Absrtact: Based on the latest literature and technical information, the status and development trend of the fabrication technology of optical fiber preform are summarized.
Keywords: optical fiber prefabricated rods;
At present, has formed the fiber optic cable global development Good climate, U.S. KMI company predicts that the next 10 years, the global fiber and cable demand will continue to grow, in order to adapt to the global demand for fiber and cable growth, the international major fiber manufacturers are carrying out a new round of expansion, at the same time, the domestic fiber industry development momentum is very strong, Some optical fiber production enterprises are expanding, but also a few large-scale fiber-optic plants will be built. Here, the choice of the technical route is very important. Based on the latest literature and international technology exchange information, this paper reviews the current status and development trend of optical fiber preform manufacturing technology. The focus is on the "two-step" process, including various core-rod manufacturing Technologies (OVD, VAD, MCVD, PCVD) and outsourced manufacturing technology (casing, plasma spraying, flame hydrolysis, Melt glue--gel method), hope to the domestic fiber industry development benefit.
The "two-step" optical fiber industry, which manufactures prefabricated rods, arose in the 70 's.
Over the past more than 20 years, the fiber-optic manufacturing process has been evolving. Because the fabrication technology of optical fiber preform is the core of optical fiber manufacturing technology, optical fiber manufacturing technology has always been used in fiber-optic preform fabrication. According to the traditional naming method, the current fiber technology market four kinds of technology coexist, namely OVD, VAD, MCVD, PCVD. However, simply using the above-mentioned process name indicates that the current production process is very incomplete. At present, the vapor-phase deposition technology of the commercial production of optical fiber preform has been developed into two-step method (two-step processes). In the current commercial production of fiber preform technology, OVD, MCVD and other process names only represent the production of the 1th step of the preform, that is, the production of Mandrel (Core-rod/primary preform/initial preform) used in the production of core rods, Not only must manufacture the core also must manufacture the partial cladding, this is in order to ensure the optical quality of the optical fiber, then can pull the mandrel into many small core rods, also can not pull thin, depending on the size of the core bar. The second step is to attach the outsourced layer (commonly known as outsourced technology or overcladding) to the mandrel to make the precast rods, which can be pulled fine or thin before drawing, depending on the size of the precast rod and The wire drawing furnace.
Therefore, the so-called "two-step" is not limited to two steps, the optical properties of optical fiber preform mainly depends on the core manufacturing technology; the cost of fiber preform is mainly dependent on outsourcing technology, so the core manufacturing technology plus outsourcing technology can fully explain the characteristics of the current fiber preform manufacturing process.
"Soot" method, commonly used in foreign literatures "soot process" to refer to Ovd, VAD and other flame hydrolysis of the outer deposition technology. In this paper, we call it: soot outsourcing technology, rather than OVD terminology, to show the difference with OVD core technology, the technology in the United States and Japan companies have been widely used.
Plasma spraying (Plasma Spray), refers to the use of high-frequency plasma flame will be fused quartz powder made of large precast rods on the technology, by Alcatel invented, used.
Sol-Gel Method (Sol-gel) is used as outsourcing technology, which was invented by Lucent, including two channels. Firstly, the synthesis of quartz tube as casing by sol-gel method, then, the casing system is used as a large precast rod; Secondly, the synthesis of quartz powder by sol-Gel method, and then the synthesis of quartz powder by high frequency plasma flame is made into the technology of large precast rods on the mandrel, so it belongs to the soot or plasma spraying method in essence.
Second, the development trend of mandrel manufacturing process
2.1 Development of various chemical vapor deposition processes from 1980 to 2000
MCVD is the earliest mature process, the early multimode optical fiber is mainly produced by the process, into the 80 's, with the conventional single-mode fiber (SMF) mature, OVD, VAD in the fiber market share of the rapid increase in the United States Corning and Japan companies have ceased to use the MCVD process, MCVD's market share has dropped rapidly, and the share of OVD and VAD technology has increased rapidly. However, the MCVD process continues to improve and incorporates a number of new technologies, thus still accounting for about 1/3 per cent of the market share.
The development of 2.2 MCVD
The initial MCVD is a typical "one-step" method, in which the cladding, core deposition, and shrinkage of the prefabricated rods are successively carried out on a lathe. At present, Alcatel has separated the deposition and melt shrinkage, after the deposition, using another special lathe to melt into a rod, and graphite induction furnace instead of hydrogen and oxygen flame as a heat source for melting and shrinking into rods.
