gure 4.1, the coupler, as well as the type of connector on the coupler, play important roles in creating an optical transmission system and are covered later in this chapter. Component Relationships An optical transmission system is similar to an electrical transmission system in that the power at the receiver must be equal to or above its sen- sitivity level to be recognized. By examining the power level of the trans- mitter, the receiver sensitivity level, and the attenuation level of couplers and connectors, we can determine the transmission distance possible prior to amplification becoming necessary. This may not appear impor- tant when installing fiber within the floor of a building; however, it becomes an important consideration for communications carriers as it pro- vides them with the ability to determine the number of amplifiers required on a long-haul circuit. Because each amplifier requires power and shelter, the ability to space amplifiers farther apart from one another will affect the initial and recurring cost of a long-haul fiber circuit. To Chapter Four illustrate a simplistic example of the relationship of components affect- ing the distance between amplifiers, let's assume that we are using a laser with 0 dBm of optical output power at the 1550-nm wavelength. As a refresher, 0 dBm means that the output power equals the input power. Let's further assume that the optical detector to be used has an input sensitivity of -20 dBm. Again as a refresher, -20 dBm means that the receiver is capable of detecting one-hundredth of the optical power injected into the fiber by the transmitter. Because we transmit at 0 dBm and have a receiver sensitivity of -20 dBm, the long-haul fiber-optic system becomes capable of supporting an attenuation of 20 dBm of light. Let's further assume that the optical fiber has an attenuation of 0.20 dBm/km at 1550 nm and the connectors at both ends of the cable have an attenuation of 0.10 dBm. From the pre- ceding observations, we can compute the long-haul drive distance before 