Fiber Optic Polishing Fixture Maintenance

To help ensure consistent polishing results, maintenance of all fiber optic polishing equipment is essential.    The Preventive Maintenance program for polishing fixtures should include periodic ultrasonic cleaning.  This is true for any fiber optic polishing fixtures, regardless of connector or ferrule type:  connector fixtures with latching mechanisms (LC, SC), ferrule-only fixtures with screw caps or cam-locks, MT ferrule fixtures, etc.

All fixtures come from the factory with very precisely milled ferrule “bores”, tailored specifically to the particular ferrule which will be polished.  These bores position the ferrule to precise angles to the polishing surface—–90-degrees for PC polishing, other angles (typically 82-degrees, to create an 8-degree finish) for various APC polishing.  (Note:  I use the term “bore” for the circular holes milled into the fiber optic polishing fixture which hold the round ferrule, but the same concepts apply to fixture for rectangular ferrules such as MT.  For simplification, this discussion will reference typical round, PC-finished ferrules, but the concepts all apply to MT fixtures as well as APC fixtures).

The level of precision to which the fixture holds the ferrules determines many of the ferrule’s geometric characteristics (Apex, Radius, Fiber Height, Ferrule Angle, etc).   Contamination of the fixture can negatively affect this precision, by either pre-maturely wearing of the fixtures dimensions, or by creating buildup in the fixture, which prevents the ferrule from seating properly.

The contamination we are discussing here is primarily a natural result of the normal polishing process.  Ferrules are polished on abrasive films or flock-pile pads impregnated with abrasives.  During polishing, some of these abrasive particles, along with the ceramic or plastic material being removed from the ferrule itself, come free and mix with the water used as lubricant within the process.  This results in an abrasive slurry that contaminates the fixture and the ferrules themselves.  Common polishing practices require the operator to clean the bottom of the fixture between polishing cycles, to remove abrasive particles that may create fiber end-face scratches in subsequent polishing steps.  However, this slurry can (and will) migrate into crevices and the bores of the fixture—places difficult or unlikely to be fully cleaned or flushed out during normal the normal polishing process.  Allowed to dry, it will harden and cake.

The 4 major effects of this contamination to consider:

Contamination within the ferrule bore is wearing the bore, creating larger bore diameter:  Ferrule bore wear is unavoidable over time—as thousands of ceramic ferrules are inserted and removed from a stainless steel fixture, the bore will wear.   However, contamination of the bore, particularly with abrasive particles naturally resulting from the polishing process (the “slurry” referred to above), can accelerate this wear.  As the bore diameter becomes larger, the ferrule is held to less than 90-degrees to the polishing surface, resulting in larger Apex Offset and Angle values.

Contamination within the ferrule bore is building up, “pushing” the ferrule to one side:  the slurry generated from polishing can accumulate in the bore or other areas of the fixture, building up to prevent the ferrule from seating at precisely 90 degrees to the polishing surface.  This can also result in large Apex Offset and Angle values.  This buildup issue is often seen in MT ferrule polishing fixtures.

Contamination within the ferrule bore is preventing the ferrule from sliding freely within the bore:  This mainly applies to connector polishing (as opposed to ferrule-only polishing) where the connector’s spring force is relied on to present equal downward pressure to the ferrules during polishing.  The ferrules in a connector fiber optic polishing fixture must be able to piston up-and-down freely in the fixture.  If contamination of the ferrule bore holds the ferrule too tightly, this may “lock up” the ferrules or prevent them from pistoning consistently / smoothly within the bore during polishing.  This, in turn, will result in different pressures being applied to the end-faces during polishing—–which creates variation in Radius values, FH values, and fiber end-face polish quality (scratches).

Contamination on the fixture prevents ferrules from protruding equal distance from the base of the fixture. This mainly applies to fixtures for polishing ferrule only (as opposed to connector polishing).  The ferrules must protrude the same amount from the bottom of the fiber optic polishing fixture, to ensure consistent pressure being applied to all ferrules.  Contamination at the top of the bore, where the ferrule flange sits on, will cause the ferrules to sit higher and protrude less.   If ferrules are protruding different length from the bottom of the fixture, this results in unequal pressures being applied to the ferrules during polishing, again resulting in variation in Radius values, FH values, and fiber end-face polish quality (scratches).

