Wavelength Switching of Asymmetric Dual Quantum Well Lasers

Monolithic laser diodes (LD's) with widerange wavelength tunablility have a great deal of possibilities in future electro-optic applications such as multi-wavelength optical communication and/or recording systems. Many studies based on distributed Bragg reflector (DBR) and distributed feedback (DFB) LD's have been done1. However, a typical range of their controllable wavelengths is less than I% of their lasing wavelengths (u.g., l}nm for L.55p,m DBR LD), because of their Bragg wavelength selectivities in a change of the efiective refractive index with carrier injectionl. To realize a wider tuning range, a method is to control an optical gain spectrum over difierent transitions between quantized levels in quantum well (QW) LD's. In this paper we propose an asymmetric dual quantum well (ADQW) LD which consists of two differen"t quantum wells effectively separated by a barrier layer within a single optical cavity as shown in Fig.l(e). We show that it is possible to control gain spectra in both two wells by current injection, thereby changing the lasing wavelength. In this experiment we demonstrate that such an ADQW LD can lase at two wavelengths and switch between them over 1-3n,rn in 0.8p,m wavelength region. A remarkable point of well-designed ADQW LD's is that the threshold current can be low. This is because the gain at a shorter wavelength can become equal to that at a longer one with a little injection current. This is different from the case D-6-1