Fiber Optic Cable Assembly – A Look behind the Scenes
Fiber Optic Cable Assembly
– A Look behind the Scenes
Fibers as Thin as a Hair
In 1995, a customer asked if it was possible for LASER COMPONENTS to provide optical fibers equipped with SMA connectors. The company founder Günther Paul did not hesitate and agreed. That was the birth of fiber manufacturing in Olching. What began 25 years ago with cabling for printing systems has since developed into an important part of the company’s broad range of products. In the 2000s, fibers for powerful industrial lasers were added to the portfolio of data cables. As requests for medical technology increased, the company set up a class 7 cleanroom to meet the hygiene requirements of this industry. A short time later, the company also entered high-precision manufacturing (e.g., spherical lenses and end caps).
“Today, data transmission is just one of many application areas,” says Florian Tächl, product manager for the fiber components division. “As it stands, our assemblies are used in material processing, medical technology, and sensor technology, etc. We also frequently receive requests for plastic fibers for use in lighting applications.”
No Entry without Shoe Covers!
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If you want to see the production facility for yourself, you first must dress appropriately. Just behind the office of production manager Dr. Stefan Hanf, you enter a room that looks like a mix between an airlock and a coatroom. The area behind it may only be entered with a lab coat and plastic overshoes. Signs hang on the door: “Please use disposable gowns and shoes;” “No food!” “No open drinks!”
“This is not the cleanroom yet,” Hanf reassures. “But it is a clean area where controlled conditions prevail. Here, too, all contamination should be avoided as much as possible.”
Finesse is a Requirement
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First and foremost, the production manager would like to clear up a misunderstanding: “LASER COMPONENTS does not manufacture fibers. We assemble fibers that we receive from our suppliers. That means we use them to manufacture cables with connectors and protective sleeves.” In doing so, his employees must proceed with the utmost care because the material is very demanding. The thinnest fibers that they deal with are about as thick as a human hair. If you bend them too much, they will break. If the end surfaces get scratched, in the worst case the fiber is useless.
Assembly takes place in four steps. Each step has its own work area where all the necessary tools are ready to use. To achieve the desired size, the fibers are first cut – or rather broken – at the required length. Before they are fitted with connectors, the outer coating must be removed with special pliers called strippers.
“Connectorization is a critical point,” explains Stefan Hanf. “After all, the connector is the point where the light leaves the cable. If the wrong coating layer is glued on here, the connector is still contaminated, the adhesive has been incorrectly dosed, or the fiber is not quite centrally located in the ferrule, this can have serious consequences. In the worst case, the fiber will burn off. And I mean that literally.”
The two-component adhesive can change the optical and mechanical properties of the fiber. That is why every milligram counts here. The dosage is performed by a special device, which has been adjusted beforehand to precisely match the amount to the fiber-connector combination at hand. The connector end is then placed in the “oven” for several hours to harden. Here, too, the temperature depends on what the customer considers necessary for his application. In extreme cases, the temperature is turned up to 300°C.
Standardized Cleanliness
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Right next door is the entrance to the cleanroom. “This is where assemblies are made that are later installed in medical devices. However, the work steps are basically the same,” explains Dr. Stefan Hanf. LASER COMPONENTS’ quality management has been certified according to EN ISO 13485 since 2016 and thus fulfills all requirements for the design and manufacture of medical devices. This also includes the existence of class 7 and class 8 cleanrooms. In addition to the filtering system, so-called “smear tests” ensure that “colony-forming units” are neither present on the product nor in the cleanroom. If such microorganisms appear, the assemblies are no longer considered sterile.
“Our fiber assemblies are primarily used in products for invasive medicine,” says Florian Tächl, “where there are now many areas of application. These range from kidney stone fragmentation to metastasectomy in cancer patients to the sclerotherapy of varicose veins. Currently, we also have more inquiries from customers in ophthalmology (i.e., eye care).”
Routine with the Microscope
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Once the connector is assembled and the assembly is complete, the fiber ends can be equipped with an anti-reflective coating upon request. To do this, Hanf and his team use the coating equipment in optics production. All they have to do is carry the cables down the stairs.
Whether coated or not, every fiber is then checked. With routine hand movements, an employee clamps one connector after the other into the holder of the measuring microscope. A few quick adjustments and the image of the fiber end face appears on the screen, magnified 300 times. Now it can spot any minor damage and assess whether the assembly should be shipped. “This is a matter of practice,” explains Stefan Hanf. “This makes it possible for skilled colleagues to check around a hundred fiber ends in an hour. If someone doesn’t have the necessary routine, it can also take 20 minutes per fiber.”
Strict specifications apply to end face inspection: LASER COMPONENTS follows a strict zero-defect policy for uncoated fibers. At signs of the smallest imperfection, the assembly will be reworked. For fiber ends with anti-reflective coatings, irregularities in the coating can occur; thus, a different basis for evaluation is required. Industry standards or similar norms do not yet exist for this. Stefan Hanf and his team therefore borrow from the ISO standard 10110, which defines the tolerances for the coating of laser optics. “Of course, we work with different scales than our colleagues who coat optics,” explains the production manager, “but the principle is the same. We use the specification 5/C3×0.005, which means there can be a maximum of three defects of level 0.005. The grade number corresponds to the square root of the defect area. That’s extremely small.”
Simulated Industrial Conditions
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We deal with completely different orders of magnitude a few rooms away. Behind a door with a whole stock of warning signs is the laser measuring station where the production team checks whether the high-power assemblies that they produce can withstand the high demands of industrial applications. Next to the optical table are two devices: the smaller one is a powerful diode laser; the larger one is a cooling unit. From this you can see that high wattages are involved here. To be precise, the lasers cover two configurations that are commonly used in industry: Fibers with a diameter of 200 µm or more are tested at a wavelength of 980 nm for laser powers of up to 130 W of cw. In addition, tests with 50 W of cw are also possible for 100 µm fibers. The laser used for this emits at a wavelength of 914 nm.
For transmission measurement, the outgoing beam is detected using a laser power detector to determine whether losses have occurred during transmission. This measurement technology detects power deviations as small as 0.1%. Temperature sensors on the connectors can also be used to detect heat. If the temperature rises above 40°C, this is an indication that light has leaked out during transmission, which is converted into heat at the end of the fiber. This means that the fiber must be discarded.
Important Key Technology
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“When we started assembling fibers 25 years ago, there was no telling where this technology would lead,” says Dr. Lars Mechold, technical director at LASER COMPONENTS. “Today, fiber optics are one of the key technologies for many future markets. Accordingly, we must be broadly positioned in manufacturing to fulfill requests from various sectors. This also includes comprehensive product control and documentation. To maintain our high-quality standards, we need two things above all else: precise measurement technology and experienced, qualified personnel.”
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