High fiber density loose fiber all-dry optical unit, its preparation method, product and optical cable

Abstract

The present invention discloses a high-fiber-density loose fiber all-dry optical unit, its preparation method, product and optical cable. The method comprises the following steps: 1) Paying off: Each optical fiber is paid off through an optical fiber pay-off frame, enters the inner cavity of a powder spraying die together and then enters an extruder after coming out of the inner cavity of the powder spraying die; 2) Extruding a sleeve: Air first enters an air dryer, and the dried air enters a constant pressure controller after being treated by a plasma generator. The air flow flowing out of the constant pressure controller blows water blocking powder and lubricating powder into the inner cavity of the powder spraying die from a first injection hole and a second injection hole of the powder spraying die respectively, and a layer of lubricating powder is distributed around the periphery of the water blocking powder in the inner cavity of the powder spraying die; 3) Cooling: After the sleeve is cooled and formed, it wraps the lubricating powder and the optical fiber, thus obtaining the optical unit. In the present invention, there is lubricating powder playing a lubricating role between the inner wall of the sleeve and the optical fiber, the surplus length consistency is good, the inner and outer diameters of the sleeve can be made smaller, the optical fiber density is larger, and the material is more saved.

Description

Technical Field

[0001] The present invention belongs to the field of optical unit preparation processes, and more specifically, relates to a high fiber density loose fiber all-dry optical unit, a preparation method thereof, a product, and an optical cable. Background Art

[0002] With the full promotion of 5G network construction and green manufacturing, a large number of optical network constructions have put forward higher requirements for low-carbon environmental protection and resource conservation. Facing the industry problems of increasingly tense pipeline network resources and large consumption of traditional optical cable resources,

[0003] The all-dry optical cable eliminates the use of ointment in traditional optical cables. It uses dry water-blocking materials to absorb water and expand in the fiber sleeve to block water. At the same time, during construction, there is no need to clean the ointment, which is green and environmentally friendly, saves the optical cable connection time, and reduces the dependence on petroleum derivatives.

[0004] During the production process of the sleeve, the water-blocking yarn or water-blocking powder is used to replace the fiber paste, and the water-blocking substance swells when encountering water to achieve the purpose of water blocking. During the reproduction process of the sleeve, when the polymer plastic material is extruded and processed into a mold, there will be processes such as cooling, crystallization, and shrinkage setting. Depending on the material, the shrinkage degree of the sleeve after setting is different, some are large and some are small. This shrinkage is the main factor for forming the fiber slack length. By adjusting auxiliary technologies such as the fiber payout tension, processing speed, extrusion temperature, take-up tension, and differential traction of the optical fiber, the fiber slack length can be within a certain appropriate range to ensure that the attenuation in the optical fiber is qualified. Moreover, optical fibers are afraid of bending. Under the condition of a large slack length, the optical fiber attenuation will be relatively large.

[0005] In a common sleeve filled with fiber paste, due to the excellent thixotropic strain and lubrication effect of the fiber paste, when the optical fiber generates a slack length due to the shrinkage of the sleeve, under the action of the rear traction of the fiber payout tension that the optical fiber can withstand, a smaller slack length range and consistent slack length performance can be well controlled.

[0006] During the production process of the sleeve, since the materials currently used in the industry for sleeve processing are all PBT or PP, the friction coefficients of the inner walls of the sleeves are relatively large, and there is a very large frictional force between the optical fiber and the inner wall of the sleeve. When the sleeve cools and forms, crystallizes and shrinks, the optical fiber in the sleeve and the inner wall cannot form a good sliding, which will cause an excessive slack length. In this case, the optical fiber is bent and stressed, and the transmission loss increases. Coupled with the existence of the post-shrinkage effect of the material, when the diameter of the sleeve is further reduced, the optical fiber attenuation will be so large that it cannot be used.

[0007] Secondly, when there are multiple optical fibers in the sleeve, some optical fibers always come into contact with the sleeve, while some do not touch the inner wall of the sleeve. This is the main reason for the inconsistent slack lengths (excessive fiber differences). Especially for sleeves with water-blocking yarn, due to the different rigidities of the optical fibers and the water-blocking yarn and the inconsistent surface friction coefficients, crosstalk will occur during the shrinkage of the sleeve, making the inconsistent slack lengths of each optical fiber even worse.

