Method and apparatus for predicting semiconductor laser failure

Abstract

A method and apparatus are disclosed for predicting the failure of semiconductor lasers. To predict the failure of a particular semiconductor laser, operational characteristics that are predictive of a laser's health are computed while the laser is in use (e.g., while the laser is transmitting a signal or pumping an optical amplifier or solid state laser). This is done by modulating the injection current of the semiconductor laser and observing changes in laser parameters such as output power and junction voltage. From these observations, various laser characteristics can be computed including current threshold, slope efficiency and dynamic resistance. By carefully selecting the injection current modulation frequency and degree, the system in which the laser is used is not significantly disturbed by the changes in output power. For example, modulating the injection current with a modulation period that is substantially less than the relaxation time of the dopant ions in a solid-state laser does not substantially affect the gain of the solid state laser. The current modulation and laser parameter sampling are controlled by a microprocessor via a controller interface. During any particular modulation cycle, the microprocessor stores multiple parameter samples in a random access memory. Once enough samples have been stored, the microprocessor computes the laser characteristics and compares them to beginning-of-life data for the same semiconductor laser, which are stored in a read only memory. If the laser characteristics are out of range with respect to the beginning-of-life data, the microprocessor outputs an alarm via a serial interface.