Narrowband Digital Forward (NDF) refers to the digitizing of an analog portion of the downstream spectrum at the headend, sending the digital samples as payload in packets to the RPD, and then re-creating the original analog stream at the RPD. NDF supports services such as FM Broadcast, DAB+. What is used to measure light in fiber optics? Fiber optic power meters are used to measure microwatts (mW), Decibels (dB), and decibel milliwatts (dBm, which are some of the most common measurements of light in fiber optics. Decibels (dB): A unit of measurement of optical power which indicates. The NDF (fiber1) simulated had an attenuation of 0. 212 dB/Km and a negative dispersion of -2. This setup is simulated using fiber length of 100 km.