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Here’s a key reason why we don’t have one standard polishing process: Single-fiber and multi-fiber ferrules are composed of different materials and have different shapes, diameters, hardness, and tolerances.
Here are two quick examples:
Single-fiber ferrules are often pre-shaped with either a flat surface or a conical tip (with various conical angles like 45-60 degrees) and pre-domed, or even pre-angled and pre-domed.
Zirconia ferrules are available in several diameters: 2.5mm, 1.58mm, 1.25mm, and 1.0mm.
Compounding this, there are many different connector components with considerations such as spring force and dimensional tolerances. For single fiber connectors, the most common material is ceramic, yet some are stainless steel. Multifiber ferrules are made of a type of plastic (a glass-filled polymer).
When properly crimped, the cable assembly has the strength to withstand a reasonable amount of pulling that occurs during the final production stages and installation.
Even after installation, the cable assembly may need to withstand a certain amount of mechanical forces. For example, a dense rack may have multiple fibers bundled with Velcro®, hanging out of a cabinet – the force of the complete bundle is distributed over all the connectors. Proper crimping ensures that force is transferred to the connector, not the delicate glass fiber.
When looking at the bigger picture of our industry, it has become clear that cabling and connectivity go hand-in-hand as a SYSTEM. Connectivity is integral to helping our industry do more – and do it faster. We are continuing to pack more cargo (data) into smaller spaces. As bandwidth on any given medium increases, decisions on how to terminate the cable to the outside world and how to transfer that cargo become increasingly critical.
At one point in time, the transmission medium itself was the biggest loss contributor. Now the connector is the biggest loss device. This is just one of many challenges our industry is tackling:
As bandwidth increases, more and more areas will migrate to optical fiber to compete in the smart world. And, as bandwidth swells, the issues related to moving light from one platform to another multiply.
In copper high-frequency connectivity, electrical laws apply and over many years have become well understood. This is best exemplified in that we move mountains of data over twisted pair that 30 years ago were unthinkable. In optical connectivity, we are moving highly intense lightwaves at one end and extremely small amounts of light are detected at the other end. The physics of light manipulation involve several disciplines from physics to electro-optics to material science. We are still learning about how the sciences that govern optical connectivity can best be used with mass data movement.
Many of the difficulties related to higher bandwidth connectivity such as back reflection issues and index mismatches require significant research and experimentation to resolve on a commercial scale and meet acceptable costs.
Driven by the internet of things, optical communication technology will move into more and more traditional copper transmission media. In many cases, the use of wireless communications would seem to be the likely next generation after optical fiber. Rather than diminish the use of fiber, it will expand that use – every wireless point of presence will require a higher bandwidth connection to the web in order to transfer the last few meters of distance into the network.
An epoxy-based connector needs a tight buffer that will not wick epoxy between the coating and the buffer material. In this fashion where true tight buffers are mechanically in intimate contact with the coating of the fiber and are not applied in a way that could draw the coating away from the glass core and cladding. There can be no small spaces that could allow the epoxy to wick into the buffer or between the coating and the glass.
If an operator forgets to and only cleans one end of a mated connector pair, the clean connector will become cross-contaminated.
Residue-based contamination will transfer from the contaminated end face to the clean end face. You can tell when this happens because you will usually see a coffee ring stain on both connector end faces.
Dust-based contamination will also transfer from the contaminated end face to the clean end face.
When this happens, the dust particles will start to break apart and spread across both ferrule end faces. Another common problem that happens with dust contamination creates pits and scratches on both ferrule end faces.
The MT plastic material requires fibers to protrude between 1 to 3.5 microns in height. The only way to achieve this is to etch away the thermoset or thermoplastic material from the fibers.
Remember, the primary task of CMP coated flock pile pads is to etch away the substrate material, leaving the fibers at a specific, controllable protrusion.
The secondary task is to provide a good polish to the glass fibers, so they meet industry requirements for visual standards and optical transmission.
Good cleaning techniques throughout your polishing process will directly impact the quality of your process and extend the life of the lapping film. This helps to provide polishing uniformity and enables you to achieve the desired polishing results.
It important to consider that when stripping multi-layer cables for connectorization, each layer must usually be stripped individually, as they all usually need to be stripped to different lengths. That is, you cannot strip the above cable in one “go”, the layers must be stripped progressively.
The Jacket must be stripped, then the Aramid Yarn, then the Buffers. (there is a slight exception with the Buffers, noted in our blog article). And thus, when stripping an outer layer, care must be taken to ensure that the layers underneath are not damaged.
Regardless of the stripping tools you use, always be sure to properly maintain the, to keep cutting edges sharp.
In most cases, cable assembly manufacturers are curing by placing their room-temperature product into pre-heated curing ovens—quite a thermal shock. Based on our observations, it seems that curing in this manner, with an oven temperature below 90 degrees C will usually not produce Core Cracking. In many cases, epoxy manufacturers will provide a range of acceptable curing time and temperature combinations for a given epoxy—-for example, the same epoxy maybe able to fully cure in 30 min @ 80 degrees C, or 5 min @ 120 degrees C. To avoid Core Cracking, choose the lower temperature.
Some cable assembly houses have had good success by curing with a “ramped” temperature profile: where the room-temperature connectors are placed in a room-temperature oven, which is then gradually heated until the curing temperature is reached. This lessens the thermal shock to the product, and may allow for curing at higher temperatures without Core Cracking. Curing with this method opens up the available range of epoxies available to use in your product, but does increase the curing time needed (ramp time + cure time), and can be more difficult to control.
When fiber optic cable assembly houses set up a new polishing machine and establish their polishing process, they often find that film slipping or coming off the pad is an issue. To provide uniform polishing, film should never move on the polishing pad. If the film moves with the revolutions of the polishing machine’s platen (the turntable), then you’re not accomplishing anything.
