The requirements for a practical module for an undersea system1 are high coupling efficiency, good stability with respect to temperature variation, high reliability, and easy fabrication. We have developed for transatlantic transmission (TAT 8) the module shown in Fig. 1, designed to satisfy these requirements. We use a buried heterostructure laser2 selected for a submarine system. High coupling efficiency (−4 dB) is achieved using a tapered single-mode fiber with a spherical tip. The optical power levels are checked by a germanium photodetector which monitors the rear laser diode output.
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