In recent years

the optical Instability output characteristics in semiconductor lasers has been studied in a number of optoelectronic devices. As the bistable devices could be used in memory units and optical switching devices. They made a great interest to researchers. However

as far as the optical bistability observed experimentally the optical output hysteresis width is narrow. A narrow hysteresis gives rise to difficulties in controlling switching states

and thus limits the practical applications of optical bistability. Many people currently are seeking ways to fabricate bistable devices with large hysteresis from both experiments and theory. The multi-segment absorptive bistable lasers are one of most important kinds of bistable devices. It is necessary to study this kind of bistable devices and to know its hysteresis width quantitively varying with structure parameters.In this paper

the active-passive tandem ridge waveguide GaAs/GaAlAs laser optical bistable output characteristics have been reported. It includes experimental results as well as its theoretical analysis. Through experiment

it is found that the bistable characteristics are dependent on the length of active region and also the length of passive region. When the length of two segments are in certain proportion

the hysteresis in optical output reaches to a maximum width. The studies on multi-segment laser optical bistability is quantitively reported for the first time. Also

that the current injection level from the third segment in a three section laser has a strong influence to the hysteresis was observed. It is seen that a small abstract current in the third part results in an increase in hysteresis width. These experimental results have the significance in finding laser exhibiting large hysteresis. A ray approximation theory has been applied to our laser

which gives out the rela-tionship between light power and injenction current. However

there is some differences between theoretical calculation and experiment test. The author believes that the differences come from the theoretical equation's invalidity indescribing the scattering loss caused by lateral roughness of ion beam-etching.The loss leads to a very high input level to pump active part and 1o mahethe carrier density high enough in passive part. So

the optical output bi-stability is obtained in a very high injenction current.In our theoretical model

we add a constant optical loss term in the ray equations that is suitable to describe the burid stripe lasers

to simulate the scattering loss in the real case. Neverthless. the scattering loss may not be uniformly distributed. To get a better theoretical model for ridge waveguide absorptive bistable laser

a z-dependent loss term should be introduced. The experimental and theoretical calculation results are shown in Fig.2 and Fig.3. in which experimental optical hysteresis ocurrs at much higher input level than theoretical one does.Summary

the ridge waveguide active-passive segment lasers were tested

the results show that the hysteresis in optical output depends on the length of two segments and this phenomenon was explained theoretically.