Fiber Optic Polishing Fixture Maintenance Ultrasonic CleaningThe most effective way to reduce the effects of such contamination is to thoroughly clean the fixtures between use, by rinsing with distilled water immediately after polishing, to prevent the “surry” from drying.   Even so, particularly with fixture having many recessed faces or “nooks and crannies”, it is good practice to give each fixture a more rigorous cleaning after use, when the fixture will be not be in use for some time (such as at end of shift).  Ultrasonic cleaning, in combination with brush-cleaning the bores, works very well for this type of cleaning, and it is recommended that cleaning be part of a daily Preventive Maintenance program for all fiber optic polishing fixtures.

Ultrasonic Cleaning:

Ultrasonic cleaners are a bath into which the object to be cleaned is submerged.  The bath is usually of distilled water, which can be augmented with detergents or solvents or other cleaners.  For cleaning of polishing fixtures, an ultrasonic bath of only distilled water is sufficient, and recommended over other solutions.

The walls of an ultrasonic cleaner vibrate and a particular high frequency, transferring pressure waves to the water. These waves have the effect of pushing-and-pulling the water molecules to create “cavitation”:  essentially “tearing” the water molecules apart, creating a very short-lasting “bubble” of vacuum within the water, which very quickly—and forcefully—implodes. The energy of this collapse, which occurs near the surface of the submerged object, is what creates the agitation to remove contaminates from the surface.

Because the cavitation occurs within the water medium only, it is important that the entire object be submerged, with no air bubbles trapped in areas to be cleaned.  As long as the surfaces to be cleaned are in contact with the water, and because the cavitation happens on the molecular level, the cleaning effect can reach into very small crevices and is ideal for fiber optic polishing fixture cleaning.

It is important to note that the cavitation is created by physical movement of the side walls of the cleaner, and that most ultrasonic cleaners are calibrated such that most of the cavitation power occurs somewhere in the middle of the bath.  It is important that objects to be cleaned are suspended within the bath water, and do NOT contact the bottom or interior walls of the ultrasonic cleaner.   Objects contacting the bottom or sidewalls of the cleaner will reduce their movement, and thus reduce the cavitation effect.

Following up the ultrasonic cleaning with brushing of the ferrule bores and blowing dry with clean, compressed air will help to ensure maximum life and performance of the fiber optic polishing fixture.

APC Polishing Advice to Improve Apex Offset and Angle Measurements

Of the two common ferrule shapes involved in APC polishing – conical and step – the step ferrule is by far the easiest in terms of controlling geometries. Step ferrules are more expensive than conical ferrules. However, from a purely process-control point of view, step ferrules are absolutely the easiest and best choice. If you are new to APC polishing, it is highly recommended to use step ferrules over conical. Step ferrules are less sensitive to minor process and material variations, and they are much easier to work with when it comes to developing and modifying polishing processes. Thus, using step ferrules results in significantly improved first-pass yields.

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 standards1. 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.

To understand APC polishing, it is helpful to start by reviewing PC polishing. The mechanisms at work affecting Apex Offset and Angle are the same, but it is simpler and more intuitive when describing PC polishing.

Apex Offset and Angles in PC polishing

Apex Offset is a fairly simple concept to understand in PC polishing. With PC ferrules, the intention is to hold the ferrule at a 0.0 degrees vertical angle during polishing (perpendicular to the polishing surface). As long as the ferrule is perfectly perpendicular to the polishing surface, the Apex (highest point) of the radiused endface will be the exact center of the ferrule, and Apex Offset value will be zero2 (Figures 1a and 1b).

