An analytical model for vertical dual-cavity quantum-dot optical amplifiers

Novel closed-form model for the threshold conditions and the optical gains of vertical dual-cavity semiconductor optical amplifier (VDC-SOA) is derived. Expressions for the transfer functions that relate the average photon density inside the two cavities to the incident photon density are derived. The model is simple, accurate and easy to use for designing dual-wavelength laser amplifiers. Good agreement is obtained between the analytical model and numerical calculations. The transmitted and reflective bistability characteristics of quantum dot VDC-SOA have been investigated. The threshold condition of each mode is expressed in terms of the top-cavity and the bottom-cavity currents. The dual modes \(\lambda_{o}^{ + }\) and \(\lambda_{o}^{ - }\) show different bistability behavior as a function of the top cavity current when the device operates at fixed operating point below the threshold curve. We find that the contrast ratio of mode \(\lambda_{o}^{ + }\) is a weak function of the device currents, and the hysteresis width increases when the top cavity current is increased. For mode \(\lambda_{o}^{ - }\) large contrast ratio and hysteresis width are obtained when the two cavities exhibit equal currents. Our analysis also reveals that the spectral characteristics of mode \(\lambda_{o}^{ + }\) are different from that of mode \(\lambda_{o}^{ - }\).