1. Introduction: CYT1550B is an external modulation optical transmitter which adopts DFB laser diode as it抯 optical supply to transmit the video and sound signals as well as telephone and data by the way of amplitude modulation. This equipment cooperating with the optical amplifier used in large and medium ring network, distribution network and long distance transmission between cites and countries. CYT1550B provides the stable power optical supply through the 1550nm DFB laser and its controlling circuit that optimize the performance of system automatically with the SBS restraining technology; the external modulator combines the excellent linear technology with its circuit and microprocessor controlling system. It has twin channel optical power output that can be used in ring optical network economically and effectively. 2. Features: A. Standard（rack mounted）case:1U 19 inch B. Advanced automatic power control (APC) and automatic temperature control (ATC) circuit to ensure the performance , C. Working bandwidth: 45-870MHz, double optical switched ports, optical power (each port) ≥ 7dB. D. Optional SBS (13dBm, 16dBm, 18dBm). E. AGC and MGC control methods F. RS485 interface G. LCD at front penal shows the working parameter and alarm