The more the ferrule is angled away from perpendicular, the farther away the Apex of the Radius will be from the ferrule’s center – thus the larger the Apex Offset value will be. Apex Offset is directly proportional to the angle with which the ferrule was polished. In fact, Apex Offset and Angular Offset are two ways to express the same thing, they just use different units of measurement. (Apex Offset is measured in microns from the fiber center, whereas Angular Offset is measured in degrees from the fiber center axis.) Since Angular Offset is a common cause of Apex Offset measurement issues, polishing process engineers can identify the following as a general Geometry Process Rule:

All other factors being equal, the bigger the difference between the intended polishing angle and the actual polishing angle, the bigger the measured Apex Offset (or Angular Offset) value will be.

Furthermore, since the endface is polished with a radiused (domed) surface, we know that the surface angle of any two points along the curve will not be equal.That is, the Angle at my Apex point and the Angle at my ferrule centerline point can never be equal (Figure 3). (We’re assuming the dome created is perfectly spherical, which is unlikely in reality but is not relevant to our discussion.)

Here’s another important concept to keep in mind: The tangent angle at my Apex point will always be exactly the angle at which I held the ferrule during polishing. If I held my ferrule at exactly 0.4 degrees from perpendicular during polishing, this will produce an angle at my Apex point of exactly 0.4 degrees from horizontal. This concept is important to remember when we discuss APC polishing.

Apex Offset and Angles in APC polishing

All of the above also applies when polishing APC ferrules – the only difference is that, with APCs, we are intending to hold the ferrule at an angle to the fiber/ferrule axis during polishing (typically 8 degrees) instead of perfectly vertical (0 degrees). This introduces other factors that have significant impact on Apex Offset and Angle measurement values – namely ferrule SHAPE, end-face RADIUS, and KEY ERROR.

Note that Key Error is a major component of measured Apex Offset values. Key Error is the “rotational component” of Apex Offset. For example, if the adapter keyway slot in my interferometer is significantly wider than the key width on my APC connector, you can imagine it is possible for me to rotate the connector slightly during measurement, resulting in erroneous measurement values. It is a complicated topic to fully explain and is worthy of its own article. Because of this complexity – and the fact that Key Error problems are less common than Angular problems – I will not discuss Key Error in great detail in this article.

First, let’s look at ferrule shape. There are two common types of APC ferrules in terms of shape: conical and step.

The conical ferrule (Image 1), naturally, has a cone shape to the polishing area of the ferrule.  The step ferrule (Image 2) has as cylindrical shape to the polishing area of the ferrule.

How to Develop a Fiber Optic Polishing Process that Produces Consistent Results

Frequently, my customers ask for guidance to develop a fiber optic polishing process.

While there are many details to consider, the process comes down to 5 basic steps.

Note that this article focuses on single-fiber (and not MT) PC ferrules. While much of my advice applies to APC polishing, those connectors require additional considerations.

Step 1. Define your objectives, especially measurement criteria and process yields.

When developing a polishing process, it’s important to clarify your acceptance criteria and targeted yields – and have the ability to accurately measure and quantify pass/fail results. For example, do your polished ferrules need to meet an end-face geometry specification such as those specified in Telcordia GR-326? Also, virtually all polished fiber optic ferrule end-faces must meet SOME visual appearance specifications. What criteria will you use to determine if your polishing results are acceptable or not?

When developing a polishing process, I highly recommend that your initial targets are to meet GR-326 geometry requirements and IEC 61300-3-35 visual requirements – with a minimum yield expectation of 95% passing.

Step 2. Ensure you have the proper equipment.

Of course, it would be ideal if you are starting with all-new polishing equipment. The precision of polishing equipment dimensions (both the fixturing as well as the machine itself) play a vital role in determining your process capabilities. Properly maintained polishing machines should last for decades, so be sure to follow the manufacturer’s maintenance recommendations.

Polishing fixtures wear out more quickly depending, of course, on the amount of use. If you follow the recommendations below and still find it impossible to get acceptable results (particularly in Apex Offset), it’s very possible you may need to procure new fixtures.

