Preparation device and preparation method of double-clad optical fiber preform

Abstract

The invention discloses a preparation device of a double-clad optical fiber preform. The preparation device comprises a bottom mold assembly and a cylindrical mold which extends vertically and is provided with openings at two ends, an outer cladding glass sleeve matched with the inner structure of the barrel mold is detachably installed in the barrel mold, the two ends of the outer cladding glass sleeve are open, the interior of the outer cladding glass sleeve is used for being squeezed into and filled with inner cladding glass melt, and a top mold in butt joint with the top end of the outer cladding glass sleeve is further arranged in the barrel mold. The top mold is provided with a first feeding channel used for allowing a fiber core glass melt to circulate and sucking and injecting the fiber core glass melt into the inner cladding glass, and the bottom end of the first feeding channel is provided with a discharging port coaxially communicated with the outer cladding glass sleeve; the bottom mold assembly is used for blocking the bottom end of the outer cladding glass sleeve, and the bottom mold assembly is matched with a cooling mechanism for cooling the inner cladding glass, so that the double-cladding optical fiber preform with an ideal interface, good fiber core diameter uniformity and wide fiber core / cladding proportion adjustable range can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber preform manufacturing, and in particular to a preparation device and a preparation method of a double-clad optical fiber preform. Background Art

[0002] Mid-infrared glass fiber has broad application prospects and research value in the fields of communications, medical treatment, military and environmental monitoring, and has been widely studied by many scholars in recent years. At present, mid-infrared glass fiber is mainly based on multi-component glass, mainly fluoride fiber, tellurite fiber and sulfide fiber. The common multi-component glass fiber is generally a single-cladding structure, while the double-cladding fiber has some unique advantages due to its structural characteristics. For example, the double-cladding fiber has a very high "surface area / volume" ratio, good heat dissipation effect, and the ambient temperature is allowed to be between -20 and 70 ° C, without the need for a large water cooling system; in addition, the double-cladding fiber is essentially a fiber device, which can be connected with the fiber devices in the current fiber-optic communication system with a high coupling efficiency; and the core diameter of the double-cladding fiber can be very small, which limits a very small number of laser modes in the core, making it easier to prepare a single-mode fiber, and it is easy to form a high power density, and the inner cladding structure can ensure high-power semiconductor pumping, thereby improving the pumping efficiency and achieving high gain.

[0003] The preparation technology of optical fiber preform is the core of optical fiber manufacturing process. Multi-component glass optical fiber preform cannot be prepared by chemical vapor deposition. The common preparation methods of single-clad optical fiber preform include tube-rod method (i.e. mechanical processing method), suction injection method and spin casting method, etc. The preparation technology of optical fiber preform with double cladding structure is based on the preparation technology of single-clad optical fiber preform. Usually, the hollow outer cladding glass sleeve is prepared by mechanical processing method or spin casting method, while the core / inner cladding rod is prepared by mechanical processing method, suction injection method or spin casting method, etc. Then, based on the idea of ​​tube-rod method, the core / inner cladding rod is inserted into the outer cladding glass sleeve to obtain double-clad multi-component glass optical fiber preform. For example, Chinese invention patent CN115395356A introduces a method for preparing an erbium-doped double-clad zirconium fluoride-based glass optical fiber preform, that is, the core / inner cladding rod is prepared by the suction injection method, the hollow outer cladding glass sleeve is prepared by the rotation method, and then the core / inner cladding rod is inserted into the outer cladding glass sleeve to prepare a double-clad optical fiber preform. Chinese invention patent CN101923189B introduces a method for preparing a thulium-doped tellurite glass double-clad optical fiber, the core and the inner and outer cladding glass sleeves are all prepared by mechanical processing, and then the core rod is inserted into the inner cladding sleeve and heated and stretched, and then inserted into the outer cladding glass sleeve to obtain a double-clad optical fiber preform.

