How to perform fiber splicing and testing?
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 clean with toilet paper, and put the optical cable into the splice box. When fixing the steel wire, it must be pressed 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, dust and fiber fragments in the mirror and V-shaped groove. . The optical fibers used in 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. After cutting, carefully place the optical fiber into the V-groove of the fusion splicer, close the windshield, and press the discharge button of the fusion splicer. The fusion splicing can be completed automatically, and it only takes 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.
2. Optical fiber test
The optical fiber is erected, and the test is done after the fusion is completed. The instruments used are mainly OTDR testers or light source optical power meters. The FTB-100B portable Chinese color touch screen OTDR tester from EXFO Canada (dynamic range is 32/31, 37.5/ 35, 40/38, 45/43db), you can test the position of the fiber breakpoint; the whole loss of the fiber link; understand the loss distribution along the length of the fiber; the splice loss of the fiber splicing point.
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, and the general location of the fault point can be found out, and then placed 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 fiber. The above method can be successfully eliminated. Multiple breakpoints and high loss points.