Optical Pulse Switch Design And Analysis Based On Nonlinear Effects In SOI Waveguides

In recent years, silicon on insulator (SOI) waveguide is concerned by the semiconductor researchers and its theoretical and experimental studies have gradually increased. Because its structure has a strong light-binding property and its material has a Kerr and two-photon absorption property, these determine that it has a variety of nonlinear effects.In this thesis, we have researched the nonlinear processes in SOI waveguide used an ultrafast picosecond or femtosecond optical pulse. Then, we have used these functions obtained in these processes to design some optical switch models and analyzed their thermal stability. The main results are as follows:(1) We have summarized the recent development about silicon-based optoelectronic devices as well as their applying trend on nonlinear optical switches. On the basis of existing theories, we obtain a better light pulse nonlinear propagation equation in the SOI waveguide.(2) The vector finite element method is introduced to the electromagnetic field theory and is applied to analyze the modes of polymer waveguide for more accurate results. This method is also used to analyze the errors about 45°total internal reflection waveguide mirror in the electro-optic printed circuit board (EOPCB), the relationship between fabrication errors and relative power change is obtained. The fabrication error tolerance is calculated, it is beneficial to direct the actual 45°total internal reflection waveguide mirror production. Moreover, this method is also applied to analyze the misalignment errors between the 45°total internal reflection waveguide mirror and waveguide in the EOPCB. The relationship between relative power change and misalignment errors is obtained. The misalignment error tolerance is achieved, it is useful to guide the actual alignment fabrication between the 45°total internal reflection waveguide mirror and waveguide.(3) The conventional solution to nonlinear Schrodinger equation, Split-step Fourier method, is introduced. But, this method requires a large amount of computer memory and time, so, we propose a Split-step multi-wavelet method for solving nonlinear Schrodinger equation. This method will sample and compress the optical pulse signal in order to save computer memory and time and preserve calculating accuracy. We have applied this method to solve the two-core nonlinear optical pulse switch. Compared with other methods, we find the power transmission efficiency do not loss significantly in the coupler, but the computational memory and time has clearly decreased. This method is beneficial to iteratively solve the differential equations.(4) We have analyzed the power transmission efficiency in the two-core linear negative tapered SOI Bragg grating directional coupler (LNTSBGDC) under etching depth perturbation. For the Gaussian, exponential and raised cosine variable coupling coefficient, when the power transmission efficiency is lower than 0.02, the performance of optical pulse switch is essentially unaffected and the etching depth tolerance is achieved. It is useful to actually guide to fabricate optical switches. Moreover, we have also designed the cascaded SOI nonlinear optical pulse switch. The coupling length and the core-distance-ratio of switch are calculated. When the function of optical pulse switch is unaffected, the tolerance of height and width in the core layer and tolerance of core-distance-ratio is calculated. In the range of tolerance, the power transmission efficiency and relative power transmission efficiency error have been not seriously affected by the variation. When four pulses with different power are input, they are switched to different output ports. Although the output pulses have a little compression and loss, these output pulse waveforms are essentially unchanged. The optical pulse switch function is achieved, so, this design is effective.(5) The thermal stability of power transmission efficiency and extinction ratio in the optical pulse switch is analyzed. The switch has a three-core asymmetric SOI variable Gaussian coupling coefficient. Because the refractive indices of Si and SiO2 are affected by temperature, the effective refractive indices in the nonlinear coupler change correspondingly. When the coupling coefficients and temperature vary, the relative transmission efficiency errors and the relative extinction ratios are obtained respectively. When temperature change during±100K, the design parameter scope of coupling coefficient is obtained. The power transmission efficiency and extinction ratio in the optical pulse switch can work stably in this area. In addition, we have researched the switch performance in the optical pulse wavelength selective switch array, which is disturbed by two-photon absorption. Because two-photon absorption can change the temperature in this array, the temperature will affect the effective refractive index of material and shift the Bragg wavelength; this will disturb the power transmission efficiency, pulse peak-amplitude-ratio and relative extinction ratio. The normalized input power range is calculated in order to minimize the variation of relative transmission efficiency. So, the switch function of optical pulses is essentially unaffected. Pulse wavelength selection function can be achieved reliably. It is useful to actually guide to fabricate optical pulse wavelength selection switch array.