[0008] The friction between multiple optical fibers, without the fiber grease in the conventional sleeve as a lubricant, and the frictional force generated by the electrostatic adsorption on the surface of the optical fibers are also one of the reasons for the inconsistent fiber differences.

[0009] Therefore, currently, the inner space of the sleeve is enlarged as much as possible to alleviate the problem of increased attenuation caused by excessive slack lengths. This makes it difficult to make the inner space of the sleeve very small and difficult to significantly increase the fiber density.

[0010] In summary, the current problems of all-dry optical cables are as follows: 1) The reduction range of the inner and outer diameters of the sleeve is limited. It cannot maintain a low transmission loss of the optical fiber like a sleeve with fiber grease when the inner and outer diameters are small. For the existing all-dry loose tube of 12-core 250um optical fibers, the outer diameter is 2.35mm ± 0.1mm, and the inner diameter is 1.8mm ± 0.05mm. If the size of the loose tube is further reduced, the attenuation of the optical fiber will increase sharply. 2) The consistency of the slack lengths of the optical fibers in the loose tube is poor and uncontrollable. It is very difficult to achieve or maintain good consistency of the slack lengths by adjusting the parameters of a specific optical fiber. This poor consistency will result in different attenuations of some optical fibers and some optical fibers, and at the same time, it will also cause problems with the mechanical performance indicators. Especially for optical fibers with small slack lengths, when the optical cable is subjected to laying tension, they will be stressed first and are prone to failure.

[0011] Chinese patent document CN105589155A provides a manufacturing method of an all-dry loose tube optical unit. By adding fine steel wires in the loose tube to control the shrinkage of the sleeve, the problem of excessive slack length is solved. At the same time, talcum powder is incorporated in the loose tube to reduce the friction between optical fiber and optical fiber, between optical fiber and water-blocking yarn, between water-blocking yarn and the sleeve, thereby solving the problems of inconsistent and uncontrollable slack lengths. However, setting fine steel wires or other strengthening members in the loose tube will cause the bending performance of the loose tube to be non-uniform in all directions, making it difficult to control the stranding during the cabling of the optical unit. Excessive strengthening members may even cause the inability to strand into a cable. Summary of the Invention

[0012] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a high fiber density loose fiber all-dry optical unit, its preparation method, product and optical cable, which contains lubricating powder for lubrication between the inner wall of the sleeve and the optical fiber, has good consistency of slack lengths, can make the inner and outer diameters of the sleeve smaller, has a greater fiber density, and saves more materials.

[0013] To achieve the above object, according to one aspect of the present invention, a method for preparing a high fiber density bulk fiber all-dry optical unit is provided, characterized in that it comprises the following steps:

[0014] 1) Pay-off: Each optical fiber is paid out through the optical fiber pay-off frame, guided by the guide wheel to form a wire bundle, enters the inner cavity of the powder spraying mold, and then enters the extruder after coming out of the inner cavity of the powder spraying mold. After coming out of the extruder, it is towed by the traction assembly;

[0015] 2) Extrusion of sleeve: the blown air first enters the air dryer to keep the humidity of the blown air within the set range. The dry air is processed by the plasma generator to form a plasma airflow and then enters the constant pressure controller. The constant pressure controller is used to keep the plasma airflow at a constant pressure. The plasma airflow flowing out of the constant pressure controller blows the water-blocking powder and the lubricating powder into the inner cavity of the powder-spraying mold from the first injection hole and the second injection hole of the powder-spraying mold respectively, and a layer of lubricating powder is distributed on the periphery of the water-blocking powder in the inner cavity of the powder-spraying mold, so that the airflow carries the water-blocking powder and the lubricating powder into the sleeve extruded by the extruder head. The lubricating powder contacts the inner wall of the sleeve, thereby increasing the crystallization speed of the sleeve and providing a layer of lubricating powder between the sleeve and the optical fiber to reduce the friction between the sleeve and the optical fiber;

[0016] 3) Cooling: After the sleeve is cooled and formed, it is wrapped with the lubricating powder, water-blocking powder and optical fiber to obtain the optical unit.

