Decibel units: dB and dBm

Decibel units are often used in fiber optics and lasers(dB), defined as shown in the following table. Due to the use of logarithmic properties, larger values can be converted into smaller numerical representations. When the ratio R=1 is equivalent to 0dB, and when the ratio is less than 1, it is expressed in negative decibel units. The decibel unit is most commonly used to express the relative power ratio, such as the loss of the optical fiber, the insertion loss of the optical fiber device, the gain multiple of the amplifier, etc. When 1mW is used as the reference power, the decibel unit of absolute power can be described in dBm, as defined in the following table. dBm can be used to describe the laser transmit power, amplifier output power, and detector received power. When the system loss and gain are described in dB, and the absolute value of optical power is described in dBm, the description and analysis of the entire system become very convenient.