MITSUBISHI

MITSUBISHI OPTICAL SEMICONDUCTORS. RELIABILITYAs the operating life time of optical devices. especially laser diodes. is important for reliability. it is explainedat this page. We sincerely hope that the "Mitsubishi semiconductor reliability handbook" will be of valuefor basic concepts for quality. quality assurance system. reliability theory and reliability tests of Mitsubishisemiconductor devices.1. Definition of life timeThe life time of laser diodes is defined as thechange of the. light output power P versus forwardcurrent IF characteristic because the P-I characteristicis the most important factor for laser diodes.In Fig. 1 (a) shows P-I characteristic under initialcondition.The laser should be operated continuously andits light output power(Po) should be kept constantby the APe drive.Operating current lop (0) at initial conditionincreases until lop (to) that is caused by decreasingslope efficiency and increasing threshold current asa result of degradation of the crystal. (Fig. 1 (b»As degradation increases, a constant light output(Po) can't be kept. (Fig. 1 (c»Fig. 2 shows an example of operating current lop(t) vs. operating time t.Life time is defined as the time at which theoperating current lop (t) is 1.5times as large as theinitial operating current lop (0).In Fig. 1, the life time of laser diodes justcorresponds to condition (b) .a.~Q Po -------­;;Q;;oc~ 1.0u10p(0)lop (to)Current IFFig. 1 Light output power vs.forward current characteristic of laser diodeOlc.;::;i 0.5o-0.~"iiiE(;z2.0~-------~--"'"OL-------~--~otoTime tFig. 2 Change in time of operating current1- 36•... . ··.MITSUBISHI...... ELECTRIC