[0017] Preferably, the powder spraying mold comprises a guide mold and an injection mold which are sequentially connected along the moving direction of the optical fiber, the first injection hole and the second injection hole are both arranged on the injection mold, and the injection mold is inserted into the head of the extruder.

[0018] Preferably, the injection mold includes a mold frame and an injection needle, the mold frame is mounted on the outside of the injection needle, the guide mold and the injection needle are connected in sequence along the moving direction of the optical fiber, the first injection hole passes through the mold frame and the injection needle, and the second injection hole passes through the mold frame and the injection needle.

[0019] Preferably, the optical unit has 12 optical fibers, and the outer diameter of the sleeve of the optical unit is 2 mm or less.

[0020] Preferably, the average particle size of the lubricating powder is 4 um to 6 um.

[0021] Preferably, the mass ratio of the lubricating powder to the water-blocking powder is not greater than 1:4.

[0022] Preferably, a lubricating powder with a mass between 0.25 mg and 1 mg is applied per meter of casing.

[0023] According to another aspect of the present invention, there is also provided a high fiber density loose fiber all-dry optical unit, which is prepared by the described preparation method.

[0024] Preferably, the optical unit is a 12-core optical unit, and the outer diameter of the sleeve is below 2.0 mm.

[0025] According to another aspect of the present invention, there is also provided an optical cable, which is stranded with the described high fiber density loose fiber all-dry optical unit as the cable core.

[0026] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0027] 1) Since the crystal structure of the lubricating powder (talcum powder, graphite powder) is layered, it has a tendency to split into scales easily and special lubricity. When the polymer material extruded by the extruder cools and shrinks in water and crystallizes, the sliding resistance of the optical fiber in the sleeve is small, and the relative adhesion force between the optical fibers is also relatively small. It can solve the problem of controlling the consistency of the extra length, and the extra length consistency is good and easier to control.

[0028] 2) The lubricating powder has lubricity, anti-adhesion, flow aid, high melting point, chemically inactive, good covering power. When it contacts with the molten sleeve polymer materials PBT and PP, it not only has excellent physical properties such as strong adsorption force, but also the chemical property that the lubricating powder can form microcrystal nuclei, disperses crystallization and improves the crystallinity of the material forming the sleeve, reduces the post-shrinkage of the sleeve. It can not only control the extra length within a suitable range to avoid excessive extra length, but also make the extra length stability of the sleeve stronger, the storage time of the sleeve longer, make the cycle of production regulation and arrangement wider, and is more conducive to production.

[0029] 3) The diameter of the sleeve can be made smaller, the fiber density is larger, and the material is more economical. The fiber density of a single sleeve optical unit can be increased to 32%.

[0030] 4) The production control of the optical unit and the optical cable products is easier, greatly reducing the overall manufacturing cost of the optical cable and making it more beneficial to promote the low-carbon and environmentally friendly sleeve optical cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the equipment system diagram of the preparation method of the present invention;

[0032] Figure 2 is the powder spraying flow chart of the preparation method of the present invention;

[0033] Figure 3 is the schematic diagram of the powder spraying die in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Reference Figures 1 to 3 , a method for preparing a high fiber density bulk fiber fully dry optical unit, comprising the following steps:

[0036] 1) Paying off: Each optical fiber 1.1 is paid out through the optical fiber 1.1 pay-off frame 1, guided by a guide wheel to form a wire bundle, enters the inner cavity of the powder spraying mold 2, and enters the extruder 3 after coming out of the inner cavity of the powder spraying mold 2. After coming out of the extruder 3, it is towed by a traction assembly; each optical fiber 1.1 can be guided by a guide wheel respectively, and the guide wheel can make the optical fiber 1.1 as concentrated as possible to form an optical fiber 1.1 bundle. The traction assembly preferably includes a wet traction device 4 and a take-up wheel 5, which can achieve good traction. After the subsequent optical unit is formed and comes out of the extruder 3, it is still towed by the traction device and then wound onto the take-up wheel 5.

