| Semiconductor optical amplifiers (SOAs) have achieved extensive research and wide applications in optoelectronic devices and optical networks after nearly half a century of development, and bulk SOAs and quantum well SOAs have already realized commercial production. However, bulk SOAs have not been widely used in practical optical communication systems due to the performance limitation. The low-dimensional nanostructure, especially the zero-dimensional quantum dot (QD) structure, is the present research focus all over the world, and it has attracted considerable interest and has been studied intensively in optoelectronic device applications. In this dissertation, in order to improve the performance of SOA and enhance the application flexibility in optical communication systems, a low-dimensional nanostructural SOA--two-section quantum well SOA is fabricated, and the performance of the SOA is analyzed. The wavelength converter using two-electrode SOA is simulated. In addition, we also investigate the structural and optical properties of the QDs and quantum dot molecules (QDMs) grown by metal-organic chemical vapor deposition (MOCVD). The research contents are summarized as follows:(1) Two-electrode quantum well SOAs are successfully fabricated. At first, strain compensated InGaAsP quantum well active region and other SOA's structures are grown by MOCVD on InP substrates, and characteristics of the wafers are measured and analyzed. Secondly, two-electrode quantum well SOAs are successfully fabricated and the performance of the SOA is measured. The results show that the peak wavelength, gain and saturated output power of the SOA can be tuned through the change of the injection current of the two segments. Therefore, the SOA with adjustable performances can adapt different applications.(2) Wavelength converter by using two-electrode SOA is theoretically investigated. According to features of two-electrode SOA, the simulation model, which takes into account carrier diffusion process, is set up on the basis of Connelly's broadband model, and the performance of wavelength converter is simulated by using this model. The results show that the carrier recovery time can be effectively reduced, and the pattern effect of converted light can be greatly suppressed.(3) The growth of InAs/GaAs QDs is studied. At first, the growth mechanism of QD growth is analyzed, and the effects of growth parameters on the QD properties are discussed. Secondly, the InAs QD characteristics with different cap layers are systematically investigated, the results show that the double cap layer structure with low-temperature and high-temperature layer can greatly improve the QDs'performance. In addition, the In graded InGaAs cap layer can increase photoluminescence intensity and improve the uniformity of the QD size. Finally, an InAs/GaAs QD structure with the full width at half maximum (FWHM) of 183nm is obtained. The influences of In composition of InGaAs strain-reducing layer and the InAs coverage on the optical properties of multi-modal QDs are studied.(4) The preparation of laterally aligned InAs/GaAs QDMs is studied. A self-assembled growth method is proposed, which does not require special template and process, and QDMs are fabricated by MOCVD through appropriately selecting growth parameters. So the method has the advantage of simple implementation. The experiment results show that the formation of QDMs is very sensitive to growth temperature and InAs coverage, and it causes the redshift of emission wavelength. The effects of InGaAs cap layer on the optical properties are also investigated, and the results show that redshift of PL wavelength is observed with increasing the In composition and thickness of InGaAs SRL. Finally, a QDM sample with high emission efficiency and FWHM of 209 nm is grown. It is very promising for the broad-spectrum QDMs to employ in broad-spectrum devices.
|
PDF Full Text Request