[0004] Most of the existing preparation technologies for double-clad optical fiber preforms are based on the idea of ​​the tube-rod method, and are combined with methods such as the suction injection method and the spin casting method. Therefore, some of the shortcomings of these methods are inevitably retained during the preparation process. For example, the tube-rod method has high requirements for the optical quality of bulk glass and the precision of mechanical processing equipment, and the inevitable gap between the core rod and the cladding sleeve will easily introduce interface defects during the optical fiber drawing process. The core diameter uniformity of the optical fiber preform prepared by the suction injection method is poor, and it will present an elongated "V"-shaped structure in the cladding sleeve. In order to avoid blockage when pouring the core glass melt, the spin casting method requires a larger diameter of the prepared cladding sleeve, resulting in a small adjustable range of the core / cladding ratio of the preform; in addition, when pouring the core glass melt into the cladding sleeve, bubbles are easily introduced, thereby increasing the interface defects between the core and the cladding sleeve. In addition, due to the size limitation of the inner diameter of the outer cladding glass sleeve, the core / inner cladding rod usually needs to undergo an additional heating and drawing process, which is very unfavorable for suppressing the crystallization phenomenon of multi-component glass. Summary of the invention

[0005] The purpose of the present invention is to provide a double-clad optical fiber preform preparation device and preparation method thereof, so as to solve the problems existing in the above-mentioned prior art and obtain a double-clad optical fiber preform with an ideal interface, good core diameter uniformity and a wide adjustable range of core / cladding ratio.

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

[0007] An outer cladding glass sleeve matching its internal structure is detachably installed in the drum mold, the two ends of the outer cladding glass sleeve are open, and the interior of the outer cladding glass sleeve is used to squeeze in and fill with the inner cladding glass melt, and the drum mold is also provided with a top mold docked at the top end of the outer cladding glass sleeve, and the top mold is provided with a first feed channel for the core glass melt to flow and be sucked and injected into the inner cladding glass, and the bottom end of the first feed channel has a discharge port 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 feed channel passes through the top mold in a vertical direction, the radial cross section of the first feed 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 in the drum mold, and a limiting component for abutting against the top end surface of the top mold is detachably inserted on the outer peripheral wall of the drum mold.

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

[0012] A liquid storage tank for accommodating the inner cladding glass melt is provided at the top of the bottom mold, the pressure head is slidably connected to the inside of the liquid storage tank along the vertical direction, and the outer peripheral wall of the pressure head and the inner peripheral wall of the liquid storage tank are slidingly and sealingly matched along the axial direction thereof, the top of the pressure head is used to dock with the bottom end of the outer cladding glass sleeve, and the pressure head is penetrated along the vertical direction to open a second feeding channel 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 docked with and connected to the outer cladding glass sleeve, and the diameter of the straight section matches the inner diameter of the outer cladding glass sleeve.

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

[0015] Preferably, the portion of the limiting tube that cooperates with the pressure head is provided with two strip-shaped through holes, the two strip-shaped through holes extend along the axis direction of the limiting tube and are symmetrically distributed along the diameter direction of the limiting tube; the limiting tube is also provided with 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 axis direction of the limiting tube, the top end of the notch extends to the bottom position of the support platform, and the bottom end thereof passes through the bottom edge of the limiting tube;

[0016] Two connecting holes are provided on the outer peripheral wall of the part where the pressure head extends into the limiting tube, and the two connecting holes are distributed along the circumference of the pressure head corresponding to the two strip-shaped through holes; a sliding rod passing through the strip-shaped through hole is detachably inserted into the connecting hole, and the sliding rod slides with the strip-shaped through hole along the extension direction thereof.

[0017] Preferably, the support platform is connected to a connecting tube coaxially connected to the top of the limiting tube, the connecting tube surrounds the outer peripheral side of the cylinder mold, and is connected to the outer wall of the cylinder mold by multiple connecting parts, and each of the connecting parts is evenly spaced along the circumference of the connecting tube.

[0018] Preferably, it further comprises a preheating component, wherein the preheating component is provided with a first heating mechanism for preheating the drum 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 cladding glass sleeve of a preset size, fix the outer cladding glass sleeve in the drum mold, install the top mold in the drum mold and dock it on the top of the outer cladding glass sleeve, install the drum mold on the support platform, and slide the pressure head to the bottom position of the limit tube through a sliding rod, then connect the bottom mold to the bottom of the pressure head, and set the second heating mechanism and the cooling mechanism at the bottom mold;

[0021] Preheating: Move the support platform downward and slide the pressure head into the liquid storage tank of the bottom mold, then set the first heating mechanism at the barrel mold, and start the first heating mechanism and the second heating mechanism according to the preset temperature for preheating;

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

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

[0024] Extrusion: Install the limit assembly on the barrel 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 squeeze the inner cladding glass melt into the outer cladding glass sleeve at a uniform speed through the second feed channel until the inner cladding glass melt reaches the bottom of the first feed channel, and the support platform stops moving;

