| Optical cross-connects(OXC's) are key elements in all-optical dense wavelength division multiplexing (DWDM) networks. To build high-speed and large-capacity DWDM networks, one of the key technologies is to study and design OXC structure with good performance. Compared with other OXC architectures, integrated optical cross-connects show many merits such as the compact dimensions and low cost, which makes them move attractive in DWDM networks. Integrated optical cross-connects generally consist of many optical waveguide devices such as demultiplexers, optical switches and multiplexers. These optical waveguide devices usually have high optical crosstalk levels, which will cause large crosstalk noise and impede their applications in OXC system. So, solution should be developed to limit the damaging effect of crosstalk in the integrated optical nodes.In this thesis an optical switching matrix with good crosstalk performance for photonic switching is proposed. Major subjects in this thesis are discussed as follows:(1) A list of different forms of optical crosstalk that may be generated in DWDM networks is presented. The crosstalk elements in an OXC node are analyzed in detail.(2) The impact of homodyne crosstalk on intensity-modulation direct-detection system is studied. The relationships between the impact and various system-factors are discussed. Instructions are provided for the design of low channel crosstalk OXC nodes. Several methods proposed to mitigate the influence of crosstalk are compared and discussed. Results show that a low channel optical switching structure is very important to design a low channel crosstalk OXC. (3) Different parameters to evaluate properties of optical switching structures are discussed. Based on the properties, the characteristics of several optical switching networks are analyzed and compared. From the results, we can see that the dilated Benes (DB) architecture has several advantage such as the fewer number of switching elements needed and rearrangeable nonblocking, which made it move attractively used to design optical cross-connects. However, when DB structure is built with optical waveguide devices, the crosstalk is very large and the signal-to-noise ratio (SNR) becomes deteriorated. So, modified methods should be proposed to improve the SNR of DB architecture.(4) To improve the SNR characteristics of DB structure, On/Off Gates are introduced in its last stage of recursion and improved dilated Benes (IDB) fabric is proposed. The On/Off Gates in IDB can switch off the crosstalk path in DB structure and decrease accumulation of crosstalk, so the SNR of IDB structure is improved. To further increase the SNR of DB, On/Off Gates can be added in other stages of DB and form Generally Improved Dilated Benes (GIDB). Compared with other optical switching matrixs, GIDB has the best SNR characteristics.(5) The crosstalk performance of 8×8 DB,IDB and GIDB are experimentally investigated.Results show that the 8×8 GIDB based on current optical waveguide devices can totally remove the influence of crosstalk.
|
PDF Full Text Request