The characteristics of the best known defect centers E' in silica optical fiber material irradiated with ray were investigated by ESR at room temperature.A mechanism model of production of the E' center defect was established.The production of E' center includes two processes creation and activation.The strained bonds(or oxygen replacement) in silica networks lead to the creation of new defects whose concentration increases linearly with the dose.The pre-existing defects produce the activation,which tends to saturation.According to this model,the relation of E' center concentration changing with irradiation dose was obtained theoretically.The results are in good agreement with the experimental results.
LUO WenyunXIAO ZhongyinWEN JianxiangYIN JianchongWU WenkaiCHEN ZhenyiWANG ZihuaWANG Tingyun
An all-optical transient waveform equivalent time sampling system based on cross-gain modulation （XGM） in semiconductor optical amplifier （SOA） is presented. Anoisy SOA dynamic model and PIN equyalent circuit function are employed for system evaluating. The results show this SOA-XGM sampler with subtracting postprocessing can achieve picosecond sampling window. The shape of sampling window can be adjusted by SOA bias current and amplitude of control pulse. Compared with amplified spontaneous emission （ASE） noise of SOA and thermal noise in PIN, the jitter of sampling control pulse causes most sampling error. Simulations show that this SOA-XGM sampler can be a capable candidate for transient waveform sampling.
Transmission properties of fractal Cantor distribution with left-handed materials （LHM） are investigated. The transmittance and reflectance spectra can be calculated by using the optical transmission matrix method. Comparing with the conventional Cantor multilayers, these structures with LHM have double functions of stopbands and defects. Through adjusting the thickness of dielectric layers, the properties of stopbands and defects can be obtained, respectively. For stopbands, a broad stopband filter is studied. For defect modes, multi-frequencies narrow passband filters are proposed.