Regardless of whether your customer or product design requires you to meet geometry specifications, it is HIGHLY recommended that you measure geometries during process development, using an interferometer. This is an expensive piece of equipment (typically $20,000 or more), but it is invaluable to developing a robust polishing process. If the cost is prohibitive, look into renting or borrowing an interferometer.

Be sure your equipment is capable of properly measuring what you need it to measure, particularly regarding visual inspection. For example, if you need to meet single-mode requirements of IEC 61300-3-35, does your microscope have a high-resolution system as defined within the spec? If you are inspecting APC ferrules, do you have an APC adapter for your scope, or just the PC adapter? (Unfortunately, it’s fairly common to find production lines inspecting APC ferrules with a PC adapter, which is improper. With the APC ferrule end-face at an angle to the microscope optics, the entire fiber end-face will never be in proper focus, making it very difficult to detect small defects.)

When developing a polishing process, be sure to use only brand-new rubber polishing pads. Rubber pads play a critical role in polish results and are often overlooked. Having a consistent hardness (durometer) across the surface of the rubber pad is CRITICAL in getting consistent polishing results. Rubber hardness will change over time, so rubber pads always need to be replaced periodically (once a year, at minimum).

Step 3. Conduct a trial run, following our recommended procedures.

Fiber Optic Center offers Recommended Polishing Procedures for Domaille and Seikoh Giken polishing machines – by far the two most popular polishing platforms used today. However, due to variations in ferrule material, connector design, and even in machine/fixturing dimensions, it is likely that you will need to modify some of the recommended machine settings. Use Fiber Optic Center’s recommended polishing settings as a starting point, and budget time to modify as needed based on your results.

Step 4. To adjust your process, start with a focus on Radius.

The ability to achieve desirable, consistent Radius values is critical to developing a fiber optic polishing process. Radius is the first geometry parameter to bring under control. Why? Because the Radius value is an excellent indicator of consistency in polishing pressure and the amount of ferrule material removed during the process – important factors that highly impact all results, including visual appearance and angle (particularly with conical-style APC ferrules). When all polished ferrules have an identical Radius after polishing, this indicates that all ferrules have undergone consistent polishing conditions.

After polishing a group of connectors, use the interferometer to measure geometry and focus on the Radius values. As a rough rule of thumb, a stable Radius variation on one plate of ferrules should be less than 2mm. If the variation is higher, you likely have a process issue or your polishing equipment is subjecting ferrules to varying pressure.

Generally speaking, the smaller your average Radius value, the smaller the deviation in results will be. It is usually a good idea to aim for the lower end of the Radius specification rather than the middle or upper end of the spec. For example, if the Radius spec limits are 7-25mm, you’ll usually have better and more consistent results if you target 10-12mm as opposed to 18-20mm.

How to decrease or increase Radius values:

Decrease Radius values by applying more pressure or using a softer rubber pad.

Increase Radius values by applying less pressure or using a harder rubber pad.

When your Radius values are under control, look at another key geometry parameter: Apex (also called Apex Offset). This reflects the angle of the polished end-face. If the Apex values are too large, this means your ferrules are being polished at an angle that is too large. All other conditions being equal, a smaller Radius value will generally result in a better Apex value. This is another reason to aim for an average Radius value toward the lower end of spec limits. If you’re already dialed-in on desired Radius values and the Apex values remain unacceptable, the cause is likely related to worn polishing fixtures or worn rubber pads. In both cases, the only fix is to replace the worn fixture or rubber pad.

Step 5. Conduct a visual inspection.

Your customers will require some type of visual inspection. (Clearly, you cannot ship a connector with a shattered fiber.) After achieving desired geometry values, measure the visual appearance of the end-face, looking for 2 types of defects: pits and scratches. Typically, pitting can be resolved by increasing time during the intermediate (diamond) polishing steps. Consistent appearance of a large quantity of fine scratches (the “skating rink” appearance) is likely due to insufficient time and/or pressure on the final polishing step. Sporadic appearance of a few scratches is likely caused by contamination, due to insufficient cleaning.

