الفهرس | Only 14 pages are availabe for public view |
Abstract The successful remote operation of equipment for maintenance and diagnostics tasks in the future International Thermonuclear Experimental Reactor (ITER) requires the development of transmission links that can withstand high total dose, ranging from 1 to 100 MGy, depending on the particular working conditions. Therefore, the feasibility of applying photonic technology in such intense radiation fields and up to very high particles fluences needs to be assessed. Although a considerable amount of radiation effects studies of laboratory experiments on individual devices exposed to a variety of radiation conditions are reported in literature, only a few theoretical models are available to describe the behaviors of the irradiated optoelectronics devices. Also, there is a scarcity of analysis of the optical, the electrical properties and the communication parameters of the devices working under the high temperature irradiation. The proposed mathematical models in this thesis provide a clearer understanding and a deeper analysis of the laboratory results and also the ability to extrapolate and predict the most accurate results for changing of the performance characteristics of irradiated optoelectronic devices. The Vertical Cavity Surface-Emitting Laser (VCSEL) is considered one of the most important devices for enabling ultra parallel information transmission in lightwave and computer systems. Neutron fluences were chosen in such a way that one gets estimates of the behavior especially in space environments and nuclear engineering. Laser Diodes show a reduction of light output power and also a shift of threshold current after irradiation. The thesis has proposed the study of the transmission bit rates and products of optical laser diode sources such as VCSEL under thermal irradiated environments. We have taken into account the performance characteristics of these devices such as the harmonic response transfer function, the resonance frequency, 3-dB bandwidth, damping frequency and the pulse rise time. Both the ambient temperature and irradiation dose as well as the spectral wavelength possess serve reduction effects on the transmission characteristics (dispersion and bandwidth) and consequently the transmitted bit rates and products. In addition, we have investigated the performance of PIN photodiodes employed in high temperature-irradiated environment. Nonlinear relations are correlated to investigate the currentvoltage and capacitance-voltage dependences of the silicon PIN photodiodes, where thermal and gamma irradiation effects are considered over the practical ranges of interest. Thermal and irradiation effects are modeled over the practical ranges of interest. Both the ambient temperature and irradiation dose as well as the spectral power of incident light possess several effects on the electro-optical PIN photodiode characteristics (dark current, photocurrent, absorption coefficient, responsivity, quantum efficiency, rise time, bandwidth and directivity)ABSTRACT vi and consequently signal to noise ratio (SNR) and bit error rate (BER) for analog and digital optical link systems. The results of each of SNR and BER show that, InGaAs PIN photodiodes more radiation hardness than Si PIN photodiode. Moreover, we have also taken into account the radiation dependent characteristics of the avalanche photodiodes (APDs). The study has presented the main irradiation effects, i.e., the multiplication gain, minority carrier life time, impact ionization, illumination and radiation damage coefficient. By comparing protons and gamma radiation effects, we will applied the model on the two different silicon APD structures. The fluence effects of 51 MeV proton irradiation on the photosensitivity and SNR are also investigated. Also, we have taken into account the effects of excess noise on the device performance and then to decrease the bit error rated that has a bad effect on the operating efficiency. The results demonstrate that the model can accurately calculate the internal parameters of the APDs and produce data that can be directly compared with measurements. Finally, we have taken into account the integrated device that is composed of a Hetrojunction Phototransistor (HPT) and a Laser Diode (LD) or Light Emitting Diode (LED). The expressions describing the transient response of the output, the rise time, and the output derivative are derived. The results show that the transient response of the two types of the device strongly depends on the optical feedback inside the device and it is found that the device works in two different modes. They are amplification for small optical feedback coefficient and switching for high optical feedback coefficient. The rise times in both types of the device are calculated in order to calculate the transmission bit rates depending on non return to zero (NRZ) and return to zero (RZ) coding formats in both modes. By increasing the optical feedback, the rise time in the amplification mode is increased along with an increasing output, while that in the switching mode can be reduced effectively with a saturated output. |