The development of compact and low-cost coherent sources in visible and infrared wavelength range can provide indispensible tools for a variety of scientific, technological and industrial applications. Great progress over the last years in material science, crystal growth and semiconductor material processing in combination with recent advances in some of the more traditional technologies, in particular nonlinear frequency conversion and parametric sources, have led to the realisation of a new generation of laser sources. Furthermore, the advent of a new generation of quasi-phase-matched, waveguided and semiconductor nonlinear materials together with novel semiconductor lasers have led to the development of new frequency conversion and parametric sources with previously unattainable performance capabilities. The research described in this thesis relates to the development and characterisation of novel semiconductor based laser sources tunable in the broad spectral ranges which are unattainable for conventional lasers due to a lack of suitable laser gain materials. In the first part of the thesis the subject matter is concerned with the direct emission from laser devices. In particular, a broadly tunable InGaAs/InP strained multi-quantum well external cavity diode laser, operating in the spectral range of 1494 nm – 1667 nm with a maximum CW output power in excess of 81 mW and side-mode suppression ratio higher than 50 dB is demonstrated. This represents the highest output power and side-mode suppression ratio ever to be generated in this spectral region. A record broadly tunable high-power external cavity InAs/GaAs quantum-dot diode laser with a tuning range of 202 nm (1122 nm - 1324 nm), a maximum output power of 480 mW and a side-mode suppression ratio greater than 45 dB, is also demonstrated. This represents a promising achievement for the development of a high-power fast swept tunable laser and compact nonlinear frequency generation schemes for the green-yellow-orange-red spectral range. The second part of the thesis relates to induced nonlinear processes, focusing on frequency doubling and optical parametric oscillation. In particular, an all-room-temperature CW second harmonic generation at 612.9 nm and 591.5 nm in periodically poled potassium titanyl phosphate waveguides pumped by a broadly-tunable quantum-dot external cavity diode laser with a conversion efficiency of 10.5% and 7.9%, respectively, is demonstrated. For the first time, a green-to-red tunable laser source with tunability of over 60 nm (567.7 nm – 629.1 nm) based on frequency doubling in a single periodically poled potassium titanyl phosphate waveguide pumped by a single broadly-tunable quantum dot laser is demonstrated. These results are an important step towards a compact tunable coherent visible light source, operating at room temperature. The possibility of nonlinear frequency conversion in orientation-patterned GaAs waveguides is also investigated. The technology of low-loss periodically poled GaAs waveguided crystals is developed and such crystals are fabricated. Second harmonic generation at 1621 nm in low-loss periodically poled GaAs waveguide is demonstrated. An optical parametric oscillator system used as the pump source for GaAs devices and based on the periodically poled 5 mol% MgO-doped Congruent Lithium Niobate crystal, generating light in the wavelength range between 1430 nm and 4157 nm, is presented. The obtained results show a great promise for realisation of efficient quasi-phase-matched optical parametric oscillator devices based on orientation-patterned GaAs waveguides, which enables the extending generated wavelength up to 16 µm.
|Date of Award||2011|
|Supervisor||Edik Rafailov (Supervisor)|
- Nonlinear Optics
- Tunable Laser