Novel Quantum Dot-Waveguide Devices by the Sol-Gel Method

摘要

Passive CW mode-locking of a Cr:forsterite laser using PbS quantum-dot glasssamples as intracavity saturable absorbers was demonstrated. This is believed to be the first application of a quantum-dot system in a practical device. Average output powers of 74 mW, 4.6 ps laser pulses at 110 MHz repetition rate, and a wide tunability range of 1207 to 1307 nm were obtained. The modelocking was made possible by the absorption saturation in the PbS quantum-dot samples, observed at room temperature. For the first time, significant optical gain was measured in quantum-dots pumped with nanosecond-pulse excitation. The samples studied were sol-gel derived CdS quantum-dots. The gain persists up to room temperature, it has a broad spectral width, and has its maximum value slightly below the absorption band edge. The measured rather surprising gain features were confirmed by theoretical calculations. Ultrashort pulse propagation in quantum dot waveguides was investigated. The measured characteristics of femtosecond pulse propagation, near two-photon resonance, in a CdS quantum-dot waveguide were theoretically explained. The new theoretical models developed open the doorway to propagation of space-time solitons in quantum-dot waveguides.