[0037] 2) Extruded sleeve 3.4: It is preferably supplied with high-pressure air. The blown air first enters the air dryer 9 to keep the humidity of the blown air within a set range. The dried air is processed by the plasma generator to form a plasma air flow and then enters the constant pressure controller 7. The constant pressure controller 7 is used to keep the plasma air flow at a constant pressure. The plasma air flow flowing out of the constant pressure controller 7 blows the water blocking powder and the lubricating powder into the inner cavity of the powder spraying die 2 from the first injection hole 6.1 and the second injection hole 6.2 of the powder spraying die 2 respectively, that is, the plasma air flow carries the water blocking powder and the lubricating powder into the inner cavity of the powder spraying die 2 from the first injection hole 6.1 and the second injection hole 6.2, and a layer of lubricating powder is distributed around the periphery of the water blocking powder in the inner cavity of the powder spraying die 2, that is, the water blocking powder can be wrapped by a layer of lubricating powder, so as to realize that the air flow carries the optical fiber 1.1, the water blocking powder and the lubricating powder into the sleeve 3.4 extruded from the head of the extruder 3. Among them, the lubricating powder is talcum powder or graphite powder. The lubricating powder can contact the inner wall of the just extruded molten sleeve 3.4. The lubricating powder serves as a microcrystal nucleus, thereby increasing the crystallization speed of the sleeve 3.4 and having a layer of lubricating powder between the sleeve 3.4 and the optical fiber 1.1 to reduce the friction between the sleeve 3.4 and the optical fiber 1.1; The head of the extruder 3 adopts a conventional structure, having a die cover 3.2 and a die core 3.3 arranged in the die cover 3.2. There is a sleeve material injection port 3.1 on the die cover 3.2. A sleeve material extrusion channel is formed between the die cover 3.2 and the die core 3.3. The sleeve material flowing out of the sleeve material extrusion channel wraps the lubricating powder, the water blocking powder and the optical fiber 1.1. Further, the average particle size of the lubricating powder is 4um to 6um, preferably 5um, which can reduce the microbending loss of the optical fiber and is more likely to become a microcrystal nucleus to increase the crystallization speed of the sleeve 3.4. In addition, the mass ratio of the lubricating powder to the water blocking powder is not greater than 1:4, and the mass of the lubricating powder applied per meter of the sleeve is between 0.25mg and 1mg, so that the cost of the added powder is moderate, does not change the main proportion of the water blocking powder, and does not reduce the waterproof effect of the optical unit.

[0038] The material of the sleeve 3.4 contacts the lubricating powder and crystallizes with the lubricating powder as the crystal nucleus. Ideally, the lubricating powder is evenly attached to the inner wall of the sleeve 3.4, so that the material of the sleeve 3.4 crystallizes rapidly and evenly, resulting in a smaller post-shrinkage of the sleeve 3.4 and avoiding excessive residual length. At the same time, the lubricating powder reduces the friction between the optical fibers and between the optical fiber and the sleeve 3.4, thus improving the problem of inconsistent and uncontrollable residual length. Therefore, whether the attachment of the lubricating powder is uniform is crucial. Under normal circumstances, it is difficult to ensure uniformity by relying on the adsorption of the lubricating powder itself and the optical fiber to bring it into the loose sleeve 3.4, and the sleeve still shrinks unevenly. It is necessary to adopt means such as threading a steel wire to control the shrinkage of the sleeve. The present invention uses a plasma air flow to carry a mixed powder of the lubricating powder and the water blocking powder. On the one hand, the plasma air flow can carry a larger amount of powder, and on the other hand, the lubricating powder is more wrapped on the surface of the water blocking powder, so that the lubricating powder contacts the inner wall of the sleeve 3.4 more fully and evenly.

[0039] The above air dryer 9 can prevent the added water-blocking powder from getting damp during air drying. The constant pressure controller 7 can ensure that the shrinkage pressure inside the sleeves 3.4 is basically balanced with the outside world, neither allowing the water-blocking powder to flow back into the inner cavity of the powder spraying die 2 nor causing excessive diameter fluctuations of the sleeves 3.4 due to underpressure. After the constant pressure air flow blown by the constant pressure controller 7 blows the water-blocking powder into the inner cavity of the powder spraying die 2, it can not only eliminate the adhesion and accumulation of the water-blocking powder and lubricating powder on the passing path and the die tube wall, but also eliminate the attenuation change caused by the static adsorption generated by the friction between the optical fibers 1.1 in the powder spraying die 2.

