Investigation On Stripe Waveguide Amplifiers And Microring Resonator Amplifiers

The amplifier is a key device in the optical fiber communication network, its function is to amplify the signal. The Er³⁺ doped waveguide amplifier is another promising one after the successful development of the Er³⁺ doped fiber amplifier and the semiconductor optical amplifier. The research as well as application of the Er³⁺ doped waveguide amplifier is a hotspot topic in the field of optical communication and optoelectronics. In the Er³⁺/Yb³⁺ co doped waveguide amplifier, Yb³⁺ has an absorption section with a higher peak value (0.8 1.1 m), it can offer higher gain, so in this way, the operation efficiency and the gain stability of the device can be improved greatly. Yb³⁺ is as a tool of transferring energy only, so the Er³⁺/Yb³⁺ co doped waveguide amplifier reserves the superior characteristics as those of the Er³⁺ doped waveguide amplifier, such as high gain, low noise, large output power ang low insertion loss.The microring resonator is a novel optoelectronic device. Because of its excellent features, including low cost, compact conformation, high integrated level, low insertion loss and low crosstalk, the microring resonator is widely applied in filtering, multi/demultiplexing, modulating, switching, sensing, lasing and so on. The microring resonator is easily integrated with other photoelectronic devices.The Er³⁺/Yb³⁺ co doped microring resonator possesses both the filtering and amplifying functions for the signal light. After the waveguide core is doped with Er³⁺ and Yb³⁺, the pump light of 0.98 m and the signal light of 1.55 m are input into the upper channel, and then coupled into the microring at the coupling point. The pump light and signal light would resonate in the microring because they meet with the resonance conditions. At the same time, the pump light transfers its power to the signal light by the Er³⁺/Yb³⁺ co doped system, as a result, the output signal light intensities in the upper and lower channels are enhanced, and then the filtering and amplifying are realized in the device.The main contents and innovations of this thesis are as follows:1. The introduction is performed on the history of the development, applications, classification, functions and fabrication technologies of the waveguide amplifier and the microring resonator.2. Based on the electric magnetic theory, the Marcatili's methed of analyzing the straight rectangular waveguide is described. By using the coupled mode theory and the transfer matrix technique, the bending coupling is analyzed between two bent rectangular waveguides or between a straight waveguide and a bent one. And the expression of amplitude coupling ratio is derived. This provides a theoretical basis of simulating the filtering and amplifying functions of the microring resonator.3. The rate equations and light propagation equations as well as the theoretical model of interrelated level structures are used to the Er³⁺ doped waveguide amplifier and the Yb³⁺ doped waveguide amplifier. The solutions of the rate equations and light propagation equations have been obtained under the steady state condition. In order to get these solutions, we introduce the overlapping factor between the light function and the dopant distribution, and neglect the amplified spontaneous emission and the loss inside the waveguide. The expressions of pump threshold, gain and optimum waveguide length are given, and some important characteristics of the devices are numerical simulated, and the simulation results are analyzed and discussed. When the input pump power is larger than the pump threshold power, the gain is larger than zero, in this case, the signal will be amplified by the device. The stronger the incident signal power, the weaker the gain is. The pump threshold power increases as the waveguide length or the dopant concentration increase. We should select the optimum length and the optimum dopant concentration to get the maximum gain at the end of the waveguide.4. Formulas for analyzing the gain characteristics of the Er³⁺/Yb³⁺ co doped waveguide amplifier is derived from the rate equations and the light propagation equations based on the energy transfer process of Er³⁺ and Yb³⁺ ions. Then by using these formulas, the effects of the pump power, signal power, dopant concentration and waveguide length on the gain characteristics are analyzed for the phosphate glass Er³⁺/Yb³⁺ co doped waveguide amplifier. The simulation process by formulas is simple, and requires little time spent on computing. Simulated results show that the Er³⁺/Yb³⁺ co doped waveguide amplifier has better gain characteristics compared with the Er³⁺ doped waveguide amplifier. This is the first innovation.5. Formulas of the transfer function and output power gain are presented, transmission characteristics are analyzed, and simulation and optimization are performed for three kinds of Er³⁺/Yb³⁺ co doped microring resonator amplifiers with single , parallel double and series double microring structures. Around the pumping wavelength of 0.98 m and the central signal wavelength of 1.55 m , the effects of the pump power, signal power, dopant concentration and amplitude coupling ratios bettwen microring and microring/channel on the output power gain are investigated, and the transmission spectra are presented. The simulated results are as follows.In the case of the amplitude coupling ratioκ= 0.092, pump power P_p0 = 8 mW, signal power P_s0 = 36.5 W, Er³⁺ concentration N_Er = 1×10²⁶ m^–3, and Yb³⁺ concentration NYb = 3×10²⁷m 3, the single microring resonator can produce the signal power gain from 10 dB even to 60 dB. The transmission spectrum of the upper channel possesses the positive gain in the whole range of the signal wavelength, while the transmission spectrum of the lower channel has the positive gain around the central resonant signal wavelength of 1.55 m, but has the negative gain far from the central signal wavelength. Therefore, we should select the upper channel to perform the signal amplification, and choose the lower channel to carry on the signal filtering in practice.In the case of the amplitude coupling ratioκ=0.064, pump power P_p0 = 8 mW, signal power P_s0 = 37.2 W, Er³⁺ concentration NEr = 1×10²⁶ m^–3, and Yb³⁺ concentration NYb = 3×10²⁷m³, compared with the single microring resonator, the transmission spectrum of the channel on parallel cascaded double microring resonator has larger gain around the central resonant signal wavelength of 1.55 m.In the case of the pump power P_p0 =10 mW, signal power P_s0 = 24 W, Er³⁺ concentration N_Er = 1×10²⁶ m^–3, and Yb³⁺ concentration N_Yb = 2×10²⁷m³; amplitude coupling ratiosκ1= 0.16 amdκ2= 0.012, for the series cascaded double microring resonator, the signal output spectrum of the right channel is much flatter, the intensity of the non resonant light (and hence the crosstalk) is much weaker, and the maximum gain is larger compared with the single microring resonator. This indicates that by adopting the series cascaded double microring resonator structure, much batter features of the device can be obtained, the wavelength control and the requirement for the fabrication technologies can be relaxed efficiently. The signal output spectrum of the left channel has a negative minimum gain at the resonant wavelength of 1.55 m, while that of the right channel possesses more than 10.16 dB positive gain in a wider range of the wavelength around the resonant wavelength of 1.55 m. Therefore, we should select the right channel to realize the filtering and amplifying functions in the practical applications of the device.6. Using the presented technique and its relative formulas of the amplitude coupling ratios, the transfer functions and output signal power gain, we can easily and conveniently perform the formulized analysis and simulation for the transmission characteristics. We think that the presented technique is useful and valuable for the parameter optimization and structural design of this kind of microring resonator amplifiers. This is the second innovation.