[0025] Pouring the core glass melt: After extrusion is completed, the core glass melt is allowed to cool for a required time, and then poured into the first feed channel of the top mold;

[0026] Suction injection: Turn on the cooling mechanism to accelerate the cooling and shrinkage of the inner cladding glass in the liquid storage tank, and quickly suck the core glass melt in the top mold into the inner cladding glass. When the liquid level in the first feeding channel drops to the specified position, turn off the cooling mechanism, then move the support platform upward and separate the pressure head from the bottom of the barrel mold, and use the sealing mechanism to seal the bottom end of the inner cladding glass in the barrel mold for the required time;

[0027] Annealing: remove the blocking mechanism, remove the barrel mold from the supporting platform, keep the barrel mold in a vertical state and perform annealing treatment;

[0028] Take out the finished product: disassemble the barrel mold and separate the top mold to obtain the double-clad optical fiber preform.

[0029] Compared with the prior art, the present invention has achieved the following technical effects:

[0030] An outer cladding glass sleeve matching its internal structure is fixed in the barrel mold, and a top mold is docked at the top of the outer cladding glass sleeve. A first feed channel is opened on the top mold for the core glass melt to flow and be sucked and injected into the inner cladding glass. The core glass melt is sucked and injected into the inner cladding glass through the first feed channel; 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; the cooling and shrinkage of the inner cladding glass is accelerated by arranging the cooling mechanism, thereby accelerating the suction and injection process of the core glass melt into the peripheral solidified inner cladding glass, avoiding the V-shaped structure with a wide top and a narrow bottom, and improving the uniformity of the core diameter. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

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

[0033] Figure 2 It is a process diagram of the preparation process of the present invention;

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

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] The purpose of the present invention is to provide a double-clad optical fiber preform preparation device and preparation method thereof, so as to solve the problems existing in the above-mentioned prior art and obtain a double-clad optical fiber preform with an ideal interface, good core diameter uniformity and a wide adjustable range of core / cladding ratio.

[0037] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] like Figure 1 to Figure 2 As shown, this embodiment provides a preparation device for a double-clad optical fiber preform, comprising a bottom mold assembly and a barrel mold 5 extending vertically and opened at both ends; preferably, the barrel mold 5 is a cylindrical structure; an outer cladding glass sleeve 4 matching its internal structure is detachably installed in the barrel mold 5, and the inner diameter of the barrel mold 5 matches the outer diameter of the outer cladding glass sleeve 4. Preferably, a fixing assembly for fixing the outer cladding glass sleeve 4 is detachably inserted on the outer peripheral wall of the barrel mold 5, and the fixing assembly can be bolts, etc. A plurality of screw holes are opened in the middle of the barrel mold 5, and the screw holes are evenly spaced along the circumference of the barrel mold 5. During operation, the outer cladding glass sleeve 4 is fixed in the barrel mold 5 by abutting against the outer peripheral wall of the outer cladding glass sleeve 4 through the bolts, and the outer cladding glass sleeve 4 is kept flush with the bottom end of the barrel mold 5. The outer cladding glass sleeve 4 is opened at both ends, and the interior of the outer cladding glass sleeve 4 is used to squeeze in and fill with the inner cladding glass melt 12. The drum mold 5 is also provided with a top mold 3 docked at the top end of the outer cladding glass sleeve 4. The top mold 3 is provided with a first feed channel for the core glass melt 13 to flow and be sucked and injected into the inner cladding glass. The bottom end of the first feed channel has a discharge port coaxially connected to the outer cladding glass sleeve 4. The core glass melt 13 is sucked and injected into the inner cladding glass through the first feed channel; the bottom mold assembly is used to be sealed at 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, during the preparation process, the barrel mold 5 and the outer cladding glass sleeve 4 are preheated first, and then the inner cladding glass melt 12 is filled into the outer cladding glass sleeve 4. After 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, so that the inner cladding glass cools and shrinks quickly, thereby accelerating the suction process of the core glass melt 13 into the inner cladding glass solidified at the periphery, avoiding the V-shaped structure with a wide top and a narrow bottom in the traditional suction method, and improving the uniformity of the core diameter. In addition, by adjusting the inner diameter of the outer cladding glass sleeve 4 and the cooling time after the extrusion is completed, the degree of freedom of setting the inner cladding and core diameters can be increased, thereby increasing the adjustable range of the core / cladding ratio.

