Experimental And Theoretical Study On Erbium-Ytterbium Doped Waveguide Amplifier Fabricated By Ion-Exchange

All-optical communication network is more popular among the individual and family consumers with the rapid development of the Internet and digital communication business. All-optical waveguide devices which have the advantages in size, compatibility and transmission capacity are very attractive recent years. Erbium-ytterbium doped waveguide amplifiers (EYDWA) are one of the important all-optical waveguide active devices, and have received great attention in optical telecommunications. In this thesis, we study the influence of the parameters of two-step ion-exchange process and the optical configurations on the performance of EYDWA both experimentally and theoretically.In the experiments, a channel optical waveguide series with different channel opening widths (COWs) were fabricated on the same erbium-ytterbium uniformly doped phosphate glass substrate by two-step ion exchange technique. The passive losses, gain, noise figure (NF) and mode characteristics of EYDWAs with different COWs are investigated experimentally. Experimental results indicate that if single-mode operation at the signal wavelength in C-band is ensured in the waveguide fabricated by ion exchange technique, high order modes of pump light at 980 nm will be excited unavoidably. The intensity profile overlap between signal and pump light is dependent on COW, and the gain of EYDWAs with different COWs will changed accordingly. The presence of higher order modes of pump light is beneficial to increase this intensity profile overlap and to improve the gain of EYDWA. A maximal value of gain is present for a COW value just after a mutation in the number of modes for the pump light in the experimental results. In addition, we investigate the gain and noise figure characteristics of EYDWA with different optical configurations under the condition of the same total pump power. Equalizing bidirectional pump scheme (EBPS) achieves evident enhancement in gain compared with backward pump only scheme (BPOS), while forward pump only scheme (FPOS) achieves large reduction in NF for single pass configuration (SPC). About 100% increment in gain and 50% less deterioration in NF can be obtained in double pass configuration (DPC) compared with SPC.The theoretical model of EYDWA system is based on thermal diffusion equation, full-vectorial wave equation and propagation-rate equations, and it can be used to analyze the performance of EYDWA fabricated by ion-exchange process. The two-dimensional graded index profile of the section of channel waveguide is obtained through solving the ion diffusion equation. The eigen-modes in the section of channel waveguide with graded index profile then can be simulated by solving the vectorial wave equation using a full-vectorial finite-difference method. The intensity profile of pump and signal light corresponding to the fiber end-coupled with waveguide are determined by the orthogonality relation between eigen-modes. Finally, the intensity profiles of pump and signal light, together with the parameters of the active characteristics for substrate material, are applied to rate-propagation equations to obtain the amplification performance of EYDWA numerically. We can simulate the gain and NF characteristics of EYDWAs with different ion-exchange parameters or optical configurations by this theoretical model.The main achievements are shown as follows:Full-vectorial finite-difference method is applied to solving the full-vectorial wave equation for the two-dimensional graded index channel waveguide. Multimode and hybrid nature of vectorial guided modes for both pump and signal light are investigated by above simulation. The theoretical model of EYDWA fabricated by ion-exchange process based on thermal diffusion equation, full-vectorial wave equation and propagation-rate equations, is presented for the first time, and can be used to accurately analyze the performance of EYDWA system.It is demonstrated both experimentally and theoretically that the optimization of the intensity profile overlap between signal and pump light in waveguide can evidently improve the gain characteristics of EYDWA. The presence of higher order modes of pump light is beneficial to increase this intensity profile overlap and to improve the gain of EYDWA while the presence of higher order modes at signal wavelength has a negative effect on both intensity profile overlap between signal and pump light and the gain of EYDWA. Therefore, we introduce a normalized overlap factor of the intensity profile between signal and pump light to the theoretical model of EYDWA, which is defined as the modified simplification model. The gain characteristics of EYDWA simulated by no simplification, modified simplification and traditional simplification model are analyzed when neglecting some effects of erbium, and then are compared with the experimental results. Results show that the introduction of the overlap factor about the intensity profile between signal and pump light has some advantages. It clarifies the physical significance of rate-propagation equations, explains the experimental results reasonably, simplifies the theoretical model, and reduces the computational complexity of simulations.The characteristics of gain and NF versus forward and backward pump power normalized by total pump power are investigated systematically in EYDWA with different optical configurations (e.g., SPC, DPC, FPOS, BPOS and EBPS). The advantages and disadvantages of each optical configuration are analyzed. The results show that a significant improvement on the performance of EYDWA can be achieved by optimizing the optical configuration.