A good dBm value for fiber optic communication typically falls within the range of -3 dBm to -10 dBm. This range indicates a strong and stable signal with minimal loss and interference. Optical loss is measured in “dB” which is a relative measurement, while absolute optical power is measured in “dBm,” which is dB relative to 1mw optical power Loss is a negative number (like –3. 2 dB) while power measurements can be either positive (greater than the reference) or negative (less than. Positive dBm values represent power greater than $1text { mW}$, while negative values, which are far more common at the receiver end, represent power less than $1text { mW}$. Since dB is a ratio, it does not provide an absolute value of power.