What are the best methods and tools for testing fiber attenuation in the field?

Attenuation is the most important measurement because it determines how much light gets to the end destination. Too little and it's too faint to interpret, too much and you can burn out the receiving optic. While some attenuation is unavoidable as the light travels over the glass, things like splice points and connectors also contribute to loss. So in essence, having poor splices or dirty connectors directly impacts the distance the signal can travel. Attenuation is measured in decibels (dB) but many people don't realize that it's a logarithmic scale. Every -3dB of attenuation equates to a 50% reduction of signal strength. At -30dB for example, the signal is 1/1000th of what it was when it left the transmitter. Clean your ports.

An insertion loss by a power meter( Source and receiver) thats referenced for the correct fibre will give the most accurate loss over a distance. An OTDR will give an indication of individual losses including all spliced fibres throughout the overall length of the fibre including , traumatic events ( damaged cable micro and macro bends etc ) , And obviously worked out along with the light loss for specific cables and fibres used .

Although as you say ILM is one of the most important tests you can provide on a system, RL is equally important, especially in today's systems where laser TX can be compromised especially if power is reflecting back. Understanding that too much power in either direction can be as bad on a system as the loss (dB) typically loss/reflection is one of the biggest culprits so you could argue a scope is equally important.

I think having initial OTDR and OLTS testing performed prior to putting a circuit into active production is vital-crucial in establishing operational benchmark readings associated with any channel. This provides several benefits. 1. Benefit #1: It helps provide a guidance or an established initial reading, (bench mark), for that channel/circuit to compare with for future scheduled maintenance or potential restoration MTBF-MTTR operational-network impacting events, SLA requirements with customers and other applicable stakeholders. 2. Benefit #2: It helps with any potential BERT/packet error related issues associated with isolating/troubleshooting and establishing the necessary steps or courses of action to fix that OSI related problem.

La atenuación de la fibra óptica debe verificarse mediante mediciones tanto en la construcción, pruebas de aceptación y durante la operación y mantenimiento del enlace óptico. Esta medida es la más importante de un enlace óptico, porque permite asegurar que la fibra óptica tiene un valor de atenuación en decibelios (dB) menor al presupuesto óptico de diseño (OLB – Optical Loss Budget) que asegura que el receptor óptico seleccionado para el enlace pueda recibir el valor de potencia óptica (dBm) dentro del rango óptimo funcionamiento, para el cual está diseñado.

The OTDR does not measure the attenuation, but the backscatter, this is then converted into attenuation. so if the Backscatter value is not set correctly the attenuation will not be correct. today we have so many different types of fibers with different backscatter values, so if we want better measurements we must measure in both directions and take the average

There are a number of ways, we can measure fiber attenuation. 1. Using an optical source meter and power meter set to test absolute link loss 2. using the actual equipment being used as transmitter and receiver to see how much attenuation the signal experienced to reach from transmitter to the receiver. This will also give us absolute link loss 3. finally test using and OTDR (Optical Time Domain Reflectometer). This test will measure estimate link loss however, it gives us actual picture of complete links and different points along the way where attenuation is faced. Therefore, this method is used for detailed link troubleshooting

If you want to measure the attenuation of a fiber you must use an optical light source and optical power meter (OLTS), placing one in the start of the fiber and the other on its end, as long as you have already calibrated them. This is the most accurate way to measure the attenuation. You can also use an OTDR to get an attenuation measurement but that will be only indicative and not that accurate. Of course OTDR will show you much more than just attenuation, like fiber length and any events (splices, reflections, connectors, splitters etc.) along the fiber path. In order to have a clear view of the fiber quality you need to take both measurements OLTS & OTDR bi-directionally.

Un OTDR est utile pour analyser notre liaison fibre optique si et seulement nous avons les compétences et la maîtrise sur le calibrage. En fonction du problème qu'on voudrait résoudre certains paramétrages de l'OTDR doivent être considérés. Distance, pulse, le temps de mesure....

La medida de atenuación de la fibra, debe efectuarse con el método LSPM, es decir inyectar en un extremo una señal óptica a la longitud de onda de trabajo (ejem. 1310nm, 1550nm) con una fuente óptica (LS) y en el otro extremo medirlo con un medidor óptico (PM). La diferencia de potencias (dBm) en será el valor de la atenuación (dB). También se puede usar referenciar el PM para obtener directo en dB, lo mismo se puede hacer con el conjunto OLTS (Optical Loss Test set) para una medida directa en dB. Para caracterizar la atenuación a lo largo de la fibra óptica, es decir para conocer las atenuaciones en los tramos y puntos se usa el reflectómetro óptico en el dominio del tiempo (OTDR)

The OTDR shows you where the event are, gives you an approximate loss value, and the possibility of finding bends or stress in the installation, In PON systems using 1650 and a filter(or live port), means you can measure without affecting the other customers using other wavelengths

An off wavelength WDM like 1625nm coupled to an OTDR with the same wavelength can be used without disruption of the channel. Use of this configuration or the use of a dark fiber in real-time in a system can detect breaks and intermittent events instantaneously. An OTDR coupled with proper software and optical switching can perform continuous system sweeping.

