Boosting Fiber Optic Links

Boosting Fiber Optic Links

The need for faster data transmission rates is an ever increasing requirement for tomorrow’s data centers, local area networks and digital communication systems. By adjusting the fiber optic communication links you can manipulate the data transmission rate of your network. These links are made up of optical and electrical components. Both components are required to work together in order to provide adequate system performance. In other words, the whole link is only as good as its weakest link. Choosing the correct fiber in conjunction with the correct transceiver is critical to achieve the desired distance and bandwidth.

Did you know that there is more than 1 approach to speed up a fiber link?

Modulation Approach

By increasing the modulation rate of the transceiver (turning the laser or LED light source on and off at a faster rate) you can “squeeze” more bits of information into the same time frame. However, this increased speed complicates the transceiver electronics which can increase the energy cost of the data center.

Encoding Scheme Approach

Another way to increase the transmission speed is to change the encoding scheme to allow each transmission to hold more information. Typically, digital data (ones and zeros) are represented by two light levels, either on or off. By adding an additional symbol (light level) you are able to send more data in the same amount of time. This is called PAM4 (pulse amplitude modulation). PAM4 is an emerging method used to double the data rate of transceivers from 10 gigabites per second to 20 gigabites per second.

Parallel Optics Approach

In many cases, simply adding more fibers to the cable (also referred to as lanes) can multiply the effective data rate. This is call “parallel optics” or Space Division Multiplexing (SDM). For instance, a common way to migrate from two-fiber 10 Gbps systems to eight-fiber 40 Gbps is to use MTP/MPO 12-fiber cable assemblies and QSFP series transceivers. While the 4 middle fibers are not used, this method is able to greatly increase the overall transmission rates.

WDM Approach

Increasing the number of wavelengths on each individual fiber is an effective method to boost system transmission capacity. This method is commonly referred to as Wavelength Division Multiplexing (WDM). Different colors of light are transmitted over a single mode fiber for telephony and outside plant applications. In the past, WDM required expensive lasers and components. However, increased availability of short wavelength VCSEL lasers and multi-mode optional fibers has made this option much more viable and affordable.

Cisco has developed a 40 Gbps bi-directional (BiDi) short wavelength system (40G-SR-BD) that transmits two different wavelengths in opposite directions over a pair of multi-mode OM3 or MO4 fibers. Legacy duplex fiber cable plants can be used with BiDi transceivers without the need to install additional fibers into the plant.

Recently, wide band multi-mode fibers (WBMMF) have been developed to extend the reach of Short Wavelength Division Multiplexing (SWDM) multi-mode fiber systems and increase the transmission capacities from 10 Gbps to 40 Gbps and 100 Gbps. These fibers are optimized for use with the VSCEL lasers and operate from 850nm to 950nm. A SWDM industry alliance has been formed to promote a new TIA-492AAAE detail specification for WBMMF. The TIA-568-3.D spec will include a cable with WVMMF as the recommended medium.

Where is this all going?

We live in a world that is becoming increasingly more dependent on data centers, local area networks and digital communication systems. By increasing transmission rates, companies are able to share more information within a shorter period of time. Using the methods we discussed in this article a company can begin to improve its data transmission speeds.

In the future, new developments in Fiber Optics Transceivers and Multi-Mode Optical Fibers will continue to boost the transmission capacity of fiber optic links. These developments will provide solutions that promote the use of multi-mode fiber as a cost effective media for data centers.

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