Abstract

Quantum well (QW) lasers operating in the long wavelength range (λ=1.3 to 1.55 μm) have been demonstrated or are expected to be superior to the conventional distributed feedback (DFB) lasers, in such aspects as (i) threshold current density (J_th)⁽¹⁾⁽²⁾, (ii) temperature dependence of J_th (the characteristic temperature, T₀)⁽¹⁾, (iii) stability in polarization (TE polarization or TM polarization)⁽³⁾, (iv) static and dynamic single mode oscillation, (v) spectral width under cw operation and under high speed modulation ⁽⁴⁾⁽⁵⁾, and (vi) upper frequency limit for direct modulation⁽⁶⁾. Furthermore, the fabrication process for QW lasers is simpler since it does not involve the corrugation formation process necessary for DFB lasers. The aspects remaining for future study with respect to this comparison are the lifetime of the devices⁽¹⁰⁾ and the temperature stability of the oscillation wavelength λ. As for the temperature dependence of λ, dλ/dT, DFB lasers exhibit a small value of dλ/dT = 0.8~1.0 Å/degree, which is determined by the temperature dependence of the refractive index of the semiconductor materials. On the other hand, little work has been done on the dλ/dT of QW lasers since the first report⁽⁷⁾ on the multiple quantum well (MQW) laser made from GaAs-AlGaAs material described that the dλ/dT of this laser was equal to 4 Å/degree, which is determined by the temperature dependence of the bandgap energy E_g of the material.

© 1989 Optical Society of America