Splicing and testing of optical fiber communication fiber engineering

Optical fiber communication technology is a new technology that has developed rapidly in the past 20 years. Because optical fiber communication transmits a large amount of information, a fast rate, and the information is digitized, it transmits digital signals, which makes it possible to transmit information such as broadband image signals and computer networking.

The measurement of optical fiber loss is very important, it is directly related to the quality of optical fiber communication, and can detect possible fault points in time.

1. Optical fiber connection

(1) Optical fiber connection. The principle that should be followed for optical fiber splicing is: when the number of cores is equal, it should be connected with the corresponding color optical fiber in the bundle tube.

(2) There are three methods of optical fiber splicing: fusion splicing, active connection, and mechanical connection. Most of the welding method is used in the project. The joint loss by this welding method is small, the reflection loss is large, and the reliability is high.

(3) The process and steps of optical fiber connection:

① Strip the optical cable and fix the optical cable into the splice box. Be careful not to injure the bundle tube, take about 1m for the stripping length, wipe the ointment with toilet paper, pass the optical cable into the splice box, and fix the steel wire tightly without loosening. Otherwise, it may cause the fiber optic cable to roll and break the fiber core.

②Split the fiber through the heat shrinkable tube. Separate the fibers of different bundles and colors and pass them through the heat-shrinkable tube. The stripped fiber is very fragile, use heat shrink tubing to protect the fiber splice.

③Turn on the power of the Furukawa s176 fusion splicer, use the preset 42 programs to splicing, and remove the dust in the fusion splicer in time and after use, especially the fixture, the dust and fiber fragments in the mirrors and v-shaped grooves. . The fibers used by catv include conventional single-mode fiber and dispersion-shifted single-mode fiber, and the operating wavelengths are also 1310nm and 1550nm. Therefore, before splicing, an appropriate splicing procedure should be selected according to the optical fiber and working wavelength used by the system. Unless there are special circumstances, the automatic welding procedure is generally used.

④ Make the fiber end face. The quality of the fiber end face will directly affect the quality of the connection, so it is necessary to make a qualified end face before fusion splicing. Use a special wire stripper to peel off the coating layer, then wipe the bare fiber with alcohol-dipped cleaning cotton several times with moderate force, and then use a precision fiber cutter to cut the fiber. For 0.25mm (outer coating) fiber, The cutting length is 8mm-16mm. For 0.9mm (outer coating) fiber, the cutting length can only be 16mm.

⑤Place the optical fiber. Put the optical fiber in the v-shaped groove of the fusion splicer, carefully press the optical fiber pressure plate and the optical fiber clamp, set the position of the optical fiber in the pressure plate according to the fiber cutting length, close the windshield, and the fusion can be automatically completed in 11 seconds.

⑥ Remove the optical fiber and heat the heat shrinkable tube with a heating furnace. Open the draft shield, take the fiber out of the fusion splicer, place the heat shrink tube in the center of the bare fiber, and place it in a heating furnace for heating. The heater can use 20mm micro heat shrink tube and 40mm and 60mm general heat shrink tube, 20mm heat shrink tube takes 40 seconds, 60mm heat shrink tube takes 85 seconds.

⑦Fix the disc. Coil the spliced ​​optical fiber onto the optical fiber receiving tray. When coiling the fiber, the larger the radius of the coil and the larger the radian, the smaller the loss of the entire line. Therefore, a certain radius must be maintained to avoid unnecessary losses when the laser is transmitted in the core.

⑧ Seal and hang. The field connection box must be sealed to prevent water from entering. After the fusion splicing box enters the water, due to the long-term immersion of the optical fiber and the optical fiber splicing point in the water, the attenuation of some optical fibers may increase first. Put on stainless steel hooks and hang on the hanging wire. At this point, the optical fiber fusion is completed.

2. Optical fiber test The optical fiber is erected, and the test work is done after the fusion is completed. The instrument used is mainly the otdr tester. Test, the position of fiber breakpoint; the whole loss of fiber link;

Understand loss distribution along fiber length; splice losses at fiber splice points. In order to test accurately, the pulse size and width of the otdr tester should be appropriately selected and set according to the index of the refractive index n value given by the manufacturer. When judging the fault point, if the length of the optical cable is not known in advance, it can be placed in the automatic otdr first to find out the general location of the fault point, and then put it in the advanced otdr. Select a smaller pulse size and width, but it should correspond to the length of the optical cable. The blind area is reduced until it coincides with the coordinate line. The smaller the pulse width, the more accurate it is.

Then there is the addition of the fiber detection disk, the purpose is to prevent the blind spot in the vicinity from being easily found. When judging the breakpoint, if the breakpoint is not at the junction box, open the nearest junction box, connect the otdr tester, test the exact distance between the fault point and the test point, and use the meter mark on the optical cable to easily find the fault point. . When using the meter scale to find faults, there is also a twist rate problem for the twisted optical cable, that is, the length of the optical cable is not equal to the length of the optical fiber, and the length of the optical fiber is about 1.005 times the length of the optical cable. The above method can be successfully eliminated Multiple breakpoints and high loss points.

Fiber splicing and testing

Optical cable construction is roughly divided into the following steps: preparation → routing project → optical cable laying → optical cable connection → project acceptance.

1. Preparation

(1) Check whether the design materials, raw materials, construction tools and equipment are complete.

(2) Form a high-quality construction team. This is very important, because optical fiber construction is much stricter than cable construction, and any negligence in construction may result in increased optical fiber loss or even broken cores.

