Designed for long distance transmission and local network coverage, it is widely used in optical modulation, optical insertion, wavelength-division multiplexing (WDM), as well as network upgrading and expansion of large and medium-sized optical transmission systems. Direct and external modulation are primarily used in the optical domain with LED and Laser devices as methods for converting electrical data into optical form. Figure 1: Laser diode used for direct modulation. The Medallion 8100 series leverages a breakthrough optical device innovation at its. Huatai is the well-known manufacture in analog externally modulated optical transmitter in the world. The transmitters feature low-noise DFB-CW lasers to reduce the dispersion effect.