When developing a polishing process, carefully evaluate other major visual defects: shattered fibers, core cracks, no visible fiber, etc. In many cases, the cause of the defect is not related to your polishing process but rather to cleaving, product handling, curing temperatures, and so forth. These defects are real and need to be corrected, but you should address the root cause of these issues by preventing them from happening and not relying on your polishing process to remove large fiber defects, which only adds to the time, cost, and instability of your polishing process.

Final thoughts:

Cleaning is critical – The act of polishing removes material, similar to sanding wood. To prevent contamination, it’s vital to thoroughly clean the fixture and ferrules between every polishing step. Contamination causes scratching and will negatively impact visual yields.

Focus on preventive action, not corrective action – As you develop your fiber optic polishing process, I encourage you to implement a statistical process control system. For example, over time, rubber pads and fixtures will wear out, and yields will begin to degrade. Record the data, track it, and actively analyze it. This will help you to prevent problems rather than fixing issues after they occur. Watch the trends and take preventive action, and you’ll consistently see high yields.

How to polish fiber connectors – Fiber connector polishing Tips and Practices

How to make your fiber optic polishing work to be correct and how to revise your fiber connector polishing

When you polishing a fiber connector or several connectors in polishing holder, by fiber polishing machine or fiber polisher, there are procedures and setting parameters designed to leverage the machines best practices as well as previous developments and experience.

Additionally, there are tips to consider applying during daily production to improve first pass yield, efficiency and results to avoid scrapping costs.

The standard polishing process includes three steps:

Epoxy Removal

Geometry checking

Final Step: finishing the fiber connector end-face, check optical surface

Below we share tips for each step of the fiber polishing process:

Epoxy removal

Pre- Polish

When connectors are loaded on the polishing fixture or fiber polishing holder jig after cleaving, there are large, sharp edge fibers and inconsistent fiber protrusion due to different fiber cleaves.  This can result in fiber breaks if polishing, by machine, is started immediately.

Tip: start polishing the connectors loaded on the jig with SC Film mounted on the rubber pad and then by hand/air delicately, with little hand pressure making few rotations (around 10).  Next the fiber protrusion has more consistent length distribution over all ferrules resulting in less fiber breakage (fiber into ferrule bore hole).  After this initial operation, one can start polishing with the machine using the same film used for air polishing.

LC Conical

The available surface of the 1.25 mm connector is small and sometimes due to this limited surface, epoxy is also going to the base of the chamfer area that you cannot remove using the polisher.

Tip: After the epoxy removal step on the polisher, if some epoxy is still present on the chamfer area, use a little scalpel to remove residues. This will allow to move to the next step (Geometry) avoiding any contamination on D films.

For other types of ferrule (2.0 or 2.5 mm) it is a good practice to check, after epoxy removal, if all the epoxy has been polished away (checking the front face of the ferrules).

Fiber Polishing Jig Holder Locking Mechanism with Individual Ferrule

A fiber polishing fixture or holder jig where the ferrules are independently moving from the each other is called Individual Pressure Control (IPC) fixture and is recognized by the use of spring loaded adapters to lock and to keep the ferrule in place.

Tip: after checking if there are not any epoxy residues left, it is a good practice to verify if all the connectors are well positioned (same height) and if the spring of each adapter is working properly with the ferrule moving freely – not stuck due to polishing residue. This guarantees each ferrule will be under the defined fiber polisher pressure in the polishing steps offering more consistent geometry results.

Geometry Checking

Air Bubble Under Fiber Polishing Film

A common occurrence after positioning on the rubber pad is air bubbles under the fiber polishing lapping film.

When this occurs, it must be removed because during the geometry polishing process as the air cushion can modify the ferrule geometry (radius and/or apex).

Tip: to avoid this effect, use a roller to press down the lapping film on the rubber pad. It is important to have a different roller for each type of film to avoid contamination especially from D film to final film.  If one uses the same roller, it is essential to clean it before moving to the smaller film grid.

Tip: when using just one roller, to avoid contamination, take two films one on top of the other (one on top upside down) and then use roller. The lapping film that will used for polishing connector will not be effected by any cross-contamination.

