Optical Fiber Fusion Splice Loss

Optical Fiber Fusion Splice Loss

1. The main factors affecting the fiber splicing loss

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

1. 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 do not match;

(3) The cross section of the fiber core 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.

2. Measures to reduce fiber splicing loss

1. 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. The installation of the optical cable is carried out according to the requirements

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

Now most of the fusion splicing is automatic fusion splicing machine, but the level of splicing personnel directly affects the size of 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 carried out 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.

6. Correct use of welding machine

The function of the fusion splicer is to fuse two optical fibers together, so the correct use of the fusion splicer is also an important measure to reduce the loss of optical fiber splicing. Correctly and reasonably set the fusion splicing parameters, pre-discharge current, time and main discharge current, main discharge time, etc. according to the fiber type, and remove the dust in the fusion splicer in time during and after use, especially the clamps, mirrors and V-shaped grooves Removal of dust and fiber debris inside. Before each use, the fusion splicer should be placed in the welding environment for at least fifteen minutes, especially in places where the placement and use environment are quite different (such as indoors and outdoors in winter), according to the air pressure, temperature, humidity and other environmental conditions at that time , reset the discharge voltage and discharge position of the fusion splicer, and reset the v-groove driver.

3. Measurement of fiber splicing point loss

Optical loss is an important index to measure the quality of a fiber optic splice. There are several measurement methods to determine the optical loss of a fiber optic splice, such as using an optical time domain reflectometer (OTDR) or a loss evaluation scheme for a fusion splice.

1. Evaluation of fusion splice loss

Some fusion splicers use a cross-section alignment system for imaging fiber optics and measuring geometric parameters. By viewing the fiber from two perpendicular directions, the computer processes and analyzes the images to determine cladding shifts, core distortions, fiber outer diameter changes, and other key parameters that are used to evaluate splice loss. Depending on the splice and its loss estimation algorithm, the resulting splice loss may differ considerably from the actual splice loss.

2. Using Optical Time Domain Reflectometer (OTDR)

Optical Time Domain Reflectometer (OTDR: OpTIcal TIme Domain Reflectometer), also known as backscattering instrument, its principle is: when the light pulse is transmitted to the optical fiber, due to the trace light scattered in the optical fiber, after returning to the light source side, the time base can be used To observe the degree of reflected return light. Since the mode field diameter of a fiber affects its backscatter, the fibers on either side of the splice may backscatter differently, masking the true loss of the splice. If the loss of the joint is measured from two directions, and the average value of these two results is obtained, the human factor error of the one-way OTDR measurement can be eliminated. However, in many cases the operator only measures the splice loss from one direction, and the result is not very accurate, in fact, the loss due to the fiber with mismatched mode field diameter can be 10 times larger than the intrinsic splice loss itself.