4. The apparatus for producing a double-clad optical fiber preform according to claim 3, wherein The second feeding channel includes a straight cylinder segment and a tapered segment communicated at the bottom of the straight cylinder segment, the radial cross section of the tapered segment gradually expands from top to bottom, the bottom of the tapered segment is provided with an opening communicated with the liquid storage groove, the top of the straight cylinder segment is provided with an opening coaxially butted and communicated with the outer cladding glass sleeve, and the diameter of the straight cylinder segment matches the inner diameter of the outer cladding glass sleeve.

5. The apparatus for producing a double-clad optical fiber preform according to claim 4, wherein The barrel die is connected with a support platform which moves synchronously, and a vertically extending limiting tube is connected below the support platform, the top end of the limiting tube is fixedly sleeved at the bottom position of the barrel die, and the bottom end of the limiting tube is slidingly sleeved at the top position of the pressure head along the axial direction.

6. The apparatus for manufacturing a double-clad optical fiber preform according to claim 5, wherein The part of the limiting tube matched with the pressure head is provided with two strip-shaped through holes, the two strip-shaped through holes extend along the axial direction of the limiting tube and are symmetrically distributed along the diameter direction of the limiting tube; two notches are further provided on the limiting tube, the two notches are located at the positions between the two strip-shaped through holes and are symmetrically distributed along the diameter direction of the limiting tube, the notches extend along the axial direction of the limiting tube, the top end of the notches extends to the bottom position of the support platform, and the bottom end of the notches penetrates the bottom edge of the limiting tube; Two connecting holes are provided on the outer peripheral wall of the part of the pressure head extending into the limiting tube, the two connecting holes are correspondingly distributed along the circumference of the pressure head and the two strip-shaped through holes; a slide rod which penetrates the strip-shaped through hole is detachably inserted in the connecting hole, and the slide rod slidingly matches the strip-shaped through hole along the extension direction of the strip-shaped through hole.

7. The apparatus for producing a double-clad optical fiber preform according to claim 6, wherein The support platform is connected with a connecting pipe coaxially communicated with the limiting pipe top end, the connecting pipe surrounds the outer periphery of the drum mold, and a plurality of connecting pieces are connected between the connecting pipe and the outer wall of the drum mold, and each connecting piece is distributed equidistantly along the circumference of the connecting pipe.

8. The apparatus for manufacturing a double-clad optical fiber preform according to claim 7, wherein The preheating assembly is further provided with a first heating mechanism for preheating the drum mold and a second heating mechanism for preheating the liquid storage tank and the pressure head.

9. A method of producing a double-clad optical fiber preform using the production apparatus of the double-clad optical fiber preform according to any one of claims 1 to 8, characterized by, The method comprises the following steps: Preparation: hollow outer cladding glass sleeve of preset size is prepared, the outer cladding glass sleeve is fixed in the drum mold, the top mold is installed in the drum mold and butts on the top end of the outer cladding glass sleeve, the drum mold is installed on the support platform, the pressure head is slidingly connected at the bottom position of the limiting pipe through the sliding rod, the bottom mold is connected below the pressure head, and the second heating mechanism and the cooling mechanism are arranged at the bottom mold; Preheating: the support platform is moved downward, the pressure head is slidingly inserted into the liquid storage tank of the bottom mold, the first heating mechanism is arranged at the drum mold, and the first heating mechanism and the second heating mechanism are started at a preset temperature for preheating; Fusion: inner cladding glass and core glass are fused; Pouring of inner cladding glass melt: the first heating mechanism and the second heating mechanism are closed, the support platform is moved upward to leave sufficient space between the pressure head and the bottom mold, the fused inner cladding glass melt is taken out and poured into the liquid storage tank of the bottom mold; Extrusion: the limiting assembly is installed on the drum mold, the support platform is moved downward to ensure that the pressure head is inserted into the liquid storage tank of the bottom mold, then the inner cladding glass melt is uniformly extruded into the outer cladding glass sleeve through the second feeding channel, and the support platform stops moving when the inner cladding glass melt reaches the bottom of the first feeding channel; Pouring of core glass melt: after the extrusion is completed, the cooling is cooled to the required time, then the core glass melt is poured into the first feeding channel of the top mold; Suction: the cooling mechanism is started to accelerate the cooling and shrinkage of the inner cladding glass in the liquid storage tank, the core glass melt in the top mold is quickly sucked into the inner cladding glass, the cooling mechanism is closed when the liquid surface in the first feeding channel drops to the specified position, then the support platform is moved upward and the pressure head is separated from the bottom of the drum mold, and the plugging mechanism is used to plug the bottom end of the inner cladding glass in the drum mold to the required time; Annealing: the plugging mechanism is removed, the drum mold is disassembled from the support platform, the drum mold is kept in a vertical state and is subjected to annealing treatment; The finished product is obtained by disassembling the drum mold and separating the top mold.

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