[0039] In a specific embodiment, the first feed channel penetrates the top mold 3 in the vertical direction, and the radial cross-section of the first feed 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 core glass melt 13 can be smoothly sucked and injected into the inner cladding glass. Specifically, the discharge port is tightly connected with the outer cladding glass sleeve 4 to avoid leakage and the like.

[0040] In a specific embodiment, the top mold 3 is slidably installed in the barrel mold 5, and a limiting component for abutting against the top end surface of the top mold 3 is detachably inserted on the outer peripheral wall of the barrel mold 5 to ensure that when the inner cladding glass melt 12 is squeezed into the outer cladding glass sleeve 4, and when the core glass melt 13 is poured into the first feeding channel of the top mold 3, the top mold 3 can abut against the top end of the outer cladding glass sleeve 4, and the top mold 3 and the top end of the outer cladding glass sleeve 4 are tightly fitted to avoid the top mold 3 and the outer cladding glass sleeve 4 from separating. Preferably, a limiting hole is provided on the outer peripheral wall of the top of the barrel mold 5, and a limiting rod 2 is slidably inserted in the limiting hole, and abuts against the top end surface of the top mold 3 through the limiting rod 2.

[0041] In a specific embodiment, the bottom mold assembly includes a bottom mold 9 and a pressure head 8; the top of the bottom mold 9 is provided with a liquid storage tank for accommodating the inner cladding glass melt 12, the pressure head 8 is slidably connected to the inside of the liquid storage tank along the vertical direction, and the outer peripheral wall of the pressure head 8 and the inner peripheral wall of the liquid storage tank are slidably sealed and matched along the axial direction thereof. Specifically, the pressure head 8 and the liquid storage tank are both cylindrical structures, and the outer diameter of the pressure head 8 is the same as the inner diameter of the liquid storage tank, so that the sliding cooperation between the pressure head 8 and the liquid storage tank is facilitated on the premise that the pressure head 8 and the liquid storage tank structure match each other, and 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 penetrates through the second feeding channel connected to the outer cladding glass sleeve 4 in the vertical direction. 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 inner cladding glass melt 12 is reversely squeezed into the outer cladding glass sleeve 4 to replace the traditional tube-rod method of plugging, which can increase the bonding strength between the inner and outer cladding glasses, eliminate the adverse effects caused by the gap between the two, and thus reduce interface defects.

[0042] In a specific embodiment, 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, and the top of the straight section is provided with an opening coaxially docked and connected to the outer cladding glass sleeve 4, and the diameter of the straight section matches the inner diameter of the outer cladding glass sleeve 4. When the inner cladding glass melt 12 is squeezed in, the outer cladding glass sleeve 4 is coaxially and sealed at the bottom to the top opening of the straight section, so that the inner cladding glass melt 12 can be squeezed into the outer cladding glass sleeve 4 quickly and smoothly.

[0043] In a specific embodiment, the drum mold 5 is connected to a support platform 6 that moves synchronously with it, and a vertically extending limit tube is connected below the support platform 6, the top end of the limit tube is fixedly sleeved at the bottom position of the drum mold 5, and the bottom end of the limit tube is slidably sleeved along its axial direction at the top position of the pressure head 8. The pressure head 8 and the drum mold 5 are connected by the limit tube to ensure that the pressure head 8 and the drum mold 5 are in a coaxial state during the operation of extrusion and suction injection. Preferably, the support platform 6 is connected to a stepping system, and the stepping system is provided with a motor, which drives the support platform 6 to move up and down in the vertical direction through the motor, thereby driving the drum mold 5 to move.

