Compact 1.3-µm laser transmitter for the SL undersea lightwave system

The mechanical, optical, and electrical design leading to a reliable, high-performance, robust, and compact transmitter are described. Reliability considerations are of paramount importance in the design of undersea systems. Main features of the laser-fiber-monitor package and the light-feedback control strategy are outlined. The functions of the laser drive circuit, consisting of a low-speed feedback IC and a high-speed modulation IC are discussed. Access to multiple test points through an edge board connector permits automated tuning and reliability testing. The transmitter circuit can provide a 200-mA bias current, about double the expected end of life laser bias requirement, and 60-mA modulation current, double the typical value, with < 0.75-ns rise and fall time. The transmitter operates up to 800 Mbit/s, far beyond the TAT-8 bit rate of 295.6 Mbit/s. Transmitter redundancy is planned to meet the extreme reliability requirements for the transatlantic system. Up to four of the compact transmitters can be mounted per regenerator, thus providing as many as three redundant transmitters for improved system reliability.