# Using alternative fibers

If you are using alternative fiber or fibers, you need to be aware of the following:

- You will decrease the coupled optical-transmit power of your Ringnode if the core diameter of your fiber is LESS THAN 62.5mm and its nominal numerical aperture is LESS THAN 0.275. More light will be lost at the Tx connector.

- You will increase the optical-transmit power of your Ringnode if the core diameter of your fiber is GREATER THAN 62.5mm and its nominal aperture is GREATER THAN 0.275. Less light will be lost at the Tx connector.

- You could affect the optical-receive sensitivity of your Ringnode, although the Rx connector on your Ringnode is big enough to capture most of the light coming out of even the biggest fiber.

The following table summarizes the potential effect on the optical-power budget of using the alternative fibers described above. (The figures in the table are relative to the 62.5/125mm fiber that we recommend.)

Fiber size (Core cladding) | Adjustment to optical-transmit power dB | Adjustment to optical-receive senitivity dB | Adjustment to optical-power budget dB
50/125 NA=0.20 | 00 to -5.0 | -1.0 to 1.0 | -6.0 to 1.0
85/125 NA=0.26 | 1.0 to 2.5 | 0.0 to -1.0 | 00 to 2.5
100/140 NA=0.29 | 2.0 to 4.0 | 0.0 to -1.0 | 1.0 to 4.0