[0044] In a specific embodiment, the part of the limiting tube that cooperates with the pressure head 8 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; the limiting tube is also provided with 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, the top ends of the notches extend to the bottom position of the supporting platform 6, and the bottom ends thereof pass through the bottom edge of the limiting tube; two connecting holes are provided on the outer peripheral wall of the part of the pressure head 8 extending into the limiting tube, the two connecting holes are distributed along the circumference of the pressure head 8 corresponding to the two strip-shaped through holes; a sliding rod 7 passing through the strip-shaped through hole is detachably inserted into the connecting hole, and the sliding rod 7 slides with the strip-shaped through hole along the extension direction thereof. During the process of extruding the inner cladding glass melt 12, when the inner cladding glass melt 12 is squeezed into the second feeding channel, the ram 8 abuts against the bottom end of the barrel mold 5 through the limiting tube, and during the entire extrusion process, the top end of the ram 8 and the bottom end of the outer cladding glass sleeve 4 always maintain a tight fit to prevent overflow and reduce the difficulty of subsequent separation of the ram 8 and the barrel mold 5. Furthermore, by setting the 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 be convenient to separate the pressure head 8 and the barrel mold 5 when the suction injection is completed: the top of the pressure head 8 and the bottom of the outer cladding glass sleeve 4 are sealed and matched, and there is no overflow. Then, after the suction injection is completed (or the cooling mechanism is turned off), the pressure head 8 and the outer cladding glass sleeve 4 are connected only by the inner cladding glass sleeve solidified at the periphery. Due to the setting of the notch, it is easy to bend and deform when knocked, thereby cutting off the inner cladding glass and separating them; on the other hand, after separation, if the preset size of the core is large, the unsolidified core glass melt 13 will spontaneously flow downward in the inner cladding glass sleeve that passes 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 is quickly solidified to achieve rapid sealing, and then it can be vertically moved to the annealing furnace for annealing. During the actual operation, the pressing head 8 and the cylinder mold 5 can be separated by knocking along the direction of the line connecting the two notches (perpendicular to the direction of the line connecting the slide rod 7) and knocking on the bottom mold 9 or the pressing head 8.

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

[0046] In a specific embodiment, the support platform 6 is connected with a connecting pipe coaxially connected to the top of the limiting pipe, the connecting pipe and the limiting pipe are respectively located at the top and bottom of the support platform 6, the connecting pipe surrounds the outer peripheral side of the cylinder mold 5, and is connected to the outer wall of the cylinder mold 5 by a plurality of connecting parts, each of which is evenly spaced along the circumference of the connecting pipe. The preferred connecting part is a bolt, and a plurality of screw holes are opened through the connecting pipe, each of which is evenly spaced along the circumference of the connecting pipe. The bolts are detachably inserted in the screw holes, and are used to abut against the outer peripheral wall of the cylinder mold 5 to complete the connection between the connecting pipe and the cylinder mold 5.

[0047] In a specific embodiment, it also includes a preheating assembly, which is provided with a first heating mechanism for preheating the barrel 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 the upper heating sleeve 1 is larger than the outer diameter of the barrel mold 5, and surrounds the outer peripheral side of the barrel 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. In the preparation process, the barrel mold 5 and the outer cladding glass sleeve 4 are first preheated by the upper heating sleeve 1, and the inner cladding glass melt 12 is filled into the outer cladding glass sleeve 4, and then the upper heating sleeve 1 is closed and removed, and after cooling for a period of time, the core glass melt 13 is poured into the first feeding 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 surrounds the outer peripheral side of the bottom mold 9. When preheating the mold, the preheating temperature of the lower heating sleeve 14 is set to be near the softening temperature of the inner cladding glass, and the preferred cooling mechanism includes a cooling plate 10 attached to the bottom end surface of the bottom mold 9, and the heating plate 11 is installed at the bottom end of the cooling plate 10. The preheating temperature of the heating plate 11 is set to be near the glass transition temperature of the inner cladding glass. Moreover, since the cooling plate 10 is arranged at the upper end of the heating plate 11, the bottom mold 9 is arranged at the upper end of the cooling plate 10, and the size of the cooling plate 10 is larger than the bottom mold 9. The bottom end of the bottom mold 9 is always in a tightly fitting state with the cooling plate 10. After the cooling plate 10 is turned on, the heat exchange process can be accelerated, and the cooling and shrinkage of the inner cladding glass in the bottom mold 9 can be accelerated, so that the core glass melt 13 can be quickly absorbed 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 cladding glass sleeve 4 of a preset size, fix the outer cladding glass sleeve 4 in the barrel mold 5, make the bottom end of the outer cladding glass sleeve 4 flush with the bottom end of the barrel mold 5, install the top mold 3 into the barrel mold 5, and dock it on the top of the outer cladding glass sleeve 4, install the barrel mold 5 on the support platform 6, specifically install it in the connecting pipe connected to the support platform 6, and the barrel 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 through the sliding rod 7. The bottom position of the tube is located below the barrel mold 5, and the bottom mold 9 is connected to the bottom of the pressure head 8, and the second heating mechanism and the cooling mechanism are arranged 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 arranged on the 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 drum mold 5, and start the first heating mechanism and the second heating mechanism for preheating according to the preset temperature; preferably, the first heating mechanism is the upper heating sleeve 1, and after the support platform 6 is moved downward so that the pressure head 8 enters the liquid storage tank, the upper heating sleeve 1 is set on the periphery of the drum mold 5, wherein the preheating temperature of the upper heating sleeve 1 and the heating plate 11 is set to be near the glass transition temperature of the inner cladding glass, and the preheating temperature of the lower heating sleeve 14 is set to be near the softening temperature of the inner cladding glass. After starting 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: close the first heating mechanism and the second heating mechanism to stop heating, move the support platform 6 upward to leave enough space between the pressure head 8 and the bottom mold 9, take out the melted inner cladding glass melt 12, and pour it into the liquid storage tank of the bottom mold 9; preferably, the first heating mechanism and the second heating mechanism are both equipped with a heating system to control the opening and closing thereof, and when it is necessary to stop preheating, turn off the heating system, and specifically during operation, remove the upper heating sleeve 1, then move the support platform 6 upward to leave enough space between the pressure head 8 and the bottom mold 9, and remove the lower heating sleeve 14, and then take out the melted inner cladding glass melt 12, and pour it into the liquid storage tank of the bottom mold 9;