A small diameter quartz tube made of large diameter synthetic quartz tube instead of natural crystal powder is used as liner bottom tube, and the diameter of synthetic quartz liner used in production is about 40mm, and the deposition length is 1.2~1.5m.
Most importantly, a variety of external deposition techniques have been used to replace the casing method for making large sticks, such as the use of flame hydrolysis outsourcing and plasma outsourcing technology to create an outsourced layer on the mandrel, forming a hybrid process combining MCVD with the external deposition process. This new technology makes up for the disadvantage of low deposition rate and poor geometrical precision of traditional MCVD process, which reduces cost, improves quality and enhances competitiveness.
Development of Low-cost, high-quality, large-scale casing manufacturing methods (such as Sol-gel method, Ovd method), for casing use.
Development of 2.3 VAD process
The VAD technology of the 70 's, the core and cladding simultaneously deposited, simultaneously sintered, called the prefabricated continuous manufacturing process.
The 80 's VAD process is to make the big diameter mandrel first, then the large diameter mandrel is drawn into many small core rods, and then the casing method is used as the precast rods, from "one step" to "two Step".
The 90 's was replaced by soot outsourcing as a fiber-optic preform rod.
Since the 90 's, the use of VAD manufacturers increased, in addition to the Japanese ancient river, Tenzang, the letter, Hitachi, Mitsubishi, Showa and other companies from NTT in Japan obtained the use of VAD process production of optical fiber licensing, and implemented a redevelopment, the commercialization of VAD technology, Lucent has also acquired a license to use the VAD process from Sumitomo Corporation, and has also established a VAD joint venture with Sumitomo in the United States, which has the opportunity to observe VAD fiber production for many years, after which Lucent introduced the VAD process to its Atlanta fiber factory. The Spectran company also acquired the VAD process while buying Ensign-bickford's assets. By the way, Spectran company was purchased by Lucent in the late 1999.
Development of 2.4 Ovd process
Deposition rate is increased exponentially from single blowtorch deposition to multiple jets.
From one device to another, a rod is deposited at the same time to deposit many sticks.
The "one step" of the precast rods made from successive sedimentary cores and cladding is developed to "two steps", that is, using a ceramic stick or graphite rod as the target only the deposition core material (with a small amount of cladding) makes the large diameter mandrel, after the water is sintered, the large diameter mandrel is drawn into a small diameter core rod, and then the small diameter core rods are used as the target rods to deposit the cladding. Fabrication of fiber-optic preform rods has greatly improved productivity and reduced costs.
Development of 2.5 PCVD process
As with MCVD, the current PCVD process also uses a large-diameter synthetic quartz tube instead of a natural crystal fused quartz tube as a substrate tube.
Dutch POF Company has developed a four-generation PVCD process, the diameter of the substrate tube from the initial 16mm to 60mm years, the deposition rate increased to 2~3g/min, deposition length 1.2~1.5m.
At present, the casing system is still made of large precast rods, but a casing weighs several kilograms.
In principle, as with MCVD, it can also form a hybrid process which combines PCVD with the outer deposition process, but has not been reported so far.
2.6 Comparison of various core rod processes
The productivity of the same fiber-optic product is significantly different in the various mandrel processes; the production of specific varieties of fiber will require the use of the most suitable mandrel process, given that in the near future the most internationally used fiber is still SMF. Therefore, the number of equipment required for the production of 1 million km of optical fiber is MCVD to be $number (set), and VAD is required for $number (set); Obviously, MCVD requires more investment in machinery and equipment. However, the unit price of various equipment is different, to MCVD equipment unit price is lowest. Therefore, the total investment of equipment will not be as different as the number of equipment.
It is predicted that in the next 10, the market share of multimode fiber (MMF) and non-0 dispersion fiber (NZDSF) will continue to increase, and the market share of SMF will decrease because the transmission characteristics of MMF and NZDSF are sensitive to the defects of radial refractive index distribution (RIP). In the core bar manufacturing process to precisely control rip, in this regard, MCVD, especially PVCD and Ovd, Vad compared with obvious advantages. The expansion of the market for NZDSF and MMF means more application of MCVD and PCVD processes. American Corning and several Japanese companies using the VAD process, such as Sumitomo, Fujikura, Gu River, and the Ovd, had abandoned MCVD in the 80 's, and it was reported that, at present, it might be considered to reactivate MCVD or introduce PCVD in its factories.