2. Routing project

(1) Before laying the optical cable, it is necessary to conduct a careful survey of the route passed by the optical cable, understand the local road construction and planning, and try to avoid potential hidden dangers such as pits, threshing fields, and gas stations. After the route is determined, the actual length is measured, accurate to within 50m. In addition, the natural bending and various reserved lengths during deployment are also added. Various reservations also include other special reservations such as bending in the insertion hole, reservation on the rod, reservation at both ends of the joint, and increase in the curvature of the horizontal plane. In order to make the optical cable reconnect when it breaks, a certain margin should be left at every 100 meters. The length of the margin is generally 5% to 10%. Order according to the actual required length and indicate when winding.

(2) Draw the path construction drawing. Number the pre-planted poles, draw a path construction drawing, and indicate the number of each pole or underground pipeline outlet pole and the length of the pipeline, and determine the length and location that need to be left behind. In this way, the length of the optical cable can be effectively used, and the reasonable configuration can minimize the fusion points.

(3) It is best to install the two optical fiber joints in a place with flat terrain and stable geology, avoiding ponds, rivers, ditches and roads, preferably at the exit of poles or pipes, and the overhead optical cable joints should be placed on the electrical outlet. About 0.5 ~ 1m next to the pole, this work is called "matching plate". Reasonable matching plate can reduce welding points. In addition, the location of the fusion splicing point should also be stated on the construction drawing. When the optical cable breaks, it is convenient to quickly find the breakpoint with the instrument for maintenance.

3. Optical cable laying

(1) The mode field diameters of the same batch of optical fibers are basically the same. After the optical fiber is disconnected at a certain point, the mode field between the two ends can be regarded as the same. Therefore, the mode field diameter can be spliced ​​to the optical fiber. The impact of losses is minimized. Therefore, optical cable manufacturers are required to use the same batch of bare fibers, continuously produce them according to the required length of optical cable, serially number them on each reel, and mark the a (red) and b (green) ends respectively, without skipping numbers. When erecting the optical cable, it should be laid out according to the number along the determined routing sequence, and ensure that the b end of the optical cable in the front coil is connected to the a end of the optical cable in the next coil, so as to ensure that the mode field diameters of the two optical fiber end faces are basically the same during the connection, so that the value of the fusion loss is the same. reach the minimum.

(2) For the aerial optical cable, 72.2mm galvanized steel strand can be used as the hanging wire for hanging the optical cable. Suspension wires and optical cables should be well grounded, and should have lightning and electric protection measures, as well as shock-proof and wind-proof mechanical properties. The horizontal and vertical distance between the overhead suspension line and the power line should be more than 2m, the minimum height from the ground is 5m, and the minimum distance from the roof is 1.5m. There are three types of hanging types of overhead optical cables: hanging wire hanging type, hanging wire winding type and self-supporting type. The self-supporting type does not use steel strand suspension wires, the optical cable sags, and the wind load capacity is poor, so the hanging type is commonly used.

(3) Aerial optical cable laying. Since the length of the reel of the optical cable is much longer than that of the cable, the length may reach several kilometers, so it is limited by the allowable rated tensile force and bending radius, and special attention should be paid to not yanking and kinking during construction. Generally, the allowable tensile force of the optical cable is about 150-200kg. The bending radius of the optical cable should be greater than or equal to 10 to 15 times the outer diameter of the optical cable when the cable is turned, and the bending radius should be greater than or equal to 20 times during construction and deployment. In order to avoid that the optical cable is placed in the middle of the road section, it is about 20m away from the pole and erected in opposite directions. The first half of the coil is erected, and the second half of the optical cable is put down from the reel, and placed on the ground in an "8" shape. Then deploy.

(4) When laying the optical cable, it is strictly forbidden to make small circles, folding and twisting of the optical cable, and a certain number of walkie-talkies should be equipped. Also pay attention to the uniform force, the traction force does not exceed 80% of the allowable optical cable, and the instantaneous maximum traction force does not exceed 100%. In addition, when erecting, there should be a special person responsible for the turning of the optical cable or the complex terrain, and it is strictly forbidden for vehicles to roll over it. Use pulleys to lay optical cables overhead, and pre-hang pulleys on the poles and suspension lines (usually one pulley is hung every 10-20m), and reduce the sag and tension at the pulleys and pulleys of the optical cable. Then put the traction rope between the pulleys, the traction rope is tied to the traction head of the optical cable, and the optical cable is allowed to climb up the pole with a certain traction force and hang on the suspension line. The distance between the optical cable hooks is 40cm, the hooks on the hanging wire should be in the same direction, and there should be a convex drip groove at each pole. Each cable should have a pole length plus 3m allowance at the joint so that the box can be connected. Ground welding operation, and there must be a certain amount of coils every few hundred meters.

4. Optical cable connection

Common optical cables include layer twisted, skeletonized and central bundled optical cables. The color of the core is divided into blue, orange, green, brown, gray, white, red, black, yellow, purple, pink, powder blue in order. This is called the full spectrum of core colors, and some fiber optic cable manufacturers replace a color in the color spectrum with "natural colors". Multi-core optical fiber cables put optical fibers of different colors in the same bundle to form a group, so that there may be several bundles in a multi-core optical cable. Facing the cross section of the optical cable, the red bundle tube is regarded as the first bundle tube of the optical cable, and the clockwise order is white one, white two, white three... The last one is the green bundle tube. The principle that should be followed for fiber splicing is: when the number of cores is equal, the fibers of the corresponding color in the same bundle tube are connected, and when the number of cores is different, connect the larger number of cores first, and then connect the smaller number of cores in order.