Everything may be spinning, but you’re not actually polishing the connectors. It’s extremely important to overcome this issue! In fact, this is the first thing I show people when I teach them how to polish connectors.
One of the concerns with automation in the optical fiber industry is that you want a stable technology. Again, fusion splicing serves as a good example: when companies began using fusion splicing (as opposed to other methods of permanent termination) that process became very stable. Whether factory or field splicing, they are using the same equipment and stability. The point is that while one process was developed (fusion splicing) the process equipment continued to upgrade and add more features but the core process did not change. We had one process, initially very operator sensitive that due to the advances in generic robotics and manufacturing automation allowed automation. An example from a different industry is the assembly of automobiles. For decades, auto manufacturers have robot welded uni-bodies together. This stable technology successfully automated a major non-stable step in the manufacturing process.
In standard Singlemode cable assembly, the two wavelengths used for Insertion Loss testing are 1310nm and 1550nm. All Singlemode fibers work very similarly in either wavelength—that is, you don’t need to buy fiber based on wavelength, one fiber fits all. So, IF your cable assembly is built properly, with good materials and good techniques, the Insertion Loss values for any given connector should be very similar when tested at either 1310 or 1550.
Most polymer plastics are inherently isotropic (that is, that is they have no directionality in their optical properties). However, when formed in the injection molding process the polymer is melted, injected and cooled, which depending on the material can induce stress that shows up as birefringence in the finished molded part.
Without question, good stripping techniques in your fiber optic cable assembly process are imperative. What happens if you damage the fiber during this production step? A tiny scratch or nick in the optical fiber is like a time bomb. Eventually, this imperfection can initiate a crack when the connector is exposed to stress or thermal cycling. (Think about how a diamond blade scratches glass – this weakens the structure and initiates a break.) If the fiber cracks in a cable assembly, the connection is weakened or lost. Your cable assembly house could face repairing or replacing connectors in the field, which could be exceedingly costly for your company.
Yes and in theory, this ensures connectors will be sufficiently clean for installation. However, there are a number of ways in which the end-face can (and do) become contaminated along the way:
When installing the dust-cap, the manufacturer accidentally touches the end-face with the dust-cap itself, leaving plastic mold-release grease or other contamination. Since the dust cap is never removed again by the manufacturer, it’s impossible to detect this.
In some poorly-designed dust-caps, the interior surface dimensions are such it permits contact with the end-face it is trying to protect, usually leaving a super-contaminated end-face.
During installation, dust caps are removed prematurely, while cables are still being organized / routed, and end-face is exposed, and prone, to contamination.
Color variation from batch to batch is a non-issue. Since epoxies are manufactured in batches, the raw materials used by manufacturers to synthesize the epoxy are subject to small variations. These slight variations in raw materials can result in mild color variations.
About the curing difference…. while it is possible for a batch of epoxy to be faulty, this is very rare. Most likely, this points to some variation in the epoxy that is allowed by the epoxy’s specification. Again, epoxies are manufactured in batches, with specified manufacturing windows for viscosity, work time, and other parameters. This means the final product can – and probably will – show some variation from batch to batch. What happens if your cable assembly process has been very specifically tailored to a given batch of epoxy and a new batch has slightly different properties? This slight variation might result in an unwelcome disruption to your production process. However, minor process adjustments can solve the issue and, happily, make for a more robust process.
To ensure optimum performance between mated pairs of APC connectors, it is important that the ferrule endface geometries meet or exceed industry-accepted endface geometry standards (1). The most common issues that polishing process engineers face regarding APC polishing geometry usually involve the Apex Offset and Angle measurements. There’s quite a bit of complex trigonometry to mathematically “prove” the geometrical consequences involved in forming and measuring a curved angle across a conical or cylindrical object (the ferrule). But it’s not necessary to delve too deeply into complex math. Simplified diagrams are sufficient to help polishing process engineers visualize the basic principles at work, enabling them to better control their polishing process to meet the product’s geometry needs.
When clean end-faces should be inspected at the installation site. It is always highly recommended to visually inspect the connector end-faces at the installation site, immediately prior to installing into any adapters. This should be common practice by any respectable installer. There are many options available in lightweight inspection systems that are designed specifically for installation and include the capability of viewing connectors after installation into an adapter.
CMP flock pile pads have gone from being a good idea – but problematic – to becoming an advanced process that offers repeatable, predictable results.
In the early days of MT process development, many types of chemical slurries were used in the polishing process. The slurry contained water or oil with a chemical compound, which was manually deposited onto a polishing pad by a technician.
(Coated flock pile pads were not available at the time.)
The CMP occurred with the addition of the mechanical action: motion, pressure, and velocity. This slurry-based polishing process was not clean and did not yield predictable results. It was tricky at best!
Today’s coated flock pile pads – pre-deposited films – make the polishing process cleaner and more efficient while providing repeatable, predictable results. Of course, the quality of the coated flock pile pad is important. Achieving the correct etching and polishing process requires manufacturers to maintain very tight quality control of critical aspects such as pile (fiber) size, length, uniformity, and density as well as controlled particle size of the abrasive chemicals.
When process engineers ask about slurries, I let them know that these are still available, but they will not get repeatable results. They WILL get repeatable, predictable results using a coated flock pile pad with chemical deposition.
Fiber Optic Center offers several epoxies for single mode and multi-mode products. Refer to the “Chart of Epoxies for Single Fiber, Single Mode and Multi-mode Terminations” to review epoxy properties that will support your specific application.
There is a high degree of detail involved with every step of the epoxy process. While you may be using an epoxy successfully in one particular application, don’t assume you can use the same epoxy and cure temperature in a different application. Carefully train your production team, and don’t take anything for granted.
