The Study Of The Total Internal Reflection Optical Waveguide Switch

The optical switch is the key component in optical switching systems. A lot of switching schemes have been proposed in the past. However, none of them can satisfy all requirements of commercial applications up to now, so developing the optical switch of high performance has become one of the most challenging problems in the area of optoelectronics. Compared with the mechanical and the microelectromechanical (MEMS) switches, the optical waveguide switch utilizing the total-internal-reflection (TIR) structure has an intrinsic advantage at the operation speed. In addition, it has merits such as the compact size, the digital response to the driving signal, the nonsensitivity to wavelength and polarization, so the TIR switch is a promising structure to meet the requirements of the optical switching system.The TIR switch has been studied for 30 years, it is designed and fabricated in a lot of material systems. However, its performance is not satisfying all along, an important reason for that is people's understanding about its operation mechanism is not exact: it is widely thought that the beam reflection in the TIR switch is the same as the ordinary reflection in the free space. In fact, the beam reflection in the TIR switch has the following four particularities: 1. the width of the incident beam is narrow; 2. the incident angle approaches 90°; 3. the beam is confined by the waveguide while it is being reflected; 4. the refractive index in the reflection region varies in two dimensions.In this thesis, analytical models are developed to describe the operation mechanism of the TIR switch, and then the results of the analytical study are used to guide the practical design and fabrication. This thesis makes innovative theoretical works mainly in the following three aspects:1. The definition of the generalized reflection and transmission of plane wave is proposed and rigorously proved in this thesis. With the definition of the generalized reflection, the controversy about the Goos-Hanchen shift in the limit of grazing incidence is solved, and then the spectrum superposition effect is studied for the incidence circumstance that the beam spread angle exceeds the complementary angle of the incident angle. This work is helpful for understanding the operation mechanism of the TIR switch, and for investigating analogical problems in optics such as the Lloyd's mirror. 2. The modal expansion method is utilized to investigate the reflection in the bounded space. The thesis points out that the essence of the reflection in the practical TIR switch is the mode degeneracy between even and odd modes. Since different modes require different refractive index decreases to achieve the degeneracy state, the thesis explores to reduce the power consumption of the TIR switch by controlling the mode excitation.3. The light reflection in the reflection region with a two-dimensional gradient refractive index distribution is studied particularly for the thermo-optical effect of polymer. Based on the analytical expression of the thermal field distribution, the thesis utilizes the method of ray optics to calculate the light reflection trace. The calculation indicates that the reflection trace varies with different horizontal planes due to the nonuniformity of the refractive index in the perpendicular direction. A direct result of that is the beam is expanded after the reflection. According to the beam expansion rule, the structure of the TIR switch should be adjusted accordingly. Since the two-dimensional gradient distribution of the refractive index is prevalent in practical reflections, the analytical method presented in this thesis is constructive for studying these problems.Based on the three theoretical models above, the thesis fabricates the practical TIR switch which operates at the optical wavelength of 1.55μm by utilizing the thermo-optical effect and the carrier injection effect. A 2×2 TIR switch is developed successfully employing the thermo-optical effect of polymer. The testing result shows that its extinction ratio exceeds 35dB at a power consumption of 80 mW, and the switching speed is about 5 ms. In addition, an improvement is made on the traditional 2×2 structure. By setting a sectional electrode, the thesis successfully fabricates a 2×3 switch which can route the light between 3 output ports. On the other hand, by collaborating with the Beijing semiconductor institute, the thesis explores to fabricate the high-speed TIR switch on GaAs/GaAlAs double heterojunction. The light switching phenomenon is observed in the primary result, and the response time is faster than 70 ns.At last, based on the cutoff characteristic of the zero-order TE mode of the W-type waveguide, the thesis proposes a cutoff modulator with tunable filtering characteristic which can be used as a gate switch or a variable optical attenuator. Compared with other schemes of the cutoff modulator, it has the advantages of a more compact size, a simpler structure and the potential for the high intensity integration.