Fiber Polishing Film Longer Life

Diamond fiber lapping film is the most expensive film we use on the polishing process and one consideration when selecting a supplier is the number of times you can use it.   There are fiber polishing films used for 10, 15, 25 times, or even longer depending on the process and specific customer specifications.

Tip: after a certain number of usage, typically 10 times, if you clean the surface with alcohol you are able to extend the life of this film (using alcohol removes debris from previous polishing).

VIEW: Diamond Films Product Matrix

Fiber Polishing Rubber Pad

In a polishing process, we use rubber pads typically 60 to 80/85 durometer.  Keeping consistent geometry can be a challenge.

In principle, a rubber pad that is too soft can help to reduce radius but effect negatively the apex.

Using a harder pad with higher pressure should be better to get positive radius and apex results.

Tip: always try to develop a process using pads with same durometer throughout the entire process. Changing the hardness of the fiber polishing pad will effect radius and/or apex and can make it difficult to bring both parameters within the specification.  Usually adjusting pressure and timing, using the same pad, can achieve desired results.  If you do need to change to a softer pad, decrease the durometer maximum by approximately 10 durometer.

Choice of APC connector holder/Jig According to Connector Style

In the market there are two different types of ferrules: Stepped and Conical.

As soon as you select the connector style, you need to consider the related fiber polishing fixture holder jig.

Tip:

Stepped Ferrule – require a jig with an APC angle of 8°

Conical Ferrule – require a jig with an APC angle of 8.3°

FINAL STEP

CLEAN, CLEAN, CLEAN

Scratches are a fiber optic assembler’s nightmare because if it occurs, they jeopardize all of the previous activities and are costly due to the waste of time and additional material.

Tip: each step requires good cleanliness to avoid contamination especially when you move from D film to Final polishing film.   Quite often this activity is underestimated but if you make this a priority, you can avoid costly issues.

Tip: use spray water to remove all the debris on the ferrule and mainly at the jig’s bottom surface.   Follow this by wiping the operation using Cleaning Wipes or similar paper moving from the center of the jig to the outside.

Final Fiber polishing Film Choice

In addition to the nice smooth surface, final film is extremely important to define the right fiber protrusion.  Based on the requested specification, you can choose different types of film that provide various results.

Tip: important to know the different specifications and what your requirement is: Fiber protrusion, Undercut, Flatness with respect to the Ferrule. Basically, fibers can protrude or stay below the ferrule surface according to the described parameter to guarantee the best fiber physical contact terminated in a connector.

Tip: if you don’t have access to different final lapping films, adjusting time and pressure, can also achieve specified results with some limitations.

Polishing-Tips-and-Best-Practices-for-Single-Fiber-Connectors-fig-1

Fiber optics requires physical contact between the two mating parts because if you have an air gap between, it will cause high back reflection.  The physical contact will happen when you have fiber protrusion but considering the compression force made by the connectors, you could have some physical deformation of the fiber and ferrule.  When that happens, there is physical contact with flat and undercut if the related values are according to the specified parameters.

One might ask, why not only use protruding fiber and the answer is that concern is about fiber breaks when the two fibers are pushed against the others?   They specify undercut or flat fiber vs. end face the ferrule to better protect the fiber but still having physical contact.  It is clear the parameters have to be according to the specifications (as seen on the graphic) otherwise you will experience air gap.

Polishing-Tips-and-Best-Practices-for-Single-Fiber-Connectors-fig-2

CONCLUSION

Hundreds of fiber optic patch cable assembly facilities around the world use Fibermart’s Fiber polishing films, including multiple Fortune 500 companies. Fibermart has polishing process technical experts on staff as well as lapping film experts.

