Multiwavelength cross-connects (WXC's) will play a key role to provide more reconfiguration flexibility and network survivability in wavelength division multiplexing (WDM) transport networks. In this paper, we utilize three different fiber Bragg grating (FBG)-based P-type, S-type, and N-type building blocks with optical circulators and related control devices for constructing large rearrangeably nonblocking N\;\times\;N WXC's. The P-type building block is composed of certain "parallel" FBG-element chains placed between the control devices of two large mechanical optical switches (OSW's). The S-type building block consists of a "series" of FBG elements and the control device of 2\;\times\;2 OSW's. The nonswitched N-type building block includes a "series" of FBG elements with appropriate stepping motor or PZT control devices. All FBG elements, each with central wavelength corresponding to equally or unequally spaced WDM channel wavelengths, with high-reflectivity are required. Large N\;\times\;N WXC structures, with minimum number of required constitutive elements, based on a three-stage Clos network are then constructed. We investigate their relevant characteristics, compare the required constitutive elements, and estimate the dimension limits for these WXC architectures. Other related issues such as capacity expansion, wavelength channel spacing, and multiwavelength amplification are also addressed.
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