Method and apparatus for monitoring performance of a laser transmitter

Abstract

A low-cost monitor includes two comparators which are adapted to form a window comparator which frames a laser transmitter's normal range of operation. An apparatus for generating an amplified back-face-monitor voltage corresponding to the laser transmitter's optical output power level is coupled to the window comparator. A reference voltage is also coupled to the window comparator which defines the upper threshold of the normal operational range. A controllable variable voltage source is coupled to the window comparator and is used to define the lower threshold of the normal operating range, where this lower threshold has two associated threshold values as described above. The lower threshold is initialized to the first threshold value which corresponds to an end-of-life operating state of the laser transmitter. When the back-face-monitor voltage signal equals or drops below the first threshold value, an alarm signal is generated by the laser monitor, and the controllable variable voltage source is switched to a second state for providing a second threshold value which corresponds to failed operating state of the laser transmitter. As the optical output power level continues to decline with temperature and time, it eventually falls belows the second threshold and a second alarm is generated to indicate failure of the laser. A variable gain instrumentation amplifier is coupled to the generating apparatus and utilized to measure the optical output power of the laser transmitter.