Research on Technology and standard of fiber optic rapid connector (1)

In the past two years, with the development of the communication industry and the implementation of national policies, China's FTTH has developed rapidly from the pilot project to the current scale deployment.

As an important part of FTTH construction, fiber connection doubles the engineering volume. Meanwhile, the extension of FTTH construction connection point to the indoor environment also brings about a significant increase in the difficulty of work. There are two increases: one is the increase in quantity, and the other is the increase in difficulty. This makes the traditional hot-melt connection method unable to adapt to the current FTTH terminal connection work. It is necessary to choose a new method that is faster and more convenient to replace hot melt. The fast connector has such advantages. The current use of the fast connector is bringing revolutionary changes to the current optical fiber connection work.

For the current connection of FTTH construction Terminal, there are some limitations in Hot Melt connection: 1. Deployment of the melting machine requires a platform and limited space; 2. Expensive melting machine and high construction costs; 3. Active construction, limited battery endurance; 4. Large Size and inconvenient carrying of Hot-melt equipment; 5. It takes a long time to separately connect FTTH terminals.

Advantages of the quick connector: 1. simple operation, only one time for optical fiber stripping, fast construction; 2. No special requirements for the operating environment; 3. Passive Construction; 4. Simple tools, easy to carry.

Fast connectors are mainly used for the following features: Wiring cables and connecting points of home leather cables (fiber distribution boxes); and Access Points of users' homes, the main reason is that the Optical Cable End is connected to a port in the optical information panel, and the cable end is connected to the home terminal ONU in the multi-media box.

Fast connector classification and analysis

At present, there are many manufacturers of fast connector in China and abroad, and their structures and materials have also formed their own characteristics. Structural classification: mechanical connection type and hot melt type. Mechanical connection type: pass-through type and pre-buried type. Straight-through type: After the optical cable is stripped and cut, it is directly worn from the end to the top of the connector, and there is no connection point in the connector. Pre-embedded type: a fiber segment is embedded in the connector core, after the optical fiber cables are stripped and cut, they are connected to the embedded optical fiber cables in the internal vslot of the connector. The matching fluid is filled in the vslot.

Disadvantages of pass-through structure:

First, it has a strong dependence on the cutting end face. Because the straight-through structure is to direct the optical fiber from the end of the connector to the top of the connector, this means that the optical fiber cutting end face is the connector end face, if the optical fiber Cutting Face is uneven, it will inevitably affect the performance indicators of the connector, especially the return loss, which is even more insecure. The traditional pigtails and jumpers in production must ensure their echo indicators, which must be ground, the end face is divided into PC, UPC, and APC based on different plug-in Cores and grinding processes. The straight-through structure only supports manual face Cutting without grinding, not to mention PC, UPC, and APC. To ensure the quality, the operator can only rely on the cutting level. Therefore, the operator is required to have strong optical fiber construction capability and experience. Second, the requirements for matching the ceramic plug-in core and the fiber diameter are strict. Likewise, the straight-through structure is to direct the fiber from the end of the connector to the top of the connector, this requires that the inner aperture of the ceramic plug-in core should be greater than or equal to the diameter of the optical fiber, otherwise it cannot be worn in. But it cannot be too large. If it is too large, it will cause the fiber to shake in the ceramic cartridge, leading to the eccentric core. This affects the performance of the connector. Third, strict requirements on the cutting length and clamping strength; If the optical fiber remains long or short, it will lead to high attenuation when the fiber is worn or not worn. In addition, even if the length is in place, the grip strength of the rear fixed optical fiber cable is also high because of the construction and user's pull during use, and as the service life increases, deformation of materials may lead to the relative displacement of optical fiber cables and connectors. The experiment shows that the loss of the connector increases greatly when the bulge or sag exceeds nm. Of course, the straight-through structure also has its advantages, that is, its connector itself is simple in structure, the factory production is easier, so the cost is low.

Advantages of pre-Embedded Fiber structure:

1. The top of the pre-embedded optical fiber in the ceramic plug-in core is ground, and the return loss is guaranteed. 2. Fill the matching fluid in the internal docking area, but it depends on the optical fiber end face Cutting. 3. The pre-embedded optical fiber is solidified through injection, it will not be shaken or eccentric;

Of course, he also has his shortcomings, that is, it is difficult to handle the problem after the fiber is broken.

At present, most manufacturers adopt pre-Embedded Fiber structures, and only a few adopt straight-through fiber structures.

The hot-melt quick connector is compared with the hot-melt one here:

The hot melt is fused to the terminal. For example, 3 is actually to connect the optical fiber cable and pigtails separately through the melting machine. After the connection, you need to use the melting disk for fixed protection;

Hot-melt fast connectors, such as 4, are actually Optical Fiber fusion, but the fusion point is inside the end of the connector, which is equivalent to saving the tail cable of the pigtail, the advantage of doing so is that no additional protection is required after the fusion is completed.

