Abstract
A dual-wavelength emission source is realized by asymmetrically pumping a two-section quantum-dot distributed feedback laser. It is found that under asymmetric bias conditions, the powers between the ground-state and excited-state modes of the two-section device can be equalized, which is mainly attributed to the unique carrier dynamics of the quantum-dot gain medium. As a result, a two-color emission with an 8-THz frequency difference is realized that has potential as a compact THz source. It is also shown that the combination of significant inhomogeneous broadening and excited-state coupled mode operation allows the manipulation of the quantum-dot states through external optical stabilization.
Highlights
Terahertz (THz) technology has a wide variety of applications in fields as diverse as generation computing and communications technologies, medical and pharmaceutical fields as well as basic material science and homeland security [1±5]
Two coherently interfering optical modes are typically generated by two single-mode lasers, and the light is absorbed in an ultrafast photoconductive semiconductor [8±10]
The dual-mode laser source for THz generation has been previously studied in bulk and Quantum-Well (QW) semiconductor lasers [15±18], but very little is known about the behavior of nanostructured active regions in these types of devices
Summary
Terahertz (THz) technology has a wide variety of applications in fields as diverse as generation computing and communications technologies, medical and pharmaceutical fields as well as basic material science and homeland security [1±5]. In order to accurately characterize the performance of the DFB device under investigation, the values of the index and gain coupling coefficients are calculated by using the numerical least-squares-fitting of the sub-threshold spectra. LAPAREX (Laser Tokyo was used to Parameter Extraction) predict the ț-value of the device under investigation [27] This program enables predictive calculation of the coupling coefficient for both the gain and index-coupled DFB structures through numerical least-squares-fitting of the measured sub-threshold spectrum with a theoretical sub-threshold fitting algorithm. Least-squares-fitting of the sub-threshold spectra measured from a 1 mm long and two-section QD LLC-DFB laser predicts a gain coupling coefficient value of țgain = 5.2 to 3.2 cm as the bias current varies from 60 mA to 70 mA, respectively. The error analyses for the coupling coefficient values are evaluated based on a one standard deviation confidence interval, and are observed to be less than 7% of the extracted values
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