Fiber optics are increasingly being used in networks. There are many reasons for this, such as low susceptibility to interference, eavesdropping security or high data throughput. Nevertheless, with optical networks, attention must be paid above all to dirty or damaged plug connections. This is because a lack of cleanliness can lead to reduced network performance or even the failure of entire transmission links.
Dirt such as oil, fingerprints or adhesive residues on connector end surfaces of fiber optic connectors repeatedly lead to errors and quality losses on transmission links. Scratches and chipping during patch processes are also not uncommon reasons for impairment, leading above all to increased reflection, recognizable in the form of a reduction in transmission power or increase in return loss at the link transitions..
To prevent this from happening, connector end faces ideally need to be inspected before every connection - and at all stages of a fiber optic network's lifecycle from installation and maintenance work to troubleshooting in the event of faults. This inspection is not possible with the naked eye. At a minimum, a simple manual handheld microscope is required to inspect areas that are in the low micron range. In addition, further equipment is necessary to perform the correct cleaning.
Standard for cleanliness: IEC 61300-3-35
The International Electrotechnical Commission (IEC) has developed a standard for cleanliness for measurement technology in the form of IEC 61300-3-35. This standard is intended to ensure optimum insertion and return loss. With its different requirements for the quality of connector surfaces (SM-PC, SM-UPC, SM-APC and MM and multi-fiber connectors), a uniform level of performance can be guaranteed if the limits are complied with.
Yet, despite these specifications, many technicians are unable to produce meaningful measurements for compliance with the IEC standard due to their aptitude, inadequate measuring equipment, difficult lighting conditions, or varying display quality. To address these many challenges and ensure compliance with the standard, a video microscope is necessary in many cases. This can be used to automate the inspection of connector end faces. Softing IT Networks offers suitable video microscopes for its certifiers, the WireXpert or FiberXpert, and its qualifier, the NetXpert XG. These devices can easily evaluate the "pass/fail" criteria of the standard using analysis software.
Measurements in practice
A certifier plus video microscope is probably used for the first time during the assembly or installation of the network. The attenuation or reflection behavior is measured. Attenuation measurements are compared with fixed limit values of, for example, the individual components, while reflection measurements show events on the fiber optic link and at the same time require documentation of the link end surfaces.
These are viewed with the video microscope, as already described. Here, the different levels of damage and contamination are examined in four different zones radially around the center of the connector. The damage and contamination are specified for each type of glass fiber (MM/SM) in individual zones according to number, size and position relative to the fiber core.
Guaranteed IEC standard with video microscopy
Only automated inspection with a video microscope guarantees compliance with the standard and eliminates the uncertainties of manual inspection. This is because the creation of a documented proof of quality of the connector end faces creates a repeatable and reliable process. Video microscopy alone can deliver on the performance promises of a fiber optic network.
However, this test method must also be integrated into a larger process. The connector end surfaces are cleaned and tested alternately. The IEC standard also specifies exactly how the individual steps are to be carried out. For this purpose, there is a flow chart to clearly define good and bad plug connections and to ensure that the inspection is always carried out correctly by adhering to the flow chart. This ultimately prevents dirty or damaged plug connections from being connected to the network.