ndow. Team-Fly® Fiber in the WAN The development of optical amplifiers during the late 1980s was based on the efforts of researchers at Bell Laboratories, then part of AT&T and NTT of Japan. As we noted earlier in this chapter, erbium amplifiers were developed by doping a length of fiber and then pump- ing the fiber at a wavelength of 980 nm. The laser pump provides the energy for the amplifier while the incoming signal results in stimulated emissions as light pulses pass through the section of the doped fiber. Because the stimulated emission results in the stimulation of additional emissions, the effect is a rapid growth in the flow of photons in the doped portion of the fiber. Figure 6.12 illustrates the components of an erbium optical amplifier. Note that the laser pump, coupler, and a small section of erbium-doped fiber are typically assembled in a common housing. The effect of the erbium amplifier can result in a gain of approximately 40 dB, or 10,000 times the received signal. The use of couplers made it relatively easy to increase the number of light sources being combined onto a common fiber. A more difficult task facing engineers was the demultiplexing of the common light source. To separate the different wavelengths coupled onto a fiber, devel- opers used a mirrorlike device known as a grating that works in essen- tially the same way as a prism. Specifically, the grating is used to sepa- rate light sources into their individual wavelengths by reflecting them at different angels. Figure 6.13 illustrates the wavelength division multiplex- ing process, which may be a tongue twister but that actually represents the process of distributing the different wavelengths to their intended destinations. Note that the grating must be extremely accurate in reflect- ing different wavelengths to applicable output fibers. Figure 6.12 An erbium amplifier consists of a pump Erbium- laser, a coupler, and a Input Doped Output small section of Signal Fiber Signal erbium-doped fiber. Coupler Filter Laser Chapter Six Figure 6.