[0040] 3) Cooling: After the sleeve 3.4 is cooled and formed, it wraps the lubricating powder, water-blocking powder and optical fiber 1.1, and then the optical unit is obtained. The optical unit preferably has 12 optical fibers 1.1, and the outer diameter of the sleeve 3.4 of the optical unit is below 2 mm.

[0041] Subsequently, through a series of conventional auxiliary processes such as differential traction, control of the winding and unwinding tension, and adjustment of the water temperature cooling, an optical unit with a small and reasonable and stable and controllable surplus length is formed.

[0042] Furthermore, the powder spraying die 2 includes a guiding die 2.1 and an injection die connected in sequence along the moving direction of the optical fiber 1.1. The first injection hole 6.1 and the second injection hole 6.2 are both arranged on the injection die. The first injection hole 6.1 and the second injection hole 6.2 are arranged in sequence along the advancing direction of the optical fiber 1.1. In short, the water-blocking powder should first contact and mix with the optical fiber 1.1, and then the lubricating powder should wrap the water-blocking powder and the optical fiber 1.1 on the periphery of the water-blocking powder. The injection die is inserted into the head of the extruder 3. The injection die includes a die holder 2.2 and an injection needle 2.3. The die holder 2.2 is sleeved outside the injection needle 2.3. The guiding die 2.1 and the injection needle 2.3 are connected in sequence along the moving direction of the optical fiber 1.1. The first injection hole 6.1 penetrates through the die holder 2.2 and the injection needle 2.3, and the second injection hole 6.2 penetrates through the die holder 2.2 and the injection needle 2.3.

[0043] The inner cavity of the powder spraying die 2 can adopt an inner and outer double-layer flow channel spraying design. The inner flow channel 6.1.1 is inside the outer flow channel 6.2.1. The water-blocking powder flows in the inner flow channel 6.1.1 and the lubricating powder flows in the outer flow channel 6.2.1, so that the lubricating powder can be distributed on the periphery of the water-blocking powder; or, the orifice of the first injection hole 6.1 on the inner wall of the powder spraying die 2 is closer to the center line of the inner cavity of the powder spraying die 2 than the orifice of the second injection hole 6.2 on the inner wall of the powder spraying die 2, that is, the distance from the center line is closer, so that the optical fiber 1.1 can first pass through the water-blocking powder for full and uniform mixing and then enter the head of the extruder 3 under the wrapping of the lubricating powder.

[0044] The powder spraying die 2 in front of the machine head sprays the water blocking powder and lubricating powder onto the optical fiber 1.1 in a pneumatic blowing manner and enters the machine head of the extruder 3 together with the optical fiber 1.1, improving the water blocking performance of the optical unit and reducing the friction between the sleeve 3.4 and the optical fiber 1.1. When using the water blocking powder, a little talcum powder can also be added to the air flow of the water blocking powder spraying, making the friction between the optical fibers 1.1 in the sleeve 3.4 smaller.

[0045] During the production and extrusion process of the sleeve 3.4 of the present invention, it is preferably to use a high-pressure plasma generator 8 to generate a plasma air flow, and through a constant pressure control device, introduce the plasma into the sleeve 3.4 using the powder spraying die 2, so that the inner diameter of the sleeve 3.4 remains at the desired threshold value, and large fluctuations in the inner diameter will not be caused due to reasons such as speed increase and decrease. At the same time, the plasma air flow can eliminate the electrostatic adsorption problem between multiple optical fibers 1.1, and can also blow the water blocking powder and lubricating powder into the sleeve 3.4 at the same time.

[0046] After the sleeve 3.4 is cooled and formed, the produced optical unit is then normally cabled and the outer sheath is extruded outside to form a fully dry optical cable.

[0047] Whether using the water blocking yarn or the water blocking powder water blocking technology, the conventional fiber difference is generally above 8 mm (relative to the 10 m long sleeve 3.4). After adopting the technology of adding lubricating powder in the present invention, the surplus length consistency can be controlled within 3 mm (relative to the 10 m long sleeve 3.4). The inner cavity of the sleeve 3.4 of the present invention can be made smaller, and the fiber density can be increased a lot. Especially, there is still lubricating powder intermittently mixed with the water blocking powder between the optical fibers 1.1, and the sliding between the optical fiber 1.1 and the sleeve 3.4 is more flexible, and the fiber length consistency of each fiber is better.

