907-0601-00 Rev. C Model 907 Video/Data Multiplexer – User’s Guide
Focal Technologies Corp. Page 7-2
7.2 System Design
One important component of the optical system design is to prepare a detailed flux (optical power) budget.
This calculation is a good indicator of the expected performance of the optical system and is useful when
selecting components and finalizing the optical design. Optical power losses in decibels (dB) for each
component are summed. This total system loss is subtracted from the difference between the transmitter
launch power and the receiver‟s sensitivity, as measured at the access bushings in the stacks, i.e. internal
WDMs and couplers are taken into account. Any remaining power is the optical power margin. Some margin
should be allocated for temperature and aging effects, typically 4-6 dB. Minimum flux budgets for 907-based
systems range from 16 dB to 26 dB available to the external cables, connectors, FORJs, etc.
For long cables, an additional 1-2 dB should be allowed for additional signal degradation due to pulse
dispersion. Component return loss (optical back reflection) is also considered when lasers are used in high
bit-rate systems, as optical back reflection can cause degradation in transceiver performance or introduce
optical crosstalk. To ensure optimum performance, the back reflection of the optical system should be less
than -25 dB.
An example flux budget calculation for a dual-fiber, 1310/1550 nm based system is provided in Table 7-1.
Table 7-1: Typical ROV System Flux Budget
0.4 dB/km @ 1310 nm, 0.3 dB/km @ 1550 nm
Rx Sensitivity for 1E-12 BER
Caution: Model 907 transceivers with high sensitivity receivers can be saturated, and therefore non-
operational, when too much power is received. All testing and operation of the 907 multiplexer system
should be conducted with a minimum 5 dB of attenuation to ensure optimum performance.
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