Precautions for fiber splicings

Splicing procedure

Before splicing, according to the material and type of the optical fiber, set the key parameters such as the optimal pre-melting main melting current and time, and the amount of fiber feeding. During the welding process, the "V" groove, electrode, objective lens, welding chamber, etc. of the welding machine should be cleaned in time, and any bad phenomena such as bubbles, too thin, too thick, virtual melting, separation, etc. should be observed during the welding at any time, and attention should be paid to the tracking and monitoring results of OTDR. Analyze the causes of the above adverse phenomena in a timely manner and take corresponding improvement measures. If virtual fusion occurs many times, check whether the materials and models of the two optical fibers to be welded match, whether the cutter and the fusion splicer are polluted by dust, and check the oxidation status of the electrodes. If there is no problem, the fusion current should be increased appropriately.

Disc fiber

Disk fiber is a technology, but also an art. The scientific fiber coiling method can make the optical fiber layout reasonable, the additional loss is small, can withstand the test of time and harsh environment, and can avoid the phenomenon of fiber breakage caused by extrusion.

Disc Fiber Rules

1) The fiber is coiled in units along the loose tube or the branching direction of the optical cable. The former is applicable to all splicing projects; the latter is only applicable to the end of the main optical cable, and it has one input and multiple outputs. Most of the branches are small logarithmic optical cables. The rule is to reel the fiber once after splicing and heat-shrinking one or several fibers in loose tubes, or fibers in a split direction cable. Advantages: It avoids the confusion of optical fibers between loose tubes of optical fibers or between different branch optical cables, making it reasonable in layout, easy to reel and dismantle, and easier to maintain in the future.

2) The heat-shrinkable tube placement unit in the reserved tray is used as the unit for fiber coiling. This rule is based on the number of heat-shrinkable tubes that can be placed in a small placement area in the reserved tray in the splice box. For example, the GLE type barrel splice box, in actual operation, every 6 cores is a plate, which is very convenient. Advantages: It avoids the unevenness of the same bundle of optical fibers caused by different placement positions, it is difficult to coil and fix the fibers, and even sharp bends and small circles occur.

3) Special circumstances, such as optical splitters, add/drop pigtails, pigtails and other special devices in the splicing, should be welded, heat-shrinked, and coiled with ordinary optical fibers first, and then deal with the above situations in turn, for safety reasons Disk operation to prevent the increase of additional losses caused by extrusion.

Disk fiber method

1) First the middle and then both sides, that is, first place the heat-shrinkable sleeves in the fixing groove one by one, and then process the remaining fibers on both sides. Advantages: It is beneficial to protect the fiber joints and avoid possible damage caused by the fiber coil. This method is often used when the space reserved for the optical fiber is small and the optical fiber is not easy to coil and fix.

2) Start fiber coiling from one end, that is, start from the fiber coil on one side, fix the heat shrinkable tube, and then process the remaining fiber on the other side. Advantages: It is convenient and quick to choose the placement position of the effective copper tube according to the length of the remaining fiber on one side, and it can avoid sharp bends and small circles.

3) Handling of special circumstances, such as individual optical fibers that are too long or too short, can be placed at the end and coiled separately; when there are special optical devices, they can be processed separately. It is lightly placed on the ordinary optical fiber, and a buffer liner is added between the two to prevent fiber breakage caused by extrusion, and the tail fiber of special optical devices should not be too long.

4) According to the actual situation, a variety of graphic disk fibers are used. According to the length of the remaining fiber and the size of the reserved disk space, it will be coiled naturally according to the trend. Do not pull it forcefully. You should flexibly use various graphics such as circle, ellipse, "CC" and "~" (note that R≥4cm), and make the fiber as large as possible. Maximize the use of reserved disk space and effectively reduce the additional loss caused by disk fiber.

Quality Assurance of Optical Cable Connection

It is of great significance to strengthen the monitoring of OTDR to ensure the quality of optical fiber fusion, reduce the additional loss caused by the fiber coil and the possible damage to the optical fiber caused by the sealing box. During the entire follow-up work, the OTDR four monitoring procedures must be strictly implemented:

1) Real-time tracking and monitoring of each core fiber during the fusion splicing process to check the quality of each splicing point;

2) After each fiber reel, perform a routine inspection on the reeled fiber to determine the additional loss caused by the reel;

3) Before sealing the splicing box, conduct a unified test on all optical fibers to find out whether there is any missing test and whether there is any extrusion on the optical fiber and the connector between the reserved optical fiber discs;

4) After sealing the box, perform a final inspection on all optical fibers to check whether the sealing box has damaged the optical fiber.

technical problem

main factors. There are many factors affecting the fiber splicing loss, which can be roughly divided into two types: intrinsic factors and extrinsic factors.