[0048] If the original conventional sleeve 3.4 with 12 roots of 250 um can only achieve an outer diameter of more than 2.3 mm through various auxiliary control means, the attenuation can be normally guaranteed, and the average fiber density is about 2.89 cores / mm 2 However, for the sleeve 3.4 with 12 roots of 250 um adopting this method, the outer diameter of the sleeve 3.4 can be made below 2.0 mm, and the average fiber density is about 3.82 cores / mm 2 The fiber density of the sleeve 3.4 of the optical unit can be increased by about 32%.

[0049] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Preparation method of high fiber density bulk fiber fully dry optical unit, It is characterized in that The following steps are involved: 1) Pay-off: Each optical fiber is paid out through the optical fiber pay-off frame, guided by the guide wheel to form a wire bundle, enters the inner cavity of the powder spraying mold, and then enters the extruder after coming out of the inner cavity of the powder spraying mold. After coming out of the extruder, it is towed by the traction assembly; 2) Extrusion of sleeve: the blown air first enters the air dryer to keep the humidity of the blown air within the set range. The dry air is processed by the plasma generator to form a plasma airflow and then enters the constant pressure controller. The constant pressure controller is used to keep the plasma airflow at a constant pressure. The plasma airflow flowing out of the constant pressure controller blows the water-blocking powder and the lubricating powder into the inner cavity of the powder-spraying mold from the first injection hole and the second injection hole of the powder-spraying mold respectively, and a layer of lubricating powder is distributed on the periphery of the water-blocking powder in the inner cavity of the powder-spraying mold, so that the airflow carries the water-blocking powder and the lubricating powder into the sleeve extruded by the extruder head. The lubricating powder contacts the inner wall of the sleeve, thereby increasing the crystallization speed of the sleeve and providing a layer of lubricating powder between the sleeve and the optical fiber to reduce the friction between the sleeve and the optical fiber; 3) Cooling: After the sleeve is cooled and formed, it is wrapped with the lubricating powder, water-blocking powder and optical fiber to obtain the optical unit.

2. The method for preparing the high fiber density bulk fiber all-dry optical unit according to claim 1, It is characterized in that The powder spraying mold includes a guide mold and an injection mold connected in sequence along the moving direction of the optical fiber, the first injection hole and the second injection hole are both arranged on the injection mold, the first injection hole and the second injection hole are arranged in sequence along the advancing direction of the optical fiber, and the injection mold is inserted into the head of the extruder.

3. The method for preparing the high fiber density bulk fiber all-dry optical unit according to claim 2, It is characterized in that The injection mold includes a mold frame and an injection needle, the mold frame is mounted on the outside of the injection needle, the guide mold and the injection needle are connected in sequence along the moving direction of the optical fiber, the first injection hole passes through the mold frame and the injection needle, and the second injection hole passes through the mold frame and the injection needle.

4. The method for preparing the high fiber density bulk fiber all-dry optical unit according to claim 1, It is characterized in that The optical unit has 12 optical fibers, and the outer diameter of the sleeve of the optical unit is 2 mm or less.

5. The method for preparing the high fiber density bulk fiber all-dry optical unit according to claim 1, It is characterized in that The average particle size of the lubricating powder is 4 um to 6 um.

6. The method for preparing the high fiber density bulk fiber all-dry optical unit according to claim 1, It is characterized in that The mass ratio of the lubricating powder to the water-blocking powder is not greater than 1:

4.

7. The method for preparing the high fiber density bulk fiber all-dry optical unit according to claim 1, It is characterized in that Lubricating powder with a mass between 0.25mg and 1mg is applied per meter of casing.

8. High fiber density bulk fiber full dry optical unit, It is characterized in that The invention is prepared by the preparation method described in any one of claims 1 to 4.

9. The high fiber density bulk fiber all-dry optical unit according to claim 8, It is characterized in that It is a 12-core optical unit with an outer diameter of the sleeve less than 2.0 mm.

10. An optical cable, characterized in that, it uses a high fiber density loose fiber all-dry optical unit as described in claim 8 or 9 to be stranded into a cable core.

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