Simple light pulses were used in the early optical fiber transmission systems to transmit data through twisted glass beams. To symbolize the zeros and units of the digital data, the light was switched on and off. Almost every wavelength (often referred to as hue or frequency) between roughly 670 nm and 1550 nm may be found in real light. Less expensive LEDs were used by fiber optic data connection modems in the 1980s to introduce near-infrared pulses onto inexpensive fibers. The requirement to boost bandwidth has grown along with the need for data. 155 Mbps data streams may be sent over extremely long distances using lasers operating at a frequency of 1310 nm in the early SONET networks. There are two types of WDM systems because of its extended bands and lower noise than other bands (DWDM & CDWM) Communication systems frequently use dense wavelength division multiplexing (DWDM) because it can multiplex more than 192 channels (80 channels on average) using the ITU- channel spacing of 0.1 nm, 0.2 nm, 0.4 nm, 0.8 nm, and 1.6 nm = 12.5 GHZ, 25 GHZ, 50 GHZ, 100 GHZ, and 200 GHZ over distances of more than 500 km. usually in the range of 1270–1610 nm with channels 20 nm intervals for every 100 km.But it was quickly exhausted. However, developments in optoelectronic components have made it can be to create systems that simultaneously transmit various light wavelengths across a fiber using latest version of optisystem21. Furthermore, by splitting various wavelengths, numerous high-bitrate data streams at 2.5 Gb/s, 10 Gb/s, and more lately at 40 Gb/s and 100 Gb/s might be multiplexed. Consequently, wavelength division multiplexing, or WDM.