[0053] Extrusion: Install the limit assembly on the barrel mold 5 so that the bottom end of the top mold 3 is closely fitted 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, and after the top end of the pressure head 8 is closely fitted with the bottom end of the outer cladding glass sleeve 4, the inner cladding glass melt 12 is uniformly squeezed 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, and the support platform 6 stops moving; the inner cladding glass melt 12 is reversely squeezed into the outer cladding glass sleeve 4 instead of the traditional tube-rod method, which can increase the bonding strength between the inner and outer cladding glasses, eliminate the adverse effects caused by the gap between the two, and thus reduce interface defects;

[0054] Pouring the core glass melt 13: After extrusion is completed, the core glass melt 13 is cooled for a desired time, preferably for 60-600 seconds, and then the core glass melt 13 is poured into the first feed channel of the top mold 3. At the moment after the core glass melt 13 is poured, 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 where the outer cladding glass is solidified but the inner cladding glass is flowable, and the diameter of the core depends on the cooling time;

[0055] Injection: Turn on the cooling mechanism to accelerate the cooling and shrinkage of the inner cladding glass in the liquid storage tank, and quickly inject the core glass melt 13 in the top mold 3 into the inner cladding glass, thereby accelerating the injection process of the core glass melt 13 into the inner cladding glass solidified at the periphery, avoiding the V-shaped structure of wide top and narrow bottom that occurs in the traditional injection method, and improving the uniformity of the core diameter; when the liquid level in the first feed channel drops to the specified position, turn off the cooling mechanism, then move the support platform 6 upward and separate the pressure head 8 from the bottom of the barrel mold 5, that is, cut off the inner cladding glass solidified at the periphery at the connection between the pressure head 8 and the outer cladding glass sleeve 4, and use the sealing mechanism to seal the bottom end of the inner cladding glass in the barrel mold 5 for the required time, preferably the sealing mechanism uses a metal knife, and the metal knife is used to abut the bottom end of the outer cladding glass sleeve 4 and wait for 10-60s to make the core glass melt 13 at the bottom solidify quickly;

[0056] Annealing: remove the blocking mechanism, remove the drum mold 5 from the supporting platform 6, keep the drum mold 5 in a vertical state and perform annealing treatment, preferably in an electric furnace;

[0057] Take out the finished product: disassemble the barrel mold 5 and separate the top mold 3 to obtain a double-clad optical fiber preform.

[0058] It should be pointed out that the existing preparation process of double-clad optical fiber preform usually includes three processes: preparation of outer cladding glass sleeve 4, preparation of core / inner cladding rod and heating and drawing. The reverse extrusion and suction injection combined method proposed in the present invention can greatly simplify the preparation process of double-clad optical fiber preform, avoiding the additional heating and drawing process required due to the inner diameter limitation of outer cladding glass sleeve 4, thereby effectively inhibiting the crystallization of glass; in addition, by adjusting the inner diameter of outer cladding glass sleeve 4 and the static cooling time after extrusion, the degree of freedom of setting the inner cladding and core diameter can be increased, thereby increasing the adjustable range of the core / cladding ratio. And the present invention has good applicability to non-sulfur mid-infrared glasses, such as fluoride glass, tellurite glass, fluorotellurite glass, etc.

