The purpose of this thesis is to fabricate 12-layer In0.75Ga0.25As quantum dot-in-a-well (In0.1Ga0.9As) structures grown by molecular-beam epitaxy (MBE) on GaAs substrate, and analyze the optical properties of laser devices for optical fiber communication systems. For the laser structures, larger Al content AlGaAs cladding layer enhance the optical confinement, but encounter much challenges to improve the quality. After we simulate and fabricate different Al content laser structures, we find the best cladding layer composition - Al0.2Ga0.8As which performs a best material gain. In the active layer, 12 layers In0.75Ga0.25As quantum dots (QDs) and QDs in a well (DWell) structure, and DWell with Be-doping in the well structure are included in this study. The well structure slows down the hot carriers speed and Be-doping decrease the carrier life time and increases the electron-hole pair recombination rate. We increase the QDs deposition coverage to move the emission wavelength to 1.3£gm, but the high temperature cladding layer growth process indirectly anneal the QDs and result in the emission wavelength blue shift to 1.24£gm. In the laser fabrication, to transport the light wave in smaller dispersion loss single mode waveguide, wet etching photolithography processes are adapted in this study to fabricate 2£gm width ridge waveguide. The as-cleaved facets are used as Fabry-Perot laser mirrors in ridge waveguide lasers. Finally, the current density of QD Laser(C528) lasing in CW mode is 581A/cm2, slope efficiency of 510mW/A and maximum power/facet of 65mW are obtained.Then the current density of DWELL+PD Laser(C540) lasing in CW mode is 880A/cm2, slope efficiency of 430mW/A and maximum power/facet of 34mW are obtained.

This thesis describes the work carried out at Brunel University to develop novel optical fibre sensors capable of monitoring the cure state of an epoxy/amine resin system. The sensors were of simple construction, consisting of an optical fibre from which the silicone cladding layer had been removed over a short length. This stripped length was embedded into the curing resin system. The sensor was successfully used in two ways: i) as an evanescent absorption sensor to monitor specific absorption bands of the resin system. The absorption of energy from the evanescent wave of the optical fibre by absorbing media allows evanescent absorption spectra to be obtained. Absorption spectra were obtained from sensors embedded in a model curing resin system over narrow wavelength ranges. These wavelength ranges corresponded to positions of known absorptions in the spectra of active components in epoxy/amine systems. By monitoring the change in these absorptions it was possible to obtain information about concentration of the amine hardener functional group throughout cure; ii) as a refractive index sensor capable of monitoring the changes in the refractive index of the resin system during cure. A laser diode was used to launch light into the sensor and the intensity of light emerging from the other end of the fibre was monitored. Changes in the resin system refractive index caused changes in the guiding properties of this the sensor. This resulted in a significant change in the intensity of light recorded by the detector and allowed the cure process to be followed. This sensor was also embedded into a unidirectional pre-preg system and was able to follow the cure of the system. The results from the two sensing methods have been compared with data obtained using FTIR spectroscopy and Abbe refractometry during the resin system cure. A theoretical model of sensor response has been developed and compared with the experimental data obtained. The sensor response has also been compared to predictions made by several models of evanescent sensor systems obtained from the literature. These models have been modified so that they can be applied to a sensor embedded into a curing resin system. An analysis of the correspondence between theory and experiment is presented.