Please note a few of our resources whether you are implementing a new polishing process, fine-tuning your process to ensure it produces repeatable results, or looking for help to resolve a polishing issue by writing to us: sales@fiber-mart.com or support@fiber-mart.com

Proper Care of Polishing Fixtures for Optical Fiber Polishing Machines

In fiber optic cable assembly, the polishing process is perhaps the most critical step to assure high-quality assemblies that meet specifications. That’s why it’s important to select the right optical fiber polishing machine – and polishing fixtures – that meet your needs. Depending on your cable assembly house product offerings, it’s likely that you have several polishing fixtures to produce different connector styles.

The quality of the polishing fixtures (also called polishing plates or jigs) is extremely important to your company. Considering the high cost of production equipment and components, your company will want to maintain these tools to produce a high volume of products with minimal quality issues over the long run.

Proper maintenance of polishing fixtures is absolutely essential

Polishing fixtures for optical fiber polishing machines are built with high-precision machining equipment. Fixtures made of steel and aluminum can flex and warp over time, which will negatively impact your polishing process and product quality. On the other hand, polishing fixtures made of hardened stainless steel avoid this wear effect. However, hardened stainless steel contains more iron in the alloy, so this does increase the risk of rusting. This is a key reason why proper maintenance is so critical.

In addition, the most common fiber optic connectors (SC, LC, and E2000) are locked onto the polishing fixture with a plastic latch or clamp, which can wear over time if not properly cleaned. Poor cleaning techniques can also prevent proper locking. This can significantly impact the polishing machine’s functionality and, therefore, product quality.

Polishing fixtures are expensive – this is a bottom-line reason why proper maintenance is so important. With daily maintenance, you can use your polishing fixtures for a long time with no variation in the quality level of your fiber optic cable assemblies.

Follow these 8 steps to clean and maintain your polishing fixtures

Whether your company is just starting to manufacture fiber optic cable assemblies – or you have years of experience – we recommend you rigorously follow these guidelines to properly clean and maintain your polishing fixtures.

It’s better to clean every day for 5 minutes rather than clean once a week for 30 minutes. In fact, we recommend you integrate a cleaning procedure throughout the daily polishing process. Cleaning the fixtures should be a regular task – and a priority – in your polishing process.

Use distilled water, because it doesn’t contain abrasive minerals. Do not use tap water – regular drinking water is different all over the world. Your company’s tap water may contain iron minerals that tend to adhere to the polishing fixture. Also, do not use alcohol. At Fiber Optic Center, we recommend the Air Cleanse Cleaning Wand. This hand-held cleaning wand has an integrated pressurized fluid and filter system for a debris-free cleaning operation. You can use the wand to clean any brand of polishing machine and fixture. Click to read the datasheet for the Air Cleanse Cleaning Wand from Domaille Engineering.

The ferrule holes (and for MT style fixtures the ferrule slots, surrounding surfaces, and top clamps) can be cleaned using dental brushes and particle‐free, distilled or deionized water. Again, do not use alcohol. We recommend using a 1.25mm nylon brush (purple-handled brush) for fixtures with 1.25mm diameter ferrule holes. Use a 2.5mm nylon brush (blue-handled brush) for fixtures with 2.5mm diameter ferrule holes. Either one will work fine for MT style fixtures.

Clean the fixture while it’s still wet from the polishing process. This makes it easy to remove the polishing debris.

To clean areas where a brush can’t reach, use an ultrasonic bath. When using an ultrasonic bath, you must change the deionized water every day. Otherwise, debris could contaminate the polishing fixture. (Again, here is the link for the Air Cleanse Cleaning Wand datasheet.)

If you have a fixture with a cam-lock interface, pay special attention to the spring slits. These are very narrow and debris can easily build up, causing the metal to flex less and interfere with the spring functionality.

After cleaning the polishing fixture, it’s important to dry it thoroughly to avoid rusting. This is especially true for polishing fixtures made of hardened stainless steel.

Over time, your polishing results may change, and the reason could be directly related to natural wear of key interfaces of the polishing machine and fixture. The EZ-Check Precision Wear Gage Kit provides precise measurements for the polishing machine mandrel, fixture mounting hole, and ferrule holes. We recommend incorporating this wear gage kit into your process control system. Call Fiber Optic Center to determine whether this tool works with your polishing machine and fixture.

