Laser Diode Reliability

Laser diodes are the main optical source in various optical fiber communication systems and indispensable for our daily lives. The wavelength of the laser diodes are set at 1300 nm or 1550 nm for most communication systems, including submarine systems corresponding to the low loss window of silica fiber. Laser diodes used in such wavelength bands are usually InGaAsP/InP lasers. Wavelength in 850-nm band is also used for short-range communication, such as intraoffice systems. The laser diodes used for the wavelengths are AlGaAs/GaAs laser diodes. In these systems, high reliability is required for those laser diodes since the communication systems are serious lifelines, and the operating conditions have been severe year by year. In those applications for communication systems, high-speed operation for trunk systems and long-term stable wavelength operation for wavelength division multiplexing (WDM) systems are required. For subscriber systems, high and wide operating temperature are required, corresponding to the environmental conditions of applications. In addition to those applications, some laser diodes have begun to be used in space for satellite communications and sensing systems. The environmental conditions of space applications are quite different from those of terrestrial applications such as land and submarine communication systems. Compared with the operating conditions in terrestrial systems, there are large variations in the ambient temperature in space, and laser diodes are possibly exposed to severe irradiation by high-energy particles and ultraviolet rays. These environmental factors are inherent features in space applications and have been added to the reliability issues of terrestrial applications. The basic reliability of laser diodes used in the communication systems is usually determined by optical output characteristics. The stability of lasing wavelength and spectral linewidth are also important in these applications.