[0059] In summary, the existing preparation process of double-clad optical fiber preform at least includes three independent processes: preparation of outer cladding glass sleeve 4, preparation of core / inner cladding rod, and inserting the core / inner cladding rod into the outer cladding glass sleeve 4 (due to size limitation, additional heating and drawing is often required). The whole preparation process is relatively cumbersome, and the interface defects of the inner / outer cladding and the heating and drawing process will have an adverse effect on the double-clad optical fiber preform. The present invention provides a preparation device for double-clad optical fiber preform, including a bottom mold assembly and a vertically extending drum mold 5 with openings at both ends. The drum mold 5 is detachably installed with an outer cladding glass sleeve 4 matching its internal structure. The outer cladding glass sleeve 4 is open at both ends, and the inner cladding glass melt 12 can be squeezed into the drum mold 5. The drum mold 5 is also provided with a top mold 3 docked at the top end of the outer cladding glass sleeve 4. The top mold 3 is provided with a first feeding channel for the core glass melt 13 to flow and be sucked into the inner cladding glass. The bottom mold assembly is used to block the outer cladding glass sleeve 4. The bottom end of the cladding glass sleeve 4; the present invention simultaneously arranges a top mold 3 and a bottom mold assembly at the upper and lower ends of the outer cladding glass sleeve 4, and adopts a reverse extrusion and suction injection combination method to prepare a double-clad optical fiber preform rod. On the one hand, it can not only greatly simplify the preparation process of the double-clad optical fiber preform rod, but also avoid the additional heating and thinning process required due to the inner diameter limitation of the outer cladding glass sleeve 4, and can effectively inhibit the crystallization phenomenon of the glass; on the other hand, the inner cladding glass melt 12 is reversely squeezed into the outer cladding glass sleeve 4 to replace the traditional tube-rod method of plugging, which can increase the bonding strength between the inner / outer cladding glass, eliminate the adverse effects of the traditional plug-in method, and reduce 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, and then accelerate the suction injection process of the core glass melt 13 into the peripheral solidified inner cladding glass, avoiding the upper wide and lower narrow V-shaped structure, and improving the uniformity of the core diameter.

[0060] Adaptive changes made according to actual needs are all within the protection scope of the present invention.

[0061] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any reference numerals in the claims should not be regarded as limiting the claims involved.

[0062] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A device for preparing a double-clad optical fiber preform, characterized in that: It includes a bottom mold assembly and a vertically extending cylinder mold with openings at both ends; An outer cladding glass sleeve matching its internal structure is detachably installed in the drum mold, the two ends of the outer cladding glass sleeve are open, and the interior of the outer cladding glass sleeve is used to squeeze in and fill with the inner cladding glass melt, and the drum mold is also provided with a top mold docked at the top end of the outer cladding glass sleeve, and the top mold is provided with a first feed channel for the core glass melt to flow and be sucked and injected into the inner cladding glass, and the bottom end of the first feed channel has a discharge port coaxially connected to the outer cladding glass sleeve; 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.

2. The device for preparing a double-clad optical fiber preform according to claim 1, characterized in that: The first feed channel penetrates the top mold in a vertical direction, the radial cross section of the first feed 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 device for preparing a double-clad optical fiber preform according to claim 2, characterized in that: The top mold is slidably installed in the drum mold, and a limiting component for abutting against the top end surface of the top mold is detachably inserted on the outer peripheral wall of the drum mold.

4. The device for preparing a double-clad optical fiber preform according to claim 2 or 3, characterized in that: The bottom mold assembly includes a bottom mold and a pressing head; A liquid storage tank for accommodating the inner cladding glass melt is provided at the top of the bottom mold, the pressure head is slidably connected to the inside of the liquid storage tank along the vertical direction, and the outer peripheral wall of the pressure head and the inner peripheral wall of the liquid storage tank are slidingly and sealingly matched along the axial direction thereof, the top of the pressure head is used to dock with the bottom end of the outer cladding glass sleeve, and the pressure head is penetrated along the vertical direction to open a second feeding channel connected to the outer cladding glass sleeve.

