How to calculate optical power budget?

The power budget is the difference between the output power of the transmitter and the input power requirements of the receiver.

Let’s as example calculate optical transceiver power budget for EDGE model CWDM-10G-SFP-40-27:

To calculate power budget we should use following formula:

Min output power - (receiver sensitivity) = Power Budget (dB)

For particular CWDM-10G-SFP-40-27 that would be:

(-3)-(-16) = 13 dB

From physical line perspective we should keep in mind following aspects:

Typical connector loss is:             0.5 dB
Typical splice loss is:                   0.5 dB

Typical fiber attenuation is:

1310nm                                      0.35 dB/km

1550nm                                      0.2 dB/km

Recommended Excess Margin:    3.0 dB

Please note that above mentioned physical aspects are only approximate. For exact numbers should refer to fiber, connector type and splicing method.

The different size fibers have different optical loss dB/km values. Fiber loss depends heavily on the operating wavelength. Practical fibers have the lowest loss at 1550 nm and the highest loss at 780 nm with all physical fiber sizes (for example, 9/125 or 62.5/125).