Abstract

Thermal effects in diode laser arrays are known to be important for the array mode selection.¹ Here, we examine in detail the role of active region heating, considering a uniform ten-strip GaAs/AlGaAs gain-guided array. The array is regarded as a perturbed broad-area laser whose modes are coupled via complex-permittivity perturbations induced by heating and injected carriers. Array modes are determined using the coupled-mode theory. The thermal perturbation is taken as a half-period cosine with center value of ΔT, vanishing at the lateral claddings. When heating-induced waveguide nonuniformity is small, the dominant array mode is ν = 10. Calculated temperature dependence of modal gain spectra reveals that with raising temperature, the highestgain mode shifts gradually from ν = 10 to ν = 13. Thus, thermal focusing results in sequential excitation of high-order modes with increasing pumping current. Calculated near- and far-field patterns for ΔT = 4°C are in excellent agreement with injection-seeding experiments,² while numerical simulations² with ΔT = 10°C give somewhat narrower near fields for ν > 10. This indicates that the active region heating may not be as severe as previously thought. Sensitivity of the high-order modes to thermal focusing can be used to establish the actual temperature increase with good accuracy.

© 1991 Optical Society of America