The digital optical transmitter converts digital electrical signals from electronic devices into optical signals and efficiently couples them into optical fiber lines. Electrical-to-optical conversion is achieved by modulating a light source with the digital electrical signal carrying information. Modulation methods include direct modulation and external modulation. Key parameters of the modulated light source include optical power, amplitude, frequency, and phase. Direct intensity (power) modulation is widely used in practical optical fiber communication systems. The optical transmitter converts AM TV signals from the headend into optical signals and transmits them over long distances via optical fiber. Based on operating frequency, optical transmitters are categorized as Class A or Class B: Class A supports 59 PAL-D analog TV channels in the 47–550 MHz band and digital modulation signals in the 550–750 MHz (up to 862 MHz) band; Class B supports 84 PAL-D analog TV channels in the 47–750 MHz band. Based on modulation type, optical transmitters are classified as frequency-modulated, amplitude-modulated, or digitally modulated. Currently, multi-channel AM optical transmitters—using either direct or external modulation—are most commonly deployed. The 1550 nm external modulation optical transmitter is widely used in CATV fiber-optic transmission systems, both analog and digital, with a key objective being extension of trunk-line transmission distance and deeper fiber penetration toward end users—enabling fiber-to-the-curb (FTTC) or fiber-to-the-home (FTTH) architectures. Model: 1550 nm Direct Modulation Optical Fiber Transmitter.