Fiber Optic PC Connectors: Single-channel vs. Multi-channel

Over the past 30 years, fiber optic technology has spanned its commitment constantly with, even more, endeavors nowadays to meet the ever-increasing networking bandwidth for high-quality Internet applications. In these applications, fiber optic connectors, serving as mousetraps, are used to couple the source, receiver and other components to the fiber optic cable. Fiber optic connectors generally use either physical contact (PC) or expanded beam technology. This article mainly discusses PC connectors from single-channel and multi-channel aspects.

It’s necessary to figure out what PC connections are first.

What Are PC Connection?

A PC connection is accomplished by terminating the optical fiber into a precise ceramic ferrule. The tip of the ceramic ferrule is polished in a precise manner to ensure that light enters and exits at a known trajectory with little scattering or optical loss. In achieving PC connection, there are two requirements for a cleaved fiber end face for PC connection. One is that the fiber end face inclination is less than 0.6°, and the other is that there is no mist on the end face.

PC Connector Types

There are countless single-channel and multi-channel fiber optic PC connector types available for telecommunication and data communication industries.

Single-channel Connectors

PC connectors are characteristic of directly mating and polishing fibers by utilizing tight tolerance ferrules and alignment sleeves and/or mating pins. This ceramic-ferruled technology permits reliable optical performance, with several designs becoming widely used as industry standards. Typically, these connectors are single fiber solutions with plastic shells. FC and ST connectors are becoming less popular but are still used in instrumentation. LC and SC connectors are commonly used in the telecommunication industry.

As a push-pull connector, LC connector, licensed by Lucent Technologies, provides a pull-proof design and small size perfect for high-density applications. It’s available in simplex or duplex versions, widely used in 10Gigabit, 40Gigabit, and 100Gigabit applications. Like Cisco QSFP-40GE-LR4 transceiver, QSFP-40GE-LR4 listed on Fiber-mart.com establishes 40Gigabit Ethernet (GbE) links with this duplex LC connector for 10km maximum link length over single-mode fiber (SMF).

SC connector, developed by Nippon Telegraph and Telephone (NTT), is recommended in the TIA/EIA-568-A Standard for structured cabling. It’s also available in simplex or duplex versions, typically used in Analog CATV (Cable Television) and other telecoms applications including point to point and passive optical networking.

Multi-channel Connectors

Multi-channel connectors house multiple fiber optic termini in a precision insertion. The termini can be configured as a pin/socket combination or genderless. MTP/MPO connectors belong to PC multi-channel connector.

The US CONEC MTP is an MPO compatible connector that exhibits quick and reliable connections for up to 12 fibers in a very small form factor. Just like LC connector, 40G links are likely to deploy this kind of MPO-12 connector for high performance. Take Cisco QSFP-40G-CSR4 for example, this QSFP-40G-CSR4 transceiver sets up 40G links in 850nm multi-mode fiber (MMF), with MPO-12 as its connector.

Optical Performance

Both single-channel and multi-channel PC connectors have optical performance characterized by return loss. The return loss of the connector is a measurement of how much light is reflected back at the connector interface. It’s affected by alignment, contamination, and polishing. For example, if the mating faces of the two fibers are not parallel, some energy reflects back to the source. Additionally, contamination at the mating interface causes reflection and scattering of light. What’s more, a poor polish may create an end-gap separation or an end angle.

Featuring by the tightest tolerance ceramic ferrules and alignment sleeves, coupled with the highest quality termination and polishing procedures, PC connections are able to deliver unrivaled optical performance.

Conclusion

Fiber optic connectors make quick fiber connection and efficient light transmission possible, gaining more and more popularity among their users. Fiber-mart.com offers hundreds of fiber optic connectors, such as FC, D4, DIN, MU, the MTP/MPO ST, SC and LC, as well as their related optic modules (eg. QSFP-40GE-LR4 and QSFP-40G-CSR4 mentioned above). You can visit Fiber-mart.com for more information about fiber optic connectors.

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