| Following is a discussion of light loss budget for our fiber-optic
devices. For further details, please consult Doug Belli of NIPG
(kali::DBelli).
+---------------------------+
| Fiber Optic Loss Budget |
+---------------------------+
The following figures represent the calculated loss budget for fiber optic
segments used to interconnect the following devices:
DECRepeater 90FA (DEFAR)
DECRepeater 90FL (DEFMR)
DECBridge 90FL (DEWGF)
DECrepeater 90FS (DEFMI)
DECrepeater 900FP (DEFMM)
These figures account for the connectors at either end of the segment.
Furthermore, these figures are calculated using the transmit and receive
optical power levels of the above equipment. When connecting to or from
different devices, the transmit and receive optical power levels of the
other devices must be taken into account.
10-Base FL Worst-case Loss Budget (0 to 50 degrees C, end of life)
------------------------------------------------------------------
Multimode, Graded
Index Fiber Size (um) 50/125 50/125 50/125 62.5/125 85/125 100/140
Numerical Aperture
(NA) - 0.20 0.21 0.22 0.275 0.26 0.30
Minimum Average
Transmit Power (dBm) -22.8 -23.3 -22.9 -19.0 -16.8 -13.5
Minimum Average
Receive Sensitivity (dBm) -32.5 -32.5 -32.5 -32.5 -32.5 -32.5
10-BaseFL Loss Budget
(Pt,avg - Pr,avg) (dB) 9.7 9.2 9.6 13.5 15.7 19.0
FOIRL Compatibility
-------------------
The older 802.3 FOIRL standard specified a -27.0 dBm minimum PEAK receive
power (Pr, avg = -30.0 dBm). This power level represents a 2.5 dB lower
receiver sensitivity. The worst-case loss budget for FOIRL compatibility
purposes should include this decrease in receiver sensitivity and is given
below.
FOIRL Worst-case Loss Budget (0 to 50 degrees C, End of Life)
-------------------------------------------------------------
Minimum Peak
Transmit Power (dBm) -19.8 -20.3 -19.9 -16.0 -13.8 -10.5
Minimum Peak
Received Power (dBm) -27.0 -27.0 -27.0 -27.0 -27.0 -27.0
FOIRL Loss Budget (dB) 7.2 6.7 7.1 11.0 13.2 16.5
The older 802.3 FOIRL standard specified a maximum -9.0 dBm PEAK receive
power, Pr,peak (Max Pr,avg = -12 dBm), and a maximum -10 dBm PEAK launch
power, Pt,peak (Max Pt,avg = -13dBm). When calculating the loss budget for
FOIRL devices, a concern is that the higher output from the DEFAR, DEFMR,
and DEWGF, in conjunction with the increased launch power into the two
largest fiber sizes (85/125, and 100/140), does not overload FOIRL
receivers. The worst case numbers for FOIRL devices should therefore
include the maximum launch power figures, which are given below.
Best Case Maximum (Peak) Launch Power (0 to 50 deg. C, )
--------------------------------------------------------
Maximum Peak
Transmit Power (dBm) -12.8 -13.3 -12.9 -9.0 -6.8* -3.5*
* Additional attenuation is required when connecting the above devices via
short lengths of 85/125 micron and 100/140 micron fiber optic cable.
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