Research On Reconfigurable Optical Add/Drop Multiplexer

As the rush development of optical communication technology, the optical network has witnessed tremendous evolution. In less than a decade, the state of art in fiber-optic transport system has evolved from simple point-o-point chains of optically amplified fiber spans to massive networks with hundreds of spans connecting transparent add/drop nodes spread over long distances. The optical network implementing all-optical switching and routing technology makes the dynamic and fast wavelength assignment possible and is being extensively studied recently. The reconfigurable optical add/drop multiplexer (ROADM) which can dynamicly and effectively configure the network resource is the enabler of the all-optical networks.Combing with our research on the National High Technology Research and Development Program ("863"Program) of China, this dissertation systematically analyzed the principle and manufacturing of ROADM components, especially the ROADM components based on micro electro-mechanical systems (MEMS) technology, including commercial WSS based on bi-axis MEMS mirror array, hybrid planar waveguide circuits (PLC)-MEMS ROADM components, as well as wavelength selective switch(WSS) based on single-axis MEMS mirror. The research of this dissertation can be helpful to the design and manufacturing of ROADM components. The main innovations of the dissertation are summarized as follows:A commercial 1x4 WSS module based on bi-axis MEMS mirror array technology and bulk diffraction grating is successfully researched and developed. This WSS module has compact size and shows its good performance in scalibility for both port number and channel number. According to the theoretical model of WSS in this dissertation, the relationship between insertion loss and the whole component design are demonstrated and researched in detail, we also investigate the relationship between bandwidth and spot size as well as the fill factor of the MEMS mirror array, extinction ratio and rotaing angle as well as spot size, attenuation range and MEMS mirror. The component packaging technology as well as driving and controlling method are also researched in this dissertation. The experimental results show that an insertion loss of less than 5.5dB, bandwidth of 0.45nm are achieved, all of these indicate a good uniformity with theoretical analysis and a promising application future. As far as we know, this is the first 1x4 commercial WSS module reported in China, and therefore it is significant for the commercialization of national ROADM industry.The "rabbit ear" phenomenon and the method to is theoretically analyzed and experimentally validated, by using Fresnel Law of Diffraction, the depth of "rabbit ear" is also evaluated. The "rabbit ear" phenomenon can be depicted as follows:the attenuation amount of the spectrum varies in the different position, in the central part of the spectrum, the attenuation amount is larger the that in the two edges of the spectrum. Because the "rabbit ear" can be harmful to the whole optical newroks, this research helps to alleviate the negative effect.PLC-based ROADM suffers from large insertion loss and polarization dependent effect, so a hybrid PLC-MEMS ROADM module with 2-D structure is theoretically and experimentally introduced which is based on the narrow-band optical switch (NBOS) technology, the so-called NBOS is a MEMS Fabry-Perot (F-P) cavity achieving the narrow-band optical switching and attenuation simutaneously. The NBOS structure has not only small incident angle and low polarization dependent loss but also small driving current. In comparison with the analyses of the current ROADM technologies, this hybrid PLC-MEMS ROADM module is proven to be cost-effective, low insertion loss, narrow-band, and has a more mature technology. It would grow to be a cost-effective commercial ROADM solution.A single-wavelength WSS module integrating with the commercial thin film filter (TFF), the collimating lens array, and also the bi-axial MEMS mirror is theoretically introduced and experimentally demonstrated. By cascading several single-wavelength module of this kind together, a 1x4 WSS can be constructed. We fabricate four single-wavelength (using four ITU-T wavelengths) modules in series in our experiment, the results show that a-0.5dB bandwidth of more than 0.40nm, an insertion loss of approximately 3dB, and an extinction ratio of more than 50dB as well as hitless switching can be achieved using the cascading structure. With this cascaded 1x4 WSS, each input wavelength or any of their combination could freely reach each output port. Since the cascaded components in the MEMS-based WSS module increases with the number of wavelengths and ports it carries, it is much better to be applied in a less add/drop wavelengths occasion, also it is more productive.Commercial WSS module based on bi-axis MEMS mirror array technology suffers from "rabbit ear" phenomenon and low fill factor, both of which will be detrimental to the whole system. A novel patent-pending WSS structure based on single-axis MEMS mirror array and MEMS-based F-P attenuator array is theoretically introduced and analyzed. The utilizing of MEMS-based F-P attenuator can release both the "rabbit ear" and the disadvantage of low fill factor in bi-axis MEMS mirror array technology. The maximum attenuation of 34dB, insertion loss of 6.4dB, maximum dispersion of 5ps/nm are reported, indicating a high uniformity with the simulation results. What's more, this novel WSS is manufactured based on mature technologies, so it is cost-effective and productive and can be an ideal candidate for commercial WSS component.