Over-attenuation: Over-attenuation can result in a signal that is too weak, leading to a low SNR and inaccurate measurements. The basic types of optical attenuators are fixed, step-wise variable, and continuously variable. Under-attenuation:. Transmitter power (TP) = 3dBm Receiver maximum optical input power (MP) = -6dBm Total losses (TL) = 5dB Minimum attenuation required = MP + TL – TP = -6dBm + 5dB – 3dBm = – 4 dB At a minimum, a 4 dB attenuator is required. However, an attenuator with a larger value could be used as long as it did. Optical Signal Attenuation is the single greatest factor limiting the distance and performance of your network. This loss happens due to a variety of factors. It is measured using decibels (dB).