This blog is the third and final in a series of blogs that overview fusion splicing equipment and methods, particularly those of interest to the cable/broadband industry. Information to support this series was sourced from Fusion Splicing Equipment and Applications for the Cable/Broadband Industry (SCTE 134 2021) — an SCTE Standard authored by UCL Swift Fiber Optic Engineer Rich Case.
Miss the previous parts? Catch up:
Methods and Practices — Single Fiber Splicing
The preparation process before inserting the fiber into the splicer is very important. Optical fibers must have the coating removed down to the bare glass. The fibers must be cleaned properly and must have a good quality cleave. It is important to be aware of and use the correct cleave length for the particular fusion splicer that is being used. This length varies with splicer manufactures, so it is recommended to consult the operating manual for the specific unit before beginning the splicing process. The three main steps to preparing the fiber are as follows.
Step 1: Strip
All coatings (900 μm, 250 μm and/or 200 μm) should be removed and bare glass exposed.
Step 2: Clean
The bare glass should be cleaned to remove all contaminants. The most common cleaning method is to use a clean lint-free wipe saturated with 99% isopropyl alcohol. This wipe is pulled over the bare glass removing any acrylate coating and other contaminants that may be on the bare glass. It is important to ensure that the glass is not touched with the bare fingers or contaminated with anything after the cleaning step, as this can adversely affect the cleaving, alignment and fusion process. Non-alcohol low-residue cleaners are increasing in popularity and can also be used.
Step 3: Cleave
The cleaving of optical fibers involves several processes. The fiber is inserted into the cleaver after being cleaned. The cleaving process is achieved through a combined movement of scoring and breaking. Both fiber ends can then be inserted into the splicer and are ready to be spliced together. The fiber’s end face quality affects the final splice result. The better and cleaner the fiber end faces are, the lower is the splice loss that can be achieved.
Methods and Practices — Multiple Fiber (Mass Splicing)
Multiple fibers may be spliced together simultaneously. This is commonly referred to as mass splicing. Mass fusion splicing is the same in principle as single-fiber splicing. There are some differences in the process.
Mass fusion splicers use the passive alignment system with a fixed v-groove. The fibers can be in ribbon form, ribbonized by the craftsperson from individual fibers or loose when used in combination with specialized holding equipment. The multiple fibers are stripped — usually with a thermal stripper — cleaned and then cleaved simultaneously to ensure the fibers are the same length.
The fibers are inserted into the fusion splicer and the process is essentially the same as with single-fiber splicing. The splice point can be protected with heat shrink sleeves.
Multiple ribbon types of different spacings (200 / 200 μm, 250/250 μm, 200 / 250 μm, etc.) require the usage of correct ribbonizing methods and equipment holders to correctly position the fibers and reduce splice loss.
Factors That Affect Splice Loss
Cleanliness: The fibers and equipment must be clean. Dirt and contaminants can cause (1) misalignment issues, (2) increased loss and (3) degradation of equipment.
Fiber Geometry: The position of the core relative to the center of the fiber will affect splice loss. If fibers with eccentricity offsets are being spliced, active core alignment units will provide the best splice loss results.
Equipment: It is important to use the correct equipment for the specific application and ensure it is used and maintained correctly. Proper maintenance of mechanical and optical systems on fusion splicing equipment is necessary to ensure it functions correctly and provides future use. Use of appropriate holders and/or clamps for the correct fiber type supports lower fiber loss.
Training/Skill Level: Fusion splicing requires proper training and personnel development to obtain consistent good quality low loss splices.
The Importance of Testing
A typical loss value is usually less than 0.1 dB (in single-mode fiber). It’s important to test optical fiber systems to:
- Verify the system works correctly
- Ensure splices are acceptable
- Identify problems
- Provide a baseline for maintenance and troubleshooting
An optical fiber system can be tested using:
- A power meter/source
- An Optical Time Domain Reflectometer (OTDR)
The meter/source method tests the entire system. It determines end-to-end loss including any components and fiber in the system. This is a good way to get actual values for the entire system; however, it does not allow individual splices or components to be singled out.
The OTDR operates on a principle known as Rayleigh backscatter. Light is input into one end of the system. A certain amount of light is reflected from events. Events can be fusion splices, connectors, mechanical splices, etc. The OTDR interprets these events and determines where they are located along the fiber and the attenuation value.
This can be used to verify specific splice loss values and where they are located in the system. This information can be saved for documentation proposes and validation of the system.
OTDR analysis is limited by the resolution of the device being used. This limitation is exhibited by the minimum measurement distance between events that can be determined. Unfortunately, for most splice-on connectors the distance between the splice and the connector end face does not allow the OTDR to measure both events; rather it will show a single event with represents a combination of the splice joint the connector end face.
As technology advances, new equipment and techniques will be created and utilized in the fiber industry. For example, laser cleaving has become more popular in the connector sector but has not yet entered the splicing field. The innovation is in the early stages in the fiber optic domain. But with a thorough understanding of these splicing basics, you’ll be ready for what’s on the horizon.