| As the key components of optical fiber network, optical switch and its arrays have been the focus of research and development. High-speed optical switch and its arrays are the essential devices for optical packet switching based all-optical network. Many types of optical switch have been developed, based on a variety of physical effects, principles and techniques. These switches have good performances in extinction ratio, insertion loss and polarization dependence, etc. However, there has not been a perfect solution for high-performance, high-speed optical switches with response time of nanoseconds and even higher.The refractive index change induced by the carrier injection effect in compound semiconductor is about two orders of magnitude greater than that by the electro-optic effect, and it is insensitive to polarization. The switching speed of carrier injection type optical switch is mainly determined by the combination life of carriers, which is about 100 picoseconds typically. GaAs-based devices are potentially advantageous in several aspects, such as the use of large-area high-quality inexpensive GaAs substrate and compatibility with the mature GaAs integrated circuit(IC) processing. GaAs-based carrier injection type optical switch is one of the promising solutions for high-speed optical switch with response time of nanoseconds and even higher..Supported by the key program of the National Natural Science Foundation of China, this thesis is intended to explore 1.55μm GaAs-based carrier injection optical switch and its array. The main efforts are currently concentrated on the development of the fabrication techniques, aiming at the fabrication characteristics of the carrier injection devices. The fabrication techniques are successfully developed and two types of 2×2 GaAs-based carrier injection optical switches are successfully fabricated. The innovative works of this thesis can be summarized as follow:1. Two-step etching technique is proposed for device fabrication on epitaxial material with thick core. This method is very simple and has lower requirement for the equipments. A 2×2 multimode interference optical switch is successfully fabricated, and the switching current is about 160mA. The confinement for the lateral diffusion of the injected carrier is studied by oxygen ion implantation technique.2. Multimode interference-Mach Zehnder (MMI-MZ) structure is employed to study the carrier injection optical switch. The fabrication avoids the commonly used doping techniques such as Zn diffusion or ion implantation, which is rather difficult. The fabrication only needs three times of photolithography therefore effectively reduced the error in photolithography. A 2×2 carrier injection MMI-MZ optical switch is successfully designed and fabricated, and its electrode is only 100-μm long. At an injection current of 80mA, the extinction ration exceeds 25dB at 1.55μm. The switch has a flat and polarization-insensitive response spectrum throughout 1542-1562nm. The fall- and rise- time of the switch is no more than 10ns.3. Three types of variable optical attenuators (VOA) are studied by employing the S-bend structure, MMI structure and five-layer W type waveguide. The additional phase change in tapered waveguides is discussed. The extinction ratio of the optical switch can be improved by integrating with these VOAs, which is verified by the polymer-based thermo-optical devices. Some exploring attempts are also performed on GaAs material by utilizing the carrier injection effect.In conclusion, a refractive index change up to -0.01 at 1.55 urn is successfully obtained by employing the free carrier absorption effect in GaAs. It provides an important experimental basis for the research of long wavelength GaAs-based devices employing the carrier injection effect. Meanwhile, it demonstrates the technology advantage of GaAs-based device. With the help of optimized designs and improved processes, more perfect performances can be obtained to satisfy the requirements of various applications.
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