An OTDR is a master tool used to test the health of an optical link and pin point almost exact location of different events or losses which contribute to overall link loss. We can use it to calculate attenuation for the whole length of the fiber and compare it with the standard to determine the health of the fiber, know losses incurred at each splice and connector along the way and find out it any unwanted pressure points exist on the link which are resulting in high link loss. Further, it gives the freedom to test from one end and longer lengths depending upon the model of the OTDR, saves time while finding and localizing the fault location.

I think this depends greatly on the scope of work involved and what you are ultimately trying to accomplish. OTDR: Provides a quick, effective, efficient way of trouble shooting and giving you a rough estimate of what the loss or attenuation is associated with any particular optic fiber permanent link, channel or circuit. Of course OPM, VFL and a light source detector are other tools that are vital for troubleshooting as well. OLTS: Are in my opinion is what should be used at helping provide a true measurement of; system loss, insertion loss, attenuation, polarity and continuity associated with any given Layer #1 optical fiber circuit, permanent link or channel.

Solo el OTDR permite caracterizar a la fibra óptica, es decir, conocer sus características de atenuación a lo largo de la fibra óptica, por ello podemos conocer la atenuación en los tramos de fibra y atenuaciones puntuales (acoplamientos, empalmes, macrocurvaturas, splitters). Otra ventaja del OTDR es que permite medir a la fibra óptica sin desconectar el servicio, si antes se ha colocado un acoplador WDM para poder medirlo con una señal óptica diferente a la longitud de onda de trabajo, generalmente los OTDR traen un puerto activo para este tipo de medidas a 1625 o 1650 nm.

In some cases, an OTDR has challenges interpreting multiple events in close proximity, like a bridge cable between splice cases in the same vault. When they’re close together, the reflections can overlap, creating a composite signal that might show a high loss even if each individual splice or connection is in spec. Adjusting the pulse width can help improve the resolution and accuracy for those specific situations. Be careful when reviewing test results though because this feature can also be used by an unethical tester to crank up the pulse width and hide bad splices. You have to make sure you check the settings a test was performed in along with the event results.

To use the OTDR properly, you need to have skilled staff members, otherwise the results may further confuse you while troubleshooting. an appropriate configuration according to the link length is necessary to get accurate results. They are expensive and you may need to get different models for different kind of networks like long haul, metro or GPON etc.

Correctly trained engineers and correctly setup OTDRs. A good understanding of how the OTDR works will help with trace analysis.

the first challenge is making the correct settings, the different auto modes can help here sometimes, but analyzing is the hard part . The OTDR only see reflective and non reflective events, and we have connecters- UPC and APC, splices , fusion and mechanical, so it transforms the reflection values into an event, and many times messes up fusion splices and APC connection, this is where the good OTDR analyzer (technician) , finishes the job, and does not rely on the red cross or green tick

For Fiber attenuation, you ALWYS want to use an OLTS( optical loss test set) that incorporates a power meter, and light source as this provides the most accurate measurement for fiber losses. OTDR too can measure attenuation but that’s based on back scatter calculations, and is not a very accurate measurement of actual loss.

The launch cable should always be used, it is not simply a recommendation. The launch cable allows the OTDR trace to "settle down" after the test pulse is sent. The large events one sees in analysis is caused by the crosstalk between the instrument and the reflectance from the connector attached to the OTDR. Additionally, the launch cable provides a reference connector for the first connector on the cable to determine its loss.

A properly trained team of technicians is crucial for having a well tested network. Some of the newer remotely adjustable parameters also helps eliminate improper tests taken with the wrong settings. Splice detection threshold vs max splice loss is one example of settings that can be changed by an ignorant technician that can drastically impact the test results.

-use launch cable and receive cable -clean ports before and after -experiment with OTDR setting to find the best for this specific fiber you are testing -If trace quality you are getting is poor, try to increase the measuring time -measure with more than 1 wavelength. Bad splice with more loss at 1310nm, while micro bend with more loss at 1550mn -For long reach fibers you may have to take several measurements with different settings to have a clearer view of specific part of the fiber. Higher analysis settings for first 30Km, Lower analysis settings for last 30Km and something in between settings for the middle 30Km -Utilize automated OTDR features to help you but never rely entirely on that

Felizmente ahora se puede contar con la posibilidad de conectar el OTDR a internet y poder ver las mediciones en tiempo real sin estar en el campo, mediante esta funcionalidad podemos disminuir la posibilidad de falsos positivos/negativos por una mala configuración y a la vez tener reporte en tiempo real de lo que sucede en campo. Por otro lado la documentación de la red es de lo más fundamental y que contenga la bitácora de acontecimientos para realizar comparativas entre otros.