However, in terms of its operation, the fusion splitters should be used as well as the active hot melt, which is essentially no different from the ordinary hot melt. Hot Melt has the same disadvantages, so this method is not widely used.

Material Classification: plastic and metal. Here, it mainly refers to the vtrough material. The materials of other parts are basically the same;

The vslot is actually the core component of the fast connector. Therefore, the selection of its materials is related to the entire fast connector. At present, there are two types of commercial materials on the market: metal and plastic. There is also a type of glass v tanks, but these materials are still under research and development.

In terms of performance, the average loss of metal vbrs is slightly better than that of plastics. This is mainly because the precision of the vbrs is restricted and the quality of the vbrs is uneven, this requires the manufacturer to take the time to select and identify. However, in terms of price, the metal V slot should be made. One is that its material itself is more expensive than plastic, and its processing difficulty is greater than that of plastic. In order to have high temperature resistance and low temperature resistance and corrosion resistance, the selection and coating of Metal V-trough are critical. As the plasma planar optical waveguide technology becomes increasingly mature, some manufacturers in the industry are using the fiber array vslot technology to research and develop glass vslots to create fast connectors. The stability of Z glass, especially the environmental resistance and corrosion resistance, is stronger than that of plastic and metal. Therefore, the fast connector made by this vswitch is worth looking forward. At present, due to the huge market demand of fast connectors, there are a large number of fast connector manufacturers in foreign and domestic markets. To compete for the market, the industry has formed a bad momentum of low price competition and vicious competition ., In order to reduce costs and even purchase low-cost inferior raw materials, some manufacturers have reduced the overall quality of the fast connector products on the market. Therefore, when selecting the fast connector product, we should focus on its quality and ease of operation, rather than simply pursuing the price. Here is an example: an important raw material for a pre-Embedded Fiber Optic rapid connector is the fiber optic matching liquid. The function of the matching fluid is to make up for the small gap caused by the uneven face during the optical fiber connection, so that the optical signal can be smoothly reflected through. The qualified matching fluid has strict requirements on its refractive index accuracy, and has good antioxidant properties and is extremely difficult to volatile. There is a misunderstanding here: Many people think that the matching liquid matches the liquid, the liquid is always volatile, in fact, the main component of the matching liquid is silicon compounds and Z particles, it is difficult to volatile. The price of high-quality matching liquid is expensive, but if some manufacturers choose inferior matching liquid to reduce the cost, it will inevitably lead to a reduction in the quality of the fast connector, at the same time, the service life will be greatly reduced. Therefore, the good structure and good materials are important to the quality of the quick connector.

So far, there are no formal industry standards for fast connector in China. There are only two temporary documents on the standard for fast connector: one is the industry standard of "the first part of the mechanical type of the on-site assembly of Optical Fiber activity connector" is being approved; the other is the interim draft of "China Telecom on-site assembly of Optical Fiber activity connector technical requirements. I personally think there are some points that can be discussed and discussed about the content and terms in these two documents. Here I will list 5 points:

First, performance indicators, mainly insert loss

China Telecom standard: IL average ≤ 0.25dB, limit ≤ 0.5dB; Industry Report: IL average ≤ 0.db, limit ≤ 0.5dB

Both files specify the average value and the limit value. Here I will explain:

When the insertion loss of a single fast connector is less than or equal to DB, but greater than or equal to DB, we are judged to be qualified according to the file. However, during sampling detection, if this is the case for 10 samples, according to the file, then it is unqualified, but when the number of samples expands to 100, the remaining 90 are both less than or equal to 0.25dB, and the average value of 100 samples is less than or equal to 0.25dB, the batch is qualified. This leads to different results of the same product under different bases. For example, the company produces a batch of 100 fast connector orders, 10 of which are only ≤0.5db, but ≥0.db, and the rest are ≤0.25db. According to the average value concept, this batch of goods is qualified, the workers packed and shipped two or three boxes, but unfortunately these 10 bad items were packed in one small box. The customer basically received the goods according to the sampling inspection and acceptance. The customer just got the box again. According to the standard, this box is unqualified, and the customer considers that this batch of goods is unqualified, and requests a return of goods, plus compensation. In this way, they are both rational and all follow the standards.

Similar to the standard of fiber-optic active connectors of conventional products, the industry prefers to compare the two. YD/T1272.3-2005 activity connector industry standards: Any plug through the standard adapter with the standard plug insertion loss ≤ 0.35dB (including repeatability), that is to say, under whatever circumstances, the insertion loss is a standard value 0.35dB, if there is no average limit, it is a value. If the limit is exceeded, it is unqualified. If the limit is lower, it is qualified. Very straightforward and well judged.

In fact, in actual engineering use, 0.5 has been fully able to meet the current construction needs, and the rapid connector itself is to replace the hot melt contact plus an active connection point to set. According to this calculation, the hot melt 0.1 and the active connection 0.35 are also 0.45dB. Therefore, I personally think you can refer to it to redefine it.