When utilizing optical fibers for high-speed communications applications, there two primary categories that fibers are grouped into, based on their construction and intended applications. In this article, we will review both Single Mode and Multimode optical fiber classifications, providing a quick introduction to both types and their key differences.

OFS recently made a splash when they announced a new hollow-core optical fiber optimized for low latency transmission.  While hollow-core fibers have existed for about 20 years, it is exciting to see such an innovative and promising fiber technology being more broadly applied to commercial applications. 

This year’s OFC conference in San Diego will be another showcase of innovative new and future technologies.  With fiber optic communication and networking equipment continuing to evolve, testing procedures and setups must also grow and change as part of the process.  Engineers are then often faced with a challenge - how can they continue to add and integrate new systems and the appropriate connectivity infrastructure in a finite amount of lab space?  While some may benefit from new facility expansions, the luxury of additional square footage and rack space isn't often the case for most.

As we enter the last quarter of the year, businesses are starting to or continuing to plan and budget for the upcoming year.  This may mean new investments, new equipment and other upgrades in technology or infrastructure to support and position the company to be competitive and successful in the upcoming year.  

Fiber optic attenuators are used in networking applications where an optical signal is too strong and needs to be reduced. There are many applications where this arises, such as needing to equalize the channel strength in a multi-wavelength system or reducing the signal level to meet the input specifications of an optical receiver. In both scenarios, reducing the optical signal strength is necessary or else system performance issues may arise.

In the previous article, I briefly explained and compared two types of optical sources used in transmitters: LED and LD. Today, I am going to discuss what happens at the other end of a fiber link -- detectors. Optical detectors, as the name implied, can detect the amount of light received. Our very own eyes are a pair of detectors as they can receive light information with the retina and transmit that light data to our brain. In the visible light spectrum, our eyes are great detectors to inspect fiber break or light leakage. However, most fiber works in the invisible wavelength spectrum where human eyes won't be able to see. That is the where the optical detectors come in .

 Under the ideal environment condition, the primary fiber attenuation in single mode fiber comes from intrinsic characteristics of the glass and is usually less than 0.2 dB/km. However, when the fiber is exposed to high radiation environment for an extended period, for example in a nuclear facility, the fiber's Radiation-Induced Attenuation (RIA) will accumulate and become fiber's dominant source of loss as the electrons are trapped in the glass due to ionizing radiation. It also takes time for the fiber to recover from the radiation after the radiation source is removed. Depending on the temperature, radiation doses, and radiation sources, the fiber may or may not recover to its original state.

Graded-Index Fiber, also known as G.651.1 under International Telecommunication Union (ITU) standards, is a type of fiber whose refractive index decreases gradually as the radial distance (distance to the core center) increases. In comparison, what we commonly have seen is G.652.D fiber which has a step-index refractive index profile. This article will compare graded-index multimode fiber with traditional step-index fiber, as well as its advantages when dealing with modal dispersion, a common signal distortion error.

The graph below shows the different refractive index profiles of the fiber core and cladding.

An important factor in the performance of fiber optic communications systems, chromatic dispersion is a topic and performance characteristic that is important to both understand and account for when operating and/or designing equipment for fiber-based networks.

When the time comes to buy spools of optical fiber for testing and demonstrating communications systems, there are a few items to consider that will help ensure you end up with an ideal setup.  Since it has been proven that following a few best practices will help you get the most out of your fiber, thinking about these four important items in advance will allow you to further qualify your needs as well as speed up the purchasing process.