Insertion loss (sometime referred to as attenuation) is the primary performance factor in fiber optic transmission. Measured in decibels (dB) using an optical loss test set that compares the power of the source signal to the power available at the far end, insertion loss is essentially the amount of power that an optical signal loses as it travels down the fiber. If too much of the signal is lost, the receiver at the far end will not be able to decipher the signal and the link won’t work.
Industry standards specify the maximum length and channel insertion loss for a given application. As transmissions speeds have increased, those limits have decreased. For example, 10GBASE-SR runs on up to 400 meters of multimode fiber with a maximum channel insertion loss of 2.9 dB compared to 100GBASE-SR4 that is only supported on up to 150 meters with a maximum loss of 1.5 dB. And it keeps getting more difficult—the latest 400GBASE-SR8 application is only supported up to 100 meters of multimode fiber to maintain adequate loss performance.
With today’s more stringent loss budgets, we thought we’d take a look at some of the ways you can reduce insertion loss to help ensure maximum performance.
#1 – Keep it Clean
As we discussed in our last blog, contaminated fiber end faces can cause insertion loss. Any tiny speck of dust will block some portion of a light signal from properly transmitting through the connection. That’s why it’s very important to use the right fiber cleaners and techniques.
#2 – Watch Your Bends and Tension
Another cause of insertion loss is the micro and macro bending of fiber that can occur during installation. Macrobends are typically caused by not maintaining the maximum bend radius when routing fiber cables through pathways and cable management. Microbends are bit trickier—these bends are typically cause by placing too much tension on the cable when pulling and can go unnoticed upon initial testing but worsen over time. Microbends can eventually cause the glass to crack, preventing signal transmission altogether.
#3 – Reduce Length and/or Number of Connections
In addition to the overall length of a link, insertion loss is also caused by any connector, splice, or splitter along the link. That’s why data center designers create their insertion loss budgets based on the length and number of connections in a channel. While concatenated links are commonly used in the data center environment, having too many connections can push the loss above the budget. Even if the loss falls within the application limits, there needs to be enough headroom to account for loss caused by contamination and bends.
Especially in longer links, designers may need to consider using interconnects for distributing fiber from equipment rather than cross connects to reduce the number of connections. As shown below, using cross connects at both ends of the channel adds four connections, while using an interconnect at one end results in a 3-connector channel, using interconnects at both ends results in a 2-connector channel, and using a direct switch connection for breakout applications results in a 1-connector channel. Additionally, splices typically have less loss than connectors, so where there are permanent connections that won’t change (such as where incoming service provider fiber comes into the data center), fusion splicing may be the way to go.
#4 – Use Innovative Technologies
In duplex applications, it’s common to use plug-and-play MPO-to-LC cassettes at fiber patch panels with MPO trunk cables between panels. These cassettes are also often used in breakout applications to transition from a high-speed parallel optic application to multiple lower-speed duplex applications, such as from an 8-fiber 100GBASE-SR4 switch to four duplex 25GBASE-SR servers (i.e., 4X25). However, these cassettes include the loss of the MPO connection at the rear and the LC connection at the front. But there is one innovation that significantly reduces the loss associated with cassettes—our HDReadyLink™ integrated cassette trunks that are part of our HD8² Ultra High Density Solution.
What’s so special about these cassettes? Because the HDReadyLink cassettes integrate the cassette and trunk into a single component, the MPO connection at the rear and its associated loss are eliminated as shown below. This allows for more connection points and/or more insertion loss headroom within a channel.
#5 – Choose Quality Components from Quality Vendors
Last but not least, insertion loss can be reduced by using quality components. Let’s face it; fiber cabling and connectivity varies from vendor to vendor. While most reputable players in the industry use quality components, there are others out there selling cheap, low-quality assemblies that may have higher insertion loss due to poor connector end face geometry, misalignment, or lack of mechanical reliability. So be sure to know who you’re buying from.
At CablesPlus, we are fully committed to providing the highest quality fiber optic connectivity solutions. That’s why we only use only premium-grade low-loss components like Senko and US Conec connectors.