III. Development trend of outsourcing technology
3.1 Development of various outsourcing technologies from 1980 to 2000
In the early 80, the world began to use the casing system for large precast rods, and for MCVD and PCVD rods, this is the most common method of outsourcing. At the same time, the VAD process also adopted the casing method, began the commercialization of the SMF production, which marks the transition of the preform manufacturing process to the "two-step", and later, Corning Company will soot outsourcing technology for industrial production, and then, with VAD production of optical fiber manufacturers also use soot outsourcing technology instead of casing law, In the entire 80 's, the share of casing law has declined yearly. In the 90 's, Alcatel used plasma spraying technology to replace the casing method; Lucent developed SOL-Gel outsourcing technology, and almost all the manufacturers using VAD and OVD to make fiber-core rods used soot outsourcing technology. These have kept the share of casing law down.
The root cause of the drop in casing law is the high price of synthetic quartz tubes. First of all, the cost analysis shows that if the casing method is to compete with other outsourced technologies, the price of the pipe must be reduced to 100$/kg. At present, the price of the pipe is unlikely to be reduced to this level. As a result, fewer manufacturers will make prefabricated rods with casing. Second, to use the casing method to enlarge the precast rods, which require large-scale thick-walled casing, and the manufacture of this specification of the casing is very difficult, so the price is very high.
As the price of optical fiber continues to decline, the cost of fiber manufacturing will determine the success or failure of competition. The manufacture of large precast rods can reduce the cost of fiber manufacturing (preform cost, wire drawing cost, and test cost will be reduced by the increase of precast rods). Therefore, for the survival of optical fiber manufacturers, the increase in the size of prefabricated rods is increasingly critical, because the casing method is difficult to large precast rods, so after Alcatel, other Single-mode fiber manufacturers will also abandon the casing method, and select the high-speed production of large precast rods of the more economical outsourcing technology. Most of them will be selected soot outsourcing, because of their equipment and technology already have merchandise.
3.2 Analysis of various outsourcing technologies
After 1985, the casing method has been declining, and the Sol-gel method has not yet formed the climate. Therefore, the main analysis of the plasma method and soot method.
Raw materials: Natural quartz powder, from high-quality Crystal Minerals, limited resources (China's current production of optical fiber and quartz tubes used in natural quartz powder still need to import); Natural quartz powder has limited purity. The silicon tetrachloride is a byproduct of the semiconductor industry and is rich in source, and the synthetic quartz material is produced by the soot process, and the purity is high, which is beneficial to the strength and life parameters of the fiber. In this respect, the soot process is superior to the plasma process.
Process: the production of chlorinated hydrogen and other waste gases (to be treated in the process of soot), and, in order to increase the deposition rate, have to sacrifice deposition efficiency (well below 50%), the need for the sintering of chlorine gas (toxic) and ammonia (expensive), which are not conducive to lower costs. The plasma process does not have the above problem, after deposition is transparent precast rods, in this respect, plasma technology is better than the soot process.
Heat Source: Plasma technology is more complex, and hydrogen-oxygen flame technology is simple, in the case of natural gas, the cost is very low. In this respect, the soot process is superior to the plasma process.
After 1985, the casing law accounted for a continuous decrease in the share of the world market, and the soot process increased year by day.
At present, a variety of processes accounted for the world market share: Casing method 28%,soot62%, Plasma 8%, Sol-Gel method 2%. The main limiting factor of casing method is the high price of synthetic quartz tube. In fact, several companies currently using casing have said they would make larger precast rods if they could get large size casing. As long as the price of synthetic quartz tube falls low enough, this method is the simplest and most practical. The main limiting factor of Alcatel plasma spraying technology is natural quartz powder with limited natural resources.
Sol-Gel method is developing, the combination of silica powder and plasma spraying by sol-gel method may be a good technique, which depends on the development of input.
The soot process has taken the absolute advantage. Because of its equipment and technology has been a commodity, its application will be increasingly extensive. For the factory has Ovd or VAD, the adoption of soot outsourcing process is very convenient, for only MCVD or PCVD manufacturers are required to invest heavily in equipment and technology.
IV. Comparison of optical fiber cost
4.1 Precast rod technology and optical fiber cost
It is believed that the cost of Ovd mandrel and soot outsourced preform technology is lowest. It is estimated that the cost of production is about 15$/km.
The production cost of VAD mandrel plus soot outsourcing is 25% higher than that of Ovd mandrel plus soot. The production cost of MCVD and casing method is 40% higher than that of Ovd mandrel plus soot.
4.2 Production scale and optical fiber cost
The effect of different capacity or scale on production cost is assumed by using the same level of technology, with VAD core rods and soot outsourcing production SMF. Large-scale production has a considerable cost advantage. As fiber prices fall and productivity increases,