1. The intrinsic factors of optical fiber refer to the factors of optical fiber itself. There are four main points.

(1) The fiber mode field diameter is inconsistent;

(2) The core diameters of the two optical fibers are mismatched;

(3) The core section is not round;

(4) The concentricity between the core and the cladding is not good.

Among them, the inconsistency of the fiber mode field diameter has the greatest impact. According to the recommendation of CCITT (Consultative Committee for International Telegraph and Telephone), the tolerance standard of single-mode fiber is as follows:

Mode field diameter: (9~10μm) ±10%, that is, the tolerance is about ±1μm;

Cladding diameter: 125±3μm;

Mode field concentricity error ≤ 6%, cladding out-of-roundness ≤ 2%.

2. The extrinsic factor affecting the fiber splicing loss is the splicing technology.

(1) Axis misalignment: The core of a single-mode fiber is very thin, and the misalignment of the axes of two butt-connected optical fibers will affect the splice loss. When the misalignment is 1.2μm, the connection loss reaches 0.5dB.

(2) Axis tilt: When the fiber section is tilted by 1°, about 0.6dB splice loss occurs. If the splice loss is required to be ≤0.1dB, the inclination angle of the single-mode fiber should be ≤0.3°.

(3) End-face separation: The connection of the movable connector is not good, and the end-face separation is easy to occur, resulting in a large connection loss. When the discharge voltage of the fusion splicer is low, it is also easy to cause end face separation. This situation can generally be found in fusion splicers with tensile test functions.

(4) End face quality: When the flatness of the end face of the optical fiber is poor, loss or even air bubbles will occur.

(5) Physical deformation of the optical fiber near the splicing point: the tensile deformation of the optical cable during the erection process, too much pressure to clamp the optical cable in the splicing box, etc., will affect the splicing loss, and even several times of welding cannot improve it.

3. The influence of other factors.

The splicing personnel's operation level, operation steps, fiber coil process level, electrode cleanliness in the fusion splicer, welding parameter settings, and cleanliness of the working environment will all affect the value of the splice loss.

Measures to reduce loss

Try to use the same batch of high-quality brand-name bare fibers on one line

For the same batch of optical fibers, the mode field diameters are basically the same. After the optical fiber is disconnected at a certain point, the mode field diameter between the two ends can be regarded as the same, so the fusion at this disconnection point can make the mode field diameter affect the fiber fusion loss. impact is minimized. Therefore, optical cable manufacturers are required to use the same batch of bare fibers to produce continuously according to the required length of optical cable, number them sequentially on each reel and distinguish A and B ends, and do not skip numbers. When laying optical cables, they must be laid out along the determined routing sequence according to the number, and ensure that the B end of the front optical cable is connected to the A end of the next optical cable, so as to ensure that the connection can be welded at the disconnection point, and the fusion loss value can be reached. minimum.

2. Optical cable erection is carried out as required

In the construction of optical cable laying, it is strictly forbidden to make small circles, folds, and twists on the optical cable. More than 80 people must be employed for the 3km optical cable, and more than 100 people must be employed for the 4km optical cable, and 6 to 8 walkie-talkies should be equipped; The unique cable laying method can effectively prevent the occurrence of back buckle. The traction force should not exceed 80% of the allowable optical cable, and the maximum instantaneous traction force should not exceed 100%, and the traction force should be added to the strength member of the optical cable. The laying of the optical cable should strictly follow the construction requirements of the optical cable, so as to minimize the probability of damage to the optical fiber during the construction of the optical cable, and avoid the increase of the fusion loss caused by the damage of the optical fiber core.

3. Select experienced and well-trained optical fiber splicing personnel for splicing

Most of the splicing is automatic splicing by the splicing machine, but the level of splicing personnel directly affects the splicing loss. Splicing personnel should perform splicing in strict accordance with the optical fiber fusion splicing process flow chart, and use OTDR to test the splicing loss of the splicing point during the splicing process. Those that do not meet the requirements should be re-spliced. For points with large splice loss values, the number of repeated splices should be 3 to 4 times. When the splice losses of multiple optical fibers are large, a section of optical cable can be cut off and spliced again.

4. The splicing of optical cables should be done in a clean environment

It is strictly forbidden to operate in the open air in a dusty and humid environment. The connection parts of the optical cable, tools and materials should be kept clean, and the optical fiber connector should not be allowed to get wet. The optical fiber to be cut must be clean and free from dirt. After cutting, the optical fiber should not be exposed to the air for too long, especially in a dusty and humid environment.

5. Choose a high-precision fiber end face cutter to prepare the fiber end face

The quality of the fiber end face directly affects the splicing loss, and the cut fiber should be a flat mirror surface without burrs or defects. The axial inclination angle of the fiber end face should be less than 1 degree. A high-precision fiber end face cutter not only improves the success rate of fiber cutting, but also improves the quality of the fiber end face. This is especially important for the fusion splices that cannot be tested by OTDR (that is, the blind spots of OTDR test) and the maintenance and repair of optical fibers.