Practical Considerations for Implementation of Encircled Flux Launch Conditions in the Field
|Publication Date:||1 August 2013|
This Telecommunications Systems Bulletin (TSB) describes two methods for implementing light sources to fulfill compliance requirements for the EF launch condition. The EF guidelines can be used for field testing optical attenuation of installed multimode cabling for 850 nm and 1300 nm containing 50 μm and, when required, 62.5 μm graded-index fibers.
Since the most common high-speed applications currently run at 850 nm on 50 μm cabling, for dual wavelength sources it's best to align the launch condition to the 850 nm EF target, then allow the 1300 nm launch to fall where it may. In almost all cases, the 1300 nm response will remain within its EF template also. This approach reduces 850 nm launch uncertainty, possibly at the expense of the 1300 nm launch. Despite this trade-off, this is an improvement over other launch conditions.
Since the EF template is different for 50 μm and 62.5 μm cabling, two diffferent launch controllers are needed. One specific launch controller adjusted for 50 μm EF response and another one adjusted for 62.5 μm EF response are needed. This applies to all types of controllers used with single or dual wavelength sources.
The purpose of this EF launch condition is to provide:
1. Consistency of field measurements when different sources are used; reducing loss measurement uncertainty from greater than 40 % to less than 10 % on a dB basis.
2. A provisional worst-case launch condition for IEEE 802.3 (Ethernet) and INCITS T11 (Fibre Channel) compliant transceivers used in high-speed networks (≥1Gbps).
3. A template for compliance at the output of launch cords.
4. Comparable insertion loss of a single connection and/or splice at both 850 nm and 1300 nm.
5. Increased harmonization of a metric that defines multimode launch conditions for testing.
Although the focus of this document is to assist field personnel in understanding alternative EF launch condition implementation options, the concepts in this TSB may be applicable to certain lab testing situations where EF launch condition compliance is required.
Note: The source launch conditions are specified for the launch cord output. It is presumed that equipment, as supplied, has been verified by the manufacturer to produce the specified launch measured per TIA-455-203-A (FOTP-203-A) or IEC 61280-1-4 Ed. 2.0..