How to Splice Fiber Optic Cables?

 

Do you really know how to splice the fiber optic cable? The intrinsic transmission loss of optical fiber is largely determined, but the splicing loss at the fiber optic connections significantly depends on the quality of the fiber and on-site construction.

Reducing the splicing loss at the connections can enhance the transmission distance of fiber optic relays and improve the attenuation margin of the fiber link.

 

Splice fiber optic cables follows these steps: stripping, cleaving, splicing, and coiling.
Tools required include: fusion splicer, cleaver, Miller stripper, alcohol pad, heat shrink tubing, etc.

A fiber optic cable consists of a core, cladding, and coating. The technique for removing the coating involves mastering the "steady, even, and quick" approach.

 

Even refers to keeping the fiber horizontal to prevent slipping;

Steady means grasping the stripper firmly;

Quick requires swift movement; the stripper should be held perpendicular to the fiber, slightly inclined toward the top, gently seize the fiber, then push it smoothly along its axis with a strong grip.

 

 

Check if all the coating has been removed from the fiber portion. If residues remain, strip again. For minimal adhesive layers that are hard to remove, use an alcohol-soaked cotton ball to gradually rub it off.
Tear the cotton into a flat, fan-shaped piece, moisten it gently with alcohol (ensuring no drip when squeezed between fingers), fold it into a V-shape around the stripped fiber, and wipe along its axis. Change the cotton after 2 or 3 uses to prevent re-contamination of the fiber core.

Keep the cleaver clean and stable. During cleaving, avoid creating bad end-faces such as breaks, angled cuts, burrs, or cracks.
The cleaning, cleaving, and splicing of bare fibers should be done consecutively without long delays, especially the prepared end-faces should not be exposed to air for too long.
When moving, handle gently to avoid touching other objects. Clean the V-groove, pressure plate, and blade of the cleaver as per the environment to prevent end-face contamination.

Before splicing, set the optimal pre-fusion, main fusion current, and fiber feed-in quantity based on the fiber material and type.
High-precision automatic fusion splicers come equipped with X, Y, Z three-dimensional imaging technology and automatic adjustment features, allowing for end-face inspection, positioning, and fiber alignment.
A pre-splice discharge test must be conducted, adjusting the machine's discharge voltage and position according to environmental conditions, thus enabling the splicer to adapt to actual on-site discharge requirements.

Insert two prepared fibers of the same color into the splicer's V-groove, maintain a 15-20μm distance, and close the protective cover. Initiate the fusion splicing by triggering the automatic splicing switch on the machine.
Pre-heat and approach. Use an electric arc to heat the fiber ends for 0.2-0.5 seconds to soften or eliminate burrs and protrusions; at the same time, push the two fibers together until the ends make direct contact under a specific compression force.
Splicing. Once the fibers cease moving, use the electric arc to melt and join the ends. Discharge time is typically 2-4 seconds for multimode fibers, and 1 second for single-mode fibers.

A fiber optic heat shrink tube is used for reinforcing the splice connection.
Insert the heat shrink tubing before stripping, and forbid inserting it after end-face preparation.
Move the pre-placed heat shrink tubing to the spliced area, ensure the splice is centered within the tube, gently straighten the joint, then heat it in the heater.

 

A systematic method of coiling can ensure a logical fiber layout, minimal additional loss, endurance to environmental conditions, and avoid breakages due to compression.
Coiling methods:

 

Start with the center and then to the sides, placing each heat-shrunk tube into fixed slots, followed by handling the excess fibers on both sides.

For overly long or short fibers, coil them separately at the end.

Coil around the largest diameter possible, ensuring uniform coil size.

 

Splice boxes come in barrel and horizontal types, with horizontal being the most common.
Various models exist, such as two-in-two-out, three-in-three-out, with capacities ranging from 12 to 156 cores.
Seal the splice box with raw rubber to ensure it's airtight.

Optical loss is a vital metric for assessing fiber optic joint quality. Tools such as the Optical Time Domain Reflectometer (OTDR) or optical power meters can measure optical loss at the fiber joints.

How to measure power with an optical power meter:
Operating an optical power meter is straightforward, provided you understand the function of each button.
Most power meters feature four buttons: power switch, measurement unit display (dBM or W), wavelength (λ) key, LED key, and LIGHT key.

 

 

Before measuring power, set the wavelength and other parameters of the power meter within specified ranges.
Once ready, connect the power meter to the transmitter or receiver end to measure power.
Finally, compare the measured values with the standard power values to determine if they fall within the allowed fluctuation range (to identify optical equipment faults).
Optical fiber loss is the power discrepancy from coupling at the transmission end to reception end. Measuring this requires not just an optical power meter, but also a light source.
For multimode fibers, use an 850/1300nm LED source, and for single-mode fibers, a 1310/1550nm laser source.
Loss measurement methods include single-ended and double-ended. Single-ended uses only a transmitting cable, while double-ended also requires a receiving cable.
Single-ended measurements can identify losses due to the connector to the transmitting cable and losses within the fiber, connectors, or other joints. Double-ended measurements can identify total losses, including those between connectors and splices.

 

The OTDR is essential for checking the integrity of fiber optic cables, measuring the length, transmission performance, connection attenuation, and detecting faults in the fiber link.

An OTDR injects a high-powered laser or light pulse from one end of the cable and receives the reflected signals from the same side.
As the light pulse travels through the cable, part of it is scattered back and reflected to the transmitter. The OTDR only measures higher-intensity signals reflected back, calculating the cable's length by recording the signal's travel time and speed.
The OTDR is designed based on the principles of backscattering and Fresnel reflection, using backscattered light to obtain attenuation information, thus indirectly measuring the fiber cable's loss and fault locations.

Fresnel Reflection

The V-notch on the blade is designed for precisely stripping 250µm, 500µm coated layers, and 900µm buffer layers.
A second slot is used for stripping the outer jacket of 3mm tail fibers.

The splicing process involves aligning the fiber cores and using a high voltage electric arc to melt and join the fibers.
Display: Currently, the Profile Alignment System (PAS) is commonly used for core alignment monitoring, with LCD displays showing X, Y directions of the fiber splicing process. The fiber's magnification can reach 200-300 times for observing the fiber status and splicing quality.
Heater: Used to heat the heat shrink tubing.
V-groove: Fixes and supports the left and right fibers during splicing.

SC (Squared Connector), generally multimode, often used in terminal boxes, media converters, and switches.

 

LC (Lucent Connector), usually single-mode, frequently utilized in optical modules.

 

FC (Ferrule Connector), generally multimode, commonly used in fiber optic trays, ODF racks, etc.