5. The device for preparing a double-clad optical fiber preform according to claim 4, characterized in that: 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 docked with and connected to the outer cladding glass sleeve, and the diameter of the straight section matches the inner diameter of the outer cladding glass sleeve.

6. The device for preparing a double-clad optical fiber preform according to claim 5, characterized in that: The cylinder mold is connected to a supporting platform that moves synchronously with it, and a vertically extending limiting tube is connected below the supporting platform. The top end of the limiting tube is fixedly sleeved at the bottom position of the cylinder mold, and the bottom end of the limiting tube is slidably sleeved along its axial direction at the top position of the pressure head.

7. The device for preparing a double-clad optical fiber preform according to claim 6, characterized in that: The portion of the limiting tube that cooperates with the pressure head is provided with two strip-shaped through holes, the two strip-shaped through holes extend along the axis direction of the limiting tube and are symmetrically distributed along the diameter direction of the limiting tube; the limiting tube is also provided with 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 axis direction of the limiting tube, the top end of the notch extends to the bottom position of the support platform, and the bottom end thereof passes through the bottom edge of the limiting tube; Two connecting holes are provided on the outer peripheral wall of the part where the pressure head extends into the limiting tube, and the two connecting holes are distributed along the circumference of the pressure head corresponding to the two strip-shaped through holes; a sliding rod passing through the strip-shaped through hole is detachably inserted into the connecting hole, and the sliding rod slides with the strip-shaped through hole along the extension direction thereof.

8. The device for preparing a double-clad optical fiber preform according to claim 7, characterized in that: The support platform is connected with a connecting tube coaxially connected to the top end of the limiting tube, the connecting tube surrounds the outer peripheral side of the cylinder mold, and is connected to the outer wall of the cylinder mold by a plurality of connecting parts, each of which is evenly spaced along the circumference of the connecting tube.

9. The device for preparing a double-clad optical fiber preform according to claim 8, characterized in that: It also includes a preheating component, which is provided with a first heating mechanism for preheating the drum mold and a second heating mechanism for preheating the heat storage tank and the pressure head.

10. A method for preparing a double-clad optical fiber preform using the apparatus for preparing a double-clad optical fiber preform according to any one of claims 1 to 9, characterized in that: The steps include: Preparation: prepare a hollow outer cladding glass sleeve of a preset size, fix the outer cladding glass sleeve in the drum mold, install the top mold in the drum mold and dock it on the top of the outer cladding glass sleeve, install the drum mold on the support platform, and slide the pressure head to the bottom position of the limit tube through a sliding rod, then connect the bottom mold to the bottom of the pressure head, and set the second heating mechanism and the cooling mechanism at the bottom mold; Preheating: Move the support platform downward and slide the pressure head into the liquid storage tank of the bottom mold, then set the first heating mechanism at the barrel mold, and start the first heating mechanism and the second heating mechanism according to the preset temperature for preheating; Melting: melting inner cladding glass and core glass; Pouring the inner cladding glass melt: turn off the first heating mechanism and the second heating mechanism, move the supporting platform upwards to leave sufficient space between the pressure head and the bottom mold, take out the melted inner cladding glass melt, and pour it into the liquid storage tank of the bottom mold; Extrusion: Install the limit assembly on the barrel 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 squeeze the inner cladding glass melt into the outer cladding glass sleeve at a uniform speed through the second feed channel until the inner cladding glass melt reaches the bottom of the first feed channel, and the support platform stops moving; Pouring the core glass melt: After extrusion is completed, the core glass melt is allowed to cool for a required time, and then poured into the first feed channel of the top mold; Suction injection: Turn on the cooling mechanism to accelerate the cooling and shrinkage of the inner cladding glass in the liquid storage tank, and quickly suck the core glass melt in the top mold into the inner cladding glass. When the liquid level in the first feeding channel drops to the specified position, turn off the cooling mechanism, then move the support platform upward and separate the pressure head from the bottom of the barrel mold, and use the sealing mechanism to seal the bottom end of the inner cladding glass in the barrel mold for the required time; Annealing: remove the blocking mechanism, remove the barrel mold from the supporting platform, keep the barrel mold in a vertical state and perform annealing treatment; Take out the finished product: disassemble the barrel mold and separate the top mold to obtain the double-clad optical fiber preform.

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